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

韧性是高度期望的材料性质，其结合了强度和抗断裂性。除了非常坚固之外，坚韧的材料在断裂之前也会经历相当大的变形。正在进行的制造坚韧材料的研究导致了各种金属合金和工程复合材料的发展。然而，这些材料的韧性是通过有限数量的“增韧机制”实现的，其中大部分我们已经知道了几十年。由于韧性是一种理想的材料特性，因此确定新的增韧机制可以推动各种新工程材料的开发。 这项研究计划的目的是通过研究一种引人注目的生物材料：胶原纤维来确定新的增韧机制。胶原纤维是人类和几乎所有其他动物体内最常见也是最重要的生物结构材料。胶原纤维是直径比人类头发小近1000倍的生物电缆。它们为肌腱、韧带、骨骼、皮肤、动脉、心脏瓣膜、软骨等提供力量。除了非常坚固外，胶原纤维也非常坚韧：比钢丝坚韧约10倍。然而，尽管它们具有令人难以置信的材料特性，但在胶原纤维中起作用的增韧机制尚未确定。 在这项研究计划的第一部分，胶原纤维和它们组成的分子的纳米级结构将在机械过载之前和之后进行研究。使用诸如透射电子显微镜的工具，其放大倍数可达300，000倍，我们将试图确定是什么使胶原纤维变坚韧。在研究计划的第二部分，我们将研究不同类型的胶原纤维，以尝试确定：（i）如果某些纤维比其他纤维更坚韧，以及（ii）如果是这样，什么结构特征导致这种差异。我们还将化学改性胶原纤维，人工连接或分裂胶原分子内包含，看看这些变化如何改变韧性。在这项研究计划的最后一部分，我们将使用我们在第一部分和第二部分收集的信息来构建新的，高性能的，可生物降解的材料。我们将致力于制造新的绷带和伤口敷料，这些绷带和敷料在使用时是柔软和可弯曲的，但随后变硬，为下面的愈合组织提供上级保护。我们还将致力于通过用矿物质浸渍胶原纤维来构建新的复合材料。我们将使用这些新的复合材料来开发新的可吸收的外科植入物。例如，为了修复严重骨折的骨骼，基于胶原蛋白的植入物可以在愈合过程中提供所需的结构支撑，然后慢慢消失，被身体分解和吸收。 虽然这项工作将需要许多年才能完成，但即使是在项目的早期阶段，其结果对许多人来说也很重要。组织工程师将能够使用我们的结果来改善他们实验室构建的肌腱，韧带，皮肤和动脉的机械性能。发现使这些工程组织更坚固的方法将有助于将它们推向市场，每年使成千上万需要人工或同种异体移植组织手术的加拿大人受益。在了解胶原纤维及其分子在过载时会发生什么后，医生和外科医生可能会想到更好的方法来治疗扭伤和拉伤，或者加速结缔组织愈合的方法。最后，材料科学家可能能够使用我们发现的独特的增韧机制来开发一系列日常使用的新材料。

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.