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PubMed2000

Surface design of orthopaedic drug delivery implants: X-ray photoelectron spectroscopy of bone-derived apatites.

Incorporation of foreign ions onto a biomineral surface as well as removal from it of native (physiological) ions during deproteination procedures, are discussed in view of surface design of orthopaedic implants serving as drug delivery carriers. Surface properties of bone-derived apatites, purified at low temperature in non-aqueous medium, and of several commercial samples are examined via XPS technique. It has been demonstrated that, in spite of the fact that the initial bone demineralized matrix is derived from the same bovine bone, different deproteination procedures lead to different surface properties. Correlation between carbon 1s deconvoluted peak and the percentage of the residual organic fraction on the bone-derived apatites' surface at different stages of purification has been established.

Journal Article↗

PubMed1999

Crystal growth of carbonate apatite using a CaCO3 flux.

Single crystals of carbonate apatite were grown using a CaCO3 flux under an Ar gas pressure of 55 MPa. The crystals obtained were observed by scanning electron microscopy, optical microscopy and X-ray diffraction. Electron probe microanalyses and thermal analyses were performed. CO3 ions in planar triangle form replaced both OH sites and PO4 tetrahedral sites in the apatite structure: in particular, the OH sites were perfectly substituted by CO3 ions using this method.

Journal Article↗

PubMed2001

Tissue responses to anti-washout apatite cement using chitosan when implanted in the rat tibia.

The tissue response to anti-washout apatite cement using chitosan (aw-AC(chi)) was evaluated by implanting aw-AC(chi) into bone defects of rat tibiae using conventional apatite cement (c-AC) as a control material. During the experimental period up to 16 weeks, the only difference between aw-AC and c-AC was found at two weeks in the tissue response of soft tissue. At two weeks, c-AC showed a moderate inflammatory response; small particles of c-AC were scattered in the cutaneous tissue and many foreign body giant cells were collected around the scattered c-AC, whereas aw-AC showed only a slight inflammatory response and few foreign body giant cells. We found no difference between aw-AC(chi) and c-AC with respect to bone tissue response. Both AC were almost completely surrounded by mature bone at eight weeks. No promotion or reduction of osteoconductivity was observed by chitosan even though it is considered to promote bone formation. We concluded, therefore, that enhancement of bone formation cannot be expected by employing chitosan to obtain anti-washout properties, at least in the concentration used in this study, even though aw-AC(chi) is much more useful than c-AC.

Journal Article↗

PubMed2001

Adsorption of vascular endothelial growth factor to two different apatitic materials and its release.

The aim of our study was to assess the ability of calcium phosphate powders to serve as growth factor carriers. Vascular endothelial growth factor (VEGF), in particular, is locally involved in the bone formation process throughout osteoblast differentiation. Two different apatitic substrates were tested: hydroxyapatite (HA), widely used as biomaterial, and nanocrystalline carbonated apatite (CA), which has a composition similar to bone mineral crystals. These materials have been compared for their VEGF adsorption and release properties. The adsorption of the growth factor was higher on CA than on HA probably due to differences of both the proteins and the powders involved. The specific activity of the VEGF released was also tested to determine the available activity for cells in contact with these materials. Interestingly, the bioactivity of the VEGF released from CA quantified on fetal bovine aortic endothelial cells (FBAE) by evaluating the proliferation activity, exhibited no marked difference compared to native VEGF. Qualitatively, VEGF adsorbed on CA material induced well-defined collagen type I immunostaining on osteoblast cells compared to the staining obtained after VEGF adsorption on HA.

Journal Article↗

PubMed1997

Effect of sodium bicarbonate amount on in vitro indomethacin release from self-setting carbonated-apatite cement.

PURPOSE: In the present study, to develop a drug delivery system with higher bioactivity in hard tissues by using the self-setting bioactive carbonate apatite cement, we have investigated the effects of sodium bicarbonate content on the in vitro drug release from a self-setting bioactive carbonate apatite cement containing indomethacin (IMC). METHODS: The cement powder systems constituted an equimolar mixture of tetracalcium phosphate (Ca4(PO4)2O) and dicalcium phosphate dihydrate (CaHPO4.2H2O), hydroxyapatite (HAP, Ca10(PO4)6(OH)2) seed crystals and sodium bicarbonate. Two types of 2% IMC loaded-cements were prepared as follows, one containing 0% HAP seed crystal and 0-10% sodium bicarbonate, and the other containing 40% HAP seed crystal and 0-10% sodium bicarbonate. The drug release profiles from 2% IMC loaded-cements were measured in simulated body fluid at pH 7.25 and 37.0 degrees C. RESULTS: The drug release profiles from the cement matrix systems with or without seed crystals were estimated using a moment analysis computer program. The mean drug release time (MDT) and the time required for 50% drug release of the cement containing 0 and 40% seed crystal decreased with an increase of sodium bicarbonate. Furthermore, after the drug release the total pore volume of the cement matrix, as measured by mercury porosimetry, increased with an increase of sodium bicarbonate. CONCLUSIONS: MDT and T50's were a function of adding the amount of sodium bicarbonate. The results of the relationship between the micropore distribution, total volume of pores after drug release and drug release supported the hypothesis that the variation in drug release from the cements resulting from the addition of sodium bicarbonate was mainly due to an increase in the diffusion of the drug in the micropores of the cement by dissolution or erosion of the cement matrix.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1997

