229
The following observations can be made on the diagrams:
∙ The initial particle size of DPPC:PNIPAM-b-PLA 1 chimeric
liposomes is lower than conventional DPPC, regardless of the
amount of polymer incorporated, and the polydispersity is
higher.
∙ After heating the liposomes, DPPC ones do not respond to the
stimulus on either the level of particle size or the size distribution. On the other hand, the chimeric liposomes with incorporated polymer respond to the increased temperature condition,
confirming their thermoresponsive behavior and functionality.
∙ The size increases after heating in a polymer-concentrationdependent manner, as predicted by DSC experiments, while
the polydispersity reaches maximum for all chimeric nanosystems. The results are accompanied by agglomerate formation,
which is macroscopically visible and increased for higher
amounts of polymer. These agglomerates are formed at high
temperature (45 °C) and more specifically above the thermoresponsive functional phase that was recorded for the chimeric
nanosystems and are ostensibly reversible after reaching room
temperature again, but depending on the polymer amount,
membrane disruption and fusion phenomena occur that in
turn alter the liposomal properties.
∙ This behavior is owed to the responsive nature of PNIPAM,
which is hydrophilic below LCST and more hydrophobic
above it, resulting in the so-called coil-to-globule transition
and the transition of the polymer chains from an extended to a
shrinked conformation, leading to thermodynamically favorable hydrophobic interactions between the chimeric nanoparticles. This transition affects the liposomal membranes because
of the incorporated PLA chain, but also because the membrane
surface is exposed and liposomes are more prone to fusion and
aggregation.
4 Notes
1. The copolymers were synthesized via reversible additionfragmentation chain-transfer (RAFT) polymerization methodology and further characterized by size-exclusion
chromatography (SEC) and nuclear magnetic resonance
spectroscopy (NMR). More details are provided in a previous
work [14].
2. The weight-average molecular weights M w of PLA and
PNIPAM blocks were 5800 and 12,200 (18,000 total) for
PNIPAM- b-PLA 1 and 3900 and 2500 (6,400 total) for
Thermodynamics and Functionality of Thermoresponsive Chimeric Nanosystems
The following observations can be made on the diagrams:
∙ The initial particle size of DPPC:PNIPAM-b-PLA 1 chimeric
liposomes is lower than conventional DPPC, regardless of the
amount of polymer incorporated, and the polydispersity is
higher.
∙ After heating the liposomes, DPPC ones do not respond to the
stimulus on either the level of particle size or the size distribution. On the other hand, the chimeric liposomes with incorporated polymer respond to the increased temperature condition,
confirming their thermoresponsive behavior and functionality.
∙ The size increases after heating in a polymer-concentrationdependent manner, as predicted by DSC experiments, while
the polydispersity reaches maximum for all chimeric nanosystems. The results are accompanied by agglomerate formation,
which is macroscopically visible and increased for higher
amounts of polymer. These agglomerates are formed at high
temperature (45 °C) and more specifically above the thermoresponsive functional phase that was recorded for the chimeric
nanosystems and are ostensibly reversible after reaching room
temperature again, but depending on the polymer amount,
membrane disruption and fusion phenomena occur that in
turn alter the liposomal properties.
∙ This behavior is owed to the responsive nature of PNIPAM,
which is hydrophilic below LCST and more hydrophobic
above it, resulting in the so-called coil-to-globule transition
and the transition of the polymer chains from an extended to a
shrinked conformation, leading to thermodynamically favorable hydrophobic interactions between the chimeric nanoparticles. This transition affects the liposomal membranes because
of the incorporated PLA chain, but also because the membrane
surface is exposed and liposomes are more prone to fusion and
aggregation.
4 Notes
1. The copolymers were synthesized via reversible additionfragmentation chain-transfer (RAFT) polymerization methodology and further characterized by size-exclusion
chromatography (SEC) and nuclear magnetic resonance
spectroscopy (NMR). More details are provided in a previous
work [14].
2. The weight-average molecular weights M w of PLA and
PNIPAM blocks were 5800 and 12,200 (18,000 total) for
PNIPAM- b-PLA 1 and 3900 and 2500 (6,400 total) for
Thermodynamics and Functionality of Thermoresponsive Chimeric Nanosystems