(721a) Protein-Based Catechol Conjugates As Aqueous Adhesives and Networks

Polymers that adhere to wet surfaces that are biocompatible, degradable, and devoid of animal-sourced materials are desired for applications as tissue adhesives. Silk from the domesticated silkworm Bombyx mori is a naturally occurring biopolymer with charged hydrophilic terminal regions that endcap a blocky core dominated by hydrophobic domains. Silk was selected for modification for use as an aqueous adhesive because of its high molecular weight, tunable mechanical and degradation properties, aqueous processability, and for its hydrophobicity that was envisioned to afford control over the mechanical properties and aqueous swelling of the modified biopolymers. Taking inspiration from mussels that produce proteins rich in L-3,4-dihydroxyphenylalanine to adhere to a variety of organic and inorganic surfaces by manipulation of oxidation states, silk was functionalized with catechol groups by carbodiimide coupling of dopamine. The silk polymers were characterized to determine composition, adhesive strength using lap shear measurements, cell compatibility and support of proliferation, and their ability to form beta sheets, which physically crosslink silk. As both aqueous and organic phase syntheses are possible with silk, several solvent systems were investigated to determine the conditions that led to successful coupling of dopamine without protein aggregation. Adhesive bonding and cell compatibility of the resulting materials were measured. Human mesenchymal stem cells were found to attach and proliferate on the silks in vitro. The formation of beta sheets was not affected by the chemistry, thus could be exploited to control the adhesive networkâ??s properties. This work developed new silk-catechol conjugates that can be triggered to crosslink by oxidation. Tuning the substitutions proved to be critical to the strength of the adhesive bond and aqueous swelling. All materials supported cell attachment and proliferation in vitro. Inducing beta sheet formation after bonding is currently under investigation as an additional route for controlling the mechanical properties of the adhesive networks. These materials thus represent a protein-based approach to water soluble, catechol-based adhesives, which we envision to have utility as biodegradable adhesives and sealants.