Microencapsulation: Dripping and jet break-up

Encapsulation is usually described as the procedure of envelopment of the desired cargo/material(s) within a defined porous or impermeable membrane which can be performed via multiple different techniques. Usually, in the encapsulation process, immobilization of the cargo material along with the protection, stabilizing, and the controlled release of it will be considered as the ultimate goals. There are two ways to locate the cargo material in the microcapsules. In the first structure, the interested cargo is mixed with the polymeric network structure and hence will be found all over the microcapsule. In the core shell microcapsule structures, on the contrary, the cargo will be located within the immiscible core of the microcapsule structures. In order to optimize and influence the functionality of the capsules and particles, there may be some tuning in their characteristics such as degree of cross-linking, size, the type of selected polymer, surface charge, and the shape of the particles (Jones and McClements, 2010; Marison et al., 2004). In order to apply in industrial fields such as the food industry, agriculture, and cosmetics, a desired method should have a high rate of production along with low cost. In contrast, applying a pharmaceutical process needs the produced particles to be more stringent criteria. In order to be employed as an optimized method of encapsulation in the pharmaceutical industry, a technology must be enabled to produce mono-dispersed particles with a spherical shape and a narrow size distribution. Moreover, ease of operation and set-up and high production rate are of great importance. There are quite a large variety of methods for producing microcapsules which can be combined in order to produce one optimized method. Chemical, physicochemical, and mechanical processes are three main methods for production of microparticles. Chemical processes routinely refer to the encapsulation procedures in which polymerization and polycondensation occur and usually the in situ formed polymers are used to form the capsule's shell region. However, the main drawback of this method is forming ultra-thin polymeric membranes. Physicochemical processes, on the other hand, refer to the method which applies performed polymers through processes such as solvent removal, gelation, or coacervation to form the capsules shell which of course needs an extra cross-linking step for hardening the coating layer (Wyss-Péters, 2005). Mechanical methods for microparticles production generally include techniques such as spray drying, spray cooling, dripping, and jet break-up. The dripping and jet break-up method is subcategorized into techniques such as simple dripping, electrostatic dispersion, flow focusing, vibrating nozzle, spinning disk atomization, and jet cutting. The present chapter will focus on the description of the involved principle, a general discussion about the theoretical aspects of droplet formation, gives the different possible applications, and finally compare the different methods, giving both their advantages and their disadvantages (Wyss-Péters, 2005; Shewan and Stokes, 2013).