Symposium SM05—Supramolecular Biomaterials for Regenerative Medicine and Drug Delivery

Living systems derive their functions from the dynamic interactions of multiple components, they operate away from equilibrium, and rely on the continuous consumption of high energy metabolites (predominantly ATP) to sustain their existence. This differentiates living systems from synthetic materials, which are mostly static, simple in composition, and they do not consume energy to support their function. The active and multi-component properties of living matter gives rise to structures with rapid-response, selective and context-dependent dynamic functions that are currently not accessible to synthetic materials. The talk will cover our recent progress in the use of peptide ensembles to produce shape changing, metabolite consuming nanostructures. We will discuss: (i) our discovery approaches used to identify peptide ensembles which recognize metabolites, including ATP, (ii) the development of peptide ensembles with conformation-induced reactivity and (iii) the integration of modular functions of assembly, catalysis and metabolite recognition to form active materials.

REFERENCES:
1. M. Kumar, N.L. Ing, V. Narang, N. Wijerathne, A.I. Hochbaum and R.V. Ulijn, Amino Acid-Encoded Biocatalytic Self-Assembly Enables the Formation of Transient Conducting Nanostructures, Nat. Chem., 2018, 10, 696-703.
2. A. Lampel, R.V. Ulijn, and T. Tuttle, Guiding Principles for Peptide Nanotechnology Through Directed Discovery, Chem. Soc. Rev., 2018, 47, 3737-3758.
3. C. Zhang, R. Shafi, A. Lampel, D. MacPherson, C. Pappas, V. Narang, T. Wang, C. Madarelli and R.V. Ulijn, Switchable Hydrolase Based on Reversible Formation of Supramolecular Catalytic Site Using a Self-Assembling Peptide, Angew. Chem. Int. Ed., 2017, 56, 14511.

Based on the recent near atomic structures of the PYRIN domain of ASC in the protein filament of inflammasomes, we rationally designed nucleopeptides to form supramolecular assemblies selectively sequester ATP in live cells and capable of delivery into cell nucleolus. We developed assemblies of nucleopeptides that selectively sequester ATP over ADP. Counteracting enzymes interconvert ATP and ADP to modulate the nanostructures formed by the nucleopeptides and the nucleotides. The nucleopeptides, sequestering ATP effectively in cells, slow down efflux pumps in multidrug resistant cancer cells, thus boosting the efficacy of doxorubicin, an anticancer drug. As the first example of assemblies of nucleopeptides that interact with ATP and disrupt intracellular ATP dynamics, this work illustrates the use of supramolecular assemblies to interact with small and essential biological molecules for controlling cell behavior. Moreover, the nucleopeptides accumulate preferentially at cell nucleolus, demonstrating the potential for nucleolus delivery for therapeutic benefits.

Modern cancer treatment relies on the discovery and use of potent drug molecules, yet many drug therapies suffer from inefficient or unoptimized delivery methods, resulting in poor on-target efficacy and significant off-target effects. Our work focuses on the development of novel, biomaterial-based drug delivery vehicles that can be used to enhance the efficacy of existing therapies and treat challenging diseases such as cancer. Recent advancements in the field of immunotherapy have yielded encouraging results for the treatment of advanced cancers. For example, cyclic dinucleotides (CDNs) are a powerful new class of immunotherapy drugs known as STING (Stimulator of Interferon Genes) agonists, currently in clinical trials. However, previous studies of CDNs in murine cancer models have required multiple high dose injections, and improve survival only in relatively nonaggressive tumor models. Therefore, we are working to improve the efficacy of CDN immunotherapy by developing a novel biomaterial strategy we call “STINGel.” This was done through the use of Multidomain peptides (MDP) carrier vehicles, which can self-assemble into networks of nanofibers that result in injectable hydrogels. Standard MDP hydrogels are biocompatible and can be loaded with various bioactive factors, facilitating cell growth in vitro and displaying complete cellular infiltration in vivo. This project studies the development of a delivery material to improve the efficacy of STING agonist anti-cancer immunotherapy, taking advantage of the charged domains of a lysine-based MDP hydrogel to achieve extended and localized drug release. STINGel has been shown to dramatically improve tumor survival over immunotherapy alone in a challenging murine cancer model, resulting in 6-fold higher survival after only a single intratumoral injection of CDN-loaded hydrogel. Continuing work seeks to develop second-generation delivery materials by synthesizing and studying new MDPs with different charge chemistries, and by characterizing their effects on drug release kinetics, immune response, and final tumor treatment efficacy. This project’s goals are to develop various new delivery biomaterials and better drug treatment methods, which will ultimately be translatable to the clinic.

MultiDomain Peptides (MDPs) are a class of self-assembling peptides which can form a nanofibrous gel under the proper environmental conditions which can be selected from cues such as pH and ionic strength. These hydrogels have convenient handling properties which allow them to be easily aspirated and subsequently delivered by syringe, even through exceptionally narrow-bore needles. Depending on the application, these hydrogel can be used loaded with small molecule drugs, proteins, cells or a combination of all these. However, the nanofibrous hydrogel can also be used unloaded where we have found that free of any bioactive agents it is rapidly infiltrated with cells in vivo and remodeled into highly vascularized tissue. One of the great advantages of MDPs are the ease with which they can be modified and tailored to a particular application. Over the past decade we have prepared over one hundred variants on this sequence and can now describe with confidence peptides that will assemble under acidic, basic and neutral pH, with or without complimentary salts and, most recently with and without charge on the nanofibers themselves. In this presentation I will discuss our generalized design criteria for self-assembling MDPs. I will also describe recent results related to their use in the treatment of a model of diabetic ulcers with and without bacterial infection. In this work we find that the innate regenerative ability of the hydrogel dramatically accelerates wound healing over a negative control as well as over a commercially available, and clinically prescribed, hydrogel. In a separate study I will describe the use of the MDP hydrogel as a small molecular delivery agent and compare it to commercially available hydrogels such as collagen, alginate, Matrigel and hyaluronic acid. Applying MDPs in a model of cancer immunotherapy we deliver a cyclic dinucleotide to dramatically improve the efficacy of this STING agonist in a challenging model of head and neck cancer.

Supramolecular peptide immunotherapies are receiving interest in a range of settings, from infectious diseases to cancer to chronic inflammation. One of the chief advantages of these materials is that their modular construction makes it possible, in principle, to adjust the strength and phenotype of the immune responses raised in different settings. Immune phenotype can be controlled grossly by the co-delivery of adjuvanting molecules, but here we sought to determine how fine differences in the nanostructures of supramolecular peptide materials also influence the strength and character of the immune responses raised. In this talk, the effect of various nanostructural aspects of supramolecular peptide materials, including size, stability, surface charge, and epitope content will be discussed. This work compared multiple self-assembling peptide systems, including beta-sheet fibrillizing peptides and alpha-helical fibrillizing systems that could be engineered to form assemblies of varying size. In mice, smaller assemblies were more capable of cross-presentation to stimulate CD8+ T-cell responses than larger assemblies, and the helical system generated stronger antibody responses for poor B-cell epitopes, likely because these materials contained T-cell epitopes within their assembly domains. In sublingual vaccination (under the tongue), peptides and peptide assemblies were found to be generally non-immunogenic, even when delivered with sublingual adjuvants; however, the addition of oligoethylene glycol moieties to the materials enabled them to elicit surprisingly strong immune responses. The necessity of achieving a carefully controlled strength and phenotype of immune response will be highlighted in the context of active immunotherapies against inflammatory cytokines such as TNF and IL-17, for which these materials continue to be in active development.

Alzheimer’s disease (AD) is a neurodegenerative disease characterized by dementia and memory loss for which no cure or prevention is available. Amyloid toxicity is a result of the non-specific interaction of toxic amyloid oligomers with the plasma membrane.
We studied amyloid aggregation and interaction of amyloid beta (1-42) peptide with lipid membrane using atomic force microscopy (AFM), Kelvin probe force microscopy and surface Plasmon resonance (SPR). Using AFM-based atomic force spectroscopy (AFS) we measured the binging forces between two single amyloid peptide molecules. We demonstrated that lipid membrane plays an active role in amyloid binding and toxicity: changes in membrane composition and properties increase amyloid binding and toxicity. Effect of lipid composition, the presence of cholesterol and melatonin are discussed. We discovered that membrane cholesterol creates nanoscale electrostatic domains which induce preferential binding of amyloid peptide, while membrane melatonin reduces amyloid-membrane interactions, protecting the membrane from amyloid attack. Using AFS we that novel pseudo-peptide inhibitors SG effectively prevent amyloid-amyloid binding on a single molecule level and thus can potentially prevent amyloid toxicity. These findings contribute to better understanding molecular mechanism of Alzheimer's disease and aid into developments of novel strategies for cure and prevention of AD.

