Using
a thermodynamic theory, we present a systematic study of
the behavior of microgels of N-isopropylacrylamide
(NIPAm) and methacrylic acid (MAA) copolymers as a function of the
temperature, pH, and salt concentration. These microgels swell with
increasing pH; the onset of this transition displaces to higher pH
values as the solution salt concentration decreases. The size of poly(NIPAm-co-MAA) microgels is a nonmonotonic function of the salt
concentration; at constant pH, increasing the salt concentration drives
particle swelling first, but a further increase of salinity leads
to deswelling. Upon increasing the temperature, these microgels deswell
and undergo a volume phase transition (VPT) around a characteristic
temperature. This VPT temperature depends on the MAA content of the
copolymer, the degree of cross-linking, the solution pH, and salt
concentration. Changing these independent variables and/or design
parameters are all means to modify the state of charge of the microgel
at the VPT. The amount of the charge inside the polymer backbone controls
the VPT temperature. Finally, we describe the absorption of two chemotherapeutic
drugs, Daunorubicin and Doxorubicin, and evaluate the best conditions
for incorporation into the multiresponsive microgels.
Polyamines such as putrescine, spermidine and spermine are required in many inter- and intra-cellular processes. There is, however, evidence of anomalously high concentrations of these polyamines around cancer cells. Furthermore,...
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