Effect of thermal treatment on apatite-forming ability of NaOH-treated tantalum metal.

The prerequisite for an artificial material to bond to living bone is the formation of bonelike apatite on its surface in the body. This apatite can be reproduced on its surface even in an acellular simulated body fluid with ion concentrations nearly equal to those of the human blood plasma. The present authors previously showed that the tantalum metal subjected to a NaOH treatment to form a sodium tantalate hydrogel layer on its surface forms the bonelike apatite on its surface in SBF in a short period. The gel layer as-formed on the metal is, however, not resistant against abrasion, and hence thus-treated metal is not useful for clinical applications. In the present study, effects of thermal treatment on the mechanical properties and apatite-forming ability of the NaOH-treated tantalum metal were investigated. The sodium tantalate gel on the NaOH-treated tantalum was dehydrated to convert into amorphous sodium tantalate by a thermal treatment at 300 degrees C in air environment and into crystalline sodium tantalates by the thermal treatment at 500 degrees C. Resistivity of the gel layer against both peeling-off and scratching was significantly improved by the thermal treatment at 300 degrees C. The high apatite-forming ability of the sodium tantalate hydrogel was a little decreased by the thermal treatment at 300 degrees C, but appreciably decreased by the thermal treatment at 500 degrees C. It is believed that the tantalum metal subjected to the 0.5 M-NaOH treatment and the subsequent thermal treatment at 300 degrees C is useful as implants in dental and orthopaedic fields, since it shows high bioactivity as well as high fracture toughness.

Antibacterial silver-containing silica glass prepared by sol-gel method.

Recently, various inorganic antibacterial materials containing silver have been developed and some of them are in commercial use. Colorless and more chemically durable materials which slowly release the silver ion for a long period are, however, desirable to be developed for medical applications such as composite resin for dental restoration. In the present study, Si(OC2H5)4, Al(NO3)3 x 9H2O, AgNO3, HNO3, C2H5OH and H2O solutions with various Al/Ag atomic ratios under a constant Si/Ag atomic ratio of 1/0.023 were kept at 40 degrees C for gelation and drying. Thus obtained gels were pulverized into fine powders with average particle size of approximately 10 microm and then heat-treated at 900-1000 degrees C for 2 h. For the composition Al/Ag = 0, a yellow-colored glass was formed, since the silver existed in the form of metallic colloids in the glass. However, for the compositions Al/Ag > or = 1, colorless glasses were successfully obtained, since the silver existed in the form of Ag+ ions in the glasses. For the composition Al/Ag = 0, the silver ions got released rapidly into the water, whereas, for the compositions Al/Ag > or = 1, they gradually got released into the water at a controlled rate. A composite of the obtained powders with Al/Ag atomic ratio of 1 with Bis-GMA/TEGDMA in 70:30 weight ratio showed excellent antibacterial property. The sol-gel derived silica glass powders containing silver with compositions Al/Ag > or = 1 are believed to be useful as an antibacterial material for medical applications such as filler of composite resin for dental restoration.

Bioactive tantalum metal prepared by NaOH treatment.

Untreated tantalum metal formed an apatite on its surface in simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. However, it took an induction period as long as 4 weeks for apatite formation. The tantalum metal formed the apatite within 1 week when it was previously soaked in a 0.2 or 0.5M NaOH aqueous solution at 60 degrees C for 24 h to form a sodium tantalate hydrogel layer on its surface. The decrease in the induction period of apatite formation was attributed to the catalytic effect of the Ta-OH groups on the surface of the tantalum metal for apatite nucleation and acceleration of the apatite nucleation by an increased ionic activity product of the apatite in the fluid due to the release of Na(+) ions. The NaOH-treated tantalum metal can form apatite in a short period even in the living body and bond to the bone through this apatite layer. This indicates that a highly bioactive tantalum metal can be obtained by a simple chemical treatment.

Composition and structure of apatite formed on organic polymer in simulated body fluid with a high content of carbonate ion.

