(598a) A Novel Nickel-Based Tyrosine Crosslinking Reaction to Generate ELP Hydrogels for Potential Tissue Engineering Applications.

Elastin like polypeptides (ELPs) are prominent candidates for designing biomaterials and possess several advantages. They are genetically encodable, which offers precise tunability at the molecular level, and they often can be expressed in high yields in a bacterial host such as Escherichia coli (E. coli). Their lower critical solution temperature (LCST) phase behavior can be easily taken advantage of and used in their purification process. Crosslinking of linear ELPs of the general form (VPGXG)_n with guest residue ‘X’, results in gelation to form hydrogels with superior biological properties. Different approaches have been used to crosslink ELPs, such as through lysine- or cysteine-based crosslinking reactions. Tyrosine based crosslinking is another approach, and it can result in biomaterials that have higher levels of mechanical and structural characteristics. For example, di-tyrosine crosslinks are found in resilin, which is a broad family of elastic proteins including elastin, and gluten, and human corneal collagen. These biomaterials can be used for numerous bioengineering applications, such as an extra cellular matrix (ECM). Crosslinking of tyrosine is often achieved using enzymes or ruthenium catalysts. Here we report a novel nickel-based reaction to crosslink tyrosine molecules. Complexes of nickel [Ni²⁺] in the presence of peracid oxidizing agent - monoperoxyphthalic acid (MMPP) catalyzed the formation of tyrosine free radicals, which then reacted with adjacent tyrosine residues to form dityrosine crosslinks. Adding GGH peptide further appended to the ELP peptides and resulted in spontaneous crosslinked ELP hydrogels. One factor at a time (OFAT) trails were performed to optimize the hydrogel preparation conditions. Optimized hydrogels were tested for their biological, mechanical, and structural characteristics. Washing the hydrogels improved the in-vitro biocompatibility of the hydrogels. In- vitro biocompatibility of the continuous washing method was proven to be efficient with upto 99% nickel removal and the hydrogels post-washing can be used directly in experimental studies as a biomaterial for various tissue engineering applications.