Novel silver containing antimicrobial coatings for implant materials. new applications of Ag(I) coordination networks

Modern medicine continuously develops new artificial short-term or permanent devices to assist in the performance of physiological functions. Implantation of medical devices represents one of the most important risk factors of all nosocomial infections, when implant materials become infected due to bacterial adhesion and subsequent formation of bio films. The latter are impossible to treat with antibiotics and represent a dramatic complication for the patient, leading to implant replacement, in the worst case to death. Therefore, prevention of bacterial adhesion and bio film formation is important.
We have developed new coordination compounds with silver ions and specially designed ligands. This way, one can tune the structure, the light stability and, most importantly for the biological application, the solubility. With an appropriate chemical linker, one is able to connect such compounds to metallic surfaces forming a nano-structured coating. We analyzed the coated surfaces and present the nano-structured surface topography. The chemical composition of the coating on Au(111) as a model surface, the antimicrobial properties of the coated implants, and, on a molecular level, the interaction of silver ions with peptide sequences and subsequent silver nanoparticle formation are presented in this thesis.
We have investigated this coating using several methods, namely powder X-ray, XPS, AFM, SEM, micro- and nano-calorimetry and antimicrobial studies with different bacteria. XPS and powder x-ray analyses have shown that the deposited compound is [Ag(L)NO3], described previously. The AFM revealed peak-like nano-structures and the SEM measurements the bigger sized crystalline structures 0.5-1000 µm. AAS method have been used to determine the silver loading on the surface in function the crystallisation time and the concentration. The results show that we are able to control the silver loading on the surface choosing the appropriate treating conditions. Our silver coordination compound was shown to form regular material coatings on different metal substrates.
Several anti-microbial tests were carried out. Flow-chamber experiments with S. sanguinis have been done to test the coating on dental implant material. The vitality of adhered bacteria was evaluated by applying a dual fluorescent staining, with the result that 99% of bacteria were killed. Plating of coated samples (Au(111) and titanium and steel restorative implant materials) in agar in presence of S. epidermis or S. aureus for 24h showed the formation of large inhibition zones of the order of >2 cm. In vivo microbiological assays show a high efficiency of the silver coating against S. epidermis. The antimicrobial properties were confirmed by microcalorimetry, measuring the bacterial cell multiplication heat. Furthermore the antimicrobial properties are proven for dental as well as general implant materials.
To study the working mechanism of the silver inside of the bacteria and determining the silver affinity of some amino acids and short amino acid sequences, on-bead screening of split-and-mix libraries have been used. It is a powerful tool for the identification of peptides that attach the silver and induce the formation of silver nanoparticles (AgNPs) when using either light or a chemical reducing agent. It allowed identifying simple tripeptides that would have been difficult to predict rationally. In addition, the study revealed peptide motives that generate AgNPs with distinctly different sizes. Some microbiological assays have been done using isothermal microcalorimetry method to test the antimicrobial effect of the generated AgNPs.
We have thus developed a new coating which is able to stop bacterial adhesion and multiplication, while being biocompatible with fibroblasts.