Polymerization of acrylic bone cement investigated by differential scanning calorimetry: Effects of heating rate and TCP content

Graphene Oxide and Graphene Reinforced PMMA Bone Cements: Evaluation of Thermal Properties and Biocompatibility

The incorporation of well-dispersed graphene oxide (GO) and graphene (G) has been demonstrated as a promising solution to improve the mechanical performance of polymethyl methacrylate (PMMA) bone cements in an attempt to enhance the long-term survival of the cemented orthopaedic implants. However, to move forward with the clinical application of graphene-based PMMA bone cements, it is necessary to ensure the incorporation of graphene-based powders do not negatively affect other fundamental properties (e.g., thermal properties and biocompatibility), which may compromise the clinical success of the implant. In this study, the effect of incorporating GO and G on thermal properties, biocompatibility, and antimicrobial activity of PMMA bone cement was investigated. Differential scanning calorimetry studies demonstrated that the extent of the polymerisation reaction, heat generation, thermal conductivity, or glass transition temperature were not significantly (p > 0.05) affected by the addition of the GO or G powders. The cell viability showed no significant difference (p > 0.05) in viability when MC3-T3 cells were exposed to the surface of G- or GO-PMMA bone cements in comparison to the control. In conclusion, this study demonstrated the incorporation of GO or G powder did not significantly influence the thermal properties or biocompatibility of PMMA bone cements, potentially allowing its clinical progression.

Mechanical and thermal behaviour of an acrylic bone cement modified with a triblock copolymer

The basic formulation of an acrylic bone cement has been modified by the addition of a block copolymer, Nanostrength(®) (NS), in order to augment the mechanical properties and particularly the fracture toughness of the bone cement. Two grades of NS at different levels of loading, between 1 and 10 wt.%, have been used. Mechanical tests were conducted to study the behaviour of the modified cements; specific tests measured the bend, compression and fracture toughness properties. The failure mode of the fracture test specimens was analysed using scanning electron microscopy (SEM). The effect of NS addition on the thermal properties was also determined, and the polymerisation reaction using differential scanning calorimetry. It was observed that the addition of NS produced an improvement in the fracture toughness and ductility of the cement, which could have a positive contribution by reducing the premature fracture of the cement mantle. The residual monomer content was reduced when the NS was added. However this also produced an increase in the maximum temperature and the heat delivered during the polymerisation of the cement.

Influence of powder-to-liquid monomer ratio on properties of an injectable iodine-containing acrylic bone cement for vertebroplasty and balloon kyphoplasty

The interventional radiological techniques of vertebroplasty (VP) and balloon kyphoplasty (BKP) are widely used in cases where the pain secondary to compression fractures of vertebral bodies is severe, persistent, and refractory to conservative treatments. In the majority of VP and BKP cases, an injectable poly(methyl methacrylate) (PMMA) bone cement and different values of powder-to-liquid monomer ratio (PLMR) are used. A systematic study of the influence of PLMR on relevant cement properties is lacking. This was the subject of the present study, with the injectable PMMA bone cement used being an experimental one whose radiopacity is provided by an iodine-containing compound in the powder. The PLMRs used-1.54, 2.22, and 3.08 g mL(-1)-are within the range used in clinical reports on VP and BKP. One property of the curing cement, namely, the polymerization rate at 37 degrees C (k'), was estimated using nonisothermal differential scanning calorimetry results. The fatigue lives (N(f)) of cured cement specimens were obtained under axial loading corresponding to axial stresses (S) of +/-20.0, 15.0, 12.5, and 10.0 MPa, at a frequency of 2 Hz. The fatigue limit of the cement was estimated from the fit of the S - N(f) results to the Olgive equation. With increase in PLMR, k' increased significantly, but the influence of PLMR on the fatigue limit and on another property also estimated from the S - ln N(f) results is not significant.

