Synthesis of an Electroconductive Hydrogel in 3D Printing Formulation for Tissue Engineering

The progress made in tissue engineering to treat damage caused by disease and traumatic injury has been accelerated by innovations in bioengineering over the last few decades. The strategy of repairing and revitalizing damaged tissues has advanced from the use of tissue transplants to the use of functional scaffolds. Three-dimensional (3D) printing which utilizes hydrogel inks, is an ideal technique used to fabricate sophisticated and biomimetic hydrogel scaffolds capable of promoting new tissue morphogenesis via interaction with human cells. Electroconductive hydrogels have emerged as a significant tissue engineering scaffold due to their ability to maintain a distinct 3D structure, provide mechanical support for the cells in the engineered tissues, and their high electrical conductivity which is needed for the regeneration of electrically excitable tissues. However, the fabrication of electroconductive hydrogel scaffolds of high conductivity with high-quality 3D printing resolution remains a great challenge. In this research project, several methods were explored to fabricate high-quality 3D printable electroconductive hydrogel inks using cellulose nanocrystals (CNC), polypyrrole (PPy), and the photo cross-linkable gelatin methacryloyl (GelMA) and galactoglucomannan methacrylate (GGMMA). As revealed by the results, the hydrogel ink synthesized with CNC, PPy, and GGMMA possessed promising properties for high-quality 3D printing. The hydrogel ink was prepared by mixing the CNC/PPy with GGMMA. Analysis of the surface charge and particle size of CNC/PPy showed an improvement in the colloidal stability of the CNC/PPy composite at a CNC concentration of 1 wt% to 2 wt%. Also, after checking the conducting properties of the CNC/PPy/GGMMA hydrogel inks with a two-point probe, a response was obtained on the multimeter for the hydrogel ink formulated with 1 wt% CNC and 0.2 M Py (CNC/PPy-3). Thus, the hydrogel fabricated with CNC/PPy-3 was used for further analysis. The incorporation of PPy was confirmed by the analysis of the hydrogel using Fourier transform infrared spectroscopy and UV-Vis spectroscopy. The electroconductivity of the hydrogel containing PPy was investigated using electrochemical impedance spectroscopy and compared to the control hydrogel without PPy. The impedance of the hydrogel decreased from 56.9 ± 1.9 kΩ for the control hydrogel to 43.3 ± 1.5 kΩ for the hydrogel containing PPy at 1 Hz. Likewise, the impedance of the hydrogel decreased from 113.4 ± 0.6 Ω for the control hydrogel to 79.9 ± 2.2 Ω for the hydrogel containing PPy at 1000 Hz. These results indicate the potential suitability of the hydrogel composed of CNC, PPy, and GGMMA for high-quality 3D printing and fabrication of tissue constructs for the regeneration of electrically excitable tissues