Flow Imaging Microscopy of a Self-Assembling Protein Polymer Material

Biological and bioinspired polymer microparticles have broad biomedical and industrial applications, including drug delivery, tissue engineering, surface modification, environmental remediation, imaging, and sensing. Full realization of the potential of biopolymer microparticles will require methods for rigorous characterization of particle sizes, morphologies, and dynamics, so that researchers may correlate particle characteristics with synthesis methods and desired functions. Toward this end, we evaluated biopolymer microparticles using dynamic imaging particle analysis, also known as flow imaging. This technology is becoming more widely used in the biopharmaceutical industry but is not yet well-known among the biomaterials community. Our polymer, a genetically engineered elastin-like polypeptide (ELP), self-assembles into micron- and submicron-scale coacervates. We performed flow imaging of ELP coacervates using two different instruments, one with a lower size limit of approximately 2 microns, the other with a lower size limit of approximately 300 nanometers. We validated flow imaging results by comparison with dynamic light scattering and atomic force microscopy analyses. We explored the effects of various solvent conditions on ELP coacervate size, morphology, and behavior, such as the dispersion of single particles versus aggregates. We found that flow imaging is a superior tool for thorough and statistically powerful particle analysis of ELP assemblies in solution. We anticipate that researchers studying many types of microscale protein or polymer assemblies will be interested in flow imaging as a tool for rapid, quantitative, solution-based characterization