髋关节软骨高、低负重区微纳结构的力学性质对比

Structure and mechanical properties of high-and low-weight-bearing areas of hip cartilage at micro and nano levels

背景:髋关节软骨具有高、低负重区域,既往研究表明2个区域的宏观弹性模量是不同的。然而在微米和纳米水平上的弹性模量尚不清楚,这些信息对于进一步理解软骨微米和纳米力学性质至关重要。此外,影响软骨2个区域机械性能的微纳结构至今仍有待阐明。目的:探究微纳层面髋关节软骨高、低负重区力学性质与结构。方法:取新鲜正常猪股骨头软骨,使用原子力显微镜直径为5μm的球形尖端测量不同负重区微米级压缩弹性模量,使用曲率半径为5 nm的ScanAsyst-Air探针测量其纳米级压缩弹性模量、纳米结构和胶原纤维直径。扫描电子显微镜用于识别软骨不同负重区微米结构。结果与结论:①股骨头软骨高负重区微米级弹性模量为(433.05±146.52)kPa,低负重区微米级弹性模量为(331.19±84.88)kPa,高负重区域在微米水平上的压缩弹性模量显著高于低负重区域(P=0.0298);②股骨头软骨高负重区纳米级弹性模量为(1.24±0.42)GPa,低负重区纳米级弹性模量为(1.28±0.41)GPa,在纳米水平上2个区域的胶原纤维的压缩弹性模量差异无显著性意义(P=0.8462);③在微米水平上,股骨头软骨高负重区域的胶原纤维排列更规则;在纳米水平上,2个负重区域的胶原纤维直径差异无显著性意义(P=0.9264);④以上结果表明,股骨头软骨高负重区胶原纤维较低负重区交联更规则,使软骨高负重区微米级压缩弹性模量高于低负重区,与宏观上压缩弹性模量趋势一致,但高负重并没有影响到纳米层面单个胶原纤维。

BACKGROUND:Articular cartilage has a high-weight-bearing area and a low-weight-bearing area.There are different macroscopic elastic moduli in the two regions,but the modulus of the two areas at the micro and nano levels is unknown.Such information is important for further understanding of cartilage micro and nano mechanics.Moreover,the micro and nano structures of the two areas,which influence the cartilage mechanical properties,should be discussed.OBJECTIVE:To investigate the mechanical properties and structure of high-and low-weight-bearing areas of the hip articular cartilage at the micro and nano levels.METHODS:Normal porcine femoral head cartilage was used.Atomic force microscopy with a spherical tip of 5μm in diameter was used to measure the microscale compressive elastic modulus of different weight-bearing areas of the cartilage.The nanoscale compressive elastic modulus,nano structure,and collagen fiber diameter were measured using a ScanAsyst-Air probe with a radius of curvature of 5 nm.Scanning electron microscopy was employed to identify the microstructure of different weight-bearing areas of the cartilage.RESULTS AND CONCLUSION:The microscale elastic modulus of the high-weight-bearing area of the femoral head cartilage was(433.05±146.52)kPa,and the microscale elastic modulus of the low-weight-bearing area was(331.19±84.88)kPa.The nanoscale elastic modulus of the high-and low-weight-bearing areas of the femoral head cartilage was(1.24±0.42)GPa and(1.28±0.41)GPa,respectively.While no statistically significant differences were found in the elastic modulus of collagen fibers at the nano level(P=0.8462).The collagen fibers of the high-weight-bearing area arranged more regularly than those of the low-weight-bearing area at the micro level.No significant differences between collagen fiber diameter of the two areas at the nano level were observed(P=0.9264).To conclude,the collagen fibers of the high-weight-bearing area are cross-linked more regularly than those of low-weight-bearing area.Therefore,the compressive elastic modulus of the high-weight-bearing area at the micro level is significantly higher than that of the low-weight-bearing area,which is consistent with the macroscopic compressive elastic modulus trend.However,high-weight-bearing has no impact on individual collagen fibers at the nano level.