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PubMed1992

Colour centres in plasma-sprayed hydroxyapatite.

Very pure hydroxyapatite is diamagnetic and shows no electron paramagnetic resonance (EPR) spectrum. Plasma-sprayed coatings made with such a pure hydroxyapatite contain paramagnetic point-defects. Irradiated deposits show a strong EPR absorption assigned to an O2- anion adjacent to a calcium vacancy, with anisotropic parameters, g1 = 2.004, g2 = 2.013 and g3 = 2.038. The EPR spectra and colour fade away following thermal annealing. These features are discussed in terms of point-defects in the hydroxyapatite crystal structure.

Color↗
PubMed1992

Osteogenic response to porous hydroxyapatite ceramics under the skin of dogs.

Soft tissue reactions to two materials of different microstructure made with porous and dense hydroxyapatite ceramic granules, were compared in this study. Each was implanted subcutaneously in the abdomen of 10 dogs. The implants were removed 1, 3 and 6 months after implantation, and examined by light microscopy. Heterotopic bone formation was only evident around porous hydroxyapatite ceramic granules in 6 of the 10 animals after 3 months, and in all cases after 6 months, but never around dense granules. These findings suggested that cellular differentiation and induction of osteogenesis may be influenced by the physical and chemical factors in the micromilieu provided by porous hydroxyapatite ceramic granules.

Animals↗
PubMed1993

Bone ingrowth and mechanical properties of coralline hydroxyapatite 1 yr after implantation.

A previous study of coralline hydroxyapatite as a bone-graft substitute was extended from 4 to 12 months to determine better the relationships between implantation time, bone ingrowth and mechanical properties. The model consisted of a 10 x 30 mm window defect in the shaft of the canine radius (a cortical site), and a 10 mm diameter cylindrical defect in the head of the humerus (a cancellous site). In the new study, these two defects were made bilaterally in eight dogs, and filled with block-form coralline hydroxyapatite. The radius defects were supported by a metal fixation plate which was removed after 9 months. After 12 months, the dogs were killed and the left-side implants were analyzed histomorphometrically and mechanically. The right-side radius and humerus were reserved for structural analysis. The results were combined with those previously measured after 4, 8, 12 and 16 wk of implantation. In the cortical site, bone ingrowth increased from 52% at 16 wk to 74% at 1 yr. In the cancellous site, bone ingrowth was 38% after 4 wk, then fell monotonically, reaching 17% at 1 yr. Bending and compressive strength and stiffness of the radius implants increased throughout the post-implantation year, but compressive strength and stiffness of the humerus implants did not change after the first 2-4 months. Mechanical properties were strongly correlated to bone ingrowth in the cortical, but not the cancellous, site. The volume fraction of the coralline hydroxyapatite material diminished significantly with time in the cortical, but not the cancellous, site.

Animals↗
PubMed1993

Effect of heat treatment on the microstructure of plasma-sprayed hydroxyapatite coating.

One of the claimed benefits of plasma-sprayed hydroxyapatite coatings on metal prostheses is the generation of enhanced bone bonding. However, plasma-sprayed hydroxyapatite undergoes a range of transformations during spraying, and the final microstructures produced are complex, with a variety of phases present. The microstructures of plasma-sprayed hydroxyapatite coatings on titanium alloy substrate which have been subjected to post-heat treatment at 950 degrees C have been characterized using transmission electron microscopy. It was demonstrated that heat treatment can modify the coating microstructure and improve adhesion between coating and substrate. The results of chemical analysis revealed an increase in the Ca:P ratios, accompanied by the transformation of calcium phosphate phases from amorphous to crystalline. These transformations are related to phosphorus diffusion into the titanium alloy substrate, which results in the formation of a Ti3P phase.

Alloys↗
PubMed1993

In vitro induction of a calcifying matrix by biomaterials constituted of collagen and/or hydroxyapatite: an ultrastructural comparison of three types of biomaterials.

