Abstract Body: Background: Vascularization, a challenge in tissue engineering strategies rely on hydrogels, which mimic the extracellular matrix, to help coordinate cellular behaviors. However, conventional hydrogels do not afford dynamic control of critical cues that drive vascular assembly.
Hypothesis: Biochemical and biophysical cues triggered in smart hydrogels via ultrasound synergistically influence microvascular assembly.
Goals: Develop smart hydrogels, termed acoustically responsive scaffolds (ARSs), that enable simultaneous release of bFGF and matrix reorganization using ultrasound.
Methods: ARSs were prepared by loading ultrasound-sensitive emulsions containing bFGF and perfluorohexane (C6) or perfluorooctane (C8) into 5 mg/mL fibrin hydrogels along with human endothelial cells and fibroblasts. ARSs were exposed to pulsed 2.5 MHz ultrasound at 4.4 MPa. Hydrogel architecture, mechanical properties, and bFGF release were characterized with confocal microscopy, rheometry, and ELISA, respectively. In vitro endothelial tubule formation was assessed after 7 days of culture with Ulex europaeus agglutinin I staining. Similar vasculogenic studies were performed with ARSs implanted subcutaneously in mice.
Results: Ultrasound generated stable bubbles in C6-ARSs, along with localized matrix compaction and an increased storage modulus. In C8-ARSs, ultrasound generated macropores, with no impact on modulus. For both ARSs, bFGF release increased significantly after ultrasound. In vitro tubule density increased 3-fold in C6-ARSs and 3.3-fold in C8-ARSs after ultrasound versus unexposed controls. In vivo, the endothelial area fraction increased 1.8-fold in C6-ARSs and 1.6-fold in C8-ARSs following ultrasound.
Conclusion: Using ultrasound, synergistic modulation of bFGF release and microarchitecture reorganization in fibrin-based ARSs enhanced microvascular assembly. Overall, this strategy could help improve vascularization of engineered constructs and ischemic tissues.