Symposium OrganizersUlrike G. K. Wegst, Thayer School of Engineering at Dartmouth
Amal M. K. Esawi, The American University in Cairo
Guy Genin, Washington University, St. Louis
Tianjian Lu, Xi'an Jiaotong University
Jonathan Wilker, Purdue University
TT2: General Interfaces II
Tuesday PM, April 10, 2012
Marriott, Yerba Buena, Salons 14-15
2:30 AM - *TT2.1
Advanced Composite Materials in Aerospace Products
Alexander Rubin 1
1The Boeing Company Saint Louis USAShow Abstract
Advanced materials have been, and will continue to be, critical, enabling technologies for aerospace innovation. Performance gains from weight reductions are driving the increased usage of composite materials for aerospace structure with the latest Boeing's 787 Dreamliner containing 50% of polymer composite structural materials by weight. Evolution of composite material usage for aircraft with standard carbon modulus fibers (approx. 33 Msi modulus and 500-600 ksi tensile strength) and intermediate modulus fibers (approx. 41 Msi modulus and 800 ksi tensile strength) with various polymer resins will be discussed. The presentation will address challenges for composites in material property optimization, affordable and scalable manufacturing processes, expended design space, and development and certification. The balancing of the critical properties to optimize structural performance, multi-functionality and enhanced process ability is a key to successful materials selection and implementation. Both monolithic and 3D complex design will be addressed. Computational tools and modeling techniques for advanced polymers development from chemistry to material structure to aircraft structure are being explored and implemented. Examples of how simulation methods (quantum mechanics models, molecular dynamics models, and others) can supplement experimental methods demonstrate the advanced development processes. The ideas on how the polymer modeling and simulation can reduce the aerospace material development and certification cycle will be discussed.
3:00 AM - TT2.2
Nanoscale Interfaces with Ice
Nino Samadashvili 1 2 Teemu Hynninen 1 2 Vili Heinonen 2 Cristiano L Dias 3 4 Mikko Karttunen 3 Tapio A Nissila 2 5 Adam S Foster 1 2
1Tampere University of Technology Tampere Finland2Aalto University School of Science and Technology Helsinki Finland3the University of Western Ontario London Canada4University of Toronto Toronto Canada5Brown University Providence USAShow Abstract
Melting and freezing of water are among the most important phase transitions in nature. Not only does the amount of ice on the planet regulate global sea levels, melting ice plays a part in phenomena as diverse as the electrification of thunderclouds, frost heave, and slippery ice surfaces. The phenomenon of ice melting when subject to high pressure and refreezing once the pressure is lifted, regelation, acts in systems ranging from massive glaciers, where it allows ice sheets to flow around obstacles, to Thomsonâ?Ts classic 19th century experiment of letting a wire pass through a block of ice. More recently, attention has become focused on the nanoscale properties of ice, where it has been shown to be important in a wide variety of processes including nucleation, adsorption, diffusion, confinement and friction. In each case, a key component has been understanding the atomic details ice interface. In this work we use atomistic molecular dynamics simulations to understand the atomic processes involved in several characteristic systems. As a first test of our simulation tools, we study regelation in bulk ice around a nanowire. In particular, we show that the symmetry and continuity of the transition from a stationary to a moving system due to increased driving force changes if a hydrophilic wire is replaced by a hydrophobic one . To further investigate different material combinations and the influence of roughness, we replace the nanowire with polystyrene (PS) and contrast the temperature and pressure dependence of the ice interface. Alongside this work, we investigate the frictional contact at ice-ice and ice-polymer interfaces, considering how the predicted forces depend on the temperature and sliding velocity. Particular emphasis is placed on understanding the formation of the liquid layer at the surface of ice and its role in the observed properties of the interface.  T. Hynninen, V. Heinonen, C. L. Dias, M. Karttunen, A. S. Foster, and T. Ala-Nissila, Phys. Rev. Lett. 105 (2010) 086102
3:15 AM - *TT2.3
Knowledge Diversty in the Emerging Global Bio-nano Sector
Elicia M. Maine 1 Martin Bliemel 3 Armstrong Murira 4 1 James Utterback 2
1Simon Fraser University Vancouver Canada2Massachusetts Institute of Technology Cambridge USA3University of New South Wales Sydney Australia4Simon Fraser University Burnaby CanadaShow Abstract
Great opportunities and radical innovation are most likely to occur at the convergence of two or more technology streams. A bio-nano sector is emerging from such a convergence and may eventually provide radical innovation and new dominant firms. As there are no comprehensive reviews on this emerging sector, this paper provides a descriptive overview, identifying what types of firms are entering, from what knowledge base, where they are located, and their strategic choices in terms of technological diversity, R&D strategy, business model, and areas of clinical focus.
3:45 AM - TT2.4
Nanotextured Material for Applications in CSF Sample Screening and Characterization
Krishna Vattipalli 1 Savindra Brandigampala 2 Claire McGraw 3 Gaurav Chatterjee 3 Srinath Kasturirangan 3 Philip Schulz 3 Michael Sierks 3 Shalini Prasad 1
1University of Texas at Dallas Richardson USA2Wichita State University Wichita USA3Arizona State University Tempe USAShow Abstract
One of the important features in the neurodegenerative diseases is the protein misfolding in addition to the aggregation. The ability to detect protein misfolding requires the design of a diagnostics assay the will enable molecular level probing. The use of nanoporous ceramic templates enables size based immobilization of the target proteins and by leveraging the principle of â?omacromolecular crowdingâ? protein association can be mapped with a high degree of resolution. By tailoring the surface functionalization within nanoporous ceramic templates, macromolecular immobilization can be selectively controlled, which in turn significantly enhances the perturbation to the electrical double layer/. The changes to the electrical double layer are measured with a high degree of sensitivity through impedance spectroscopy. Presence of soluble oligomeric aggregates of proteins including various AÎ² and a-syn aggregate species can be correlated to the onset and progression of many neurodegenerative diseases. Pre symptomatic diagnosis and distinction between these diseases can be achieved by the specific detection and quantification of levels of each of these different toxic protein species in CSF. Detection using highly selective morphology specific reagents in conjunction with the ultrasensitive nanoporous electronic biosensor showed the presence of different protein morphologies in human CSF samples Furthermore, we show that these morphology specific reagents can readily classify between post-mortem CSF samples from AD, PD and cognitively normal sources. These studies suggest that detection of specific oligomeric aggregate species holds great promise as sensitive biomarkers for neurodegenerative disease.
4:30 AM - TT2.5
The Role of Interfaces on Shock-induced Damage in Two-phase Metals
Saryu Jindal Fensin 1 Ellen K Cerreta 1 Steven M Valone 1 George T Gray 1 Adam M Farrow 1 Carl P Trujillo 1
1Los Alamos National Laboratory Los Alamos USAShow Abstract
For ductile metals, the process of dynamic fracture during shock loading is thought to occur through nucleation of voids, void growth, and then coalescence that leads to material failure. Particularly for high purity metals, it has been observed by numerous investigators that voids appear to heterogeneously nucleate at grain boundaries. However, for materials of engineering significance, those with inclusions, second phase particles, or chemical banding; it is less clear what the role of grain boundaries versus other types of interfaces in the metal will be on nucleation of damage. To approach this problem two materials have been systematically investigated: (1) high purity copper, (2) copper with 1% lead. The role of lead at grain boundaries and its behavior during shock loading will be discussed in conjunction with the results from experiments and Molecular Dynamics simulations.
4:45 AM - *TT2.6
The Importance of Interfaces in Nuclear Energy Systems
Todd Allen 1 Kumar Sridharan 1
1U. Wisconsin Madison USAShow Abstract
The safe and efficient operation of a nuclear energy system depends to a great extent on the performance of materials. Among the key degradation modes that challenge materials in nuclear systems are oxidation and stress corrosion cracking, radiation damage, and inter-diffusion between components in mechanical contact. This is true for current light water reactors as well as proposed advanced systems that have even more stringent materials performance requirements. In this presentation, examples of designing interfaces to improve material performance in nuclear systems will be provided, specifically: engineering grain boundaries to improve oxidation performance, understanding the relationship between grain boundary structure and radiation-induced segregation, and using electrophoretic deposition to establish barriers between nuclear fuel an cladding.
5:15 AM - TT2.7
Morphology-induced Hydrophobic Behavior of Electrospun Polyhydroxyalkanoate Membranes
Maraolina Domiacute;nguez-Diacute;az 1 Angel Romo-Uribe 1 Araceli Flores 2 Rodolfo Cruz-Silva 3
1Universidad Nac A de Mexico Cuernavaca Mexico2Consejo Superior Inv Cientifica Madrid Spain3Universidad Autoacute;noma del Estado de Morelos Cuernavaca MexicoShow Abstract
Biodegradable poly(3-hydroxybutyrate) -PHB- and the copolymers with poly (3-hydroxyvalerate) -PHB/HV, containing 5 and 12 mol% valerate (denoted PHB/5HV and PHB/12HV, respectively) were electrospun from chloroform solution at room temperature. The results showed that relatively low voltage and concentrations favored uniform filament formation in PHB, with filament diameters ranging from 3 to 7 micrometers. On the other hand, low molecular weight and solution concentration favored uniform filament formation in the PHB/5HV copolymer. Strikingly, morphology of filaments and beads favored the membranes hydrophobic behavior, the membrane from PHB/12HV exhibited a water contact angle of 112Â°. Solution cast films from the PHAs exhibited water contact angles in the range of 65Â°. Analyses on the membranes morphology via scanning electron microscopy revealed that filament diameter drives the degree of porosity and the hydrophobic behavior of the electrospun membranes.
TT3: Poster Session: Interfaces
Tuesday PM, April 10, 2012
Moscone West, Level 1, Exhibit Hall
6:00 AM - TT3.1
Patterning of Conjugated Polymer with Enhanced Photoluminescence via Self-assembly at the Air/Water Interface
Lei Zhao 1 Xinchang Pang 1 Chaowei Feng 1 Zhiqun Lin 1
1Georgia Institute of Technology Atlanta USAShow Abstract
A novel PtBA-P3HT multi-arm star-like diblock copolymer (BCP) was synthesized via a combination of atom transfer radical polymerization, quasi-living polymerization and click reaction. The self-assembly of PtBA-P3HT multi-arm star-like BCP at the air/water interface was systematically explored using the Langmuir Blodgett (LB) technique. The hydrophobic star-like BCP has 21 arms, with PtBA as the core and P3HT as the shell. At the air/water interface, the BCP molecules gradually assembled into domains composed of bundle-like structures under surface pressure, and finally formed the network structure in a way controlled by PtBA chain folding and P3HT chain stacking. The photoluminescence measurement showed that the formation of P3HT bundle in LB film led to enhanced luminescence due to the reduced inter-chain coupling.
6:00 AM - TT3.10
Mineral Density Gradients in Healthy and Diseased Human Tissues
Sabra Djomehri 1 Susan Candell 2 Siew H Lau 2 Grayson W Marshall 1 Sally J Marshall 1 Samuel Webb 3 Sunita P Ho 1
1University of California, San Francisco San Francisco USA2Xradia Inc. Pleasanton USA3Stanford Linear Accelerator Center Menlo Park USAShow Abstract
Mineralization is essential to the load-bearing nature of most tissues such as skeletal and alveolar bones, and cementum, dentin and enamel within a tooth. All five mineralized tissues are composites with heterogeneous mixtures of two basic constituents; organic and inorganic. While organic contains fibrillar and globular proteinacious matter, inorganic is dominated by apatite. Within tissue growth the epigenetic factors such as disease and load perturbations influence the organic-to-inorganic ratios which will be examined by X-ray computed tomography (micro-CT) of healthy and diseased dentoalveolar structures. A micro-CT system (MicroXCT-200, Xradia) was calibrated using hydroxyapatite (HA) phantoms in an epoxy resin matrix ranging in mineral densities from 0 and 3080 mg/cc (CIRS, Norfolk, VA; Ratoc System Engineering, Inc Ltd, Tokyo, Japan; Gammex RMI, Middleton, WI). A selected region of interest (ROI) within each sample was used to correlate intensity to Hounsfield units (HU). Enamel, dentin, cementum and alveolar bone beams (~1mm diameter) from healthy and diseased human specimens (male patients: aged 40 to 60 years, N=5) were sectioned. Cementum affected with periodontitis and carious dentin specimens were investigated. Each isolated tissue was scanned at a peak voltage of 40KVp and 60KVp using a 10X magnification. Mean intensity profiles from virtual sections of experimental specimens provided HU values for ROIs. Subsequently, the HU values were mapped to mineral densities from known mineral density phantoms. The mineral density ranges for enamel, dentin and alveolar bone are within the range as reported in literature and were found to be 2800 to 3180 mg/cc (3010Â±80), 1450 to 1600 mg/cc (1520Â±50), and 1220 to 1410 mg/cc (1330Â±80), respectively. The mineral density of cementum was 1240 to 1380 mg/cc (1290Â±20) which overlaps the range of alveolar bone, while cementum affected by periodontitis showed a slightly lower mineral density range of 950 to 1320 mg/cc (1170Â±100); a Studentâ?Ts t-test revealed statistical significance between these three groups (P < 0.05). Diseased dentin samples with effects of hypomineralization or hypermineralization were also analyzed. It was determined that moderately affected dentin regions > 1mm away from a lesion site had mineralization closely matching that of normal dentin,from 1430 to 1610 mg/cc (1530Â±80, P > 0.05) while hypomineralized dentin at the lesion site fell within a large range of 314-1210 mg/cc (630Â±400). The mineral density of hypermineralized dentin was found to be between normal dentin and enamel at 2320 mg/cc. Spatial mapping of calcium and phosphorus X-ray fluorescence mapping using microprobe (2-3 Beam line, SSRL) and mineral content from ongoing ash studies will also be reported to validate calibration accuracy. SUPPORT: NIH-NIDCR R00DE018212 (SPH); S10RR026645 (SPH); Depts. Of PRDS and OFS, UCSF
6:00 AM - TT3.11
Revealing Interfaces in Natural Materials
M. Josefina Arellano-Jimenez 1 Erica Pehmoeller 1 C. Barry Carter 1
1University of Connecticut Storrs USAShow Abstract
Structural materials in nature have long been subjects of technological interest; besides providing support to live organisms, those materials exhibit exceptional properties that made them potentially useful in engineering applications. Recently, the study of natural ceramics has been increased due to new perspectives. Extensive reports on how these materials are ordered, from the nano to the macroscopic scale, provide useful insights for design and engineering; photoconductive behavior and optical properties offer new perspectives for applications in sensors or electronic devices. The natural assembly of organic and inorganic phases, which form at room temperature, make them a valuable model in the study of composite materials, biomineralization and self-assembly processes. Sea sponges and seashells are examples of these materials. Sea sponges, the so-called glassy sponges, are essentially polymerizing silica and generating fibers (spicules) that exhibit a concentric lamellar structure with alternate organic and inorganic layers when observed in cross section. On the other hand, nacre is formed by alternate layers of aragonite platelets and organic layers. Several investigations have been carried out to study the optical and mechanical properties of these materials, however the role of organic molecules in growth mechanisms is still not fully understood. In this context, improved methods that allows the study of organic-inorganic interfaces are necessary to develop a better understanding of such biomineralization processes. Preliminary VLM, SEM and TEM results focused on developing a consistent methodology were obtained in spicules of E. aspergillum and Abalone seashell. Fracture surfaces of spicules and seashell fragments were analyzed using SEM without additional preparation. A second group of spicules and seashell fragments was embedded, cross-sectioned and polished previous to SEM analysis. Effects of sample preparation methods and chemical etch were observed on the polished surfaces. Results will be compared after the incorporation of additional techniques and methods.
