Ink Deposition Research Articles

3D Printing of Conversion Cathodes for Enhanced Custom-Form Lithium Batteries

Additive manufacturing techniques can enable the fabrication of batteries in nonconventional form factors, enabling higher practical energy densities due to improved power source packing efficiency. Furthermore, energy density can be improved by transitioning from conventional Li-ion materials to lithium metal anodes and conversion cathodes. Iron disulfide (FeS2) and iron trifluoride (FeF3) are two promising conversion cathodes of commercial and academic interest, but the 3D printing of inks made from these materials for custom-form battery applications has yet to be demonstrated. In this work, the deposition of FeS2 and FeF3 inks are investigated and optimized using direct-ink-write (DIW) 3D printing, in addition to the development of printable separators and packages to produce custom-form batteries. Two distinct custom form-factors, one on wave-shaped current collectors and the other on cylindrical rod current collectors, are demonstrated and shown to exhibit performance similar to coin cells when conventional Celgard separators are used. Additionally, FeF3 cells were integrated with a DIW printed separator consisting of an electrolyte exchanged PVDF-HFP based ionogel [1]. In the case of FeS2, it was found that cathodes with a ridged surface, produced from the filamentary extrusion of highly concentrated inks (60-70% solids w/w%) exhibited optimal power, uniformity, and stability [2]. Finally, progress toward fully-printing custom-form batteries using metal powder bed printed cases and stereolithographically printed gaskets is demonstrated. Overall, the additive manufacturing of conversion electrodes, separators, and battery packaging is shown to be a viable path toward the making of custom-form cells. More broadly, electrode ridging is found to optimize rate capability, a finding that may have broad impact beyond FeS2, FeF3 and additive manufacturing.[1] A.S. Lapp, L.C. Merrill, B.R. Wygant, D.S. Ashby, A.S. Bhandarkar, A. Zhang, E.J. Fuller, K.L. Harrison, T.N. Lambert, and A.A. Talin. Room Temperature Pseudo-Solid State Iron Fluoride Conversion Battery with High Ionic Conductivity. ACS Applied Materials & Interfaces 15, 893-902, 2022.[2] J.A. Cardenas, J.P. Bullivant, I.V. Kolesnichenko, D.J. Roach, M.A. Gallegos, E.N. Coker, T.N. Lambert, E. Allcorn, A.A. Talin, A.W. Cook, and K.L. Harrison. 3D Printing of Ridged FeS2 Cathodes for Improved Rate Capability and Custom-Form Lithium Batteries. ACS Applied Materials & Interfaces 14, 45342-45351. 2022.

Automated Production of Catalyst Coated Membranes for PEM Water Electrolysis Using a Direct Ultra-Sonic Spray Coating Approach

The production of green hydrogen through polymer electrolyte water electrolysis (PEMWE) has attracted attention in recent years for its potential to enable the widespread use of green hydrogen [1, 2]. This technology particularly impacts important sectors of today’s society such as the agricultural and mobility sectors. Among the different components of an electrolysis cell, the membrane electrode assembly (MEA) is regarded as the most important component for its operation, since it is where the water-splitting reaction takes place. For this reason, the choice of materials and production approach play a highly important role to optimize its lifetime, performance, and cost [3]. Within this context, the MEA production via ultra-sonic spray coating has been lately gaining relevance due to its potential to yield high-activity electrode layers with a low catalyst loading.Conventionally, electrodes for PEMWE have been fabricated using other catalyst deposition techniques such as the doctor blade, airbrush spray coating or rod coating on a separate substrate, which is then transferred onto the membrane via hot pressing. However, the shortcomings of these approaches which include an additional hot press step were recently reported, particularly due to the complexity associated with electrodes with low catalyst loadings due to their sensitivity towards mechanical stress [1, 4]. On the other hand, effective approaches involving a direct ink deposition onto the membrane using ultra-sonic spray coating have been long reported for fuel cell applications [5, 6].In this work, we take the approach of direct ink deposition via ultra-sonic spray coating to produce iridium based MEAs for PEMWE. Furthermore, the dependency of the MEA electrochemical activity on the process and material choice are studied in an iterative manner. Of particular interest for this study is the material transfer rate from the catalyst ink to the membrane, the reproducibility of the developed spray coating process and the variation of materials used for the MEA fabrication. The spray process was performed with an ultra-sonic spray nozzle attached to an automized 3-axis rig and coupled with a syringe pump. The fabricated MEAs were characterized using a single cell setup with an active area of 4 cm2. The results of the first generation of the fabricated MEAs show that the material ratios in ink composition play an important role in the ink flowability through the piping which carries the ink to the ultra-sonic nozzle. Furthermore, this behavior has a direct and strong influence on the final composition of the catalyst layer, which consequently directly affects the cell performance.

