Bone-bonding behavior of alumina bead composite.

Previously we developed an alumina bead composite (ABC) consisting of alumina bead powder (AL-P) and bisphenol-alpha-glycidyl methacrylate (Bis-GMA)-based resin and reported its excellent osteoconductivity in rat tibiae. In the present study, are evaluated histologically and mechanically the effect of alumina crystallinity on the osteoconductivity and bone-bonding strength of the composite. AL-P was manufactured by fusing crushed alpha-alumina powder and quenching it. The AL-P was composed mainly of amorphous and delta-crystal phases of alumina. Its average particle size was 3.5 microm, and it took a spherical form. Another composite (alpha ALC), filled with pure alpha-alumina powder (alpha AL-P), was used as a referential material. The proportion of powder added to each composite was 70% w/w. Mechanical testing of ABC and alpha ALC indicated that they would be strong enough for use under weight-bearing conditions. The affinity indices for ABC, determined using male Wistar rat tibiae, were significantly higher than those for alpha ALC (p < 0.0001) up to 8 weeks. Composite plates (15 x 10 x 2 mm) that had an uncured surface layer on one side were made in situ in a rectangular mold. One of the plates was implanted into the proximal metaphysis of the tibia of a male Japanese white rabbit, and the failure load was measured by a detaching test 10 weeks after implantation. The failure loads for ABC on its uncured surface [1.91+/-1.23 kgf (n = 8)] were significantly higher than those for alpha ALC on its uncured surface [0.35+/-0.33 kgf (n = 8); (p < 0.0001)], and they also were significantly higher than those for ABC on the other (cured surface) side (p < 0.0001). Histological examinations using rabbit tibiae revealed bone ingrowth into the composite only on the uncured surface of ABC. This study revealed that the amorphous phase of alumina and formation of an uncured surface layer are needed for the osteoconductive and bone-bonding ability of ABC. ABC shows promise as a basis for the development of a highly osteoconductive and mechanically strong biomaterial.     

Composites consisting of poly(methyl methacrylate) and alumina powder: an evaluation of their mechanical and biological properties

We developed new composites consisting of comparatively high molecular weight poly(methyl methacrylate) (hPMMA) and delta-alumina powder or alpha-alumina powder (designated delta-APC and alpha-APC, respectively) that allowed direct bone formation on their surfaces in vivo. delta-Alumina powder was manufactured by the fusing and quenching of pulverized alumina powder. It was composed mainly of delta-crystal phases of alumina. The purpose of this study was to evaluate the static mechanical properties and biological properties of these composites. The hPMMA itself was used as a reference material. The bending strength and Young's modulus of both delta-APC and alpha-APC were significantly higher than those of hPMMA, and the alumina composites are believed to be strong enough for use under weight-bearing conditions. The three types of composites were packed into the intramedullary canals of rat tibiae to evaluate osteoconductivity, as determined by an affinity index. Rats were sacrificed 4 and 8 weeks after surgery. The affinity index, equal to the length of bone in direct contact with the composite surface and expressed as a percentage of the total length of the composite surface, was calculated for each composite at each interval. Histologically, new bone had formed along the surfaces of both delta-APC and alpha-APC within 4 weeks. The affinity indices for both delta-APC and alpha-APC increased significantly with time up to 8 weeks. At 8 weeks, the affinity index for delta-APC was significantly higher than the indices for alpha-APC and hPMMA. This study revealed that the excellent osteoconductivity of delta-APC was due to the delta-crystal phases of alumina and the high molecular weight of hPMMA. delta-APC shows promise as a base for developing a highly osteoconductive and mechanically strong biomaterial.     

Ultrastructure of the interface between alumina bead composite and bone

We developed a composite (ABC) consisting of alumina bead powder as an inorganic filler and bisphenol-a-glycidyl dimethacrylate (Bis-GMA)-based resin as an organic matrix. Alumina bead powder was manufactured by fusing crushed alpha-alumina powder and quenching it. The beads took a spherical form 3 microm in average diameter. The proportion of filler in the composites was 70% w/w. The composite was implanted into rat tibiae and cured in situ. Specimens were prepared 1, 2, 4, and 8 weeks after the operation and observed by transmission electron microscopy. The results were compared with those of a bone composite made of alpha-alumina powder (alpha-ALC). In ABC-implanted tibiae, the uncured surface layer of Bis-GMA-based resin was completely filled with newly formed bonelike tissue 2 weeks after implantation. The alumina bead fillers were surrounded by and in contact with bonelike tissue. No intervening soft tissue was seen. In alpha-ALC-implanted tibiae, a gap was always observed between the alpha-ALC and the bonelike tissue. These results indicate that the ABC has osteoconductivity, although the precise mechanism is still unclear.     

