ABSTRACT
Due to good mechanical properties and biocompatibility, tissue engineering scaffolds have become the vital method for repairing and regenerating articular cartilage defects. With the continuous development of tissue engineering technology, many scaffolds preparation and formation methods have been developed and tested in the past decade, however, the preparation of ideal regenerative scaffolds remain controversial. As load-bearing tissue inside the body joints, the matrix structure and cell composition of articular cartilage are hierarchical, and there are several smooth natural gradients from the cartilage surface to the subchondral bone layer, including cell phenotype and number, specific growth factors, matrix composition, fiber arrangement, mechanical properties, nutrient and oxygen consumption. Therefore, in the design of regenerative scaffolds, it is necessary to achieve these gradients to regenerate articular cartilage in situ. In recent studies, many new biomimetic gradient scaffolds have been used to simulate the natural gradient of articular cartilage. These scaffolds show different mechanical, physicochemical or biological gradients in the structure, and have achieved good repair effects. The related articles on tissue engineering for the treatment of articular cartilage defects were retrieved by searching databases with key wordsarticular cartilage injury, cartilage repair and gradient scaffolds. In this work,the structural, biochemical, biomechanical and nutrient metabolism gradients of natural articular cartilage were studied and summarized firstly. Then, the latest design and construction of articular cartilage gradient scaffolds were classified. Besides that, the material composition (such as hydrogels, nanomaterials, etc.) and the preparation process (such as electrospinning, 3D printing, etc.) of grandient scaffolds were further enhanced. Finally, the prospect and challenge of biomimetic gradient scaffolds in cartilage engineering are discussed, which provides a theoretical basis for the successful application of gradient scaffolds in clinical transformation.
ABSTRACT
The treatment of articular cartilage (AC) injury caused by various reasons is still a major clinical problem. The emergence of cartilage tissue engineering brings new hope for the treatment of AC injury. In general, AC tissue engineering can be divided into two categories, including cell-based tissue engineering and cell-free tissue engineering. Although cell-based tissue engineering can repair cartilage damage to a certain extent, existing therapeutic strategies still suffer from limited cell sources, high costs, risk of disease transmission, and complex procedures. However, the cell-free tissue engineering avoids these shortcomings and brings hope for in-situ AC regeneration. Non-cellular tissue engineering is mainly used to recruit endogenous stem cells/progenitor cells (SCPCs) to reach the site of cartilage injury, and provide a suitable regenerative microenvironment to promote cell proliferation and chondrogenic differentiation, then the maturation of new cartilage tissue was promoted. Therefore, it is also called as cell-homing in situ tissue engineering. Successful recruitment of endogenous SCPCs is the first step in in-situ cartilage tissue engineering. This review aims to introduce chemokine response of cartilage injury, systematically summarize traditional chemoattractant (chemokines and growth factors etc.) and emerging chemoattractant (functional peptides, exosomes and nucleic acid adapters etc.), evaluate the combination mode between chemoattractant and delivery devices, discuss the prospects and challenges of chemoattractant-mediated in situ tissue engineering and provide theoretical basis for the design of endogenous SCPCs homing-based in situ tissue engineering.
ABSTRACT
BACKGROUND:With the development of tissue engineering technology, repairing large-area bone defects using tissue-engineered bone has become a hot spot. OBJECTIVE:To introduce the bone tissue engineering seed cel s, cytokines, as wel as the characteristics of scaffold materials and their vascularization. METHODS:With the key words of“bone tissue engineering, scaffold, vascularization”in Chinese and in English, respectively, a computer-based search of articles published from January 2000 to January 2012 was performed in CNKI and PubMed databases. Articles with the summary of bone tissue engineering, bone tissue engineering scaffolds and scaffold vascularization were included. RESULTS AND CONCLUSION:The selection of seed cel s, application of cytokines, scaffold material performance and degree of vascularization in bone tissue engineering has an important influence on the repair of bone injuries. Appropriate seed cel s is the study foundation in bone tissue engineering, cytokines serve as catalysts, and scaffold materials with good three-dimensional structure can promote cel growth and proliferation, tissue ingrowth, osteogenesis and vascularization. Each scaffold has its own inadequacies, so the combination of a variety of materials can reach a combined effect to meet the clinical demand. In addition, it is important to actively seek new material preparation technology and improve the existing methods, in order to create a more excel ent scaffold. But the vascularization is stil a major test for bone tissue engineering. Current methods to promote vascularization of tissue-engineered bone have some defects. For examples, the use of growth factors to promote vascularization can lead to disease progression in patients with metabolic abnormalities during;microsurgical techniques for tissue engineering bone vascularization are easy to cause trauma and deformity at other parts, which is not conducive to the patient’s physical rehabilitation.