Process fundamentals and quality investigation in extrusion 3D printing of shear thinning materials: extrusion process based on Nishihara model

Abstract

Due to the complexity of extrusion 3D printing objects and lack of universal parameters, there are few classi ed statistics or quantitative description for the "extrudability" of material with shear thinning properties. In order to systematically study the rheological properties of extrudable materials and establish a uni ed criterion or quality evaluation standard from the basic process theory, a Nishihara rheological constitutive model based on visco-elastic and visco-plastic characteristics of materials is explored to predict and investigate the extrusion performance of four typical dispersed-continuous phase binary mixture. The creep model result shows that, expect for the gelatin network-water system with almost complete elastic behavior, the material with shear thinning property based on Nishihara model is in good agreement with the experimental results. In the extrusion process, the shear stress is related to the advancing speed, material viscosity and nozzle size. The effects of advancing speed and nozzle size on shear stress show antagonistic characteristics in a certain range, that is, the velocity gradient is the dominant factor at lower extrusion speed, and the dynamic viscosity is the dominant factor at higher extrusion speed. In terms of extrusion properties, the material system with smaller yield strain/stress has the least obvious extrusion delay characteristics, and is easier to extrude under the condition of the same material strength.

Self‐healing mineralized hydrogel scaffolds for stretch‐triggered dye release

“…For example, LVER region for Na‐SHMH 1.0 was observed in the range of 0.1%–6.0% and that of Na‐SHMH 2.0 was extended up to 30.0%. The findings convey the Na‐SHMH with more amount of K 2 CO 3 need more strain to change their rheological properties that is, Newtonian to Non‐Newtonian (shear thinning) behavior, which could limit the wide applicability of such hydrogels in tissue engineering, bioprinting, drug delivery, and so on 17 …”

“…The findings convey the Na-SHMH with more amount of K 2 CO 3 need more strain to change their rheological properties that is, Newtonian to Non-Newtonian (shear thinning) behavior, which could limit the wide applicability of such hydrogels in tissue engineering, bioprinting, drug delivery, and so on. 17 In addition, the step strain rheological test was performed to determine the effect of K 2 CO 3 concentration on the thixotropic and self-healing ability of the Na-SHMH hydrogels. The test was carried out by giving the strain in a stepwise manner that is, low strain of 1.0% for 60 s followed by high strain of 100% for another 60 s. The same cycle was repeated for up to 20 min.…”

Material Extrusion Filament Width and Height Prediction via Design of Experiment and Machine Learning

“…Presently, massive methods for AM are prevalent, including vat photopolymerization [4], material inkjet [5], binder jetting [6], powder bed fusion [7], and direct energy deposition [8], among others. Material extrusion, also known as direct ink writing (DIW) or robot-casting, is a processing technology that uses pneumatic pressure or mechanical loads as driving forces to extrude a semi-solid material from a nozzle, then solidifies the extruded material and bonds it to the previously extruded material to form a solid structure [9,10]. The processed materials are referred to as 'inks', which typically manifest as viscoelastic non-Newtonian fluids characterized by shear thinning behavior [11,12].…”