Meeting the unmet: from traditional to cutting-edge techniques for poly lactide and poly lactide-co-glycolide microparticle manufacturing - Journal of Pharmaceutical Investigation

Needle-free injection device injecting a high-speed jet of liquid (a) or of powder (b). In the first case, a piston pushes the liquid through a nozzle, which produces a jet at > 100 m/s (velocity); the jet starts the formation of a hole on the skin through surface erosion, fracture, or other skin disruptive processes; a few tens of microseconds of prolonged impingement of the jet provokes progressive increase of hole depth; the liquid accumulates in the skin hole slowing down the jet and further increase of the hole is stopped; the consequent stagnation favors diffusion of the liquid into the skin. In the case of powder injections, a chamber filled with the powder is pressurized with a gas and a jet is generated by rupture of a membrane set; the particles impinge the skin surface leading to formation of a hole into the skin depositing in a spherical pattern, penetrate across the stratum corneum, and distribute completely into the stratum corneum and the viable epidermis; to produce a proper powder jet, particle densities of about 1 g/cc and a mean diameter > 20 μm are desirable. Adapted from Kale and Momin (2014)

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