Effect of heat treatment on apatite-forming ability of Ti metal induced by alkali treatment.

The present authors previously showed that titanium metal forms a bone-like apatite layer on its surface in a simulated body fluid (SBF), when it has been treated with a NaOH solution to form a sodium titanate hydrogel layer on its surface. This indicates that the NaOH-treated Ti metal bonds to living bone. The gel layer as-formed is, however, mechanically unstable. In the present study, the NaOH-treated Ti metal was heat treated at various temperatures in order to convert the gel layer into a more mechanically stable layer. The gel layer was dehydrated and transformed into an amorphous sodium titanate layer at 400-500 degrees C, fairly densified at 600 degrees C and converted into crystalline sodium titanate and rutile above 700 degrees C. The induction period for the apatite formation on the NaOH-treated Ti metal in SBF increased with the transformation of the surface gel layer by the heat treatment. Ti metal heat treated at 600 degrees C, however, showed a fairly short induction period as well as high mechanical stability, since it was covered with a fairly densified amorphous layer.

Journal Article↗

PubMed1997

Characterization of hydroxyapatite and carbonated apatite by photo acoustic FTIR spectroscopy.

An understanding of the interfacial relationship between a bioceramic implant and the adjacent bone tissue is facilitated by precise characterization of the associated structures. The structure of different commercial synthetic hydroxyapatite powders and a novel carbonated apatite have been studied with photo-acoustic (PAS) Fourier transform infrared (FTIR) spectroscopy. The PAS technique is an ideal method for analysing biomaterials, as materials can be analysed without the need to reduce the particle size or to dilute with KBr. Spectra from carbonated apatite appear to be different from those of commercial hydroxyapatite powders, with the main difference lying in the carbonate and phosphate ratio. Commercial hydroxyapatite powders from different sources have also been analysed and compared.

Journal Article↗

PubMed2004

Doping strategies to optimise the oxide ion conductivity in apatite-type ionic conductors.

The apatite-type phases, La(9.33+x)(Si/Ge)(6)O(26+3x/2), have recently been attracting considerable interest as potential electrolytes for solid oxide fuel cells. In this paper we report results from a range of doping studies in the Si based systems, aimed at determining the key features required for the optimisation of the conductivities. Systems examined have included alkaline earth doping on the rare earth site, and P, B, Ga, V doping on the Si site. By suitable doping strategies, factors such as the level of cation vacancies and oxygen excess have been investigated. The results show that the oxide ion conductivities of these apatite systems are maximised by the incorporation of either oxygen excess or cation vacancies, with the former producing the best oxide ion conductors. In terms of samples containing cation vacancies, conductivities are enhanced by doping lower valent ions, Ga, B, on the Si site. The presence of higher valent ions on these sites, e.g. P, appears to inhibit the incorporation of excess oxygen within the channels, and so limits the maximum conductivity that can be obtained. Overall the results suggest that the tetrahedral sites play a key role in the conduction properties of these materials, supporting recent modelling studies, which have suggested that these tetrahedra aid in the motion of the oxide ions down the conduction channels by co-operative displacements.

Journal Article↗

PubMed1993

Influence of carbonate on sintering of apatites.

Sintering of carbonate apatite, prepared at 100 degrees C and pH 9.0 for 3 days, was studied by thermal analysis, x-ray diffraction, and infrared spectroscopy. The sintering temperature, at which the linear thermal shrinkage of isostatically compacted specimens increased sharply, decreased in proportion to the amount of carbonate initially present in the apatite. For example, specimens with over 8 wt% carbonate could be sintered at a temperature (650 degrees C) which was nearly 400 degrees C lower than that needed for sintering a specimen with no carbonate. Amounts of carbonate lost at the end of sintering, estimated chemically and by infra-red spectroscopy, were approximately equal to sample weight losses estimated thermogravimetrically.

Carbonates↗

PubMed1998

Potassium is involved in apatite biomineralization.

