Engineering MRI-detectable protein polymer hydrogels for in vivo biomaterial analysis.

摘要

Protein polymers show great potential as biomaterials due to the ability to specify their sequence and length and consequently control mechanical, structural, and chemical properties. These proteins consist of tandem repeated blocks of an amino acid sequence and are produced through genetic engineering and recombinant protein expression. This research focuses on engineering protein polymers for hydrogels for tissue engineering and contrast agents (CAs) for Magnetic Resonance Imaging (MRI) for in vivo biomaterial analysis.;Scaffolds have been developed to aid islet transplantation as a cure for type I diabetes, an autoimmune disease that destroys insulin-producing beta islet cells, to provide physicochemical stimuli to preserve cell viability and function. The biocompatibility and ability to support beta cell survival were analyzed in protein polymer hydrogels to develop them for islet cell transplantation. The level of bacterial endotoxins associated with the protein polymers was elevated and a phase separation protocol was developed to remove them. By reducing endotoxins, the in vitro and in vivo biocompatibility improved, but they still evoked a considerable immune response. PEGylation and the inclusion of dexamethasone were strategies aimed at decreasing immunogenicity; PEGylation led to a dramatic improvement in vivo with a biocompatible response. Different protein formulations were evaluated for their material properties and effect on beta cell viability. Despite differences in microscale gelation time, protein polymer hydrogels of varying protein concentrations all supported high cell viability.;Lysine-containing protein polymers also served as a macromolecular backbone for multivalent MRI CAs that can be incorporated into hydrogels. They demonstrated high relaxivity, a measure of contrast enhancement, which improved with decreased lysine spacing and increased length. Values of up to ∼15 mM -1s-1 per Gd(III) and ∼584 mM-1s -1 per molecule were achieved. Additionally, protein polymer CAs (PPCAs) were biodegradable and non-toxic to cells. The PPCAs were covalently incorporated into protein polymer hydrogels, implanted into mice, and serially imaged to track the hydrogel over time. In comparison to a control gel without PPCA, the PPCA-containing hydrogels had a significantly higher contrast-to-noise ratio. The PPCAs were necessary for enabling the use of MRI to quantify degradation and distinguish the gel from the surrounding inflammatory tissue.