@article{bai_sandukas_appleford_ong_rabiei_2012, title={Antibacterial effect and cytotoxicity of Ag-doped functionally graded hydroxyapatite coatings}, volume={100B}, ISSN={["1552-4981"]}, DOI={10.1002/jbm.b.31985}, abstractNote={Functionally graded hydroxyapatite coatings (FGHA) doped with 1, 3, and 6.5 wt % silver (Ag) have been deposited on Titanium using ion-beam-assisted deposition. Scanning transmission electron microscopy on coating cross sections confirmed the presence of FGHA coating with mostly amorphous layers at the top and mostly crystalline layers toward the coating interface as well as the existence of 10–50 nm Ag particles distributed throughout the thickness of the coatings. Calcium release in phosphate buffered saline solution showed a high release rate of Ca at the beginning of the test, and a gradual decrease in release rate thereafter to a minimum level until day 7. Similarly, the release rate of Ag in ultra pure water was initially high in the first 4 h and then gradually decreased over a 7 days period. Antibacterial tests have shown a reduction in the viability of S. aureus in Ag-doped coatings particularly in samples with higher Ag concentrations of 3 and 6.5 wt %. Cytotoxicity tests using an osteoblast cell line, on the other hand, have demonstrated that the samples with 6.5 wt % Ag have a negative effect on osteoblast cell response, proliferation, and apoptosis as well as a negative effect on protein and osteocalcin production. It is notable that the samples with 3 wt % Ag or less presented minimal cytotoxicity compared with control surfaces. Considering both the antibacterial and cytotoxicity effects, it is suggested that the 3 wt % of Ag in FGHA coatings can be favorable. © 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 100B: 553–561, 2012.}, number={2}, journal={JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART B-APPLIED BIOMATERIALS}, author={Bai, Xiao and Sandukas, Stefan and Appleford, Mark and Ong, Joo L. and Rabiei, Afsaneh}, year={2012}, month={Feb}, pages={553–561} }
 @article{bai_more_rouleau_rabiei_2010, title={Functionally graded hydroxyapatite coatings doped with antibacterial components}, volume={6}, ISSN={["1878-7568"]}, DOI={10.1016/j.actbio.2009.12.002}, abstractNote={A series of functionally graded hydroxyapatite (FGHA) coatings incorporated with various percentages of silver were deposited on titanium substrates using ion beam-assisted deposition. The analysis of the coating’s cross-section using transmission electron microscopy (TEM) and scanning transmission electron microscopy equipped with energy dispersive X-ray spectroscopy has shown a decreased crystallinity as well as a distribution of nanoscale (10–50 nm) silver particles from the coating/substrate interface to top surface. Both X-ray diffraction and fast Fourier transforms on high-resolution TEM images revealed the presence of hydroxyapatite within the coatings. The amount of Ag (wt.%) on the outer surface of the FGHA, as determined from X-ray photoelectron spectroscopy, ranged from 1.09 to 6.59, which was about half of the average Ag wt.% incorporated in the entire coating. Average adhesion strengths evaluated by pull-off tests were in the range of 83 ± 6 to 88 ± 3 MPa, which is comparable to 85 MPa for FGHA without silver. Further optical observations of failed areas illustrated that the dominant failure mechanism was epoxy failure, and FGHA coating delamination was not observed.}, number={6}, journal={ACTA BIOMATERIALIA}, author={Bai, Xiao and More, Karren and Rouleau, Christopher M. and Rabiei, Afsaneh}, year={2010}, month={Jun}, pages={2264–2273} }
 @article{bai_sandukas_appleford_ong_rabiei_2009, title={Deposition and investigation of functionally graded calcium phosphate coatings on titanium}, volume={5}, ISSN={["1878-7568"]}, DOI={10.1016/j.actbio.2009.05.013}, abstractNote={A series of calcium phosphate coatings with graded crystallinity were deposited onto heated titanium substrates using ion beam assisted deposition. The microstructure of the coating was examined using transmission electron microscopy (TEM). The coating thickness was observed to be in a range of 594-694 nm. The degree of crystallinity and microstructural grain size of the coating showed a clear decrease with increasing distance from the substrate-coating interface. