Jean S. Stephens Luna Innovations
John F. Rabolt University of Delaware
Gregory C. Rutledge Massachusetts Institute of Technology
Gary E. Wnek Case Western Reserve University
B1: Applications of Polymer Nanofibers to Tissue Engineering I
Tuesday AM, November 28, 2006
Room 206 (Hynes)
9:30 AM - **B1.1
Synthesis and Processing of Biodegradable Thermoplastic Elastomers for Soft Tissue Engineering.
William Wagner 1 2 , John Stankus 1 , Jianjun Guan 1 , Michael Sacks 1 2 , Todd Courtney 1 2 , Yi Hong 1 Show Abstract
1 McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Dept. of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Scaffolds that mechanically mimic the tissue targeted for regeneration are desirable for tissue engineering approaches reliant upon cell ingrowth or development in vivo, as well as approaches where mechanical training and development is pursued prior to implantation. We have focused on developing biodegradable thermoplastic elastomers based on poly(ester urethane)ureas that possess elastomeric behavior mechanically compatible with soft tissues and that are amenable to processing to create scaffolds for a variety of functions. By altering the polymer backbone composition, peptide sequences can be introduced that introduce specific lability for enzymes that would be expressed at the site of tissue remodeling.One type of polymer processing that has been investigated with these elastomers is electrospinning. With this technique collagen and extracellular matrix components have been blended to generate fibrillar scaffolds. Scaffolds can be created over the complete range from pure polymer to pure collagen, with the attractive feature of greatly increasing the scaffold mechanical properties of pure collagen by the introduction of relatively low mass fractions of polymer. Electrospinning also offers the opportunity to create scaffolds of controlled anisotropy by controlling motion of the collecting target surface. Here it is possible to approximate the mechanical properties of complex anisotropic tissue such as cardiac valves. Finally, electrospinning provides the potential to create microintegrated scaffolds by concurrently depositing elastomeric fibers and cells. With this method, smooth muscle cell laden scaffolds have been generated that exhibit high cellular viability and growth in culture, with attractive elastic properties present throughout the early culture period. The combination of this thermoplastic elastomer polymer platform and a variety of processing techniques offers the potential to address many needs in soft tissue engineering applications.
10:00 AM - B1.2
Laminin-Coated Nanofiber Scaffold Improves NSC Adhesion and Proliferation
Gregory Christopherson 1 , Hongjun Song 2 , Hai-Quan Mao 1 3 Show Abstract
1 Department of Materials Science & Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 Department of Neurology and Institute for Cell Engineering, Johns Hopkins School of Medicine, Baltimore, Maryland, United States, 3 Whitaker Biomedical Engineering Institute, Johns Hopkins University, Baltimore, Maryland, United States
The existence of neural stem cells (NSCs) in the adult central nervous system (CNS) of all mammals, including humans, provides an exciting opportunity to replace damaged and lost neurons in the adult CNS by engineering endogenous NSCs, and transplanting in vitro expanded NSCs and/or their progeny. Realizing this potential requires effective expansion methodology. NSCs are regulated by an array of physical, biochemical and topographical cues that constitute an essential part of their microenvironment in vivo, called the neural stem cell niche. A growing body of evidence suggests that nanoscale topography, in synergy with the biochemical cues, plays a crucial role in controlling the adhesion, proliferation, survival, migration and differentiation of cultured cells in vitro. In order to study the effects of nanotopography and biochemical cues on NSC proliferation and self-renewal, we prepared polyethersulfone (PES) nanofiber scaffolds with an average diameter of 273 ± 43 nm by electrospinning, and coated the fiber surface with laminin (LN), a key extracellular matrix protein in the naturally occurring NSC niche. LN-coated glass coverslips were prepared as a 2-dimensional substrate control to the nanofiber substrates. Rat NSCs were seeded on both substrates in triplicate and cultured for 5 days in DMEM/F-12 medium supplemented with a range of FGF-2 concentrations (0 to 20 ng/ml). FGF-2 is the most critical growth factor to promote NSC proliferation and differentiation in a concentration dependent manner. Clonal assay was used to characterize NSC proliferation by comparing the size of colonies and total number of colonies on each substrate. On the LN-coated 2D surfaces, the majority of the cells remained nestin+ in the presence of FGF-2, indicating phenotype maintenance. The clonal size for both LN-coated 2D and nanofiber scaffolds increased with FGF-2 concentration, peaking at 5 ng/ml, before slightly declining at 20 ng/ml of FGF-2. Interestingly, NSC expansion efficiency was higher on the PES nanofiber scaffolds than 2D controls, but this improved proliferation rate was a function of FGF-2 concentration; the highest increase was observed in the presence of 1 ng/ml and 20 ng/ml of FGF-2. Qualitative analysis indicated that cell adhesion to the nanofiber surface was much stronger than to LN-coverslips; SEM images clearly showed extensive binding of NSCs to nanofibers, as evidenced by filopodia extension and attachment to multiple fibers. Additionally, NSCs cultured on LN-coated nanofiber scaffolds yielded a higher total number of colonies than those on LN-coated coverslips. This preliminary study demonstrated that nanofiber topography enhanced NSC expansion efficiency and, furthermore, this response was related to the enhanced cell-substrate adhesion.
10:15 AM - B1.3
pH-gated Drug Releasing of Polyelectrolyte Nanofibers
Lei Zhai 1 Show Abstract
1 NanoScience Technology Center and Department of Chemistry, Univeristy of Central Florida, Orlando, Florida, United States
Electrospun nanofibers have attracted much attention for medical applications such as tissue engineering and drug releasing due to their large surface area. In our studies, pH-gated drug releasing properties of the nanofibers electrospun from a mixture of polyelectrolytes with opposite charges-poly(acrylic acid)(PAA) and poly(allylamine hydrochloride) (PAH) have been investigated. Charged dyes such as methylene blue and rose bengel were used to model the loading and releasing of hydrophilic drugs. The loading of hydrophobic drugs were achieved via mixing the drugs with polyelectrolyte mixture followed by electrospinning. The nanofibers loaded with hydrophobic drugs showed a linear, long term releasing profile in PBS.
10:30 AM - B1.4
Electrospun Hydroxyapatite Bio-composites for advanced Prosthetic Devices.
A. Bishop 1 , J. Yang 1 , Cs. Balazsi 2 , P. Gouma 1 Show Abstract
1 Materials Science and Engineering, State University of New York at Stony Brook, Stony Brook, New York, United States, 2 Ceramics and Composites Laboratory, Research Institute for Technical Physics and Materials Science, Budapest Hungary
In this study, polymer based composites were prepared by electrospinning hydroxyapatite with a biocompatible polymer for the development of a structurally stable casing for prosthetic devices. Presented in this paper is the morphological study of electrospun polymer-hydroxyapatite mats to discern the effects of acidic additives and electrospinning on the production of hydroxyapatite (HA) based scaffolds for bone regeneration.
10:45 AM - B1.5
Electronic Transport Measurements in Tin Oxide Microfibers Created From a Polymer Solution.
Maria Taku 1 , Chris Rodd 2 , Jorge Santiago-Avilés 1 Show Abstract
1 Electrical & Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Materials Science & Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Tin oxide microfibers were created through electrospinning using a precursor solution consisting of poly(ethylene oxide) (PEO) and chloroform (CHCl3) which was then mixed with its tin precursor, dimethyldineodecanoatin (C22H44O4Sn). Since the conductivity of SnO2 is affected by any chemisorbed oxygen molecules on its surface, this semiconductor has high potential for use as a gas sensor for both oxidizing and reducing gases. Due to the fact that a greater surface area will produce gas sensors with improved sensitivity, work is underway to reduce the fibers into the nanoscale range. Additionally, this study determines various electronic transport characteristics—such as the conductivity and magnetoresistance—of the tin oxide microfibers.
The electrospun fibers were sintered in the air at 600°C for 2 hours in order to form the rutile phase structure of the tin oxide. The I-V characteristics were then plotted in order to determine the resistivity of the fibers and also to prove the ohmic nature of the contact. XRD and Raman spectroscopy were used to determine the composition and phase of the microfibers. The initial resistivity of the fibers subsequent to the heat treating was in the range of 10-100 MΩ. Optical and scanning probe microscopes were then utilized to determine the length and cross sectional area of the fibers. The area of the fibers was not circular in shape due to the fact that the fibers would collapse upon annealing. The long axis would range from a few micrometers to tenths of a micrometer in length, while the short axis was nanometric in size. From this information, the dimensions and conductivity of the fibers were determined. Lastly, the magnetogalvanic effects were studied by measuring the resistance of the fibers at different temperatures while being subjected to a transverse magnetic field which ranged from -9 to 9 Tesla. The system in which this was performed was a cryostat capable of raising the temperature from 1.7 K to room temperature.
B2: Functionalizing Polymer Nanofibers
Tuesday AM, November 28, 2006
Room 206 (Hynes)
11:30 AM - **B2.1
Preprocessing Functionalization of Electrospun Fibers for Applications in Biomaterials.
Cheryl Casper 1 2 , Nori Yamaguchi 1 2 , Ronak Maheshwari 1 , John Rabolt 1 2 , Kristi Kiick 1 2 Show Abstract
1 Department of Materials Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 , Delaware Biotechnology Institute, Newark, Delaware, United States
12:00 PM - B2.2
Encapsulation and Release of Bioactive Agents Using Novel Microfiber Scaffolds Produced Through Electrostatic Processing.
