Bioactivity of calcium phosphate coatings prepared by electrodeposition in a modified simulated body fluid

The purpose of this study was to investigate bioactivity of calcium phosphate coatings prepared by electrodeposition in a modified simulated body fluid (SBF). Calcium phosphates were electrodeposited on commercially pure titanium substrates in the modified SBF at 60 °C for 1 h maintaining the cathodic potentials of − 1.5 V, − 2 V, and − 2.5 V (vs. SCE). Subsequently, the calcium phosphate coatings were transformed into apatites during immersion in the SBF at 36.5 °C for 5 days. The apatites consisted of needle-shaped crystallites distributed irregularly with different grain sizes. As the coatings were electrodeposited at higher cathodic potential, the crystallite of the apatites got denser and the grain sizes of the apatites became bigger during subsequent immersion in the SBF. However, as the coatings were electrodeposited at higher cathodic potential, the coatings were transformed into apatites with lower crystallinity and the Ca/P atomic ratio of the apatites got higher than 1.67, that of stoichiometric hydroxyapatite, after subsequent immersion in the SBF. In addition, CO₃²⁻ ions contained in the modified SBF were incorporated in the calcium phosphate coating during electrodeposition and had an influence on transforming the calcium phosphate into bonelike apatite during subsequent immersion in the SBF showing that CO₃²⁻ incorporated in the apatites disturbed crystallization of the apatites. These results revealed that the coating electrodeposited at − 2.0 V (vs. SCE) in the modified SBF containing CO₃²⁻ ions was the most bioactive showing transformation into carbonate apatite similar to bone apatite.     

Comparative study of apatite formation on CaSiO<Subscript>3</Subscript> ceramics in simulated body fluids with different carbonate concentrations

Apatite formation on CaSiO₃ ceramics was investigated using two different simulated body fluids (SBF) proposed by Kokubo (1990) and Tas (2000) and three sample/SBF (S/S) ratios (1.0, 2.5 and 8.3 mg/ml) at 36.5°C for 1–25 days. The CaSiO₃ ceramic was prepared by firing coprecipitated gel with Ca/Si = 0.91 at 1400°C. The bulk density was 2.14 g/cm³ and the relative density about 76%. The two SBF solutions contain different concentrations of HCO₃^– and Cl^– ions, the concentrations of which are closer to human blood plasma in the Tas SBF formulation than in the Kokubo formulation. The pH values in the former solution are also more realistic. The CaSiO₃ ceramics show apatite formation in SBF (Kokubo) after soaking for only 1 day at all S/S ratios whereas different phases were formed at each S/S ratio in SBF (Tas). The crystalline phases formed were mainly apatite at S/S = 1.0 mg/ml, carbonate-type apatite at 2.5 mg/ml and calcite at 8.3 mg/ml. At higher S/S ratios the increase in the Ca concentration became higher while the P concentration became lower in the reacted SBF. These changes in SBF concentrations and increasing pH occurred at higher S/S ratios, producing more favorable conditions in the SBF for the formation of carbonate bearing phases, finally leading to the formation of calcite instead of apatite in the higher HCO₃^– ion concentration SBF (Tas). Apatite is, however, formed in the lower HCO₃^– ion concentration SBF (Kokubo) even though the Ca and P concentrations change in a similar manner to SBF (Tas).     

Apatite deposition on polyamide films containing carboxyl group in a biomimetic solution

The development of organic–inorganic hybrids composed of hydroxyapatite and organic polymers is attractive because of their novelty in being materials that show a bone-bonding ability, i.e. bioactivity, and because they have mechanical properties similar to those of natural bone. The biomimetic process has received much attention for fabricating such a hybrid, where bone-like apatite is deposited under ambient conditions on polymer substrates in a simulated body fluid (SBF) having ion concentrations nearly equal to those of human extracellular fluid or related solutions. It has been shown that the carboxyl group is effective for inducing heterogeneous nucleation of apatite in the body. In the present study, apatite deposition on polyamide films containing various numbers of carboxyl groups was investigated in 1.5 SBF, which had ion concentrations 1.5 times those of a normal SBF. The effect of incorporation of calcium chloride on the formation of apatite was examined. Polyamide films containing 33 mol % CaCl₂ did not form apatite, even after soaking in 1.5 SBF for 7 days, and even when the polymer film contained 50 mol % carboxyl group. On the other hand, those modified with 40 mass % CaCl₂ formed apatite on their surfaces in 1.5 SBF. The ability of the modified film to form an apatite layer increased, and the adhesion of the apatite layer bonded to the film improved, with increasing carboxyl group content. It is concluded that novel apatite–polyamide hybrids can be prepared by a biomimetic process.     

