Schematic and micrographs of antibacterial spider-silk 6mer-HNP1 coating on commercial silk sutures.
Schematic and micrographs of antibacterial spider-silk 6mer-HNP1 coating on commercial silk sutures.

Over 4 million EU patients acquire infections while in hospital, with over a fifth arising from surgery. Coating silk sutures with proteins derived from spider silk could alleviate the problem of post-surgical infection, according to a team of scientists from Portugal and the USA [Franco et al., Acta Biomaterialia (2019),].

“Silk sutures are often used for the closure of soft tissue and can be employed to enhance healing in tendon/ligament repairs,” explains first author of the study Albina R. Franco from 3B’s Research Group, University of Minho. “However, sutures can harbor bacteria, leading to the formation of biofilms and related infections, which can be problematic to treat. Furthermore, the exponential increase in microbes resistant to antibiotics or antibacterial agents has pushed research to look for alternative substances with antimicrobial properties.”

Together with David L. Kaplan at Tufts University and Rui L. Reis at 3B’s Research Group, the team has developed drug-free antimicrobial coatings for silk sutures based on spider silk. This natural material boasts a range of unique mechanical properties, as well as biocompatibility, limited immunogenicity, and controllable degradability. More importantly, spider silk is amenable to recombinant DNA technology, which allows the introduction of antimicrobial peptides (AMP). The researchers used this approach to bioengineer human-derived antimicrobial HNP1 peptides into the spider silk protein 6mer to create an antibacterial drug-free coating for commercial silk sutures.

Silk sutures were simply dip-coated with the bioengineered 6mer-HNP1 spider silk coating and tested against Gram-positive and Gram-negative bacteria, fungi, viruses, and multi-resistant organisms such as MRSA. The coated sutures show a marked improvement in resistance to MRSA and Escherichia coli, showing similar behavior to commercial non-silk antibacterial sutures. The 6mer-HNP1 coating appears to reduce the ability of bacteria to stick to the surface of silk sutures and form biofilms. Moreover, the coated sutures retain their mechanical properties and biocompatibility, with no adverse effect on cells or hemolytic activity, which is a common complication with materials in contact with blood.

The researchers’ findings indicate that spider silk proteins functionalized with antimicrobial peptides can be used to create an effective coating for commercial silk sutures to reduce, prevent, or eliminate bacterial adhesion and biofilm formation, which lead to infection.

“The main advantage of this novel coating is that it can be used as a substitute for antimicrobial agents like silver, triclosan, and others, avoiding systemic exposure to antibiotics,” says Franco. “One of the beauties of silk-based materials is that they can be introduced into different medical devices through various processes, rendering them useful for other medical applications such as orthopedics,” she adds. 

The 3B’s Research Group is now undertaking in vivo studies of the coated silk sutures to uncover their immunological effect.