Pyrolyzed Ultrasharp Glassy Carbon Microneedles

Area of Science:

• Biomaterials Science
• Nanotechnology
• Otolaryngology

Background:

• Polymeric microneedles fabricated via two-photon polymerization (2PP) offer potential for safe inner ear access.
• Expanding material options for 2PP microneedles is crucial for diverse biomedical applications.

Purpose of the Study:

• To develop and characterize novel glassy carbon microneedles derived from 2PP-fabricated polymeric precursors.
• To evaluate the efficacy of these glassy carbon microneedles for controlled round window membrane perforation and inner ear drug delivery.

Main Methods:

• Fabrication of polymeric microneedles using two-photon polymerization (2PP) lithography.
• Pyrolysis of polymeric microneedles to form glassy carbon structures.
• Material characterization using energy-dispersive X-ray spectroscopy, Raman spectroscopy, and mechanical testing (Young's modulus, Weibull distribution for strength).
• In vitro assessment of microneedle performance on guinea pig round window membrane (RWM).

Main Results:

• Glassy carbon microneedles were successfully produced with significant shrinkage (up to 81%) while maintaining structural integrity under specific surface-area-to-volume ratio conditions.
• Characterization confirmed the glassy carbon composition and revealed a Young's modulus of 9.0 GPa, with a characteristic strength of 710 MPa (Weibull modulus 3.1).
• In vitro studies demonstrated that the glassy carbon microneedles effectively created controlled perforations in the guinea pig RWM without self-damage, facilitating predictable therapeutic diffusion.

Conclusions:

• Pyrolysis of 2PP-fabricated polymeric microneedles is a viable method to create robust glassy carbon microneedles.
• These glassy carbon microneedles are suitable for creating precise perforations in the RWM, enabling enhanced and predictable inner ear drug delivery.
• The developed microneedles represent a promising tool for therapeutic interventions in the inner ear.