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PubMedDate not supplied

Hydroxyapatite-gelatin films: a structural and mechanical characterization.

Composite films of gelatin and hydroxyapatite were prepared and characterized by mechanical tests, scanning electron microscopy and X-ray diffraction investigation. The mechanical properties of the films are greatly affected by the presence of hydroxyapatite and change as a function of inorganic phase content. On stretching, the long axis of the collagen molecular portions align parallel to the direction of deformation and the gelatin coarse layered structure becomes more evident and ordered. Furthermore, under deformation the inorganic crystals, which are embedded in the gelatin layers, seem to squeeze out in the interlayer spaces and assume a preferential orientation parallel to the force trajectories. Thus, as the inorganic phase stiffens the gelatin films, the macromolecular matrix distributes the stress promoting the preferential orientation of the apatitic crystals. The results indicate that this experimental approach can be used to prepare composites with anisotropic properties, which can be modulated through variation in composition and mechanical deformation in order to get biomaterials suitable to fulfill specific mechanical functions.

Animals↗

PubMed1991

Coralline hydroxyapatite as an ocular implant.

Fifty patients received a coralline hydroxyapatite sphere as a buried integrated ocular implant after enucleation or evisceration surgery. The surgical technique is described and the results discussed. All patients obtained final prosthetic motility superior to that possible with simple spherical methylmethacrylate implants. After a follow-up of 2 to 27 months (mean, 10.4 months) there have been no cases of migration or extrusion. Complications have been minimal and easily managed. The hydroxyapatite implant appears to offer excellent cosmetic reconstruction without the unacceptable infection and extrusion rates seen with other integrated implants.

Durapatite↗

PubMed1992

Rate of vascularization of coralline hydroxyapatite ocular implants.

Twelve patients received a coralline hydroxyapatite sphere as a buried integrated ocular implant after enucleation surgery. The implant was modified by drilling 5 access holes, 1 mm in diameter, to the center of the sphere to allow more rapid host tissue ingrowth. 99Tc MDP static and dynamic bone scan studies were performed at various intervals after implantation to confirm the time course for vascularization. Complete vascularization was noted in 1 of 2 patients at 8 weeks after surgery, in 7 of 7 patients at 10 to 12 weeks, and in 3 of 3 patients at 16 weeks. This modified technique allows the hydroxyapatite ocular implants to be drilled for the final motility peg at an earlier time than currently possible, thereby resulting in more rapid cosmetic rehabilitation and obviating the need for secondary modification or replacement of the prosthesis.

Bone and Bones↗

PubMed2004

[Cranial reconsctruction with titanium mesh and hydroxyapatite cement].

We report the case of a 45 year old patient who was affected by an infectious disease of the temporal bone, after the surgical treatment of a meningioma in the greater sphenoid wing. This infection healed after the resection of the craniotomy flap. The remaining bone defect was reconstructed using a titanium mesh covered by hydroxyapatite cement (Norian). The result was excellent due to the strength of the titanium mesh and the volume and contour offered by the hydroxyapatite cement.

Humans↗

PubMedDate not supplied

Correlation between hydroxyapatite osseointegration and Young's Modulus.

From the standpoint of hard tissue response to implant materials, calcium phosphate is probably the most compatible of materials known. During the last few years, much attention has been paid to hydroxyapatite and beta-tricalcium phosphate as potential biomaterials for a bone substitute. Good implantation of biomaterials in the skeleton is evidenced by an ability to reach full integration of the non-living implant with living bone. The aim of this study is to correlate hydroxyapatite osseointegration with Young's Modulus. Cylinders (5-6 mm in diameter) of these ceramics were packed into holes made in the femur diaphysis of a mature sheep. At 2, 4, 8, 12, 16, 20, 28, 36 and 48 weeks after the operation, samples of the bone/implant interface were embedded in polymethylmethacrylate. We used the PIXE method (Particles Induced X-rays Emission) to measure the distribution of mineral elements (Ca, P, Sr, Zn, Mn and Fe) at the bone/implant interface. At 4, 8, 12, 16, 20, 28, 36 and 48 weeks after implantation we studied Young's Modulus on a biopsy of the ceramic. Young's Modulus increased with time after implantation and is linked with biomaterials integration into cortical bone.

Animals↗

PubMed1997

Effects of strontium ions on growth and dissolution of hydroxyapatite and on bone mineral detection.

