Effect of calcium salt content in the poly(epsilon-caprolactone)/silica nanocomposite on the nucleation and growth behavior of apatite layer

The effect of calcium salt content in the poly(epsilon-caprolactone) (PCL)/silica nanocomposite on the nucleation and growth behavior of apatite layer in simulated body fluid (SBF) was investigated. The specimens were prepared with low (L) and high (H) concentrations of calcium nitrate tetrahydrate through a sol-gel method. After soaking in the SBF at 36.5 degrees C for 1 week, a densely packed apatite layer that had a smooth surface and a Ca/P ratio similar to bone was formed on specimens containing a low concentration of calcium salt while a loosely packed apatite layer with a rugged surface and a higher Ca/P ratio than that of bone occurred on specimens containing a high concentration of calcium salt. The results are explained in terms of the degree of supersaturation of apatite in the SBF, as determined by the concentrations of constituent ions of apatite and pH. The practical implication of the results is that a dense and bone-like apatite layer on the PCL/silica nanocomposite in vitro, and perhaps in vivo, can be achieved by adopting an appropriate calcium salt content.     

Effect of molecular weight of poly(epsilon-caprolactone) on interpenetrating network structure,apatite-forming ability,and degradability of poly(epsilon-caprolactone)/silica nano-hybrid materials

The effect of molecular weight of poly(epsilon-caprolactone) (PCL) on the bioactivity of a PCL/silica nano-hybrid containing calcium salt was investigated. Two hybrids were prepared with low and high molecular weight PCLs, respectively, through a sol-gel method. Their bioactivities were evaluated using a simulated body fluid (SBF), which had almost the same ion concentrations with human blood plasma. Fast and uniform nucleation and growth of the apatite crystals were observed to occur all through the hybrid surface when low molecular weight PCL was used, while slow and random nucleation and growth of the apatite crystals were observed to occur when high molecular weight PCL was used, after soaking for 3 days in the SBF. This phenomenon was explained in terms of the distribution and dispersion of silica phase in the hybrid and the ionic activity product of the apatite in the SBF, which were dependent on the free volume and degradation rate of non-bioactive PCL phase, respectively.     

The effect of temperature and initial pH on biomimetic apatite coating

Bone-like apatite coatings were prepared using a biomimetic method in a simulated body fluid (SBF). The effect of initial pH values and immersing temperatures on biomimetic apatite coating formation was studied. Three different temperatures were used in this study: 24 (room temperature), 40, and 60 degrees C. At each temperature, SBF solutions with three different initial pHs were chosen: low, medium, and high. The total inorganic carbon (TIC) content and pH-time profile of each coating system were recorded during the coating formation. The apatite coatings were characterized using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), and Fourier transform infra-red (FTIR). It has been found that SBF temperature has a great effect on the bicarbonate decomposition rate. The bicarbonate ions tend to decompose faster as the temperature increases. The decomposition of bicarbonate ions results in a pH increase in the SBF. With different initial SBF pHs, the decomposition of different amounts of bicarbonate ions is required to reach the critical pH range of apatite formation. With different amounts of bicarbonate ions in the SBF, the surface morphology of the biomimetic apatite coating formed is different. Therefore, the initial pH of the SBF solution plays a vital role in controlling the surface morphology of the biomimetic apatite coating. Also, it was found that as the SBF temperature increased, the critical pH range at which biomimetic apatite coating forms decreased. The critical pH range for the SBF prepared at 24, 40, and 60 degrees C was 6.65-6.71, 6.55-6.65, and 6.24-6.42, respectively.     

Formation of CaTiO3/TiO2 composite coating on titanium alloy for biomedical applications

Plasma electrochemical oxidation (PEO) was used to prepare TiO2-based coating containing Ca and P on titanium alloy. After alkali- and then heat-treatment at 800 degrees C of the PEO coating, a CaTiO3/TiO2 composite (CTC) coating was obtained. The current results indicate that the apatite-forming ability of the CTC coating is higher than that of the PEO coating. During the simulated body fluid (SBF) incubation, Ca of the CTC coating is released into the SBF. An ionic exchange between Ca(2+) ions of the CTC coating and H(3)O(+) ions of the SBF may take place during the SBF incubation. As a result, the abundant Ti--OH groups are formed on the surface of the CTC coating. The hydroxyl functionalized surface greatly enhances the nucleation and growth of apatite, leading to the high apatite-forming ability of the CTC coating. The apatite induced by the CTC coating exhibits a porous and carbonated structure.     

