Abstract:

The adequate perfusion of blood and exchange of metabolites are crucial for maintaining organoid homeostasis and supporting cell survival, growth, and functionality. Therefore, vascularization of organoids is an essential step towards improving their functionality and long-term survival. This review provides a comprehensive overview of recent advances in the field of organoid vascularization, highlighting various construction approaches and biomaterials used to promote blood vessel formation within organoids. There are various approaches for constructing vascularized organoids, with co-differentiation and co-culture being widely utilized. Co-differentiation enables simultaneous development of both organ-specific and vascular cells from stem cells, while co-culture involves growing stem or progenitor cells together with vascular cells to promote the formation of vascular networks through self-assembly. Transplantation strategies, such as introducing microvascular fragments into organoids or engrafting organoids into specific organs, can also promote the formation of a natural and efficient vascular system within the organoid. Moreover, bioengineering strategies offer promising alternatives for organoid vascularization. Techniques like microarray fabrication and electrospinning enable the creation of micro-surface and biomimetic structures that support vascular network formation. Meanwhile, 3D bioprinting allows for the incorporation of endothelial cells and supporting biomaterials in a spatially controlled manner, facilitating the development of vascular networks within organoids. Microfluidic systems provide precise control over fluid, nutrient, and signaling factors within microscale channels, allowing for the manipulation of vascular networks in a controlled and dynamic environment. The construction of vascularized organoids often involves the utilization of biocompatible materials to incorporate pro-angiogenic factors and to create suitable microenvironments for different cell types. Hence, this review also encompasses the application cases of both natural and synthetic biomaterials in the development of vascularized organoids. Hydrogels are widely utilized in the construction of both organoids and vascularized organoids. They can be categorized into natural hydrogels, such as Matrigel, decellularized matrix, collagen, etc., and synthetic hydrogels like polyethylene glycol. Natural hydrogels are biocompatible and biologically active but with limited mechanical strength, while synthetic hydrogels offer long-term stability and tunable mechanical properties albeit with the potential lack of biocompatibility. Combining the natural and synthetic hydrogels can facilitate the creation of stable and tunable microenvironments for vascularization. Despite significant advancements, challenges in organoid vascularization continue to exist. The complex structure of organ-specific blood vessels and the underlying mechanisms of angiogenesis are still not fully understood. Additionally, accurately replicating of the in vivo microenvironment, the technical complexities of bioengineering methods, and the instability of organoid cultures hamper the generation of functional vascularized organoids. Ongoing research focusing on deciphering the key mechanisms of vascularization, combined with advancements in biotechnology, offers promising prospects for significantly enhancing the structural and functional maturity of vascularized organoids. These advancements are expected to pave the way for the widespread utilization of organoid technology in both basic and clinical fields of medicine.

Key words: stem cells, organoids, vascularization, bioengineering methods, biomaterials

摘要：

类器官血管化是完善类器官结构、功能及支持其体外长期存活的关键问题。近年来，随着类器官培养及生物工程技术的发展，类器官血管化有了长足的进步。本文综述了血管化类器官领域的最新进展，总结了目前用于血管化的构建策略与方法，包括干细胞共分化、多细胞共培养、微血管片段，移植后体内再血管化等生物技术，以及微制造、静电纺丝、三维生物打印、微流控技术等工程技术手段在血管化类器官方面的应用。血管化类器官的构建通常会辅以生物材料来负载血管化相关因子或提供不同类型细胞生长的微环境，本文对构建血管化类器官中应用的天然及合成生物材料也做了相应讨论。虽然类器官血管化目前还存在一定的局限性，但随着对血管化关键机制的解析及生物工程技术的进步，多种构建方法及生物材料的联合应用，将极大促进结构及功能完善的血管化类器官构建，并实质性地推动类器官技术在基础及临床医学领域的应用。

关键词: 干细胞, 类器官, 血管化, 生物工程学方法, 生物材料