Chemical and Physical Properties of Polymeric Contact Surfaces

Chemical and Physical Properties of Polymeric Contact Surfaces 

In order to determine the composition and structure of a biomaterial surface different methods which provide varying degrees of information are commonly used (Fig. 6). Surface-sensitive infrared spectroscopy suppHes the characteristic absorption bands of functional groups with an informational depth of 0.1-10 pm by measurement in attenuated total reflectance (IR-ATR). In the case of samples with rough surfaces photoacoustic spectroscopy (PAS), which allows an informational depth of approximately 20 pm, can be used [72]. The achieved informational depths are usually larger than the thickness of the modified interface, so that the spectra include information on the bulk composition as well. As a consequence, surface-sensitive infrared spectroscopy is often not sensitive enough for the characterization of the modified surfaces. 

X-ray photoelectron spectroscopy (XPS) is a more surface-sensitive analytical method which suppHes information not only about the type and amount of elements present but also about their oxidation state and chemical surroundings. Applying this method informational depths of approximately 10 nm can be achieved, which means about 50 atomic layers. In secondary ion mass spectroscopy (SIMS) primary ions interact with the polymer surface and the mass spectra of the formed secondary ions are obtained which give information about the chemical composition of the outermost atomic layers (approximately 1 nm in thickness). 

Electron spin resonance (ESR) spectroscopy is not applied as a surface-sensitive method. Based on its sensitivity, however, it is possible to detect covalently bound molecules at the polymer surface if these molecules are labeled with a spin marker such as 4-amino-TEMPO. The application of atomic force microscopy (AFM) in comparison to scanning electron microscopy (SEM) delivers information about surface properties as far as molecular dimensions. Another advantage of AFM compared with SEM is that the sample is investigated in the original state (no sputtering) [73]. The full characterization of the surface of a 

Several methods are available to determine the physical parameters of polymer surfaces. Biomaterials penetrate liquids like blood or water present in soft tissue. It is known that the free surface energy at the biomaterial/water interface is the driving force for the reorientation processes of the polar groups of the uppermost molecular layers of the polymer surface towards the aqueous phase. The chemical composition of the surface of the biomaterial is different depending on its contact with an aqueous medium or with air. Hydrophilic domains of polymer systems like those found in block copolymers, for example, are mostly located at the aqueous interface, while the hydrophobic ones tend to remain at the air interface. The investigation of surface wettability by means of contact angle determination and the measurement of the streaming potential ( -potential) is of special interest in the characterization of the polymer surface. 

---