Device for producing very small polymer beads (100200 mm)

Designed by Yoav Bashan, Juan-Pablo Hernandez, and Angel Carrillo

Environmental Microbiology Group, Northwestern Center for Biological Research (CIBNOR), La Paz, B.C.S., Mexico

Microbead-producing device

Entrapment of microorganisms in a polymer matrix was invented three decades ago by the fermentation industry to produce industrial products with microorganisms for fermentation units, without losing the microorganisms when the product was harvested.

In 1986, this technology was modified in Israel to produce microbial inoculants of plant growth-promoting bacteria for agriculture. In the mid-1990s, this technology was further modified to immobilize microalgae for wastewater treatment. In 2000, the technology was further modified to allow immobilization of microalgae with beneficial bacteria for enhanced wastewater treatment. This is an experimental technology in all its modifications that is used in research laboratories worldwide. The use of beads is reported in numerous scientific publications and is a widely-accepted research tool.

The main limitation of the technology is the slow rate of bead production because it involves dropping the viscous polymer solution (mostly alginate) through a small opening in a large syringe, which is a tiresome procedure for lab personnel.

A tool was designed to overcome the basic problem of the excessive manual labor and increase production of beads ( Nonetheless, their relatively large size is a disadvantage for agricultural uses because there is a need for additional, specialized treatment during sowing. Therefore, the microbead concept was conceived. By making the beads small enough but still capable of encapsulating a sufficient number of bacteria, it would be possible to produce an almost powder-like formulation to be used for coating seeds. To reach this objective, the technology was improved in 2002.

To produce very small beads, two possibilities exist: (1) Mechanically crush large beads or solid alginate sheets and sieve the powder to the desired size. (2) Produce microbeads with an appropriate technology. This website describes the technical details of such a tool.

The main advantages of the macro-bead producing tool are:
  1. Produces liters of beads with very little effort.
  2. Can be easily modified to produce fewer beads.
  3. Is easily constructed from common materials with common machine shop tools.
  4. It is inexpensive.
  5. It will not rust.
  6. Can be cleaned with running tap water.
  7. Can be sterilized for axenic cultures.
  8. Requires about 30 minutes to train personnel.

A major advantage of the microbeads technology is the possibility to produce dry beads. In the dry, agricultural preparation, the bacteria are inactive but alive, as is preferable since their activities are needed only after germination of the seeds and decomposition of the beads.

A minor disadvantage of microbead production is that the immobilizing procedure (see technical description) sometimes kills a large number of bacteria (mainly depending on the bacterial species). However, it is easy to avoid this problem by secondary incubation of the microbeads in a new growth medium. The surviving bacteria will multiply and restore the concentration to that in the original growth medium.

This website contains technical specifications and construction of the tool, technical diagrams, a photograph of the device, a PowerPoint tutorial of the procedure (2.7 MB) for rapidly producing large quantities of beads and their application on seeds, photographs (in the photo gallery), and a PDF file of the publication that describes the entire procedure, the device, and its use for bacterial inoculant in agriculture.

Related page: Device for producing large polymer beads (24 mm).