Calcium phosphate coatings for medical and dental implants

β-pyrophosphate: A potential biomaterial for dental applications

Tooth hypersensitivity is a growing problem affecting both the young and ageing population worldwide. Since an effective and permanent solution is not yet available, we propose a new methodology for the restoration of dental enamel using femtosecond lasers and novel calcium phosphate biomaterials. During this procedure the irradiated mineral transforms into a densified layer of acid resistant iron doped β-pyrophosphate, bonded with the surface of eroded enamel. Our aim therefore is to evaluate this densified mineral as a potential replacement material for dental hard tissue. To this end, we have tested the hardness of β-pyrophosphate pellets (sintered at 1000°C) and its mineral precursor (brushite), the wear rate during simulated tooth-brushing trials and the cytocompatibility of these minerals in powder form. It was found that the hardness of the β-pyrophosphate pellets is comparable with that of dental enamel and significantly higher than dentine while, the brushing trials prove that the wear rate of β-pyrophosphate is much slower than that of natural enamel. Finally, cytotoxicity and genotoxicity tests suggest that iron doped β-pyrophosphate is cytocompatible and therefore could be used in dental applications. Taken together and with the previously reported results on laser irradiation of these materials we conclude that iron doped β-pyrophosphate may be a promising material for restoring acid eroded and worn enamel.

Delivery of a therapeutic protein for bone regeneration from a substrate coated with graphene oxide

The therapeutic efficacy of drugs often depends on the drug delivery carrier. For efficient delivery of therapeutic proteins, delivery carriers should enable the loading of large doses, sustained release, and retention of the bioactivity of the therapeutic proteins. Here, it is demonstrated that graphene oxide (GO) is an efficient carrier for delivery of therapeutic proteins. Titanium (Ti) substrates are coated with GO through layer-by-layer assembly of positively (GO-NH₃⁺) and negatively (GO-COO⁻) charged GO sheets. Subsequently, a therapeutic protein (bone morphogenetic protein-2, BMP-2) is loaded on the GO-coated Ti substrate with the outermost coating layer of GO-COO⁻ (Ti/GO⁻). The GO coating on Ti substrate enables loading of large doses and the sustained release of BMP-2 with preservation of the structure and bioactivity of the drug. The extent of in vitro osteogenic differentiation of human bone marrow-derived mesenchymal stem cells is higher when they are cultured on Ti/GO- carrying BMP-2 than when they are cultured on Ti with BMP-2. Eight weeks after implantation in mouse models of calvarial defects, the Ti/GO-/BMP-2 implants show more robust new bone formation compared with Ti, Ti/GO-, or Ti/BMP-2 implants. Therefore, GO is an effective carrier for the controlled delivery of therapeutic proteins, such as BMP-2, which promotes osteointegration of orthopedic or dental Ti implants.

Influence of substrate metal alloy type on the properties of hydroxyapatite coatings deposited using a novel ambient temperature deposition technique

Hydroxyapatite (HA) coatings are applied widely to enhance the level of osteointegration onto orthopedic implants. Atmospheric plasma spray (APS) is typically used for the deposition of these coatings; however, HA crystalline changes regularly occur during this high-thermal process. This article reports on the evaluation of a novel low-temperature (<47°C) HA deposition technique, called CoBlast, for the application of crystalline HA coatings. To-date, reports on the CoBlast technique have been limited to titanium alloy substrates. This study addresses the suitability of the CoBlast technique for the deposition of HA coatings on a number of alternative metal alloys utilized in the fabrication of orthopedic devices. In addition to titanium grade 5, both cobalt chromium and stainless steel 316 were investigated. In this study, HA coatings were deposited using both the CoBlast and the plasma sprayed techniques, and the resultant HA coating and substrate properties were evaluated and compared. The CoBlast-deposited HA coatings were found to present similar surface morphologies, interfacial properties, and composition irrespective of the substrate alloy type. Coating thickness however displayed some variation with the substrate alloy, ranging from 2.0 to 3.0 μm. This perhaps is associated with the electronegativity of the metal alloys. The APS-treated samples exhibited evidence of both coating, and significantly, substrate phase alterations for two metal alloys; titanium grade 5 and cobalt chrome. Conversely, the CoBlast-processed samples exhibited no phase changes in the substrates after depositions. The APS alterations were attributed to the brief, but high-intensity temperatures experienced during processing.

