Quantitative comparison of osteoconduction of porous, dense A-W glass-ceramic and hydroxyapatite granules (effects of granule and pore sizes).

The osteoconductive potentials of dense, small porous and large porous apatite- and wollastonite-containing glass-ceramic (A-W GC) granules of various sizes implanted in rat tibiae were evaluated quantitatively, by determining their affinity indices. The average affinity indices of all types of A-W GC were high. The dense A-W GC granules had the highest values (97.0+/-5.5%), followed by the large porous (87.1+/-8.4%) and then the small porous granules (79.0+/-8.4%). There were no significant differences among the osteoconductive potentials of the different sizes of each form of A-W GC granule. The osteoconductive potentials of four types of commercially available porous hydroxyapatite (HA) granules were compared with those of the small porous A-W GC granules, using the affinity index and the proportion of newly formed bone relative to that of the granules in the bone defect. The values of the former parameter for three types of HA and those of the latter for four were significantly inferior to those of A-W GC. The difference between the osteoconductive potentials of A-W GC and HA was considered to be related to the rate of surface apatite layer formation.     

Effect of silane treatment and different resin compositions on biological properties of bioactive bone cement containing apatite-wollastonite glass ceramic powder.

In methylmethacrylate (MMA)-based cements containing bioactive particles, polymethylmetacrylate (PMMA) is known to suppress the bioactivity of Bioglass(R) and apatite-wollastonite glass ceramic (AW-GC). Little is known about the effect of different silane treatment methods on the bioactivity of AW-GC. MMA-based cement plates containing dry silanated AW-GC particles and PMMA particles of different molecular weights (12,000-900,000) were immersed in simulated body fluid (SBF). Cements containing PMMA particles of high molecular weight formed an apatite layer on the surface after 24 h. Using PMMA particles with a molecular weight of 60,000 and AW-GC particles silanated with different methods (dry method vs. slurry method), cement plates were made and immersed in SBF. Only cement plates containing dry silanated AW-GC particles showed apatite formation in SBF after 3 days. In vivo implantation in rat tibias of MMA-based cement containing dry silanated AW-GC particles and PMMA particles (molecular weight 900,000) demonstrated an affinity index of 32.1 +/- 15.8% after 8 weeks of implantation compared to 89.4 +/- 10.7% achieved by bisphenol-A-glycidyl methacrylate based cement containing the same bioactive powder. By using a dry method of silane treatment and high molecular weight PMMA particles, the bioactivity of cement based on MMA monomer was achieved; but further effort is needed to improve the mechanical properties of the composite.     

Al2O3 doped apatite-wollastonite containing glass ceramic provokes osteogenic differentiation of marrow stromal stem cells.

Fresh marrow cells were obtained from femora of Fischer rats and cultured in a medium containing 15% fetal calf serum (FCS) until confluence. After trypsinization, cells were subcultured at a cell density of 100 x 10(3)/35-mm well in the presence of FCS, beta-glycerophosphate, and ascorbic acid phosphate on four different culture substrata. The period of subculture was 2 weeks; the substrata used were the culture dish, apatite-wollastonite containing glass ceramic (AW), hydroxyapatite coated AW (HA/AW), and Al2O3 doped AW (Al/AW). The HA coating was attained by the incubation of AW in simulated physiological solution. The glass matrix of AW and HA/AW contained MgO, CaO, P2O5, and SiO2; Al/AW contained Al2O3 in addition to these components. The subculture on Al/AW substratum showed many alkaline phosphatase (ALP) positive nodules and the highest ALP activity. On a Northern blot analysis the housekeeping gene of beta-actin mRNA was evenly detected from the cells cultured on all substrata; however, bone-specific osteocalcin mRNA was only detected from the cells on Al/AW. These results indicate that Al/AW provokes the osteoblastic differentiation of marrow stromal stem cells.     

Mechanical properties of bone after implantation of apatite-wollastonite containing glass ceramic-fibrin mixture

Mechanical properties of bone implanted with a mixture of apatite-wollastonite containing glass ceramic (A-W.GC) granules and fibrin were examined by compression testing. A 1:1 mixture of A-W.GC granules and fibrin (Group 1), 1:4 mixture of A-W.GC granules and fibrin (Group 2), and 1:1 mixture of hydroxyapatite (HA) granules and fibrin (Group 3) were implanted in the distal femoral metaphyses of rabbits. Histomorphometric analysis suggested that A-W.GC has a greater osteoconductive potential than HA. Trabeculalike structures were observed 24 weeks after the operation in all groups but were most notable in Group 2. Twenty-four weeks after the operation, in Groups 1 and 3, the compressive strength and compressive stiffness were higher than that of normal cancellous bone, and the fracture toughness was comparable with that of normal cancellous bone. In Group 2, all three values were similar to those of normal cancellous bone. Implantation of A-W.GC granules at a low density induces the formation of bone tissue which is similar to normal bone in both mechanical properties and morphology.     

