Silver exhibits good anti-bacterial properties and in recent years has been used on medical devices ranging from wound dressings to catheters. Silver coatings can be deposited by magnetron sputtering however the associated substrate heating (200- 300°C) causes considerable difficulty when coating medical devices many of which contain thermally sensitive polymer components. This paper reports on a magnetron deposited silver coating treatment where the maximum substrate temperature obtained during deposition was 70°C.

This low temperature deposition was achieved by combining magnetron sputtering with a neutral atom beam (Saddle Field) plasma source. The neutral atom beam was used both to activate the polymer surface prior to coating deposition and to enhance the silver coating adhesion by bombarding the surface during film deposition. Both sources were operated simultaneously at 10ⁿ4 mbar in argon plasma. Films and tubes of polyurethane and silicone were coated with silver thicknesses in the range 5 to 50 nm. The film thickness measurements were obtained using both glancing angle XRD and variable angle ellipsometry on glass slide substrates coated adjacent to the polymers. The silver film growth rate was 10±2 nm / minute. The adhesion of the coating was examined using pull tests, tape tests and leaching tests in water at 40°C.

The anti-bacterial performance of silver is dependent on the balance between the activity of the Agⁿ+ ions which kill bacteria and the total amount of silver released from the coating, which if too high results in cytoxicity. The bacterial adhesion and bactericidal effects of the coated polymers was assessed using Sraphylococcus epidermidis and the cytotoxicity using fibroblast cells. Up to a 3 log reduction in bacterial adhesion was achieved for coatings, which did not exhibit cytotoxicity.