Effect of bioactive filler content on mechanical properties and osteoconductivity of bioactive bone cement.

We took three types of bioactive bone cement (designated AWC, HAC, and TCPC), each with a different bioactive filler, and evaluated the influence of each filler on the mechanical properties and osteoconductivity of the cement. The cements consisted of bisphenol-a-glycidyl methacrylate-based (Bis-GMA based) monomers as an organic matrix, with a bioactive filler of apatite/wollastonite containing glass-ceramic (AW-GC) or sintered hydroxyapatite (HA) or beta-tricalcium phosphate (beta-TCP) powder. Each filler was mixed with the monomers in proportions of 50, 70, and 80% (w/w), giving a total of nine cement subgroups. The nine subgroups were designated AWC50, AWC70, AWC80, HAC50, HAC70, HAC80, TCPC50, TCPC70, and TCPC80. The compressive and bending strengths of AWC were found to be higher than those of HAC and TCPC for all bioactive filler contents. We also evaluated the cements in vivo by packing them into the intramedullary canals of rat tibiae. To compare the osteoconductivity of the cements, an affinity index was calculated for each cement; it equaled the length of bone in direct apposition to the cement, expressed as a percentage of the total length of the cement surface. Microradiographic examination up to 26 weeks after implantation revealed that AWC showed a higher affinity index than HAC and TCPC for each filler content although the affinity indices of all nine subgroups (especially the AWC and HAC subgroups) increased with time. New bone had formed along the AWC surface within 4 weeks, even in the cement containing AW-GC filler at only 50% (w/w); observation of the cement-bone interfaces using a scanning electron microscope showed that all the cements had directly contacted the bone. At 4 weeks the AWC had bonded to the bone via a 10 micron-thick reactive layer; the width of the layer, in which partly degraded AW-GC particles were seen, became slightly thicker with time. On the other hand, in the HAC- and TCPC-implanted tibiae, some particles on the cement surface were surrounded by new bone and partly absorbed or degraded. The results suggest that the stronger bonding between the inorganic filler and the organic matrix in the AWC cements gave them better mechanical properties. The results also indicate that the higher osteoconductivity of AWC was caused by the higher reactivity of the AW-GC powder on the cement surface.     

Ultrastructure of the interface between bioactive composite and bone: comparison of apatite and wollastonite containing glass-ceramic filler with hydroxyapatite and beta-tricalcium phosphate fillers.

We have developed a bioactive bone cement that consists of apatite and wollastonite containing glass-ceramic (AW-GC) powder and bisphenol-a-glycidyl dimethacrylate (Bis-GMA)-based resin. In this study, we made three types of composite (designated AWC, HAC, and TCPC) consisting of AW-GC, hydroxyapatite (HA,) or beta-tricalcium phosphate (beta-TCP) powder as the inorganic filler and Bis-GMA-based resin as the organic matrix. The proportion by weight of the filler mixed into the cement was 70%. Rectangular plates (10 x 15 x 2 mm) of each composite were made and abraded with 2000 alumina powder. These composites were implanted into tibial metaphyses of rabbits. Specimens were prepared 10 and 25 weeks after implantation and examined using transmission electron microscopy (TEM). AWC was in direct contact with bone 10 weeks after implantation, and AW-GC particles were partially absorbed at the surface. HAC was in contact with partially mineralized extracellular matrix 10 weeks after implantation. In TCPC-implanted specimens, randomly oriented mineral was observed 10 weeks after implantation; however, collagenous extracellular matrix rarely was observed. In 25-week specimens, AW-GC particles were completely absorbed and replaced by new bone, and there was no intervening soft tissue. Both HAC and TCPC were in contact with bone at 25 weeks. These results indicate that AWC has higher bioactivity than either HAC or TCPC.     

