Biomedical Engineering Reference
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makes stronger interactions between the inter- and intra- hydrogen
bonds and that makes it difficult for the reaction to happen. Also
when the MW of the HA was kept unchanged, the DS gets smaller
as the length of the alkyl chains gets shorter. This may be because
the longer chains may cause steric hindrance which makes the DS
lower. Out of all the combinations tested, they reported that the HA
(9.6 kDa)-LA-SP micelles encapsulated siRNA most efficiently at a
ratio of 2:1 (siRNA:HA-LA-SP).
Similarly, another group from South Korea demonstrated targeted
delivery of the HA nanoparticles (NP) to CD44 expressing cells [7].
They conjugated 5β-cholanic acid to HA using the EDC chemistry.
They have also shown that by varying the degree of substitution
of the hydrophobic moiety, they could control the size of the self-
assembled particles. Another group from Korea demonstrated
how the percentage of chemical modification of HA changed the
distribution of those HA particles in mice [16]. According to their
real time imaging study using quantum dots (QDots), they reported
that the HA-QDots with 35 mol% HA modification maintaining
enough binding sites for HA receptors were mainly accumulated
in liver, kidney and tumours (tissues with higher CD44 expression
levels), while those with 68 mol% HA modification lost much of the
HA characteristics and were evenly distributed to the tissues in body.
Jiang and co-workers, another group from Korea, also developed and
investigated the effect of HA modification on the receptor-mediated
endocytosis by labeling HA derivatives with QDots [21]. Based on
their real time imaging study of their HA-QDot conjugates, they
have reported that the HA-QDots with a degree of modification less
than 25 mol% appeared to be more efficiently taken up by CD44
expressing cells by receptor-mediated endocytosis. Based on this,
they managed to derivatise the HA with branched PEI through the
formation of amide linkage by an EDC coupling reaction just like we
did in our laboratory [22]. By gel permeation chromatogram (GPC)
analysis, Jiang and co-workers determined that the hydrodynamic
volume of the HA-PEI derivative they made was smaller than that of
HA which was probably due to the electrostatic neutralisation. They
also confirmed with
1
H-NMR that the product that they obtained was
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