Biomaterials Tutorial

Biofilms

Misty Noble
University of Washington Engineered Biomaterials                                 

A certain fraction of all medical devices and implants used each year fail due to device-centered or biofilm-related infections. There are hundreds of thousands of infection problems with medical devices each year. These infections are believed to be caused by the introduction of foreign organisms, primarily bacteria, during the device insertion or implantation into the body, or from the attachment of blood-borne organisms onto the surface of the newly-inserted device.

Once on the surface, these organisms secrete a slimy or glue-like substance (polysaccharides) that allows them to securely anchor themselves on the surface and form connections with other organisms. After attachment, these organisms divide and expand into multi-cellular communities or microcolonies and create a protective barrier commonly known as a biofilm. 

Figure 1. Biofilm formation. Reproduced by permission of Montana State University Center for Biofilm Engineering.

Biofilms may be composed of a single or multiple species of bacteria, as well as fungi, algae, protozoa, debris, and corrosion products. Depending on the type of device, infection rates can reach up to 5-10 % in dental implants, 10-30 % in bladder cathethers, and 25-50 % in heart-assist devices. Once established, the films are very difficult to get rid of−it will take 1000 times more antibiotic dose to eliminate bacteria attached to a surface in a biofilm compared to normal free-floating bacteria.

Aside from biomedical occurrences, biofilms can also develop in other aqueous locations.  The slime that accumulates on the inner walls of sink drains leading to clogs is a biofilm. Corrosive films in oil pipelines and plaque that can cause cavities on teeth are other examples. A more positive example of biofilms includes using their degradative nature in treatment methods for biohazardous wastes.

There are many biomaterials approaches to reducing biofilm formation and device-centered infection. Within the UWEB program, we have successfully explored non-fouling surfaces that resist bacterial attachment, surfaces that release potent antibiotics at a slow but efficacious rate and antibiotic release from biomaterials controlled by focused ultrasound stimulation.

For more information:

Montana State University Center for Biofilm Engineering (an NSF ERC)

http://www.erc.montana.edu/CBEssentials-SW/bf-basics-99/default.htm

References:

Burrows LL, Khoury AE. Infection of medical devices.  In: Encyclopedia of biomaterials and biomedical engineering. New York: Marcel Dekker Inc; 2001. p. 839-848.

Costerton B, Cook G, Shirtliff M, Stoodley P, Pasmore M.  Biofilms, biomaterials, and device-related infections. In: Ratner BD, Hoffman AS, Schoen FJ, Lemons JE, editors. Biomaterials science: An introducion to materials in medicine, 2nd edition.  San Francisco, CA: Elsevier Academic Press; 2004. p. 345-354.

Donlan RM. Biofilms and device-associated infections. Emerging Infect Dis 2001; 7(2): 277-281.