Relative influence of composition and viscosity of acrylic bone cement on its apparent fracture toughness

The composition and viscosity of an acrylic bone cement have both been identified in the literature as being parameters that affect the mechanical properties of the material and, by extension, the in vivo longevity of cemented arthroplasties. The objective of the present study was to determine the relative influence of these parameters on a key cement mechanical property; namely, its fracture toughness. Two sets of cements were selected purposefully to allow the study objective to be achieved. Thus, one set comprised two cements with very similar compositions but very different viscosities (Cemex RX, a medium-viscosity brand, and Cemex Isoplastic, a high-viscosity brand) while the other set comprised two cements with similar viscosities but with many differences in composition (Cemex Isoplastic and CMW 1). Values of the fracture toughness (as determined using chevron-notched short rod specimens) [K(ISR)] obtained for Cemex RX and Cemex Isoplastic were 1.83 +/- 0.12 and 1.85 +/- 0.12 MPa square root(m), respectively, with the difference not being statistically significant. The K(ISR) values obtained for Cemex Isoplastic and CMW 1 were 1.85 +/- 0.12 and 1.64 +/- 0.18 MPa square root(m), respectively, with the difference being statistically significant. Thus, the influence of cement composition on its K(ISR) is more marked relative to the influence of cement viscosity. Explanations of this finding are offered, together with comments on the implications of the results for the in vivo longevity of cemented arthroplasties.     

Comparison of the mechanical properties of Simplex P, Zimmer Regular, and LVC bone cements

The mechanical properties of the three cement preparations most widely used in the United States were compared by conducting tensile and fatigue tests on Simplex P, LVC, and Zimmer Regular bone cements. Specimens of all three cement preparations were prepared for mechanical testing with and without centrifugation of the cement immediately after mixing. Although the results of the tensile testing revealed a few specific instances of significant differences in the tensile properties of the three cement preparations, there was no consistent evidence that one cement was superior in tension to the others. However, the fatigue properties of Simplex P were consistently and significantly superior to the fatigue properties of both LVC and Zimmer Regular bone cements. Centrifugation of the cement immediately after mixing significantly improved both the tensile and fatigue properties of all three bone cements. However, the fatigue strength of centrifuged Simplex P was substantially and significantly superior to the fatigue strength of the centrifuged LVC and Zimmer Regular bone cements. Since in total joint replacements bone cement is subjected to cyclic loading, these data suggest that centrifuged Simplex P is a preferable bone cement to LVC and to Zimmer Regular cement with or without centrifugation.     

Platelet activation after in vitro contact with seven acrylic bone cements

Seven acrylic bone cements were evaluated: Cemex Rx (Tecres S.p.a., Italy), Cemex Isoplastic (Tecres S.p.a., Italy), Zimmer Low Viscosity Cement (L.V.C. , Zimmer, IN, USA), Zimmer bone cement—dough type (Zimmer, IN, USA), CMW 3 (DePuy International Ltd., UK), Cerim LT (Cremascoli S.r.l., Italy), and Palacos R (Merck, Wehreim, Germany). The cements after polymerization were put in contact in vitro with platelet-rich plasma. Plasma in contact only with siliconated glass was used as the negative control. After contact, platelet number, β-thromboglobulin (β-TG), and transforming growth factor-β1 (TGF-β1) were determined. The Wilcoxon signed rank test showed Palacos R and L.V.C. induced a significant decrease of platelet number compared with the negative control. All cements determined a significant increase in β-TG. CMW 3 , Palacos , L.V.C. , and Zimmer dough type determined a significant increase in TGF-β1 compared with the negative control.     