A mesoporous bioactive glass/polycaprolactone composite scaffold and its bioactivity behavior

Composite scaffolds of mesoporous bioactive glass (MBG)/polycaprolactone (PCL) and conventional bioactive glass (BG)/PCL were fabricated by a solvent casting-particulate leaching method, and the structure and properties of the composite scaffolds were characterized. The measurements of the water contact angles suggest that the incorporation of either MBG or BG into PCL can improve the hydrophilicity of the composites, and the former is more effective than the later. The bioactivity of the composite scaffold is evaluated by soaking the scaffolds in a simulated body fluid (SBF) and the results show that the MBG/PCL composite scaffolds can induce a dense and continuous layer of apatite after soaking in SBF for 3 weeks, as compared with the scattered and discrete apatite particles on the BG/PCL composite scaffolds. Such improvements (improvements of the hydrophilicity and apatite forming ability) should be helpful for the extensive applications of PCL scaffold in tissue engineering.     

A comparative study of in vitro apatite deposition on heat-, H(2)O(2)-, and NaOH-treated titanium surfaces

Commercially pure titanium specimens are subjected to three different treatments, and their bioactivity are evaluated by immersing the specimens in a simulated body fluid (SBF, Kokubo's recipe) for various periods up to 7 days, with particular attention being paid to the differences in apatite deposition between surfaces open to SBF and surfaces in contact with the container's bottom. The treatment with a H(2)O(2)/HCl solution at 80 degrees C for 30 min followed by heating at 400 degrees C for 1 h produces an anatase titania gel layer on the specimen surface. This gel layer deposits apatite both on the contact and on open surfaces, and apatite deposition ability does not change with pre-staking in distilled water. The treatment with a NaOH solution at 60 degrees C for 3 days produces a sodium titanate gel layer. This gel layer can deposit apatite only on the contact surface, and the apatite deposition ability is completely lost after 1 day of pre-staking in distilled water. It is concluded, therefore, that the bioactivity of the titania gel originates from the favorable structure of the gel itself while the bioactivity of the sodium titanate gel depends heavily on ion release from the gel. The third treatment, a simple heat treatment at 400 degrees C for 1 h, produces a dense (not porous) oxide layer on the specimen surface. The specimens can deposit apatite on the contact surface after only 3 days of staking in SBF, but they cannot deposit apatite on the open surface for up to 2 months of staking. The implications of such apatite deposition behavior have been discussed in relation to the environments of titanium implants in bone as well as to the methodology of the SBF staking experiment.     

Preparation of porous composite implant materials by in situ polymerization of porous apatite containing epsilon-caprolactone or methyl methacrylate

Biodegradable and biostable composite foams were formed from porous apatite cement infiltrated with epsilon-caprolactone (CL) or methylmethacrylate (MMA) using a high over vacuum. For CL composites in situ polymerization was induced using trace water as an initiator and heating at 120 degrees C for up to 10 days or at 80 degrees C for 60 days. MMA composites were polymerized using AIBN initiator at 70 degrees C for 8 h. CL preparations gave composites with a polycaprolactone (PCL) number average of molecular weight (Mn) up to the maximum of 7.1 x 10(3) g/mol after 10 days and 16.8 x 10(3) g/mol after 60 days. The PCL and PMMA contents were close to 50 and 40 wt%, respectively, polymer was present as a thin coating on the apatite crystal plates and was evenly distributed throughout the samples. Re-evacuation of apatite saturated with monomer during preparation ensured that the upwards of 200 nm microchannels within the apatite cement were largely free of polymer, and the overall macroporous structure of the apatite foams was partly retained. Maximum compressive strengths increased from 9 MPa to 37 and 64 MPa for PCL and PMMA composites, respectively. The water drop contact angle of the PCL composite was 64 degrees, and therefore suitable for cell attachment. PMMA composite surfaces were more hydrophobic. Composites were subjected to corona discharge to induce suitable moderate hydrophilicity at the surface.     