Effects of apatite and wollastonite containing glass-ceramic powder and two types of alumina powder in composites on osteoblastic differentiation of bone marrow cells

Previously we developed a composite consisting of apatite and wollastonite containing glass-ceramic (AW-GC) powder and bisphenol-a-glycidyldimethacrylate (Bis-GMA)-based resin (designated AWC), and demonstrated that AWC showed direct contact with living bone. Another new composite consisting of mainly the delta-crystal phase of alumina bead powder and Bis-GMA-based resin (designated ABC) was developed. Although alumina ceramics are bioinert and a composite filled with the pure alpha-crystal phase of alumina powder (designated alphaALC) did not allow direct bone formation in vivo, ABC was shown to have excellent osteoconductivity. One purpose of this study was to investigate whether AW-GC powder in a composite promotes osteoblastic differentiation of rat bone marrow cells as AW-GC bulk did. Another purpose was to evaluate the effects of the delta-crystal phase of alumina powder in a composite on osteoblastic differentiation. In a cell culture with dexamethasone, alkaline phosphatase (AP) activity at both days 7 and 14, and the levels of osteocalcin mRNA and alpha1(I) collagen mRNA at day 14 and osteopontin mRNA at day 7, were highest on AWC, followed by ABC, and finally alphaALC. Scanning electron microscopy showed more abundant mineralized globules and a fibrous collagen matrix on AWC at day 14, followed by ABC. In a cell culture without dexamethasone, AP activity at both days 7 and 14, and the level of osteopontin mRNA at day 7, were higher on ABC than on any other composite, whereas osteocalcin mRNA could not be detected. These results indicate that AW-GC powder in a composite promotes osteoblastic differentiation of bone marrow cells intensively when supplemented with dexamethasone. The delta-crystal phase of alumina powder in a composite promotes greater osteoblastic differentiation than the alpha-crystal phase of alumina powder.     

Mechanical properties and osteoconductivity of new bioactive composites consisting of partially crystallized glass beads and poly(methyl methacrylate)

New bioactive composites consisting of partially crystallized glass beads as inorganic fillers and poly(methyl methacrylate) (PMMA) as an organic matrix were developed. Two kinds of partially crystallized glass beads, designated Cry820 and Cry850, were newly prepared by the heating of MgO-CaO-SiO(2)-P(2)O(5) glass at 820 and 850 degrees C, respectively. The glass beads were mixed with PMMA to form two new composites designated Cry820C and Cry850C, respectively. The goal of this study was to produce a highly osteoconductive and mechanically strong composite cement with these new fillers. A previously reported composite cement designated AWC, which was composed of apatite- and wollastonite-containing glass ceramic (AW-GC) as a powder filler and the same PMMA polymer used in the new composites, was used as a reference material. The quantity of filler added to each composite was 70 wt %. The bending strength of Cry820C was significantly higher than that of Cry850C. Composites were packed into intramedullary canals of rat tibiae to evaluate their osteoconductivity, as determined by an affinity index. The affinity index, which equaled the length of bone in direct contact with the composite surface expressed as a percentage of the total length of the composite surface, was calculated for each composite. The rats were euthanized at 4, 8, and 25 weeks after implantation. At each time interval studied, Cry820C showed a significantly higher affinity index than AWC up to 25 weeks after implantation. Cry850C showed a significantly higher affinity index than AWC up to 8 weeks and a higher affinity index than AWC at 25 weeks, although the difference was not significant. The values for each composite increased significantly with time up to 25 weeks. Our study revealed that the higher osteoconductivity of the new composites was due to the larger quantity of the glassy phase of the crystallized glass beads at the composite surface and the lower solubility of the PMMA powder to methyl methacrylate monomer. In addition, the spherical shape of the crystallized glass beads gave the new composites strong enough mechanical properties to be useful under weight-bearing conditions. The new composites show promise as alternatives, with improved properties, to conventional PMMA bone cement.     

Osteoconductivity and bone-bonding strength of high- and low-viscous bioactive bone cements.

