Determination of Fracture Toughness of Bone Cement by Nano-Indentation Test

The nano-indentation test was used to measure fracture toughness of the bone cement. The cement sample was prepared using two different mixing methods i.e., hand mixing and vacuum mixing. For this purpose, some cubic specimens, each of the size 10×10×5?mm³ were produced and then the nano-indentation test was performed on both the hand-mixed and the vacuum-mixed specimens by nano-indenter setup and atomic force microscopy observation. The fracture toughness values obtained from the hand-mixed and vacuum-mixed cements were compared. The results indicate that the vacuum-mixed cement has significantly higher fracture toughness compared with the hand-mixed ones. Since the nano-indentation test method needs less sample material, decreases costs and obtains reliable results, it can be considered as a suitable technique for determination of the mechanical properties of bone cements instead of the macroscale test methods.     

The effect of gentamicin sulphate on the fracture properties of a manually mixed bone cement

This work investigates the effect of adding gentamicin, an antibiotic, on the fracture properties of bone cement. Endurance limit, fatigue crack propagation and fracture toughness were determined for a polymethylmethacrylate‐based cement, containing 10% w/w of barium sulphate as radiopacifying agent, and the same formulation modified by the addition of 4.22% w/w of gentamicin sulphate. The antibiotic does not affect the endurance limit nor the fracture toughness of the material. There are significant differences in the parameters of the Paris' law fitting the crack growth data: once the main crack is nucleated, it initially propagates at a lower rate but thereafter accelerates faster in gentamicin loaded bone cement. Despite this difference, the growth rate for the same stress intensity factor remains of the same order of magnitude in both formulations. The addition of 4.22% w/w of gentamicin sulphate to radiopaque bone cement has a negligible total effect on the fracture properties of the material.     

Dynamic fracture of bovine bone

True clinical fracture of bones in bovine, race horses or humans occur predominantly during impact loading (e.g. car accidents, falls or physical violence). Although static fracture tests provide an estimate of fracture toughness or R-curve behavior in bones, the static toughness values may be ill suited for predicting failure under dynamic loading conditions due to the visco-elastic response of bone (i.e. strain rate dependent properties). Despite decades of the study on deformation rate dependency of bone properties such as compression and fracture toughness, high-quality dynamic fracture data remain limited. Preliminary tests (compression and fracture toughness) have been conducted on dry and wet bovine bone under both static and dynamic loading conditions. While compression tests have been conducted with loading direction parallel and perpendicular to the bone axis (longitudinal and transverse, respectively), fracture tests were performed only in the transverse direction. The strain rate in compression tests varied between 10^− 3 and 10³ s^− 1, and the stress intensity rate varied between ∼10^− 3 and 10⁵ MPa√m/s. While low strain rate tests were conducted on conventional mechanical testing machines, high strain rate experiments were conducted on a split-Hopkinson bar under compression and a novel three-point bend configuration. The fracture morphology and the extent of damage of bone in each case were characterized using SEM, and an attempt is made to relate these to the rate dependent fracture toughness of the bone. It is believed that such understanding is crucial for mechanistic interpretation of bone fracture phenomenon and eventually for predicting bone failure reliably.     

Fracture toughness of acrylic bone cements

Clinical experience has shown that fracture of PMMA-based bone cements is a significant factor in the failure of orthopaedic joint replacements. Earlier studies of the fracture toughness properties of bone cement have been limited to relatively large test specimens — ASTM standard test methods require the use of specimens with dimensions considerably larger that those associated with bone cement in clinical use. In this study, a miniature short-rod specimen was used to measure the fracture toughness (K _IC) or two bone cements (Simplex-P and Zimmer LVC). The dimension of our mini specimens approaches the cross-section of bone cements as usedin vivo. The short-rod elastic-plastic fracture toughness test method introduced by Barker was utilized to ascertain the effect of specimen preparation and ageing in distilled water on fracture toughness. Our study indicated that slow hand-mixed specimens possess comparable fracture toughness to centrifuged specimens. After ageing in water, however, centrifuged and slow hand-mixed specimens are more fracture resistant than specimens prepared by mixing the cement quickly. An optimum void content for the bone cements studied was suggested by the experimental results; for Simplex-P bone cement it appeared to be less than 1.6% whereas it was between 1.6 and 3.6% for Zimmer LVC cement. Simplex-P bone cement also showed superior fracture toughness compared to Zimmer LVC cement after storage in water for 60 days at 37° C.     

