Multiple orifices in customized microsystem high-pressure emulsification: The impact of design and counter pressure on homogenization efficiency

A continuous production of nanoernulsions (or solid lipid nanoparticles) via a single passage through a homogenization device is a challenging, yet essential prerequisite of upstream or downstream processes in an integrated overall microsystem. Multiple orifice microsystems with consecutive orifice arrangements were identified as especially efficient tools for this purpose. Design, process, and formulation parameters were studied to evaluate their influence on the process efficiency and the underlying mechanisms affecting the droplet breakup and droplet stabilization efficiency. The application of multiple orifices in one microsystem reduces the coalescence of broken up droplets due to the establishment of a turbulent mixing zone. Therein, the frequency of droplet collision is elevated and, in turn, their collision time is shorter than the coalescence time. Thus, the droplets are fluid dynamically stabilized against coalescence. Double orifices are found more efficient than triple orifices because the breakup is superior due to higher energy density. The combination of differently wide orifices as well as the orifice order and the inter-orifice distances also influence the homogenization result. The combination of orifices must be selected to yield a counter pressure in the range of Thoma numbers between 0.1 and 0.4, as described for common two-stage homogenizers. The variation of formulation parameters displayed that the improved double orifice efficiently produces small particle sizes virtually independent of the emulsifier properties and the viscosity of the continuous phase.