Smart Materials for Edible Devices

Edible devices are an emergent technology which seek to provide researchers and health professionals with smart constructs to monitor the gastrointestinal tract without the traditional risks of retention as they are constructed from bioresorbable materials. However, this field is very much still in its infancy and as such, simple materials development to enable these ingestible technologies needs to be explored. To aid in the state-of-the-art of this scientific field a variety of edible materials were modified to display smart functionalities such as conductivity, actuation, solvent extraction and self-healing were developed. Using a gellan gum/gelatin ionic-covalent entanglement (ICE) hydrogel and ionic salts, a simple method of producing conductive, robust, edible hydrogels was developed. It was found that addition of NaCl after crosslinking was able to produce ICE gels with a conductivity of 200 ± 20 mS/cm and a compressive stress at failure of 1.4 ± 0.2 MPa. Using this optimised formulation, a variety of edible devices were developed. Hand-held reactive printing was utilised to pattern highly conductive, versatile, edible ICE hydrogel wires which showed no loss in conductivity when printed compared to cast samples. A simple, robust, edible resistive strain gauge/pressure sensor and a more complex edible capacitive pressure sensor were developed using this ICE gel formulation which showed repeatable and high sensitivities to applied stresses. An ingestible actuator was developed using non-toxic poly(acrylic acid) and antacid calcium hydroxide. When exposed to simulated gastric fluid the neutralisation reaction of the calcium hydroxide preserved the poly(acrylic acid)/calcium hydroxide hydrogel samples from degradation and induced an actuation mechanism. Furthermore, this actuation was demonstrated to be reversible using sodium citrate