A fabric-based approach for wearable haptics

In recent years, wearable haptic systems (WHS) have gained increasing attention as a novel and exciting paradigm for human-robot interaction (HRI).These systems can be worn by users, carried around, and integrated in their everyday lives, thus enabling a more natural manner to deliver tactile cues.At the same time, the design of these types of devices presents new issues: the challenge is the correct identification of design guidelines, with the two-fold goal of minimizing system encumbrance and increasing the effectiveness and naturalness of stimulus delivery.Fabrics can represent a viable solution to tackle these issues.They are specifically thought “to be worn”, and could be the key ingredient to develop wearable haptic interfaces conceived for a more natural HRI.In this paper, the author will review some examples of fabric-based WHS that can be applied to different body locations, and elicit different haptic perceptions for different application fields.Perspective and future developments of this approach will be discussed

Finite element modeling and validation of a soft array of spatially coupled dielectric elastomer transducers

Dielectric elastomer (DE) transducers are suitable candidates for the development of compliant mechatronic devices, such as wearable smart skins and soft robots. If many independently-controllable DEs are closely arranged in an array-like configuration, sharing a common elastomer membrane, novel types of cooperative and soft actuator/sensor systems can be obtained. The common elastic substrate, however, introduces strong electro-mechanical coupling effects among neighboring DEs, which highly influence the overall membrane system actuation and sensing characteristics. To effectively design soft cooperative systems based on DEs, these effects need to be systematically understood and modeled first. As a first step towards the development of soft cooperative DE systems, in this paper we present a finite element simulation approach for a 1-by-3 silicone array of DE units. After defining the system constitutive equations and the numerical assumptions, an extensive experimental campaign is conducted to calibrate and validate the model. The simulation results accurately predict the changes in force (actuation behavior) and capacitance (sensing behavior) of the different elements of the array, when their neighbors are subjected to different electro-mechanical loads. Quantitatively, the model reproduces the force and capacitance responses with an average fit higher than 93% and 92%, respectively. Finally, the validated model is used to perform parameter studies, aimed at highlighting how the array performance depends on a relevant set of design parameters, i.e. DE-DE spacing, DE-outer structure spacing, membrane pre-stretch, array scale, and electrode shape. The obtained results will provide important guidelines for the future design of cooperative actuator/sensor systems based on DE transducers

Study on conductive hydrogels in flexible and wearable triboelectric devices towards energy-harvesting and sensing applications (エネルギーハーベスティングおよびセンシングに向けたフレキシブルでウェアラブルな摩擦発電デバイスにおける導電性ハイドロゲルに関する研究)

信州大学(Shinshu university)博士（工学）この博士論文は、次の学術雑誌論文を一部に使用しています。 / ACS Applied Materials Interfaces 14(7) :9126-9137(2022); doi:10.1021/acsami.1c23176 / Advanced Fiber Materials 4(6) :1486-1499(2022); doi:10.1007/s42765-022-00181-4 / Chemical Engineering Journal 457 :141276(2023); doi:10.1016/j.cej.2023.141276ThesisDONG, LI. Study on conductive hydrogels in flexible and wearable triboelectric devices towards energy-harvesting and sensing applications (エネルギーハーベスティングおよびセンシングに向けたフレキシブルでウェアラブルな摩擦発電デバイスにおける導電性ハイドロゲルに関する研究). 信州大学, 2023, 博士論文. 博士（工学）, 甲第802号, 令和05年03月20日授与.doctoral thesi

Electronic Skin in Robotics and Healthcare: Towards Multimodal Sensing and Intelligent Analysis

Skin-interfaced electronics is gradually transforming robotic and medical fields by enabling noninvasive and continuous monitoring of physiological and biochemical information. Despite their promise, current wearable technologies face challenges in several disciplines: Physical sensors are prone to motion-induced noise and lack the capability for effective disease detection, while existing wearable biochemical sensors suffer from operational instability in biofluids, limiting their practicality. Conventional electronic skin contains only a limited category of sensors that are not sufficient for practical applications, and conventional data processing methods for these wearables necessitate manual intervention to filter noise and decipher health-related information. This thesis presents advances in electronic skin within robotics and healthcare, emphasizing multimodal sensing and data analysis through machine intelligence. Chapter 1 introduces the concept of electronic skin, outlining the emerging sensor technologies and a general machine learning pipeline for data processing. Chapter 2 details the development of multimodal physiological and biochemical sensors that enable long-term continuous monitoring with high sensitivity and stability. Chapter 3 explores the application of integrated electronic skin in robotics, prosthetics, and human machine interactions. Chapter 4 showcases practical implementations of integrated electronic skin with robust sensors for wound monitoring and treatment. Chapter 5 highlights the transformative deployment of artificial intelligence in deconvoluting health profiles on mental health. The last chapter, Chapter 6, delves into the challenges and prospects of artificial intelligence-powered electronic skins, offering predictions for the evolution of smart electronic skins. We envision that multimodal sensing and machine intelligence in electronic skin could significantly advance the field of human machine interactions and personalized healthcare.</p