6:00 AM - TT3.12
Electrochemical Deposition and Evaluation of Conductive Polymer Coating on Biodegradable Magnesium Implants for Neural Applications
Meriam Sebaa 1 Shan Dhillon 1 Huinan Liu 1
1University of California, Riverside Riverside USAShow Abstract
In an attempt to develop a conductive, biocompatible material for neural applications, pure magnesium (Mg) substrates were coated with the conductive polymer, poly(3,4ethylenedioxythiophene) (PEDOT). The reason for coating the Mg is due to its high degradation rate which has been shown to cause cell death in cell culture studies. The hypothesis is that the coating of Mg with this conductive polymer will slow its degradation rate in simulated body fluid, provide a good substrate for neuronal cell interactions, and allow for attachment and possible differentiation of stem cells. This is due to the microstructure of PEDOT and its conductive properties. A series of electrochemical deposition conditions were explored to produce a uniform, consistent PEDOT coating on Mg. Both chronoamperometry and cyclic voltammetry (CV) were investigated to compare the coverage and uniformity of the coating. Different durations and number of cycles were tested for both of the coating methods, in an attempt to develop an optimal deposition process. The high cost platinum and silver-silver chloride electrodes and low cost copper and stainless steel electrodes were tested to determine whether the low-cost electrodes can produce similar outcomes. Different concentrations of EDOT (monomer form of PEDOT) were tested to identify the concentration necessary for a desirable coating. Finally, different surface conditions of Mg substrate and post-deposition treatment were examined for their effects on coating quality. The stainless steel and copper electrodes were able to coat the Mg substrate as effectively as the platinum and silver-silver chloride pair. A concentration of 1M EDOT in ionic liquid was sufficient for coating Mg substrate with a 0.5cm2 surface area. Ten cycles of CV ranging from 2V to -0.5V or a constant 2000 second chronoamperometric coating at 1.2V were used. A quick rinse with deionized water, and ethanol followed by vacuum drying was necessary to cure the coating to yield an adequate bond to the Mg. SEM images were taken to show morphology of the coatings and EDAX showed how well coated the samples were. Tape tests were conducted using 3M 710 tape according to ASTM-D 3359 and the results showed the coating adhesion was within the classifications of 3B to 4B. Tafel tests of the coated magnesium show a corrosion current (Icorr) of around 8e-5A and critical voltage of -1.1V, lower than the Icorr of pure magnesium of around 8e-4A with a critical voltage of around -1.25V. Future studies will determine the proper thickness of coatings to satisfy requirements for cytocompatibility, cell interactions during degradation, and long term degradations tests will be conducted.
6:00 AM - TT3.13
Hydroxyapatite Mineralization on Functionalized Porous Silicon Surfaces Using a pH Stat System
Amy Richter Blakeley 1 Adele Boskey 2 Lara Estroff 1
1Cornell University Ithaca USA2Hospital For Special Surgery New York USAShow Abstract
Development of materials for the repair of mineralized tissues and interfaces relies on understanding the tight control of crystal nucleation and growth that results in intricate biomineralized structures. For example, tooth enamel has a defined, nucleating surface at which crystal growth is initiated within a gel-like matrix. However, in many in vitro models of hydroxyapatite mineralization, nucleation is not controlled at surface interfaces. We have investigated the nucleation and growth of hydroxyapaptite (HA; the mineral component of bone) as a function of surface chemistry by integrating porous silicon substrates (pSi) with tunable surface chemistry into a statically-controlled, pH-based system (pH Stat). The pH Stat system allows for the study of the effects of surface chemistry on HA nucleation by tightly regulating the temperature and adding calcium/phosphate solutions in a 5:3 molar ratio to maintain a constant pH without the use of solution buffers. Surfaces chemistries, as confirmed via infrared spectroscopy, included simple functional groups such as methyl, carboxylate, and hydroxyl, as well as more complicate molecules, including proteins such as osteopontin (OPN), which were coupled to the surface via NHS/EDC chemistry. HA formation on the functionalized pSi surfaces was confirmed by XRD while nucleation density and morphology were analyzed via scanning electron microscopy (SEM). Nucleation density of HA varied as a function of surface chemistry on the pSi surfaces, with the highest density observed on OPN-functionalized surfaces. Analysis of the titration and pH curves provide additional insight into the nucleation of HA on the functionalized surfaces. This system demonstrates that tailoring the individual surface chemistries in vitro can provide clues to the nucleation and growth of HA mineralization at surface interfaces in biomineralized structures.
6:00 AM - TT3.15
Fabrication of a 3D Glass Optrode Array for Optical Neural Stimulation
Tanya Vanessa Abaya 1 Mohit Diwekar 1 Steve Blair 1 Prashant Tathireddy 1 Loren Rieth 1 Florian Solzbacher 1
1University of Utah Salt Lake City USAShow Abstract
This paper reports techniques for wafer-scale fabrication of a three-dimensional high-aspect ratio glass microneedle array intended for high resolution optical neural stimulation. Each array is composed of 100 needles, called optrodes, bulk-micromachined from a 2-inch fused silica wafer that is 2.6 mm thick. Optrodes are approximately 1 mm long and spaced 400 Î¼m apart in a 10x10 grid. Optrodes are suitable for use in optogenetics and infrared neural stimulation (INS). Tapered optical fibers serving as tissue-penetrating optrodes to excite genetically targeted neurons expressing light-sensitive channels (i.e. ChR2) have been reported in literature. A single optrode was inserted in mouse cortical slices to trigger localized epileptiform events, while a 2D array of four optrodes was used to achieve stimulation with high spatial and temporal precision. The developed fused silica optrode array, which transmits visible wavelengths, will further facilitate high-channel-count stimulation. For INS, optical fibers have intially been placed outside the nerve, but intrafascicular stimulation has been demonstrated to outperform extraneural INS using 3D optrode arrays made from undoped silicon. Silicon optrodes have already been fabricated and characterized for INS, but fused silica edge-coupled to an optical fiber of the same material will transmit more power for the same input, as supported by ray tracing simulations results. The fabrication method of the glass arrays is designed based on waferscale processing of the Utah Electrode Array (UEA). The goal is to create glass arrays similar to the silicon UEA architecture. First, the glass substrate is diced into square columns by running the blade in orthogonal directions. Sacrificial rows are placed to enhance uniformity in geometry of the 10x10 grid within each unit during subsequent etching. Initially, the glass arrays were subjected to the two-step wet etching technique of shaping silicon shanks â?" dynamic and static etching. For glass, the etchant used is 49% HF, which was found to have an etch rate of about 2.3 Î¼m/min. Dynamic etching strengthened attachment of the optrodes to the backplane by rounding the base, but retained the sharp edges of the shank. Moreover, static etching was not strongly preferential at the tips and acted in the same manner as dynamic etching. These etching results are obtained because of the nature of the etching reaction not being diffusion-limited. Tapering the optrodes is then accomplished by static etching to give the optrodes a durable base junction and applying HF meniscus techiniques to sharpen the tips. Non-uniformity within an array and across five arrays are 1.73% and 2.3%, respectively. An analysis of the mechanical strength of the optrodes is also presented to validate use of fused silica arrays.
6:00 AM - TT3.16
Poly(lactic-co-glycolic acid) Density Affects in Carbon Nanofiber Composites for Myocardial Tissue Engineering Applications
David Andrew Stout 1 Adriana N Santiago-Miranda 2 Thomas J Webster 1 3
1Brown University Providence USA2University of Puerto Rico, Mayaguuml;ez Mayaguuml;ez Puerto Rico3Brown University Providence USAShow Abstract
During a myocardial infarction part of the myocardium (cardiac muscle) is deprived of blood, and therefore oxygen, destroying cardiomyocytes (cardiac contractile muscle cells) and leaving dead myocardium tissue which results in heart failure for millions of heart attack survivors worldwide. One area that has been largely omitted in cardiovascular research is the exploration of nanotechnology (or materials with one dimension less than 200nm). Recent research (in vitro) has shown that one can increase cardiomyocyte adhesion and proliferation using poly(lactic-co-glycolic acid) (PLGA) (50:50 wt.%) polymers with carbon nanofibers (CNFs). To better understand the promoted growth of cardiomyocytes, this research was to determine human cardiomyocytes functions on PLGA:CNF composites with varying PLGA densities and CNF weight ratios.
Purified conductive CNFs (99.9% by weight %, Catalytic Materials, MA) with diameters of 200nm and PLGA (50:50 PLA:PGA wt.) (Polysciences Cat #23986) were used to make the novel cardiovascular composites. The PLGA and CNF solutions were prepared individually; CNFs were sonicated in chloroform and PLGA (50:50 PLA:PGA wt.%) was diluted in THF. PLGA:CNF weight ratios (100:0, 75:25, 50:50, 25:75, and 0:100) were made by adding the required amount of CNFs in solution to the PLGA solution of different densities (0.1, 0.05, 0.025 and 0.0125g/mL). Human cardiomyocytes (Celprogen, Cat #36044-15) were seeded in human cardiomyocyte complete stem cell culture growth media (Celprogen, Cat #M36044-15S) at a cell concentration of 5.0 x 103 cells/cm2.
Cell adhesion (after 4hrs) and proliferation (at 24, 72 and 120hrs after seeding) assays (MTT), scanning electron microscopy, atomic force micrscopy, tensile tests and contact angle experiments were performed on all samples to fully characterize composite.
All experiments were performed at least in triplicate and results were compared to a control and plotted as mean Â± standard error of the mean and statistical analyses were performed. When data were compared, ANOVA software and a student T-test were used. A p-value of < 0.05 was considered to be significant.
Results and Discussions:
Results indicated an inverse relationship between PLGA density and cell adhesion/proliferation; as PLGA density increased, less cell density was observed. It was determined that the 25:75 ratio [PLGA:CNF; (wt:wt)] with a 0.25g/mL PLGA density had the highest cardiomyocytes. This may be due to the tensile tests indicating closer material characteristics of that of the normal human myocardium (heart tissue). SEM images exhibited uniform CNF dispersion within the PLGA matrix indicating close interactions between cardiomyocytes and substrates. Contact angle experiments suggested changes in wettability while conductivity experiments presented a significance conductivity difference between the composites with different PLGA densities.
6:00 AM - TT3.2
Mechanical Model of Cell Membrane Penetration by Vertical Nanowires
Xi Xie 1 Nicholas A Melosh 1
1Stanford University Stanford USAShow Abstract
For many therapeutic and scientific applications, direct access into a cellâ?Ts interior is the key for delivering various biomolecules to alter cell behavior or for intracellular assays. However, the lipid membrane presents a challenging barrier that prevents biomolecular species from entering the cytosol. Cell viability despite plasma membrane penetration by vertical nanowires (NWs) has opened new avenues for direct intracellular access to a large number of cells in parallel. Vertical nanowire array has served as universal and efficient platforms for introducing various biomolecules into a broad range of cell types. However, the exact microscopic mechanisms of the membrane penetration are still lacking. In this work, a mechanical model is proposed to predict cell membrane penetration through two mechanisms, namely â?oimpaling mechanismâ? and â?oadhesion mechanismâ?, which represent the initial contact of the cell as they land upon the NW substrate and adhesion after initial cell deposition respectively. The cell membrane tension due to indentation by nanowire is calculated using an elastic model of axisymmetric deformation of an elastic membrane indented by a probe with a hemispherical tip. The critical membrane rupture conditions are determined under tension criteria. Our results reveal that the minimum force required to induce membrane penetration is highly dependent on the membrane shape. The impaling mechanism suggests that the penetration ability linearly decreases with increasing NW radius, while NW spacing and NW height play very little effect. On the other hand, the adhesion mechanism suggests very different conclusions that small NW radius (R<100 nm), shorter NW height and large NWs spacing are all very important for penetrations. Our results provide a practical guide to designing nanowires for applications in cell membrane penetration and to optimizing the interactions between biological cells and nanofabricated structures for lab-on-chip applications.