Meghan Smith 1 , Gary Wnek 1 Show Abstract
1 Chemical Engineering, Case Western Reserve University, Cleveland, Ohio, United States
Polymers have been employed as materials for drug delivery applications due to several advantages that they hold over more traditional delivery systems, including low toxicity, controlled degradation, ease of manufacturing, tailored release profiles and targeted or stimuli sensitive delivery. However, although polymers have radically improved the range and diversity of drug delivery technology there is considerable room for further development. Electrostatic processing, including electrospinning and electrospraying, has been investigated as a means of polymer processing to form non-woven mats of small-diameter fibers or particles for use in delivery of bioactive agents, as it allows for control of the properties of the fibrous mats, which may provide for the development of specific degradation and release profiles. Described herein is the development of an inventive fibrous structure created by novel electrostatic processing techniques. Micron diameter fibers were made from a variety of polymer solutions, within which aqueous domains have been incorporated. Upon electrospinning, the polymer solution forms a Taylor cone from which a jet is emitted, stabilized by polymer chain entanglements. The aqueous domains in these biphasic systems are hypothesized to also undergo deformation during the electrospinning process, elongating into extended aqueous columns which then break into uniformly spaced droplets within the fiber via a Rayleigh instability mechanism. Using this biphasic electrospinning method, bioactive molecules, including enzymes and growth factors, have been incorporated into these aqueous domains. We have also obtained release of these agents from the fibers into the surrounding environment via diffusion. In addition, we have also determined that the encapsulated molecules have retained biological activity. This method to produce encapsulated biomolecules in aqueous domains within a polymer fiber may have considerable application in drug delivery as well as in the development of biologically active tissue engineering scaffolds.
12:15 PM - **B2.3
Taking Advantage of Supramolecular Structure in Melt and Solution Electrospinning
Timothy Long 1 , Matthew Hunley 1 , Matthew McKee 1 Show Abstract
1 Chemistry, Virginia Tech, Blacksburg, Virginia, United States
Our research efforts have focused on the role of polymer entanglements in the prediction of the feasibility of electrospinning nanoscale polymeric fibers. Moreover, intermolecular interactions including electrostatic and multiple hydrogen bonding result in deviations from our semi-empirical models for electrospinning non-associating polymers. Polyelectrolytes, which offer promise in antimicrobial and drug delivery applications, result in 20-30 nm fiber diameters. On the other hand, multiple hydrogen bonding including the ureido pyrimidone result in higher than predicted fiber diameters. Recent efforts have demonstrated the ability to electrospin star-shaped polymeric blends containing molecular recognition sites, and fiber diameters were a function of the presence of terminal adenine and thymine base pair recognition. In addition, the electrospinning of phospholipids in both solution and melt have resulted in novel families of biocompatible fibers for cell impregnation and drug delivery.
12:45 PM - B2.4
A Simple Method to Grow Polymer Nanofibers from Superglue®.
Pratik Mankidy 1 , Ramakrishnan Rajagopalan 2 , Carlo Pantano 2 , Henry Foley 1 2 3 Show Abstract
1 Chemical Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Research Institute, Penn State University, University Park, Pennsylvania, United States, 3 Department Of Chemistry, Penn State University, University Park, Pennsylvania, United States
B3: Composite Polymer Nanofibers
Tuesday PM, November 28, 2006
Room 206 (Hynes)
2:30 PM - **B3.1
Nanostructured Materials Enabled by Electrospinning.
Younan Xia 1 Show Abstract
1 Chemistry, University of Washington, Seattle, Washington, United States
Electrospinning is a simple and versatile technique for producing fibers with nanoscale diameters and long lengths. Traditionally this method is used to create randomly-oriented, non-woven mats of fibers from polymer solutions or melts. By co-spinning sol-gel precursors with an ethanol-soluble polymer, we have extended this system to spin composite fibers with excellent size control down to tens of nanometers. Additionally, we have made a number of important modifications to the electrospinning setup. Using a coaxial spinneret, we have been able to manufacture porous, hollow, and core-sheath nanofibers and control the surface chemistry of resultant fibers by tuning the core and sheath solutions. We have also used patterned collectors to uniaxially align arrays of nanofibers. These arrays could be readily stacked into structures for device fabrication. This talk will cover these advances, concentrating on the fabrication of functional fibers and architectures relevant to various applications.
3:00 PM - B3.2
Enhanced Photoluminescence in Electrospun PPV Nanofibers owing to Molecular Orientation.
Meghana Kakade 1 , John Rabolt 1 , Bruce Chase 2 Show Abstract
1 Material Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 Central Research and Development, DuPont, Wilmington, Delaware, United States
Various efforts have been made recently to obtain uniaxially aligned nano-fibers via electrospinning as many electrical, optical, mechanical and biological applications require unique structural orientation. Recently we have been able to orient PEO chains in nanofibers at the molecular level by electrospinning onto electrically charged aluminum plates. This method is very simple and doesn’t involve any moving parts, e.g., a rotating mandrel. Polyphenylene vinylene (PPV) is an electroactive polymer which has application in light emitting diodes, biological and chemical sensors due to its inherent photo-luminescent properties. Lately, a few attempts have been made to enhance the fluorescence efficiency in ionic PPV via interaction with polyelectrolyte in solution, resulting in extended and ordered PPV chains. We present a novel approach to uniaxially orient MPS-PPV (Poly[5-methoxy-2-(3-propyloxysulfonate)-1,4-phenylenevinylene] potassium salt solution in water) nano-fibers at the molecular level via the use of electrospinning. Electrospinning MPS-PPV in a PEO matrix onto electrically charged plates leads to partial alignment of polymer chains at the molecular level and hence also at the macroscopic level, when nanofibers are aligned with charged aluminum plates. This oriented MPS-PPV architecture is proposed to have higher fluorescence efficiency compared to un-oriented polymer. The orientation of polymer chains in PPV have been observed using polarized resonance Raman spectroscopy, whereas the enhanced photoluminescence will be measured using the fluorescence spectroscopy.
3:15 PM - B3.3
PVdF/MWCNT Electrospun Nanocomposite Fibers.
Kris Behler 1 , Mickael Havel 1 , Frank Ko 1 , Yury Gogotsi 1 Show Abstract
1 Materials Science Engineering, Drexel, Philadelphia, Pennsylvania, United States
Electrospinning is a cost effective technique that is exponentially evolving due to its simplicity and efficiency in producing fibers down to the nano-range. Here, we report a study on the electrospinning of PolyVinyliDene Fluoride (PVdF) (Arkema North America, Inc.). We demonstrate that while a PVdF/DMF (dimethyl formamide) solution yields ~500 nm fibers diameter, the addition of tetramethylammonium chloride (organo-soluble salt) at very low concentration (0.01 wt%) gives uniform and ultra thin fibers (~40 nm) as seen by scanning electron microsopy (SEM). It is also shown that the fiber diameter can be tuned from 40 nm to hundreds of nanometers by changing the viscosity of the solution which depends on the polymer concentration, molecular weight, and Multi-walled Carbon Nanotubes (MWCNTs) loading content. As-received MWCNTs (Arkema, France) have been incorporated into the polymer solution to increase the mechanical and electrical properties of the nanofibers. The possible property enhancements related to increased dispersibility of the MWCNTs were investigated. Two methods have been selected: chemical modification of the MWCNTs by air oxidation and surfactant-assisted dispersion using poly(vinyl pyrrolidone). The resulting nanocomposites provide a potential for tuning electrical and mechanical properties.
3:45 PM - B3.5
Polymer Nanofibers Containing Isolated and Aligned Single Wall Carbon Nanotubes
Robert Young 1 , Stephen Eichhorn 1 , Kannan Prabhakaran 1 Show Abstract
1 Materials Science Centre, University of Manchester, Manchester United Kingdom
It is well established that carbon nanotubes have potentially impressive mechanical properties and it is thought that one of the best ways to realize these properties is to incorporate them in composites. The highest levels of stiffness and strength are obtained for composites when the reinforcing fibers are aligned in one direction. It has also been generally recognized that for any nanocomposite to realize its full potential in terms of mechanical properties the nanophase has to be well-dispersed. Hence, the isolation of reinforcing phases and their alignment are critical stages in the development of these potentially useful materials.Electrospinning from aqueous solution has been used to prepare poly(vinyl alcohol) (PVA) nanofibers, with diameters ranging from 1 micron down to 20 nm, that contain dispersions of isolated, well-aligned, single wall carbon nanotubes (SWNTs). The nanofibers were characterized by Raman spectroscopy and single radial breathing modes (RBMs) were found for the SWNTs in the nanofibers indicating debundling of the original SWNT ropes. In some nanofibers a split G’ band was found, characteristic of isolated SWNTs. Moreover when the nanofibers were rotated by an angle φ relative to the axis of laser polarization, the intensity of the G band varied as a function of cosφ to the power 4 when the analyzer was parallel to the axis of original polarization (VV) and as sinφcosφ to the power 2 when the analyzer was perpendicular to the axis of original polarization (VH). This is characteristic of the presence of isolated SWNTs, highly aligned along the nanofiber axes.This microstructure can be considered to be that of the ultimate model nanocomposite of a nanotube within a nanofiber, with a large number of potential applications. Current research is being undertaken into looking at the effect of SWNT loading, both higher and lower than that used in the present study, upon the microstructure produced. Different processing conditions are being employed, by varying the solution concentration, solvents, types of polymer etc. Stress transfer between the PVA matrix and the SWNTs is being followed from the shift of the SWNT G’ band by deforming the nanofibers in a Raman spectrometer. Nanotube-based structures will be produced by micromanipulating the nanofibers into position and then depolymerizing the polymer matrix. Consistent alignment of nanotubes within the nanofiber may also lead to the development of nanowires for electronic applications, or for the generation of artificial nerves.
B4: Conducting Polymer Nanofibers
Tuesday PM, November 28, 2006
Room 206 (Hynes)
4:30 PM - **B4.1
Electrospinning Technique And Life Quality.
Ce Wang 1 Show Abstract
1 Alan G. MacDiarmid Institute, Jilin University, Changchun, Jilin, China
Electrospinning technique is a very versatile and effective technology for continuously obtaining nanomaterials such as nanoparticles, nanofibers, nanowires, nanotubes, and various nanoparticle/nanofiber composites. They can exist in forms of hollow, core/shell, and solid forms and will play a big role in our daily life. For example, the solid and core/shell nanoparticles can be used as quantum dots and photonic crystals, while the hollow nanoparticles can be used as drug release. The nanofiber mates are suitable to applications in not only filtration and separation membranes, biomaterials for wound dressings and scaffolds for tissue engineering, but also spacecraft coatings, reinforcement in bulk materials. The (n/p) nanowires are expected to be used as a part of nanodevice and their ordered assembly is found applications in anisotropic conductivity, nanocomputer, which would raise high density information storage enormously. The nanotubes are perspective for blood vessel, hydrogen storage, and so on. Moreover, the nanoparticles/nanofiber composites may solve a catastrophic problem we are facing – nanodusts brought by development of nanoscience. Through anchoring the nanoparticles on/in the nanofibers, the floatage of the nanoparticles in air can be avoided. In such the composite types, a series of nanocomposites can be prepared such as green catalysts applied in decomposition of poise gases and synthesis of health-friendly materials. Unassailably, the electrospinning technique will bring a higher life quality for human being. Keywords: nanofiber; electrospinning; life quality
5:00 PM - B4.2
Polythiophene Nano and Micro fibers from Electrostatic Spinning and the Melt.
