Creep properties of three low temperature-curing bone cements: a preclinical assessment

The mechanical characteristics of new bone cements should be assessed before these cements are released on the orthopedic market in great quantities. In this study, we present the deformational response of 3 relatively new, low-curing temperature bone cements (Cemex RX, Cemex System, and Cemex Isoplastic) to a dynamic compressive force in comparison to Simplex P bone cement. For this purpose, dynamic compressive creep tests were performed on cylindrical shaped specimens at a maximal load level of 20 MPa for a period of 250,000 cycles. The results showed that Cemex System and Cemex RX produced creep rates that were higher (20% and 30%, respectively) as compared to Simplex P bone cement. The creep behavior of Cemex Isoplastic was very similar to that of Simplex P. It was concluded that although Cemex RX and Cemex System produced higher creep rates than Simplex P, these differences were not considered excessive. Hence, although other tests are required to assess the safety and efficacy of these new cements, the dynamic creep properties under compression can be considered adequate for clinical use.     

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.     

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.     

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.     

Fatigue and fracture toughness of acrylic bone cements modified with long-chain amine activators

The composition of acrylic bone cement has been identified as one of the important parameters affecting its mechanical properties and may, in turn, ultimately influence the longevity of a cemented arthroplasty. Our aim in this study was to determine the influence of change of one compositional variable, the activator, on the fatigue performance and fracture toughness of specimens of the fully cured cement. To that end, three sets of cements were prepared, containing either the conventional activator, 4-N,N dimethyl p-toluidine (DMPT), or novel ones that are tertiary amines based on long-chain fatty acids, that is, 4-N,N dimethylaminobenzyl oleate (DMAO) and 4-N,N dimethylaminobenzyl laurate (DMAL). In the fatigue tests, the specimens were subjected to tension-tension loading, and the results (number of cycles to failure, Nf) were analyzed using the linearized form of the three-parameter Weibull equation. The fracture toughness (KIc) tests were conducted with rectangular compact tension specimens. All fracture surfaces were subsequently examined with scanning electron microscopy. We found that the Weibull mean fatigue lives for specimens fabricated using the DMPT, DMAL, and DMAO containing cements were 272,823, 453,551, and 583,396 cycles, respectively. The corresponding values for KIc were 1.94 +/- 0.05, 2.06 +/- 0.09, and 2.00 +/- 0.07 MPa radical m, respectively. Statistical analyses showed that for both the DMAL- and DMAO-containing cements, the mean values of Nf were significantly higher compared to the corresponding value for the DMPT-containing cement (Mann-Whitney test; alpha < 0.10). This result is attributed to the higher molecular weights of the former cements compared to the latter. The same trend was found for the mean KIc values (Mann-Whitney test; alpha < 0.05), with the trend being explained in terms of the differences seen in the crack morphologies. These results thus demonstrate that these novel amines are viable alternatives to DMPT for incorporation into acrylic bone cement formulations in the future.     

Influence of strontia on various properties of surgical simplex P acrylic bone cement and experimental variants

The fact that the composition of acrylic bone cement, as used in cemented primary arthroplasties, is not optimal has been highlighted in the literature. For example: (i) deleterious effects of the radiopacifier (BaSO₄ or ZrO₂ particles in the powder) have been reported; (ii) there is an indication that pre-polymerized poly(methylmethacrylate) (PMMA) beads in the powder may be dispensed with; and (iii) there is a strong consensus that the accelerator commonly used, N,N-dimethyl-p-toluidine (DMPT), is toxic and has many other undesirable properties. At the same time, the effectiveness of drugs that contain a strontium compound in treating the effects of osteoporosis has been explained in terms of the role of strontium in bone formation and resorption. This indicates that strontium compounds may also have desirable effects on osseointegration of arthroplasties. The present study is a detailed evaluation of 24 acrylic bone cement formulations comprising different relative amounts of BaSO₄, strontia (as an alternative radiopacifier), pre-polymerized PMMA beads and DMPT. A large number of properties of the curing and cured cement were determined, including setting time, polymerization rate, fracture toughness and fatigue life. The focus was on the radiopacifier, with the finding being that many properties of formulations that contained strontia were about the same or better than those for cements that contained BaSO₄. Thus, further developmental work on strontia-containing acrylic bone cements is justified, with a view to making them candidates for use in cemented primary arthroplasties.     

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.     

Staphylococcus aureus biofilm formation on different gentamicin-loaded polymethylmethacrylate bone cements

