PDMS-based flexible and conductive composite films containing modified PEDOT:PSS coated channels as a potential neural conduit†

Abstract

Neurological injuries cause the nervous system to malfunction, significantly impacting living standards. Conductive polymers aim to ensure the continuity of nervous system activities and their treatments through specially designed materials. Their soft structure, ability to combine with other polymers, load transfer capacity and biochemical composition enable them to be used in living tissues. Within the scope of this study, conductive and flexible composite films based on PEDOT:PSS aqueous dispersion (PPAD) (poly(3,4-ethylene dioxide thiophene):poly(styrene sulfonate)) were synthesized and combined in different proportions using bis(trifluoromethane)sulfonimide lithium (LiTFSI) salt as a chemical additive. Films were formed by pouring the PDMS polymer into a mold with a special electronic design printed with a 3D printer. Afterwards, the film channels were coated with modified PPAD and PPAD-LiTFSI by dip-coating and spin-coating methods and 1.1 mm thick composite films with channels 0.4 mm wide, 62.8 mm long and 0.1 mm deep were obtained. Several modifications including ion exchange, lyophilization, redispersion, and ethylene glycol (EG) addition have been applied to dispersions. As a consequence, particle size distribution, zeta potential, pH of dispersions, film conductivities and film biocompatibilities were modified as desired. Additionally, lyophilization and redispersion processes have been shown to mostly preserve material properties and extend the shelf life. Furthermore, analyses applied to normal materials were also conducted on samples kept for 12 months (12M), and the effects of time on the materials under different storage conditions were compared. Moreover, as a result of conductivity measurements, it was seen that the PPAD-RAL-EG had a conductivity of 4.67561 S m⁻¹ and was among the values that can be used in nerve tissue. Finally, we investigated the in vitro cell culture behaviour of the films using MTT analysis, LDH analysis, ethidium bromide calcein staining and alamar blue assay with the L929 and SH-SY5Y cell lines. The composite films were found to be biocompatible. In conclusion, the shelf life of PEDOT:PSS has been extended, allowing it to be used when necessary, and a composite production and modification method that has the potential to be used in peripheral nerve injuries has been introduced to the literature.