Polymerization, Self-Bridging, and Degradation of Acryloyl- and Methacryloyl-l-proline Methyl Esters Induced by Radiation and Characteristics of Gel Swelling

Synthesis and characterization of poly [N-acryloyl-(D/L), (+/−)-phenylalanine-co-(D/L), (−/+)N-methacryloyloxyethyl-N′-2-hydroxybutyl(urea)] copolymers

Two monomers of (D/L), (+/−)-N-methacryloyloxyethyl-N′-2-hydroxybutyl(urea) methacrylate (D/L-MABU) type were prepared and further polymerized through free radical polymerization with optically active monomers containing phenylalanine sequences such as N-acryloyl-(D/L), (−/+)-phenylalanine (A-D/L-Phe). The resulting copolymers, i.e., poly[N-acryloyl-(D/L), (−/+)-phenylalanine-co-(D/L), (+/−)-N-methacryloyloxyethyl-N′-2-hydroxybutyl(urea)], A-D/L-Phe-co-D/L-MABU, were characterized by FT-IR, 1D/2D NMR (1H and 13C), UV-vis, and circular dichroism (CD) spectroscopies, differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). The copolymers obtained with a molar fraction of 0.76: 0.24 / 0.64: 0.36 monomer units had optical rotation values of −25° and +15°, respectively. Upon chemical modification of the phenylalanine-based copolymers with fluorescein-isothiocyanate, new fluorescent copolyacrylates (A-D/L-Phe-co-D/L-MABU-F) were synthesized and further studied for pH measurements in DMF solutions using HCl and NaOH 10−1M. It was found that sterioselectivity of the A-L-Phe-co-L-MABU-F copolymer is higher than of its dextro-form, especially at basic pH.

Controlled synthesis of thermoresponsive polymers derived from l-proline via RAFT polymerization

Well-defined polymers derived from L-proline are synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization and the amino acid-based polymers exhibit thermosensitive phase separation at lower critical solution temperatures (LCST = 15-45 degrees C) in aqueous medium.

Release behavior of ketoprofen from poly(acryloyl-L-proline methyl ester) gels having different crosslinked networks

In order to clarify the relationship between the crosslinked structure of thermo-responsive polymer and drug release profile, polymer gels based on acryloyl-L-proline methyl ester (A-ProOMe) were synthesized in a mixture of water and acetone by the following two methods: a simultaneously occurring process of radiation-induced polymerization and crosslinking without a crosslinker (self-bridging method), and radiation-induced polymerization in the presence of the crosslinker tetradecaethylene glycol dimethacrylate (crosslinker method). The pronounced gap in thermo-response between two A-ProOMe gels, with an apparent degree of crosslinking of 11 for 1-propanol, shows a different shrinking pattern in the initial stage of time. The gels, which were obtained with the self-bridging method and the crosslinker method, were kept constant at a swelling ratio of 17 in water at 0 degree C for all systems. However, those values fell to 0.5 and 4, respectively, at 10 min after the temperature was increased to 37 degrees C. The release mechanism of ketoprofen from two gel devices showed an anomalous (non-Fickian) transport, in which the release of ketoprofen with a low water-solubility could be directly related to the rapid release of water accompanying a gel shrinkage.

Controlled release of biomolecules from temperature-sensitive hydrogels prepared by radiation polymerization

Poly(acryloyl-L-proline methyl ester)-based hydrogels containing 1 and 5% of a crosslinking agent were studied as drug delivery systems. The drug loading properties were investigated by matrix incubation into solutions containing biomolecules with molecular weight ranging between 300 and 65,000 Da. The loading yield was found to depend on both the crosslinking degree and the molecular weight of the drug. In vitro release studies were carried out with both swollen and dry matrices loaded with gentamicin, isoniazid and insulin. Gentamicin and isoniazid were released by a bimodal Fickian diffusion with a remarkable burst that was found to depend on both matrix crosslinking degree and physical state. In vivo, the subcutaneous implantation into mice of the isoniazid loaded matrices allowed for an efficient drug release for 800 h. In vitro insulin was released from the swollen matrices for 1500 h by diffusional Fickian mechanism while the dry ones displayed a lag time followed by Fickian diffusion release. The subcutaneous implantation of the insulin-loaded matrices into diabetic mice induced a remarkable decrease in the glucose concentrations in blood. In particular, the dry 1% matrices were found to maintain a low glucose level for 700 h.