Novel mechanisms of strain energy dissipation in collagen polymers: their characterization, control, and application

Toughness is a highly desirable material property, combining both strength and fracture resistance. In addition to being very strong, tough materials can also undergo considerable deformation before breaking. Ongoing research to create tough materials has led to the development of a wide variety of metallic alloys and engineered composites. However, the toughness of these materials is achieved through a limited number of "toughening mechanisms", most of which we have known about for decades. Because toughness is such a desirable material property, identifying new toughening mechanisms could drive the development of a wide range of new engineering materials. *The aim of this research program is to identify new toughening mechanisms by studying a remarkable biomaterial: the collagen fibril. Collagen fibrils are the most common-and important-structural biomaterial within humans and almost all other animals. Collagen fibrils are biological cables that are nearly 1000 times smaller in diameter than a human hair. They are what gives strength to your tendons, ligaments, bones, skin, arteries, heart valves, cartilage, and more. In addition to being very strong, collagen fibrils are also very tough: approximately 10 times tougher than steel wire. Yet, despite their incredible material properties, the toughening mechanisms that function within collagen fibrils have not yet been identified.*In the first part of this research program, the nanoscale structure of both collagen fibrils and the molecules that they are composed of will be studied before and after mechanical overload. Using tools such as transmission electron microscopy, with which magnifications of up to 300,000x are possible, we will attempt to determine what makes collagen fibrils tough. In the second part of the research program, we will study different types of collagen fibrils to try and determine: (i) if some fibrils are tougher than others, and (ii) if so, what structural characteristics account for this difference. We will also chemically modify collagen fibrils, artificially joining or breaking apart the collagen molecules contained within to see how these changes alter toughness. In the final part of this research program, we will use the information that we have gathered in parts one and two to build new, high-performance, biodegradable materials. We will work toward building new bandages and wound dressings that are soft and bendable when applied, but then harden giving superior protection to the healing tissue beneath. We will also work toward building new composite materials by impregnating collagen fibrils with minerals. We will use these new composite materials to develop new, resorbable surgical implants. For repairing a badly fractured bone, for example, a collagen-based implant could provide the structural support required during healing and then slowly disappear, being broken down and absorbed by the body.*While this work will take many years to complete, the results, even from the project's early stages, will be important to many people. Tissue engineers will be able to use our results to improve the mechanical performance of their laboratory-built tendons, ligaments, skin, and arteries. Discovering ways to make these engineered tissues tougher would help bring them to market, benefiting the thousands of Canadians each year who require surgeries involving artificial or allograft tissue. After learning what happens to collagen fibrils and their molecules when overloaded, doctors and surgeons may think of better ways to treat sprains and strains, or ways to accelerate connective tissue healing. And finally, material scientists may be able to use the unique toughening mechanisms that we discover to develop a whole range of new materials for everyday use.