The induction of a calcifying matrix was studied in vitro and compared for three biomaterials (collagen sponge, hydroxyapatite material and a mixture of both (Biostite)) cultured with human osteoblast-like cells. The influence of biomaterials on organic matrix synthesis and the calcification process was analysed at the ultrastructural level (transmission electron microscopy and X-ray microanalysis). Biomaterials were well tolerated by bone cells. Whichever biomaterial was used, osteoblasts proliferated and synthesized a new matrix constituted of fibrillar and non-fibrillar elements. This activity appeared earlier and was more intense with Biostite than with collagen sponge alone. A deposition of a mineral substance in this newly formed matrix was observed with the collagen sponge and Biostite, but never with hydroxyapatite alone. The mineral deposits were identified as hydroxyapatite crystals, similar to those observed and analysed in bone tissue. These in vitro observations clearly demonstrated the property of Biostite to produce a calcified collagenous matrix similar to bone tissue. However, in vivo confirmation is required before extending the use of this biomaterial to periodontology.

Biocompatible Materials↗
PubMed1995

Hydroxyapatite-based porous aggregates: physico-chemical nature, structure, texture and architecture.

At the request of medical teams from the maxillofacial sector, a highly porous ceramic support based on hydroxyapatite of around 70-80% porosity was produced with a pore size distribution similar to bone texture (< 10 microns, approximately 3 vol%; 10-150 microns, approximately 110 vol%; > 150 microns, approximately 86 vol%). The ceramic substrates were conceived not only as a fillers for bone cavities, but also for use as drug dispensers and as supports to host cells to produce particular therapeutic agents. A method is suggested to obtain a substrate of high porosity, exploiting the impregnation of spongy substrate with hydroxyapatite ceramic particles. X-ray and scanning electron microscopy analyses were carried out to evaluate the nature of the new ceramic support in comparison with the most common commercial product; pore size distribution and porosity were controlled to known hydroxyapatite ceramic architecture for the different possible uses.

Biocompatible Materials↗
PubMed1996

Pre-conditioning and dual constant composition dissolution kinetics of pulsed laser deposited hydroxyapatite thin films on silicon substrates.

The kinetics of dissolution of pulsed laser deposited crystalline and amorphous thin films of hydroxyapatite on silicon substrates were measured at 37 degrees C and a pH value of 6.5 using the dual constant composition method. Solutions in which the pulsed laser deposited films were pre-conditioned (0.15 M NaCl) remained undersaturated or slightly supersaturated with respect to hydroxyapatite after equilibrium was reached, indicating only a very small coating release and the absence of re-precipitation on the surfaces. The amorphous films released more calcium and phosphate during pre-conditioning than the more crystalline films. Dual constant composition dissolution rates decreased as film crystallinity increased. The film with the lowest dissolution rate (approximately one sixth that of a crystalline film deposited using a hydroxyapatite powder target) was fabricated using a human tooth as the laser target. During pre-conditioning of plasma-sprayed coatings, more calcium and phosphate were released than for pulsed laser deposited films, and dual constant composition dissolution rates were much higher.

Calcium Phosphates↗
PubMed1987

The versatility of hydroxyapatite blocks in maxillofacial surgery.

There is considerable interest at present in the potential role of calcium hydroxyapatite as a biomaterial for bone augmentation in oral and maxillofacial surgery. Most of the published work has been on the particulate form, mainly in alveolar ridge procedures. However, hydroxyapatite is also available as solid or porous blocks. The blocks are more predictable in their use than are the particles, and are adaptable and versatile. This paper reviews the biological behaviour of the material and discusses the role of hydroxyapatite blocks in alveolar ridge augmentation and orthognathic surgery.

Alveolar Ridge Augmentation↗
PubMed1989

Two-stage combined vestibuloplasty and partial mandibular ridge augmentation with hydroxyapatite.

The preliminary results of a new two-stage technique for partial augmentation of the edentulous mandibular ridge with hydroxyapatite are reported. The technique, which has been applied to five patients, can be performed under local analgesia, and involves initial placement of temporary silicone spacers, together with submucous vestibuloplasty to preserve sulcus depth. The spacers are later replaced by dense particulate hydroxyapatite, and the connective tissue capsules that remain after removal of the spacers allow control of particle migration and minimize the amount of hydroxyapatite required.

Alveolar Ridge Augmentation↗
PubMed1980

An octacalcium phosphate intermediate in the synthesis of chromatographic hydroxyapatite.

In the laboratory synthesis of hydroxyapatite for liquid column chromatography different procedures give varying amounts of a transient intermediate, identified by X-ray diffraction as octacalcium phosphate. The intermediate is most abundant in a recently-developed method involving conversion from brushite at neutral pH; well-crystallized hydroxyapatite is then produced without the boiling previously found necessary. The results are relevant to hydroxyapatite biosynthesis, where a similar intermediate has been postulated. Methods are described for the laboratory synthesis of octacalcium phosphate.

