Lane Dwight D, Kaur Sarbjit, Weerasakare G Mahika, Stewart Russell J
Department of Bioengineering, University of Utah, Salt Lake City, UT 84112, USA.
Soft Matter. 2015 Sep 21;11(35):6981-90. doi: 10.1039/c5sm01297j. Epub 2015 Aug 3.
Aquatic caddisworm silk is a tough adhesive fiber. Part of the toughening mechanism resides in serial, Ca(2+)-phosphate crosslinked nano-domains that comprise H-fibroin, the major structural protein. To mimic the toughening mechanism, a synthetic phosphate-graft-methacrylate prepolymer, as a simple H-fibroin analog, was copolymerized within a covalent elastic network of polyacrylamide. Above a critical phosphate sidechain density, hydrogels equilibrated with Ca(2+) or Zn(2+) ions displayed greatly increased initial stiffness, strain-rate dependent yield behavior, and required 100 times more work to fracture than hydrogels equilibrated with Mg(2+) or Na(+) ions. Conceptually, the enhanced toughness is attributed to energy-dissipating, viscous unfolding of clustered phosphate-metal ion crosslinks at a critical stress. The toughness of the bioinspired hydrogels exceeds the toughness of cartilage and meniscus suggesting potential application as prosthetic biomaterials. The tough hydrogels also provide a simplified model to test hypotheses about caddisworm silk architecture, phosphate metal ion interactions, and mechanochemical toughening mechanisms.
水生石蛾丝是一种坚韧的粘性纤维。其增韧机制的一部分在于由主要结构蛋白H-丝心蛋白组成的串联式磷酸钙交联纳米域。为了模拟这种增韧机制，一种合成的磷酸接枝甲基丙烯酸酯预聚物作为简单的H-丝心蛋白类似物，在聚丙烯酰胺的共价弹性网络中共聚。在临界磷酸侧链密度以上，用Ca(2+)或Zn(2+)离子平衡的水凝胶显示出初始刚度大幅增加、应变率依赖性屈服行为，并且与用Mg(2+)或Na(+)离子平衡的水凝胶相比，断裂所需的功要多100倍。从概念上讲，增强的韧性归因于在临界应力下成簇的磷酸-金属离子交联的能量耗散、粘性展开。这种仿生水凝胶的韧性超过了软骨和半月板的韧性，表明其作为修复生物材料具有潜在应用价值。这种坚韧的水凝胶还提供了一个简化模型，用于测试关于石蛾丝结构、磷酸金属离子相互作用和机械化学增韧机制的假设。
