Abstract
The synthesis of stimulus-responsive poly(N-isopropylacrylamide-co-N-isopropylmethacrylamide)/chitosan core/shell nanohydrogels made by batch emulsion polymerization in the presence of chitosan (CS) micelles is reported. The ratio of monomers required to obtain copolymers with a volume phase transition temperature (TVPT) in the range of the temperatures observed in the human body in response to an infection (38 to 40 °C) was estimated with the Fox equation. The conversion was determined by gravimetry; mean particle size, size distribution, and thermal response were measured by quasi-elastic light scattering (QLS). The core/shell structure was confirmed by TEM, and FTIR showed the presence of N-isopropyl acrilamide (NIPA), N-isopropyl methacrylamide (NIPMA), and CS in the nanohydrogels. The nanohydrogels were loaded with the drug doxycycline hyclate, and their release kinetic profile was determined at pH = 2.0 and 7.4 at their volume phase transition temperatures (TVPT). A higher amount of drug was released at acidic pH. Some mathematical models described in the literature were used to fit the experimental drug release data.
Highlights
Stimuli-responsive polymers are materials that have the ability to significantly change a property in response to external environmental conditions [1,2]
The nanohydrogels were loaded with the drug doxycycline hyclate, and their release kinetic profile was determined at pH = 2.0 and 7.4 at their volume phase transition temperatures (TVPT ) and compared with the predictions of models commonly used in drug release studies
N-isopropyl acrilamide (NIPA)/NIPAM displays an lower critical solution temperature (LCST) of 36.8 ◦ C at pH = 7.4 employing a phosphate buffer solution
Summary
Stimuli-responsive polymers are materials that have the ability to significantly change a property (or properties) in response to external environmental conditions [1,2]. Stimuli-responsive polymers can be designed to act as biosensors [4] in ion-exchange chromatography [5], in micromechanical materials [6], in chemotherapy [7,8], in drug delivery [9,10], in photo-responsive coating materials [11] and in photonics [12]. Because there are specific conditions (temperature and pH, among others) to which stimuli-responsive nanoparticles loaded with specific drugs can respond, the importance of these nanoparticles is evident, when they respond to more than one stimulus simultaneously [14]. Hyperthermia commonly occurs in diseased tissues compared to normal tissues, so several temperaturesensitive nanohydrogels have been developed for drug delivery purposes [15,16]
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