A study was conducted to evaluate the osteoconductivity and bone-bonding ability of two types of bioactive bone cement, both consisting of apatite and wollastonite containing glass-ceramic powder (AW-P), fused silica glass powder (SG-P), submicron fumed silica as an inorganic filler, and bisphenol-a-glycidyl methacrylate (Bis-GMA) based resin as an organic matrix. The cements had two kinds of formulas: one (dough-type cement; designated DTC) composed of 85% (w/w) filler and 15% resin, which was developed for fixation of the acetabular component in total hip arthroplasty and could be handled manually; and one (injection-type cement; designated ITC) composed of 79% (w/w) filler and 21% resin. ITC was developed for fixation of the femoral component and, because it had a lower viscosity than DTC, could be injected. The DTC and ITC both contained 73% AW-P, 25% SG-P, and 2% fumed silica in the weight ratio of the filler component. Two other types of cement, both of which consisted of 83.3% AW-P or SG-P, 1.7% fumed silica, and 15% resin, were used as reference material (designated AWC or SGC) for a detaching test. Following the packing of bone defects in the rat tibiae with either DTC or ITC, histological examination revealed that the DTC and ITC had both directly contacted the bone and were almost completely surrounded by bone by 16 weeks after the surgery and that no marked biodegradation had occurred at 52 weeks postimplantation. Rectangular plates (2 x 10 x 15 mm) of AWC, DTC, ITC, and SGC were implanted into the metaphysis of the tibia of male rabbits and the failure load was measured by a detaching test at 10 and 25 weeks after implantation. The failure loads of AWC, DTC, ITC, and SGC were 3.65, 2.21, 2.44, and 0.04 kgf at 10 weeks and 4.87, 2. 81, 2.82, and 0.13 kgf at 25 weeks, respectively. Observation of the bone-implant interface by scanning electron microscopy and energy dispersive X-ray microanalysis revealed that all the samples except SGC formed direct contact with the bone and that only AWC-implanted tibiae had a layer of a low calcium and phosphorus level at the bone-implant interface. Results showed that DTC and ITC have excellent osteoconductivity and bone-bonding ability under non-weight-bearing conditions.     

Bioabsorbable scaffolds for guided bone regeneration and generation

Several different bioabsorbable scaffolds designed and manufactured for guided bone regeneration and generation have been developed. In order to enhance the bioactivity and potential osteoconductivity of the scaffolds, different bioabsorbable polymers, composites of polymer and bioactive glass, and textured surface structures of the manufactured devices and composites were investigated in in vitro studies and experimental animal models. Solid, self-reinforced polyglycolide (SR-PGA) rods and self-reinforced poly L-lactide (SR-PLLA) rods were successfully used as scaffolds for bone formation in muscle by free tibial periosteal grafts in animal experiments. In an experimental maxillary cleft model, a bioabsorbable composite membrane of epsilon-caprolactone and L-lactic acid 50/50 copolymer (PCL/LLA) film and mesh and poly 96L,4D-lactide (PLA96) mesh were found to be suitable materials for guiding bone regeneration in the cleft defect area. The idea of solid layer and porous layer combined together was also transferred to stiff composite of poly 70L,30DL-lactide (PLA70) plate and PLA96 mesh which structure is introduced. The osteoconductivity of several different biodegradable composites of polymers and bioactive glass (BG) was shown by apatite formation in vitro. Three composites studied were self-reinforced composite of PLA70 and bioactive glass (SR-(PLA70 + BG)), SR-PLA70 plate coated with BG spheres, and Polyactive with BG.     

PMMA-based bioactive cement: effect of glass bead filler content and histological change with time.

A new bioactive bone cement (designated GBC), which is a polymethyl methacrylate (PMMA)-based composite consisting of bioactive glass beads as an inorganic filler and high molecular-weight PMMA as an organic matrix, has been developed. The purpose of the present study was to evaluate the effect of the filler content on the mechanical properties and osteoconductivity of GBC, to decide the most suitable filler proportion, and to evaluate the degree of cement degradation with time. The bioactive beads, consisting of MgO-CaO-SiO(2)-P(2)O(5)-CaF(2) glass, were added to the cement in various proportions (40-70 wt %). The bending strength of GBC did not differ among the proportions (approximately 136 MPa), but the elastic modulus of bending of GBC increased as the glass bead filler content increased (approximately 4.1-7.2 GPa). The all types of GBC were packed into the intramedullary canals of rat tibiae to evaluate osteoconductivity, as determined by an affinity index calculated as the length of bone in direct contact with the cement surface expressed as a percentage of the total length of the cement surface. Rats were sacrificed at 4, 8, 25, and 39 weeks after implantation, and the affinity index was calculated for each type of GBC at each time point. Histologically, new bone had formed along the surface of all types of GBC within 4 weeks, even in GBC containing only 40 wt % of glass beads. The affinity indices of GBC tended to increase as the proportion of glass bead filler increased and as the implantation period increased. In GBC containing 60 or 70 wt % of glass beads, significant rapid increases in the affinity indices were found from 4 to 8 weeks, and the high values (approximately 70%) were maintained up to 39 weeks. A sign of glass bead degradation was observed at the bone-cement interface in the rat tibiae at 39 weeks. We conclude that, when mechanical properties and osteoconductivity are both taken into consideration, GBC containing 60 or 70 wt % of glass beads is the most suitable formulation, but that further studies are needed to investigate and overcome the degradation.     

