Tissue Engineering Strategies to Revitalize Bone Allografts

描述(由申请人提供)：由于先天性畸形、创伤、感染和肿瘤切除而导致的骨缺损重建的选择有限。每年有近100万例骨移植手术，临床上的“黄金标准”是使用脱细胞同种异体骨移植。在这些同种异体移植手术中，近60%的移植手术在植入后10年内失败，原因是移植物-宿主整合不良和微裂纹扩展。与同种异体移植物不同，自体移植物在骨膜的介导下完全愈合并整合在骨周围的薄层组织和骨膜细胞(PC)中，其中的愈合由包括基质和旁分泌因素在内的各种背景线索来协调。在自体移植物愈合期间仅存活约21天的PC，其表型类似于骨髓来源的间充质干细胞(MSCs)。然而，在治疗方面，与PC相比，MSCs更受青睐，因为它们是从骨髓中分离出来的，减少了PC分离导致的骨组织发病率。在识别协调自体移植物愈合的关键线索(旁分泌因子、基质相互作用等)方面存在着关键的知识缺口，而同种异体移植物中缺乏这些关键提示，阻碍了有效振兴同种异体移植物的治疗方法的转化。我们的目标是开发由合成水凝胶(聚乙二醇)组成的骨膜模拟物用于骨髓间充质干细胞移植，以(1)促进细胞介导的同种异体移植物的愈合/整合，(2)分离骨膜愈合中的关键因素，以及(3)开发导致同种异体移植物完全愈合和整合的无细胞疗法。水凝胶将被用来包围同种异体移植物，利用同种异体移植物的结构完整性，并通过重建骨膜来改善愈合和整合不足的地方。我们假设，水凝胶纳米结构可以通过改变降解和生化功能来促进MSC介导的同种异体移植物愈合和整合。我们进一步假设，MSCs通过简单地释放旁分泌因子来促进愈合，因此，可以开发无细胞振兴方法。这项工作的基本原理是根据关键的愈合因素确定可翻译的疗法，以改善美国每年进行的30万次大规模同种异体移植手术的愈合和整合。目标1：开发模拟骨膜的聚乙二醇水凝胶，以支持体内MSC介导的同种异体移植物愈合。目的2：确定水凝胶移植骨髓间充质干细胞产生的调节同种异体移植物愈合的关键旁分泌因子。目的3：研制旁分泌因子释放水凝胶，以增强同种异体移植物在无细胞移植情况下的活力。这些目标的成功实现将极大地促进我们对MSCs如何协调同种异体移植物的愈合和整合以及如何设计合成聚合物支架以促进自然骨再生过程的理解。这种材料平台应该容易地为骨以外的组织再生应用而定制，并为未来细胞输送载体的设计提供特定的优势。

DESCRIPTION (provided by applicant): There are limited options for reconstruction of bone defects resulting from congenital anomaalies, trauma, infection, and oncologic resection. Nearly one million bone graft procedures are performed annually, with the clinical 'gold standard' being the use of decellularized allografts. Of these allograft implantation procedures, nearly 60% fail within 10 years of implantation due to poor graft-host integration and microcrack propagation. Unlike allografts, autografts fully heal and integrate, mediated by the periosteum, a thin layer of tissue and periosteal cells (PCs) surrounding bone, where healing is coordinated by a variety of contextual cues including matrix and paracrine factors. PCs, which persist during autografts healing for only ~21 days, are phenotypically similar to bone marrow-derived mesenchymal stem cells (MSCs). Therapeutically, however, MSCs are favored compared to PCs as they are isolated from bone marrow, reducing bone tissue morbidity resulting from PC isolation. A critical knowledge gap exists in identifying the critical cues (paracrine factors, matrix interactions, etc. that orchestrate autograft healing and are absent in allografts, preventing the translation of therapies to effectively revitalize allografts. Our objective is to develop periosteum mimetics composed of synthetic hydrogels (poly(ethylene glycol), PEG) for MSC transplantation to (1) promote cell-mediated allograft healing/integration, to (2) isolate the critical factors of the periosteum in healing, and to (3) develop cell-free therapies that result in complete allograft healing and integration. Hydrogels will be used to surround allografts, taking advantage of structural integrity of allografts and improving what is insufficient in healing and integration by recreating the periosteum. We hypothesize that hydrogel nanoarchitectures can be tuned through alterations in degradation and biochemical functionalities to promote MSC-mediated allograft healing and integration. We further hypothesize that MSCs promote healing through simple release of paracrine factors, thus, cell-free revitalization approaches can be developed. The rationale for this work is to identify translatable therapies, based on critical healing factor, to improve healing and integration of the 300,000 massive allograft procedures performed annually in the US. Three specific aims are outlined: Aim 1: Develop periosteum- mimetic PEG hydrogels to support MSC-mediated allograft healing in vivo. Aim 2: Identify critical paracrine factors produced by hydrogel-transplanted MSCs that modulate allograft healing. Aim 3: Develop paracrine factor-releasing hydrogels to enhance allograft revitalization in the absence of cell transplantation. Successful completion of these Aims will significantly advance our understanding of how MSCs coordinate allograft healing and integration and of how to design synthetic polymer scaffolds to promote natural bone regeneration processes. This material platform should be readily tailored for applications towards regenerating tissues beyond bone, as well as providing specific advantages for future directions in the design of cell delivery vehicles.