Light Scattering Characterization of Salt Dependent Thermoreversible Micelles Synthesized from Elastin-Like Polypeptides

Environmentally responsive nanoparticles synthesized from Elastin-Like Polypeptides (ELP) present a promising system for applications such as biosensors, drug delivery vehicles, and viscosity modifiers. These nanoparticles undergo a transition from a soluble state at Troom to micellar aggregates above the transition. The ELP micelles have been found to be sensitive to various outside stimuli including pH, salt concentration, and solvent. Dynamic and Static Light Scattering were used to study structure and dynamics of ELP nanoparticles below the transition and of formed ELP micelles above the transition. Micelles were found to generally depend strongly on solution pH, however, in the pH window of 10.1-10.4 their size stayed constant. The apparent radius and molecular weight of micelles in this pH range strongly depend on salt concentration with three apparent regimes. At low salt (0-15mM), largely spherical micelles were found with Rh=15nm, which corresponds to the size of folded ELP hydrophilic tail; and molecular weight of 5000-6000kg/mol. At the intermediate salt (15-30mM) the observed particles are spherical micelles that increase in size (by about 3 fold) and molecular weight (by about 50 fold) as salt concentration increases. At high salt concentrations (30-60mM), Rg/Rh∼ 1.3, indicating the micelles behave as elongated particles with Rh∼75nm that corresponds to the size of a stretched ELP chain with an apparent molecular weight of 300000-600000kg/mol

Exploring Structure, Shape, and Dynamics of Elastin-like Polypeptide Nanoparticles

Environmentally responsive nanoparticles synthesized from elastin-like polypeptides (ELP) present a promising system for applications as biosensors, drug delivery vehicles, and viscosity modifiers. These nanoparticles undergo a transition from a soluble state at room temperature to micellar aggregates above the transition. The size, shape, and dynamics of micelles above the transition as well as effects of the solvent salt concentration and pH on the transition are important to understand from a fundamental science point of view as well as for potential applications. The system has been characterized with high resolution multiangle Dynamic and Static Light Scattering Spectroscopies. It was confirmed that the system undergoes a transition from mixture of ELP extended trimers and their non-spherical formations to a solution of micelles. It was discovered that micellar size and structure are very sensitive to solution\u27s pH. The micelles were generally found to exhibit properties of the hyperbranched spheres below pH of 10 and above pH of 10.3 with their shape becoming significantly elongated in the pH window of 10 to 10.3. It was also found that the size of micelles strongly depends on salt concentration displaying at least two size regimes (20-45nm at 0-20mM and 100-150nm at 25-40mM) with different salt concentration dependences

Apparent Sphere to Elongated particle transition of Elastin-Like Polypeptide Thermoreversible Micelles

Biosynthesized polymers can be designed to assemble into environmentally responsive nanoparticles. Such a system consisting of an oligomerization domain connecting three elastin-like polypeptide (ELP) chains has been developed. These polypeptides reversibly transition from aqueous soluble polymers to amphiphiles when the temperature is raised above the ELP transition temperature. As amphiphiles these can assemble into micelles under appropriate solution conditions. A particular system has been designed to reversibly form micelles at a neutral pH. However, the shape and size of micelles was found to depend strongly on salt concentration. We used polarized and depolarized dynamic light scattering to study temperature-driven formation of micelles of various geometries under different solvent conditions. We also monitored the sphere-to-elongated particle transition of the ELP micelles with addition of salt. The apparent dimensions, shape, and dynamics of micelles strongly depend on salt concentration, with two distinct salt regimes and a broad transition region observed. At low salt concentration (0-15 mM), largely spherical micelles were found with a hydrodynamic radius of 10-15 nm. At intermediate salt concentration (15-35 mM) the transition from spherical to elongated micelles is observed. At high salt concentrations (above 35 mM), the micelles again reach a stable structure consisting of highly anisotropic particles with an aspect ratio of higher than 10

Apparent Sphere to Elongated particle transition of Elastin-Like Polypeptide Thermoreversible Micelles

Biosynthesized polymers can be designed to assemble into environmentally responsive nanoparticles. Such a system consisting of an oligomerization domain connecting three elastin-like polypeptide (ELP) chains has been developed. These polypeptides reversibly transition from aqueous soluble polymers to amphiphiles when the temperature is raised above the ELP transition temperature. As amphiphiles these can assemble into micelles under appropriate solution conditions. A particular system has been designed to reversibly form micelles at a neutral pH. However, the shape and size of micelles was found to depend strongly on salt concentration. We used polarized and depolarized dynamic light scattering to study temperature-driven formation of micelles of various geometries under different solvent conditions. We also monitored the sphere-to-elongated particle transition of the ELP micelles with addition of salt. The apparent dimensions, shape, and dynamics of micelles strongly depend on salt concentration, with two distinct salt regimes and a broad transition region observed. At low salt concentration (0-15 mM), largely spherical micelles were found with a hydrodynamic radius of 10-15 nm. At intermediate salt concentration (15-35 mM) the transition from spherical to elongated micelles is observed. At high salt concentrations (above 35 mM), the micelles again reach a stable structure consisting of highly anisotropic particles with an aspect ratio of higher than 10

Size and Shape Characterization of Thermoreversible Micelles of Three-Armed Star Elastin-Like Polypeptides

Three-armed star elastin-like polypeptides are shown to have the capability of self-assembling into micellar constructs at certain environmental conditions. Here, a study of the size distribution, shape, and molecular weight of these micelles at different salt concentrations and pH values is presented. Multiangle dynamic light scattering was used to study the formation, reversibility, and size of the micelles at different environmental conditions. On the basis of the salt concentration of the solution, two distinct size distribution regimes and a transition region were observed. Static light scattering was performed to study the molecular weight and geometrical anisotropy of the micelles in each regime. The anisotropic behavior and elongation of the particles were independently confirmed by depolarized dynamic light scattering, and a model for micelles at each regime was proposed. The size and molecular weight of the micelles were verified using viscosity measurements. The results of this study suggest that there is big jump in the size and molecular weight of the micelles from the first salt-dependent regime to the other, and the shape of the micelles changes from spheres to cylindrical micelles with a higher than 10:1 axis ratio