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PubMed1995

Interaction of human gallbladder mucin with calcium hydroxyapatite: binding studies and the effect on hydroxyapatite formation.

Calcium hydroxyapatite (HAP) crystals formed in vitro in the presence of polymeric human gallbladder mucin (1.0 mg/mL) were smaller (0.75 +/- 0.39 microns) than control crystals (7.86 +/- 2.76 microns), but the mucin did not affect the kinetics of crystal formation or alter the amount of mineral phase present at equilibrium. In contrast, glycopeptide subunits produced by proteolysis of the native mucin had no effect on HAP crystal size. Both native mucin and glycopeptides bound to mature HAP crystals, but the glycopeptides were much more readily displaced by phosphate ions. Therefore, in experiments where HAP was being formed, the phosphate ions inhibited the interaction of glycopeptides with the nascent HAP. These results indicate that gallbladder mucin may modulate HAP formation in vivo, and that this ability may be altered during pathological states, such as neutrophil infiltration or bacterial colonization, that may cause the release of proteinases capable of digesting mucin.

Amino Acids↗
PubMed1996

Processing and mechanical properties of hydroxyapatite reinforced with hydroxyapatite whiskers.

Hydrothermally synthesized HAp fine crystals/HAp whiskers mixtures have been used for the preparation of HAp/0-30% (whiskers) composites. The composites have been fabricated by pressureless sintering and hot-pressing. The best mechanical properties and the highest densities have been achieved for composites hot pressed at 1000 degrees C (2 h, 30 MPa in flowing Ar). Their density was in the range of 90-97% of the theoretical density. Fracture toughness (Klc) of the composites reflected their microstructure and had the value of 1.4 MPa m1/2 (as compared with Klc = 1.0 MPa m1/2 for the non-reinforced HAp matrix). Compressive prestressing of the HAp matrix and crack deflection (both derived from the residual stress field) contributed to the increase of fracture toughness. Other toughening mechanisms have not been observed. HAp/HAp (whiskers) composites exhibited improved toughness without degradation of biocompatibility, because the HAp whiskers acted both as a reinforcement and as a biocompatible phase. Problems related to biocompatibility and mechanical properties of available HAp-based composites were also discussed.

Biocompatible Materials↗
PubMed1992

Reaction of bone to HA, carbonate-HA, hydroxyapatite + calcium orthophosphate and to hydroxyapatite + calcium ortho- and pyrophosphate.

Slip cast conical implants of HA, carbonate-HA, calcium orthophosphate/hydroxyapatite and hydroxyapatite/calcium pyrophosphate/calcium orthophosphate with weight ratios 75/25 and 50/30/20 were implanted in rabbit tibia. The bone-implant interfaces were evaluated histologically, by means of SEM/EDX analysis and by push-out test. Thirty-six implanted samples were investigated after 2, 8, and 24 weeks. The triphasic calcium phosphate showed a moderate disintegration. This material showed 2 weeks after implantation a bonding between new bone and implant could be seen in parts of the operation site by SEM. Eight weeks after implantation an intimate relationship between the bone tissue and all specimens of each material was found. After 24 weeks the Ca/P ratio in the bone had reached the Ca/P ratio of mature bone determined by SEM/EDX analysis.

Animals↗
PubMed1986

Adherence of Streptococcus sanguis to hydroxyapatite coated with lysozyme and lysozyme-supplemented saliva.

The adherence of [3H]thymidine-labeled Streptococcus sanguis strains to bare hydroxyapatite and to hydroxyapatite coated with a range of concentrations of lysozyme, poly-L-lysine, poly-L-glutamic acid, whole saliva supernatant, and combinations of some of the above was studied. Adherence of several strains of S. sanguis to bare hydroxyapatite and saliva-coated hydroxyapatite was compared. Saliva present as a pellicle on the hydroxyapatite inhibited adherence of some strains (903, M-5, 73X11) and stimulated that of others (S35, B-4, 66X49). Strains 903 and S35 were chosen for further study. Adherence of both strains was stimulated up to fivefold by the presence of adsorbed lysozyme or poly-L-lysine on the hydroxyapatite, whereas poly-L-glutamic acid inhibited adherence (80 to 95%). Adherence of strain S35 to hydroxyapatite coated with combinations of saliva and (i) lysozyme, (ii) poly-L-lysine, or (iii) poly-L-glutamic acid was unaffected compared with adherence to hydroxyapatite coated with saliva alone. In contrast, adherence of strain 903 to hydroxyapatite coated with combinations of saliva and either lysozyme or poly-L-lysine was inhibited up to ca. 90% compared with hydroxyapatite coated with saliva alone. Strain 903 was also unaffected by combinations of poly-L-glutamic acid and saliva on the hydroxyapatite. Adherent cells of both strains were completely (greater than 90%) eluted with high-ionic-strength buffer from either bare hydroxyapatite or hydroxyapatite coated with lysozyme alone. Adherent cells of strain S35 were only poorly eluted (25%) from hydroxyapatite coated with either saliva alone or saliva and lysozyme. Strain 903 elution from hydroxyapatite coated with either saliva alone or saliva and lysozyme was essentially complete. These observations were taken to indicate that the two test strains adhered to saliva-coated hydroxyapatite by different mechanisms. Protein-coated hydroxyapatite was shown not to be saturated under the conditions described here. Examination by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the variously supplemented salivary pellicles formed on the hydroxyapatite demonstrated that major changes in salivary protein composition did not occur when lysozyme, poly-L-lysine, or poly-L-glutamic acid was used to supplement saliva. Lysozyme-dependent aggregation of strain 903 was shown not to occur under the conditions of our experiments. We suggest that the basis for stimulation of adherence to hydroxyapatite coated only with lysozyme is an increase in the cationic surface area available for electrostatic adherence of the microorganisms.(ABSTRACT TRUNCATED AT 400 WORDS)