In this in vitro study, the formation of a Staphylococcus aureus biofilm on six gentamicin-loaded bone cements (CMW1, CMW3, CMW Endurance, CMW2000, Palacos, and Palamed) was determined in a modified Robbins device over a 3 days time span and related with previously (Van de Belt et al., Biomaterials 21 (2000) 1981) measured kinetics of antibiotic release by these cement brands. The influence of gentamicin release on biofilm formation was quantified by expressing the number of colony-forming units on gentamicin-loaded cement relative to the number of viable organisms on unloaded cement of the same brand. Biofilms formed on all gentamicin-loaded cements, despite the release of antibiotics, followed a consistent pattern in time with a maximum number of colony-forming units per unit cement area found between 24 and 30 h after inoculation. None of the gentamicin-loaded cements showed a reduction in biofilm formation relative to unloaded cements within 6 h after inoculation, whereas only gentamicin-loaded CMW1 and Palacos reduced biofilm formation 24 h after inoculation. Alternatively, CMW Endurance, CMW2000, and Palamed did not exhibit any initial reductions in biofilm formation, but effects started after 72, 48, and 72 h, respectively. Biofilm reduction by gentamicin-loaded CMW3 lasted the longest from 24 to 72 h. Interestingly, each cement seemed to have a different "window-of-effectiveness" with regard to reduction in biofilm formation that did not relate with the gentamicin-release kinetics. Summarising, this study demonstrates that although gentamicin loading of bone cements yields reductions in biofilm formation, S. aureus is able to grow on gentamicin-loaded bone cements.     

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.     

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.     

Production of TNF-alpha and bone resorbing activity by macrophages in response to different types of bone cement particles

We have compared the capacity of clinically relevant wear debris from seven different cement types to activate macrophages to produce TNF-alpha, IL-1beta, IL-6 and bone resorbing activity in vitro. The bone cements were: CMW 1 original (PMMA only); CMW 1RO (1 microm BaSO4; 9.2%); CMW copolymer bone cement 1 (10 microm BaSO4; 10%); CMW copolymer bone cement 2 (1 microm BaSO4; 10%); Palacos R (10 microm ZrO2; 15.6%); CMW Calcium phosphate cement 20% (10 microm tri-calcium phosphate; 20%) and CMW calcium phosphate cement 30% (10 microm tri-calcium phosphate; 30%). Cement debris was produced aseptically using a simple configuration wear test. The majority of particles were in the size range 0.1-0.5 microm for each cement type. The cement particles were co-cultured with the U937 macrophage cell line at ratios of 10 and 100 microm3 particle volumes to macrophage cell numbers for 24 h. At the 10:1 ratio the particles had no effect on the cells. At the 100:1 ratio, the major cytokine produced was TNF-alpha and there were no statistical differences between the different types of cement debris. The bone resorption activity of the co-culture supernatants was significantly greater than the control (U937 cells without particles) for particles of CMW 1RO, CMW copolymer bone cement 1, CMW copolymer bone cement 2 and Palacos R (P < 0.05, ANOVA). However there were no statistical differences between the levels of bone resoprtion evoked by these four cement types. The CMW1 original and CMW calcium phosphate containing cements failed to induce the macrophages to elaborate bone resorption activity at the 100:1 ratio. These data suggest that the addition of radio-opaque additives to bone cement may increase the capacity of the debris to induce osteolysis.     

Effect of loading rate on the apparent fracture toughness of acrylic bone cement

In this study, a determination is made of the effect of loading rate, v (0.1 mm min(-1) versus 1.0 mm min(-1) versus 10 mm min(-1)) on the value of the plane strain fracture toughness, K(Ic), of three commercial formulations of acrylic bone cement (Osteopal), CMW3, and Copal), that are characterized as "low-", "medium-", and "high-" viscosity brands, respectively). For all formulations, K(Ic) increases with increase in v. However, while this trend is statistically significant for CMW3 and Copal, this is not so for Osteopal. The CMW3 and Copal results are explained in terms of changes of the molecular relaxation transitions in the cement and the thermal state at the crack tip of the test specimen. Two implications of the findings are discussed. In the case of Osteopal, a recommendation for further study is made.     

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.     

Comparison of the response of human peripheral blood mononuclear cells to challenge with particles of three bone cements in vitro

This study compared the effects of different sizes of three clinically relevant endotoxin free bone cement particles on primary human macrophage TNF-alpha production in vitro. The bone cements used were CMW original, CMW1RO and Palacos R. The cement wear debris was generated aseptically and then sequentially filtered to produce the size ranges 0.1-1 microm, 0.1-10 microm, 1-10 microm and >10 microm. The debris was cultured with human peripheral blood mononuclear cells at particle volume (microm(3)) per cell ratios of 100:1, 10:1 and 1:1. TNF-alpha production was determined by ELISA and cell viability by MTT conversion. CMW1RO particles induced increased TNF-alpha production by PBMNCs when tested in the size range 0.1-1 microm, and also to a lesser degree in the sizes 0.1-10 microm and 1-10 microm at the particle volume (microm(3)) to cell number ratios of 100:1 and 10:1.The increase in TNF-alpha production induced by Palacos R debris was only observed with the particle size ranges less than 10 microm at the ratio of 100:1. This study demonstrated that bone cement particles are capable of inducing raised TNF-alpha production in vitro. This is dependent upon cement particle size, volume and cement particle type, with cement particles containing radio-opaque additives being the most active.     

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.     