References:

E.Drolle, K.Hammond, A.Negoda, E.Pavlov, Z.Leonenko, Changes in lipid membranes may trigger amyloid toxicity in Alzheimer's disease. PLOS ONE, 2017, 12(8), e0182194.
B.Mehrazma, M.Robinson, S.K.A.Opare, A.Petoyan, J.Lou, F.T.Hane, A.Rauk, Z.Leonenko. Pseudo-peptide amyloid-β blocking inhibitors: molecular dynamics and single molecule force spectroscopy study. Biochimica et Biophysica Acta (BBA)-Proteins and Proteomics 1865 (11), 1707-1718.
M.Robinson, B.Y.Lee, Z.Leonenko, Drugs and Drug Delivery Systems Targeting Amyloid-β
in Alzheimer’s Disease. AIMS Molecular Science, 2015, 2(3): 332-358.
E.Drolle, R.M.Gaikwad, Z.Leonenko, Nanoscale electrostatic domains in cholesterol-laden lipid membranes create a target for amyloid binding. Biophysical Journal, 2012, 103(4), L27-L29.
F.Hane, E.Drolle, R.Gaikwad, E.Faught, Z.Leonenko. 2011. Amyloid-β aggregation on model lipid membranes: an atomic force microscopy study. J. Alzheimer’s Dis. 26: 485-494.
E.Drolle, F.Hane, B.Lee, Z.Leonenko, Atomic force microscopy to study molecular mechanisms of amyloid fibril formation and toxicity in Alzheimer’s disease. J. of Drug Metabolism Reviews, 2014, 46(2): 207-223.
E.Drolle, N. Kučerka, M.I.Hoopes, Y.Choi, J. Katsaras, M. Karttunen, Z.Leonenko, Effect of melatonin and cholesterol on the structure of DOPC and DPPC membranes, Biochimica & Biophysica Acta: Biomembranes, 2013, 1828 (9): 2247-2254.
F.T.Hane, S.J.Attwood, Z.Leonenko. Comparison of three competing dynamic force spectroscopy models to study binding forces of Amyloid-β 1-42. Soft Matter, 2014, 10(1): 206-213.
F.T. Hane, B.Y. Lee, A.Petoyan, A.Rauk, Z.Leonenko, Testing Synthetic Amyloid-β Aggregation Inhibitor Using Single Molecule Atomic Force Spectroscopy. Journal of Biosensors and Bioelectronics, 2014, 54, 492–498.

Diabetes Mellitus is one of the most common metabolic disorders in the world, representing a significant health problem and economic issue. Approximately 15% of diabetic patients develop chronic wounds in their lower extremities due to complicating symptoms. Wounds in diabetic patients have relatively longer healing periods than normal wounds. Specifically, diabetic wounds exhibit delayed wound closure, prolonged inflammation, and are often infected with bacteria. The gold standard of treatment for diabetic patients with chronic wounds consists of debridement of the wound, infection control, offloading of weight, and patient education. Despite these efforts, chronic wounds frequently lead to amputation, an outcome that strongly motivates the development of new treatments. One approach to address these issues is to load cells, growth factors, or other biomolecules into scaffold materials to control release kinetics and achieve treatment localization.The difficulty here is the complex interplay between delivery material, diffusing soluble agents, and loaded cells. The wound healing process consists of a delicate sequential cascade of cell types and growth factors, and deviation from the proper sequence can adversely affect the biological efficacy of wound healing. A more attractive solution would be to create a single component hydrogel to initiate a healthy healing response without the aforementioned complexity. We utilize a self-assembling peptide hydrogel, termed multidomain peptide (MDP). MDPs contain a core of alternating hydrophilic and hydrophobic amino acids flanked by charged amino acids. This primary sequence results in the formation of nanofibers with a bilayer of β-sheets. The addition of multivalent salts, such as those found in common buffers, allows nanofiber elongation and cross-linking to form a viscoelastic hydrogel. MDPs have shown significant promise for tissue engineering applications due to their customizable chemical design and desirable biocompatibility. MDP hydrogels are made simply from amino acids, have predictable degradation in vivo, and can be easily delivered by a syringe. With compositional and structural similarity to the native extracellular matrix, MDP hydrogels are readily infiltrated by cells, vascularized, and innervated. Because of these excellent biomaterial properties, we investigate the effect of the MDP hydrogel on the healing of full-thickness dermal wounds in genetically diabetic mice. We find wound healing is substantially accelerated with the use of this MDP hydrogel compared to a clinically used hydrogel, or a buffer-only control. The work presented herein shows the MDP hydrogel supports cells present in the wound healing process and thereby accelerates the healing of diabetic wounds by increasing granulation tissue formation, re-epithelialization, vascularization, and innervation.

Antimicrobials remain the main means to treat and control bacterial infections, but their efficacy is now compromised due to overuse in humans, animals, agriculture, with bacteria developing resistance that renders certain antibiotics ineffective. With very few antibiotics in the pipeline and given the difficulty in bringing novel antimicrobial agents to the market, antimicrobial resistance (AMR) poses one of the biggest threat to global health. Tackling the problem of AMR requires a multidisciplinary approach focused in repurposing and revitalizing older drugs.
In this talk, I will present a supramolecular engineering approach to develop antimicrobial nanoformulations able to enhance the efficacy of known antimicrobials toward multi-drug resistant Gram-negative pathogens (Enterobacteriaceae, Pseudomonas, Acinetobacter) by improving their pharmacokinetic profiles, whilst minimizing the risks of adverse systemic effects and potential development of resistance. We will show an extensive characterization of these nanoformulations from nanostructure to antimicrobial activity and pharmacokinetics.

Many disease processes are driven by “undruggable” protein-protein interactions (PPIs) inside cells. In cancer, for example, tumor suppressor proteins are often inactivated by upregulation of their protein binding partners. Despite the promise of therapeutic peptides for disrupting PPIs, their delivery to and into cells remains a major obstacle to clinical translation. Peptides amphiphiles (PAs), a peptide conjugated to a hydrophobic tail, are one tool for facilitating intracellular peptide delivery. PAs self-assemble into micellar nanoparticles, protect peptides during delivery to diseased cells, and facilitate cell-uptake of peptides that would otherwise not be internalized. However, after internalization, PAs remain trapped in endosomes, which prevents them from reaching their cytoplasmic targets and reduces therapeutic efficacy. To facilitate their intracellular delivery, we have designed cleavable PAs to release therapeutic peptides after internalization and have explored strategies to facilitate their endosomal escape. We have explored this delivery system in two PPI systems frequently hijacked by cancer cells: the guardian of the genome (i.e. p53) and the gatekeepers of apoptosis (i.e. the BCL-2 family of proteins).

Covalent modification of a therapeutic agent represents an effective means to improve the drug’s pharmacokinetic profile for enhanced therapeutic outcomes. Incorporating the concept of molecular assembly into the prodrug design provides a new dimension for tailored synthesis of supramolecular medicine to address specific clinical needs. This self-assembling prodrug strategy uniquely and specifically exploits the self-assembling potential of therapeutic agents to achieve improved treatment efficacy. In this presentation, I will detail our rational design of monodisperse, amphiphilic anticancer drugs—which we term drug amphiphiles (DAs)—that can spontaneously associate into discrete, stable supramolecular nanostructures with a 100% drug loading. Our results suggest that formation of nanostructures provides protection for both the drug and the biodegradable linker from the external environment and offers a mechanism for controlled release.

The balance between charge and intermolecular hydrogen bonding is considered critical in determining the cellular effects of self-assembled peptide amphiphile (PA) materials. These two parameters have been tuned to induce cell membrane disruption, promote neuronal development, and amplify response to growth factors. To conjugate an alkyl tail at the C-terminus of the peptide in the PA, a lysine residue is commonly used as a linker. In this work, we show that the orientation of this lysine residue relative to the peptide chain and the alkyl tail plays an important role in determining PA’s ability to induce programmed cell death. When the alkyl tail is conjugated to the side chain amine of lysine linker, the resulting PA induced oncotic type of programmed death on cervical cancer cells, evidenced by loss of mitochondrial membrane potential, decrease in intracellular ATP level, and formation of giant blebs. Cell viability was rescued when the lysine orientation was reversed (the alkyl tail was attached to the primary amine) even though the nanostructure retained very similar morphology. Further investigation suggests that the oncosis could be triggered by an alteration in the cell membrane properties resulting from sequestration of cholesterol by membrane-associated PA nanofibers. Our results demonstrate how a subtle difference in the molecular design can be utilized to tailor the assembled nanostructure to elicit specific cell response.

