Needle-free jet injection allows delivery of liquid drugs through the skin in the form of a narrow fluid jet traveling at high speed, minimizing the risk of accidents. The use of a controllable actuator to drive this process has many advantages, but the voice coil actuators previously used are too large and heavy for practical use with common injection volumes (1 mL). We instead propose a compact slotless tubular linear permanent magnet synchronous motor design for jet injection. The design was determined by utilizing a semi-analytical electromagnetic modeling technique to predict the performance of any given motor design, an optimization scheme for the motor mass at a given power dissipation, and an automated routine for estimating cogging force using finite-element analysis. A prototype motor was constructed, with a nominal mass of 322 g, a stroke of 80 mm, and a target operating power of 1.2 kW; experimental data show that the motor constant is within 10% of the target, and that the cogging force is in close agreement with the model. Test ejection of water into a force sensor verified that the motor is fit for needle-free injection. The design methodology explained here shows the benefits to integrated design optimization of both the actuator and the load, particularly in systems that drive fluid pressure loads, and also opens the door to controllable injector designs for larger volumes.
Needle-free jet injection (NFJI) is a drug delivery technique that requires the application of a brief (10 ms to 100 ms) pulse of high force to pressurize a liquid drug and force it through the skin. To provide control over this force using an electric motor, high drive power is needed from a compact system. This work outlines the design process of an untethered power and motor drive system that is estimated to weigh approximately 2.5 kg, capable of supplying 1.6 kW at 210 V peak-peak. The device is used to drive a linear synchronous motor to deliver up to 31 large volume (1 mL) needle-free jet injections (NFJI) within a single recharge. The system architecture, gathering of detailed functional requirements, selection of energy storage, and the studies of power electronics and motor drive via system simulation are discussed. Inspired by electric vehicles' battery boosted motor drives and cascaded interleaved boost converters for high step-up conversion ratio, the proposed design employs a battery-powered boost converter which then energize a 3-level inverter with the peak to peak voltage of 210 V. The design utilizes the latest gallium nitride (GaN) transistors as well as the latest lithium-ion capacitors (LIC) for energy storage. The power electronic topology introduced in this work is also adaptable for other high energy pulsed applications such as plasma generation, or MRI gradient coils.
Needle-free jet injection allows delivery of a liquid drug through the skin in the form of a narrow fluid jet traveling at high speed, minimizing the risks of accidents. Doing this in a controlled way requires an actuator with exceptionally high force density. We propose the use of linear permanent magnet fluxswitching motors for this task, and describe their characteristics relative to the needs of jet injection. This paper will introduce a design process which involves the use of artificial neural networks as a means of response surface modelling, combined with nonlinear constraint optimization, to deduce a motor design that satisfies all of the challenging linear motor requirements for needle-free jet injection applications.
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