Hydroxyapatite Specimens Research Articles

Influence of sintering temperature on the mechanical properties and biocompatibility of titanium-nano hydroxyapatite functionally graded materials

Titanium-hydroxyapatite functionally graded materials (Ti/HA FGMs) exhibit potential for specific mechanical and biological properties. Spark plasma sintering (SPS) has attracted considerable attention in recent years as a flexible process for manufacturing Ti/HA FGMs with accurate gradients of composition and microstructure. However, little information has been discovered about how the sintering temperature affects the mechanical behavior and biocompatibility of Ti/HA FGMs produced via SPS. In this study, the relationship between sintering temperature and the mechanical and biocompatibility properties of the Ti/HA FGM created by SPS is explored. 6-Layer functionally graded Titanium-Nano hydroxyapatite specimens were produced at three sintering temperatures of 850, 1000, and 1150 °C. To investigate the properties of the specimens, various techniques including compression test, Vickers hardness, X-ray diffraction (XRD), toxicity (MTT), and cell adhesion were performed. According to the results, TiO2 and TCP phases formed in the structure of FGM by raising the sintering temperature to 1150 °C, which decreased the compressive strength from 265 to 167 MPa and increased the maximum hardness from 419 to 894 HV. In addition, increasing the sintering temperature to 1150 °C enhanced the biocompatibility of the fabricated Ti/HA FGM. The optimum sintering temperature for generating Ti/HA FGM with appropriate mechanical and biocompatibility properties was 1000 °C.

Alkaline-Activation Technique to Produce Low-Temperature Sintering Activated-HAp Ceramic

The fabrication of hydroxyapatite (HAp) ceramics prepared by existing conventional sintering requires high-temperature sintering of 1250 °C to 1300 °C. In this paper, the activated metakaolin (MK)/HAp specimens were prepared from varied mix design inputs, which were varied solid mixtures (different amounts of MK loading in HAp) and liquid-to-solid (L/S) ratios, before being pressed and sintered at 900 °C. Phase analysis, thermal analysis, surface morphology, and tensile strength of the specimens were investigated to study the influences of the Al, Si, Fe, Na, and K composition on the formation of the hydroxyapatite phase and its tensile strength. XRD analysis results show the formation of different phases was obtained from the different mix design inputs HAp (hexagonal and monoclinic), calcium phosphate, sodium calcium phosphate silicate and calcium hydrogen phosphate hydrate. Interestingly, the specimen with the addition of 30 g MK prepared at a 1.25 L/S ratio showed the formation of a monoclinic hydroxyapatite phase, resulting in the highest diametrical tensile strength of 12.52 MPa. Moreover, the increment in the MK amount in the specimens promotes better densification when sintered at 900 °C, which was highlighted in the microstructure study. This may be attributed to the Fe2O3, Na2O, and K2O contents in the MK and alkaline activator, which acted as a self-fluxing agent and contributed to the lower sintering temperature. Therefore, the research revealed that the addition of MK in the activated-HAp system could achieve a stable hydroxyapatite phase and better tensile strength at a low sintering temperature.

Effect of electric field strength stimulation on phase evolution in flash sintered hydroxyapatite at high-temperature range

ABSTRACT Flash sintering (FS) is becoming a popular densification route for high-temperature oxide ceramics because of its rapid sintering performance. In the current study, bar-shaped hydroxyapatite (HA) specimens were hung between two Pt wire electrodes and consolidated by FS through a direct electric field at a constant furnace temperature (1000°C or 1100°C) in air. The electric field facilitated the sintering of HA at relatively lower furnace temperatures than that obtained using the conventional sintering method. The voltage required for the onset of the flash decreased with increasing furnace temperature. The effects of the DC electric field strength at different sintering furnace temperatures were examined in terms of the phase evolution and stability of HA. HA phase dissociation was not observed regardless of the electric field strength or furnace temperature because of the very short FS time. Higher grain growth with fast densification in the flashed-sintered HA samples occurred with increasing electric field strength at each furnace temperature.

