Abstract
Poly-N-isopropylacrylamide (polyNIPA) is an extensively studied polymer in the field of controlled drug delivery. PolyNIPA contains carbonyl and amide groups along a hydrophobic chain. In an aqueous environment, crosslinked polyNIPA forms a gel characterized by a reversible volume phase transition temperature (VPTT), in response to changes in the external environment excited by the temperature factor. NIPA-based polymers were synthesized by a surfactant-free precipitation polymerization (SFPP) method at a temperature of 70 °C using the free radical initiator potassium persulfate (KPS) and at 35 °C using redox initiator system KPS with N,N,N’,N’-tetramethylethylenediamine (TEMED). The synthesized products were evaluated via dynamic light scattering (DLS), nuclear magnetic resonance (NMR) and Fourier-transform infrared spectroscopy (FTIR). The chemical structure, molecular mass, and hydrodynamic diameter of obtained particles, as well as the effects of synthesized polymers on the release of the active substance, naproxen sodium (NS), from hydroxypropyl methyl cellulose (HPMC)-based hydrogels were assessed. The use of the TEMED activator affected the particle size, as well as the release kinetics of NS. The insertion of TEMED into reactant mixtures may be applied to modify the release kinetics of NS from hydrogel preparations.
Highlights
The 1 H-nuclear magnetic resonance (NMR) spectra of the products are presented in poly(ethylene glycol) dimethacrylate (PEG-DMA) is elucidated by a characteristic multiplet of ethylene groups (δ: 3.4 ppm–3.9 ppm)
The proposed synthesis scheme is given on Figure 5
Application of the TEMED activator at a temperature of 35 ◦ C enabled the synthesis of nano-range particles, with pronounced volume phase transition temperature (VPTT), between 28 and 32 ◦ C
Summary
The high water content in hydrogels results in good biocompatibility of the systems prepared on the basis of the hydrophilic polymers. Hydrogels were first used to make contact lenses; later they were applied as controlled drug delivery systems. Hydrogels were designed to protect the drug molecule against adverse environmental conditions or to form a depot preparation, slowly releasing the drug substance. The intensive development of polymer chemistry has gone further in the synthetic applications of hydrogels and has led to the emergence of “intelligent polymers” that react to several external stimuli [1,2,3,4]. Hydrophilic gels have been known to change their properties in response to temperature changes, pH, light intensity, mechanical pressure or electrical impulses [5,6,7]
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