Can the Wet – State Conductivity of Hydrogels be Improved by Incorporation of Spherical Conducting Nanoparticles?

Abstract

In nerve and muscle regeneration applications, the incorporation of conducting elements into biocompatible materials has gained interest over the last few years, as it has been shown that electrical stimulation of some regenerating cells has a positive effect on their development. A variety of different materials, ranging from graphene to conducting polymers, have been incorporated into hydrogels and increased conductivities have been reported. However, the majority of conductivity measurements are performed in a dry state, even though material blends are designed for applications in a wet state, in vivo environment. The focus of this work is to use polypyrrole nanoparticles to increase the wet-state conductivity of alginate to produce a conducting, easily processable, cell-supporting composite material. Characterization and purification of the conducting polymer nanoparticle dispersions, as well as electrochemical measurements, have been performed to assess conductivity of the nanoparticles and hydrogel composites in the wet state, in order to determine whether filling an ionically conducting hydrogel with electrically conductive nanoparticles will enhance the conductivity. It was determined that the introduction of spherical nanoparticles into alginate gel does not increase, but rather slightly reduces conductivity of the hydrogel in the wet state. ABSTRACTIn nerve and muscle regeneration applications, the incorporation of conducting elements into biocompatible materials has gained interest over the last few years, as it has been shown that electrical stimulation of some regenerating cells has a positive effect on their development. A variety of different materials, ranging from graphene to conducting polymers, have been incorporated into hydrogels and increased conductivities have been reported. However, the majority of conductivity measurements are performed in a dry state, even though material blends are designed for applications in a wet state, in vivo environment. The focus of this work is to use polypyrrole nanoparticles to increase the wet-state conductivity of alginate to produce a conducting, easily processable, cell-supporting composite material. Characterization and purification of the conducting polymer nanoparticle dispersions, as well as electrochemical measurements, have been performed to assess conductivity of the nanoparticles and hydrogel composites in the wet state, in order to determine whether filling an ionically conducting hydrogel with electrically conductive nanoparticles will enhance the conductivity. It was determined that the introduction of spherical nanoparticles into alginate gel does not increase, but rather slightly reduces conductivity of the hydrogel in the wet state.

Electrically Conductive and 3D‐Printable Oxidized Alginate‐Gelatin Polypyrrole:PSS Hydrogels for Tissue Engineering

“…The drop of conductivity for 0.4 m PPy might be a result from electrolyte being expelled and replaced by the PPy:PSS matrix in the ADA‐GEL hydrogel, leading to a significant decrease in overall ionic conductivity (Figure 3D) and ion mobility, overall influencing the electrical performance of the composite. [ 87 ] Others have demonstrated a similar drop of both electrical conductivity and stiffness for high PPy‐content (100 m m Py, in situ oxidized) hyaluronic acid hydrogels, [ 82 ] which was associated to structural instability and non‐uniformity of the final PPy hydrogel. [ 82 ] Consistent with these results, 0.4 m PPy showed similarly decreased electrical conductivity and elastic modulus, suggesting that this modification is not feasible for further investigation.…”

“…Previous studies have identified that incorporation of spherical conductive PPy nanoparticle fillers inside ALG hydrogels does not increase but slightly decreases the electrical hydrogel conductivity until forming a percolating PPy network. [87] An increased PPy formation in the ADA-GEL network repels water content from the overall hydrogel volume, due to the higher ratio of Py to PSS, and therefore, lowering of the amount of free sulfonates to interact with water. The ionic conductivity of the electrolyte-swollen hydrogel (≈1 S m −1 , Figure 3), which is close to the range of culture medium (≈1.5 S m −1 [88][89][90] at 37°C), has a non-neglectable contribution to the overall hydrogel conductivity.…”