Hybrid functional microfibers for textile electronics and biosensors

Background

Fibers can be woven or twisted into two- and three-dimensional patterns without losing deformability, which makes them candidate substrates for wearable electronics, electronic skin and implantable devices. Metallic wires conduct well but oxidize under ambient conditions, are dense and bend poorly. The review argues that hybrid fibers combining polymers with carbon or metallic nanomaterials, or with biomaterials such as hydrogels, can add electrical, sensing and biological functions while keeping the mechanical character of the fiber.

How the review is organized

The review first classifies functional nanofibers made of metals, metal oxides, ceramics and polymer composites, including luminescent, magnetic and gas-sensing electrospun fibers. It then describes materials strategies: carbon-based fibers (carbon nanotube yarns, graphene fibers and graphene woven fabrics), metal-polymer composites with nanoparticle fillers or coatings, and biomaterial fibers for biosensing and tissue engineering. Device configurations follow, covering fiber transistors, light-emitting textiles, textile pressure sensors, stretchable conductors and thread-based diagnostic devices, and the final sections cover energy fibers, smart garments, electrospun fibers for drug delivery and optical microfiber sensors.

Scope of the review

As a review, the article compiles representative studies and the performance values they reported, with Figure 1 to Figure 4 reproduced from the cited work: graphene woven fabrics grown by chemical vapor deposition on copper mesh, a capacitive textile pressure sensor made from cross-stacked PDMS-coated conductive fibers tested at loads of 0.05, 0.1 and 0.5 N, a printable elastic conductor with in situ formed silver nanoparticles, and a thread-based pH sensor characterized in an in vitro skin model.

Main points of the review

For sensing fibers and electronic skin, the review cites a graphene/PEDOT nanohybrid e-skin with a gauge factor of 320 and a pressure detection limit of 0.5 Pa, a polymer composite fiber with a linear glucose response from 1 to 15 mM and a response time under 6 s, and ZnO nanofibers of 150 nm average diameter that detected ethanol at 300 °C with response and recovery times of about 3 s and 8 s. Electrospun nanofibers offer specific surface areas about one to two orders of magnitude larger than flat films, which the review links to higher sensitivity.

For conductive and energy fibers, polyaniline nanowire arrays raised the capacitance of carbon nanotube yarn supercapacitors from 2.3 to 38 mF/cm2, and spun carbon nanotube fibers retained reversible torsional actuation after 2400 cycles. Graphene woven fabrics reached sheet resistances of 500 to 2500 Ω/sq that improved after HNO3 treatment but did not meet transparent conductor criteria. A textile triboelectric nanogenerator produced 120 V and 65 μA, a four-layer version 170 V and 120 μA, with no significant drift after 120 000 cycles, and a fiber nanogenerator had an expected output of 20 to 80 mW per square meter of fabric.

For textile devices, a printed elastic conductor with fluorine surfactant showed 4919 S/cm without strain and 719 S/cm at 300% strain, against 3727 and 297 S/cm without surfactant; annealing above 130 °C raised conductivity further at the expense of stretchability. One fiber organic field-effect transistor used 45 μm metal fibers with an approximately 1 μm polyimide layer, and the cross-stacked capacitive textile sensor gave stable responses under repeated loading.

For biomedical fibers, a thread-based diagnostic device measured pH with a slope of −59.63 mV per pH, a response time under 30 s and a drift of 2.5 mV/h during 4 h at pH 7.4. Prussian blue-TiO2 nanowire interfaces detected H2O2 with a detection limit of 20 nM and a response under 5 s. In tissue engineering, cell-laden hydrogel fibers were woven with a microweaving machine or built around a mechanically strong synthetic core, and electrospun fibers were noted for high drug loading and potentially lower initial burst release, particularly in core-shell geometries.

Open questions

The review states that most fiber-shaped electronic prototypes remain far from final application. It names three challenges: solid-state fiber devices with high flexibility and performance, small electronics on fibers such as transistors, and integration into textiles with a comfortable human-textile interface. Many commercial fibers other than carbon fibers conduct poorly, reports focus on electrochemical performance rather than mechanical properties, and the lack of a unified evaluation system makes capacitance and energy values hard to compare. For sensors and scaffolds, the review notes limited control of fiber size and arrangement in electrospinning and poor control of graphene size, thickness and defects.

How it connects to other research

The stretchable carbon nanotube strain sensor by Yamada and colleagues, cited in this review, applies aligned nanotube films to garments for motion detection, whereas the review centers on building conductive, sensing and biological functions into individual fibers and yarns.