Mechanical characterization of commercially made carbon-fiber-reinforced polymethylmethacrylate

Carbon Fiber Biocompatibility for Implants

Carbon fibers have multiple potential advantages in developing high-strength biomaterials with a density close to bone for better stress transfer and electrical properties that enhance tissue formation. As a breakthrough example in biomaterials, a 1.5 mm diameter bisphenol-epoxy/carbon-fiber-reinforced composite rod was compared for two weeks in a rat tibia model with a similar 1.5 mm diameter titanium-6-4 alloy screw manufactured to retain bone implants. Results showed that carbon-fiber-reinforced composite stimulated osseointegration inside the tibia bone marrow measured as percent bone area (PBA) to a great extent when compared to the titanium-6-4 alloy at statistically significant levels. PBA increased significantly with the carbon-fiber composite over the titanium-6-4 alloy for distances from the implant surfaces of 0.1 mm at 77.7% vs. 19.3% (p < 10⁻⁸) and 0.8 mm at 41.6% vs. 19.5% (p < 10⁻⁴), respectively. The review focuses on carbon fiber properties that increased PBA for enhanced implant osseointegration. Carbon fibers acting as polymer coated electrically conducting micro-biocircuits appear to provide a biocompatible semi-antioxidant property to remove damaging electron free radicals from the surrounding implant surface. Further, carbon fibers by removing excess electrons produced from the cellular mitochondrial electron transport chain during periods of hypoxia perhaps stimulate bone cell recruitment by free-radical chemotactic influences. In addition, well-studied bioorganic cell actin carbon fiber growth would appear to interface in close contact with the carbon-fiber-reinforced composite implant. Resulting subsequent actin carbon fiber/implant carbon fiber contacts then could help in discharging the electron biological overloads through electrochemical gradients to lower negative charges and lower concentration.

Incorporation of MWCNTs to PMMA Bone Cements: Effects on Fatigue Properties

All the commercially available plain acrylic bone cement brands, which are used incemented arthroplasties, are based on poly (methyl methacrylate). With a few exceptions, have the same constituents. It is well known that these brands are beset with many drawbacks, such as high maximum exotherm temperature, lack of bioactivity, and volumetric shrinkage upon curing. The aim of this study was to investigate the fatigue properties of MWCNTs-PMMA bone cement composites. Multi-walled carbon nanotubes (unfunctionalised and carboxyl functionalised), which was synthesized by infusion chemical vapor deposition, and PMMA bone cement were used to produce pastes. The mixing amount of MWCNTs ranged from 0.1 wt.% to 1wt.%. The fatigue properties of the MWCNTs-PMMA bone cement was characterised with the type and wt.% loading of MWCNTs used having a significant influence on the number of cycles to failure. The condition and degree of dispersion of the MWCNTs in the matrix at different length scales were studied using field emission scanning electron microscopy. Improvements of the fatigue properties were attributed to the MWCNTs arresting or retarding crack propagation through the cement by a bridging effect and hindering crack propagation. MWCNTs agglomerates were evident in the cement microstructure and the degree of agglomeration depended on the level of the mixing amount and the ability of the MWCNTs.

Fatigue and biocompatibility properties of a poly(methyl methacrylate) bone cement with multi-walled carbon nanotubes

Composites of multi-walled carbon nanotubes (MWCNT) of varied functionality (unfunctionalised and carboxyl and amine functionalised) with polymethyl methacrylate (PMMA) were prepared for use as a bone cement. The MWCNT loadings ranged from 0.1 to 1.0 wt.%. The fatigue properties of these MWCNT-PMMA bone cements were characterised at MWCNT loading levels of 0.1 and 0.25 wt.% with the type and wt.% loading of MWCNT used having a strong influence on the number of cycles to failure. The morphology and degree of dispersion of the MWCNT in the PMMA matrix at different length scales were examined using field emission scanning electron microscopy. Improvements in the fatigue properties were attributed to the MWCNT arresting/retarding crack propagation through the cement through a bridging effect and hindering crack propagation. MWCNT agglomerates were evident within the cement microstructure and the degree of agglomeration was dependent on the level of loading and functionality of the MWCNT. The biocompatibility of the MWCNT-PMMA cements at MWCNT loading levels upto 1.0 wt.% was determined by means of established biological cell culture assays using MG-63 cells. Cell attachment after 4h was determined using the crystal violet staining assay. Cell viability was determined over 7 days in vitro using the standard colorimetric MTT assay. Confocal scanning laser microscopy and SEM analysis was also used to assess cell morphology on the various substrates.

