Biomedical Engineering Reference
In-Depth Information
new crystallites between the parent HA particles in the P3HB/HA composite,
as well as at the surface of the parent HA particles [155].
With respect to the mechanical properties and the tissue response, P3HB-
20%HV films were more suitable than PLLA, PDLLA, and PCL to separate
mucoperiostum and bone in a dog model for closure of palatal defects [156].
In contrast, P3HB-3HV reinforced with polyglactin was not useful as an oc-
clusive barrier over dental implants in dogs, since the material prevented
bone healing due to an increased inflammatory reaction [157].
P3HB-22%3HV coated onto a tantalum stent implanted for 4 weeks in the
porcine coronary artery induced a marked inflammatory and foreign body
response, thrombosis as well as extensive fibromuscular proliferation leading
to eccentric stenosis [158]. Intense inflammatory reactions and proliferations,
thrombosis, and in-stent lumen narrowing have also been reported after im-
plantation of P3HB stents (plasticized with 30% TEC) into the rabbit iliac
artery for up to 30 weeks. The polymer degradation process was suggested to
be the main reason for the significant chronic inflammation induced by these
stents [159]. Another explanation might be the fast leaching of the water-
soluble plasticizer [79], together with polymer crystallization induced by the
laser-cutting in the stent manufacturing process [160] leading to polymer
stiffness and brittleness, which may cause the tissue irritation and early stent
rupture observed in the study.
Blood Compatibility
In vitro studies have confirmed that P3HB is a polymer with a high blood
compatibility [139]. For example, a good thromboresistance of the P3HB sur-
face has been concluded from the adsorption and desorption characteristics
of albumin and fibrinogen, the latter playing a major role in stimulating
thrombus formation [161]. Furthermore, the blood compatibility of P3HB,
P3HB-9%3HV, and P3HB-22%3HV films has been compared by studying the
adsorption of these proteins. An increasing fibrinogen adsorption has been
observed with increasing 3HV content (increasing hydrophobicity) while al-
bumin adsorption decreased [162].
The protein adsorption that precedes and probably determines the sub-
sequent coagulation process was also evaluated on unmodified P3HB films
and on films modified by perfluorohexane plasma. It was ascertained that
the adsorption of fibrinogen strongly decreased on the plasma-treated P3HB
films, resulting in prolonged blood coagulation times in vitro. Perfluorohex-
ane plasma modification leads to very smooth and hydrophobic surfaces [138,
139]. Surface roughness was found to be more significant for protein ad-
sorption than surface energy [139]. The same was concluded after alkaline
treatment of P3HB-8%3HV films leading to strong surface erosion and in-
creasing area accessible to proteins [122].
The release of molecules of the inflammation cascade was evaluated in
vitro after contact of P3HB films with fresh human blood. The activation of
 
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