Chemistry Reference
In-Depth Information
Thus, at physiological temperature the crystallinity, measured during
degradation by XRD technique has an slightly extreme character. On the
initial stage of PHB degradation the crystalline/amorphous ratio is in-
creased owing to additional crystallization through involvement of poly-
mer molecules situated in amorphous fields. In contrast, at 70 °C after
reaching the critical MW values (see Section 2), the following desorption
of water-soluble intermediates occurs. On the following stage, as the deg-
radation is developed till film disintegration, the crystallinity drop must
takes place as result of crystallite disruption.
5.3.4 THE ANALYSIS OF FILM SURFACES FOR PHB BY AFM
TECHNIQUE
Morphology and surface roughness of PHB film exposed to corrosive me-
dium (phosphate buffer) have been studied by the AFM technique. This
experiment is important for surface characterization because the state of
implant surface determines not only mechanism of degradation but the
protein adsorption and cell adhesion, which are responsible for polymer
biocompatibility [30]. As the standard sample we have used the PHB film
with relatively low MW=170 kDa. The film casting procedure may lead
to distinction in morphology between two surfaces when the one plane of
the polymer film was adjacent with glass plate and the other one was ex-
posed to air. Really, as it is shown in Fig. 5.4 the surface exposed to air has
a roughness formed by a plenty of pores with the length of 500-700 nm.
The opposite side of the film contacted with glass (Fig.5.4b) is character-
ized by minor texture and by the pores with the less length as small as 100
nm. At higher magnification (here not presented) in certain localities it can
see the stacks of polymer crystallites with width about 100 nm and length
500-800 nm Fig. 5.4.