The biogenetic formation of mineral crystals, one aspect of biomineralization, is a multistep process of apatite formation throughout the growth of dentin tissue. An important step is the transformation of the non-mineralized predentin matrix to mineralizing dentin matrix and its biological control. In this study, the high capacity of elemental mapping is combined with single x-ray point measurements to elucidate whether special elements are involved in initiation or regulation of mineral nucleation. Directly at the mineralization front, micro-areas with a strong co-enrichment of phosphorus (e.g., as phosphate) and potassium are found. During the beginning of the calcium enrichment and the subsequent apatite mineral formation in the characteristic micro-areas, the content of potassium decreases significantly. These findings indicate that potassium is involved in the process of dentin mineralization.

Animals↗

PubMed2003

How does fluoride concentration in the tooth affect apatite crystal size?

Despite fluoride's (F) well-documented ability to prevent caries, the effects of F concentrations on enamel and dentin apatite crystals are unknown. The present study examined the hypothesis that tooth F concentration and tooth crystallite size correlate. One hundred human unerupted third molars were studied-53 from Fortaleza-Brazil (F water 0.7 ppm), 23 from Toronto (1.0 ppm), and 24 from Montreal (0.2 ppm). F concentration was analyzed by Neutron Activation Analysis and apatite crystal size by powder x-ray diffraction. A positive correlation between dentin F concentration and enamel crystallite length and width was found. Enamel crystallite length was significantly greater in teeth from Fortaleza than in teeth from Toronto (p = 0.011) and Montreal (p = 0.003). Enamel crystallite widths were significantly greater in Fortaleza teeth compared with those from Toronto (p = 0.020) and Montreal (p < 0.001). No difference in the dentin crystallite size was seen in the 3 regions. Thus, tooth F concentration and crystallite size correlate.

Analysis of Variance↗

PubMed2000

A methodological study for the analysis of apatite-coated dental implants retrieved from humans.

The stability of thermally processed hydroxyapatite coatings for oral and orthopedic bioprostheses has been questioned. Information on the chemical changes, which occur with hydroxyapatite biomaterials post-implantation in humans, is lacking. The purpose of this investigation was to begin to examine post-implantation surface changes of hydroxyapatite-coated implants using scanning electron microscopy (SEM), x-ray microanalysis (EDAX), Fourier transform infrared spectroscopy (FTIR), and x-ray diffraction (XRD). Three retrieved dental implant specimens from humans following clinical failure due to peri-implantitis were examined. Unimplanted cylinders served as controls. Clinically, the retrieved specimens were all enveloped by a fibrous tissue capsule with bone present at the apical extent of the implant. SEM analysis showed that the retrieved surfaces were coated with both calcified and proteinaceous deposits. EDAX scans of the retrieved specimens demonstrated evidence of hydroxyapatite coating loss reflected by increasing titanium and aluminum signals. Other foreign ions such as sodium, chloride, sulfur, silica, and magnesium were detected. XRD of the control specimens showed that the samples were predominantly apatite; however, two peaks were detected in the diffraction pattern, which are not characteristic of hydroxyapatite, indicating that small amounts of one or more other crystalline phases were also present. The retrieved specimens showed slightly larger average crystal size relative to the control sample material, and the non-apatite lines were not present. FTIR evaluation of the retrieved specimens revealed the incorporation of carbonate and organic matrix on or into the hydroxyapatite. Narrowing of and increased detail in the phosphate peaks indicated an increase in average crystal size and/or perfection relative to the controls, as did the XRD results. Based on these results, we conclude that chemical changes may occur within the coating, with the incorporation of carbonate and concomitant reduction in hydroxyapatite coating thickness. Thermodynamic dissolution-reprecipitation of the coating itself and subsequent surface insult by bacterial and local inflammatory components may be involved with these changes.

Aluminum↗

PubMed2004

Effects of added sodium alginate on mechanical strength of apatite cement.

Effects of added sodium alginate on the mechanical strength of Biopex, one type of apatite cement, were investigated since sodium alginate addition is very effective for Biopex to acquire anti-washout property. Addition of sodium alginate into the liquid phase of Biopex resulted in a slower transformation to apatitic monolith. As a result, mechanical strength of set Biopex in terms of diametral tensile strength (DTS) decreased when it was hardened in an incubator kept at 37 degrees C and 100% relative humidity for 7 days. However, DTS value increased with increase in the amount of added sodium alginate when the Biopex paste was immersed in 0.9% saline at 37 degrees C for 7 days. Set Biopex with less sodium alginate also showed larger porosity. Based on these findings, we concluded that added sodium alginate was effective in increasing the mechanical strength of Biopex by inhibiting liquid penetration into its paste when it is exposed to body fluids.