Apatite layer was formed on polyethyleneterephthalate (PET) substrate by the following biomimetic process. The PET substrate was placed on granular particles of a CaO, SiO2-based glass in simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma to form apatite nuclei on their surfaces. The apatite nuclei was then grown into a continuous layer by subsequently soaking the substrate in SBF under air or CO2 atmosphere in which CO2 partial pressure in the ambient was adjusted to 14.8 kPa to increase the content of carbonate ion to a level nearly equal to that of blood plasma. The increase in the content of carbonate ions in SBF changed the Ca/P atomic ratio of the apatite from 1.51 to 1.63, content of CO(3)2- ions from 2.64 to 4.56 wt %, and lattice constants a from 94.32 to 94.23 nm and c from 68.70 to 68.83 nm, respectively. The Ca/P ratio and lattice constants of the apatite formed in SBF under CO2 atmosphere were approximately identical to those of bone apatite, i.e. Ca/P atomic ratio 1.65, content of CO(3)2- ion 5.80 wt % and lattice constants a 94.20 and c 68.80 nm. This indicates that an apatite with composition and structure nearly identical to those of bone apatite can be produced in SBF by adjusting its ion concentrations including the content of carbonate ions to be equal to those of blood plasma.

Formation of bioactive functionally graded structure on Ti-6Al-4V alloy by chemical surface treatment.

An Al- and V-free sodium titanate hydrogel layer with a graded structure where the sodium titanate gradually decreases toward the interior, was formed on the surface of Ti-6Al-4V alloy, when the alloy was exposed to 5M NaOH solution at 60 degrees C for 24 h. This gel layer was transformed into an amorphous sodium titanate layer without giving considerable change in the graded structure, except a little increase in the depth of the oxygen distribution by a heat treatment at 600 degrees C for 1 h. The sodium titanate layer formed Ti-OH groups on its surface by exchanging its Na+ ion with H3O+ ion in simulated body fluid when soaked in the fluid, and thus formed Ti-OH groups induced the apatite nucleation. The apatite layer also formed a graded structure toward the substrate. The strong bond of the apatite layer to the substrate was attributed to this graded structure.

Enhancement of bone-bonding strengths of titanium alloy implants by alkali and heat treatments.

The purpose of this study is to evaluate the bone-bonding ability of alkali- and heat-treated titanium alloys. Smoothed-surface rectangular plates of Ti6Al4V, Ti6Al2Nb1Ta, and Ti15Mo5Zr3Al were prepared. The plates were inserted transcortically into the proximal metaphyses of bilateral rabbit tibiae, with alkali- and heat-treated plates inserted on the right side, and untreated plates on the left. The tensile failure loads between the implants and the bones were measured after 8, 16, and 24 weeks by a detaching test. The untreated implants showed almost no bonding even at 16 weeks, and only weak bonding at 24 weeks. In contrast, treated implants showed bonding to bone at all time periods. Histological examination showed that alkali- and heat-treated alloys bonded directly to the bone. Conversely, the untreated implants had an intervening layer of fibrous tissue between the bone and the plate, or only partial direct contact with the bone. This study demonstrates that alkali and heat treatments enhance the bone-bonding strength of these titanium alloys. Although in this study even tentative conditions of the treatments enhance the bonding strength of the titanium alloys, further work is required to determine the optimum conditions for treatment to give the highest bonding strength. These new bioactive titanium alloys are available for weight-bearing and bone-bonding orthopedic devices.

Graded surface structure of bioactive titanium prepared by chemical treatment.

An NaOH treatment of pure titanium (Ti) forms a sodium titanate hydrogel surface layer with a smooth graded interface structure to the Ti metal substrate. Subsequent heat treatment at 600 degrees C of the NaOH-treated Ti forms an amorphous sodium titanate surface layer with a smooth graded interface structure similar to the Ti metal substrate. These treated Ti metals both form an apatite surface layer with a smooth graded interface structure to the Ti metal substrates in simulated body fluid (SBF). The smooth graded interface structures give a tight bond of the apatite layer to the substrates. Heat treatment at 800 degrees C of the NaOH-treated Ti forms crystalline sodium titanate and a rutile surface layer with a graded interface structure to the Ti metal substrate, which is intervened by a thick titanium oxide. This substrate forms an apatite layer with a graded interface structure to the Ti metal substrate, which is intervened by a thick titanium oxide in SBF. This irregular graded structure gives a less tight bond of the apatite layer to the substrate.

Bonelike apatite coating on organic polymers: novel nucleation process using sodium silicate solution.

A bonelike apatite layer was formed on organic polymers when sodium silicate was used as a catalyst for the apatite nucleation, and modified simulated body fluid was used as a medium for the apatite growth. The apatite-forming ability was the highest when the SiO2 concentration and SiO2/Na2O mole ratio of the sodium silicate solution were above 2.0 M and 1.0-1.5, respectively. It is assumed that particular silicate oligomers with structures such as dimer, linear trimer and cyclic tetramer contribute to the apatite nucleation the most. The apatite layer was formed not only on limited surfaces but also on the whole surfaces of fine PET fibers constituting a fabric. This method is expected to enable the bonelike apatite coating on various kinds of materials with complex shapes.