Gregory Sotzing 1 , Arvind Kumar 1 , Chris Asemota 1 , Jia Choi 1 , Yogesh Ner 1 Show Abstract
1 Institute of Material Science, Univ of Connecticut, Storrs, CT , Connecticut, United States
Conducting polymer nanofibers have tremendous potential in electronic, optoelectronic and biological applications as sensors, drug delivery devices, and electrochromic textile, to name a few. High surface area provided by nanofibers would provide optimization for devices by which diffusional processes limit device characteristics. Here, we report the preparation of conducting polymer nanofibers from precursor nanofibers via Solid-state Oxidative Conversion (SOC). Precursor polymers have been prepared by both living and step-growth polymerizations producing different electroactive groups such as thiophenes, 3,4-alkylenedioxythiophenes, and their oligomers as either pendant groups or within the backbone of the precursor polymer. Precursor polymers are soluble in common organic solvents, and thus, were spun into nano-fibers via electrostatic spinning. Fibers of precursors having melting transitions were prepared by melt drawing. Two different approaches viz. electrochemical and vapor induced SOC have been performed to convert precursor polymer nano and micro fibers into polythiophene fibers. Optimized systems show no change in morphology upon the SOC process. Desired alignment of fibers and cospinning to produce core/shell fiber onto the substrate during electrostatic spinning was obtained. Electrochemical, optoelectronic and redox switching behavior of these fibers will be presented.
5:30 PM - B4.4
Electrical Conductivity Measurements of Nanofibers from PAni.HCSA in the PEO Matrix Fabricated with Electrospinning Method.
Saima Khan 1 , Martin Kordesch 1 Show Abstract
1 Physics & Astronomy and CMSS Program, Ohio University, Athens, Ohio, United States
5:45 PM - B4.5
Nanometal Containing Nanocomposites and PhotolithographicPolyaniline Nanofibers.
Massimo Bertino 1 Show Abstract
1 physics, university of missouri-Rolla, Rolla, Missouri, United States
B5: Poster Session: Structure, Processing, and Properties of Polymer Nanofibers
Tuesday PM, November 28, 2006
Exhibition Hall D (Hynes)
9:00 PM - B5.1
Supramolecular Selectivity of Poly(ethylene oxide) in Semicrystalline Polymer Nanocomposites.
Peng He 1 Show Abstract
1 Chemistry, North Carolina State University, Raleigh, North Carolina, United States
9:00 PM - B5.10
Polymers Derived Ceramic and UV-sensitive Polymer Nanofibers by Electrospinning Technique.
Saima Khan 1 , Aurangzeb Khan 1 , Martin Kordesch 1 Show Abstract
1 Physics & astronomy and CMSS Program, Ohio University, Athens, Ohio, United States
9:00 PM - B5.11
Prospects for Using Liquid Crystals to Affect Polymer Chain Alignment in Electrospun Fibers.
Chris Snively 1 , John Rabolt 1 , Bruce Chase 2 Show Abstract
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 , DuPont Inc., Wilmington, Delaware, United States
It is well-known that liquid crystals undergo reorientation and alignment under the application of electric fields. This effect is commonly exploited in a variety of electrooptical display devices. Here, we explore the possibility of using liquid crystals to cause changes in the extent of molecular orientation of polymer chains in electrospun fibers. The effect that varying amounts of liquid crystal has on chain alignment will be presented for a variety of polymer molecular structures. Also, this effect will be explored as a function of the extent of solubility of the liquid crystal in the polymers. The possibility of employing the residual dissolved liquid crystal molecules in conjunction with Raman spectroscopy will also be presented as an external probe of molecular orientation.
9:00 PM - B5.12
Formation of Nanoscale Palladium Combining Electrospinning and dc Sputtering.
Víctor Pantojas 1 , Carlo Otaño 2 , Ariel Otero 1 , José Otaño 2 , Carlos Ortiz-Rodriguez 1 , Jorge Santiago 3 , Wilfredo Otano 1 Show Abstract
1 Department of Physics, University of Puerto Rico at Cayey, Cayey, Puerto Rico, United States, 2 Department of Mechanical Engineering, University of Puerto Rico at Mayaguez, Mayaguez, Puerto Rico, United States, 3 Department of Electrical and System Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
9:00 PM - B5.13
Two-Layer Electrospun Composite
Kristin Sisson 1 Show Abstract
1 MSEG, University of Delaware, Newark, Delaware, United States
Electrospinning is a technique, which is currently undergoing a significant resurgence in interest. It offers a route to the production of small diameter fibers, which requires minimal amounts of material. Fiber diameters in the range of 100 nanometers to several microns are readily spun. These nanofibers can potentially play a significant role in composite materials due to the small diameters and high surface areas. We have utilized the electrospinning process to create very small fibers in the form of a two-layer composite using two different polymers. Polycaprolactone and Pellethane(Dow) were selected for their durability. An appropriate solvent system, such as THF and DMF in different volume ratios, was determined to create the desired fiber properties. Upon examination of the interface of the two electrospun layers using Scanning Electron Microscopy, there is evidence of physical crosslinking present. This composite electrospinning process can be used in more specific applications, such as a multi-layered synthetic blood vessel, in the future.
9:00 PM - B5.14
Crystal Structure and Piezoelectric Properties of Electrospun PVDF Ultrafine Fiber Mats.
Onur Yordem 1 , Mert Gulleroglu 1 , Erdem Ogut 1 , Yusuf Menceloglu 1 , Melih Papila 1 Show Abstract
1 , Sabanci University, Istanbul Turkey
9:00 PM - B5.15
Micropatterned Polythiophene Nanofibers via Electrostatic Spinning and Photolithography
Chris Asemota 1 , Arvind Kumar 1 , Gregory Sotzing 1 Show Abstract
1 , University of Connecticut, Willimantic, Connecticut, United States
Fabrication of nanometer dimension devices is a strong area for active research today. The control of feature size in the submicron and particularly the nanoscale level is very important in many areas of nanotechnology, especially but not limited to the semiconductor industries. Research in polymer nanotechnology has also grown tremendously, particularly in areas where nanoscale control of feature size is important like printable and flexible electronic displays, OLEDs, to name a few. These materials are economical in cost, and weight, in comparison to their inorganic counterparts, and can also be preprocessed with very simple and cheap techniques before they are converted into conducting polymers. We report the processing of a conducting polymer precursor into submicron scale fibers, as well as the photo-controlled micron scale and submicron scale patterning of nanometer and micron sized fiber mats. We show that the patterned fibers remain a fibrous mat, and the features retained in post photolytic operation is easily converted into the conducting polymer, with no observable loss in structural integrity. We believe this work adds to the growing research contributions towards design of controlled nanoscale devices.
9:00 PM - B5.16
Characterization of Electrospun poly (methyl methacrylate) Scaffolds for Three-dimensional in vitro Biological Studies.
Ying Liu 1 , Yuan Ji 1 , Jonathan Sokolov 1 , Miriam Rafailovich 1 Show Abstract
1 Material Science and Engineering, SUNY at Stony Brook, Stony Brook, New York, United States
9:00 PM - B5.2
Electrospun Novel Structured Polymer and Polymer/Carbon Nanotube Composite Materials.
Jing Liu 1 , Satish Kumar 1 Show Abstract
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
9:00 PM - B5.3
The Size Dependence of Polymeric Materials in Confined Geometries:NNanofibers.
Sezen Curgul 1 , Gregory Rutledge 2 Show Abstract
1 DMSE/PPST, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
In this project, we have developed the necessary modeling tools to characterize and quantify the size dependence of polymeric materials in one-dimensionally (1-D) confined geometries, in particular nanofibers. The main goal is to provide a means to evaluate the size dependence of fiber properties, and thereby understand the origin of the transition from the regime of bulk-like behavior to that of nanomaterial behavior in 1-D nanomaterials (i.e. “how small is nano?”) Our method also allows estimation and prediction of properties that may be hard to measure due to limitations of experimental capabilities.For the molecular dynamics (MD) simulation of the nanofiber, we are using LAMMPS (Large-Scale Atomic/Molecular Massively Parallel Simulator), a classical molecular dynamics code designed to run efficiently on parallel computers.Using a parallelized code gives the opportunity to simulate realistic size nanofibers such as those made in the lab by electrospinning or similar technologies. Construction of the polymer fiber from bulk consists of two main steps. First, a bulk simulation is run until an equilibrium structure is reached. Then the box size is increased in two perpendicular directions such that the parent polymer molecules do not interact with their periodic images in the directions along which extension occurs. Thus, the periodic boundary condition applies only in one direction. A new equilibrium structure is acquired in the new simulation box. We call the equilibrated structure that is formed in this periodic box as “fiber”.To date, we have simulated prototypical polymers that mimic polyethylenes of sizes between C50 and C300. These nanofibers have diameters in the range 1.86-8.8 nm. In these fibers, the density approaches the bulk density of the polymer towards the center of the fiber, even in the smallest fibers. The fiber diameter is determined using the Gibbs dividing surface method. The interface thickness, which can be defined as the distance over which the density of the fiber decreases from 90% to 10% of its bulk value, is between 0.89-1.3 nm for all fibers and shows little dependence on the fiber size. Significant chain end segregation at the surface of the fiber is observed, with the end beads being more abundant than the middle beads at the interface. Chain conformations, as characterized by the ratio of the mean squared end to end distance to radius of gyration, is unperturbed in fibers with diameters larger than 3.0 nm, comparable to the unperturbed size of the molecules, but shows signs of confinement for smaller fibers. This confinement is pronounced more for fibers that are composed of longer chains. Further analysis of the radius of gyration shows that the chains become flattened towards the surface of the fiber. The surface energy as a function of fiber size has also been determined and exhibits size dependence. It’s observed that the mobility of chains increases toward the free surface.