Alginates↗

PubMed2003

Evaluation of apatite ceramics containing alpha-tricalcium phosphate by immersion in simulated body fluid.

The purpose of this study was to estimate the availability of alpha-tricalcium phosphate (alpha-TCP) on/in hydroxyapatite (HAP) ceramics for bioactivity as bone-substitute materials by immersion in a simulated body fluid (SBF; Hanks' solution) containing ion concentrations similar to those in human blood plasma. Two alpha-TCP-surface-modified HAP and alpha-TCP-HAP composite materials were prepared by orthophosphoric acid treatment of sintered HAP and controlling the crystal phases of calcium phosphate cement, respectively. After immersion in SBF, the sintered HAP modified on the surface in an approximately 0.2 microm alpha-TCP layer was more effective for the precipitation of carbonated apatites than an approximately 2 microm alpha-TCP layer and HAP-only layer. In the calcium phosphate cements consisting of HAP and alpha-TCP phases, after immersion for 1 week, the specimens precipitated large amounts of apatites having alpha-TCP contents of approximately 25% and 50% in the cement. The results of immersion tests imply the possibility that the alpha-TCP on/in HAP ceramics may be a bioactive agent for bone-substituting HAP materials.

Biomimetic Materials↗

PubMed1991

[Apatite tenosynovitis of the hand].

Three cases of apatite tenosynovitis of the hands are presented. This rare condition has often a dramatic outset with an intense inflammation that could suggest an infectious process. The radiographic feature is characteristic, and the examination of the material removed from synovial sheath or from calcific deposits allows apatite crystals to be identified. The process is self-limited, but immobilization and local infiltrations of steroids shorten the duration of disability.

Adult↗

PubMed1995

X-ray diffraction studies on the lattice perfection of human bone apatite (Crista iliaca).

The lattice perfection of human bone apatite (iliac crest of 117 individuals aged 0-90 years) was systematically investigated by means of combined X-ray diffraction procedures--profile fitting and line-broadening analysis--correlated with age, sex, type of tissue (corticalis, spongiosa), and position (superior, middle, and inferior) for different crystallographic directions [length axis using reflection (002), basal plane by means of reflections (300), (210), and (310)]. Bone specimens within age group 0-30 were strongly affected by an increased crystallinity in the direction of the c-axis (domain size increasing by 5-7 nm, strain decreasing respectively), whereas in the direction of the a-axis crystallinity decreased significantly (domain size shortening by 5-7 nm, strain increasing respectively) in correlation with some heteroionic substitutions within the apatitic structure. Within age group 30-80 a certain balance seemed to exist between processes of ordering and disordering such that statistically only a slight increase of crystallinity within the basal plane was observed. Age as main fixed effect was highly significant for all investigated parameters. Crystallinity was well correlated with type of tissue (corticalis, spongiosa) in the direction of the length axis of the bone crystallite.

Adolescent↗

PubMed1996

Effect of crystallization on apatite-layer formation of bioactive glass 45S5.

The bioactive glass 45S5 was crystallized to 8-100 vol % of crystals by thermal treatments from 550-680 degrees C. The micro-structure of the glass-ceramics had a very uniform crystal size, ranging from 8 to 20 microns. Fourier-transform infrared (FTIR) spectroscopy was used to determine the rate of hydroxycarbonate apatite (HCA) formation that occurs on bioactive glass and glass-ceramic implants when exposed to simulated body fluid (SBF) solutions. Crystallization did not inhibit development of a crystalline HCA layer, but the onset time of crystallization increased from 10 h for the parent glass to 22 h for 100% crystallized glass-ceramic. The rate of surface reactions was slower when the percentage of crystallization was > or = 60%.

Apatites↗

PubMed1997

Apatite as carrier for growth hormone: in vitro characterization of loading and release.

Previous studies concerning bone drug delivery systems have provided little data about the amount of drug loaded, one of the essential factors for determining the dose/effect relationship. To investigate this factor, an adsorption method involving a therapeutic agent was tested in vitro on an apatitic calcium phosphate (AP). One milligram of human growth hormone (hGH) was deposited onto 0.1, 0.15, and 0.2 g of AP powder over a period of 24 h at 37 degrees C. The amount of hGH loaded was determined by subtracting the dose recovered from that applied on AP. The results show that 1 g of AP absorbed 9.48 mg of hGH. From 0.1 and 0.15 g of hGH-loaded AP, hGH was released in vitro for 2 and 3 weeks, respectively, with a 50% time release (T1/2) at 30 h and 72 h, respectively, for the two quantities. The amount of drug loaded and the determined release kinetics were compatible with the action pattern of hGH, indicating that hGH-loaded calcium phosphate supports are suitable for bone-growth promotion.

Apatites↗