Bead size is influenced by following parameters:

• Nozzle size - major influence
• Liquid flow rate - moderate influence
• Vibration frequency - moderate influence
• Physico-chemical properties of the encapsulation mixture - minor influence.

The most important parameter for bead production is the nozzle size. In general final bead diameter is about twice the size of the nozzle aperture.

Capsule size is influenced by the following parameters:

• Shell (external) nozzle size - major influence
• Core (internal) nozzle size – moderate influence
• Liquid flow rate for shell - moderate influence
• Liquid flow rate for core material – minor influence
• Vibration frequency - moderate influence
• Physico-chemical properties of the encapsulation mixture - minor influence.

The most important parameter for capsule production is the size of the shell nozzle. In general final capsule diameter is about twice the size of the shell nozzle aperture. What influences the core size within core-shell capsules.

• Shell (external) nozzle size - minor influence
• Core (internal) nozzle size – major influence
• Liquid flow rate for shell - minor influence
• Liquid flow rate for core material – major influence
• Vibration frequency - moderate influence
• Physico-chemical properties of the encapsulation mixture - minor influence.

The most important parameter for core size within capsules is the size of the core nozzle and the flow rate of the core material. In general final core diameter within capsules is about 1-2.5 times the size of the core nozzle aperture with increasing with increasing flow rates resulting in larger diameters.

Scale up is simply done by multiplying the number of nozzles on the machine, and is referred to as the multi-nozzle system. The parameters used for the one nozzle system should also apply to the multi-nozzle system. Therefore a special scale-up development is not required. However the process must work and be stable when using the one nozzle system before switching to a multi-nozzle system: Buchi offers such a multi-nozzle system which enables between 1 and 6 nozzles to be operated simultaneously by the operator.

The optimal frequency and amplitude ranges for different nozzle sizes are given in the following table.  

• Nozzle Diameter : 1.0 mm          Frequency Range: 40 to 200 Hz      Amplitude Range: 6 to 9
• Nozzle Diameter : 750 microns  Frequency Range: 40 to 300 Hz       Amplitude Range: 5 to 9
• Nozzle Diameter : 500 microns  Frequency Range: 100 to 400 Hz     Amplitude Range: 2 to 5
• Nozzle Diameter : 400 microns  Frequency Range: 200 to 500 Hz     Amplitude Range: 1 to 4
• Nozzle Diameter : 300 microns  Frequency Range: 400 to 800 Hz     Amplitude Range: 1 to 3
• Nozzle Diameter : 200 microns  Frequency Range: 600 to 1200 Hz   Amplitude Range: 1 to 3
• Nozzle Diameter : 150 microns  Frequency Range: 800 to 1800 Hz   Amplitude Range: 1 to 4
• Nozzle Diameter : 80 microns    Frequency Range: 1300 to 3000 Hz Amplitude Range: 4 to 4

The viscosity of the encapsulation mixture has the following effects:

• The higher the viscosity the higher the minimal jet velocity
• The higher the viscosity the higher the working flow rate
• The higher the viscosity the lower the optimal frequency
• The higher the viscosity the larger the beads/capsules

A range of natural and synthetic polymers are commercial available either from Buchi or chemical suppliers. Some of the common materials are follows:

• Natural polymers: Na-Alginate, Gelatin, lamda-Carragennan, Agar, Agrose, Chitosan, Cellulose, Whey protein, Collagen, Pectin
• Synethtic polymers: Polyacrylamide, Polyvinyl Alcohol (PVA), poly(lactic-co-glycolic acid) (PLGA), Cellulose sulphate, polyDADMAC, poly-l-lysine, Polyethylene Glycol (PEG)
• In additional  range of waxes can also be used to produce the capsules

Alginate is a natural polymer deviated from the cell wall of various different seaweed plants. On account of its natural origin the type of alginate supplied by different suppliers can vary extensively and this variable composition can have a negative effect on the quality of the alginate. This can result in the production of low quality particles or in some cases beads/capsules cannot be produced, while it also affects reproducibility of experiments. Buchi now supplies high quality alginate with a consistent composition. Each batch of alginate is pre-tested by scientists at Buchi to ensure customers can consistently produce high quality beads/capsules in a reproducible manner.

In this case either the nozzle or the bead producing unit is blocked with dried polymer. Cleaning nozzle: See nozzle cleaning section

• Cleaning bead production unit: If alginate is being used, soak the unit in 0.1 M NaOH for 1 hour and then pump the NaOH through the unit using a syringe pump or place the unit within a sonication bath for 1 – 5 minutes to loosen the alginate. For gelatin either soak in hot water (> 60 °C) and flush or sonication as above.
• For most materials, sonication will help to unblock it and the unit should be flushed with a liquid with can dissolve the entrapped material i.e. for PGLA this can be dichloromethane.
• Blocking of the pre-filter in the producing unit can also prevent the pumping of the polymer material through the bead producing unit and should be changed. See YouTube videos for more details.