Platelet activation after in vitro contact with seven acrylic bone cements

Seven acrylic bone cements were evaluated: Cemex Rx (Tecres S.p.a., Italy), Cemex Isoplastic (Tecres S.p.a., Italy), Zimmer Low Viscosity Cement (L.V.C., Zimmer, IN, USA), Zimmer bone cement - dough type (Zimmer, IN, USA), CMW (DePuy International Ltd., UK), Cerim LT (Cremascoli S.r.l., Italy), and Palacos (Merck, Wehreim, Germany). The cements after polymerization were put in contact in vitro with platelet-rich plasma. Plasma in contact only with siliconated glass was used as the negative control. After contact, platelet number, beta-thromboglobulin (beta-TG), and transforming growth factor-beta1 (TGF-beta1) were determined. The Wilcoxon signed rank test showed Palacos R and L.V.C. induced a significant decrease of platelet number compared with the negative control. All cements determined a significant increase in beta-TG. CMW 3, Palacos, L.V.C., and Zimmer dough type determined a significant increase in TGF-beta1 compared with the negative control.     

Tensile characteristics of ten commercial acrylic bone cements

The mechanical properties of acrylic bone cement, used in orthopedic surgery, are very influential in determining successful long-term stability of a prosthesis. A large number of commercial formulations are available, differing in chemical composition and physical properties of both powder and monomer constituents. In this study, the static and dynamic tensile characteristics of a number of the most commonly used bone cements (Palacos R, Simplex P, CMW 1 & 3, Sulfix-60, Zimmer Dough), along with some newer formulations (Endurance, Duracem 3, Osteobondtrade mark and Boneloc), have been investigated under the same testing regimes. Testing was performed in air at room temperature. Significant differences in both static and fatigue properties were found between the various bone cements. Tensile tests revealed that Palacos R, Sulfix-60, and Simplex P had the highest values of ultimate tensile strength, closely followed by CMW 3, while Zimmer Dough cement had the lowest strength. Fatigue testing was performed under stress control, using sinusoidal loading in tension-tension, with an upper stress level of 22MPa. The two outstanding cements when tested in these cyclic conditions were Simplex P and Palacos R, with the highest values of Weibull median cycles to failure. Boneloc bone cement demonstrated the lowest cycles to failure. While the testing regimes were not designed to replicate exact conditions experienced by the bone cement mantle in vivo, there was a correlation between these results and clinical outcome.     

Graft copolymers of methyl methacrylate and poly([R]-3-hydroxybutyrate) macromonomers as candidates for inclusion in acrylic bone cement formulations: Compression testing

Graft copolymers of methyl methacrylate and biodegradable, biocompatible bacterial poly([R]-3-hydroxybutyrate) (PHB) blocks were synthesized and evaluated as possible constituents in acrylic bone cements for use in orthopaedic applications. The copolymers were produced by conventional free radical copolymerization and incorporated in one commercially available acrylic bone cement brand, Antibiotic Simplex (AKZ). Cements with formulations containing 6.7 and 13.5 wt % of PMMA-graft-PHB were prepared. The morphology of the graft copolymer particles was suggested to influence the ability of the modified cement to be processed. Formulations containing more than about 20 wt % of the graft copolymer resulted in cement doughs that, both after first preparation and several hours later, were either sandy or soft spongy in texture and, thus, would be unacceptable for use in orthopaedic applications. The morphologies of the powders and the volumetric porosity (p) and ultimate compressive strength (UCS) of the cured cements were determined. Micro computed tomography showed that the cements presented average porosities of 13.5-16.9%. It was found that, while the powder particle shape and size for the experimental cements were markedly different from those of AKZ, there was no significant difference in either p or UCS for these cements. The latter was determined to be about 85 MPa for the modified cements and 84 MPa for Antibiotic Simplex. Furthermore, the UCS of all the cements exceeded the minimum level for acrylic bone cements, as stipulated by ASTM F-451.     

Influence of antibiotic impregnation on the fatigue life of Simplex P and Palacos R acrylic bone cements, with and without centrifugation