Influence of two changes in the composition of an acrylic bone cement on its handling, thermal, physical, and mechanical properties

This study is a contribution to the growing body of work on the influence of changes in the composition of an acrylic bone cement on various properties of the curing and cured material. The focus is on one commercially-available acrylic bone cement brand, Surgical Simplex P, and three variants of it and a series of properties, namely, setting time, maximum exotherm temperature, activation energy and frequency factor for the polymerization reaction, diffusion coefficient for the uptake of phosphate buffered saline, at 37 degrees C, ultimate compressive strength (UCS), plane-strain fracture toughness, fatigue life (under fully-reversed tension-compression stress), hardness (H) and elastic modulus (both determined using quasi-static nanoindentation), and the variation of the storage and loss moduli with frequency of the applied force in a dynamic nanoindentation test. It was found that (a) a 68% reduction in the volume of the activator, N,N dimethyl-4-toluidine, relative to the total volume of the liquid monomer (the amounts of all the constituents in the powder and of the hydroquinone in the liquid monomer remaining unchanged) led to, for example, a significant decrease in the rate of the polymerization reaction, at 37 degrees C (c') and a significant increase in H; and (b) the elimination of the pre-polymerized poly (methyl methacrylate) beads in the powder (the amounts of all the other powder constituents and those of the liquid monomer remaining unchanged) led to, for example, a significant drop in c' and a significant increase in UCS. Thus, these findings suggest a strategy for optimizing the composition of an acrylic bone cement.

Influence of changes in the composition of an acrylic bone cement on its polymerization kinetics

It has been suggested in the literature that a lower polymerization rate of an acrylic bone cement is favorable for the in vivo longevity of a cemented arthroplasty. The present work was a study of the influence of three changes in the composition of an acrylic bone cement (when taken separately) on the cement polymerization rate at 37 degrees C (assumed to be the temperature in the bone bed during a cemented arthroplasty) [k']. The changes were the amount of copolymer as a proportion of the total powder weight (in cements in which there is a copolymer in the powder), the amount of DMPT as a proportion of the total volume of the liquid monomer, and the accelerator. k' was calculated using values of the activation energy and the frequency factor (assuming the polymerization reaction is Arrhenius in nature) that were computed from measurements made using the nonisothermal mode of differential scanning calorimetry. Statistical analysis (one-way ANOVA, with Bonferroni correction, and factorial ANOVA) of the k' values showed that the change in accelerator had a significant influence on k'. The importance of this finding, together with results from two relevant literature reports, is discussed within the context of the use of modified bone cements in cemented arthroplasties.

Influence of the activator in an acrylic bone cement on an array of cement properties

In all but one of the acrylic bone cement brands used in cemented arthroplasties, N,N-dimethyl-4-toluidine (DMPT) serves as the activator of the polymerization reaction. However, many concerns have been raised about this activator, all related to its toxicity. Thus, various workers have assessed a number of alternative activators, with two examples being N,N-dimethylamino-4-benzyl laurate (DMAL) and N,N-dimethylamino-4-benzyl oleate (DMAO). The results of limited characterization of cements that contain DMAL or DMAO have been reported in the literature. The present work is a comprehensive comparison of cements that contain one of these three activators, in which the values of a large array of their properties were determined. These properties range from the setting time and maximum exotherm temperature of the curing cement to the variation of the loss elastic modulus of the cured cement with frequency of the applied indenting force in dynamic nanoindentation tests. The present results, taken in conjunction with those presented in previous reports by the present authors and co-workers on other properties of these cements, indicate that both DMAL and DMPT are suitable alternatives to DMPT.

Influence of a pre-blended antibiotic (gentamicin sulfate powder) on various mechanical, thermal, and physical properties of three acrylic bone cements

The aim of this work was to determine an array of mechanical, physical, and thermal properties of three pairs of commercially available acrylic bone cement brands, with the brands in each pair having the same compositions except that one contains 4.22 wt/wt% gentamicin sulfate blended with the powder by the manufacturer and the other one does not. The difference between the pairs was in the viscosity of the curing cement dough, with one pair of 'low-viscosity', one pair of 'medium-viscosity', and one pair of 'high-viscosity' brands being used. Thus, the brands studied cover the range of those used in anchoring some total joint replacements (TJRs). The properties determined were the strength, modulus, and work-to-fracture (all under four-point bending), plane-strain fracture toughness, Weibull mean fatigue life (fatigue conditions: 15 MPa; 2 Hz), activation energy and frequency factor for the cement polymerization process (both determined, using differential scanning calorimetry, at heating rates of 5, 10, 15, and 20 K min (1)), and the diffusion coefficient for the absorption of phosphate-buffered saline at 37 C by the cured cement. For each property determined, there was no significant difference in the mean values for the brands in each of the pairs. These results indicate that over the range of cement brands that are widely used in the anchoring of cemented TJRs, the addition of gentamicin sulfate powder does not degrade the properties of the cement, and, hence, may not adversely affect the in vivo longevity of the replacement.

