Bone Cement Formulations Research Articles

Characterization of new acrylic bone cement based on methyl methacrylate/1-hydroxypropyl methacrylate monomer.

New formulations of acrylic bone cement based on methyl methacrylate/1-hydroxypropyl methacrylate (MMA/HPMA) monomers were developed with the purpose of obtaining more ductile materials with reduced polymerization shrinkage. In this way, the ductility of such materials increased, but the introduction of high percentages of the hydrophilic component produced an important decrease in Young's modulus and strength. To ascertain the reason for the deterioration of the tensile parameters, an analysis by scanning electron microscopy of these formulations was carried out; it revealed poor adhesion between the matrix and poly(MMA) beads. We also observed that the polymerization shrinkage increased as the amount of hydrophilic monomer in the formulation decreased, and the 50% (v/v) HPMA modified bone cement compensated for this volume reduction with its water uptake swelling. Measurements taken on the setting time and polymerization exotherm showed a decrease in the former and an increase in the latter, because of the introduction of a more reactive monomer in the bone cement formulation.

Acrylic bone cements incorporating polymeric active components derived from salicylic acid: curing parameters and properties.

A methacrylic monomer derived from salicylic acid, 5-hydroxy-2-methacrylamido benzoic acid, 5-HMA, was incorporated with 2-hydroxyethyl methacrylate, (HEMA), in different proportions to the liquid phase of classical bone cement formulations. The monomer 5-HMA shows the ability to form molecular complexes with calcium atoms in order to improve osteointegration in the application of bone cement formulations used for the fixation of joint prostheses such as knee and hip. Kinetic parameters, peak temperature and setting time of the bone cement formulations prepared were determined, obtaining lower peak temperature values when 5-HMA was incorporated, with respect to classical acrylic bone cements based on PMMA. Mechanical and thermal properties as well as surface energy values, have been determined for all cured bone cement formulations.

The apparent fracture toughness of acrylic bone cement: effect of three variables.

In cemented arthroplasties, pores are almost invariably present at one or more of the so-called 'weak-link' zones (namely, the bone-cement interface, the cement mantle and the cement-implant interface). In the clinical milieu, arthroplasties are frequently subjected to cyclical loading. These conditions underscore the significance of the apparent fracture toughness (KISR) of the cement. The present work is an investigation of the effect of three variables on KISR of three commercial formulations of bone cement (namely, CMW3, PalacosR and Osteopal) measured using straight-sided chevron notched short rod specimens. For CMW3, the effect of mixing method was studied, with all cement constituents having been stored at ambient laboratory environment prior to being mixed. The highest KISR was obtained from material that was obtained from exposing the cement constituents to a passive vacuum for 20 s and then mixing them in a machine that subjected them to simultaneous mechanical mixing and centrifugation. For Palacos R, the effects of two variables [storage temperature of the cement constituents prior to being mixed (4 degrees C versus 21 degrees C) and mixing method (hand mixing versus vacuum mixing)] (taken individually) were studied. It was found that only mixing method exerts a significant effect on KISR. When room-temperature stored constituents were vacuum mixed, the KISR values for a low-viscosity cement (Osteopal) and a medium-viscosity cement of very similar composition (Palacos R) are not significantly different, indicating that the fracture resistance of bone cement is influenced more by its composition than its viscosity.

Effect of crosslinking agents on acrylic bone cements based on poly(methylmethacrylate)

Three different crosslinking agents were added to the monomer content of the bone cement formulation based on poly(methylmethacrylate), PMMA, in various concentrations, and their effects on the curing parameters and mechanical properties were determined. The different crosslinking agents were dimethacrylates containing a range of chain lengths and degrees of flexibility. For the parent formulation of the bone cement, PMMA powder was used, and the properties and kinetics of curing were compared for the same system with and without crosslinking agents. It was found that at low concentrations of crosslinking agents, the mechanical properties were superior but steadily decreased with increasing concentrations. Poly(ethyleneglycoldimethacrylate), EGDMA(400), even when used at very low concentrations, produced a steady improvement in the mechanical properties and could be used in cement formulations with a view to reducing creep and improving mechanical properties.

Optimization of benzoyl peroxide concentration in an experimental bone cement based on poly(methyl methacrylate).

The effect of the concentration of benzoyl peroxide in poly(methyl methacrylate) bone cement formulations on their setting characteristics, particularly peak temperature and setting time, were studied. An optimization of the concentration of benzoyl peroxide was made with respect to curing parameters and compared with the residual monomer content. The mechanical properties of the different formulations were also determined and the results indicated that a composition of 1.5% wt/wt and 0.82% wt/wt of benzoyl peroxide and N,N-dimethyl-p-toluidine concentrations, respectively, gave the highest yield strength. Studies on the preparation of bone cement formulations containing different amounts of barium sulphate were also performed to assess the effect on the polymerization process and mechanical properties of the cements.

Radio-opaque agents in bone cement increase bone resorption.

