Critical factors for the bulk adhesion of engineered elastomeric proteins

Many protein-based materials, such as soy and mussel adhesive proteins, have been the subject of scientific and commercial interest. Recently, a variety of protein adhesives have been isolated from diverse sources such as insects, frogs and squid ring teeth. Many of these adhesives have similar amino acid compositions to elastomeric proteins such as elastin. Although elastin is widely investigated for a structural biomaterial, little work has been done to assess its adhesive potential. In this study, recombinant elastin-like polypeptides were created to probe the factors affecting adhesion strength. Lap shear adhesion was used to examine the effects of both extrinsic factors (pH, concentration, cross-linker, humidity, cure time and cure temperature) and intrinsic factors (protein sequence, structure and molecular weight). Of the extrinsic factors tested, only humidity, cure time and cure temperature had a significant effect on adhesion strength. As water content was reduced, adhesion strength increased. Of the intrinsic factors tested, amino acid sequence did not significantly affect adhesion strength, but less protein structure and higher molecular weights increased adhesion strength directly. The strengths of proteins in this study (greater than 2 MPa) were comparable to or higher than those of two commercially available protein-based adhesives, hide glue and a fibrin sealant. These results may provide general rules for the design of adhesives from elastomeric proteins.