Contact killing antimicrobial acrylic bone cements: preparation and characterization

Novel antimicrobial poly(methyl methacrylate) (PMMA)-based bone cement was synthesized by co-polymerizing PMMA/MMA with various percentages of quaternary amine dimethacrylate (QADMA) by free radical bulk polymerization technique at room temperature using benzoyl peroxide and N,N-dimethyl-p-toulidine (DMPT) as a redox initiator. The modified bone cement was characterized by FT-IR and 1H-NMR spectral studies. The thermal and physical properties of the bone cements of varying composition of QADMA were evaluated by thermogravimetric analysis (TGA), differential calorimetry (DSC) and contact angle measurements. Peak exothermic temperature was observed to decrease, while setting time increased with increase in QADMA content in the bone cement formulations. The antibacterial activity of the synthesized bone cement containing quaternary amine dimethacrylate against Escherichia coli and Staphylococcus aureus was studied by zone of inhibition, colony count method and scanning electron microscopy (SEM). QADMA containing acrylic bone cement showed a broad spectrum of contact killing antimicrobial properties. Retention of E. coli onto the surface of PMMA bone cement was observed, whereas there was complete prevention of retention of E. coli onto the modified PMMA bone cement with 15% QADMA. The studies were compared with the acrylic bone cement synthesized using 15% N-vinyl-2-pyrrolidone (NVP) in place of QADMA to which iodine was added as an antimicrobial agent during co-polymerization.     

Contact killing antimicrobial acrylic bone cements: preparation and characterization

Novel antimicrobial poly(methyl methacrylate) (PMMA)-based bone cement was synthesized by co-polymerizing PMMA/MMA with various percentages of quaternary amine dimethacrylate (QADMA) by free radical bulk polymerization technique at room temperature using benzoyl peroxide and N, N-dimethyl-p-toulidine (DMPT) as a redox initiator. The modified bone cement was characterized by FT-IR and ¹H-NMR spectral studies. The thermal and physical properties of the bone cements of varying composition of QADMA were evaluated by thermogravimetric analysis (TGA), differential calorimetry (DSC) and contact angle measurements. Peak exothermic temperature was observed to decrease, while setting time increased with increase in QADMA content in the bone cement formulations. The antibacterial activity of the synthesized bone cement containing quaternary amine dimethacrylate against Escherichia coli and Staphylococcus aureus was studied by zone of inhibition, colony count method and scanning electron microscopy (SEM). QADMA containing acrylic bone cement showed a broad spectrum of contact killing antimicrobial properties. Retention of E. coli onto the surface of PMMA bone cement was observed, whereas there was complete prevention of retention of E. coli onto the modified PMMA bone cement with 15% QADMA. The studies were compared with the acrylic bone cement synthesized using 15% N-vinyl-2-pyrrolidone (NVP) in place of QADMA to which iodine was added as an antimicrobial agent during co-polymerization.     

The effect of cross-linking agents on acrylic bone cements containing radiopacifiers.

Poly(methylmethacrylate) PMMA, based cements are the most widely used bone cements in joint replacement surgery. Although, there are some disadvantages in the use of these cements, the clinical success rate is fairly high. Intrinsic radiopacity is difficult to achieve in these cements due to the constituent elements of the PMMA polymer. As radiopacity is an essential requirement, PMMA bone cements have been rendered radiopaque by blending heavy metal ion salts, which tend to adversely affect the mechanical and biological properties of the bone cement. In this study, dimethacrylate cross-linking agents were added to the monomer phase in order to generate a cross-linked matrix, with barium sulphate as a radiopaque agent. The results suggest that the mechanical properties can be improved or retained with the addition of such cross-linking agents.     

Characterization of new acrylic bone cements prepared with oleic acid derivatives

