Silk

In the following section, you can get to know more about what silk really is and what features it has.

Silk is defined as protein polymers that are spun into fibers, e.g. by: silkworms, spiders and scorpions PADOL, A. R., JAYAKUMAR, K., SHRIDHAR, N. B., NARAYANA SWAMY, H. D., NARAYANA SWAMY, M. & MOHAN, K. 2011. Safety evaluation of silk protein film (a novel wound healing agent) in terms of acute dermal toxicity, acute dermal irritation and skin sensitization. Toxicol Int, 18, 17-21.. Silk is characterized by a highly repetitive primary sequence, leading to homogeneity in secondary structure (triple helices and beta-sheets), and giving important mechanical properties ALTMAN, G. H., DIAZ, F., JAKUBA, C., CALABRO, T., HORAN, R. L., CHEN, J., LU, H., RICHMOND, J. & KAPLAN, D. L. 2003. Silk-based biomaterials. Biomaterials, 24, 401-416.. Due to its chemical structure, it is highly compatible and absorbed easily by the human skin PADOL, A. R., JAYAKUMAR, K., SHRIDHAR, N. B., NARAYANA SWAMY, H. D., NARAYANA SWAMY, M. & MOHAN, K. 2011. Safety evaluation of silk protein film (a novel wound healing agent) in terms of acute dermal toxicity, acute dermal irritation and skin sensitization. Toxicol Int, 18, 17-21.. Silks differ widely in composition and structure, allowing different properties. It is made up of 25-30% sericin and 70-75% fibroin proteins. These are the wound healing agents and antioxidants of the silk PADOL, A. R., JAYAKUMAR, K., SHRIDHAR, N. B., NARAYANA SWAMY, H. D., NARAYANA SWAMY, M. & MOHAN, K. 2011. Safety evaluation of silk protein film (a novel wound healing agent) in terms of acute dermal toxicity, acute dermal irritation and skin sensitization. Toxicol Int, 18, 17-21.. The silk from Bombyx mori, a domesticated silkworm, has been used for biomedical suture material for centuries and has been much characterized. We ended up choosing silk from the spider Nephila clavipes, which is another extensively characterized silk LTMAN, G. H., DIAZ, F., JAKUBA, C., CALABRO, T., HORAN, R. L., CHEN, J., LU, H., RICHMOND, J. & KAPLAN, D. L. 2003. Silk-based biomaterials. Biomaterials, 24, 401-416.

The many properties of silk have been used in tissue engineering and regenerative medicine. It has been shown to be biocompatible, have material versatility and mechanical robustness GIL, E. S., PANILAITIS, B., BELLAS, E. & KAPLAN, D. L. 2013. Functionalized silk biomaterials for wound healing. Adv Healthc Mater, 2, 206-17. It has also been suggested that spider silk has bactericidal properties WENDT, H., HILLMER, A., REIMERS, K., KUHBIER, J. W., SCHAFER-NOLTE, F., ALLMELING, C., KASPER, C. & VOGT, P. M. 2011. Artificial skin--culturing of different skin cell lines for generating an artificial skin substitute on cross-weaved spider silk fibres. PLoS One, 6, e21833..

Spider silk has not been used as much as cocoon silk for commercialization due to the restrained production. It has always been more complicated to produce spider silk compared to harvesting it from cocoons. N. clavipes' silk line is characterized by polyalanine and glycine-glycine-X regions, where X is often tyrosine, glutamine or leucine. This gives the dragline toughness, stiffness, strength and extensibility. It is noticeable that this silk line can supercontract. This feature is though lost when embedded in a material ALTMAN, G. H., DIAZ, F., JAKUBA, C., CALABRO, T., HORAN, R. L., CHEN, J., LU, H., RICHMOND, J. & KAPLAN, D. L. 2003. Silk-based biomaterials. Biomaterials, 24, 401-416..

Silk is stable in the environment due to the extensive hydrogen bonding, the hydrophobic nature of much of the protein, and the crystallinity ALTMAN, G. H., DIAZ, F., JAKUBA, C., CALABRO, T., HORAN, R. L., CHEN, J., LU, H., RICHMOND, J. & KAPLAN, D. L. 2003. Silk-based biomaterials. Biomaterials, 24, 401-416.. It is also degradable, as a protein, it is susceptible to proteolytic degradation and can over longer time be absorbed in vivo ALTMAN, G. H., DIAZ, F., JAKUBA, C., CALABRO, T., HORAN, R. L., CHEN, J., LU, H., RICHMOND, J. & KAPLAN, D. L. 2003. Silk-based biomaterials. Biomaterials, 24, 401-416..

Several biomedical products have already been made due to silks’ many properties, e.g. wound dressings. There has likewise been conducted a study, which investigates the dermal toxicity, dermal irritation and sensitization potential. It was shown that the silk products would not cause any of the named consequences PADOL, A. R., JAYAKUMAR, K., SHRIDHAR, N. B., NARAYANA SWAMY, H. D., NARAYANA SWAMY, M. & MOHAN, K. 2011. Safety evaluation of silk protein film (a novel wound healing agent) in terms of acute dermal toxicity, acute dermal irritation and skin sensitization. Toxicol Int, 18, 17-21.. Recombinant silk will therefore be a good material for our Bacto-Aid.