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PubMed1988

High-performance adsorption chromatography of proteins on 2-micron spherical beads of hydroxyapatite.

Chromatographic studies have been done with a 100 mm x 7.5 mm I.D. high-performance liquid chromatographic column of hydroxyapatite beads of diameters as small as 2 micron. The high resolving power was demonstrated by a gradient fractionation of nine model proteins and an isocratic fractionation into two immunologically active components of a highly purified toxic shock syndrome toxin-1 preparation which was homogeneous upon both ion-exchange and molecular sieve chromatography as well as isoelectric focusing. The resolution of the toxin preparation thus attests to the unique separation mechanism of hydroxyapatite. Characteristic of hydroxyapatite is that all proteins can be desorbed by phosphate ions but few are affected by chloride ions. gamma-Globulins are the only serum proteins which belong to the latter category. This property of gamma-globulin has been utilized in a simple procedure for its specific purification directly from whole serum; for the isolation of gamma-globulin on a large scale the hydroxyapatite can be replaced by brushite, CaHPO4.2H2O, which is simpler and cheaper to prepare. In a set of isocratic elution experiments with cytochrome c the peak width was determined at different flow-rates. As expected with macroporous beads, the peaks became much narrower as the flow-rate was lowered. For maximum resolution, low flow-rates must be used.

Blood Proteins↗
PubMed2000

Direct and indirect effects of P2O5 glass reinforced-hydroxyapatite composites on the growth and function of osteoblast-like cells.

Human osteoblast-like cells were plated on hydroxyapatite and P2O5-glass reinforced hydroxyapatite composite discs. They were also cultured in the presence of media obtained by incubating the discs in the absence of cells. The effects of these direct and indirect interactions were examined by measuring cell proliferation and the expression of certain key extracellular matrix antigens. One composite was found to initially delay cell growth, while the extract of a different composite appeared to down-regulate DNA synthesis. Flow cytometry analysis showed that growth directly on the discs had little effect on collagen type I, but reduced fibronectin and osteocalcin levels. The extracts of the materials generally had less effect, although one extract obtained from the glass-reinforced hydroxyapatite significantly down-regulated fibronectin. These in vitro studies thus suggest that there were only few differences overall in the growth of the cells directly on the glass-reinforced compared with the hydroxyapatite discs and also only relatively small effects of the extracts on the cells. However, the flow cytometry results suggest that both the materials and the extracts may have a potentially important influence on connective tissue production, and that these effects are both material- and antigen-specific.

Antigens↗
PubMed2002

Synthesis of hydroxyapatite via mechanochemical treatment.

Hydroxyapatite powder was synthesized with calcium pyrophosphate (Ca2P2O7) and calcium carbonate (CaCO3) through solid-state reaction. The two powders were mixed in acetone and water, respectively, and the single phase of hydroxyapatite was observed to occur only in the powder milled in water, without the additional supply of water vapor during heat-treatment at 1100 degrees C for 1 h. The results were explained in terms of the mechanochemical reaction that could supply enough amount of hydroxyl group to the starting powders to form a single phase of hydroxyapatite. Practical implication of the results is that the powder of high crystalline hydroxyapatite can be obtained by the simple milling in water and subsequent heat-treatment.

Bone Substitutes↗
PubMed1997

Mechanical and chemical consequences of the residual stresses in plasma sprayed hydroxyapatite coatings.

The residual stresses in thick hydroxyapatite coatings, deposited by plasma spraying, have been determined experimentally using Raman piezo-spectroscopy. The stress dependence of the centre position of the 980 cm 1 Raman band, owing to the symmetric stretching of the phosphate ion, PO3(4), has been established and found to be 2.47 cm 3 GPa 1. Using this calibration, the residual stresses in hydroxyapatite coatings deposited onto Ti-6A1-4V substrates in air have been found to be 100 MPa (tensile), whereas those deposited in a vacuum have been found to be 60 MPa (compressive). Although desirable from a mechanical point of view, it is shown that coating under residual compression are thermodynamically more stable and, hence, the dissolution of the ionic species, necessary in the exchange between bone and hydroxyapatite coating, can be impeded. It is calculated that for the coating under examination the stresses have an effect comparable with almost an order of magnitude change of the [OH] concentration. The analysis explains the dissolution behaviour of hydroxyapatite coatings subject to cyclic stress reported previously.