Influence of the method of blending an antibiotic powder with an acrylic bone cement powder on physical, mechanical, and thermal properties of the cured cement

Two variants of antibiotic powder-loaded acrylic bone cements (APLBCs) are widely used in primary total joint replacements. In the United States, the antibiotic is manually blended with the powder of the cement at the start of the procedure, while, in Europe, pre-packaged commercially-available APLBCs (in which the blending is carried out using an industrial mixer) are used. Our objective was to investigate the influence of the method of blending gentamicin sulphate with the powder of the Cemex XL formulation on a wide collection of properties of the cured cement. The blending methods used were manual mixing (the MANUAL Set), use of a small-scale, easy-to-use, commercially-available mechanical powder mixer, OmoMix 1 (the MECHANICAL Set), and use of a large-scale industrial mixer (Cemex Genta) [the INDUSTRIAL Set]. In the MECHANICAL and MANUAL Sets, the blending time was 3 min. In preparing the test specimens for each set, the blended powder used contained 4.22 wt% of the gentamicin powder. The properties determined were the strength, modulus, and work-to-fracture (all obtained under four-point bending), plane-strain fracture toughness, Weibull mean fatigue life (fatigue conditions: +/-15 MPa; 2 Hz), activation energy and frequency factor for the cement polymerization process (both determined using differential scanning calorimetry, at heating rates of 5, 10, 15, and 20 Kmin(-1)), the diffusion coefficient for the absorption of phosphate buffered saline, PBS, at 37 degrees C, and the rate of elution of the gentamicin into PBS, at 37 degrees C (E). Also determined were the particle size, particle size distribution, and morphology of the blended powders and of the gentamicin. For each of the cured cement properties (except for E), there is no statistically significant difference between the means for the 3 cements, a finding that parallels the observation that there are no significant differences in either the mean particle size or the morphology of the blended cement powders. Notwithstanding these results, it is suggested that when the powder mixture is blended in the operating room, using the OmoMix 1 is more likely to produce a more consistent and reproducible mixture than when manual mixing is used.

Influence of the radiopacifier in an acrylic bone cement on its mechanical, thermal, and physical properties: Barium sulfate-containing cement versus iodine-containing cement

In all acrylic bone cement formulations in clinical use today, radiopacity is provided by micron-sized particles (typical mean diameter of between about 1 and 2 microm) of either BaSO(4) or ZrO(2). However, a number of research reports have highlighted the fact that these particles have deleterious effects on various properties of the cured cement. Thus, there is interest in alternative radiopacifiers. The present study focuses on one such alternative. Specifically, a cement that contains covalently bound iodine in the powder (herein designated the I-cement) was compared with a commercially available cement of comparable composition (C-ment3), in which radiopacity is provided by BaSO(4) particles (this cement is herein designated the B-cement), on the basis of the strength (sigma(b)), modulus (E(b)), and work-to-fracture (U(b)), under four-point bending, plane-strain fracture toughness (K(IC)), Weibull mean fatigue life, N(WM) (fatigue conditions: +/-15 MPa; 2 Hz), activation energy (Q), and frequency factor (ln Z) for the cement polymerization process (both determined by using differential scanning calorimetry at heating rates of 5, 10, 15, and 20 K min(-1)), and the diffusion coefficient for the absorption of phosphate-buffered saline at 37 degrees C (D). For the B-cement, the values of sigma(b), E(b), U(b), K(IC), N(WM), Q, ln Z, and D were 53 +/- 3 MPa, 3000 +/- 120 MPa, 108 +/- 15 kJ m(-3), 1.67 +/- 0.02 MPa check mark m, 7197 cycles, 243 +/- 17 kJ mol(-1), 87 +/- 6, and (3.15 +/- 0.94) x 10(-12) m(2) s(-1), respectively. For the I-cement, the corresponding values were 58 +/- 5 MPa, 2790 +/- 140 MPa, 118 +/- 45 kJ m(-3), 1.73 +/- 0.11 MPa check mark m, 5520 cycles, 267 +/- 19 kJ mol(-1), 95 +/- 9, and (3.83 +/- 0.25) x 10(-12) m(2) s(-1). For each of the properties of the fully cured cement, except for the rate constant of the polymerization reaction, at 37 degrees C (k'), as estimated from the Q and ln Z results, there is no statistically significant difference between the two cements. k' for the I-cement was about a third that for the B-cement, suggesting that the former cement has a higher thermal stability. The influence of various characteristics of the starting powder (mean particle size, particle size distribution, and morphology) on the properties of the cured cements appears to be complex. When all the present results are considered, there is a clear indication that the I-cement is a viable candidate cement for use in cemented arthroplasties in place of the B-cement.

