Three-Dimensional Self-Healable Touch Sensing Artificial Skin Device

Beclomethasone loaded liposomes enriched with mucin: A suitable approach for the control of skin disorders

Inflammatory skin disorders are the fourth leading cause of chronic non-fatal conditions, which have a serious impact on the patient quality of life. Due to their treatment with conventional corticosteroids, which often result in poor therapeutic efficacy, relapses and systemic side effects from prolonged therapy, these diseases represent a global burden that negatively impacts the global economy. To avoid these problems and optimize corticosteroid benefits, beclomethasone was loaded into liposome formulations specifically tailored for skin delivery. These formulations were enhanced with mucin (0.1 and 0.5 % w/v) to further ensure prolonged formulation permanence at the site of application. The addition of 0.5 % w/v mucin resulted in the formation of small unilamellar vesicles and multicompartment vesicles. Liposomes and 1mucin-liposomes were smaller (∼48 and ∼61 nm, respectively) and more monodispersed (PI ∼ 0.14 and ∼ 0.17, respectively) than 5mucin-liposomes, which were larger (∼137 nm), slightly polydispersed (PI ∼ 0.23), and less stable during storage (4 months in the dark at 25 °C). Liposomes were negatively charged (∼ -79 mV) irrespective of their composition, and capable of incorporating high amount of beclomethasone (∼ 80 %). In vitro studies on skin fibroblasts and keratinocytes confirmed the high biocompatibility of all formulations (viability ≥ 95 %). However, the use of mucin-liposomes resulted in higher efficacy against nitric oxide production and free radical damage. Finally, topical applications using 12-O-tetradecanoylphorbol-13-acetate-injured skin in vivo experiments showed that only the mucin-enriched formulations could restore healthy conditions within 4 days, underscoring promise as a treatment for skin disorders.

3D Printing of Self-Healing Materials

This review article presents a comprehensive overview of the latest advances in the field of 3D printable structures with self-healing properties. Three-dimensional printing (3DP) is a versatile technology that enables the rapid manufacturing of complex geometric structures with precision and functionality not previously attainable. However, the application of 3DP technology is still limited by the availability of materials with customizable properties specifically designed for additive manufacturing. The addition of self-healing properties within 3D printed objects is of high interest as it can improve the performance and lifespan of structural components, and even enable the mimicking of living tissues for biomedical applications, such as organs printing. The review will discuss and analyze the most relevant results reported in recent years in the development of self-healing polymeric materials that can be processed via 3D printing. After introducing the chemical and physical self-healing mechanism that can be exploited, the literature review here reported will focus in particular on printability and repairing performances. At last, actual perspective and possible development field will be critically discussed.

Structural Electronic Skin for Conformal Tactile Sensing

The conformal integration of the electronic skin on the non-developable surface is in great demand for the comprehensive tactile sensing of robotics and prosthetics. However, the current techniques still encounter obstacles in achieving conformal integration of film-like electronic skin on non-developable surfaces with substantial curvatures for contact pressure detection and tactile mapping. In this paper, by utilizing the 3D printing technology to prepare the 3D electrode array in the structural component following its surface curvature, and covering it with a molded functional shell to form the pressure sensitive iontronic interface, a device is proposed to achieve high-sensitive pressure detection and high-fidelity tactile mapping on a complicated non-developable surface, called structural electronic skin (SES). The SES is prepared in a 3D printed fingertip with 46 tactile sensing units distributed on its curved surface, achieving the integration of both structural and tactile functions in a single component. By integrating the smart fingertip into a dexterous hand, a series of demonstrations are presented to show the dead-zone free pressure detection and tactile mapping with high sensitivity, for instance, 2D pulse wave monitoring and robotic injection in a medical robot, object recognition and compliant control in a smart prosthesis.

