Cytocompatibility studies of a biomimetic copolymer with simplified structure and high-strength adhesion.

The development of adhesives suitable for biomedical applications has been challenging given that these materials must exhibit sufficient adhesion strengths and biocompatibility. Biomimetic materials inspired by mussel adhesive proteins appear to contain many of the necessary characteristics for biomedical adhesives. In particular, poly[(3,4-dihydroxystyrene)-co-styrene] has been shown to be a high strength adhesive material with bonding comparable to or even greater than several commercial glues. Herein, a thorough study on the cytocompatibility of this copolymer provides insights on the suitability of a mussel-mimicking adhesive for applications development. The cytotoxicity of poly[(3,4-dihydroxystyrene)-co-styrene] was evaluated through assessment of the viability, proliferation rate, and morphology of NIH/3T3 fibroblasts when cultured with copolymer extracts or directly in contact with the adhesive. After 1 and 3 days of culture, both the copolymer alone and copolymer cross-linked with periodate exhibited minimal effects on cell viability. Likewise, cells cultured on the copolymer displayed proliferation rates and morphologies similar to cells on the poly-L-lysine control. These results indicate that poly[(3,4-dihydroxystyrene)-co-styrene] is highly cytocompatible and therefore a promising material for use where biological contact is important.

Molecular weight effects upon the adhesive bonding of a mussel mimetic polymer.

Characterization of marine biological adhesives are teaching us how nature makes materials and providing new ideas for synthetic systems. One of the most widely studied adhering animals is the marine mussel. This mollusk bonds to wet rocks by producing an adhesive from cross-linked proteins. Several laboratories are now making synthetic mimics of mussel adhesive proteins, with 3,4-dihydroxyphenylalanine (DOPA) or similar molecules pendant from polymer chains. In select cases, appreciable bulk bonding results, with strengths as high as commercial glues. Polymer molecular weight is amongst several parameters that need to be examined in order to both understand biomimetic adhesion as well as to maximize performance. Experiments presented here explore how the bulk adhesion of a mussel mimetic polymer varies as a function of molecular weight. Systematic structure-function studies were carried out both with and without the presence of an oxidative cross-linker. Without cross-linking, higher molecular weights generally afforded higher adhesion. When a [N(C4H9)4](IO4) cross-linker was added, adhesion peaked at molecular weights of ~50,000-65,000 g/mol. These data help to illustrate how changes to the balance of cohesion versus adhesion influence bulk bonding. Mussel adhesive plaques achieve this balance by incorporating several proteins with molecular weights ranging from 6000 to 110,000 g/mol. To mimic these varied proteins we made a blend of polymers containing a range of molecular weights. Interestingly, this blend adhered more strongly than any of the individual polymers when cross-linked with [N(C4H9)4](IO4). These results are helping us to both understand the origins of biological materials as well as design high performance polymers.