Assessment of Cavitation Intensity in Accelerating Syringes of Spring-Driven Autoinjectors

Area of Science:

• Biomedical Engineering
• Fluid Dynamics
• Pharmaceutical Technology

Background:

• Cavitation, a phenomenon of vapor-filled bubble formation and collapse due to pressure changes, can occur in autoinjectors (AIs).
• This collapse generates shock waves, potentially damaging sensitive protein drug molecules and the device itself.
• Understanding and mitigating cavitation is crucial for ensuring AI functionality and drug integrity.

Purpose of the Study:

• To investigate the influence of key design parameters on the risk and severity of cavitation in autoinjectors.
• To analyze the effects of air gap size, syringe filling volume, fluid viscosity, and drive spring force on cavitation dynamics.
• To quantify cavitation intensity using the extension rate as a key metric.

Main Methods:

• Development of a model autoinjector platform to record syringe and cavitation dynamics.
• Estimation of cavitation intensity through the measurement of the extension rate.
• Systematic variation of design parameters to study their impact on cavitation severity.

Main Results:

• Cavitation collapse generates intense shock waves and high extension rates.
• Higher syringe acceleration and filling volume increase the extension rate.
• Increased fluid viscosity and larger air gap size decrease the extension rate.

Conclusions:

• The most severe cavitation is observed with higher drive spring force and smaller air gap size.
• Less viscous fluids and larger filling volumes exacerbate cavitation severity.
• Optimizing AI design parameters is essential to minimize cavitation and protect drug products.