Characterization of PEDOT:PSS Nanofilms Printed via Electrically Assisted Direct Ink Deposition with Ultrasonic Vibrations.

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has emerged as a promising conductive polymer for constructing efficient hole-transport layers (HTLs) in perovskite solar cells (PSCs). However, conventional fabrication methods, such as spin coating, spray coating, and slot-die coating, have resulted in PEDOT:PSS nanofilms with limited performance, characterized by a low density and non-uniform nanostructures. We introduce a novel 3D-printing approach called electrically assisted direct ink deposition with ultrasonic vibrations (EF-DID-UV) to overcome these challenges. This innovative printing method combines programmable acoustic field modulation with electrohydrodynamic spraying, providing a powerful tool for controlling the PEDOT:PSS nanofilm's morphology precisely. The experimental findings indicate that when PEDOT:PSS nanofilms are crafted using horizontal ultrasonic vibrations, they demonstrate a uniform dispersion of PEDOT:PSS nanoparticles, setting them apart from instances involving vertical ultrasonic vibrations, both prior to and after the printing process. In particular, when horizontal ultrasonic vibrations are applied at a low amplitude (0.15 A) during printing, these nanofilms showcase exceptional wettability performance, with a contact angle of 16.24°, and impressive electrical conductivity of 2092 Ω/square. Given its ability to yield high-performance PEDOT:PSS nanofilms with precisely controlled nanostructures, this approach holds great promise for a wide range of nanotechnological applications, including the production of solar cells, wearable sensors, and actuators.

A comparison of conductive ink usage optimization techniques used in fabrication of epidermal UHF radio frequency identification tags for medical and sensing applications.

The aim of this work is to assess the performance of various inkjet printing techniques. These techniques are aimed at optimizing the volume of conductive ink used in the fabrication of inkjet printed Radio Frequency Identification tags. It is also possible that they can be used in fabricating other electronic and electromagnetic devices and structures. Three ink optimization approaches were examined viz. gridded (meshed) designs, conductive area trimming and selective ink deposition. The volume of conductive ink utilized in tag fabrication and the measured on-body (forearm) read range of the tag were used to develop a figure of merit which determined the best printing approach. Although the longest read range was obtained from the tag with 48% conductive area trimming (Trim 1), the best figure of merit, that is, the tag with the best balance between measured read range and utilized conductive ink, was obtained from the tag that had its surface area trimmed by 65% (Trim 2). It is however suggested that optimum use of conductive ink would be achieved with a combination of 65% surface area trimming and selective ink deposition technique.

Go with the flow: Rheological requirements for direct ink write printability

The rapid development of additive manufacturing, also known as three-dimensional (3D) printing, is driving innovations in both industry and academia. Direct ink writing (DIW), an extrusion-based 3D printing technology, can build 3D structures through the deposition of custom-made inks and produce devices with complex architectures, excellent mechanical properties, and enhanced functionalities. A paste-like ink is the key to successful printing. However, as new ink compositions have emerged, the rheological requirements of inks have not been well connected to printability, or the ability of a printed object to maintain its shape and support the weight of subsequent layers. In this review, we provide an overview of the rheological properties of successful DIW inks and propose a classification system based on ink composition. Factors influencing the rheology of different types of ink are discussed, and we propose a framework for describing ink printability using measures of rheology and print resolution. Furthermore, evolving techniques, including computational studies, high-throughput rheological measurements, machine learning, and materiomics, are discussed to illustrate the future directions of feedstock development for DIW. The goals of this review are to assess our current understanding of the relationship between rheological properties and printability, to point out specific challenges and opportunities for development, to provide guidelines to those interested in multi-material DIW, and to pave the way for more efficient, intelligent approaches for DIW ink development.

