Bacterial biofilms often can cause chronic infections because they show increased tolerance to antibiotics and disinfectant chemicals. To this end, there is an urgent need for innovative biomaterials with a broad application spectrum capable of providing the desired antimicrobial properties to prevent the emergence of these deadly pathogens. Over the last years, research has focused on developing microbe-killing or repellant agents to address this threat. In another context, silk-based materials have drawn interest as potential candidates for use in the biomedical field owing to their excellent mechanical strength, biocompatibility and nonimmunogenicity properties. Today, most research on silk-based materials seek to reveal and understand the fundamental mechanisms behind their biomedical properties. All the available silks exhibit slightly different mechanisms and properties that can be attributed to many years of evolution that have led to different physio-chemical properties adapted to the specific application in accordance with the lifestyle of the respective species. The wide range of potential applications of such natural materials has fueled the production of numerous strategies for producing sufficient amounts of silk proteins.
Herein, Mr. David Sonnleitner, Mr. Christoph Sommer, Professor Thomas Scheibel and Professor Gregor Lang from the University of Bayreuth provided an expert opinion review of the research progress on inhibiting the formation of biofilm through applying silk-based materials. The authors described the biofilm formation process and the most commonly used methods to prevent it. These methods were divided into three: effects on surface topography, integrated additive and material modification. Different silk properties were detailed, and conclusions were drawn on the crucial parameters for the effective design of silk-based materials. The work is currently published in the journal, Materials Science and Engineering C. It is noteworthy to mention that the research group at University of Bayreuth has published extensively in engineering new silk-based materials.
Although the review mainly focused on spider silks and silkworm silks that have dominated scientific interests, the results demonstrated the existing diversity emanating from the matrix of the silk origin, their production, processing, and additives. This required the use of different organisms and testing methods. Antimicrobial silk properties were found to be sensitive to external factors like sampling design and testing methods. It is speculated that microbe adhesion can be inhibited by homogeneously distributed hydrophobic patches formed by the assembly of beta-sheet crystals because they do not provide adequate anchoring sites for microbes. However, the patches must be < 10 nm like in the case with spider silks. On the other hand, the crystalline size of Bombyx mori fibroin is sufficiently big enough (~ 14nm) to be applied for microbes as adhesion sites. The hypothesis of a nano-structural mechanism was strengthened using biotechnologically produced spider silk proteins. It was shown that slight changes in the amino acid sequence of silk proteins can cause loss of anti-fouling properties as attributed to nano-structural changes in the distribution of crystalline patches.
In summary, the research team critically reviewed the recent state-of-the-art developments in artificial and natural silk-based materials with antimicrobial properties. Overall, the authors reported that not all silks are the same, the obtained results are based on the measured parameters and research design and the function of the silk is dependent on its structure. Furthermore, it was worth noting that the most currently valid theory is associated with the attributions of silk properties to well-defined nanocrystalline structures. However, more research is necessary to validate it. In a statement to Advances in Engineering, Professor Gregor Lang explained their study pave the way for the design of new polymeric materials with remarkable and improved antimicrobial properties. Progress in this field is of high significance to create sustainable material innovations contributing to the required reduction of conventional antibiotic overuse in the health care sector.
Sonnleitner, D., Sommer, C., Scheibel, T., & Lang, G. (2021). Approaches to inhibit biofilm formation applying natural and artificial silk-based materials. Materials Science and Engineering: C, 131, 112458.