Pressure and stress transients in autoinjector devices

Area of Science:

• Biomedical Engineering
• Fluid Dynamics
• Materials Science

Background:

• Spring-actuated autoinjectors are used for viscous drug delivery.
• High drug concentrations necessitate large spring forces, increasing risks.
• Device failure can occur due to extreme pressures and stresses.

Purpose of the Study:

• Investigate the origins of peak pressures and stresses in autoinjector syringes.
• Understand the role of mechanical impacts, acceleration, and cavitation.
• Analyze the influence of air gaps on pressure dynamics.

Main Methods:

• Utilized novel instrumentation for precise measurements.
• Employed numerical simulations for detailed analysis.
• Examined the effects of component acceleration and liquid tension waves.

Main Results:

• Identified mechanical impacts and high acceleration as primary stress sources.
• Discovered cavitation, driven by tension waves, contributes significantly to peak pressures.
• Demonstrated that air gap dynamics critically affect cavitation and pressure.
• Observed shock wave focusing in the conical syringe section causing localized high pressures.

Conclusions:

• Autoinjector failure is linked to cavitation and shock wave phenomena.
• Optimizing air gap parameters can mitigate extreme pressure events.
• Understanding these mechanisms is crucial for designing more reliable autoinjectors.