Actuation waveform auto-design of drop-on-demand inkjet for ejection droplet without satellite

Designing the actuation waveform is a key step for the piezoelectric inkjet printing technology, which controls the deposition quality of the material. However, the current design of actuation waveforms remains laborious and reliant on repetitive experimentation, resulting in a suboptimal match between the actuation waveform and ink properties, which may cause material deposition defects such as satellite. In this study, the influences of the ink physical properties, nozzle diameter, and ejection behavior on the kinetics of droplet formation were investigated. Further, the transition boundaries of three droplet formation modes for different types of inks, namely, no droplet, single droplet, and satellite droplet, were determined. An actuating waveform auto-design method for creating a single droplet without satellite was constructed based on the physical properties of the ink, which can easily achieve the formation and volume control of a single droplet. The efficacy of the method was validated through monitoring the droplet forming processes of four standard reagents. Moreover, the printing of an interdigitated electrode and micro-patterns was precisely controlled under well-formed droplets. This study could facilitate a comprehensive understanding of droplet formation dynamics, enabling the rapid creation of actuation waveforms for high-quality deposition of functional inks and enhancing the performance of piezoelectric inkjet-based fabrication equipment.

Ultrafast and Large-Scale Fabrication of PEDOT:PSS Nanofilms Using Electrical-Field-Assisted Direct Ink Deposition.

The importance of conductive polymers has significantly increased over the decade due to their various applications, such as in electronic devices, sensors, and photovoltaics. Poly(3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) is one of the most successfully and widely used polymers in practical applications. Spin coating is extensively used to fabricate these conductive films; however, it has disadvantages. It is inherently a batch process with relatively low output and high solution wastage. To address these issues, we developed a novel printing process called electrical-field-assisted direct ink deposition (EF-DID), which yields a continuous, homogenous film with high electrical conductivity. In this process, we studied the formation of nanodroplets under an electrical field and their effects on film characteristics. Furthermore, dimethyl sulfoxide (DMSO) was considered as an additive solvent to increase the conductivity and wettability of the films. We then compared EF-DID-printed PEDOT:PSS films with spin-coated films to better understand the film properties. Finally, inverted perovskite solar cell devices were fabricated and compared, where the PEDOT:PSS layers were prepared by EF-DID printing and spin coating. Based on the experimental results, a solution of 20% PEDOT:PSS in DMSO (vol/vol) printed by EF-DID for 15 s provided optimal morphology.

Over 13% Efficient, Ambient Air‐Processed CuIn(S,Se)2 Solar Cells via Compositional Engineering of Molecular Inks

A dimethylformamide (DMF) and thiourea (TU)‐based ink deposition route is used to fabricate narrow bandgap (≈1.0 eV) CuIn(S,Se)2 (CISSe) films with Cu‐poor ([Cu]/[In] = 0.85), stoichiometric ([Cu]/[In] = 1.0), and Cu‐rich ([Cu]/[In] = 1.15) compositions for photovoltaic applications. Characterization of KCN‐ or (NH4)2S‐treated Cu‐rich absorber films using X‐ray diffraction and scanning electron microscopy confirms the removal of copper‐selenide phases from the film surface, while electron backscatter diffraction measurements and depth‐dependent energy‐dispersive X‐ray spectroscopy indicate remnant copper‐selenides in the absorber layer bulk. Contrary to best practice for vacuum‐processed cells, optimum [Cu]/[In] ratios appear to be stoichiometric, rather than Cu‐poor, in DMF–TU‐based CISSe devices. Accordingly, stoichiometric film compositions yield large‐grained (≈2 μm) absorber layers with smooth absorber surfaces (root mean square roughness <20 nm) and active area device efficiencies of 13.2% (without antireflective coating). Notably, these devices reach 70.0% of the Shockley–Queisser limit open‐circuit voltage (i.e., 526 mV at Eg of 1.01 eV), which is among the highest for ink‐based CISSe devices.