Physical and mechanical properties of PMMA bone cement reinforced with nano-sized titania fibers

X-ray contrast medium (BaSO(4) or ZrO(2)) used in commercially available PMMA bone cements imparts a detrimental effect on mechanical properties, particularly on flexural strength and fracture toughness. These lower properties facilitate the chance of implant loosening resulting from cement mantle failure. The present study was performed to examine the mechanical properties of a commercially available cement (CMW1) by introducing novel nanostructured titania fibers (n-TiO(2) fibers) into the cement matrix, with the fibers acting as a reinforcing phase. The hydrophilic nature of the n-TiO(2) fibers was modified by using a bifunctional monomer, methacrylic acid. The n-TiO(2) fiber content of the cement was varied from 0 to 2 wt%. Along with the mechanical properties (fracture toughness (K (IC)), flexural strength (FS), and flexural modulus (FM)) of the reinforced cements the following properties were investigated: complex viscosity-versus-time, maximum polymerization temperature (T (max)), dough time (t (dough)), setting time (t (set)), radiopacity, and in vitro biocompatibility. On the basis of the determined mechanical properties, the optimized composition was found at 1 wt% n-TiO(2) fibers, which provided a significant increase in K (IC) (63%), FS (20%), and FM (22%), while retaining the handling properties and in vitro biocompatibility compared to that exhibited by the control cement (CMW1). Moreover, compared to the control cement, there was no significant change in the radiopacity of any of the reinforced cements at p = 0.05. This study demonstrated a novel pathway to augment the mechanical properties of PMMA-based cement by providing an enhanced interfacial interaction and strong adhesion between the functionalized n-TiO( 2) fibers and PMMA matrix, which enhanced the effective load transfer within the cement.

Augmentation of acrylic bone cement with multiwall carbon nanotubes

Acrylic bone cement, based on polymethylmethacrylate (PMMA), is a proven polymer having important applications in medicine and dentistry, but this polymer continues to have less than ideal resistance to mechanical fatigue and impact. A variety of materials have been added to bone cement to augment its mechanical strength, but none of these augmentative materials has proven successful. Carbon nanotubes, a new hollow multiwalled tubular material 10-40 nm in diameter, 10-100 microm long, and 50-100 times the strength of steel at 1/6 the weight, have emerged as a viable augmentation candidate because of their large surface area to volume ratio. The objective of this study was to determine if the addition of multiwall carbon nanotubes to bone cement can alter its static or dynamic mechanical properties. Bar-shaped specimens made from six different (0-10% by weight) concentrations of multiwall carbon nanotubes were tested to failure in quasi-static 3-point bending and in 4-point bending fatigue (5 Hz). Analyses of variance and the 3-Parameter Weibull model were used to analyze the material performance data. The 2 wt % MWNT concentration enhanced flexural strength by 12.8% (p=0.003) and produced a 13.1% enhancement in yield stress (p=0.002). Bending modulus increased slightly with the smaller (<5 wt % MWNT) concentrations, but increased 24.1% (p<0.001) in response to the 10 wt % loading. While the 2 wt % loading produced slightly improved quasi-static test results, it was associated with clearly superior fatigue performance (3.3x increase in the Weibull mean fatigue life). Weibull minimum fatigue life (No), Weibull modulus (alpha), and characteristic fatigue life (beta) for bone cement augmented with carbon nanotubes were enhanced versus that observed in the control group. These data unambiguously showed that the bone cement-MWNT polymer system has an enhanced fatigue life compared to "control" bone cement (no added nanotubes). It is concluded that specific multiwall carbon nanotube loadings can favorably improve the mechanical performance of bone cement.

Bending and fracture toughness of woven self-reinforced composite poly(methyl methacrylate)

Loosening remains an impediment to the long-term success of total hip replacements despite numerous improvements in the materials used. In cemented prostheses, fatigue and fracture of bone cement have been implicated in the failure of these devices. A new material, self-reinforced composite poly(methyl methacrylate). (SRC-PMMA), has been developed. SRC-PMMA is formed by a novel processing method that will be described. The composite consists of high strength, highly oriented PMMA fibers embedded in a matrix of PMMA. Using a woven form of SRC-PMMA, an in vitro physical and mechanical evaluation was performed to assess the feasibility of its use in an orthopedic prosthesis. Three different weaves of SRC-PMMA were evaluated in bending and fracture toughness in air, after immersion for 30 days in 37 degrees C saline, and after gamma irradiation followed by immersion. Bending modulus and strength were decreased by gamma irradiation followed by saline immersion. The effect of saline immersion alone on bending strength and modulus was negligible. Saline immersion and gamma irradiation followed by saline immersion was shown to have little or no effect on the fracture toughness of woven SRC-PMMA. Differences in the fracture processes of the different weaves were found and can be related to the differing orientation of fibers to the fracture toughness pre-crack. Optimally incorporated SRC-PMMA absorbs the same amount of water as bone cement. Comparison to previous and current work with bone cement controls shows that SRC-PMMA is a material equal to or better than bone cement in all tests performed. It deserves further consideration as a candidate biomaterial.

