Research on the Microstructure Construction Technology of Fully Degraded Polymer Vascular Stent Based on Electric Field Driven 3D Printing

The so-called fourth-generation biodegradable vascular stent has become a research hotspot in thefield of bioengineering because of its good degradation ability and drug-loading characteristics.However,the preparationof polymer-degraded vascular stents is affected by known problem such as poor processflexibility,low formingaccuracy,large diameter wall thickness,limited complex pore structure,weak mechanical properties of radial support and high process cost.In this study,a deposition technique based on a high-voltage electric-field-driven continuous rotating jet is proposed to fabricate fully degraded polymer vascular stents.The experimental results showthat,due to the rotation of the deposition axis,the deposition direction of PCL(polycaprolactone)micro-jet isalways tangent to the surface of the deposition axis.The direction of the viscous drag force is also consistent withthe deposition direction of the jet.It is shown that by setting different rotation speeds of deposition axisωandlinear motion speeds of the nozzle V,the direction of rotation,pitch and angle of the individual printed spiralcurve can be precisely tuned.In the process of multiple spiral curves matching the deposition forming thin walltube mesh,the mesh shape and size of the thin wall tube can be accurately controlled by changing the number ofmatching spiral curves and the size of the matching position bias distance.Finally,the characteristics of a PCLtubular stent sample(with uniform-size microfibers and mesh shape),fabricated under the appropriate processparameters are described in detail.

Design and Experimental Testing of an Electric Field-Driven Droplet Injection Device

The properties of droplets produced by existing on-demand injection systems are typically determined by the nozzle diameter,i.e.,only droplets with size larger than this diameter can be obtained.To solve this problem,a system for electricfield-driven droplet injection and deposition was developed,and the related performances were compared with those of a standard pneumatic system.The results show that the diameter of droplets gen-erated accordingly can be significantly smaller than the nozzle diameter.In particular,the effects of frequency and duty ratio on the number of droplets were studied by assuming microcrystalline wax as work material.A deposi-tion matrix was obtained by using a nozzle with a diameter of 200μm.The average diameter of the matrix was 80.17μm with a standard deviation of 2.65μm and the average spacing was 301.25μm with a standard deviation of 6.80μm.Four deposition states after droplet injection were considered and verified under different velocities of F60,F10,F3,and F0.We also provide an explanation for the existence of a series of inclined columns showing up during the deposition processs.

Experimental Analysis of a Pneumatic Drop-on-Demand(DOD)Injection Technology for 3D Printing Using a Gallium-Indium Alloy

Many liquid metals have a high boiling point,strong electrical conductivity,high thermal conductivity,and nontoxic properties,which make them ideal targets for applications in different fields such as optics,microcircuits,electronic switches,micro-electromechanical System(MEMS)devices and 3D printing manufacturing.However,owing to the generally high surface tension of these liquids,achieving uniform micro-droplets is often a challenge due to the inherent difficulties in controlling their size and shape.In this study,a gallium indium alloy(GaIn24.5)has been used in combination with a pneumatic drop-on-demand(DOD)injection technology to carry out a series of experiments.The micro-droplet forming process has been explored for different pressure and pulse width conditions.Uniform metal droplets(diameter 1080μm)have been obtained with a 1.5 kPa jet pressure,100 ms pulse width,and 50%duty ratio.The standard deviation of the measured metal droplets diameter has been found to be approximately 20μm.