9:00 PM - B5.4
Core-Sheath, Hollow, Porous and Surface-Functionalized Nanofibers by Coaxial Electrospinning
Jesse McCann 1 , Dan Li 1 , Younan Xia 1 Show Abstract
1 Department of Chemistry, University of Washington, Seattle, Washington, United States
Electrospinning is an inexpensive technique for the production of nanofibers with extremely long lengths. Traditionally the technique was developed for generating non-woven mats of organic fibers from polymer solutions or melts. Using a coaxial spinneret, we have been able to manufacture porous, hollow, and core-sheath nanofibers and control the surface chemistry of these fibers by tuning the composition of the core and sheath solutions. Our coaxial methods have enhanced the utility of electrospinning as the spinneret can be loaded with a carrier polymer that is amenable to electrospinning and doped with polymers that can not be electrospun individually. Following electrospinning, the carrier polymer can be removed by selective dissolution. This poster will cover these advances, concentrating on the fabrication of functional fibers and architectures relevant to nanoscale devices.
9:00 PM - B5.5
High Flux, Anti-fouling Three-tier Ultra-filtration Membrane of the Electrospun PAN/PES Nanofibers Coated with Polyurethane
ChanHee Park 1 , Kwang Sok Kim 2 , In-Joo Chin 1 Show Abstract
1 Polymer Science and Engineering, Inha University, Incheon Korea (the Republic of), 2 , Small Business Training Institute, Kyungsan Korea (the Republic of)
We propose a new structure for the three-tier ultra-filtration membrane, which could provide high flux and anti-fouling characteristics. This three-tier membrane is composed of the mixed cellulose ester micro-porous substrate, the electrospun nanofibrous membrane of the poly(acrylonitrile) (PAN)/poly(ether sulfone) (PES) blend as the mid layer, and the UV- curable polyurethane top-coating. In order to reduce interaction with natural organic matter (NOM) and the fouling caused by NOM, polyurethane was modified. UV-curable polyurethane was synthesized by using modified urethane prepolymer with methacrylate, prepared from the polyaddition of isophorone diisocyanate, poly(ethylene glycol), dimethylol propionic acid and hydroxyethyl methacrylate. The chemical structures were analyzed by FT-IR and NMR, and the thermal stability was measured by TGA and DSC. As the ultra-filtration membrane, electrospun nanofibrous polymer blends were used, which can provide high flux efficiency owing to the high porosity and a solid connection between the pores. The blend of PAN and PES was electrospun into the nanofibrous membrane using DMF as a solvent. The microstructure and morphology of the electrospun fibers were characterized by SEM. Fiber diameter and morphology of the PAN/PES nanofibrous membranes were found to depend on the solution concentration and the blend ratio. The thermal property of the PAN/PES membrane was examined via TGA, and the surface tension was estimated by the contact angle measurement. The filtering characteristics of the three-tier membrane were also characterized.
9:00 PM - B5.6
Characterization of Electrospun Polymer Fibers with Dyes
Carl Giller 1 , Keun-Hyung Lee 1 , John Rabolt 1 , Bruce Chase 2 1 Show Abstract
1 MSEG, University of Delaware, Newark, Delaware, United States, 2 , Dupont, Wilmington, Delaware, United States
In this study we examine fundamental interactions between small diameter fibers(100 nanometer to several microns) and azo dyes, notably methyl yellow and copper (II) phthalocyanine. Hydrocarbon polymeric fibers (eg. PP, PB PMP, PS) were successfully prepared from solutions via electrospinning from multi-component solvent systems. These polymer solutions prepared with and without dyes were electrospun under identical conditions. Fiber morphologies were observed with FE-SEM, and interactions between polymer and dyes have been characterized by FT-IR and Raman spectroscopy. Fiber morphologies were changed as evidenced by FE-SEM. Preliminary observations from FT-IR spectroscopy indicate possible polymer-dye interactions.
9:00 PM - B5.7
Isotactic Poly(1-butene) (i-PB) Fibers by Electrospinning
Keun-Hyung Lee 1 , Steven Givens 1 , Bruce Chase 2 , John Rabolt 1 Show Abstract
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 Experimental Station, Dupont, Wilmington, Delaware, United States
A electrospinning study utilizing poly(1-butene) (PB) in various solvent systems was performed. In this study, the effects of a mixture of good solvent and/or non-solvent(s) on the electro-spinnability and morphological appearance of PB electrospun fibers have been investigated. Interesting various shapes such as star, collapsed circle with fiber and hollow hemisphere (HHS)-on-a-string have been observed by FE-SEM. Fiber morphologies and fiber spinnability are strongly dependent on the non-solvent used and non-solvent mixing ratio. Fibrous membranes have been compared with films made from the same polymer solution as used for electrospinning. Fourier transform infrared spectroscopy, Raman spectroscopy as well as wide angle x-ray diffraction and differential scanning calorimetry were chosen as appropriate techniques to investigate PB fibrous membranes and solvent cast films.
9:00 PM - B5.8
Characteristics of PB/PMP blend Fibers via Electrospinning
Keun-Hyung Lee 1 , Christopher Snively 1 2 , Steven Givens 1 , Bruce Chase 3 , John Rabolt 1 Show Abstract
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 Chemical Engineering, University of Delaware, Newark, Delaware, United States, 3 Experimental Station, Dupont, Wilmington, Delaware, United States
Polymer blending is an alternative method to develop new materials exhibiting combinations of properties that could not be obtained from any one polymer. Their properties depend on the compatibility of the blends as well as individual component. In this study, all blends (0 to 100%) were successfully prepared in the form of nonwoven mats via electrospinning. All electrospun blends were made using identical conditions at room temperature. As demonstrated by FE-SEM, fiber morphologies have the twisted ribbon shape. Also, their crystallization behavior and thermal properties have strongly depended on the blend ratio. All blend samples has been characterized with FE-SEM, DSC, TGA, and WAXD as well as FT-IR and Raman spectroscopy.
9:00 PM - B5.9
Stretched Polymer Nanohairs by Tailored Capillarity and Adhesive Force
Hoon Eui Jeong 1 , Sung Hoon Lee 1 , Pilnam Kim 1 , Kahp Y. Suh 1 Show Abstract
1 School of Mechanical and Aerospace Engineering, Seoul National University, Seoul Korea (the Republic of)
Jean S. Stephens Luna Innovations
John F. Rabolt University of Delaware
Gregory C. Rutledge Massachusetts Institute of Technology
Gary E. Wnek Case Western Reserve University
B6: Unique Processing Strategies for Polymer Nanofibers
Wednesday AM, November 29, 2006
Room 206 (Hynes)
9:30 AM - **B6.1
Coaxial Electrospinning for Nanostructured Advanced Materials.
Ignacio Loscertales 1 , Juan E. Díaz Gómez 2 , Manuel Lallave 3 , Jorge Bedía 4 , José Rodriguez-Mirasol 4 , Tomás Cordero 4 , Manuel Márquez 5 , Suresh Shenoy 6 , Gary Wnek 7 , Todd Thorsen 8 , Antonio Barrero 3 Show Abstract
1 Dep. Ingenieria Mecanica y Mecanica de Fluidos, Universidad de Malaga, Malaga Spain, 2 , Yflow S.L., Campanillas, Malaga, Spain, 3 Dep. Ingeniería Energetica y Mecanica de Fluidos , Universidad de Sevilla, Sevilla Spain, 4 Dep.Ingeniería Química, Universidad de Málaga, Málaga Spain, 5 Harrington Department Bioengineering, Arizona State University, Tempe, Arizona, United States, 6 Chemical and Life Sciences Engineering, Virginia Commonwealth University, Richmond, Virginia, United States, 7 Department of Chemical Engineering, Case Western Reserve University, Cleveland, Ohio, United States, 8 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
10:00 AM - B6.2
Controlling the Confined Assembly of Coaxially Electrospun Poly(styrene-block-isoprene) Fibers.
Vibha Kalra 1 , Sergio Mendez 1 , Jung Lee 1 , Huy Nguyen 1 , Manuel Marquez 2 , Yong Joo 1 Show Abstract
1 School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York, United States, 2 INEST Group, Research Center, Philip Morris USA Inc., Richmond, Virginia, United States
Recently, we have reported the formation of self-assembled structures in electrospun poly (styrene-block-isoprene) (PS-b-PI) nanofibers . Despite clear phase-separated domain structures, we were unable to induce any long-range ordered structure because annealing the nanofibers above the glass transition temperature (Tg) resulted in melting and therefore the loss of the fiber morphology. In the present study, our electrospinning set up with a coaxial spinneret system has been combined with sol gel synthesis to produce PS-b-PI fibers enveloped by a silica sheath, and the development of self assembled structures of nearly symmetric poly (styrene-block-isoprene) (PS-b-PI) nanofibers under cylindrical confinement has been investigated. Due to the thermally stable silica shell, we are able to anneal the fibers at high temperatures to obtain long-range ordered structures. Stacked lamellar discs have been shown along the fiber axis for both low and high molecular symmetric copolymers using Transmission Electron Microscopy (TEM). This orientation of lamellar structures with the unit normal along the flow direction seems a consequence of the relaxation of deformation during electrospinning and cylindrical confinement  by the silica sheath. On annealing at higher temperatures yet below the ODT (order disorder transition temperature) for long times lamellae blocks are seen to relax to an orientation parallel to the cylindrical silica wall forming alternating concentric cylinders of PI and PS. We believe that this coaxial electrospinning scheme of self-assembling block copolymer and thermally stable silica as the core and the sheath together with annealing can provide a useful means to control the confined assembly of block copolymers.1.Kalra, V.; Kakad, P.A.; Mendez, S.; Ivannikov, T.; Kamperman, M.; Joo, Y.L. Macromolecules 2006 (in press).2.Shin, K.; Xiang, H.; Moon, S.I.; Kim, T.; McCarthy, T.J.; Russell, T.P. Science 2004, 306, 76.