Acrylic bone-cement formulations were prepared with the use of a new tertiary aromatic amine derived from oleic acid, and also by incorporating an acrylic monomer derived from the same acid with the aim of reducing the leaching of toxic residuals and improving mechanical properties. 4-N,N dimethylaminobenzyl oleate (DMAO) was used as an activator in the benzoyl-peroxide radical cold curing of polymethyl methacrylate. Cements that contained DMAO exhibited much lower polymerization exotherm values, ranging between 55 and 62 C, with a setting time around 16--17 min, depending on the amine/BPO molar ratio of the formulation. On curing a commercial bone cement, Palacosreg R with DMAO, a decrease of 20 C in peak temperature and an increase in setting time of 7 min were obtained, the curing parameters remaining well within limits permitted by the standards. In a second stage, partial substitution of MMA by oleyloxyethyl methacrylate (OMA) in the acrylic formulations was performed, the polymerization being initiated with the DMAO/BPO redox system. These formulations exhibited longer setting times and lower peak temperatures with respect to those based on PMMA. The glass transition temperature of the experimental cements were lower than that of PMMA cement because of the presence of long aliphatic chains of both activator and monomer in the cement matrix. Number average molecular weights of the cured cements were in the range of 1.2x10(5). PMMA cements cured with DMAO/BPO revealed a significant (p<0.001) increase in the strain to failure and a significant (p<0.001) decrease in Young's modulus in comparison to Palacosreg R, whereas ultimate tensile strength remained unchanged. When the monomer OMA was incorporated, low concentrations of OMA provided a significant increase in tensile strength and elastic modulus without impairing the strain to failure. The results demonstrate that the experimental cements based on DMAO and OMA have excellent promise for use as orthopaedic and/or dental grouting materials.     

Radiopacity in bone cements using an organo-bismuth compound

In a joint replacement surgery it is vital for bone cement to be radiologically detectable. Consequently, heavy metal salts of barium and zirconia are incorporated as a contrast medium for this purpose. The addition of such particulate additives, however, can be detrimental to some of the physical, mechanical and biological properties. The present study reports the feasibility of using an organo-bismuth compound, namely. triphenyl bismuth (TPB) as a radiopaque agent for orthopaedic bone cements. TPB was incorporated in the bone cement matrix by two methods, (i) blending: TPB was added to the polymer phase of the bone cement and (ii) dissolution: by dissolving TPB in the monomer phase methylmethacrylate. The results showed that the inclusion of TPB at concentrations of 15% and 25% by weight of the polymer, in the bone cement matrix did not affect the polymerisation exotherm temperature and setting time. Furthermore, the addition of TPB via the dissolution method provided a statistically significant increase in the strain to failure in comparison to commercial acrylic cements containing barium sulphate, thus reducing the brittleness of the cement. The detrimental effects on the mechanical properties post conditioning in water, was also much less pronounced in the homogeneous TPB cements in comparison to barium sulphate containing cements. These observations can be attributed to the formation of a homogeneous and continuous matrix of the resultant bone cement with a much lower porosity.     

Mechanical and histological evaluation of a PMMA-based bone cement modified with gamma-methacryloxypropyltrimethoxysilane and calcium acetate

Polymethylmethacrylate (PMMA) bone cement is widely used for prosthetic fixation in orthopaedic surgery; however, the interface between bone and cement is a weak zone. We developed a bioactive PMMA cement through modification with gamma-methacryloxypropyltrimethoxysilane (MPS) and calcium acetate. The purpose of this study was to compare the handling, mechanical and histological properties of the modified bone cement with those of the conventional cement. The modified specimens exhibited higher bonding strength between bone and implant. Histological observation and micro-focus X-ray computed tomogram (micro-CT) images showed that the modified cement exhibited osteoconduction, which the conventional PMMA bone cement lacked. The modification was found to be effective in enabling osteoconduction with PMMA bone cement, thus providing stable fixation for a long period after implantation.     

Surface and chemical properties of surface-modified UHMWPE powder and mechanical and thermal properties of it impregnated PMMA bone cement, III: effect of various ratios of initiator/inhibitor on the surface modification of UHMWPE powder

From our previous study, 3 wt% of ultra-high-molecular-weight polyethylene (UHMWPE) powder surface-modified by various ratios of methyl methacrylate (MMA) and poly(methyl methacrylate) (PMMA) solution was impregnated to improve the poor mechanical and thermal properties of conventional PMMA bone cement. In this study, various amounts of benzoyl peroxide (BPO) and hydroquinone were used for the adhesion reinforcement of UHMWPE powder with PMMA polymerized from MMA monomer (polyMMA) by the mixture of BPO and hydroquinone and ultimately to strengthen the poor mechanical and thermal properties of conventional PMMA bone cement. The tensile strengths of 3 wt% of UHMWPE powders surface-precoated with polyMMA prepared by various amounts of BPO- and hydroquinone-impregnated composite PMMA bone cements were similar to that of conventional PMMA bone cement. In particular, 3 wt% of UHMWPE powder surface precoated with polyMMA prepared with 0.75 wt% of BPO and 300 ppm of hydroquinone impregnated composite PMMA bone cement revealed the maximum tensile strength. However, no obvious significant difference was revealed, although the curing temperatures of the composite PMMA bone cements decreased from 103 degrees C to 91-97 degrees C. From these results, it was determined that the mixture of BPO and hydroquinone plays an important role in improving the poor mechanical properties of conventional PMMA bone cement. However, the thermal properties of the composite PMMA bone cements were not remarkably improved. The mechanical, chemical and thermal properties were individually confirmed using a scanning electron microscope (SEM), universal transverse mercator (UTM), Fourier transform infrared-attenuated total reflectance (FT-IR-ATR) and digital thermometer, respectively.     

