Optimizing Nutrient Supply in Large Engineered Cartilage Tissue Constructs

描述(由申请人提供)：骨关节炎(OA)是一种衰弱的退行性疾病，估计有2700万25岁及以上的美国人患有此病。这种疾病导致腹股沟关节的关节层进行性退化，显著损害作为承重材料的软骨的主要功能，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，作为一种方式，极大地扩大了这种疾病有限的治疗选择。虽然软骨退变偶尔局限于关节层内的小灶区，但当退化扩散到更大的表面区(如关节层的25%以上)时，骨关节炎通常会出现症状。不幸的是，大型软骨结构的功能组织工程在很大程度上受到营养运输和消耗平衡的限制。一些研究表明，基质沉积和功能特性的形成优先发生在结构的外围，那里来自周围培养介质的营养供应最丰富，而内部细胞获得的营养物质较少，产生的基质较少，功能特性较差。在这一应用中，提出了一种工程解决方案，通过优化整个构造层的狭窄通道的数量和间距，为大型工程化软骨构建提供充足的营养，从而概括了软骨通道在发育早期提供的营养供应。渠道在不同维度的结构中的放置必须进行优化，以平衡相互竞争的需求：增加渠道密度在逻辑上会增加总的营养供应，使其更均匀地分布在整个结构中。然而，通道密度的增加可能会有效地降低细胞密度，并增加合成的基质产物在与细胞外基质结合之前丢失的途径。这种类型的优化分析，其中相互竞争的需求必须得到平衡，非常适合于一种工程方法，该方法解释了调节组织生长的主要机制。这项工程技术的发展将通过四个具体目标进行：(1)将现有模型中的溶质扩散/结合/消耗和组织生长方程应用到定制的有限元软件中，用于组织工程构造的分析。(2)对工程化软骨的营养供应和基质生长模型所需参数进行实验表征。(3)利用这些计算工具和实验数据，对大型圆柱形和髌骨状关节层结构中的通道布置进行了优化分析。(4)使用理论上最优(N)和次优(N/2和2N)的通道数以及无通道控制来培养大型构建物；比较基质沉积和功能特性以测试N是最佳值；必要时改进模型。 公共卫生相关性：膝关节和髋关节的骨关节炎(OA)最常与关节层相对较大区域的软骨丢失有关。骨性关节炎患者的治疗选择有限：早期干预主要针对疼痛管理，而晚期疾病通常采用关节置换治疗，这种治疗受到患者预期寿命与植入物存活率的限制。软骨组织工程提供了一个机会，提供一种生物植入物作为一种中间治疗方式，遵循保守的疼痛治疗，但推迟(或可能消除)关节置换的需要。在这项申请中提出的技术将促进大软骨组织结构的工程化，所需的软骨组织结构用于修复骨关节炎关节的表面缺陷。

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.