Recent advances in 3D printable conductive hydrogel inks for neural engineering

Recently, the 3D printing of conductive hydrogels has undergone remarkable advances in the fabrication of complex and functional structures. In the field of neural engineering, an increasing number of reports have been published on tissue engineering and bioelectronic approaches over the last few years. The convergence of 3D printing methods and electrically conducting hydrogels may create new clinical and therapeutic possibilities for precision regenerative medicine and implants. In this review, we summarize (i) advancements in preparation strategies for conductive materials, (ii) various printing techniques enabling the fabrication of electroconductive hydrogels, (iii) the required physicochemical properties of the printed constructs, (iv) their applications in bioelectronics and tissue regeneration for neural engineering, and (v) unconventional approaches and outlooks for the 3D printing of conductive hydrogels. This review provides technical insights into 3D printable conductive hydrogels and encompasses recent developments, specifically over the last few years of research in the neural engineering field.

Preparation and Characterization of Poly(Acrylic Acid)-Based Self-Healing Hydrogel for 3D Shape Fabrication via Extrusion-Based 3D Printing

The three-dimensional (3D) printing of hydrogel is an issue of interest in various applications to build optimized 3D structured devices beyond 2D-shaped conventional structures such as film or mesh. The materials design for the hydrogel, as well as the resulting rheological properties, largely affect its applicability in extrusion-based 3D printing. Here, we prepared a new poly(acrylic acid)-based self-healing hydrogel by controlling the hydrogel design factors based on a defined material design window in terms of rheological properties for application in extrusion-based 3D printing. The hydrogel is designed with a poly(acrylic acid) main chain with a 1.0 mol% covalent crosslinker and 2.0 mol% dynamic crosslinker, and is successfully prepared based on radical polymerization utilizing ammonium persulfate as a thermal initiator. With the prepared poly(acrylic acid)-based hydrogel, self-healing characteristics, rheological characteristics, and 3D printing applicability are deeply investigated. The hydrogel spontaneously heals mechanical damage within 30 min and exhibits appropriate rheological characteristics, including G'~1075 Pa and tan δ~0.12, for extrusion-based 3D printing. Upon application in 3D printing, various 3D structures of hydrogel were successfully fabricated without showing structural deformation during the 3D printing process. Furthermore, the 3D-printed hydrogel structures exhibited excellent dimensional accuracy of the printed shape compared to the designed 3D structure.

Microstructure and Self-Healing Capability of Artificial Skin Composites Using Biomimetic Fibers Containing a Healing Agent

The aging and damage of artificial skin materials for artificial intelligence robots are technical problems that need to be solved urgently in their application. In this work, poly (vinylidene fluoride) (PVDF) fibers containing a liquid agent were fabricated directly as biomimetic microvasculars, which were mixed in a glycol-polyvinyl alcohol-gelatin network gel to form biomimetic self-healing artificial skin composites. The self-healing agent was a uniform-viscous buffer solution composed of phosphoric acid, acetic acid, and sodium carboxymethyl cellulose (CMC-Na), which was mixed under 40 °C. Microstructure analysis showed that the fiber surface was smooth and the diameter was uniform. SEM images of the fiber cross-sections showed that there were uniformly distributed voids. With the extension of time, there was no phenomenon of interface separation after the liquid agent diffused into the matrix through the fiber cavity. The entire process of self-healing was observed and determined including fiber breakage and the agent diffusion steps. XRD and FT-IR results indicated that the self-healing agent could enter the matrix material through fiber damage or release and it chemically reacted with the matrix material, thereby changing the chemical structure of the damaged matrix. Self-healing behavior analysis of the artificial skin indicated that its self-healing efficiency increased to an impressive 97.0% with the increase in temperature to 45 °C.