Dual setting α-tricalcium phosphate cements

An extension of the application of calcium phosphate cements (CPC) to load-bearing defects, e.g. in vertebroplasty, would require less brittle cements with an increased fracture toughness. Here we report the modification of CPC made of alpha-tricalcium phosphate (α-TCP) with 2-hydroxyethylmethacrylate (HEMA), which is polymerised during setting to obtain a mechanically stable polymer-ceramic composite with interpenetrating organic and inorganic networks. The cement liquid was modified by the addition of 30–70 % HEMA and ammoniumpersulfate/tetramethylethylendiamine as initiator. Modification of α-TCP cement paste with HEMA decreased the setting time from 14 min to 3–8 min depending on the initiator concentration. The 4-point bending strength was increased from 9 MPa to more than 14 MPa when using 50 % HEMA, while the bending modulus decreased from 18 GPa to approx. 4 GPa. The addition of ≥50 % HEMA reduced the brittle fracture behaviour of the cements and resulted in an increase of the work of fracture by more than an order of magnitude. X-ray diffraction analyses revealed that the degree of transformation of α-TCP to calcium deficient hydroxyapatite was lower for polymer modified cements (82 % for polymer free cement and 55 % for 70 % HEMA) after 24 h setting, while the polymerisation of HEMA in the cement liquid was quantitative according to FT-IR spectroscopy. This work demonstrated the feasibility of producing fracture resistant dual-setting calcium phosphate cements by adding water soluble polymerisable monomers to the liquid cement phase, which may be suitable for an application in load-bearing bone defects.     

Toughening performance of glass fibre composites with core–shell rubber and silica nanoparticle modified matrices

The fracture energies of glass fibre composites with an anhydride-cured epoxy matrix modified using core–shell rubber (CSR) particles and silica nanoparticles were investigated. The quasi-isotropic laminates with a central 0°/0° ply interface were produced using resin infusion. Mode I fracture tests were performed, and scanning electron microscopy of the fracture surfaces was used to identify the toughening mechanisms.The composite toughness at initiation increased approximately linearly with increasing particle concentration, from 328 J/m² for the control to 842 J/m² with 15 wt% of CSR particles. All of the CSR particles cavitated, giving increased toughness by plastic void growth and shear yielding. However, the toughness of the silica-modified epoxies is lower as the literature shows that only 14% of the silica nanoparticles undergo debonding and void growth. The size of CSR particles had no influence on the composite toughness. The propagation toughness was dominated by the fibre toughening mechanisms, but the composites achieved full toughness transfer from the bulk.     

The effect of adding 10% of barium sulphate radiopacifier on the mechanical behaviour of acrylic bone cement

Barium sulphate (BaSO₄) is commonly used in bone cement as a radiopacifier. The addition of the BaSO₄ to the polymeric matrix may cause a decrease in the mechanical properties of the cement. In this work, the effect of adding 10%w/w BaSO₄ to a plain polymethylmethacrylate based bone cement was evaluated in terms of endurance limit, fatigue crack propagation and fracture toughness. A lower endurance limit (?13%), as well as a lower fracture toughness (?13%), was found for the radiopaque bone cement in comparison with the plain formulation. Conversely, a substantial decrease (66%) in the crack growth rate was found due to the radiopacifier addition. These are all effects that reflect the weakening of the polymeric matrix, caused by the addition of the radiopacifier.     

Investigation of the mechanical properties of DGEBA-based epoxy resin with nanoclay additives

The present study investigated the effect of nanoclay additives on the mechanical properties of diglycidyl ether of bisphenol A (DGEBA) epoxy resin. The resin was cured with diethyltoluene diamine (DETDA) hardener and four material variations produced through the addition of four types of nanoclays, respectively. The nanocomposites were prepared by the in situ polymerisation method with the aid of mechanical shearing. The properties of the nanocomposites investigated included tensile modulus, tensile strength, tensile strain and fracture toughness (K_IC). It was observed that while the addition of nanoclay significantly increased the elastic modulus and fracture toughness of DGEBA epoxy resin, it also significantly reduced the failure strength and failure strain with increasing nanoclay level. Possible mechanisms for the improvement and degradation of these properties of the epoxy–clay nanocomposite materials are discussed.     

