Thermoresponsive Starch Nanoparticles
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Thermosensitive or thermoresponsive polymers (TRPs) that undergoes an abrupt change in aqueous solubility with temperature have numerous potential commercial applications. The vast majority of TRPs reported to date are synthetic, petroleum-based, polymers. TRPs based on benign natural polymers such as cellulose and starch have garnered some attention recently due to their biodegradability, biocompatibility, low toxicity and low production costs. A protocol for the modification of Ecosphere® Starch Nanoparticles (ENPs) with various epoxides under environmentally preferable conditions was developed. The temperature-dependent aggregation behaviour of thermoresponsive ENPs (TRENPs) was examined. The lower critical solution temperatures (LCSTs) of the thermoresponsive TRSNPs increased with the molar substitution (MS) of the modifying group. The temperature-dependent aggregation behaviour of the TRSNPs changed depending on the concentration of NaCl or various alcohols. The LCSTs of the TRSNPs decreased with increasing NaCl concentration and with increasing n-propanol and n-butanol concentration. Low concentrations of methanol and ethanol decreased the LCST. Higher concentrations of these alcohols broadened the thermal transitions and increased the LCST. At sufficiently high concentrations of methanol and ethanol, the nanoparticles no longer exhibited a thermal transition. The TRENPs discussed in this work represent a novel class of thermoresponsive biopolymer nanoparticles with tunable critical temperatures.