Drug Delivery from PCL/Chitosan Multilayer Coatings for Metallic Implants.

Implant-related infections, mainly caused by Staphylococcus aureus, are a major health concern. Treatment is challenging due to multi-resistant strains and the ability of S. aureus to adhere and form biofilms on bone and implant surfaces. The present work involved the preparation and evaluation of a novel dual polymeric film coating on stainless steel. Chitosan and polycaprolactone (PCL) multilayers, loaded with poly(methyl methacrylate) (PMMA) microspheres encapsulating vancomycin or daptomycin, produced by the dip-coating technique, allowed local antibiotic-controlled delivery for the treatment of implant-related infections. Enhanced adhesion of the film to the metal substrate surface was achieved by mechanical abrasion of its surface. Studies have shown that for both drugs the release occurs by diffusion, but the release profile depends on the type of drug (daptomycin or vancomycin), the pH of the solution, and whether the drug is freestanding (directly incorporated into the films) or encapsulated in PMMA microspheres. Daptomycin freestanding films reached 90% release after 1 day at pH 7.4 and 4 days at pH 5.5. In comparison, films with daptomycin encapsulated microspheres reached 90% release after 2 h at pH 5.5 and 2 days at pH 7.4. Vancomycin encapsulated and freestanding films showed a similar behavior reaching 90% release after 20 h of release at pH 5.5 and 2 and 3 days, respectively, at pH 7.4. Furthermore, daptomycin-loaded films showed activity (assessed by agar diffusion assays) against sensitive (ATCC 25923) and clinically isolated (MRSA) S. aureus strains.

Cellulose acetate fibres loaded with daptomycin for metal implant coatings.

Multifunctional polymeric coatings containing drug delivery vehicles can play a key role in preventing/reducing biofilm formation on implant surfaces. Their requirements are biocompatibility, good adhesion, and controllable drug release. Although cellulose acetate (CA) films and membranes are widely studied for scaffolding, their applications as a protective coating and drug delivery vehicle for metal implants are scarce. The reason is that adhesion to stainless steel (SS) substrates is non-trivial. Grinding SS substrates enhances the adhesion of dip-coated CA films while the adhesion of electrospun CA membranes is improved by an electrosprayed chitosan intermediate layer. PMMA microcapsules containing daptomycin have been successfully incorporated into CA films and fibres. The released drug concentration of 3 × 10-3 mg/mL after 120 min was confirmed from the peak luminescence intensity under UV radiation of simulated body fluid (SBF) after immersion of the fibres.

CuI p-type thin films for highly transparent thermoelectric p-n modules.

Developments in thermoelectric (TE) transparent p-type materials are scarce and do not follow the trend of the corresponding n-type materials - a limitation of the current transparent thermoelectric devices. P-type thermoelectric thin films of CuI have been developed by three different methods in order to maximise optical transparency (>70% in the visible range), electrical (σ = 1.1 × 104 Sm-1) and thermoelectric properties (ZT = 0.22 at 300 K). These have been applied in the first planar fully transparent p-n type TE modules where gallium-doped zinc oxide (GZO) thin films were used as the n-type element and indium thin oxide (ITO) thin films as electrodes. A thorough study of power output in single elements and p-n modules electrically connected in series and thermally connected in parallel is inclosed. This configuration allows for a whole range of highly transparent thermoelectric applications.