Controlling the Size and Shape of Polypeptide Colloidal Particles: Characterization by Light Scattering

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Undergraduate Research Posters


Temperature-dependent polymer surfactants have been developed by connecting three elastin-like polypeptide (ELP) chains to a charged protein domain (foldon), forming a three-armed star polymer. At low temperatures, the polymer is soluble, while at higher temperatures, the ELP phase separates into a hydrophilic head group and hydrophobic tails, forming micelles. These particles have potential applications in drug delivery, as they are both small and biocompatible. The behavior of mixtures of the three-armed star ELP (E20-Foldon) and H-40 linear ELP chains was analyzed under different salt and protein concentrations, as well as with various foldon to linear ratio combinations using Dynamic Light Scattering (DLS) and Depolarized Dynamic Light Scattering (DDLS). Pure E20-Foldon solutions with the same protein and salt concentrations were also analyzed and compared to their respective mixtures. It was expected that under certain conditions, the pure E20-Foldon would form spherical micelles, and that by adding the linear ELP, those micelles would increase in size and the conditions under which they formed would change. It was determined that the pure E20 did indeed form largely spherical micelles with an apparent size of about 10nm in solutions with salt concentration between 15mM and 100mM and protein concentration between 10μM and 100μM. It was also determined that low salt (up to 25mM) mixtures of E20-Foldon and H-40 linear ELPs yielded large colloidal particles with an apparent radius of 200-500nm and properties of non-spherical particles above the transition.