GC-MS Silylation Derivative Method to Characterise Black BIC® Ballpoint 2-Phenoxyethanol Ratio Evaporation Profile-A Contribution to Ink Ageing Estimation.

One of the major challenges in forensic document analysis is estimating the age of ink deposition on a manually written document. The present work aims to develop and optimise a methodology, based on the evaporation of 2-phenoxyethanol (PE) over time, that can contribute to ink age estimation. A black BIC® Crystal Ballpoint Pen was purchased in a commercial area, and ink deposition began in September 2016 over 1095 days. For each ink sample, 20 microdiscs were subjected to n-hexane extraction in the presence of an internal standard (ethyl benzoate) followed by derivatisation with a silylation reagent. A gas chromatography-mass spectrometry (GC/MS) method was optimised for PE-trimethylsilyl (PE-TMS) to characterise the ageing curve. The developed method presented good linearity between 0.5 and 50.0 μg mL-1, as well as limits of detection and quantification of 0.026 and 0.104 μg mL-1, respectively. It was possible to characterise PE-TMS concentration over time, which reveals a two-phase decay behaviour. First, there was a substantial decline between the 1st and the 33rd day of deposition, followed a by a stabilisation of the signal, which allowed to detect the presence of PE-TMS up to 3 years. Two unknown compounds were also present and allowed to identify three dating time frames for the same ink stroke: (i) between time 0 and 33 days, (ii) between time 34 and 109 days, and (iii) more than 109 days. The developed methodology allowed to characterise the behaviour of PE over time and to establish a relative dating of three-time frames.

Novel and Efficient Methodology for Drop Placement Accuracy Testing of Robot-Guided Inkjet Printing onto 3D Objects

Robot-guided inkjet printing technology offers a new way for the digital and additive deposition of low-viscous inks to be made directly onto arbitrary surfaces and, thus, enables the production of individualized printed electronics on large-scale objects. When compared to conventional flatbed printing, the distance between the nozzle plate and the object’s surface varies and needs to be considered in order to match the accuracy requirements needed for the positioning of single drops. Knowledge about applicable distance limits and the influence of tunable print parameters is crucial for improving the print process and results. This study discusses the sources of errors in the inkjet printing process onto 3D objects and presents extensive results about position accuracy in relation to jetting distance for different parameter sets of functional inks, drop volumes, and piezo voltages. Additionally, an efficient novel method was applied to determine the drop position accuracy of inkjet droplets in relation to the jetting distance. The method relies on cylinder geometry for the object and an inkjet head that is guided by a six-axis robot manipulator along the cylinder’s axis. For the determination of drop placement accuracy, the position of single dots on the surface was compared to a model which considered the cylinder radii, drop velocity, and the movement speed of the guided inkjet printhead. The method and the extensive research results can be utilized for the prediction of achievable drop placement accuracy and the prior definition of distance limits.

2D characterisation and evaluation of multi-material structures towards 3D hybrid printing

ABSTRACT Multi-material manufacturing through the hybridisation of printed electronics and additive manufacturing has gained great interest recently. However, such hybridisation attempts are not trivial due to the need for functional material development and compatible process identification, as well as further performance understanding, comprehensive characterisation and long-term reliability evaluation of multi-material parts. While some multi-material structures from functional materials such as silver inks have been demonstrated via the integration of direct writing systems into stereolithography or material extrusion platforms, the performance assessment and characterisation of parts manufactured using such integrated systems is still required. Therefore, this research presents a comprehensive assessment of multi-material structures manufactured using syringe deposition and material extrusion platforms. Test specimens were subjected to various characterisation activities such as thickness measurement, resistance measurement, roughness tests, wettability measurement, adhesion tests, and morphological analysis. Results and statistical analyses suggested that the dry thickness and conductivity of deposited films were dependent on the substrate material. Adhesion between the conductive film and substrate was affected by both substrate material and ink deposition angle. Also, the interaction of conductive films with polycarbonate substrate was found to be noticeably better among all substrates due to low resistivity and enhanced adhesion at low thicknesses.

