A versatile alginate droplet generator applicable for microencapsulation of pancreatic islets

Abstract

Alginate beads for immunoisolation of pancreatic islets by microencapsulation should be small, smooth, and spherical in order to ensure that around the islets a strong alginate-polylysine-alginate capsule will be formed with optimal biocompatibility and diffusion of nutrients and hormones. However, the preparation of small capsules around islets is difficult. Our newly designed air jet droplet generator allows for variations in the length and diameter of the alginate nozzle and the air jacket and is in this way adaptable to a required bead size. Alginate droplets are converted into rigid beads in a 100 mM CaCl 2 solution. Their size depends upon the diameter of the jacket, the air flow rate, and the outer diameter of the nozzle, whereas the production rate depends upon the pressure on the alginate, and on the diameter and the length of the nozzle. When the air flow or the alginate flow surpasses a certain rate, the droplets are fragmented. This study describes the mutual relationship of these variables and defines their optimal range for reproducible production of smooth and spherical beads for microencapsulation of islets at an acceptable production rate.

Long-term biocompatibility, chemistry, and function of microencapsulated pancreatic islets

“…First, we produced rigid Ca-alginate beads, by converting an alginate solution into droplets using an air-driven droplet generator as previously described [19]. The droplets were collected in a Ca-rich solution to gelify into rigid Ca-beads.…”

Association between macrophage activation and function of micro-encapsulated rat islets

“…This immunoprotection by encapsulation allows for successful transplantation of cells in the absence of immunosuppression. A commonly used procedure for immunoprotection is microencapsulaThe alginate solution was converted into droplets using an air-driven droplet generator as previously described [20]. Polylysine-alginate encapsulation was carried out as described elsewhere [21].…”

Encapsulation and Surface Engineering of Pancreatic Islets: Advances and Challenges

“…Two forces are usually used to control the size of droplets: an air flow that builds around the tip of the needle (Wolters et al, 1992), and a high voltage pulse around the needle tip (Halle et al, 1994;Hsu et al, 1994), the formed droplets very often require an additional stabilization via gelation and beads formation (Stabler et al, 2001). Cross-linking with metal ions, calcium and barium, and chemical or covalent cross-linking are the two methods generally used in microbead or microcapsule formation.…”