Context-dependent signaling, as a ubiquitous phenomenon in nature, is a dynamic molecular process at nano- and microscales, but how to mimic its essence using non-covalent synthesis in cellular environment has yet to be developed. Here we discuss two examples of instructed-assembly (iA) for controlling cell fates: (1) a dynamic continuum of non-covalent filaments formed by instructed-assembly (iA) of a supramolecular phosphoglycopeptide (sPGP) as context-dependent signals for morphogenesis of cells; (2) enzymatic morphology/phase transition of isopeptides effectively delivery cargos to mitochondria in a cell selective manner. In the first case, while enzymes (i.e., ectophosphatases) on cancer cells catalyze the formation of the filaments of the sPGP to result in cell death, damping the enzyme activity induces 3D cell spheroids. Similarly, relying on the ratio of stromal and cancer cells in a co-culture to modulate the expression of the ectophosphatase, the iA process enables cell spheroids. The spheroids act as a mimic of tumor microenvironment for drug screening. In the second case, consisting of DYKDDDDK (Flag, a substrate of enterokinase (ENTK)) as the branch and a phenylalanine rich short peptide as the backbone, the isopeptides (Mito-Flag) form micelles, which, upon the cleavage of the Flag catalyzed by ENTK, turn into a gel made of nanofibers. Entering cells mainly via clathrin mediated endocytosis, the micelles interact with the mitochondria having ENTK and high membrane potential. The mitochondrial ENTK cleaves the Flag of the isopeptides, thus turning the micelles to nanofibers on the mitochondria. Mixing the Mito-Flags and cargos (drug molecules, proteins, and genes) allows the selective delivery of the cargos into mitochondria of cancer cells. These results provides a new way to control cell fates and to target organelles for biomedicine.

Homochiral assembly of amphiphilic peptides consisting either D- or L-enantiomers inside the living cells are emerging as an attractive strategy for different biological implications including therapeutics. However, less attention is given for the heterochiral assembly of peptides consisting both D- and L-isomers. Heterochiral assembly containing both D- and L-isomers (racemates) could create wonders in their biological impact since the assembly of racemates often results in altered properties compared with enantiomers such as faster kinetics, higher mechanical strength and enzymatic stability. In here, we have monitored altered morphological and biological properties of a short peptide amphiphile, Mito-FF upon their co-assembly with mirror pair, Mito-ff. Mito-FF is an intra mitochondrial self-assembling peptide amphiphile, which induce cancer cell apoptosis followed by mitochondrial damage upon intra mitochondrial fibrillation. Mito-FF upon co-assembly with Mito-ff induced thick fibrous bundle of diameter upto 100 nm, while enantiomers form fiber of diameter ~ 10 nm. The co administration of Mito-FF and Mito-ff in the cell induced drastic mitochondrial disruption than enantiomers both in vitroand in vivoas a result of intra mitochondrial racemic co-assembly to form thicker Mito-rac fibrous bundles.

Bladder cancer is the costliest cancer to treat, requiring long-term follow-up and repeat interventions, because almost 70% of patients with non-muscle-invasive disease will develop tumor recurrence, and about 25% will progress to the muscle invasive stage. One of the major shortcomings associated with current intravesical chemotherapy is the short residence time of the drug in the bladder since much of it is lost upon the first voiding of urine. Our research focus is on the development of protein drug nanocarriers in the form of albumin molecules (~6 nm) and nanoparticles (~100 nm) that can target and be readily taken in by tumor cells via targeting receptors that are highly expressed on bladder cancer cells. Peptides that target fibroblast growth receptor 3 (FGFR3), epidermal growth factor receptor (EGFR) and CD47 on human bladder tumor cells were designed and the uptake of these peptides by bladder cancer cells were investigated. The uptake of the peptide targeting CD47 was the highest followed by those targeting EGFR and FGFR3. Thus, our subsequent drug delivery study centered on protein nanocarriers conjugated with the CD47 targeting peptide, and loaded with drugs commonly used for non-muscle invasive bladder cancer therapy. Our in vitro experiments showed that within the exposure time expected for intravesical therapy (2 h), the killing of bladder cancer cells treated with these receptor-targeting drug-loaded nanocarriers was significantly enhanced (drug IC₅₀ reduced by a factor of ~3 to >10) compared to the free drug or the drug-loaded non-functionalized nanocarriers. Thus, CD47-targeting drug-loaded protein nanocarriers are a promising candidate for intravesical chemotherapy against non-muscle-invasive bladder cancer.

The emergence of drug-resistance among pathogenic bacteria constitutes one of the paramount challenges to the human heath worldwide. This threat is further exacerbated by biofilm-associated infections that are even more challenging to treat. Conventional antibiotic-therapies are ineffective due to their inability to penetrate biofilm matrix coupled with the rapidly growing number of antibiotic-resistant strains. Host-defence peptide mimicking synthetic polymeric have emerged as promising novel antimicrobials that can disrupt the microbial membrane and readily penetrate biofilm matrix. However, their lack of specificity towards mammalian hosts limits their widespread therapeutic application. Here, we report synergistic antimicrobial therapy using engineered polymeric nanoparticles with colistin antibiotic for combating MDR bacterial and biofilm infections. We observed an 8-16-fold decrease in antibiotic dosage in presence of polymeric nanoparticles to combat planktonic cells and eradicate pre-formed biofilms of multiple MDR species. The synergy observed on planktonic bacteria was attributed to the ability of NPs (at sub-lethal concentrations) to create small pores on bacterial membrane that increased influx of antibiotics inside the microbes. Moreover, antibiotic accumulation inside biofilms increased by ~3.5 times in presence of NPs, resulting in a synergistic effect to kill the constituent microbes. Overall, this strategy demonstrates the ability of polymeric NPs to minimize the side-effects caused by high doses of ‘lethal’ antibiotics while simultaneously rejuvenating the antibiotics rendered ineffective due to development of drug-resistance in bacteria.

Bioorthogonal transformation of prodrugs and profluorophores using transition metal catalysts (TMC) offers a promising strategy for imaging and therapeutic applications. However, maintaining activity and controlling the localization of TMCs make their use in biomedical applications challenging. Here we report the engineering of nanoparticles of gold nanoparticles (AuNPs) with encapsulated TMCs (nanozymes) to provide specific intra- and extracellular localization. We used membrane-penetrating cationic nanoparticles for catalysis inside and ‘stealth’ zwitterionic particles to limit catalysis to outside of mammalian cells. Specific localization of nanozyme activity was demonstrated through profluorophore activation. Therapeutic efficacy was demonstrated through intra- and extracellular activation of a prodrug. The ability to control nanozyme localization was further shown by targeting biofilms in a complex bio-system using a co-culture model. We designed pH-switchable nanozymes that effectively localize in the acidic microenvironment of biofilms. These nanozymes generate imaging agents through bioorthogonal
activation of profluorophores inside biofilms demonstrating potential for early detection of biofilm-associated infections. Taken together, these studies demonstrate a new level of spatial control for TMC-mediated bioorthogonal catalysis for diagnostic and therapeutic purposes.

Nearly half of newly discovered active pharmaceutical ingredients (APIs) suffer from poor dissolution in water. After finding a successful “hit” using high throughput screening methodologies, many promising APIs must undergo subsequent chemical modification to improve the dissolution behavior. Pharmaceutical cocrystals are of growing interest as a means of controlling the release of an active pharmaceutical ingredient (API) without modifying its molecular structure.
Pharmaceutical cocrystals are typically defined as a combination of two organic compounds in solid form, held together by hydrogen bonds and van der Waals forces and simple stoichiometries (e.g., 1:1, 1:2, etc. molar ratios) of API and coformer. By choosing an appropriate coformer, the dissolution behavior of the API (i.e. its concentration over time) can be controlled and even enhanced significantly over the pure form and can have many functional advantages. Current methods of creating pharmaceutical cocrystals, however, are limited by the necessity for a liquid solvent during synthesis, required post-processing, and compatible delivery methods.
We have developed a novel, solvent-free method for synthesizing organic cocrystals. The method, organic vapor cocrystalization (OVCC), involves subliming the API and co-former into a carrier gas, followed by jetting the gas mixture onto a temperature-controlled substrate, where the organic materials condense to form the cocrystal film. As proof of concept, we demonstrate for the first time the synthesis of the cocrystal system of caffeine and succinic acid, whose isolation has not been previously obtained by conventional methods. X-ray diffraction and differential scanning calorimetry are used to confirm the presence of the cocrystal phase, while scanning electron microscopy studies show that the cocrystal forms an elongated morphology comprised of long needles, whose length and orientation depend on process parameters.
Because a liquid solvent is not needed, OVCC opens the door to new cocrystal systems and printing applications. The new OVCC process enables excellent process control and automation, andautomation and is highly scalable for the manufacturing of cocrystal products.

