Over the last 30 years, scientific and technological progress has boosted the development of medical devices that can assist patients and support medical staff. With regard to the rehabilitation of patients who have suffered from traumas, robotic systems can be an aid for rapid patient recovery. This paper focuses on studying and implementing a system for measuring the finger position of one hand with the aim of giving feedback to the rehabilitation system. It consists of a glove where sensors are mounted suitably configured and connected to an electronic conditioning and acquisition unit. The information regarding the position is then sent to a remote system. The objective of this paper is to provide a sensorized glove for monitoring the rehabilitation activities of the hand. The glove can have several other applications such as: 1) the recognition of sign language; 2) the diagnostic measurement of the finger movement at a distance; and 3) the interaction with virtual reality.

Printing sensors and electronics directly on the objects is very attractive for producing smart devices, but it is still a challenge. Indeed, in some applications, the substrate that supports the printed electronics could be non-planar or the thermal curing of the functional inks could damage temperature-sensitive substrates such as plastics, fabric or paper. In this paper, we propose a new method for manufacturing silver-based strain sensors with arbitrary and custom geometries directly on plastic objects with curvilinear surfaces: (1) the silver lines are deposited by aerosol jet printing, which can print on non-planar or 3D surfaces; (2) photonic sintering quickly cures the deposited layer, avoiding the overheating of the substrate. To validate the manufacturing process, we printed strain gauges with conventional geometry on polyvinyl chloride (PVC) conduits. The entire manufacturing process, included sensor wiring and optional encapsulation, is performed at room temperature, compatible with the plastic surface. At the end of the process, the measured thickness of the printed sensor was 8.72 μm on average, the volume resistivity was evaluated 40 μΩ∙cm, and the thermal coefficient resistance was measured 0.150 %/°C. The average resistance was (71 ± 7) Ω and the gauge factor was found to be 2.42 on average.

Printed electronics is an expanding research field that can reach the goal of reducing the environmental impact on electronics exploiting renewable and biodegradable materials, like paper. In our work, we designed and tested a new method for fabricating hybrid smart devices on cellulose substrates by aerosol jet printing (AJP) and photonic curing, also known as flash lamp annealing (FLA), capable to cure low temperature materials without any damage. Three different cellulose-based materials (chromatographic paper, photopaper, cardboard) were tested. Multilayer capability and SMDs (surface mount devices) interconnections are possible permitting high flexibility in the fabrication process. Electrical and geometrical tests were performed to analyze the behavior of printed samples. Resulted resistivities are 26.3 × 10⁻⁸ Ω⋅m on chromatographic paper, 22.3 × 10⁻⁸ Ω⋅m on photopaper and 13.1 × 10⁻⁸ Ω⋅m on cardboard. Profilometer and optical microscope evaluations were performed to state deposition quality and penetration of the ink in cellulose materials (thicknesses equal to 24.9, 28.5, and 51 μm respectively for chromatographic paper, photopaper, and cardboard). Furthermore, bending (only chromatographic paper did not reach the break-up) and damp environment tests (no significant variations in resistance) where performed. A final prototype of a complete functioning multilayer smart devices on cellulose 3D-substrate is shown, characterized by multilayers, capacitive sensors, SMDs interconnections.

Industry 4.0 has radically been transforming the production processes and systems with the adoption of enabling technologies, such as Internet of things (IoT), big data, additive manufacturing (AM), and cloud computing. In this context, sensors are essential to extract information about production, spare parts, equipment health, and environmental conditions necessary for improving many aspects of industrial processes (flexibility, efficiency, costs, etc.). Sensors should be placed everywhere (on machines, smart devices, objects, and tools) inside the factory to monitor in real-time physical quantities such as temperature, vibrations, deformations that could affect the production. Printed electronics (PE) offers techniques to produce unconventional sensor and systems or to make conventional objects “smart”. This work aims to analyze innovative PE technologies—inkjet printing and aerosol jet printing in combination with photonic curing—as manufacturing technologies for electronics and sensors to be integrated into objects, showing a series of sensors fabricated by PE as applications that will be adopted for smart objects and Industry 4.0.

The growing diffusion and usability of additive printing techniques have created new manufacturing scenarios for products. Printed electronics is playing a key role in the design of next-generation objects. These objects are no longer only able to fulfill their original function, but through specific sensors and circuits can measure physical quantities in the surrounding environment. In this way, a conventional object is made smart, being able to communicate with other objects or remote units. This kind of change fits perfectly into the context of Industry 4.0, where the ability to collect additional information can increase efficiency in the production, transportation, and storage of products. Smart objects can be manufactured with numerous different technologies and materials depending on the performance required and on the specific application. The purpose of this review is to provide an analysis of printed technologies that enable resistive sensors printing on complex surfaces for smart objects fabrication. First, an explanation of the technologies under consideration is provided. Then, an analysis of the aspects that affect the final print quality for each technique is provided, highlighting advantages and disadvantages. The paper also indicates the limitations and potential of these printed technologies for smart objects.