A 12 month in vivo study on the response of bone to a hydroxyapatite-polymethylmethacrylate cranioplasty composite

We investigated the osteoconductivity and biocompatibility in vivo of a new hydroxyapatite-polymethylmethacrylate (HA-PMMA) composite developed for use as an implant material for cranioplasty, which is expected to have the good osteoconductivity of HA together with the strength and ease of handling of PMMA. The HA-PMMA composites were implanted in eight full-grown beagles and then 6, 12, 24 weeks and 1 year after implantation, the animals were sacrificed and the implanted materials removed along with the surrounding tissues. Extirpated specimens were studied using an optical microscope and micro-computed tomography (micro-CT). Fibrous connective tissue was prominent in the interface of the composite at 6 weeks. New bone formation was seen around the implant, 12 and 24 weeks after operation. At 1 year, new bone filled in the interface of the HA-PMMA composite and adhered to the surrounding autogenous bone. Mixing HA and PMMA did not interfere with the osteoconductivity of the HA component. In micro-CT findings, the new bone growing on the HA-PMMA composite could be seen attaching preferentially to HA particles exposed at the composite surface, rather than the PMMA. This study demonstrated that this HA-PMMA composite is a good candidate for cranial bone implants due to its good osteoconductivity and biocompatibility.     

Bioactive polymethyl methacrylate-based bone cement: comparison of glass beads, apatite- and wollastonite-containing glass-ceramic, and hydroxyapatite fillers on mechanical and biological properties

A new bioactive bone cement (designated GBC) consisting of polymethyl methacrylate (PMMA) as an organic matrix and bioactive glass beads as an inorganic filler has been developed. The bioactive beads, consisting of MgO-CaO-SiO(2)-P(2)O(5)-CaF(2) glass, have been newly designed, and a novel PMMA powder was selected. The purpose of the present study was to compare this new bone cement GBC's mechanical properties in vitro and its osteoconductivity in vivo with cements consisting of the same matrix as GBC and either apatite- and wollastonite-containing glass-ceramic (AW-GC) powder (designated AWC) or sintered hydroxyapatite (HA) powder (HAC). Each filler added to the cements amounted to 70 wt %. The bending strength of GBC was significantly higher than that of AWC and HAC (p < 0.0001). Cements were packed into intramedullar canals of rat tibiae in order to evaluate osteoconductivity as determined by an affinity index. Rats were sacrificed at 2, 4, and 8 weeks after operation. An affinity index, which equaled the length of bone in direct contact with the cement expressed as a percentage of the total length of the cement surface, was calculated for each cement. At each time interval studied, GBC showed a significantly higher affinity index than AWC or HAC up to 8 weeks after implantation (p < 0.03). The value for GBC increased significantly with time up to 8 weeks (p < 0.006). The handling property of GBC was comparable with that of PMMA bone cement. Our study revealed that the higher osteoconductivity of GBC was due to the higher bioactivity of the bioactive glass beads at the cement surface and the lower solubility of the new PMMA powder to MMA monomer. In addition, it was found that the smaller spherical shape and glassy phase of the glass beads gave GBC strong enough mechanical properties to be useful under weight-bearing conditions. GBC shows promise as an alternative with improved properties to the conventionally used PMMA bone cement.     

Effects of ceramic component on cephalexin release from bioactive bone cement consisting of Bis-GMA/TEGDMA resin and bioactive glass ceramics