Inkjet‐Printed Microlenses Integrated onto Organic Photodiodes for Highly Accurate Proximity Sensing

AbstractThe current needs for optical detectors in industrial and consumer electronics require sensors with thin form‐factors, high performance and a facile fabrication and integration. In this work, the integration of inkjet printed microlenses onto solution‐processed organic photodiodes is demonstrated to enable high‐accuracy proximity sensing via the focused induced photoresponse (FIP) effect. By precisely controlling the ink deposition and substrate properties, it is able to tune the microlens focal length from 150 to 775 μm. This allows to the appropriate microlens design to be chosen to take advantage of the FIP effect. By comparing the photocurrent ration of a device with and without microlenses, absolute proximity measurements in the range of 100 μm to 4 mm are achieved. Champion devices yield an accuracy of down to ±50 μm within three standard deviations (3σ). These results highlight the potential of the microlens‐OPD integration for highly accurate and close‐distance proximity applications in a variety of fields.

C8‐BTBT‐C8Thin‐Film Transistors Based on Micro‐Contact Printed PEDOT:PSS/MWCNT Electrodes

AbstractAdvances in organic materials manufacturing have enabled the creation of electronic devices using solution‐processing techniques by employing soluble materials with high conductivity grade. In this exploratory study, the use of micro‐contact for poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) polymer ink deposition as high‐quality structured electrodes for organic field‐effect transistors (OFETs) in top‐contact geometry is demonstrated. The optimized OFET's solution‐processed fabrication is a promising strategy to be realized in the simple, cost‐effective roll‐to‐roll manufacturing processes. The electrical performance of the fabricated devices is comparable to transistors with gold electrodes prepared via vacuum deposition, and even exceeding the values of the charge carriers’ mobilities and featuring lower contact resistance (Rc), due to lower charge‐carrier injection barrier for carbon‐based organic electrodes. An addition of multi‐walled carbon nanotubes to the PEDOT:PSS decreasesRceven further, changing the work function for better energy alignment with semiconductor materials.

Transient deformation and swelling of paper by aqueous co-solvent solutions.

Inkjet printing inks frequently contain polar liquids of low volatility such as glycerol or poly(ethylene glycols) in addition to the main solvent water. The deposition of these liquids on paper sheets induces swelling of the cellulose fibers, which leads to an overall, anisotropic deformation of the sheet. We characterized the corresponding strain components by means of a grid projection method and white light interferometry. For pure water, most of the hydroexpansion strain vanishes again after drying is complete. However, for aqueous solutions of non-volatile co-solvents, a large fraction of the deformation persists after the water has evaporated. Because swelling occurs only after liquid enters the cellulose fibers, monitoring the dynamics of expansion provides insight into the pore-fiber distribution of co-solvents. The corresponding timescales of pore-fiber transport strongly depend on the co-solvent concentration, as a sufficient quantity of water is needed to plasticize the fiber walls.

Ultraviolet-assisted direct-write printing strategy towards polyorganosiloxane-based aerogels with freeform geometry and outstanding thermal insulation performance

Developing aerogels with a tailored geometric feature is of prime importance for enlarging their functional effects in application scenarios. However, conventional manufacturing techniques have remained challenging in the on-demand shaping of aerogels due to their costly and time-consuming fabrication process and poor designability of casting molds. Herein, an ultraviolet-assisted direct-write printing strategy has been proposed for fabricating polyorganosiloxane-based aerogels with tunable molecular triple-crosslinks consisting of hydrogen bonds, hydrocarbon chains, and polysiloxanes. The implementation of direct-write printing depends on the close synergy of consecutive ink deposition and instantaneous photopolymerization, appearing as a considerable characteristic of solidification-while-printing, which is conducive to constructing spatially freeform geometries with high structural complexity and shape fidelity. The resultant 3D-printed polyorganosiloxane-based aerogels exhibit outstanding nanoporous performances, such as low density (0.14 g·cm−3), high surface area (484 m2·g−1), superhydrophobicity (water contact angle, 150°), high specific modulus (27.9 kN·m·kg−1), and low thermal conductivity (37.48 mW·m−1·K−1), which are ideal materials for shape-dominated thermal insulation applications. This work would provide an alternative printing strategy to fabricate nanoporous materials with arbitrary architectures for wider applications.

