Characterization of a Peptide Amphiphile Hydrogel Model System

Organic phase change materials (PCM) release large quantities of heat during phase changes and can store significant amounts of thermal energy. Unlike inorganic PCMs, which are commonly used to store thermal energy in buildings, organic PCMs show potential for biomedical applications. Current PCMs, including fatty acids or paraffins, can be difficult to synthesize, exhibit low tunability, or display poor physical properties. One prospective PCM, peptide-amphiphiles (PA), may show enhanced tunability and a simplified synthesis. Experimental PAs contained a lipid tail bound to a short peptide containing between 0 and 5 leucine residues. PAs were synthesized using an automated peptide synthesizer, purified by HPLC, and their purity was confirmed by MALDI-MS analysis. The efficacy of PAs as PCMs can be evaluated by determining the critical gelation concentration (CGC), or the concentration of peptide required to form a hydrogel, using a dilution assay. Based on preliminary data, it is anticipated that the CGC will be between 4 and 10% weight. To observe the influence of pH and the number of leucine residues on micelle formation, a fluorescence-based critical micelle concentration (CMC) assay was conducted using the micelle sensitive dye 1,6-diphenyl-1,3,5-hexatriene. Increased pH and peptide length decreased the CMC. Compiling CGC and CMC data will provide valuable information about the effect of modifying the quantity of leucine residues on PA properties and the ability of PAs to act as PCMs. These tunable PA hydrogels could be applied in biomedical settings to improve drug delivery or wound healing.