Biomaterial processing for organ-on-a-chip engineering

组织工程为旁分泌信号、组织功能和化合物的发现提供了微生物芯片平台。干细胞生物学的最新进展使得能够通过将多能干细胞（PSC）分化成专门的谱系（例如心肌细胞（CM）、肝细胞等）来获得几乎所有的人类细胞类型。然而，整个领域面临两个关键限制：1）与将几种细胞类型整合到高保真组织芯片模型中相关的复杂性仍然存在。2)缺乏对体外构建功能器官的结构-功能关系和设计规则的理解。利用生物材料和聚合物科学，材料加工，微细加工和化学工程的方法，该研究计划将克服这两个限制。 大多数当前的片上器件利用聚（二甲基硅氧烷）PDMS，其因吸收和浸出小分子而臭名昭著。片上器件具有封闭的构造，通常组织密封在PDMS层和玻璃基板之间，需要泵驱动的流动。这使得直接进入组织变得困难，并且各种隔室的整合呈指数级复杂，需要庞大的外部设备。 在体内，代谢物通过对流输送通过连接不同器官的脉管系统，穿过内皮进入实质空间。在项目1中，为了设计一个强大的组织，然后是器官芯片平台，我们将首先建立一个通用的功能性血管床来支持，然后连接不同的组织。为此，我们将开发一种新的3D微冲压技术，以创建基于聚酯的可灌注分支脉管系统，该脉管系统适应两个相反的标准：机械稳定的壁，但可渗透小分子，蛋白质和最终迁移的细胞。将在无PDMS的生物反应器中用实质细胞接种血管床，该生物反应器具有孔板的占地面积和用于液体分配的开放入口。 我们的目标是将心脏、肝脏和乳腺肿瘤组织整合到一个平台上。在项目2中，我们假设功能性心脏左心室（LV）可以通过生物打印多层3D构建体来工程化，该构建体通过使用微流体生物打印机在水凝胶片中指定用于CM附着的粘合剂和非粘合剂区域来重现天然LV的复杂纤维取向。我们预期具有适当纤维取向的LV能够与天然心室同步扭转和收缩，而各向同性或周向排列的纤维则不能。项目1和2相互关联，因为项目1的分支血管系统可用于项目2的规模扩大研究。这两个项目都将使用从人类诱导PSC分化的细胞。3名博士，2名硕士和5名本科生将通过拟议的研究进行培训。

Tissue engineering may provide microhpysiological on-a-chip platforms for studies of paracrine signaling, tissue function and compound discovery. Recent advances in stem cell biology enable procurement of virtually all human cell types by differentiation of pluripotent stem cells (PSC) into specialized lineages e.g. cardiomyocytes (CM), hepatocytes, etc. However, the entire field is faced with two critical limitations: 1) Complexities related to integrating several cell types into high-fidelity tissue-on-a-chip models still remain. 2) Lack of understanding of structure-function relationships and design rules for building functional organs in vitro. Using approaches from biomaterial and polymer sciences, materials processing, microfabrication and chemical engineering this research program will overcome both limitations. Most current on-a-chip devices utilize poly(dimethylsiloxane), PDMS, which is notorious for absorption and leaching of small molecules. The on-a-chip devices have a closed configuration, usually with the tissue sealed between the PDMS layer and a glass substrate, requiring a pump driven flow. This makes direct access to the tissue difficult and integration of various compartments exponentially complex, requiring bulky external equipment. In vivo, metabolites are delivered by convection through the vasculature connecting different organs, passing through the endothelium into the parenchymal space. In Project 1, to engineer a robust tissue then organ-on-a-chip platform, we will first build a generic and functional vascular bed to support and then connect different tissues. For this purpose, we will develop a new 3D micro-stamping technique to create polyester-based perfusable branching vasculature that accommodates two opposing criteria: mechanically stable walls yet permeable to small molecules, proteins and ultimately migrating cells. The vascular bed will be seeded with parenchymal cells in a PDMS-free bioreactor, with a footprint of a well plate and open access for liquid dispensing. We aim to integrate cardiac, liver and breast tumor tissue onto a single platform. In Project 2 we hypothesize that a functional heart left ventricle (LV) can be engineered by bioprinting a multilayer 3D construct that recapitulates complex fiber orientation of the native LV, by specifying adhesive and non-adhesive regions for CM attachment in a hydrogel sheet using a microfluidic bioprinter. We expect the LV with appropriate fiber orientation to be capable of synchronously twisting and contracting as the native ventricle, while isotropic or circumferentially aligned fibers will not. Project 1 and 2 are interconnected as branching vasculature from Project 1  could be used in scale-up studies for Project 2. Both Projects will use cells differentiated from human induced PSC. Three PhD, 2 MASc and 5 undergraduate students will be trained through the proposed studies.