Transient modelling of impact driven needle-free injectors

• Published in: Computers in biology and medicine 2021-08, Vol.135, p.104586-104586, Article 104586
• Main Authors: Rane, Yatish S., Marston, Jeremy O.
• Format: Article
• Language: English
• Subjects: Actuation; Cartridges; Cavitation; Computational fluid dynamics; Drug delivery; Fluid flow; Free jets; Geometry; Hydrodynamics; Hypodermic needles; Injection; Injector; Injectors; Jet streams (meteorology); Mathematical models; Mathematics; Nozzle geometry; Partial differential equations; Peak pressure; Penetration depth; Pressure; Pressure impulse; Pressure loss; Reynolds number; Rheology; Simulation; Stagnation pressure; Tissues; Transient; Validation; Velocity; Velocity distribution; Viscosity
• ISSN: 0010-4825; 1879-0534
• DOI: 10.1016/j.compbiomed.2021.104586

Needle-free jet injectors (NFJIs) are one of the alternatives to hypodermic needles for transdermal drug delivery. These devices use a high-velocity jet stream to puncture the skin and deposit drugs in subcutaneous tissue. NFJIs typically exhibit two phases of jet injection – namely – an initial peak-pressure phase (< 5 ms), followed by a constant jet speed injection phase (≳ 5 ms). In NFJIs, jet velocity and jet diameter are tailored to achieve the required penetration depth for a particular target tissue (e.g., intradermal, intramuscular, etc.). Jet diameter and jet velocity, together with the injectant volume, guide the design of the NFJI cartridge and thus the required driving pressure. For device manufacturers, it is important to rapidly and accurately estimate the cartridge pressure and jet velocities to ensure devices can achieve the correct operational conditions and reach the target tissue. And thus, we seek to understand how cartridge design and fluid properties affect the jet velocity and pressure profiles in this process. Starting with experimental plunger displacement data, transient numerical simulations were performed to study the jet velocity profile and stagnation pressure profile. We observe that fluid viscosity and cartridge-plunger friction are the two most important considerations in tailoring the cartridge geometry to achieve a given jet velocity. Using empirical correlations for the pressure loss for a given cartridge geometry, we extend the applicability of an existing mathematical approach to accurately predict the jet hydrodynamics. By studying a range of cartridge geometries such as asymmetric sigmoid contractions, we see that the power of actuation sources and nozzle geometry can be tailored to deliver drugs with different fluid viscosities to the intradermal region. [Display omitted] •For manufacturers, it is important to design needle-free jet injector cartridges tailored to a given drug/fluid rheology and target tissue penetration depth.•Using CFD, we develop the geometry-specific correlations of Euler number (Eu) and Reynolds number (Re) to modify existing analytical models.•The geometry-specific correlations can be used for non-Newtonian fluids such as novel DNA vaccines with the use of generalized Reynolds number.•The increase in fluid viscosity reduces the plunger friction coefficient, and thus increases cartridge pressure.•Novel cartridge geometries (using Richard's function) increase the mechanical efficiency, especiall