Transdermal Mechanical Loading for Cell Therapy-Based Bone Repair

用于骨修复的细胞疗法与水凝胶组合，交联聚合物链的网络具有非常高的 水含量，作为基于支架的组织工程的潜在替代方案， 特别是对于可以通过微创方法治疗的较小规模的缺陷。将细胞注射 在临床上， 指出了一旦在缺损部位，细胞在水凝胶内基本上不受干扰，因为缺损本身 需要稳定以允许愈合，这一要求违背了 物理加载骨形成细胞。正是这种矛盾推动了本提案中概述的工作。 非侵入性的低强度脉冲超声已被证明是有效的透皮治疗， 新鲜骨折（临床和影像学愈合时间缩短38%）和骨折不愈合。而 LIPUS的作用机制知之甚少，我们已经开发出一种高度可调的超声 在临床相关超声强度下演示可测量声辐射力的系统， 已经表明这种力能够物理地偏转细胞和水凝胶。但迄今 LIPUS产生的声辐射力尚未与用于骨修复的细胞负载水凝胶配对。 本提案的目标是将联合收割机LIPUS产生的声辐射力和基于水凝胶的细胞结合起来 相信这两种方法结合在一起会比单独使用任何一种方法都能增强修复。使用LIPUS- 产生的负载能够赋予细胞物理力，这是我们的意图，设计水凝胶支架 其1）能够在体内递送包封的活细胞，2）可以通过产生的LIPUS物理负载， 植入后和愈合过程中的声辐射力，以及3）可以被修改以转移 改变从水凝胶到细胞的物理力，使得愈合将被优化。 本研究的目的是：1）评估LIPUS产生的声辐射的效果 随着交联密度的增加，包埋在水凝胶中的细胞上的力，2）评估 对包封在不同机械性质的胶原水凝胶中的细胞的辐射力，以确定 施加的力和水凝胶刚度对细胞行为的关系，以及3）使用施加的辐射力 涉及已装载细胞并植入骨缺损模型中的水凝胶。植入水凝胶 将使用声辐射力经皮加载包含细胞的容器。预计该 在体外研究中定义的参数将导致水凝胶中的增强的体内缺损愈合， 声辐射力时，相比之下，任何参数单独。

Cell therapy for bone repair combined with hydrogels, networks of crosslinked polymer chains with very high water content, is gaining in acceptance as a potential alternative to scaffold-based tissue engineering, especially for smaller scale defects that may be treatable through minimally invasive methods. Injecting cells into a bony defect with a small incision may be preferable to more invasive surgical procedures when clinically indicated. Once at the defect site the cells are left largely unperturbed within the hydrogel as the defect itself would require stabilization to permit healing, a requirement that goes against the therapeutic benefit of physically loading bone forming cells. It is this contradiction that has driven the work outlined in this proposal. Non-invasive, low-intensity pulsed ultrasound has been shown to be effective for transdermal treatment of fresh fractures (38% reduction in clinical and radiographic healing time) and fracture nonunions. While the mechanism through which LIPUS acts is poorly understood we have developed a highly tunable ultrasound system that demonstrates a measurable acoustic radiation force at clinically relevant ultrasound intensities and have shown this force to be capable of physically deflecting both cells and hydrogels. However, to date LIPUS-generated acoustic radiation force has not been paired with cell-loaded hydrogels for bone repair. The goal of this proposal is to combine LIPUS-generated acoustic radiation force and hydrogel-based cell therapy with the belief that both approaches together will enhance repair over either one alone. Using LIPUS- generated loading capable of imparting physical forces on cells, it is our intention to design hydrogel scaffolds that 1) are able to deliver encapsulated viable cells in vivo, 2) can be physically loaded by LIPUS generated acoustic radiation force after implantation and during the healing process and 3) can be modified to transfer varied physical forces from the hydrogel to cells such that healing would be optimized. The objectives of the present research are 1) to evaluate the effect of LIPUS-generated acoustic radiation force on cells embedded in hydrogels with increasing crosslinking densities, 2) to evaluate the effect of radiation force on cells encapsulated in collagen hydrogels of varying mechanical properties to determine the relationship between applied force and hydrogel stiffness on cell behavior, and 3) to use radiation force applied to hydrogels that have been loaded with cells and implanted in bone defect models. Implanted hydrogels containing cells will be loaded transdermally using acoustic radiation force. It is anticipated that the parameters defined in the in vitro studies will result in enhanced in vivo defect healing in hydrogels under acoustic radiation force when compared to either parameter alone.