Material characterisation and in vitro biological investigation into acrylic bone cements incorporating multi-walled carbon nanotubes (MWCNTs)

Acrylic bone cements, based on poly(methylmethacrylate) (PMMA), have been widely used in orthopaedic surgery for the fixation and force distribution of joint prostheses in cemented arthroplasties. However, PMMA continues to have less than ideal in vivo performance. A variety of materials have been added to bone cement to enhance its performance. Multi-Walled Carbon Nanotubes (MWCNTs) have emerged as a viable augmentation candidate because of their superior properties. This study investigated if the incorporation of small amounts of MWCNTs to a commercially available Simplex-P® bone cement matrix can improve its properties and in vivo performance. The MWCNTs examined were unfunctionalised, hydroxyl and carboxyl functionalised MWCNTs with weight loading varied from 0 to 0.5 wt.%. In most Total Joint Arthroplastry (TJA) there exists a state of biaxial loading: a combination of hoop, axial, and flexural loading, thus evaluating the stress within the cement mantle by traditional uniaxial tests may not provide accurate material characterisation. To address this issue, biaxial flexural test was used to determine the strength and stiffness of the resultant bone cement nanocomposites. Furthermore, finite element analysis (FEA) was performed to verify the analytical biaxial theory. Along with the mechanical properties of the reinforced nanocomposites, the rate of reaction exotherm generated, and the degree of polymerisation attained, thus, the residual monomer content were investigated by differential scanning calorimetry (DSC) using isothermal and dynamic modes. The maximum polymerisation temperature (Tmax) and the thermal necrosis index (TNI) values were also measured using a k-type thermocouple wire according to (ISO 5833:02) specifications. In order to investigate the in vivo biomedical potential of these bone cement nanocomposites, the influence of MWCNTs chemical functionality and loadings in bone cement composites on the adhesion and viability of an in vitro model of human osteoblast cells was studied. On the basis of the determined mechanical properties, this work demonstrated that the biaxial flexural test can be used for testing orthopaedic bone cement nanocomposites, and that specific MWCNTs loading (≤ 0.1 wt.%) can favourably improve the performance of acrylic bone cement. The thermal analysis demonstrated that the chemically functionalised MWCNTs altered the bone cement polymerisation kinetics, reducing the exothermic polymerisation reaction for acrylic bone cement, which could potentially reduce the hyperthermia experienced in vivo. The in vitro biocompatibility investigation showed that the biological response of osteoblasts onto the surface of MWCNTs reinforced Simplex-P® bone cement nanocomposites was not cytotoxic and exhibited good cell functionality related to cellular adhesion, growth, and viability.