The purpose of this study was to elucidate the effect of amount of ceramic cement powder on drug release from bioactive bone cement. The associated bone-bonding strength was also investigated. The bioactive bone cement under investigation consisted of bisphenol-alpha-glycidyl methacrylate (Bis-GMA), triethylene-glycol dimethacrylate (TEGDMA) resin and a combination of apatite- and wollastonite-containing glass-ceramic (A-W GC) powder. A-W GC powder (50%, 70% and 80% w/w) containing 5% cephalexin (CEX) powder hardened within 5 min after mixing with Bis-GMA/TEGDMA resin. The compressive strength of the cement with or without drug increased with increasing the amount of ceramic powder. The compressive strength of the 80% ceramic cement without the incorporation of cephalexin was 194 MPa. This compressive strength was about 3 times higher than that for polymethylmethacrylate cement. After the cement was implanted in the proximal metaphysis of the tibiae of male rabbits, the failure load for the cement was found to increase with increasing of the amount of ceramic powder. This finding suggested that the cement formed a bonding with bone. In vitro CEX release from bioactive bone cement pellets in a simulated body fluid at pH 7.25 and 37 degrees C continued for more than 2 weeks. Drug release profile followed the Higuchi equation initially, but not at later stages. The drug release rate increased with increasing amount of ceramic powder in the mixture. Since the pore volume of the cement increased with increasing of amount of ceramic powder, the drug diffused in the pores between the ceramics particle and polymer matrix. As hydroxyapatite precipitated on the cement surface, the drug release rate decreased, as observed at the later release stage. These results suggest that varying the amount of ceramic powder in the cement system could control the drug release rate from bioactive bone cement.     

Evaluation of cytocompatibility and bending modulus of nanoceramic/polymer composites

In an attempt to simulate the microstructure and mechanical properties of natural bone, novel nanoceramic/polymer composite formulations were fabricated and characterized with respect to their cytocompatibility and mechanical properties. The bending moduli of nanocomposite samples of either poly(L-lactic acid) (PLA) or poly(methyl methacrylate) (PMMA) with 30, 40, and 50 wt % of nanophase (<100 nm) alumina, hydroxyapatite, or titania loadings were significantly (p < 0.05) greater than those of pertinent composite formulations with conventional, coarser grained ceramics. The nanocomposite bending moduli were 1-2 orders of magnitude larger than those of the homogeneous, respective polymer. For example, compared with 0.06 GPa for the 100% PLA, the bending modulus of 50/50 nanophase alumina/PLA composites was 3.5 GPa. Osteoblast adhesion on the surfaces of the nanophase alumina/PLA composites increased as a function of the nanophase ceramic content. Most importantly, osteoblast adhesion on the 50/50 nanophase alumina/PLA substrates was similar to that observed on the 100% nanophase ceramic substrates. Similar trends of osteoblast adhesion were observed on the surfaces of the nanophase titania/polymer and nanophase hydroxyapaptite/polymer composites that were tested. In contrast, fibroblast adhesion on the nanophase composites was either similar or lower than that observed on the conventional composites with either PLA or PMMA and minimum on all tested neat nanophase substrates. The calcium content in the extracellular matrix of cultured osteoblasts was also enhanced on the nanoceramic/PLA composite substrates tested as a function of the nanophase ceramic loading and duration of cell culture. The results of the present in vitro study provide evidence that nanoceramic/polymer composite formulations are promising alternatives to conventional materials because they can potentially be designed to match the chemical, structural, and mechanical properties of bone tissue in order to overcome the limitations of the biomaterials currently used as bone prostheses.     

A new bioactive bone cement: effect of glass bead filler content on mechanical and biological properties.

A new bioactive bone cement (designated GBC), consisting of bioactive glass beads as an inorganic filler and polymethylmethacrylate (PMMA) as an organic matrix, has been developed. The purpose of the present study was to examine the effect of the amount of glass bead filler added to GBC on its mechanical and biological properties, and to decide the most suitable content of filler. Serial changes in GBC with time were also examined. The newly designed bioactive beads, consisting of MgO-CaO-SiO2-P2O5-CaF2 glass, were added to the cement in the proportions 30, 40, 50, 60, and 70 wt %. These cements were designated GBC30, GBC40, GBC50, GBC60, and GBC70, respectively. The compressive strength and the elastic modulus of bending of GBC increased as the glass bead content increased. The various types of GBC were packed into the intramedullar canals of rat tibiae to evaluate osteoconductivity, as determined by an affinity index calculated as the length of bone in direct contact with the cement expressed as a percentage of the total length of the cement surface. Rats were killed at 4 and 8 weeks after the operation and the affinity index was calculated for each type of GBC. Histologically, new bone had formed along the surface of all types of GBC within 4 weeks, even in GBC30 containing only 30 wt % of glass beads. At each time interval studied, there was a trend for the affinity index of GBC to increase as the glass bead filler content increased. There was no significant increase of affinity index between GBC60 and GBC70. The affinity indices for all types of GBC increased significantly with time up to 8 weeks. The handling properties of GBC were comparable to those of conventional PMMA bone cement. We conclude that when mechanical properties and osteoconductivity are both taken into consideration, GBC60 is the most suitable formulation; it shows excellent osteoconductivity and sufficient mechanical strength for clinical use.     

