Electrospinning Machine| Novel stable and biocompatible poly L-lactide/β-glycine films for in vivo bone repairing by using nanogenerator with high piezoelectricity

With the advancement of wearable devices and implantable medical technologies, piezoelectric materials are increasingly being used in vivo for applications such as monitoring physiological signals, powering implanted devices, and promoting tissue regeneration. Clinically, such piezoelectric biomaterials are required to possess high piezoelectricity, flexibility, biocompatibility, and degradability. Compared to traditional inorganic piezoelectric materials (e.g., piezoelectric ceramics) and certain piezoelectric polymers (e.g., polyvinylidene fluoride—PVDF), piezoelectric biomaterials exhibit superior biocompatibility and can achieve complete degradation within the body.

Poly-L-lactic acid (PLLA) is widely used as an implantable material due to its excellent flexibility, ease of processing, and biodegradability. However, its low piezoelectric constant limits its application as a piezoelectric biomaterial. On the other hand, β-phase glycine, with its ultrahigh shear piezoelectricity (178 pm/V), is an ideal candidate for in vivo piezoelectric materials. Yet, its thermodynamic instability, complex fabrication process, and water solubility pose challenges for practical applications.

Recently, Professor Fan Huiqing's team at Northwestern Polytechnical University developed PLLA composite fibers encapsulating highly piezoelectric β-glycine via unique coaxial electrospinning. During the process, the 3D confinement effect of PLLA controlled glycine crystallization into the β-phase, aligned along the (100) direction under a high electric field. The PLLA/β-glycine composite film demonstrated high piezoelectric performance, structural stability under PLLA encapsulation, sufficient flexibility, and long-term degradability. In vitro and in vivo experiments confirmed that the novel composite film effectively promotes cell proliferation and bone tissue repair.

The research, titled "Novel stable and biocompatible poly L-lactide/β-glycine films for in vivo bone repairing by using nanogenerator with high piezoelectricity," was published in Nano Energy.

Fig. 1: Morphology and structure (a–f), preparation mechanism (g–i) of PLLA-glycine films.

The PLLA/β-glycine composite film was prepared via coaxial electrospinning, with β-glycine as the core and PLLA as the shell (Fig. 1g). During fiber formation, glycine solution in the core layer was ionized and confined by the outer PLLA solution, limiting its size to micro/nanoscale and favoring the metastable β-phase. XRD, FTIR, and Raman spectroscopy confirmed β-glycine in the optimal PL4G1 composite film. SEM and TEM (Figs. 1b, d) revealed a pod-like structure in PL4G1 fibers, with convex diameters of ~1 μm, confirming β-glycine's micro/nano-scale size.

For comparison, uniaxial electrospinning of a PLLA-glycine mixture (PLG, same ratio as PL4G1) yielded α-glycine due to the absence of PLLA confinement (Fig. 1c).

Fig. 2: Piezoelectric/mechanical properties.

Fig. 3: PENG performance of PLLA vs. PL4G1.

The PL4G1 composite membrane demonstrated outstanding electrical performance, achieving a maximum open-circuit voltage (Voc) of approximately 14 V, short-circuit current (Isc) of 0.95 μA, and instantaneous power density of 0.92 mW/cm². The incorporation of β-glycine significantly enhanced the piezoelectric properties compared to pure PLLA films. This superior piezoelectric performance enabled effective energy harvesting, allowing the membrane to serve as a power source for capacitor charging and LED illumination. During capacitor charging tests, PL4G1 exhibited 2-3 times faster charging rates and higher maximum voltages than pure PLLA.

Remarkably, the PL4G1 samples maintained stable short-circuit current output throughout 1000 pressure cycles, demonstrating exceptional durability and reliability for piezoelectric nanogenerator (PENG) applications. Under ultrasound stimulation, the PL4G1-based nanogenerator showed substantial improvements, with voltage and current outputs increasing by 1 V and 0.65 mA respectively compared to pure PLLA devices. Mechanical characterization revealed that while β-glycine incorporation increased the elastic modulus, values remained relatively low (<0.45 GPa), preserving the material's flexibility.

These comprehensive results confirm that the composite membrane-based nanogenerator can efficiently harvest and convert both biomechanical motion and ultrasound energy, highlighting its tremendous potential as an implantable power source for microdevices or as a tissue regeneration material. The system's ability to maintain performance under physiological conditions while preserving mechanical flexibility makes it particularly suitable for biomedical applications.

Fig. 4: Stability and degradability of PL4G1.

Fig. 5: Cytotoxicity and antibacterial evaluation.

Fig. 6: Histological assessment of bone repair.

Long-term stability tests confirmed that the PL4G1 membrane maintained consistent piezoelectric output after 30 days, demonstrating exceptional stability for in vivo applications. The composite film's biological properties ensured complete degradability, with natural degradation observed during prolonged PBS immersion.

In vitro and in vivo biological evaluations revealed that the fibrous architecture and enhanced piezoelectric response of the composite membrane synergistically improved biocompatibility. Most notably, the material exhibited remarkable efficacy in promoting bone regeneration, as validated through histological assessments.

Paper link: https://doi.org/10.1016/j.nanoen.2025.111275