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BACKGROUND: Self-healing hydrogels are scaffold materials with superior self-healing capability and biocompatibility, and are widely used in bone tissue engineering. OBJECTIVE: To introduce the gelatin mechanism and composition of self-healing hydrogels and summarize their applications in bone tissue engineering. METHODS: The first author searched both Chinese and English articles with key words "self-healing hydrogels; bone tissue engineering; bone regeneration" on CNKl, Wanfang, VIP, PubMed, Embase and Web of Science databases published from 2000 to 2020. Totally 69 eligible articles were selected for review. RESULTS AND CONCLUSION: The gelation mechanisms of self-healing hydrogels include dynamic covalent bonds, supramolecular bonds and multi-mechanism cross-links. Self-healing hydrogels can be composed of natural polymers, synthetic polymers and nanocomposites. Self-healing hydrogels have been found to be applied in bone tissue engineering through scaffold modification as stem cells delivery vehicle. The application of self-healing hydrogels in bone tissue engineering can be broaden by enhancing the mechanical properties of the hydrogel while maintaining its self-healing capability. Additionally, the specific mechanism for better superiority of self-repairing hydrogels over traditional hydrogels in bone tissue engineering is still unclear. [ABSTRACT FROM AUTHOR]

BACKGROUND: Angiogenesis is a key component of bone reconstruction. Promoting bone vascularization thereby can accelerate bone repair. There are numerous research methods for promoting angiogenesis, and significant progress has been made in the field of bone defect repair in recent years. OBJECTIVE: To review several cutting-edge methods and developments in promoting angiogenesis and repairing bone defects in recent years, as well as their applications in bone tissue engineering. METHODS: The first author used the Chinese search terms “angiogenesis, osteogenesis, bone defect, tissue engineering, exosomes” and English search terms “angiogenesis, osteogenesis, bone defect, exosomes, vascularization” to find relevant publications in CNKI, WanFang, PubMed, and Web of Science databases. After screening and excluding articles irrelevant to the research purpose and repetitive articles, 69 articles were finally selected for review. RESULTS AND CONCLUSION: At present, promising results have been achieved in the bone defect remodeling research. Bone vascularization can be promoted by growth factors, delivery genes, biologically active ions, small molecule active peptides, and Chinese medicine monomers. Each has its own advantages and challenges, and faces different challenges. The synthesis of small molecule active peptides has low cost, high efficiency and safety, with obvious advantages. It has the potential to generate new ideas and methods for vascularization in bone tissue engineering. [ABSTRACT FROM AUTHOR]

BACKGROUND: The exosomes are one of important active components of adult stem cells paracrine, providing the basis for stem cell “non-cellular” treatment. Exosomes from stem cells can play different roles in the wound through different mechanisms to promote the healing of diabetic wounds. OBJECTIVE: To summarize the main mechanism and application of stem cell derived exosomes in the treatment of diabetic wounds. METHODS: Computers were used to retrieve English databases such as PubMed database, Web of Science database, FMRS foreign language medical information resource retrieval platform, and Chinese databases such as CNKI and Wanfang Data Knowledge Service Platform. The retrieval scope was from the inception of the database to September 2020. The English and Chinese search terms were “stem cells, exosomes, wound healing, cell proliferation, neovascularization, inflammation, extracellular matrix, therapeutic use”. According to the inclusion and exclusion criteria, 66 articles were included and the results were analyzed. RESULTS AND CONCLUSION: (1) It is summarized that stem cell-derived exosomes can promote diabetic wound healing by regulating inflammation, promoting neovascularization, re-epithelialization and remodeling of extracellular matrix. (2) The application of stem cell-derived exosomes in diabetic wounds was listed. (3) The exosomes from stem cells can avoid the immune response of stem cells in the treatment of diabetic wounds, and the genetic material of stem cells carried by them is more widely regulated and more effective than that from ordinary cells in the treatment of diabetic wounds. (4) At present, the application of stem cell derived exosomes in diabetes wounds still has some problems, such as low purity, high cost of separation, low production efficiency, and the way to reach the target area, loss rate and diffusion efficiency. [ABSTRACT FROM AUTHOR]

