Super-Elastic Phenylalanine Dipeptide Crystal Fibers in Wearable and Implantable Bioelectronics

Background

With the rapid development of flexible bioelectronics, the development of piezoelectric materials and devices with high elasticity, breathability, and the ability to achieve conformal deformation with the human body has become an important research topic. Traditional inorganic piezoelectric ceramics (such as zinc oxide, barium titanate, and lead zirconate titanate) have high piezoelectric coefficients, but their mechanical properties mismatch with human tissues, limiting their practical applications. Organic piezoelectric polymers (such as polyvinylidene fluoride and polylactic acid) have good biocompatibility, but their piezoelectric effects are weak, and their stretchability is limited. Therefore, finding a material that can maintain high piezoelectric performance while also having good elasticity, breathability, and biocompatibility has become a focus of current research.

Phenylalanine dipeptide (FF) is considered an ideal material for preparing wearable and implantable devices due to its excellent piezoelectric performance and mechanical characteristics. However, the inherent rigidity, brittleness, and monodispersity of FF crystals limit their application in flexible devices. To address these issues, researchers have developed a novel FF crystal fiber (FF-CFs) based on a nanoconfinement self-assembly strategy, aiming to combine elasticity, flexibility, stability, and breathability.

Source of the Paper

This research was conducted by Juan Ma, Lili Qian, Fei Jin, Weiying Zheng, Tong Li, Zhidong Wei, Ting Wang, and Zhang-Qi Feng from the School of Chemistry and Chemical Engineering at Nanjing University of Science and Technology, and was published in 2025 in the journal Advanced Fiber Materials (Volume 7, Pages 338–350). The research was supported by the National Natural Science Foundation of China, the China Postdoctoral Science Foundation, and the Fundamental Research Funds for the Central Universities.

Research Process and Results

1. Preparation and Characterization of FF Crystal Fibers

The research team developed a nanoconfinement self-assembly strategy by combining FF crystals with oriented styrene-butadiene-styrene (SBS) molecular beams, forming a unique mortise-tenon structure. This resulted in FF crystal fibers with elasticity (≈1200%), flexibility (Young’s modulus: 0.409 ± 0.031 MPa), piezoelectricity (macroscopic d33: 10.025 ± 0.33 pC N⁻¹), breathability, and physical stability. The specific steps are as follows:

• Electrospinning of SBS Fibers: SBS (25 wt%) was dissolved in 1,2-dichloroethane and stirred for 4 hours, followed by electrospinning to prepare SBS fibers.
• Preparation of FF Acetonitrile Solution: 20 mg of FF was dissolved in 100 μl of hexafluoroisopropanol and diluted with acetonitrile to a concentration of 0.2% w/v.
• Preparation of FF Crystal Fibers: FF acetonitrile solution was combined with SBS fibers via a micro-permeation pulling method to form FF crystal fibers.

2. Performance Characterization of FF Crystal Fibers

The research team characterized the morphology, functional groups, and self-assembly mechanism of FF crystal fibers using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and steady-state/lifetime fluorescence spectroscopy (PL). The results showed that FF crystal fibers exhibit excellent elasticity, flexibility, and physical stability, enabling conformal deformation with human skin and high-fidelity collection of biological information during various human activities.

3. Piezoelectric Performance of FF Crystal Fibers

The longitudinal piezoelectric coefficient (d33) of FF crystal fibers was 10.025 ± 0.33 pC N⁻¹, higher than commonly used piezoelectric materials (such as glycine, polylactic acid, and collagen fibers). The research team integrated FF crystal fibers with a liquid metal (Ga-In alloy) coating and wireless electronic transmission components to develop a flexible human physiological motion sensing system. This system achieved high-sensitivity detection of human movements and detected subtle pressure changes during heartbeats, respiration, and diaphragm movements under different physiological states.

4. Animal Experiments

The research team implanted FF crystal fiber sensors into the hearts, chest muscles, and diaphragms of mice to monitor signal changes under different physiological states. The experimental results showed that the sensors could accurately capture heart rate and respiratory patterns and exhibited good biocompatibility in long-term implantation experiments.

Conclusions and Significance

This study successfully prepared super-elastic FF crystal fibers using a nanoconfinement self-assembly strategy, addressing the rigidity, brittleness, and monodispersity issues of FF crystals in flexible device applications. FF crystal fibers combine excellent elasticity, breathability, and stability and have been successfully applied in flexible human physiological motion sensing systems, achieving high-fidelity detection of human movements. Additionally, the sensors exhibited good biocompatibility and long-term stability in animal experiments, providing a new solution for future wearable and implantable bioelectronic devices.

Research Highlights

1. Super-Elastic FF Crystal Fibers: FF crystal fibers prepared via the nanoconfinement self-assembly strategy exhibit tensile strains of up to 1200%, breaking the limitations of traditional piezoelectric materials.
2. High-Sensitivity Sensing System: The flexible sensing system integrated with a liquid metal coating and wireless transmission components enables high-sensitivity detection of human movements and physiological signals.
3. Excellent Biocompatibility: Animal experiments showed that FF crystal fiber sensors maintained good biocompatibility after long-term implantation, ensuring the safety of implantable devices.

Additional Valuable Information

The study also proposed that future research could further enhance device performance by functionalizing FF molecules and optimizing the self-assembly process, while integrating deep learning technology to achieve intelligent health monitoring and emotion recognition functions, promoting innovative development in the field of intelligent healthcare.

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This research not only provides new ideas for the design of flexible piezoelectric materials but also opens new avenues for the development of wearable and implantable bioelectronic devices, holding significant scientific value and practical application prospects.