A successful modification of titanium dioxide (TiO2) nanoparticles surfaces by a grafting-to polymer technique combining catalytic chain transfer and thiol-ene click chemistry is reported. Vinylic end functional polymers were first prepared by catalytic chain transfer polymerization (CCTP) using oligo(ethylene glycol) methacrylate as a monomer. The presence of vinylic end groups was then exploited to attach the polymers to thiol functionalized TiO2 nanoparticles via thiol-ene Michael nucleophilic reactions. X-ray photoelectron spectroscopy (XPS), attenuated total reflectance-infrared (ATR-IR), dynamic light scattering (DLS), and thermogravimetric analyses (TGA) were used to verify the successful modification of the TiO2 surface. The modified TiO2 nanoparticles were stable in cell culture media and formed smaller aggregates when compared to non-surface modified nanoparticles. Cellular toxicity of the hybrid TiO2-polymer particles towards human lung cell lines A549 and H1299 in vitro was evaluated. Results from one-dimensional gel electrophoresis show the presence of polymer layers around the particles affects the adsorption of protein onto the TiO2 surface. The reduction in particle aggregate size and changes to the particle surface chemistry, following polymer grafting, was found to reduce cellular uptake and diminish cytotoxicity for both human lung cell lines tested.