coating would intrinsically imply a certain degree of replication of biological apatites,
featuring nano-crystalline structures in bone and dentin materials. Above all, surface
morphology with nano-scale features and excellent island uniformity, appears to be a
critical factor in promoting bio-molecule/protein - surface interactions.
Thus, fabrication of a graded bioceramic-implant structure capable of simultaneously sat-
isfying the basic requirements for the interfacial stability at the coating-implant interface,
controllable stoichiometry and crystallinity in the bulk, and the optimized, from the point
of view of sustained protein attachment and growth, nano-scaled surface morphology, is a
critical problem in the biomaterials research. In particular, a large number of the existing
techniques for CaP-based films (including HA) deposition suffer from poor coating-metal
implant interfacial bonding strength, excessive amorphosity or larger, than in natural apa-
tites, crystal size in the bulk, as well as irregular surface morphology features typically in
the micrometer range.
EXPERIMENTAL DETAILS
Here, we report on a new and efficient technique for synthesis of a graded CaP-based
biocompatible interlayer on orthopedic alloy Ti-6Al-4V, consistently satisfying all the
above requirements. The essential part of the method is a concurrent low-temperature
plasma-assisted Rf magnetron sputtering (PA-RFMS) of crystalline HA and metallic tita-
nium targets in low-pressure discharges of reactive gas mixtures of argon and water va-
por sustained in PSAC/PA-RFMS facility. The titanium target has purposely been intro-
duced to create a titanium-rich layer adjacent and stronger adhering to the implant-
simulating metallic sample. The discharges were sustained in the range of Rf powers of
P
in
= 300 - 700 W applied to a water-chilled Rf magnetron electrode with several rows of
concentrically positioned permanent magnets with specific polarities. The working pres-
sure p
0
was typically maintained in the range of 10 to 70 mTorr. In this pressure and
power range, large DC sheath potentials near the HA/Ti target surface, promoting high
sputtering yields, and eventually high film deposition rates, can be achieved. An electri-
cally floating substrate heater powered by an external temperature controller supports the
Ti-6Al-4V samples, with the surface being coated facing downwards, approximately 6
cm above the HA/Ti sputtering target. In the experiments, the substrates were negatively
biased with V
b
= 25 - 200 V. Chemical composition and elemental bonding states in the
interlayer were studied by VG ESCALAB 220i-XL spectrometer (XPS). The crystal
structure was characterized using SIEMENS D5005 X-Ray diffractometer (XRD) in a
lock coupled (θ − 2θ) mode with an incident x-ray wavelength of 1.540A (Cu Kα line).
Cross-sectional structure of the functionally graded structure was examined with the
Field Emission Scanning Electron Microscopy (FESEM). Nano-scaled features of the
surface morphology were studied by the Atomic Force Microscope in a contact mode
(AFM). Bio-ceramic-metal interfacial bonding strength was assessed via a Micro-scratch
teste. Further details of the PSAC/PA-RFMS sputtering facility, routine steps in pre-
deposition substrate treatment, as well as film characterization instruments and tech-
niques, can be found elsewhere [7,8].
F3.42.2