Calcium Phosphates↗
PubMed1991

Primary closure of median sternotomy with interposition of hydroxyapatite blocks. A new approach in pediatric cardiac surgery.

Chest closure after correction of congenital heart disease with subsequent enlargement of the heart has been a problem encountered throughout departments performing pediatric cardiac surgery. Present techniques using Rehbein struts or an open chest with a Gore-Tex patch skin closure have not solved this issue satisfactorily. Between January 1989 and September 1990, median sternotomies could not be closed primarily due to hemodynamic consequences in nine patients age 3 months to 19 years operated upon in our department. In three children, a conduit exchange, in two a Mustard correction, in two a correction of Fallot's tetralogy, in one a prosthetic valve exchange and in one, a new implantation of a homograft was performed. Primary chest closure was achieved by interposing hydroxyapatite blocks (50 mm x 15 mm x 6 mm) without hemodynamic consequences. In a follow-up period of 10 +/- 8 months, all children are alive and well. There was no complication resulting from the implanted blocks. Due to the excellent functional and cosmetic results of this technique and the outstanding histomorphological characters of hydroxyapatite, we regard the implantation of hydroxyapatite blocks as a superb method for primary sternotomy closure especially in pediatric cardiac surgery.

Adolescent↗
PubMedDate not supplied

Sintered hydroxyfluorapatites. Part III: sintering and resultant mechanical properties of sintered blends of hydroxyapatite and fluorapatite.

The presence of chemically dissimilar apatites occurs widely in biological systems as a result of exposure to chemically enriched media, but also to optimize the mechanical properties. The use of mechanical blends of apatites can be used to manufacture high temperature processed fluoride containing hydroxyapatites with improved properties. Mechanical blends of fluorapatite and hydroxyapatite were produced with 0%, 20%, 40%, 60%, 80% and 100% fluorapatite. Pellets were sintered at 1150 degrees C, 1200 degrees C and 1250 degrees C and the density determined by the Archimedes method. Mechanical properties including hardness, elastic modulus and fracture toughness were measured using indentation. It was found that mechanical blends of 150 nm sized hydroxyapatite and 300 nm sized fluorapatite lead to solid solutions after sintering. The mechanical blends do not sinter as effectively as homogeneous hydroxyfluorapatite solid solutions and exhibit a minimum density at 80 wt.% fluorapatite. The hardness, elastic modulus and brittleness decreases with a higher flourapatite content, attributed primarily to a decrease in density. The higher fracture toughness for mechanical blends indicates that these materials are more crack resistant and provide a means for improving mechanical properties.

Apatites↗
PubMed2006

Synthetic and biological hydroxyapatites: crystal structure questions.

Experimental and theoretical studies have demonstrated that biological and synthetic hydroxyapatites display crystal structure similarities and differences that affect greatly the bioactivity of the synthetic materials. Recent developments in structure research of bioapatites report experimental values of the hydroxyl concentration in biological apatites in the range of 20-0% of the amount in synthetic hydroxyapatite. Theoretical calculations find the hexagonal space groups energetically unfavorable for hydroxyapatite crystallization. Different configurations are proposed for the carbonate substitution in B-type carbonate apatites.

Biocompatible Materials↗
PubMed2005

STEM and EDXS characterisation of physico-chemical reactions at the periphery of sol-gel derived Zn-substituted hydroxyapatites during interactions with biological fluids.

With its good properties of biocompatibility and bioactivity hydroxyapatite (HA) is highly used as bone substitutes and as coatings on metallic prostheses. In order to improve the bioactive properties of HA, we have elaborated Zn2+ doped hydroxyapatite. Zn2+ ions substitute for Ca2+ cations in the HA structure and four Zn concentrations (Zn/Zn+Ca) were prepared at 0.5, 1, 2 and 5 at.%. To study physico-chemical reactions at the materials periphery, we immersed the bioceramics into biological fluids for intervals from 1 day to 20 days. The surface changes were studied at the nanometer scale by scanning transmission electron microscopy associated with energy dispersive X-ray spectroscopy. After 20 days of immersion, we observed the formation of a calcium-phosphate layer at the periphery of the HA doped with 5% zinc. This layer contains magnesium and its thickness was around 200 nm. Formation of this Ca-P-Mg layer represents the bioactive properties of 5% Zn-substituted hydroxyapatite. This biologically active layer improves the properties of HA and will permit a chemical bond between the ceramic and bone.

