at the surface down into the material approximately 1 3 micrometers the oxidized surface remains stable at ambient conditions for at least 3 months more particularly about 6 months polypropylene materials with a high degree of crystallinity can provide stability for up to 1 year the phrase u201c stable u201d is intended to mean that the oxidized polypropylene mesh materials do not appreciably change in physical characteristics over a given period of time that is the ability to promote tissue in growth is not effected if the material is left at ambient conditions for a period of time prior to use e g for at least about 3 month more particularly about 4 to about 6 months the surface treatment to the polypropylene mesh does not lose its ability to promote tissue in growth over such a period of time and as such the physical make up of the oxidized polypropylene mesh does not appreciably change to an extent that tissue in growth would not be improved over a native untreated sample of polypropylene mesh generally the process noted above involve a gas cloud that has been excited by the application of energy a cloud of fast moving particles is produced including electrons ions atoms free radicals molecules and other metastable species this energetic cloud is capable of reacting with the polypropylene surface in a variety of ways specific examples of these processes include corona discharge.