6:00 AM - TT3.3
Two-step Growth Method for Ge Epitaxial Layer on (100) GaAs Substrate by Rapid Thermal Chemical Vapor Deposition (RTCVD)
Yeon-Ho Kil 1 Woong-Ki Hong 1 Min-Woo Seo 2 Yang-Kyu Park 1 Chel-Jong Choi 2 1
1Semiconductor Physics Research Center Jeonju Republic of Korea2Department of BIN Fusion Technology JeonJu Republic of KoreaShow Abstract
We have demonstrated two-step growth method for Ge epitaxial layer on GaAs substrate by rapid thermal chemical vapor deposition (RTCVD). In order to minimize strain caused by lattice mismatch between Ge and GaAs and the outdiffusion of Ga and As atoms in the Ge/GaAs interface, low temperature Ge seed layer was introduced in first-step growth before high temperature second-step growth. A thin Ge layer was deposited at 400 oC in the first growth constituting a buffer which enables strain relaxation and reduces the outdiffusion of Ga and As atoms. During second-step growth at 500 oC, the isolated Ge islands grew larger to impinge with other islands, and eventually coalesced into a continuous Ge film with a thickness of ~ 2 um. Finally, annealing process at 600 oC was employed to improve the surface morphology of Ge epitaxial layer. Threading dislocations density, estimated using etch pit density with the help of optical microscopy, was calculated to be 7.4 x 105 /cm2. The root mean square (RMS) roughness was measured to be 0.07 nm.
6:00 AM - TT3.4
Mechanics without Muscles: Rapid Motion of the Venus Flytrap
Qiaohang Guo 1 2 Zi Chen 3 4 Huang Zheng 5 Wenzhe Chen 1 6
1Fuzhou University Fuzhou China2FuJian University of Technology Fuzhou China3Princeton University Princeton USA4Princeton Institute for the Science and Technology of Materials Princeton USA5Fujian Radio and Television University Fuzhou China6FuJian University of Technology Fuzhou ChinaShow Abstract
The rapid motion of the Venus flytrap has intrigued scientists for centuries. Plants do not have nerves or muscles, and yet the Venus flytrap can close its trap in a fraction of a second to catch insects for nutrients. Darwin was the first to systematically study the trap closure mechanism, and commented the plant was "one of the most wonderful in the world". Several physical mechanisms have been proposed thereafter, such as the rapid loss of turgor pressure, an irreversible acid-induced wall loosening mechanism, and the snap-through model by mechanical instability, yet with no unanimous agreement among researchers. In our study, a mechanical bistable mechanism is proposed which reasonably explains the rapid closure of the Venus flytrap in a comprehensive manner, consistent with a series of experimental observations. Such bistability is theoretically modeled and validated with table-top experiments. A biomimetic flytrap robot is designed with principles learned from the Venus flytrap. Our study will provide important insights into mechanotransduction and scaling up of movements in plants in absence of nerves and muscles. By studying the mechanics of the Venus flytrap, it is also promising to design smart bio-mimetic materials and devices with snapping mechanisms as sensors, actuators, artificial muscles and biomedical devices (e.g., drug delivery systems) with a broad range of engineering applications.
6:00 AM - TT3.5
Single-molecule Heaters for Biomedical Intervention
Iris Kramberger 1 Michael Inkpen 1 Shuoren Du 1 Nicholas J Long 1 Tim Albrecht 1
1Imperial College London London United KingdomShow Abstract
A certain class of fulvalene-bridged organometallics can be switched reversibly between different conformers. Optical absorption leads to bond formation and the storage of significant amounts of energy. Thermal or catalytic back-conversion is used to restore the initial state, liberating this energy. Hence such molecules have been proposed as target systems for solar energy storage.  One of the most promising organometallic compounds that can cycle through energy conversion and release is tetracarbonyl-diruthenium fulvalene. When exposed to light with wavelengths from 325-375 nm it can store up to 30 kcal/mol in energy.  We have synthesized this compound and structurally less complex analogs to explore whether their properties can also be exploited in a biological context, for example for controlled, local release of heat at a cell membrane or attached to a particular biomolecule such as DNA. References: Vollhardt K.P.C., Weidman T.W. Synthesis, Structure, and Photochemistry of Tetracarbonyl(fulvalene)diruthenium. Thermally Reversible Photoisomerization Involving Carbon-Carbon Bond Activation at a Dimetal Center. J. Am. Chem. Soc. 1983, 105, 1676-1677
6:00 AM - TT3.6
Photophysical Properties and Antibacterial Effect of Fabricated Photofunctional Nanoporous Membrane
Bong Jin Kim 1 Kang Kyun Wang 1 Yong Rok Kim 1
1Yonsei University Seoul Republic of KoreaShow Abstract
Fabrication and photophysical study of photofunctional nanoporous alumina membrane (PNAM) were performed, and its application of photodynamic antimicrobial chemotherapy (PACT) was investigated. Nanoporous alumina membrane (NAM) was fabricated by two-step aluminium anodic oxidation process. The surface of the fabricated NAMs have controllable pore diameters (40â?"80 nm, 250nm) and unidirectionally ordered pore direction. The NAM was modified with organo-silane agent to induce covalent bonding and ionic bonding between NAM and photosensitizers. PtCP ([5,10,15-triphenyl-20-(4-methoxycarbonylphenyl)-porphyrin] platinum) was covalently bonded to the surface of the modified NAM and TSPP (tetrakis(psulfonatophenyl)porphyrin) was ionic bonded to the membrane surface. The morphology and the photophysical properties of the fabricated PNAM were studied with field emission scanning electron microscope (FE-SEM), thermo gravimetric analysis (TGA), steady-state spectroscopies, and nanosecond laser-induced time-resolved spectroscopy. For the efficacy study of PNAM in PACT, an enveloped animal virus, vesicular stomatitis virus (VSV), was utilized as a target organism. The antiviral effect of the PNAM-PACT was measured by the extent of suppression of plaque-forming units (PFU) after the activation of photosensitizers by light irradiation. In the cultures inoculated with PACT-treated VSV, the suppression of PFU was prominent, which demonstrated that PNAM was a potential bio clean-up material.
6:00 AM - TT3.7
Biomedical Application of Nanocrystalline Diamond Films Deposited by Low Temperature PE Linear Antennas MW CVD System for Orthodontical Devices
Jana Fendrychova 1 7 Vit Kopelent 2 Marie Kalbacova 3 Ladislav Senolt 4 Pavel Fendrych 5 7 Jan Vlcek 6 Andy Taylor 7 Milos Nesladek 8
1Second Faculty of Medicine, Charles University Prague Prague 5 Czech Republic23M UNITEK CZ Ltd. Prague Czech Republic3Institute of Inherited Metabolic Disorders, Charles University, 1st Faculty of Medicine Prague Czech Republic4Department of Revmathology, First Faculty of Medicine, Charles University Prague Czech Republic5Faculty of Biomedical Engineering, Czech Technical University Prague Czech Republic6Department of Physics and Measurements, Institute of Chemical Technology Prague Czech Republic7Institute of Physics, Academy Sciences CR Prague Czech Republic8Hasselt University, Institute for Materials Research (IMO) Hasselt BelgiumShow Abstract
In contemporary medicine, the explosive development of biomedical technologies and novel materials is recorded. Dentistry and its special disciplines are not excepted. In our research, we focus our attention on the dental implants. It is made of commercially pure titanium (Ti) or titanium alloy. Dental implants are used at most in two disciplines: prosthodontiscs and orthodontics. Its role in these lines differs. In prosthodontics, dental implants replace missing teeth and therefore a long term stability and strong osseointegrity is demanded. In orthodontics, dental implants play the role as the skeletal anchorage devices. Temporary Anchorage Device (TAD) is a device that is temporarily fixed to bone for the purpose of enhancing orthodontic anchorage. It allows for a fixed anchorage point that can be used to move teeth individually or en masse. Its period of use is limited, in average for six months (orthodontical treatment in general takes two years in average). For this type of implants, on the contrary, it is demanded, that the strength of osseointegrity would not be as high as in prosthodontical type of implants. The reason is, above all, an easy removal of it out of the bone, when the treatment goal is achieved. Unfortunately, it often happens, that the implant grows into the alveolar bone. 3M UNITEK Company handled the problem of overgrowing of TADs into the alveolar bone by a special mechanical configuration of the thread. The IMTECâ"¢ ORTHO Implant (TAD) has a modified buttress thread form: 1.8 mm diameter designed for strength and a 45 degree lead-in angle and 90 degree trailing angle, this thread form assists in insertion and retention of the implant. Our research is focused on improvement of TADs conditions in aspect of prevention of its overgrowing into the alveolar bone without loose of its biocompatibility and mechanical thread benefites. We have been solving this problems by coating of the IMTECâ"¢ ORTHO Implant by pure or boron doped nanocrystalline diamond (NCD) films using a unique pulsed plasma enhanced linear antennas microwave CVD (PELAMWCVD) system which was designed and constructed in the Institute of Physics ASCR Prague in cooperation with Leybold Optics Dresden GmbH. This unique apparatus enables to cover the IMTECâ"¢ ORTHO Implant with thin (200-400nm), smooth (Rms~10nm), adhesive and fully biocompatible NCD film at condition of low temperature (<350C). It prevents any structural or phase degradations of special titanium alloy implant. In this paper we present technological details and physical properties of IMTECâ"¢ ORTHO Implants coated with NCD films deposited by low temperature PELAMWCVD system. In addition we bring out our biomedical testing results of HUMAN FIBROBLASTS cultivation in MTT colorometric assay and HUMAN OSTEOBLASTS cultivation in McCoys medium on original TADs surface comparing with TADs coated with NCD films.
6:00 AM - TT3.8
Effect of Iron Oxide Nanoparticles on Germination and Growth of Raphanus Sativus
N. Pariona 1 2 Arturo I Martinez 1 Dale L Perry 3 R. Castro-Rodriguez 4
1Cinvestav Unidad Saltillo, Carr, km. 13 Ramos Arizpe Mexico2Universidad de la Sierra Juarez Oaxaca Mexico3Lawrence Berkeley National Laboratory Berkeley USA4Cinvestav-Merida Merida MexicoShow Abstract
Iron oxide nanoparticles (NP) have attracted great interest because of their fascinating properties and potential applications in many fields, such as in the biomedical and environmental applications . Articles published on nanotoxicology impacts have focused on animals and bacteria [2, 3]. Additionally, there is a growing interest in the environmental consequences of how nanomaterials affect plantâ?Ts growth. It has been reported that ZnO and Al2O3 NP have toxic effects at high concentrations in different plants . The present study evaluates the effect of four types of iron oxide NP on germination and growth of Raphanus sativus. In particular, we used citrate coated and uncoated Fe3O4 NP, with different critical sizes, that were prepared in our laboratory by different techniques. Six different concentrations were evaluated for each type of NP. This study concludes that the presence of iron oxide NP permits the germination of Raphanus sativus; additionally, larger plants were observed at high concentrations of iron oxide NP. It indicates that iron oxide NP promote a rapid growth of Raphanus sativus plants. Based on different materials characterization techniques such as magnetometry, transmission electron microscopy, and X-ray fluorescence, an outline of the effects of iron oxide nanoparticles on Raphanus sativus was developed. References  X. Ma, J. Geiser-Lee, Y. Deng, A. Kolmako, Science Total Environment 408 (2010) 3053â?"3061.  E. Corredor et al., BMC Plant Biology 2229 (2009) 9-45.  S.A. Blaser, M. Scheringer, M. Macleod, K. Hungerbuhler, Sci Total Environ 390 (2008) 396â?"409.  B. Nowack, T.D. Bucheli, Environ Pollut 150 (2007) 5â?"22.
TT1: General Interfaces I
Tuesday AM, April 10, 2012
Marriott, Yerba Buena, Salons 14-15
9:00 AM - *TT1.1
Cell Entry of One-dimensional Nanomaterials Occurs by Tip Recognition and Rotation
Xinghua Shi 1 Annette Von dem Bussche 1 Robert Hurt 1 Agnes Kane 1 Huajian Gao 1
1Brown University Providence USAShow Abstract
Materials with high aspect ratio, such as carbon nanotubes and asbestos fibres, have been shown to cause length-dependent toxicity in certain cells because these long materials prevent complete ingestion and this frustrates the cell1â?"3. Biophysical models have been proposed to explain how spheres and elliptical nanostructures enter cells4â?"8, but one-dimensional nanomaterials have not been examined. Here, we show experimentally and theoretically that cylindrical one-dimensional nanomaterials such as carbon nanotubes enter cells through the tip first. For nanotubes with end caps or carbon shells at their tips, uptake involves tip recognition through receptor binding, rotation that is driven by asymmetric elastic strain at the tubeâ?"bilayer interface, and near-vertical entry. The precise angle of entry is governed by the relative timescales for tube rotation and receptor diffusion. Nanotubes without caps or shells on their tips show a different mode of membrane interaction, posing an interesting question as to whether modifying the tips of tubes may help avoid frustrated uptake by cells.
