Study On Photocured 3D Printing Natural Polyphenols-based Photosensitive Gel

Acrylamide(AM)has been widely used in 3D printing as a promising photosensitive gel ink material due to its good properties,including chemical inertness,adjustable elasticity,optical transparency and adhesion.However,there are still some drawbacks,such as the toxicity of free radical residues generated by photoinitiators and the biological inertness of the material itself,which greatly limit the application of AM in biomedical fields.Tannic acid(TA),as a green natural polyphenolic material with excellent antibacterial and antioxidant properties,can effectively solve these problems.However,the contradiction between radical-based photopolymerization and radical scavenging by TA introduces new problems for the preparation of TA-based acrylamide.Based on this,this project successfully introduced TA into the AM ink system using a glycerol-water binary system as a solvent to prepare multifunctional hydrogels that can be used for 3D printing based on polyphenols.The main findings are as follows.(1)First,precursor solutions composed of AM and TA were prepared by the one-pot method using TA as the second cross-linking agent and glycerol as the shielding agent for TA.It was demonstrated by FTIR that the radicals generated by the photoinitiator play a key role in determining the kinetics of photopolymerization.The effects of TA and glycerol concentrations on the photocuring efficiency of the gels were investigated.The results showed that the addition of glycerol significantly improved the photocuring efficiency of the gels.Scend,the printability of the photosensitive gel ink was evaluated.The PAM-TA gel could prepare hollow models with complex structure,and the printed models had high resolution with an average error of 38 μm.In addition,the effect of TA concentration on printing was also explored,and it was found that the appropriate concentration of TA(3-6 wt%)could also be used as a masking agent to improve the printing accuracy of the gel.(2)TA as a cross-linking agent also improves the mechanical properties and biological inertness of PAM-TA gels.The interpenetrating polymer network of TA and glycerol gives PAM-TA gels good toughness,and the printed nose models can still recover to their initial shape when subjected to 85% compressive strain.The tensile properties of the hydrogels with different addition ratios were investigated,and it was found that the mechanical properties of the hydrogels could be controlled by adjusting the concentration of each component to meet the needs of different applications.The elongation at break of the gel increased from 380% to 997%with the increase of glycerol concentration.In terms of bioactivity,the antibacterial,antioxidant and biocompatible properties of the gels were evaluated by in vitro studies.The results showed that the introduction of TA allowed the PAM-TA gels to possess good biological properties.(3)Polyphenols,as a polymerization inhibitor,not only prevent photosensitive gel inks from curing under natural light,but also ensure successful 3D printing at specific wavelengths and intensities.Polyphenols,including Tannic acid,protocatechuic acid(PA),gallic acid(GA)and hydroquinone(HQ),have good free radical scavenging ability and can reach 90%scavenging efficiency within 10 min.So their use as a polymerization inhibitor can effectively retard polymerization.The photosensitive gel ink containing TA was barely affected by continuous exposure to simulated sunlight,while the photosensitive gel ink without free radical inhibitors polymerized in less than one hour.Furthermore,by appropriately setting the concentration of polyphenols,the DLP-based 3D printing process was not affected by the radical scavenging properties of polyphenols.When printing hollow structures,the addition of TA significantly improved the internal over-crosslinking phenomenon.In summary,this paper considered the application of natural polyphenols as crosslinkers and polymerization inhibitors in photosensitive ink materials.Natural polyphenols as a polymerization inhibitor can improve the stability of photosensitive gels and extend the storage time.As cross-linking agents not only can enable high-precision printing,but also impart tough and stretchable mechanical properties,anti-dehydration,anti-oxidation and anti-bacterial properties to the gels.Our research is expected to provide the basis for the development of other polyphenol-based gels and expand the application of 3D printed PAM polyphenol gels in the fields of soft wearable devices,robotics and tissue engineering.