Osteoinductive Injectable Degradable Polymeric Scaffold

描述(申请人提供)：可生物降解的聚合物支架可以注射到骨缺损处并原位交联，可以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脊柱后路融合。支架设计参数包括生物相容性、决定可注射性的流变性、降解率和最终产品、机械性能和骨诱导性。我们假设(1)含有不饱和双键的富马酸丙二酸酯(PPF)与主链上含有柔性聚己内酯大分子的新型聚己内酯(PCLF)在没有交联剂的情况下可以自交联形成互穿聚合物网络(IPN)，(2)使用可降解的水凝胶微球作为造孔方法，既改善了支架的可注入性，又消除了产生孔的淋滤技术所需的固体致孔剂扩散的步骤。(3)骨形态发生蛋白(BMP-2)从骨再生部位的支架中的控制输送可以被优化，以最大限度地利用该分子的骨诱导特性。因此，我们建议解决自交联性、降解性、可注射性和生长因子的受控传递等问题。在第一个目标中，将研究一种新型的PPF/PCLF互穿网络的自交联性和降解特性，以避免在可注射体系中使用交联剂。为此，我们还将合成天然和合成的可生物降解水凝胶作为造孔剂，以改善支架在注射过程中的流变性。第二个目标是将BMP-2包裹在可生物降解的PPF/PLGA共混微球中，将微球固定在IPN/水凝胶复合支架中，并研究其生长因子的释放动力学和生物活性。在第三个目标中，将通过测量骨髓基质细胞(MSC)在候选造孔剂中的体外迁移率来优化作为造孔剂的水凝胶的组成。利用MSCs的体外功能，优化BMP-2微球在复合支架中的载药量。这将通过测量MSC的增殖和碱性磷酸酶和骨钙素的分泌来实现，以响应从支架释放的BMP。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负载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.