A guide to solution‐based additive manufacturing of polymeric structures: Ink design, porosity manipulation, and printing strategy

Abstract

Three-dimensional (3D) printing of polymer solution is a rising research topic as it can utilize polymers without photoreactivity or melting points. Solution-based additive manufacturing (SBAM) was recently reported to fabricate polymeric objects by depositing ternary polymeric inks (eg, solutions comprising polymer, volatile solvent, and nonvolatile nonsolvent), which undergo rapid phase inversion upon evaporation of a relatively small fraction of the volatile component, resulting in hierarchically porous filaments (eg, pores of diameters ranging from 2 nm to 10 μm). SBAM is conceptually compatible with any solution-processable polymer, which significantly extends the 3D-printable polymeric material spectrum. In addition to the architecture of the printed object, its internal porosity can be manipulated for different applications. Compared with typical direct ink writing of binary polymeric inks, which typically only contain the polymer and a volatile solvent, SBAM is capable of (a) eliminating evaporation-induced shrinkage, and (b) creating nanopores without the need for templating additives or nanoscale nozzles. The development of SBAM processes involves optimization of polymer solution thermodynamics, rheological engineering and mass transfer control, which makes it challenging to develop an SBAM protocol for a new polymer. This paper provides a practical guide toward the development of ternary polymeric inks, the design of 3D printer hardware for SBAM, and the posttreatment of printed objects for desired porosity. It also discusses solutions to common challenges encountered during this new polymer processing technology. A case study of developing the optimal SBAM protocol for a commercial polyimide is provided to illustrate the process design.

Direct ink write 3D printing of high solids loading bimodal distributions of particles

“…Care must be taken to avoid vaporization during ink handling, and some have even exposed extruding material to inert gas flows during printing to further control the solvent evaporation rate. 19 Additionally, for optimal shape fidelity of printed parts, binder/solvent formulations must be carefully selected to avoid shrinkage on evaporation and residual solvent, especially when considering highly volatile solvents. Careful characterization of the interplay of solid loadings, binder type, and solidification processes can enable successful printing, even for more complex geometries such as scaffolds.…”

“…For example, highly fluid inks extrude easily but are vulnerable to gravitational deformation, causing poor shape retention, structural sagging, and low final printing resolution. [19][20][21] However, high viscosity inks, which can retain their printed shape, require higher pressure and are vulnerable to nozzle clogging during deposition. 8 Designing inks for DIW that have good shape fidelity requires careful selection of the materials, which may include polymers, monomers, particles, and solvents and the composition of the mixture.…”

Editorial

“…Alongside the theme of process intensification, we have also published articles on 3D printing and additive manufacturing, [10][11][12] which we see as a multidisciplinary topic requiring the skills of multiple domains of science and engineering for successful innovation. We encourage further submissions in this area, particularly those that can connect fundamental material properties to processing outcomes and connect design and control to fabrication constraints.…”

Welcome to the second year of the Journal of Advanced Manufacturing and Processing

“…We also look forward by including articles from this issue that are connected specifically to the themes of the first year. [1][2][3][4] We want authors to explore a range of subjects related to advanced manufacturing and processing, so this is not meant to be prescriptive with regards to the subjects that will be covered. In particular, we would like to encourage reviews of topics in advanced manufacturing and we are pleased that we have already published three of these.…”

“…Another connected theme is the construction of "digital twins" for better manufacturing system operation. [15] Process intensification and modularization continues to be of interest in the journal with papers in this issue on threedimensional printing of polymers from solution [4] and a potential way to intensify CO 2 capture with a phaseseparating absorbent. [1] A theme that we highlighted in our first editorial was advanced manufacturing of biologics, particularly living systems such as cells or cellular constructs.…”