Nanogel formation from dilute solutions of clickable elastin-like recombinamers and its dependence on temperature: two fractal gelation modes.

Diluted, complementary, click-reactive elastin-like recombinamer (ELR) solutions have been prepared and mixed at two different temperatures, one below and one above the characteristic transition temperature (Tt) of these chemically modified ELRs. FTIR measurements, size, aspect ratio, zeta potential, and microrheological measurements have been carried out on the nanostructures formed under these dilute conditions as a way to better understand the relationship between the final macroscopic properties of ELR-based hydrogels and the molecular conditions governing the initial stages of the chemical cross-linking process that occurs, especially its dependence on the preparation temperature relative to Tt. As a result, two different fractal modes of gel formation have been found at the two temperatures studied (above and below Tt). Thus, when the reaction mixture is prepared below Tt, essentially one-dimensional linear nanogels with a high aspect ratio are obtained. In contrast, 3D nanogels are formed above Tt, with spherical shapes predominating. These different structures seem to reflect the two molecular organizations of the single components of the mixture under these conditions, namely extended chains below Tt and a spherical arrangement above Tt. In addition to the interest in these nanogels as models for understanding the formation of microscopic structures and differential macroscopic properties under more conventional hydrogel-formation conditions, these nanogels are of interest because of their thermoresponsiveness and biocompatibility, which provide them with potential uses for drug delivery and other biomedical applications in living systems.

Effect of surfactants on the self-assembly of a model elastin-like block corecombinamer: from micelles to an aqueous two-phase system.

Recent advances in genetic engineering now allow the synthesis of protein-based block corecombinamers derived from elastin-like peptide sequences with complete control of chemistry and molecular weight, thereby resulting in unique physical and biological properties. The individual blocks of the elastin-like block corecombinamers (ELbcR's) display different phase behaviors in aqueous solution, which leads to the thermally triggered self-assembly of nano-objects ranging from micelles to vesicles. Herein, the interaction of cationic surfactant dodecyl trimethylammonium bromide (DTAB), anionic surfactant dodecyl sodium sulfate (SDS), and nonionic surfactant octyl-ß-glucopyranoside (OG) with an ELbcR has been investigated by dynamic light scattering (DLS), the ζ potential and cryo-transmission electron microscopy (cryo-TEM). At 65 °C and neutral pH in aqueous solution, the ELbcR (E50A40) is associated into micelles with a diameter of 150 nm comprising a hydrophobic (A) core and a hydrophilic (E) anionic (from the glutamic acid residues) corona. The size of these self-assemblies can be controlled by adjusting the cosurfactant concentrations. Although the effects of surfactants on the self-assembly behavior of ELbcR's depend on the hydrocarbon chain length and headgroup of the surfactants, a general tendency to increase in size, which in some cases leads to flocculation and a phase-separated state, is observed. These results support the use of surfactants as a highly interesting means of controlling the self-assembly of ELbcR's in aqueous solution as well as their use in drug delivery and purification processes.