Quantitative comparison of bone growth behavior in granules of Bioglass, A-W glass-ceramic, and hydroxyapatite

The hypothesis that bioactive glass particulate increases the rate of bone proliferation over that of synthetic hydroxyapatite and bioactive glass-ceramic was tested in these experiments. Three types of bioactive particles-45S5 Bioglass(R), synthetic hydroxyapatite, and A-W glass-ceramic-were implanted in 6-mm-diameter holes drilled in the femoral condyles of mature rabbits. Bone growth rate was measured using an image processor. 45S5 Bioglass(R) produced bone more rapidly than either A-W glass-ceramic or hydroxyapatite. At the later time periods, 45S5 Bioglass(R) was resorbed more quickly than A-W glass-ceramic. Synthetic hydroxyapatite was not resorbed at all. Backscattered electron imaging suggested that the resorption process occurred by solution-mediated dissolution, which produced chemical changes in the enclosed particulate. It was concluded that the rate of bone growth correlates with the rate of dissolution of silica as the particles resorb.     

Fretting wear properties of hydroxyapatite, alumina containing high density polyethylene biocomposites against zirconia

Considering the importance of wear on the materials performance in biomedical applications, the major objective of the present work is to investigate the friction and fretting wear behavior of various HDPE-based composites against zirconia counterbody, both in air and simulated body fluid (SBF) environment. Both Al(2)O(3) and/or HAp fillers (upto 40 vol %) have been incorporated in HDPE to improve the hardness and elastic modulus of HDPE. The fretting wear study indicates that extremely low COF (approximately 0.055-0.075) as well as higher wear resistance (wear rate in the order of approximately 10(-6) mm(3)/N m) can be achieved with the newly developed composites in SBF. A low wear depth of 3-7 microm is recorded, irrespective of fretting environment. Besides reporting the phenomenological tribological data, major focus has been on to understand the underlying mechanism of material removal at fretting contacts. Such understanding has been established in discussing the wear mechanisms in terms of deformation of polymer matrix, tribolayer formation, and wear debris generation.     

Study on glass infiltrated alumina(GIA) ceramic for CAD/CAM

With the rapid development of computer technique,Computer aided design( CAD) and computer aided manufacturing( CAM) or computer integrated manufac-turing( CIM) has became an alternative to the conventional technique for producingdental restorations. and the increasing demand for esthetic restoration during thelast decade has led to the development of several new ceramic system.One of theseis In Ceram( Vita Zahnfabrik,S ckingen,Germany) ,a high-strength ceramic basedon a skeleton of parti…     

Resorption of apatite-wollastonite containing glass-ceramic and beta-tricalcium phosphate in vivo

Apatite-wollastonite containing glass ceramic is considered to be difficult to resorb, but we experienced the disappearance of the porous type of Apatite-wollastonite glass ceramic particles . In this study, the resorption of porous apatite-wollastonite glass-ceramic implanted in the femurs of rabbits was investigated, and the process was compared with beta-tricalcium phosphate, a resorbable ceramics. Porous apatite-wollastonite glass-ceramic (70, 80, and 90% porosity) and beta-tricalcium phosphate (75% porosity) were implanted in the femurs of Japanese white rabbits. Samples were harvested and examined 0, 4, 8, 12, 24 and 36 weeks after implantation. Quantitative analysis of the radiographic and histologic findings was performed with NIH Image software. Radiographic examination demonstrated that the radiopacity and size of the porous apatite-wollastonite glassceramic cylinders decreased gradually after implantation. Histologic examination revealed that the surface area of the apatite-wollastonite glass-ceramic cylinders decreased continuously, and approached 20% of the original area 36 weeks after implantation. However, the resorption rate of porous apatite-wollastonite glass-ceramic was slower than that of beta-tricalcium phosphate. Toluidine blue staining showed abundant new bone formation on the surface of the apatite-wollastonite glassceramic matrix. Considering its mechanical strength, gradual resorption characteristics, and good osteochonductive activity, porous apatite-wollastonite glass-ceramic appears to be a suitable artificial bone substitutes.     

