Collagen is a structural protein that is widely present in vertebrates, being usually distributed in tissues in the form of fibers. In living organisms, fibers are organized in different orientations in various tissues. As the structural base in connective tissue and load-bearing tissue, the orientation of collagen fibers plays an extremely important role in the mechanical properties and physiological and biochemical functions. The study on mechanics role in formation of oriented collagen fibers enables us to understand how discrete cells use limited molecular materials to create tissues with different structures, thereby promoting our understanding of the mechanism of tissue formation from scratch, from invisible to tangible. However, the current understanding of the mechanism of fiber orientation is still insufficient. In addition, existing fabrication methods of oriented fibers are varied and involve interdisciplinary study, and the achievements of each experiment are favorable to the construction and improvement of the fiber orientation theory. To this end, this review focuses on the preparation methods of oriented fibers and proposes a model explaining the formation process of oriented fibers in tendons based on the existing fiber theory.

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Collagen, as a structural protein, is widely distributed in the human body. Many factors influence collagen self-assembly in vitro, including physical-chemical conditions and mechanical microenvironment, and play a key role in driving the structure and arrangement. However, the exact mechanism is unknown. The purpose of this paper is to investigate the changes in the structure and morphology of collagen self-assembly in vitro under mechanical microenvironment, as well as the critical role of hyaluronic acid in this process. Using bovine type I collagen as the research object, collagen solution is loaded into tensile and stress-strain gradient devices. The morphology and distribution of collagen is observed using an atomic force microscope while changing the concentration of collagen solution, mechanical loading strength, tensile speed, and ratio of collagen to hyaluronic acid. The results demonstrate that the mechanics field governs collagen fibers and changes their orientation. Stress magnifies the differences in results caused by different stress concentrations and sizes, and hyaluronic acid improves collagen fiber orientation. This research is critical for expanding the use of collagen-based biomaterials in tissue engineering.