Understanding counter pressure during syringe injections

Injection of drug into the skin is a common therapeutic process. Development of injection devices for efficient drug delivery requires a detailed understanding of the characteristic forces and tissue resistance pressure of which the injectors need to overcome. The pain felt during injection, typically delivered via a hypodermic needle as a single bolus, is associated with the pressure build-up around the site of injection. Recently, Multi-needle injection system has got attention to overcome the technical and clinical limitations of single needle injections, such as- large volume and concentrated drug delivery, sustained release rate and pain during injection. It is hypothesized that this counter-pressure is a function of the target tissue as well as fluid properties. Given that novel vaccines target different tissues (muscle, adipose, and skin) and can exhibit a wide range of fluid properties, we conducted a study of the effect of volumetric flow rate, needle size, viscosity and rheology of fluid, and hyaluronidase as an adjuvant on counter-pressure build-up in porcine skin and muscle tissues. We also used a double-needle injection system to see the effect of needle distance on tissue counter pressure. In particular, for a single-needle injection system, we found a significant increase in counter-pressure for intradermal ({ID}) injections compared to intramuscular (IM) injections, by an order of magnitude in some cases. We also showed that the addition of adjuvant affected the tissue back pressure only in case of subcutaneous (SC) injections. We observed that the volumetric flow rate plays an important role along with the needle size. For the double-needle injection system, we found that the volumetric flow rate has a significant effect on tissue counter-pressure. This study aims to improve the current understanding and limitations of liquid inject-ability via hypodermic needles, however, the results also have implications for other technologies, such as intradermal jet injection where a liquid bleb is formed under the skin.

Embargo status: Restricted until 06/2022. To request the author grant access, click on the PDF link to the left.