Enhancing compliance and extracellular matrix properties of tissue-engineered vascular grafts through pulsatile bioreactor culture

Abstract

Biofabrication techniques represent a promising avenue for the production of small diameter vascular grafts. However, while current tissue-engineered vascular grafts (TEVGs) fulfil certain functional requirements of native blood vessels, most exhibit very poor mechanical compliance, directly reducing patency in vivo. Here, highly compliant TEVGs were cultured in a dynamic pulsatile bioreactor which ensured enhanced compliance, using biomimetic melt electrowritten (MEW) tubular scaffolds as substrates for tissue growth. Through 6-week in vitro culture, we investigated differences in extracellular matrix (ECM) production and mechanical performance of TEVGs cultured with placental mesenchymal stem cells (MSCs) and smooth muscle cells (SMCs) in static and dynamic conditions. Pulsatile stimulation successfully maintained the high compliance (12.4 ± 0.8 % per 100 mmHg) of our biomimetic scaffolds, substantially greater than existing small diameter grafts. Dynamic TEVGs demonstrated physiologically relevant burst pressure (1125 ± 212 mmHg) and suture pull-out force (3.0 ± 0.4 N), while also accumulating greater ECM components than static TEVGs. To assess off-the-shelf suitability, grafts were decellularized and lyophilised to produce d-TEVGs, which exhibited negligible loss of mechanics or ECM integrity. Finally, rehydrated d-TEVGs were seeded with endothelial cells in vitro, with an intimal endothelial lining forming after 7 days. These findings demonstrate the production of TEVGs with specifically engineered mechanical compliance which has been maintained by dynamic in vitro culture, supporting continued work toward biofabrication of the next generation of vascular grafts.