Smart Textiles as the Digital Interface of the Future

The growing field of smart textiles could change everyday life, adding an element of interactivity to commonly used items such as clothing and furniture. Smart textiles measure then respond to external stimuli. For scalability in the future, smart textiles must be produced using conventional textile manufacturing craftsmanship. The resulting textile must be durable and comfortable while retaining electrical capabilities. Smart textiles can be fabricating through embroidery, weaving, and knitting using conductive threads. Electronics can also be printed onto textiles. Researchers are also creating higher-order electronics, such as the transistor, on the fiber-level to make the technology in smart textiles as discreet as possible. A variety of sensors can be produced with smart textile technology, and these sensors can be utilized in medical and protective applications. Smart textiles can then communicate a response through output devices such as lighting displays. As smart textiles develop, the ethics of manufacturing must be considered. Lightweight sources of power generation besides batteries are needed to make textiles systems more robust. As the smart textile market continues to grow, there are several obstacles in the way of smart textiles entering everyday life. Two traditionally different sectors—textiles and electronics—must converge. Consumers must also be motivated to trade up to smart textile products through increased electronic functions. As smart textiles continue to mature, more applications will be accepted by society and begin impacting day to day life

Electroactive Materials for Applications in the Field of Wearable Technologies

The objective of this PhD thesis is to present the most performing EAP-based materials, technologies and devices developed by our lab (Ch.4, 5 and 6) also in collaboration with other research groups (Ch.1 and 2) for sensing, actuating and energy harvesting, with reference to their already demonstrated or potential applicability to electronic textiles and wearable technologies in general. Over the last decade great strides have been made in the field of wearable technology: thanks to new discoveries in materials science and miniaturized electronics, tissues and "smart" devices for monitoring vital parameters, rehabilitation and tele-assistance were born. However, a complete and self-powered system, able to exchange information with the external environment, to generate power using the usual movements of the human body (walking, work, sport) and to drive wearable devices, is not yet available on the market and it would find a considerable number of applications (monitoring physiological parameters for athletes and special forces officers in emergency situations, etc.). After a first survey of the state of the art concerning the so-called "smart materials” and technologies currently available for " wearable " activities, the work has developed on three major directives consisting in: energy generation and storage, sensing and actuation. Energy generation and storage. An experimental study, conducted mainly during the first year of PhD, has identified possible candidate materials (piezoelectric PVDF, electret PP) for the energy harvesting and subsequent generation of power from movement and gestures by exploiting the piezoelectric properties of selected materials. These materials have been either found on the market or processed in laboratory. In collaboration with the University of Pavia, a circuit for the storage of electric charges generated was made. Both the commercial materials and those obtained in laboratory were electromechanically tested and the generation of electric charges has been used to develop a demonstrator generator-LED embedded in a shoe. Sensing. During the first and second year, different sensor configurations of "dry" piezoelectric PVDF sensors were tested for the monitoring of vital parameters (heart and breathing rate). Such sensors, prepared in collaboration with the University of Lodz (TUL, Poland), our partners in the PROETEX European project (6th FP 2006-2009), were woven into fabrics to be easily integrated into clothing, and their response was studied. Signal intensities comparable to those of common 3M medical electrodes have been observed. A further development of these materials should be turn to reduce noise, while a computational study might deal with the signal filtering and elimination of motion artifacts. Along with the study of piezoelectric sensors mentioned above, during the third PhD year the production and characterization of dielectric elastomers for sensing applications (artificial skin) was developed too, in collaboration with the Genoa DIST (Dipartimento di Informatica, Sistemistica e Telematica). Such elastomers, characterised by high dielectric constants and restrained compressive elastic moduli, were develop in order to act as dielectric medium in piezocapacitive sensing devices. The obtained materials will be used as artificial skin in robotic systems. Actuating. In parallel with the two lines described above, the activity was concentrated, throughout the period of PhD, on the development of new dielectric elastomer actuators, to be used as high dielectric constant, low elastic modulus and, especially, low electric driving fields devices so that they can be used once inserted inside the clothing (simplified prototype actuators able to change the porosity / texture of different textiles were developed during the first year of activity for the FLEXIFUNBAR European project (6th FP 2005-2008)). The "blend" approach has been privileged over the "composite" approach, previously studied in the master thesis, and has led to promising results both from the applicative point of view, with an increase in the electromechanical performance, and on a fundamental level, for the implications emerging from the interaction between different phases in the study of dielectric response of partially heterogeneous systems. Electromechanical encouraging results were then obtained during the second year of activity with the development of silicone/polyurethane (SI/PU) blends prepared by appropriate volume fractions. Further improvements have also been achieved during the third year of doctoral studies, when it was introduced in the same mixtures a third component, the conjugated polymer poly-(3-hexylthiophene-2,5-dyil) (P3HT), already used by our group for its high polarizability in order to increase the dielectric constant of silicon actuators. The obtained samples, dielectrically, mechanically and electromechanically tested, showed that the conjugated polymer leads to a further significant increase in the electromechanical response of the blend only when added at levels of 1 wt%. This polymer shows, in fact, a certain influence on the microscopic distribution of the SI and PU "phases" in the blend. This effect is maximized for the 1 wt% concentration at which the presence of interfaces is maximized and thus a larger surface polarization, combined with the characteristic high polarizability of P3HT, leads to dielectric constant and strain further implementations. Similar increases in performance, compared to pure components, were also found in mixtures prepared using other polyurethanes and silicones adopting, when necessary, appropriate steps to modify the kinetics of reaction (addition of solvents). The results obtained with this "blending" approach are supported by the Intephase Theory (IT), recently introduced to complete the well known Effective Medium Theory (EMT) which, although applicable to a variety of particle composite structures, is not suitable to describe the behaviour of systems where the presence of an interphase between filler and matrix is significant. The EFT demonstrates that border regions, showing dielectric characteristics different from those of the starting components, can strongly influence the system performance. Through theoretical and experimental evidence, in fact, it is known that, while the inner parts of the matrix polymer chains are able to adopt a configuration that minimizes spontaneous conformational energy, at the interface they are linked or otherwise conditioned in their movements, giving rise to a region where the electrical properties (in some cases also thermal and mechanical) are different from those of both the pure material composing the mixture. During the third year, the production and characterization of elastomeric foams with dielectric properties suitable for sensing (artificial skin) and actuating applications were also developed. The electromechanical performance of these polyurethane-based foams, after appropriate polarization under very high electric fields (Corona poling), were compared with those of two commercial products, which were also subjected to corona poling. Studies have been conducted also on the life of the induced polarization produced by poling in the foam and on the influence of electric field exposure time on the final response of the material. The slightly positive results obtained in terms of increased dielectric constants and strains have opened a new line of activity that represents an innovation in the field of dielectric elastomers, that is the preparation of elastomeric foams with electret properties

