3D Printing of Compositional Gradients Using the Microfluidic Circuit Analogy

Abstract

multimaterial DIW printer uses two separate ink dispensers joined at a single nozzle junction to simultaneously 3D print two viscoelastic inks through a single nozzle. Some models have been established to help control the printing of viscoelastic inks, but they have not been applicable for use in structures with complex compositional gradients. [18,22,23] As illustrated in Figure 1A, the toolpath of the printer is directly coupled with a desired composition (Φ) in order to determine the dispensing rate of each material. A distinction between the programmed dispensing rate of an ink (Q i ) and the measured flow rate out of the nozzle (Q Ni ) must be made when considering how to obtain an accurate compositional profile. Ideally, the increases and decreases in the measured ink flow rate synchronously follow the programmed dispensing rate. In reality, a number of factors introduce significant differences between the ideal ink dispensing rates and the realized outputs. Achieving accurate compositional 3D printing involving gradient transitions requires that we account for more complex behaviors, such as hydraulic compliance and non-Newtonian ink response, that result in significant differences between the programmed Q i and the realized Q Ni ( Figure 1B). For binary compositional changes within the same component, a combination of ink retraction and over extrusion can be used to account for these nonidealities. [22] For gradient compositional changes, the microfluidic circuit analogy (MCA) can be used to model and inform the ink dispensing profile that is required to achieve accurate compositional control ( Figure 1C).Here, we first describe the MCA model that is used to prescribe the ink-dispensing profile for improved compositional deposition accuracy in 3D-printed geometries with compositional gradients. We outline a calibration procedure to extract the MCA model parameters, which are then used in the MCA model to quantitatively guide the ink-dispensing profile for the desired compositional gradients to be printed. We finally validate the model in a DIW system using viscoelastic polydimethylsiloxane (PDMS) inks with time-dependent compositional changes. The ability to print multiple materials with accurate compositional profiles in a programmable manner enables the fabrication of new functional materials that were previously inaccessible.We use a model based on the microfluidic circuit analogy to determine the correct ink dispensing profiles required for 3D printing of structures with compositional gradients requires accurate dispensing control to achieve desired profiles. Here, empirical data are used with a model based on the microfluidic circuit analogy (MCA) to project dispense rate profiles that yield improved compositional accuracy in the printed part. Since minor variation in the experimental setup for each printing session can result in significant changes, a calibration procedure is developed to measure the system response. This calibration enables the extraction of the empirical MCA model parameters speci...

3D printed gradient index glass optics

“…The nozzle was held in a fixed position, while the material was deposited onto a silicone sheet, which was clamped to a threeaxis motion positioning stage (Aerotech). Before each print, a calibration procedure was performed to quantify the flow characteristics of the system, which was then used to calculate the flow rates necessary to achieve a desired compositional profile for a given geometry, as described previously (39). Typical print speeds were 10 mm/s.…”

“…On the other hand, the mixer design must also provide a rapid response to changes in the programmed ink composition, which necessitates a shorter residence time. However, the latter requirement can also be accounted for by implementing strategic compensation of the dispense rates into the toolpath (39). Hence, the micromixer used in this work was optimized for longer residence time to ensure complete mixing within the filament.…”

Mechanical Properties Tailoring of 3D Printed Photoresponsive Nanocellulose Composites

“…However, local compositional changes in the matrix as well as local density patterns are still difficult to produce with single‐nozzle DIW printing since they require in situ mixing of materials with different viscoelastic responses. [ 11 ] Such features might be achieved via multimaterial 3D printing approaches, [ 12 ] but these are usually time consuming due to the complexity of manufacturing and require careful selection of compatible materials. Indeed, multimaterial printing often introduces incoherent interfaces with abrupt changes of elastic modulus between materials to the manufactured composites, hence leading to stress concentration sites and defects that weaken the printed structure.…”

3D Printing of Core–Shell Capsule Composites for Post‐Reactive and Damage Sensing Applications

“…[ 2 ] Structural components different from the extruded polymer are conventionally introduced directly as a mixture within the extruded polymer via the incorporation of particles, fibers, or nanoparticles to improve structural stability. In particular by use of photopolymerization a large plethora of different and highly complex structures have been addressed such as the 3D printing of compositional gradients for microfluidics, [ 3 ] 3D printing of ionogels for stretchable sensors, [ 4 ] shape‐deformable hydrogels, [ 5 ] or specific methodological developments such as the removal of overhanging structures without the need for supportive materials. [ 6 ] There is also ample application of 3D printing in the areas of energy materials (thin film solar cell technology, super capacitors, multilayered systems), where many different components (solids and liquids) are required to be printed into one and the same material.…”