Biocompatibility and other properties of acrylic bone cements prepared with antiseptic activators

Acrylic bone cements prepared with activators of reduced toxicity have been formulated with the aim of improving the biocompatibility of the final material. The activators used were N,N-dimethylaminobenzyl alcohol (DMOH) and 4,4'-dimethylamino benzydrol (BZN). The toxicity, cytotoxicity, and antiseptic action of these activators were first studied. DMOH and BZN presented LD50 values 3-4 times higher than DMT, were less cytotoxic against polymorphonuclear leucocytes, and possessed an antimicrobial character, with a high activity against the most representative microorganisms involved in postoperative infections. The properties of the acrylic bone cements formulated with DMOH and BZN were evaluated to determine the influence of these activators on the curing process and the physicochemical characteristics of the cements. A decrease of the peak temperature was observed for the curing with DMOH or BZN with respect to that of one commercially available formulation (CMW 3). However, residual monomer content and mechanical properties in tension and compression were comparable to those of CMW 3. The biocompatibility of acrylic bone cements containing DMOH or BZN was studied and compared with CMW 3. To that end, intramuscular and intraosseous implantation procedures were carried out and the results were obtained from the histological analysis of the surrounding tissues at different periods of time. Implantation of rods of cement into the dorsal muscle of rats showed the presence of a membrane of connective tissue, which increased in collagen fibers with time of implantation, for all formulations. The intraosseous implantation of the cements in the dough state in the femur of rabbits, revealed a higher and early osseous neoformation, with the presence of osteoid material surrounding the rest of the cured material, for the cement prepared with the activator BZN in comparison with that obtained following the implantation of the cement cured with DMOH or DMT (CMW 3).     

Effect of four acrylic bone cements on transforming growth factor-beta1 expression by osteoblast-like cells MG63.

Based on the hypothesis that bone cements cause changes in the production of transforming growth factor-beta 1 (TGF-beta1) by bone cells, the effects of four acrylic bone cements (Sulfix-60, CMW 1, CMW 2 and CMW 3) were examined using the osteoblast-like cell line MG63. The extracts in MEM of the cements were tested, following 1 h- and 7 day-curing. MG63 cells seldom expressed mRNA specific for TGF-beta1 in basal conditions. The cultures expressed mRNA constantly after incubation with the extract of CMW 1 cured for 1 h. TGF-beta1 specific mRNA was seldom expressed after incubation with the other cement extracts. The release of TGF-beta1 into the conditioned medium was increased significantly by CMW 1 extract at 1 h-curing, but was not changed significantly by CMW 1 extract at 7 day-curing and by the extracts of the other cements, at both curing times. The stimulating effect of CMW 1 on the secretion of TGF-beta1, even with all the restrictions of an in vitro study of continuous cell lines, if confirmed in vivo, might favor the development of the synovial-like membrane around the implant, and therefore impair the chance of success of the prosthesis.     

The fracture toughness of titanium-fiber-reinforced bone cement.

Fracture of the poly(methyl methacrylate) bone cement mantle can lead to the loosening and ultimate failure of cemented total joint prostheses. The addition of fibers to the bone cement increases fracture resistance and may reduce, if not eliminate, in vivo fracturing. This study discusses the effect of incorporating titanium (Ti) fibers on fracture toughness. Essential characteristics of the composite bone cement included a homogeneous and uniform fiber distribution, and a minimal increase in apparent viscosity of the polymerizing cement. Ti fiber contents of 1%, 2%, and 5% by volume increased the fracture toughness over non-reinforced bone cement by up to 56%. Bone cements of two different viscosities were used as matrix material, but when reinforced with the same fiber type and content, they showed no difference in fracture toughness. Four different fiber aspect ratios (68, 125, 227, 417) were tested. At 5% fiber content, there was no statistically significant dependence of fracture toughness on fiber aspect ratio. Scanning electron microscopy revealed important toughening mechanisms such as fiber/matrix debonding, local fracture path alteration, and ductile fiber deformation and fracture. Fiber fracture was evidence that the critical fiber length was exceeded. The surfaces of the Ti fibers were rough and irregular, indicating that a high degree of mechanical interlock between matrix and fiber was likely. The energy absorption contribution of plastic deformation and ductile fracture is absent in brittle fibers, like carbon, but is a distinction of the Ti fibers used in this study.     

PMMA bone cement containing a quaternary amine comonomer with potential antibacterial properties

An iodinated quaternary amine dimethacrylate monomer was synthesized and incorporated as a comonomer in acrylic bone cements. Bone cement is used in orthopaedic surgery and imparting antibacterial properties to the cement can be beneficial in the lowering of bacterial infection post surgery. PMMA based bone cements were modified by copolymerising the monomer methylmethacrylate (MMA) with a quaternary amine dimethacrylate by using the redox initiator activator system as used for curing commercial bone cements. The cements were prepared using the commercial PMMA bone cement CMW and the liquid component was modified with the amine to render antimicrobial properties to the cement. The physical, mechanical, and antimicrobial properties of the modified cements were evaluated; in addition, the viability of the cement to function as a orthopaedic cement was also established, especially with an advantage of it being radiopaque, due to the inclusion of the iodine containing quaternary amine. The cytotoxicity of the modified cements were tested using a human cell model and the results indicated that the cells remained metabolically active and proliferated when placed in direct contact with the experimental cement specimens. The cements and their eluants did not evoke any cytotoxic response.     

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.