Electroactive Tissue Engineering Scaffolds Fabricated By Conductive Hydrogels Via Three Dimensional Bioprinting Technique

Cell-based multiple functions, such as adhesion, proliferation, migration and differentiation, can be regulated by electrical stimulation. Conducting polymer can intelligently transfer or control cell electrochemistry by its unique electrical activity or conductivity. It is widely used in the field of tissue engineering. Through physical or chemical bonds, hydrogel the three-dimensional cross-linked network structure is formed in water with a water-soluble or hydrophilic polymer of hydrophilic groups or molecular chains. As a kind of cell-friendly material, it is known as the "bio-ink" in the field of biofabrication. We prepare to combine them and make a conductive hydrogel, and then the electroactive tissue engineering scaffold controllable in shape and pore size with 3D printing.In this paper, aniline tetramer grafted polyethyleneimine copolymer(AT-PEI) was synthesized by two methods. The first is the carboxyl-terminated aniline tetramer(AT-COOH) by oxidative coupling of aniline dimer and aniline dimer is modified by carboxylation. Another, AT-COOH was prepared by oxidative coupling of aniline dimer and then carboxylation. Both of AT-PEI are formed by the amidation reaction between the carboxyl group on AT-COOH and the amino group on polyethyleneimine. Their structures were characterized by Fourier transform infrared spectroscopy(FT-IR), nuclear magnetic resonance(1H-NMR) and X-ray diffraction(XRD). Ultraviolet Absorption Spectroscopy(Uv-vis), cyclic voltammetry was used to detect its redox properties and electroactivity. The morphology was observed by scanning electron microscopy(SEM) and transmission electron microscopy(TEM). Then AT-PEI was blended with a temperature-sensitive hydrogel of Pluronic F127 to prepare F/AT-PEI conductive hydrogel. Through the rheological test, conductive hydrogel had shear thinning and elastic behavior suitable for 3D printing. And the electroactive tissue engineered scaffold was successfully printed. The conductivity of scaffolds was measured at 10-3 S /cm by AC impedance method, which satisfied the requirement of most micro-current stimulated cell proliferation and differentiation.In addition, we prepared the silk fibroin hydrogel induced by F127 and modified the AT-PEI complex by DNA to form conductive composite hydrogel. FT-IR and XRD showed that F127 could induce ?-sheet structure of silk protein. AT-PEI / DNA complex(AD) had further enhanced effect. From the rheological data, the prepared composite hydrogels had shear thinning and elastic behavior. With the increase of AD content, the hydrogel gelation time was shortened and the gel strength was also improved. And electroactive tissue engineering scaffolds were fabricated by 3D printing. The electrical conductivity was the highest with AD of 5% and then decreased. The pore size of the micrographs of freeze-dried silk fibroin composite hydrogels decreased with the increase of AD content, and the swell ratio was also the corresponding result.In conclusion, two kinds of conductive hydrogels are obtained, which can meet the need of micro-current stimulation and can be used to stimulate the growth of electroresponsive tissue(such as myocardium, nerve, etc.).