Multiphysics modeling of frontal polymerization-assisted layer-by-layer additive manufacturing of thermoset polymer components

Frontal polymerization (FP) is a novel curing strategy that relies on a self-propagating exothermic reaction front to polymerize thermoset resins rapidly. Due to its energy-efficiency and rapid curing of thermosets, a series of applications related to polymer and polymer composite manufacturing have been developed based on FP, in particular additive manufacturing (AM). While the current research demonstrates successful printing of 1D, 2D and 3D structures based on FP, a key challenge is the determination of the printing parameters through trial-and-error, which hinders its large-scale application. To better understand how different process parameters affect the front behavior and the printing process, and eventually enable fast printing of complex parts without trial-and-error, computational modeling of the printing process is highly desired. For the first time, we develop a multiphysics finite element model for simulating FP-assisted AM which accounts for both the thermal-chemical process and the ink deposition in a real printing process. To simulate the dynamic ink deposition process, element activation is used that constantly adds elements to the simulation domain following a predefined printing path and velocity. A coupled thermo-chemical partial differential equation system is solved over the changing ink domain to simulate the heat transfer and chemical reaction during the printing process. The model is first validated by comparing the front temperature history during the printing process with the experimental infrared thermal measurements. The validated model enables the determination of proper printing velocity range, within which the polymerization front can follow the printing such that the ink will not deform before curing, which is critical to ensure printing accuracy. Furthermore, the simulation reveals the change of front temperature and degree of cure between different layers, and their dependency on layer length and printing velocity, providing insights into the printing experiments for processing parameters selection.

PGM-Free Catalysts and Electrodes for Anion Exchange Membrane Water Electrolyzers

Recent progress in the development of anion exchange membranes (AEMs) with improved performance and durability has opened the way for the application of the AEM-based electrolyzers in low-temperature water electrolysis (LTWE),1 an important technology for producing “green” hydrogen.2 AEM-LTWEs can potentially operate on pure water, i.e., without highly concentrated and corrosive supporting electrolyte, and they allow for replacement of electrocatalysts based on platinum group metals (PGMs) with PGM-free ones, thus addressing the main drawbacks of the liquid-alkaline (LA) and proton exchange membrane (PEM) electrolyzers.3 Consequently, the development of PGM-free electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media is of primary importance for the deployment of AEM-LTWEs that has attracted significant attention of researchers.4–6 Besides improving the catalytic activity, the integration of PGM-free HER and OER electrocatalysts into electrodes for operation in AEM electrolyzers is crucial to achieving satisfactory electrolyzer performance and making them competitive with the LA and PEM systems.7,8 In this work, we measured electrocatalytic activity of a series of OER and HER catalysts in a three-electrode cell and then implemented these catalysts in electrodes for testing in an AEM electrolyzer. We investigated different classes of OER catalysts, including commercial IrO2 (a PGM ORR benchmark), LaxSr1-xCoO3-δ oxides, Ni-Fe nanofoam oxides, Ni-Fe aerogel-derived oxides, and MOF-derived Co oxides. In the HER-catalyst part of the study, we compared a commercial PtRu/C (a PGM HER benchmark) with an aerogel NiMo/C catalyst. Catalysts and electrodes before and after testing were characterized by XRD, SEM, EDS, and XPS.In addition to exploring different catalysts, we investigated the impact of several fabrication variables such as the ink deposition method, amount of ionomer, incorporation of a binding agent, and the type of anode porous transport layer on performance. The tests were carried in an electrolyzer operating with pure water and two electrolyte solutions, 0.1 M KOH and 1% K2CO3. The results show that, in addition to the OER and HER electrocatalytic activity, the electrode fabrication is an important factor affecting AEM electrolyzer performance, especially in the pure-water operation mode, in which case assuring an effective transport of the OH– ions within the catalyst layer is especially challenging. References Y. S. Kim, ACS Appl. Polym. Mater. (2021).C. Santoro et al., ChemSusChem, 202200027 (2022).H. A. Miller et al., Sustain. Energy Fuels, 4, 2114–2133 (2020).D. Xu et al., ACS Catal., 9, 7–15 (2019).H. Shi et al., Adv. Funct. Mater., 2102285, 1–10 (2021).H. Doan et al., J. Electrochem. Soc., 168, 084501 (2021).N. U. Hassan, M. Mandal, B. Zulevi, P. A. Kohl, and W. E. Mustain, Electrochim. Acta, 409, 140001 (2022).G. A. Lindquist et al., ACS Appl. Mater. Interfaces (2021).