Chemical surface treatment of silicone for inducing its bioactivity

It has been confirmed that the apatite nucleation is induced by silanol (Si–OH) groups formed on the surfaces of materials and/or silicate ions adsorbed on them.It was previously shown that apatite nuclei are formed on organic polymers when the polymers are placed on CaO, SiO2-based glass particles soaked in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma, and that they grow spontaneously to form a dense and uniform apatite layer together with high adhesive strength to the substrates when the polymers are soaked in another solution with ion concentrations 1.5 times the SBF. In the present study, silanol groups bonded covalently to the surface of the silicone substrate were formed and its apatite-forming ability was examined. When silicone substrates were treated with 5 or 10 M NaOH with pH 7.25 at 36.5°C for more than 3 h, silanol groups were formed on the surfaces of the substrates. When thus NaOH-treated substrates were soaked in 1.5SBF at 36.5°C, a bone-like apatite was formed on the substrates in a short period. © 1998 Chapman & Hall.     

Apatite coated on organic polymers by biomimetic process: improvement in adhesion to substrate by HCl treatment

A dense, uniform and highly biologically active bone-like apatite layer can be formed in arbitrary thickness on any kind and shape of solid substance by the following biomimetic method at normal temperature and pressure: first, a substrate is set in contact with particles of CaO-SiO₂-based glass soaked in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. Second, the substrate is soaked in another solution with ion concentrations 1.5 times those of SBF (1.5 SBF). In the present study, organic polymer substrates were treated with 1 m HCl solution, then subjected to the above mentioned biomimetic process. The induction periods for the apatite nucleation on polyethyleneterephthalate, polymethylmethacrylate, polyamide 6 and polyethersulfone substrates were reduced from 24 to 12 h with the HCl treatment. The adhesive strength of the formed apatite layer to the polyethyleneterephthalate, polymethylmethacrylate and polyamide 6 substrates were increased from 3.5 to 7.0 MPa from 1.1 to 2.8 MPa and from 0.6 to 3.1 MPa, respectively, with the HCl treatment. It is supposed that highly polar carboxyl group formed by the HCl hydrolysis reaction of ester group in polyethyleneterephthalate and polymethylmethacrylate or amide group in polyamide 6 increased the affinity of the substrates with a silicate ion to decrease the induction period, and also increased the affinity of the substrate with the apatite to increase the adhesive strength. The apatite-organic polymer composites thus obtained are expected to be useful as bone-repairing materials as well as soft-tissue-repairing materials.     

Synthesis and structure of cerium-substituted hydroxyapatite

The aim of this study was to explore the effect of cerium ions on the formation and structure of hydroxyapatite (HAP). All particles, prepared by hydrothermal method, were synthesized at varied X_Ce = Ce/(Ca + Ce) (from 0 to 10%) with the atomic ratio (Ce + Ca)/P fixed at 1.67. Their morphology, composition and crystal structure were characterized by TEM, EPMA, XRD and FTIR. The results showed that in this composition range the apatite structure is maintained, Ce^{3 +} ions could enter the crystal lattice of apatite and substitute Ca^{2 +} ions. The doping of Ce^{3 +} ions resulted in the decrease of the crystallite size with increase in X_Ce. The HAP particles without doping were short rods having a diameter from 10 to 20 nm and a length from 30 to 50 nm. They grew into long needles upon increasing X_Ce.     

Effects of ions dissolved from bioactive glass-ceramic on surface apatite formation

Non-bioactive glass-ceramic A-W(Al) containing apatite and wollastonite in a MgO–CaO–SiO₂–Al₂O₃ glassy matrix did not form an apatite layer on its surface in a simulated body fluid with ion concentrations nearly equal to those of human blood plasma and also in the fluids with small amounts of the calcium and silicate ions added individually, but formed the apatite layer in the fluid with the calcium and silicate ions added simultaneously. This indicates that the calcium and silicate ions dissolved from bioactive glass-ceramic A-W containing the apatite and wollastonite in a MgO–CaO–SiO₂ glassy matrix play a cooperative and important role in forming an apatite layer on its surface in the body, to give the glass-ceramic bioactivity. The calcium ion might increase the degree of the supersaturation of the surrounding body fluid, and the silicate ion might provide favourable sites for nucleation of the apatite on the surfaces of glass-ceramic.     

