Abstract: A medical device having body contacting surfaces provided with a film of amorphous calcium phosphate having a thickness of 1 nm to 10000 nm and an average dissolution rate calculated as the time taken to remove 95% of the film of at least 1 nm h?1 as determined in accordance with ASTM Standard P1926-03. The characteristics of the film are such that the film is relatively rapidly dissolved from the surface by body fluids. This dissolution of the surface film of amorphous calcium phosphate is sufficiently fast to prevent the attachment of bacteria, thus preventing them forming a biofilm and keeping the cells in a planktonic (non-biofilm) state where they are more vulnerable to the body's defences. The invention is particularly applicable to implants (e.g. orthopaedic implants such as prosthetic hips) but may also be applied to “non-implanted” devices such as surgical instruments.