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In the past decade, the booming smart skin electronic product industry has promoted the application of electronic skin in many fields such as healthcare, Internet of Things, human-computer interaction, artificial intelligence and soft robotics. Among them, flexible humidity sensors respond quickly to humidity changes and play an important role in human health monitoring and non-contact sensing. However, existing humidity sensors are uncomfortable to wear, complex to prepare and expensive, and have low sensitivity and slow response time, which limits their application in continuous real-time detection of human physiological signals and dynamic humidity measurement.
Recently, the team of Associate Professor Wang Bin and Professor Zhang Xiuqin from the School of Materials Design and Engineering of Beijing Institute of Fashion Technology, in collaboration with Researcher Liu Xiaoni from Beijing You'an Hospital Affiliated to Capital Medical University, published a research result entitled "A Biomimetic Asymmetric Structured Intelligent Wound Dressing with Dual-modality Humidity-pressure Sensing for Non-invasive and Real-time Wound Healing Monitoring" in Advanced Fiber Materials. Based on MXene materials and electrospinning technology, this work designed and prepared a multifunctional flexible humidity sensor with excellent sensing performance, breathability and lightness. It has the characteristics of high sensitivity, pressure-humidity dual-mode response, all-weather antibacterial, and is comfortable. It has potential application value in respiratory monitoring, non-contact response, and smart wound dressings.
The main point of this paper
In order to reduce the secondary damage caused by traditional wound dressings, this study pioneered a smart wound dressing method. The preparation process and structure are shown in Figure 1. The use of dual-modal sensors can monitor the healing process in real time without invasiveness. The dressing uses electrospinning and screen printing technology to construct a three-layer structure with asymmetric wettability. When simulating the dermal environment, the sensitivity of the MXene@sodium alginate (SA)/polylactic acid (PLA) humidity sensor is 99%, the response time is 0.6 s, and the performance can last for 28 days. The chitosan (CS) sponge middle layer with a loose porous structure prepared by freeze-drying technology can effectively manage wound exudate and accelerate wound healing. The outer layer is a hydrophobic PLA@Ag3PO4 membrane that can eliminate 99.99% of bacteria.
In addition, this sandwich structure dressing can also serve as a highly sensitive capacitive pressure sensor (199.22 kPa-1), which can last for more than 1,500 cycles and capture subtle pressure fluctuations during wound healing. The in vivo experimental results in Figure 2 show that the dressing can prevent infection, accelerate angiogenesis, epithelial regeneration and open wound healing.
The introduction of the binder SA into the MXene layer increases the interfacial interaction of MXene, and at the same time, the MXene@SA composite particles are combined with the PLA segments through hydrogen bonds. The hydrophilic functional groups on the surface of MXene and the -OH and -COOH on the SA molecular chain are used to adsorb external water molecules through hydrogen bonding. Since the electrospun PLA nanofiber membrane has a large specific surface area and a porous network structure, water molecules are captured by the MXene@SA composite particles on the PLA nanofibers, forming a layer of liquid water on the surface. Water molecules are ionized in the water layer and undergo a Grotthuss chain reaction, and migration occurs between ions to reduce the resistance of the device. As can be seen from Figure 5, the sensor exhibits excellent humidity responsiveness, indicating that the introduction of SA improves the humidity responsiveness and stability of the device and is not affected by deformation such as bending.
An obvious antibacterial zone appeared around the Ag3PO4-loaded PLA nanofiber membrane. After 20 minutes, only 20 bacteria were left per 100 µL, and the bacteria completely disappeared within 60 minutes. The antibacterial rate reached 99.99%, proving that PLA@Ag3PO4 has excellent antibacterial properties. The wettability test of the smart wound dressing showed that the hydrophobic outer layer of the dressing can effectively block the invasion of external bacteria, and the hydrophilic inner layer of the dressing is conducive to the rapid transmission of wound tissue fluid from the inside to the outside through the asymmetric surface energy gradient and spread on the outer layer.
The experimental results show that this smart wound dressing not only promotes wound healing and recovery, but also can monitor the humidity and pressure sensing signals of the wound in real time during the healing process, reducing secondary damage. The dressing can provide an optimal healing environment by accurately monitoring the moisture changes of the wound surface, while its pressure sensing function ensures that excessive pressure and friction are avoided when treating the wound; in addition, this real-time monitoring capability enables medical staff to adjust the treatment plan in a timely manner, improve the overall treatment effect and patient comfort, showing great potential in clinical applications and providing an effective solution for the management of open wounds.
In summary, this study used the MXene interlayer confinement effect to combine sodium alginate (SA) with MXene to prepare humidity-sensitive composite nanoparticles (MXene@SA), and used electrospinning and screen printing technology to manufacture a resistive flexible humidity sensor with polylactic acid (PLA) nanofiber membrane as the substrate. The sensor has high sensitivity (99%), fast response/recovery time (0.6 s/1.4 s) and wide detection range (11% RH~98% RH), is not affected by deformation, and has good stability (4 weeks). Based on the above-mentioned MXene@SA/PLA resistive flexible humidity sensor, a sandwich-structured smart wound dressing with both humidity and pressure sensing functions was constructed to monitor the healing of open wounds. The surface layer of this dressing is a PLA nanofiber membrane anchored with silver phosphate (Ag3PO4) nanoparticles, which has all-weather antibacterial function; the middle layer is a chitosan (CS) sponge with a loose porous structure prepared by freeze-drying technology, which provides excellent absorption and conduction of liquid and compression resilience; the bottom layer is a MXene@SA/PLA nanofiber membrane with humidity response function, which can detect changes in wound humidity in real time and quickly. At the same time, this sandwich-structured dressing also has a capacitive pressure sensing function, which is conducive to monitoring the healing of wounds and shows broad application prospects in the field of smart medical care.
Electrospinning Nanofibers Article Source:
https://link.springer.com/article/10.1007/s42765-024-00473-x