Porcine-derived xenogeneic bone/poly(glycolide-co-lactide-co-caprolactone) composite and its affinity with rat OCT-1 osteoblast-like cells

Porcine-derived xenogeneic bone (PDXB) was derived from cancellous bone of adult porcine. Its morphology and structure were characterized by SEM, FTIR and XRD. A series of composite films consisting of PDXB and poly(glycolide-co-lactide-co-caprolactone) (PGLC) polymer were prepared. Because of the introduction of PGLC polymer, the PDXB/PGLC composites especially PDXB/PGLC(30/70) and PDXB/PGLC(50/50) showed good processability and mechanical properties. In addition, the hydrophilicity of the composites was enhanced as well since the PDXB component was hydrophilic. Osteoblast-like cells (OCT-1) were used as an in-vitro model to assess the affinity of the PDXB/PGLC composites. It was found that compared with the pure PGLC film, PDXB/PGLC(30/70) and PDXB/PGLC(50/50) composite films promoted cell attachment, proliferation and ALP (alkaline phosphatase) activity obviously. In addition, the cells preferred growing on the areas of exposed PDXB. It was considered that the hydrophilicity, osteoconductivity and appropriate surface roughness (Sa=3.30, 4.00 microm) induced by PDXB facilitate cell growth. However, the introduction of too much PDXB, such as PDXB/PGLC(70/30) film, would obtain an adverse effect on the cell growth since the value of Sa was up to 7.33 microm. It indicated that only the composites with appropriate surface topography could favor cell growth. Surface topography probably has a more important effect on cell growth process than surface chemistry.     

In vivo evaluation of a novel porous hydroxyapatite to sustain osteogenesis of transplanted bone marrow-derived osteoblastic cells

Biosynthetic bone grafts are considered to contain one or more of three critical components: osteoprogenitor cells, an osteoconductive matrix, and osteoinductive growth factors. The basic requirements of the scaffold material are biocompatibility, mechanical integrity, and osteoconductivity. A major design problem is satisfying these requirements with a single composite. In this study, we hypothesize that one composite that combines bone marrow-derived osteoblasts and a novel mechanical reinforced porous hydroxyapatite with good biocompatibility and osteoconductivity (HA/BMO) can reach these requirements. A novel sintered porous hydroxyapatite (HA) was prepared by the following procedures. The HA slurry was foamed by adding polyoxyethylenelaurylether (PEI) and mixing. The pores were fixed by crosslinking PEI with diepoxy compounds and the HA porous body was sintered at 1200 degrees C for 3 h. The HA sintered porous body had a high porosity (77%), and was completely interconnected. Average pore diameter was 500 microm and the interconnecting path 200 microm in diameter. The compressive (17 MPa) and three-point bending (7 MPa) strengths were high. For in vivo testing, the 2-week subcultured HA/BMO (+) composites were implanted into subcutaneous sites of syngeneic rats until 8 weeks after implantation. These implants were harvested at different time points and prepared for the biochemical analysis of alkaline phosphatase activity (ALP) and bone osteocalcin content (OCN), and histological analysis. ALP and OCN in the HA/BMO group were much higher than those in the HA without BMOs control group 1 week after implantation (p < 0.001). Light microscopy revealed mature bone formation in the HA/BMO composite 4 weeks after implantation. In the SEM study, mineralized collagenous extracellular matrix was noted in HA/BMO composite 2 weeks after implantation with numbers of active osteoblasts. We conclude that the composite of the novel HA and cultured BMOs has osteogenic ability in vivo. These results provide a basis for further studies on the use of this composite as an implant in orthopaedic surgery.     