10:15 AM - B6.3
Production and Characterization of Core-Sheath Electrospun Nanofibers doped with Carbon Nanotubes
Satyajeet Ojha 1 , Jamal Irving 1 , Russell Gorga 1 Show Abstract
1 Textile Engineering, Chemistry and Science, North Carolina State University, Raleigh, North Carolina, United States
Electrospinning is a process to develop fibers with diameters at the nanometer range. Recently much interest has been generated in this technique due to the large number of potential biomedical uses such as tissue engineering and drug delivery applications. Our effort has been to produce composite fibers utilizing carbon nanotubes for enhanced electrical conductivity. The optimization of the solution and process parameters such as solution viscosity and feed rate and polymer concentration, electric field, and the distance between needle and grounded collector are discussed. In addition, the fabrication of a core-sheath fiber structure is presented, with a core of poly (ethylene oxide) (PEO) and a sheath of PEO doped with carbon nanotubes (CNTs). Since the addition of CNTs increases the viscosity of the polymer solution, fabrication of such a structure is a complex process in which rheology, surface tension, polymer concentration of the two solutions must be optimized for successful spinning. Finally, we investigate the effect dispersing agents, such as Gum Arabic, have on the process as well as the fiber properties. As expected, our research shows that the addition of Gum Arabic has reduced the CNT concentration necessary to attain percolation.
10:30 AM - B6.4
Plasma-radiation Enhanced Nanofiber-thermoplastic Composites.
Aflal Mohamed 1 , Yossef Elabd 1 , Giuseppe Palmese 1 Show Abstract
1 Chemical and Biological Engineering, Drexel University, Philadelphia, Pennsylvania, United States
10:45 AM - B6.5
Gradient Nanobtubes by Wetting of Ordered Porous Templates.
Marc Milbradt 1 , Olaf Kriha 2 , Martin Steinhart 3 , Andreas Greiner 2 , Joachim Wendorff 2 , Ralf Wehrspohn 1 Show Abstract
1 Department of Physics, University of Paderborn, Paderborn Germany, 2 Department of Chemistry, University of Marburg, Marburg Germany, 3 , Max-Planck-Institute of Microstructure Physics, Halle Germany
B7: Processing of Polymer Nanofibers: Fundamentals
Wednesday AM, November 29, 2006
Room 206 (Hynes)
11:30 AM - **B7.1
Nanofibers Collected Reproducibly.
Darrell Reneker 1 , Tao Han 1 Show Abstract
1 Polymer Science, The University of Akron, Akron, Ohio, United States
The determination of the behavior of the jet path in the vicinity of the onset of the first bending instability is important for the orderly collection of the nanofibers produced by electrospinning. Adjustments of the fluid flow, the electrical current, and the shape of the region from which the jet issued, produced a stable jet which was observed with a high frame rate, short exposure time video camera. The collection process was complicated but predictable within limits, so the design and creation of two or three dimensional structures of nanofibers is feasible, if the considerations described below are incorporated into the design and production processes. The fluid jet in the straight segment of the path, and the more solid nanofibers in the coils of the first bending instability were collected on stationary and moving surfaces. The diameter and characteristic path of the collected jet depended on the exact distance between the tip and the collector, if other parameters were not changed. The moving surfaces caused the various coils that were collected to be displaced rather than landing on and thereby obscuring each other. The fiber collected on the moving surfaces preserved a record of the mechanical and electrical instabilities that occurred. If the straight segment was fluid, it formed a series of small sessile drops on the collector, but when the jet was more solid, buckling occurred and produced small, complicated loops close to point at which the jet hit the surface. Buckling was observed during collection of the straight segment and the first coils of the electrically driven bending instability. The second electrically driven bending instability produced a series of smaller coils on the larger coils of the first bending instability. Both a rotating drum and an inclined plane were used to collect the fibers. Surface velocities of up to about 5 meters per second were used. These velocities are commensurate with the velocities at which the solidifying jet approached the surface. A variety of structures of loops, both conglutinated and not, associated with the instabilities can be created.The jets used in this work were formed from solutions of polyethylene oxide, nylon-6, polycaprolactone, polyacrylonitrile, and other polymers. Several solvents were used for some of the polymers, and details of the jet path changed when the solvent or the concentration changed. The jets issued from a glass capillary with an orifice diameter of about 60 microns. Relatively low voltages, in the range of 500 to 5000 volts were used. With proper illumination, interference colors associated with jet diameter around 10 microns were observed in the straight segment. The color patterns were stable, indicating that the process was running within reproducible limits.
12:00 PM - B7.2
Characterization of Electrospinning Fiber Diameter Distributions and Process Dynamics for Development of Real-Time Control.
Xuri Yan 1 , Michael Gevelber 1 , Jian Yu 2 , Gregory Rutledge 2 Show Abstract
1 Manufacturing Engineering, Boston University, Boston, Massachusetts, United States, 2 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
In many emerging electrospinning applications, the fiber diameter distribution has important implications for yield, material utilization, and production rate. This paper reports our results on analyzing the relation between the operating point and the resulting diameter distributions, as well as the dynamic process characteristics which can be used for developing a closed-loop system for controlling diameter distribution.A computer based data acquisition and actuator control system is used to map the operating conditions for achieving a steady cone-jet shape for a range of Poly(ethylene oxide) concentrations. A vision system is used to dynamically measure the variations in the upper cone-jet volume and the upper jet diameter. At any pump flow rate, there is a range of voltages that result in a steady upper jet, although the volume has periodic variations but remains bounded stable. The relation between variations in upper cone volume and jet diameter to the fiber diameter distribution is studied, and it is observed that large variations occur when the system is not operated at a stable operating point. Variations are also analyzed in terms of operating at different flow rates, concentration levels, and polymer molecular weight. The fundamental dynamics of the process are determined as a function of operating point, and the implications for developing real time process control system are discussed.
12:15 PM - B7.3
Electrostatic Processing of Polyolefins.
Steven Givens 1 , Keun-Hyung Lee 1 , D. Bruce Chase 1 , John Rabolt 1 Show Abstract
1 Material Science, University of Delaware, Newark, Delaware, United States
12:30 PM - B7.4
Highly Porous Nanofibers by Electrospinning into a Cryogenic Liquid
Jesse McCann 1 , Manuel Marquez 2 , Younan Xia 1 Show Abstract
1 Department of Chemistry, University of Washington, Seattle, Washington, United States, 2 INEST, PMUSA, Richmond, Virginia, United States
There has been much interest recently in extending electrospinning to fabricate fibers of novel compositions and morphologies. By immersing the collector in a bath of liquid nitrogen, porous nanofibers can be obtained from polymer solutions as a result of thermally induced phase separation (TIPS) between solvent-rich and solvent-poor regions in the fiber, followed by removal of solvent in vacuo. This method is versatile in that it can be readily used with non-volatile solvents and does not require selective dissolution of phase-separated polymers. The porosity and resultant morphology of the fibers can be controlled by altering the collection distance and freeze-dying protocol. As this method is dependent on the presence of residual solvent to induce phase separation, it is also applicable to electrospray in order to generate hollow and/or porous particles in a simple and inexpensive fashion. In addition, the fibers are porous throughout, thus making them suitable for encapsulation of active substances or catalysts. By altering the surface properties of the fibers, it is possible to control the adhesion and growth of cells to the fibers, thus enhancing the properties of nanofiber assemblies for applications such as tissue engineering. In addition, the increased surface area of the fibers can be used to create superhydrophobic coatings.
12:45 PM - B7.5
One Dimensional Nanocomposites
Nikhil Sharma 1 , Darrin Pochan 1 Show Abstract
1 Materials Science & Engineering, University of Delaware, Newark, Delaware, United States
Tailoring the structure of hybrid materials at the nanoscale in order to enhance their properties can result in advanced materials with remarkable attributes and poses significant research challenges. One-dimensional nanoparticle assemblies are an interesting class of materials that may provide an insight into the fundamentals of quantum mechanics of nanomaterials and have potential applications as sensors, in drug-delivery, and in the conduction of novel signals such as phonons and spin states. Experimental work with electrospinning of polyethylene oxide fibers with inorganic particles (silica and silver) is underway that utilizes a coaxial capillary electrospinning apparatus for the formation of one-dimensional assemblies of nanoparticles encapsulated within the polymer nanofiber. The method has been demonstrated in the successful creation of 1D assemblies of differently sized silica nanoparticles. The effect of change in solution concentrations and relative flow rates in internal and external channels of the coaxial electrospinning apparatus on the inter-particle distance are being investigated.
B8: Structure, Processing, Property Relationships in Polymer Nanofibers
Wednesday PM, November 29, 2006
Room 206 (Hynes)
2:30 PM - **B8.1
Electrospinning of Nanofibers and Beyond: Towards New Techniques, Functions and Applications.
Joachim Wendorff 1 , Andreas Greiner 1 Show Abstract
1 Department of Chemistry, Philipps-University, Marburg Germany
Nanofibers, core shell nanofibers as well as hollow nanofibers and nanotubes based on polymers serve as a platform for a broad range of applications as filters, textiles, in photonics, sensorics, catalysis or in medicine and pharmacy. Such nanoobjects become available by techniques such as the well known electrospinning and the more recently developed co-electrospinning of nanofibers. Electrospinning takes place in the latter case via two or more concentrically arranged dies yielding core shell fibers or fibers with droplet –like inclusions arranged along the center of the fibers, where the inclusions are composed of polymers, low molar mass synthetic functional units or molecules of biological origins such as proteins. Furthermore template methods have been developed utilizing electrospun nanofibers or porous substrate which yield core shell fibers of complex architectures, with or without gradient structures or hollow nanofibers and nanotubes. These techniques are not restricted to polymers of synthetic and natural origin, but are able – based on precursor substances - to deliver nanofibers and nanotubes composed of metals, glasses, ceramics. These preparation techniques allow furthermore to introduce into these nanostructures specific functional compounds such as semiconductor or catalytic nanoparticles, chromophores but also enzymes, proteins, microorganism etc. directly during the preparation process in a very gentle way. Biological objects such as, for instance, proteins can be immobilized in this way in a fluid environment within these polymer based nanoobjects in such a way that they keep their native conformation and the corresponding functions among them biosensoric functions. Of particular interest are such nanostructures, composed of biocompatible polymers or even biodegradable polymers, in medicine and pharmacy for instance as scaffolds for tissue engineering, as drug delivery systems among others for tumor therapy and inhalation therapy or as surface modifiers for implants acting as drug release systems for specific drugs.