Precipitation of carbonate crystal on surface active glasses

Anions, such as CO₃ ^2– and SO₄ ^2– ions, in industrial wastewater can cause serious scale problem in drainage pipes and vessels, when combined with other metal ions in the water. In this study, it was attempted to remove CO₃ ^2– ions from an aqueous solution by using surface active glasses. Glasses with various compositions of SiO₂-Na₂O-B₂O₃-RO (R = Mg, Ca, Sr, Ba) system were reacted in a CO₃ ^2– ion-containing solution with various pH, then the glass surfaces were analyzed by XRD and SEM, and CO₃ ^2– ions in the reacted solution were also measured. CO₃ ^2– ions in the solution were combined with alkaline earth metal ions, which were leached out of the glass, and were precipitated on the glass surface as carbonate crystals. In this way, the carbonate ions could be removed from the solution. The removal capacity of CO₃ ^2– ions is closely related to the surface reactivity of the glass and solubility product constants of the newly formed carbonate crystals. Glass containing either SrO or BaO showed a strong uptake capacity of CO₃ ^2– ions from the solution.     

Mechanical properties and apatite forming ability of TiO<Subscript>2</Subscript> nanoparticles/high density polyethylene composite: Effect of filler content

Composite materials consisting of TiO₂ nanoparticles and high-density polyethylene (HDPE), designated hereafter as TiO₂/HDPE, were prepared by a kneading and forming process. The effect of TiO₂ content on the mechanical properties and apatite forming ability of these materials was studied. Increased TiO₂ content resulted in an increase in bending strength, yield strength, Young’s modulus and compressive strength (bending strength = 68 MPa, yield strength = 54 MPa, Young’s modulus = 7 GPa, and compressive strength = 82 MPa) at 50 vol% TiO₂. The composite with 50 vol% TiO₂ shows a similar strength and Young’s modulus to human cortical bone. The TiO₂/HDPE composites with different TiO₂ contents were soaked at 36.5°C for up to 14 days in a simulated body fluid (SBF) whose ion concentrations were nearly equal to those of human blood plasma. The apatite forming ability, which is indicative of bioactivity, increased with TiO₂ content. Little apatite formation was observed for the TiO₂/HDPE composite with 20 vol% content. However, in the case of 40 vol% TiO₂ content and higher, the apatite layers were formed on the surface of the composites within 7 days. The most potent TiO₂ content for a bone-repairing material was 50 vol%, judging from the mechanical and biological results. This kind of bioactive material with similar mechanical properties to human cortical bone is expected to be useful as a load bearing bone substitute in areas such as the vertebra and cranium.     

Functionalization of different polymers with sulfonic groups as a way to coat them with a biomimetic apatite layer

Covalent coupling of sulfonic group (–SO₃H) was attempted on different polymers to evaluate efficacy of this functional group in inducing nucleation of apatite in body environment, and thereupon to design a simple biomimetic process for preparing bonelike apatite-polymer composites. Substrates of polyethylene terephthalate (PET), polycaprolactam (Nylon 6), high molecular weight polyethylene (HMWPE) and ethylene-vinyl alcohol co-polymer (EVOH) were subjected to sulfonation by being soaked in sulfuric acid (H₂SO₄) or chlorosulfonic acid (ClSO₃H) with different concentrations. In order to incorporate calcium ions, the sulfonated substrates were soaked in saturated solution of calcium hydroxide (Ca(OH)₂). The treated substrates were soaked in a simulated body fluid (SBF). Fourier transformed infrared spectroscopy, thin-film X-ray diffraction, and scanning electron microscopy showed that the sulfonation and subsequent Ca(OH)₂ treatments allowed formation of –SO₃H groups binding Ca²⁺ ions on the surface of HMWPE and EVOH, but not on PET and Nylon 6. The HMWPE and EVOH could thus form bonelike apatite layer on their surfaces in SBF within 7 d. These results indicate that the –SO₃H groups are effective for inducing apatite nucleation, and thereby that surface sulfonation of polymers are effective pre-treatment method for preparing biomimetic apatite on their surfaces.     

