Osteoinductive Injectable Degradable Polymeric Scaffold

描述（由申请人提供）：可注射到骨缺损中并原位交联的生物可降解聚合物支架可为外科医生提供几种临床情况的微创治疗选择，其中包括节段性骨缺损和后路脊柱融合。支架设计参数包括生物相容性、决定可注射性的流变特性、降解速率和最终产物、机械特性和骨诱导性。我们假设：（1）通过聚乙烯的相互交联形成互穿聚合物网络（IPN（富马酸丙二醇酯）（PPF），其含有用于原位交联的不饱和双键，和一种新型聚（富马酸己内酯）（PCLF），其中含有柔性聚（己内酯）大分子单体，可以在不存在交联剂的情况下自交联，（2）使用可降解的水凝胶微球作为孔隙产生方法将改善支架的可注射性并消除用于孔产生的浸出技术中所需的固体致孔剂从支架扩散的步骤，和（3）骨形态发生蛋白（BMP-2）从支架在骨再生部位的受控递送可以被优化以最大限度地利用该分子的骨诱导性质。因此，我们建议解决生长因子的自交联、降解、注射性和受控递送等问题。在第一个目标中，将研究新型PPF/PCLF IPN的自交联和降解特性，以消除在注射系统中使用交联剂。在这个目标中，我们还将合成天然和合成的可生物降解的水凝胶，用作致孔剂，以改善支架在注射过程中的流变性能。第二个目标是将BMP-2包埋在可生物降解的PPF/PLGA共混微球中，将微球固定在IPN/水凝胶复合支架中，研究BMP-2的释放动力学及其生物活性。在第三个目标中，作为致孔剂的水凝胶的组成将通过测量骨髓基质细胞（MSC）通过候选致孔剂的体外迁移速率来优化。利用MSCs在体外的功能，优化复合支架中BMP-2微球的负载量。这将通过测量MSC的增殖和碱性磷酸酶和骨钙素两者的分泌来响应从支架释放的BMP而发生。在第四个目标中，将使用大鼠节段性缺损模型和兔后外侧脊柱融合模型来评估具有负载的BMP-2微球的IPN/水凝胶复合支架在体内诱导骨形成的能力。

DESCRIPTION (provided by applicant): Biodegradable polymeric scaffolds that can be injected into a bone defect and crosslinked in situ may provide surgeons with minimally invasive treatment options for several clinical situations, among them segmental skeletal defects and posterior spinal fusion. Scaffold design parameters include biocompatibility, rheologic properties that determine injectability, degradation rate and end products, mechanical properties, and osteoinductivity. We hypothesize that (1) interpenetrating polymer networks (IPN) formed by inter-crosslinking of poly(propylene fumarate) (PPF), which contains unsaturated double bonds for in situ crosslinking, and a novel poly(caprolactone fumarate) (PCLF), which contains flexible poly(caprolactone) macromers in its backbone, may self-crosslink in the absence of a crosslinking agent, (2) the use of degradable hydrogel microspheres as the porosity generating method would both improve the scaffold's injectability and eliminate the step of solid porogen diffusion from the scaffold needed in leaching techniques for pore generation, and (3) controlled delivery of bone morphogenic protein (BMP-2) from the scaffold at the bone regeneration site could be optimized to take maximum advantage of this molecule's osteoinductive properties. Therefore, we propose to address the issues of self-crosslinking, degradation, injectability, and controlled delivery of growth factors. In the first aim, the self-crosslinking and degradation characteristics of a novel PPF/PCLF IPN will be investigated to eliminate the use a crosslinking agent in injectable systems. In this aim, we will also synthesize natural and synthetic biodegradable hydrogels for use as porogens to improve the scaffold's rheological properties during injection. In the second aim, BMP-2 will be encapsulated in biodegradable PPF/PLGA blend microspheres, the microspheres will be immobilized in the IPN/hydrogel composite scaffold, and we will study the release kinetics of the growth factor as well as its bioactivity. In the third aim, the composition of the hydrogel as the porogen will be optimized by measuring the in vitro migration rate of marrow stromal cells (MSC) through candidate porogens. The function of MSCs in vitro will be used to optimize the loading dose of BMP-2 microspheres in the composite scaffold. This will occur by measuring the MSC's proliferation and secretion of both alkaline phosphatase and osteocalcin in response to BMP released from the scaffold. In the fourth aim, a rat segmental defect model and a rabbit posterolateral spine fusion model will be used to assess the ability of the IPN/hydrogel composite scaffold with loaded BMP-2 microspheres to induce bone formation in vivo.