A computational model of a controllable needle-free jet injector

Area of Science:

• Biomedical Engineering
• Fluid Dynamics
• Robotics and Control Systems

Background:

• Needle-free jet injectors (NFJIs) offer an alternative drug delivery method, bypassing traditional needles.
• Understanding the precise dynamics of NFJIs is crucial for optimizing drug delivery to dermal, subcutaneous, and muscular tissues.
• Previous NFJI designs relied on servo-controlled Lorentz-force motors for actuation.

Purpose of the Study:

• To develop and validate a mathematical model simulating the dynamics of a Lorentz-force motor-based needle-free jet injector (NFJI).
• To predict the fluid jet speed and piston movement during the injection process.
• To assess the model's accuracy against experimental high-speed video measurements.

Main Methods:

• A mathematical model was formulated to simulate the NFJI's dynamics.
• The model incorporated the electrical response of the motor coil, mechanical response of the piston and ampoule, and frictional forces.
• High-speed video recordings of piston displacement under a step input were used for model validation.

Main Results:

• The model accurately predicted piston-tip position with a Root Mean Square (RMS) error of 287 µm compared to experimental data.
• The model predicted a jet speed of 180 m·s⁻¹ during injection.
• A maximum jet speed overshoot of 205 m·s⁻¹ was also predicted by the model.

Conclusions:

• The developed mathematical model provides a reliable tool for predicting NFJI performance, specifically jet speed and piston dynamics.
• Model validation against experimental data confirms its accuracy for simulating the complex interplay of electrical, mechanical, and frictional forces.
• This predictive capability can aid in the design and optimization of future needle-free jet injection systems for enhanced drug delivery.