Physical Fundamentals of Biomaterials Surface Electrical Functionalization.

This article is focusing on electrical functionalization of biomaterial’s surface to enhance its biocompatibility. It is an overview of previously unpublished results from a series of experiments concerning the effects surface electrical functionalization can have on biological systems. Saccharomyces cerevisiae cells were used for biological experiments. The hydroxyapatite (HAp) specimens were used to investigate influence of structural point defects on the surface electrical charge. Threshold photoelectron emission spectroscopy was used to measure the electron work function of HAp and biologic samples. The density functional theory and its different approximations were used for the calculation of HAp structures with defects. It was shown that the electrical charge deposition on the semiconductor or dielectric substrate can be delivered because of production of the point defects in HAp structure. The spatial arrangements of various atoms of the HAp lattice, i.e., PO4 and OH groups, oxygen vacancies, interstitial H atoms, etc., give the instruments to deposit the electrical charge on the substrate. Immobilization of the microorganisms can be achieved on the even surface of the substrate, characterized with a couple of nanometer roughness. This cells attachment can be controlled because of the surface electrical functionalization (deposition of the electrical charge). A protein layer as a shield for the accumulated surface charge was considered, and it was shown that the protein layer having a thickness below 1 µm is not crucial to shield the electrical charge deposited on the substrate surface. Moreover, the influence of surface charge on the attachment of microorganisms, when the surface roughness is excluded, and the influence of controlled surface roughness on the attachment of microorganisms, when surface charge is constant, were also considered.

In-Vitro Assessment of Synthesized Hydroxyapatite Specimen in Simulated Body Fluid (SBF)

Recently, the patient that requires bone replacement has increase, especially the patients who suffering from bone cancer, trauma and ageing. This attracts attention of researchers related to biomaterial fields to synthesis materials from biomaterials waste for bone tissue replacements. Hydroxyapatite was identified as a suitable source for bone substitution due its excellent bioactivity and biocompatibility. The strategies for tissue engineering include developing those cells to form the required tissue/organ in-vitro before inserting them into the body. This study is aimed to investigate In-Vitro properties of hydroxyapatite (HAp) specimens synthesize from the clamshells via precipitation method. HAp moulded specimen were immersed in the simulated body fluid (SBF). It displayed that the development of apatite layers materialized in the surface of HAp after being immersed for 25 days in the 1.5SBF.

Direct 3-D printing of Ti-6Al-4V/HA composite porous scaffolds for customized mechanical properties and biological functions.

Customized scaffold plays an important role in bone tissue regeneration. Precise control of the mechanical properties and biological functions of scaffolds still remains a challenge. In this study, metal and ceramic biomaterials are composited by direct 3-D printing. Hydroxyapatite (HA) powders with diameter of about 25 μm and Ti-6Al-4V powders with diameter of 15-53 μm were mixed and modulated for preparing 3-D printing inks formulation. Three different proportions of 8, 10, and 25 wt.% HA specimens were printed with same porosity of 72.1%. The green bodies of the printed porous scaffolds were sintered at 1,150°C in the atmosphere of argon furnace and conventional muffle furnace. The porosities of the final 3-D-printed specimens were 64.3 ± 0.8% after linear shrinkage of 6.5 ± 0.8%. The maximum compressive strength of the 3-D-printed scaffolds can be flexibly customized in a wide range. The maximum compressive strength of these scaffolds in this study ranged from 3.07 to 60.4 MPa, depending on their different preparation process. The phase composition analysis and microstructure characterization indicated that the Ti-6Al-4V and HA were uniformly composited in the scaffolds. The cytocompatibility and osteogenic properties were evaluated in vitro with rabbit bone marrow stromal cells (rBMSCs). Differentiation and proliferation of rBMSCs indicated good biocompatibility of the 3-D-printed scaffolds. The proposed 3-D printing of Ti-6Al-4V/HA composite porous scaffolds with tunable mechanical and biological properties in this study is a promising candidate for bone tissue engineering.

