Investigation of topography effect on antibacterial properties and biocompatibility of nanohydroxyapatites activated with zinc and copper ions: In vitro study of colloids, hydrogel scaffolds and pellets

In the present work, nanohydroxyapatites (nHAp) doped with copper and/or zinc ions were investigated for the assessment of its antibacterial activity and biocompatibility. Three forms of material with diverse surfaces were tested: nanopowder in colloidal suspension, galactose hydrogel (3,6-Anhydro-α-l-Galacto-β-d-Galactan) scaffold and pellet. The structural and morphological properties of the obtained biomaterials were comprehensively determined by using: XRPD, FT-IR, SEM-EDS, AAS, XPS and EPR techniques. The antimicrobial active ions, mostly Cu2+, were successfully released from the apatite structure despite the material being suspended in the porous galactose hydrogel matrix. The colloidal solutions of nanohydroxyapatites on bacterial viability revealed moderate activity of Cu2+-doped materials against Escherichia coli strain and significant activity against Pseudomonas aeruginosa strain. The comparative study of bacterial attachment to the hydrogel and pellet surface indicated that hydrogels were more prone to be colonized by both tested strains. Moreover, an additive of the Cu2+ ion modified bacterial attachment and biofilms forming on nHAp:Cu2+ and nHAp:Cu2+-Zn2+ materials. In the case of hydrogels, the biofilms were scattered while these forming on other materials were more clumped. The cytotoxicity evaluation of tested biomaterials showed biocompatible properties of both nanomaterial colloidal solutions as well as galactose hydrogel eluates toward normal mouse osteoblast cell lines (7F2) and human chondrocytes (TC28A2) and osteosarcoma cell line (U2OS). The biocompatibility of tested materials was additionally confirmed by conducting a hemolysis assay which showed full hemocompatibility of nanopowder colloidal solutions and galactose-based materials. Furthermore, unaltered red blood cell morphology was visible after a short and long time of incubation with the obtained biomaterials by using confocal laser scanning microscopy (CLSM). The comparison research provided data of 7F2, TC28 and U2OS cell attachment to the galactose hydrogel surface.