Nanoscale technologies and its applications in medicine for disease diagnosis, treatment and prevention, has gained considerable attention during the past decade. Nanomaterials have been widely used in drug delivery systems as nanotubes, nanomachines, nanofibers and nanomembranes since they can mimic or alter biological processes. Nanospheres have been widely investigated as transport vehicles due to the ease and efficiency of uptake in the cells. Peptide-based carriers are a promising candidate for drug delivery due to ease of synthesis via self-assembly, biocompatibility, biodegradability, and tunable chemical structures. Such peptide-based nanospheres have the potential to be targeted for a specific organ as well as increasing the half-life in systemic circulation, enhancing bioavailability, improved retention time of the therapeutic molecules and intracellular penetration.

In this study, the fabrication of peptide-based nanospheres by electrospraying technique have been demonstrated, and their potential as carriers for targeted delivery of cranberry extracted flavonoids such as proanthocyanidins, and triterpenoids such as quercetin and ursolic acid have been evaluated. For this purpose, triphenylalanine nanospheres containing the drugs have been fabricated using a coaxial electrospraying set-up. Probiotic bacteria such as L. acidophilus, L. casei and Akkermansia were also encapsulated in such micro-carriers to improve their viability in the gut and intestinal tract. The effect of encapsulation of bacteria in stimuli-responsive peptide-based carriers, which can assist with on-demand release and the co-encapsulation of proanthocyanidins and triterpenoids was studied to understand their influence on bacterial cell survivability. The self-assembly and secondary structure of the fabricated tripeptide spheres have been analyzed through SEM, FTIR, Raman and CD analysis. The morphology and chemical structure of drug and bacteria enclosed carriers have also been characterized. The nanospheres carriers have then been modified to be targeted specifically for colon cancer. The efficiency of the carriers was analyzed by observing the release behavior of each of the drugs with and without post crosslinking treatment. The extent of their delivery to cells and their influence on reduction in tumor cell proliferation has been analyzed.

The central nervous system (CNS) plays a central role in the control of sensory and motor functions, and the disruption of its barriers can result in severe and debilitating neurological disorders. Neurotrophins are promising therapeutic agents for neural regeneration in the damaged CNS. However, their penetration across the blood–brain barrier remains a formidable challenge, representing a bottleneck for brain and spinal cord therapy. We developed a nanocapsule–based delivery system that enables intravenously injected nerve growth factor (NGF) to enter the CNS in healthy mice and non–human primate. The encapsulation of NGF is achieved by in situ polymerization, which grows a thin layer of polymer around individual NGF molecules, forming NGF nanocapsules. These nanocapsules can efficiently penetrate the blood–brain barrier and enter the CNS after intravenous administration via the endogenous neurotransmitter transport pathway. In pathological conditions, the delivery of NGF enables neural regeneration, tissue remodeling, and functional recovery in mice with spinal cord injury. This technology can be utilized to deliver other neurotrophins and growth factors to the CNS, opening a new avenue for tissue engineering and the treatment of CNS disorders and neurodegenerative diseases.

A novel multifunctional β-cyclodextrin macrocrosslinker-based self-healable hydrogel is developed by crosslinking β-cyclodextrin oligomer allyl ether [C(βCD−OM)AE], a β-cyclodextrin oligomer with allyl groups and quaternary ammonium groups formed from epichlorohydrin and another epoxide, with adamantly guest units and acrylic acid moieties. The covalent bonds between the allyl groups and hydrogel backbones are designed to increase the stability of supramolecular hydrogels without losing their self-repairing attribute by introducing a macrocrosslinker concept. This new hydrogel shows a trebling in the storage modulus and a high tensile strain up to 1590%. The tensile strength of the C(βCD−OM)AE@Ad hydrogel is more than double that of the monomeric βCD hydrogel without cationic groups. The volume magnitude of the C(βCD−OM)AE@Ad hydrogel can be stably changed by swelling, and it can increase in volume by more than eight times on a shift in the pH from 1.2 to 7.4. In addition, the hydrogel shows good cytocompatibility. The C(βCD−OM)AE@Ad hydrogel also showed ibuprofen sustained-release property depending on the pH. This multifunctional βCD macrocrosslinker-based self-healable hydrogel designed to combine chemical links, the host–guest interactions of macrocrosslinkers, and electrostatic attractions could provide good stability, improved mechanical strength, and beneficial self-healing performances for further applications in a wide variety of fields, including biomedicine.

Electrospinning is a versatile technique for producing composite micro-/nano-fibers from various functional materials. The properties of electrospun nanofiber membranes provide many versatile elements that can be excellent resources for biomedical applications, such as drug delivery, tissue enginering and wound healing. In addition, coaxial electrospinning produces core-sheath fibers that provides even more advanced features, such as (a) independent combination of two or more functional materials; (b) encapsulating functional molecules and their controlled release; (c) protection of incorporated drugs from the outer environment. In the initial stages of applying electrospinning fibers in the biomedical area, core-sheath fibers enabled the incorporation of two separate polymers into a single fiber in order to combine good mechanical properties from synthetic polymers and cell biocompatibility from biomaterials.¹ In the past decade, coaxial electrospinning has become one of most popular techniques for developing novel drug delivery vehicles, enabling the controlled and sustained release of the drug from the fiber core. Moreover, multiple drugs can be individually incorporated into either the core or sheath layers (or both layers) enabling synergistic effect from two or more different drugs².
Moving beyond sustained release, “on-demand” release triggered by external stimuli has emerged recently. In this report, we present on-demand triggered release using stimuli-responsive materials, such as self-immolative polymer (SIP)³ and pH-responsive Eudragit polymers⁴. We also introduce bio-responsive SMART nanofiber membranes for developing non-hormonal contraceptive devices. For triggered release by external stimuli, we have produced nanofibers with SIP in the sheath encapsulating core materials. In the absence of stimuli, no drug release is observed, whereas abrupt core release was observed upon SIP depolymerization is triggered by external stimuli. Controlled multi-pH response has also been demonstrated using core-sheath fibers made of two different Eudragit polymers. Core-sheath fibers made of Eudragit L 100 (EL100) core and Eudragit S 100 (ES100) sheath provide three-phase responses depending on evironmental pH within physiological range. At pH < 5, no release was observed from either core or sheath layer. At pH within 5-6 range, while release from the sheath is minimal, the controlled release from the core can be obtained by adjusting the sheath thickness. For pH > 6, all core and sheath materials are quickly released. This three-phase responses within physiological range is very useful for targeted drug delivery in because the environment in human orgians have different pH values. For all cases, due to the high surface-to-volume ratio of nanofiber membranes, their response rates to external stimuli or environmental pH is much quicker ( > 25 x) than that of the cast film equivalent. Finally, we will introduce bio-responsive nanofiber devices for the contraceptive application without using any hormonal agent. The fiber device is made of HPMC and Carbopol 974P composite polymers. HPMC provides a mucoadhesive and highly viscous hydrogel network and Carbopol polymers provide the pH buffering capacity with high viscosity. Upon contact with seminal fluid (pH ~ 8), HPMC/Carbopol nanofiber membranes convert into hydrogel, providing a physical barrier by swelling, with a low pH value of ~ 4, which acts as a spermicidal agent. This non-hormonal bio-responsive contraceptive device is highly attractive for women’s health, providing excellent spermcidal performance without affecting user’s hormonal conditions.
1. Han, D.; Boyce, S. T.; Steckl, A. J., MRS Proc. 2008, 1094, 1094-DD06-02.
2. Han, D.; Steckl, A. J., ACS Appl. Mater. Interfaces 2013, 5, 8241.
3. Han, D.; Yu, X.; Ayres, N.; Steckl, A. J., ACS Appl. Mater. Interfaces 2016, 9, 11858.
4. Han, D.; Steckl, A. J., ACS Appl. Mater. Interfaces 2017, 9, 42653.

