Dynamic elastic modulus of porcine articular cartilage determined at two different levels of tissue organization by indentation-type atomic force microscopy
Dynamic elastic modulus of porcine articular cartilage determined at two different levels of tissue organization by indentation-type atomic force microscopy
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DOI：
10.1016/s0006-3495(04)74375-1
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发表时间：
2004-05-01
影响因子：
3.4
通讯作者：
Aebi, U
中科院分区：
文献类型：
--
作者：
Stolz, M;Raiteri, R;Aebi, U
在微米和纳米尺度下离体测量腕关节刚度，以探索比以前更小尺度下的结构-机械性能关系。提出了一种利用压痕型原子力显微镜（IT AFM）测量材料动态弹性模量E * 的方法。球形压头尖端（半径=类似于2.5 μ m）和尖锐的锥形尖端（半径=类似于20 nm）分别用于探测微米级和纳米级响应。在3 Hz下，从在猪股骨髁的表面下软骨上的给定位置处记录的1024条卸载响应曲线获得E* 值。使用微球尖端时，平均模量接近2.6 MPa，与可用的毫米级数据一致，而使用尖锐的金字塔尖端时，平均模量通常低100倍。与软骨相反，在琼脂糖凝胶（一种分子上无定形得多的生物材料）上进行的测量导致两种压痕尖端的平均模量相同。从软骨的AFM成像的结果，微米级的球形尖端解决no.ne结构，除了一些软骨细胞，而纳米级的金字塔尖解决个别胶原纤维和它们的67 nm轴向重复距离。这些结果表明，球形AFM针尖是足够大的，以测量总的动态弹性模量的软骨，而尖锐的AFM针尖描绘其弹性特性。ne结构。酶作用后软骨硬度的其他测量结果显示，胶原蛋白部分的弹性蛋白酶消化降低了微米级的模量。相比之下，组织蛋白酶D消化的蛋白聚糖部分在微米尺度上对\E*\几乎没有影响，但在纳米尺度上产生了明显的硬化。因此，由于精细的纳米尺度结构，与在微米和更大尺度下测量的整体结构刚度相比，软骨压缩刚度在纳米尺度下是不同的，并且酶诱导的结构变化可以不同地影响这种尺度依赖性刚度。
Cartilage stiffness was measured ex vivo at the micrometer and nanometer scales to explore structure-mechanical property relationships at smaller scales than has been done previously. A method was developed to measure the dynamic elastic modulus, \E*\, in compression by indentation-type atomic force microscopy (IT AFM). Spherical indenter tips (radius=similar to2.5 mum) and sharp pyramidal tips (radius=similar to20 nm) were employed to probe micrometer-scale and nanometer-scale response, respectively. \E*\ values were obtained at 3 Hz from 1024 unloading response curves recorded at a given location on subsurface cartilage from porcine femoral condyles. With the microsphere tips, the average modulus was similar to2.6 MPa, in agreement with available millimeter-scale data, whereas with the sharp pyramidal tips, it was typically 100-fold lower. In contrast to cartilage, measurements made on agarose gels, a much more molecularly amorphous biomaterial, resulted in the same average modulus for both indentation tips. From results of AFM imaging of cartilage, the micrometer-scale spherical tips resolved no. ne structure except some chondrocytes, whereas the nanometer-scale pyramidal tips resolved individual collagen fibers and their 67-nm axial repeat distance. These results suggest that the spherical AFM tip is large enough to measure the aggregate dynamic elastic modulus of cartilage, whereas the sharp AFM tip depicts the elastic properties of its. ne structure. Additional measurements of cartilage stiffness following enzyme action revealed that elastase digestion of the collagen moiety lowered the modulus at the micrometer scale. In contrast, digestion of the proteoglycans moiety by cathepsin D had little effect on \E*\ at the micrometer scale, but yielded a clear stiffening at the nanometer scale. Thus, cartilage compressive stiffness is different at the nanometer scale compared to the overall structural stiffness measured at the micrometer and larger scales because of the fine nanometer-scale structure, and enzyme-induced structural changes can affect this scale-dependent stiffness differently.