Preparation and analyses of a series of hydroxyapatites (HA) containing 1-10 mol % of Ca2+ replaced by Sr2+ is reported. The solubility of these apatites is found to increase with increasing content of Sr2+, 10% SrHA dissolves faster than CaHA at given values of Ca2+ and phosphate concentrations, but with a similar rate at the same degree of saturation. Sr2+ is found to inhibit the rates of both dissolution and growth of CaHA and 10% SrHA at pH 7.2, CaHA being more strongly inhibited by Sr2+ than 10% SrHA. The effect of partial substitution of Ca2+ in hydroxyapatite by Sr2+ on bone mineral content (BMC) and bone mineral density (BMD) measured by dual energy X-ray absorptiometry has been studied using three commercial densitometers. Extrapolating the absorption data for up to 10% replacement of Ca2+ by Sr2+ to 100% substitution of Ca2+ by Sr2+ in HA leads to an apparent increase in BMC or BMD of about a factor of 10. This factor is in agreement with theoretical calculations using attenuation coefficients of the atoms concerned. It is concluded that existing BMC scanners register artificially high values of BMC if the bone contains significant amounts of Sr2+ or other metal ions with atomic number larger than calcium.

Absorptiometry, Photon↗

PubMed1979

The binding of beta-casein to hydroxyapatite: the effect of phosphate content and location.

The elution behaviour of beta-casein from columns of hydroxyapatite has been studied and the effect examined of the enzymic addition of an extra phosphate residue. When the additional phosphate is located near pre-existing phosphate residues stronger binding to hydroxyapatite is observed. When the additional phosphate is remote from the pre-existing phosphates no increase in strength of binding is observed. It is suggested that the clustering of phosphate residues which characterizes alphas- and beta-caseins can be rationalized on the basis that it facilitates co-operative interactions between these phosphates and the Ca phosphate of the casein micelle and/or basic residues within casein polypeptide chains.

Amino Acid Sequence↗

PubMed1977

Fractionation of whole casein on hydroxyapatite. Application to a study of buffalo kappa-casein.

When whole caseins from cow and Italian buffalo (Bubalus arnee) were fractionated by chromatography on a column of hydroxyapatite they behaved in a similar manner. kappa-Casein was eluted with 5 mM phosphate buffer, pH 6-8, containing 0-2 M-KCl, 4-5 M-urea and 2 mM-2-mercaptoethanol, but beta- and alphas-caseins were retained and could be eluted successively by a linear gradient from 5 mM to 250 mM-phosphate buffer. Buffalo kappa-casein preparations, obtained from bulk milk or from milks of individual animals by chromatography on hydroxyapatite, produced identical electrophoretic patterns at pH 8-6. By further fractionation of these kappa-caseins on DEAE-cellulose, in each case, at least 7 components were purified; they had different electrophoretic mobilities but were all sensitive towards chymosin. The major fraction migrated like component 1 of bovine kappa-casein B.

Animals↗

PubMed1986

Inhibition of hydroxyapatite crystal growth by bone-specific and other calcium-binding proteins.

Mineralization of bone matrix may be influenced by the presence of specific, noncollagenous bone proteins. The quantitative influence of two bone-specific proteins--bone gamma-carboxyglutamic acid (Gla) protein and osteonectin--and other proteins that decreased the rate of crystal growth was measured by adding seed crystals of hydroxyapatite to a solution of CaCl2 and KH2PO4, pH 7.4 at 37 degrees C. The molar concentrations of proteins needed to inhibit the rate of crystal growth by 50% were as follows: osteonectin, 0.15 microM; bone Gla protein, 0.8 microM; prothrombin, 0.9 microM; prothrombin fragment 1, 1.0 microM; soybean trypsin inhibitor, 3 microM; prethrombin 1, 9 microM; cytochrome c, 30 microM. Calmodulin and parvalbumin were found to be less active than prothrombin fragment 1 and had no activity in the micromolar range. The combination of two inhibitors resulted in a mixture with an inhibitory activity that was the sum of the two inhibitors. Decarboxylation of bone Gla protein significantly reduced its inhibitory activity. These results indicate that the inhibitory activity of a protein does not correlate with Ca2+-binding affinity under these conditions, that the mixture of inhibitors has an additive effect, and that gamma-carboxyglutamic acid residues enhance the ability of a protein to inhibit hydroxyapatite-seeded crystal growth.

Animals↗

PubMed1980

The caries resistance of human teeth is determined by the spatial arrangement of hydroxyapatite microcrystals in the enamel.

Teeth from different people differ in their susceptibility to caries. The beginning and the development of tooth decay depend on the presence of bacterial plaque and on the structure of the tooth enamel. But it has not been established whether the organic or the inorganic component of the enamel (which is comprised principally of hydroxyapatite microcrystals organized in a firm matrix), is responsible for most of the resistance of teeth to caries. We report here that the electron spin resonance (ESR) lines of the (CO3)3 defect of samples of enamel prepared from caries-resistant teeth differ significantly from the corresponding spectra of the caries-sensitive samples. We have traced these differences to the hydroxyapatite microcrystalline alignment in the tooth enamel, and found that this alignment is specific to individuals and is therefore probably nutritionally or genetically determined.

