Natural Coatings on Titanium Surfaces to Improve Their Biological Response

Biomolecules and extracts from natural products are gaining increasing interest due totheir beneficial properties for human health, low toxicity, environmental compatibility andsustainability. In this work, keratin, chitosan and peppermint essential oil have been used for thepreparation of coatings on titanium substrates for biomedical implants/devices. All these coatingswere obtained from local natural products/byproducts: keratin from discarded wool, chitosan fromshrimp shells and peppermint essential oils from a local production. The above cited moleculeswere selected for their ability to stimulate soft tissue adhesion (keratin), anti-inflammatory activity(chitosan) and antibacterial activity (keratin after metal ion doping, chitosan and mint oil). Thecoatings were characterized by means of SEM-EDS, FTIR, zeta potential, wettability, tape andscratch tests, and cell and bacteria cultures. The coatings were successfully obtained for all theconsidered natural substances with good adhesion to the titanium substrates. All the coatings arechemically stable in water and the continuous coatings are mechanically resistant and protectivefor the metallic substrates. The keratin coatings are hydrophilic while the mint oil and chitosancoatings are hydrophobic; nanofibers, instead of continuous coatings, behave as morehydrophobic. At the physiological pH, the keratin and mint oil coatings are negatively chargedwhen in contact with an aqueous environment, while the chitosan ones are positively charged. Theoriented keratin fibers are able to drive fibroblast alignment. The Ag-doped keratin fibers and mintcoating show antibacterial properties.