Improvement of the mechanical properties of acrylic bone cements by substitution of the radio-opaque agent

Acrylic bone cements become radio-opaque by the addition of an inorganic compound, commonly BaSO₄ or ZrO₂. However, the use of these additives has some negative effects such as loss of mechanical properties, risk of release and bone resorption. The use of the monomer 2,5-diiodo-8-quinolyl methacrylate (IHQM), which shows adequate polymerization and radio-opacity properties, is proposed as a new X-ray opaque, methacrylate iodine-containing agent. The aim of this study is to determine the effect of this new radio-opaque agent on the mechanical properties of acrylic bone cements. The addition of the iodine-containing methacrylate provides a statistically significant increase in the tensile strength, fracture toughness and ductility, with respect to the barium sulphate-containing cement. This effect can be attributed to the fact that the use of a radio-opaque monomer eliminates the porosity associated with the barium sulfate particles, which show no adhesion to the matrix. However, some reinforcing effect must also be attributed to the iodine-containing monomer, since the tensile and fracture toughness values reached are even higher than those shown by the radiolucent cement. © 1999 Kluwer Academic Publishers     

Effect of iodixanol particle size on the mechanical properties of a PMMA based bone cement

Iodixanol (IDX) is a water soluble opacifier widely used in radiographical examinations of blood vessels and neural tissue, and it has been suggested as a potential contrast media in acrylic bone cement. The effect of the iodixanol particle size on the polymerisation process of the bone cement, the molecular weight, and the quasi-static mechanical properties have been investigated in this article. The investigation was performed using radiolucent Palacos powder mixed with 8 wt% of iodixanol with particle sizes ranging from 3 to 20 μm MMD, compared with commercial Palacos R (15 wt% ZrO₂) as control. Tensile, compressive and flexural tests showed that smaller particles (groups with 3, 4, and 5 μm particles) resulted in significantly lower mechanical properties than the larger particles (groups with 15, 16, and 20 μm particles). There was no difference in molecular weight between the groups. The thermographical investigation showed that the IDX cements exhibit substantially lower maximum temperatures than Palacos R, with the 4 μm IDX group having the lowest maximum temperature. The isothermal and the constant rate differential scanning calorimetry (DSC) did not show any difference in polymerisation heat (ΔH) or glass transition temperature (T _g) between radiolucent cement, or cement containing either IDX, or ZrO₂. The findings show that the particle size for a bone cement containing iodixanol should be above 8 μm MMD.     

Determination of interfacial fracture toughness of bone-cement interface using sandwich Brazilian disks

The long-term stability of cemented total hip replacements critically depends on the lasting integrity of the bond between bone and bone cement. Conventionally, the bonding strength of bone-cement is obtained by mechanical tests that tend to produce a large variability between specimens and test methods. In this work, interfacial fracture toughness of synthetic bone-cement interface has been studied using sandwiched Brazilian disk specimens. Experiments were carried out using polyurethane foams as substrates and a common bone cement as an interlayer. Selected loading angles from 0° to 25° were used to achieve full loading conditions from mode I to mode II. Finite element analyses were carried out to obtain the solutions for strain energy release rates at given phase angles associated with the experimental models. The effects of crack length on the measured interfacial fracture toughness were examined. Microscopic studies were also carried out to obtain the morphology of the fractured interfaces at selected loading angles.The implication of the results on the assessment of fixation in acetabular replacements is discussed in the light of preliminary work on bovine cancellous bone-cement interface.     

