Modulating the Gelation Properties of Self-Assembling Peptide Amphiphiles

Abstract

Peptide amphiphiles (PAs) are self-assembling molecules that form interwoven nanofiber gel networks. They have gained lots of attention because of their excellent biocompatibility, adaptable peptide structure that allows for specific biochemical functionality, and nanofibrous assembly that mimics natural tissue formation. However, variations in molecule length, charge, and intermolecular bonding between different bioactive PAs cause contrasting mechanical properties. This potentially limits cell-delivery therapies because scaffold durability is needed to withstand the rigors of clinician handling and transport to wound implant sites. Additionally, the mechanical properties have critical influence on cellular behavior, as the elasticity and stiffness of biomaterials have been shown to affect cell spreading, migration, contraction, and differentiation. Several different PAs have been synthesized, each endowed with specific cellular adhesive ligands for directed biological response. We have investigated mechanical means for modulating and stabilizing the gelation properties of PA hydrogels in a controlled manner. A more stable, biologically-inert PA (PA-S) was synthesized and combined with each of the bioactive PAs. Molar ratio (Mr = PA/PA-S) combinations of 3:1, 1:1, and 1:3 were tested. All PA composites were characterized by observed nanostructure and rheological analysis measuring viscoelasticity. It was found that the PAs could be combined to successfully control and stabilize the gelation properties, allowing for a mechanically-tunable scaffold with increased durability. Thus, the biological functionality and natural degradability of PAs can be provided in a more physiologically-relevant microenvironment using our composite approach to modulate the mechanical properties, thereby improving the vast potential for cell encapsulation and other tissue engineering applications. KeywordsPeptide amphiphile; hydrogel; viscoelasticity; biomimetic material; ECM (extracellular matrix)With ever expanding research into synthetic biomaterials, the importance of recapitulating the innate characteristics of biological tissue microenvironments, including the biochemical and mechanical properties, has gained greater importance. In particular, synthetic microenvironments need to provide both the spatial and temporal complexities necessary to guide cell-specific tissue development and function. 1 Peptide-based hydrogels offer one such promising biomaterial, crafted to simplistically mimic the native extracellular matrix (ECM). *Corresponding author: Dr. Ho-Wook Jun; hwjun@uab.edu; University of Alabama at Birmingham, Shelby 806, 1825 University Blvd., Birmingham, AL 35294-2182, United States; office: 205-996-6938; fax: 205-974-6938. Supporting Information Available: (1) Macroscopic gelation properties of peptide amphiphile composite hydrogels modulated at a 3:1 molar ratio. (2) Viscoelastic characterization using dynamic oscillatory rheometry to measure storage modulus in relation to frequency for peptide amphiphile compo...

Experimental and Computational Investigation of the Effect of Hydrophobicity on Aggregation and Osteoinductive Potential of BMP-2-Derived Peptide in a Hydrogel Matrix

“…Peptides have recently been used to generate tubular, fibrillar, micellar, or vesicular nanostructures due their amphiphilic nature. [14][15][16][17] For example, peptides with a hydrophilic head and a hydrophobic tail spontaneously self-assemble to form vesicular structures in aqueous solution. 18 Peptide aggregation may alter the overall conformation and presentation of the amino acid sequence that interacts with cell surface receptors, which adversely affects the osteoinductive potential of the peptide.…”

Peptide conjugate hydrogelators

“…Such triggers include light, 171,172 heparin, 173 calcium, 174 cis-platin 175 and counter ion screening. 176 In contrast to the Fmoc-peptide derivatives discussed in section 4.1, PAs have not been used extensively to create 90 particularly strong gels (G′ typically around 200 Pa or lower, 127 although there are exceptions 77 ) and have generally been used as biomedical scaffolds. Some work has been undertaken, however, to optimise the strength of PA hydrogels.…”

“…This carefully controlled study showed, for the first time, that additives can be used to strengthen PA hydrogels at no 10 detriment to structural conformation. More recently, Anderson et al 127 showed that a biologically inert PA could be effectively mixed with a bioactive PA to enhance structural stability of the final hydrogel whilst maintaining the material"s biological function. In some cases, the cell-binding 15 PAs were not able to form standing hydrogels without the incorporation of the structural PA additive, demonstrating the value of this approach for cell encapsulation and other tissue engineering applications.…”

Enhanced MIN-6 beta cell survival and function on a nitric oxide-releasing peptide amphiphile nanomatrix

“…11,13 The nanomatrix can be self-assembled into two-dimensional coatings or three-dimensional nanomatrix gels. [18][19][20] It has been shown to promote endothelial cell adhesion and proliferation 11,12 as well as endothelial progenitor cell adhesion and differentiation.…”

“…14 CONH-GTAGLIGQ-KKKKK] were prepared using the Fmoc chemistry in the Advanced Chemtech Apex 396 peptide synthesizer (AAPPTec, Louisville, KY, USA) and subsequently were alkylated at the N-termini with palmitic acid by a manual coupling reaction for 24 hours at room temperature. 18,20 To alkylate with palmitic acid, a mixture of o-benzotriazole-N,N,N,N′-tetramethyluronium hexafluorophosphate, diisopropylethylamine, and dimethylformamide was used, and cleavage and deprotection were achieved using a mixture of trifluoroacetic acid, deionized water, triisopropylsilane, and anisole (40:1:1:1) for 3 hours at room temperature. The peptide amphiphiles precipitated in cold ether were lyophilized and characterized by matrix-assisted laser desorption ionization time of flight mass spectrometry.…”