Abstract
In the presence of water, poly(N-acryloyl glycinamide) homopolymers form highly swollen hydrogels that undergo fast and reversible gel↔sol transitions on heating. According to the literature, the transition temperature depends on concentration and average molecular weight, and in the case of copolymers, composition and hydrophilic/hydrophobic character. In this article, we wish to introduce new copolymers made by free radical polymerization of mixtures of N-acryloyl glycinamide and of its analog optically active N-acryloyl l-alaninamide in various proportions. The N-acryloyl l-alaninamide monomer was selected in attempts to introduce hydrophobicity and chirality in addition to thermo-responsiveness of the Upper Critical Solubilization Temperature-type. The characterization of the resulting copolymers included solubility in solvents, dynamic viscosity in solution, Fourrier Transform Infrared, Nuclear Magnetic Resonance, and Circular Dichroism spectra. Gel→sol transition temperatures were determined in phosphate buffer (pH = 7.4, isotonic to 320 mOsm/dm3). The release characteristics of hydrophilic Methylene Blue and hydrophobic Risperidone entrapped in poly(N-acryloyl glycinamide) and in two copolymers containing 50 and 75% of alanine-based units, respectively, were compared. It was found that increasing the content in N-acryloyl-alaninamide-based units increased the gel→sol transition temperature, decreased the gel consistency, and increased the release rate of Risperidone, but not that of Methylene Blue, with respect to homo poly(N-acryloyl glycinamide). The increase observed in the case of Risperidone appeared to be related to the hydrophobicity generated by alanine residues.
Highlights
Polymeric hydrogels are swollen 3D matrices composed of at least 50% or more of aqueous medium
We have shown that drug-containing PNAGA hydrogels present an
This work shows that thermo-responsive PNAGA-co-N-acryloyl L-alaninamide chiral analog (NALALA) copolymers can be synthesized by radical polymerization in aqueous medium, as was the case for PNAGA homopolymers
Summary
Polymeric hydrogels are swollen 3D matrices composed of at least 50% or more of aqueous medium. Two domains of applications of hydrogels are drug delivery and tissue engineering [1,2,3,4,5,6]. In such hydrogels, water is entrapped in a 3D network of chemically or physically cross-linked macromolecules. Contrary to chemical cross-linking, physical cross-linking can be reversible under the action of a change in environmental conditions. The reversibility of the physical cross-linking present in hydrogels results in gel↔sol transition. PH, ionic strength, and temperature changes have been proposed as a means to modify water-polymer interactions and lead to sol↔gel reversible
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