Biocompatible Materials↗
PubMed1998

Hydroxyapatite-polyethylene composites for bone substitution: effects of ceramic particle size and morphology.

Synthetic hydroxyapatite particles of two median sizes and different morphologies have been used to manufacture hydroxyapatite reinforced high density polyethylene composites (HAPEX) for medical applications. The effects of hydroxyapatite particle size on properties of the resultant composites were investigated using various techniques. It was found that composites with smaller hydroxyapatite particles had higher torsional modulus, tensile modulus and tensile strength, but lower strain to failure. Examination of fracture surfaces revealed that only a mechanical bond existed between the filler and the matrix. It was shown that dynamic mechanical analysis is useful in studying the viscoelastic behaviour of the composite.

Bone Substitutes↗
PubMed2000

Microstructural dependence of Young's and shear moduli of P2O5 glass reinforced hydroxyapatite for biomedical applications.

P2O5 glass reinforced hydroxyapatite composite materials were prepared through a liquid-phase sintering process. Secondary phases, beta- and alpha-tricalcium phosphates (beta-TCP and alpha-TCP), were formed in the microstructure of the composites, due to the reaction between the liquid glassy phase and the hydroxyapatite matrix. The dynamic Young's modulus (E) and shear modulus (G) of these composites were determined using an impulse excitation method. By applying the Duckworth-Knudsen equation, the elastic property results were correlated with the relative proportion of beta-TCP and alpha-TCP phases and with the porosity percentage present in the microstructure. Glass reinforced hydroxyapatite composites showed lower Young's and shear moduli than unmodified hydroxyapatite, mainly due to the presence of beta-TCP phase. The Duckworth-Knudsen model demonstrated an exponential dependence of E and G modulus with porosity and mathematical equations were derived for composite materials with porosity correction factors (b) of 4.04 and 4.11, respectively, indicating that porosity largely decreased both E and G moduli.

Biocompatible Materials↗
PubMed1992

Role of magnetic resonance imaging in the evaluation of the hydroxyapatite orbital implant.

The role of magnetic resonance imaging (MRI) in the assessment of fibrovascular ingrowth in the integrated hydroxyapatite orbital implant is evaluated. Fifteen patients who underwent enucleation and placement of a hydroxyapatite orbital implant were evaluated for degree of implant vascularity with gadolinium-DPTA-enhanced MRI with surface coil before drilling the implant. On T1-weighted images, the hydroxyapatite sphere appeared with intermediate signal. After gadolinium-DPTA administration, all patients showed an enhancement in the implant consistent with the presence of fibrovascular ingrowth. The enhancement was most notable in the peripheral portions of the sphere and was seen as early as 5 months after implantation. Comparison of gadolinium-DPTA-enhanced MRI with contrast-enhanced computed tomography, ultrasonography, and color Doppler imaging suggests that these latter techniques are not as helpful in the detection of the fibrovascular tissue in the orbital implant. Bone scan, a technique used by many surgeons, demonstrates fibrovascular ingrowth, but it is limited by its one-dimensional low-resolution image. Because of its three-dimensional capability and its highest resolution, contrast-enhanced MRI with surface coil appears to be the best imaging method for evaluating the hydroxyapatite orbital implant and its fibrovascular ingrowth.

Adolescent↗
PubMed1995

Coralline hydroxyapatite spheres as secondary orbital implants in anophthalmos.

