Current Status of Liquid Metal Printing

A Guide to Printed Stretchable Conductors

Printing of stretchable conductors enables the fabrication and rapid prototyping of stretchable electronic devices. For such applications, there are often specific process and material requirements such as print resolution, maximum strain, and electrical/ionic conductivity. This review highlights common printing methods and compatible inks that produce stretchable conductors. The review compares the capabilities, benefits, and limitations of each approach to help guide the selection of a suitable process and ink for an intended application. We also discuss methods to design and fabricate ink composites with the desired material properties (e.g., electrical conductance, viscosity, printability). This guide should help inform ongoing and future efforts to create soft, stretchable electronic devices for wearables, soft robots, e-skins, and sensors.

A Review of the Metal Additive Manufacturing Processes

Metal additive manufacturing (AM) is a layer-by-layer process that makes the direct manufacturing of various industrial parts possible. This method facilitates the design and fabrication of complex industrial, advanced, and fine parts that are used in different industry sectors, such as aerospace, medicine, turbines, and jewelry, where the utilization of other fabrication techniques is difficult or impossible. This method is advantageous in terms of dimensional accuracy and fabrication speed. However, the parts fabricated by this method may suffer from faults such as anisotropy, micro-porosity, and defective joints. Metals like titanium, aluminum, stainless steels, superalloys, etc., have been used-in the form of powder or wire-as feed materials in the additive manufacturing of various parts. The main criterion that distinguishes different additive manufacturing processes from each other is the deposition method. With regard to this criterion, AM processes can be divided into four classes: local melting, sintering, sheet forming, and electrochemical methods. Parameters affecting the properties of the additive-manufactured part and the defects associated with an AM process determine the method by which a certain part should be manufactured. This study is a survey of different additive manufacturing processes, their mechanisms, capabilities, shortcomings, and the general properties of the parts manufactured by them.

Manipulating liquid metal flow for creating standalone structures with micro-and nano-scale features in a single step

Standalone structures with periodic surface undulations or ripples can be spontaneously created upon flowing a liquid metal, e.g. Ga, over a metallic film, e.g. Pt, Au, etc, through a complex 'wetting-reaction'-driven process. Due to the ability of 3-dimensional patterning at the small length scale in a single step, the liquid metal 'ripple' flow is a promising non-conventional patterning technique. Herein, we examine the effect of a few process parameters, such as distance away from the liquid reservoir, size of the liquid reservoir, and the geometry, thickness, and width of substrate metal film, on the nature of the ripple flow to produce finer patterns with feature sizes of ≤ 2μm. The height and the pitch of the pattern decrease with distance from the liquid reservoir and decrease in the reservoir volume. Furthermore, a decrease in the thickness and width of the substrate film also leads to a decrease in the height and pitch of the ripples. Finally, the application of an external electric field also controls the ripple patterns. By optimizing various parameters, standalone ripple structures of Ga with the height and pitch of ≤ 500 nm are created. As potential applications, the ripple patterns with micro-and nano-scopic features are demonstrated to produce a diffraction grating and a die for micro-stamping.

Liquid Phase 3D Printing: How This New Technology Can Help Bring 3D Printing to the Operating Room

PURPOSE OF REVIEW

The purpose of this review is to discuss the state of technology in liquid phase three-dimensional (3D) metal printing, how this has affected the field of orthopedic surgery, and changes that we can expect in the future with the rise of this printing technology. We will also discuss how liquid phase metal printing can possibly bring three-dimensional printing to the operating room.

RECENT FINDINGS

The use of liquid phase 3D metal printing may become commonplace for manufacturing orthopedic implants and devices. Traditional metal printing involved powder-based metals and high-energy beam technologies that are expensive, time-consuming, and potentially wasteful. This unfortunately leaves them out of reach for most end consumers such as orthopedic surgeons. Liquid phase metal printing is less expensive and faster. However, there is still major work required to bring this technology to the operating room and benefit patients. While major strides have been made in the field of liquid phase metal three-dimensional printing, there are still significant developments in the pipeline. These could lead to future production of personalized orthopedic implants and devices with optimal material properties for patients.

Microfluidics-enabled functional 3D printing

Microfluidic technology has established itself as a powerful tool to enable highly precise spatiotemporal control over fluid streams for mixing, separations, biochemical reactions, and material synthesis. 3D printing technologies such as extrusion-based printing, inkjet, and stereolithography share similar length scales and fundamentals of fluid handling with microfluidics. The advanced fluidic manipulation capabilities afforded by microfluidics can thus be potentially leveraged to enhance the performance of existing 3D printing technologies or even develop new approaches to additive manufacturing. This review discusses recent developments in integrating microfluidic elements with several well-established 3D printing technologies, highlighting the trend of using microfluidic approaches to achieve functional and multimaterial 3D printing as well as to identify potential future research directions in this emergent area.

Influence of Salt Support Structures on Material Jetted Aluminum Parts

Like most additive manufacturing processes for metals, material jetting processes require support structures in order to attain full 3D capability. The support structures have to be removed in subsequent operations, which increases costs and slows down the manufacturing process. One approach to this issue is the use of water-soluble support structures made from salts that allow a fast and economic support removal. In this paper, we analyze the influence of salt support structures on material jetted aluminum parts. The salt is applied in its molten state, and because molten salts are typically corrosive substances, it is important to investigate the interaction between support and build material. Other characteristic properties of salts are high melting temperatures and low thermal conductivity, which could potentially lead to remelting of already printed structures and might influence the microstructure of aluminum that is printed on top of the salt due to low cooling rates. Three different sample geometries have been examined using optical microscopy, confocal laser scanning microscopy, energy-dispersive X-ray spectroscopy and micro-hardness testing. The results indicate that there is no distinct influence on the process with respect to remelting, micro-hardness and chemical reactions. However, a larger dendrite arm spacing is observed in aluminum that is printed on salt.