Zargarian, Seyed Shahrooz (Institute of Fundamental Technological Research, Polish Academy of Sciences )


Recently, conductive hydrogels have garnered significant attention and permitted momentous improvements in neuroscience due to their tissue-like softness, chemical steadiness, and sufficient electrical conductivity.(1) They have been utilized as interfaces for neural electrode arrays to improve their biocompatibility and lower protein adsorption. In particular, these materials have the potential to circumnavigate the mechanical mismatch between the neural probes and the implanted tissue.(2) Therefore, the transition from rigid to soft interfaces can improve the performance of the recording/stimulating devices by minimizing tissue irritation and neuronal cell loss. Alas, the chronic application of such interfaces is still challenging due to the poor adhesion of soft hydrogels to metallic electrodes and their relatively low stimuli-responsive characteristics.
The utilization of porous, high surface area and stimuli-responsive hydrogels may compensate for these physiochemical shortcomings, offering multifunctional properties such as low electrical impedance, better mechanical properties, lower thickness, and on-demand controlled release of bioactive agents.
To this end, a conductive hydrogel with semi-interpenetrating polymer network (semi-IPN) structure comprised of temperature-responsive poly(N-isopropyl acrylamide) (PNIPAAm)-based copolymer and polythiophene (PT) was synthesized in this study and miniaturized via a nanofabrication method to be used as a neural interface.
The electrospinability of the solution was facilitated by the high molecular weight of the synthesized PNIPAAm-based block copolymer and its narrow molecular weight distribution. A cytocompatible and degradable dendrimer was used as the crosslinking agent of the semi-IPN with ample surface groups, which allowed a dual-hardening physical and chemical gelation process. Consequently, a lowered curing temperature was necessary to attain structural robustness at molecular and macroscopic levels. The copolymerization process reduced the volume phase transition temperature (VPTT) of pure PNIPAAm, and the resulted block copolymer showed lower overall transition energy. The fibrous hydrogel gave water molecules rapid access to the whole material and switched on a fast responsive characteristic. As the water impregnated the xerogel, the porosity and fiber diameter increased substantially. The developed material showed fast swelling and de-swelling responses triggered by temperature changes. Repeated hydration/dehydration cycles did not affect the physical integrity of produced electrospun fibers.
Furthermore, the conductive fibrous semi-IPN displayed a high electrical conductivity and charge storage capacitance compared to the conductive bulk hydrogel. This occurrence was attributed to the formation of a large electrochemical surface area that resulted from system miniaturization. The impedance of the developed material was in the range of physiologically relevant frequencies.
The incorporation of PT chains in the stimuli-responsive hydrogel network promoted the synergetic effect between the two components leading to the fabrication of a superior fibrous interpenetrating network neural interface with remarkable electrochemical properties.
This study was supported by the First TEAM grant number POIR.04.04.00-00-5ED7/18-00, which is conducted within the framework of the First TEAM programme of the Foundation for Polish Science (FNP) and co-financed by the European Union under the European Regional development Fund.
1. Sung, C. et al., J. Mater. Chem. B, Mater. Biol. Med. 8, 6624 (2020).
2. Park, S. et al., Nat. Commun. 12, 3435 (2021).


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