The study of biomaterials based on injectable hydrogels has increased over the past years due to their potential medical application in non-invasive treatments for tissue engineering and drug delivery systems. These hydrogels can be adjusted to deliver drugs in vivo for long periods without activating the immune system. Thermosensitive hydrogels, as poly(N-vinylcaprolactam) (PNVCL), when heated above a determined temperature (called lower critical solution temperature, LCST) change from a state where the chains are swollen in an aqueous medium (by hydrophilic interactions) to a state in which they self-aggregate by predominant hydrophobic interactions [1]. In this transition, hydrogen bonds between the polymer chains and the water molecules break and the hydrogel aggregates expelling these molecules, creating a phase separation. By understanding the physicochemical aspects of the swelling-collapse transition, it is possible to evaluate the suitability of PNVCL as smart delivery systems [2]. PNVCL is biocompatible facilitating its use as a biomaterial. In this way, PNVCL was synthesized by radical polymerization in the presence of azobisisobutyronitrile (AIBN) initiator, dimethyl sulfoxide (DMSO) as solvent, for 4 h at 70 °C and N₂ atmosphere. The hydrogel was purified using dialysis membrane to remove DMSO and monomers unreacted. The LCST and energies involved during the swollen to aggregate states were calculated from the analysis of a PNVCL aqueous suspension (1% m/v) by UV-vis spectrophotometry. The material changes from a transparent system to opaque when heated, allowing to be studied by its transmittance in different temperatures. The polymers synthesized showed a LCST of 33.6 °C, which results in the gel formation in the body temperature. The calculated enthalpy and entropy changes during the phase transition were 6000 kJ mol^-1 and 20 kJ K^-1 mol^-1, respectively. The FTIR spectrum of PNVCL showed bands relatives to the functional groups C=O (1617 cm^-1), C-H (2930 cm^-1) and water adsorbed by the amide cyclic group (3300 cm^-1). For applications as a drug delivery system, the hydrogels capacity to adsorb drugs was evaluated by varying the concentration of Methylene blue-MB (5, 10, 25, 50, 100 e 200 ppm). In this study, methylene blue was used as a model for hydrophobic drugs, which are usually difficult to be released in a controlled manner by hydrogels with a typical hydrophilic character. The advantage of PNVCL comes from its amphiphilicity, which hydrophilic groups interact with the medium and the hydrophobic chains agglomerated above LCST interact with the drug. PNVCL suspensions (5% m/v) in the presence of MB were heated at 37 °C for 5 min, centrifuged and the supernatant was measured by UV-vis spectrophotometry. Two adsorption mechanisms were tested: Langmuir and Freundlich. The best model fitted was Freundlich, which can be used to describe non-ideal systems with heterogeneous surface. The amount of dye adsorbed varying the PNVCL concentration (5,10 and 20% m/v) was also studied. The adsorption of 50 ppm MB was up to 40% and increased linearly with polymer concentration. Thereby, PNVCL can be a suitable injectable delivery system for hydrophobic drugs with different concentrations.
References:
[1] – Ponce-Vargas, S. M., et al., Macromolecular Symposia, 2013. 325-326 (1).
[2] – Fucinos, C., et al., PLoS ONE, 2014. 9(2).

Understanding the mechanisms, extent, and consequences of receptor co-localization and inter-receptor communication is critical for the design and development of therapeutic nanoparticles and proper biomaterial scaffolds. Nature orchestrates specificity and selectivity in ligand–receptor targeting by introducing multivalency to control binding affinities. Cell-cell interactions, signaling, cell-matrix binding and immune activation all are controlled through multiple weak interactions between one or more types of ligand-receptor pairs. Over the past decades, the fields of nanoparticle and nano-engineering have utilized this concept to achieve targeted delivery, increased specificity and selectivity of therapeutic and diagnostic ligand-functionalized nanoparticles.Numerous ligand-presenting materials have been developed yet the translation to clinical success is limited. The main cause hereof is a lack of control in particle shape, size, ligand-spacing and ligand-number, resulting in a distribution of particles with varying functionality. Precision engineering of functional materials is required to acquire insight into these fundamental natural mechanisms.

Here, we aim to develop a precision-engineered materials platform to gain quantitative insights into the fundamental mechanisms of complex multivalency that can lead to super-specificity. We show how the development of multivalent particles with controlled ligand spacing, heterogeneity, stoichiometry and positioning are needed to accurately study the role of these parameters in overall binding affinity on model surfaces and on the cell membrane. Understanding mechanisms and consequences of receptor co-localization and inter-receptor communication is critical for the design and development of therapeutic particles and functional biomaterial scaffolds. We will touch upon the parallels of multivalency as tool to develop uniform and well-defined hydrogels that can subsequently be equipped with the above mentioned cell-interacting functionalities to develop artificial cell environments with functionality indistinguishable from nature. Together with new analysis methods, theory and simulations we aim to introduce an unmet level of accuracy and control in functional materials self-assembly and truly be super-specific.

Antibody drugs are a rapidly growing set of therapeutics that increasingly prove effective for clinical applications spanning from macular degeneration treatments, to targeted cancer therapies, and to passive immunization. These antibody treatments can be engineered to target almost any cell surface moiety and their production has since been scaled to an industrial level. Despite these advances, parenteral administration of antibodies is severely constrained by high viscosities at desirable doses, poor long-term antibody stability, high required frequency of administration, and therapeutically suboptimal pharmacokinetics. In this work, we demonstrate the development of supramolecular polymer-nanoparticle (PNP) interactions to engineer shear-thinning, self-healing hydrogels capable of stabilizing and delivering high concentrations of antibodies over prolonged timeframes. The PNP interactions underpinning the behavior of these materials afford injectability and tunable mechanical properties, while also controlling antibody release kinetics. We investigate how the thermodynamics of the PNP interaction affect in vitro and in vivo antibody release kinetics, pharmacokinetics, and bioavailability. Analysis of nanoparticle surface chemistry, polymer network hydrophobicity, and hydrogel formulation reveal explicit design handles relating PNP thermodynamics to in vivo antibody release kinetics via subcutaneous injection. Overall, this work presents a robust set of design parameters to tune PNP interactions to develop a materials platform for long-term, controlled antibody delivery.

The natural extracellular matrix (ECM) is a highly dynamic, supramolecular structure composed of various bioactive molecules held together by specific interactions. The ECM directly interacts with cells and dictates cell behavior to a large extend. Our goal is to synthetically mimic this intricate natural system using supramolecular materials based on hydrogen bonding units. The dynamics of the supramolecular system is shown to be important in the presentation of bioactive epitopes to cells. By design, highly dynamic supramolecular fibrous particles decorated with cell adhesive RGD motifs were made and studied in solution. It was shown that these soluble particles interact with the cell surface, and that the dynamics of bioactive presentation is dependent on the method of supramolecular incorporation. Transient networks and hydrogels composed of similar molecules were shown to have slowed down dynamics, compared to the particles in solution. These hydrogels, when formulated in the right way, were able to enhance cell viability and adhesion. When highly robust solid materials were made using the same supramolecular motif, cell adhesion and migration could be tuned. However, the ECM displays a plethora of bioactive peptide signals. Therefore, a high throughput screening approach was taken using a design of experiments set up, to investigate a library of natural ECM proteins as coatings, and a synthetic library of ECM peptides supramolecularly incorporated as additives in the base material. It was found that the several sequences and/or combinations outperformed others, showing the importance of the high throughput screening appraoch. The proposal that both the dynamics and presentation of bioactive sequence determines cell behavior is currently being investigated. In this way we aim to make steps towards the design of a synthetic ECM analogue.

Most biological materials exist in non-equilibrium states driven by the irreversible consumption of high-energy molecules like ATP or GTP. These energy-dissipating structures are governed by the kinetics of energy dissipation. They are thus endowed with unique properties which include spatiotemporal control over their presence, the ability to repair damage or the ability to form higher-order structures driven by reaction-diffusion fronts. Most of these properties would be desirable in human-made materials.

We and others have thus set out to explore the use of dissipative self-assembly for the use of supramolecular (bio)-materials.[1-7] In this work, I will discuss design criteria fro dissipative supramolecular materials. I will focus on our recently described system and its application as a vehicle that can control cellular uptake, or deliver drugs.