Mechanical properties of natural hydroxyapatite using low cold compaction pressure: Effect of sintering temperature

This study describes the effect of sintering temperature on the microstructural, calcium/phosphorus (Ca/P) ion ratios and mechanical properties of non-separated biowastes processed hydroxyapatite (HAp) prepared through a low cold compaction protocol. The HAp was produced by a sintering temperature of 900 °C. Furthermore, HAp sintered at 900 °C was subjected to sintering temperatures of 1000 and 1100 °C.The structural and morphological evolution of the fabricated biomaterials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with electron dispersive X-ray analysis (EDX) respectively. Uniaxial compaction using a pressure of 500 pa was used to produce rectangular shaped pellets to investigate the influence of sintering temperature on the mechanical properties of the produced pellets. From XRD analysis, it was found that hydroxyapatite derived from the biowastes showed good thermal stability and did not exhibit phase instability with traces of other calcium phosphates. The SEM micrographs showed microporous structure of the biomaterials and an increase in temperature reduced the porosity and enhanced the mechanical properties. It was also noticed that the trend of transformation of the average shape of pores was from strongly flattened to round at higher sintering temperatures. Electron dispersive X-ray analysis (EDX) revealed that the atomic Ca/P ratios of the as-sintered HAp specimens ranged from 1.58 to 1.79 for sintering temperatures of 900–1100 °C. The synthesized hydroxyapatite powder showed inclusion of the fluorapatite phase at sintering temperature of 1000 °C with a reduction in the crystallite size. For both scenarios (sintering temperature and compaction pressure), a consistent trend in mechanical properties (microhardness, fracture toughness and Young's modulus) is noticed at every point of measurement except for compressive strength. The reduction in compressive strength when compaction pressure was applied could be as a result of the stress induced in the HAp powders during compaction which may have made it more susceptible to cracks. The hardness value obtained for the synthesized hydroxyapatite pellets is in the range of that of actual human femoral cortical bone.

Evolution of the microstructural and mechanical properties of hydroxyapatite bioceramics with varying sintering temperature

Abstract This study highlights the effects of sintering temperature on the microstructures, densification, grain sizes/boundaries, calcium/phosphorus (Ca/P) ion ratios, mechanical and bioactive properties of biocompatible hydroxyapatite (HA) ceramics prepared via cold isostatic pressing. X-ray diffraction refinement analysis revealed that the phase ratios of hexagonal HA and secondary phases were sensitive to the sintering temperature. Grain sizes, densities, and shrinkages of the as-sintered HA ceramics increased with increasing sintering temperature. The Ca/P ratios of the as-sintered HA specimens ranged from 1.63 to 1.71 for sintering temperatures of 900–1300 °C. The maximum mechanical hardness was achieved in the specimen sintered at 1200 °C due to the dense matrix formed with a smaller grain size and fewer flawed grain boundaries, as determined by high-resolution transmission electron microscopy. Ion release analysis (in a simulated body fluid solution) indicated that phosphorus ions were absorbed and rapid deposition of calcium ions occurred after immersion periods of above 4 days.

