Systemic low-dose erythropoietin administration improves the vascularization of collagen-glycosaminoglycan matrices seeded with adipose tissue-derived microvascular fragments

Engineered dermis loaded with confining forces promotes full-thickness wound healing by enhancing vascularisation and epithelialisation

Tissue-engineered skin is ideal for clinical wound repair. Restoration of skin tissue defects using tissue-engineered skin remains a challenge owing to insufficient vascularisation. In our previous study, we developed a 3D bioprinted model with confined force loading and demonstrated that the confined force can affect vascular branching, which is regulated by the YAP signalling pathway. The mechanical properties of the model must be optimised to suture the wound edges. In this study, we explored the ability of a GelMA-HAMA-fibrin scaffold to support the confined forces created by 3D bioprinting and promote vascularisation and wound healing. The shape of the GelMA-HAMA-fibrin scaffold containing 3% GelMA was affected by the confined forces produced by the embedded cells. The GelMA-HAMA-fibrin scaffold was easy to print, had optimal mechanical properties, and was biocompatible. The constructs were successfully sutured together after 14 d of culture. Scaffolds seeded with cells were transplanted into skin tissue defects in nude mice, demonstrating that the cell-seeded GelMA-HAMA-fibrin scaffold, under confined force loading, promoted neovascularisation and wound restoration by enhancing blood vessel connections, creating a patterned surface, growth factors, and collagen deposition. These results provide further insights into the production of hydrogel composite materials as tissue-engineered scaffolds under an internal mechanical load that can enhance vascularisation and offer new treatment methods for wound healing. STATEMENT OF SIGNIFICANCE: Tissue-engineered skin is ideal for use in clinical wound repair. However, treatment of tissue defects using synthetic scaffolds remains challenging, mainly due to slow and insufficient vascularization. Our previous study developed a 3D bioprinted model with confined force loading, and demonstrated that confined force can affect vascular branching regulated by the YAP signal pathway. The mechanical properties of the construct need to be optimized for suturing to the edges of wounds. Here, we investigated the ability of a GelMA-HAMA-fibrin scaffold to support the confined forces created by 3D bioprinting and promote vascularization in vitro and wound healing in vivo. Our findings provide new insight into the development of degradable macroporous composite materials with mechanical stimulation as tissue-engineered scaffolds with enhanced vascularization, and also provide new treatment options for wound healing.

Electrospun gelatin-based biomimetic scaffold with spatially aligned and three-layer architectures for vascular tissue engineering

The spatial cellular alignment and multi-layer structure are vitally important for the physiological functions of natural blood vessels. However, the two features are difficult to be constructed in one scaffold simultaneously, especially in the small-diameter vascular scaffold. Here we report a general strategy to construct a gelatin-based biomimetic three-layer vascular scaffold with spatial alignment features mimicking the natural structure of blood vessels. By using a sequential electrospinning strategy combined with folding and rolling manipulation, a three-layer vascular scaffold with inner and middle layers spatially perpendicular to each other was obtained. The special features of this scaffold could fully mimic the natural multi-layer structures of blood vessels and also possess great potential for spatial arrangement guidance of corresponding cells in blood vessels.

Expanding tubular microvessels on stiff substrates with endothelial cells and pericytes from the same adult tissue

Endothelial cells (ECs) usually form a monolayer on two-dimensional (2D) stiff substrates and a tubular structure with soft hydrogels. The coculture models using ECs and pericytes derived from different adult tissues or pluripotent stem cells cannot mimic tissue-specific microvessels due to vascular heterogeneity. Our study established a method for expanding tubular microvessels on 2D stiff substrates with ECs and pericytes from the same adult tissue. We isolated microvessels from adult rat subcutaneous soft connective tissue and cultured them in the custom-made tubular microvascular growth medium on 2D stiff substrates (TGM2D). TGM2D promoted adult microvessel growth for at least 4 weeks and maintained a tubular morphology, contrary to the EC monolayer in the commercial medium EGM2MV. Transcriptomic analysis showed that TGM2D upregulated angiogenesis and vascular morphogenesis while suppressing oxidation and lipid metabolic pathways. Our method can be applied to other organs for expanding organ-specific microvessels for tissue engineering.

Adipose tissue-derived microvascular fragments promote lymphangiogenesis in a murine lymphedema model

Chronic lymphedema after cancer treatment is common and there is still no cure for this disease. We herein investigated the lymphangiogenic capacity of adipose tissue-derived microvascular fragments (MVF), which contain stem cells and lymphatic vessel fragments. Secondary lymphedema was induced in the hindlimbs of C57BL/6J mice. Green fluorescence protein (GFP)+ MVF were isolated from transgenic C57BL/6Tg (CAG-EGFP)1Osb/J mice, suspended in collagen hydrogel, and injected in the lymphadenectomy defect of wild-type animals. This crossover model allowed the detection of MVF-derived blood and lymphatic vessels after transplantation. The MVF group was compared with animals receiving collagen hydrogel only or a sham intervention. Lymphangiogenic effects were analyzed using volumetry, magnetic resonance (MR) lymphography, histology, and immunohistochemistry. MVF injection resulted in reduced hindlimb volumes when compared to non-treated controls. MR lymphography revealed lymphatic regeneration with reduced dermal backflow after MVF treatment. Finally, MVF transplantation promoted popliteal angiogenesis and lymphangiogenesis associated with a significantly increased microvessel and lymphatic vessel density. These findings indicate that MVF transplantation represents a promising approach to induce therapeutic lymphangiogenesis.

Microvascular fragments in microcirculation research and regenerative medicine

Adipose tissue-derived microvascular fragments (MVF) are functional vessel segments, which rapidly reassemble into new microvasculatures under experimental in vitro and in vivo conditions. Accordingly, they have been used for many years in microcirculation research to study basic mechanisms of endothelial cell function, angiogenesis and microvascular network formation in two- and three-dimensional environments. Moreover, they serve as vascularization units for musculoskeletal regeneration and implanted biomaterials as well as for the treatment of myocardial infarction and the generation of prevascularized tissue organoids. Besides, multiple factors determining the vascularization capacity of MVF have been identified, including their tissue origin and cellular composition, the conditions for their short- and long-term storage as well as their implantation site and the general health status and medication of the recipient. The next challenging step is now the successful translation of all these promising experimental findings into clinical practice. If this succeeds, a multitude of future therapeutic applications may significantly benefit from the remarkable properties of MVF.