Body Fluids↗
PubMed2006

Cadmium fixation by synthetic hydroxyapatite in aqueous solution--thermal behaviour.

This study deals with the mechanism of the cadmium uptake by synthetic hydroxyapatite (HA: Ca10(PO4)6(OH)2) in aqueous solution. The rate of cadmium fixation by hydroxyapatite was investigated at 10 and 50 degrees C using batch experiments. Inductively coupled plasma atomic emission spectrometry, X-ray diffraction, FT-IR spectroscopy and electron microscopy were used to characterize the starting HA and the samples. The thermal behaviour of the powders was determined with the help of three thermoanalytical techniques (TGA, DTA, and MS) and temperature programmed X-ray diffraction. Cadmium immobilization kinetics can be divided into two steps: substitution of Ca2+ ions by Cd2+ in the HA lattice at the particle's surface, followed by their incorporation into the hydroxyapatite bulk. This results in the formation of an apatite solid solution, which is very important because in this way decontamination and storage can be performed with the same material.

Cadmium↗
PubMed2004

Reconstruction of skull bone defects using the hydroxyapatite cement with calvarial split transplants.

PURPOSE: We sought to present a new method for primary reconstruction of traumatic or tumor calvarial defects. PATIENTS AND METHODS: Forty-one patients underwent reconstruction of calvarial bone defects between October 1998 and December 2001. Among them were 19 patients who needed reconstruction of the calvaria due to traumatic bone loss. Five of these trauma cases had insufficient primary reconstruction of the calvaria. Tumor resection caused calvarial defects in 22 patients. For primary reconstruction of the skull bone defects, calvarial split grafts were used to cover the defect as accurately as possible. The monocortical layers of the calvaria were fixed with titanium miniplates. Irregular defects surrounding the transplanted regions were filled with hydroxyapatite cement. In one case of posttraumatic bone loss, hydroxyapatite cement alone was sufficient to reconstruct the defect. RESULTS: The follow-up of each patient was at least 6 months; the longest period was 38 months. Evaluated clinical and radiologic results are stable, showing no measurable side effects. CONCLUSION: Hydroxyapatite cement alone or in combination with calvarial split grafts gave clinically and aesthetically stable results in the reconstruction of skull bone defects. The cement can be used for many reconstruction possibilities in craniofacial surgery.

Adult↗
PubMed2005

Bone regeneration in osseous defects using a resorbable nanoparticular hydroxyapatite.

PURPOSE: This animal study examined the de novo bone formation in bony defects following the insertion of autogenous bone alone versus an injectable nanoparticle hydroxyapatite alone and in combination with 25% autogenous bone. The regenerative potentials of the tested materials were compared with each other. MATERIALS AND METHODS: A model with biological similarity to humans with regard to bone regeneration was a prerequisite for the transferability of the results to clinical practice. Therefore, the adult domestic pig was the animal of choice. A total observation period of 6 months was selected. Microradiographic and histologic evaluation of the bone specimens was completed at 8 defined times. RESULTS: Microradiography indicated mineralization rates in the 2 bone substitute groups that were not significantly lower than those found in the autogenous bone group. Histologically, there was suitable osseointegration and osteoconduction of the used material. Complete resorption of the nanoparticle hydroxyapatite had taken place after 12 weeks. CONCLUSIONS: It can be concluded that the evaluated nanoparticular hydroxyapatite met the clinical requirements for a bone substitute material within the limits of this experimental setting. Due to its microstructure, complete resorption took place during the course of this study.

Absorbable Implants↗
PubMed2003

Hydroxyapatite cement scaffolds with controlled macroporosity: fabrication protocol and mechanical properties.

Precipitated hydroxyapatite cement scaffolds with macroporosity of controlled size and shape were successfully built using a solid freeform fabrication process. The negative macroporosity was designed using CAD software and built with an inkjet machine. A slip casting process using a plaster mold was used to precipitate the cement and manufacture samples for mechanical testing. The negative macroporosity was then extracted from the samples using a thermal process. Compression, tension and torsion tests were completed successfully on the precipitated hydroxyapatite cement samples in moist condition. Elastic and strength properties were measured for these three loading cases and compared to the plain hydroxyapatite cement properties reported in a previous study. Homogenization theory was applied to estimate the elastic properties of the manufactured scaffolds. A good correlation was obtained between the experimental data and the theory.

Bone Cements↗