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PubMed1992

Hydroxyapatite orbital implant after enucleation. Experience with initial 100 consecutive cases.

The hydroxyapatite orbital implant is designed to provide the enucleated patient with improved motility of the prosthesis. We report the results of our first 100 consecutive cases of hydroxyapatite implantation in eyes enucleated primarily for intraocular neoplasms. During a median of 11 months' follow-up, there have been no cases of orbital infection, implant extrusion, or implant migration. Minor postoperative problems have included transient orbital pain in six patients, Tenon's fascia edema and buried peg from tissue overgrowth in two patients each, wound erosion and peg extrusion in one patient each, and audible click of the peg in three patients. Movement of the socket and fornices was excellent in 99% of patients. Motility was cosmetically satisfactory with 10 degrees to 15 degrees rapid darting prosthesis movement present in 96% of patients regardless of whether the peg had been placed. Large-degree prosthesis motility (greater than 15 degrees) was present in 24% of all patients and was most impressive in those adults who had the peg in place and in children. The hydroxyapatite implant appears to be well tolerated and provides prosthesis motility with few problems.

Adolescent↗
PubMed2001

Sphenoethmoid cerebrospinal fluid leak repair with hydroxyapatite cement.

Despite advances in neurological, reconstructive, and endoscopic sinus surgery, sphenoethmoid cerebrospinal fluid (CSF) fistulae continually pose difficult management problems. Standard surgical techniques for fistulae closure succeed approximately 78% to 90% of the time. To improve this success rate, hydroxyapatite cement (HAC), a Food and Drug Administration-approved substance for cranial defect repair, was applied to this problem in a clinical setting. Twenty-one patients with spontaneous, posttraumatic, or postoperative CSF leaks of the sphenoid sinus, cribriform plate, or ethmoid region were treated with HAC. Study participants were prospectively accrued at 5 tertiary care medical centers in the eastern United States. The CSF leaks of all 21 patients treated with HAC were successfully sealed by its initial application. The sites of CSF leakage included the nasal cavity (n = 2) and sphenoid sinus (n = 19). Fifteen of the patients had previously undergone a failed repair by standard methods. There have been no recurrent CSF leaks with a maximum follow-up of 72 months, and an average follow-up of 36 months. All patients have survived to date. The only HAC-related morbidity was the extrusion of the HAC when placed in the nasal cavity. Hydroxyapatite cement is an effective method of repair for postoperative, posttraumatic, and spontaneous sphenoid CSF leaks. The efficacy of HAC in sealing the CSF leak was unaffected by previous attempts at leak closure by standard methods or by its origin. Hydroxyapatite cement should not be applied transnasally for the treatment of an ethmoid region fistula owing to its high probability of extrusion. Correct patient selection and technical familiarity with HAC are necessary for successful application.

Cerebrospinal Fluid Rhinorrhea↗
PubMed1998

Interaction of amelogenin with hydroxyapatite crystals: an adherence effect through amelogenin molecular self-association.

At the secretory stage of tooth enamel formation the majority of the organic matrix is composed of amelogenin proteins that are believed to provide the scaffolding for the initial carbonated hydroxyapatite crystals to grow. The primary objective of this study was to investigate the interaction between amelogenins and growing apatite crystals. Two in vitro strategies were used: first, we examined the influence of amelogenins as compared to two other macromolecules, on the kinetics of seeded growth of apatite crystals; second, using transmission electron micrographs of the crystal powders, based on a particle size distribution study, we evaluated the effect of the macromolecules on the aggregation of growing apatite crystals. Two recombinant amelogenins (rM179, rM166), the synthetic leucine-rich amelogenin polypeptide (LRAP), poly(L-proline), and phosvitin were used. It was shown that the rM179 amelogenin had some inhibitory effect on the kinetics of calcium hydroxyapatite seeded growth. The inhibitory effect, however, was not as destructive as that of other macromolecules tested. The degree of inhibition of the macromolecules was in the order of phosvitin > LRAP > poly(L-proline) > rM179 > rM166. Analysis of particle size distribution of apatite crystal aggregates indicated that the full-length amelogenin protein (rM179) caused aggregation of the growing apatite crystals more effectively than other macromolecules. We propose that during the formation of hydroxyapatite crystal clusters, the growing apatite crystals adhere to each other through the molecular self-association of interacting amelogenin molecules. The biological implications of this adherence effect with respect to enamel biomineralization are discussed.