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of PO(4)(3-), and X-ray photoelectron spectroscopy (XPS) analysis on the coating top surface showed that the atomic Ca/P ratio was in the range of 1.52+/-0.15 to 1.61+/-0.07. The biological response to the coatings was also evaluated using an osteoblast precursor cell culture test. More cells and a higher integrin expression of cell attachment sites were observed on the coating surface when compared to the control group (blank titanium surface). The pull-off test showed average adhesion strengths at the coating-substrate interface to be higher than 85.12+/-5.37 MPa. Nanoindentation tests indicated that the Young's moduli of all coatings are higher than 91.747+/-3.641 GPa and microhardness values are higher than 5.275+/-0.315 GPa. While the adhesion strength results helped us to identify the best setup for substrate temperature and processing parameters to begin the deposition, the culture test and XPS results helped identifying the optimum parameters for the last stage of deposition. TEM, X-ray diffraction, FTIR and nanoidentation results were used to further evaluate the quality of the coating and optimization of its processing parameters.}, number={9}, journal={ACTA BIOMATERIALIA}, author={Bai, Xiao and Sandukas, Stefan and Appleford, Mark R. and Ong, Joo L. and Rabiei, Afsaneh}, year={2009}, month={Nov}, pages={3563–3572} }
 @article{blalock_bai_narayan_rabiei_2008, title={Effect of substrate temperature on mechanical properties of calcium phosphate coatings}, volume={85B}, ISSN={["1552-4981"]}, DOI={10.1002/jbm.b.30917}, abstractNote={The effect of substrate temperature and processing parameters on mechanical properties of nanoscale calcium phosphate coatings are being studied in order to refine the processing technique for Functionally Graded Hydroxyapatite (FGHA) coatings. Coatings were deposited on titanium substrates with a set substrate temperature of 450, 550, 650, or 750 degrees C in an Ion Beam Assisted Deposition (IBAD) system using a sintered hydroxyapatite (HA) target. Mechanical properties of the coatings deposited with a set substrate temperature such as, bonding/adhesion strength to the substrate, nanohardness, and Young's Modulus as well as coating thickness were evaluated and compared with commercial plasma spray HA coatings. It is concluded that depositing FGHA coatings would better be started at 550-650 degrees C to maintain superior properties of the film at the interface. It can also be concluded that the residual stresses caused by different Coefficient of Thermal Expansions (CTEs) between the substrate and coatings are not the only factor controlling the bonding strength and mechanical properties of these samples. Other parameters such as the nature of the interface layers and their bonding to each other as well as the density and grain structure of the coatings must be taken into consideration for an appropriate evaluation of mechanical properties of calcium phosphate coatings deposited on heated substrate.}, number={1}, journal={JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART B-APPLIED BIOMATERIALS}, author={Blalock, Travis L. and Bai, Xiao and Narayan, Roger and Rabiei, Afsaneh}, year={2008}, month={Apr}, pages={60–67} }
 @article{blalock_bai_rabiei_2007, title={A study on microstructure and properties of calcium phosphate coatings processed using ion beam assisted deposition on heated substrates}, volume={201}, ISSN={["0257-8972"]}, DOI={10.1016/j.surfcoat.2006.10.039}, abstractNote={In this study a set of thin Hydroxyapatite (HA) [Ca 10 (PO 4 ) 6 (OH) 2 ] coatings was deposited on heated silicon and titanium substrates using Ion Beam Assisted Deposition (IBAD). The effects of substrate temperature and processing parameters on the microstructural properties and composition of the coatings are being studied. Analytical techniques include transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) with an energy dispersive X-ray spectroscopy (EDS), as well as scanning electron microscopy (SEM) with EDX, X-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). The current results indicate that as substrate temperature increases the Ca/P ratio of the coatings both on titanium and silicon substrates increases. The crystallinity of the coatings and the number of calcium phosphate compounds within the coating including HA also increases. STEM–EDS revealed an atomically diffused intermediate layer at the interface between the coating and substrate. XRD results along with TEM selected area diffraction (SAD) revealed that the coatings are composed of HA, other calcium phosphate, and calcium oxide compounds.}, number={12}, journal={SURFACE & COATINGS TECHNOLOGY}, author={Blalock, Travis and Bai, Xiao and Rabiei, Afsaneh}, year={2007}, month={Mar}, pages={5850–5858} }