Adhesiveness↗
PubMed2004

A 1-year study of osteoinduction in hydroxyapatite-derived biomaterials in an adult sheep model: part II. Bioengineering implants to optimize bone replacement in reconstruction of cranial defects.

The present study investigated hydroxyapatite biomaterials implanted in critical-size defects in the calvaria of adult sheep to determine the optimal bioengineering of hydroxyapatite composites to facilitate bone ingrowth into these materials. Five calvarial defects measuring 16.8 mm in diameter were made in each of 10 adult sheep. Three defects were filled with cement paste composites of hydroxyapatite and beta-tricalcium phosphate as follows: (1) 100 percent hydroxyapatite-cement paste, (2) 60 percent hydroxyapatite-cement paste, and (3) 20 percent hydroxyapatite-cement paste. One defect was filled with a ceramic composite containing 60 percent hydroxyapatite-ceramic, and the fifth defect remained unfilled. One year after implantation, the volume of all biomaterials was determined by computed tomography, and porosity and bone replacement were determined using backscatter electron microscopy. Computed tomography-based volumetric assessment 1 year after implantation demonstrated that none of the unfilled cranial defects closed over the 1-year period, confirming that these were critical-size defects. There was a significant increase in volume in both the cement paste and ceramic implants containing 60 percent hydroxyapatite (p < 0.01). There was no significant change in volume of the remaining cement paste biomaterials. Analysis of specimens by backscatter electron microscopy demonstrated mean bone replacement of 4.8 +/- 1.4 percent (mean +/- SEM) in 100 percent hydroxyapatite-cement paste, 11.2 +/- 2.3 percent in 60 percent hydroxyapatite-cement paste, and 28.5 +/- 4.5 percent in 20 percent hydroxyapatite-cement paste. There was an inverse correlation between the concentration of hydroxyapatite and the amount of bone replacement in the cement paste for each composite tested (p < 0.01). Bone replacement in 60 percent hydroxyapatite-ceramic composite (13.6 +/- 2.0 percent) was not significantly different from that in 60 percent hydroxyapatite-cement paste. Of note is that the ceramic composite contained macropores (200 to 300 microm) that did not change in size over the 1-year period. All cement paste composites initially contained micropores (3 to 5 nm), which remained unchanged in 100 percent hydroxyapatite-cement paste. Cement paste implants containing increased tricalcium phosphate demonstrated a corresponding increase in macropores following resorption of the tricalcium phosphate component. Bone replacement occurred within the macropores of these implants. In conclusion, there was no significant bone ingrowth into pure hydroxyapatite-cement paste (Bone Source, Stryker-Leibinger Inc., Dallas, Texas) in the present study. The introduction of macropores in a biomaterial can optimize bone ingrowth for reconstruction of critical-size defects in calvaria. This was demonstrated in both the ceramic composite of hydroxyapatite tested and the cement paste composites of hydroxyapatite by increasing the composition of a rapidly resorbing component such as beta-tricalcium phosphate.

Animals↗
PubMed2002

A 1-year study of osteoinduction in hydroxyapatite-derived biomaterials in an adult sheep model: part I.

