A Multifunctional Wearable Device with a Graphene/Silver Nanowire Nanocomposite for Highly Sensitive Strain Sensing and Drug Delivery

Abstract

Advances in wearable, highly sensitive and multifunctional strain sensors open up new opportunities for the development of wearable human interface devices for various applications such as health monitoring, smart robotics and wearable therapy. Herein, we present a simple and cost-effective method to fabricate a multifunctional strain sensor consisting of a skin-mountable dry adhesive substrate, a robust sensing component and a transdermal drug delivery system. The sensor has high piezoresisitivity to monitor real-time signals from finger bending to ulnar pulse. A transdermal drug delivery system consisting of polylactic-co-glycolic acid nanoparticles and a chitosan matrix is integrated into the sensor and is able to release the nanoparticles into the stratum corneum at a depth of~60 µm. Our approach to the design of multifunctional strain sensors will lead to the development of cost-effective and well-integrated multifunctional wearable devices. C 2019, 5, 17 2 of 16the development of mobile devices where increasing functionalities are being integrated into single devices, multifunctional wearable devices [2,10,11] open new tech logical possibilities in areas such as human-machine interaction, health monitoring and drug delivery [12]. For example, a single device might be fabricated which can simultaneously deliver drugs and monitor the physiological response. Despite the clear promise of such multifunctional wearable devices, further improvements related to the fabrication process and cost-effectiveness are needed for their adoption.In terms of materials selection, there have been various approaches utilizing nanomaterials (e.g., silver nanowires [13], carbon nanotubes [14] and chemical vapor deposition (CVD) graphene [15]) as sensing components and elastomeric polymers or textiles as flexible and stretchable substrates [16,17]. Graphene nanoplatelets (GnPs) have been widely used in various polymer nanocomposites because of their superior electrical and mechanical properties [18][19][20]. Each GnP is typically 2-5 nm in thickness and may contain 3-10 graphene layers [21]. Upon reaching the percolation threshold in a matrix, the individual GnP forms a physically connected network where the overall resistance of the nanocomposites becomes limited by the interlayer contact resistance of the GnPs [4,22]. A strategy to reduce the contact resistance is to combine GnPs with silver nanowires (AgNWs). AgNWs employed in this work are around 40 nm in diameter and 20-60 µm in length. Under low strain, nanowires might change wave amplitudes and slide across each other, thus facilitating and maintaining a conducting network to accommodate the strain [23].Transdermal drug delivery is a promising drug delivery strategy to complement the limitations of traditional oral-and injectable-based methods. Transdermal drug delivery might potentially realize convenient and painless drug delivery and a sustained release profile with reduced side effects [24]. Advances in nanotechnology have led to the development of drug nanocarriers whi...

A versatile PDMS submicrobead/graphene oxide nanocomposite ink for the direct ink writing of wearable micron-scale tactile sensors

“…3D printing has recently emerged as a solution for creating PDMS-based structures [5,[11][12][13][14][15][16][17][18]. Direct ink writing (DIW), a type of 3D printing, can construct 3D microstructures via layerby-layer deposition of polymer composite ink of typically high viscosity [19,20].…”

“…It offers a controlled way to introduce the elastic component to inks via the water-dispersible PDMS beads [27,28]. In terms of the conductive component of inks, while silver is often used in PDMS composites [5,13,16], for larger scale/commercial implementation, lower cost nanofillers would ideally be used.…”

Silver Nanowires in Stretchable Resistive Strain Sensors

“…High sensitivity, high stretchability, low resolution, fast response time, high linearity, and low hysteresis are the desired features of any stretchable strain sensors. In recent times, self-healing ability [ 43 ], biocompatibility [ 44 ], and multifunctional sensing [ 45 ] have become a few additional features realized with these sensors.…”

A Flexible Strain Sensor Based on Embedded Ionic Liquid

“…Due to the emerging trend in wearable technologies, flexible strain sensors that can withstand large deformation have received a considerable amount of interest in recent years. Compared with conventional strain gauges made of metal or semiconductive material, polymer-based strain sensors exhibit significantly higher mechanical flexibility, making them favorable candidates for a wide range of wearable applications such as human–machine interfaces [ 1 , 2 ], motion detection systems [ 3 , 4 ], soft robotics [ 5 , 6 ], and healthcare monitoring devices [ 7 , 8 ]. Currently, flexible strain sensors are developed using various approaches.…”