Apatite deposition on thermally and anodically oxidized titanium surfaces in a simulated body fluid

By application of a special specimen set-up, thermally oxidized titanium specimen pairs were found able to deposit apatite on the contact surfaces after soaking for 7 days in the simulated body fluid (SBF) of Kokubo's recipe. The specimens oxidized at 400 degrees C and 500 degrees C showed the highest ability of apatite deposition. Both increase and decrease in oxidation temperature from this range caused the apatite deposition ability to decrease. The specimen without treatment failed to deposit any apatite. Specimens anodically oxidized in electrolytes of H(3)PO(4), H(2)SO(4) and acetic acid exhibited very low ability of apatite deposition. Furthermore, the specimen thermally oxidized at 400 degrees C was even able to help the surfaces of PTFE and silicone deposit apatite in the PTFE-Ti and silicone-Ti pairs. This in vitro experimental results indicated that the difference in apatite deposition among various titanium oxides does exist and can be distinguished by applying the present specimen set-up. The mechanism of the apatite deposition on the contact surfaces was discussed in relation to the passive dissolution of titanium in SBF. The release of titanium hydroxide and OH(-) ions from the titanium surfaces and their accumulation inside the confined space between the two contact surfaces were suggested to be responsible for the apatite deposition.     

Process and kinetics of bonelike apatite formation on sintered hydroxyapatite in a simulated body fluid

The surfaces of two hydroxyapatites (HA), which have been sintered at different temperatures of 800 and 1200 degrees C, was investigated as a function of soaking time in simulated body fluid (SBF) using transmission electron microscopy (TEM) attached with energy-dispersive spectrometry (EDX) and laser electrophoresis spectroscopy. The TEM-EDX indicated that after soaking in SBF, both the HAs form bonelike apatite by undergoing the same surface structural change, i.e., formations of a Ca-rich amorphous or nano-crystalline calcium phosphate (ACP) and a Ca-poor ACP, which eventually crystallized into bonelike apatite. Zeta potential characterized by the electrophoresis indicated that during exposure to SBF, the HA surfaces reveal negative surface charge, thereby interacting with the positive calcium ions in the fluid to form the Ca-rich ACP, which gains positive surface charge. The Ca-rich ACP on the HAs then interacts with the negative phosphate ions in the fluid to form the Ca-poor ACP, which stabilizes by being crystallized into bonelike apatite with a low solubility in the SBF. The exposure times for formations of these phases of the Ca-rich ACP, the Ca-poor ACP as well as the apatite were, however, all late on HA sintered at 1200 degrees C, compared with the HA sintered at 800 degrees C. This phenomenon was attributed to a lower initial negative surface charge of the HA sintered at 800 degrees C than of that one sintered at 1200 degrees C, owing to poverty in surface hydroxyl and phosphate groups which are responsible for the surface negativity of the HA. These indicate that sintered temperature of HA might influence not in terms of the process but in terms of the rate of formation of biologically active bonelike apatite on its surface, through which the HA integrates with living bone.     

In vitro and in vivo studies of alkali- and heat-treated Ti-6Al-7Nb and Ti-5Al-2Nb-1Ta alloys for orthopedic implants

In vitro studies of Ti-6Al-7Nb and Ti-5Al-2Nb-1Ta alloys were carried out by treating the specimens with 10 M NaOH at 60 degrees C for 24 h and subsequently heat-treated at 600 degrees C for 1 h. After the alkali and heat treatments, and on subsequent soaking in simulated body fluid (SBF), the morphological and compositional changes on the surface of the specimens were examined using scanning electron microscope attached with an energy-dispersive electron probe X-ray analyzer. The results revealed a dense and uniform bonelike apatite layer on the surface of treated substrates immersed in SBF solution. In vivo studies were carried out in rats to evaluate osteoconduction of Ti-6Al-7Nb and Ti-5Al-2Nb-1Ta alloys surface after alkali and heat treatments compared with untreated titanium alloys as the control. The following titanium implants were prepared from these species: (1) control without implant; (2) untreated titanium implant; (3) alkali- and heat-treated implant--the implants were immersed in 10 M NaOH solution at 60 degrees C for 24 h and subsequently heated at 600 degrees C for 1 h. The specimens were inserted into the medial side of each tibia of rats. Histologically, direct bone contact with the implant surface was significantly higher in the alkali heat-treated implants than the untreated titanium implants.     