Comparison of the material properties of PMMA and glass-ionomer based cements for use in orthopaedic surgery

The intrisic benefits of low exotherm and bioactivity have generated interest in utilizing glass-ionomer cements (GIC) as a bone cement replacement in orthopaedic surgery. This paper is concerned with evaluating the mechanical properties of compressive strength, flexural strength, and fracture toughness for two traditional GICs, one resin-modified GIC (an experimental bone cement) and two polymethylmethacrylate (PMMA) cement systems. To determine the suitability of a GIC system for use in the clinical orthopaedic setting, the additional characteristics of setting exotherm and setting time have also been evaluated. The characterization of these two vastly different cement systems has raised some concern as to the applicability of using the current orthopaedic standards for the testing of GIC systems. In particular, issues relating to the strain rate dependence of PMMA cement and the exothermic basis for determining setting time are not applicable as these factors are not characteristic of GIC systems. Whilst the intrinsic benfits of current GIC systems are well understood and generally accepted, this study has shown their intrinsic mechanical properties to be inferior to current PMMA cements. Improvement in the mechanical properties of traditional GICs have been achieved with the addition of a resin component (HEMA). © 2001 Kluwer Academic Publishers     

Computational modeling of debonding behavior at the bone/cement interface with experimental validation

Both clinical examinations and in vitro physical experiments have shown that the fixation interfaces of cemented components are actually critical sites affecting the long-term stability and survival of prosthetic implants after implantation. This study aims to investigate the interfacial debonding behavior of bone/cement composite structures and attempts to establish an analysis model for clinical applications involving cemented prosthetic components. The mechanical properties of the bonded interface were characterized by interfacial strength, interfacial stiffness, and fracture toughness; the measured values of tensile strength, shear strength, and fracture toughness were 4.94 MPa, 5.94 MPa, and 0.34 MN/m^3/2, respectively. The measured strengths of the different configurations from this study are in good agreement with the experimental results available in the literature. In addition, we generated a finite element model with the same geometry as that of the experimental specimen used in the fracture test. The extent of interfacial debonding was further determined by means of the surface damage criteria and the fracture characteristics of the interface crack. The finite element model with an elastic interface predicted that the stress intensity factor (SIF) at the bone/cement interface crack varies nonlinearly with the applied load, which shows that the interface disintegrates at the load level, as was measured in the fracture experiments. It was possible to verify that the proposed simulation model was capable of describing the interfacial mechanical behavior of cemented components.     

Processing and characterization of a lightweight concrete using cenospheres

A study has been conducted in which a lightweight concrete was processed using ceramic microspheres, known as cenospheres, as a primary aggregate. The mechanical properties, including compressive strength, tensile strength, flexural strength and fracture toughness, were tested and cataloged. It was determined that the addition of high volumes of cenospheres significantly lowered the density of concrete but was also responsible for some strength loss. This strength loss was recovered by improving the interfacial strength between the cenospheres and the cement. The interfacial properties were quantified using interfacial fracture mechanics techniques. These techniques were also employed to find a suitable surface modifier with which to improve this interface. The admixture silica fume and the coupling agent Silane were found to be suitable candidates and both performed well in small-scale compression testing. Silica fume was eventually isolated as a prime candidate. The concrete produced with this admixture was tested and compared to a concrete with an equal volume fraction of cenospheres. The addition of silica fume improved the compressive strength of cenosphere concrete by 80%, tensile strength by 35%, flexural strength by 60% and fracture toughness by 41%.     

Improved mechanical properties of acrylic bone cement with short titanium fiber reinforcement

Acrylic bone cements are widely used in total joint arthroplasties to grout the prosthesis to bone. The changes in the tensile properties and fracture toughness of polymethylmethacrylate (PMMA) bone cements obtained by the addition of control and heat treated short titanium fibers are studied. Heat treatment of titanium fibers is conducted to precipitate titania particles on the fiber surface, which may improve the biocompatibility of the metal. Control (non-heat treated) and heat treated short titanium fibers (250 μm long and 20μm diameter) were used as reinforcements at 3 volume %. X-ray diffraction indicated the presence of a rutile form of titania due to the heat treatments. Results indicate that the tensile and fracture properties of unfilled bone cement were improved by the addition of control and heat-treated fibers. The fracture properties of bone cements reinforced with control titanium fibers were at least 10% higher than those reinforced with heat treated titanium fibers. Therefore, we recommend further studies on the use of non-heat treated titanium fibers to reinforce acrylic bone cement.     

