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1.  Photodynamic Control of Bioactivity in a Nanofiber Matrix 
ACS nano  2012;6(12):10776-10785.
Self-assembling peptide materials have been used extensively to mimic natural extracellular matrices (ECMs) by presenting bioactive epitopes on a synthetic matrix. Although this approach can facilitate a desired response from cells grown in the matrix, it lacks the capacity for spatial or temporal regulation of the presented signals. We describe here a photo-responsive, synthetic ECM using a supramolecular platform comprised of peptide amphiphiles (PAs) that self-assemble into cylindrical nanofibers. A photocleavable nitrobenzyl ester group was included in the peptide backbone using a novel Fmoc-amino acid that is compatible with microwave-assisted solid phase peptide synthesis. The placement of the photolabile group on the peptide backbone enabled efficient removal of the ECM-derived cell adhesion epitope RGDS from PA molecules upon exposure to light (half-life of photolysis ~ 1.9 min) without affecting the nanofiber assembly. Fibroblasts cultured on RGDS-presenting PA nanofiber substrates demonstrated increased cell spreading and more mature focal adhesions compared with unfunctionalized and control (RGES-presenting) surfaces, as determined by immunostaining and cell morphological analysis. Furthermore, we observed an arrest in fibroblast spreading on substrates containing a cleavable RGDS epitope when the culture was exposed to light; in contrast, this dynamic shift in cell response was absent when the RGDS epitope was attached to the PA molecule by a light-insensitive control linker. Light-responsive bioactive materials can contribute to the development of synthetic systems that more closely mimic the dynamic nature of native ECM.
PMCID: PMC3528833  PMID: 23153342
Supramolecular Nanofibers; Cell Morphological Analysis; Nitrobenzyl; Projected Cell Area; Photodegradable; RGDS Epitope
2.  Controlled Release of Dexamethasone from Peptide Nanofiber Gels to Modulate Inflammatory Response 
Biomaterials  2012;33(28):6823-6832.
New biomaterials that have the ability to locally suppress an immune response could have broad therapeutic use in the treatment of diseases characterized by acute or chronic inflammation or as a strategy to facilitate improved efficacy in cell or tissue transplantation. We report here on the preparation of a modular peptide amphiphile (PA) capable of releasing an anti-inflammatory drug, dexamethasone (Dex), by conjugation via a labile hydrazone linkage. This molecule self-assembled in water into long supramolecular nanofibers when mixed with a similar PA lacking the drug conjugate, and the addition of calcium salt to screen electrostatic repulsion between nanofibers promoted gel formation. These nanofiber gels demonstrated sustained release of soluble Dex for over one month in physiologic media. The Dex released from these gels maintained its anti-inflammatory activity when evaluated in vitro using a human inflammatory reporter cell line and furthermore preserved cardiomyocytes viability upon induced oxidative stress. The ability of this gel to mitigate the inflammatory response in cell transplantation strategies was evaluated using cell-surrogate polystyrene microparticles suspended in the nanofiber gel that were then subcutaneously injected in a mouse. Live animal luminescence imaging using the chemiluminescent reporter molecule luminol showed a significant reduction in inflammation at the site where particles were injected with Dex-PA compared to the site of injection for particles within a control PA in the same animal. Histological evidence suggested a marked reduction in the number of infiltrating inflammatory cells when particles were delivered within Dex-PA nanofiber gels and very little inflammation was observed at either 3 days or 21 days post-implantation. The use of Dex-PA could facilitate localized anti-inflammatory activity as a component of biomaterials designed for various applications in regenerative medicine and could specifically be a useful module for PA-based therapies. More broadly, these studies define a versatile strategy for facile synthesis of self-assembling peptide-based materials with the ability to control drug release.
PMCID: PMC3445268  PMID: 22748768
Inflammatory Response; Peptide Amphiphiles; Controlled drug release; Self-assembly; Immune response; Cell therapy
3.  Nanostructure-templated control of drug release from peptide amphiphile nanofiber gels 
Soft matter  2012;8(13):3586-3595.
