Voelcker Academy

Research Symposium 2010


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Ian A. Hardy

Endocytosis of Ultra-high Molecular Weight Polyethylene Particles by Osteoblasts is Dependent on Particles Size, Dose, and Treatment Time

Ian A. Hardy

Mentor: Dr. David Dean

Ultra-high molecular weight polyethylene (UHMWPE) is widely used to make components of orthopaedic implants. Although this biomaterial has good mechanical properties, wear debris particles are produced at the articulating surfaces. These particles have been implicated in implant loosening. Cell response to UHMWPE particles depends on particle number and size, with more particles and smaller size associated with a more robust response. Biological response to submicron size particles has been widely studied, but there are no detailed studies examining cell response to particles <0.2µm in size. A primary reason for this gap in our understanding is that UHMWPE particles tend to aggregate in suspension. This makes them virtually impossible to fractionate into different sizes. Our laboratory has developed a method for fractionating UHMWPE particles by adjusting the pH and surfactant content of the solvent in which the particles are suspended. Once suspended, the particles don’t reaggregate; this allows the separation of the particles into different size fractions by vacuum filtration. This fractionation technique allows study of the biological effects of different size ranges of UHMWPE particles. Prior studies have shown that UHMWPE particles stimulate osteoblast proliferation and inhibit osteoblast differentiation in a dose-dependent manner. The results have employed fractionated particles to compare the response of MG63 osteoblast like cells to particles of three different size ranges. Future studies will examine the effect of particle size on the rate and mechanism of particle endocytosis.