DEVELOPMENT OF FUNCTIONAL NANOCOMPOSITE MATERIALS TOWARDS BIODEGRADABLE SOFT ROBOTICS AND FLEXIBLE ELECTRONICS

World population is continuously growing, as well as the influence we have on the ecosystem\u2019s natural equilibrium. Moreover, such growth is not homogeneous and it results in an overall increase of older people. Humanity\u2019s activity, growth and aging leads to many challenging issues to address: among them, there are the spread of suddenly and/or chronic diseases, malnutrition, resource pressure and environmental pollution. Research in the novel field of biodegradable soft robotics and electronics can help dealing with these issues. In fact, to face the aging of the population, it is necessary an improvement in rehabilitation technologies, physiological and continuous monitoring, as well as personalized care and therapy. Also in the agricultural sector, an accurate and efficient direct measure of the plants health conditions would be of help especially in the less-developed countries. But since living beings, such as humans and plants, are constituted by soft tissues that continuously change their size and shapes, today\u2019s traditional technologies, based on rigid materials, may not be able to provide an efficient interaction necessary to satisfy these needs: the mechanical mismatch is too prohibitive. Instead, soft robotic systems and devices can be designed to combine active functionalities with soft mechanical properties that can allow them to efficiently and safely interact with soft living tissues. Soft implantable biomedical devices, smart rehabilitation devices and compliant sensors for plants are all applications that can be achieved with soft technologies. The development of sophisticated autonomous soft systems needs the integration on a unique soft body or platform of many functionalities (such as mechanical actuation, energy harvesting, storage and delivery, sensing capabilities). A great research interest is recently arising on this topic, but yet not so many groups are focusing their efforts in the use of natural-derived and biodegradable raw materials. In fact, resource pressure and environmental pollution are becoming more and more critical problems. It should be completely avoided the use of in exhaustion, pollutant, toxic and non-degradable resources, such as lithium, petroleum derivatives, halogenated compounds and organic solvents. So-obtained biodegradable soft systems and devices could then be manufactured in high number and deployed in the environment to fulfil their duties without the need to recover them, since they can safely degrade in the environment. The aim of the current Ph.D. project is the use of natural-derived and biodegradable polymers and substances as building blocks for the development of smart composite materials that could operate as functional elements in a soft robotic system or device. Soft mechanical properties and electronic/ionic conductive properties are here combined together within smart nanocomposite materials. The use of supersonic cluster beam deposition (SCBD) technique enabled the fabrication of cluster-assembled Au electrodes that can partially penetrate into the surface of soft materials, providing an efficient solution to the challenge of coupling conductive metallic layers and soft deformable polymeric substrates. In this work, cellulose derivatives and poly(3-hydroxybutyrate) bioplastic are used as building blocks for the development of both underwater and in-air soft electromechanical actuators that are characterized and tested. A cellulosic matrix is blended with natural-derived ionic liquids to design and manufacture completely biodegradable supercapacitors, extremely interesting energy storage devices. Lastly, ultrathin Au electrodes are here deposited on biodegradable cellulose acetate sheets, in order to develop transparent flexible electronics as well as bidirectional resistive-type strain sensors. The results obtained in this work can be regarded as a preliminary study towards the realization of full natural-derived and biodegradable soft robotic and electronic systems and devices