Fracture toughness of steel-fiber-reinforced bone cement

Fractures in the bone-cement mantle (polymethyl methacrylate) have been linked to the failure of cemented total joint prostheses. The heat generated by the curing bone cement has also been implicated in the necrosis of surrounding bone tissue, leading to loosening of the implants. The addition of reinforcements may improve the fracture properties of bone cement and decrease the peak temperatures during curing. This study investigates the changes in the fracture properties and the temperatures generated in the ASTM F451 tests by the addition of 316L stainless steel fibers to bone cement. The influence of filler volume fraction (5-15% by volume) and aspect ratios (19, 46, 57) on the fracture toughness of the acrylic bone cement was assessed. Increasing the volume fraction of the steel fibers resulted in significant increases in the fracture toughness of the steel-fiber-reinforced composite. Fracture-toughness increases of up to 2.63 times the control values were obtained with the use of steel-fiber reinforcements. No clear trend in the fracture toughness was discerned for increasing aspect ratios of the reinforcements. There is a decrease in the peak temperatures reached during the curing of the steel-fiber-reinforced bone cement, though the decrease is too small to be clinically relevant. Large increases in the fatigue life of acrylic bone cement were also obtained by the addition of steel fibers. These results indicate that the use of steel fibers may enhance the durability of cemented joint prostheses.

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.

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.

Effect of MMA-g-UHMWPE grafted fiber on mechanical properties of acrylic bone cement

Ultrahigh molecular weight polyethylene (UHMWPE) fibers were treated with argon plasma for 5 min, followed by uv irradiation in methyl methacrylate (MMA)-chloroform solution for 5 h to obtain MMA-g-UHMWPE grafted fiber. The grafting content was estimated by the titration of esterification method. The grafting amount of 5280 nmol/g was the largest for the MMA concentration at 18.75 vol%. To improve the mechanical properties of acrylic bone cement, pure UHMWPE fiber and MMA-g-UHMWPE fiber were added to the surgical Simplex. P radiopaque bone cement. The mechanical properties including tensile strength, tensile modulus, compressive strength, bending strength, and bending stiffness were measured. Dynamic mechanical analysis was also performed. By comparing the effect of the pure UHMWPE fiber and MMA-g-UHMWPE grafted fiber on the mechanical properties of acrylic bone cement, it was found that the acrylic bone cement with MMA-g-UHMWPE grafted fiber had a more significant reinforcing effect than that with untreated UHMWPE fiber. This might be due to the improvement of the interfacial bonding between the grafted fibers and the acrylic bone cement matrix.

Study of polymerization of acrylic bone cement: effect of HEMA and EGDMA

The polymerization reaction of standard surgical Simplex-P radiopaque bone cement was investigated by differential scanning calorimetry to determine the influence of hydroxyethyl methacrylate (HEMA) and ethylene glycol dimethacrylate (EGDMA) on the polymerization reaction. From the kinetic analysis, the polymerization reaction of the modified acrylic bone cement was found to be approximately a first-order reaction. The reaction rate constants (k) were determined. It was found that the effects of HEMA and EGDMA contents on the rate and the heat of polymerization can be explained by the frequency factor and the activation energy. An increase in HEMA content tends to result in an increase in the values of both frequency factor and activation energy, whereas an increase in EGDMA content tends to induce a decrease in the frequency factor and activation energy.

Polymerization of acrylic bone cement using differential scanning calorimetry

The polymerization of acrylic bone cement using differential scanning calorimetry (DSC) was investigated. The polymerization reaction of the acrylic bone cement was found to be an approximately first order reaction. Two kinds of reaction rate constants for the polymerization reaction were observed. Both rate constants were calculated before and after the peak time. The effects of the addition of tricalcium phosphate (TCP) on the polymerization reaction of standard Surgical Simplex-P Radiopaque Bone Cement have been investigated by DSC. The TCP content had a strong retardation effect on the rate constants. The thermal stability of the acrylic bone cement was also studied by thermogravimetric analysis.