Biomaterial processing for organ-on-a-chip engineering

组织工程可以为研究旁分泌信号、组织功能和化合物发现提供微生理芯片平台。干细胞生物学的最新进展使得通过多能干细胞（PSC）分化为特化谱系，如心肌细胞（CM）、肝细胞等，几乎可以获得所有人类细胞类型。然而，整个领域面临着两个关键的限制：1)将几种细胞类型整合到高保真组织芯片模型中的复杂性仍然存在。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。利用生物材料和高分子科学、材料加工、微加工和化学工程的方法，这个研究项目将克服这两个限制。目前大多数芯片上设备使用聚（二甲基硅氧烷），PDMS，这是臭名昭著的吸收和浸出的小分子。片上器件具有封闭配置，通常将组织密封在PDMS层和玻璃基板之间，需要泵驱动流。这使得直接接触组织变得困难，各个隔间的整合变得指数复杂，需要笨重的外部设备。在体内，代谢物通过连接不同器官的脉管系统通过对流传递，通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和器官芯片平台，我们将首先建立一个通用的、功能性的血管床来支持和连接不同的组织。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渗透分支血管系统，以适应两个相反的标准：机械稳定的壁，同时可渗透小分子，蛋白质和最终迁移的细胞。血管床将在无pdms的生物反应器中播种实质细胞，具有孔板的足迹和开放的液体分配通道。我们的目标是将心脏、肝脏和乳房肿瘤组织整合到一个平台上。在项目2中，我们假设可以通过生物打印多层3D结构来设计功能心脏左心室（LV），该结构再现了天然左心室的复杂纤维方向，通过使用微流体生物打印机在水凝胶片上指定CM附着的粘附和非粘附区域。我们预计具有适当纤维取向的左室能够像天然心室一样同步扭曲和收缩，而各向同性或周向排列的纤维则不能。项目1和项目2是相互关联的，因为项目1的分支血管系统可以用于项目2的规模研究。这两个项目都将使用从人类诱导的PSC分化而来的细胞。拟培养博士生3人，硕士生2人，本科生5人。

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.