1. Tena-Solsona, M., Rieß, B., Grötsch, R. K., Löhrer, F. C., Wanzke, C., Käsdorf, B., Bausch, A. R., Müller-Buschbaum, P., Lieleg, O. & Boekhoven, J. Non-equilibrium dissipative supramolecular materials with a tunable lifetime. Nat. Commun. 8, 15895 (2017).
2. Grötsch, R. K., Angi, A., Mideksa, Y. G., Wanzke, C., Tena-Solsona, M., Feige, M. J., Rieger, B. & Boekhoven, J. Dissipative Self-Assembly of Photoluminescent Silicon Nanocrystals. Angew. Chem. Int. Ed. Engl. (2018), ASAP: DOI:10.1002/anie.201807937
3. Rieß, B. & Boekhoven, J. Applications of Dissipative Supramolecular Materials with a Tunable Lifetime. ChemNanoMat 4, 710-719 (2018).
4. Tena-Solsona, M., Wanzke, C., Riess, B., Bausch, A. R. & Boekhoven, J. Self-selection of dissipative assemblies driven by primitive chemical reaction networks. Nat. Commun. 9, 2044 (2018).
5. Rieß, B., Wanzke, C., Tena-Solsona, M., Grötsch, R. K., Maity, C. & Boekhoven, J. Dissipative assemblies that inhibit their deactivation. Soft Matter. 14, 4852-4859 (2018).
6. Merindol, R. & Walther, A. Materials learning from life: concepts for active, adaptive and autonomous molecular systems. Chem. Soc. Rev. 46, 5588-5619 (2017).
7. Debnath, S., Roy, S. & Ulijn, R. V. Peptide Nanofibers with Dynamic Instability through Non-Equilibrium Biocatalytic Assembly. J. Am. Chem. Soc. 16789 (2013).

The fullerenes are a unique carbon allotrope family that boast many desirable properties for therapeutic and diagnostic applications in nanomedicine, such as improved magnetic resonance imaging (MRI) contrast agents, photodynamic therapy (PDT) agents and enzyme inhibitors, for example. These highly hydrophobic cages, however, must be modified in order to enter the human body safely and effectively, and avoid rejection. One such method is exohedral functionalisation: the covalent attachment of water-solubilising groups to the fullerene cage.

PEGylation (the covalent attachment of polyethylene glycol (PEG) chains) is often used to functionalise nanoparticles with the aim of negating rejection by the body. Inspired by this, but looking to reduce the dominance of the long PEG chain, we functionalised fullerenes C₆₀, C₇₀, C₈₄ and C₉₀ with triethylene glycol based chains. We have characterised the resultant molecular structures. Strikingly, depending on the size of the fullerene cage, these molecular building blocks self-assemble in aqueous solution to give complex hierarchical structures with porous architectures defined by a network of tubular fibrils. The mechanical properties of these hydrogels have been investigated using atomic force microscopy. Not only are these findings of interest to the study of the fundamentals of self-assembly processes, but the resultant structures hold great promise for the utility of fullerenes in the field of nanomedicine.

Multi-drug resistant diseases are one of the biggest challenges society is facing in the domain of healthcare. Contraction of a multi-drug resistant disease, whether through a microbial infection or the loss of chemotherapeutic effectiveness, results in an extremely poor patient prognosis given the severely limited treatment options. The rapid resistance development in microbes, for instance, has completely eviscerated the current antimicrobial drug pipeline. The resistance development of a variety of cancer cell lines has rendered treatment with a single therapeutic agent completely ineffective. Instead, chemotherapeutic treatments must rely on a bevy of chemotherapeutic agents and chemosensitizers to achieve remission, most often at the cost of the patient’s well-being, owing to significant toxicity.

Traditional, small-molecule drug therapy usually targets highly specific cellular processes or interactions, enabling resistance development through simple mutations in the pathogen’s genome. In contrast, macromolecular therapeutics consist of polymeric assemblies that exhibit selective but non-specific interactions with the pathogen, making resistance development extremely difficult. In fact, macromolecular therapeutic agents developed at IBM have shown no resistance development in the treatment of bacteria and viruses, in preliminary in vitrostudies. Additionally, these agents have been found to be highly effective against drug-resistant bacteria and cancer cell lines, while maintaining very low toxicity towards healthy cells. Given these impressive features, macromolecular therapeutics hold significant promise for disease treatment.

Various RNAs, such as siRNA, microRNA, and mRNA, play pivotal roles in biological functions and have gained increasing importance for therapeutic applications. However, the lack of safe and efficient delivery vehicles remains the major challenge to RNA-based therapeutics. Our lab designs both small molecule and polymer-based molecular carriers for safe and efficient delivery of both short and long RNAs into cells. Using natural building blocks such as amino acids, we have developed dendronized bolaamphiphiles and polypeptides that are biocompatible, biodegradable, and highly efficient for RNA delivery. Our systematic investigation into structure–property relationships revealed important correlations between molecular design, self-assembled nanostructure, and biological activity. Through collaborations with biomedical researchers, we further investigate RNA delivery for various therapeutic applications including diabetes, vaccine development, immunotherapy, and CRISPR-Cas based gene editing. In this talk, I will discuss the design, synthesis, biological studies, and biomedical applications of our new vectors.

Glioblastoma multiforme (GBM) is the most common primary cancer in adults and one of the most aggressive cancers with extremely poor survival statistics owing to high rates of disease recurrence. GBM infiltrates the brain tissue diffusely making complete surgical excision impossible. Current standard of care involves surgical resection of the tumour, concomitant radiotherapy and alkylating chemotherapy, followed by adjuvant chemotherapy. Chemotherapeutic choices are limited on account of most drugs’ poor propensity to cross the blood brain barrier. Systemic treatment with unspecified concentrations of chemotherapy is ineffective and risks adverse side effects. A localised and sustained delivery of patient-tailored chemotherapy to the resection cavity walls could significantly enhance patient survival opportunities by circumventing the BBB to eradicate the local, residual disease.

We describe the utilisation of a peptide-functionalised hyaluronic acid hydrogel cross-linked by the host-guest interactions of cucurbit[8]uril (CB[8]) as a drug-delivery vehicle for the treatment of GBM. The resulting material (98 wt% water) exhibits extraordinary tailorability and biocompatibility and can be produced to closely match the rheological properties of GBM tumour tissue.[1-3] The shear-thinning and self-healing capability of the hydrogel is successfully achieved through the use of CB[8] as a supramolecular cross-linker,[4] allowing the hydrogel to mold itself to an ex vivo resection cavity, maintaining tight apposition whilst releasing therapeutic compounds up to 950 μm in 1 h. The hyaluronic acid cysteine-phenylalanine (HA-CF) hydrogel shows no toxicity towards in vitro cell lines, with up-regulation of inflammatory markers seen only in samples loaded with chemotherapeutics. Importantly, these supramolecular hydrogels demonstrate superior release properties compared to conventional carmustine-impregnated wafers, Gliadel^TM. HA-CF supramolecular hydrogels represent a class of physically cross-linked biocompatible materials that open a crucial window into post-operative treatment for glioma resection patients.

In vitro release studies of various drug compounds encapsulated in the hydrogel have been performed and efficacy against multiple patient-derived human GBM cell lines determined. In vivo experiments with a mouse model are currently underway. We envisage that access to such drug-delivery technology will lead to clinical studies in the near future with an overall goal to prevent disease recurrence and improve patient survival rates.

References:
[1] Rowland, M.J.; Appel, E.A.; Coulston, R.J.; Scherman, O.A. J. Mater. Chem. B, 2013, 1, 2904-2910.
[2] Rowland, M.J.; Atgie, M.; Hoogland, D.; Scherman, O.A. Biomacromolecules, 2015, 16, 2436-2443.
[3] Rowland, M.J.; Parkins, C.C.; McAbee, J.H.; Kolb, A.K.; Hein, R.; Loh, X.J.; Watts, C.; Scherman, O.A. Biomaterials 2018, 179, 199-208.
[4] Appel, E.A.; del Barrio, J.; Loh, X.J.; Scherman, O.A., Chem. Soc. Rev., 2012, 41, 6195-6214; Liu, J.; Lan, Y.; Scherman, O.A. et al., Acc. Chem. Res. 2017, 50, 208-217; Liu, J.; Tan, C.S.Y.; Lan, Y. Scherman, O.A., Macromol. Chem. Phys., 2016, 217, 319-332.