Effect of solid/solution ratio on apatite formation from CaSiO<Subscript>3</Subscript> ceramics in simulated body fluid

The effect of the solid/solution (S/S) ratio on apatite formation from CaSiO₃ ceramics in simulated body fluid (SBF) was investigated. CaSiO₃ ceramics with a Ca/Si ratio of 0.91 were prepared by sintering CaSiO₃ powder coprecipitated from ethanol solutions of Ca(NO₃)₂⋅4H₂O and Si(OC₂H₅)₄ using NH₄OH as the precipitant. These ceramics were reacted with SBF at S/S ratios of 1.0, 2.5 and 8.3 mg/ml at 36.5 ^∘C for various times. Formation of apatite was observed at all the S/S ratios after soaking for 1 day. The amount and microstructure of the apatite obtained at a S/S ratio of 8.3 mg/ml, however, differed largely from the product formed at the other two S/S ratios. The apatite formed at S/S = 8.3 mg/ml was of smaller particle size, formed in smaller amount and with less preferred orientation of the (00l) of apatite crystals compared with those formed at S/S = 1.0 and 2.5 mg/ml. An increase of Ca and decrease of the P components occurred in the soaked SBF at S/S = 8.3 mg/ml, the changes being much more marked than with the other two S/S ratios. These differences in the concentration changes in SBF at different S/S ratios are attributed to the difference in the apatite formation from the CaSiO₃ ceramics.     

Surface modification of Ti–Nb–Zr–Sn alloy by thermal and hydrothermal treatments

Surface modifications by thermal and hydrothermal treatments in solution with calcium ions were investigated with the aim of improving bioactivity and wear resistance of a Ti–Nb–Zr–Sn alloy. The results showed that the first step of thermal treatment at 600 °C significantly increases the surface hardness and energy by forming oxides of Ti and Nb. The second step of hydrothermal treatment in a boiled supersaturated Ca(OH)₂ solution induces a bioactive layer containing CaTiO₃, CaCO₃, Ca(OH)₂ and TiO₂. Using this treatment, a complete Ca–P layer can be formed within 3 days of soaking in simulated body fluid (SBF). The origin of such fast apatite formation was analyzed by comparison with single step thermal or hydrothermal treatment and with thermal plus hydrothermal treatment without calcium ions. The results suggest that the increase of surface energy by thermal treatment and the incorporation of calcium ions by the hydrothermal treatment in calcium ion solution play important roles in the formation of bioactive apatite.     

Manganese in apatites,chemical, ligand-field and electron paramagnetic resonance spectroscopy studies

Hydroxapatites precipitated with different amounts of carbonate and Mn²⁺ were studied. Infrared spectra, X-ray diffraction lattice parameters and thermal behaviour indicate that the presence of Mn²⁺ does not have any effect on the formation and properties of the carbonate apatites obtained. Interaction of apatite with a Mn²⁺-containing aqueous solution reveals that the molar uptake of Mn²⁺ by the apatite is higher than the Ca²⁺ released by it. Ligand-field and electron paramagnetic resonance spectroscopy results show that in Mn²⁺-doped Cd₅(PO₄)₃Cl, Mn²⁺ replaces Ca²⁺ in the apatite lattice, but in precipitated carbonate apatite it is in an MnO phase. The conclusion that Mn²⁺ in precipitated carbonate apatites is not incorporated in the apatite crystal is discussed in the light of the size differences between Mn²⁺ and Ca²⁺.     

Carbonated hydroxyapatite nanopowders for preparation of bioresorbable materials

Incorporation of carbonate ions to the crystal structure of carbonated hydroxyapatite (CHAp) leads to the formation of point defects (vacancies) in Ca‐ and OH‐sublattices as well as to microstrains revealed in CHAp nanocrystals. Various techniques, such as XRD, FTIR, TEM, FESEM/EDX, TG/DTA, AES (ICP), wet chemical analysis, Ca‐ionometry, microvolumetric analysis of evolved CO₂, BET adsorption, were applied to determine an efficiency of carbonate substitution, and to quantify the elemental composition, as well as to characterize the structure of the carbonated hydroxyapatite and the site(s) of carbonate substitution. It was shown that there is insignificant incorporation of Na into the crystal structure of HAp. Over the range of 0–4 % wt. (x<0.25), the substitution of OH‐ by CO₃^2‐ takes place leading to A‐Type of CHAp, further increase of CO₃^2‐‐content enhances PO₄^3‐‐substitution giving AB‐type of CHAp. According to in vitro test, the bioactivity of the samples is increasing with the growth of carbonate content due to accumulation of the defects in CHAp nanocrystals.     

