Institute of Biomaterials and Biomedical Engineering, University of Toronto, Canada.
J Tissue Eng Regen Med. 2011 Feb;5(2):119-29. doi: 10.1002/term.296.
A major obstacle in tissue engineering is overcoming hypoxia in thick, three-dimensional (3D) engineered tissues, which is caused by the diffusional limitations of oxygen and lack of internal vasculature to facilitate mass transfer. Modular tissue engineering is a bio-mimetic strategy that forms scalable, vascularized and uniform 3D constructs by assembling small (sub-mm), cell-containing modules. It was previously assumed that mass transfer resistance within the individual modules was negligible, due to their small size. In the present study, this assumption was tested using theoretical analysis of oxygen transport within the module (effectiveness factor) and experimental studies. Small (400 µm diameter post-contraction) and large (700 µm diameter post-contraction) HepG2-collagen modules were made for a range of seeding densities (2 × 10(6) -1 × 10(7) cells/ml collagen). Cell density, distribution and morphology within the modules showed that the small modules were capable of sustaining high cell densities (8.0 × 10(7) ± 4.4 × 10(7) cells/cm(3) ) with negligible mass transfer inhibition. Conversely, large modules developed a necrotic core and had significantly (p < 0.05) reduced cell densities (1.5 × 10(7) ± 9.2 × 10(6) cells/cm(3) ). It was also observed that the embedded cells responded quickly to the oxygen availability, by proliferating or dying, to reach a sustainable density of approximately 8000 cells/module. Furthermore, a simple effectiveness factor calculation was successful in estimating the maximum cell density per module. The results gathered in this study confirm the previous assumption that the small-diameter modules avoid the internal mass transfer limitations that are often observed in larger constructs.
组织工程中的一个主要障碍是克服厚的三维（3D）工程组织中的缺氧，这是由氧气的扩散限制和缺乏内部脉管系统来促进质量传递引起的。模块化组织工程是一种仿生策略，通过组装小（亚毫米）、含细胞的模块来形成可扩展的、血管化的和均匀的 3D 结构。以前假设由于模块的小尺寸，单个模块内的质量传递阻力可以忽略不计。在本研究中，通过对模块内氧传递的理论分析（有效因子）和实验研究来检验这一假设。为了一系列的接种密度（2×10^6-1×10^7 个细胞/ml 胶原蛋白），制作了小（收缩后直径 400μm）和大（收缩后直径 700μm）HepG2-胶原蛋白模块。模块内的细胞密度、分布和形态表明，小模块能够维持高细胞密度（8.0×10^7±4.4×10^7 个细胞/cm^3），几乎没有质量传递抑制。相反，大模块形成了坏死核心，细胞密度显著降低（1.5×10^7±9.2×10^6 个细胞/cm^3）（p<0.05）。还观察到，嵌入的细胞对氧气的可用性迅速做出反应，通过增殖或死亡，达到大约 8000 个细胞/模块的可持续密度。此外，简单的有效因子计算成功地估计了每个模块的最大细胞密度。本研究的结果证实了以前的假设，即小直径模块避免了在较大构建体中经常观察到的内部质量传递限制。