Pure hydroxyapatite as a substitute for enamel in erosion experiments

ObjectivesThe study evaluated the suitability of pure crystalline hydroxyapatite (HA) as a substitute for human (H) and bovine (B) enamel in erosion experiments. MethodsHuman and bovine enamel and hydroxyapatite specimens (n = 18 each) were submitted to demineralisation by HCl at pH values of 3.0, 2.6 and 2.0 (1.0, 2.5, and 10 mmol/l concentration). Specimens were eroded in a superfusion chamber for 7 min (flow rate: 1 μl/s). Multiple fluid samples were taken per specimen throughout the exposure period. The dissolved calcium content was measured using a colorimetric assay with Arsenazo III reagent, to serve as surrogate for erosive substance loss. Additionally, erosive tissue loss was quantified by profilometry. Differences in erosive substance loss were assessed by the Kruskal-Wallis and Conover’s posthoc test. ResultsGood agreement in erosive substance loss between HA and human specimens was found at pH 2.6, as no statistically significant difference and considerable overlap of their respective interquartile ranges was observed. At pH 2.0 and 3.0, a statistically significant difference between HA and human and bovine enamel was determined. HA consistently tended to have lower mean dissolution rates, with a maximum deviation from human enamel of -16% at pH 3. It displayed lower specimen variability with an average coefficient of variation of 17%, compared to 25% (H) and 25% (B), respectively. ConclusionsCrystalline hydroxyapatite may not be suitable for full substitution of biologic enamel in erosion experiments focusing on absolute measurement values, but is useful for establishing consistent relative trends between erosive agents due to biosimilar erosion behavior and lower experimental variability. This is especially true for preliminary studies where approval for use of biological samples is restricted. Clinical significanceCrystalline hydroxyapatite is a useful substitute of human or bovine enamel in experiments studying chemical aspects of dental erosion.

Evaluation of Naturally Derived Hydroxyapatite Tissue Engineering Scaffold Coated With Chitosan-Carbon Nanotubes Composite

Objective; This study aimed to valuate the effect of f-CNTs (functionalized carbon nanotubes) and chitosan (CS) composite on the mechanical properties and cell biocompatibility of carbonated HAp (hydroxyapatite) derived from cuttlefish bone. Methods; The microstructure characterization of carbonated HAp after hydrothermal treatment showed complete transformation into highly crystalline structure. The prepared CS/f-CNTs composite was introduced into HAp specimens under vacuum. A compressive load was applied till failure using a universal testing machine to evaluate compressive strength and elastic modulus of aragonite (CaCO3) and treated HAp with CS/f-CNTs composite. The proliferating number and percentage of MSCs (mesenchymal stem cells) in direct contact with tested materials were used as indication of cytotoxic effect after 24, 36 and 72 hours in addtion alkaline phosphatase activity (ALP) after 12 days was used as indication of osteogenic effect. Results; The HAp group with deposition of CS/f-CNTs composite showed a statistically significant higher compressive strength (0.82 ± 0.17 MPa) and elastic modulus (11.1 ± 1.06 MPa) and a statistically significant lower value for cell viability percentage (225,590 ± 8030.503, 32.95%) after 72 hours and ALP activity (85.51 ± 5.67 μU/μg protein) after 12 days of incubation. Conclusions; Carbonated HAp scaffolds reinforced with CS/f-CNTs composite can be used in low stress bonny defects.

In vivo and in vitro assessment of the bleaching effectiveness of a brush-off patch containing 3.0% hydrogen peroxide.

To evaluate the efficacy of a brush-off patch containing 3.0% hydrogen peroxide, which is a new over-the-counter (OTC) product for tooth whitening, and determine the optimal protocol for use. We performed an in vitro study using hydroxyapatite specimens and a clinical trial involving 140 volunteers. The brush-off patch was applied to the specimens (in vitro) or the maxillary anterior teeth (in vivo; 14days) for 10min twice daily (case 10 group) or 30min once daily (case 30 group). We also included control groups in both experiments. Lightness (L*), redness (a*), and yellowness (b*) values were measured using a colorimeter. In the in vivo study, color changes were measured at baseline and 7 and 14days after the start of patch application. The overall color change (ΔE) was statistically analyzed. In the in vitro study, the color change (ΔE*) after the experiment was significantly different between the two case groups and the control group (p < 0.001). In the in vivo study, the case groups showed color changes at both 7 and 14days after patch application. In particular, the change in the case 30 group was significantly more prominent on day 14 than on day 7 (p < 0.05). Our findings suggest that brush-off patches containing 3.0% hydrogen peroxide are effective OTC products for tooth whitening. For best results, brush-off patches containing 3.0% hydrogen peroxide can be applied once daily for 30min.