Contact nanofatigue shows crack growth in amorphous calcium phosphate on Ti, Co-Cr and Stainless steel

Fatigue testing of load-bearing coated implants is usually very time-consuming and so a new contact nanofatigue test using a nanoindenter has been evaluated. A cube corner indenter provided the fastest indication of failure, through crack formation, compared to a spherical indenter. Contact nanofatigue was performed on a sintered hydroxyapatite and then on amorphous calcium phosphate splats produced on titanium, stainless steel and Co-Cr surfaces, made either at room temperature or on 250°C preheated surfaces. Sintered hydroxyapatite showed continual plastic deformation, but this is not that apparent for splats on metal surfaces. Substrate preheating was found to induce cracking in splats, explained by greater thermal residual stresses. Endurance during contact nanofatigue, measured as time to crack formation, was the lowest for splats on titanium followed by Co-Cr and stainless steel. The splat on titanium showed both cracking and plastic deformation during testing. Good agreement has been reached with previous studies with cracking directed to the substrate without splat delamination. Contact nanofatigue with the nanoindenter easily and quickly identifies cracking events that previously required detection with acoustic emission, and shows good feasibility for mechanical testing of discs and splats produced by thermal spraying, spray forming, laser-ablation, aerosol jet and ink jet printing.

Comparison between the SBF Response of Hydroxyapatite Coatings Deposited Using both a Plasma-Spray and a Novel Co-Incident Micro-Blasting Technique

This paper reports on the response of hydroxyapatite (HA) coatings, fabricated using two deposition technologies, to immersion in simulated body fluid (SBF). The deposition methods used were: plasma spray, a commercial standard, and CoBlast, a novel low temperature microblast technique. In the case of the latter, HA coatings are deposited by simultaneous blasting HA and abrasive powders concentrically at a metallic substrate, resulting in a thin layer of HA (approx. 2.5 µm thick). Groups of the CoBlast and plasma spray HA coatings were immersed in 7 ml of SBF solution for 1, 2, 4, 7, 14 and 28 days, and were subsequently removed and examined for any alterations caused by the SBF solution. It was noted from this study that the CoBlast HA coatings appeared to undergo a two step calcium phosphate recrystallisation process; initial homogenous nucleation and subsequent heterogeneous nucleation. Conversely recrystallisation on the plasma spray coatings appeared to proceed largely through a heterogeneous nucleation process. Two factors that may influence the differences in HA recrystallisation is the presence of amorphous HA resulting in rapid dissolution, and/or the significantly lower surface area (roughness) offered to the SBF solution by the CoBlast coatings. The interpretation of recrystallisation mechanisms from this preliminary study is limited however by the differences in coating morphology and thickness (27 versus 2 µm) for the plasma spray and CoBlast HA coatings respectively.

Selection of the implant and coating materials for optimized performance by means of nanoindentation

Mechanical compatibility between a coating and a substrate is important for the longevity of implant materials. While previous studies have utilized the entire coating for analysis of mechanical compatibility of the surface, this study focuses on the nanoindentation of a uniformly thermally sprayed splat. Hydroxyapatite was thermally sprayed to create a homogeneous deposit density, as confirmed by microRaman spectroscopy, of amorphous calcium phosphate. Substrates were commercially pure Ti, Ti-6Al-4V, Co-Cr alloy and stainless steel. Nanoindentation revealed that splats deposited on the different metals have similar hardness and elastic modulus values of 4.2 ± 0.2 GPa and 80 ± 3 GPa, respectively. The mechanical properties were affected by the substrate type more than residual stresses, which were found to be low. It is recommended that amorphous calcium phosphate is annealed to relieve the quenching stress or that appropriate temperature histories are chosen to relax the stress created in cooling the coating assembly.

