222
exogenous stimuli, including pH and temperature fluctuations.
The concept for targeted and controlled drug delivery suggests the
release of the incorporated therapeutic moiety, e.g., the drug molecule, in a site- and time-specific manner. The result is the increased
bioavailability of drugs, their accumulation in diseased tissues
instead of healthy ones, and therefore increased efficacy and safety
[4, 5].
A thermoresponsive macromolecule that has drawn attention
in biomedical applications is poly(N-isopropylacrylamide)
(PNIPAM). This polymer has the distinct property of reversible
phase transition from water soluble to water insoluble, when
heated above a certain temperature value (32 °C) that is known as
the lower critical solution temperature (LCST). The transition is
also called coil-to-globule transition, since the polymer changes its
conformation, from hydrated and extended to dehydrated and
shrinked [6]. The LCST of PNIPAM and other thermoresponsive
materials can be tailored close to the physiological temperature
(37 °C), which makes them very promising candidates for therapeutic and other human-related bioapplications [7, 8].
PNIPAM has been combined with liposomal technology, leading to thermoresponsive chimeric nanosystems. One of the
approaches involves attaching PNIPAM to another polymer that is
hydrophobic, producing an amphiphilic diblock copolymer and
incorporating it inside lipidic bilayers [9, 10]. This integration has
in turn been studied on a thermodynamic and physicochemical
basis, which aims to delineate the thermodynamic and biophysical
properties of these combinatorial platforms, with the final aim of
predicting their stability and functionality for drug delivery applications [11–13].
2 Materials
The materials described below concern the preparation of thermoresponsive chimeric/mixed bilayers, by utilizing a phospholipid
and two different thermoresponsive amphiphilic block copolymers;
the DSC analysis of the samples in 40 μL aluminum pans, hydrated
with phosphate-buffered saline (PBS) medium; the development
of thermoresponsive chimeric/mixed liposomes, by utilizing the
same phospholipid and one of the two copolymers that presented
the most promising functional properties; and finally the use of
dynamic light scattering for measurement of their physicochemical
properties, for which dilution was achieved with HPLC-grade
H 2 O.
1. DPPC (M w = 734.039) (Fig. 1A).
2.1 Preparation
of Thermoresponsive
Chimeric Bilayers
Nikolaos Naziris et al.
exogenous stimuli, including pH and temperature fluctuations.
The concept for targeted and controlled drug delivery suggests the
release of the incorporated therapeutic moiety, e.g., the drug molecule, in a site- and time-specific manner. The result is the increased
bioavailability of drugs, their accumulation in diseased tissues
instead of healthy ones, and therefore increased efficacy and safety
[4, 5].
A thermoresponsive macromolecule that has drawn attention
in biomedical applications is poly(N-isopropylacrylamide)
(PNIPAM). This polymer has the distinct property of reversible
phase transition from water soluble to water insoluble, when
heated above a certain temperature value (32 °C) that is known as
the lower critical solution temperature (LCST). The transition is
also called coil-to-globule transition, since the polymer changes its
conformation, from hydrated and extended to dehydrated and
shrinked [6]. The LCST of PNIPAM and other thermoresponsive
materials can be tailored close to the physiological temperature
(37 °C), which makes them very promising candidates for therapeutic and other human-related bioapplications [7, 8].
PNIPAM has been combined with liposomal technology, leading to thermoresponsive chimeric nanosystems. One of the
approaches involves attaching PNIPAM to another polymer that is
hydrophobic, producing an amphiphilic diblock copolymer and
incorporating it inside lipidic bilayers [9, 10]. This integration has
in turn been studied on a thermodynamic and physicochemical
basis, which aims to delineate the thermodynamic and biophysical
properties of these combinatorial platforms, with the final aim of
predicting their stability and functionality for drug delivery applications [11–13].
2 Materials
The materials described below concern the preparation of thermoresponsive chimeric/mixed bilayers, by utilizing a phospholipid
and two different thermoresponsive amphiphilic block copolymers;
the DSC analysis of the samples in 40 μL aluminum pans, hydrated
with phosphate-buffered saline (PBS) medium; the development
of thermoresponsive chimeric/mixed liposomes, by utilizing the
same phospholipid and one of the two copolymers that presented
the most promising functional properties; and finally the use of
dynamic light scattering for measurement of their physicochemical
properties, for which dilution was achieved with HPLC-grade
H 2 O.
1. DPPC (M w = 734.039) (Fig. 1A).
2.1 Preparation
of Thermoresponsive
Chimeric Bilayers
Nikolaos Naziris et al.