New Trends in Polymers - Progress in Organic and Physical Chemistry: Structures and Mechanisms - page 205

with an endothelium-like lining, neomedia with smooth muscle cells, collagenous,
and elastic tissue, and a layer with polynucleated macrophages surrounding istets of
PHB, capillaries and collagen tissue. Lymphocytes were rare one. It were concluded
that PHB nonwoven patches can be used as a scaffold for tissue regeneration in low
pressure systems. The regenerated vessel had structural and biochemical qualities
in common with the native pulmonary artery [56]. Biodegradable PHB patches im-
planted in atrial septal defects promoted formation of regenerated tissue that macro-
scopically and microscopically resembled native atrial septal wall. The regenerated
tissue was found to be composed of three layers: monolayer with endothelium-like
cells, a second layer with ¿ broblasts and some smooth muscle cells, collagenous tis-
sue and capillaries, and a third layer with phagocytizing cells isolating and degrad-
ing PHB. The neointima contained a complete endothelium-like layer resembling
the native endothelial cells. The patch material was encapsulated by degrading mac-
rophages. There was a strict border between the collagenous and the phagocytizing
layer. Presence of PHB seems to stimulate uniform macrophage in¿ ltration, which
was found to be important for the degradation process and the restoration of func-
tional tissue. Lymphocytic in¿ ltration as foreign body reaction, which is common
after replacement of vessel wall with commercial woven Dacron patch, was wholly
absent when PHB. It was suggested that the absorption time of PHB patches was
long enough to permit regeneration of a tissue with suf¿ cient strength to prevent
development of shunts in the atrial septal position [53]. The prevention of postop-
erative pericardial adhesions by closure of the pericardium with absorbable PHB
patch was demonstrated. The regeneration of mesothelial layer after implantation
of PHB pericardial patch was observed. The complete regeneration of mesothelium,
with morphology and biochemical activity similar to ¿ nding in native mesothelium,
may explain the reduction of postoperative pericardial adhesions after operations
with insertion of absorbable PHB patches [55]. The regeneration of normal ¿ lament
structure of restored tissues was observed by immunohistochemical methods after
PHB devices implantation [54]. The immunohistochemical demonstration of cyto-
keratine, an intermediate ¿ lament, which is constituent of epithelial and mesodermal
cells, agreed with observations on intact mesothelium. Heparan sulfate proteogly-
can, a marker of basement membrane, was also identi¿ ed [54].
The PHB patches for the gastrointestinal tract were tested using animal model. The
patches are made from PHB sutured and PHB membranes were implanted to close
experimental defects of stomach and bowel wall. The complete regeneration of tissues
of stomach and bowel wall was observed at 6 months after patch implantation without
strong inÀ ammatory response and ¿ brosis [11, 70].
Recently an application of biodegradable nerve guidance channels (conduits) for
nerve repair procedures and nerve regeneration after spinal cord injury was demon-
strated. Polymer tubular structures from PHB can be modulated for this purpose. Suc-
cessful nerve regeneration through a guidance channel was observed as early as after
1 month. Virtually all implanted conduits contained regenerated tissue cables centrally
located within the channel lumen and composed of numerous myelinated axons and
Schwann cells. The inÀ ammatory reaction had not interfered with the nerve regenera-
tion process. The progressive angiogenesis was present at the nerve ends and through