BACKGROUND: Secondary reconstruction of the anophthalmic socket is frequently challenging. A number of surgical techniques are described to improve the cosmetic and functional outcome. Recently, the use of hydroxyapatite as a primary orbital implant after enucleation has gained popularity and yielded encouraging surgical results. There are no published reports concerning the use of hydroxyapatite as a secondary orbital implant in anophthalmos. METHODS: The authors reviewed the charts of 17 patients who received a secondary hydroxyapatite orbital implant to rehabilitate the anophthalmic socket. Each patients' preoperative and postoperative photographs, socket appearance, implant and prosthetic motility, and overall impressions of the surgical outcome were analyzed. Complications of surgery and secondary procedures were reviewed. RESULTS: All except one patient attained an improved prosthetic appearance postoperatively and 76% achieved improved implant and prosthetic motility. Four patients undergoing surgery early in the series had worsening of pre-existing ptosis. In two patients, implant exposure developed; a socket infection with subsequent loss of the implant developed in one of these patients. Eight patients underwent additional eyelid and orbital surgery at the time of secondary implant surgery, whereas nine patients required additional staged procedures. CONCLUSION: Secondary orbital implantation with the coralline hydroxyapatite sphere is an encouraging alternative to traditional secondary orbital implant surgery. Surgical outcomes in this study were excellent with few complications and high patient satisfaction.

Adolescent↗
PubMed1999

La ions in precipitated hydroxyapatites.

Hydroxyapatites were synthesized by precipitation from an aqueous solution with La3+ (0-0.75%) and with carbonate (0-6.1%) at controlled pH 7.0. Uptake of La3+ was 90-95% complete. Relatively low Ca/P (1.54-1.63) ratios were attributed to nonstoichiometry. Carbonate in samples was identified by IR spectroscopy as B-type carbonate. Lattice parameters of the hexagonal apatite structure were not affected by the La3+ content. Noncarbonated samples heated to 800 degrees C transform partially to beta-Ca3(PO4)2. Thermogravimetric analysis showed release of 0.4 mol adsorbed and 1 mol crystalline water up to 400 degrees C and decomposition of carbonate up to 900 degrees C in the samples. Luminescence data obtained for Gd-containing hydroxyapatites prove that Gd3+ ions are not incorporated in the precipitated hydroxyapatite. These findings suggest that, in the La-containing samples, La3+ is surface absorbed and not incorporated in hydroxyapatite.

Calcium↗
PubMed1992

The critical role of geometry of porous hydroxyapatite delivery system in induction of bone by osteogenin, a bone morphogenetic protein.

The collagenous extracellular matrix of bone obtained after dissociative extraction with 4 M guanidine-HCl is an optimal substratum for bone induction by osteogenin, a bone morphogenetic protein. As a proteinaceous substratum, this matrix and other collagen-based materials may be immunogenic. Thus, the search and discovery of a non-immunogenic substratum is a necessary prerequisite for the therapeutic application of the principle of bone induction to skeletal repair. Bovine osteogenin, purified greater than 50,000-fold and with an apparent molecular mass of 28-42 kilodaltons, was delivered into nonresorbable porous hydroxyapatite in granular and disc configuration. A total of 328 preparations were bioassayed for osteogenic activity by subcutaneous implantation into 164 Long-Evans rats. Specimens were harvested at day 7, 11 and 21 after implantation and subjected to alkaline phosphatase activity determination and histologic analysis. Osteogenin combined with discs of porous hydroxyapatite induced in vivo differentiation of the osteogenic phenotype in mesenchymal cells invading the three-dimensional porous space of the inorganic substratum. The geometry of the substratum had a profound influence on bone induction, since the expression of the osteogenic phenotype was solely confined in porous hydroxyapatite with disc configuration. Osteogenin did not induce bone differentiation when combined with granules of porous hydroxyapatite with identical pore dimensions. The finding that the biological activity of osteogenin can be restored and delivered by a substratum with defined geometry other than the insoluble collagenous matrix may form the basis of the potential therapeutic application of bone morphogenetic proteins.

Animals↗
PubMedDate not supplied

Instrumented posterolateral lumbar fusion using coralline hydroxyapatite with or without demineralized bone matrix, as an adjunct to autologous bone.