Crystallography↗

PubMed1991

Porous block hydroxyapatite in orthognathic surgery.

Seventy-six nonconsecutive patients undergoing orthognathic surgery, in whom blocks of porous hydroxyapatite were implanted into osteotomy gaps in lieu of autogenous bone grafts, are the subjects of this report. Surgical procedures include inferior maxillary repositioning (10 patients), maxillary advancement (24 patients), transverse maxillary expansions (17 patients) and inferior repositioning of the chin (25 patients). A total of 140 anatomic sites were implanted. Eleven patients later consented to open biopsy of the implant material at a mean 10.2 months following implantation. At the time of follow-up, mean 16.3 months, excellent osseous stability was observed. Three patients developed complications relative to the presence of the implant. Twenty-one of 24 biopsy specimens demonstrated an osseous union of implant to bone with osseous deposition within the implant pores. Radiographic follow-up revealed implant blocks to maintain their volume with no change in density or discreteness. The biological behavior and biomechanical properties of porous block hydroxyapatite are discussed. These implant characteristics make it a feasible bone graft substitute in orthognathic surgery and justify its continued use in this context.

Adolescent↗

PubMed2003

Development of interface in hydroxyapatite implanted in the middle ear of the rat: a light and scanning microscopy study.

OBJECTIVE: The aim of this work is to study the chronology in the biological covering of the hydroxyapatite bioprostheses in the healthy middle ear of the rat. STUDY DESIGN AND SETTING: Dense hydroxyapatite is implanted into the middle ear of 45 Long-Evans rats, between stapes and tympanic membrane. The sample was divided into 3 groups for morphologic, functional, and chemical studies at 15 days, 3 months, and 6 months after surgery, respectively. RESULTS: The short-term studies reveal that the prostheses is surrounded by a fibrous epithelial tissue referred as the interface; it presents a marked inflammatory reaction that decreases gradually in the medium-term and long-term studies; in this way, we observe a progressive adhesion between implant and the contact tissues. CONCLUSIONS AND SIGNIFICANCE: This model has enabled us to study the cell reaction produced by the contact of the prostheses with bone and soft tissue and their impact on the functional qualities of the prostheses.

Animals↗

PubMed1974

Fractionation of DNA on hydroxyapatite with a base-specific complexing agent.

We describe a chromatographic technique for separating mixtures of DNA of varying G + C content. The method employs a specially prepared high-capacity hydroxyapatite and a G.C-specific DNA ligand (2-methyl-3-amino-7-dimethylamino-5-phenyl-phenazinium cation, abbreviated PNR). DNA molecules rich in G.C pairs bind larger amounts of this dye and are eluted earlier from the hydroxyapatite column than are molecules rich in A.T pairs. The dye can easily be removed from DNA by dialysis or solvent extraction after the chromatographic separation. The resolution of the method approaches that of CsCl density gradient separation, and the capacity of the column is much larger than that of a typical density gradient experiment. Elution of the DNA is not dependent on molecular weight, so samples of different molecular weight can be separated on the basis of G + C content. The technique should be especially useful for separating G.C-rich minor components from DNA obtained form eukaryotic cells, as demonstrated by a fraction of DNA from calf thymus.

Animals↗

PubMed2005

Impaction bone grafting with hydroxyapatite: increased femoral component stability in experiments using Sawbones.

BACKGROUND: Substantial bone loss and bone defects increase the amount of allografting required in hip revision surgery. Thus, the use of a synthetic material to limit the amount of allograft tissue required for impaction grafting is desirable. We evaluated the potential of hydroxyapatite (HA) mixtures to provide initial mechanical stability to a polished tapered femoral stem. MATERIAL AND METHODS: We determined the initial stability of a polished tapered femoral stem after reconstructing a cavitary femoral bone defect by impaction bone grafting with cement in Sawbones composite femurs. Three types of graft material were tested for their ability to improve initial rotational stability. The graft materials investigated were pure allograft, a mixture of 50% allograft and 50% hydroxyapatite (HA), and pure HA. RESULTS: We found a statistically significant difference between the three groups as regards torsional micromotion and failure load. INTERPRETATION: Our findings suggest that reconstruction of femoral bone defects with pure HA or a mixture of allograft and HA provides adequate initial stability for femoral revision arthroplasty using impaction grafting.

Arthroplasty, Replacement, Hip↗

PubMed1993

Effects of radiation on the use of hydroxyapatite for orbital reconstruction in the rabbit.