The study presented here investigated hydroxyapatite biomaterials implanted in soft-tissue sites in adult sheep to determine whether these materials are osteoinductive and whether the rate of osteoinduction can be increased by manipulating the composition and porosity of the implants. For the study, 16.8-mm x 5-mm discs were prepared from mixtures of hydroxyapatite and beta-tricalcium phosphate. Five mixtures of hydroxyapatite-ceramic and hydroxyapatite-cement paste forms were studied: 100 percent hydroxyapatite-ceramic (Interpore), 60 percent hydroxyapatite-ceramic, 100 percent hydroxyapatite-cement paste, 60 percent hydroxyapatite-cement paste, and 20 percent hydroxyapatite-cement paste. Biomaterials were implanted in subcutaneous and intramuscular soft-tissue pockets in 10 adult sheep. Cranial bone grafts of equal dimension were implanted as controls. One year after implantation, the volume of all biomaterials and bone grafts was determined from a computed tomographic scan, and porosity and bone formation were determined using backscatter electron microscopy. Cranial bone and the 20 percent hydroxyapatite-cement paste implants demonstrated significant volume reduction in all sites after 1 year (p < 0.001). No significant difference in volume of the remaining four biomaterials was found. There was no significant change in pore size in the ceramic implants (range, 200 to 300 micro) and in the cement-paste implants containing 60 percent hydroxyapatite or more (range, 3 to 5 nm). Pore size in the cement-paste implants containing 20 percent hydroxyapatite increased significantly with resorption of the tricalcium-phosphate component, reaching a maximum of 200 to 300 micro in the periphery, where the greatest tricalcium-phosphate resorption had occurred. Both ceramic biomaterials demonstrated lamellar bone deposition within well-formed haversian systems through the entire depth of the implants, ranging from a mean of 6.6 percent to 11.7 percent. There was minimal bone formation in the cement-paste implants containing 60 percent hydroxyapatite or more. In contrast, cement-paste implants containing 20 percent hydroxyapatite demonstrated up to 10 percent bone replacement, which was greatest in the periphery of the implants where the greatest tricalcium-phosphate resorption had occurred. This study confirms the occurrence of true osteoinduction within hydroxyapatite-derived biomaterials, when examined using backscatter techniques. In this study, the rate of osteoinduction was greatest when a porous architecture was maintained, which was best achieved in ceramic rather than cement-paste forms of hydroxyapatite. Porosity and resultant bone formation in cement-paste implants can be improved by combining hydroxyapatite with a rapidly resorbing component, such as tricalcium phosphate.

Animals↗
PubMed2006

Comparison of periodontal ligament cells responses to dense and nanophase hydroxyapatite.

Hydroxyapatite, a synthetic calcium phosphate ceramic, is used as a biomaterial for the restoration of human hard tissue as well as in techniques which aim to regenerate periodontal tissues. Generally, hydroxyapatite is believed to have osteoconductive effects and to be non-bioresorbable but not to induce to periodontal tissue regeneration. No report has been found on responses of periodontal ligament cells (PDLC), the main contributor to periodontal tissue regeneration, to nanoparticles of hydroxyapatite. The objective of this study was to investigate the possible effects of nanophase powder of hydroxyapatite on proliferation of periodontal ligament cells. Using a sol-gel method, the nanophase hydroxyapatite powders were fabricated. These powders were proved to comprise nanoparticles by transmission electron microscope examination. The primary periodontal ligament cells were cultured on dense particle hydroxyapatite and nanometer particle hydroxyapatite. The effects on proliferation of periodontal ligament cells on dense and nanoparticle hydroxyapatite were examined in vitro using a methyl thiazolil tetracolium (MTT) test. The intercellular effects were studied with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX). In addition, the influence of the two materials on osteogenic differentiation was determined through measurement of alkaline phosphatase activity and flow cytometry. About 2, 3, and 4 days after treatment with nanoparticles of hydroxyapatite, the proliferation activity of the PDLC increased significantly compared with those proliferating on dense hydroxyapatite and of control PDLC, but no significant difference was found between the PDLC proliferation on dense hydroxyapatite and the control PDLCs. After 3 and 5 days' incubation with nanoparticles of hydroxyapatite, alkaline phosphatase activity was significantly increased as compared to PDLCs incubated with dense hydroxyapatite and control PDLCs. Intracellular engulfment was found in the cultured cells with nanophase hydroxyapatite under electron microscopy. The results suggest that nanophase hydroxyapatite can promote proliferation and osteogenic differentiation of periodontal ligament cells and further that it may be used as a bioresorbable agent in osseous restoration.

Alkaline Phosphatase↗
PubMed1999

The use of coralline hydroxyapatite with bone marrow, autogenous bone graft, or osteoinductive bone protein extract for posterolateral lumbar spine fusion.

