# Effect of Driving Pressure Modes on Microjet Dispersion Characteristics in Tissue-Mimicking Gels for Large-Volume Needle-Free Injection

## TL;DR

A new needle-free injection system uses a two-phase pressure mode to improve drug dispersion in gels, enabling controlled delivery of large-volume formulations.

## Contribution

A novel two-phase pneumatic system is introduced to enhance microjet dispersion for large-volume needle-free injections.

## Key findings

- The two-phase driving mode produces a larger dispersion width compared to the single-phase mode at equivalent pressures.
- The two-phase mode achieves more uniform lateral drug distribution and higher drug delivery percentages in gels.
- Optimal pressure combinations were identified for different injection volumes, aiding clinical parameter optimization.

## Abstract

Needle-free injection (NFI) technology is a promising alternative to conventional syringe injection, as it mitigates needle-related complications and enhances patient compliance. However, achieving the controlled and efficient dispersion of larger-volume formulations (>1 mL) within tissues remains a significant challenge. This study presents a novel pneumatic NFI system that uses a two-phase driving mode to regulate driving pressure and duration with an ejection volume of 1.0–2.0 mL. The integrated pressure stabilization unit significantly reduces pressure fluctuations during the initial injection phase, generating a more stable and uniform spray distribution. It is designed to produce an ideal elliptical dispersion effect while eliminating splatter, enabling controlled large-volume delivery. Jet impact experiments were conducted to investigate the dynamic characteristics of microjets generated by conventional single-phase and novel two-phase driving modes. Furthermore, the influence of the driving mode on the dispersion behaviors of microjets in agarose gels was explored through high-speed imaging of gel injections. The results demonstrate that the two-phase driving mode produces a distinct two-phase jet pressure profile. Compared to the single-phase mode, the two-phase mode produced a significantly larger dispersion width at equivalent initial driving pressures. This promotes more uniform lateral drug distribution and achieves a higher percentage of liquid drug delivery in gels. Furthermore, favorable driving pressure combinations were identified for different volumes: (1.25–0.25) MPa for 1.0 mL, (1.25–0.50) MPa for 1.5 mL, and (1.50–0.50) MPa for 2.0 mL. This provides a practical basis for optimizing clinical parameters and advancing the development of controllable NFI systems.