Forwood M R, Bennett M B, Blowers A R, Nadorfi R L
Department of Anatomical Sciences, University of Queensland, Brisbane, Australia.
Bone. 1998 Sep;23(3):307-10. doi: 10.1016/s8756-3282(98)00090-8.
We modified the noninvasive, in vivo technique for strain application in the tibiae of rats (Turner et al., Bone 12:73-79, 1991). The original model applies four-point bending to right tibiae via an open-loop, stepper-motor-driven spring linkage. Depending on the magnitude of applied load, the model produces new bone formation at periosteal (Ps) or endocortical surfaces (Ec.S). Due to the spring linkage, however, the range of frequencies at which loads can be applied is limited. The modified system replaces this design with an electromagnetic vibrator. A load transducer in series with the loading points allows calibration, the loaders' position to be adjusted, and cyclic loading completed under load control as a closed servo-loop. Two experiments were conducted to validate the modified system: (1) a strain gauge was applied to the lateral surface of the right tibia of 5 adult female rats and strains measured at applied loads from 10 to 60 N; and (2) the bone formation response was determined in 28 adult female Sprague-Dawley rats. Loading was applied as a haversine wave with a frequency of 2 Hz for 18 sec, every second day for 10 days. Peak bending loads were applied at 33, 40, 52, and 64 N, and a sham-loading group was included at 64 N. Strains in the tibiae were linear between 10 and 60 N, and the average peak strain at the Ps.S at 60 N was 2664 +/- 250 microstrain, consistent with the results of Turner's group. Lamellar bone formation was stimulated at the Ec.S by applied bending, but not by sham loading. Bending strains above a loading threshold of 40 N increased Ec lamellar bone formation rate, bone forming surface, and mineral apposition rate with a dose response similar to that reported by Turner et al. (J Bone Miner Res 9:87-97, 1994). We conclude that the modified loading system offers precision for applied loads of between 0 and 70 N, versatility in the selection of loading rates up to 20 Hz, and a reproducible bone formation response in the rat tibia. Adjustment of the loader also enables study of mechanical usage in murine tibia, an advantage with respect to the increasing variety of transgenic strains available in bone and mineral research.
我们改进了在大鼠胫骨中施加应变的非侵入性体内技术（Turner等人，《骨》12:73 - 79，1991）。原始模型通过开环、步进电机驱动的弹簧连杆对右胫骨施加四点弯曲。根据所施加负荷的大小，该模型在骨膜（Ps）或骨内膜表面（Ec.S）产生新骨形成。然而，由于弹簧连杆，能够施加负荷的频率范围有限。改进后的系统用电磁振动器取代了这种设计。与加载点串联的负荷传感器允许进行校准、调整加载器的位置，并在负荷控制下作为闭环完成循环加载。进行了两项实验以验证改进后的系统：（1）将应变片应用于5只成年雌性大鼠右胫骨的外侧表面，并在10至60 N的施加负荷下测量应变；（2）在28只成年雌性Sprague - Dawley大鼠中确定骨形成反应。负荷以频率为2 Hz的正弦波形式施加18秒，每隔一天施加一次，共施加10天。峰值弯曲负荷分别为33、40、52和64 N，并包括一个64 N的假负荷组。胫骨中的应变在10至60 N之间呈线性关系，60 N时Ps.S处的平均峰值应变为2664 +/- 250微应变，与Turner团队的结果一致。施加的弯曲刺激了Ec.S处的板层骨形成，但假负荷未产生此效果。高于40 N负荷阈值的弯曲应变增加了Ec板层骨形成率、骨形成表面和矿物质沉积率，其剂量反应与Turner等人报道的相似（《骨矿物质研究杂志》9:87 - 97，1994）。我们得出结论，改进后的加载系统在0至70 N的施加负荷方面具有精度，在高达20 Hz的加载速率选择上具有通用性，并且在大鼠胫骨中具有可重复的骨形成反应。加载器的调整还能够研究小鼠胫骨中的机械使用情况，这对于骨与矿物质研究中可用的转基因品系种类不断增加而言是一个优势。
