BUCHI Encapsulator B-390 - Manual (Page 18)

4 Description of function
18 B-390 Operation Manual, Version C
The main parts of the Encapsulator B-390 are the control unit, the bead producing unit, and the pres-
sure bottle. All parts of the instrument which are in direct contact with the immobilization mixture can
be sterilized by autoclaving.
The product to be encapsulated (active ingredients, enzymes, chemicals and cells) is mixed with an
encapsulating polymer (typically alginate) and the mixture put into the pressure bottle a see figure
4-1. The polymer-product mixture is forced into the bead producing unit  by air pressure (P). The
liquid then passes through a precisely drilled nozzle  and separates into equal size droplets on
exiting the nozzle. These droplets pass through an electrical field between the nozzle  and the elec-
trode  resulting in a surface charge. Electrostatic repulsion forces disperse the beads as they drop
to the polymerization bath. The polymerization bath must be electrically grounded.
Bead size
The bead size is controlled by several parameters including the vibration frequency, nozzle size, flow
rate, and physical properties of the encapsulation mixture. In general, the bead size is twice the nozzle
diameter. But, by varying the jet velocity and the vibration frequency, the range can be adjusted by
about 1 - 15 %.
Optimal parameters for bead formation are indicated by visualization of real-time bead formation in the
light of a stroboscope lamp . When optimal parameters are reached, a standing chain of droplets is
clearly visible. Once established, the optimal parameters can be preset for subsequent bead produc-
tion runs with the same encapsulating mixture.
Depending on several variables, up to 6000 beads are generated per second and collected in the
polymerization bath , which is continuously mixed by a magnetic stir bar. In addition, the reaction
solution must be electrically grounded to eliminate the electrostatic charges coming from the charged
bead surface. At the conclusion of the production run, the hardening solution is drained off, washing
solutions, or other reaction solutions, are added to further process the beads if needed.
4 .2 Connections at the Encapsulator B-390
Front connections (See figure 5-2)
• Main switch
• Air out
• Electrode
• Ground
Rear connections (See figure 5-1)
• Electric supply
• Air inlet
• Vibration
• Optional plug(s)