Poly(amino acid) bioadhesives for tissue repair

We report here on poly(amino acid)-based bioadhesives with potential to bond to soft tissues. The systems investigated included homopolymer poly(amino acids), mixtures of poly(amino acids) and amino acids, and blends of different poly(amino acids). Adhesive performance was tested in tension on glass surfaces, chondroitin sulfate surfaces, as well as bovine cartilage surfaces. The amino acid structural units contained acidic, basic, or polar side chains and were found to adhere reasonably well to the surfaces of glass and chondroitin sulfate. The formation of polymer-monomer complexes with the addition of a basic monomer such as L-lysine to negatively charged polymers such as poly(L-aspartic acid) and poly(L-glutamic acid) was found to result in greater adhesive strength relative to homopolymers. Further improvement in adhesion was observed in blends of poly(L-lysine) with polar poly(amino acids) such as poly(L-asparagine). Adhesion on wet cartilage surfaces was the weakest measured but a priming approach designed to form electrostatic or hydrogen bonds appears promising. We believe the strength of the adhesives studied here is based on the ability of their constituent polymers and monomers to form molecular entanglements and crosslinks for load transfer. We also believe hydrogen bonds and electrostatic forces play a role in the adhesion of the systems to the substrates probed in this work.