Modification of Polyhydroxyalkanoates (PHAs) - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 161

thrombosis condition. 83 The monoacrylate of polyethylene glycol metha-
crylate (PEGMA) was grafted with poly(3-hydroxyundecenoate) (PHU) 84 and
PHO 83 by UV irradiation of the homogeneous PHA solutions containing
PEGMA. In both studies, the surface adsorption tendencies of both graft
copolymers towards blood proteins and platelet adhesion were reduced
significantly in comparison to the control i.e. poly (L-lactide) surface. Fur-
thermore, the grafted copolymers exhibited excellent blood compatibility
with increasing PEGMA fraction. 83,84 A higher PHA molecular weight (M w )is
associated with a lower degradation rate thus limiting its application as a
short-lived drug carrier for molecules such as DNA and functionalized
polypeptides. Instead of cross-linking and grafting the PHA, Shangguan
et al. 101 used UV irradiation to achieve controlled degradation of PHBHHx
leading to oligomers bearing reactive radical groups with a quick degrad-
ation rate. The authors found the decrement of the M w to be dependent upon
the UV radiation exposure time. The degradation mechanism was extensively
reviewed. 9

d n 2 r 4 n g | 1

7.3.3 Ion Implantation
Ion implantation is another physical method employed in polymer surface
modification. Its advantage over other polymer modification methods is
that it only modifies the polymer surface layer, without upsetting the bulk
polymer's properties. 102 Ion implantation has been successfully applied in
several polymer modifications thereby expanding its applications. 102-106
Hou et al. 85 successfully implanted hydroxyl ions on the surface of PHB
using an electron ion implantation energy of 40 keV when an implantation
flux ranging from 1 10 12 to 1 10 15 ions per cm 2 was applied. The study
reported that the modified PHB showed a better proliferative activity of
mouse embryo fibroblast (3T6) cells compared to non-modified PHB.
However, it was observed that the ion implantation caused polymer cracks
proportional to the intensity of fluence or flux of the hydroxyl ion bom-
bardment. 85 In a similar study, Santos et al. 107 improved the hydrophilicity
of PHB and PHB-graft-polyvinylacetate copolymers by implanting H 1 ,Ag 1 ,
and Na 1 ions at different fluences. In both polymers, the treatment re-
sulted in increased hydrophilic characteristics. PHB and PHBHHx wett-
ability was shown to be significantly improved upon implantation with
carboxyl ions at an electron implantation energy of 150 keV and ion
bombarding fluences ranging from 5 10 12 to 1 10 15 ions per cm 2 . 102 In
comparison to the non-implanted PHA, the polymer surface analysis re-
vealed a decrease in the intensities of C C , C Oand C ¼ O
groups in the COO implanted polymer, thus improving its hydrophilicity.
Likewise, PHB, PHBV and PHBHHx implanted with C 1 ions revealed im-
proved cytocompatibility when used as supports for culturing mouse em-
bryo fibroblast (3T6) cells. 105 In all polymer samples, it was found that an
implantation ion flux of 1 10 12 ions per cm 2 was the optimal in conferring
better cytocompatibility.

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