Risan Jared, Jain Gaurav, Pendola Martin, Evans John Spencer
Nano Surfaces Division, Bruker Corporation, 9625 W. 76th Street, Eden Prairie, MN 55344, USA.
J Mater Chem B. 2018 Jul 7;6(25):4191-4196. doi: 10.1039/c8tb01156g. Epub 2018 Jun 14.
The fracture toughness of mollusk shell nacre has been attributed to many factors, one of which is the intracrystalline incorporation of nacre-specific proteins. Although mechanical force measurements have been made on the nacre layer and on individual calcium carbonate crystals containing occluded organic molecules and macromolecules, there are few if any studies which examine the impact of occluded proteins on the mechanical properties of calcium carbonate crystals. To remedy this, we performed microcompression studies of calcite crystals grown in the presence and absence of two recombinant nacre proteins, r-AP7 (H. rufescens, intracrystalline proteome) and r-n16.3 (P. fucata, framework proteome), both of which are known aggregators that form hydrogel nanoinclusions within in vitro calcite. We find that, relative to protein-free calcite, the intracrystalline inclusion of either r-AP7 or r-n16.3 nacre protein hydrogels within the calcite crystals leads to a reduction in strength. However, nacre protein-modified crystals were found to exhibit elastic deformation under force compared to control scenarios, with no discernable differences noted between intracrystalline or framework protein-modified crystals. We conclude from our in vitro microcompression studies that the intracrystalline incorporation of nacre proteins can contribute to fracture-resistance of the crystalline phase by significantly reducing both modulus AND critical strength.
软体动物贝壳珍珠层的断裂韧性归因于多种因素，其中之一是珍珠层特异性蛋白质在晶体内部的掺入。尽管已经对珍珠层以及含有封闭有机分子和大分子的单个碳酸钙晶体进行了机械力测量，但几乎没有研究考察封闭蛋白质对碳酸钙晶体力学性能的影响。为了弥补这一点，我们对在存在和不存在两种重组珍珠层蛋白（r-AP7，红鲍的晶体内部蛋白质组；r-n16.3，合浦珠母贝的框架蛋白质组）的情况下生长的方解石晶体进行了微压缩研究，这两种蛋白都是已知的聚集剂，可在体外方解石中形成水凝胶纳米内含物。我们发现，相对于不含蛋白质的方解石，方解石晶体内部包含r-AP7或r-n16.3珍珠层蛋白水凝胶会导致强度降低。然而，与对照情况相比，发现珍珠层蛋白修饰的晶体在受力时表现出弹性变形，晶体内部或框架蛋白修饰的晶体之间没有明显差异。我们从体外微压缩研究中得出结论，珍珠层蛋白在晶体内部的掺入可通过显著降低模量和临界强度来提高晶相的抗断裂能力。