STUDY DESIGN: A posterolateral lumbar arthrodesis animal model using coralline hydroxyapatite as a bone graft substitute. OBJECTIVE: To determine the effectiveness of coralline hydroxyapatite as a bone graft substitute for lumbar spine fusion when used with bone marrow, autogenous bone graft, or an osteoinductive bone protein extract. SUMMARY OF BACKGROUND DATA: Coralline hydroxyapatite is commonly used as a bone graft substitute in metaphysial defects but its use in a more challenging healing environment such as the posterolateral spine remains controversial. There are no published animal studies in which the use of coralline hydroxyapatite has been evaluated in a posterolateral lumbar arthrodesis model. METHODS: Single-level posterolateral lumbar arthrodesis was performed at L5-L6 in 48 adult New Zealand White rabbits. Rabbits were assigned to one of three groups based on the graft material they received: 3.0 mL coralline hydroxyapatite 1.5 mL plus bone marrow; 1.5 mL coralline hydroxyapatite plus 1.5 mL autogenous iliac crest bone; and, 3.0 mL coralline hydroxyapatite plus 500 micrograms bovine-derived osteoinductive bone protein extract on each side. Rabbits were killed after 2, 5, or 10 weeks, and the spines were excised and evaluated by manual palpation, radiographs, tensile biomechanical testing, and nondecalcified histology. RESULTS: Fusions were assessed by manual palpation at 5 weeks for comparisons among the three groups of graft materials. The coralline hydroxyapatite used with bone marrow produced no solid fusions (0/14). When combined with an equal amount of autogenous iliac crest bone, coralline hydroxyapatite resulted in solid fusion in 50% (7/14) of the rabbits (P < 0.05). When combined with the osteoinductive growth factor extract, the coralline hydroxyapatite resulted in solid fusion in 100% (11/11) of the rabbits (P < 0.05). The fusion masses in the growth factor group were significantly stronger (1.8 +/- 0.2 vs. 1.3 +/- 0.1; P = 0.02) and stiffer (1.5 +/- 0.2 vs. 1.2 +/- 0.1, P = 0.04) based on tensile testing to failure when normalized to the adjacent unfused level. CONCLUSION: These data indicate that coralline hydroxyapatite with bone marrow was not an acceptable bone graft substitute for posterolateral spine fusion. When combined with autogenous iliac crest bone graft-coralline hydroxyapatite served as a graft extender yielding results comparable to those obtained with autograft alone. Coralline hydroxyapatite served as an excellent carrier for the bovine osteoinductive bone protein extract yielding superior results to those obtained with autograft or bone marrow.

Animals↗
PubMed1995

Reaction of hydroxyapatite-sol in bone marrow.

Hydroxyapatite-sol was prepared by dispersing hydroxyapatite microcrystals into saline. The hydroxyapatite microcrystals were synthesized by neutralization reaction of calcium hydroxide suspension and phosphoric acid solution. Sizes of the hydroxyapatite microcrystals were less than 0.1 microns, and the mean value was 0.05 microm. The 0.2 ml hydroxyapatite-sol with a concentration of 14.8 mg/ml was injected into medullary cavities of rat femurs. Both sintered hydroxyapatite powder suspension and saline as comparative materials were injected into the medullary cavities in the same way. Reaction of the hydroxyapatite-sol in the bone medullary cavities was investigated histologically using light and transmission electron microscopes. After 3 days, new bone formation was observed by injection of hydroxyapatite-sol, while no bone formation was observed by injection of sintered hydroxyapatite powder and saline. Osteoblasts were observed endocytosing the hydroxyapatite-sol in the medullary cavities of the rats. Macrophages and undifferentiated osteoblasts were found around the hydroxyapatite-sol aggregation by transmission electron microscope. After 5 days, amounts of new bone increased and matured, forming trabeculae. Many osteoblasts were observed in a line along the surface of the bone. On the other hand, 5 days after injection of sintered hydroxyapatite powder and saline to bone formation was observed while at 10 days after injection, some immature new bone formation started to be observed. New bone increased and matured at 15 days postoperatively. From these results, it was concluded that hydroxyapatite-sol only quickly promotes the formation of new bone in bone marrow and can be used as injection liquid of new biomaterials for bone formation.

Animals↗
PubMed1991

The mechanical properties and solubility of strontium-substituted hydroxyapatite.

The mechanical properties and solubility of sintered Sr-substituted hydroxyapatites were examined in order to investigate the influences of Sr incorporation into hydroxyapatite in bones and teeth on them. Hydroxyapatite (HAp), Sr-substituted hydroxyapatite (Ca.SrAp), and strontium-hydroxyapatite (SrAp) were synthesized and sintered. The bending strength and Young's modulus were measured. Also, solubility in isotonic NaCl solution was examined. The Young's modulus of Sr-substituted hydroxyapatite (Sr wt% = 1.0) and hydroxyapatite surface treated with Sr ion were greater than that of hydroxyapatite. The bending strengths of Sr-substituted hydroxyapatites (Sr/Ca = 4/6 and less) were reduced slightly compared to that of hydroxyapatite. The bending strength of hydroxyapatite surface treated with Sr ion was increased compared to that of hydroxyapatite. The solubility in isotonic NaCl solution at 37 degrees C was increased with an increase in Sr content. The effects of Sr on the mechanical properties and solubility of bones and/or teeth are discussed.

Biomechanical Phenomena↗