Lawrence J. Ellison Musculoskeletal Research Laboratory, Department of Orthopaedic Surgery, UC Davis School of Medicine & Biomedical Engineering Graduate Group, UC Davis, United States.
J Biomech. 2013 Sep 27;46(14):2411-8. doi: 10.1016/j.jbiomech.2013.07.026. Epub 2013 Jul 31.
Bone is biphasic with an organic matrix and an inorganic mineral component. As we age bone's susceptibility to fracture increases. It has been shown that there is no change in mean mineralization with aging, but bone nevertheless becomes less tough. This aging effect is therefore likely related to the organic phase. Under mechanical loading, immediately prior to failure, bone has been observed to visually become more opaque and has been termed stress-whitening. Stress-whitening is known to make materials tougher. The goal of this investigation was to investigate stress-whitening in the collagenous matrix of bone. Hydrogen bonds play a key role in collagen stability and we hypothesize that changes in hydrogen bonding will significantly affect matrix stiffness, toughness and stress whitening. Demineralized bone specimens were loaded in tension and stress-whitening was monitored. The effect of hydrogen bonding on mechanical properties and stress-whitening process was probed by altering the Hansen's hydrogen bonding parameter (δh) of the immersing solution. The Hansen's hydrogen bonding parameter of the immersing fluid affected the morphology, mechanical properties and stress whitening of specimens. Specimens were visually whiter in the absence of mechanical load in low δh solvents (the specimens solvent-whitened). Both the observed stress-whitening and solvent-whitening were reversible and repeatable processes. The observed solvent-whitening that occurred without the presence of load was consistent with solvent-induced optical clearing (the opposite of whitening) in skin caused by collagen fibril swelling. Stress whitening and solvent whitening can be explained by a common mechanism, collagen fibril densification and thinning, leading to an increased distinction between the collagen fibrillar phase and immersing fluid, ultimately leading to more scattering. Bones may be at a greater risk for fracture as we age because solubility of the matrix changes, thus making the collagen less hydrated (and more brittle) even in the same solvent.
骨组织具有两相特性,包括有机基质和无机矿物质成分。随着年龄的增长,骨组织的骨折易感性增加。研究表明,随着年龄的增长,平均矿化程度没有变化,但骨组织的韧性却降低了。因此,这种衰老效应可能与有机相有关。在机械加载下,在失效之前,骨组织已经被观察到肉眼变得更加不透明,并被称为应力致白。应力致白已知会使材料更坚韧。本研究的目的是研究骨胶原基质中的应力致白现象。氢键在胶原稳定性中起着关键作用,我们假设氢键的变化将显著影响基质的刚度、韧性和应力致白。将脱矿骨标本在张力下加载,并监测应力致白。通过改变浸泡溶液的 Hansen 氢键参数(δh)来探究氢键对力学性能和应力致白过程的影响。浸泡液的 Hansen 氢键参数影响了标本的形态、力学性能和应力致白。在低 δh 溶剂中(标本溶剂致白),没有机械负载时,标本肉眼看起来更白。观察到的应力致白和溶剂致白都是可逆和可重复的过程。在没有负载的情况下发生的观察到的溶剂致白与由胶原纤维肿胀引起的皮肤中溶剂诱导的光学透明(与致白相反)一致。应力致白和溶剂致白可以用一个共同的机制来解释,即胶原纤维的密集化和变薄,导致胶原纤维相和浸泡液之间的差异增加,最终导致更多的散射。随着年龄的增长,骨骼可能更容易骨折,因为基质的溶解度发生了变化,因此即使在相同的溶剂中,胶原也会变得不那么水合(更脆弱)。