Through dynamic supramolecular recognition, it is possible to create materials rationally designed beginning at the molecular level with specific, dynamic, and tunable non-covalent interactions. Certain benefits to this approach are precise control of composition, improved routes for targeting drugs, and new strategies to create materials that respond to a variety of stimuli with concomitant changes in their properties. The modularity of supramolecular interactions also facilitates opportunities to combine multiple payloads within a single delivery platform, as well as a route to the facile incorporation of specific targeting motifs that enable recognition in complex biological milleu. Using macrocyclic host-guest recognition, dynamic and tunable heterodimeric interactions enable precise control over the properties and availability of small molecule and protein drugs. This includes the ability to design new materials with affinity-directed dynamics, stimuli-responsive properties, or user-directed changes in mechanical properties. Furthermore, the ability to precisely tune affinity leads to a spectrum of different dynamics in topologically identical materials, as well as facilitating recognition even in complex or contaminated environments. By leveraging this affinity axis, a new route to precisly target therapies may also be achieved. We are very excited about this approach to creating new functional biomaterials through engineered supramolecular interactions, and will highlight these advances accross several material platforms.

Efforts to engineer polymer material mechanics is increasingly coupled to the design of transient crosslink dynamics. We have sought to gain a deeper understanding of how polymer gel mechanical properties can be controlled over multiple hierarchical time-scales via design of bio-inspired metal-coordinate crosslink structure on multiple length-scales. By utilizing metal ion-coordination complexes and metal nanoparticle-coordination junctions as supra-molecular crosslink structures, we have gained unique access to network dynamics on the microscopic scale, and thereby opportunities to broadly shape the distribution of network stress relaxation on the macroscopic scale. Our findings offer deeper insights on how to engineer gel stress relaxation mechanics directly via design of supramolecular crosslink structure dynamics, and could help improve our understanding of spatio-temporal molecular hierarchy in loadbearing biological materials.

Supramolecular complex systems are composed the host and guest molecules by noncovalent interaction such as hydrogen bonding, dipole-dipole interaction, van der Waals forces, hydrophobic interaction, and electrostatic interactions between molecules. Cyclic oligosaccharides, including derivatives of β-cyclodextrin (βCD) and cyclosophoraose (Cys), generally used as host molecules in biotechnology. These carbohydrate-based host molecules can enhance the stability, mechanical strength, effective loading capacity of hydrophobic drug, sustain release properties, pH responsive release and self-healing properties in hydrogels. In this study, we developed a hydrogel based on cyclic oligosaccharides using epichlorohydrin (ECH). The cyclic oligosaccharides were incorporated into the hydrogel to change the water-swelling ability of the hydrogel and to enhance the ability to complex hydrophobic drug such as galangin, tetracycline and ibuprofen. We used Cys and carboxmethyl βCD (CmβCD) to increase the drug loading capacity of the hydrogel without reducing the water-swelling of the hydrogel. They also improved mechanical strength of hydrogel. Poly-acrylic acid based hydrogel containing cationic βCD oligomer was also devised by triple cross-linking strategy combining electrostatic interactions, host-guest complexation, and C-C chemical bonds and the macrocrosslinker concept in one hydrogel. This cationic βCD oligomer was prepared by ECH, allyl glycidyl ether and glycidyltrimethylammonium chloride. These hydrogels show multi-functionality of high mechanical strength, enhanced stability, cytocompatibility, and pH-responsive drug release as well as self-healing property. These results suggest that cyclic oligosaccharide-based supramolecular complex system can enhance the various functionality of hydrogels for the effective hydrophobic drug delivery.

Heart failure is one of the most leading causes of death worldwide, with myocardial infarction (MI) having a significant morbidity and mortality rate. After MI, the artery occlusion eventually leads to scar tissue formation and malfunctioning of the heart. Cardiac regeneration could be initiated by delivering drugs to the damaged tissue.¹ However, without retentive properties the drugs are washed out due to pumping of the heart.² Therefore, a drug release system is needed to retain the drugs at the damaged tissue site and provide sustained drug release. Hydrogels are often used for drug delivery at various sites in the human body, thereby reducing the drug toxicity and increasing the drug release at target site. The question remains whether these gels can be applied in the heart.

A special class of hydrogels are supramolecular hydrogels, which offer unique dynamic and useful properties that could not be realized by traditional covalent biomaterials. These hydrogels benefit from the modular approach by allowing functionality and bioactivity, mimicking the ECM structure.³ In our group, hydrogels are designed using four-fold hydrogen bonding ureido-pyrimidinone (UPy) moieties, which dimerizes through strong and specific hydrogen bonds.⁴ These supramolecular hydrogels are composed of poly(ethylene glycol) (PEG) functionalized with UPy-units protected by alkyl spacers. These supramolecular hydrogels show pH- and temperature responsive behavior facilitating injection in the liquid state at a pH > 8.5, showing fast gelation when in contact with physiological pH.⁵

Our research goal is to develop these UPy-hydrogels into suitable drug delivery vehicles for the heart. Therefore, three goals have to be reached:
1. Control of drug-hydrogel affinity
2. Retention of the hydrogel in the heart
3. Introduction of imaging modules

To control the drug-hydrogel affinity different anchors were introduced in the hydrogel network, being dodecyl-, cholesterol-, and UPy-moieties. These moieties are proposed to show different affinities towards the hydrogel network, therefore having different release profiles. These moieties could be further functionalized with an RNA or drug molecule of interest. Furthermore, adhesive ligands based on collagen were introduced in the hydrogel to increase the retention of the hydrogel in the heart. An MRI detectable imaging module UPy-DOTA-gadolinium(III) was introduced in the UPy-hydrogel. Retention of the gel was examined in vivo in a porcine heart model after injection in the left ventricle. Future studies focus on UPy-DOTA complexed with indium-111 label that will be introduced in the hydrogel to furthermore examine the retention and biodistribution.
In conclusion, we ultimately envision a multi-functional supramolecular drug delivery system that is able to control drug release, shows retention in the heart and can be imaged with MRI.


1. Nielsen, S. H., Lindsey M.L. et al. Matrix Biol. (2017).
2. Feyen, D. A. M. Sluijter, J.P.G. et al. Eur. Heart J. 38, 184–186 (2017).
3. Webber, M. J., Appel, E. A., Meijer, E. W., & Langer, R. Nat. Mater. 15, 13 (2015).
4. Sijbesma, R. P., Meijer, E.W. et al. Science (80-. ). 278, 1601 LP-1604 (1997).
5. Bastings, M. M. C., Dankers, P.Y.W. et al. Adv. Healthc. Mater. 3, 70–78 (2014).

The "printing," or layer-by-layer extrusion, of cell-laden hydrogels results in the fabrication of 3D tissue-like structures. These fabricated tissues have potential applications in regenerative medicine and as in vitro tissue prototypes for drug screening. Bioinks for 3D bioprinting of synthetic tissues must fulfill three criteria: they must have rheological properties appropriate for extrusion printing, they must be cyto-compatible during the printing process, and they must include biological cues to control cell behavior after printing. Here we report on a recently developed family of bioinks that meet these requirements and can be further customized to achieve a range of mechanical properties. These hydrogel-based bioinks are produced from blends of engineered recombinant proteins and peptide-modified, naturally occurring biopolymers such as alginate. These materials undergo two-stages of crosslinking: (i) weak, peptide-based, supra-molecular assembly to homogeneously encapsulate cells in a shear-thinning hydrogel within the ink cartridge and (ii) stimuli-responsive crosslinking post-printing to rapidly stabilize the construct. Benefits of this two-stage crosslinking strategy include the prevention of cell sedimentation within the ink cartridge, mechanical shielding of the cell membrane from damaging extrusion forces during printing, rapid post-print self-assembly within an aqueous bath that prevents cell dehydration, and fine-tuning of the printed scaffold mechanical properties for optimal cell-matrix interactions. We demonstrate that tuning of the hydrogel material properties can be used to identify bioinks suitable as scaffolds for the large-scale expansion of neural stem cells.