Amelogenin↗
PubMed1997

Variations in solution chemistry during calcium-deficient and stoichiometric hydroxyapatite formation from CaHPO4.2H2O and Ca4(PO4)2O.

This study explores the mechanistic paths taken when calcium-deficient hydroxyapatite, CDHAp (Ca/P = 1.50), and stoichiometric hydroxyapatite, SHAp (Ca/P = 1.67), form by reaction between particulate calcium phosphate salts. The acidic reactant was CaHPO4.2H2O (DCPD) and the basic reactant was Ca4(PO4)2O (TetCP). Variations in pH, calcium and phosphate concentrations, and the solids present during apatite formation, were determined as functions of reaction temperature (25.0 degrees, 37.4 degrees, and 50.0 degrees C) and time. It was found that the dissolution of TetCP was rate limiting for both hydroxyapatite (HAp) compositions at all three temperatures. However, the retrograde solubility and incongruent dissolution of DCPD became increasingly important in influencing the kinetics as the reaction temperature was increased. An amorphous intermediate phase was observed regardless of the HAp stoichiometry. The solutions from which the SHAp formed approached equilibrium at much shorter reaction times (1-2 days) than those from which the CDHAp formed. The latter continued to display changes in pH and in calcium and phosphate concentrations for 6 months. CDHAp was shown to be a thermodynamically stable phase. The dissolution of CDHAp is incongruent, showing a Ca/P molar ratio in solution less than 0.5.

Biocompatible Materials↗
PubMed1999

Structure-function relationships for coralline hydroxyapatite bone substitute.

To improve the understanding of the functional requirements of trabecular bone substitutes, the structure-function relationships of coralline hydroxyapatite were determined and compared to those of trabecular bone from a variety of anatomic sites. Mechanical properties and permeability of cylindrical coralline hydroxyapatite specimens were measured and related to various morphological parameters that were obtained from analysis of high-resolution (20 microm) computer reconstructions of each specimen. Results indicated the average (+/-SD) Young's modulus (2900 +/- 1290 MPa, n = 20) and permeability (0.50 +/- 0.19 x 10(-9) m2, n = 21) of the coralline hydroxyapatite were within the range of values exhibited by high density trabecular bone; ultimate stress (5.87 +/- 1.92 MPa, n = 13), while in the range of mid-density trabecular bone, was low considering its high volume fraction (31.3 +/- 1.9%, n = 49); and ultimate strain (0.22 +/- 0.03%, n = 13) was much lower than that of trabecular bone from any anatomic site. The only correlation found between mechanical and morphological parameters was between Young's modulus and "fabric" (a scalar measure of architecture that combined the degree of microstructural anisotropy with orientation). These results provide insight into the in vivo performance of this implant, as well as the biomechanical requirements for successful trabecular bone substitutes in general.

Animals↗
PubMed1999

Early events associated with periodontal connective tissue attachment formation on titanium and hydroxyapatite surfaces.

Endosseous dental implants can support at least three types of biomaterial/connective tissue interfaces: osseointegration, fibro-osseous integration, and periodontal connective tissue attachment. Although a periodontal connective tissue attachment offers distinct advantages, only osseointegration and fibro-osseous integration are at present clinically achievable. Recent studies indicate a periodontal regeneration-competent cell population and an appropriate biomaterial substrate both are required for periodontal connective attachment formation on biomaterial surfaces. We therefore have developed an in vitro model to characterize the effects of various biomaterial substrates on the early events of periodontal connective tissue attachment formation. Primary cultures of periodontal ligament and gingival connective tissue cells were cultured on uncoated (control) and coated (titanium- and hydroxyapatite-coated) tissue culture plastic, and the level of cell proliferation, collagen, and noncollagen protein synthesis, alkaline phosphatase activity, and expression of a 42 kD cementum extracellular matrix protein were measured over 5, 7, and 9 days in culture. While all three substrates supported cell attachment, proliferation, and protein synthesis, only uncoated and titanium-coated tissue culture plastic supported expression of the cementum extracellular matrix protein after 9 days of culture. In addition, the levels of cell proliferation and collagen and noncollagen protein synthesis for cells grown on hydroxyapatite-coated surfaces lagged behind cells cultured on the control or titanium-coated surfaces at each of the three time points. These data suggest that biomaterial substrates markedly can influence the temporal sequence of extracellular matrix proteins associated with periodontal connective tissue attachment formation. In addition to surface composition (titanium versus hydroxyapatite), surface properties (e.g., topography) also may have an effect on periodontal connective tissue attachment formation. This model may be of use in designing biomaterials to support the formation of periodontal connective tissue attachment in vivo.

