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Special Issue "Flexible Sensors and Actuators for Novel Wearable Solutions"

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Smart Materials".

Deadline for manuscript submissions: 31 December 2019

Special Issue Editors

Guest Editor
Dr. Carlos Marques

I3N and Physics Department, Instituto de Telecomunicações, University of Aveiro, Portugal
Website | E-Mail
Interests: optical fiber sensors; polymer and silica fiber devices; sensing and data applications; flexible sensor solutions; data processing; low-cost polymer optical solutions for sensing; IoT; biomedical devices; integrated optics
Guest Editor
Prof. Dr. Anselmo Frizera-Neto

Electrical Engineering Department; Graduate Program on Electrical Engineering Federal University of Espirito Santo; Vitoria-ES, Brazil
Website | E-Mail
Interests: wearable robotics; sensor technologies; actuator; soft robotics; data processing

Special Issue Information

Dear Colleagues,

Locomotion plays a crucial role on the capacity to perform activities of daily living, personal functional abilities, and independent development in the community. However, such ability can be impaired due to clinical conditions. In order to overcome or attenuate gait disorders, assistance devices, such as wearable robots and smart walkers, as well as systems for the assessment and control of a person’s physical incapacities, have been proposed. In addition, a trend in wearable robotics involves the use of flexible materials in the robot’s structure and actuation aiming to obtain a user-friendly interface that can extend the capabilities of conventional rigid robots, so-called soft robotics. An emerging technology for the instrumentation of gait assistance and rehabilitation devices are optical sensors which include mainly optical fiber sensors. Some of the advantages of such sensors are their electromagnetic field immunity, chemical stability, compactness and multiplexing capabilities. To that extent, different technologies for optical fiber sensing have been proposed, ranging from low-cost systems to approaches with high multiplexing capabilities. For these reasons, different polymers have been studied for the development of, not only the actuators for soft robotics applications, but also for the instrumentation of these devices. Therefore, in this Special Issue, the development, characterization and application of flexible sensors and actuators for novel wearable solutions will be presented.  

In this context, wearable robotics is a growing research and application area at the intersection of health and engineering. The next generation of robots and devices for rehabilitation purposes points towards the application of flexible and more transparent structures and actuators that adapt better to the human body. Sensing and control technologies for such devices also include some important challenges.

Further, advanced sensing materials are at the core of the next generation of robots and devices for rehabilitation and linked areas with a close intersection of health and engineering are the aim of this Special Issue as is the development of novel concepts of multifunctional and interactive solutions.

It is our pleasure to invite you to submit original research papers, short communications or state-of-the-art reviews within the scope of this Special Issue. Contributions can range from fundamental properties of materials, their processing and characterization, as well as innovations in processing technologies for the development of applications.

Dr. Carlos Marques
Prof. Dr. Anselmo Frizera-Neto
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Optical fiber sensors
  • Flexible materials in bulk
  • Polymer and silica fiber devices
  • Sensing applications
  • Flexible sensor solutions
  • Data processing for wearable robotics
  • Low cost optical solutions for flexible sensing
  • Wearable Robotics
  • Sensor technologies
  • Actuator
  • Soft robotics

Published Papers (6 papers)

