Hydroxyapatite nanoparticles/polyimide-coated platinum electrodes for improved heat-insulating and heavy metal ion diffusion properties

Polyimide is a promising shell polymer for platinum electrodes because of good biocompatibility, excellent corrosion resistance, mechanical, thermal and chemical stabilities. Herein, hydroxyapatite (HAP) nanoparticles were coated on polyimide encapsulated platinum electrodes to overcome the adverse effects of electrical stimulation. SEM, TEM, XRD and EDS analyses indicated that the coating was homogeneous and dense consisting of nano-hydroxyapatite. The HAP/polyimide coating presented good stability under the conditions of moist heat, high temperature or high shear stress (10 dyn/cm 2 ). Differential thermal analysis revealed that the nano-hydroxyapatite coating could significantly reduce the thermal diffusion from electrical stimulation its thermal elimination rate was about 96 times and 310 times smaller than that of polyimide encapsulated platinum electrode and bare platinum electrode, respectively. Atomic absorption spectroscopy measurement showed that the nano-hydroxyapatite coatings could prohibit the diffusion of platinum ions caused by electrical stimulation. CCK-8 test, neutral red uptake measurement and Tunel analysis revealed that the nano-hydroxyapatite coating could significantly attenuate the cytotoxicity of heavy metal ion from long-term stimulation. The in vivo biocompatibility evaluation by H&E measurement in a rabbit subcutaneous implantation model clearly showed that the nano-hydroxyapatite coating had good tissue response in 6 months. All these data supported that the nano-hydroxyapatite coating improved the biocompatibility of platinum electrodes by prohibiting thermal injury and heavy metal ions diffusion.