Shuichi Shinzato

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 GBCs 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.

Biological and mechanical properties of PMMA-based bioactive bone cements

We reported previously that a bioactive PMMA-based cement was obtained by using a dry method of silanation of apatite-wollastonite glass ceramic (AW-GC) particles, and using high molecular weight PMMA particles. But handling and mechanical properties of the cement were poor (Mousa et al., J Biomed Mater Res 1999;47:336-44). In the present study, we investigated the effect of the characteristics of PMMA powder on the cement. Different cements containing different PMMA powders (CMW1, Surgical Simplex, Palacos-R and other two types of PMMA powders with Mw 270,000 and 1,200,000) and AW-GC filler in 70 wt% ratio except Palacos-R (abbreviated as B-CMW1 and B-Surg Simp, B-Palacos 50 [50 wt% AW-GC filler] and B-Palacos 70 [70 wt% AW-GC filler], B-270 and B-1200) were made. Dough and setting times of B-CMW1, B-Surg Simp B-270 and B-1200 were similar to the commercial CMW1 cement which did not contain bioactive powder (C-CMW1), but B-palacos which contained large PMMA beads with high Mw had delayed setting time. B-270 had the highest bending strength among the tested cements. After 4 and 8 weeks of implantation in the medullary canals of rat tibiae, the bone-cement interface was examined using SEM. The affinity index of B-1200 was significantly higher than the other types of cements. B-270 showed good combination of handling properties, high mechanical properties and showed higher bioactivity with minimal soft tissue interposition between bone and cement compared with commercial PMMA bone cement. This may increase the strength of the bone-cement interface and increase the longevity of cemented arthroplasties.

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.

Bioactive bone cement : Effect of silane treatment on mechanical properties and osteoconductivity

A novel bioactive bone cement (GBC) was developed with newly designed bioactive MgO-CaO-SiO(2)-P(2)O(5)-CaF(2) glass beads as the inorganic filler and high molecular weight poly(methyl methacrylate) as the organic matrix. The purpose of this study was to examine the relationship between the amount of the silane coupling agent (gamma-methacryloxy propyl trimethoxy silane) used to treat the glass beads and the mechanical and biological properties of the resultant bone cement. Serial changes in the cement over time were also investigated. Five different kinds of cement, in which the glass beads were treated with different amounts of the coupling agent, were prepared. The quantities of the coupling agent were 0 (control), 0.1, 0.2, 0.5, and 1.0% (w/w) of the glass beads, and the cements were designated GBCs0, GBCs0.1, GBCs0.2, GBCs0.5, and GBCs1.0, respectively. After soaking in water at 75 degrees C for 5 days, GBCs0.1 and GBCs0.2 had significantly higher bending strengths than the other cements. Each GBC was packed into intramedullar canals of rat tibiae to evaluate osteoconductivity, as determined by affinity indices. Rats were killed 4 and 8 weeks after the operation. The affinity index was calculated for each GBC and equaled the length of bone in direct contact with the cement and was expressed as a percentage of the total length of the cement surface. Histologically, new bone had formed along all of the GBC surfaces within 4 weeks. At each time interval, a decreasing trend in the affinity index of GBC was found as the amount of the coupling agent increased. At 8 weeks, no significant change in the affinity index occurred when the amount of the coupling agent increased from 0 to 0.2%, whereas a significant decrease in the affinity index was observed when the amount of the coupling agent increased from 0 to 0.5 or 1.0%. The affinity indices for all the GBCs increased significantly up to 8 weeks. When both the mechanical properties and osteoconductivity were taken into consideration, GBCs0.1 and GBCs0.2 were the best cements, and they showed excellent osteoconductivity and strong enough mechanical properties for clinical use.

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.

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.

Bioactive bone cement: Effects of phosporic 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 Youngs 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.

Bioactive bone cement: effect of filler size on mechanical properties and osteoconductivity.

A bioactive bone cement (designated GBC), consisting of bioactive glass beads as an inorganic filler and poly(methyl methacrylate) (PMMA) as an organic matrix, has been developed. The purpose of the present study was to examine the effect of the size of the glass beads added as a filler to GBC on its mechanical properties and osteoconductivity. Serial changes in GBC with time were also examined. Four different sizes of beads (mean diameters 4, 5, 9, and 13 microm) consisting of MgO-CaO-SiO(2)-P(2)O(5)-CaF(2) glass were added to four GBC mixes in a proportion of 70 wt %. The bending strength of GBC increased as the mean size of the glass beads decreased. The four GBC mixes were packed into the intramedullary canals of rat tibiae to evaluate osteoconductivity, as determined by an affinity index. Rats were sacrificed at 4 and 8 weeks after surgery. The affinity index, which equaled the length of bone in direct contact with the cement surface expressed as a percentage of the total length of the cement surface, was calculated for each cement at each interval. Histologically, new bone had formed along the surface of all types of GBC within 4 weeks. At each time interval, there was a trend for the affinity index of GBC to increase as the mean glass bead size decreased. 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 concluded that, considering both mechanical properties and osteoconductivity, GBC made with smaller sized glass beads as filler was the most suitable cement. GBC shows promise as an alternative bone cement with improved properties compared to conventional PMMA bone cement.

Alumina powder/bis-GMA composite : Effect of filler content on mechanical properties and osteoconductivity

Three composites consisting of alumina powder dispersed in a bisphenol-a-glycidyl methacrylate (Bis-GMA) matrix were prepared and evaluated to assess the effect of alumina powder content on the mechanical properties and osteoconductivity of the composite. The alumina powder composites (APC) consisted of alumina powder (AL-P) as the inorganic filler dispersed in a Bis-GMA matrix that was solidified by a radical polymerization process. Prior to polymerization the AL-P was mixed with the monomers in proportions of 50%, 70%, and 80% by weight (APC50, APC70, and APC80). A fused silica-glass-filled composite containing 70% glass by weight (SGC70) was used as a control. The compressive and bending strengths, the elastic modulus in bending, and the bending strain of the composites increased as the AL-P content increased. We also evaluated the composites in vivo by implanting them into the medullary canals of rat tibiae. To compare the osteoconductivity of the composites, an affinity index was calculated for each composite; the affinity index equals the length of a bone in direct apposition to the composite and is expressed as a percentage of the total length of the composite surface. Microradiographic examination for periods of up to 26 weeks after implantation revealed that APC50, APC70, and APC80 all exhibited excellent osteoconductivity and made direct contact with the bone with no interposed soft tissues. However, the higher the AL-P content of the composite, the higher the osteoconductivity, especially at 4 weeks after the operation. Moreover, the amount of bone directly apposed to the composite surface increased with time. In contrast, little bone formation was seen on the surface of SGC70, even after 26 weeks. Observation by scanning electron microscope-energy dispersive X-ray microanalysis demonstrated that bone made direct contact with the APC surface through a layer containing calcium, phosphorus, and alumina powder. These results suggest that APC shows promise as a basis for developing mechanically strong and highly osteoconductive composites.

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.