Effects of solid loadings and silica addition on microstructure and compressive strength of hydroxyapatite specimens fabricated by freeze casting technique

Attributed to its bioactivity, osteoconductivity, and chemical compositions similarly to those of human bones, hydroxyapatite (HAp, Ca10(PO4)6(OH)2) is a well-known material suitable for bone graft applications. To achieve physical and mechanical properties desired for the practical applications, microstructure of the HAp specimen needs to be controlled. This study therefore aimed at fabricating freeze-cast hydroxyapatite specimens with the porosity, pore sizes and compressive strength with acceptable values for the applications. Effects of solids loadings and silica addition on compressive strength were also examined in this study. Experimental results indicated that enhanced strength could be obtained in the specimens prepared from slips with higher solids loadings. The results also revealed that the HAp specimens achieved average porosity, pore sizes, and compressive strength in the ranges of 43.3–72.8%, 94.2–128.4 µm, and 1.29–29.35 MPa, respectively. The highest compressive strength was evident in the specimens prepared from silica-added slip with 35 vol% solids loading. The pH value of simulated body fluid solution was relatively stable upon sample submersion. Slight increase of specimen weight and formation of apatite layer were observed. The findings suggested that the specimens could be potential candidates for biomedical applications.

Glass-ceramic coating material for the CO2 laser based sintering of thin films as caries and erosion protection

ObjectivesThe established method of fissure-sealing using polymeric coating materials exhibits limitations on the long-term. Here, we present a novel technique with the potential to protect susceptible teeth against caries and erosion. We hypothesized that a tailored glass-ceramic material could be sprayed onto enamel-like substrates to create superior adhesion properties after sintering by a CO2 laser beam. MethodsA powdered dental glass-ceramic material from the system SiO2-Na2O-K2O-CaO-Al2O3-MgO was adjusted with individual properties suitable for a spray coating process. The material was characterized using X-ray fluorescence analysis (XRF), heating microscopy, dilatometry, scanning electron microscopy (SEM), grain size analysis, biaxial flexural strength measurements, fourier transform infrared spectroscopy (FTIR), and gas pycnometry. Three different groups of samples (each n=10) where prepared: Group A, powder pressed glass-ceramic coating material; Group B, sintered hydroxyapatite specimens; and Group C, enamel specimens (prepared from bovine teeth). Group B and C where spray coated with glass-ceramic powder. All specimens were heat treated using a CO2 laser beam process. Cross-sections of the laser-sintered specimens were analyzed using laser scanning microscopy (LSM), energy dispersive X-ray analysis (EDX), and SEM. ResultsThe developed glass-ceramic material (grain size d50=13.1mm, coefficient of thermal expansion (CTE)=13.310−6/K) could be spray coated on all tested substrates (mean thickness=160μm). FTIR analysis confirmed an absorption of the laser energy up to 95%. The powdered glass-ceramic material was successfully densely sintered in all sample groups. The coating interface investigation by SEM and EDX proved atomic diffusion and adhesion of the glass-ceramic material to hydroxyapatite and to dental enamel. SignificanceA glass-ceramic material with suitable absorption properties was successfully sprayed and laser-sintered in thin films on hydroxyapatite as well as on bovine enamel. The presented novel technique of tooth coating with a dental glass-ceramic using a CO2-laser holds a great potential as a possible method to protect susceptible teeth against caries and erosion.

MG63 osteoblast cell response on Zn doped hydroxyapatite (HAp) with various surface features

The clinical success of implant is governed by implant-surface and bone cell interaction that promote osseointegration and long term stability. Calcium hydroxyapatite (HAp) is a widely used bioceramic material for orthopedic and dental applications, which promotes bone tissue generation. Doped hydroxyapatite using various metallic ions is often reported to enhance this osteoconductive property. The objective of this study was to synthesize zinc doped HAp, to investigate the osteoblast cell response on this doped HAp and find out separately the effect of doping and different surface parameters on cell response. Slip casting technique was used to prepare pure and doped HAp specimens which were sintered at 1100°C and 1250°C. Different porosities, pore sizes were generated along with different surface roughness so as to understand the effect of these extrinsic parameters on cell culture. MG63 osteoblast cells were used for a maximum period of two weeks. Metabolic activity, adhesion and proliferation rate study of osteoblast cells on doped HAp showed significantly better response than pure HAp. Effect of doping was found to be more prominent than the effect of surface roughness.

