Intl. Research Center for Advanced Structural and Biomaterials, School of Materials Science and Engineering, Beihang University, Beijing, 100191, China.
Beijing Inst Aeronaut Mat, Beijing 100095, China.
Acta Biomater. 2021 Apr 15;125:57-71. doi: 10.1016/j.actbio.2021.02.018. Epub 2021 Feb 16.
Hydrogels are an attractive class of materials that possess similar structural and functional characteristics to wet biological tissues and demonstrate a diversity of applications in biomedical engineering. Silk fibroin (SF) is a unique natural polymer due to its fibrous protein nature, versatile formats, biocompatibility, tunable biodegradation and is thus a good hydrogel candidate for bio-applications. Compared to synthetic polymer hydrogels, poor mechanical performance is still a fatal drawback that hinders the application of SF hydrogels as structural materials. Researchers have attempted to develop strategies to construct silk fibroin-based high-strength hydrogels (SF-HSHs). Herein, we firstly provide an overview of the approaches of processing SF-HSHs with a focus on the physical/non-covalent crosslinking mechanisms. The examples of SF-HSHs are discussed in detail under four categories, including physical-crosslinked, dual-crosslinked, double network and composite hydrogels respectively. A brief section follows to elucidate on the gelation mechanisms of SF-HSHs before a description of the utility of SF-HSHs in biomedicine and devices is presented. Finally, the potential challenges and future development of SF-HSHs are briefly discussed. This review aims to enhance our understanding of the structure-mechanical property-function relationships of soft materials made from natural polymers and guide future research of silk fibroin-based hydrogels for biomedical applications. STATEMENT OF SIGNIFICANCE: Silk fibroin (SF) extracted from silk fibres is increasingly applied in the biomedical field, and SF hydrogel has been an emerging area for frontier bio-research. Since SF biopolymer has an intrinsic tendency to form regular β-sheet stacks, it can be processed into purely physically crosslinked hydrogels, thus avoiding the use of chemical crosslinkers. Nevertheless, akin to other natural polymers, lab-produced SF is variable (i.e. the molecular weight and distribution), and the gelation of SF hydrogel is challenging to control. In addition, hydrogels made from SF are usually weak and brittle, which hinders the wide use of this biofriendly and biodegradable hydrogel. Recently, there is a pressing need for high strength hydrogels from natural polymers for biomedical applications, and SF is proposed as a strong candidate. Therefore, we have studied the literature in the past 10 years and would like to focus on the gelation mechanism and mechanical strength of SF hydrogels for the review.
水凝胶是一类具有类似结构和功能特性的材料，与湿生物组织相似，并在生物医学工程中具有多种应用。丝素蛋白（SF）是一种独特的天然聚合物，由于其纤维状蛋白质性质、多种形式、生物相容性、可调节的生物降解性，因此是生物应用的良好水凝胶候选材料。与合成聚合物水凝胶相比，较差的机械性能仍然是阻碍 SF 水凝胶作为结构材料应用的致命缺点。研究人员已经尝试开发构建丝素蛋白基高强度水凝胶（SF-HSH）的策略。在此，我们首先提供了一种处理 SF-HSH 的方法概述，重点介绍了物理/非共价交联机制。分别详细讨论了物理交联、双重交联、双网络和复合水凝胶这四类 SF-HSH 的实例。接下来简要介绍了 SF-HSH 的凝胶化机制，然后介绍了 SF-HSH 在生物医学和器件中的应用。最后，简要讨论了 SF-HSH 的潜在挑战和未来发展。本综述旨在增强我们对天然聚合物软材料结构-机械性能-功能关系的理解，并指导基于丝素蛋白的水凝胶在生物医学应用中的未来研究。
意义声明：从丝纤维中提取的丝素蛋白（SF）越来越多地应用于生物医学领域，SF 水凝胶已成为前沿生物研究的新兴领域。由于 SF 生物聚合物具有形成规则β-折叠堆叠的内在趋势，因此它可以被加工成纯物理交联水凝胶，从而避免使用化学交联剂。然而，与其他天然聚合物一样，实验室生产的 SF 是可变的（即分子量和分布），并且 SF 水凝胶的凝胶化难以控制。此外，SF 制成的水凝胶通常较弱且易碎，这阻碍了这种生物友好且可生物降解的水凝胶的广泛使用。最近，对用于生物医学应用的天然聚合物的高强度水凝胶有迫切的需求，SF 被提议为一种强有力的候选材料。因此，我们研究了过去 10 年的文献，希望重点关注 SF 水凝胶的凝胶化机制和机械强度。
