Tissue Engineering Strategies to Revitalize Bone Allografts

描述（由申请人提供）：由于先天性异常，创伤，感染和肿瘤切除导致的骨缺损的重建选择有限。每年进行近100万例骨移植手术，临床“金标准”是使用脱细胞异体移植物。在这些同种异体移植物植入过程中，由于移植物与宿主融合不良和微裂纹扩展，近60%的移植物在植入10年内失败。与同种异体移植物不同，自体移植物完全愈合和整合，由骨膜介导，骨膜是骨周围的薄层组织和骨膜细胞（PCs），其中愈合由各种环境因素协调，包括基质和旁分泌因素。PCs在自体移植物愈合过程中仅持续约21天，其表型与骨髓来源的间充质干细胞（MSCs）相似。然而，在治疗上，与骨髓干细胞相比，MSCs更受青睐，因为它们是从骨髓中分离出来的，减少了骨髓干细胞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）方面存在关键的知识缺口，而这些线索在同种异体移植物中却不存在，这阻碍了治疗方法的转化，从而有效地使同种异体移植物恢复活力。我们的目标是开发由合成水凝胶（聚乙二醇，PEG）组成的模拟骨膜，用于MSC移植，以：(1)促进细胞介导的同种异体移植物愈合/整合，(2)分离骨膜愈合的关键因素，以及(3)开发无细胞疗法，导致完全的同种异体移植物愈合和整合。水凝胶将用于同种异体移植物的周围，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融合不足的地方。我们假设水凝胶纳米结构可以通过降解和生化功能的改变来调节，以促进msc介导的同种异体移植物愈合和整合。我们进一步假设MSCs通过简单释放旁分泌因子促进愈合，因此可以开发无细胞再生方法。这项工作的基本原理是确定基于关键愈合因子的可翻译疗法，以改善美国每年30万例大规模同种异体移植手术的愈合和整合。概述了三个具体目标：目标1：开发骨膜模拟PEG水凝胶，以支持msc介导的同种异体移植物体内愈合。目的2：确定水凝胶移植的间充质干细胞产生的调节同种异体移植愈合的关键旁分泌因子。目的3：开发旁分泌因子释放水凝胶，在没有细胞移植的情况下增强同种异体移植物的再生。这些目标的成功完成将极大地促进我们对间充质干细胞如何协调同种异体移植物愈合和整合以及如何设计合成聚合物支架来促进自然骨再生过程的理解。这种材料平台可以很容易地用于骨外组织的再生，并为未来设计细胞递送载体的方向提供特定的优势。

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.