Development of a biodegradable load-bearing DBM carrier

骨节段性缺损通常难以治疗，需要多期手术才能达到足够的愈合和功能。目前的治疗选择包括自体移植物、同种异体移植物和牵张成骨已经取得了成功，但仍有许多局限性。在治疗失败的情况下，替代治疗可能涉及严重的后果，如腿缩短或截肢。为了克服这些治疗方案的局限性，我们正在探索组织工程。组织工程方法使用可生物降解的支架来携带生物因子和/或细胞，以促进组织再生。这种方法在保护脚手架不受载荷的情况下是成功的。由于支架的力学性能相对较低，因此在载荷作用下支架的骨再生一直具有挑战性。在这个项目中，我们建议使用一种承重的、可生物降解的、携带脱矿骨基质（DBM）的载体来再生大节段性骨缺损。与传统多孔支架不同的是，可降解载体在初始愈合阶段可以通过髓内针稳定并参与承重功能。在提供生物力学稳定性和DBM输送后，载体将在稍后的时间降解。我们对这个建议的假设是：1。负重载体联合DBM可缩短大鼠股骨节段缺损骨愈合所需时间。2. 负重载体联合DBM对大鼠股骨缺损骨形成有促进作用。3. 负重载体联合DBM可改善大鼠股骨节段缺损再生后的最终力学性能。45只Long-Evans大鼠将被用来测试这些假设。可生物降解的载体将由聚（己内酯）三甲丙烯酸酯/磷酸三钙复合材料制成。将低剂量（0.05ml）和高剂量（0.3 ml）的腻子型DBM （DBX(r), Densply）掺入载体中。将载体植入大鼠股骨5毫米节段性缺损内24周。植入后1周、3周、6周、15周和24周用x线评估骨愈合时间。股骨将在植入24周后取出。采用双能x线吸收仪（DXA）测量骨矿物质含量（BMC; g），外周计算机断层扫描（pQCT）测量骨横截面积（CSA; mm2）、体积骨密度（vBMD; mg/cm3）和骨矿物质含量（BMC; mg/cm）。然后将标本包埋在石蜡中，脱钙，切片，并用McNeals四色染色和Safarin-0染色，交替进行骨和软骨切片。比较对照组与低剂量组、对照组与高剂量组的BMC、CSA和vBMD。每组10根大腿骨在材料试验机上进行四点弯曲弯曲强度测试。比较对照组和DBM处理组的极限力（Fu； N）、刚度（S; N/mm）和能量与极限力之比（U； N.mm）。

Segmental defects in bones often are difficult to manage and require multiple-phase surgery to achieve adequate union and function. Current treatment options including autografts, allografts, and distraction osteogenesis have brought forth successes, yet are still with many limitations. In case of treatment failure, alternative treatment may involve serious consequences such as leg shortening or amputation. To overcome the limitations in these treatment options, we are exploring tissue engineering. Tissue engineering approach uses a biodegradable scaffold to carry biological factors and/or cells to facilitate tissue regeneration. This approach has been successful when scaffold is protected from load bearing. Bone regeneration in scaffolds subjected to loading has been challenging due to the relatively low mechanical properties in scaffolds. In this project, we propose to regenerate bone in large segmental bone defects using a load-bearing, biodegradable carrier carrying demineralized bone matrix (DBM). Unlike traditional porous scaffolds, the degradable carrier can be stabilized by intramedullary pin and participate in load-bearing function in the initial healing phase. After providing biomechanical stability and DBM delivery, the carrier will degrade at a later time. The hypotheses we have for this proposal are: 1. Load-bearing carrier combined with DBM shortens the time required for bone union to take place in rat femoral segmental defects. 2. Load-bearing carrier combined with DBM improves bone formation in rat femoral segmental defects. 3. Load-bearing carrier combined with DBM improves final mechanical properties of the rat femur after segmental defect regeneration. Forty-five Long-Evans rats will be used to test the hypotheses. Biodegradable carriers will be manufactured from poly(caprolacton) trimethacrylate/tricalcium phosphate composites. Low (0.05ml) and high (0.3 ml) dose of putty type DBM (DBX(r), Densply) will be incorporated into the carrier. The carrier will be implanted in a 5 mm segmental defect in rat femurs for 24 weeks. The time for unions to occur will be evaluated with x-ray at week 1, 3, 6, 15 and 24 weeks after implantation. The femurs will be retrieved after 24 weeks of implantation. Five femurs from each group will be evaluated with dual energy X-ray absorptiometry (DXA) for bone mineral content (BMC; g) and with peripheral computed tomography (pQCT) for the bone cross sectionaj area (CSA; mm2), volumetric bone density (vBMD; mg/cm3), and bone mineral content (BMC; mg/cm). The specimens will then be embedded in paraffin, decalcified, sectioned, and stained with McNeals Tetrachrome and Safarin-0 in alternating sections for bone and cartilage. The BMC, CSA, and vBMD of control versus low dose and control versus high dose groups will be compared. Ten femurs from each group will be tested with four-point-bending on a material testing machine for bending strength. The ultimate force (Fu; N), stiffness (S; N/mm) and energy to ultimate force (U; N.mm) will be compared between the control and the DBM treated groups.