Composition and structure of the apatite formed on PET substrates in SBF modified with various ionic activity products.

An apatite layer was formed on polyethyleneterephthalate (PET) substrates by the following biomimetic process. PET substrates were placed on granular particles of a CaO-SiO2-based glass in simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma to form apatite nuclei on their surfaces (first treatment). They then were soaked in modified SBFs, the ion concentrations of which were changed to give a variation in ionic activity product of apatite (IP), in order to make the apatite nuclei grow (second treatment). The Ca/P atomic ratio and the lattice constant c of the formed apatite decreased from 1.54 to 1.40 and from 6.880 to 6.838 A, respectively, with increasing ion concentrations from 0.75 to 2.00 times those of SBF, that is, with increasing IP from 10(-96.6) to 10(-91.9). This was attributed to an increase in the concentration of HPO4(2-) ion substituting for the PO4(3-) ion sites, which gave an increase in the Ca2+ in the apatite. Even the apatite formed in 1.00 SBF showed a Ca/P ratio of 1.51 and lattice constants a of 9.432 A and c of 6.870 A. The Ca/P ratio and lattice constant c were smaller and the lattice constant a was larger than those of the bone apatite; its Ca/P ratio and its lattice constants a and c, were 1.65, 9.419 A, and 6.88 A, respectively. This was attributed to the lower content (2.64 wt%) of the CO3(2-) ion substituting for the PO4(3-) ion sites of the apatite compared to that of the bone apatite (5.80 wt%). The lower content of the CO3(2-) ion in the apatite might be caused by the lower concentration of HCO3- ion in 1.00 SBF compared to that in human blood plasma.

Apatite formation on PDMS-modified CaO-SiO2-TiO2 hybrids prepared by sol-gel process.

Dense and homogeneous monolithics of polydimethylsiloxane (PDMS)-modified CaO-SiO2-TiO2 hybrids were successfully synthesized by sol-gel process. They were assumed to be composed of a silica and titania network incorporated with PDMS and the calcium ion ionically bonded to the network. Among them, the hybrids containing relatively larger amounts of the calcium in their surfaces formed an apatite on their surfaces within only 1 or 0.5 day in a simulated body fluid with ion concentrations nearly equal to those of human flood plasma. This indicates that they are highly bioactive. Organic-inorganic hybrids synthesized by a sol-gel process usually exhibit high ductility, low elastic modulus and high mechanical strength. The present hybrids are, therefore, expected to be useful as a new kind of bone-repairing material, because of their high bioactivity and unique mechanical properties.

The effect of heat treatment on bone-bonding ability of alkali-treated titanium.

The purpose of this study was to evaluate the bone-bonding ability of alkali-treated titanium with and without heat treatment. Three groups of smooth titanium plate were prepared: control, or pure titanium, alkali-treated titanium, and alkali- and heat-treated titanium. The plates were inserted transcortically into the proximal metaphyses of bilateral rabbit tibiae. The tensile failure loads between implants and bones were measured at two time intervals using a detaching test. The tensile failure loads of the alkali- and heat-treated titanium group were 2.71 and 4.13 kgf, at 8 and 16 weeks, respectively, and significantly higher than those of the other titanium groups. Histological examination revealed that alkali- and heat-treated titanium was in direct contact with bone, but the other titanium groups had a thin intervening fibrous tissue. This result indicated that the alkali-treated titanium without heat treatment had no bone-bonding ability due to the unstable reactive surface layer of alkali-treated titanium. In conclusion, both alkali and heat treatment are essential for preparing bioactive titanium and this bioactive titanium is thought to be useful for orthopedic implants with cementless fixation.

Sol-gel modification of silicone to induce apatite-forming ability.

Silicones formed with silanol groups on their surfaces were prepared by partial hydrolysis and polycondensation of tetraethoxysilane (TEOS) dispersed in silicones in molecular scale. Although the silanol-modified silicones thus prepared formed no apatite in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma within 21 d, they formed a bone-like apatite layer in situ on their surfaces in a solution (1.5 SBF) with ion concentrations 1.5 times the SBF within 7 d. This indicates that the silanol groups formed on the silicones by the present method can induce the apatite nucleation in 1.5 SBF and hence, apatite-coated silicones can be fabricated by a biomimetic process. Apatite-silicone composites thus prepared could exhibit mechanical properties analogous to the natural bone as well as bioactivity.