Compositionally graded hydroxyapatite/tricalcium phosphate coating on Ti by laser and induction plasma

In this study we report the fabrication of compositionally graded hydroxyapatite (HA) coatings on Ti by combining laser engineering net shaping (LENS) and radio frequency induction plasma spraying processes. Initially, HA powder was embedded in the Ti substrates using LENS, forming a Ti-HA composite layer. Later, RF induction plasma spraying was used to deposit HA on these Ti substrates with a Ti-HA composite layer on top. Phase analysis by X-ray diffraction indicated phase transformation of HA to β-tricalcium phosphate in the laser processed coating. Laser processed coatings showed the formation of a metallurgically sound and diffused substrate-coating interface, which significantly increased the coating hardness to 922 ± 183 Hv from that of the base metal hardness of 189 ± 22 Hv. In the laser processed multilayer coating a compositionally graded nature was successfully achieved, however, with severe cracking and a consequent decrease in the flexural strength of the coating. To obtain a structurally stable coating with a composition gradient across the coating thickness a phase pure HA layer was sprayed on top of the laser processed single layer coatings using induction plasma spray. The plasma sprayed HA coatings were strongly adherent to the LENS-TCP coatings, with adhesive bond strength of 21 MPa. In vitro biocompatibility of these coatings, using human fetal osteoblast cells, showed a clear improvement in cellular activity from uncoated Ti compared with LENS-TCP-coated Ti and reached a maximum in the plasma sprayed HA coating.

Induction Plasma Sprayed Nano Hydroxyapatite Coatings on Titanium for Orthopaedic and Dental Implants

This paper reports preparation of a highly crystalline nano hydroxyapatite (HA) coating on commercially pure titanium (Cp-Ti) using inductively coupled radio frequency (RF) plasma spray and their in vitro and in vivo biological response. HA coatings were prepared on Ti using normal and supersonic plasma nozzles at different plate powers and working distances. X-ray diffraction (XRD) and Fourier transformed infrared spectroscopic (FTIR) analysis show that the normal plasma nozzle lead to increased phase decomposition, high amorphous calcium phosphate (ACP) phase formation, and severe dehydroxylation of HA. In contrast, coatings prepared using supersonic nozzle retained the crystallinity and phase purity of HA due to relatively short exposure time of HA particles in the plasma. In addition, these coatings exhibited a microstructure that varied from porous and glassy structure at the coating-substrate interface to dense HA at the top surface. The microstructural analysis showed that the coating was made of multigrain HA particles of ~200 nm in size, which consisted of recrystallized HA grains in the size range of 15- 20 nm. Apart from the type of nozzle, working distance was also found to have a strong influence on the HA phase decomposition, while plate power had little influence. Depending on the plasma processing conditions, a coating thickness between 300 and 400 μm was achieved where the adhesive bond strengths were found to be between 4.8 MPa to 24 MPa. The cytotoxicity of HA coatings was examined by culturing human fetal osteoblast cells (hFOB) on coated surfaces. In vivo studies, using the cortical defect model in rat femur, evaluated the histological response of the HA coatings prepared with supersonic nozzle. After 2 weeks of implantation, osteoid formation was evident on the HA coated implant surface, which could indicate early implant- tissue integration in vivo.

Apatite formation on titanium substrates by electrochemical deposition in metastable calcium phosphate solution

An apatite layer was successfully formed on titanium substrates by electrochemical deposition in a metastable calcium phosphate solution, which had 1.5 times the ion concentrations of a normal simulated body fluid, but did not contain MgCl(2).6H(2)O, at 41 degrees C for 40 or 60 min at 13 mA. The current did not produce large effects on the crystalline size of the apatite, but the thickness of the apatite layer could be controlled by deposition conditions such as electrolyte temperature, current and deposition time. It is expected that the present electrochemical deposition will be useful to rapidly coat apatite on metallic materials.

Effect of substrate temperature on mechanical properties of calcium phosphate coatings

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.

In vitro anti-bacterial and biological properties of magnetron co-sputtered silver-containing hydroxyapatite coating