The biocompatibility and osteoconductivity of a cement containing beta-TCP for use in vertebroplasty

A new composite bone cement designated "G2B1" was developed for percutaneous transpedicular vertebroplasty. G2B1 contains beta tricalcium phosphate particles and methylmethacrylate-methylacrylate copolymer as the powder components, and methylmethacrylate, urethane dimethacrylate, and tetrahydrofurfuryl methacrylate as the liquid components. Biocompatibility and osteoconductivity were evaluated using scanning electron microscopy, contact microradiography, and Giemsa surface staining 4, 8, 12, 26, and 52 weeks after implantation into rat tibiae. To evaluate osteoconductivity, affinity indices (%) were calculated. Scanning electron microscopy and contact microradiography revealed that bone contact with G2B1 was attained within 4 weeks (affinity index: 50.2 +/- 11.8 at 4 weeks) and at most of the margin within 26 weeks (affinity index: 87.4 +/- 7.2 at 26 weeks). Specifically, G2B1 contacted bone via a wide calcium-phosphate-rich layer, and its degradation started within 8 weeks, mainly in the marginal area. Giemsa surface staining showed that there was almost no inflammatory reaction around the G2B1. These results indicate that G2B1 is a biocompatible and osteoconductive bone cement.     

Bioactive bone cement: effects of phosphoric ester monomer on mechanical properties and osteoconductivity

A new bioactive bone cement, designated GBC, has been developed. It consists of polymethyl methacrylate (PMMA) as an organic matrix and bioactive glass beads as an inorganic filler. The bioactive beads, consisting of MgO--CaO--SiO(2)--P(2)O(5)--CaF(2) glass, have been newly designed, and a novel PMMA powder was selected. The purpose of the present study was to evaluate the effects on mechanical properties and osteoconductivity of adding a phosphoric ester (PE) monomer to the cement as an adhesion-promoting agent. Four kinds of cements were prepared: GBC, GBC with PE (designated GBC/PE), a cement consisting of the same PMMA used in GBC with apatite- and wollastonite-containing glass-ceramic (AW-GC) powder (designated AWC), and AWC with PE (designated AWC/PE). Each filler was added to the cement at 70 wt %. Adding PE to either GBC or AWC resulted in increases in the bending strength and decreases in the Young's modulus compared with the unmodified cements. Cements were packed into the intramedullar canals of rat tibiae to evaluate osteoconductivity as determined by an affinity index. Rats were sacrificed at 4 and 8 weeks after operation. The affinity index (length of bone in direct contact with the cement expressed as a percentage of the total length of the cement surface) was calculated for each cement. Adding PE to either GBC or AWC resulted in significant increases in the affinity index compared with the unmodified cements. The affinity index for GBC was significantly higher than that of AWC, and that for GBC/PE was also significantly higher than that of AWC/PE. The affinity indices for each cement increased significantly with time up to 8 weeks. Our study revealed that the higher osteoconductivity of GBC/PE was due to the large alkyl group in the PE monomer, to the hydrophilicity of the phosphoric acid in the PE monomer, and to the higher bioactivity of the bioactive glass beads at the cement surface. GBC/PE shows promise as an alternative bone cement with improved properties compared with conventional PMMA bone cement.     

Transmission electron microscopic study of interface between bioactive bone cement and bone: comparison of apatite and wollastonite containing glass-ceramic filler with hydroxyapatite and beta-tricalcium phosphate fillers.

We developed a bioactive bone cement that consists of apatite and wollastonite containing glass-ceramic (AW-GC) powder and bisphenol-a-glycidyl methacrylate (Bis-GMA) based resin. In this study, we made three types of cement (designated AWC, HAC, and TCPC) consisting of either AW-GC, hydroxyapatite (HA), or beta-tricalcium phosphate (beta-TCP) powder as the inorganic filler and Bis-GMA based resin as the organic matrix. These cements were implanted into rat tibiae and cured in situ. Specimens were prepared 1, 2, 4, and 8 weeks after the operation and observed using transmission electron microscopy. Each of the bone cements was in direct contact with the bone. In AWC-implanted tibiae, the uncured surface layer of Bis-GMA based resin was completely filled with newly formed bone-like tissue 2 weeks after implantation. The AW-GC particles were surrounded by bone and were in contact with bone through an apatite layer. No intervening soft tissue was seen. In HAC-implanted tibiae, it took 4 weeks for the uncured layer to completely fill with newly formed bonelike tissue. The HA particles were also in contact with bone through an apatite layer. In TCPC-implanted tibiae, it took 8 weeks for the uncured layer to fill with newly formed bone-like tissue. The new bone that formed on the TCPC was not as dense as that on the AWC or HAC, and an intervening apatite layer was not evident. Results indicated that AWC had higher bioactivity than either HAC or TCPC.