Antimicrobial activity of hydroxyl radicals generated by hydrogen peroxide photolysis against Streptococcus mutans biofilm

Prevention of dental caries with maximum conservation of intact tooth substance remains a challenge in dentistry. The present study aimed to evaluate the antimicrobial effect of H2O2 photolysis on Streptococcus mutans biofilm, which may be a novel antimicrobial chemotherapy for treating caries. S. mutans biofilm was grown on disk-shaped hydroxyapatite specimens. After 1–24 h of incubation, growth was assessed by confocal laser scanning microscopy and viable bacterial counting. Resistance to antibiotics (amoxicillin and erythromycin) was evaluated by comparing bactericidal effects on the biofilm with those on planktonic bacteria. To evaluate the effect of the antimicrobial technique, the biofilm was immersed in 3% H2O2 and was irradiated with an LED at 365 nm for 1 min. Viable bacterial counts in the biofilm were determined by colony counting. The thickness and surface coverage of S. mutans biofilm increased with time, whereas viable bacterial counts plateaued after 6 h. When 12- and 24-h-old biofilms were treated with the minimum concentration of antibiotics that killed viable planktonic bacteria with 3 log reduction, their viable counts were not significantly decreased, suggesting the biofilm acquired antibiotic resistance by increasing its thickness. By contrast, hydroxyl radicals generated by photolysis of 3% H2O2 effectively killed S. mutans in 24-h-old biofilm, with greater than 5 log reduction. The technique based on H2O2 photolysis is a potentially powerful adjunctive antimicrobial chemotherapy for caries treatment.

A novel 1540 nm light emission from erbium doped hydroxyapatite/β-tricalcium phosphate through co-precipitation method

This paper reports a novel way for the synthesis of erbium (Er) doped hydroxyapatite (HA) nanostructure to achieve strong and stable near-infrared light emission at ∼1540nm of hydroxyapatite, particularly, by applying an optimum annealing temperature. The Er doped HA was observed to have a nanowire structure. As annealed 600°C specimens, the XRD diffraction peaks were to be hydroxyapatite; however a mixture of hydroxyapatite and β-tricalcium phosphate phase (β-TCP) when annealed temperatures of 800–1200°C were used. The formation of HA/β-TCP of the Er doped HA specimens resulted in a significantly enhanced light emission at ∼1540nm, which was potential application in waveguide telecommunication and biomedicine.

유효성분들을 배합한 치약제의 실험실적 및 임상적 치아미백유지 효과

Objectives: The purpose of this study was to investigate tooth whitening maintenance efficacy of several dentifrices containing effective ingredients for tooth whitening. Methods: Hydroxyapatite specimens(HAPs) staining was done by using modified Stookey’s methods. HAPs were treated with 2.9% hydrogen peroxide containing strip for whitening, and were shaken with several dentifrice slurry(dentifrice 1 : artificial saliva 2) for 30 minutes. The HAPs were finally dipped in staining solution for an hour. Shaking and dipping were repeated 4 times and lightness values were measured by colorimeter at each step. In clinical test, test 4 dentifrice and control dentifrice were evaluated by 21 subjects for 2 months after receiving institutional review board(IRB) approval. Organoleptic(vita shade guide) and instrumental(SHADEEYENCC) evaluation were performed for whiteness change of teeth. Statistical analysis was performed using repeated measures ANOVA, Tukey's post hoc test and χ2-test(p 0.05). Conclusions: Dentifrice containing sodium pyrophosphate, sodium metaphosphate, candelilla wax and sodium fluoride was more effective in keeping teeth white.