Preparation of phosphorus-containing silica glass microspheres for radiotherapy of cancer by ion implantation.

A chemically durable glass microsphere containing a large amount of phosphorus is useful for in situ irradiation of cancers, since they can be activated to be a beta-emitter with a half-life of 14.3 d by neutron bombardment. When the activated microspheres are injected to the tumors, they can irradiate the tumors directly with beta-rays without irradiating neighboring normal tissues. In the present study, P+ ion was implanted into silica glass microspheres of 25 microm in average diameter at 50 keV with nominal doses of 2.5 x 10(16) and 3.35 x 10(1)6 cm(-2). The glass microspheres were put into a stainless container and the container was continuously shaken during the ion implantation so that P+ ion was implanted into them uniformly. The implanted phosphorus was localized in deep regions of the glass microsphere with the maximum concentration at about 50 nm depth without distributing up to the surface even for a nominal dose of 3.35 x 10(16) cm(-2). Both samples released phosphorus and silicon into water at 95 degrees C for 7 d. On the basis of the previous study on P+-implanted silica glass plates, the silica glass microspheres containing more phosphorus which is desired for actual treatment could be obtained, without losing high chemical durability, if P+ ion would be implanted at higher energy than 50 keV to be localized in deeper region.

Surface structural change of bioactive inorganic filler-resin composite cement in simulated body fluid: effect of resin.

Recently much attention has been paid to bioactive filler-resin composite cements because they can solidify in a few minutes to give high mechanical strengths and they can bond to living bone. In this study the dependence on resin of apatite-forming ability in simulated body fluid (SBF) was investigated for the composite cements of bioactive CaO-SiO2-P2O5-CaF2 glass with polymethyl methacrylate (PMMA) or bisphenol-a-glycidyl methacrylate/triethyleneglycol (Bis-GMA/TEGDMA) resin. The PMMA-containing composite cement did not show the apatite-forming ability in SBF because the reaction of the glass grains with SBF was inhibited due to the complete covering of the grains with PMMA. To the contrary, the Bis-GMA/TEGDMA-containing cement exhibited high apatite-forming ability in SBF; these monomers significantly dissolved from the composite surface into SBF, causing a direct exposure of the glass grains to SBF to convert into silica gel. It is assumed that thus formed silica gels, and the silicate ions that were dissolved and adsorbed onto the composite surface, induced the apatite nucleation between the spaces of the glass grains and on the composite surface, respectively. A continuous bone-like apatite layer was formed on the top surface of the glass-Bis-GMA/TEGDMA composite cement in a short period.

[Postpartum depression and social support].

OBJECTIVES: To ascertain the state of a mother's depression three months after childbirth and to what sort of or to whose social support it is related. METHOD: In October 1993, a questionnaire survey was conducted on the attributes, state of depression by Zung Self-rating Depression Scale, and social support of 300 mothers who received health examinations of their 3 to 4 months' old infants at five health centers in Tokyo. Relationship between depression and social support of 256 mothers (rate of valid answer 85.3%) was examined by one-way analysis of variance, Pearson's product moment correlation coefficient and multiple regression analysis. RESULTS: The depression score averaged 37.3 points, with 73 persons (28.5%) scoring 40 to 47 points (light) and 27 persons (10.5%) scoring 48 or more points (medium level or higher). The following were the variables which individually showed a significant relationship to the depression score after controlling for age, education, number of children, type of family, and whether or not the mother was working: The emotional support score from the husband and his parents, such as the frequency in which the husband "listened to the mother's worries and anxieties" "was attentive or considerate to the mother" and "helped in feeding the child", the frequency in which the husband's parents "could be consulted on worries the mother had about childbirth, child care and child development" and "nursed and played with the child". It was found that the better the state of such support, the less the state of depression. On the other hand, support from the mother's parents, neighbors, and friends had no bearing on depression. CONCLUSION: The level of depression of the surveyed group was the same as that of the general female public. Postpartum depression was related to emotional support from the husband and emotional and practical support from the husband's parents. Therefore, from the aspect of preventing depression, we believe it is important that, firstly, the mother and family should understand the importance of support and improve the support by the family, and, secondly, the mother herself should improve her ability to cope.

Apatite formation on silica gel in simulated body fluid: effects of structural modification with solvent-exchange.

