Team:UFRGS Brazil/Alginate

Alginate

As discussed in the ‘About biological filters’ section, the media filter has the role to ensure the optimized contact between the contaminated material and the biological agent. In a traditional sewage treatment filter, it provides the best specific surface and oxygenation of the organic matter, but as a synthetic biology and engineering project, we care about the biosafety and efficiency of the system, so there are some different patterns we have to think about. So our media is not only about enabling the reaction, but it is also about encapsulating the modified agent.

We started searching for polymer fibers for an electrospinning approach, but we found experimental complications, such as sensibility of the equipment, relatively high costs and a considerable bacterial death rate when these organisms are subjected to the process (Bhardwaj N. 2010, Liu Y. 2009, Patel S. 2019). To get around these problems, another strategy was devised: alginate beads.

Among polymers used for encapsulation of bacteria, one of the most common is alginate. Alginate is a naturally occurring binary linear heteropolymer that contains 1,4-linked β-D-mannuronic and α-L-guluronic acid residues. Its immobilization procedure can be carried out in a single-step process under very mild conditions and therefore is capable of forming a very versatile matrix, biocompatible and non-toxic. Compared to fibers made by an electrospinning method, sodium alginate stands out by the ease of handling and its low-cost. Most cell types are suitable for immobilization by this technique, such as bacteria (e.g. Escherichia coli).

The cell suspension is mixed with a \({Na}^{+}\) alginate solution, and the mixture dripped into a solution containing multivalent cations (usually \({Ca}^{2+}\)). The droplets form gel spheres instantaneously, entrapping the cells in a three-dimensional lattice of ionically cross-linked alginate, allowing the functionality of our biological filter approach.

References

ZHANG, Y. W., PRABHU, P., & LEE, J. K. (2010). Alginate immobilization of recombinant Escherichia coli whole cells harboring l-arabinose isomerase for l-ribulose production. Bioprocess and Biosystems Engineering, 33(6), 741–748. https://doi.org/10.1007/s00449-009-0397-7

BHARDWAJ, N.; KUNDU, S. C. Electrospinning: a fascinating fiber fabrication technique. Biotechnol Adv, 28, n. 3, p. 325-347, 2010 May-Jun 2010.

LIU, Y.; RAFAILOVICH, M. H.; MALAL, R.; COHN, D. et al. Engineering of bio-hybrid materials by electrospinning polymer-microbe fibers. Proc Natl Acad Sci U S A, 106, n. 34, p. 14201-14206, Aug 2009.

PATEL, S.; PATEL, G. A Review and Analysis on Recent Advancements in Bubble Electrospinning Technology for Nanofiber Production. Recent Pat Nanotechnol, Mar 2019.