Search

The recent advent of biodegradable materials has offered huge opportunity to transform healthcare technologies by enabling sensors that degrade naturally after use. The implantable electronic systems made from such materials eliminate the need for extraction or reoperation, minimize chronic inflammatory responses, and hence offer attractive propositions for future biomedical technology. The eco-friendly sensor systems developed from degradable materials could also help mitigate some of the major environmental issues by reducing the volume of electronic or medical waste produced and, in turn, the carbon footprint. With this background, herein we present a comprehensive overview of the structural and functional biodegradable materials that have been used for various biodegradable or bioresorbable electronic devices. The discussion focuses on the dissolution rates and degradation mechanisms of materials such as natural and synthetic polymers, organic or inorganic semiconductors, and hydrolyzable metals. The recent trend and examples of biodegradable or bioresorbable materials-based sensors for body monitoring, diagnostic, and medical therapeutic applications are also presented. Lastly, key technological challenges are discussed for clinical application of biodegradable sensors, particularly for implantable devices with wireless data and power transfer. Promising perspectives for the advancement of future generation of biodegradable sensor systems are also presented.

This work presents a biodegradable flexible pressure sensor using a piezoelectric layer sandwiched between Mg electrodes. The active layer of the sensor is a piezoelectric composite of β-glycine amino acid and natural chitosan polymer, fabricated by self-assembly of glycine molecules inside polymer. As a result, a one-step solution casting method have been used to fabricate the biodegradable piezoelectric composite. The x-ray diffraction confirms the structure and crystalline nature of β-glycine crystals inside the chitosan matrix and hence its piezoelectric nature. The sensitivity of the fabricated pressure was about ~ 1.42 mV in the range of 5-25 kPa. The in-vitro degradability of the device has been confirmed in cell culture medium. The fabricated biodegradable sensor offers potential for point-of-care and implantable healthcare applications.

A sweat-based flexible supercapacitor (SC) for self-powered smart textiles and wearable systems is presented. The developed SC uses sweat as the electrolyte and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the active electrode. With PEDOT:PSS coated onto cellulose/polyester cloth, the SC shows specific capacitance of 8.94 F g-1 (10 mF cm-2 ) at 1 mV s-1 . With artificial sweat, the energy and power densities of the SC are 1.36 Wh kg-1 and 329.70 W kg-1 , respectively for 1.31 V and its specific capacitance is 5.65 F g-1 . With real human sweat the observed energy and power densities are 0.25 Wh kg-1 , and 30.62 W kg-1 , respectively. The SC performance is evaluated with different volumes of sweat (20, 50, and 100 µL), bending radii (10, 15, 20 mm), charging/discharging stability (4000 cycles), and washability. With successful on-body testing, the first demonstration of the suitability of a sweat-based SC for self-powered cloth-based sensors to monitor sweat salinity is presented. With attractive performance and the use of body fluids, the presented approach is a safe and sustainable route to meet the power requirements in wearable systems.

This paper presents flexible pressure sensors based on free-standing and biodegradable glycine-chitosan piezoelectric films. Fabricated by the self-assembly of biological molecules of glycine within a water-based chitosan solution, the piezoelectric films consist of a stable spherulite structure of β-glycine (size varying from a few millimeters to 1 cm) embedded in an amorphous chitosan polymer. The polymorphic phase of glycine crystals in chitosan, evaluated by X-ray diffraction, confirms formation of a pure ferroelectric phase of glycine (β-phase). Our results show that a simple solvent-casting method can be used to prepare a biodegradable β-glycine/chitosan-based piezoelectric film with sensitivity (∼2.82 ± 0.2 mV kPa-1) comparable to those of nondegradable commercial piezoelectric materials. The measured capacitance of the β-glycine/chitosan film is in the range from 0.26 to 0.12 nF at a frequency range from 100 Hz to 1 MHz, and its dielectric constant and loss factor are 7.7 and 0.18, respectively, in the high impedance range under ambient conditions. The results suggest that the glycine-chitosan composite is a promising new biobased piezoelectric material for biodegradable sensors for applications in wearable biomedical diagnostics.

This work presents an advanced soft robotic finger with integrated strain sensor based on carbon nanotubes (CNTs). The interdigitated strain sensor is obtained by dielectrophoretic assembled CNT network. The sensor is connected to stretchable interconnects to ensure robust electrical connection during movements of the soft finger. The sensor is highly sensitive with up to 1300% change in the resistance for 11% strain. Finally, the CNT strain sensor is integrated with a soft robotic finger to monitor the bending for real time kinesthetic tactile feedback.

The application of controlled mechanical stress on a wound site can accelerate the wound healing by improving the cellular proliferation during tissue regeneration. To facilitate this there is need to monitor the applied stress around the wound site and hence there is need to develop a biocompatible stress sensor. Here we present the glycine-based biocompatible and flexible piezoelectric stress sensor. The sensor is based on novel piezoelectric composite comprising of piezoelectric y-glycine micro-crystals embedded in PDMS. On application of external force the sensor generates an average output voltage of 250 mV, with current density of 0.010 µA/cm2 and a power density of 2.5 nW/cm2. While the produced piezoelectric voltage helps accelerate the wound healing, the energy generation by the sensor could also find potential applications in self-powered touch sensors. The successful demonstration of presented stress sensor, we will pave the way for their integration on compression bandages and dressings used for chronic wound management.