Preparation And 3D Bioprintability Of Electroactive Hydrogels Based On Schiff Base Bonds

Hydrogels can mimic natural extracellular matrix and allow cell encapsulation in a highly hydrated and mechanically supportive three-dimensional environment.Additionally,they effectively promote cell adhesion,proliferation and differentiation and then forming functional tissue.Therefore,they are often used as a scaffold material for 3D bio-printing technology.We prepared two electroactive composite hydrogels based on Schiff base bonds and studied their 3D bioprintability in detail.Firstly,konjac glucomannan?KGM?which has less attention was oxidized by reacting with sodium periodate to produce oxidized konjac polysaccharide?OKGM?.Through the oxidation reaction,the KGM molecular chain are cleaved and generate reactive aldehyde.The oxidation product was characterized by Fourier transform infrared spectroscopy?FT-IR?.Polyethyleneimine?PEI?is a polymer with a large number of amino groups.The three-dimensional network structure of OKGM/PEI composite hydrogel can be formed throught chemically cross-linking via Schiff-base reaction between the free amino groups of PEI and the aldehyde groups of OKGM.The reaction process is simple and rapid,and the composite hydrogel can be formed within 3minutes.Moreover,the OKGM/PEI composite hydrogel has self-healing ability and pH sensitivity due to the presence of imine bonds.Through the rheological test,OKGM/PEI hydrogel showed shear thinning capability,which is suitable for 3D bio-printing technology.The OKGM/PEI electroactive composite hydrogel was prepared by adding carbon nanotubes before the OKGM/PEI composite hydrogel was gelatinized.Then the rheological behavior and morphology of the electroactive hydrogel were characterized.The results showed that the mechanical strength of the OKGM/PEI composite hydrogel was improved by the addition of carbon nanotubes,however the structure and size of microporous inside the gel were not affected,which still meet the requirements on pore size for cell adhesion and growth.The conductivity of OKGM/PEI electroactive composite hydrogels increased with the addition of carbon nanotubes by AC impedance method.With an less addition of 2%carbon nanotubes,the conductivity of the electroactive hydrogel can reach 10^-4 S/cm,which satisfies the needs of cells for micro-current stimulation.In addition,the rheological behavior and 3D bioprintability of the electroactive hydrogel were also tested.It was found that the addition of carbon nanotubes can also improve the bioprintability of the OKGM/PEI composite hydrogel.In addition,FT-IR and ¹H-NMR were used to characterize the methacrylamidated gelatin?GelMA?and the dialdehyde-functionalized Poly?ethylene glycol?.Then,the GelMA/DF-PEG electroactive composite hydrogel which is stable at 37?was prepared via Schiff-base reaction between the free amino groups of the GelMA and the aldehyde groups of the DF-PEG,and the carbon nanotube was added at the same time.The results of in vitro degradation showed that,the hydrogel can be completely degraded;rheological tests showed that the hydrogel has shear thinning and viscoelastic behavior,which can meet the requirements of 3D bio-printing.And the electroactive composite hydrogel has good bioprintability and can be successfully printed by3D-Bioprinter.The conductivity of electroactive composite hydrogel i.e.above 10^-4 S/cm was suitable for the needs of micro-currentIn summary,two electroactive composite hydrogels were prepared based on Schiff base bonds,which have good 3D bioprintability.And their conductivity was above10^-4S/cm,Therefore,they were expected to construct electroresponsive tissues such as myocardium tissue,nerve tissue,etc.by 3D bio-printing technology.