Bacterial infection after implant placement is a significant rising complication. In order to reduce the incidence of implant-associated infections, several biomaterial surface treatments have been proposed. In this study, the effect of in vitro antibacterial activity and in vitro cytotoxicity of co-sputtered silver (Ag)-containing hydroxyapatite (HA) coating was evaluated. Deposition was achieved by a concurrent supply of 10 W to the Ag target and 300 W to the HA target. Heat treatment at 400 degrees C for 4 h was performed after 3 h deposition. X-ray diffraction, contact angles measurements, and surface roughness were used to characterize the coating surfaces. The RP12 strain of Staphylococcus epidermidis (ATCC 35984) and the Cowan I strain of Staphylococcus aureus were used to evaluate the antibacterial activity of the Ag-HA coatings, whereas human embryonic palatal mesenchyme cells, an osteoblast precursor cell line, were used to evaluate the in vitro cytotoxicity of the coatings. X-ray diffraction analysis performed in this study indicated peaks corresponding to Ag and HA on the co-sputtered Ag-HA surfaces. The contact angles for HA and Ag-HA surfaces were observed to be significantly lower when compared to Ti surfaces, whereas no significant difference in surface roughness was observed for all groups. In vitro bacterial adhesion study indicated a significantly reduced number of S. epidermidis and S. aureus on Ag-HA surface when compared to titanium (Ti) and HA surfaces. In addition, no significant difference in the in vitro cytotoxicty was observed between HA and Ag-HA surfaces. Overall, it was concluded that the creation of a multifunctional surface can be achieved by co-sputtering the osteoconductive HA with antibacterial Ag.

Dissolution behavior and in vitro evaluation of sputtered hydroxyapatite films subject to a low temperature hydrothermal treatment

Hydroxyapatite (HA) was coated onto titanium substrates using radio frequency sputtering. Some of the as-sputtered films were hydrothermally recrystallized at 110 degrees C. In immersion tests, the as-sputtered film completely dissolved after 2 days in a culture medium, whereas the thickness of hydrothermally treated films increased with an increase in immersion period, reaching a thickness of 127% after a period of 4 weeks. The proliferation and alkaline phosphatase (ALP) activity of MC3T3-E1 osteoblast-like cells on the as-sputtered and hydrothermally treated films were investigated, and the cell morphology was also observed using scanning electron microscopy. The proliferation of MC3T3-E1 cells on the as-sputtered films was suppressed, whereas proliferation on the hydrothermally treated films was comparable to that on control and titanium substrate. The suppression of cell proliferation is associated with an increase in pH of the culture medium caused by dissolution of the as-sputtered film. After a 96-h culture time, the ALP activity of the cells on the hydrothermally treated film was higher than that on the control, titanium substrate, and as-sputtered film samples. From scanning electron microscopic observations, it was found that the MC3T3-E1 cells on the hydrothermally treated films were elongated and had established more intricate filopodia networks with each other, which were also observed for MC3T3-E1 cells on the as-sputtered films after a period of 24 h.

The Effect of Sputtered Calcium Phosphate Coatings of Different Crystallinity on Osteoblast Differentiation

BACKGROUND

Coating titanium implants with hydroxyapatite (HA) has been suggested to increase osseointegration by stimulating early osteoblast function. The goal of this study was to determine the extent to which the crystalline content of the HA surface affected osteoblast function in vitro.

METHODS

Osteoblasts were isolated from fetal rat calvaria. Titanium coupons were sputter coated and analyzed. Mineralized nodule formation on plastic using von Kossa staining was compared to tetracycline and procion dye labeling. Cell proliferation, adhesion, alkaline phosphatase activity, morphology and spreading, and cytoskeletal arrangement were analyzed. Reverse transcription-polymerase chain reaction (RT-PCR) was used to determine the expression of mRNA for specific proteins.

RESULTS

The percent crystallinity of coatings was 0% (HA1), 1.9% +/- 0.4% (HA2), and 66.4% +/- 2.8% (HA3). The nodule formation and cell number were greatest on titanium and HA3 compared to HA1 and HA2 (P < 0.01). At weeks 2 to 4, all samples showed strong alkaline phosphatase, osteocalcin, monocyte-colony stimulating factor (M-CSF), and receptor activator of nuclear factor kappa B ligand (RANKL) expression, but the specific activity of alkaline phosphatase decreased. Cell adherence was greater than 60% of applied cells for all surfaces except HA3. The cells were significantly more elongated on titanium, with no difference on the HA-coated surfaces. Actin filaments were arranged peripherally at 5 hours but arranged parallel to the long axis of the cell at 20 hours.

CONCLUSIONS

Procion labeling is a valid method for evaluating mineralized nodule formation on opaque surfaces. There were no major differences in osteoblast function using titanium or high-crystalline coatings, and most functions were decreased on amorphous or low-crystalline coatings.

