Structural Variation and Enzymatic Susceptibility of Collagen Fibril Extracted from Native and Overloaded Tail Tendons

Abstract

The mechanical overload of collagen based connective tissues is a common cause of injuries, resulting in the loss of locomotion. In the case of overloaded tendons, the transmission of forces between muscle and bone are affected, impeding the function associated with the localized musculoskeletal system. The result is a reduction in locomotion and quality of life of the injured person. Novel work performed in 2012 discovered a new damage motif along collagen fibrils sourced from tendon loaded until rupture in vitro. This damage motif, termed discrete plasticity, consists of characteristic, repetitive kink structures along the collagen fibril axis, and a fuzzy shell layer when imaged by SEM. Limitations of SEM to characterize discrete plasticity led to the development of a novel AFM technique to improve understanding of discrete plasticity. This body of work describes the; development, physical basis of its function, and application to discrete plasticity, of such a technique. The unique aspect of the developed technique is the nano-scale mechanical characterization of hydrated collagen fibrils, and its increased sensitivity to structural variations. Four major studies were performed. The first analyzed sample collagen fibrils and explored the technique’s ability to measure structural changes in fibrils following thermal treatments, as well as comprehend the physical mechanism that provides the increased sensitivity of the technique. The second, characterized the alteration of the collagen fibril associated with discrete plasticity. The third study revealed a connection between a natural, novel, variation along unloaded fibrils and the spacing of the kink structures along fibrils displaying discrete plasticity. The thesis culminates with a study of individual discrete plasticity and unloaded fibrils post and prior to incubation with either trypsin and MMP-9, a critical enzyme in initial stages of inflammation in injured tendon. In summary, this work encompasses the development and application of a novel technique which permits nano-scale studies of, biological, mechanical and thermal changes to collagen fibrils, in particular, fibrils displaying discrete plasticity. The development of such a technique should have far reaching application in understanding the fundamental response of protein aggregates to chemical, biological, and physical exposures.