Human umbilical vein endothelial cells (HUVECs) and human aortic smooth muscle cells (HASMCs) were coaxially and continuously extruded without ultraviolet illumination using a microfluidic-based nozzle. Type I collagen (3 mg ml−1) containing HUVECs and a crosslinking reagent (100 mM CaCl2) were supplied as the core material. A mixture of 3 mg ml−1 of type I collagen (25%) and 1.8% weight volume−1 of sodium alginate (75%) was provided as the shell layer material surrounding the core material. The HUVECs were well proliferated at the core and reshaped into a monolayer formation along the axial direction of the scaffold. The HASMCs showed more than 90% cell viability in the shell layer. Fluorescent beads were passed through the inside channel of the scaffold with the HUVEC core and HASMC shell using an in-house connector. This double-layered scaffold showed higher angiogenesis in growth factor-free medium than the scaffold with only a HUVEC core. The HASMCs in the shell layer affected angiogenesis, extracellular matrix secretion, and outer diameter. The proposed technique could be applied to three-dimensional bioprinting for the production of high-volume vascularised tissue.
In the current study, a method is proposed to supply culture medium into a two-layered cell-laden tubular scaffold in order to enhance cell proliferation, confluence, and viability. The two-layered cell-laden tubular scaffold was made of calcium-alginate mixed with fibroblast cells (NIH/3T3) using a lab-made doublecoaxial laminar-flow generator. Afterwards, the tubular scaffold was connected to a syringe pump system using a polydimethylsiloxane (PDMS) micro-connector for long-term cell culture. Three medium pumping conditions were applied and compared: a heartbeat mimicking pumping (20 µL/s, 1 s period, and 50 % pulse width), a continuous pumping (20 µL/s) and a non-pumping. Non-leaky connections between the tubular scaffolds and the micro-connector outlet were sustained for 13.5 ± 0.83 d in heartbeat-mimicking pumping and 11.8 ± 0.33 d in continuous pumping condition, due to the elasticity of the tubular scaffolds. Importantly, the two pumping conditions resulted in more cell proliferation, confluence, and viability than the non-pumping condition. Furthermore, analysis of newly-produced type-I collagen matrix indicated that the cells under the two pumping conditions formed a tissue-like structure. The proposed technique could further be applied to vascular co-culturing for vascular engineered tissue.
Rapid construction of pre-vascular structure is highly desired for engineered thick tissue. However, angiogenesis in free-standing scaffold has been rarely reported because of limitation in growth factor (GF) supply into the scaffold. This study, for the 1st time, investigated angiogenic sprouting in free-standing two-vasculature-embedded scaffold with three different culture conditions and additional GFs. A two-core laminar flow device continuously extruded one vascular channel with human umbilical vein endothelial cells (HUVECs) and a 3 mg/ml type-1 collagen, one hollow channel, and a shell layer with 2% w/v gelatin-alginate (70:30) composite. Under the GF flowing condition, angiogenic sprouting from the HUVEC vessel had started since day 1 and gradually grew toward the hollow channel on day 10. Due to the medium flowing, the HUVECs showed elongated spindle-like morphology homogeneously. Their viability has been over 80% up to day 10. This approach could apply to vascular investigation, and drug discovery further, not only to the engineered thick tissue.
Digital light processing (DLP) bioprinting can be used to fabricate volumetric scaffolds with intricate internal structures, such as perfusable vascular channels. The successful implementation of DLP bioprinting in tissue fabrication requires using suitable photo‐reactive bioinks. Norbornene‐based bioinks have emerged as an attractive alternative to (meth)acrylated macromers in 3D bioprinting owing to their mild and rapid reaction kinetics, high cytocompatibility for in situ cell encapsulation, and adaptability for post‐printing modification or conjugation of bioactive motifs. In this contribution, we report the development of gelatin‐norbornene (GelNB) as a photocrosslinkable bioink for DLP 3D bioprinting. Low concentrations of GelNB (2‐5 wt%) and poly(ethylene glycol)‐tetra‐thiol (PEG4SH) were DLP‐printed with a wide range of stiffness (G' ∼120 to 4,000 Pa) and with perfusable channels. DLP‐printed GelNB hydrogels were highly cytocompatible, as demonstrated by the high viability of the encapsulated human umbilical vein endothelial cells (HUVECs). The encapsulated HUVECs formed an interconnected microvascular network with lumen structures. Notably, the GelNB bioink permitted both in situ tethering and secondary conjugation of QK peptide, a vascular endothelial growth factor (VEGF)‐mimetic peptide. Incorporation of QK peptide significantly improved endothelialization and vasculogenesis of the DLP‐printed GelNB hydrogels, reinforcing the applicability of this bioink system in diverse biofabrication applications.This article is protected by copyright. All rights reserved
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