The prerequisite for glasses and glass-ceramics to bond to living bone is the formation of biologically active bone-like apatite on their surfaces. It has been shown that even a pure silica gel forms the bone-like apatite on its surface in a simulated body fluid. In the present study, pore structure of silica gels prepared by hydrolysis and polycondensation of tetraethoxysilane in an aqueous solution containing polyethylene glycol was modified by 1M HNO3, and 0.1M and 1M NH4OH solution treatments. The three kinds of resultant gels all contained large amounts of silanol groups and trisiloxane rings, but differ greatly in pore structure of nanometre pore size. Irrespective of these differences, all the gels formed the bone-like apatite on their surface in the simulated body fluid. It was speculated that a certain type of structural unit of silanol groups, which is easily formed in the presence of the polyethylene glycol, is effective for the apatite formation.

Apatite-organic polymer composites prepared by a biomimetic process: improvement in adhesion of the apatite layer to the substrate by ultraviolet irradiation.

A dense and uniform layer of highly bioactive apatite can be formed in arbitrary thickness on any kind and shape of organic polymer substrates by the following biomimetic process. The substrate is first placed in contact with granular particles of CaO, SiO2-based glass soaked in a simulated body fluid with ion concentrations nearly equal to those of human blood plasma for forming apatite nuclei, and then soaked in another fluid highly supersaturated with respect to the apatite for making the apatite nuclei grow. In the present study, the polymer substrates were pretreated with ultraviolet (UV) light, and then subjected to the biomimetic process described above. By UV irradiation, the induction period for the apatite nucleation of poly(ethylene terephthalate) (PET), poly-ether sulphone (PESF), polyethylene (PE), poly(methyl methacrylate) (PMMA) and polyamide 6 (N6) substrates were reduced form 24 h to 10 h. The adhesive strengths of the apatite layer to the substrates increased from 2.5-3.2 MPa to 4.5-6.0 MPa for PET, PESF and PMMA, and from about 1.0 MPa to 4.0-6.5 MPa for PE and N6 substrates. These results have been explained by assuming that silicate ions, which induce apatite nucleation, are easily adsorbed on the substrates due to the formation of polar groups, with an improved hydrophilic nature, on the polymer surfaces by UV irradiation.

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 degrees 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 degrees C, a bone-like apatite was formed on the substrates in a short period.

Bonding of chemically treated titanium implants to bone.

A study was undertaken in rabbit tibiae to determine the effects of chemical treatments and/or surface-induced bonelike apatite on the bone-bonding ability of titanium (Ti) implants. Smooth-surfaced plates (10 x 10 x 2 mm) of pure Ti, alkalil- and heat-treated Ti, and bonelike apatite-formed Ti after the treatments were implanted into the tibial metaphyses of mature rabbits. The tibiae containing the implants were harvested at 4, 8, and 16 weeks after implantation and subjected to a tensile testing and histologic evaluation. Biomechanical results showed that both treated implants exhibited significantly higher failure loads compared with untreated Ti implants at all time periods. Histologic examination by Giemsa surface staining, contact microradiography (CMR), and scanning electron microscopy (SEM) in backscatter mode revealed that both treated Ti implants directly bonded to bone tissue during the early postimplantation period, whereas untreated Ti implants formed direct contact with the bone only at 16 weeks. SEM-electron-probe microanalysis (EPMA) examination showed a Ca-P-rich layer at the interface between the treated implants and bone, although the Ca-P-rich layer was not detected on the surface of untreated implants during observation periods. The results of this study suggest that chemical treatments may accelerate the bone-bonding behavior of titanium implants and enhance the strength of bone-implant bonding by inducing a bioactive surface layer on Ti implants.

Bioactivity of ferrimagnetic glass-ceramics in the system FeO-Fe2O3-CaO-SiO2.

Bioactive and ferrimagnetic glass-ceramics are useful as thermoseeds for hyperthermia treatment of cancer. A heat treatment of a 40(FeO, Fe2O3)-60CaO x SiO2 wt% glass gives a ferrimagnetic glass-ceramic containing 36 wt% magnetite in a CaO x SiO2 matrix. However, it does not show bioactivity since a small amount of iron ion remains in the matrix. In the present study, bioactivities of ferrimagnetic glass-ceramics which were prepared by heat treatment of glasses of the composition 40(FeO, Fe2O3)-60CaO x SiO2 (wt%) with various components added at 100:3 weight ratio were evaluated in vitro by examining bone-like apatite formation on their surfaces in a simulated body fluid. It was found that glass-ceramics with Na2O or B2O3 added in combination with P2O5 show bioactivity.