Simulation And Experiment Studies Of Multi-degree Of Freedom Micro-vibration Assisted Hydrogel 3D Printing

In recent years,hydrogel 3D printing technology has been widely used in biomedicine,software drive,flexible sensing and many other fields,but it also faces some difficulties.In the biomedical field,when micro-extrusion hydrogel 3D printing is used to print active cells,excessive printing shear stress will lead to the decline of cell vitality;Using low-viscosity materials or large-diameter needles can reduce shear stress,but low-viscosity materials are not conducive to printing,and large-diameter needles can reduce printing resolution.Therefore,it is necessary to study a hydrogel 3D printing method with high printing resolution and low shear stress.In this paper,a micro-vibration assisted hydrogel 3D printing method is proposed,which utilizes the shear thinning characteristics of hydrogel materials to ensure the resolution and reduce the viscosity of printing materials and shear stress during printing.(1)The non-Newtonian fluid model of hydrogel material was established.According to the model,the shear stress of conventional hydrogel extrusion process was analyzed,and the influence of needle diameter and inlet speed on shear stress was studied.The results show that the shear stress decreases with the increase of needle diameter and increases with the increase of inlet velocity.(2)Based on the fluid-structure coupling theory,the effects of single-degree-of-freedom vibration and multi-degree-of-freedom vibration on the viscosity and shear stress of hydrogel are studied.The simulation results show that radial vibration can effectively reduce the viscosity and printing shear stress of the material in the needle tube,and the shear stress fluctuates with the cycle under axial vibration,and the peak value of the shear stress in the cycle will exceed the shear stress during conventional printing.The shear stress of double radial vibration is basically the same as that of single radial vibration,but the fluctuation range of viscosity decreases;The shear stress of axial-radial vibration and three-degree-of-freedom vibration fluctuates periodically,and its peak value will exceed that of conventional printing.Compared with uniaxial vibration,the fluctuation range of shear stress and viscosity is reduced.(3)The parameters of hydrogel 3D printing were optimized,and the effects of needle diameter and entrance velocity on viscosity and shear stress during micro-vibration assisted3 D printing were studied.The printing parameters were designed by Latin hypercube experiment,and the parameters were fitted based on polynomial response surface optimization method,and the relationships between needle diameter and inlet speed and the maximum viscosity difference and shear stress reduction percentage were obtained.A set of optimal parameter solutions were obtained by solving and analyzing through non-inferior genetic algorithm.The results showed that the shear stress reduction percentage increased from 16.68% to 16.94%,and the maximum viscosity difference decreased from 9.40Pa·s to8.36Pa·s after optimization.(4)A micro-vibration auxiliary device for hydrogel 3D printing is designed,and the static analysis and modal analysis of the device are carried out.The 3D printing platform was built,and the 3D printing experiment was carried out by using micro-vibration auxiliary device.By comparing the weight and shape of printed materials between vibration-assisted printing and conventional printing,it was found that vibration-assisted printing can effectively reduce the viscosity of printed materials in needle tubes,improve printing resolution and reduce printing shear stress,which verified the feasibility of micro-vibration-assisted printing method.