Tiruvannamalai Annamalai Ramkumar, Rioja Ana Y, Putnam Andrew J, Stegemann Jan P
Department of Biomedical Engineering, University of Michigan, Ann Arbor.
ACS Biomater Sci Eng. 2016 Nov 14;2(11):1914-1925. doi: 10.1021/acsbiomaterials.6b00274. Epub 2016 Sep 27.
Microvascular endothelial cells (MVEC) are a preferred cell source for autologous revascularization strategies, since they can be harvested and propagated from small tissue biopsies. Biomaterials-based strategies for therapeutic delivery of cells are aimed at tailoring the cellular microenvironment to enhance the delivery, engraftment, and tissue-specific function of transplanted cells. In the present study, we investigated a modular tissue engineering approach to therapeutic revascularization using fibrin-based microtissues containing embedded human MVEC and human fibroblasts (FB). Microtissues were formed using a water-in-oil emulsion process that produced populations of spheroidal tissue modules with a diameter of 100-200 µm. The formation of MVEC sprouts within a fibrin matrix over 7 days in culture was dependent on the presence of FB, with the most robust sprouting occurring at a 1:3 MVEC:FB ratio. Cell viability in microtissues was high (>90%) and significant FB cell proliferation was observed over time in culture. Robust sprouting from microtissues was evident, with larger vessels developing over time and FB acting as pericyte-like cells by enveloping endothelial tubes. These neovessels were shown to form an interconnected vascular plexus over 14 days of culture when microtissues were embedded in a surrounding fibrin hydrogel. Vessel networks exhibited branching and inosculation of sprouts from adjacent microtissues, resulting in MVEC-lined capillaries with hollow lumens. Microtissues maintained in suspension culture aggregated to form larger tissue masses (1-2 mm in diameter) over 7 days. Vessels formed within microtissue aggregates at a 1:1 MVEC:FB ratio were small and diffuse, whereas the 1:3 MVEC:FB ratio produced large and highly interconnected vessels by day 14. This study highlights the utility of human MVEC as a cell source for revascularization strategies, and suggests that the ratio of endothelial to support cells can be used to tailor vessel characteristics. The modular microtissue format may allow minimally invasive delivery of populations of prevascularized microtissues for therapeutic applications.
微血管内皮细胞（MVEC）是自体血管再生策略中一种理想的细胞来源，因为它们可以从小组织活检中获取并增殖。基于生物材料的细胞治疗递送策略旨在调整细胞微环境，以增强移植细胞的递送、植入和组织特异性功能。在本研究中，我们研究了一种模块化组织工程方法，用于使用含有嵌入式人MVEC和人成纤维细胞（FB）的纤维蛋白基微组织进行治疗性血管再生。微组织通过油包水乳液工艺形成，产生直径为100 - 200 µm的球形组织模块群体。在培养7天内，纤维蛋白基质中MVEC芽的形成依赖于FB的存在，在MVEC:FB比例为1:3时芽生最为旺盛。微组织中的细胞活力很高（>90%），并且在培养过程中观察到FB细胞有显著增殖。微组织有明显的旺盛芽生，随着时间的推移会形成更大的血管，并且FB通过包裹内皮管起到类周细胞的作用。当微组织嵌入周围的纤维蛋白水凝胶中培养14天时，这些新血管形成了一个相互连接的血管丛。血管网络表现出相邻微组织芽的分支和吻合，形成具有中空管腔的MVEC内衬毛细血管。悬浮培养的微组织在7天内聚集形成更大的组织块（直径1 - 2 mm）。在微组织聚集体中以1:1的MVEC:FB比例形成的血管小且分散，而在第14天时，1:3的MVEC:FB比例产生大且高度相互连接的血管。本研究突出了人MVEC作为血管再生策略细胞来源的实用性，并表明内皮细胞与支持细胞的比例可用于调整血管特性。模块化微组织形式可能允许以微创方式递送预血管化微组织群体用于治疗应用。