Effect of post-deposition heating temperature and the presence of water vapor during heat treatment on crystallinity of calcium phosphate coatings

In this study, radiofrequency sputtered calcium phosphate (CaP) coatings were evaluated after 1h post-deposition heat treatment at either 350 degrees C, 400 degrees C, 450 degrees C, 500 degrees C or 600 degrees C in the presence or absence of water vapor. X-ray diffraction analyses indicated the as-sputtered coatings to be amorphous. With different post-deposition heat treatments used, in this study, crystallinity of CaP coatings was observed to be in the range of 0-68%. The 400 degrees C and 450 degrees C heat-treated CaP coatings in the absence of water vapor were poorly crystalline, exhibiting a crystallinity of 2+/-1%. In comparison to heat treatments at 450 degrees C in the absence of water vapor, the presence of water vapor at 450 degrees C heat treatment resulted in a significant increase in coating crystallinity. However, this effect was not observed at higher temperatures. A coating crystallinity of 60-68% was observed for coatings heat treated at 450 degrees C in the presence of water vapor, and at 500 degrees C and 600 degrees C in the presence or absence of water vapor. In addition, increases in the degree of coating crystallinity were observed to be consistent with the increasing number of PO(4) peaks observed as a result of different post-deposition heat treatments. It was concluded that the presence of water vapor at 450 degrees C post-deposition heat treatment significantly affect the crystallinity of CaP coatings, whereas an increase to temperature higher than 450 degrees C and in the presence of water vapor has no significant effect on crystallinity.

Osteoblast precursor cell attachment on heat-treated calcium phosphate coatings

The influence of properties of calcium phosphate (CaP) coatings on bone cell activity and bone-implant osseointegration is not well-established. This study investigated the effects of characterized CaP coatings of various heat treatments on osteoblast response. It was hypothesized that heat treatments of CaP coatings alter the initial osteoblast attachment. The 400 degrees C heat-treated coatings were observed to exhibit poor crystallinity and significantly greater phosphate or apatite species compared with as-sputtered and 600 degrees C heat-treated coatings. Similarly, human embryonic palatal mesenchyme (HEPM) cells, an osteoblast precursor cell line, seeded on 400 degrees C heat-treated coatings, exhibited significantly greater cell attachment compared with Ti surfaces, as-sputtered coatings, and 600 degrees C heat-treated coatings. The HEPM cells on Ti surfaces and heat-treated coatings were observed to attach through filopodia, and underwent cell division, whereas the cells on as-sputtered coatings displayed fewer filopodia extensions and cell damage. Analysis of the data suggested that heat treatment of CaP coatings affects cell attachment.

Bone response to radio frequency sputtered calcium phosphate implants and titanium implants in vivo

The objective of this study was to evaluate the effect of radio frequency sputtered calcium phosphate (CaP) coatings of titanium (Ti) implants on the bond strength at the bone-implant interface and percent bone contact length. Cylindrical coated or noncoated implants (4.0-mm diameter by 8-mm long) were implanted for 3 and 12 weeks. At 3 weeks after implant placement, the ultimate interfacial strengths for as-deposited CaP-coated and heat-treated CaP-coated implants were 2.29 +/- 0.14 MPa and 1.28 +/- 0.04 MPa, respectively. These ultimate interfacial strength values at 3 weeks were statistically greater than the mean ultimate interfacial strength for control Ti implants (0.67 +/- 0.13 MPa). At 12 weeks after implant placement, no statistical differences in the mean ultimate interfacial strengths were observed between the as-deposited CaP-coated, heat-treated CaP-coated, and control Ti implants. Histomorphometric evaluation indicated greater percent bone contact lengths for the as-deposited CaP-coated implants compared with the heat-treated CaP-coated and control Ti implants 3 and 12 weeks after implant placement.

