Liquid-cell transmission electron microscopy for imaging of thermosensitive recombinant polymers.

Various polymers used in controlled release applications exhibit solution-based thermal responses. Unfortunately, very few characterization and imaging techniques permit resolution of individual polymers during their thermally-triggered phase transitions. Here, we demonstrate the use of temperature-ramp liquid-cell transmission electron microscopy (LCTEM) for real-time evaluation of the solution and interfacial behavior of elastinlike polypeptides (ELPs) and their self-assembled nanostructures over a temperature range incorporating their intrinsic lower critical solution temperatures (LCSTs). Individual polymers and supramolecular assemblies were discriminated dependent upon solubility states. The recombinant polymers were shown to adsorb to the silicon-nitride chip window from the buffered saline solution and desorb in a temperature-dependent manner. Silk-elastinlike protein block copolymers (SELPs) (composed of repeat peptide motifs of silk and elastin) differed from ELPs in thermal behavior. While both polymers were shown to cluster, only SELPs formed robust amyloid-like fibers upon heating.