Animals↗
PubMed2001

Ultrasonic characterization of the curing process of hydroxyapatite-modified bone cement.

Ultrasonic parameters such as velocity of sound and broad-band ultrasonic attenuation (BUA) are sensitive to changes in the viscoelastic properties of a material. Bone cement undergoes changes is these properties as it cures. By monitoring the propagation of ultrasonic pulses through a sample of curing bone cement, the curing reaction of polymethylmethacrylate-based (PMMA) bone cement was investigated for hydroxyapatite (HA) concentrations of 0, 10, and 30% (by weight). As the material hardens, the velocity of sound increases by 70%. BUA shows a large peak at the midpoint of the velocity transition. These data are used to compare the cure time and cure duration for PMMA bone cement mixed with hydroxyapatite particles. Measurements of the final sound velocity and BUA were also performed to investigate the mechanical properties of the fully cured cement, and to compare to compression testing data. This is the first time the curing process of bone cement has been investigated as a function of hydroxyapatite concentration. Results indicate that the cure time is not significantly affected by the addition of HA particles, and that both velocity of sound and BUA are sensitive to the curing process.

Bone Cements↗
PubMed1984

Hereditary joint disorder in progressive ankylosis (ank/ank) mice. I. Association of calcium hydroxyapatite deposition with inflammatory arthropathy.

Progressive ankylosis (ank), a murine autosomal recessive mutation, produces an inflammatory joint disorder associated with intraarticular calcium hydroxyapatite deposition and culminates in fusion of the joints. Joints in the feet become stiffened and swollen with milky white fluid containing polymorphonuclear leukocytes, large mononuclear macrophage-like cells, and calcium hydroxyapatite. The joints develop a proliferative synovitis, sometimes associated with marginal erosions of the articular cartilage and periosteal bone. Subsequently, cartilaginous osteophytes, extending outward from the subchondral bone, bridge the margins of the joint and undergo ossification. The progressive ankylosis mutation provides a useful system for investigating calcium hydroxyapatite-associated arthropathies.

Animals↗
PubMed1986

Hereditary joint disorder in progressive ankylosis (ank/ank) mice. II. Effect of high-dose hydrocortisone treatment on inflammation and intraarticular calcium hydroxyapatite deposits.

Mice homozygous for the progressive ankylosis trait develop an inflammatory joint disorder associated with the intraarticular deposition of calcium hydroxyapatite. When affected (ank/ank) mice were treated with high doses of hydrocortisone, synovitis receded, development of cartilaginous and bony osteophytes halted, and calcium hydroxyapatite accumulated in and distended the synovial spaces. No changes, however, occurred in the joint morphology of hydrocortisone-treated normal (ank/+) mice. Since inhibition of inflammation by hydrocortisone treatment did not block apatite accumulation, intraarticular deposition of hydroxyapatite occurs independent of inflammation in progressive ankylosis.

Animals↗
PubMed1979

A resonance frequency technique to determine elastic modulus of hydroxyapatite.

A resonance frequency technique was applied to determine the elastic modulus of hydroxyapatite. A Free-Free Vibration Transducer was designed to determine elastic modulus in a longitudinal direction. A Fixed-Free Vibration Transducer was also designed to study elastic modulus of materials were specimens longer than 3 cm in length were not available. Six lots of hydroxyapatite were prepared utilizing the same process. The elastic modulus of hydroxyapatite varied between 3.94 x 10(10) (dyn/cm2) and 6.30 x 10(10) (dyn/cm2) in a longitudinal direction. For the same six lots, it varied between 1.95 x 10(10) (dyn/cm2) and 3.20 x 10(10) (dyn/cm2) in a cross direction. The elastic modulus values of cortical bone from dog tibias, fibulas, and femurs were also determined.

