THE MECHANICAL-PROPERTIES OF SIMULATED COLLAGEN FIBRILS

Previous theoretical studies of the mechanical properties of tissues s uch as skin, bone and tendon, have used approaches based on composite materials and have tended to neglect the contribution of individual mi croscopic components. In this paper, we examine the relationship betwe en the fine structure of a collagen fibril and its relative tensile st rength. Collagen is a fibrous protein which provides associated tissue s with the majority of their tensile strength. It is present in the fo rm of elongated structures termed fibrils which are created by the sel f-assembly of rod-like collagen molecules in an entropy-driven process termed fibrillogenesis. Mutations that alter the primary structure of the collagen molecule, interfere with this assembly process and can l ead to the potentially fatal brittle bone disease, osteogenesis imperf ecta. Here we investigate the mechanical properties of a range of comp uter-generated aggregates. The aggregates, created by the diffusion li mited aggregation of rods, were subjected to a simple tensile test bas ed on local rules of damage accumulation. In the test, core samples ar e 'extracted' from the aggregates, and the network of particles involv ed in the transmission of stress resolved. Increasing stress applied t o the core leads to the removal of individual rods from this network; the tensile strength is determined from the Force necessary to form a discontinuous network. Using this approach, we have shown that collage n fibril morphology is critical in determining its tensile strength. W e suggest a possible mechanism to account for the increasing severity of osteogenesis imperfecta associated with the distance of mutation fr om the N-terminal of the collagen molecule. (C) 1997 Elsevier Science Ltd.