Biomimetic modification of poly-L-lysine and electrodeposition of nanocomposite coatings for orthopaedic applications

Abstract

For the first time, a biomimetic method has been developed for the chemical modification of poly-l-lysine (PLL) with catechol in order to improve polymer adhesion to inorganic particles and surfaces. The method is based on the Schiff base reaction of amino groups of PLL monomers and aldehyde groups of 3,4-dihydroxybenzylaldehyde (DHBA) molecules. It was found that adherent PLL-DHBA films can be prepared by cathodic electrophoretic deposition (EPD). Nanocomposite coating with dual micro-nano topography has been developed for orthopaedic and dental coating applications. The catechol groups of PLL-DHBA facilitated its adsorption on hydroxyapatite (HA) and rutile (TiO2) and allowed the fabrication of stable suspensions for EPD. PLL-DHBA was used as both a charging and film-forming agent for EPD of HA and TiO2. Moreover, the methods allowed co-deposition of HA and TiO2 and fabrication of composite films, which allows the benefits of both bioceramics to be combined. In addition to having dual scale topography, the films exhibited both sub-micron surface roughness and hydrophilic behaviour, which both have been found to promote osteoblast adhesion and proliferation. in vitro studies revealed that the fabricated coatings showed increased cell metabolism and alkaline phosphatase activity over the period studied, with PLL-DHBA-TiO2 showing the greatest increase. This work paves the way for both the development of the next generation of biomedical implant coatings, with improved osseointegration and lifespan, as well as one-step low-temperature processing.