9:30 AM - TT1.2
DNA-coated Microbubbles with Tunable Ultrasound Contrast Activity for Thrombin Sensing
Matthew A. Nakatsuka 1 Mark J Hsu 2 Sadik C Esener 1 2 Jennifer N Cha 1 Andrew P Goodwin 1
1University of California, San Diego La Jolla USA2University of California, San Diego La Jolla USAShow Abstract
Ultrasound imaging is a critical tool for diagnosis, treatment, and monitoring of disease. Because it is safe, non-invasive, and inexpensive, it is one of the most widely used imaging modalities in the world. In order to enhance image signal-to-noise ratios, ultrasound contrast agents with high echogenicity such as gas-filled lipid microbubbles have been adopted. When insonated at specific resonance frequencies, these microbubble contrast agents oscillate and generate signals that can be easily distinguished from the surrounding tissues. These acoustic properties are highly dependent on the physical properties of the encapsulating shell at the interface between the gas and the surrounding environment; stiffer shells provide weaker signals. However, using contrast agents to identify growing areas of inflammation has proven a difficult challenge. To address this problem, we have developed a novel microbubble formulation that changes its acoustic properties in the presence of thrombin, a precursor to the potentially deadly deep venous thrombosis. The formulation incorporates DNA-poly(acrylic acid)-lipid conjugates into the encapsulating shell. Hybridization of the DNA side groups via a thrombin binding aptamer creates crosslinks within the shell, increasing its stiffness, which prevents microbubble oscillation and mutes the resulting signal. Once exposed to thrombin, the aptamer preferentially binds to the biomarker, removing crosslinks within the shell and allowing the bubble to oscillate freely. Thus, the acoustic properties of this smart imaging agent are controlled by how its interface interacts with specific biomarkers within its environment. We have demonstrated that this enhancement can be achieved with nanomolar concentrations of thrombin in serum, and have demonstrated up to 100-fold imaging signal enhancement after activation with complementary DNA strands as sample analytes. Further work will include activation and imaging within live rabbit models to study the unique properties of this new contrast agent.
9:45 AM - TT1.3
Multiscale Modeling of Organic-Inorganic Interface: From Molecular Dynamics Simulation to Finite Element Modeling
Denvid Lau 1 Oral Buyukozturk 1 Markus J Buehler 1
1MIT Cambridge USAShow Abstract
Bi-layer material systems are found in various engineering applications ranging from nanoscale components, such as thin films in circuit boards, to macroscale structures, such as adhesive bonding in aerospace and civil infrastructure. They are also found in many natural and biological materials such as nacre or bone. The structural integrity of a bi-layer system depends on properties of both the interface and the constitutive materials. In particular, interfacial delamination has been observed as a major integrity issue. Here, we present a model to predict the intrinsic shear strength between organic and inorganic materials, based on a molecular dynamics (MD) simulation approach combined with the metadynamics method, used to reconstruct the free energy surface between attached and detached states of the bonded system. We apply this technique to model an epoxy-silica system that primarily features non-bonded and non-directional van der Waals and Columbic interactions. The intrinsic strength between epoxy and silica derived from the molecular level is used to predict the structural behavior of epoxy-silica interface at the macroscopic length scale by applying a finite element approach using a cohesive zone model (CZM). The behavior of the CZM is governed by the traction-separation relationship which includes the definition of the initial stiffness, damage initiation threshold, and damage evolution properties. The corresponding parametric studies on these three parameters have been conducted which show that the interfacial properties are strongly correlated with the morphology of material at the epoxy-silica interface. Experiment for quantifying interfacial fracture toughness of epoxy-silica system using superlayer approach was conducted for verifying the applicability of our proposed multiscale model. Our prediction shows a good agreement with experimental data of the interfacial fracture toughness and the associated morphology of material captured under the scanned electronic microscope (SEM). The method used here provides a powerful new approach to link nano to macro for complex heterogeneous material systems.
10:00 AM - TT1.4
Ultrafast Nano Scale Solution Patterning Utilizing Solvent Evaporation Driven Double-dewetting Edge Lithgoraphy
Kwang-Ho Lee 1 Gun-Young Jung 1 2
1GIST Gwangju Republic of Korea2GIST Gwangju Republic of KoreaShow Abstract
During the last few decades, researchers have been investigating simple, inexpensive, and easy patterning technologies. Nowadays, conventional patterning technologies such as photolithography and metal deposition systems have been developed and are now widely used in modern electronics industry for the mass production of micro- and nanoscale patterns. With the advent of organic electronics age, the conventional photography methods are not appropriate for organic functional polymer. So, direct solution-processable and printable methods such as micro contact printing (Î¼CP), dewetting, ink-jet printing and capillary force lithography (CFL) have been developed for the patterning of organic functional materials.1 Recently, other researches on edge lithography have been explored, in which nanoscale patterns can be produced at the edges of microscale patterns.2 The solution-processable edge lithography techniques developed to date typically utilize a PDMS stamp to make channels to confine the precursor solution at a certain external pressure, which may cause distortion of pattern resolution due to the sagging or pairing effects while being pressed for the process duration.3 To overcome these problems, we develop an innovative solution processable edge lithography, what we call, double-dewetting edge lithography (DDEL). The polymer solution spontaneously dewets the hydrophobic regions and covers only hydrophilic regions on a surface energy-engineered substrate, which is achieved by combination of the conventional photolithography and a subsequent hydrophobic treatment of the exposed areas. Then, the secondary dewetting occurs through coffee stain effect during the solvent evaporation, leaving polymer edge patterns behind. The whole double-dewetting phenomena complete within 1 sec. This technique is a fast, cost-effective and easy direct solution patterning method, which enables nanoscale polymer edge patterns from various micron-scale platforms including lines, angular and irregular shapes.  E. Menard, M. A. Meitl, Y. Sun, J-U. Park, D. J. L Shir, Y-S. Nam, S. Jeon, and J. A. Rogers, Chem. Rev. 107, 117-1160 (2007).  B. Radha and G. U. Kulkarni, Small, 2009, 5, 2271.  Y. Xia and G. M. Whitesides, Angew. Chem. Int. Ed., 1998, 37, 550. Acknowledgments This work was supported by basic science research program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. R15-2008-006-03002-0, CLEA, NCRC) and the IT R&D program of MKE/KEIT (10030559, Development of next generation high performance organic/nano materials and printing process technology). The integrated molecular system program at GIST also partially supported this project.
10:15 AM - *TT1.5
Hirarchical Scaffolds and Composites with Practical Dimensions
Eduardo Saiz 1 Claudia Walter 1 Suelen Barg 1 Cecilia Mattevi 1 Antoni P Tomsia 2
1Imperial College of London London United Kingdom2Lawrence Berkeley National Laboratory Berkeley USAShow Abstract
One of the major challenges faced by materials science today is the development of new, stronger and tougher lightweight structures needed to support advances in strategic fields as diverse as building, transportation, energy or healthcare. The idea of answering this challenge by using complex hierarchical designs, including some that replicate structures found in nature, has enormous appeal but also high risk. This is primarily due to the current lack of processing techniques able to implement these structural hierarchies in practical dimensions. In this talk we will describe new approaches towards the fabrication of hierarchical composites and porous structures. In particular, we will discuss the use of freeze casting. This technique can be used to create scaffolds and hybrid, hard-soft composites with unique layered and brick-and-mortar structures that can exhibit unusual combination of mechanical properties. For example, freeze-casted Al2O3-PMMA composited can exhibit fracture toughness that are up to 300 times higher (in terms of energy) than those of their main component, alumina. In specific terms their mechanical properties are comparable to those of aluminium alloys. These results will be discussed and the possibilities of freeze casting, its advantages and drawbacks, will be compared with those of alternative techniques. The goal is to summarize the state of the art and point out future research directions.
10:45 AM - TT1.6
Long-term Adhesion Studies of Polyimide to Inorganic and Metallic Layers
Juan Sebastian Ordonez 1 Boehler Christian 1 Martin Schuettler 1 Thomas Stieglitz 1 2
1University of Freiburg Freiburg Germany2Bernstein Focus Neurotechnology - Freiburg/Tuebingen Freiburg GermanyShow Abstract
Delamination between thin-film metal and substrate is a major cause of failure in polyimide based neural microelectrode arrays. Adhesion defines to which extent a mechanical force applied to the metal will be dissipated by the much more robust polymer substrate. Since noble metals donâ?Tt provide a proper bond to polyimide, adhesion promotion techniques are necessary to create reliable neural interfaces that withstand mechanical and electrical loads over decades implanted in the body. Chemical adhesion is the only way to establish a long-term bond that will allow two materials to stick to each other even in a wet environment, given that the adhesion is not affected by the presence of water. This study assesses, by means of peel and shear tests, a long-term quantitative and comparative study of the adhesion and adhesionâ?Ts behavior of polyimide to various metallic and other inorganic layers of interest. Polyimide (BPDA-PPD) is cured on the layers, which involve platinum, gold and tungsten-titanium as commonly used implant metals and diamond-like carbon (DLC), silicon carbide (SiC), silicon oxide (SiO2) and silicone nitride (SiN) as potential adhesion promoters to be used later as intermediate layers between metal and polyimide. The adhesion was observed over one year under accelerated-aging conditions by storing the specimens in 60Â°C saline (40000 hrs at 37Â°C). Only silicon carbide and amorphous carbon showed almost unaffected adhesion to polyimide over the testing period. No water intrusion in the interface is observed and the strong bond is almost fully maintained even after one year of incubation. This suggests that carbon binding occurring between polyimide and layers of DLC, SiC, SiO2 or SiN is responsible for a stable bond. The platinum-polyimide interface shows bubble formation at the interface after some weeks of incubation and a decrease in the adhesion force. While gold, SiN and SiO2 show a week initial bond strength and absolute delamination after short time of incubation, WTi does provide a strong but decreasing bond. However, the change in the mechanical properties of the polyimide on top of the WTi is much more interesting, turning into a brittle layer after 750 hours in saline. DLC provides the strongest bond, nevertheless is silicon carbide a better adhesion promoter for platinum metallizations as it offers a chemical bond partner (Si) for the metal structures (mostly platinum) required in neural interfaces. Furthermore, the implementation of an inorganic adhesion promoter is advantageous for neural interfaces, as it avoids the fabrication of bimetallic layer combinations that can lead to galvanic corrosion, hence preventing failure of the device and protecting the biological environment from potentially toxic agents. The study successfully analyses the decay of adhesion during long-term accelerated aging, retrieving information on the chemical nature of the bond of polyimide to selected other materials.
11:30 AM - TT1.7
Molecular and Surface Interactions of Comb-type Polymer Polystyrene-graft-Polyethylene Oxide (PS-g-PEO)
Ling Zhang 1 Qingxia Liu 1 Hongbo Zeng 1
1University of Alberta Edmonton CanadaShow Abstract
Molecular and surface interactions of well-defined comb-type polymer polystyrene-graft-polyethylene oxide (PS-g-PEO) were measured using a surface forces apparatus (SFA). The impact of two different end-function groups â?"OH and â?"COOH on PEO side chains on the interaction forces were investigated in both symmetric (polymer vs. polymer) and asymmetric (polymer vs. mica) configurations. Long-range repulsive forces were measured between the polymer brushes in aqueous solutions, which were shown to have a steric origin and could be well described using the Alexander-de Gennes model. Contact angle measurement showed the water contact angle on PS-g-PEO surface decreased by over 15 degrees in about one min after the water droplet in contact with the polymer surface, which indicates that the PEO side chains are able to extend into water due to the strong van der Waals forces and hydrogen bonding between hydrophilic PEO side chains and water. The extended PEO side chains can act as a swelling brush, leading to the strong steric forces measured by SFA. Atomic force microscope (AFM) was employed to provide complementary information regarding the surface morphology before and after the polymer is exposed to water. Variation of the solution pH and ionic strength showed stronger impact for PS-g-PEO with â?"COOH end-function group than that with â?"OH end-function group on the surface forces. Our results provide important insight into the design and development of novel functional polymers and coatings with strong antifouling capabilities, i.e., preventing the non-specific binding of bacteria, cells and proteins with significant engineering and biomedical applications.
11:45 AM - TT1.8
Direct Probing of Micromechanical Properties of Hydrogen-bonded LbL Microcapsule Shells with Different Chemical Compositions
Milana O Lisunova 1 Irina Drachuk 1 Olga Shchepelina 1 Vladimir V Tsukruk 1
1Gatech Atlanta USAShow Abstract
The mechanical properties of hydrogen-bonded layer-by-layer (LbL) microcapsule shells constructed from tannic acid (TA) and poly(vinylpyrrolidone) (PVPON) components have been studied in both the dry and swollen states. In the dry state, the value of the elastic modulus was measured to be within 0.6-0.7 GPa, which is lower than the typical elastic modulus for electrostatically assembled LbL shells. Three-fold swelling of the LbL shells in water results in a significant reduction of the elastic modulus to values well below 1 MPa. The increase of the molecular weight of the PVPON component from 55 kDa to 1,300 kDa promotes chain entanglements and causes a stiffening of the LbL shells with a more than twofold increase in elastic modulus value. Moreover, adding a polyethyleneimine prime layer to the LbL shell affects the growth of hydrogen-bonded multilayers which consequently results in dramatically stiffer, thicker, and rougher LbL shells with the elastic modulus increasing, up to 4.3 MPa. Such an ability to alter the elastic modulus in a wide range is critically important for the design of highly compliant microcapsules with tunable mechanical stability, loading ability, and permeability.
12:00 PM - *TT1.9
Morphometric Analysis of Complex Interfaces
Klaus Mecke 1 Gerd Schroeder-Turk 1
1University Erlangen-Nuremberg Erlangen GermanyShow Abstract
The 'shape' of interfaces imbedded in space is a remarkably unprecise defined concept which mainly depends on applications in mind. One systematic approach is provided by integral geometry which furnishes a suitable family of morphological descriptors, so-called tensorial Minkowski functionals. They are related geometrically to curvature integrals and physically to thermodynamic properties of structured materials, what makes them most suitable to derive structure-property relations for condensed matter bounded by complex interfaces. This analysis is applied to biopolymer networks, to granular bead packs, to biomaterials such as bone and wood as well as to triply-periodic minimal surfaces which are often used as structural models for self-assembled amphiphilic phases.
