The use of silver-doped keratin nanofibers to prevent infection and promote soft tissue healing onto titanium dental implants

Introduction: in the oral cavity, peri-implantitis is the main condition associated to dental implant failure due to the infection that causes inflammation of the surrounding connective tissue. In this scenario, fibroblasts have a key role in promoting the inflammatory process, counteracting the release of metalloproteinases by bacteria and produce an effective gum sealing [1-2]. Accordingly, it is of great interest to develop innovative surface treatments effective in counteracting bacterial infection and promoting fibroblasts repopulation. Aim: an innovative approach based on keratin nanofibers enriched with silver ions is here presented as strategy to improve the surface of titanium (Ti) dental implants in contact with soft tissues. Keratin nanofibers are aimed to guide and promote fibroblasts repopulation while silver is added to introduce antibacterial properties and prevent infection. Materials and Methods: keratin was extracted from wool by sulfitolysis and used to achieve a nanofiber layer onto mirror polished Ti surfaces by means of electrospinning [1]. Then, keratin-coated surfaces were doped with silver ions (Ag) using different concentrations of silver nitrate as a precursor. Specimens were characterized by means of FESEM and XPS, while Ag release in cells/bacteria medium was evaluated by ICP. Antibacterial properties were tested against a multidrug-resistant Staphylococcus aureus biofilm while cytocompatibility and cells spread orientation were evaluated on human primary gingival fibroblasts (HGFs) by means of metabolic assay (XTT) and morphological observation (FESEM and fluorescence staining) [2]. Results and Discussion: FESEM and XPS analysis confirmed that keratin nanofibers were randomly and homogeneously distributed onto Ti surface as well as Ag was successfully coated to the fibers. ICP results revealed that Ag was continuously released into the culture media in a range of 1-10 mg/L within a 72 hrs immersion. The viability of S. aureus biofilm cultivated onto specimens' surface was reduced of >70% in comparison with mirror polished controls (p<0.05) after 72 hrs of direct contact. Finally, HGFs viability was not affected by the presence of Ag and keratin (p>0.05 vs mirror controls) whereas cytoskeleton spread showed that cells adhesion and alignment were strongly influenced by nanofibers topography. Moreover, cells were able to deposit matrix within keratin nanofibers as a large amount of collagen was detected by fluorescence observation. Conclusions: the here proposed strategy appears to be very promising to improve dental implants surfaces, thus meeting the needed requirements to preserve their integrity.