Tissue Engineering Strategies to Revitalize Allografts

由于先天性异常、创伤、 感染和肿瘤切除。全世界每年进行超过200万例骨移植手术， 临床的“金标准”是使用自体移植物。自体移植物完全愈合和整合，由 骨膜，一薄层组织和骨膜细胞（PC）围绕骨。然而，自体移植物是有限的， 由于组织可用性和供体部位发病率。因此，通常采用脱细胞同种异体移植物。 然而，缺乏骨膜的同种异体移植物重塑和与宿主组织整合的能力有限 直接导致植入后2年和10年内约35%和60%的失败率。骨膜介导 愈合是由各种背景线索协调的，包括基质重塑和粘附， 旁分泌因子的明确释放。我们的总体假设是同种异体移植物的愈合将显著 通过捕获组织工程骨膜（TEP）中的关键愈合线索来改善。在第一个供资周期， 我们率先开发了TEP，它将间充质干细胞（MSC）和OP整合在 - 可水解降解的聚（乙二醇）（PEG）基水凝胶，其在同种异体移植物周围形成， 类似于天然骨膜。TEP显示出增强小鼠同种异体移植物愈合的突出前景， 植入后9周，与未修饰同种异体移植物相比，最大骨折扭矩增加300%。 然而，愈合受到纤维化组织的困扰，这导致同种异体移植物仅为自体移植物的约50 最大扭矩纤维化与宿主血管/组织对TEP浸润的不良支持一致， 由大量水解TEP降解导致的限制，其导致结构上的不相容性，以支持 完全的宿主组织浸润因此，这种更新的焦点是细胞重塑的TEP， 局部的、细胞需要的降解，同时保持大体积水凝胶性质以支持宿主组织 浸润概述了三个具体目标：具体目标1：调节TEP基质线索（粘附肽和 MMP-可降解交联），以协调组织浸润和改善同种异体移植物愈合。具体目标二： 表征TEP介导的宿主组织募集。具体目标3：利用优化的TEP矩阵提供 肽模拟骨膜旁分泌线索作为一个可翻译的，非细胞TEP。成功完成这些 目的将显著提高我们对骨膜如何协调同种异体骨愈合和移植物愈合的理解。 设计工程骨膜以促进这些骨再生过程。开发的材料 平台和一般方法也可容易地应用于其它组织工程应用。

There are limited options for reconstruction of bone defects resulting from congenital anomalies, trauma, infection, and oncologic resection. Over 2 million bone graft procedures are performed annually worldwide, with the clinical ‘gold standard’ being the use of autografts. Autografts fully heal and integrate, mediated by the periosteum, a thin layer of tissue and periosteal cells (PCs) surrounding bone. However, autografts are limited due to tissue availability and donor site morbidity. Thus, decellularized allografts are commonly employed. However, the limited ability of allografts, which lack periosteum, to remodel and integrate with the host tissue directly contributes to ~35% and 60% failure rates within 2 and 10 years of implantation. Periosteal-mediated healing is coordinated by a variety of contextual cues including matrix remodeling and adhesion and temporally defined release of paracrine factors. Our overarching hypothesis is that allograft healing will be dramatically improved by capturing critical healing cues in a tissue engineered periosteum (TEP). In the first funding cycle, we pioneered development of the TEP, which incorporates mesenchymal stem cells (MSCs) and OPs within hydrolytically degradable poly(ethylene glycol)(PEG)-based hydrogels, which are formed around allografts, similar to native periosteum. TEP shows outstanding promise to enhance murine allograft healing, resulting in a 300% increase in maximum fracture torque versus unmodified allografts at 9 weeks post-implantation. However, healing was plagued by fibrotic tissue, which results in the allograft limited to ~50% of autograft maximum torque. Fibrosis is consistent with poorly supported infiltration of TEP by host vessel/tissue, a limitation resulting from bulk hydrolytic TEP degradation which results in structural insufficiencies to support complete host-tissue infiltration. Thus, the focus of this renewal is a cellularly remodeled TEP, which enables localized, cell-demanded degradation while maintaining bulk hydrogel properties to support host-tissue infiltration. Three specific aims are outlined: Specific Aim 1: Tune TEP matrix cues (adhesive peptides and MMP-degradable crosslinks) to coordinate tissue infiltration and improve allograft healing. Specific Aim 2: Characterize TEP-mediated host-tissue recruitment. Specific Aim 3: Exploit the optimized TEP matrix to deliver peptides emulating periosteal paracrine cues as a translatable, acellular TEP. Successful completion of these Aims will significantly advance our understanding of how the periosteum coordinates allograft healing and the design of engineered periosteum to promote these bone regeneration processes. The developed material platforms and general approach are also readily applicable in other tissue engineering applications.