In vitro behavior of fluoridated hydroxyapatite coatings in organic-containing simulated body fluid

A dense and pure hydroxyapatite [HA, Ca₁₀(PO₄)₆(OH)₂] coating and a fluoridated HA [Ca₁₀(PO₄)₆(OH)_0.67F_1.33] are deposited on Ti6Al4V substrates by sol-gel dip coating method. Glucose and bovine serum albumin have been added in standard simulated body fluid (SBF) to form organic-containing SBF in simulation of the physiological blood plasma. The HA and the fluoridated HA coatings are immersed in the standard and modified SBF for time periods of 2, 4, 7, 14 and 28 days at 37 ± 0.1°C. After soaking, the coating surface is examined for nucleation and growth of apatite using SEM morphological observation. The post-soaking SBF solutions are analyzed via Inductively Coupled Plasma spectroscopy for calcium ion concentration. The results show that at concentration of 40 g/L, bovine serum albumin has significant retardation effect on apatite precipitation from SBF onto pure or fluoridated HA coatings; Fluorine-incorporation in HA has positive bio-activation effect in both standard SBF and organic-containing SBF. However, glucose addition in SBF does not generate significant influence on the bioactivity of HA and fluoridated HA.     

A nitrogen doped TiO<Subscript>2</Subscript> layer on Ti metal for the enhanced formation of apatite

Biomedical titanium metals subjected to gas under precisely regulated oxygen partial pressures (P_O2) from 10⁻¹⁸ to 10⁵ Pa at 973 K for 1 h were soaked in a simulated body fluid (SBF), whose ion concentrations were nearly equal to those of human blood plasma, at 36.5°C for up to 7 days. The effect of oxygen partial pressures on apatite formation was assessed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) measurements. After heating, the weight of the oxide layer (mainly TiO₂) formed on the titanium metal was found to increase with increased oxygen partial pressure. Nitrogen (N)-doped TiO₂ (Interstitial N) was formed under a P_O2 of 10⁻¹⁴ Pa. At lower P_O2 (10⁻¹⁸ Pa), only a titanium nitride layer (TiN and Ti₂N) was formed. After soaking in SBF, apatite was detected on heat-treated titanium metal samples. The most apatite was formed, based on the growth rate calculated from the apatite coverage ratio, on the titanium metal heated under a P_O2 of 10⁻¹⁴ Pa, followed by the sample heated under a P_O2 of 10 and 10⁴ Pa (in N₂). The titanium metal heated under a P_O2 of 10⁵ Pa (in O₂) experienced far less apatite formation than the former three titanium samples. Similarly, very little weight change was observed for the titanium metal heated under a P_O2 of 10⁻¹⁸ Pa (in N₂). During the experimental observation period (5 days, 36.5°C, SBF), the following relationship held: The growth rate of apatite decreased in the order P_O2 of 10⁻¹⁴ Pa > P_O2 of 10 Pa ≥ P_O2 of 10⁴ Pa > P_O2 of 10⁵ Pa > > P_O2 of 10⁻¹⁸ Pa. These results suggest that N-doped TiO₂ (Interstitial N) strongly induces apatite formation but samples coated only with titanium nitride do not. Thus, controlling the formation of N-doped TiO₂ is expected to improve the bioactivity of biomedical titanium metal.     

生物活性钛涂层

真空等离子喷涂的钛涂层经 ５．０ｍｏｌ／Ｌ ＮａＯＨ溶液处理后,将其浸泡在含 Ｃａ^２＋、ＨＰＯ_４^２－的模拟生理体液（ＦＣＳ和ＳＢＦ）中,考察涂层诱导羟基磷灰石生长过程,并评价其生物活性．用ＳＥＭ观察碱处理前后和在模拟生理体液中浸泡后钛涂层的形貌,用ＡＥＳ分析了碱处理前后钛涂层的表面成分;用ＸＲＤ、ＦＴ－ＩＲ和ＥＤＳ表征浸泡后涂层表面生长物的结构和成分;并测量了处理后钛涂层在浸泡过程中溶液中离子浓度和ｐＨ值的变化．结果表明,经处理的钛涂层在模拟生理体液中能诱导羟基磷灰石在其表面生长;在ＳＢＦ和ＦＣＳ分别形成碳酸羟基磷灰石层和含氧磷灰石的羟基磷灰石层．钛涂层的活性是由于碱处理后表面形成了网状和纤维状结构的Ｎａ－Ｔｉ－Ｏ化合物．这种化合物在模拟生理溶液中释放Ｎａ^＋,吸收Ｈ^＋;形成水化钛酸盐,诱导羟基磷灰石成核生长．     

