Uskoković Vuk, Rau Julietta V
Advanced Materials and Nanobiotechnology Laboratory, Department of Biomedical and Pharmaceutical Sciences, Center for Targeted Drug Delivery, Chapman University School of Pharmacy, Irvine, CA 92618-1908, USA.
Department of Bioengineering, University of Illinois, Chicago, IL 60607-7052, USA.
RSC Adv. 2017;7(64):40517-40532. doi: 10.1039/C7RA07395J. Epub 2017 Aug 21.
Here we report on the nonlinear, oscillatory dynamics detected in the evolution of phase composition during the setting of different calcium phosphate cements, two of which evolved toward brushite and one toward hydroxyapatite as the final product. Whereas both brushite-forming cements contained ion-doped β-tricalcium phosphate as the initial phase, the zinc-containing one yielded scholzite as an additional phase during setting and the oscillations between these two products were pronounced throughout the entire 80 h setting period, long after the hardening processes was over from the mechanical standpoint. Oscillations in the copper-containing system involved the amount of brushite as the main product of the hardening reaction and they progressed faster toward an equilibrium point than in the zinc-containing system. Initially detected with the use of energy-dispersive X-ray diffractometry, the oscillations were confirmed with a sufficient level of temporal matching in an Fourier transform infrared spectroscopic analysis. The kinetic reaction analysis based on the Johnson-Mehl-Avrami-Kolmogorov model indicated an edge-controlled nucleation mechanism for brushite. The hydroxyapatite-forming cement comprised gelatin as an additional phase with a role of slowing down diffusion and allowing the detection of otherwise rapid oscillations in crystallinity and in the amount of the apatitic phase on the timescale of minutes. A number of possible causes for these dynamic instabilities were discussed. The classical chemical oscillatory model should not apply to these systems unless in combination with less exotic mechanisms of physicochemical nature. One possibility is that the variations in viscosity, directly affecting diffusion and nucleation rates and accompanying growth and transformation from the lower to the higher interfacial energy per the Ostwald-Lussac rule, are responsible for the oscillatory dynamics. The conception of bone replacement materials and tissue engineering constructs capable of engaging in the dynamics of integration with the natural tissues in compliance with this oscillatory nature may open a new avenue for the future of this type of medical devices. To succeed in this goal, the mechanism of these and similar instabilities must be better understood.
在此，我们报告了在不同磷酸钙骨水泥固化过程中相组成演变过程中检测到的非线性振荡动力学。其中两种骨水泥最终产物演变为透钙磷石，一种演变为羟基磷灰石。虽然两种形成透钙磷石的骨水泥都含有离子掺杂的β - 磷酸三钙作为初始相，但含锌的那种在固化过程中产生了磷锌矿作为额外相，并且在整个80小时的固化期间，这两种产物之间的振荡都很明显，从力学角度来看，硬化过程早已结束之后依然如此。含铜体系中的振荡涉及作为硬化反应主要产物的透钙磷石的量，并且它们朝着平衡点的进展比含锌体系更快。这些振荡最初是通过能量色散X射线衍射法检测到的，在傅里叶变换红外光谱分析中通过足够程度的时间匹配得到了证实。基于约翰逊 - 梅尔 - 阿夫拉米 - 科尔莫戈罗夫模型的动力学反应分析表明透钙磷石的成核机制为边缘控制型。形成羟基磷灰石的骨水泥包含明胶作为额外相，其作用是减缓扩散，并使得能够在几分钟的时间尺度上检测到结晶度和磷灰石相含量原本快速的振荡。讨论了这些动态不稳定性的一些可能原因。经典的化学振荡模型不适用于这些体系，除非与不太奇特的物理化学性质机制相结合。一种可能性是，粘度的变化直接影响扩散和成核速率，并伴随着按照奥斯特瓦尔德 - 卢萨克规则从较低界面能到较高界面能的生长和转变，这是振荡动力学的原因。能够按照这种振荡性质与天然组织进行整合动力学的骨替代材料和组织工程构建体的概念，可能为这类医疗设备的未来开辟一条新途径。为了实现这一目标，必须更好地理解这些以及类似不稳定性的机制。
