Polymer surface can be modified by chemical or physical methods. By using these routes, antimicrobial and antibiofilm surfaces can be deposited onto several polymer devices, including metals, polymers, composites, or even ceramics and glasses.
Since early 1990s, Leung et al. (1992) proposed how to reduce the bacterial adherence onto polymer. For this purpose, they used polyurethane discs that were coated with silver, and they found that the number of adhered bacteria decreased between 10- and 100-fold compared with the uncoated polyurethane discs. Rosch and Lugauer (1999) proposed silver-impregnated catheters for urological applications. Monolithic or composite copper or silver were extensively studied from this point of view. Daniel et al. (2009) used plasma-enhanced chemical vapor deposition (PE-CVD)-sputtering for depositing copper containing organo-silicon thin layer with a mean content of Cu of 38%. The as-obtained coating exhibited good antimicrobial activity.
Prosthetic tubular devices
The use of prosthetic tubular devices is associated with the treatment of many diseases, these devices being designed for short- or long-term use. These devices are intended for certain liquid flow through them and are in direct contact with specific tissues or organs. So, the interface is of great importance and usually it is desired that no deposition occurs during their use. In Fig. 7.4 the evolution of the inner surface of a catheter is presented, since the appearance of the infection until the failure of the tubular device. In the first stage the microorganisms are flowing through the tubular devices and can adhere onto the surface. The adherence to the surface is dependent
Figure 7.4 Transversal view through the catheter from the initial stage of infection to catheter failure.
on two main factors: nature and morphology of the surface. Usually, hydrophobic surfaces are antiadherent, as well as smooth surfaces. Starting from these ideas, catheters were improved by developing new materials with antiadherent properties and smooth surfaces (Lewis and Klibanov, 2005).
Once the planktonic cells are adhered onto the surface, the adherence rate of the other cells increases and biofilms are rapidly formed. During the biofilm life, new cells attach to the surface as well as cells detach from the biofilm, and via the flowing liquid can infect other tissues/organs. Usually, the planktonic cells cannot alter too much the pH of the flowing solution. The crystallization of the organic and inorganic matters (calcium oxide and oxalates; calcium phosphates; proteins; blood clots; and so on) mainly occurs after the biofilm formation (Laube et al., 2008; Tenke et al., 2006).
The antimicrobial catheters are effective in avoiding or reducing catheter-associated infections, the nosocomial urinary tract infections being extremely widespread. The catheter-associated urinary tract infection is often urease positive. In this case, the pH of the urine increases up to 8.5 or even higher and a direct consequence of this pH increase is the decrease in solubility of many naturally occurring salts from urine and their deposition onto the catheter wall. So, in reality, the failure is fast because the biofilm formation is associated with massive salt deposition, which also favors organic and inorganic matter deposition (Edinliljegren et al., 1994).
A typical layered tubular prosthetic device is presented in Fig. 7.5. The presence of the intermediate layer is not mandatory, its role being facilitating the adhesion of the active layer(s). Because these devices are intended to replace natural vessels from the body and to take over its functions, the active layer should be in contact with the fluids flowing there through, which is usually the inner layer. For certain application, two active layers can isolate the TPD in relation to the surrounding body tissue or the normally flowing fluids.