Chemical and Bio-molecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, United States.
Chemical and Bio-molecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, United States.
J Mech Behav Biomed Mater. 2019 Mar;91:315-325. doi: 10.1016/j.jmbbm.2018.12.031. Epub 2018 Dec 24.
Bone derives its mechanical strength from the complex arrangement of collagen fibrils (type-I primarily) reinforced with hydroxy-apatite (HAp) mineral crystals in extra- and intra-fibrillar compartments. This study demonstrates a novel approach to obtain organic matrix of bone through its demineralization as well as mechanically characterize it at small length scales using static and dynamic indentation techniques. Sample surface preparation protocol used in the present work maintained the surface integrity of demineralized bone samples which resulted sample surface of roughness (RMS) magnitude of approximately 14 nm (averaged over 1 × 1 μm area duly verified by atomic force microscope (AFM)). Elemental composition analysis via energy dispersive X-ray spectroscopy (EDX) (for probed depth upto 2 μm) confirmed the complete removal of HAp mineral from bone samples during their demineralization using EDTA leaving collagen molecule assemblies unaffected as represented by Second Harmonic Generation (SHG) imaging. The modulus magnitudes of organic matrix obtained using from quasistatic as well as dynamic indentations (at constant frequency of 30 Hz) as ∼2.6 GPa and 4.5 GPa respectively, demonstrated the influence of loading rate on the estimated mechanical properties. For indentation depth to surface roughness ratio greater than ∼5:1, interestingly, measured material properties of organic matrix were found to depend on increasing magnitude of indentation depth of up to ∼500 nm value which probed from few collagen fibrils to next level of hierarchy i.e. collagen fibers. These findings are very useful to accurately determine the elastic and visco-elastic response of organic matrices of mineralized tissues for various applications including tissue engineering, bio-mimetics, etc.
骨骼的机械强度来源于胶原纤维（主要是 I 型）的复杂排列，这些纤维被羟基磷灰石（HAp）矿物质晶体在纤维内外间隙中增强。本研究展示了一种通过脱矿作用获得骨有机基质的新方法，并通过静态和动态压痕技术在小尺度上对其进行力学特性表征。本工作中使用的样品表面制备方案保持了脱矿骨样品的表面完整性，导致样品表面粗糙度（RMS）约为 14nm（在经过原子力显微镜（AFM）验证的 1×1μm 面积上平均）。通过能量色散 X 射线光谱（EDX）的元素组成分析（探测深度可达 2μm）证实，EDTA 脱矿作用可完全去除骨样品中的 HAp 矿物质，而胶原分子组装不受影响，如二次谐波产生（SHG）成像所示。通过准静态和动态压痕（恒定频率为 30Hz）获得的有机基质的模量值分别约为 2.6GPa 和 4.5GPa，表明加载速率对估计的机械性能有影响。对于压痕深度与表面粗糙度比大于约 5:1，有趣的是，发现有机基质的测量材料性能取决于压痕深度的增加，最大可达约 500nm，这从几个胶原纤维探测到下一个层次，即胶原纤维。这些发现对于准确确定矿化组织的有机基质的弹性和粘弹性响应非常有用，适用于各种应用，包括组织工程、仿生学等。