Macropore tissue ingrowth: a quantitative and qualitative study on hydroxyapatite ceramic

The aim of this study was to obtain more information about macropore tissue ingrowth into the pores of sintered hydroxyapatite implanted in the rat middle ear, for the assessment of the usefulness of this material in reconstructive middle-ear surgery. The exudate filing the pores during the early post-operative period was gradually replaced by equal amounts of fibrous tissue and bone. The percentage of the macropore area occupied by bone was directly correlated with the macropore size. Bone was deposited not only from the pore wall towards the pore centre, but also in the opposite direction. Bonding osteogenesis was demonstrated. At sites of mechanical irritation, the presence of multinucleated cells and proliferatively active mononuclear phagocytes persisted for as long as a year. Under appropriate conditions hydroxyapatite seems to be a promising material for bone substitution in reconstructive middle-ear surgery.     

Calcium phosphate materials containing alumina: Raman spectroscopical, histological, and ultrastructural study

Variable alumina quantities were added to two types of calcium phosphate materials-hydroxyapatite ceramics with Ca/P = 1.67 and calcium metaphosphate glass with Ca/P = 1--in order to increase their mechanical properties. Raman spectroscopy shows that alumina interacts with the phosphate group of these materials, while thermomechanical analysis shows that their elastic modulus has a value similar to that of bone. Histological sections demonstrate that the surface in close contact with ceramic materials shows a good integration between bone and biomaterial. All ceramic specimens are penetrated by well-stained, presumably glycoprotein, matrix, that consistently forms a thin network in close contact with the implant. After 6 weeks bone growing on both ceramic and glass shows signs of maturation with a lamellar structure and an apparently normal mineralization. In the case of the glass, inside this newly formed bone, were often observed two layers, the internal one showing a well defined lamellar structure.     

Clinical and simulator wear study of alumina ceramic THR to 17 years and beyond

Three THAs with cementless monolithic alumina ceramic sockets and cementless Co-alloy stems were retrieved because of aseptic loosening after 17 and 24 years. At revision heads and cups were marked for orientation. Maps were drawn of wear patterns with the use of light microscopy and surveyed by SEM. In a simulator experiment 28-mm-diameter alumina heads and liners were used. The cups were mounted inverted in a hip simulator and run with calf serum as the lubricant. The hip loads were 2 kN maximum and a 1-Hz frequency for 20 million cycles. Wear severity was classified into five grades. In retrieved implants, SEM analysis showed that the main wear zones (MWZ) had Grade 4 wear. The peripheral wear zones (PWZ) showed grain pull-out regions (Grade 5 wear). These corresponded to neck-socket impingement and head-acetabular cup separation. Gray was due to transferred CoCr particles from the stem. In the simulator study, the MWZ had only localized areas of grain pull out surrounded by polished surface regions (Grade 4 wear) at 20 million cycles; stripe wear was not seen. The alumina ceramic bearings proved excellent up to 22 years in simulator studies and clinical studies. However, microseparation kinematics would be necessary in the simulator to duplicate the more peripheral wear zones.     

Early osseointegration of a strontium containing glass ceramic in a rabbit model

The most important property of a bone cement or a bone substitute in load bearing orthopaedic implants is good integration with host bone with reduced bone resorption and increased bone regeneration at the implant interface. Long term implantation of metal-based joint replacements often results in corrosion and particle release, initiating chronic inflammation leading onto osteoporosis of host bone. An alternative solution is the coating of metal implants with hydroxyapatite (HA) or bioglass or the use of bulk bioglass or HA-based composites. In the above perspective, the present study reports the in vivo biocompatibility and bone healing of the strontium (Sr)-stabilized bulk glass ceramics with the nominal composition of 4.5SiO₂–3Al₂O₃–1.5P₂O₅–3SrO–2SrF₂ during short term implantation of up to 12 weeks in rabbit animal model. The progression of healing and bone regeneration was qualitatively and quantitatively assessed using fluorescence microscopy, histological analysis and micro-computed tomography. The overall assessment of the present study establishes that the investigated glass ceramic is biocompatible in vivo with regards to local effects after short term implantation in rabbit animal model. Excellent healing was observed, which is comparable to that seen in response to a commercially available implant of HA-based bioglass alone.     