12:30 PM - TT1.10
In-situ Raman Spectroscopy of H2 Gas Interaction with Layered Pd/MoO3 at Different Temperatures
Jian Zhen Ou 1 Sivacarendran Balendhran 1 David Yao 1 Kay Latham 1 Kourosh Kalantar-zadeh 1
1RMIT University Melbourne AustraliaShow Abstract
MoO3 is a well-known semiconducting metal oxide used for H2 sensing applications especially while combined with catalytic metals such as Pt or Pd. However, the H2 interaction mechanism is still not well understood. In this work, we employ in-situ Raman spectroscopy to investigate the H2 gas interaction with the layered Pd/MoO3 film at different temperatures. Layered MoO3 is prepared via a conventional thermally evaporative method. 10 mg of the MoO3 powder is placed at the centre of a horizontal furnace. Transparent silica substrate is located at a 16 cm distance from the central hot spot, where the temperature is 460Â°C. Thermal deposition is carried out for 1 hr using argon gas at a constant flow rate of 800 sccm. Later, Pd films of approximately 25 Ã. are DC sputtered onto the sample. The scanning electron microscopy (SEM) image indicates that the film consists of hexagonal plates with the average width and length of 0.7 and 1 Î¼m, respectively. Each of these plates is composed of nanometer-thick layers with the average thickness of â^¼30 nm. X-ray diffraction (XRD) pattern reveals that the crystal structure of the film is dominated by orthorhombic structure. Raman spectrum of the film further confirms the outcome obtained from XRD study as strong peaks are observed at 284, 671, 821 and 995 cm-1. The 284 cm-1 peak represents the bending for the double bond (Mo=O) vibration. The 671 cm-1 peak is assigned to the triply coordinated oxygen (Mo3â?"O) stretching mode. The 821 cm-1 peak is for the doubly coordinated oxygen (Mo2â?"O) stretching mode, and the peak at 995 cm-1 is assigned to the terminal oxygen (Mo6+=O) stretching mode. Other peaks at 339 and 381 cm-1 can be assigned to Moâ?"O bending modes, while the peak at 477 cm-1 represents the same mode as that of 671 cm-1. In addition, the peak at 160 cm-1 assigns to the lattice mode. The Raman spectra of the film are investigated after exposure towards 1% H2 at 23 and 100Â°C. At 23Â°C, Raman intensities of the strong peaks at 284, 671 and 821 cm-1 are greatly reduced by 87.5%, 86.5% and 97%, respectively. The blue shift of the peak at 821 back to 815 cm-1 and the appearance of small new HxMoO3 peaks at 204 (deformation mode), 441 (Mo3-O stretching mode) and 1006 cm-1(Mo=O stretching mode), all indicate the crystal transformation from original orthorhombic structure into HxMoO3 in the presence of H2. A new peak which appears at 718 cm-1 suggests that the traces of MoO3-x also appear. Other noticeable peaks, which appear at 393, 483, 866 and 962 cm-1, can be assigned to the deformation mode, Mo3-O, and Mo=O stretching modes of MoO3-x, respectively. However, at 100Â°C, the Raman intensity response decreased. There is no clear evidence of new peaks formation in the presence of H2. This could be due to the significant enhancement of decomposition of HxMoO3 and oxygen vacancies recombination processes at high temperature (>100Â°C).
12:45 PM - TT1.11
Molecular Recognition of Solid Interfaces by Engineered Peptides
Mehmet Sarikaya 1
1University of Washington Seattle USAShow Abstract
Proteins enable biology to be viable through molecular interactions (such as in antigen-antibody, ligand-receptor, and drug-target) with
Symposium OrganizersUlrike G. K. Wegst, Thayer School of Engineering at Dartmouth
Amal M. K. Esawi, The American University in Cairo
Guy Genin, Washington University, St. Louis
Tianjian Lu, Xi'an Jiaotong University
Jonathan Wilker, Purdue University
Wednesday PM, April 11, 2012
Marriott, Yerba Buena, Salons 14-15
2:30 AM - TT5.1
Interactions of Osteoclasts with Nanostructured Biomimetic Bone
Douglas Rodriguez 1 Edgardo J Toro 2 Shannon Holliday 2 Laurie Gower 1
1University of Florida Gainesville USA2University of Florida Gainesville USAShow Abstract
Bone is a hierarchical composite based on the fundamental unit of a mineralized collagen fibril. The crystals of hydroxyapatite (HA) are extremely small and embedded within the interstices of the collagen fibril, leading to an interpenetrating organic-inorganic composite structure. The hydroxyapatite nanocrystals are also uniaxially aligned parallel to the long axis of the fibril, which leads to the anisotropy of mechanical properties. With roughly 50:50 volume percent organic:inorganic phases, bone can be considered either a particle-reinforced organic matrix composite (HA nanocrystals within collagen matrix), or it can be considered a fiber-reinforced ceramic matrix composite (collagen fibrils in HA matrix). It is this nanostructured architecture which provides bone with unique mechanical properties and biological activity. In the latter case, while bone can be resorbed and remodeled, synthetic HA is very insoluble and generally slow to degrade in the body. But the nanocrystals of HA in bone are metastable and can be resorbed once the protective collagen is removed. This is accomplished by osteoclasts, which secrete enzymes for removal of the collagen, and a weak acid to resorb the mineral. Our group has been able to duplicate the interpenetrating nanostructured architecture of bone, providing us with the unique opportunity to examine osteoclast interactions with a biomimetic bone substrate. We are able to achieve intrafibrillar mineralization of collagen using a polymer-induced liquid-precursor (PILP) mineralization process, where synthetic polyaspartic acid peptides or osteopontin, a polyaspartic acid rich protein, is used to induce a hydrated amorphous precursor to HA. This PILP precursor can infiltrate the interstices of the collagen fibrils, which upon solidification and crystallization, leaves the collagen fibrils embedded with nanocrystals of hydroxyapatite. We have utilized this PILP process to mineralize a variety of collagen-based scaffolds, and then examined the interactions of osteoclasts with the scaffolds by measuring markers of osteoclastic bone resorption, actin rings and ruffled border formation. We confirmed the results by examining resorption pits by scanning electron. One key finding is that the polymeric process-directing agent, such as osteopontin versus polyaspartic acid, can have a pronounced effect on osteoclast behavior. In conclusion, these biomimetic bone substrates provide a useful platform for examining cell-biomaterial interactions. Our ultimate goal is to identify bone biomimetics in which both structural characteristics and the ability to integrate with bone cells are optimized for clinical purposes.
2:45 AM - TT5.2
Study of a Novel ALD Al2O3-parylene Bi-layer Encapsulation for Biomedical Implants
Xianzong Xie 1 Loren Rieth 1 Florian Solzbacher 1 2
1University of Utah Salt Lake City USA2University of Utah Salt Lake City USAShow Abstract
Atomic layer deposited (ALD) Al2O3 has been widely used as encapsulation material for organic LEDs and solar cells due to its low water vapor transmission rate (WVTR) (~5Ã-10-6 g-H2O/m2-day). However, its coating performance for implantable devices still needs investigation. Parylene has been commonly used as encapsulation for biomedical implants, such as Utah Electrode Arrays (UEAs). The idea of combing Al2O3 and parylene is based on the concept that Al2O3 works as moisture barrier and parylene as ion barrier. Parylene also prevent direct contact of water with Al2O3. In this paper, Al2O3 was deposited by both thermal and plasma-enhanced ALD on interdigitated electrodes (IDEs) for comparison using Fiji F200 (Cambridge NanoTech). AFM micrographs show that Al2O3 films deposited on silica substrate (RMS surface roughness of 0.17 nm) by thermal and plasma-enhanced ALD have RMS surface roughness of 0.51 nm and 0.48 nm, respectively. XPS shows that plasmaâ?"enhanced ALD films had oxygen to aluminum ratio of 1.41 while thermal ALD Al2O3 is 1.36, showing both are close to stoichiometric value of 1.5. A 6-Âµm thick parylene-C layer was deposited by CVD using Gorman process on top of Al2O3 and saline A-174 (Momentive Performance Materials) was used as adhesion promoter. The samples were soaked in 1Ã- PBS at 37 Â°C and 57 Â°C, 67 Â°C and 80 Â°C for accelerated lifetime testing over 6 months. Electrochemical impedance spectroscopy (EIS) and chronoamperometry were used to evaluate the performance of the encapsulation. Our study showed that the leakage current remained at small (~ 20 pA) and the electrochemical impedance was consistently high (~ 3.5 MÎ© at 1 kHz) after 6 months of soaking test at 67 Â°C (equivalent to approximate 48 months of soak testing at 37 Â°C). Comparing with parylene and Al2O3 control samples, the Al2O3-parylene coated sample showed lower leakage current and higher insulation impedance. The Al2O3 coated samples failed immediately after being soaked in PBS due to water corrosion. The phase of parylene-C coated sample declined after 5 days of soaking test, suggesting water absorption of parylene film. The Al2O3-parylen C coated samples had phase close to 90Â° during the whole soak testing, indicating no obvious water absorption. Samples at higher temperature are expected to fail faster. However, no obvious difference has been observed yet for samples soaked at different temperatures. This is because the coating would last much longer than the current testing period and long-term soak testing is needed for observing the temperature effect on lifetime. In conclusion, in-vitro soaking tests show that the Al2O3-parylene bi-layer encapsulation scheme is promising encapsulation in terms of insulation performance. Long-term in-vitro soaking tests are being performed to further investigate the suitability of this novel encapsulation scheme for biomedical implants.
3:00 AM - *TT5.3
Development of Tough and Adhesive Hydrogels for Biotechnology and Tissue Regeneration
Gudrun Schmidt 1 Chia-Jung Wu 1 Akhilesh Gaharwar 1 Patrick Schexnailder 1
1Purdue University West Lafayette USAShow Abstract
We have developed a series of poly(ethylene glycol) - silicate nanocomposite hydrogels with unique chemical, mechanical and biological properties. The injectable nanocomposite precursor solutions can be covalently cross-linked via photopolymerization. The resulting hydrogels have interconnected pores, high elongation and toughness. These properties can be tuned by changing the hydrogel composition, controlling polymer-nanoparticle interactions and degree of cross-linking (both physical and covalent). Covalent cross-linking of polymer chains leads to the formation of an elastic hydrogel network, whereas additional physical cross-linking between nanoparticles and polymer chains induces viscoelastic properties. At high deformations covalent bonds may be broken but reversible and physical bonds rebuild and self-heal the overall network structure. Addition of silicate nanoparticles (or hydroxyapatite) also enhances bulk adhesiveness of the hydrogel as these materials stick to soft tissue as well as to hard surfaces. In addition, mammalian cells readily attach, spread and proliferate on the hydrogel surfaces. Collectively, the property combinations such as toughness, interconnected network, bulk adhesiveness as well as cell attachment and growth provide inspiration and opportunities to engineer mechanically strong and elastic hydrogel matrixes for biotechnology and tissue engineering applications.
3:30 AM - TT5.4
Time Study of Ultraviolet Grafting of Poly (N-isopropylacrylamide-co-acrylamide) Grafted onto Tissue Culture Polystyrene Surface for Cell Sheet Engineering
Paranee Traichedtakul 1 Nguyen T Thuyen 1 Nontapat Teekeng 1 Thanakom Klaewvitkij 1 Wanwipa Siriwatwechakul 1
1Siridhorn Institute of Technology, Thammasat University Pathumthani ThailandShow Abstract
This study introduces a new technique to graft temperature sensitive poly(N-isopropylacrylamide-co-acrylamide), PNIAM-co-AM, onto a tissue culture polystyrene (TCP) surface for tissue engineering application. At 37Â°C, the grafted surface exhibits hydrophobic characteristics, which allow cells to adhere and proliferate. When the temperature of the environment drops below 32Â°C, the surface characteristic changes to hydrophilic. As a result, the adherent cells detach from the substrate without using any digestive enzymes. The different UV exposure times were investigated, and the optimized exposure time was found to be one hour. The characterization of PNIAM-co-AM grafted surfaces has been studied by Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR), Atomic Force Microscopy (AFM) and Contact Angle Measurement. The contact angle of the grafted and control TCP surfaces was measure for temperatures ranging from 20 - 45Â°C. The results showed the hydrophilic-to-hydrophobic transition at temperature around 30-32Â°C. The Atomic Force Microscopy (AFM) results have further supported for contact angle data. Applications of the grafted TCP in tissue engineering were investigated by using L929 cell line in cell attachment, cell proliferation, and cell sheet detachment. The cytoxicity of PNIAM-co-AM grafted TCP was also tested to ensure that the grafted TCP was non-toxic. L929 cells were found to be able to detach from the PNIAM-co-AM grafted TCP surface at 20 Â°C, and they could proliferate on a new commercial TCP surface.
4:15 AM - *TT5.5
Structure, Biomechanics, and Mechanobiology in the Attachment of Tendon to Bone
Stavros Thomopoulos 1
1Washington University St. Louis USAShow Abstract
The attachment of dissimilar materials is a major challenge because of the high levels of localized stress that develop at such interfaces. An effective biologic solution to this problem can be seen at the attachment of tendon (a compliant, structural â?osoft tissueâ?) to bone (a stiff, structural â?ohard tissueâ?). The unique transitional tissue that exists between uninjured tendon and bone is not recreated during healing, so surgical reattachment of these two dissimilar biologic materials often fails (e.g., the incidence of recurrent tears after rotator cuff repair may be as high as 94%). Tissue engineering strategies hold promise for improving the healing process and include the use of mechanical stimulation as a means to promote matrix synthesis. To develop successful strategies for tissue engineering at the tendon-to-bone insertion site we must first understand how the cells at the insertion respond to changes in their mechanical environment, i.e., their â?omechanobiology.â? Our research explores structure-function relationships at the natural tendon-to-bone insertion and the role of mechanobiology for the development, healing, and tissue engineering of the tendon-to-bone insertion site. Our recent work has shown that: 1) the tendon-to-bone insertion is a functionally graded material with regard to its extracellular matrix composition, its structural organization, its mineral content, and its mechanical properties, 2) mechanical loading is necessary for the maturation of the insertion into a functionally graded material, 3) low levels of mechanical load are beneficial to tendon-to-bone healing while high levels of load are detrimental to healing, and 4) mechanobiology factors control collagen fiber orientation, matrix synthesis, and mechanical properties of tissue engineered constructs for tendon-to-bone repair. Taken together, these results provide guidance and a theoretical framework for our ongoing efforts to apply mechanobiologically-based tissue engineering strategies to improve healing and surgical repair of the tendon-to-bone insertion.
