Computational Fluid Dynamics modeling and experimental studies of multi-port needles for optimization of drug delivery to multiple tissue layers

Transdermal injections remain the most efficient way of delivering drugs to the circulatory system to circumvent the barriers typically associated with enteral routes. However, the therapeutic or immunologic response can be limited due to either (a) poor drug diffusion, or inaccurate deposition/location of drug. Or (b) the need for electroporation to enhance cellular uptake. Sustained progress in the development of new formulation technologies have successfully introduced macro-molecules into therapeutic treatment: protein, RNA and DNA based vaccines brought a new potential of tapping into heightened immune response; those, however, suffer with poor efficacy in part due to the difficulties of properly delivering these macro-molecules at high concentration, which often result in high-viscosity injectables.

Whilst the hypodermic needle remains the vanguard method of delivery, we sought to improve the delivery with a modified flow regime by placing the outlets along the length of the needle, to create a so-called “sprinkler needle” effect. With the aid of CFD based simulations, we created 3D models of 22 gauge hypodermic needles modified with side-ports along the length of its body. With viscosity at the forefront of drug-delivery hindrance, we focused on substituting the conventional beveled outlet for multiple outlets varying in size and number: those were the variables attributed to the side-ports with the goal of being monitored throughout our studies where the outflow distribution was the target output. In this first phase of our study, the number of side-ports is the main variable of focus, along with the effects of fluid viscosity variation. Utilizing both simulations and experiments, we were able to study numerous high-viscosity injections and determine the volumetric flow rates through each port and ultimately design geometries to achieve a given flow distribution.