Seeded growth of hydroxyapatite in simulated body fluid

The precipitation of calcium phosphates was investigated, in simulated body fluid (SBF), pH 7.40 and 37°C. The kinetics of the mineral phase forming in the SBF was measured using the constant supersaturation method. The approach provides a detailed investigation in the processes taking place in the SBF which is widely used for the study of biomineralization. The pH adjustment was done by a pH-stat instead of Tris-Buffer [Tris (hydroxymethyl) Aminomethane] to avoid the presence of organic soluble compounds. The stability of SBF was investigated and the stable supersaturated solutions were seeded. The technique of seeded precipitation was employed for the achievement of accurate and reproducible kinetics measurements. The crystal growth experiments in which SBF solutions of variable supersaturations were seeded with hydroxyapatite [Ca₅(PO₄)₃OH, HAP] crystals showed that the precipitation of calcium phosphates took place exclusively on specific active sites provided on the surface of the synthetic seed crystals. The crystal growth mechanism showed that the process was controlled by surface diffusion. The phase formed was HAP in the lattice of which CO₃²⁻ and Mg²⁺ ions were incorporated. SBF was the source of these ions. Moreover it was found that the less stable calcium phosphate dihydrate (CaHPO₄·2H₂O, DCPD) may form as a transient phase hydrolyzing rapidly into the more stable HAP. Morphological examination of the carbonated apatites formed in the SBF showed appreciable aggregation.     

Improved stability of plasma-sprayed dicalcium silicate/zirconia composite coating

Dicalcium silicate/zirconia composite coatings were produced on Ti-6Al-4V substrates using atmospheric plasma spraying. Different weight ratios of zirconia (50 wt.%, 70 wt.%, 90 wt.%) were mechanically blended with dicalcium silicate (C₂S) powders as feedstocks. The composite coatings were immersed in a simulated body fluid (SBF) and a Tris-HCl solution for the in vitro appraisement of stability and long-term performance in a biological environment. The ion concentration changes of Ca, Si, and P in SBF and Tris-HCl solution were monitored using inductively-coupled plasma atomic emission spectroscopy (ICP-AES). Compared to the pure C₂S coating, our results show that the dissolution rate of the composite coatings is effectively reduced and the stability is improved by the addition of zirconia. The high content of zirconia in the coatings ensures the long-term performance in biological environment, while dissolution of C₂S in the coatings results in a higher Ca ion concentration in SBF and rapid precipitation of bone-like apatite on the composite coating surfaces indicating good bioconductivity of the coatings.     

Apatite formation from simulated body fluid on various phases of TiO2 thin films prepared by filtered cathodic vacuum arc deposition

Hydroxyl (OH⁻)-free TiO₂ thin films with amorphous and crystalline phases were deposited onto (100) silicon substrates using filtered cathodic vacuum arc deposition in order to investigate the in vitro apatite formation in simulated body fluid (SBF). The surface morphology, composition and structure of the TiO₂ thin films were characterized. The X-ray photoelectron spectroscopy results confirmed the presence of calcium and phosphorus on all TiO₂ thin film surfaces after immersion in SBF at 37 °C. Fourier transform infra red results showed the presence of carbonated apatite on the surface of these films. Amorphous structured TiO₂ thin film showed poor ability to form apatite on its surface in SBF. Apatite formation was more pronounced on the surfaces of the anatase films in comparison to those of rutile. The carbonated apatite deposition rate increased significantly when the TiO₂ film was illuminated with UV light prior to immersing in the SBF. In particular, the UV-treated anatase and rutile films showed increased rates of carbonated apatite formation on their surfaces in comparison to samples not treated with radiation. The increase in hydrophilicity due to UV treatment appears beneficial for the apatite growth on these surfaces.