BACKGROUND CONTEXT: Autogenous posterolateral fusion with and without instrumentation has been reported with good results. However, difficult-to-fuse patients, such as smokers, elderly patients with poor bone quality and/or quantity, or patients with prior posterior surgeries, may have somewhat lower fusion rates. PURPOSE: To determine the efficacy of coralline hydroxyapatite with or without demineralized bone matrix as a bone graft extender in a human clinical model with long-term follow-up. STUDY DESIGN/SETTING: A retrospective series of 40 patients undergoing instrumented autogenous posterolateral lumbar fusion augmented with coralline hydroxyapatite with or without demineralized bone matrix. PATIENT SAMPLE: Long-term clinical and radiographic follow-up were examined for 40 patients who underwent an instrumented posterolateral fusion only. Patients undergoing anterior lumbar interbody fusion (ALIF) procedures were not considered part of the sample. METHODS: All patients underwent successful transpedicular fixation with autogenous posterolateral lumbar fusion. Fifteen cc of Pro Osteon 500 coralline hydroxyapatite (Interpore Cross International, Irvine, CA) was used at each level. An additional 10 cc of Grafton demineralized bone matrix gel (Osteotech, Eatontown, NJ) was used in 70% of these patients. RESULTS: An overall fusion rate of 92.5% was achieved. Pain and function improvement were good but somewhat age dependent and correlated with the number of comorbidities. Patients with Grafton DBM gel had a lower fusion rate of 89.3%. CONCLUSIONS: Based on this small retrospective review, coralline hydroxyapatite is an effective bone graft extender in difficult-to-fuse patients as an adjunct to autologous bone for posterolateral fusion of the lumbar spine when combined with rigid instrumentation.

Adult↗
PubMedDate not supplied

Anterior lumbar interbody fusion with titanium mesh cages, coralline hydroxyapatite, and demineralized bone matrix as part of a circumferential fusion.

BACKGROUND CONTEXT: Anterior lumbar interbody fusion (ALIF) has become one of the primary choices for eliminating motion between vertebral segments in patients with severe discogenic pain and other lumbar pathologies. Autograft is the gold standard for spinal fusion. However, multiple authors have reported complication and morbidity rates associated with iliac crest harvesting to be as high as 25%. Drawbacks to the use of allograft in the anterior column include slower incorporation rates, the possibility for disease transmission, increasing cost resulting from stringent processing and unavailability on a worldwide basis resulting from religious and economic concerns. PURPOSE: To determine the clinical and arthrodesis efficacy of coralline hydroxyapatite as an osteoconductive bone graft substitute in the anterior lumbar spine using a titanium mesh cage. STUDY DESIGN: A series of 50 patients returning for long-term prospective follow-up, implanted with titanium mesh cages filled with coralline hydroxyapatite and demineralized bone matrix for ALIF as part of a circumferential fusion. PATIENT SAMPLE: Long-term clinical and radiographic follow-up were examined for the first 50 patients undergoing this technique by one surgeon. OUTCOME MEASURES: Pain was measured with a visual analog scale and function was measured with the Oswestry Disability Index. METHODS: All 50 patients underwent successful ALIF with titanium mesh cages, coralline hydroxyapatite and demineralized bone matrix, as well as an autologous posterolateral fusion with rigid posterior instrumentation. Patients filled out follow-up questionnaires and appropriate radiographs were taken. RESULTS: A solid fusion rate of 96% was achieved. Mean pain decrease was 60% overall. A total of 70% of all patients either returned to work or to full home activities at a mean of 8 months after surgery. Ninety percent felt the surgery was successful. CONCLUSIONS: The combination of titanium mesh cages, coralline hydroxyapatite and demineralized bone matrix is effective for anterior interbody fusion of the lumbar spine when used as part of a rigidly instrumented circumferential fusion.