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Research

Open AccessFeature PaperArticle
Fluoride Fiber-Based Plasmonic Biosensor with Two-Dimensional Material Heterostructures: Enhancement of Overall Figure-of-Merit via Optimization of Radiation Damping in Near Infrared Region
Materials 2019, 12(9), 1542; https://doi.org/10.3390/ma12091542
Received: 29 March 2019 / Revised: 1 May 2019 / Accepted: 7 May 2019 / Published: 10 May 2019
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Abstract
Two-dimensional (2D) heterostructure materials show captivating properties for application in surface plasmon resonance (SPR) sensors. A fluoride fiber-based SPR sensor is proposed and simulated with the inclusion of a 2D heterostructure as the analyte interacting layer. The monolayers of two 2D heterostructures (BlueP/MoS [...] Read more.
Two-dimensional (2D) heterostructure materials show captivating properties for application in surface plasmon resonance (SPR) sensors. A fluoride fiber-based SPR sensor is proposed and simulated with the inclusion of a 2D heterostructure as the analyte interacting layer. The monolayers of two 2D heterostructures (BlueP/MoS2 and BlueP/WS2, respectively) are considered in near infrared (NIR). In NIR, an HBL (62HfF4-33BaF2-5LaF3) fluoride glass core and NaF clad are considered. The emphasis is placed on figure of merit (FOM) enhancement via optimization of radiation damping through simultaneous tuning of Ag thickness (dm) and NIR wavelength (λ) at the Ag-2D heterostructure–analyte interfaces. Field distribution analysis is performed in order to understand the interaction of NIR signal with analyte at optimum radiation damping (ORD) condition. While the ORD leads to significantly larger FOM for both, the BlueP/MoS2 (FOM = 19179.69 RIU−1 (RIU: refractive index unit) at dm = 38.2 nm and λ = 813.4 nm)-based sensor shows massively larger FOM compared with the BlueP/WS2 (FOM = 7371.30 RIU−1 at dm = 38.2 nm and λ = 811.2 nm)-based sensor. The overall sensing performance was more methodically evaluated in terms of the low degree of photodamage of the analyte, low signal scattering, high power loss, and large field variation. The BlueP/MoS2-based fiber SPR sensor under ORD conditions opens up new paths for biosensing with highly enhanced overall performance. Full article
(This article belongs to the Special Issue Flexible Sensors and Actuators for Novel Wearable Solutions)
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Open AccessArticle
Large-Range Polymer Optical-Fiber Strain-Gauge Sensor for Elastic Tendons in Wearable Assistive Robots
Materials 2019, 12(9), 1443; https://doi.org/10.3390/ma12091443
Received: 1 April 2019 / Revised: 19 April 2019 / Accepted: 29 April 2019 / Published: 3 May 2019
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Abstract
This paper presents the development and validation of a polymer optical-fiber strain-gauge sensor based on the light-coupling principle to measure axial deformation of elastic tendons incorporated in soft actuators for wearable assistive robots. An analytical model was proposed and further validated with experiment [...] Read more.
This paper presents the development and validation of a polymer optical-fiber strain-gauge sensor based on the light-coupling principle to measure axial deformation of elastic tendons incorporated in soft actuators for wearable assistive robots. An analytical model was proposed and further validated with experiment tests, showing correlation with a coefficient of R = 0.998 between experiment and theoretical data, and reaching a maximum axial displacement range of 15 mm and no significant hysteresis. Furthermore, experiment tests were carried out attaching the validated sensor to the elastic tendon. Results of three experiment tests show the sensor’s capability to measure the tendon’s response under tensile axial stress, finding 20.45% of hysteresis in the material’s response between the stretching and recovery phase. Based on these results, there is evidence of the potential that the fiber-optical strain sensor presents for future applications in the characterization of such tendons and identification of dynamic models that allow the understanding of the material’s response to the development of more efficient interaction-control strategies. Full article
(This article belongs to the Special Issue Flexible Sensors and Actuators for Novel Wearable Solutions)
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Open AccessArticle
A Validation Study of a Polymer Optical Fiber Sensor for Monitoring Lumbar Spine Movement
Materials 2019, 12(5), 762; https://doi.org/10.3390/ma12050762
Received: 15 January 2019 / Revised: 22 February 2019 / Accepted: 1 March 2019 / Published: 6 March 2019
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Abstract
This study aims to investigate the validity and reliability of a novel plastic optical fiber (POF) sensor, which was developed to measure the angles of flexion, extension and lateral bend at the lumbar region. The angles of flexion, extension and lateral bend for [...] Read more.
This study aims to investigate the validity and reliability of a novel plastic optical fiber (POF) sensor, which was developed to measure the angles of flexion, extension and lateral bend at the lumbar region. The angles of flexion, extension and lateral bend for a standing position were measured simultaneously using both the novel POF sensor of this investigation and the commercial Biometrics goniometer instrument. Each movement had two steps of bending which were 10° and 20° based on inclinometer readings. The POF sensor had good intra-rater reliability (Intraclass correlation coefficient, ICC = 0.61 to 0.83). Bland–Altman plots were used to study the agreement using these two sensors. There were proportional differences and bias between the POF sensor and Biometrics goniometer, as the zero points did not lie in the percentage difference region in the Bland–Altman plots. The proportional difference between these two likely reflects the different sizes and thus, measurement regions of the two sensors. There was also strong correlation between the two sensors (r > 0.77). Hence, the POF sensor could be of potential utility in measuring lumbar range of motion (ROM) in a manner which is minimally invasive, and where discrete sections of the spine are under specific investigation. Full article
(This article belongs to the Special Issue Flexible Sensors and Actuators for Novel Wearable Solutions)
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Open AccessArticle