含氟羟基磷灰石的合成与性能研究

采用湿法合成羟基磷灰石和两种不同氟含量的含氟羟基磷灰石粉,在300,600,900度热处理,并将900度热处理的两种含氟羟基磷灰石及羟基磷灰石的压片在模拟体液内浸泡,采用扫描电镜及溶液离子浓度测定法观察其体外生物活性,红外光谱分析显示通过热处理可去除含氟痉基磷灰石及羟基磷灰石内的杂质成分,获得标准比的羟基磷灰石,X线衍射分析显示含氟羟基磷灰石的热稳定性差,900度出现很弱的β－Ca3(PO4)2衍射峰,在模拟体液中羟基磷灰石和氟含量低的磷灰石表面可沉淀出骨状磷灰石。     

Study on the heat resistant property of Ag/4A antibacterial agent

The heat resistant property of silver-loading zeolite 4A antibacterial agent (SLZ) was investigated by heat treatment methodology. The morphological and structural changes of the specimens were characterized by using differential thermal analyzer (TG-DTA), scanning electron microscopy, and X-ray diffraction techniques. The particle size of the specimens was measured by Malvern instruments zetasizer systems, and silver content of specimens was determined by inductively coupled plasma spectrometer. Escherichia coli (E. coli) was chosen as indicators of fecal contamination to evaluate the antibacterial effect of the specimens by minimum inhibitory concentration method. The service life of the specimens was also tested. The experimental results indicated that as heat-treatment temperature increases, the particle size increases, more aggregating occurs, silver content decreases, the color of SLZ gradually changes from white to brown, and the antibacterial ability falls. The release rate of Ag(+) cation from SLZ became slow after heat treatment at 400, 450, and 500 degrees C, thus resulting in prolonged service life of SLZ. When the heat-treatment temperature approached 800 degrees C, the collapse of SLZ structure occurred, and the crystals of SiO(2) and Al(2)O(3) were formed after recrystallization. Consequently, the heat resistant temperature of SLZ can be as high as 500 degrees C. SLZ could be used in antibacterial plastics, antibacterial fibers, or biomedical materials.     

Formation of bone-like apatite on poly(L-lactic acid) fibers by a biomimetic process.

Bone-like apatite coating on poly(L-lactic acid) (PLLA) fibers was formed by immersing the fibers in a modified simulated body fluid (SBF) at 37 degrees C and pH 7.3 after hydrolysis of the fibers in water. The ion concentrations in SBF were nearly 1.5 times of those in the human blood plasma. The apatite was characterized by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), thin-film X-ray diffraction, and Fourier transform infrared spectroscopy. After 15 days of incubation in SBF, an apatite layer with about 5-6 microm thickness was formed on the surface of the fibers. This apatite had a Ca/P ratio similar to that of natural bone. The mass of apatite coated PLLA fibers increased with extending the incubation time. After 20 days incubation, the fibers increased their mass by 25.8 +/- 2.1%. The apatite coating had no significant effect on the tensile properties of PLLA fibers. In this article, the bone-like apatite coating on three-dimensional PLLA braids was also studied. The motivation for this apatite coating was that it might demonstrate enhanced osteoconductivity in the future studies when they serve as biodegradable scaffolds in tissue engineering.     