BACKGROUND: Hyaluronic acid is a natural polysaccharide and a common glycosaminoglycan in human body. It has the highest concentration in eyes and joints. It is made into hydrogels because of its biocompatibility, degradability, and low immunogenicity, and is widely used in tissue engineering. OBJECTIVE: To introduce the characteristics of various hyaluronic acid composite hydrogels and their application in the repair of cartilage damage caused by osteoarthritis. METHODS: CNKI and Wanfang databases were searched with the key words of “hyaluronic acid, hydrogel, cartilage repair, osteoarthritis” in Chinese. PubMed and Web of Science databases were searched with the key words of “hyaluronic acid, hydrogel, cartilage repair, osteoarthritis” in English. The articles published from January 1995 to July 2020 were searched and further analyzed and summarized. RESULTS AND CONCLUSION: The excellent biological properties of hyaluronic acid hydrogel have made it widely studied in the cartilage repair of osteoarthritis, especially through the combination of biological factors, natural materials, synthetic materials, 3D printing technology, polypeptides, mechanical stimulation, etc., which improved the performance of hyaluronic acid hydrogel and promoted its application in cartilage tissue engineering. Although hyaluronic acid composite hydrogels have been studied more, with the comprehensive development of chemistry, materials, physics, biology and other disciplines in the future, a deeper understanding of the degradation mechanism of hyaluronic acid hydrogels and an exploration of the cartilage damage mechanism in osteoarthritis, the hyaluronic acid composite hydrogel is expected to be designed with high efficiency, no side effects and more suitable for cartilage tissue engineering. [ABSTRACT FROM AUTHOR]

BACKGROUND: With the development of bone tissue engineering, the role of scaffold materials has become more and more important. Polycaprolactone and its composite materials have also increasingly attracted researchers to become one of the research highlights in this field. OBJECTIVE: To introduce the basic properties and synthesis methods of polycaprolactone, to summarize the research status of polycaprolactone and its composite materials in the field of bone tissue engineering, and to prospect the future development and research direction. METHODS: These articles published from 1950 to 2020 in Web of Science database were retrieved by using the search terms “PCL, PCL composites, bone tissue engineering, scaffold, bone, PCL synthesis”, taking “and” as the logical combination relationship. Totally 253 articles were initially obtained, and finally 52 articles were reviewed and analyzed after careful reading and selection. RESULTS AND CONCLUSION: (1) Pure polycaprolactone materials have certain shortcomings in bone tissue engineering. Due to their easy chemical modification and physical modification, polycaprolactone composite undoubtedly has become one of the candidate materials for bone tissue engineering scaffolds. (2) Due to the excellent solubility and thermal properties of polycaprolactone, it can be applied to a variety of scaffold preparation technologies. The appropriate scaffold preparation technology can be selected according to the application site. A variety of scaffold preparation technologies also broaden the application field of polycaprolactone, and there are also developed some novel technologies, so scaffold preparation technology should also attract the attention researchers. (3) For the modification direction of polycaprolactone, the modification of inorganic substances and natural or synthetic polymers has received extensive attention. (4) In terms of experimental research methods, researchers should pay attention to introducing more kinds of experimental cells and experimental models in accordance with clinical needs. [ABSTRACT FROM AUTHOR]

BACKGROUND: How to recruit endogenous seed cells to promote osteogenesis, provide appropriate bone regeneration microenvironment for cells and ensure the vascularization process of new bone are the difficulties of bone tissue engineering research. OBJECTIVE: To review the osteogenesis and vasculogenesis from the aspects of hierarchical microchanneled bone scaffold. METHODS: The first author searched relevant literature on the promoting effect of hierarchical microchanneled bone scaffold on osteogenesis and angiogenesis from China National Knowledge Infrastructure, Wanfang, PubMed and Web of Science databases from 1950 to 2020. The key words were “hierarchical microchanneled scaffolds, osteogenesis, and angiogenesis” in Chinese and English. Finally, a total of 52 articles meeting the inclusion criteria were selected. RESULTS AND CONCLUSION: Hierarchical microchanneled bone scaffold has a good role in promoting osteogenesis and vascularization, and has a good application prospect in bone tissue engineering. At present, hierarchical microchanneled bone scaffold is mature in the theory of bone tissue engineering. In vitro experiments have confirmed that the hierarchical microchanneled bone scaffold can promote the adhesion and differentiation of mesenchymal stem cells into osteoblasts, but the osteogenic effect in vivo is still poor, and it is still possible to further improve the osteogenic effect. In the future, we should focus on the construction of hierarchical microchanneled bone scaffold complexes, such as chemokines or cytokines, which can further improve the osteogenic efficiency in vivo. [ABSTRACT FROM AUTHOR]