## 7 Guidelines on Developing Biopolymeric Microparticles
### Recommended Guidelines to Prepare Microparticles Loaded with Chemical and Biological Agents  
This section brings some important aspects to prepare microparticles, not only for agroindustrial purposes, but also for other fields as food engineering or pharmaceutical science. Sodium alginate is used as a carrier biopolymer, and when a solution of the latter encounters divalent or trivalent cations, a rapid, strong, and irreversible formation of the gel matrix occurs, respectively. Residues from sodium alginate blocks react cooperatively with cations forming a gel network. Because of the rapid and irreversible reaction, controlled conditions of preparation should be achieved [138; 139]. The procedure of microparticle preparation vary, and the essential need is to achieve high encapsulation efficiency, loading capacity, alongside chemical stability. It is also important to achieve good swelling properties, surface, and core morphology, all of which influence the controlled release of encapsulated agents (Figure 4). Nevertheless, with regards to the preparation of biopolymer-based microparticles, universal microparticles for any purpose do not exist. It is important to tailor microparticles based on the intended use, and therefore, appropriate procedures need to be developed and applied. To achieve desirable microparticle efficiency for the prolonged release of chemical and biological agents, it is important to choose sodium alginate with a higher content of guluronic acid residues. High guluronic acid content results in more rigid and porous gels and can maintain their integrity for longer periods. One of the most important things to consider when tailoring microparticles is choosing a proper concentration of gelling cation alongside a used biopolymer [133]. The ratio between gelling cations and sodium alginate determines the kinetics of gelation, and in the end, physicochemical characteristics of the formed gel matrix [140]. Research reveals that the decrease in sodium alginate concentration increases mechanical stability, but when the concentration is too low, mechanical stability starts to decrease [138; 140; 141]. The sodium alginate solution is viscous, depending on the concentration. The minimum viscosity of sodium alginate solution to form microspheres via the ionic gelation method is 0.03 Pa-s [142]. Spherical microparticles may be obtained over a wide range of viscosity of the latter solution. Usually, the viscosity of aqueous sodium alginate solution does not go over 1 Pa-s [133]. Microparticle size mainly depends on the polymer concentration. An increase in the particle size correlates with the higher initial concentrations of biopolymers, because of the functional groups' proportions. It should be noted that encapsulation efficiency decreases with an increase in polymer concentration, which ends with less space for encapsulated material [46]. The concentration of both sodium alginate and gelling cation significantly affects cation binding and kinetics of gel matrix formation. This review discusses the impact of Cu2+ or Ca2+ cations in various concentrations on the physicochemical characteristics of formed microparticles with regards to the constant concentration of sodium alginate (1.5% \(w/v\)). Respectively, the preparation procedure of microparticles consists of two steps. The first step being ionic gelation, where sodium alginate interacts with cation to form a gel network--microspheres, and the second step involving the additional coating of microspheres with chitosan via polyelectrolyte complexation [143]. Figure 4: Schematic representation of recommended observations when tailoring microparticles for specific purposes, a case of chemical and biological agents. The process of preparation starts with the addition of a biological agent (_T. viride_) to the sodium alginate solution and homogenization of the suspension. Filtration through the muslin cloth is recommended to filter out only spores (to not clog the machine used in the process of preparation--mentioned later in the discussion).