Foundations of plasma surface functionalisation of polymers for industrial and biological applications

Abstract Polymer materials are widely employed in many fields due to the ease with which they can be formed into complex shapes, their versatile mechanical properties, light weight, and low cost. However, many applications can be hindered by the chemical compatibility of the polymer surface, which is generally hydrophobic and bonds poorly to other media such as paints, glues, metals and biological samples. While polymer surfaces can be treated by wet chemical processes, the aggressive reagents employed are detrimental to the environment, limiting the range of modifications that can be achieved in an industrial context . Plasma functionalisation is an attractive alternative, offering great versatility in the processed surface characteristics, and often using only environmentally benign rare gases, oxygen and nitrogen, as well as organic precursors. Since the modified surface is only a few monolayers thick, the processes are extremely rapid and low in cost. The first industrial process to be developed was plasma oxidation, increasing the surface energy of the polymer to allow adhesion of paint, glue and metal to the component. This polymer surface functionalisation can be achieved with both low-pressure plasmas and with atmospheric pressure discharges. Subsequently many other processes have emerged, allowing other functional groups to be grafted, including amines, hydroxyl and carboxylic acid groups. Plasma polymerisation, starting from gaseous monomers, allows a whole new family of surface chemistries to be created. These processes have many exciting applications in the biomedical field due to the control they give on biocompatibility and selective interaction with living cells. This article will present the fundamentals of plasma interactions with polymers, the plasma devices employed (both at low-pressure and at atmospheric pressure), their advantages and drawbacks, and a range of current and future applications.