Inhibition of Ni release from NiTi alloy by hydroxyapatite,alumina, and titanium sputtered coatings

To alleviate the effects of Ni allergy from NiTi alloy implants, hydroxyapatite (Ca10(PO4)6(OH)2; HA), alumina (Al2O3), or titanium (Ti) was coated onto NiTi alloy plates to form 1-microm thick films using radio frequency magnetron sputtering. The coatings on the plates were characterized using XRD. After the plates had been immersed in physiological saline for periods of one, four, or eight weeks, the concentration of Ni ions released in each solution was detected using a microwave induced plasma mass spectrometer. After eight weeks, the concentration of Ni ions released from the non-coated, the Ti-coated, the HA-coated, and the alumina-coated plates were 238, 19.7, 183, and 106 ppb, respectively. The bonding strength of the Ti film, the HA film, and the alumina film to the NiTi substrate were 3.8 +/- 1.2, 2.6 +/- 0.7, and 3.1 +/- 1.2 MPa, respectively.The non-coated, the HA-coated, the alumina-coated, and the Ti-coated plates were implanted into the femurs of a dog for four weeks for histological observation. In case of the non-coated plates, connective tissue more than 300 microm thick was observed, whereas for the coated plates the thickness of the connective tissue was around 100 microm.     

The biocompatibility of hydroxyapatite ceramic: a study of retrieved human middle ear implants

The biocompatibility of 11 hydroxyapatite auditory canal-wall prostheses and 4 hydroxyapatite incus prostheses implanted for 4 to 40 months was evaluated by light microscopy, scanning electron microscopy, transmission electron microscopy, and R?ntgen microanalysis. These 15 prostheses representing 4% of 375 prostheses, has been removed because of unresolved chronic middle ear infection, residual cholesteatoma, or poor fit. The findings confirmed earlier reports on the biocompatibility of hydroxyapatite in vitro, in animals, and in man. An electron-dense layer was found at the interface with bone and fibrous tissue, and a firm bond between the ceramic and bone at the hydroxyapatite ceramic/bone interface developed. Macropores became filled with bone and fibrous tissue, and the tissue in the individual pores was interconnected. Furthermore the incus prostheses were covered with an epithelium similar to that found in the human middle ear. Findings diverging from those made in other studies were the relatively large amount of exudate in the pores, an apparent increase of degradation during infection, and the accumulation of trace elements in one of the canal-wall prostheses. In all likelihood these three phenomena may be attributed to the unfavorable conditions to which these prostheses were exposed during implantation.     

Behaviour of tricalcium phosphate and hydroxyapatite granules in sheep bone defects

Granules of hydroxyapatite (HA) and tricalcium phosphate (TCP) were implanted in separate holes drilled in mandibular bone of sheep to check the bone growth and in vivo behaviour of the materials. The experiment was performed in three sheep, killed respectively at 4, 8, 12 month. Samples of bone with the materials were explanted, microradiographed and sectioned to evaluate the interface under optical and electron scanning electron microscope. The hole, left empty as a reference, showed no full repair; whereas 4 month after implantation the TCP granules induce total repair of the hole. HA granules crumbled and no new bone induction was seen even 12 month after implantation.     

Release of silica, calcium, phosphorus, and fluoride from glass ionomer cement containing bioactive glass

The aim of this study was to examine the release of silica (Si), calcium (Ca), phosphorous (P), and fluoride (F) from conventional glass ionomer cement (GI) and resin-modified glass ionomer cement (LCGI), containing different quantities of bioactive glass (BAG). Further aim was to evaluate in vitro biomineralization of dentine. The release of Si increased with the increasing immersion time from the specimens containing BAG, whereas the amount of Ca and P decreased indicating in vitro bioactivity of the materials. LCGI with 30wt% of BAG showed highest bioactivity. It also showed CaP-like precipitation on both the surface of the test specimens and on the dentin discs immersed with the material. Within the limitations of this study, it can be concluded that a dental restorative material consisting of glass ionomer cements and BAG is bioactive and initiates biomineralization on dentin surface in vitro.     

Preparation and in vitro characterization of scaffolds of poly(L-lactic acid) containing bioactive glass ceramic nanoparticles

Porous nanocomposite scaffolds of poly(l-lactic acid) (PLLA) containing different quantities of bioactive glass ceramic (BGC) nanoparticles (SiO(2):CaO:P(2)O(5) approximately 55:40:5 (mol)) were prepared by a thermally induced phase-separation method. Dioxane was used as the solvent for PLLA. Introduction of less than 20wt.% of BGC nanoparticles did not remarkably affect the porosity of PLLA foam. However, as the BGC content increased to 30wt.%, the porosity of the composite was observed to decrease rapidly. The compressive modulus of the scaffolds increased from 5.5 to 8.0MPa, while the compressive strength increased from 0.28 to 0.35MPa as the BGC content increased from 0 to 30wt.%. The in vitro bioactivity and biodegradability of nanocomposites were investigated by incubation in simulated body fluid (SBF) and phosphate-buffered saline, respectively. Scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and X-ray diffraction were employed to monitor the surface variation of neat PLLA and PLLA/BGC porous scaffolds during incubation. PLLA/(20wt.%)BGC composite exhibited the best mineralization property in SBF, while the PLLA/(10wt.%)BGC composite showed the highest water absorption ability.     

