Electrostatic spray deposition (ESD) of calcium phosphate coatings, an in vitro study with osteoblast-like cells

Electrostatic spray deposition (ESD) is a recently developed technique to deposit a calcium phosphate (CaP) coating upon substrates. With this technique, an organic solvent containing calcium and phosphate is pumped through a nozzle. Between the nozzle and substrate a high voltage is applied. As a consequence, droplets coming out the nozzle disperse into a spray, and this spray is deposited upon the substrate. When the solvent has evaporated, a coating is formed on the substrate. ESD allows for a variation in coating composition and morphology. Titanium alloy (TiAl6V4) substrates were coated with a CaP layer using two different methods; radio frequency magnetron sputtering, and ESD. These surfaces were characterized with X-ray diffraction, Fourier transform infrared spectroscopy, an universal surface tester, scanning electron microscopy, and energy dispersive spectrometry. Subsequently, bone marrow cells were isolated from rat femora and cultured 1, 4, 8, 14 and 16 days. Cell proliferation, alkaline phosphatase activity, and osteocalcin concentration were assayed. RT-PCR was done for collagen type I and osteocalcin. SEM was also performed to observe cellular behaviour during culture. Two separate runs of the experiment were performed. In the first run, osteoblast-like cells on both CaP coatings showed similar results in all assays. In the second run, proliferation and osteogenic expression had increased on ESD coatings. On basis of these results, we conclude that the novel ESD coating behaved similar to, or even better than the known RF magnetron sputter coating. Thus, ESD could be a valid addition to already existing CaP coating processes.