A heavy infiltrate of foreign-body macrophages is commonly seen in the fibrous membrane which surrounds an aseptically loose cemented implant. This is in response to particles of polymethylmethacrylate (PMMA) bone cement and other biomaterials. We have previously shown that monocytes and macrophages responding to particles of bone cement are capable of differentiating into osteoclastic cells which resorb bone. To determine whether the radio-opaque additives barium sulphate (BaSO4) and zirconium dioxide (ZrO2) influence this process, particles of PMMA with and without these agents were added to mouse monocytes and cocultured with osteoblast-like cells on bone slices. Osteoclast differentiation, as shown by the presence of the osteoclast-associated enzyme tartrate-resistant acid phosphatase (TRAP) and lacunar bone resorption, was observed in all cocultures. The addition of PMMA alone to these cocultures caused no increase in TRAP expression or bone resorption relative to control cocultures. Adding PMMA particles containing BaSO4 or ZrO2, however, caused an increase in TRAP expression and a highly significant increase in bone resorption. Particles containing BaSO4 were associated with 50% more bone resorption than those containing ZrO2. Our results suggest that radio-opaque agents in bone cement may contribute to the bone resorption of aseptic loosening by enhancing macrophage-osteoclast differentiation, and that PMMA containing BaSO4 is likely to be associated with more osteolysis than that containing ZrO2.

Improved cortical histology after cementation with a new MMA‐DMA‐IBMA bone cement: An animal study

The histological response of bone to inert bone wax, conventional polymethylmethacrylate (PMMA), and a new formulation of bone cement, methylmethacrylate/n-decylmethacrylate/isobornylmethacrylate (MMA/DMA/IBMA) was investigated in canine tibial diaphysis. The new formulation of cement is characterized by a reduced exothermic temperature at curing and reduced leakage of chemicals to the adjacent bone. In comparison with bone wax, the MMA/DMA/IBMA bone cement did not differ significantly with respect to periosteal apposition and bone remodeling, although a tendency to inhibit the biological response was encountered. The MMA/DMA/IBMA was clearly superior to PMMA bone cement in respect to both bone necrosis and repair, as well as bone remodeling.

Polyisobutylene-toughened poly(methyl methacrylate): III. PMMA-l-PIB networks as bone cements.

A series of novel polyisobutylene (PIB)-toughened poly(methyl methacrylate) (PMMA) networks consist of rubbery PIB domains covalently bonded to a glassy PMMA matrix. Materials containing 8.5-17 wt.% PIB (Mn = 18,000 g/mol) in a PMMA matrix (PIB/PMMA) were evaluated to assess their feasibility as the powder component along with methyl methacrylate (MMA) as the liquid component in a standard powder/liquid bone cement formulation. A standard ISO four-point bend test, commonly used for testing bone cements, was employed to investigate flexural properties. The mixing time and powder/liquid (P/L) ratio were studied to formulate novel PIB/PMMA cements for optimum toughness. Appropriate formulations led to improved toughness while adequate flexural strength and modulus were maintained. An experimental PIB/PMMA-system exhibited approximately 57 MPa flexural strength and approximately 2000 MPa flexural modulus.

Acrylic bone cements: Residuals and extractability of methacrylate monomers and aromatic amines

AbstractA new formulation of acrylic bone cement [methylmethacrylate/n‐decylmethacrylate/isobornylmethacrylate (MMA/DMA/IBMA)] developed with the purpose of reducing the biologic adverse effects of bone cements was analyzed by high performance liquid chromatography for residual content of monomers and aromatic amines from the accelerator system [dimethyl‐p‐toluidine (DMPT), dihydroxypropyl‐p‐toluidine (DHPPT)] in the cured cement and for concentrations of these constituents in hydrophilic and lipophilic eluates. In comparison with conventional polymethyl‐methacrylate acrylics a considerable reduction of both released and residual MMA was experienced, being about 10‐ to 15‐fold. The residual content of the new DMA and IBMA monomers were 0.35% and 0.66%, respectively, in cured cement after 72 h and these could only be detected in the paraffin eluates. The residual content of aromatic amines was considerably reduced with the new cement formulation. No DMPT could be detected and the DHPPT represented a 3‐ to 4‐fold reduction in cured cement and a 8‐ to 10‐fold reduction in eluates. The residual DHPPT content of about 0.07% was found to be practically constant with time. It is concluded that MMA/DMA/IBMA cement cures faster and more completely.

Genotoxicity of Acrylic Bone Cements

The genotoxicity of conventional polymethylmethacrylate (PMMA) and a new formulation of bone cement: methylmethacrylate/n-decylmethacrylate/isobornylmethacrylate (MMA/DMA/IBMA) were tested by micronucleus test and reverse mutation assays of Salmonella typhimurium (Ames test). In extracts from cement pellets (37 degrees, 72 hr) with water and water/ethanol the concentration of MMA was reduced by 13-19 times with the new formulation and the concentrations of accelerators were reduced by 4-5 times. New chemical constituents (DMA, IBMA, dihydroxy-propyl-p-toluidine) were found in negligible concentrations. In the micronucleus test all three cement brands were found non-mutagenic and in the Ames test scattered increased revertant ratios were found without differences between the three brands. The new formulation does not possess any increased risk of genotoxicity.

Anchorage of the femoral head prosthesis to the shaft of the femur.

Anchorage of the femoral head prosthesis to the shaft of the femur.