Properties of an injectable low modulus PMMA bone cement for osteoporotic bone

The use of polymethylmethacrylate (PMMA) cement to reinforce fragile or broken vertebral bodies (vertebroplasty) leads to extensive bone stiffening. Fractures in the adjacent vertebrae may be the consequence of this procedure. PMMA with a reduced Young's modulus may be more suitable. The goal of this study was to produce and characterize stiffness adapted PMMA bone cements. Porous PMMA bone cements were produced by combining PMMA with various volume fractions of an aqueous sodium hyaluronate solution. Porosity, Young's modulus, yield strength, polymerization temperature, setting time, viscosity, injectability, and monomer release of those porous cements were investigated. Samples presented pores with diameters in the range of 25-260 microm and porosity up to 56%. Young's modulus and yield strength decreased from 930 to 50 MPa and from 39 to 1.3 MPa between 0 and 56% porosity, respectively. The polymerization temperature decreased from 68 degrees C (0%, regular cement) to 41 degrees C for cement having 30% aqueous fraction. Setting time decreased from 1020 s (0%, regular cement) to 720 s for the 30% composition. Viscosity of the 30% composition (145 Pa s) was higher than the ones received from regular cement and the 45% composition (100-125 Pa s). The monomer release was in the range of 4-10 mg/mL for all porosities; showing no higher release for the porous materials. The generation of pores using an aqueous gel seems to be a promising method to make the PMMA cement more compliant and lower its mechanical properties to values close to those of cancellous bone.     

Bone marrow modified acrylic bone cement for augmentation of osteoporotic cancellous bone

The use of polymethylmethacrylate (PMMA) cement to reinforce fragile or broken vertebral bodies (vertebroplasty) leads to extensive bone stiffening. This might be one reason for fractures at the adjacent vertebrae following this procedure. PMMA with a reduced Young's modulus may be more suitable. The goal of this study was to produce and characterize PMMA bone cements with a reduced Young's modulus by adding bone marrow. Bone cements were produced by combining PMMA with various volume fractions of freshly harvested bone marrow from sheep. Porosity, Young's modulus, yield strength, polymerization temperature, setting time and cement viscosity of different cement modifications were investigated. The samples generated comprised pores with diameters in the range of 30-250 μm leading to porosity up to 51%. Compared to the control cement, Young's modulus and yield strength decreased from 1830 to 740 MPa and from 58 to 23 MPa respectively by adding 7.5 ml bone marrow to 23 ml premixed cement. The polymerization temperature decreased from 61 to 38 °C for cement modification with 7.5 ml of bone marrow. Setting times of the modified cements were lower in comparison to the regular cement (28 min). Setting times increased with higher amounts of added bone marrow from around 16-25 min. The initial viscosities of the modified cements were higher in comparison to the control cement leading to a lower risk of extravasation. The hardening times followed the same trend as the setting times. In conclusion, blending bone marrow with acrylic bone cement seems to be a promising method to increase the compliance of PMMA cement for use in cancellous bone augmentation in osteoporotic patients due to its modified mechanical properties, lower polymerization temperature and elevated initial viscosity.     

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.     

