Polymer-coated silicone rubber surfaces

Antifouling activity is one of the most important properties that catheters should ideally exhibit in order to prevent catheter-associated infections. To quantitatively investigate bacterial fouling on polymer-coated silicone rubber surfaces, the number of viable bacterial cells on the surfaces was measured [102]. After 1 day of incubation, there was a high number of viable Staphylococcus aureus and Escherichia coli cells on both pristine and thiol-functionalised surfaces (Staphylococcus aureus 8.8 and 8.6 log colony forming units (CFU), respectively Escherichia coli 8.5 and 8.2 log CFU, respectively) (Figure 6.1). 

Chemical alternation of the surface layer and deposition of a new layer on top of the silicone mbber can be achieved by physical techniques. For the inert surface of silicone rubber, the former requires the generation of high-energy species, such as radicals, ions, or molecules in excited electronic states. In the latter case, coatings of atoms or atomic clusters are deposited on polymer surfaces using technique such as plasma (sputtering and plasma polymerization) or energy-induced sublimation, like thermal or electron beam-induced evaporation. 

The top-coats are responsible for the durability and resistance to water and chemical impacts from the environment. Mainly acrylic and fiuori-nated polymers are used for top-coats on various base coats (PVC, PUR, PTFE, silicone rubber, etc.) to enhance resistance to soiling and ageing. Certain additives for UV protection can be added. Due to its self-cleaning non-adhesive surface the top-coat is often hard and brittle. On PVC coatings the top-coat gives not only protection against environmental infiuences but also a barrier against emission of plasticizer out of the PVC. 

Actual potentiometric biosensors are commonly designed on the basis of ISFETs, i.e. they are ENFETs. Inclusion in hydrogels is no longer done. Covalent bonding, preferably at carbon surfaces, is preferred. Alternatively, embedding in polymer layers is performed, today preferably in polymers generated elec-trochemically. Also widespread are P VC coatings with specific softeners (as solvents for active substances) as well as layers of silicon rubber and polyurethane. 

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