Design and development of electroconductive and stimuli-responsive coatings for wearable smart textiles

Electroconductive and stimuli-responsive coatings were realized on textile fabrics by sol-gel technique and grafting polymerization for developing smart materials able to sense environmental stimuli, respond, and adapt intelligently due to specific functionalities integrated into their structure. Functionalized and high aspect ratio multiwalled carbon nanotubes (CNTs) were immobilized in hybrid coatings to obtain electroconductive cotton fabrics to be used for environmental and heart rate monitoring, respectively. The developed CNTs-based fabrics efficiently detected simultaneous environmental humidity and temperature changes as a function of resistance variations even after four consecutive exposure cycles. Whereas high aspect ratio CNTs-based cotton strips were able to reliably transmit electrical signals for heart rate monitoring through photoplethysmography by providing a signal reasonable fitted with that obtained from commercial metal wires. Stimuli-responsive fabrics for sweat pH monitoring were realized using nitrazine yellow (NY) and alizarin red S (ARS). NY was involved in a two-step procedure for the efficient immobilization on cotton fabrics: (a) the covalent functionalization of NY molecules by catalyzed epoxy ring-opening of a bifunctional precursor followed by (b) the radical grafting of the modified dye on cellulose. Conversely, ARS was covalently linked to a silica-based sol-gel precursor and then immobilized on cotton and polyester samples. For both stimuli-responsive coatings, UV-Vis diffuse reflectance spectroscopy and CIELAB color space analysis confirmed the dyestuffs immobilization on cotton fabrics, by preserving the typical halochromic response, and that grafting or sol-gel techniques were efficient in reducing the dye leaching after laundering cycles, compared to conventional dyeing techniques. Moreover, experimental findings demonstrated the reversibility and reliability of pH changes of NY-based cotton fabrics and the low affinity of polyester substrates towards ARS-silica based coating. The sol-gel technology was confirmed as a suitable approach also for designing hybrid networks for controlled drug release, thus further ensuring biocompatibility and drug reservoir. Indeed, a palmitoylethanolamine derivative as an antioxidant/anti-inflammatory molecule was encapsulated in a silica-based polyethylene oxide 3D network. In vitro diffusion test performed on treated cotton fabrics demonstrated to efficiently release the drug molecule through the medium due to the weak bonding of the molecule in the sol-gel matrix. The two prototypes, "ELECT" (a T-shirt realized by the deposition of CNT-electroconductive tracks) and "Health Belt" (a belt integrated with a halochromic fabric), were developed as a practical application of electroconductive and stimuli-responsive coatings, respectively to monitor the heart rate and the sweat pH of human being due to the integrated electronic devices. The reported studies are a step forward for the integration between electronics and textile materials by real application processes, industrially scalable, usable for the development of high-performance wearable e-textiles.