PLGA-PEG-PLGA thermogel mechanism and molecular weight effects detailed
PolySciTech
division of Akina, Inc. (www.polyscitech.com)
provides a wide array of biodegradable block copolymers including thermogelling
PLGA-PEG-PLGA polymers with varying molecular weights and block constituents (PolyVivo
AK012, AK024, AK097, etc.). Unlike normal materials, these polymers when
dissolved in aqueous solution for a liquid at cold temperature and solidify
when the temperature is increased. The primary mechanism for this lies in the
competing forces between water-molecule binding attraction to the PEG block and
entropic forces encouraging water to be free of the PEG block. Recently a paper
was published detailing the effects of polymer block sizes, concentration, and
temperature on the gelation and precipitation behavior of these types of
polymers. Read more: Chen, Liang, Tianyuan Ci, Lin Yu, and Jiandong Ding.
"Effects of Molecular Weight and Its Distribution of PEG Block on
Micellization and Thermogellability of PLGA–PEG–PLGA Copolymer Aqueous
Solutions." Macromolecules (2015). http://pubs.acs.org/doi/abs/10.1021/acs.macromol.5b00168
“Abstract: While
amphiphilic block copolymers have been extensively investigated, little is
known about the effect of molecular weight distribution (MWD) of the
hydrophilic blocks on corresponding physical gelation behaviors. Herein, we
employed thermogelling poly(d,l-lactide-co-glycolide)-b-poly(ethylene
glycol)-b-poly(d,l-lactide-co-glycolide) (PLGA–PEG–PLGA) as the model system.
We synthesized the block copolymer and prepared a series of copolymers with
similar PLGA blocks but varied lengths and distributions of the PEG block. The
micellization in dilute solutions was detected by light scattering and
fluorescence spectroscopy using the probe 1-anilino-8-naphthalenesulfonate
(ANS) specifically for the micelle coronae. Vial-inverting observations and
rheological measurements were carried out to judge sol or gel states for the
concentrated aqueous systems. The gel-to-sol transition or sol-to-gel
transition occurred only with appropriate molecular weight (MW) and molar mass
dispersity (ĐM). In this study, we denote the normal hydrogel with a sol-to-gel
transition upon cooling as gel-1, and gel-2 refers to the thermogel with a
reversed physical gelation in a sol-to-gel transition upon heating. We found
that wider MWD of PEG block sometimes even led to coexistence of normal gel
(gel-1) and reversed gel (gel-2). The corresponding concentrated aqueous system
of copolymers underwent gel-1-to-sol-to-gel-2 transitions with an increase of
temperature. The macroscopic physical gelation was further discussed based upon
the mesoscopic micellization and the micellar aggregation.”
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