Melt electrowriting (MEW) is an emerging additive process for high‐fidelity, microscale fibrous scaffold fabrication. However, achieving precise multilayered MEW‐enabled scaffolds is limited by the entrapped residual charges owing to charge‐based mechanisms. Specifically, the semi‐conductive nature of processed materials causes retainment of net positive charges and jet–fiber repulsion, while exposure to the electric field yields charge polarization with resultant jet–fiber attraction. These competing effects work in tandem to determine the distinctive features of jet–fiber interaction. To deconstruct various charge‐related phenomena, the collector temperature is manipulated as a key process variable to investigate its effect on printing outcomes in two printing modes. Moreover, energy analysis is introduced to explain how collector temperature affects the polarization extent, along with the jet–fiber interaction and printing outcomes. In single fiber printing mode, sets of two parallel fibers with variable set interfiber distances (
- Award ID(s):
- 1663095
- NSF-PAR ID:
- 10291819
- Date Published:
- Journal Name:
- Processes
- Volume:
- 8
- Issue:
- 11
- ISSN:
- 2227-9717
- Page Range / eLocation ID:
- 1440
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract sS f) are printed at different collector temperatures. At a lowsS fthreshold, significant fiber attraction is observed, but no significant difference is observed among the cases at different collector temperatures. In scaffold printing mode, 200‐layer scaffolds are printed at different collector temperatures, and the wall morphologies are found to vary with location, layer number, and collector temperature. -
more » « less
Abstract The printing accuracy of the melt electrowriting (MEW) process is adversely affected by residual charge entrapped within the printed fibers. To mitigate this effect, the residual charge amount (
Q r) must first be accurately determined. In this study,Q ris measured by a commercial electrometer at a nanocoulomb scale for MEW‐enabled scaffolds. Based on this enabling measurement, the effects of various design parameters (including substrate surface conductivityσ , printing timet , layer numberN ), and process parameters (including voltageU , translational stage speedv , and material temperatureT m), onQ rare investigated. An increase ofσ or decrease ofN helps to decreaseQ r. The effects of different process parameters on the residual charge can be either dependent or independent of fiber morphologies. Moreover, the fiber‐morphology dependent and independent effect can be either synergistic (U andT m) or antagonistic (e.g.,v ) for different process parameters. Under same conditions,Q rin the interweaving scaffold design is generally smaller than that in the non‐interweaving scaffold design. These results help to furnish necessary insights into the charge dissipation process for a melt‐based electrohydrodynamic printing process while providing a systematic methodology to mitigate the residual charge accumulation. -
null (Ed.)Abstract Pellet-based extrusion deposition of carbon fiber-reinforced composites at high material deposition rates has recently gained much attention due to its applications in large-scale additive manufacturing. The mechanical and physical properties of large-volume components largely depend on their reinforcing fiber length. However, very few studies have been done thus far to have a direct comparison of additively fabricated composites reinforced with different carbon fiber lengths. In this study, a new additive manufacturing (AM) approach to fabricate long fiber-reinforced polymer (LFRP) was first proposed. A pellet-based extrusion deposition method was implemented, which directly used thermoplastic pellets and continuous fiber tows as feedstock materials. Discontinuous long carbon fibers, with an average fiber length of 20.1 mm, were successfully incorporated into printed LFRP samples. The printed LFRP samples were compared with short fiber-reinforced polymer (SFRP) and continuous fiber-reinforced polymer (CFRP) counterparts through mechanical tests and microstructural analyses. The carbon fiber dispersion, distribution of carbon fiber length and orientation, and fiber wetting were studied. As expected, a steady increase in flexural strength was observed with increasing fiber length. The carbon fibers were highly oriented along the printing direction. A more uniformly distributed discontinuous fiber reinforcement was found within printed SFRP and LFRP samples. Due to decreased fiber impregnation time and lowered impregnation rate, the printed CFRP samples showed a lower degree of impregnation and worse fiber wetting conditions. The feasibility of the proposed AM methods was further demonstrated by fabricating large-volume components with complex geometries.more » « less
-
null (Ed.)Abstract Aerosol jet printing (AJP) is a direct-write additive manufacturing technique, which has emerged as a high-resolution method for the fabrication of a broad spectrum of electronic devices. Despite the advantages and critical applications of AJP in the printed-electronics industry, AJP process is intrinsically unstable, complex, and prone to unexpected gradual drifts, which adversely affect the morphology and consequently the functional performance of a printed electronic device. Therefore, in situ process monitoring and control in AJP is an inevitable need. In this respect, in addition to experimental characterization of the AJP process, physical models would be required to explain the underlying aerodynamic phenomena in AJP. The goal of this research work is to establish a physics-based computational platform for prediction of aerosol flow regimes and ultimately, physics-driven control of the AJP process. In pursuit of this goal, the objective is to forward a three-dimensional (3D) compressible, turbulent, multiphase computational fluid dynamics (CFD) model to investigate the aerodynamics behind: (i) aerosol generation, (ii) aerosol transport, and (iii) aerosol deposition on a moving free surface in the AJP process. The complex geometries of the deposition head as well as the pneumatic atomizer were modeled in the ansys-fluent environment, based on patented designs in addition to accurate measurements, obtained from 3D X-ray micro-computed tomography (μ-CT) imaging. The entire volume of the constructed geometries was subsequently meshed using a mixture of smooth and soft quadrilateral elements, with consideration of layers of inflation to obtain an accurate solution near the walls. A combined approach, based on the density-based and pressure-based Navier–Stokes formation, was adopted to obtain steady-state solutions and to bring the conservation imbalances below a specified linearization tolerance (i.e., 10−6). Turbulence was modeled using the realizable k-ε viscous model with scalable wall functions. A coupled two-phase flow model was, in addition, set up to track a large number of injected particles. The boundary conditions of the CFD model were defined based on experimental sensor data, recorded from the AJP control system. The accuracy of the model was validated using a factorial experiment, composed of AJ-deposition of a silver nanoparticle ink on a polyimide substrate. The outcomes of this study pave the way for the implementation of physics-driven in situ monitoring and control of AJP.more » « less
-
more » « less
Abstract Melt electrowriting (MEW), an emergent additive manufacturing process, shows significant potential in fabricating high‐fidelity fibrous scaffolds for tissue engineering applications. However, fiber deviation can deteriorate the printing accuracy of MEW. To evaluate the printing accuracy, an evaluation protocol along with an index (
I p) is proposed. For the first time, 0–90 patterned and 0–θ patterned scaffolds with varying inter‐fiber distances along different printing directions are fabricated to establish the dependence ofI pon two distinct printing sequences. One sequence is the small–large sequence, which first prints the fibers separated by a small inter‐fiber distance, followed by fibers separated by a large inter‐fiber distance. Alternatively, for the large–small sequence, the fibers separated by a large inter‐fiber distance are printed prior to the fibers separated by a small inter‐fiber distance. The small–large sequence contributes to largerI presults compared to the large–small sequence. Moreover, the printing sequence has more significant effects on theI pfor the 0–θ pattern compared to the 0–90 pattern. These differences can be attributed to different fiber morphologies at the intersection points, accompanied by resultantly varying charge amounts, which gives an insight into the cause of fiber deviation phenomena.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/pr8111440