Acoustics↗
PubMed1988

The effect of glass-ceramic bone implant materials on the in vitro formation of hydroxyapatite.

The extracts of four glass-ceramic bone implant materials were investigated for dissolved material, for effects on in vitro formation of hydroxyapatite, and for surface morphology of glass-ceramic particles in scanning electron microscopy. In vitro leaching released substances that affected in vitro formation of hydroxyapatite, i.e., initiation time and growth of crystals. Leaching also changed the surface morphology of the materials. The ability of the materials to bond to bone did not correlate with the inhibition of hydroxyapatite formation by the released substances. Surface morphology and other factors at present not yet known are probably involved in controlling the bonding to bone of these ceramics.

Bone and Bones↗
PubMed1992

Tensile strength of the interface between hydroxyapatite and bone.

Tensile strength of the interface between hydroxyapatite (HA) and bone was tested. Scanning electron microscopy was used to observe the tensile failure mode and the morphological change of hydroxyapatite ceramic surface in bone. The porosity of hydroxyapatite is 14% and pore size less than 2 microns. After 2 weeks of implantation, the tensile strength of the interface is 0.72 MPa. After 4, 8, and 16 weeks, the average tensile strength stayed at 1.5 MPa. SEM showed that tensile failure occurred at the HA-bone interface at the second week, but after 4 weeks, the failure occurred between HA particles within the bulk, and not at the HA-bone interface. Calcified tissue was directly deposited on the HA ceramic surface and exits also in the micropores. Near the interface, sintered necks among HA ceramic particles were subjected to biodegradation.

Animals↗
PubMed1995

Influence of discharge power level on the properties of hydroxyapatite films deposited on Ti6A14V with RF magnetron sputtering.

The effects of discharge radiofrequency (RF) power and film thickness were studied on the characteristics of Ca5(PO4)3OH (hydroxyapatite) thin films fabricated by RF magnetron sputtering. The structure and chemical composition were investigated with alpha-step (thickness), scanning electron microscopy (SEM), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), and infrared absorption spectrometry (FTIR). The films were analyzed as-sputtered and after annealing at 550 degrees C under argon flow. SEM showed that the film surfaces had no cracks or other defects. X-ray diffraction showed that the deposited films were amorphous with low-discharge RF power, and crystalline with high-discharge RF power. After annealing, all the films had the same crystalline structure as apatite. However, the RBS measurements revealed that all films had a higher calcium-phosphate ratio than standard synthetic hydroxyapatite. Furthermore, statistical testing of the RBS data revealed the existence of only a weak correlation between the Ca/P ratio and the discharge power level. Although all sputtered films showed phosphate bonds in the infrared spectrum, only after annealing did the OH bonds of hydroxyapatite become visible.

Alloys↗
PubMed2003

Preparation, characterization, and in vitro release of gentamicin from coralline hydroxyapatite-alginate composite microspheres.

In this work, composite microspheres were prepared from bioactive ceramics such as coralline hydroxyapatite [Ca(10)(PO(4))(6)(OH)(2)] granules, a biodegradable polymer, sodium alginate, and an antibiotic, gentamicin. Previously, we have shown a gentamicin release from coralline hydroxyapatite granules-chitosan composite microspheres. In the present investigation, we attempted to prepare composite microspheres containing coralline hydroxyapatite granules and sodium alginate by the dispersion polymerization technique with gentamicin incorporated by absorption method. The crystal structure of the composite microspheres was analyzed using X-ray powder diffractometer. Fourier transform infrared spectra clearly indicated the presence of per-acid of sodium alginate, phosphate, and hydroxyl groups in the composite microspheres. Scanning electron micrographs and optical micrographs showed that the composite microspheres were spherical in shape and porous in nature. The particle size of composite microspheres was analyzed, and the average size was found to be 15 microns. The thermal behavior of composite microspheres was studied using thermogravimetric analysis and differential scanning calorimetric analysis. The cumulative in vitro release profile of gentamicin from composite microspheres showed near zero order patterns.

Alginates↗
PubMed2007

Laser microfabrication of hydroxyapatite-osteoblast-like cell composites.

