Measuring the Physical Properties of Synthetic Cement Derived Barnacle Adhesive Nanomaterials from the Barnacle Amphibalanus amphitrite

Abstract

Barnacles, a common biofouling organism, produce a micron-thick layer of long-lasting, proteinaceous, amyloid-like underwater adhesive. The barnacle triggers assembly and delivery of glue materials from a liquid, which set as a bulk adhesive gel in seawater environments. To accomplish this, barnacles use an organized co-block arrangement of sequence domains to dictate material formation, cohesive strength, and adhesive bonding properties of larger protein components. To understand physical properties of barnacle glue and construct a new class of underwater adhesive biomaterials, we have established a materials library from barnacle protein sequences for study. Derived from consensus barnacle cement sequences of Amphibalanus amphitrite natural glue proteins, we use eight synthetic barnacle cement peptides (BCPs), with patterned sequence motifs from the natural adhesive, for materials processing and testing. To understand how barnacle adhesive is fabricated, we looked closely at the BCP sequence to evaluate its function in delivery, polymerization, curing, and adhesion. Bulk gel materials, characterized by atomic force microscopy and profilometry, are shown to form dependent upon a BCP sequence pattern. The adhesive properties of assembled BCP gels were measured using adhesion testing of pull off (normal force) and push off (shear force). In shear force, patterned sequences behave differently demonstrating the structuring of fibrils enhances resistance to shear. Bulk BCP gels are shown to be pressure sensitive and have similar strength to natural barnacle glue. The alternating patterns identified suggest glue chemistries are displayed in the BCPs. Using BCPs, we link distinct peptide sequences to polymerization, recognition, formation of fibrils, and the physical properties of bulk gel materials. We offer a means to develop and test a protein library to establish the relationship between dry adhesion and biomaterial structure for insights into how natural barnacles adhere.