Influence of coating strain on calcium phosphate thin-film dissolution

The success of calcium phosphate (CaP) coatings used to accelerate initial bone growth onto dental implants can vary depending on the CaP phases present in the coating. In this study, the effect of CaP coating crystal structure and morphology on dissolution rates was investigated. RF magnetron-sputtered CaP coatings (NTC) were compared to a less strained coating (HTC) obtained from heat treatment of sputtered samples at 550 degrees C. Coating strain differences were apparent in XRD spectra where hydroxyapatite-like planes shifted by 0.5 degrees 2theta and 0.05 degrees 2theta for the NTC and HTC coatings, respectively. HTC XRD peak widths were broader than NTC peak widths, indicating smaller crystals or grain sizes. These differences in grain size were corroborated by imaging with scanning probe microscopy. NTC coatings dissolved at a 300% faster rate than HTC coatings. A major factor contributing to this kinetic effect was the level of strain in both coatings. These results suggest an alternate design for CaP coatings can be obtained through the manipulation of coating strain. Using this approach, delivery of different ionic gradients from CaP coatings to surrounding tissue environments can be obtained from surfaces having similar chemistries.

Effects of cyclic bending and physiological solution on plasma-sprayed hydroxylapatite coatings of varying crystallinity

This study investigated the effects of cyclic bending stress levels and testing in simulated physiological solutions or air on the integrity of plasma-sprayed hydroxylapatite (HA) coatings of two different crystallinities. Hydroxylapatite-coated commercially pure (CP) Ti rods were evaluated by immersion testing in Hank's Balanced Salt Solution (HBSS) and by rotating bending in air and HBSS. Static immersion testing of nonstressed specimens resulted in significant microcracking of coating surfaces after 42 days. Specimens cyclically tested at bending stresses above the yield strength of Ti experienced low cycle fatigue failure of the Ti substrates prior to spallation of the HA coatings. Coatings tested at 1 x 10(6) cycles with interface bending stresses of 180 MPa displayed increased surface microcracking, but no bulk coating spallation. Coatings cycled in HBSS displayed greater amounts of microcracking and surface alteration than samples cycled in air. There was no apparent relation between HA crystallinity and mechanical integrity under cyclic bending stresses.

Proteoglycans at the bone-implant interface

The widespread success of clinical implantology stems from bone's ability to form rigid, load-bearing connections to titanium and certain bioactive coatings. Adhesive biomolecules in the extracellular matrix are presumably responsible for much of the strength and stability of these junctures. Histochemical and spectroscopic analyses of retrievals have been supplemented by studies of osteoblastic cells cultured on implant materials and of the adsorption of biomolecules to titanium powder. These data have often been interpreted to suggest that proteoglycans permeate a thin, collagen-free zone at the most intimate contact points with implant surfaces. This conclusion has important implications for the development of surface modifications to enhance osseointegration. The evidence for proteoglycans at the interface, however, is somewhat less than compelling due to the lack of specificity of certain histochemical techniques and to possible sectioning artifacts. With this caveat in mind, we have devised a working model to explain certain observations of implant interfaces in light of the known physical and biological properties of bone proteoglycans. This model proposes that titanium surfaces accelerate osseointegration by causing the rapid degradation of a hyaluronan meshwork formed as part of the wound-healing response. It further suggests that the adhesive strength of the thin, collagen-free zone is provided by a bilayer of decorin proteoglycans held in tight association by their overlapping glycosaminoglycan chains.

Osteoblast precursor cell activity on HA surfaces of different treatments

The clinical success of dental implants is governed by implant surfaces and bone cell responses that promote rapid osseointegration and long-term stability. The specific objective of this study was to investigate osteoblast precursor cell responses to hydroxyapatite (HA) surfaces of different treatments. Since the nature of bone cell responses in vitro is influenced by the properties of HA ceramics, this study was divided into two components: a chemical and crystallographic characterization of the HA ceramics and an in vitro cell culture study. The sintered HA samples were observed to have the highest crystallite size as compared to the as-received HA and calcined HA samples. No differences in the surface roughness and chemical composition were observed among the sintered, calcined, and as-received HA surfaces. In concurrence with the X-ray diffraction, high resolution XPS resolution of Ca 2p also indicated a higher crystallinity on sintered HA samples as compared to the calcined and as-received HA samples. As indicated by increased alkaline phosphatase-specific activity, increased cell-surface and matrix-associated protein, and 1.25 (OH2) vitamin D3-stimulated osteocalcin production, a more differentiated osteoblast-like phenotype was observed on the sintered HA surfaces compared to the as-received HA and calcined HA surfaces. An increased osteoblast-like cell activity on the sintered HA surfaces suggested that the crystallite size of HA surfaces may play an important role in governing cellular response.