The Application of Carbon Nanotube to Bone Cement

Abstract

Bone cement is used as a grouting agent between the prosthesis and the bone as well as a method to anchor prosthesis in orthopedic implants such as total hip replacement. Basically, bone cement consists of two portions: (1) powder portion including pre-polymerized methylmethacrylate (PMMA) and initiator (benzoyl peroxide) and (2) liquid portion including methylmethacrylate (MMA) monomer and promoter (N, N-dimethyl-p-toluidine). When two portions are mixed, the initiation is activated by promoters that make the free radicals (initiators). The free radicals react with monomers for polymerization (Park & Lakes, 1992). Some disadvantages of PMMA bone cement are found such as significant poor mechanical properties which may cause failure of the cement. For instance, PMMA bone cement is considerably weaker than bone (Saha & Pal, 1984) and the tensile stresses of PMMA bone cement are comparatively low (Saha & Pal, 1986). Vallo et al. used cross-linked PMMA beads to prepare cements by replacing 30% of the PMMA powder and showed an increase in the flexural strength value of 22.4%. The cross-linked beads resulted in more effective reinforcing filler than plain PMMA beads (Vallo et al., 2004). Basgorenay et al. modified acrylic bone cement by addition of hydroxyapatite and ammonium nitrate. A linear relation was observed in compression strength (from 98 to 111 MPa) and in tensile strength (from 27 to 21 MPa) upon HA addition, and in the compression strength (from 103 to 85 MPa) and in the tensile strength (from 22 to 17 MPa) with NA addition (Basgorenay et al., 2006). Kwon et al. prepared bone cements incorporated with montmorillonite (MMT) to improve their mechanical properties. The measured compressive strength of the bone cement with 1 wt % MMT was 113.6 ± 3.9 MPa, which is higher than that of the bone cement without MMT (110.1 ± 2.0 MPa). The measured tensile strength of the control bone cement with 1 wt % MMT was 27.2 ± 4.4 MPa, which is higher than that of the bone cement without MMT (22.3 ± 3.8 MPa) (Kwon et al., 2007). Carbon nanotube is known for a larger aspect ratio and higher modulus (Iijima, 1991). Kearns and Shambaugh found that the tensile strength of polypropylene fibers reinforced with carbon nanotube could increase 40% (Kearns & Shambaugh, 2002). There are several studies related to the preparation and characterization of carbon nanotube/poly(methyl methacrylate) composites. For example, Jin et al. studied muti-walled carbon nanotube/poly(methyl methacrylate) composites fabricated by melting blending and found that the nanotube was well dispersed in the polymer matrix and the storage modulus of the