The fatigue properties of Simplex P and Palacos R bone cements were compared to their antibiotic impregnated counterparts AKZ* and Palacos R with gentamycin. The effect of porosity reduction by centrifugation of all four cement types was also assessed. Fifteen specimens of each cement type were prepared according to manufacturer's instructions and 15 additional specimens of each cement type were prepared by mixing the powder with chilled monomer (0 degrees C) and then centrifuging the cement immediately after mixing. Fifteen fully reversed tension-compression fatigue tests were performed at 15 MPa in stress control for each cement preparation in vitro while simulating the in vivo state (37 degrees C and 100% humidity). The number of cycles to failure were recorded. There was no significant difference in the fatigue life of Palacos R and Simplex P when both cements were prepared in the standard fashion. The addition of 1/2 g of gentamycin to Palacos R did not significantly alter its fatigue properties. The addition of 0.5 g of erythromycin and 0.24 g of colistin did not decrease the fatigue life of Simplex P. Centrifugation significantly improved the fatigue properties of Simplex P and AKZ. The fatigue lives of Palacos R and Palacos R with gentamycin were not improved by centrifugation. The fatigue life of centrifuged Simplex P was significantly greater than the fatigue life of Palacos R and of Palacos R with gentamycin, whether the Palacos R based cements were centrifuged or not.     

Antibiotic bone cement for the treatment of Pseudomonas aeruginosa in joint arthroplasty: comparison of tobramycin and gentamicin-loaded cements

One hundred clinical isolates of Pseudomonas aeruginosa were collected from 22 medical centers throughout Europe and were challenged with two aminoglycoside-loaded bone cements, employing a modified in vitro Kirby-Bauer susceptibility model. The results of this study show that Simplex P with tobramycin exhibits antibacterial activity against 98% of the strains tested, compared to 93% for Palacos with gentamicin. Additionally, for strains that were susceptible to the antibiotic bone cement formulations, the average zone of inhibition produced around the tobramycin-loaded cement disks was approximately 25% greater than that seen around the gentamicin-loaded cement disks. This difference was statistically significant (p < 0.01). Tobramycin-loaded bone cement is therefore the preferred formulation when addressing Pseudomonas aeruginosa in septic joint arthroplasty.     

Preparation of epoxy-SiO2 hybrid sol-gel material for bone cement

An organic-inorganic hybrid material, epoxy-SiO(2), was prepared by incorporating epoxy structure units covalently into a SiO(2) glass network via the sol-gel approach. The precursor was obtained by the reaction of diglycidyl ether of bisphenol A (DGEBA) with 3-aminopropyl trimethoxysilane (APTS). The precursor was then hydrolyzed and co-condensated with tetraethyl orthosilicate (TEOS) in tetrahydrofuran (THF) at room temperature to yield epoxy-SiO(2) hybrid sol-gel material having a 50 wt % SiO(2) content. Thermal properties of the hybrid material were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The hybrid sol-gel material epoxy-SiO(2) was the solid, powder component of bone cement. The liquid component contains bis-phenol-A glycidyl methacrylate (Bis-GMA), triethyleneglycol dimethacrylate (TEGDMA), and methyl methacrylate (MMA) with 25, 55, and 20 vol %, respectively. We discuss the comparison between the new epoxy-SiO(2) bone cement and the commercial Simplex P bone cement. Mechanical properties such as Young's modulus, compressive strength, hardness, and impact strength of the new epoxy-SiO(2) bone cement exceeded those of Simplex P bone cement. The tensile and bending strengths of the new epoxy-SiO(2) bone cement were approximately the same as those of Simplex P bone cement. In order to evaluate the biocompatibility of the new bone cement, an MTT test and optical microscopy were conducted in cell culture. Results indicated that the new epoxy-SiO(2) bone cement exhibits very low cytotoxicity compared with Simplex P bone cement.     

Structural degradation of acrylic bone cements due to in vivo and simulated aging

Acrylic bone cement is the primary load-bearing material used for the attachment of orthopedic devices to adjoining bone. Degradation of acrylic-based cements in vivo results in a loss of structural integrity of the bone-cement-prosthesis interface and limits the longevity of cemented orthopedic implants. The purpose of this study is to investigate the effect of in vivo aging on the structure of the acrylic bone cement and to develop an in vitro artificial aging protocol that mimics the observed degradation. Three sets of retrievals are examined in this study: Palacos brand cement retrieved from hip replacements, and Simplex brand cement retrieved from both hip and knee replacement surgeries. In vitro aging is performed using oxidative and acidic environments on three acrylic-based cements: Palacos, Simplex, and CORE. Gel permeation chromatography (GPC) and Fourier transform infrared spectroscopy (FTIR) are used to examine the evolution of molecular weight and chemical species within the acrylic cements due to both in vivo and simulated aging. GPC analysis indicates that molecular weight is degraded in the hip retrievals but not in the knee retrievals. Artificial aging in an oxidative environment best reproduces this degradation mechanism. FTIR analysis indicates that there exists a chemical evolution within the cement due to in vivo and in vitro aging. These findings are consistent with scission-based degradation schemes in the cement. Based on the results of this study, a pathway for structural degradation of acrylic bone cement is proposed. The findings from this investigation have broad applicability to acrylic-based cements and may provide guidance for the development of new bone cements that resist degradation in the body.     