We have developed a novel approach for layer-by-layer growth of tissue-engineered materials using a direct writing process known as matrix assisted pulsed laser evaporation direct write (MAPLE DW). Unlike conventional cell-seeding methods, this technique provides the possibility for cell-material integration prior to artificial tissue fabrication. This process also provides greater flexibility in selection and processing of scaffold materials. In addition, MAPLE DW offers rapid computer-controlled deposition of mesoscopic voxels at high spatial resolutions. We have examined MAPLE DW processing of zirconia and hydroxyapatite scaffold materials that can provide a medical device with nearly inert and bioactive implant-tissue interfaces, respectively. We have also demonstrated codeposition of hydroxyapatite, MG 63 osteoblast-like cells, and extracellular matrix using MAPLE DW. We have shown that osteoblast-like cells remain viable and retain the capacity for proliferation when codeposited with bioceramic scaffold materials. Our results on MG 63-hydroxyapatite composites can be extended to develop other integrated cell-scaffold structures for medical and dental applications.

Cell Line, Tumor↗
PubMed1989

Different effects of mechanical vibration on bone ingrowth into porous hydroxyapatite and fracture healing in a rabbit model.

The effects of mechanical vibration on bone ingrowth into porous hydroxyapatite implants and fracture healing were examined radiographically, histomorphometrically, and biomechanically in a rabbit model. Fifty-three female NZW rabbits were used in this study. These rabbits were divided into four separate studies to assess the effects of 20 and 60 min of vibration/day in both implant and osteotomy models as compared with the respective non-vibrated controls. For the implant model, coral hydroxyapatite goniopora rods were implanted bilaterally into tibiae and for the osteotomy model, bilateral fibulae were osteotomized. A resonant frequency of 25 Hz mechanical vibration was used. After periods of 2, 3, 4, and 6 weeks of vibration, the rabbits were killed and examined. For the implant model, there was no significant difference between control, 20, or 60 min of vibration/day with respect to the rate or amount of new bone ingrowth. For the fracture model, 60 min of vibration/day produced a significantly larger callus as compared with the non-vibrated controls (p less than 0.05), whereas 20 min of vibration/day did not. Although biomechanical testing demonstrated a general trend for increased strength in the vibrated animals, it failed to reach significance. These results suggest that the mechanical vibration used in the present study had a beneficial effect on callus volume, possibly due to the stimulation of secondary bone healing processes, but does not appear to promote bone ingrowth into a porous hydroxyapatite implant.

Animals↗
PubMed1979

Potassium permanganate induced calcergy: a model to study the effects of drugs on hydroxyapatite crystal deposition.

Hydroxyapatite crystal deposition is thought to play a role in the inflammatory episodes of osteoarthritis. A plaque of hydroxyapatite crystals was produced by local subcutaneous injection of a potassium permanganate solution. Transmission electron microscopy with X-ray energy spectroscopy was used to identify the crystal deposits as hydroxyapatite. The effects of dexamethasone, indomethacin, ethane 1-hydroxy-1, 1-diphosphonate (EHDP) and dichloromethylene diposphonate (Cl2MDP) on the development of the apatite plaque was studied. EHDP strongly inhibited the apatite deposition. Cl2MDP slowed the natural resorption of the apatite plaque. Dexamethasone and indomethacin failed to affect the crystal deposition process. The results suggest that EHDP could inhibit crystal deposition in the osteoarthritic joint and that Cl2MDP might have a role in slowing apatite crystal shedding from osteoarthritic cartilage and so reduce the synovitis seen in Osteoarthritis.

Animals↗
PubMed1993

Initiation of heterotopic osteogenesis in primates after chromatographic adsorption of osteogenin, a bone morphogenetic protein, onto porous hydroxyapatite.

The chromatographic adsorption of partially purified osteogenin, a bone morphogenetic protein (BMP), onto porous hydroxyapatites for the construction of an osteogenic delivery system was investigated. Osteogenin fractions, with osteogenic activity in rats, were chromatographically adsorbed onto porous hydroxyapatites and implanted intramuscularly in baboons (Papio ursinus). Histology showed extensive bone differentiation within the porous spaces as early as 30 days after implantation in baboons. The unbound eluate from the porous hydroxyapatites showed lack of osteogenic activity when bioassayed in rats. These findings in primates may help to construct custom made porous ceramic as carriers for BMPs resulting in predictable bone formation for treatment of human bone defects.

Adsorption↗