DE VIVO, ANGELA (2020) An industrial oriented technology for core-shell alginate microbeads production. [Tesi di dottorato]

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Ionotropic alginate microgels are commonly used as an encapsulation medium for biomedical, bioprocessing, pharmaceutical and food applications. The purpose is to encapsulate several substances, which in their raw form may be sensitive to heat, light, moisture, pH, toxins, oxidation, mechanical shear, or pressure. Microgels are produced via ionotropic cross-linking gelation resulting from the interaction between alginate molecules and calcium or barium cations. In order to obtain microgels with a size range that is appropriate for the desired application, various considerations come into play in the designing phase including high efficiency and production rates, the scale-up possibilities with no quality concerns, possibility of contamination and the cost constraints. The extrusion of a liquid encapsulating material through a nozzle (dripping method) is relatively simple, size-controlled, low-cost, and scalable formation method for microgels. The setup based on the use of external force as pressurized air provide shear force in order to improve the production rate and the reduction of the microbead diameter. A new “industrial oriented” technology was developed in this thesis. More in detail, an extrusion air system connected with a micro-air flow nozzle resulting in an integration of a feed pump and a co-flow microfluidic device was designed. The microfluidic device was made of hybrid 3D printing technology for the scale-up ability based on the massive parallelization. The low values of the air density and viscosity require higher velocities, in order to ensure the appearance of sufficiently high tangential stress and pressure perturbations. At the same time, higher velocity values lead to complex jet break-up dynamics, including the formation of satellites drops and consequently the increase in microbeads size dispersion that makes extremely difficult operating especially in core-shell configuration. Hence, the understanding of the fundamental phenomena involved in the formation of a pendant droplet or a jet at the nozzle was obtained using numerical modeling approach. The application of the described air-liquid focusing device was tuned in order to perform both matrix and core-shell configurations of microencapsulation. The obtained results showed that the extrusion system coupled with a micro-air co-flow nozzle allowed to produce microgels with a mean diameter (D50) in the range of 27.1–87.5 µm and 64.6–334.8 µm for the matrix and core-shell microencapsulation systems, respectively. Furthermore, the proposed research was aimed to optimize the geometric parameters of the designed device and to analyze the influence of the process parameters on the microcapsules particle size distribution by varying the alginate solution and air-flow rate.

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