Thrombogenicity and biocompatibility studies of reduced graphene oxide modified acellular pulmonary valve tissue

Current strategies in tissue engineering seek to obtain a functional tissue analogue by either seeding acellular scaffolds with cells ex vivo or repopulating them with cells in vivo, after implantation in patients. To function properly, the scaffold should be non-thrombogenic and biocompatible. Especially for the case of in vivo cell repopulation, the scaffold should be prepared in a manner that protects the tissue against platelet activation and adhesion. Anti-thrombogenicity can be achieved by chemical or physical surface modification. The aim of our study was to evaluate the platelet activation and thrombogenic properties of an acellular tissue scaffold that was surface modified with reduced graphene oxide (rGO). Graphene oxide was prepared by a modified Hummers method. For the study, an acellular pulmonary valve conduit modified with rGO was used. The rGO modified tissue samples were subjected to in vitro testing through interaction with whole blood under simulated laminar flow conditions. The following cellular receptors were then analysed: CD42a, CD42b, CD41a, CD40, CD65P and PAC-1. In parallel, the adhesion of platelets (CD62P positive), leukocytes (CD45 positive) and platelet-leukocyte aggregates (CD62P/CD45 positive) on the modified surface was evaluated. As a reference, non-coated acellular tissue, Poly-l lysine and fibronectin coated tissue were also tested. The rGO surface was also analysed for biocompatibility by performing a cytotoxicity test, TUNEL assay and Cell Cycle analysis. There was no significant difference in platelet activation and adhesion between the study groups. The only significant difference was observed for the PAC-1 receptor between Poly-l lysine group and rGO and the percentage of PAC-1 positive cells was 6% and 18% respectively. The average number of activated platelets (CD62P) in the field of view was 1, while the average number of leukocytes in the field of view was 3. No adherent platelet-leukocyte aggregates were observed. There were no significant differences in the DNA fragmentation. No significant effect of rGO on the amount of cells in different phases of the cell cycle was observed. Cytotoxicity indicates that the rGO can damage cells in direct contact but have no effect on the viability of fibroblasts in indirect contact.