Laboratory of Biomechanical Orthopedics, EPF Lausanne, Lausanne, Switzerland.
Bone. 2011 Dec;49(6):1357-64. doi: 10.1016/j.bone.2011.09.040. Epub 2011 Sep 18.
A successful bone tissue engineering strategy entails producing bone-scaffold constructs with adequate mechanical properties. Apart from the mechanical properties of the scaffold itself, the forming bone inside the scaffold also adds to the strength of the construct. In this study, we investigated the role of in vivo cyclic loading on mechanical properties of a bone scaffold. We implanted PLA/β-TCP scaffolds in the distal femur of six rats, applied external cyclic loading on the right leg, and kept the left leg as a control. We monitored bone formation at 7 time points over 35 weeks using time-lapsed micro-computed tomography (CT) imaging. The images were then used to construct micro-finite element models of bone-scaffold constructs, with which we estimated the stiffness for each sample at all time points. We found that loading increased the stiffness by 60% at 35 weeks. The increase of stiffness was correlated to an increase in bone volume fraction of 18% in the loaded scaffold compared to control scaffold. These changes in volume fraction and related stiffness in the bone scaffold are regulated by two independent processes, bone formation and bone resorption. Using time-lapsed micro-CT imaging and a newly-developed longitudinal image registration technique, we observed that mechanical stimulation increases the bone formation rate during 4-10 weeks, and decreases the bone resorption rate during 9-18 weeks post-operatively. For the first time, we report that in vivo cyclic loading increases mechanical properties of the scaffold by increasing the bone formation rate and decreasing the bone resorption rate.
一项成功的骨组织工程策略需要生产出具有足够机械性能的骨支架结构。除了支架本身的机械性能外，支架内形成的骨骼也会增加结构的强度。在这项研究中，我们研究了体内周期性负载对骨支架机械性能的影响。我们将 PLA/β-TCP 支架植入 6 只大鼠的股骨远端，对右腿施加外部周期性负载，左腿作为对照。我们使用时变微计算机断层扫描（CT）成像在 35 周内的 7 个时间点监测骨形成。然后，我们使用这些图像构建了骨-支架结构的微有限元模型，用其估计了每个样本在所有时间点的刚度。我们发现，在 35 周时，负载使刚度增加了 60%。负载支架的骨体积分数比对照支架增加了 18%，这与刚度的增加相关。骨支架中体积分数和相关刚度的这些变化是由两个独立的过程——骨形成和骨吸收来调节的。使用时变微 CT 成像和新开发的纵向图像配准技术，我们观察到机械刺激在术后 4-10 周内增加了骨形成率，在 9-18 周内降低了骨吸收率。我们首次报告，体内周期性负载通过增加骨形成率和降低骨吸收率来提高支架的机械性能。