A 3D printable, highly stretchable, self-healing hydrogel-based sensor based on polyvinyl alcohol/sodium tetraborate/sodium alginate for human motion monitoring

Self-healing hydrogels have great application potential in the field of bio-sensors due to their self-healing, flexibility and excellent tensile properties. However, most hydrogel-based sensors are processed by template method, which is unable to fabricate complex three-dimensional (3D) structures, and limits the development of hydrogel-based sensor devices. A simple yet efficient one-pot method was proposed to fabricate polyvinyl alcohol/sodium tetraborate/sodium alginate hydrogel inks (SPB), also a fabricating process of self-healing hydrogel based on 3D printing technology has been proposed. The SPB hydrogel rapidly healed (<30 s) at room temperature, while its mechanical properties and conductivity also recovered quickly after healing. Besides, it could be used as wearable strain sensors, whose high stretchability (>2800 % strain) and sensitivity (gauge factor: 18.56 at 2000 % strain) could not only detect very large stretch deformations, but also detect the tiny pressure changes in the human body, such as finger flexion, knee flexion, and respiration. This study provides a method for the rapid fabrication of complex-structured hydrogel-based sensors, which is helpful for the hydrogel-based sensor applications in human motion detection and wearable devices.

Recent Advances in Touch Sensors for Flexible Wearable Devices

Many modern user interfaces are based on touch, and such sensors are widely used in displays, Internet of Things (IoT) projects, and robotics. From lamps to touchscreens of smartphones, these user interfaces can be found in an array of applications. However, traditional touch sensors are bulky, complicated, inflexible, and difficult-to-wear devices made of stiff materials. The touch screen is gaining further importance with the trend of current IoT technology flexibly and comfortably used on the skin or clothing to affect different aspects of human life. This review presents an updated overview of the recent advances in this area. Exciting advances in various aspects of touch sensing are discussed, with particular focus on materials, manufacturing, enhancements, and applications of flexible wearable sensors. This review further elaborates on the theoretical principles of various types of touch sensors, including resistive, piezoelectric, and capacitive sensors. The traditional and novel hybrid materials and manufacturing technologies of flexible sensors are considered. This review highlights the multidisciplinary applications of flexible touch sensors, such as e-textiles, e-skins, e-control, and e-healthcare. Finally, the obstacles and prospects for future research that are critical to the broader development and adoption of the technology are surveyed.

See Me, Feel Me, Touch Me, Heal Me: A Contextual Overview of Conductive Polymer Composites as Synthetic Human Skin

The fields of polymer science, conductive composites, materials engineering, robotics, and human perception intersect at the development and application of synthetic human skin. To be accepted by human users, artificial human skin must meet several requirement benchmarks. Synthetic human skin must look realistic, but not be eerie or creepy, upsetting those using or interacting with the material. Synthetic skin must feel like human skin, including mechanical response, thermal conductivity, and tactile properties. Realistic synthetic human skin must be electrically conductive, so that the user may experience accurate sensations of touch and feel. Finally, synthetic human skin should possess some degree of self-healing behavior. This review provides a brief description of advances in these disparate aspects of synthetic skin science, from the perspective of a practicing conductive polymer composite scientist and engineer.

Flexible and Wearable Zinc-Ion Hybrid Supercapacitor Based on Double-Crosslinked Hydrogel for Self-Powered Sensor Application

The rapidly growing Internet of Things (IoT) has brought about great demand for high-performance sensors as well as power supply devices for those sensors. In this respect, the integration of sensors and energy storage devices, or the development of multifunctional devices having both energy storage and sensing properties, is of great interest in the development of compact sensing systems. As a proof of concept, a zinc-ion hybrid supercapacitor (ZHS) based on a double-crosslinked hydrogel electrolyte is developed in this work, which can be employed not only as an energy storage device, but also as a self-powered sensor for human movement and breathing detection. The ZHS delivers a capacitance of 779 F g⁻¹ and an energy density of 0.32 mWh cm⁻² at a power density of 0.34 mW cm⁻², as well as sensitive resistance response to strain. Our work provides a useful basis for future designs of self-powered sensing devices and function-integrated systems.