Bone bonding ability and handling properties of a titania-polymethylmethacrylate (PMMA) composite bioactive bone cement modified with a unique PMMA powder

One of the challenges of using bioactive bone cements is adjusting their handling properties for clinical application. To resolve the poorer handling properties of bioactive bone cements we developed a novel bioactive bone cement containing a unique polymethylmethacrylate (PMMA) powder, termed SPD-PMMA (40 μm in diameter), composed of cohered minute particles of PMMA (0.5 μm). The present study aimed to examine the mechanical and handling properties and the in vivo bone bonding strength of this cement. The titania content of the cement varied from 10 to 30 wt.% (Ts10, Ts20, and Ts30). The mechanical and thermal properties of Ts10 and Ts20 exceeded those of commercially available PMMA cements (PMMAc). The setting properties of Ts20, including a shorter dough time and a working time that was comparable with that of PMMAc, were adequate for clinical application. Hardened cylindrical cement specimens were inserted into rabbit femurs and the interfacial shear strengths were measured by a push-out test at 6, 12, and 26 weeks after the operation. The interfacial shear strength values (in Newtons per square millimeter) of Ts10, Ts20, and Ts30 at 12 weeks and those of Ts20 and Ts30 at 26 weeks were significantly higher than that of PMMAc (P < 0.05). These results show that a bioactive titania–PMMA composite bone cement modified by SPD-PMMA particles possesses adequate mechanical and handling properties, as well as osteoconductivity and in vivo bone bonding ability, and can be used for prosthesis fixation.     

Preparation and characterization of bone cements incorporated with montmorillonite

Bone cements incorporated with montmorillonite (MMT) were prepared in an attempt to improve their mechanical properties. The cements were characterized using particle size analysis, gel permeation chromatography, viscosity measurements, unreacted monomer analysis, X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and mechanical properties. The average particle size and molecular weight of the PMMA powders used were 47 microm and 100,000 g/mol, respectively. The incorporation of MMT led to an increase in viscosity of the bone cement but did not severely affect its setting temperature or the amount of residual monomer. Regardless of the MMT mixing methods used, in this case MMT being mixing in liquid and powder components, sodium MMT (SMMT) was not well dispersed in the bone cements, which was believed to be due to its hydrophilicity. Organophilic MMT (OMMT) was better dispersed in the liquid component than in the powder component. The compressive and tensile strength of the bone cement containing the OMMT mixed into the liquid component were significantly higher than those of the bone cement without MMT (p < 0.05).     

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.     

Improved fatigue life of acrylic bone cements reinforced with zirconia fibers

Poly(methyl methacrylate) (PMMA) bone cements have a long and successful history of use for implant fixation, but suffer from a relatively low fracture and fatigue resistance which can result in failure of the cement and the implant. Fiber or particulate reinforcement has been used to improve mechanical properties, but typically at the expense of the pre-cured cement viscosity, which is critical for successful integration with peri-implant bone tissue. Therefore, the objective of this study was to investigate the effects of zirconia fiber reinforcement on the fatigue life of acrylic bone cements while maintaining a relatively low pre-cured cement viscosity. Sintered straight or variable diameter fibers (VDFs) were added to a PMMA cement and tested in fully reversed uniaxial fatigue until failure. The mean fatigue life of cements reinforced with 15 and 20 vol% straight zirconia fibers was significantly increased by ～40-fold, on average, compared to a commercial benchmark (Osteobond?) and cements reinforced with 0–10 vol% straight zirconia fibers. The mean fatigue life of a cement reinforced with 10 vol% VDFs was an order of magnitude greater than the same cement reinforced with 10 vol% straight fibers. The time-dependent viscosity of cements reinforced with 10 and 15 vol% straight fibers was comparable to the commercial benchmark during curing. Therefore, the addition of relatively small amounts of straight and variable diameter zirconia fibers was able to substantially improve the fatigue resistance of acrylic bone cement while exhibiting similar handling characteristics compared to current commercial products.     

Antibacterial and mechanical properties of bone cement impregnated with chitosan nanoparticles

Although total joint replacement has become commonplace in recent years, bacterial infection remains a significant complication following this procedure. One approach to reduce the incidence of joint replacement infection is to add antimicrobial agents to the bone cement used to fix the implant. In this in vitro study, we investigated the use of chitosan nanoparticles (CS NP) and quaternary ammonium chitosan derivative nanoparticles (QCS NP) as bactericidal agents in poly(methyl methacrylate) (PMMA) bone cement with and without gentamicin. The antibacterial activity was tested against Staphylococcus aureus (S. aureus) and Staphylococcus epidermidis (S. epidermidis). A 10(3)-fold reduction in the number of viable bacterial cells upon contact with the surface was achievable using QCS NP at a nanoparticle/bone cement weight ratio of 15%. The inhibition of S. aureus and S. epidermidis growth on the surface of the CS NP and QCS NP-loaded bone cements was clearly shown using the LIVE/DEAD Baclight bacterial viability kits and fluorescence microscopy. The CS NP and QCS NP also provided a significant additional bactericidal effect to gentamicin-loaded bone cement. The antibacterial effectiveness remained high even after the modified bone cements had been immersed for 3 weeks in an aqueous medium. No cytotoxic effect of the CS NP- and QCS NP-loaded cements was shown in a mouse fibroblast MTT cytotoxicity assay. Mechanical tests indicated that the addition of the CS and QCS in nanoparticulate form allowed the retention of a significant degree of the bone cement's strength. These results indicate a new promising strategy for combating joint implant infection.     

