Biomedical Engineering Reference
In-Depth Information
Amongst the chitosan-grat ed polymers, the more important polymers
in the biomedical i eld are chitosan-grat ed-PEG and chitosan-grat ed-
PEI. PEG is commonly used in the biomedical sector due to its hydrophi-
licity and biocompatibility. It is non-toxic, does not cause irritation and is
odourless, making it an ideal polymer which has been used in pharmaceu-
ticals as a solvent, ointment and tablet excipient [27]. h e grat ing of PEG
onto chitosan promotes solubility at physiological pH and the stability
of the polymer
in vivo
. In addition, PEG delays the host immune system
from degrading the polymers leading to a longer blood residence time.
As a result of these advantageous properties, this co-polymer has been
applied in the development of carriers for transmucosal drug delivery
[41, 42]. PEG has been approved by the Food and Drug Administration
for human intravenous, oral, and dermal application which is favourable
for the development of biomedical applications of the chitosan-PEG co-
polymer [43]. h ese chitosan-PEG co-polymers are typically synthesized
via
reductive amination or through the use of activated esters. PEGylation
can proceed at the amino (C2) or hydroxyl groups (C3/C6) present on chi-
tosan depending on the reaction conditions used. h ese chitosan-PEG co-
polymers can be further functionalized to incorporate functional groups
which of er advantageous properties [28]. Grat ing of PEI onto chitosan
lowers the cytotoxicity associated with PEI polyplexes while increasing
transfection ei ciency associated with chitosan polyplexes. h ese co-poly-
mers can be synthesized
via
many dif erent routes which include peri-
odate oxidation of the chitosan backbone together with imine formation
and Michael addition [28].
5.4 Nanoparticles
When moving to the nanoscale, certain properties are improved due to
the higher surface area to volume ratio [44]. Nanoparticles are dei ned as
ultrai ne particles which range from 1 to 100 nm in size.
Polymeric nanoparticles (NPs) are of great interest in many areas
although much ef ort has been focused on the application of these par-
ticles in the biomedical sector. Biodegradable polymeric NPs are the main
focus of scientists which have been studied mainly as carriers of drugs or
bioactive compound agents due to their favourable properties [45]. h ese
include a longer half-life (sustained release), stability
in vivo
, higher drug
loading, enhanced permeation (due to small size), targeted delivery, pro-
tection of the drug and improvement of pharmacokinetics [45, 46]. In
addition, release of the bioactive compounds in response to a trigger such
