Needle-less electrospinning employed for calcium and magnesium phosphate coatings on titanium substrates

The needle-less electrospinning method was employed for a preparation of calcium phosphate (CP) and magnesium calcium phosphate (MgCP) fibers as biocompatible coatings on Ti substrate. The polyvinylalcohol, triethyl phosphite, calcium and magnesium nitrates were used for a preparation of spun solutions and subsequent precursor fiber formation. The citric acid of 10 wt% was added to the spun solution in order to increase conductivity as well as a convenient complexing agent. A possible mechanism of complexation process of triethyl phosphite with calcium and magnesium nitrates with citric acid is presented. The optimization of calcination temperatures was defined according to the results obtained from TG/DSC analysis. The XRD analysis confirmed the formation of hydroxyapatite and Mg-whitlockite phases at both used temperatures 600 and 800 °C. The final morphology and thickness of prepared CP and MgCP fibrous coatings was designed by a suitable choice of the used sols, spinning time and calcination temperature. The SEM/FIB observations revealed that the average thickness of the CP coating was around 1 μm, which is almost two times thinner than the MgCP coating with the approximate width 2 μm. The in vitro cytotoxicity tests of the substrate surfaces revealed that the osteoblastic MC3T3-E1 cells have a good proliferation activity when cultured on the 600 °C calcined substrates covered by smooth and uniform fibrous nets. A strong cytotoxic cell response was observed in the samples treated at 800 °C, where the fibrous coatings were disrupted by the newly formed sharp rutile (TiO2) micro-crystals. Such surface topography acts against the initial adhesion and proliferation of osteoblast like cells.