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.     

Effect of triphenyl bismuth on glass transition temperature and residual monomer content of acrylic bone cements

Self-curing acrylic bone cements are widely used in the fixation of prosthetic implants in orthopaedic surgery. Commercial bone cements are rendered radiopaque by the addition of heavy metal salts of barium and zirconia. The addition of barium sulphate adversely affects the mechanical strength and fracture toughness of bone cement and despite the fact that it has low solubility in water; its slow release and subsequent toxicity have caused concern. In an earlier study triphenyl bismuth (TPB) was found to be a viable alternative as a radiopaque agent in acrylic bone cements, which provided enhanced homogeneity. In this study we report the effect of the inclusion of TPB on the thermal properties of PMMA-based bone cements using both conventional DSC and Modulated Temperature DSC. Furthermore, analysis of the residual monomer contents is reported analysed by NMR spectroscopy in order to ascertain the influence of TPB on the polymerisation reaction. The glass transition temperature (Tg) determined by DSC showed that the values decreased with the addition of increasing amounts of TPB through both blending and dissolution methods; however, the method of incorporating TPB did not influence Tg. The magnitude of reduction was dependent of the amount of TPB and was greatest in the case of highest concentration of TPB used. A TPB melting peak was observed in the 25 wt% TPBBC, suggesting a limit to the solubility of TPB. The residual monomer analysis showed that at 10 and 15% by weight of TPB in the cement caused no significant changes in the residual monomer content but 25 wt% of TPB exhibited a significantly higher residual monomer content.     

Reinforcement of bone cement using zirconia fibers with and without acrylic coating

Acrylic (polymethylmethacrylate or PMMA) bone cement was modified by the addition of high-strength zirconia fibers with average lengths of 200 microm and diameters of 15 microm or 30 microm. A novel emulsion polymerization process was developed to encapsulate individual fibers in PMMA. Improvements in tensile and compressive properties as well as in fracture toughness were investigated upon incorporation of uncoated and acrylic coated zirconia fibers. Bone cements were reinforced with 2% by volume of the 15 microm diameter and 5% by volume of the 30 microm fibers. Results indicate that elastic modulus and ultimate strength of bone cements reinforced with zirconia fibers were higher than controls, being the largest for cements reinforced with 30 microm diameter fibers. The fracture toughness of the cement increased by 23% and 41% by the addition of 15 microm and 30 microm fibers, respectively. Coating of individual zirconia fibers did not result in improved material properties of bone cements. The use of uncoated or acrylic coated 30 microm fibers is recommended based on the significant increases in ultimate strength and fracture toughness of the cements.     

Incorporation of multiwalled carbon nanotubes to acrylic based bone cements: Effects on mechanical and thermal properties

Polymethyl methacrylate (PMMA) bone cement–multiwalled carbon nanotube (MWCNT) nanocomposites with a weight loading of 0.1% were prepared using 3 different methods of MWCNT incorporation. The mechanical and thermal properties of the resultant nanocomposite cements were characterised in accordance with the international standard for acrylic resin cements. The mechanical properties of the resultant nanocomposite cements were influenced by the type of MWCNT and method of incorporation used. The exothermic polymerisation reaction for the PMMA bone cement was significantly reduced when thermally conductive functionalised MWCNTs were added. This reduction in exotherm translated in a decrease in thermal necrosis index value of the respective nanocomposite cements, which potentially could reduce the hyperthermia experienced in vivo. The morphology and degree of dispersion of the MWCNTs in the PMMA matrix at different scales were analysed using scanning electron microscopy. Improvements in mechanical properties were attributed to the MWCNTs arresting/retarding crack propagation through the cement by providing a bridging effect into the wake of the crack, normal to the direction of crack growth. MWCNT agglomerations were evident within the cement microstructure, the degree of these agglomerations was dependent on the method used to incorporate the MWCNTs into the cement.     

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.