Effect of initiation chemistry on the fracture toughness, fatigue strength, and residual monomer content of a novel high-viscosity, two-solution acrylic bone cement.

Porous-free, two-solution bone cements have been developed in our laboratory as an alternative to commercial powder/liquid formulations. Each pair of solutions consist of poly(methyl methacrylate) (PMMA) powder dissolved in methyl methacrylate (MMA) monomer, with benzoyl peroxide (BPO) added to one solution as the initiator and N,N-dimethyl-p-toluidine (DMPT) added to the other as the activator. When mixed, the solutions polymerize via a free radical reaction, which is governed by the concentrations of initiator and activator and their molar stoichiometry. Previous work by the authors has demonstrated that these two-solution cement compositions are comparable to Simplex P bone cement in polymerization exotherm, setting time, and flexural mechanical properties. This study was designed to evaluate the effect of BPO and DMPT concentrations, along with their molar ratio, on the fracture toughness, fatigue strength, and residual monomer content of the experimental compositions. The results showed that fracture toughness and fatigue strength for the solution cements were comparable to Simplex P and were not significantly affected by the BPO concentration or the BPO:DMPT molar ratio; however, the highest DMPT concentration yielded significantly lower values for both variables. Residual monomer content was significantly affected by both the individual concentrations of BPO and DMPT and their molar ratios. The two-solution cements had significantly higher residual monomer contents versus Simplex P; however, this can be attributed to their higher initial monomer concentration rather than a lower degree of conversion.     

A simple method of determining the modulus of orthopedic bone cement

Accurate determination of the elastic modulus of surgical bone cements is of primary importance, when evaluating the stresses within the cement mantle in Total Joint Arthroplasty. This article presents a new method of determining the modulus of surgical bone cements from the biaxial flexural test. The biaxial flexural test is not currently employed in mainstream orthopedic mechanical testing, which is surprising because most loading in orthopedic applications is biaxial in nature. Nor has this method been utilized for dental materials, even though the biaxial flexure test has been used for many years in this field. It has been demonstrated that the modulus of surgical bone cements can be determined from the biaxial flexural test, and these results are in agreement with results from compressive and bending tests.     

Kinetic study of citric acid influence on calcium phosphate bone cements as water-reducing agent

Most of the research performed on calcium phosphate bone cements (CPBCs) has dealt with the improvement of bone cement formulations for new, demanding bone-filling applications. In particular, the development of injectable bone cements is of real interest for the biomedical community. The aim of this work was to study the effect of citric acid on the injectability and the setting properties of alpha-tricalcium phosphate-based cements. A comparative kinetic study was performed on cements with and without citric acid relating the hardening curves and the hydration rates using a mathematical approach. Citric acid behaved as a fluidificant during the first stages of the cement mixing. The dissolution-precipitation reactions of the alpha-tricalcium phosphate were retarded with the addition of citric acid and the compressive strength at saturation increased. In conclusion, citric acid can behave as a water-reducing admixture.     