One of the grand challenges for science in this century is to create strategies to regenerate parts of the human body in order to achieve longer “healthspans”. Materials science has a central role to play in this quest, which is both a highly desired and critical societal outcome given shifting demographics. The ultimate role, but not the only one, of materials in regenerative biology is to act as a bioactive medium with finite half-life that traffics signals in dynamic fashion. This in fact imitates the function of extracellular matrices as tissues develop or repair after injury, and requires molecular design of soft materials to directly activate signaling pathways via cell receptors or protein signals such as growth factors. This lecture will describe a broad platform of supramolecular biomaterials built with a toolbox of peptides, peptide amphiphiles, glycans, and nucleic acids that exhibit various forms of dynamic bioactivity toward neural or musculoskeletal cells. In one example it is possible to switch biological signals on and off through external cues, and in another one there is capacity in the material to adapt to the living structure for optimal signaling. In a third example an unprecedented soft material that exhibits reversible self-assembly of superstructures is found to modulate the phenotype of cells involved in tissue repair.

Induced pluripotent stem cells (iPSCs) differentiated to a mixture of kidney cell types are observed to rearrange into kidney nephron-like structures when aggregated, spotted and cultured in a media/air interface.¹ Although kidney like structures were observed, organoid growth is limited. No further growth or rearrangement was observed after 18 days in media/air interface cell culture. Moreover, preliminary results within our group showed overexpression of extracellular matrix (ECM) proteins, which is due to a fibrosis reaction. Here we hypothesized a possible need for a 3D environment, which mimics the in vivo surrounding matrix of the developing kidney in the fetus. Hence, the use of supramolecular hydrogels.
Conventional supramolecular hydrogel cross-linking methods mostly rely on static covalent chemistry, such as thiol-ene chemistry. Although these hydrogels show similarities to the in vivo ECM structural characteristics, they do not mimic the dynamic behavior of the natural ECM. Cells within the natural ECM are constantly stimulated by physical and chemical cues, which change over time.² For example, the repair of injured tissue occurs in multiple stages. Initially provisional matrix is deposit at the injured tissue side after which matrix modification restores the tissue. However, small difference in environment cues can result in excessive secretion of collagen by the cells, which subsequently results in fibrosis or scar tissue. The dynamic cues and interactions of matrix composition, biochemical molecules and matrix mechanics all play a significant role to the cellular behavior and induced pathways to healthy or diseased tissues. Therefore, there is a need for scientists to the design hydrogel that mimic this dynamic behavior beside structural composition.
New dynamic visco-elastic cross-linked supramolecular hydrogels of reversible covalent chemistry offer a novel approach to mimic the natural dynamic ECM behavior. Within our lab we observed a significant different in hydrogel stiffness, stress relaxation time and self-healing characteristics with different cross-linkers. This shows the possibility of tuning these materials for the desired dynamic behavior for the required cellular response.

Here we encapsulated the formed kidney organoids in the design reversible covalent chemistry cross-linked supramolecular hydrogels. Organoid cell arrangement, ECM expression, proliferation, and metabolic response were investigated in the designed dynamic hydrogels. These results were compared with to the encapsulation of organoids in a conventional thiol-ene static covalent cross-linked hydrogel.

1. Takasato, M.; Er, P. X.; Chiu, H. S.; Little, M. H., Generation of kidney organoids from human pluripotent stem cells. Nature Protocols 2016, 11 (9), 1681-1692.
2. Rosales, A. M.; Anseth, K. S., The design of reversible hydrogels to capture extracellular matrix dynamics. Nature reviews. Materials 2016, 1, 15012.

Articular cartilage lacks the intrinsic ability to regenerate following injury or disease. Biomaterials scaffolds can improve cartilage healing by supporting cell infiltration and guiding new matrix deposition, yet these materials must withstand dynamic shear in the articulating joint. Transforming growth factor β-1 (TGFβ-1) binding peptide amphiphile (PA) matrices have been shown to improve cartilage healing in a laprine model; however, these materials lacked the mechanical integrity necessary for use in load-bearing large-animal joints. To improve material retention, we developed a PA-hyaluronic acid (HA) hybrid material, which improved the mechanical toughness of scaffolds. Combining these two materials formed a biocompatible gel with a highly porous microstructure containing bundled supramolecular polymers. Because of its improved mechanical properties, the material was well retained in shallow osteochondral defects in the load-bearing ovine condyle. Four weeks following implantation, joints treated with TGFβ-1 loaded scaffolds revealed an improved level of tissue infiltration and integration with surrounding cartilage relative to control defects treated with only the growth factor alone. The observed improvements early in the healing process suggest the possible use of these covalent-supramolecular polymer hybrids as scaffolds for cartilage repair.

The extracellular matrix (ECM) is the non-cellular component present within all tissues and provides essential biological and mechanical cues required for tissue growth. Traditional synthetic covalent hydrogels (a network of hydrophilic polymers) have been investigated for 3D cell culture and probing cell-matrix interactions as they mimic the mechanics of soft tissues and support cell adhesion. However, these hydrogels are elastic and lack the viscoelasticity found in native ECM and soft tissues and can only allow tissue formation via degradation, since they are built from covalent bonds. To overcome these limitations, hydrogels with reversible crosslinks are developed which could respond cell stresses by rapidly breaking and reforming the bonds while maintaining uniform biophysical properties.

In our lab, we are working with 1,3,5-benzenetricarboxamide (BTA) supramolecular hydrogels. BTA molecules stack over each other through 3-fold hydrogen bonding and hydrophobic interactions to form long self-assembled BTA fibres, resulting in the hydrogel. BTAs are of interest for us owing to their cell-relevant timescales, protein-like fibrous structures and the ease of adjusting viscoelastic properties by controlling interactions at the molecular level. In addition, these gels exhibit injectability, showing a potential for bioprinting, and can serve as a platform for the generation of spatiotemporal dynamic co-cultures.

For cell viability, cultured cells within gels were stained with calcein-AM and ethidium homodimer-1 and imaged using fluorescence microscopy. Minimal cytotoxicity was observed over 7 days. To be more quantitative, an absorbance-based LDH and CyQUANT assays were carried out. LDH assay showed approximately 10% dead cells and results are comparable to alginate control sample, Ca²⁺ crosslinked. The CyQUANT assay showed that cell number fairly stayed constant and gels did not enhance the proliferation. Interestingly, chondrocytes aggregation within gels were observed over time which was visualized with actin and nuclei staining. Currently, cell culture experiments are being carried out to investigate cartilage matrix formation by chondrocytes within BTAs hydrogels with varying viscoelastic timescales.

Furthermore, to expand the current BTA hydrogelator library (with different architectures) work was carried out towards desymmetrization of BTAs; a penta-fluorophenol BTA synthon (BTE-F₅Ph) has been synthesized and desymmetrized using hexylamine as a model reaction. This work enables the creation of a small library of hydrogels with varying dynamicity and viscoelasticity that can help in developing a better understanding of cell-ECM interactions and directing cell fate.

Statically crosslinked hydrogels poorly recapitulate the complex and responsive behavior of a cell’s native extra cellular matrix (ECM). Cells have a difficult time growing, migrating, and fusing to form tissue within a densely crosslinked covalent hydrogel, yet covalently crosslinked hydrogels are the most widely used material for 3D printing of cell laden hydrogels (bioinks). Consequently, in order to create more complex and biomimetic 3D tissue engineering constructs, the there is a noticeable need for the creation and use of dynamically crosslinked hydrogels within biofabrication and 3D printing.
Recently, our lab has developed both supramolecular and dynamic covalently crosslinked hydrogels which show high cell viability upon encapsulation, tunable network dynamics and mechanical properties, and exhibit self-healing, injectability, and 3D printability. In this talk, I will mainly focus on the dynamic covalent crosslinked hydrogels based on imine type crosslinking. These imine cross links are dynamic under physiologic conditions, resulting in appreciable on/off rates depending on the molecular structure of the crosslinker. Furthermore, these hydrogels are easily functionalized with biological cues using oxime ligation strategies. Several cell types (HDF, ATDC5, pancreatic islets) show good cell viability within these hydrogels. We observe noticeable changes in cellular function (proliferation, morphology, etc.) depending on the dynamics of the hydrogel formulation, enabling the matching of network dynamics with the desired cellular response. These hydrogel formulations also show good 3D printability, allowing the creation of spatially defined cell-laden constructs with enhanced function (as compared to other covalent bioinks).
These developed hydrogels represent new classes of dynamic bioinks for 3D printing and the construction or large tissue engineering constructs. The ability to fabricate appreciable size and spatially defined objects with biomimetic network dynamics enables the creation of complex multicellular constructs that can facilitate inter-cellular communication. Current efforts in the lab are focused on using these dynamically remodelable networks to study the interactions of cells and migration through reversible networks in complex geometries.