Engineering Microvascular Networks in LED Light-Cured Cell-Laden Hydrogels

The success of tissue engineering inevitably depends on the fabrication of tissue constructs that can be vascularized and that anastomose with the host vasculature. In this report, we studied the effects of light-emitting diode (LED) photopolymerized gelatin methacryloyl hydrogels (GelMA), encapsulated with stem cells from the apical papilla (SCAP) and human umbilical vein endothelial cells (HUVECs), in promoting vasculature network formation as a function of hydrogel physical and mechanical properties, as well as total cell density. Lithium acylphosphinate (LAP) was used as the photoinitiator in concentrations of 0.05, 0.075, 0.1% (w/v). GelMA hydrogel precursors of 5% (w/v) were encapsulated with cocultures of SCAPs and HUVECs at different cell densities (1×, 5×, and 10 × 10⁶ cells/mL) and photo-cross-linked for 5 s. Results suggested that the compressive modulus of GelMA hydrogels increased as a function of LAP concentration, and had a maximum stiffness of 3.2 kPa. GelMA hydrogels photopolymerized using 0.05 or 0.075% LAP, which had an average of 1.5 and 1.6 kPa of elastic modulus respectively, had the most efficient vasculature formation after 5 days, and these results were further enhanced when the highest cell density (10 × 10⁶ cells/mL) was used. Immunofluorescence images showed that SCAP cells spread in close contact with endothelial networks and expressed alpha smooth muscle actin (αSMA), which is suggestive of their differentiation into pericyte-like cells. αSMA expression was also apparently higher in hydrogels polymerized with 0.05% LAP and 10 × 10⁶ cells/mLl. In conclusion, photopolymerization of GelMA hydrogels using an LED-light source can be an effective method for potential chair-side/in situ procedures for engineering of vascularized tissue constructs in regenerative medicine.