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International audience; We report on printed flexible micro-hotplates operating at high temperature at lower power consμmption than ever reported using aerosol jet printing of fine metallic conductor features. Efficient heating (i.e., 40 mW at 325 °C) was produced by reducing the effective heating area and substrates thickness. Gold (Au) nanoparticles solution was used for printing micro-hotplates of two different sizes, i.e., 500 × 500 μm2 and 300 × 300 μm2, on 50 μm- and 13 μm-thick PI substrates, respectively. Comsol simulations were used to optimize the thermal design of micro-hotplates. Their power consμmption at 325 °C was of 54 mW for the large hotplate and of 40 mW for the smaller design. These results validate the simple manufacturing of high temperature and power efficient flexible micro-hotplates for applications such as in portable gas and chemical sensors, thermal metrology, etc.

Triboelectric motion sensors, based on the generation of a voltage across two dissimilar materials sliding across each other as a result of the triboelectric effect, have generated interest due to the relative simplicity of the typical grated device structures and materials required. However, these sensors are often limited by poor spatial and/or temporal resolution of motion due to limitations in achieving the required device feature sizes through conventional lithography or printing techniques. Furthermore, the reliance on metallic components that are relatively straightforward to pattern into fine features limits the possibility to develop transparent sensors. Polymers would allow for transparent devices, but these materials are significantly more difficult to pattern into fine features when compared to metals. Here, we use an aerosol-jet printing (AJP) technique to develop triboelectric sensors using a wide variety of materials, including polymers, which can be directly printed into finely featured grated structures for enhanced sensitivity to displacement and speed of motion. We present a detailed investigation highlighting the role of material selection and feature size in determining the overall resolution of the resulting motion sensor. A 3-channel rotary sensor is also presented, demonstrating the versatility of the AJP technique in developing more complex triboelectric motion sensors.

Highlights • Aerosol-jet printing is used to fabricate microfluidic devices with customised geometries, including steps and slopes. • A rapid prototyping method for producing bespoke molds for microfluidic devices with precise channel functionalization. • The functionalization capability is demonstrated by rendering a section of a microfluidic channel hydrophilic using PVA., Microfluidics has emerged as a powerful analytical tool for biology and biomedical research, with uses ranging from single-cell phenotyping to drug discovery and medical diagnostics, and only small sample volumes required for testing. The ability to rapidly prototype new designs is hugely beneficial in a research environment, but the high cost, slow turnaround, and wasteful nature of commonly used fabrication techniques, particularly for complex multi-layer geometries, severely impede the development process. In addition, microfluidic channels in most devices currently play a passive role and are typically used to direct flows. The ability to “functionalize” the channels with different materials in precise spatial locations would be a major advantage for a range of applications. This would involve incorporating functional materials directly within the channels that can partake in, guide or facilitate reactions in precisely controlled microenvironments. Here we demonstrate the use of Aerosol Jet Printing (AJP) to rapidly produce bespoke molds for microfluidic devices with a range of different geometries and precise “in-channel” functionalization. We show that such an advanced microscale additive manufacturing method can be used to rapidly design cost-efficient and customized microfluidic devices, with the ability to add functional coatings at specific locations within the microfluidic channels. We demonstrate the functionalization capabilities of our technique by specifically coating a section of a microfluidic channel with polyvinyl alcohol to render it hydrophilic. This versatile microfluidic device prototyping technique will be a powerful aid for biological and bio-medical research in both academic and industrial contexts.

Thermoelectric generators (TEGs) operate in the presence of a temperature gradient, where the constituent thermoelectric (TE) material converts heat into electricity via the Seebeck effect. However, TE materials are characterised by a thermoelectric figure of merit (ZT) and/or power factor (PF), which often has a strong dependence on temperature. Thus, a single TE material spanning a given temperature range is unlikely to have an optimal ZT or PF across the entire range, leading to inefficient TEG performance. Here, we demonstrate compositionally graded organic-inorganic nanocomposites, where the composition of the TE nanocomposite is systematically tuned along the length of the TEG, in order to optimise the PF along the applied temperature gradient. The nanocomposite composition can be dynamically tuned by an aerosol-jet printing method with controlled in-situ mixing capability, thus enabling the realisation of such compositionally graded thermoelectric composites (CG-TECs). We show how CG-TECs can be realised by varying the loading weight percentage of Bi2Te3 nanoparticles or Sb2Te3 nanoflakes within an organic conducting matrix using bespoke solution-processable inks. The enhanced energy harvesting capability of these CG-TECs from low-grade waste heat (