Epoxy modified with triblock copolymers: morphology, mechanical properties and fracture mechanisms

The morphology, fracture toughness and mechanical properties of an anhydride-cured diglycidylether of bisphenol-A epoxy polymer modified with poly(methyl methacrylate)-b-poly(butylacrylate)-b-poly(methyl methacrylate) (MAM) have been investigated. The addition of three different MAM triblock copolymers (M22N, M52N and M52) to the epoxy polymer gives two different microstructures. A nanostructure with well-dispersed worm-like micelles (or a bicontinuous gyroid structure if the micelles are connected into a network) was obtained using M22N. The addition of M52N or M52 gives dispersed micron-size particles in the epoxy matrix for ≤7 wt% MAM, and a co-continuous microstructure at higher MAM contents. These triblock copolymers toughen the epoxy polymer significantly, with only slight reductions in the mechanical and thermal properties of the epoxy polymer. The maximum values of fracture toughness and fracture energy (1.22 MPa m^1/2 and 450 J/m², respectively) were measured using 12 wt% M22N, which is an increase of 100 and 350%, respectively, compared with the unmodified epoxy. The M52- and M52N-modified materials show a maximum toughness when a co-continuous microstructure is formed. The potential toughening mechanisms are identified and discussed.     

超细玻璃纤维改性PMMA骨水泥力学性能研究

为了提高PMMA骨水泥的机械力学强度,用超细玻璃纤维对其进行改性.采用扫描电子显微镜等手段研究了超细玻璃纤维的含量以及处理方式对骨水泥拉伸强度和冲击韧性等力学性能的影响.研究表明,玻璃纤维含量(质量分数)为10%左右时材料的抗冲及抗拉性能好,同时此含量时材料的弹性模量低.用硅烷偶联剂偶联过的玻璃纤维其改性效果要优于没有偶联过的,球磨混合玻璃纤维与PMMA粉料比手工混合玻璃纤维在PMMA基体中的分散性要好,其力学性能也较手工混合的要好.     

Development and cytotoxicity evaluation of SiAlONs ceramics

SiAlONs are ceramics with high potential as biomaterials due to their chemical stability, associated with suitable mechanical properties, such as high fracture toughness and fracture resistance. The objective of this work was to investigate the mechanical properties and the cytotoxicity of these ceramic materials. Three different compositions were prepared, using silicon nitride, aluminum nitride and a rare earth oxide mixture as starting powders, yielding Si₃N₄–SiAlON composites or pure SiAlON ceramics, after hot-pressing at 1750 °C, for 30 min. The sintered samples were characterized by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). Furthermore, hardness and fracture toughness were determined using the Vicker's indentation method. The biological compatibility was evaluated by in vitro cytotoxicity tests. Ceramic with elevated hardness, ranging between 17 and 21 GPa, and high fracture toughness of 5 to 6 MPa m^1/2 were obtained. Since a nontoxic behavior was observed in the cytotoxicity tests, it may be assumed that SiAlON-based ceramics are viable materials for clinical applications.     

Real time monitoring of the polymerisation of PMMA bone cement using Raman spectroscopy

In this investigation Raman spectroscopy was shown to be a method that could be used to monitor the polymerisation of PMMA bone cement. Presently there is no objective method that orthopaedic surgeons can use to quantify the curing process of cement during surgery. Raman spectroscopy is a non-invasive, non-destructive technique that could offer such an option. Two commercially available bone cements (Palacos^® R and SmartSet^® HV) and different storage conditions (4 and 22°C) were used to validate the technique. Raman spectroscopy was found to be repeatable across all conditions with the completion of the polymerisation process particularly easy to establish. All tests were benchmarked against current temperature monitoring methods outlined in ISO and ASTM standards. There was found to be close agreement with the standard methods and the Raman spectroscopy used in this study.     

Compositional influence on toughness of structural acrylic adhesives

The fracture behaviour and toughness of modified acrylic adhesives, based on mixtures of various acrylic monomers and rubbers polymerized by a radical mechanism have been investigated. The influence of the matrix and rubber composition on bulk morphology and mechanical properties is analysed by means of transmission and scanning electron microscopy, and dynamic-mechanical measurements. Both microtexture of the material and resin-rubber compatibility have been found to significantly influence the fracture behaviour in tension-impact tests.