The effect of pH on the structural evolution of accelerated biomimetic apatite

The classic biomimetic apatite coating process can be accelerated by first immersing substrates into concentrated simulated body fluid, 5x SBF (SBF1), at 37 degrees C, to form an initial coating of precursor apatite spheres, and subsequently transferring to a second 5x SBF (SBF2) solution which is devoid of crystal growth inhibitors to promote phase transformation of SBF1-derived precursor apatite spheres into final crystalline apatite plates. Since SBF1 governs the formation kinetics and composition of the initial precursor spheres, we hypothesized that the pH of the SBF1 solution will also influence the final structure of the SBF2-derived crystalline apatite. To test this hypothesis, polystyrene substrates were immersed into SBF1 with different pH (5.8 or 6.5), and then immersed into the identical SBF2 (pH=6.0). The resultant apatites exhibited similar 2 theta XRD peaks; FTIR spectra in terms of hydroxyl, phosphate and carbonate groups; and Ca/P atomic ratio (1.42 for SBF1(5.8) apatite; 1.48 for SBF1(6.5) apatite). SEM, TEM and electron diffraction show that while SBF1(6.5) (pH 6.5) precursor spheres transform into larger, single crystals plates, SBF1(5.8) (pH 5.8) precursor spheres developed minute, polycrystalline plate-like structures over predominantly spherical precursor substrate.     

Processing of HA-coated Ti-6Al-4V by a ceramic slurry approach: an in vitro study

Hydroxyapatite-coated titanium alloy composite powders (Ti-6Al-4V/HA) was produced by a ceramic slurry approach. The aim was to evaluate the stability of the coating when subjected to a physiological medium simulated body fluid (SBF). Three consolidation conditions (700 degrees C for 5 h, 700 degrees C for 8 h and 700 degrees C for 11 h) were used in the production of the Ti-6Al-4V/HA composite powders. Results showed that biodissolution followed by apatite precipitation had taken place after soaking in SBF. In addition, it was found that consolidation at 700 degrees C for 5 h resulted in a weak mechanical locking of calcium phosphate on the Ti-6Al-4V surfaces; and the formation of small crystallites, which would increase the dissolution rate.     

Bioactive glass sol-gel foam scaffolds: Evolution of nanoporosity during processing and in situ monitoring of apatite layer formation using small- and wide-angle X-ray scattering

Recent work has highlighted the potential of sol-gel-derived calcium silicate glasses for the regeneration or replacement of damaged bone tissue. The work presented herein provides new insight into the processing of bioactive calcia-silica sol-gel foams, and the reaction mechanisms associated with them when immersed in vitro in a simulated body fluid (SBF). Small-angle X-ray scattering and wide-angle X-ray scattering (diffraction) have been used to study the stabilization of these foams via heat treatment, with analogous in situ time-resolved data being gathered for a foam immersed in SBF. During thermal processing, pore sizes have been identified in the range of 16.5-62.0 nm and are only present once foams have been heated to 400 degrees C and above. Calcium nitrate crystallites were present until foams were heated to 600 degrees C; the crystallite size varied from 75 to 145 nm and increased in size with heat treatment up to 300 degrees C, then decreased in size down to 95 nm at 400 degrees C. The in situ time-resolved data show that the average pore diameter decreases as a function of immersion time in SBF, as calcium phosphates grow on the glass surfaces. Over the same time, Bragg peaks indicative of tricalcium phosphate were evident after only 1-h immersion time, and later, hydroxycarbonate apatite was also seen. The hydroxycarbonate apatite appears to have preferred orientation in the (h,k,0) direction.     