A highly radiopaque vertebroplasty cement using tetraiodinated o-carborane additive

Bone cements for vertebroplasty must have a much better radiocontrast level than cements for knee or hip arthroplasty. This is generally accomplished by adding a relatively large portion of BaSO(4), although this affects the physical-mechanical and biological properties of the cement. This prompted us to develop an alternative radiopaque cement, on the basis of unique highly radiopaque methacrylic microspheres. These contain iodine in two modalities: (i) covalently linked to the methacrylic polymer, and (ii) as constituent of the stable tetraiodocarborane 8,9,10,12-I(4)-1,2-closo-C(2)B(10)H(8). The total iodine content in these particles exceeded 30% by mass. These radiopaque microspheres as well as the cement made thereof were characterized extensively, e.g., by scanning electron microscopy, X-ray contrast measurements, X-ray photoelectron spectroscopy, measurements of compressive strength, infrared spectroscopy, and solid state (11)B{(1)H} NMR spectroscopy. Furthermore, the new cement was subjected to several biocompatibility tests in vitro. The results show that the new bone cement fulfills all physico-chemical criteria for use in vertebroplasty. Further data on the cement's biocompatibility (in vitro), as well as on the handling parameters and doughviscosity, indicate that this material has a potential to become an alternative to vertebroplasty cements with a high BaSO(4) content. The new cement provides two significant advantages: (i) controlled viscosity in the dough phase, which facilitates precise injection during the vertebroplasty procedure; (ii) excellent structural stability, which precludes leaching of contrast post-implantation.     

聚甲基丙烯酸甲酯骨水泥与Cortoss骨水泥生物力学性能及聚合温度比较

背景：聚甲基丙烯酸甲酯骨水泥是其最常用的一种填充材料,但由于其存在聚合时放热、单体毒性等缺点,所以目前出现了以Cortoss为代表的生物新型骨水泥。 目的：对比两种骨水泥在体外的力学性能。 方法：将聚甲基丙烯酸甲酯与新型骨水泥Cortoss按照ISO5833:2002标准分别制作成抗压及抗弯模型,将制作的模型使用生物力学机测试两种骨水泥的抗弯及抗压模量,同时在制模过程中测量骨水泥聚合温度。 结果与结论：与聚甲基丙烯酸甲酯骨水泥比较,Cortoss骨水泥在聚合过程中最高温度较低、抗压强度较强、抗弯模量降低,差异均有显著性意义(P < 0.05),而抗弯强度间差异无显著性意义(P > 0.05)。说明Cortoss生物力学强度优于聚甲基丙烯酸甲酯骨水泥,由于Cortoss在聚合时放热较少,所以其用于手术时有较好的安全性。      

Effect of choice of surgical gloves on dough time measurements of acrylic bone cement

In this study we investigated the effect of the brand of surgical gloves on the dough time determination for acrylic bone cements. Four different brands of powder-free latex surgical gloves were tested. Two commercial bone cements, Surgical Simplex P and Palacos R, were used for dough time measurement following standard test methods for acrylic bone cements (ASTM F-451 and ISO 5833). The results show that the measured dough time depended largely on the brand of gloves used, and could vary by nearly 250%. The surface morphological structures of gloves, determined by SEM, probably contribute to the differences in the measured dough time. This study provides experimental evidence that supports the need to describe the type of gloves used, in detail, when dough time is reported. It also illustrates the importance of the glove brand, when bone cement is to be handled as a dough in the clinical setting.     

Comparative study of bone cements prepared with either HA or alpha-TCP and functionalized methacrylates

The properties of bone cements prepared with both hydroxyapatite (HA) and alpha-tricalcium phosphate (alpha-TCP) and methacrylates containing acidic or basic groups are the main interest of this article. The presence of methacrylic acid or diethyl amino ethyl methacrylate as comonomers in the bone cement and both ceramic types as filler were found not to affect the amount of residual monomer, which was generally less than 4.5 wt%. In contrast, setting times, maximum temperature, and glass transition temperature were found to be composition dependent. For samples with acidic comonomer, a faster setting time, a higher maximum temperature, and higher glass transition temperatures were observed compared to those with the basic comonomer. The presence of the fillers slightly increased the setting time but did not affect the other parameters. The mechanical properties of the filled bone cements depended mainly on composition and type of testing. Both HA or alpha-TCP filled systems fulfilled the minimum compressive strength required for bone cement application, although a significantly lower value was observed for the alkaline comonomer systems. The minimum bending strength was not satisfied by any of these formulations. The tensile and shear strength of these composites ranged from 20 to 37.9 and from 18 to 27 MPa, respectively. In all cases it was higher for bone cements containing methacrylic acid. The results of this study suggest that the properties of dry unfilled bone cements prepared with MAA are comparable to CMW 3 in mechanical terms but inferior in their setting properties.     

