Optimizing Nutrient Supply in Large Engineered Cartilage Tissue Constructs

描述（由申请人提供）：骨关节炎（OA）是一种使人衰弱的退行性疾病，折磨着大约2700万25岁及以上的美国人。这种疾病导致腹泻关节关节层的进行性退化，严重损害软骨作为承重材料的主要功能，导致疼痛和限制日常生活活动。软骨功能组织工程是一项非常有前途的技术，旨在为磨损的关节层提供生物替代品，作为一种模式，大大扩展了治疗这种疾病的有限选择。虽然软骨退行性变偶尔局限于关节层内的小病灶区域，但当退行性变扩散到更大的表面区域（如大于关节层的25%）时，OA通常会出现症状。不幸的是，大型软骨结构的功能性组织工程明显受到营养运输和消耗平衡的限制。几项研究表明，基质沉积和功能特性的形成优先发生在结构体的外围附近，那里来自周围培养基的营养供应最丰富，而内部细胞接受的营养较少，产生的基质较少，功能特性较差。在本应用中，提出了一种工程解决方案，通过优化通过全层构建层的窄通道的数量和间距，为大型工程软骨构建体提供充足的营养，从而概括了软骨管道在早期发育期间提供的营养供应。必须优化各种尺寸结构中的通道位置，以平衡竞争需求：增加通道密度从逻辑上讲会增加总营养供应，使其更均匀地分布在整个结构中。然而，通道密度的升高可能会有效地降低细胞密度，并增加合成基质产物在与细胞外基质结合之前的损失途径。这种类型的优化分析，其中竞争需求必须得到平衡，非常适合工程方法，说明调节组织生长的主要机制。该工程技术的发展将通过四个具体目标进行：(1)将溶质扩散/结合/消耗和组织生长方程从现有模型实现到定制编写的有限元软件中，用于分析组织工程结构。(2)实验表征了模拟工程软骨中营养供应和基质生长所需的参数。(3)利用这些计算工具和实验数据对大型圆柱形和髌骨形关节层结构的通道放置进行优化分析。(4)使用理论上最优(N)和次优（N/2和2N）通道数以及无通道控制培养大型构建体；对比基体沉积和功能性能，N为最优值；必要时改进模型。

DESCRIPTION (provided by applicant): Osteoarthritis (OA) is a debilitating degenerative disease that afflicts an estimated 27 million Americans age 25 and older. This disease leads to the progressive degradation of the articular layers of diarthrodial joints, significantly compromising the main function of cartilage as a load bearing material, leading to pain and limiting activities of daily living. Cartilage functional tissue engineering is a highly promising technology that aims to provide a biological replacement to worn articular layers, as a modality that considerably expands the limited options in the treatment of this disease. Though cartilage degeneration is occasionally limited to small focal areas within articular layers, OA generally becomes symptomatic when degradation has spread over much greater surface areas (such as greater than 25 percent of the articular layer). Unfortunately, functional tissue engineering of large cartilage constructs is significantly constrained by the balance of nutrient transport and consumption. Several studies have shown that matrix deposition and elaboration of functional properties preferentially occurs near the periphery of constructs, where nutrient supply from the surrounding culture medium is most abundant, whereas cells in the interior receive less nutrients and produce less matrix, with poorer functional properties. In this application, an engineering solution is proposed for the technical challenge of supplying plentiful nutrients for large engineered cartilage constructs by optimizing the number and spacing of narrow channels through the full thickness of construct layers, thus recapitulating the nutrient supply provided by cartilage canals during early development. The placement of channels in constructs of various dimensions must be optimized to balance competing needs: Increasing the channel density would logically increase the total nutrient supply, spreading it more evenly across the entire construct. However, an elevated channel density may effectively decrease the cell density and increase the pathways for loss of synthesized matrix products before they bind to the extracellular matrix. This type of optimization analysis, where competing needs must be balanced, is very well suited for an engineering approach that accounts for the dominant mechanisms regulating tissue growth. The development of this engineering technology will proceed through four specific aims: (1) Implement solute diffusion/binding/consumption and tissue growth equations from existing models into custom-written finite element software for the analysis of tissue engineered constructs. (2) Experimentally characterize the parameters needed for modeling nutrient supply and matrix growth in engineered cartilage. (3) Use these computational tools and experimental data to perform the optimization analysis for channel placement in large cylindrical and patella-shaped articular layer constructs. (4) Culture large constructs using theoretically optimal (N) and sub-optimal (N/2 and 2N) number of channels, as well as channel-free controls; compare matrix deposition and functional properties to test that N is the optimal value; refine model if necessary. PUBLIC HEALTH RELEVANCE: Osteoarthritis (OA) of the knee and hip is most often associated with loss of cartilage over relatively large regions of the articular layers. OA patients have limited treatment options: Early interventions mostly address pain management, whereas advanced stages of the disease are generally treated with joint replacement, a treatment constrained by the life expectancy of patients in relation to the survival rate of implants. Cartilage tissue engineering offers an opportunity to provide a biological implant as an intermediate treatment modality that follows conservative pain management but postpones (or possibly eliminates the need for) joint replacement. The technology proposed in this application will facilitate engineering of large cartilage tissue constructs needed to resurface defects in OA joints.