High aspect ratio peptide nanofibers have potential as biodegradable vehicles for drug delivery. We report here the synthesis of four self-assembling peptide amphiphiles (PAs) containing a lysine ε-amine-derivatized hydrazide that was systematically placed at different positions along the backbone of the peptide sequence C16V2A2E2 (where C16 = palmitic acid). Hydrazones were formed from each hydrazide by condensation with the solvatochromic dye 6-propionyl-2-dimethylaminonaphthalene (Prodan), which is typically used to probe cell membranes. All four compounds were found to self-assemble into nanofibers, and Prodan release was measured from filamentous gels prepared by screening PA charges with divalent cations. Near zero-order release kinetics were observed for all nanofibers, but release half-lives differed depending on the position of the fluorophore in the PA sequence. Dye release kinetics were rationalized through the use of cryogenic transmission electron microscopy, small-angle X-ray scattering, fluorescence spectroscopy, fluorescence anisotropy, circular dichroism, and partition coefficient calculations. Relative release rates were found to correlate directly with fluorophore mobility, which varied inversely with packing density, degree of order in the hydrophobic PA core, and the β-sheet character of the peptide.
PMCID: PMC3487392  PMID: 23130084
4.  Self-assembling peptide scaffolds for regenerative medicine 
Biomaterials made from self-assembling, short peptides and peptide derivatives have great potential to generate powerful new therapies in regenerative medicine. The high signaling capacity and therapeutic efficacy of peptidic scaffolds has been established in several animal models, and the development of more complex, hierarchical structures based on peptide materials is underway. This highlight discusses several classes of self-assembling peptide-based materials, including peptide amphiphiles, Fmoc-peptides, self-complementary ionic peptides, hairpin peptides, and others. The self-assembly designs, bioactive signalling strategies, and cell signalling capabilities of these bioactive materials are reported. The future challenges of the field are also discussed, including short-term goals such as integration with biopolymers and traditional implants, and long term goals, such as immune system programming, subcellular targeting, and the development of highly integrated scaffold systems.
PMCID: PMC3355058  PMID: 22080255
5.  A Peptide-Based Material for Therapeutic Carbon Monoxide Delivery 
Soft matter  2012;8(25):2689-2692.
We report on the preparation of the first material for therapeutic delivery of CO. A peptide amphiphile was synthesized with a covalently attached ruthenium tricarbonyl. Self-assembled nanofiber gels containing this peptide spontaneously released CO with prolonged release kinetics compared to soluble CO donors. Oxidatively stressed cardiomyocytes had improved viability when treated with this peptide, demonstrating its potential as a biodegradable gel for localized therapeutic CO delivery.
PMCID: PMC3374652  PMID: 22707978
6.  Peptide Self-Assembly for Crafting Functional Biological Materials 
Self-assembling, peptide-based scaffolds are frontrunners in the search for biomaterials with widespread impact in regenerative medicine. The inherent biocompatibility and cell signaling capabilities of peptides, in combination with control of secondary structure, has led to the development of a broad range of functional materials with potential for many novel therapies. More recently, membranes formed through complexation of peptide nanostructures with natural biopolymers have led to the development of hierarchically-structured constructs with potentially far-reaching applications in biology and medicine. In this review, we highlight recent advances in peptide-based gels and membranes, including work from our group and others. Specifically, we discuss the application of peptide-based materials in the regeneration of bone and enamel, cartilage, and the central nervous system, as well as the transplantation of islets, wound-healing, cardiovascular therapies, and treatment of erectile dysfunction after prostatectomy
PMCID: PMC3224089  PMID: 22125413
Peptide amphiphiles; Self-assembly; Bioactive materials; Regenerative medicine; Bone regeneration; Enamel regeneration; Cartilage regeneration; Angiogenesis; Islet transplantation; Bioactive membranes
7.  Antisense Oligonucleotides Delivered to the Mouse CNS Ameliorate Symptoms of Severe Spinal Muscular Atrophy 
Science translational medicine  2011;3(72):72ra18.
Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by mutations in the SMN1 gene that result in a deficiency of SMN protein. One approach to treat SMA is to use antisense oligonucleotides (ASOs) to redirect the splicing of a paralogous gene, SMN2, to boost production of functional SMN. Injection of a 2′-O-2-methoxyethyl–modified ASO (ASO-10-27) into the cerebral lateral ventricles of mice with a severe form of SMA resulted in splice-mediated increases in SMN protein and in the number of motor neurons in the spinal cord, which led to improvements in muscle physiology, motor function and survival. Intrathecal infusion of ASO-10-27 into cynomolgus monkeys delivered putative therapeutic levels of the oligonucleotide to all regions of the spinal cord. These data demonstrate that central nervous system–directed ASO therapy is efficacious and that intrathecal infusion may represent a practical route for delivering this therapeutic in the clinic.
