Functional regeneration at the blood-biomaterial interface.

The use of cardiovascular implants is commonplace in clinical practice. However, reproducing the key bioactive and adaptive properties of native cardiovascular tissues with an artificial replacement is highly challenging. Exciting new treatment strategies are under development to regenerate (parts of) cardiovascular tissues directly in situ using immunomodulatory biomaterials. Direct exposure to the bloodstream and hemodynamic loads is a particular challenge, given the risk of thrombosis and adverse remodeling that it brings. However, the blood is also a source of (immune) cells and proteins that dominantly contribute to functional tissue regeneration. This review explores the potential of the blood as a source for the complete or partial in situ regeneration of cardiovascular tissues, with a particular focus on the endothelium, being the natural blood-tissue barrier. We pinpoint the current scientific challenges to enable rational engineering and testing of blood-contacting implants to leverage the regenerative potential of the blood.

Calcification in Pulmonary Heart Valve Tissue Engineering: A Systematic Review and Meta-Analysis of Large-Animal Studies.

Tissue-engineered heart valves (TEHVs) are emerging alternatives to current valve prostheses and prospectively a lifelong replacement. Calcification, a pathological complication for biological protheses, has been reported in preclinical TEHV studies. Systematic analysis of its occurrence is missing. This review aims to: 1) systematically review reported calcification of pulmonary TEHVs in large-animal studies; and 2) analyze the influence of engineering methodology (choice of scaffold material, cell preseeding) and animal model (animal species and age) on calcification. Baseline analysis included 80 studies, of which 41 studies containing 108 experimental groups were included in meta-analysis. Inclusion was low because only 55% of studies reported on calcification. Meta-analysis showed an overall average calcification event rate of 35% (95% CI: 28%-43%). Calcification was more prominent (P = 0.023) in the arterial conduit region (34%; 95% CI: 26%-43%) than in the valve leaflets (21%; 95% CI: 17%-27%), and was mostly (42% in leaflets, 60% in conduits) present in a mild form. Time-analysis showed an initial surge within 1 month after implantation, decreased calcification between 1 and 3 months, and then progression over time. There were no significant differences in degree of calcification between TEHV strategy nor animal models. Much variability between individual studies was observed in degree of calcification as well as quality of analysis and reporting thereof, hampering adequate comparisons between studies. These findings underline the need for improved analysis and better reporting standards of calcification in TEHVs. It also necessitates control-based research to further enlighten the risk of calcification for tissue-engineered transplants compared to current options. This can bring the field of heart valve tissue engineering forward toward safe clinical use.