Abstract
With a promising import-substituting alternative of electromyography (EMG) needle electrodes used in spasticity treatment, this research aimed to investigate polymer types and polymer coating technologies that were suitable for coating on the needle shaft of the common hypodermic needles. Previous study of the EMG needle electrodes with accessible data of related coating products and Thailand’s commercially available raw materials data revealed a potential technique of implementing the dip-spinning process of aqueous fluoropolymer dispersion coating onto the surface of 316 stainless steel needle shaft. As a result of the former research on topic “a study of polymer coating on needle for medical application” financially supported by National Research Council of Thailand, the newly designed dip-spin coating equipment was used to coat FEP and PTFE on the needle shafts of the common hypodermic needles. Various characterizations and testing of the polymer-coated surfaces were conducted. Depended on predetermined coating parameters, thicknesses of FEP and PTFE could be coated on the needle shafts in the range of 5-10 μm. Both FEP- and PTFE- coated needles showed good adhesion with no polymer film detachment after insertion the needles into a piece of pork shoulder. In addition, the results of penetrating the FEP- and PTFE- coated needles to the injection vial stoppers showed low friction forces and good adhesion. Film adhesion qualities were in agreement with measuring adhesion by using tape test on the FEP- and PTFE- coated flat surfaces of 316 stainless steel plates that showed no detachment. As results of penetrating the FEP- and PTFE- coated needles to the injection vial stoppers, their drag forces were compared with the commercially available EMG needles. Drag forces of the FEP- and PTFE- coated needles were, respectively, 1880-1900 mN and 2650-3000 mN while the commercially available EMG needles from companies A and B were, respectively, 1450-1520 mN and 1400-1900 mN. However, the coats from company A were detached from the needle shafts during penetrating the injection vial stoppers with possible cause of poor adhesion of the coat on the needle shaft. Biological evaluation testing was complied with Thailand’s TIS-1398 sterile hypodermic needles for single use and TIS-2395 Biological evaluation of medical devices. Seven sets of the biological evaluation testing included cytotoxicity testing, irritation testing, sensitization testing, pyrogen testing, haemocompatiblity testing, systematic toxicity testing, and intracutaneous testing.