Surface microcracks signal osteoblasts to regulate alignment and bone formation

Microcracks are present in bone and can result from fatigue damage due to repeated, cyclically applied stresses. From a mechanical point, microcracks can dissipate strain energy at the advancing tip of a crack to improve overall bone toughness. Physiologically, microcracks are thought to trigger bone remodeling. Here, we examine the effect of microcracks specifically on osteoblasts, which are bone-forming cells, by comparing cell responses on microcracked versus non-microcracked hydroxyapatite (HA) specimens. Osteoblast attachment was found to be greater on microcracked HA specimens (p<0.05). More importantly, we identified the preferential alignment of osteoblasts in the direction of the microcracks on HA. Cells also displayed a preferential attachment that was 75 to 90μm away from the microcrack indent. After 21days of culture, osteoblast maturation was notably enhanced on the HA with microcracks, as indicated by increased alkaline phosphatase activity and gene expression. Furthermore, examination of bone deposition by confocal laser scanning microscopy indicated preferential mineralization at microcrack indentation sites. Dissolution studies indicate that the microcracks increase calcium release, which could contribute to osteoblast responses. Our findings suggest that microcracks signal osteoblast attachment and bone formation/healing.

Characterization of sintered hydroxyapatite samples produced by 3D printing

Purpose – The purpose of this study is to characterize sintered hydroxyapatite (HA) samples produced by three-dimensional printing (3DP). This study is part of a project concerned with the fabrication of calcium phosphates implants by 3DP. However, before considering a more complex structure, like scaffolds or implants, a thorough knowledge of the role played by the sintering temperature on physical and mechanical the properties of porous HA is necessary. Design/methodology/approach – The characteristics of sintered HA samples have been analyzed by means of x-ray diffraction, scanning electron microscope (SEM) and uniaxial compression tests. The 3DP parameters used to produce the HA samples were those who led to higher accuracy and mechanical stability. Findings – Sintering temperature and powder morphology are critical factors influencing densification behavior, porosity, phase stability, mechanical strength and tangent modulus of the HA samples produced by 3DP. This study allowed us to conclude about the 3DP parameters to be used to produce porous HA specimens with the required integrity and dimensional accuracy, and the optimal post-processing sintering temperature which led to the best results in terms of porosity, microstructure, phase stability of HA and mechanical properties. Originality/value – This paper provides a method to evaluate the manufacturability of calcium phosphate models produced by 3DP.

Fabrication of hydroxyapatite targets in radio frequency sputtering for surface modification of titanium dental implants

The purpose of this study was to explore the properties of sintered hydroxyapatite specimens for developing a suitable hydroxyapatite target and a fabrication process for the radio frequency sputtering of implants. Using a compound surface treatment of sand blasting and acid etching followed by hydroxyapatite radio frequency sputtering, this work planned to develop a commercial dental implant system in the near future. First, in addition to producing hydroxyapatite parts using hot isostatic pressing, this study examined the properties of hydroxyapatite parts produced through cold pressing followed by sintering in vacuum and air. The experimental results showed that the index of crystallization, density, and Vickers hardness of the parts sintered in air were more favorable than those of parts sintered in vacuum, and that the parts sintered in vacuum could crack or break. Second, hydroxyapatite sputtering was performed on the hot isostatic pressing–produced and cold pressing–produced targets on titanium dental implant surfaces at power levels of 50 and 90 W. The results showed no cracks in the cold pressing–produced hydroxyapatite targets when the sintering condition was at 1050 °C. By contrast, cracks occurred in the hot isostatic pressing hydroxyapatite targets at a relative density in excess of 93.35%. Observing scanning electron microscopy cross-sectional images revealed that the sputtering deposition rate was approximately 0.456 nm/min at the sputtering power level of 50 W and 1.139 nm/min at 90 W.