Transdermal Mechanical Loading for Cell Therapy-Based Bone Repair

骨修复的细胞疗法结合水凝胶，具有非常高的交联聚合物链网络 水含量，作为基于支架的组织工程的潜在替代方案，正在被越来越多的人接受， 尤其是对于可以通过微创方法治疗的较小规模的缺陷。注射细胞 在临床上，小切口植入骨缺损可能比更具侵入性的外科手术更可取。 已注明。一旦到达缺陷部位，细胞在水凝胶中基本上不受干扰，就像缺陷本身一样 需要稳定才能治愈，这一要求违背了 物理负载骨形成细胞。正是这种矛盾推动了本提案中概述的工作。 非侵入性、低强度脉冲超声已被证明是有效的经皮治疗 新鲜骨折(临床和放射学愈合时间缩短38%)和骨折不愈合。而当 LIPUS的作用机制尚不清楚，我们已经开发出一种高度可调的超声波 在临床相关超声强度下演示可测量的声辐射力的系统，以及 已经证明这种力能够在物理上使细胞和水凝胶偏转。然而到目前为止， Lipus产生的声辐射力还没有与细胞负载水凝胶配对用于骨修复。 该方案的目标是将LIPUS产生的声辐射力和基于水凝胶的细胞相结合 治疗，相信这两种方法一起使用将比单独使用其中任何一种方法更能促进修复。使用LIPUS- 能够对细胞施加物理力的产生载荷，这是我们设计水凝胶支架的意图 1)能够在体内运送封装的活细胞，2)可以通过LIPUS产生的物理负载 植入后和愈合过程中的声辐射力以及3)可以修改以传递 从水凝胶到细胞的不同物理作用力，从而使愈合得到优化。 本研究的目的是：1)评估LIPUS产生的声辐射的影响 随着交联度的增加，包埋在水凝胶中的细胞所受的力，2)评估 不同力学性质的胶原水凝胶包裹细胞的辐射力 外力与水凝胶硬度对细胞行为的影响；3)外加辐射力 到已经装载了细胞并植入骨缺损模型的水凝胶。植入水凝胶 含有细胞的细胞将使用声辐射力经皮加载。据预计， 体外研究中定义的参数将导致水凝胶在以下条件下体内缺陷愈合的增强 单独与任一参数比较时的声辐射力。

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.