Biomedical Engineering Reference
In-Depth Information
A slow polymer degradation has also been suggested from a long-term
implantation study of P3HB-3HV (7%, 14%, 22% 3HV) i.m. in sheep. The
copolymer containing 22% 3HV appeared to be more sensitive to the in vivo
degradation than the copolymers having a lower 3HV content [100].
P3HB samples implanted s.c. and i.p. in rats showed a fast initial degra-
dation in the first 4 weeks. The molecular weight had halved 1 year after
implantation [201]. P3HB-7%3HV showed a decrease in the molecular weight
to about 40% of the initial value 15 months after implantation s.c. into rab-
bits [184]. In a 4-week implantation study of P3HB-12.6%3HV films s.c. in
rats it was shown that the polymer degradation can be accelerated by incor-
poration of a basic drug [182].
No mass loss of P3HB fibers was observed after s.c. implantation in rats for
180 days [202]. A slow resorption of P3HB fibers has also been reported after
i.m and i.p. implantation in rats. The maximum breaking force was between
94%(i.m.)and81% (i.p.) of the initial values 12 weeks postoperatively [203].
Nonwoven P3HB patches were implanted for closure of an atrial sep-
tal defect [144], as transannular patches for the enlargement of the right
ventricular outflow tract and pulmonary artery [145] and as pericardial
patches [142] in sheep. At 12 months postoperatively, no remaining polymer
could be observed by light microscopy in the atrial septal defect study but
small particles appeared in polarized light. The transannular patches disap-
peared microscopically after about 12 months; however, macrophages were
still present 24 months postoperatively. The pericardial patches degraded
more slowly. Some polymer particles remained 24 months after implanta-
tion, but disappeared after 30 months leaving behind some macrophages
marking the implant region at this time. In clinical use, P3HB pericardial
patches showed a significant reduction in size, by an average of 27%, in
the 24-month follow-up group [33]. The complete absorption of a P3HB
pericardial patch, 16 months after implantation in a patient, has also been
reported [204].
Bioresorbable intravascular stents made of P3HB plasticized with TEC
were nearly completely dissolved 16-26 weeks after implantation into the iliac
arteries of rabbits [205, 206]. P3HB conduits for nerve regeneration showed
softening [36] or fragmentation and size reduction [34] after a 12-month
implantation in cats. In another study, the canine urethra was replaced by
a polyglactin mesh coated with P3HB. The complete resorption of the graft
was observed 8-12 months postoperatively [207].
Gastrointestinal patches made of P3HB/at-P3HB (70
30) blends tested for
repair of a bowel defect in rats showed a fast initial degradation followed by
a deceleration after 2 weeks [38]. Interestingly, this time period corresponds
to the occurrence of mRNA encoding of pancreatic enzymes after implanta-
tion of P3HB patches onto the gastric wall of rats [150]. Material remnants
were found only in one out of four test animals 26 weeks after implantation,
and had a molecular weight of about 38% of the initial value (Fig. 11a) [38].
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