Biomedical Engineering Reference
In-Depth Information
Tests have been made on patches made either from P3HB films [150], P3HB
films blended with at-P3HB in order to reduce stiffness and enhance hydro-
lysis [38], or from P3HB film/textile composites [214]. A similar asymmetric
patch, made either from P3HB/at-P3HB (70
50) blends, has re-
cently been tested in minipigs and shown to support healing of a dural defect
on its porous surface and prevent adhesions to brain tissue on its smooth
surface [39].
Furthermore, P3HB tubes have been described that are intended to sup-
port tissue healing of vessels and hollow organs. P3HB was selected as a ma-
terial that can resist the aggressive secretions of the intestinal tract for a suf-
ficiently long time but will finally degrade [31]. It was demonstrated in a rat
model that high-risk anastomoses under the condition of general peritonitis
can be significantly protected by an intraluminal bypass with P3HB-7%3HV
tubes. No postoperative complications due to adhesions and no signs of toxic
reactions, as well as a good healing process with excellent revascularization of
the anastomotic region have been observed [215].
/
30) or (50
/
Nerve Conduits
Conduits for peripheral nerve regeneration were formed from nonwoven
P3HB sheets having polymer fibers oriented in one direction. These sheets
were wrapped around a 2-3 mm gap of the transected superficial radial nerve
in cats, and were sealed with fibrin glue [34, 36]. The fibers were oriented lon-
gitudinally in order to provide contact guidance and mechanical support for
growing axons. The slow degradation of P3HB was considered to be of advan-
tage, supporting the nerve during a period long enough for regeneration to
takeplaceandreducingtheriskofaccumulationoflargeamountsofacidic
degradation products. Axonal regeneration was found to be similar to that
observed with epineural repair, which was used as a control.
P3HB tubes with unidirectional fiber orientation were prepared by rolling
a sheet of nonwoven P3HB around a cannula and sealing it with cyanoacrylate
glue. These tubes were successfully used to bridge a 10 mm gap in the sciatic
nerve of rats [35]. An increased axonal regeneration was found by filling the
tubes with transplanted Schwann cells [216]. Allogenic Schwann cells, embed-
ded in an alginate/fibronectin matrix inside the P3HB conduit, were shown to
enhance axonal regeneration of the transected rat sciatic nerve without elic-
iting a deleterious immune response [217, 218]. Additionally, P3HB conduits
filled with leukemia inhibitory factor in an alginate/fibronectin matrix en-
hanced the repair of the rat sciatic nerve in comparison to conduits without
growth factor, but still did not perform as well as autografts [219].
Tubes made from P3HB sheets were also tested as conduits for long-gap
peripheral nerve repair. P3HB tubes used to bridge up to 40 mm-long gaps
in the transected peroneal nerve in rabbits supported nerve regeneration, al-
thoughnotaswellasautografts.TheauthorsconcludedthatemptyP3HB
conduits may not be optimal for long-gap repair, and improvements might
