The present invention relates to a process of treating an implant, comprising a step of treating the surface of the implant with at least one phosphonic acid compound or a pharmaceutically acceptable salt, ester or amide thereof under sonication at a temperature of about 50° C. to about 90° C. This process is highly advantageous in that it allows the formation of a monolayer of the phosphonic acid compound on the implant surface, having a particularly dense surface coverage which, in turn, results in an improved implant biocompatibility and improved osseointegration. The invention further relates to a surface-treated implant obtainable by this process and, in particular, it provides an implant having a surface made of a metal, a metal alloy or a ceramic, wherein a phosphonic acid compound or a pharmaceutically acceptable salt, ester or amide thereof is bound to the surface of the implant and forms a monolayer having an implant surface coverage, in terms of the ratio of the phosphorus content to the metal content as determined by X-ray photoelectron spectroscopy (XPS), of at least 70% of a reference maximum surface coverage.
