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== Plasma modification of biomaterials ==
Plasma modification is one way to alter the surface of biomaterials to enhance their properties. During plasma modification techniques, the surface is subjected to high levels of excited gases that alter the surface of the material. Plasma's are generally generated with a [[Radio frequency|radio frequency (RF)]] field. Additional methods include applying a large (~1KV) DC voltage across electrodes engulfed in a gas. The plasma is then used to expose the biomaterial surface, which can break or form chemical bonds. This is the result of physical collisions or chemical reactions of the excited gas molecules with the surface. This changes the surface chemistry and therefore surface energy of the material which affects the adhesion, biocompatibility, chemical inertness, lubricity, and sterilization of the material. The table below shows several biomaterial applications of plasma treatments.<ref>{{cite web |last=Loh |first=Ih-Houng |work=AST Technical Journal |title=Plasma Surface Modification In Biomedical Applications |url=http://www.astp.com/PDFs/PSBiomed.pdf |deadurl=yes |archiveurl=https://web.archive.org/web/20080514091530/http://www.astp.com/PDFs/PSBiomed.pdf |archivedate=2008-05-14 |df= }}</ref>
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=== Adhesion of Coatings ===
In general, the lower the surface tension of a liquid coating, the easier it will be to form a satisfactory wet film from it. The difference between the surface tension of a coating and the surface energy of a solid substrate to which a coating is applied affects how the liquid coating flows out over the substrate. It also affects the strength of the adhesive bond between the substrate and the dry film. If for instance, the surface tension of the coating is higher than the surface tension of the substrate, then the coating will not spread out and form a film. As the surface tension of the substrate is increased, it will reach a point to where the coating will successfully wet the substrate but have poor adhesion. Continuous increase in the coating surface tension will result in better wetting in film formation and better dry film adhesion.<ref name=SurfaceTension>{{cite web |url= http://www.pra-world.com/technical_services/laboratory/testing/surface-tension |title= Surface Tension, Surface Energy, Contact Angle and Adhesion |year= 2013 |work= Paint Research Association |accessdate= 22 May 2013 |deadurl= yes |archiveurl= https://web.archive.org/web/20130109105050/http://www.pra-world.com/technical_services/laboratory/testing/surface-tension |archivedate= 9 January 2013 |df= }}</ref>
More specifically whether a liquid coating will spread across a solid substrate can be determined from the surface energies of the involved materials by using the following equation:
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