Non-planar embedded 3D printing for complex hydrogel manufacturing

Embedded bioprinting as a tissue engineering method has expanded the ability to bioprint complex geometry of native tissue. Print bath support in these methods allows the biomaterial to solidify in place, mitigating the possibly negative effects of low viscosity and gravity. This material stability also permits for non-planar deposition of the biomaterial. Here, we developed a non-planar 3D print slicer for non-planar embedded bioprinting. We quantified the changes in ink deposition properties with respect to non-planar movement to understand printability in the system. Alginate prints in a FRESH support bath were used to quantify the capability of the slicer to create tunable mechanical properties. Mechanical testing reveals that geometric changes to the printed models can tune stiffness, failure stress and strain, and Poisson's ratio. These results demonstrate that using non-planar manufacturing can produce mechanically tunable properties with a homogeneous biomaterial. This may strengthen our ability to precisely match mechanical properties of native tissues to improve tissue engineering outcomes.

3D Printing of Largescale Functional Nanofilm using Electrically assisted Direct Ink Deposition

Functional nanofilms show significant importance for various applications in different fields, such as sustainable energy, biomedicine, electronics, and optics. However, there are still many challenges in the fabrication of nanostructured films with tailored properties using traditional manufacturing technologies. A novel 3D printing approach called electrical field-assisted direct ink deposition (EF-DID) was developed to produce large-scale nanofilms with controllable nanostructures and patternable features. In the proposed method, the formation of nanodroplets in the direct ink deposition was investigated under an electrostatic field with high voltage. Critical printing parameters, including solution concentration, deposition height, applied voltage, and ink flow rate, were studied systematically to understand fundamental mechanisms of the nanostructures generation during the printing. In addition, the scientific relationship between deposition parameters and nanofilm properties, including film thickness, electrical conductivity, and contact angle, were explored. Finally, patterned nanofilms with well-organized nanostructures were fabricated to demonstrate potential application prospects in the field of nanotechnology.

Tuning Electrode-Membrane Interface for Highly Efficient Polymer Electrolyte Membrane Fuel Cells

Polymer electrolyte membrane fuel cells (PEMFCs) are typically comprised of porous electrodes with randomly distributed mixtures of Pt/C catalyst and ionomer formed during the ink deposition process. The randomness of catalyst particles, ionomer films, and voids, create a non-ideal disordered electrode structure with high tortuosity. These intrinsic characteristics of conventional electrodes create significant challenges during PEMFC operation. These challenges include: 1) low catalyst utilization; 2) high O2 transport resistance to catalyst through the ionomer and pores of carbon support; and 3) limited electronic/protonic conductivities. To improve the performance of the PEMFC electrode, we have previously shown that structured electrodes based on a patterned membrane surface can increase the interfacial area between the electrode and the membrane, enhancing mass transport at high current densities, and augmenting its ionic conductivity.[1][2] In this work, we will present further optimization of these type of structured electrodes using free-standing architectures, reduced ionomer content, and new catalyst deposition processes. More importantly, these newly tuned electrode structures can improve the performance of PEMFCs by maximizing three-phase boundaries and optimizing the electron, proton, gas, and water transport paths. Acknowledgement: We gratefully acknowledge support from the Laboratory Directed Research & Development Program at Los Alamos National Laboratory. Reference: [1] S. K. Babu, R. Mukundan, D. A. Cullen, and J. S. Spendelow, “Co-Axial Nafion Nanowire Electrode.” ECS, Oct. 15, 2019.[2] S. K. Babu, J. S. Spendelow, and R. L. Borup, “Meso-Structured Array Electrode for Polymer Electrolyte Fuel Cells.” ECS, Oct. 03, 2017.