Protective coatings on extensible biofibres

Abstract

Formulating effective coatings for use in nano- and biotechnology poses considerable technical challenges. If they are to provide abrasion resistance, coatings must be hard and adhere well to the underlying substrate. High hardness, however, comes at the expense of extensibility. This property trade-off makes the design of coatings for even moderately compliant substrates problematic, because substrate deformation easily exceeds the strain limit of the coating. Although the highest strain capacity of synthetic fibre coatings is less than 10%, deformable coatings are ubiquitous in biological systems. With an eye to heeding the lessons of nature, the cuticular coatings of byssal threads from two species of marine mussels, Mytilus galloprovincialis and Perna canaliculus, have been investigated. Consistent with their function to protect collagenous fibres in the byssal-thread core, these coatings show hardness and stiffness comparable to those of engineering plastics and yet are surprisingly extensible; the tensile failure strain of P. canaliculus cuticle is about 30% and that of M. galloprovincialis is a remarkable 70%. The difference in extensibility is attributable to the presence of deformable microphase-separated granules within the cuticle of M. galloprovincialis. The results have important implications in the design of bio-inspired extensible coatings.

Three intrinsically unstructured mussel adhesive proteins, mfp‐1, mfp‐2, and mfp‐3: Analysis by circular dichroism

“…The cuticle is both hard and reversibly extensible up to 100% strain. 6,28 How these peculiar mechanical properties of the cuticle are related to mfp-1's unusual structure continues to intrigue. A variety of techniques have been performed to elucidate the structure of mfp-1.…”

“…Recruitment of the atomic force microscope, nanoindentation, and the surface force apparatus (SFA) has contributed much to understanding the physical and mechanical properties of mussel byssus and byssal proteins particularly the mfps. [5][6][7][8][9] However, structural studies at different length scales have been hampered by considerable challenges, including a menagerie of peculiar post-translational modifications, mfp sequence polymorphism, 2,10 the inability to crystallize any of the mfps, difficulty of purifying mg quantities, and the instability of mfps in solution. 11 This has lead to a variety of experimental approximations, which may or may not be biologically relevant.…”

“…Mfp-1 (from Mytilus californianus) is the only protein known to be present in the byssal cuticle remarkable for its combination of high stiffness and high extensibility. 6 Mfp-1 has a mass between 88 and 92 kDa, a basic isoelectric point (8)(9)(10), and 60 or more tandem repeats of a decapeptide sequence (PKISYO*OTY*K in which Y* is 3,4-dihydroxyphenyl-L-alanine (Dopa), O is trans-4-hydroxproline, and O* denotes trans-2,3-cis-3,4-dihydroxyproline (diHyp). 15 Mfp-2 (from M. edulis) is an abundant protein in the plaques ($25% of adhesive plaque by dry weight) with a mass of 45 kDa and consists of 11 tandem repeats of a 40-res long epidermal growth factor (EGF) motif.…”

Surface-initiated self-healing of polymers in aqueous media

“…Despite recent progress in the design of self-mending polymeric materials based on crack-activated crosslinking 1 , light 2 , heat 3 or other external stimuli 4 , these remain less than perfectly healed, and, in the case of polymers in wet environments, self-healing technologies are even more limited than those engineered for dry conditions. Mussel adhesive holdfasts exhibit significant self-healing capabilities 11,12 , although the molecular mechanisms involved are poorly understood. Notwithstanding this, the selfmending adhesion and cohesion of isolated dopa (3,4-dihydroxyphenyl-L-alanine)-containing adhesive proteins were shown to rely critically on maintaining dopa in an acidic and reducing environment 13,14 .…”

Multiscale monitoring of interface failure of brittle coating/ductile substrate systems: A non-destructive evaluation method combined digital image correlation with acoustic emission

“…[1][2][3][4] Owing to mismatch of thermo-mechanical properties between film/coating and substrate, however, such a system is always subjected to residual stresses, which would eventually lead to a structural degradation of coating near interfacial regions. Therefore, how to evaluate the interface adhesion performance of a system and predict its reliability has attracted ever-increasing attention in recent years.…”