Schmidt Stephanie M, McCready Mark J, Ostafin Agnes E
Department of Chemical and Biomolecular Engineering, 182 Fitzpatrick Hall, University of Notre Dame, Notre Dame, IN 46556-5637, USA.
J Biomech. 2005 Dec;38(12):2337-43. doi: 10.1016/j.jbiomech.2004.10.013. Epub 2004 Dec 16.
The consequences of an oscillatory fluid shear mechanism on nutrient transport in bone during physical activity and ultrasonic therapy are discussed. During movement, periodic stress on bone creates transient pressure gradients that circulate interstitial fluid through calcified bone. A transport model derived from oscillatory Taylor-Aris dispersion phenomena was used to predict a ratio of effective-to-molecular diffusivity, K/D, for solutes of varying sizes up to 50 nm in diameter, in pores filled with interstitial fluid and pericellular matrix. The magnitude of the estimated transport enhancement depended on the molecular size, pore dimension, applied frequency and the displacement of the fluid during pressurization. For oscillation frequencies and amplitudes corresponding to those experienced during normal human activity, transport enhancements of up to 100 fold are expected for molecules larger than 5 nm in diameter. Enhancements of up to one order of magnitude, due to ultrasound stimulations in the MHz frequency range, are also expected for 7-nm-sized solutes. No effects are anticipated for ions, whose molecular diffusion time is too fast relative to the oscillation frequency. This model is expected to be useful for understanding differences in bone growth as a function of type of movement or to develop new physical therapies.
本文讨论了振荡流体剪切机制在身体活动和超声治疗过程中对骨营养物质运输的影响。在运动过程中，骨骼上的周期性应力会产生瞬态压力梯度，使组织液在钙化骨中循环。利用从振荡泰勒-阿里斯弥散现象推导出来的传输模型，预测了直径达50nm的不同大小溶质在充满组织液和细胞周基质的孔隙中的有效扩散率与分子扩散率之比K/D。估计的传输增强幅度取决于分子大小、孔隙尺寸、施加频率以及加压过程中流体的位移。对于与正常人类活动中所经历的频率和振幅相对应的情况，预计直径大于5nm的分子的传输增强可达100倍。对于7nm大小的溶质，由于兆赫兹频率范围内的超声刺激，预计传输增强可达一个数量级。对于离子，预计不会有影响，因为其分子扩散时间相对于振荡频率太快。该模型有望用于理解不同类型运动对骨生长的影响差异或开发新的物理治疗方法。
