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Thermo-responsive polysaccharidic hydrogels were designed and synthesized by a free radical induced grafting procedure. Chitosan was chosen as biopolymer to impart biocompatibility and biodegradability to the macromolecular systems, while N-isopropylacrylamide (NIPAAm) was selected as co-monomer responsive for the thermo-sensitive properties. Ammonium persulfate was the initiator system and different polymeric networks have been synthesized by modulating the amount of NIPAAm in the polymerization feed. The resulting hydrogels were proposed as drug delivery devices and their performance was evaluated by using Diclofenac sodium salt as a model drug. Hydrogels were carefully characterized by FT-IR spectrophotometry, calorimetric analyses and swelling behavior in a temperature range of 15-45°C. Finally, to verify the suitability of these hydrogels as thermo-responsive devices, the drug release profiles were studied performing in vitro experiments around the swelling-shrinking transition temperatures of the macromolecular systems. [ABSTRACT FROM AUTHOR]

Two types of hydrogel microspheres have been developed. Fast ionotropic gelation of sodium alginate (Na-alg) in the presence of calcium ions was combined with slow covalent cross-linking of poly(ethylene glycol) (PEG) derivatives. For the first type, the fast obtainable Ca-alg hydrogel served as spherical matrix for the simultaneously occurring covalent cross-linking of multi-arm PEG derivative. A two-component interpenetrating network was formed in one step upon extruding the mixture of the two polymers into the gelation bath. For the second type, heterobifunctional PEG was grafted onto Na-alg prior to gelation. Upon extrusion of the polymer solution into the gelation bath, fast Ca-alg formation ensured the spherical shape and was accompanied by cross-linker-free covalent cross-linking of the PEG side chains. Thus, one-component hydrogel microspheres resulted. We present the physical properties of the hydrogel microspheres and demonstrate the feasibility of cell microencapsulation for both types of polymer networks. [ABSTRACT FROM AUTHOR]

A novel flavonoid-polysaccharide conjugate was synthesized by free radical grafting of quercetin on starch. The covalent insertion of quercetin in the polymeric chain was confirmed by FT-IR, DSC and fluorescence analyses, while an estimation of the amount of quercetin bound per g of polymer was obtained by the Folin-Ciocalteu assay. The conjugate shows improved UV stability and retains the antioxidant properties of free quercetin, such as scavenging activity towards free radicals (DPPH and peroxynitrite); inhibition of the free radical formation (peroxidation of linoleic acid) and total antioxidant activity. The conjugate also prevented drug degradation and shows potential health functionality in the treatment of Alzheimer disease, diabetes and as skin-whitening agent. [ABSTRACT FROM AUTHOR]

Abstract: This study has the goal to evaluate the stability of B complex vitamins, loaded into catechin-based crosslinked hydrogels, in aqueous medium at accelerated conditions of oxidative stress. The formulations were prepared by coupling polyacrylic acid with catechin in the presence of dicycloexylcarbodiimide. Folic acid (FA) and Thiamine (TH) were chosen within the B complex vitamins because of the well-known oxidative degradation characteristics. The protective role of the hydrogels against the oxidation damage was monitored inducing oxidative stress, by means of UV irradiation and t-butyl hydroperoxide treatment for FA and TH, respectively. The characterization of the hydrogels was obtained by morphological, calorimetric, FT-IR analyses, antioxidant assays and evaluation of the swelling behavior in aqueous media at different pH. The experimental results confirmed the suitability of the hydrogels as pH-responsive devices, furthermore the presence of oxidative condition proved the protective effect of the hydrogels. Catechin-based polymers gave a pronounced improvement in the stability of vitamins compared to hydrogels prepared by the coupling reaction of polyacrylic acid in the presence of 1,6-hexandiol. Under oxidative conditions, FA and TH were preserved by 96% and 60% respectively. [Copyright &y& Elsevier]

A novel polymeric material with antioxidant properties and suitable for ophthalmic application was synthesized by free radical grafting reaction between 2-hydroxyethyl methacrylate and quercetin. The presence of quercetin in the polymeric chain was confirmed by FT-IR and UV-Vis analyses, while an estimation of the amount of quercetin bound per gram of polymer was obtained by the Folin-Ciocalteu assay. The conjugate shows high biocompatibility (HET-CAM assay) and antioxidant and anti-inflammatory properties which were extensively investigated by specific in vitro tests.

Goal of the present study was the characterization of the biological properties of a gelatin-gallic acid conjugate (Gel-GA) to evaluate its applicability in biomedicine and pharmacy. The macromolecular conjugate was synthesized by free radical grafting reaction between gelatin and gallic acid (GA) to form a covalent conjugate that was found to retain the antioxidant and enzymatic activities of free GA. In particular, the peroxynitrite scavenging power was found to be consistent with a IC(50) value of 2.17 ± 0.4 mg mL(-1). The enzymatic capacities of GA, which are regarded beneficial for cell functions, are partly retained in the Gel-GA conjugate. In particular, acetylcholinesterase inhibition (IC(50) of 7.1 ± 1.3 mg mL(-1)) implies the conjugate's usefulness in the chemoprevention of Alzheimer's disease, while the inhibition of α-amylase (IC(50) of 9.8 ± 1.1 mg mL(-1)) suggests that the conjugate can be a preferred alternative for inhibition of carbohydrate breakdown and control of glycemic index of food products. Finally, the anticancer activity of Gel-GA was proven in prostate carcinoma and renal cell carcinoma cell lines, confirming the potential of the proposed protein-polyphenol conjugate in medicine.