Effect of methylene blue on the fracture toughness of acrylic bone cement

It has been advocated that the use of contrast acrylic bone cement (namely, a cement in which a suitable additive is included) for the fixation of a cemented arthroplasty will facilitate its revision (should this be necessary). It is useful, therefore, to determine the extent to which each of the relevant mechanical properties of the cement is affected by the presence of such an additive. It is shown, in the present work, that the addition of one contrast agent (an aqueous methylene blue solution) to a cement has no statistically significant effect on its mode-I plane-strain fracture toughness. This strengthens the case for the use of contrast cement for the aforementioned application.

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.

Cellular events in the mechanisms of prosthesis loosening

The functional restoration of a joint damaged by trauma or disease is obtained by prosthetic surgery. In particular the implantation of hip prostheses is regarded as routine in orthopedic surgery and thorough research has been developed in this field. The prosthetic replacement of the knee and even more so the ankle and elbow occurs less frequently in clinical practice and has been studied less intensively. The results of artifical hip replacement are generally good, both in terms of pain relief and the restoration of satisfactory joint function. Nevertheless, as time passes, a high rate of failures have been recorded due to prosthesis infections, fracture and wearing of the prosthetic components and prosthesis loosening by various causes. The use of ultra-filtered air and laminar flow in operating theatres and antibiotic prophylaxis have dramatically reduced the incidence of infections in total hip arthroplasty. Thanks to the setting up of new stem configurations and the use of superalloys that are highly resistant to fatigue failure, the fracture of the femoral component has been virtually eliminated as a complication of total hip arthroplasty replacements. Loosening is thus the most frequent complication in total hip replacement.

Study of the mineral-organic linkage in an apatitic reinforced bone cement

In order to increase mechanical properties of surgical cements, an apatitic filler has been linked to the polymethylmethacrylate (PMMA) matrix. We report here the study of the linkage between the mineral and organic components by a dielectric spectroscopy: Thermally Stimulated Current. First, the mineral-organic interface between apatitic-octocalcic phosphate and hydroxyethylmethacrylate (HEMA) has been investigated. Second, the filler-matrix interface between grafted apatite and PMMA has been examined. It has been shown that the filler is chemically linked to the matrix and stiffens the PMMA bone cement.

Calcium phosphate and polymer interfaces in orthopaedic cement

In order to increase the mechanical properties and the bioactivity of surgical cement, the linkage of two monomers, namely hydroxyethylmethacrylate (HEMA) and methylmethacrylate (MMA), by copolymerization to a modified apatite has been studied. This linkage is obtained by grafting an organic molecule containing an ethylenic bond onto the apatite surface. These two studies have shown that after polymerization more than 70% of the modified apatite is irreversibly linked to the polymers. This linkage is due not to an adsorption but to the existence of a stable covalent bond between apatite and polymers. From these results, it should be possible to develop a new orthopaedic cement which will be more biocompatible and will have good mechanical properties.

Use of high-performance polyethylene fibres as a reinforcing phase in poly(methylmethacrylate) bone cement

First results are presented concerning the elastic and ultimate mechanical behaviour of p(MMA) bone cement reinforced with as-received and surface-modified Spectra 900 polyethylene fibres. Even though the surface chemistry and reactivity of the fibres was modified, the surface oxidation and surface grafting treatments of the polyethylene fibres apparently did not significantly affect the mechanical properties of the polyethylene-reinforced p(MMA) bone cement or improve the interfacial bonding. This may be attributed to the rather unfavourable area-to-volume ratio of PE fibres for such treatments, as well as to the necessarily low content of PE fibres in the bone cement which does not allow a clear differentiation between the various samples.

Elastic and ultimate properties of acrylic bone cement reinforced with ultra-high-molecular-weight polyethylene fibers

A study of the fracture behavior of poly-(methyl methacrylate) (PMMA) bone cement reinforced with short ultra-high-molecular-weight polyethylene (Spectra 900) fibers is presented. Linear elastic and nonlinear elastic fracture mechanics results indicate that a significant reinforcing effect is obtained at fiber contents as low as 1% by weight, but beyond that concentration a plateau value is reached and the fracture toughness becomes insensitive to fiber content. The flexural strength and modulus are apparently not improved by the incorporation of polyethylene fibers in the acrylic cement, probably because of the presence of voids, the poor mixing practice and the weakness of the fiber/matrix interfacial bond. The present polyethylene/PMMA composite presents several advantages as compared to other composite cements, but overall the mechanical performance of this system resembles that of Kevlar 29/PMMA cement, with a few differences. Scanning electron microscopy reveals characteristic micromechanisms of energy absorption in Spectra 900/PMMA bone cement. A scheme for the strength of random fiber-reinforced composites, which is a simple extension of the Kelly and Tyson model for the strength of unidirectional composites, is presented and discussed. Young's modulus and the fracture toughness results are discussed in the framework of existing theories. More fundamental modeling treatments are needed in terms of fracture micromechanisms to understand and optimize the various mechanical properties with respect to structural parameters and cement preparation technique.