The gross and histopathologic effects of external beam radiation on host response to subperiosteal implantation of dense hydroxyapatite (HA) blocks along the superior orbital rim was investigated, using the rabbit as an experimental model. Three study groups were employed: those with no radiation, those receiving 500 cGy, and those receiving 1,500 cGy. The hydroxyapatite blocks were surgically implanted 2 weeks after administration of the radiation. The pathologic specimens, including the HA block and the neighboring bone segment, were harvested and examined at either the fourth or 12th postsurgical week. There was essentially no inflammatory reaction stimulated by the implanted HA blocks, nor was there any evidence of abnormal bone remodeling in the underlying orbital rim segments. The most secure bonding between the HA block and bone was found in the specimens having received either 500 cGy or 1,500 cGy and harvested at 12 weeks. We conclude that HA serves as an acceptable bone graft substitute in areas previously treated with radiation. The various properties of HA are also reviewed.

Animals↗

PubMedDate not supplied

Biological apatite vs hydroxyapatite at the atomic level.

Known differences in chemical content of biological apatites, specifically the dense (sp.g. greater than 2.95) portion of human tooth enamel (TE), and of stoichiometric hydroxyapatite (OHAp) imply atomic-scale crystal-structural differences, via major and minor substitutions, which can impart very different characteristics to the two materials. Further, some substitutions are shown to produce important effects not predictable from study of pure materials alone. A number of crystal-detail differences between TE and OHAp, both at room temperature and in response to heating (which occurs to some degree locally in hard tissue in vivo as a result of grinding, laser action, etc.), are tabulated. They include CO3 content and incorporation, lattice parameters, water content, non OHAp phases formed on heating, structural OH deficiency, and hydrogen-bonding of F and Cl "impurities" to OH. The significance of these differences is such that it is clearly misleading to speak of tooth enamel, and by inference other biological apatites, as "hydroxyapatite" without considerable qualification of the statement. The differences between biological apatite and OHAp are, in fact, of greater current interest and probable biological significance than are the similarities.

Apatites↗

PubMed2000

A new technique for cranioplasty with L-shaped titanium plates and combination ceramic implants composed of hydroxyapatite and tricalcium phosphate (Ceratite).

OBJECTIVE: The use of hydroxyapatite-based ceramics for cranioplasties has recently increased in Japan, because of the good cosmetic outcomes, biocompatibility, strength, osteoconductive properties, and lack of risk of disease transmission associated with these materials. However, miniplate fixation has not been possible for ceramic implants. We describe a new technique for miniplate fixation of ceramic implants. METHODS: Combination ceramic implants composed of hydroxyapatite and tricalcium phosphate (Ceratite; NGK Spark Plug Co., Aichi, Japan) were used for cranioplasties. A slot and a pair of holes were cut in each Ceratite implant, for use as a fixation unit. We have also developed a new L-shaped titanium plate (HOMS Engineering Inc., Nagano, Japan) that fits into the fixation unit. We first insert an L-shaped titanium plate through the slot from the back surface of the Ceratite implant. We then bend the plate outward at the front surface of the Ceratite implant and fix it to the cranium of the patient with titanium screws. The Ceratite implant is usually firmly fixed to the cranium of the patient with three L-shaped titanium plates. RESULTS: Using L-shaped titanium plates and Ceratite implants, we successfully performed cranioplasties for seven patients with cranial defects resulting from external decompression craniotomies. The Ceratite implant exactly fit the bone window for each patient. Surgical maneuvers were simple and easy for all patients, permitting shorter operating times. All Ceratite implants were firmly fixed, and no postoperative infections have occurred. CONCLUSION: Our new technique for cranioplasty is simple and allows rigid fixation of Ceratite implants.

Adolescent↗

PubMed2003

Different fibrovascularization rate between coralline hydroxyapatite and high density porous polyethylene (Medpore) measured by 99mTc-MDP bone scintigraphy 6 months after intraorbital implantation.

Many materials and types of implant have been used to achieve a cosmetic effect and prosthesis motility in the anophthalmic socket. Hydroxyapatite remains the implant material of choice for producing the most natural prosthesis motility while porous polyethylene shows promising characteristics as another useful material. The aim of this study was to compare the fibrovascular ingrowth rates of orbital implants between coralline hydroxyapatite and high density porous polyethylene (Medpore). The fibrovascularization rate is determined by bone imaging using 99mTc methylene diphosphonate (99mTc-MDP) 6 months after implantation. Our study included 29 patients with coralline, and nine patients with Medpore implants. Our results showed that groups with coralline implants appearing to achieve complete fibrovascularization at a much more rapid rate than those with Medpore. The differences in rate were statistically significant.

Adolescent↗