Smart and functional materials processed by printing technologies reveal an increasing interest due to small cost assembly, easy integration into devices and the possibility to obtain multifunctional materials over flexible and large areas. After introducing smart materials, printing technologies and inks, this review discusses the materials that are already being printed, mainly piezoelectric, piezoresistive, magnetostrictive, shape memory polymers (SMP), pH sensitive and chromic system materials. Since polymer-based smart materials are particularly attractive for device implementation, this review will focus on printed polymer-based smart materials. Finally, critical challenges and future research directions will be addressed.

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Printing electronic passive components suffer from the lack of a wide variety of appropriate materials for developing components with specific characteristics, for specific dimensions. This paper introduces a multilayer approach for the inkjet printing of resistors, inductors and capacitors, showing that it is possible to manufacture tailored passive circuit elements and therefore their implementation into functional printed electronics. The materials and process steps for the manufacturing, the individual component characteristics and the equivalent circuit is provided for all passive devices.

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Printed sensors find an increasing interest essentially due to their characteristics of flexibility and low cost per unit area. In this work a screen printed Wheatstone bridge is presented, suitable for strain sensing applications. A piezoresistive ink composite based on biocompatible thermoplastic elastomer styrene-ethylene/butylene-styrene (SEBS) as matrix and multi-walled carbon nanotubes (MWCNT) as nanofillers was used as a piezoresistive sensing material. Different deposition techniques, such as, screen printing, spray painting and drop casting were evaluated in order to optimize the resistance variation related to the piezoresistive effect. Several Wheatstone bridges with one and two sensors were designed to obtain an output sensitivity as a function of the strain submitted to the sensors. Further, different sensor geometries were evaluated to maximize the strain output sensitivity. Electro-mechanical bending tests showed a good linearity and a sensitivity up to 18 mV/V in the all screen printed half Wheatstone bridge output with two MWCNT/SEBS sensors.

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Printed electronics represent an alternative solution for the manufacturing of low-temperature and large area flexible electronics. The use of inkjet printing is showing major advantages when compared to other established printing technologies such as gravure, screen or offset printing, allowing the reduction of manufacturing costs due to its efficient material usage and the direct-writing approach without requirement of any masks. However, several technological restrictions for printed electronics can hinder its application potential, e.g. the device stability under atmospheric or even more stringent conditions. Here, we study the influence of specific mechanical, chemical, and temperature treatments usually appearing in manufacturing processes for textiles on the electrical performance of all-inkjet-printed organic thin-film transistors (OTFTs). Therefore, OTFTs where manufactured with silver electrodes, a UV curable dielectric, and 6,13-bis(triisopropylsilylethynyl) pentance (TIPS-pentacene) as the active semiconductor layer. All the layers were deposited using inkjet printing. After electrical characterization of the printed OTFTs, a simple encapsulation method was applied followed by the degradation study allowing a comparison of the electrical performance of treated and not treated OTFTs. Industrial calendering, dyeing, washing and stentering were selected as typical textile processes and treatment methods for the printed OTFTs. It is shown that the all-inkjet-printed OTFTs fabricated in this work are functional after their submission to the textiles processes but with degradation in the electrical performance, exhibiting higher degradation in the OTFTs with shorter channel lengths (L = 10 μm)