3:00 PM - B8.2
Texture Engineering in Nanotubes Consisting of Partially Crystalline Polymers.
Nitin Shingne 2 1 , Markus Geuss 1 , Martin Steinhart 1 , Lili Zhao 1 , Ulrich Goesele 1 , Elke Hempel 2 , Thomas Thurn-Albrecht 2 Show Abstract
2 Institute of Physics, Martin Luther University, Halle (Saale) Germany, 1 , Max-Plank-Institute of Microstructure Physics, Halle (Saale) Germany
3:15 PM - B8.3
A Novel Method to Measure the Mechanical Properties of Electrospun Polyacrylonitrile Nanofibers
Ioannis Chasiotis 1 , Mohammad Naraghi 1 , Hal Kahn 2 , Yuris Dzenis 3 Show Abstract
1 Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Materials Science and Engineering, Case Western Reserve University, Cleveland, Ohio, United States, 3 Department of Engineering Mechanics , University of Nebraska , Lincoln, Nebraska, United States
Electrospun polymeric nanofibers are expected to demonstrate mechanical behavior very different from bulk due to their small diameters and high surface-to-volume ratios. However, their small dimensions and high compliance have posed so far a major challenge in characterizing their elastic, plastic, and failure properties.In this presentation we report on a method to measure the mechanical behavior of electrospun polyacrylonitrile (PAN) nanofibers (150,000 MW) as a function of strain rate and fiber diameter. The PAN nanofiber test specimens were 300-800 nm in diameter and 12-90 μm in length. The novel test platform was a microelectromechanical (MEM) tensile testing device fabricated with a combination of surface micromachining and a focused ion beam. It allowed for independent measurement of the applied force and the fiber elongation with 80 nm displacement resolution. The fiber properties were measured at three different strain rates: 0.00025 s-1, 0.0025 s-1, 0.025 s-1. Their stress-strain response was linear up to 2% strain that was followed by a stress plateau. The elastic modulus was as high as 3.8 GPa being rather insensitive to loading rate and fiber diameter. The nanofibers demonstrated a remarkable ultimate strain that varied between 70-120% for saturation stresses in the range of 20-130 MPa depending on loading rate and fiber diameter. The ultimate strain decreased with increasing strain rate while the saturation stress increased for the slowest strain rate. Fibers with larger diameters demonstrated a reduced saturation stress for most strain rates. Finally, the deformation and failure mechanisms pertaining to these PAN nanofibers will be discussed in connection to electron and atomic force microscopy images.
3:30 PM - B8.4
A Novel Test and Characterization Device for obtaining the Nano-mechanical Behavior of Electrospun Polyaniline Micro/nano-scale Fibers.
Pankaj Kaul 1 , Liangti Qu 2 , Vikas Prakash 1 , Alexis Abramson 1 , Liming Dai 2 Show Abstract
1 Mechanical and Aerospace Engineeering, Case Western Reserve University , Cleveland, Ohio, United States, 2 Chemical and Materials Engineering, University of Dayton, Dayton, Ohio, United States
3:45 PM - B8.5
Structure and Nanomechanical Characterization of Well-aligned Electrospun Polystyrene/MWCNT Composite Nanofibers
Yuan Ji 1 , Jaseung Koo 1 , Shouren Ge 1 , Bingquan Li 1 , Batya Herzberg 2 , Toby Klein 2 , Jonathan Sokolov 1 , Miriam Rafailovich 1 Show Abstract
1 Materials Science and Engineering, SUNY at Stony Brook, Stony Brook, New York, United States, 2 , SKA High School for Girls, Hewllett Bay Park, New York, United States
Carboxyl-functionalized multi-wall carbon nanotubes (MWCNTs) were incorporated into polystyrene(PS)/DMF solutions and electrospun to form PS/MWCNT composite nanofibers. The fiber diameters were adjusted from 80 nm to 4 μm by changing the solution concentration. The electropsun nanofibers were collected onto a high-speed rotator where they became well aligned. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the surface morphology and interior structure of the electrospun nanofibers. The MWCNTs were well aligned along the fiber axis direction, which can be attributed to the high shear flow during the electrospinning process. A three-point bending test, using atomic force microscopy (AFM), was utilized to measure the Young’s moduli of the nanofibers as a function of fiber diameter and MWCNT concentration. Shear modulation force microscopy (SMFM) was employed to measure the surface glass transition temperature of an individual PS/MWCNT composite nanofiber. The existence of MWCNTs inside the electrospun fibers enhanced the Young’s moduli and increased the glass transition temperature by nearly 10 degrees. Supported by NSF-MRSEC
B9: Properties of Polymer Nanofiber Membranes
Wednesday PM, November 29, 2006
Room 206 (Hynes)
4:30 PM - **B9.1
Electrospinning: An Industrial Perspective.
H. Young Chung 1 Show Abstract
1 Corp. Technology, Donaldson Co., Inc., Minneapolis, Minnesota, United States
5:00 PM - B9.2
Prediction of Electrospinning Parameters for Targeted Fiber Diameter and Applications to Superhydrophobicity
Eren Simsek 1 , Sinan Yordem 1 , Melih Papila 1 , Yusuf Menceloglu 1 Show Abstract
1 Materials Science and Engineering Program, Sabanci University, Istanbul Turkey
In this study, how material and process parameters affect the diameter of electrospun fibers of polyacrylonitrile was investigated. Design of the experiments was performed via response surface methodology (RSM) at the settings of solution concentration, voltage and tip-to-ground distance. Effect of applied voltage and solution concentration on fiber diameter was investigated as two-variable process domains of several collector distances which varied at a fixed polymer molecular weight. The mean diameter and coefficient of variation were modeled by polynomial response surfaces as functions of solution concentration and voltage at each collector distance. This allowed the evaluation of the significance of each parameter on the fiber diameter. It was determined that, in the corresponding domain, effect of applied voltage in micro-scale fiber diameter was almost negligible at high solution concentrations and collector distances. However, all three parameters were found statistically significant for the production of fibers in the nano-scale. The predictions also showed that there is a negative correlation between the mean diameter and coefficient of variation for the fiber diameter. These results led us to investigate the effect of the same parameters on the hydrophobicity of electrospun fibers. Surfaces prepared by electrospinning have morphologies of micro and nano-scale structures which limit contact area between the low surface energy solid substrate and water by introducing large surface roughness. Being able to create bead-only, bead on the string, nano and micro fiber morphologies as a function of concentration and applied voltage alone brings up the question of their interactive influences on the morphology, so the hydrophobicity. We investigated the transition between bead-only and micro-fiber morphology and resultant hydrophobicity via contact and sliding angles of the electrospun surfaces (of a low surface energy polymer) as a function of applied voltage and solution concentration at a fixed collector distance, again via RSM which this time provided the determination of the significance of the parameters on the hydrophobic properties. The main parameter determining the contact and sliding angle of a superhydrophobic electrospun surface was found to be the concentration of the solution. The applied voltage was determined to have very slight effect on hydrophobicity for both nano and microfiber morphologies.
5:15 PM - B9.3
Superhydrophobic Surfaces with Optical Functionalities.
Minglin Ma 1 , Malancha Gupta 1 , Randal Hill 2 , Karen Gleason 1 , Gregory Rutledge 1 Show Abstract
1 cheme, MIT, Cambridge, Massachusetts, United States, 2 , MIT, Cambridge, Massachusetts, United States
Superhydrophobic surfaces with large water contact angle (>150 deg) and a low hysteresis or sliding angle (<10 deg) have a number of applications involving water proof and self-cleaning. Incorporating optical functionalities into superhydrophobic surfaces considerably enlarges their applications. Here we report the fabrication of superhydrophobic surfaces with special optical properties such as transparency, fluorescence and structure color based on an electrostatic spraying or spinning technique. The transparent superhydrophobic surfaces were obtained by electrospraying a dilute polyacrylonitrile (PAN) solution onto transparent glass substrates followed by a surface treatment using an initiated chemical vapor deposition (iCVD). The electrosprayed PAN nanoparticle thin layer coatings have sufficient surface roughness for superhydrophobicity while maintaining the transparence of the glass substrates due to the relatively low light absorption and scattering. The superhydrophobic surface with fluorescent property was composed of hat-like porous microparticles of a phenyleneethynylene conjugated polymer (PPE) made by electrospraying its solution in chloroform. The superhydrophobicity is due to combined effects of the low surface energy of PPE and the high roughness of the surface. Finally, we report the superhydrophobic surface with structure colors made by electrospinning a phenyl-siloxane-resin PMMA hybrid material and a subsequent surface hydrophobization. The structure color is angle-dependent to the observer and probably due to the interference of the reflected or transmitted light.
5:30 PM - B9.4
Polarizing Energy Transfer Luminescence From Single Polymer Nanowires by Control of Internal Molecular Arrangements
Gareth Redmond 1 Show Abstract
1 Nanotechnology Group, Tyndall National Institute, Cork Ireland
We have investigated template-assisted formation of poly(9,9-dioctylfluorenyl-2,7-diyl), PFO, nanowires with respect to effects of internal molecular structure on the processes of light emission from the wires. We used template wetting to form high-yields of pristine nanowires with controlled dimensions. By selective template removal, wires could be freed and dispersed yielding ~10e9 discrete nano-optical elements of uniform cylindrical morphology, 200–300 nm diameter and 5–50 µm length. Epi-fluorescence microscopic imaging indicated that the nanowires luminesced under UV excitation with intense blue light emission and strong radial out-coupling of emission from the wire bodies. Absorption spectra of nanowire arrays indicated that ~40% of the polymer strand segments within the wires existed in the planar, energetically favourable β-phase conformation and that the remainder of the strand segments existed in the higher-energy, normal (glassy) phase. Raman micro-spectroscopy confirmed the presence of β-phase PFO within the wires. Given the presence of so much β-phase within the nanowires, optically excited luminescence spectra of the wires were completely dominated by emission from this phase. The large β-phase fraction present in the wires was attributed to mechanical stresses imposed on the polymer molecules during template synthesis, i.e., during template pore wetting and/or solvent evaporation following pore filling, since it is largely accepted that β-phase is formed by stress-induced planarization of the PFO molecular backbone. Importantly, polarized optical microscopic studies of nanowire birefringence with supporting X-ray diffraction studies further indicated axial alignment of PFO molecules within the wires. We therefore employed high spatial resolution polarized emission microscopy to investigate the effect of such internal molecular organisation on nanowire luminescence. Data acquired for single nanowires revealed polarized, on-axis emission, only from β-phase segments, with emission dichroic ratios of up to 9. This anisotropy was attributed to the forced axial alignment of the β-phase strand segments during wire synthesis. In addition, only a weak dependence of the emission dichroic ratio on the excitation light polarization direction was observed. This large excitation polarization independent emission anisotropy was attributed to efficient polarizing energy transfer from randomly aligned polymer strand segments to aligned β-phase strand segments within the wires. This suggested that the nanowires act as photophysical machines that harvest and convert excitation light of any polarization to highly polarized on-axis light emission. To create optically functional nanowire structures, a simple, non-destructive micromanipulation tool was developed for positioning of wires on a substrate. The effectiveness of the technique was demonstrated by fabrication of a PFO nanowire based polarized emissive microstructure.
