* Synthesis and Characterization of Electroactive Gellan Gum Spongy-Like Hydrogels for Skeletal Muscle Tissue Engineering Applications.

Advances on materials' research for tissue engineering (TE) applications have shown that animal cells respond directly to the material physical, chemical, mechanical, and electrical stimuli altering a variety of cell signaling cascades, which consequently result in phenotypic and genotypic alterations. Gellan gum (GG) spongy-like hydrogels (SLH) with open microstructure, mechanical properties, and cell performance have shown promising results for soft TE applications. Taking advantage of intrinsic properties of GG-SLH and polypyrrole (PPy) electroactivity, we developed electroactive PPy-GG-SLH envisaging their potential use for skeletal muscle TE. Three different methods of in situ chemical oxidative polymerization were developed based on the availability of pyrrole: freely dissolved in solution (method I and III) or immobilized into GG hydrogels (method II). PPy was homogeneously distributed within (method I and III) and on the surface (method II) of GG-SLH, as also confirmed by Fourier Transform infrared spectra. PPy-GG-SLH showed higher conductivity than GG-SLH (p < 0.05) whereas PPy-GG-SLH (method I and II) showed the best conductivity among the 3 methods (∼1 to 2 × 10-4 S/cm). The microarchitecture of PPy-GG-SLH (method I) was similar to GG-SLH but PPy-GG-SLH (method II and III) presented smaller pore sizes and lower porosity. PPy-GG-SLH (method I and II) compressive modulus (∼450-500 KPa) and recovering capacity (∼75-90%) was higher than GG-SLH, nevertheless the mechanical properties of PPy-GG-SLH (method III) were lower. The water uptake of PPy-GG-SLH was rapidly up to 2500% and were stable along 60 days of degradation being the maximum weight loss 20%. Mechanically stable and electroactive PPy-GG-SLH (method I and II) were analyzed regarding cellular performance. PPy-GG-SLH were not cytotoxic for L929 cells. In addition, L929 and C2C12 myoblast cells were able to adhere and spread within PPy-GG-SLH, showing improved spreading in comparison to GG-SLH performance. Overall, PPy-GG-SLH show promising features as an alternative electroactive platform to analyze the influence of electrical stimulation on skeletal muscle cells.