New Trends in Polymers - Progress in Organic and Physical Chemistry: Structures and Mechanisms - page 197

the microstructure on the surface and in volume of sutures [18]. It was shown that PHB
nonwoven patches (made to close atrial septal defect in calves) was slowly degraded
by polynucleated macrophages, and 12 months postoperatively no PHB device was
identi¿ able but only small particles of polymer were still seen. The absorption time
of PHB patches was long enough to permit regeneration of a normal tissue [53]. The
PHB sheets progressive biodegradation was demonstrated qualitatively at 2, 6. and 12
months after implantation as weakening of the implant surface, tearing/cracking of the
implant, fragmentation and a decrease in the volume of polymer material [15, 37, 59].
The complete biodegradation of PHB (M w = 150-1000 kDa) thin ¿ lms (10-50 —m)
for 3-6 months was shown and degradation process was described. The process of
PHB biodegradation consists of several phases. At initial phase PHB ¿ lms was cov-
ered by ¿ brous capsule. At second phase capsulated PHB ¿ lms very slowly lost their
weight with simultaneous increase of crystallinity and decrease of M w and mechani-
cal properties of PHB. At third phase PHB ¿ lms were rapidly disintegrated and then
completely degraded. At forth phase empty ¿ brous capsule resolved (Figure 5) [24,
25]. Interesting data were obtained for biodegradation in vivo of PHB microspheres
(0.5-0.8 —m in diameter). It was demonstrated indirectly that PHB loss about 8% of
weight of microspheres accumulated in liver after 2 month of intravenous injection.
It was demonstrated also a presence of several types PHB degrading enzymes in the
animal tissues extracts [19].
FIGURE 5 Biodegradation of PHB films in vivo . Connective tissue capsule with PHB thin
films (outlined with broken line) 2 weeks (98% residual weight of the film) (left photograph)
and 3 months (0% residual weight of the film) (left photograph) after subcutaneous implantation
[24, 25].