Design of solid powder particles for a needle-free injection

ABSTRACT

Background: In 2020, the COVID19 pandemic has shown the medical need for vaccinations. The conventional method of vaccine application is intravascular injection of a liquid solution. However, this method is associated with some disadvantages, such as a high risk of infection. Purpose(s) The approach of a needle-free ballistic administration accelerates solid powder particles to a sufficient speed so that they are able to penetrate into the skin and address target Langerhans cells. For this purpose, the particles require certain characteristics (Weissmueller et al., 2017). The main criteria for a successful application is the particle size as well as the density (Maa et al., 2004). Method(s) One potential production process is freeze-drying out of a solution with a subsequent milling step (abbreviated to FD). Another modified approach is spray-freeze drying (abbreviated to SFD). Dried powders are treated afterwards by ultrasonic microsieving (6000 vibrations per seconds for ten minutes) in order to segregate a useable fraction (38 mum to 75 mum). Tap density was determined according to the protocol by Ph.eur. guidelines. Helium pycnometry determines the true density. The magnitude of density is described by the quotient of tap density rho tap and pycometric density rho He-pycnometer. Result(s) Estimated density of examined samples containing trehalose and mannitol could not exceed 50%. Conclusion(s) The described techniques reveal a quite porous structure of the product. This structure might not be sufficient for particles to successfully penetrate into the skin. These powder particles might burst upon the surface. However the dimension of the speed has to be considered as well as it plays a crucial role as well.