Mechanically Stiff Hydrogels for Osteochondral Tissue Engineering

虽然水凝胶提供了一种简便的细胞原位传递方法，但它们不利于同时 耐受关节中的巨大力量(需要高模数)并促进干细胞分化 (需要低模数)。此外，脚手架与相邻脚手架之间的力学性能不匹配 组织会导致机械失稳，并最终导致周围关节组织的退化。这 指出需要一种机械坚固的脚手架，能够承受正常的关节载荷。在骨软骨中 组织、细胞驻留在它们自己的小环境中，并在很大程度上受到细胞外基质的保护，不受大力的影响。 提出的组织工程解决方案在于模仿大自然对这一复杂问题的解决方案。 具体地说，我们将把结构(即承载)组件从我们的 水凝胶设计。坚硬的、功能梯度的、承重的结构水凝胶组件将经受住 大的力，并将适当的应变(即，机械信号)传递到每个细胞生态位。独立地， 三个细胞壁龛将捕捉与钙化的透明软骨相适应的化学物质和降解 软骨和骨头。当与从结构传递机械提示的动态加载相结合时 每个细胞生态位，干细胞介导的OC组织再生将会实现。我们的方法是 通过数字投影光刻和高度可调的光点击使能技术成为可能 水凝胶。因此，这项研究的首要假设是：结构僵化，功能分级 嵌入在含有干细胞的软材料中的材料支持正常的关节载荷，将损害降至最低 到周围组织，并促进OC组织再生。为了验证这一假设，我们概述了 三个具体目标。在具体目标#1中，我们将设计建筑控制的3D OC模拟水凝胶 支持与体内天然OC组织相似的应力并将适当的应变传递到每一层OC组织的材料 OC模拟水凝胶。我们将测试一种无细胞和机械稳定的OC模拟水凝胶的能力 以最大限度地减少对猪膝关节OC缺损区周围组织的损害。在具体目标2中，我们将调查 骨髓间充质干细胞在软组织成分中的诱导分化和OC组织再生 它的设计具有适合每个OC利基的生化和机械线索，并在定制中培养 模拟体内负载环境的生物反应器。在具体目标3中，可降级和 将含有自体骨髓间充质干细胞的机械刚性OC模拟水凝胶植入猪OC膝关节缺损处 12周，并评估工程化OC组织和对缺损区周围组织的损害。vt.在.的基础上 完成这个项目，我们希望已经展示了一种机械僵硬的水凝胶与胶囊 骨髓间充质干细胞能够(A)承受较大的力，(B)促进干细胞介导的OC组织再生和 (C)维持缺陷周围组织的健康。从长远来看，我们正在开发一种小型化 以及便携式打印技术，外科医生可以通过关节镜平台轻松获得。

While hydrogels offer a facile method for in situ delivery of cells, they are not conducive to simultaneously withstanding the large forces found in joints (requiring high moduli) and promoting stem cell differentiation (requiring low moduli). Moreover, a mismatch in mechanical properties between scaffold and the adjacent tissue can lead to mechanical destabilization and eventually degeneration in the surrounding joint tissue. This points to the need for a mechanically robust scaffold that can withstand normal joint loads. In osteochondral tissues, cells reside in their own niche and are largely protected from large forces by the extracellular matrix. The proposed tissue engineering solution lies in mimicking nature's solution to this complex problem. Specifically, we will decouple the structural (i.e., load-bearing) component from the cellular niche within our hydrogel design. A stiff and functionally graded, load-bearing structural hydrogel component will withstand large forces and transfer appropriate strains (i.e., mechanical signals) to each cellular niche. Independently, three cellular niches will capture chemistries and degradation appropriate to hyaline cartilage, calcified cartilage and bone. When combined with dynamic loading that transfers mechanical cues from the structural component to each cellular niche, stem cell mediated OC tissue regeneration will be achieved. Our approach is possible by the enabling technologies of digital projection photolithography and highly tunable photoclickable hydrogels. Thus the overarching hypothesis for this research is: a structurally stiff and functionally graded material embedded within a soft material containing stem cells supports normal joint loads, minimizes damage to the surrounding tissue, and promotes OC tissue regeneration. To test this hypothesis, we have outlined three specific aims. In specific aim #1, we will design architecturally-controlled 3D OC mimetic hydrogel materials to support stresses similar to native OC tissue in vivo and transfer appropriate strains to each layer of the OC mimetic hydrogel. We will test the ability of an acellular and mechanically stable OC mimetic hydrogel to minimize damage to tissue surrounding an OC defect in swine knees. In specific aim #2, we will investigate MSC differentiation and OC tissue regeneration when MSCs are incorporated in the soft cellular component that is designed with biochemical and mechanical cues appropriate to each OC niche and cultured in custom bioreactors that mimic aspects of the in vivo loading environment. In specific aim #3, degradable and mechanically stiff OC mimetic hydrogels with autologous MSCs will be implanted in a swine OC knee defect for 12 weeks and evaluated for engineered OC tissue and damage to tissues surrounding the defect. Upon completion of this project, we expect to have demonstrated a mechanically stiff hydrogel with encapsulated MSCs is capable of (a) withstanding large forces, (b) promoting stem cell mediated OC tissue regeneration and (c) maintaining the health of the tissue surrounding the defect. Long-term, we are developing a miniaturized and portable printing technology that will be easily accessible to surgeons via an arthroscopic platform.