Biomedical Engineering Reference
In-Depth Information
hyperbranched polyacylhydrazone (HPAH) through the A 2 + B 3 polyconden-
sation of butane-2,3-dione and 1-(2-aminoethyl)piperazine tripropionylhydra-
zine. 35 This hyperbranched dynamer HPAH was regarded as an excellent
carrier for drug delivery, since it featured good aqueous solubility and low
cytotoxicity. On the one hand, since the acylhydrazone bonds are stable in
physiological conditions (pH # 7.4), the HPAH-doxorubicin (DOX)
nanosized micelles can avoid removal by the reticuloendothelial system
(RES), kidneys, and intestines, perform the enhanced permeability and
retention (EPR) effect, and reduce systemic side effects. On the other hand,
after the endocytosis of HPAH-DOX micelles, the acidic lysosomes (pH # 5-
6) trigger cleavage of the acylhydrazone bonds, resulting in the release of
DOX.
From the aforementioned examples, the pH sensitivity endows delivery
systems with controlled release behavior.
d n 4 y 3 n g | 1
5.3.1.2 Thermo-responsiveness
In response to the environmental temperature alteration, thermo-responsive
HBPs exhibiting unique changes of chemical and physical properties are
promising materials for various biomedical applications, especially in smart
drug/gene delivery systems and tissue engineering. HBPs with a lower critical
solution temperature (LCST) are readily soluble in water below their LCST,
and their aqueous solutions undergo a phase transition to an insoluble state
with the increasing temperature. In particular, polymers with a LCST around
37 uC have received much attention due to their phase transition close to body
temperature.
The
most
well-known
class
of
thermo-responsive
polymer,
poly(N-isopropylacrylamide)
(PNIPAM),
exhibits
a
rapid
coil-to-globule
conversion at its LCST around 32 uC in aqueous solution.
Through PTP of triethanolamine, trimethylolpropane, and glycidyl metha-
crylate with potassium hydride as a catalyst, novel thermo-responsive
hyperbranched poly(amine-ester)s were successfully designed and synthesized
in one pot by Pang et al. 36 As shown in Figure 5.3, in vitro evaluation
suggested that hyperbranched poly(amine-ester)s exhibited low cell cytotoxi-
city and efficient cell internalization against COS-7 cells. Moreover, DOX as a
model
drug
was
encapsulated
into
hyperbranched
poly(amine-ester)s
in
aqueous
solution,
availing
of
a
phase
transition
at
the
LCST.
Thermo-
responsive
hyperbranched
poly(amine-ester)s
can
be
utilized
to
construct
promising drug delivery systems for cancer therapy.
The combination of temperature-sensitive polymer nanoparticles (nanogel)
and magnetically activated superparamagnetic nanoparticles has realized
reversible, on-off drug or gene release by means of exertion and removal of
an oscillating magnetic field. 37,38 The external oscillating magnetic field
activates the superparamagnetic nanoparticles, which behave as local heat
sources. When arriving at the phase transition temperature, the temperature-
sensitive vehicles collapse and subsequently release their cargoes (drug or gene)
 
Search WWH ::




Custom Search