4:45 AM - TT5.6
Titania Nanodots Film for Cell Culture Application
Kui Cheng 1 Yi Hong 1 Mengfei Yu 2 Wenjian Weng 1
1Zhejiang University Hangzhou China2Zhejiang University Hangzhou ChinaShow Abstract
Cell culture is an important technique in many biological researches. One of the key issues of cell culture is how to harvest the cells. So far, trypsin digestion and mechanical way are the most prevalent methods. However, both methods caused cell damage to certain extent. Recently, T. Okanoâ?Ts group developed a new way to harvest cells through a temperature-sensitive polymer modified surface, which is rather hydrophobic at body temperature and turns into hydrophilic when temperature goes down. Cells initially attach on such surfaces and then detach spontaneously at lower temperature owing to the wettability variation. With such method, cells, or even cell membranes, which contain both cells and extracellular matrix, could be easily obtained. In this work, surfaces consist of nanostructured titania, which could transform from rather hydrophobic to hydrophilic upon UVA irradiation, were prepared and utilized for cell culture. The results indicated that the surfaces with different nanodots parameters could eventually modulate the wettability surface, absorption of UVA and cell attachment. After one week cell culture, a continuous osteoblast cell membrane could form, and easily harvested after 30 min UVA irradiation. The detached cells showed good activity and could be used for further subculture. Moreover, biocompatibility test indicated that no detrimental effects were found for titania nanodots under UVA irradiation. Such photo induced cells detachment showed good potential in cell culture.
5:00 AM - *TT5.7
Forensic Finite Simulations of Case Specific Skull Fracture
Lars Pilgaard Mikkelsen 1 Tina L Skytte 1 Niels Lynnerup 2
1Technical University of Denmark Roskilde Denmark2University of Copenhagen Copenhagen DenmarkShow Abstract
An important issue in forensic medicine is to determine how a certain skull fracture arose. This information can be critical to establishing if a criminal offense has taken place. Even though all suspicious death cases as a standard already now is proceed through a CT-scan, the achieved data is mainly used as a visualization and documentation tool. Today, the medical examiner chiefly relies on his experience since only a few scientific methods are considered sufficiently reliable. Nevertheless, during the latest decade computers and finite element codes have reached a stage where accurate numerical finite element predictions of complex fracture processes in large 3-D structures are possible, e.g. in a full 3-D finite element simulation of a skull fracture. In addition, tools are available transfer CT-scan data to a 3-D finite element model making it possible to base the analysis on a person specific skull. In the presented study, this procedure is demonstrated using the software Simpleware on a CT-scan from a specific forensic case. Based on this, a 3-D finite element model of the skull is extracted where the skull material as a first step is considered as a homogeneous isotropic linear elastic material. Even though, only a rather simple geometrical part of the skull is considered, some manual work improving the achieved mesh is necessary in order to get a workable model. In the subsequently finite element simulation, a simple element removing algorithm describing the fracture process is used and the specific skull is simulated using a commercial dynamic finite element code, Abaqus/Explicit. The skull is exposed for a short dynamic impact from a blunted object. Based on the simulations, large sensitivity of the fracture modes is found for small changes in the initial speed of the incoming object. It was found that the time scale for the fracture process in the present simulations is found to be order of magnitude larger than the stress wave propagation. Therefore a more advanced skull fracture prediction could be performed using the Abaqus/Standard implementation of the extended finite element method XFEM in a quasi-dynamic simulation. In both cases, the fracture path is found to differ somehow from the observed fracture path in the specific case. This may do to some of the simplifications used in the model. A more realistic simulation should take into account the influence of the actually sandwich structure where the skull is build up by a spongy bone layer with a low density between two compact bone layers as well as the effects of the sutures between the bones building up the skull should be included as well as a more realistic fracture process simulation.
5:30 AM - *TT5.8
Microscale Technologies for Regeneration of Functional 3D Tissue Models In vitro
Utkan Demirci 1
1Harvard Medical School Boston USAShow Abstract
Most tissues in organisms are composed of repeating cellular structures (i.e., functional units), such as the lobule in the liver and kidney, islets in the pancreas. In vivo, the cells in these functional units are imbedded in a three-dimensional (3D) microenvironment composed of extracellular matrix (ECM) and neighboring cells with defined spatial distribution. Tissue engineering approaches therefore attempt to recreate the native 3D architecture in vitro. Recently, the convergence of nano and microscale technologies and hydrogels has resulted in the emergence of bottom-up methods where cell-laden microgels can be used as building blocks for tissue engineering and regenerative medicine. Although various microgel fabrication and assembly methods have been developed based on modifying interfaces and using microfluidics, so far, two main challenges remain: (1) to fabricate microgels composed of multiple cell types spatially confined in 3D as functional units, and (2) to assemble microgels into large complex 3D constructs rapidly in an efficient way. In the past several years, our lab has been focusing on addressing these two challenges. (1) As for fabrication of functional units, we developed a simple, multilayer photolithography method to fabricate co-culture microgels as tissue units (co-culture units) in a high throughput manner, with control over composition of cell types and their microscale spatial organization. We demonstrate the utility of this method by fabricating four different types of co-culture units, where the quality of the units was optimized by the photomask design (i.e., via overlap ratio). (2) As for assembly of microgels, we developed several different methods based on magnetics, acoustics and printing technology. We developed a magnetic assembler that utilizes nanoparticles and microscale hydrogels as building blocks to create 3D complex multi-layer constructs via external magnetic fields using different concentrations of magnetic nanoparticles. In this method, MNPs were incorporated into microgels to create a new biomaterial that maintains the biocompatibility of hydrogels, while contributing additional capabilities for culture, magnetic manipulation, and complex 3D assembly of microgels. We also developed a simple, non-invasive acoustic assembler for cell-encapsulating microgels with maintained cell viability. The microgels were assembled via acoustic field in seconds in a non-invasive manner. Besides, we developed novel cell printing technologies where microgel fabrication and assembly are integrated into one system. With cell printing, we have successfully regenerated muscle tissues, created in vitro cancer co-culture models, and engineered controlled niches for embryoid stem cells. These methods that we present would enable a better biologically relevant in vitro platform to investigate cellâ?"cell interactions in a 3D microenvironment, holding great potential in various areas, spanning tissue engineering, regenerative medicine, pharmacological studies and high throughput applications.
TT4: Interfaces Plus Biomaterials
Wednesday AM, April 11, 2012
Marriott, Yerba Buena, Salons 14-15
9:15 AM - *TT4.1
Iron/Iron Oxide Core/Shell Nanoparticles for Magnetic Hyperthermia Treatment
Ian Baker 1 Katsiaryna Kekalo 1
1Dartmouth College Hanover USAShow Abstract
Magnetic nanoparticles accumulated in tumors either by direct injection or by using tumor-targeted antibodies introduced though the vasculature and subjected to an alternating magnetic field (AMF) are being pursued for cancer therapy. The localized heating of the tumor, via nanoparticle heating from the AMF, to 44-45oC for sufficient time causes apoptosis of the tumor cells. This presentation will discuss the preparation of novel iron/iron oxide core/shell nanoparticles for this purpose using a microemulsion method and their characterization using scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometry. The particles are produced with a cetyl trimethyl ammonium bromide coating, which is subsequently replaced with either a phospholipid or dextran coating. The effects of these coatings as well as influence of additions of cobalt on both the nanoparticlesâ?T magnetic properties and heating behavior in an alternating magnetic field will be discussed. A comparison with the behavior of dextran-coated iron oxide nanoparticles will be presented. Supported by NIH grant 1U54CA151662-01.
9:45 AM - *TT4.2
Electrospun Nanofibers for Regenerative Medicine
Younan Xia 1
1Georgia Institute of Technology Atlanta USAShow Abstract
I will discuss how electrospinning can be modified to engineer the composition, structure and alignment of nanofibers. For example, by mixing a sol-gel precursor with an alcohol soluble polymer, my group has extended the capability of electrospinning to fabrication of composite and ceramic fibers with excellent size control down to tens of nanometers. Additionally, my group has made a number of important modifications to the electrospinning setup. Using a coaxial spinneret, my group shows that it is feasible to manufacture porous, hollow, and core-sheath nanofibers and control the surface chemistry of resultant fibers by tuning the core and sheath solutions. My group has further used patterned electrodes as collectors to uniaxially align arrays of nanofibers. These arrays could be readily stacked into structures for device fabrication and tissue engineering. In the second part of this talk, I will discuss the use of electrospun nanofibers as scaffolds for both neural and bone tissue engineering. Specifically, I will focus on the use of aligned nanofibers to control the differentiation of embryonic stem cells into different types of neural lineages and to guide the outgrowth of neurites for peripheral nerve repair. I will also discuss how nanofiber scaffolds can be designed for injury repair at the insertion site between tendon and bone, and as substitutes for dura mater in brain surgery.
10:15 AM - TT4.3
Correlative Microscopy Study of FIB Patterned Stainless Steel Surfaces as Novel Nano-structured Stents for Cardiovascular Applications
Michael Schmidt 1 Feroze Nanzeen 2 Gregoire Herzog 2 Paul Galvin 2 Justin D Holmes 1 Nikolay Petkov 1
1Tyndall National Institute, University College Cork Cork Ireland2Tyndall National Institute, University College Cork Cork IrelandShow Abstract
Coronary artery disease is a major problem worldwide causing 7.2 million deaths worldwide annually , resulting from vascular occlusion, myocardial infarction and its complications. Stent implantation is a percutaneous interventional procedure that mitigates vessel stenosis, providing mechanical support within the artery. However, stenting causes physical damage to the arterial wall. It is well accepted that a valuable route to reduce in-stent re-stenosis can be based on promoting cell response to nano-structured stainless steel (SS) surfaces such as, for example, by patterning nano-pits in SS . In this regard patterning by Focus Ion-Beam (FIB) milling offers several advantages for flexible prototyping (i) practically any substrate material that is able to withstand high vacuum conditions of the microscope chamber can be used, (ii) there is high flexibility in the obtainable shapes and geometries by modulating the ion beam current and the patterning conditions, (iii) reduced complexity of the pattering process e.g. it is a single-step process with a possibility of real-time monitoring of the milling progression. On the other hand FIB patterning of polycrystalline metals is greatly influenced by channelling effects and re-deposition . Correlative microscopy methods present an opportunity to study such effects comprehensively and derive structure-property understanding that is important for developing improved pattering. In this report we present a FIB patterning protocol for nano-structuring features (concaves) ordered in rectangular arrays on pre-polished 316L Stainless Steel (SS) surfaces. Comprehensive investigation based on correlative microscopy approach of the size, shape and depth of the developed arrays in relation to the crystal orientation and size of the underlying SS domains, is presented. The correlative microscopy protocol is based on cross-correlation of top-view Scanning Electron Microscopy (SEM), Electron Backscattered Diffraction (EBSD), Atomic Force Microscopy (AFM) and cross-sectional SEM and TEM imaging. Additionally, various dose tests were performed, aiming at improved productivity by preserving nano-size accuracy of the patterned process. The optimal FIB patterning conditions for achieving reasonably high throughput (patterned rate of about 0.03 mm2 per hour) and nano-size accuracy in dimensions and shapes of the features, are discussed as well.  http://www.who.int/mediacentre/factsheets/fs317/en  Dalby M J, Gadegaard N, and Wilkinson, C D W 2008 J Biomed Mater Res Part A 4 973-979  Kempshall B W, Schwarz S M, Prenitzer B I, Giannuzzi L A, Irwin R B, Stevie F A 2001 J Vac Sci Technol B 19 749-754
11:00 AM - TT4.4
Hybrid Titanium/Biodegradable Polymer Implants with an Hierarchical Pore Structure
Engin Vrana 1 Agnegrave;s Dupret-Bories 1 2 Christelle Coraux 3 Dominique Vautier 1 Chrisitan Debry 1 2 Philippe Lavalle 1 2
1INSERM UMR 977 / University of Strasbourg Strasbourg France2Hocirc;pitaux Universitaires de Strasbourg Strasbourg France3INSERM U903 Reims FranceShow Abstract
In order to improve implant success rate, it is important to enhance the responsiveness of the implants to the prevailing conditions following implantation. Uncontrolled movement of inflammatory cells and fibroblasts is one of these in vivo problems and the porosity properties of the implant have a strong effect on these movements. Here, we describe a hybrid system composed of a macroporous titanium structure filled with a microporous biodegradable polymer poly(L-lactic acid) (PLLA)1. This polymer matrix has a distinct porosity gradient to accommodate different cell types (fibroblasts and epithelial cells). Overall, such a system would enable spatial and temporal control over cell migration by a gradient ranging from macroporosity to nanoporosity within the implant. Moreover, mechanical properties will be dependent mainly on the macroporous titanium frame. This will make it possible to create a polymeric environment most suitable for cell activity without the need to meet mechanical requirements with the polymeric structure against collapse. The immediate clinical application of such a system will be the prevention of restenosis due to excessive fibroblast migration and proliferation in the case of tracheal implants.2 Hybrid microporous PLLA/ Titanium tracheal implants which were designed to decrease initial stenosis and to provide a surface for epithelialization have been implanted in new Zealand white rabbits and compared to intramuscular implantation samples. Moreover, a basement membrane like modification of the implant surface was also done by Layer-by-Layer (LbL) method3,4 with Collagen and Alginate. The results showed that the commencement of stenosis can be prevented by the microporous PLLA. Following 3 weeks the implant would be ready for epithelialization with respect to the amount of tissue integration. Epithelial cell seeding shows that after 3 weeks implant surfaces were suitable for their attachment. Crosslinked Collagen/Alginate multilayers showed nanofibrillarity and they form uniform films over the implant surfaces without damaging the microporosity of the PLLA body. Human respiratory epithelial cells proliferated and migrated on these surfaces. In conclusion, Collagen/Alginate LbL coated hybrid PLLA/Titanium implants are viable options for tracheal replacement, together with in situ epithelialization. References 1. Vrana N.E., Dupret A., Coraux C., Vautier D., Debry C., Lavalle Ph., Plos One, 2011, 6, e20480. 2. Muller S., Koenig G., Charpiot A., Debry C., Voegel J.-C., Lavalle Ph., Vautier D., Advanced Functional Materials, 2008, 18: 1767â?"1775. 3. Mertz D., Vogt C., HemmerlÃ© J., Mutterer J., Ball V., Voegel J.-C., Schaaf P., Lavalle P., Nature Mater., 2009, 8, 731-735. 4. Zhang J., Senger B., Vautier D., Picart C., Schaaf P., Voegel J.-C., Lavalle Ph., Biomaterials, 2005, 26, 3353-3361.
