(23h) New Synthetic Route to Produce TiO2-PMMA Nanocomposites for Orthopedic Applications

Our longer living population is requiring a new generation of implant biomaterials for orthopedic applications as bone cements for total joint replacements. Polymer-nanoceramic composites provide unique combinations of properties such as significantly increased mechanical strength and radioopacity when compared to commercial reinforced composites. The challenge for preparing nanocomposites is the agglomeration of the nanofillers in the polymer matrix that leads to poor performance of the composite.

In this study, we present a new method of functionalizing novel titania nanostructures with a bifunctional molecule and synthesizing a nanocomposite by bulk polymerization with methyl methacrylate (MMA) monomer. Methacrylic acid (MA), a functionalization agent that can chemically link TiO2 nanomaterials (n-TiO2) and polymer matrix, was used to modify the surface of n-TiO2 using a Ti-carboxylic coordination bond. Various morphologies of n-TiO2 were studied including nanospheres, nanofibers, and nanotubes with various anatase/rutile ratios and with bimetallic integration of ZrO2. Then, the double bond in MA was copolymerized with methyl methacrylate (MMA) to form the n-TiO2-PMMA nanocomposites. The resulting materials were characterized by electron microscopy and mechanical analysis. To functionalize the surface of the nanofibers, calcined nanotitania powder was dispersed in 2-propanol, followed by reacting with methacrylic acid at 85 °C in a controlled environment at pH 5.5. The nanocomposites were synthesized at room temperature using PMMA powder and MMA liquid. The functionalized n-TiO2 (2 to 15 wt%) was dispersed in the liquid monomer portion by ultrasonic agitation for one hour. The resulting materials were then hand-mixed with the powder portion into a dough state and then injected into a polysiloxane mold (diameter: 16 mm, height: 2mm). After complete curing at room temperature, specimens were taken out of the mold and aged for 24 h at room temperature. For wet tests, the samples were conditioned for 1 week in distilled water at 37C. Electron microscopy results show excellent dispersion of the nanofillers in the polymer matrix.

Composites with functionalized titania nanotubes were shown to possess the highest compressive strength, fracture toughness, tensile modulus, and dynamic Young's and shear moduli, compared to other studied composites and commercial bone cements. The improved mechanical properties are due to the strength of the titania nanotubes, their high aspect ratio, and ability to chemically modify for bonding to the polymer. Moreover, the chemical bonding between the functionalized titania nanotubes and the PMMA matrix illustrates strong adhesion between the functionalized nanofibers and surrounding polymer matrix in allowing an external load to be effectively transferred from the polymer matrix.

As titania is an established radiopaque material, the resulting nanocomposites containing functionalized n-TiO2 exhibit a unique combination of radiopacity and mechanical strength for application as a bone cement.