关键词: 干细胞, 类器官, 血管化, 生物工程学方法, 生物材料

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