11:15 AM - *TT4.5
Real-time Characterization of Protein Interactions with Surfaces
Matthew Dixon 1
1Biolin Scientific Linthicum Heights USAShow Abstract
There is a growing need for new technologies to quantitatively measure biologically relevant interactions with different types of materials in real-time. One technique in particular, Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D), fulfills the need for monitoring real-time dynamic adsorption and desorption phenomena. Capable of operating in liquid environments, QCM-D provides a powerful approach to analyze the in situ thickness, structural, and viscoelastic properties of both protein deposition at interfaces and also protein-protien self-association interactions. These types of interactions have implications to a wide variety of different fields and this presentation will focus on the application of the QCM-D technology to monitoring protein - surface interactions relevant to protein therapeutics. This includes antibody storage considerations with multiple container materials and adverse behavior such as protein aggregation as a result of increased concentration or additives.
11:45 AM - TT4.6
Engineering Electrospun Nanofibers for Biomedical Applications
Sha He 1 Xingyu Jiang 1
1National Center for Nanoscience and Technology Beijing ChinaShow Abstract
Electrospinning is a facile strategy to generate fibers with diameters from a few nanometers to several micrometers. Researchers could obtain various micro-/nanostructures, such as bead-on-string, tubes, cages and meshes by carefully tuning relevant parameters. These nanofibers could be assembled to form fibrous membranes with different features as well. Electrospun nanofibers and related structures have drawn considerable interest in biomedical engineering due to its simplicity and versatility. Our group has made a few explorations on the fabrication and assembly of electrospun nanofibers. For instance, we added magnetic nanoparticles into the polymer solution and electrospun nanofibers using a pair of magnetic collectors. The resulting nanofibers are uniformly aligned in one direction on collectors. We could generate necklace-like or blackberry-like nanostructures by simply tuning the ratio between polymer solution and silica nanoparticles. Besides bare nanofibers, we considered to tailor the surfaces of nanofibers to fit for more applications. We combined surface-initiated atom transfer radical polymerization and bio-inspired silicification process to tune the surface chemistry of the nanofibers, introducing versatile functional groups onto their surfaces. These tailored surfaces allowed diverse biomolecular entrapment in high payload while substantially retaining their biological activities. By taking advantage of the large surface-to-volume ratio, we used as-spun fibrous membranes as novel solid supports for immunoassays as well as protein microarrays, finding that electrospun nanofibrous membrans have great protein adsorption capacity. Compared to conventional planar substrates, electrospun nanofibrous membranes with delicate structures showed apparently promoted efficiency. Also, in order to utilizing the aligned fiber structures, we tried to replicate them with polydimethylsiloxane and the well-defined, parallel grooves were proved to be excellent guidance for neurite outgrowth.
12:00 PM - *TT4.7
Interfacial Mechanics from a Molecular Perspective
Markus J Buehler 1
1MIT Cambridge USAShow Abstract
The challenge of attaching dissimilar materials is ubiquitous in biology and across engineering materials applications, and also across length scales. Nature presents coping strategies that extend across multiple spatial hierarchies. A primary framework nature applies is the universality-diversity paradigm, wherein identical, universal units are arranged to create materials with diverse properties. This talk will highlight the structure and role of nanoscale features of various associations of such units -- itself a problem of attachment of dissimilar entities -- and challenges and opportunities associated with understanding how nanoscale and hierarchical features can toughen macroscale attachments. We review applications in two biological interfaces, focused on biomineralized materials (bone and specifically collagen-mineral interfaces) as well as spider web attachment structures.
12:30 PM - *TT4.8
Probing Chemistry and Bonding at Interfaces in Organic and Hybrid Structures with High Spatial Resolution
David W. McComb 1
1Ohio State University Columbus USAShow Abstract
Electron energy-loss spectroscopy (EELS) when performed in the scanning transmission electron microscope (STEM) is, arguably, the only technique that can provide information of chemistry and bonding in solid materials with near atomic scale spatial resolution. In the past this method has been applied extensively to the study of atomically abrupt engineered interfaces grown by thin film deposition methods. The results have been impressive, establishing that the method can be used to reveal changes in oxidation state, coordination environment and electronic structure at such interfaces. Applying STEM-EELS to the study of interfaces in organic, hybrid and biomaterials system is complicated by many factors. In this contribution I will use a number of examples to illustrate the insights that can be gained into the structure-property relationships in mineralised tissue, inorganic wear debris in periprosthetic tissue and organic solar cells. The common aspect in all of these studies is the need to probe hard/soft or soft/soft interfaces between inorganic and organic materials. This presents considerable challenges associated with sample preparation, electron beam damage and achievable spatial resolution. I will show that it is possible in many cases to obtain both qualitative and quantitative chemical information that can significantly enhance our understanding in these complex systems.
Symposium OrganizersUlrike G. K. Wegst, Thayer School of Engineering at Dartmouth
Amal M. K. Esawi, The American University in Cairo
Guy Genin, Washington University, St. Louis
Tianjian Lu, Xi'an Jiaotong University
Jonathan Wilker, Purdue University
TT7: Biology and Biomimetics II
Thursday PM, April 12, 2012
Marriott, Yerba Buena, Salons 14-15
2:30 AM - TT7.1
Motile Liposomes: Hybrids of Nature and Engineering
Nienke Geerts 1 T. Kyle Vanderlick 1
1Yale University New Haven USAShow Abstract
Liposomes are artificially prepared, small membrane-enclosed sacks that can store or transport substances. As liposomes encapsulate an aqueous solution inside a partly hydrophobic membrane, they can carry both hydrophobic molecules and hydrophilic molecules. To deliver the molecules to sites of action, the lipid bilayer can fuse with other bilayers, thus delivering the liposome contents. Due to its unique properties, liposomes are often used for drug-delivery. But, this is certainly not the only field where they found their usage. Liposomes can also be used as carriers for the delivery of dyes to textiles, pesticides to plants, enzymes and/or nutritional supplements to foods, and cosmetics to the skin. One factor all these applications have in common is the word delivery that naturally brings up the concept of transport. Transport requires movement. And yet, besides Brownian motion, liposomes by itself are non-moving objects. In the case of drug-delivery this is of lower consequence as the bloodstream provides sufficient movement for the goods to be delivered. The same holds for applying cosmetics either by hand or pesticides in a spray. However, somehow this seems to hold liposomes back in fulfilling all their potential. What if we could make them motile? In nature there are numerous examples of micro-organisms that are motile. Most obtain their motility through their flagella. This tail-like projection propels the organism via rotation or lashing back and forth. It is made up of about 40 proteins. Unfortunately, at the moment it is not possible to reconstruct this machinery in vitro. This however, does not mean we cannot use it. Here we present the first hybrids between various micro-organisms and liposomes. By showing that whole organisms can be used to transport liposomes we would like to open the floor for numerous applications.
2:45 AM - TT7.2
Differentiation and Identification of Epicuticular Waxes on Arabidopsis thaliana Organs and Cells by TOF-SIMS Chemical Imaging
Gregory L Fisher 1 Scott R Bryan 1 Philip C Wong 2 Christopher Buschhaus 2 Reinhard Jetter 2
1Physical Electronics Chanhassen USA2University of British Columbia Vancouver CanadaShow Abstract
TOF-SIMS has emerged as an important tool for imaging mass spectrometry of biological samples due to its unique capability to detect molecular, molecular fragment and elemental ions at sub-micron spatial resolution and without the sample treatments required by e.g. MALDI imaging. For many biological specimens, the ability to image samples having a large degree of surface topography is also highly desired. The resulting elemental and molecular images provide important information regarding the composition of biointerfaces, for example between plant tissues and their natural environment. This TOF-SIMS study involves the differentiation, identification and spatial characterization of epicuticular waxes present at the surfaces of wild-type Arabidopsis thaliana organs including the flower, stem, adaxial (top) leaf surface and the abaxial (bottom) leaf surface. We also characterize the differences in wax composition among the specialized cells of Arabidopsis thal. organs. We have characterized and identified several of the components that comprise the waxes. Moreover, we have observed that the wax compositions of specific, specialized cells within an organ exhibit remarkable variation. Â¶ Images obtained from the flower, adaxial leaf surface and abaxial leaf surfaces, revealing spores, trichomes and stomates, respectively, demonstrate the capability of TOF-SIMS to image molecular species at a resolution of0.3 microns. Total ion images, and molecular ion images of individual wax components, demonstrate the capability to image entire organ surfaces without topographic artifacts. High mass range spectra reveal that the surface of each Arabidopsis thal. organ is comprised of several molecular components. Mass spectra acquired from specialized cells reveal a striking variability in the epicuticular wax composition. The differences in wax composition among organs and cells of Arabidopsis thal. will be presented and discussed. Structural assignments for characteristic mass spectrometric features related to the wax composition will also be presented and discussed.
3:00 AM - *TT7.3
Nature-inspired Ceramic Structural Materials Containing a ``Lubricating'' Second Phase
Robert O. Ritchie 1 2 Antoni P Tomsia 2
1University of California Berkeley USA2Lawrence Berkeley National Laboratory Berkeley USAShow Abstract
Directional freezing of ceramic suspensions is used to create lamellar scaffolds with structural features controlled by the freezing conditions. The resulting porous scaffolds, comprising ~1 to 100 Âµm thick lamellae of a â?ohardâ? ceramic phase oriented over macroscopic dimensions, are then infiltrated with a second metallic or organic â?osoftâ? phase to generate hybrid structures with lamellar or â?obrick-and-mortarâ? architectures, in the latter case involving cold pressing prior to final infiltration. Our approach here is to process high-toughness/high-strength structural ceramic materials, with only minimal volume fractions of the second phase which serves solely as a â?olubricantâ? between the ceramic layers. We have applied this technology initially to the fabrication of up to 80 vol.% alumina ceramics, containing polymethylmethacrylate; these â?obrick-and-mortarâ? structures display remarkable fracture toughness exceeding 35 MPaâ^sm. Our current work is focused on higher strength ceramic scaffolds involving silicon nitride and silicon carbide, infiltrated with either a polymeric or Al-Si metallic phase. The exceptional fracture resistance of these materials derives from a confluence of mechanisms acting at multiple length scales with the microstructural damage and resulting toughening distributed over very large (millimeter) dimensions.
3:30 AM - TT7.4
Mineralized Collagen Coatings on Titanium with Sustained Antibiotic Release
Wenjian Weng 1 Ting Ling 1 Kui Cheng 1
1Zhejiang University Hangzhou ChinaShow Abstract
Recently, the prevention of peri-implant infections in orthopedic surgeries becomes increasingly important. On-site drug delivery is considered as an effective approach. A mineralized collagen coating on metallic orthopedic implant has been proven to be not only highly bioactive and rapidly improve bone growth, but also porous, which means it could be a good carrier for antibiotic delivery. In this study, mineralized collagen coatings were prepared on titanium substrate through electrolytic deposition. The deposition was done through applying a constant potential to the electrochemistry cell that contained an electrolytic solution (pH4.3â?"4.4) of collagen, calcium and phosphate ions. Vancomycin hydrochloride was loaded by distributing its droplets on the coatings after the deposition. Scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier-transformed infrared spectroscopy (FTIR) were utilized to analyze the coating morphology, crystal structure and compositions, trying to adjust microstructures of mineralized collagen coatings. In vitro drug release was carried out by immersing the drug-loaded specimens in the phosphate buffered solution (PBS) and then detecting the release of vancomycin hydrochloride by ultraviolet-visible light detector at fixed time intervals. The result showed an initial burst release of the drug followed by a sustained slow release. The drug delivery behavior was dependent on the microstructure of the coatings. The study showed the potential of the mineralized collagen coatings as a good drug carrier.
4:15 AM - TT7.5
Nanofabricated Stealth Patch Clamp Arrays for Probing Neuronal Electrical Activities
Katie Chang 1 Vijay Narasimhan 1 Nicholas Melosh 1
1Stanford Unversity Stanford USAShow Abstract
Intracellular electrophysiological measurements form the foundation for understanding ion channel behavior, neural signaling and pharmaceutical activity. However, intra-cellular patch clamps lead to cell death in less than 2 hrs and are not amenable to fabrication into large arrays, significantly limiting their applicability. Extra-cellular electrodes traditionally have many electrodes in parallel, yet suffer from poor data quality and limited electrical stimulation. Here we report that metallic electrodes that mimic transmembrane protein hydrophobicity spontaneously fuse into cell membranes during cell culture, providing direct, robust electrical access into cells without damage. These â?~Stealth electrodesâ?T are fully functional intracellular patch-clamps, providing current-clamp, voltage-clamp, stimulation and recording capabilities for more than 3 days continuously on primary rat hippocampal neurons. These devices can be fabricated using standard semiconductor processing techniques.
