Reverse Process Embedded 3D Printing Based On Photocurable Hydrogel Materials

Embedded 3D printing is an emerging additive manufacturing strategy that is most notable for the fact that the printing process takes place in the support medium rather than in the air,and the printed ink can be embedded in the support medium,making the embedded 3D printing process virtually immune to gravity and does not require additional support structures to be generated for the digital model prior to printing.Embedded 3D printing has been of great value in many fields in recent years.This paper focuses on a renewed innovation of its printing strategy,proposing a novel strategy for the inverse process embedded 3D printing of hydrogels with multiple internal surface features,and performing the necessary characterization and testing.In parallel with this,finite element analysis based on special rheological materials,instrument construction,and the design and fabrication of long-needle equipment were also carried out.A full range of instrument and material development was done to achieve inverse process embedded 3D printing based on yield stress support media,providing a new fast and efficient solution for the printing of surgical organ models,with the following results.(1)A photocrosslinkable Herschel-Bulkley fluid with yield stress based on Carbopol rheology modifier was prepared and the corresponding release ink was fabricated;the Carbopol system with different concentrations was characterized using a rheometer and its yield stress,consistency coefficient and power rate index were obtained.The strength and elasticity of the photocurable hydrogel precursors were controlled by mixing the content of polyethylene glycol diacrylate.The prepolymer system cured at very low concentrations(0.2wt.%)of photoinitiator and achieved very high transparency(>90%).This material has a yield stress characteristic shear thinning behavior in the fluid state and is an ideal support medium.After curing by UV radiation,it is characterized by high transparency and high elasticity and is able to simulate the feel of human organs.(2)Based on the H-bot structural algorithm with Marlin open source firmware,an extruded 3D printer specifically designed for embedded 3D printing was designed and built,and targeted with a remote syringe pump and a proximity syringe pump,the pump device can be converted by a specially designed quick disassembly device.Longer printed microneedles were prepared using a needle puller with capillary glass tubing.Combining rheological data from hydrogel precursors with different parameters,a solid-liquid coupling based finite element analysis of the long needles and media was performed using the Flow Simulation finite element analysis tool and found that the largest print volume with acceptable deformation was achieved using barge glass capillary long needles.0.2 wt.% Carbopol rheology modified media had the least resistance and was the most suitable for embedded 3D printing.(3)Two viscosities of pure silicone oil release inks were tested and the possible reasons for their self-polymerization in the media were explained.Based on this phenomenon,emulsion release inks with different oil-to-water ratios and light-blocking inks were also prepared using surfactants.In practical printing,it was tested that the 1:1 oil-to-water ratio release inks lose less peel energy when stripping and are more suitable for the new strategy of inverse process embedded 3D printing.A particle image analysis device was set up to characterize the "wall effect" during printing,which was found to be independent of the printing depth.Finally,a fluid finite element analysis tool was used to reproduce this effect and a possible explanation was provided using existing theory.(4)A novel inverse process embedded 3D printing approach is proposed to print hydrogel models with multiple internal surfaces,soft,highly transparent and cuttable.This new strategy integrates new materials,machines and inks,and has advantages in hydrogel organ printing that cannot be replaced by conventional additive manufacturing methods,with potential applications especially for the preoperative simulation of giant liver tumors.From a practical point of view,its printing speed involves only thin walls without filling,which greatly reduces the printer’s work path and increases efficiency;its support media material,in addition to having various desirable properties,is extremely cheap at less than 20 RMB/liter and easy to land;the printing process does not require the design of additional digital models as support,which can virtually eliminate gravitational interference and has good resolution for complex models.