天美传媒

Bioprinting; Endothelial cells; Vascularization; Tissue engineering; Bioink; Microvascular networks; Regenerative medicine; 3D scaffolds; Cell viability; Angiogenesis

Introduction

Bioprinting has emerged as a transformative technology in tissue engineering, enabling the creation of three-dimensional (3D) tissue constructs that mimic the complexity of native biological tissues. One of the critical challenges in engineering thick tissue constructs is the integration of a functional vascular network to ensure adequate nutrient diffusion and waste removal. Without vascularization, tissues larger than a few hundred microns suffer from hypoxia and necrosis, limiting their clinical translation. Among the numerous strategies to overcome this barrier, the incorporation of endothelial cells directly into bioinks during the bioprinting process offers a promising solution. These cells have the natural capacity to form capillary-like networks and facilitate the development of microvasculature within engineered tissues [1-5].

Bioinks, composed of biocompatible hydrogels and living cells, are the core materials used in 3D bioprinting. The choice of hydrogel not only influences the printability and mechanical strength of the construct but also affects the biological behavior of encapsulated cells. Hydrogels such as gelatin methacryloyl (GelMA), alginate, and fibrin are frequently used for endothelial cell-laden bioinks due to their cell-supportive properties. When extruded through a bioprinter and crosslinked under controlled conditions, these bioinks create spatially organized, cell-laden structures capable of supporting tissue maturation and vascularization [6-10].

In this study, we explore the fabrication of vascularized tissue constructs using 3D bioprinting technology combined with bioink-embedded endothelial cells. We investigate how various bioink compositions affect endothelial cell viability, proliferation, and network formation. Additionally, we assess the capability of these constructs to develop perfusable microvascular channels when cultured in vitro, a crucial step toward achieving functional tissue implants suitable for regenerative medicine applications.

Discussion

The integration of endothelial cells within bioinks has shown a significant impact on enhancing vascularization in engineered tissues. Endothelial cells encapsulated within hydrogels can spontaneously organize into interconnected capillary-like networks under appropriate culture conditions. In our study, the use of GelMA and fibrin-based hydrogels provided a highly supportive matrix for cell spreading, migration, and angiogenic sprouting. The crosslinking density and degradation rate of the hydrogels were found to influence the rate and extent of vascular network formation. Specifically, moderately crosslinked hydrogels allowed better matrix remodeling and cell invasion, leading to denser and more branched vascular networks.

One of the primary observations was the increased cell viability in constructs that included vascular endothelial growth factor (VEGF) as a bioactive cue. VEGF enhanced endothelial cell functionality and promoted lumen formation within the hydrogel. Moreover, co-culturing endothelial cells with supporting stromal cells, such as mesenchymal stem cells (MSCs), further improved vascular stability and organization, likely due to paracrine signaling and matrix remodeling capabilities of MSCs.

Another significant factor contributing to vascular development was the printing resolution and geometry of the constructs. Fine-tuned nozzle diameter and printing speed allowed the creation of intricate channels and patterns that mimic natural vascular architectures. These structural cues guided endothelial cell alignment and tubulogenesis. Over time, perfusion assays demonstrated the ability of these networks to support fluid flow, confirming their potential for nutrient and oxygen delivery in larger constructs.

While in vitro results are promising, translation to in vivo models poses additional challenges. Host integration, immune compatibility, and the long-term stability of the printed vasculature need thorough investigation. Nevertheless, the combination of 3D bioprinting with bioactive hydrogels and endothelial cells presents a powerful platform to address vascularization—a major bottleneck in tissue engineering.

Conclusion

The bioprinting of vascularized tissue constructs using bioink-embedded endothelial cells represents a significant advancement in regenerative medicine and tissue engineering. Our findings demonstrate that the strategic formulation of cell-laden bioinks and the use of pro-angiogenic factors such as VEGF can result in the successful formation of functional microvascular networks within 3D printed constructs. Hydrogels like GelMA and fibrin not only support high cell viability but also facilitate the organization of endothelial cells into perfusable channels.

By optimizing printing parameters and incorporating supportive cell types, it is possible to create biomimetic constructs that closely resemble native tissue architecture and function. These vascularized constructs are promising candidates for future applications in organ repair, transplantation, and disease modeling. However, further studies, particularly involving in vivo implantation and long-term functional assessments, are necessary to validate their clinical utility. With continued innovation in bioprinting technology and biomaterial science, the goal of fabricating fully vascularized, functional tissues is becoming increasingly attainable.

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