5:45 PM - B9.5
Development of Novel Materials for Proton Exchange Membrane Fuel Cells.
Burak Birkan 1 , Albert Levi 1 , Cenk Gumeci 1 , Yusuf Z Menceloglu 1 Show Abstract
1 Material Science and Engineering, Sabanci University, Istanbul Turkey
Fuel cells are electrochemical devices that convert the chemical energy of a reaction directly into electrical energy. Among them, Proton Exchange Membrane Fuel Cells (PEMFC) delivers the highest power density, which offers low weight, cost, and volume. Because of these reasons, PEMFC’s have a wide application areas as an environmentally friendly energy source but also have limitations for larger-scale commercial use because of their poor ionic conductivities at low humidity and/or elevated temperatures, susceptibilities to chemical degradation at elevated temperatures and finally membrane cost.In this research, the aim is to synthesize porous structures from polyacrylonitrile based carbon fibres bearing nanosize metal particles with high specific surface areas. The polymeric fibres will be produced using electrospinning technique from different types of copolymers of polyacrylonitrile at varying ratios of co-monomers. By optimization of comonomer/polymer and metal/polymer ratio and varying the carbonization procedures we target to characterize the effect of pendant ionic side chain on the size of metal particle on the polymer fibre.By the application of this technique it is possible to decrease the catalytic material concentration up to 0.2 mg catalytic material/cm2 area of the carbon fiber structure by enhancing catalytic performance and/or enabling by using less catalytic material for equivalent catalytic performance which can lead to cost savings, amongst other advantages. These materials can be used in fuel cells, conductors, solar cells, sensors, electrochemical actuators, thin film transistors, reflectors and compact disks.
Jean S. Stephens Luna Innovations
John F. Rabolt University of Delaware
Gregory C. Rutledge Massachusetts Institute of Technology
Gary E. Wnek Case Western Reserve University
B10: Applications of Polymer Nanofibers to Tissue Engineering II
Thursday AM, November 30, 2006
Room 206 (Hynes)
9:30 AM - **B10.1
Elastomeric Biodegradable Electrospun Polymers for Tissue Engineering and Regeneration
Kimberly Woodhouse 1 Show Abstract
1 Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada
The goal of tissue engineering devices is to mimic natural systems for therapeutic treatment of failing tissue. Polymers are being studied to either induce tissue growth or to provide temporary scaffolds for cells to be implanted . In vivo, the extracellular matrix (ECM) is a network of fibrous proteins and adhesion molecules that provide structural support for cells. In many application including cardiac patches and cardiovascular implants, polymers with elastomeric mechanical properties are required as scaffolds for tissue engineered constructs. Two such polymeric materials are a biodegradable polyurethane and an elastin like polypeptide based fiber. The segmented-polyurethane has been synthesized using an amino acid-derived diisocyanate and a phenylalanine-based chain extender. The chemical architecture of this polymer joins the necessary functional components (i.e., hydrolyzable groups) to promote in vivo degradation. The segmented nature of the polyurethane allows for elastomeric behavior thus providing the mechanical properties required to respond to physiological stresses in a cardiac patch application. The second polymer to be described is a recombinant human elastin-like polypeptide that has been shown to form materials of different architectures in vitro. Elastin is an extracellular matrix protein found in tissues requiring elastic recoil and is the complement to collagen which provides structural rigidity. Using E-coli, ESI has expressed, produced and purified a family of recombinant human elastin polypeptides. We have shown that such polypeptides contain self-assembly information promoting the spontaneous formation of highly stable fibrils in a concentration/temperature dependent manner. These fibers can be cross-linked with agents including peroxidase, glutaraldehyde, and carbodiimides. The resulting materials have mechanical properties very similar to natural elastin, with high extensibility, rubber-like recoil and a long half-life. They can be produced using commercially available processes including electrospinning. Embryonic stem (ES) cells are an attractive source of cells for many applications. In our laboratory we have created a model for cardiac tissue by seeding ES cell-derived cardiomyocytes onto the biodegradable polyurethane processed using both thermally induced phase segregation and electrospining. Most promising is the ability of ES cell-derived cardiomyocytes to contract the polymer scaffold with each beat. Both the polyurethane and elastin based polymers can impart elastomeric properties to materials allowing their use in cardiac and cardiovascular applications. These polymers and their impact on cardiomyocyte morphology and gene expression will be described with a view to highlighting their flexible and diverse properties.
10:00 AM - B10.2
Aligned Biofunctionalized Nanofibrous Scaffolds for Neural Stem Cell Differentiation.
Shawn Lim 1 , Hongjun Song 2 , Hai-Quan Mao 3 Show Abstract
1 Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States, 2 Institute for Cell Engineering, Departments of Neurology and Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States, 3 Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States
A current and persistent obstacle to the treatment of neurodegenerative diseases has been the availability of a suitable cellular population. A subpopulation of constantly renewing neural stem cells (NSCs) has been found in the subventricular and hippocampal subgranular zones of the adult mammalian brain, that exhibit the potential to differentiate into the various neural subtypes. Signals from the local environment are crucial in dictating the fate choice of these neural progenitors, whether it be promoting proliferation and phenotype maintenance, or stimulation of neurogenesis[2,3]. In order to develop effective cellular therapies in vitro for disease treatment, it is crucial to gain a clearer insight into the mechanisms controlling NSC behavior as well as their response to an artificial extracellular matrix (ECM). In this study, we investigate the influence of contact guidance from aligned nanofibrous meshes, in combination with surface-bound adhesive molecules, on the differentiated fate choice of adult rat NSCs.Aligned fibrous meshes of poly(ε-caprolactone) (PCL), a biocompatible polymer, were prepared by electrospinning a PCL solution onto the edge of a rotating aluminum collecting disc. A coating of poly-L-ornithine/laminin or fibronectin, both important components of the natural ECM, was adsorbed onto the surface of the meshes prior to cell seeding. Following five days of culture in differentiation medium, NSCs were fixed and immunostained for the appropriate neural subtype-specific markers – neurons, astrocytes and oligodendrocytes. The relative proportion of each subtype was determined by cell counting under confocal and fluorescence microscopy, in order to evaluate the effect of cell alignment and surface adhesion. Three sets of meshes with average diameters of 890 nm, 550 nm and 380 nm, and a high degree of alignment were obtained by variation of electrospinning parameters. A greater extent of NSC adhesion was observed on uncoated meshes than on uncoated films; however, adhesion was equally good on all coated substrates. NSCs cultured on aligned meshes were clearly guided by the topography of the underlying substrate – the majority of neurites extended from cells were aligned in parallel to the axis of fiber alignment. In contrast, no such directionality was observed in cells cultured on the thin films. The effect of ECM adhesion signal presentation in conjunction with nanofiber contact guidance on NSC differentiation potential is currently under investigation. Our surface-functionalized nanofibrous substrates present a novel approach to dissect the individual effects of various cues on NSC adhesion and fate choice, and paves the way for evaluating their synergistic impact in combination. Palmer TD, Takahashi J, Gage FH. Mol. Cell Neurosci. 1997; 8(60):389-404 Gage FH. Science 2000; 287:1433-1438 Temple S. Nature 2001; 414:112-117
10:15 AM - B10.3
Electrospun Polymer Fibers for Tissue Engineered Scaffolds
Danielle Rockwood 1 , Robert Akins 2 , Kimberly Woodhouse 4 , Joanna Fromstein 4 , D. Chase 3 1 , John Rabolt 1 Show Abstract
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 Biomedical Research, A.I. duPont Hospital for Children, Wilmington, Delaware, United States, 4 Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada, 3 Corporate Center for Analytical Sciences, DuPont de Nemours Company, Wilmington, Delaware, United States
The goal of this research is to fabricate a cardiac patch using a synthetic scaffold as a vehicle to transport cells to the site of an injury. In particular, a segmented-polyurethane was synthesized with blocks of polycaprolactone as the soft segment and a hard segment made of lysine diisocyanate and phenylalanine residues. Throughout the polymer backbone there are ester linkages to promote hydrolytic cleavage and the phenylalanine groups are recognized by enzymes to aid in degradation. Therefore, this polymer is biodegradable but it still maintains elastomeric properties that will be desirable for applications in the heart. In order to construct a tissue engineering scaffold, this material was electrospun to make a fibrous mat to mimic the structure of the extracellular matrix. Scanning electron microscopy revealed the architecture of the polyurethane mats and showed that inter-fiber junctions were prevalent. Woodhouse and co-workers previously examined the properties and degradation of the bulk material. Current work is focused on investigating the material properties of the electrospun scaffolds and the degradation rate of the fibrous mats in the presence of enzymes. Preliminary cell work focused on seeding murine derived-skeletal myoblasts (C2C12) onto the electrospun polyurethane. These studies showed that cells were able to attach and proliferate on the material. Further studies aim to show that primary cardiac cells from neonatal rats can also attach, form gap junctions, beat, and excrete collagen.Another promising material being studied is poly(N-isopropyl acrylamide) (pNIPAM) which is known for its thermoresponsive behavior. Recent work by Okano and co-workers has shown that monolayers of cells can be grown on oligomers of pNIPAM that have been immobilized on polystyrene dishes. When the temperature of the dish is lowered to 25 οC, below the lower critical solution temperature of the pNIPAM, the sheet of cells can be lifted from the dish without the use of enzymes. We have electrospun pNIPAM in order to create a three-dimensional network of fibers. Current work is focusing on seeding cells onto these matrices with the intention of removing the polymer once cells begin to excrete their own proteins and form intercellular junctions.