Adult↗
PubMed1985

Inhibition of hydroxyapatite formation in collagen gels by chondroitin sulphate.

Crystal growth in native collagen gels has been used to determine the role of extracellular matrix macromolecules in biological calcification phenomena. In this system, type I collagen gels containing sodium phosphate and buffered at pH 7.4 are overlayed with a solution containing CaCl2. Crystals form in the collagen gel adjacent to the gel-solution interface. Conditions were determined which permit the growth of crystals of hydroxyapatite [Ca10(PO4)6(OH)2]. At a Ca/P molar ratio of 2:1, the minimum concentrations of calcium and phosphate necessary for precipitation of hydroxyapatite are 10 mM and 5 mM, respectively. Under these conditions, precipitation is initiated at 18-24h, and is maximal between 24h and 6 days. Addition of high concentrations of chondroitin 4-sulphate inhibits the formation of hydroxyapatite in collagen gels; initiation of precipitation is delayed, and the final (equilibrium) amount of precipitation is decreased. Inhibition of hydroxyapatite formation requires concentrations of chondroitin sulphate higher than those required to inhibit calcium pyrophosphate crystal formation.

Calcium↗
PubMed2002

Titanium mesh and hydroxyapatite cement cranioplasty: a report of 20 cases.

PURPOSE: This article describes the use of titanium mesh and hydroxyapatite cement constructs for the treatment of large through-and-through calvarial defects. PATIENTS AND METHODS: Twenty consecutive calvarial defects (10 to 156 cm(2)) that resulted from surgical removal of neoplasms or were secondary to trauma were reviewed retrospectively after reconstruction with titanium mesh and hydroxyapatite cement. All patients were followed up by clinical examination and periodic radiographic studies for a minimum of 6 months (range, 6 months to 3 years). Three patients underwent biopsy of the construct at various points during their follow-up. RESULTS: There was no evidence of adverse healing, wound infection, or implant exposure or extrusion in any of the patients reviewed. Adequate 3-dimensional aesthetic restoration of calvarial contour was noted in each case. There was evidence of osseous ingrowth into the titanium mesh and hydroxyapatite cement construct in all 3 patients who underwent biopsy. CONCLUSION: Titanium mesh and hydroxyapatite cement cranioplasty appears to be a reasonable method for the reconstruction of significant calvarial defects.

Bone Cements↗
PubMed1986

Effects of calcium carbonate and hydroxyapatite on zinc and iron retention in postmenopausal women.

We measured the effect of calcium carbonate and hydroxyapatite on whole-body retention of zinc-65 in 11 and iron-59 in 13 healthy, postmenopausal women. In a single-blind, controlled, crossover study, each subject, on three occasions, ingested a standard test meal supplemented with iron-59 or zinc-65 and capsules containing placebo or 500 mg elemental calcium as calcium carbonate or hydroxyapatite. Whole-body countings were performed prior to, 30 min after, and 2 wk after each meal. Mean (SEM) zinc retention was 18.1 +/- 1.0% with placebo (control) and did not vary significantly with calcium carbonate (110.0 +/- 8.6% of control) or hydroxyapatite (106.0 +/- 7.9% of control). Iron retention, 6.3 +/- 2.0% with placebo, was significantly reduced with both calcium carbonate (43.3 +/- 8.8% of control, p = 0.002) and hydroxyapatite (45.9 +/- 10.0% of control, p = 0.003). Iron absorption may be significantly reduced when calcium supplements are taken with meals.

Aged↗
PubMed2005

Hydroxyapatite cement in pediatric craniofacial reconstruction.

