Electrospinner: Superelastic phenylalanine dipeptide crystal fibers: flexible, highly elastic, wearable, and implantable for sensitive monitoring

Background

The development of self-powered electronic devices based on electromechanical conversion of piezoelectric materials has promoted many innovations in medical diagnosis and sensing technologies. However, developing electronic devices with excellent elasticity, flexibility, stability, biocompatibility and breathability, and achieving conformal deformation and synchronous electromechanical coupling with human physiological movements, so as to collect biological information with high fidelity, is still a major challenge in the current field of functional materials and nanotechnology.

Recently, Feng Zhangqi from Nanjing University of Science and Technology and Wang Ting's team from Southeast University published a research result entitled "Super-Elastic Phenylalanine Dipeptide Crystal Fibers Enable Monolithic Stretchable Piezoelectrics for Wearable and Implantable Bioelectronics" in Advanced Fiber Materials. A nanometer-limited self-assembly strategy for the preparation of elastic phenylalanine dipeptide crystal fibers (FF-CFs) is reported. The FF crystals are combined with styrene-butadiene-styrene (SBS) fibers in a unique mortise and tenon structure, which has ultra-high elasticity (≈1200%), flexibility (Young's modulus: 0.409±0.031 MPa), and excellent physical stability, thus solving the thorny problem of the natural rigidity and brittleness of FF piezoelectric crystals. Under cyclic tension and compression conditions, the FF crystal fibers can maintain structural integrity and stable piezoelectric properties, and the integrated liquid metal coating and wireless electronic transmission components can capture biometric information from human motion with high fidelity and monitor subtle pressure changes in the body with high sensitivity. Therefore, this elastic FF crystal fiber has potential for application in the field of flexible electromechanical sensors, suitable for precise medical diagnosis and efficient energy harvesting.

The main point of this paper

First, the difference between wet electrospinning and traditional electrospinning is introduced. From the perspective of fiber formation, traditional electrospinning is to stretch the polymer solution into fibers with diameters ranging from micrometers to nanometers under a high-voltage electrostatic field, as shown in Figure 1a. In contrast, wet electrospinning technology is to squeeze the polymer solution into a thin stream, which is then coagulated into fibers in a coagulation bath (Figure 1b). This method is controllable during the fiber forming process, so it has unique advantages in preparing ordered fibers and specific functional short fibers.

Secondly, the principle of wet electrospinning technology is introduced. Wet electrospinning mainly includes an injection propulsion device, a high-voltage power supply, and a coagulation bath collection device, as shown in Figure 2. The wet electrospinning process generally includes four consecutive stages: (1) charge excitation; (2) jet linear propagation; (3) coil jet dynamics; (4) coagulation. During the coagulation process, a chemical reaction occurs between the polymer and the coagulant, and the solvent diffuses from the raw material solution to the coagulation bath, resulting in a double diffusion effect, thereby accelerating the formation of ultrafine fibers. The coagulation bath is the key to the unique advantages of wet electrospinning over traditional electrospinning in terms of fiber morphology, surface modification and functionalization, and yarn preparation. Coagulation bath devices usually include plate, drum, vortex, and disc collection.

Then, the potential of wet electrospinning in the preparation of patterned fibers is summarized. The coagulation bath in the wet electrospinning process is beneficial to the transformation of the fiber from liquid to solid. This allows for better control of the coagulation rate of the spinning solution and the phase separation process inside the fiber. The increase in the concentration of the coagulation bath improves the uniformity of fiber coagulation and reduces the formation of macropores, thereby reducing the porosity of the native fiber. These characteristics can be used to design and manufacture patterned fibers for biomedical or industrial devices, such as core-sheath fibers for drug delivery, highly porous fibers, beaded fibers, or adhesive films.

Finally, the advantages, current challenges, and future developments of wet electrospinning are summarized. Advantages of wet electrospinning technology: (1) Adjustable fiber diameter; (2) Diverse materials and strong scalability; (3) Controllable fiber structure; (4) Wide application. However, the rapid development of wet electrospinning technology has also exposed some problems, making its industrial development face challenges: (1) Low industrial production efficiency; (2) Insufficient control of fiber morphology and microstructure, limited performance; (3) Complex equipment operation and high cost; (4) Solvent recovery and environmental pollution.

summary

In summary, this study developed FF-CFs based on the nano-limited threshold method, which exhibits extremely high elasticity, flexibility, excellent piezoelectric properties, good air permeability and physical stability, and is suitable for wearable and implantable bioelectronic devices that synchronize with human physiological movements and require high-precision collection of biological information. This mortise and tenon structure not only improves material performance, but also provides a novel general strategy for designing and manufacturing advanced hierarchical electronic devices, which is expected to promote the further development of flexible electronic technology.