Tuning the Size of Elastin-like Polypeptide Nanoparticles

The ability to control the size of biologically-based, environmentally-sensitive colloidal nanoparticles can advance their application in areas such as drug delivery, tissue engineering, and biosensors. Controlling size is a primary task in engineering nanomaterials because many of their properties depend on size. With the aim of fine- tuning the size of particles, we characterize mixtures of two elastin-like polypeptide structures: a linear and a trimer configuration. Both constructs undergo aggregation above their inverse transition temperatures, but the linear ELP forms large aggregates which coalesce into a protein-rich phase, while the ELP trimer with polar head groups forms stable polymer micelles in low salt concentrations. The mixing of these two constructs makes possible a range of sizes of stable particles through the formation of a microemulsion. The linear ELP fills the cores of the micelle aggregates, resulting in larger stable particles. We determined the dependence of particle size on both the salt and linear ELP concentration across a range of temperatures using UV-vis spectroscopy and dynamic light scattering (DLS). We find that a given mixture of linear and trimer constructs has two temperature-based transitions and therefore displays three predominant size regimes. The results help elucidate the mechanisms of ELP aggregation.https://engagedscholarship.csuohio.edu/u_poster_2015/1048/thumbnail.jp

Light Scattering Study of Mixed Micelles Made from Elastin-Like Polypeptide Linear Chains and Trimers

Temperature sensitive nanoparticles (E20F) were generated from a construct of three chains of Elastin- Like Polypeptides (ELP) linked to a negatively charged foldon domain. This ELP system was mixed at different ratios with a single linear chain of ELP (H40L) which was deprived of the foldon domain. The mixed system is soluble at room temperature and at a transition temperature will form swollen micelles with the hydrophobic linear chains hidden inside. This system was studied using Depolarized Dynamic Light Scattering (DDLS) and Static Light Scattering (SLS) to model the size, shape, and internal structure of the mixed micelles. The mixed micelle in equal parts of E20F and H40L show a constant apparent hydrodynamic radius of 40-45 nm at the concentration window from 25:25 to 60:60 μM (1:1 ratio). At a fixed 50 μM concentration of the E20F with varying H40L concentrations from 5 to 80 μM, a linear growth in the hydrodynamic radius is seen from about 11 to about 62 nm, along with a 1000-fold increase in VH signal. A possible simple model explaining the growth of the mixed micelles is considered. Lastly, the VH signal can indicate elongation in the geometry of the particle or could possibly be a result from anisotropic properties from the core of the micelle. Static Light Scattering was used to study the molecular weight, and the radius of gyration of the micelle to help identify the structure and morphology of mixed micelles and the tangible cause of the VH signal.https://engagedscholarship.csuohio.edu/u_poster_2016/1039/thumbnail.jp

Light Scattering Characterization of Elastin-Like Polypeptide Trimer Micelles

Elastin-Like Polypeptides (ELP) can be used to form thermo-reversible vehicles for drug delivery systems. The ELP nanoparticles are composed of three-armed star polypeptides. Each of the three arms extending from the negatively charged foldon domain includes 20 repeats of the (GVGVP) amino acid sequence. The ELP polymer chains are soluble at room temperature and become insoluble at the transition temperature (close to 50 oC), forming micelles. The size and shape of the micelle is dependent on the temperature and the pH of solution, along with the concentration of the Phosphate Buffered Saline (PBS) solvent. The technique of Depolarized Dynamic Light Scattering (DDLS) was employed to study the structure and dynamics of micelles at 62 oC; the solution was maintained at an approximate pH level of 7.3 - 7.5, while varying the concentration of the solvent (PBS). At low salt concentrations (\u3c 15 mM), the micellar size is not very reproducible due to unstable pH levels, arising from low buffer concentration. At intermediate salt concentrations (15 - 60 mM), the system formed spherically-shaped micelles exhibiting a steady growth in the hydrodynamic radius (Rh) from 10 to 21 nm, with increasing PBS concentration. Interestingly, higher salt concentrations (\u3e 60 mM) displayed an apparent elongation of the micelles evident by a significant VH signal, along with a surge in the apparent Rh. A model of micelle growth (and potentially elongation) with increase in salt concentration is considered.https://engagedscholarship.csuohio.edu/u_poster_2016/1038/thumbnail.jp

Tuning the Size of Elastin-like Polypeptide Nanoparticles

The ability to control the size of biologically-based, environmentally-sensitive colloidal nanoparticles can advance their application in areas such as drug delivery, tissue engineering, and biosensors. Controlling size is a primary task in engineering nanomaterials because many of their properties depend on size. With the aim of fine- tuning the size of particles, we characterize mixtures of two elastin-like polypeptide structures: a linear and a trimer configuration. Both constructs undergo aggregation above their inverse transition temperatures, but the linear ELP forms large aggregates which coalesce into a protein-rich phase, while the ELP trimer with polar head groups forms stable polymer micelles in low salt concentrations. The mixing of these two constructs makes possible a range of sizes of stable particles through the formation of a microemulsion. The linear ELP fills the cores of the micelle aggregates, resulting in larger stable particles. We determined the dependence of particle size on both the salt and linear ELP concentration across a range of temperatures using UV-vis spectroscopy and dynamic light scattering (DLS). We find that a given mixture of linear and trimer constructs has two temperature-based transitions and therefore displays three predominant size regimes. The results help elucidate the mechanisms of ELP aggregation.https://engagedscholarship.csuohio.edu/u_poster_2015/1048/thumbnail.jp