In vivo behavior of zirconia hydroxyapatite (ZH) ceramic implants in dogs: a clinical, radiographic, and histological study

The main goal of this study is to evaluate potential applications of two zirconia-hydroxyapatite composites, Z4H6 and Z6H4, as bone substitutes. Composite plugs were implanted into the distal femoral metaphysis and also onto the longissimus dorsi of 18 adult mixed-breed dogs in order to assess in vivo biocompatibility by immediate clinical and radiographic evaluation 30, 90, and 120 days after implantation. Radiographic examination revealed radiolucency on the defect site. However, a progressive increase in bone density was observed over time, reaching a radiopacity similar to that of bone 120 days after implantation. Histological study revealed that a thin layer of fibroblasts was observed at the implant-bone interface in addition to osteoblastic activity 30 days after implantation, whereas bone neoformation around the implants was detected for the subsequent implantation times (90 and 120 days). Otherwise, the histological evaluation of the implant-muscle interface showed the presence of an initially thick fibrous tissue layer 30 days after implantation, which decreased with longer investigation times (90 and 120 days). The numbers of plasmocytes, lymphocytes, and macrophages gradually reduced as a function implantation time, being completely absent 120 days after implantation with a resulting complete osteointegration process. The zirconia phase content did not affect the bioactive behavior of the implants investigated and did not induce bone formation when implanted into muscle either.     

Proliferation and differentiation of osteoblast-like cells on apatite-wollastonite/polyethylene composites

Glass-ceramic apatite-wollastonite (A-W)/high-density polyethylene composite (AWPEX) materials have been designed to match the mechanical strength of human cortical bone and to provide favourable bioactivity, with potential use in many orthopaedic applications. To better understand AWPEX properties, the effects of surface finish and ceramic filler size and content on osteoblast-like cell attachment, proliferation, and differentiation were examined. Glass-ceramic content was tested at 30 and 50 vol% and median particle size at 4.5 and 7.7 microm. Samples were prepared as 1 x 10 x 10 mm(3) tiles with polished or rough surfaces, sterilized by gamma irradiation (2.5 Mrad), and characterized by scanning electron microscopy (SEM) and surface profilometry. Saos-2 human osteoblast-like cells were cultured on each surface at an initial concentration of 4500 cells/cm(2) for 1, 3, or 7 days. At each time point, adenosine triphosphate and alkaline phosphatase levels were measured to assess cell number and osteoblast differentiation. SEM imaging of cells on the composite surfaces showed preferential cell attachment to filler particles within the polymer matrix. Significant biochemical assay differences were found at 7 days, confirmed by ANOVA post-hoc testing using Bonferroni's correction. Overall, increased exposure of the glass-ceramic A-W phase in AWPEX through surface polishing, higher volume fraction and/or larger particle size was found to lead to an improved cell response.     

On the feasibility of phosphate glass and hydroxyapatite engineered coating on titanium

In this report, bioactive calcium phosphate (CaP) coatings were produced on titanium (Ti) by using phosphate-based glass (P-glass) and hydroxyapatite (HA), and their feasibility for hard tissue applications was addressed in vitro. P-glass and HA composite slurries were coated on Ti under mild heat treatment conditions to form a porous thick layer, and then the micropores were filled in with an HA sol-gel precursor to produce a dense layer. The resultant coating product was composed of HA and calcium phosphate glass ceramics, such as tricalcium phosphate (TCP) and calcium pyrophosphate (CPP). The coating layer had a thickness of approximately 30-40 microm and adhered to the Ti substrate tightly. The adhesion strength of the coating layer on Ti was as high as 30-33 MPa. The human osteoblastic cells cultured on the coatings produced by the combined method attached and proliferated favorably. Moreover, the cells on the coatings expressed significantly higher alkaline phosphatase activity than those on pure Ti, suggesting the stimulation of the osteoblastic activity on the coatings. On the basis of these observations, the engineered CaP coating layer is considered to be potentially applicable as a hard tissue-coating system on Ti-based implants.