Flexible wearable sensors - an update in view of touch-sensing

Nowadays, much of user interface is based on touch and the touch sensors have been common for displays, Internet of things (IoT) projects, or robotics. They can be found in lamps, touch screens of smartphones, or other wide arrays of applications as well. However, the conventional touch sensors, fabricated from rigid materials, are bulky, inflexible, hard, and hard-to-wear devices. The current IoT trend has made these touch sensors increasingly important when it added in the skin or clothing to affect different aspects of human life flexibly and comfortably. The paper provides an overview of the recent developments in this field. We discuss exciting advances in materials, fabrications, enhancements, and applications of flexible wearable sensors under view of touch-sensing. Therein, the review describes the theoretical principles of touch sensors, including resistive, capacitive, and piezoelectric types. Following that, the conventional and novel materials, as well as manufacturing technologies of flexible sensors are considered to. Especially, this review highlights the multidisciplinary approaches such as e-skins, e-textiles, e-healthcare, and e-control of flexible touch sensors. Finally, we summarize the challenges and opportunities that use is key to widespread development and adoption for future research.

3D Antidrying Antifreezing Artificial Skin Device with Self-Healing and Touch Sensing Capability

Hydrogels are attractive, active materials for various e-skin devices based on their unique functionalities such as flexibility and biocompatibility. Still, e-skin devices are generally limited to simple structures, and the realization of optimal-shaped 3D e-skin devices for target applications is an intriguing issue of interest. Furthermore, hydrogels intrinsically suffer from drying and freezing issues in operational capability for practical applications. Herein, 3D artificial skin devices are demonstrated with highly improved device stability. The devices are fabricated in a target-oriented 3D structure by extrusion-based 3D printing, spontaneously heal mechanical damage, and enable stable device operation over time and under freezing conditions. Based on the material design to improve drying and freezing resistance, an organohydrogel, prepared by solvent displacement of hydrogel with ethylene glycol for 3 h, exhibits excellent drying resistance over 1000 h and improved freezing resistance by showing no phase transition down to -60 °C while maintaining its self-healing functionality. Based on the improved drying and freezing resistance, artificial skin devices in target-oriented optimal 3D structures are presented, which enable accurate positioning of touchpoints even on a complicated 3D structure stably over time and excellent operation at temperatures below 0 °C without losing their flexibility.

Self-Healing Soft Sensors: From Material Design to Implementation

The demand for interfacing electronics in everyday life is rapidly accelerating, with an ever-growing number of applications in wearable electronics and electronic skins for robotics, prosthetics, and other purposes. Soft sensors that efficiently detect environmental or biological/physiological stimuli have been extensively studied due to their essential role in creating the necessary interfaces for these applications. Unfortunately, due to their natural softness, these sensors are highly sensitive to structural and mechanical damage. The integration of natural properties, such as self-healing, into these systems should improve their reliability, stability, and long-term performance. Recent studies on self-healing soft sensors for varying chemical and physical parameters are herein reviewed. In addition, contemporary studies on material design, device structure, and fabrication methods for sensing platforms are also discussed. Finally, the main challenges and future perspectives in this field are introduced, while focusing on the most promising examples and directions already reported.

Kouzani A, Mosadegh B, Gharaie S. Blood Pressure Sensors: Materials, Fabrication Methods, Performance Evaluations and Future Perspectives

Advancements in materials science and fabrication techniques have contributed to the significant growing attention to a wide variety of sensors for digital healthcare. While the progress in this area is tremendously impressive, few wearable sensors with the capability of real-time blood pressure monitoring are approved for clinical use. One of the key obstacles in the further development of wearable sensors for medical applications is the lack of comprehensive technical evaluation of sensor materials against the expected clinical performance. Here, we present an extensive review and critical analysis of various materials applied in the design and fabrication of wearable sensors. In our unique transdisciplinary approach, we studied the fundamentals of blood pressure and examined its measuring modalities while focusing on their clinical use and sensing principles to identify material functionalities. Then, we carefully reviewed various categories of functional materials utilized in sensor building blocks allowing for comparative analysis of the performance of a wide range of materials throughout the sensor operational-life cycle. Not only this provides essential data to enhance the materials' properties and optimize their performance, but also, it highlights new perspectives and provides suggestions to develop the next generation pressure sensors for clinical use.