Biomimetic deposition of apatite coating on surface-modified NiTi alloy

TiO(2) coatings were prepared on NiTi alloy by heat treatment in air at 300, 400, 600 and 800 degrees C. The heat-treated NiTi alloy was subsequently immersed in a simulated body fluid for the biomimetic deposition of the apatite layer onto the surface of TiO(2) coating. The apatite coatings as well as the surface oxide layer on NiTi alloy were characterized using scanning electron microscopy equipped with energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. Results showed the samples heat-treated at 600 degrees C produced a layer of anatase and rutile TiO(2) on the surface of NiTi. No TiO(2) was detected on the surface of NiTi after heat treatment at 300 and 400 degrees C by X-ray diffraction, while rutile was formed on the surface of the 800 degrees C heat-treated sample. It was found that the 600 degrees C heat-treated NiTi induced a layer consisted of microcrystalline carbonate containing hydroxyapatite on its surface most effectively, while 300 and 400 degrees C heat-treated NiTi did not form apatite. This was due to the presence of anatase and/or rutile in the 600 and 800 degrees C heat-treated NiTi which could provide atomic arrangements in their crystal structures suitable for the epitaxy of apatite crystals, and anatase had better apatite-forming ability than rutile. XPS and Raman results revealed that this apatite layer was a carbonated and non-stoichiometric apatite with Ca/P ratio of 1.53, which was similar to the human bone. The formation of apatite on 600 degrees C heat-treated NiTi following immersion in SBF for 3 days indicated that the surface modified NiTi possessed excellent bioactivity.     

Characterization of wollastonite-reinforced HAp--Ca polycarboxylate composites

The effects of wollastonite on the mechanical properties and in vitro behavior of hydroxyapatite-Ca polyacrylate composites were studied. Powder mixtures of tetracalcium phosphate, poly(acrylic-co-itaconic), and wollastonite fibers (< or =75% by weight) were hot-pressed for 30 min at 300 degrees C and 60 kpsi. Tensile strengths, elastic moduli, and microstructures of the composites were investigated. The tensile strengths of these composites were improved by the addition of wollastonite fibers, whereas the elastic moduli decreased. The highest value of tensile strength (approximately 155 MPa) was achieved by the addition of 40% wollastonite. Composites were immersed in simulated body fluid (SBF) for up to 14 days and then in 1.5 SBF for a week. The changes in the concentrations of Ca, Si, and P ions and the pH of these solutions indicate bioactivity. An evaluation of the microstructures of the composites after SBF immersion indicated that apatite layers had formed on the surfaces of the composites.     

Apatite formation on zirconium metal treated with aqueous NaOH.

Previous studies by the authors have shown that titanium metal, titanium alloys and tantalum metal which were subjected to aqueous NaOH solution and subsequent heat treatments form an apatite surface layer upon immersion in a simulated body fluid (SBF) with ion concentrations nearly equal to those in human blood plasma. These metals form the apatite surface layer even in living body, and bond to living bone through the apatite layer. In the present study, the apatite-forming ability of NaOH-treated zirconium metal in SBF has been investigated. A hydrated zirconia gel layer was formed on the surface of the zirconium metal on exposure to 1-15 M NaOH aqueous solutions at 95 degrees C for 24h. It was observed that the metals treated in NaOH aqueous solutions with concentrations above 5 M form an apatite layer on their surface in SBF. This indicates that the Zr-OH group of the zirconia gel induces apatite nucleation. The present study points to the possibility of obtaining bioactive zirconium after treatment by NaOH.     

Preparation and characterization of bioactive mesoporous wollastonite – Polycaprolactone composite scaffold

A well-defined mesoporous structure of wollastonite with high specific surface area was synthesized using surfactant P123 (triblock copolymer) as template, and its composite scaffolds with poly(?-caprolactone) (PCL) were fabricated by a simple method of solvent casting-particulate leaching. The measurements of the water contact angles suggest that the incorporation of either mesoporous wollastonite (m-WS) or conventional wollastonite (c-WS) into PCL could improve the hydrophilicity of the composites, and the former was more effective than the later. The bioactivity of the composite scaffold was evaluated by soaking the scaffolds in a simulated body fluid (SBF) and the results show that the m-WS/PCL composite (m-WPC) scaffolds can induce a dense and continuous layer of apatite after soaking for 1 week, as compared with the scattered and discrete apatite particles on the c-WS/PCL composite (c-WPC) scaffolds. The m-WPC had a significantly enhanced apatite-forming bioactivity compared with the c-WPC owing to the high specific surface area and pore volume of m-WS. In addition, attachment and proliferation of MG₆₃ cells on m-WPC scaffolds were significantly higher than that of c-WPC, revealing that m-WPC scaffolds had excellent biocompatibility. Such improved properties of m-WPC should be helpful for developing new biomaterials and may have potential use in hard tissue repair.