Stem Cell-based Human Placenta-on-a-Chip Using 3D Bioprinting

作为母体和胎儿血液供应的接口，胎盘向胎儿输送营养物质和氧气，并将代谢废物和二氧化碳排出胎儿；它还产生建立和维持妊娠所必需的激素。为了实现这些不同的功能，胎盘由称为绒毛膜绒毛的功能单位组成，绒毛膜绒毛由被基质细胞包围的胎儿毛细血管环组成，然后是细胞滋养细胞，整个被合胞滋养细胞单层包裹。随着胎盘的成熟，间质细胞和细胞滋养层的数量显著减少，导致在足月时，交换界面主要由靠近合胞滋养层的胎儿毛细血管组成。胎盘功能异常与常见和临床显著的妊娠并发症有关，包括先兆子痫和胎儿生长受限。鉴于人类胎盘的结构和功能与实验可处理的动物模型存在显著差异，以及胎母界面的复杂微结构，迫切需要能够用于实验探索人类胎盘功能的体外模型。传统的系统，如绒毛膜癌细胞系、原代细胞滋养层细胞、胎盘外植体培养和胎盘组织的体外灌注，在使用恶性细胞来模拟非恶性细胞、无法重建不同细胞类型之间复杂的3D关系和/或实验寿命短等方面存在显著的局限性。最近，胎盘芯片技术得到了应用，但现有的实现方法缺乏对胎盘原生微环境、解剖结构和长期功能进行详细机制研究的能力。

As the interface between the maternal and fetal blood supplies, the placenta transports nutrients and oxygen to, and metabolic waste products and carbon dioxide away from, the fetus; it also produces hormones necessary for establishment and maintenance of pregnancy. To carry out these diverse functions, the placenta is comprised of functional units, called chorionic villi, which consist of loops of fetal capillaries surrounded by stromal cells, followed by cytotrophoblast, with the whole encased in a syncytiotrophoblast monolayer. As the placenta matures, the number of stromal cells and cytotrophoblast decrease significantly, resulting, at term, in an exchange interface composed primarily of fetal capillaries adjacent to the syncytiotrophoblast monolayer. Abnormalities in placental function are associated with common and clinically significant complications of pregnancy, including preeclampsia and fetal growth restriction. Given marked differences in placental structure and function between humans and experimentally tractable animal models, and the complex microarchitecture of the feto-maternal interface, there is a pressing need for in vitro models that can be used to experimentally probe the function of the human placenta. Traditional systems, such as choriocarcinoma cell lines, primary cytotrophoblast, placental explant cultures, and ex vivo perfusion of placental tissue, have significant limitations related to use of malignant cells to model non-malignant cells, failure to recreate the complex 3D relationships among different cell types, and/or short experimental life-span. Recently, placenta-on-a-chip approaches have been applied, but existing implementations lack the ability to recapitulate the native microenvironment, anatomical structure, and long-term function needed for detailed mechanistic studies. We will address these challenges by engineering a novel human placenta-on-a-chip in a microfluidic platform, which will recapitulate human placental microstructure and function. By using a rapid 3D bioprinting method, we are able to better replicate the intricate microarchitecture of the native maternal-fetal placental interface at term and incorporate each of the key human placental cell types, including placental microvascular endothelial cells, and primary cytotrophoblast or human trophoblast stem cells. The work will be accomplished in two aims by: (1) building the 3D placenta-on-a-chip and confirming the spatial placement, viability, and identity of the component cell types, and (2) performing detailed evaluation of our platform as a biomimetic model of placental function, including assessment of barrier formation, and the effects of varying glucose concentration and oxygen tension on biomolecular transport, production of placental hormones, and intracellular and extracellular RNA expression. Where appropriate, these results will be compared to those obtained from placental explants cultured in the same conditions. This work will produce a validated novel 3D bioprinted placental model that can be used to reveal the mechanisms of placental function and dysfunction in normal and complicated pregnancies.