Tao Jinhui, Battle Keith C, Pan Haihua, Salter E Alan, Chien Yung-Ching, Wierzbicki Andrzej, De Yoreo James J
Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352;
Department of Chemistry, University of South Alabama, Mobile, AL 36688;
Proc Natl Acad Sci U S A. 2015 Jan 13;112(2):326-31. doi: 10.1073/pnas.1404481112. Epub 2014 Dec 24.
The remarkable properties of bone derive from a highly organized arrangement of coaligned nanometer-scale apatite platelets within a fibrillar collagen matrix. The origin of this arrangement is poorly understood and the crystal structures of hydroxyapatite (HAP) and the nonmineralized collagen fibrils alone do not provide an explanation. Moreover, little is known about collagen-apatite interaction energies, which should strongly influence both the molecular-scale organization and the resulting mechanical properties of the composite. We investigated collagen-mineral interactions by combining dynamic force spectroscopy (DFS) measurements of binding energies with molecular dynamics (MD) simulations of binding and atomic force microscopy (AFM) observations of collagen adsorption on single crystals of calcium phosphate for four mineral phases of potential importance in bone formation. In all cases, we observe a strong preferential orientation of collagen binding, but comparison between the observed orientations and transmission electron microscopy (TEM) analyses of native tissues shows that only calcium-deficient apatite (CDAP) provides an interface with collagen that is consistent with both. MD simulations predict preferred collagen orientations that agree with observations, and results from both MD and DFS reveal large values for the binding energy due to multiple binding sites. These findings reconcile apparent contradictions inherent in a hydroxyapatite or carbonated apatite (CAP) model of bone mineral and provide an energetic rationale for the molecular-scale organization of bone.
骨骼的非凡特性源于在纤维状胶原基质中高度有序排列的纳米级共线磷灰石血小板。这种排列的起源尚不清楚，仅羟基磷灰石（HAP）和非矿化胶原纤维的晶体结构无法提供解释。此外，关于胶原 - 磷灰石相互作用能知之甚少，而这种相互作用能会强烈影响复合材料的分子尺度组织及其最终的力学性能。我们通过结合对结合能的动态力谱（DFS）测量、结合的分子动力学（MD）模拟以及对骨形成中四个潜在重要矿相的磷酸钙单晶上胶原吸附的原子力显微镜（AFM）观察，来研究胶原 - 矿物质相互作用。在所有情况下，我们都观察到胶原结合存在强烈的优先取向，但将观察到的取向与天然组织的透射电子显微镜（TEM）分析进行比较后发现，只有缺钙磷灰石（CDAP）提供了与胶原一致的界面。MD模拟预测的胶原优先取向与观察结果相符，MD和DFS的结果都揭示了由于多个结合位点导致的较大结合能值。这些发现调和了骨矿物质的羟基磷灰石或碳酸化磷灰石（CAP）模型中固有的明显矛盾，并为骨的分子尺度组织提供了能量学依据。
