Nanosize and surface charge effects of hydroxyapatite nanoparticles on red blood cell suspensions

In this paper, the effects of size and surface charge of hydroxyapatite (HAP) particles on a red blood cell (RBC) suspension were studied. Results showed that the HAP particles exhibited nanosize and surface charge effects on the RBC suspension. Differing from HAP microparticles, HAP nanoparticles induced some aggregation of the RBCs in the unstructured agglutinates. HAP nanoparticles were adhered to the surface membrane of the RBCs due to their remarkably higher adsorption capacity than the HAP microparticles, resulting in the formation of a sunken appearance ("caves") on the surface membrane of the RBCs without rupturing the lipid bilayer. In the case of high negatively charged HAP nanoparticles after heparin modification, the aggregation of the RBCs induced by the HAP nanoparticles was inhibited. Such HAP nanoparticle-induced aggregation of the RBCs could be attributed to the bridging force via the electrostatic interaction between the positively charged binding sites on the HAP surface and the negatively charged groups on the surface of the RBCs. The surface charge of the HAP nanoparticles is thus a crucial factor influencing the interaction between the HAP nanoparticles and the RBCs.