The gold standard for closing small cranial defects is autogenous bone: iliac crest, rib, or split calvarial grafts. Autogenous grafts result in donor site morbidity, increased operative time, blood loss, and additional cost, and they are limited in quantity. Hydroxyapatite cements are alternative bone substitutes that eliminate these restrictions. Although the use of hydroxyapatite is well accepted in completely developed crania, its use in the growing pediatric skull is limited. The purpose of the current study was to address the safety and long-term efficacy of this bone substitute for the repair of craniofacial bone defects in the growing pediatric skull. Safety is measured dually by resistance of bone substitute to infection and its tolerability by lack of a foreign body reaction. Efficacy is evaluated as structural skull integrity, volume stability with time, aesthetic quality, and most importantly, the ability to integrate adequately into a growing cranium without subsequent deformity or complications. This is a retrospective review of all pediatric patients at the authors' institution who underwent reconstruction of cranial defects using hydroxyapatite cement between May 1997 and March 2001. Eight patients who underwent 11 operations between the ages of 25 and 100 months (mean, 55 months) were followed up between 23 and 72 months (mean, 38 months). No mortalities or significant morbidities were encountered in the study population. It has been the authors' experience that hydroxyapatite cement is both biocompatible and resistant to infection when used in sites not contiguous with sinus mucosa; and that it is a good alternative to autogenous bone in pediatric craniofacial reconstruction.

Biocompatible Materials↗
PubMed2002

Bovine hydroxyapatite orbital implant: a preliminary report.

PURPOSE: To determine the safety and efficacy of bovine hydroxyapatite as an orbital implant material. METHODS: Prospective, consecutive case series of patients undergoing enucleation, evisceration, or secondary orbital implantation. A motility peg was placed in all consenting candidates. Patients were followed 1 week, 1 month, and several months after surgery for signs of inflammation, infection, extrusion, or other complication. RESULTS: Twenty-seven patients received a bovine hydroxyapatite orbital implant. Magnetic resonance imaging was obtained in 3 patients (3 orbits) approximately 4 weeks after surgery and showed signs of peripheral fibrovascular ingrowth in all three cases. Magnetic resonance imaging was obtained in 9 patients (9 orbits) 4 to 12 months after surgery and showed signs of incomplete fibrovascular ingrowth in 1 of 9 (11%) cases, subtotal fibrovascular ingrowth in 2 of 9 (22%) cases, and complete fibrovascular ingrowth in 6 of 9 (67%) of cases. Complications included postoperative chemosis in 3 cases (11%) and exposure requiring reoperation in 2 cases (7%). Motility peg placement was performed successfully in 5 patients (5 orbits). CONCLUSIONS: Bovine hydroxyapatite appears to be a safe and effective orbital implant material. The material appears to be biocompatible and nonallergenic. Bovine hydroxyapatite allows for fibrovascular integration and motility peg placement.

Adolescent↗
PubMed1988

Porous hydroxyapatite as a bone graft substitute in cranial reconstruction: a histometric study.

To assess the potential of a porous hydroxyapatite matrix to serve as a bone graft substitute, bilateral 15 X 20 mm craniectomy defects were reconstructed in 17 dogs with blocks of implant and split-rib autografts. Specimens were retrieved at 3, 6, 12, 24, and 48 months, and undecalcified sections were prepared for microscopy and histometry. The implant and graft cross-sectional areas did not change with time, documenting their equivalent ability to maintain cranial contour. Bone ingrowth extended across the implant from one cranial shelf to the other in 15 specimens. Little apparent bone ingrowth was seen in most graft specimens. Two implants and three grafts were nonunited, possibly due to lack of fixation or the orientation of the histology sections. The implant specimens were composed of 39.3 percent hydroxyapatite matrix, 17.2 percent bone ingrowth, and 43.5 percent soft-tissue ingrowth. The graft specimens were composed of 43.7 percent bone and 56.3 percent soft tissue. This study supported the thesis that a porous hydroxyapatite matrix may function in part as a bone graft substitute. The brittle hydroxyapatite matrix undoubtedly became stronger with bone ingrowth, but the degree of cranial protection achieved was not measured in this study. The size of the cranial defect used in this study did not permit estimation of the distance over which bone ingrowth may be reliably expected. There remains a need for greater understanding of the causes of nonunion, the extent of predictable ingrowth depth, and the strength of the resultant implant-bone composite.

Animals↗