Bioceramics are biocompatible ceramic materials, that interact with biological systems
of the body to treat, strengthen or replace body functions. Most conventional bioceramics
are oxide ceramics, glass ceramics and calcium phosphate ceramics. Among
these calcium phosphates, synthetic hydroxyapatite has been extensively studied due
to its biomimetic properties similar to that of natural bone. One approach to prepare
synthetic hydroxyapatite is to first deposit amorphous Ca-P-O thin film and then by
means of post deposition annealing initiate the formation of hydroxyapatite crystals
to the film. In addition to the correct film composition and crystalline structure, other
surface properties such as wettability and surface nano- and microtopography are very
significant for the biocompatibility.
In this study Ca-P-O thin films were deposited using two different techniques, ion
beam sputtering and atomic layer deposition (ALD). Films deposited using both techniques
were amorpho
us after deposition. For sputter deposited films, the Ca/P atomic
ratio determined by means of ion beam analysis approached stoichiometric hydroxyapatite
when hydroxyapatite powder doped with extra phosphorous was used as the
sputtering target. Though the sputtered films showed good biocompatibility in cell
attachment studies, the dissolution of as-deposited films in cell culture medium is
a disadvantage. The surface of as-deposited and annealed thin films deposited using
ALD were locally modified by high and low energy irradiation. After low energy
ion irradiation the as-deposited films showed an increase in hydrophilicity, which was
determined using contact angle measurements, and also greater spreading of mouse
pre-osteoblast cells.
The effect of surface topography was studied by abrading Ti metal substrates to
different roughnesses before depositing 2–50 nm thick ALD Ca-P-O films on them. Ti
was selected in order to combine the biocompatibility of Ca-P-O thin-films with the
mechanical strength of the Ti metal substrate. Ca-P-O films deposited on smoother
substrates showed higher Ca/P atomic ratios than those on the rough substrates,
demonstrating the influence of roughness on the film growth during the deposition.
As-deposited Ca-P-O films acted as equally good cell culture substrate as untreated
Ti samples used as a control.
After post deposition annealing at 800 C, Ca-P-O films were crystallized on Si substrates
and showed filopodic morphology of pre-osteoblast cells. Films on Ti showed
also filopodic morphology of cells after 700 C annealing but at 800 C the number of
cells substantially dropped, most likely due to formation of a less biocompatible TiO2
rutile phase on the surface.
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