Micromechanical testing of interfacial protein networks demonstrates ensemble behavior characteristic of a nanostructured biomaterial

摘要

We develop and use novel instrumentation, the Cambridge Interfacial Tensiometer (CIT), to characterize the micromechanical response of a beta-lactoglobulin network adsorbed at the air-water interface. The technique is an interfacial two-dimensional analogy of conventional materials testing methodology but is conducted with high spatial resolution and requires the measurement of micro-Newton forces. Here we characterize interfacially adsorbed networks using an elasticity modulus (Et) derived from the gradient of the stress-strain plot at low strain. Measured Et values were of order 200 mN/m at the air-water interface, consistent with a calculated ensemble average estimated using atomic force microscopy derived data on the unfolding of individual protein molecules, Hydrophobic intermolecular interactions were identified as a possible dominant mechanism by which networks transmit force laterally in the interfacial plane. Covalent disulfide linkages did not significantly contribute to network rigidity in these tests, as the addition of the reducing agent dithiothreitol did not affect force transmission. Networks demonstrated a clear ability for "repair" that is dependent on bulk protein concentration and hence the rate of transport into the interfacial region during tensile testing. Importantly, this study suggests that network mechanical response is determined by residual protein tertiary structure and that adsorbed networks should therefore be analyzed as nanostructured biomaterials. The CIT technique complements existing surface rheology approaches for the characterization of interfacial protein networks and advantageously does not require a priori assumptions about network properties and behavior. [References: 42]