Flexible and stretchable strain sensors are in great demand for many applications like wearables and home health. This work reports a strain sensor fabricated using aerosol jet printing technology on a commercially available bandage to be used as a low-cost wearable. Laser light is explored to sinter the silver nanoparticle ink on low-temperature bandage substrate. The laser parameters, their effects on the microstructure of the film, and the resulting sensor performance are systematically investigated. The results showed that the sensor is stretchable, has good sensitivity, and stability for 700 cycles of repeated bending.

Carbon nanotubes (CNTs) are 1D nanostructured materials with unique mechanical, optical, and electrical properties which can be potentially exploited for fabricating wide variety of devices. In addition, the biocompatibility of CNTs makes it attractive for wearable and implantable technology applications. Well‐aligned CNT structures show enhanced properties such as superior electron mobility, strain sensitivity, better mechanical property, and enhanced performance and reproducibility that are absent in their disordered counterparts, thus allowing more promising applications in various fields. With aligned CNTs, devices can be optimized to exhibit better performance with lesser materials and more miniature designs. This review summarizes the landscape of CNTs alignment, either during the growth or post‐growth processing. This paper delineates various CNTs alignment mechanism, process parameters, and challenges of each technique. A comparative discussion on the advantages, disadvantages, and degree of alignment of each technique is presented. A detailed discussion on the various applications that utilize properties of aligned CNTs devices is presented. The advent of 3D printing techniques for printing CNTs for novel and futuristic applications is also discussed.

3D printing, also known as additive manufacturing, is a manufacturing process in which the materials are deposited layer by layer in an additive manner. With the advancement in materials and manufacturing technology, 3D printing has found its applications in the field of electronics manufacturing. Initially, 3D printing is used for the fabrication of electronic components with single material designs such as resistors, inductors, circuits, antennas, strain gauges, etc. Recently, there are many works involving the use of 3D printing fabrication techniques for advanced electronic components and devices such as parallel plate capacitors, inductors, organic light‐emitting diodes, photovoltaics, transistors, displays, etc. which involve multilayer multimaterial printing. Despite these many works, there has been no review on the design and fabrication consideration for the 3D printing of multilayered and multimaterial (MLMM) electronics. As such, this review aims to summarize the current landscape of 3D printing of MLMM electronics and provide some insights on the design consideration, fabrication strategies, and challenges of 3D printing of MLMM electronics. In particular, the focus will be placed on discussing the interface conditions between different materials such as surface wettability, surface roughness, material compatibility, and the considerations for postprocessing treatments.

Three-dimensional (3D) bioprinting systems serve as advanced manufacturing platform for the precise deposition of cells and biomaterials at pre-defined positions. Among the various bioprinting techniques, the drop-on-demand jetting approach facilitates deposition of pico/nanoliter droplets of cells and materials for study of cell-cell and cell-matrix interactions. Despite advances in the bioprinting systems, there is a poor understanding of how the viability of primary human cells within sub-nanoliter droplets is affected during the printing process. In this work, a thermal inkjet system is utilized to dispense sub-nanoliter cell-laden droplets, and two key factors – droplet impact velocity and droplet volume – are identified to have significant effect on the viability and proliferation of printed cells. An increase in the cell concentration results in slower impact velocity, which leads to higher viability of the printed cells and improves the printing outcome by mitigating droplet splashing. Furthermore, a minimum droplet volume of 20 nL per spot helps to mitigate evaporation-induced cell damage and maintain high viability of the printed cells within a printing duration of 2 min. Hence, controlling the droplet impact velocity and droplet volume in sub-nanoliter bioprinting is critical for viability and proliferation of printed human primary cells.

The alignment of carbon nanotubes (CNTs) is of great importance for the fabrication of high-speed electronic devices such as a transistor as the electron mobilities can be greatly enhanced with aligned CNT architectures. Here, we report, for the first time, a methodology to obtain preferentially aligned CNT traces on a flexible polyimide substrate utilizing the high-resolution aerosol jet printing technique and evaporation-driven self-assembly process. A self-assembled twin-line of CNT (“coffee-ring” effect) is observed in the deposit patterns, and the field-emission scanning electron microscopy (FESEM) images reveal highly self-ordered CNT in the resulting CNT twin-line. Various aerosol jet parameters have been investigated to obtain printed tracks in the range of 30–80 μm and conductive tracks (single CNT twin-line width) in the range of 600–1500 nm. The smallest CNT twin-line obtained in this experiment is found to be approximately 16 μm using a suitable sheath-to-atomizer flow ratio. Image analysis of FESEM images confirms the formation of aligned CNT traces at the ink periphery. The effect of the line width on the degree of alignment of the CNT is studied and evaluated. The electrical resistance of the CNT trace is adjustable by controlling the number of print passes and print speed.

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A study of evaporation dynamics of the CNT suspensions and CNT alignment via sessile drop experiments on a flexible substrate.

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