4:30 AM - *TT7.6
Bio-inspired Synthetic Materials with Brick and Mortar Microstructures
Matthew Begley 1
1University of California, Santa Barbara Santa Barbara USAShow Abstract
The surprising strength and ductility of nacre (in light of its largely ceramic composition) can be attributed to its unique microstructure, which consists of precisely aligned ceramic platelets (bricks) bonded together with nanoscale organic layer (mortar). The underlying composites concepts are arguably straight-forward: (i) high stiffness is maintained by limiting volume fraction of the compliant phase, (ii) high strength is achieved by utilization of small-volume ceramics and an interlocking brick architecture, and (iii) ductility is promoted by brick pull-out. This talk will describe the opportunities and challenges related to the development of synthetic materials that aim to simultaneously implement these concepts. Micromechanical models and large-scale parallelized simulations will be used to describe the key scaling relationships between constituent properties and geometry that control competing deformation mechanisms and govern macroscopic properties. These scaling relationships will be used to identify microstructrual processing targets for high performance materials. The opportunities and challenges relating to realizing these targets will be briefly described in the context of three-dimensional printing of hierarchical structural materials.
5:00 AM - *TT7.7
Integration of Mineralized and Soft Tissues Facilitate Effective Function of the Bone-cartilage Interface
Virginia Ferguson 1
1University of Colorado Boulder USAShow Abstract
Interactions between cells and the tissues in which they reside depend heavily on tissue mechanical properties. These tissue properties arise from a myriad of factors including structural hierarchical organization, underlying microstructure, and composition. In regions joining tissues of dissimilar properties, such as the boneâ?"cartilage interface, stress concentrations are minimized to prevent failure. Yet this particular interface defies logic. It consists of a thin (~10 to 100 Âµm) layer of articular calcified cartilage (ACC) that anchors stiff (~20 GPa) bone to the significantly more compliant (~100â?Ts of MPa) hyaline articular cartilage (HAC). We have recently shown that an abrupt edge exists between the hard, mineralized ACC and overlying soft HAC. While such layering of stiff and soft materials should produce devastating stress concentrations, this complex, layered region rarely fails in healthy tissues. The ACC is thought to possess a lower modulus than the neighboring bone and thus functionally grade properties form the HAC to the SCB; however, we find that the ACC material possesses nanoindentation moduli and mineral volume fractions that are on par with the SCB and which far exceed properties of the HAC. Continuous parallel-aligned collagen fibrils within the HAC are oriented perpendicular to and penetrate the mineralized ACC to anchor the two tissues. These fibrils become mineralized within the ACC to form a highly anisotropic structure, where stiffness is greatest along the fibrils (i.e., normal to the jointâ?Ts surface). The mineral particles within the ACC are less well connected between adjacent particles than in bone, and may thus enable lateral motion when compressed to reduce stress concentrations at the mineralized tissue edge. This talk will explore how microstructural linkages and compositional gradients contribute to the effective function of the boneâ?"cartilage interface. An improved understanding of this region will enable biomimetic development of layered engineered materials and will improve our understanding of progression and treatment of a range of cartilaginous diseases.
5:30 AM - *TT7.8
Full-field Inflation Experiments of Soft Fibrous Tissues
Thao Vicky Nguyen 1
1The Johns Hopkins University Baltimore USAShow Abstract
We have developed inflation experiments with full-field deformation measurements using 2D and 3D digital image correlation (DIC) to measure the mechanical behavior of a variety of soft fibrous tissues, including the human sclera, mouse sclera, and human dermis. This presentation provides an overview of the experimental methods and analysis methods to determine the anisotropic material properties of the tissues. We have developed analytical and computational methods to analyze the DIC measurements for the anisotropic properties of the tissue specimens. The computational approach uses finite elements coupled with an optimization algorithm to fit the parameters of a distributed fiber constitutive models to the DIC displacement field. The finite element models are constructed from DIC reconstruction of the specimen surface and thickness maps measured during the inflation experiments. The simulations also incorporate at the element level X-ray diffraction maps of the collagen orientation distribution. We use gradient-based methods with analytical gradient calculations for computational efficiency, while selectively probing the parameter space with the starting conditions to ensure a globally optimized solution. The analytical methods determine the strain field from the DIC displacement field and the stress field from the curvature of the deformed surface in regions away from the boundaries. Skin, which is anisotropic, inflates from a flat membrane to an ellipsoidal dome. For this tissue, we also calculate an average dominant fiber orientation from the orientation of the inflated ellipsoidal shape.
TT6: Biology and Biomimetics I
Thursday AM, April 12, 2012
Marriott, Yerba Buena, Salons 14-15
9:00 AM - *TT6.1
Adhesion of Eukaryotic Cells and the Influence of Cytoskeletal Contractility
Robert M McMeeking 1 2 3 Vikram S Deshpande 4 Amit Pathak 5 Will Roman 6 Patrick McGarry 6
1University of California, Santa Barbara Santa Barbara USA2University of California Santa Barbara USA3University of Aberdeen, King's College Aberdeen United Kingdom4Cambridge University Cambridge United Kingdom5University of California Berkeley USA6National University of Ireland Galway IrelandShow Abstract
Almost all eukaryotic cells are capable of adhering to an extra-cellular matrix, to other cells, to hard and soft tissue and to artificial substrates, e.g. coated glass slides. Such adhesion occurs by specific and non-specific interactions between substrate ligands and cellular trans-membrane protein complexes. An additional phenomenon that is often coupled to cellular adhesion is cytoskeletal contractility driven by protein motors, with the commonest example being that due to myosin cross-bridging with actin filaments. Cases include smooth muscle cells, fibroblasts, endothelial cells and cardiac muscle cells. Observations indicate that the size of adhesive protein complexes, known as focal adhesions, is proportional to the degree of cell contractility, and the magnitude of the forces applied are also similarly controlled. Such phenomena have been incorporated into a chemo-mechanical model for cell adhesions interacting with ligands that are subject to contractile forces from the cytoskeleton. This model has been used successfully to simulate various cellular phenomena. These include the sensitivity of cell contractile forces to substrate stiffness, the orientation of cytoskeletal stress-fibres in smooth muscle cells that are cyclically stretched, and the location of focal adhesions and stress-fibers in cells adhering to patterned shapes of fibronectin, a ligand bearing protein. The model is also used to simulate the process of a spherical cell developing adhesion to a flat surface, and the shearing of an adhered cell on a flat surface where the cell body is forced sideways by a blunt tool.
9:30 AM - TT6.2
A Method to Monitor Biofilm Formation from Single Cells to Multicellular Communities in Food Processing Systems
Ozlem Istanbullu 1 Jerome Babauta 1 Ryan Renslow 1 Haluk Beyenal 1
1Washington State University Pullman USAShow Abstract
Biofilms are a mode of survival for microorganisms when environmental growth conditions are harsh. By forming biofilms, microorganisms adapt to and are able to survive in various unwanted places, especially in the food industry. Biofilm-related problems in the food industry cause losses in efficiency, downtime of processes, damage to equipment, obstruction of pipelines, and decreases in the competence of heat exchangers. Post-processing contamination lowers shelf life and increases transmission of diseases, resulting in sickness, lost lives, and millions of dollars of extra costs annually. Biofilm formation has become one of the most important food safety issues and monitoring biofilm formation in-situ will lead to control methods that mitigate biofilm-related problems. In this study, we developed a method to monitor biofilm formation on opaque surfaces. We managed to monitor in-situ biofilm formation starting from single cells to multicellular communities. We designed a flow cell in which opaque coupons were inserted. The system was operated continuously and an inverted microscope with a mounted camera was used to monitor biofilm formation. By capturing images during biofilm formation, we were able to evaluate the effect of environmental conditions on biofilm formation starting from single cells. Lastly, we developed software to calculate the number of cells per image automatically.
9:45 AM - TT6.3
Biofilm Growth on Untreated (Hydrophobic) and Plasma Treated (Hydrophilic) Polydimethylsiloxane (PDMS)
Li Hong Zhao 1 Pabitra N Sen 1
1University of North Carolina Chapel Hill USAShow Abstract
We find biofilms grow poorly on Polydimethylsiloxane (PDMS), which is inherently hydrophobic, a property that remains to be an obstacle in numerous scientific applications. Oxygen plasma treatment is a non-toxic, low cost method to render PDMS hydrophilic and copious biofilms form. We find sterilizing PDMS with alcohol after plasma treatment makes it resistant to biofilm. We find that storing PDMS samples, immediately after plasma treatment, under water and Luria-Bertani broth (LB), a common growth medium for bacteria, retards hydrophobic recovery considerably. We study the thickness and structure of biofilm using confocal microscopy and Scanning electron microscopy (SEM) and correlate that with the contact angles. Results will be presented for various scenarios of curing, oxidation and storage times.
10:00 AM - TT6.4
Behavior of Surface Adsorbed Bioluminescent Bacteria
Satoshi Sasaki 1
1Tokyo University of Technology Hachioji JapanShow Abstract
Photobacterium kishitanii, blue-green glowing bacteria, were collected from the skin of a cuttlefish and Todarodes pacificus and were purified. Different volume of oscillation broths were placed in a reactor cell in order to examine the effects of the air-liquid interface area/volume. Oxygen concentration inside the cell was thought to be critical for the dynamic behavior. We focused therefore on the cell density (optical density) in the suspension as an index of cell activity. Simultaneous measurement of luminescence and dissolved oxygen concentration during oscillation was performed using a self-made luminescence meter and an optical fibre-based DO sensor placed into the bacterial suspension. Then we performed simultaneous measurements of the luminescence and cell density. A self-made luminescence meter was attached on the reactor cell, and an optical density meter was used for the continuous measurement of the optical density (OD) of the bacterial suspension. The generated voltage was measured and recorded by the data logger. Apart from the characteristics of the luminescence from the whole bacterial suspension, we focused on the luminescence from single cells. As luminescence from the suspension with a volume of several tens - hundreds of mL might contain luminescence from cells of different conditions, a study of single cell luminescence is also thought to be necessary. We therefore examined luminescence from single cells adsorbed on a glass or agar plate surfaces. Images of single cell luminescence were captured using EM-CCD camera attached to a microscope. Difference in the luminescent characteristics of each cells were observed. Using the single-cell luminescence image, we finally searched for a model that can describe the oscillation phenomena. A model often used to characterize predator-prey interactions was chosen, by regarding that 1. one bright cell divides into two bright cells with the supply of infinite broth; 2. one bright cell becomes a dark cell as a result of interaction with a dark cell (both cells consume oxygen as a result of respiration and become dark ones); 3. a dark cell becomes a dead cell. A numerical solution of the two equations, i.e., the time course of bright cell density and dark cell density through the simulation was performed using a common spreadsheet software. A possible hypothesis of the oscillation in the luminescence was proposed.
10:15 AM - TT6.5
Titania Nanotubes for Growth Improvement of Biological Cells
Tolou Shokuhfar 1 Craig Friedrich 1 Chang Choi 1 Jen-Young Chang 1
1Michigan Technological University Houghton USAShow Abstract
In this study a self-assembled arrays of titanium dioxide nanotube was used to investigate the adhesion, spreading and substrate interaction of osteoblast cells. Focused ion beam (FIB), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and optical microscopy observation of osteoblast were used to investigate the cell proliferation, morphology and adhesion at the nanotube interfaces. Chemical analysis from the osteoblasts, osteoblast-nanotube interface, and milled areas of cell attached to nanotubes, revealed that the lipid bilayer of the cells has been grown inside the nanotubes, resulting in complete coverage and clogging of the nanotubes. The results indicated that osteoblasts spreading, adhesion and substrate interaction is higher in surfaces covered by nanotubes compared to bare surfaces of commonly used surgical pure Ti and Ti6Al4V alloys.
11:00 AM - *TT6.5
The Hierarchical Structure and Mechanics of Plants
Lorna J. Gibson 1
1MIT Cambridge USAShow Abstract
The cell walls in plant tissues are made up of just four basic building blocks: cellulose, the main structural fiber of the plant kingdom, hemicellulose, lignin and pectin. Although the microstructure of plant cell walls varies in different types of plants, broadly speaking, cellulose fibers reinforce a matrix of hemicellulose and either pectin or lignin. The cellular structure of plants varies from the honeycomb-like cells of wood to the closed-cell, liquid-filled foam-like parenchyma cells of apples and potatoes. The arrangement of the four basic building blocks plant cell walls and the variations in cellular structure give rise to a remarkably wide range of mechanical properties: the Youngâ?Ts moduli span 4 orders of magnitude while the compressive strengths span over 2 orders of magnitude. Here, we review the microstructure of both the cell wall and the cellular structure in four plant materials (wood, arborescent palm stems, bamboo and parenchyma) to explain the wide range in mechanical properties in plants.
11:30 AM - TT6.6
The Mechanics of the Plant Cell/Cell Wall Interface: Effects of Osmotic Challenge
Lihong Zhou 1 Feng Xu 3 Barbara G Pickard 1 David Ehrhardt 2 Guy M Genin 1 3
1Washington University St Louis USA2Carnegie Institute Stanford USA3Xi'an Jiaotong University Xi'an ChinaShow Abstract
The plant cell periphery -- the interface between membrane and cell wall -- is central to the ability of plants to maintain and recover polarity following drought. Turgor pressure is maintained by the membrane-bounded cytoplasm against the relatively stiff cell wall, and recent evidence suggests that this depends not only on membrane functions but also on how subcellular architectural units organize and regulate these functions at the cell membrane/wall interface (periphery). Recently we have used advanced microscopy to identify a peripheral cytoskeletal structure that is a candidate for an important role in turgor regulation. We present recent results on the dynamics of these interfacial structures.