Characterization of bone cements prepared with functionalized methacrylates and hydroxyapatite

Bone cements prepared with methyl methacrylate and either methacrylic acid or diethyl amino ethyl methacrylate as comonomers were characterized by infrared spectroscopy, nuclear magnetic resonance, gel permeation chromatography, dynamic mechanical thermal analysis, and mechanical testing. Selected formulations containing these functionalized methacrylates were filled with hydroxyapatite and studied in terms of their properties in tension, compression and bending, and X-ray diffraction. It was found that residual monomer was not greatly affected by the presence of either acid or basic comonomers in the unfilled bone cements. In contrast, molecular weight, curing times, and glass transition temperature were composition dependent. For samples with acidic comonomer, a faster curing time, higher molecular weight, and higher glass transition temperatures were observed with respect to those with the basic comonomer. X-ray diffraction revealed that the crystalline structure was not affected by the nature of comonomer in the bone cement while scanning electron microscopy showed that hydroxyapatite remained as clusters in the bone cement.The mechanical properties of filled bone cements depended mainly on composition and type of testing. Hydroxyapatite-filled bone cements fullfilled the minimum compressive strength (70 MPa) required for bone cement use. However, the minimum tensile strength (30 MPa) was only fullfilled by cements prepared without comonomer and those containing methacrylic acid. The minimum bending strength requirement (50 MPa) was not satisfied by any of the formulations studied.     

硅酸钙-磷酸盐复合骨水泥的制备及其性能研究

分别以α-磷酸三钙（α—TCP）、磷酸四钙（TTCP）为基本原料，添加羟基磷灰石（HAP）、磷酸氢钙（DCPD）、碳酸钙（CaCO2）、氧化钙（CaO）等其它辅料，并与一定量的无定形硅酸钙（CaSiO3）进行复合，确定了钙磷比均为1．50的六种骨水泥配方，对其基本性能进行了研究。对固化骨水泥样品进行了Ringer’S模拟液浸泡实验，研究了浸泡液pH值、样品的抗压强度随浸泡时间的变化。结果表明：调和液0．25MK2HPO4／KH2PO4和无定形CaSiO3对骨水泥有促凝作用，缩短骨水泥的终凝时间，其中初凝时间为4～5．5min，终凝时间为18～19．5min；同时添加适量无定形CaSiO3可以显著提高骨水泥的抗压强度，其中添加适量无定形CaSiO3的以α—TCP为主要原料的骨水泥Ringer’s模拟液浸泡两周后抗压强度可达45．3MPa。     

Viscoelastic properties of injectable bone cements for orthopaedic applications: state-of-the-art review

Injectable bone cements (IBCs) are used for a variety of orthopaedic applications, examples being poly (methyl methacrylate) (PMMA) bone cements used for anchoring total joint replacements (TJRs) (high load-bearing application), PMMA bone cements used in the vertebral body augmentation procedures of vertebroplasty (VP) and balloon kyphoplasty (BKP) (medium load-bearing application), and calcium phosphate-based and calcium sulfate-based cements used as bone void fillers/bone graft substitutes (low load-bearing application). For each of these applications, the viscoelastic properties of the cement are very important. For example, (1) creep of the cement has an influence on the longevity of a cemented TJR (for example, creep allows the cement to remodel, thereby maximizing the contact area of the cement-bone interface and, hence, minimizing stress concentration at that interface); and (2) in VP and BKP, the likelihood of cement extravasation is directly related to the profile of the viscosity-versus-time elapsed from commencement of mixing of the cement. There are a few reviews of the literature on a number of viscoelastic properties of some IBCs but a comprehensive review of the literature on all viscoelastic properties of all IBCs is lacking. The objective of this contribution is to present such a review. In addition, a number of ideas for future study in the field of viscoelastic properties of IBCs are described.