10:30 AM - B10.4
Bioresorbable Core-Sheath Bicomponent Nanofibrous Scaffolds for Tissue Engineering.
Ajit Moghe 1 , Bhupender Gupta 1 Show Abstract
1 , North Carolina State University, Raleigh, North Carolina, United States
It has been shown that the nanofibrous scaffolds produced by electrospinning, very closely resemble the native extracellular matrix in that they provide extremely high specific surface area for cell anchoring and interconnected pore network for optimum cell growth and proliferation [1,2]. The use of biodegradable synthetic and natural polymers in scaffolds for tissue engineering has been reported in the literature. The primary reasons for using natural polymers have been their biocompatibility, and inherent capability to bind cells, owing to the presence of the cell recognition compounds, e.g. a protein sequence RGD . Synthetic biodegradable polymers, on the other hand, provide the necessary mechanical properties, such as viscoelasticity and strength, and their degradation rate can be controlled positively . Accordingly, for tissue engineering, an ideal structure thought of is a biodegradable bicomponent nanofiber with the sheath of natural polymer and the core of synthetic polymer. Such composite structure involving combinations of polymers may prove to be valuable for a variety of other applications as well, such as drug delivery, optical fibers, and nanowires.Using a novel co-axial electrospinning set up, uniform core-sheath nanofibers have been produced using collagen (type I) and gelatin as natural and polycaprolactone as synthetic polymers. Electron microscopic analyses clearly demonstrated the presence of core-sheath morphology of the nanofibers. The applied voltage was found to be a governing factor in the bicomponent fiber formation process, the role of which will be discussed. Polymer concentrations, polymer extrusion rates as well as the difference between the sheath and core extrusion rates were found to affect morphology and uniformity of the resulting bicomponent structure, which is expected to have an effect on cell activity. Since the uniqueness of these structures lie in their being able to degrade at a controlled rate, optimum for cell growth, factors affecting degradation and the parameters controlling it and the effect of degradation on the human mesenchymal stem cell activity will be presented. References: Yashimoto et al., Biomaterials 2003;24(12):2077-2082. Wnek et al., Nano Letters 2003;3(2):213-216. Boland et al., Frontiers in Bioscience 2004;9:1422-1432. Hakkarainen, Adv. Polym. Sci. 2002;157:113-138
B11: Applications of Polymer Nanofibers to Tissue Engineering III
Thursday AM, November 30, 2006
Room 206 (Hynes)
11:15 AM - **B11.1
Biomimetic and Bioactive Nano-fibrous Scaffolds for Regeneration.
Peter Ma 1 Show Abstract
1 Biologic and Materials Sciences, University of Michigan, Ann Arbor, Michigan, United States
11:45 AM - B11.2
Degradation of Electrospun Nanofiber Scaffold by Short Wave-Length Ultraviolet Radiation Treatment and Its Potential Applications in Tissue Engineering
Yixiang Dong 1 , Thomas Yong 1 , Casey Chan 1 2 , Seeram Ramakrishna 1 3 4 Show Abstract
1 Division of Bioengineering, National University of Singapore, Singapore Singapore, 2 Dept. of Orthopedic Surgery, National University of Singapore, Singapore Singapore, 3 Dept. of Mechanical Engineering, National University of Singapore, Singapore Singapore, 4 NUS Nanoscience and Nanotechnology Initiative (NUSNNI), National University of Singapore, Singapore Singapore
Development in the field of tissue engineering has brought much attention in the fabrication and preparation of scaffold with biopolymers and/or biodegradable synthetic polymers nanofibers. The rationale for using nanofibers is based on the theory that cells attach and organize well around fibers with diameters smaller than the diameter of the cells. The non-woven polymeric meshwork is a mimic to the nano-scale protein fiber meshwork in native extracellular matrix. Electrospun biodegradable polymeric nanofiber is increasingly being used to fabricate scaffolds for tissue engineering applications as it provides high surface area to volume ratio and possesses high porosity. For in vitro experiments, the most common way to sterilize polymeric nanofiber scaffolds is either by using 75% ethanol or UV sterilization. In this study, we aim to evaluate the effects of UV radiation, commonly used to sterilize polymer nanofiber scaffolds, on the degradation rate in polymer nanofibers, and potentially capitalizing on UV photolithography in patterning polymeric nanofiber scaffolds for tissue engineering applications. The co-polymers poly(DL-lactic-glycolic) acid [PLGA, 75:25] and poly(L-lactic acid)-co-poly(ε-caprolactone) [P(LLA-CL), 70:30] were chosen for this study. PLGA and P(LLA-CL) were dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol at 20% and 12% weight/volume ratio, respectively, and electrospun at 12.5 and 10 kV with a feed rate of 1 and 1.5 ml/hr, respectively, at a distance of 15 cm between the spinneret and the grounded collector, to fabricate nanofiber scaffolds. The scaffolds were irradiated with 254 nm UV with intensity of 170μW/cm2 at various treatment durations, and followed by mechanical test and molecular weight analysis. We found that UV sterilization of polymer nanofibers for tissue engineering studies at 254 nm will induce degradation with varying rates. At one hour UV treatment, the average molecular weight of PLGA and PLLA-CL were reduced by 47% and 43%, respectively, with corresponding reduction in the tensile strength of 26% for PLGA and 28% for PLLA-CL. Hence, precautions may have to be taken into consideration when sterilizing biodegradable polymers by UV treatment. However, we can capitalize on the accelerated degradation of scaffolds following UV-irradiation to produce and/or design defined patterns on the scaffolds. By placing specially designed masks over the scaffolds followed by UV treatment, we were able to fabricate patterned structures on the scaffold to meet defined requirements in tissue engineering applications. We have shown that patterned scaffolds produced by UV irradiation were able to support cell in-growth into the scaffolds. In conclusion, UV treatment of polymeric nanofiber scaffolds increases the degradation rate but allowing one to produce patterned scaffolds with potentials in tissue engineering applications.
12:00 PM - B11.3
Electrospun Mesoporous Molecular Sieves
Kenneth Balkus 1 , Chunrong Xiong 1 , Minedys Macias 1 , Nadia Khanam 1 Show Abstract
1 Chemistry, University of Texas at Dallas, Richardson, Texas, United States
Mesoporous molecular sieves comprise a growing family of nanoporous materials. The evolution of new molecular sieves and associated applications has generated a greater demand for new ways to manipulate and configure these porous materials. The required form of a molecular sieve may involve dramatically different length scales, ranging from shaped particles to fibers and continuous coatings. We first reported the formation of DAM-1 and SBA-15 type mesoporous silica fibers using the technique known as electrospinning. Subsequently, we extended this work to include a variety of mesoporous metal oxides. For example, the formation of mesoporous TiO2 fibers as spider webs and papers has been achieved by electrostatic deposition. The mesoporous fibers and other forms such as shaped particles and films have been employed as templates to grow TiO2 nanofibers in various configurations. Molecular sieves in these configurations have also been prepared with various organic functional groups as well as reactive species such as enzymes and carbon nanotubes. Polymer fibers have been co-spun with the molecular sieves using multiple spinnerets. Recent Progress in electrospinning mesoporous molecular sieves and hybrid frameworks will be presented including apllications in tissue engineering.
12:15 PM - B11.4
Crosslinked Chitosan Nanofibers.
Caroline Schauer 1 , Jessica Schiffman 1 Show Abstract
1 Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States
Electrospinning chitosan is an inexpensive scalable processing method for creating continuous, randomly oriented, nanofibrous meshes. Chitin is a high-molecular weight linear polymer composed of N-acetyl-D-glucosamine (N-acetyl-2-amino-2deoxy-D-glucopryanose) units linked by β-D (1→4) bonds. A nitrogen-rich polysaccharide, chitin is abundant in crustaceans, mollusks, insects, and fungi and is the second most abundant organic material (produced by biosynthesis) second to cellulose. Chitosan, the N-deacetylated derivative of chitin is environmentally friendly, non-toxic, biodegradable, and anti-bacterial. These characteristics in conjunction with the beneficial effects of increased surface area from its nanofiberous form make electrospun chitosan ideal for medical, packaging, agricultural, and automotive applications. In the present study, we have electrospun various grades of chitosan and crosslinked them. Chemical, structural, and mechanical analyses have been conducted utilizing FTIR, SEM, and Kawabata microtensile testing respectively.
12:30 PM - B11.5
Characterization of Fibers Electrospun from an Organometallic Tin Precursor in Different Polymer Binders.
Christopher Rodd 1 , Maria Taku 2 , Jorge Santiago-Avilés 2 Show Abstract
1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Electrospinning has been thought of as an effective, low cost technique for producing nanofibers for use in gas sensor applications with nanofibers of tin oxide showing particular promise in this area. Critical to the success of tin oxide in these applications are nanowires with a rutile phase structure and well defined current-voltage characteristics which requires controlled fiber diameters. This paper reports on the fiber sizes of three different concentrations of organometallic tin precursor (dimethyl tin dineodecanoate) electrospun from two different polymer matrices (polyethylene oxide / chloroform and polystyrene / THF) used to control viscosity using a homemade electrospinning setup. Fibers were spun on silicon wafers to give differing mat densities depending on characterization technique and sintered at 600 centigrade for 2 hours. Phase structure was determined by combination of Raman spectroscopy and X-ray diffraction. Auger spectroscopy (AES) was used to investigate the general purity of the resulting fibers. Scanning electron microscopy (SEM) was used to determine fiber diameters and used in an attempt to model fiber geometry (i.e. degree of ovality). Fibers were found to have the necessary rutile phase structure across both binder systems and all organometallic concentrations. Polystyrene / THF solutions where found to have better fiber diameter control along with fibers that were more circular in cross section than the polyethylene oxide / chloroform solutions. Fiber diameters were found to be in the micron size range with future work dedicated to reducing these diameters to the nanoscale size range.