Titanium Dioxide Nanotube-Based Oxygen Indicator for Modified Atmosphere Packaging: Efficiency and Accuracy
Materials 2018, 11(12), 2410; https://doi.org/10.3390/ma11122410
Received: 4 November 2018 / Revised: 21 November 2018 / Accepted: 27 November 2018 / Published: 29 November 2018
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Abstract
Colorimetric oxygen indicators can be applied for non-destructive testing in packaging; especially in modified atmosphere packaging (MAP). In this paper; titanium dioxide (TiO2) nanotube; which is used as a semiconductor photocatalyst in oxygen indicators; was synthesized via a microwave-assisted hydrothermal method. [...] Read more.
Colorimetric oxygen indicators can be applied for non-destructive testing in packaging; especially in modified atmosphere packaging (MAP). In this paper; titanium dioxide (TiO2) nanotube; which is used as a semiconductor photocatalyst in oxygen indicators; was synthesized via a microwave-assisted hydrothermal method. X-Ray Diffraction (XRD) was used to analyze its crystal form and Scanning Electron Microscope (SEM).to characterize its morphology. Its properties were studied using Brunauer-Emmett-Teller (BET), Diffuse Reflection Spectrum (DRS), and Bluebottle experiments. The results showed that the synthesized TiO2 nanotube was a mixture of rutile and anatase; with a specific surface area of 190.35 m2/g; and a wide band gap of 3.34 eV. Given the satisfactory performance; the TiO2-based oxygen indicator was prepared and combined with glycerol; methylene blue; and hydroxyethyl cellulose (HEC). The oxygen indicator demonstrated excellent photocatalytic performance and effectively avoided excitation by visible light. We studied the rheological properties; thixotropic properties; and wettability of the indicator. The results demonstrated the printability of the indicator solution; which was then printed in the polyethylene terephthalate (PET) film by screen printing and applied to MAP. The application results showed that the prepared oxygen indicator was able to provide visual support to judge whether the packaging was intact and the food was safe. Full article
(This article belongs to the Special Issue Flexible Sensors and Actuators for Novel Wearable Solutions)
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Open AccessArticle
Fiber Bragg Gratings in CYTOP Fibers Embedded in a 3D-Printed Flexible Support for Assessment of Human–Robot Interaction Forces
Materials 2018, 11(11), 2305; https://doi.org/10.3390/ma11112305
Received: 15 October 2018 / Revised: 31 October 2018 / Accepted: 13 November 2018 / Published: 16 November 2018
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Abstract
We developed a flexible support with embedded polymer optical fiber (POF) sensors for the assessment of human–robot interaction forces. The supports were fabricated with a three-dimensional (3D) printer, where an acrylonitrile butadiene styrene (ABS) rigid structure was used in the region of the [...] Read more.
We developed a flexible support with embedded polymer optical fiber (POF) sensors for the assessment of human–robot interaction forces. The supports were fabricated with a three-dimensional (3D) printer, where an acrylonitrile butadiene styrene (ABS) rigid structure was used in the region of the support in which the exoskeleton was attached, whereas a thermoplastic polyurethane (TPU) flexible structure was printed in the region where the users placed their legs. In addition, fiber Bragg gratings (FBGs), inscribed in low-loss, cyclic, transparent, optical polymer (CYTOP) using the direct-write, plane-by-plane femtosecond laser inscription method, were embedded in the TPU structure. In this case, a 2-FBG array was embedded in two supports for human–robot interaction force assessment at two points on the users’ legs. Both FBG sensors were characterized with respect to temperature and force; additionally, the creep response of the polymer, where temperature influences the force sensitivity, was analyzed. Following the characterization, a compensation method for the creep and temperature influence was derived, showing relative errors below 4.5%. Such errors were lower than the ones obtained with similar sensors in previously published works. The instrumented support was attached to an exoskeleton for knee rehabilitation exercises, where the human–robot interaction forces were measured in flexion and extension cycles. Full article
(This article belongs to the Special Issue Flexible Sensors and Actuators for Novel Wearable Solutions)
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Open AccessArticle
Flexible Strain Sensor Based on Carbon Black/Silver Nanoparticles Composite for Human Motion Detection
Materials 2018, 11(10), 1836; https://doi.org/10.3390/ma11101836
Received: 24 August 2018 / Revised: 21 September 2018 / Accepted: 25 September 2018 / Published: 27 September 2018
Cited by 2 | PDF Full-text (2548 KB) | HTML Full-text | XML Full-text
Abstract
The demand for flexible and wearable electronic devices with excellent stretchability and sensitivity is increasing, especially for human motion detection. In this work, a simple, low-cost and convenient strategy has been employed to fabricate flexible strain sensor with a composite of carbon black [...] Read more.
The demand for flexible and wearable electronic devices with excellent stretchability and sensitivity is increasing, especially for human motion detection. In this work, a simple, low-cost and convenient strategy has been employed to fabricate flexible strain sensor with a composite of carbon black and silver nanoparticles as sensing materials and thermoplastic polyurethane as matrix. The strain sensors thus prepared possesses high stretchability and good sensitivity (gauge factor of 21.12 at 100% tensile strain), excellent static (almost constant resistance variation under 50% strain for 600 s) and dynamic (100 cycles) stability. Compared with bare carbon black-based strain sensor, carbon black/silver nanoparticles composite-based strain sensor shows ~18 times improvement in sensitivity at 100% strain. In addition, we discuss the sensing mechanisms using the disconnection mechanism and tunneling effect which results in high sensitivity of the strain sensor. Due to its good strain-sensing performance, the developed strain sensor is promising in detecting various degrees of human motions such as finger bending, wrist rotation and elbow flexion. Full article
(This article belongs to the Special Issue Flexible Sensors and Actuators for Novel Wearable Solutions)
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