Facile and cost-effective fabrication of wearable alpha-naphtholphthalein-based halochromic sensor for wound pH monitoring.

The sensor, designed to be worn directly on the skin, is suitable for real-time monitoring of the recovery level of not only general wounds, but also difficult-to-heal wounds, such as those with chronic inflammation. Notably, healthy skin has a pH range of 4-6. When a wound occurs, the pH is known to be approximately 7.4. In this study, alpha-naphtholphthalein (Naph) was immersed in a cotton-blended textile to produce a wearable halochromic sensor that clearly changed color depending on the pH of the skin in the range 6-9, including pH 7.4, which is the skin infection state. The coating was performed without using an organic solvent by dissolving it in micelle form using cetyltrimethylammonium bromide, a surfactant, in water. Naph-based halochromic sensor shows light yellow, which is the dye's own color, at pH 6, which is a healthy skin condition, and gradually showed a clear color change to light green-green-blue as pH increased. Even after washing and drying by rubbing with regular tap water, the color change due to pH was maintained more than 10 times. Naph-based halochromic sensors use a simple solution production and coating method and are not only reusable sensors that can be washed with water but also use environmentally friendly water, making them very suitable for developing commercial products for wound pH monitoring. In addition, it can be easily applied to medical supplies, such as medical gauze, patient clothes, and compression bandages, as well as everyday wear, such as clothing, gloves, and socks. Therefore, it is expected to be widely used as a wound pH sensor, allowing real-time monitoring of the skin condition of individuals with chronic skin inflammation, including patients requiring wound recovery.

Reversible thermochromic fibers with excellent elasticity and hydrophobicity for wearable temperature sensors.

Color-changing fibers, which can intuitively convey information to the human eye, can be used to facilely add functionality to various types of clothing. However, they are often expensive and complex, and can suffer from low durability. Therefore, in this study, we developed highly elastic and hydrophobic thermochromic fibers as wearable temperature sensors using a simple method that does not require an electric current. A thermochromic pigment was embedded inside and outside hydrophobic silica aerogel particles, following which the thermochromic aerogel was fixed to highly elastic spandex fibers using polydimethylsiloxane as a flexible binder. In particular, multi-strand spandex fibers were used instead of single strands, resulting in the thermochromic aerogels penetrating the inside of the strands upon their expansion by solvent swelling. During drying, the thermochromic aerogel adhered more tightly to the fibers by compressing the strands. The thermochromic fiber was purple at room temperature (25 °C), but exhibited a two-stage color change to blue and then white as the temperature increased to 37 °C. In addition, even after 100 cycles of tension-contraction at 200%, the thermochromic aerogel did not detach and was strongly attached to the fiber. Additionally, it was confirmed that color change due to temperature was stable even after exposure to 1 wt% NaCl (artificial sweat) and 0.1 wt% detergent solutions. The developed thermochromic fiber therefore exhibited excellent elasticity and hydrophobicity, and is expected to be widely utilized as an economical wearable temperature sensor as it does not require electrical devices.

Cesium tungsten oxide-carbon nanotube-hydroxypropyl cellulose thermoresponsive display.

Among different heat-responsive polymers, hydroxypropyl cellulose (HPC) is biodegradable and is widely used in products that are harmless to the human body, such as food and pharmaceuticals. When the temperature of the hydrogel-type HPC increases, the hydrophilic bonds between the HPC molecules break, and the HPC molecules aggregate owing to the hydrophobic bonds. Therefore, light transmittance may vary because the aggregated HPC molecules scatter light. This study investigated the implementation of a display using the thermoreversible phase transition of HPC. Herein, a near-infrared (NIR) laser was irradiated only to a local area to control the surface temperature and enable the effective operation of the thermoreversible phase transition of HPC. For this, cesium tungsten oxide (CTO), which absorbs NIR light and generates heat, was mixed with the HPC hydrogel to improve the photothermal effect. Moreover, by additionally mixing carbon nanotubes (CNTs) with high thermal conductivity, the heat generated from the CTO is quickly transferred to the HPC hydrogel, and the heat of the HPC hydrogel is quickly cooled through the CNTs after stopping the NIR laser irradiation. The produced NIR-writing CTO-CNT-HPC (CCH) thermoresponsive display exhibited a fast thermoresponsive time. The CCH thermoresponsive display developed in this study can be applied in situations that require fast display response times, such as interactive advertising, property exhibitions, navigation systems for car, schedule information, event information, and public announcements.