PMCID: PMC3140425  PMID: 21368223
9.  End-functionalized glycopolymers as mimetics of chondroitin sulfate proteoglycans† 
Glycosaminoglycans are sulfated polysaccharides that play important roles in fundamental biological processes, such as cell division, viral invasion, cancer and neuroregeneration. The multivalent presentation of multiple glycosaminoglycan chains on proteoglycan scaffolds may profoundly influence their interactions with proteins and subsequent biological activity. However, the importance of this multivalent architecture remains largely unexplored, and few synthetic mimics exist for probing and manipulating glycosaminoglycan activity. Here, we describe a new class of end-functionalized ring-opening metathesis polymerization (ROMP) polymers that mimic the native-like, multivalent architecture found on chondroitin sulfate (CS) proteoglycans. We demonstrate that these glycopolymers can be readily integrated with microarray and surface plasmon resonance technology platforms, where they retain the ability to interact selectively with proteins. ROMP-based glycopolymers are part of a growing arsenal of chemical tools for probing the functions of glycosaminoglycans and for studying their interactions with proteins.
PMCID: PMC3026345  PMID: 21274421
10.  Monotelechelic Poly(oxa)norbornenes by Ring-Opening Metathesis Polymerization using Direct End-Capping and Cross Metathesis 
Macromolecules  2010;43(1):213-221.
Two different methodologies for the synthesis of monotelechelic poly(oxa)norbornenes prepared by living ring-opening metathesis polymerization (ROMP) are presented. The first method, termed direct end-capping, is carried out by adding an internal cis-olefin terminating agent (TA) to the reaction mixture immediately after the completion of the living ROMP reaction. The second method relies on cross metathesis (CM) between a methylene-terminated poly(oxa)norbornene and a cis-olefin TA mediated by the ruthenium olefin metathesis catalyst (H2IMes)(Cl)2Ru(CH-o-OiPrC6H4) (H2IMes = 1,3-dimesitylimidazolidine-2-ylidene). TAs containing various functional groups, including alcohols, acetates, bromides, a-bromoesters, thioacetates, N-hydroxysuccinimidyl esters and Boc-amines, as well as fluorescein and biotin groups, were synthesized and tested. The direct end-capping method typically resulted in >90% end-functionalization efficiency, while the CM method was nearly as effective for TAs without polar functional groups or significant steric bulk. End-functionalization efficiency values were determined by 1H NMR spectroscopy.
PMCID: PMC2943665  PMID: 20871800
11.  Pulsed-Addition Ring-Opening Metathesis Polymerization: Catalyst-Economical Syntheses of Homopolymers and Block Copolymers 
Poly(tert-butyl ester norbornene imide) homopolymers and poly(tert-butyl ester norbornene imide-b-N-methyl oxanorbornene imide) copolymers were prepared by pulsed-addition ring-opening metathesis polymerization (PA-ROMP). PA-ROMP is a unique polymerization method that employs a symmetrical cis-olefin chain transfer agent (CTA) to simultaneously cap a living polymer chain and regenerate the ROMP initiator with high fidelity. Unlike traditional ROMP with chain transfer, the CTA reacts only with the living chain end, resulting in narrowly dispersed products. The regenerated initiator can then initiate polymerization of a subsequent batch of monomer, allowing for multiple polymer chains with controlled molecular weight and low polydispersity to be generated from one metal initiator. Using the fast-initiating ruthenium metathesis catalyst (H2IMes)(Cl)2(pyr)2RuCHPh and cis-4-octene as a CTA, the capabilities of PA-ROMP were investigated with a Symyx robotic system, which allowed for increased control and precision of injection volumes. The results from a detailed study of the time required to carry out the end-capping/initiator-regeneration step were used to design several experiments in which PA-ROMP was performed from one to ten cycles. After determining the rate of catalyst death, a single, low polydispersity polymer was prepared by adjusting the amount of monomer injected in each cycle, maintaining a constant monomer/catalyst ratio. Additionally, PA-ROMP was used to prepare nearly perfect block copolymers by quickly injecting a second monomer at a specific time interval after the first monomer injection, such that chain transfer had not yet occurred. Polymers were characterized by gel permeation chromatography with multi-angle laser light scattering.
PMCID: PMC2787826  PMID: 19215131

Results 1-11 (11)