A series of polyurethane (PU) films were synthesized via one-shot bulk polymerization with polyethylene glycol, castor oil, hexamethylene diisocyanate, and 1,4-butanediol (BD) at three different chain extender ratios. Since it was found in our previous study that hard segment content is more effective on shape memory property than soft segment length (Bonfil, M., Sirkecioglu, A., Bingol-Ozakpinar, O., Uras, F., Güner, F. S. J. Appl. Polym. Sci. 2014, 131, 1-12), in this study the effects of BD amount on some physical properties, thermal properties, and shape memory performance of the films were investigated. Shape fixity and shape recovery were achieved under two different cooling/heating regimes.The amount of BD is an important parameter affecting the physical properties, chemical structure, and thus shape memory performance. Decreasing the BD amount increased the crystallinity and the films, being of relatively high crystallinity, showed the highest shape recovery ratio. Increasing BD amount in PU films increases the hydrogen-bonded structure and the films having a relatively high degree of hydrogen-bonded structure showed the highest shape fixity ratio. The samples showed higher shape memory performance at high cooling and heating rates. IntroductionSince the first shape memory polyurethanes were discovered in 1988 by Mitsubishi Heavy Industry, the research area has developed rapidly. In recent years, smart textile and biomedical applications have become the most promising fields for shape memory polyurethanes.Polyurethane (PU) is a special polymer composed of soft and hard segments in its structure. Hard segments consist of diisocyanate and chain extender. Soft segments are formed by long chain polyether or polyester glycols. Urethane groups have an ability to self-associate via hydrogen bonds between interurethane and urethane-ester or urethane-ether groups. 1 Due to the aggregation of hard segments via hydrogen bonds to form hard segment domains, which disperse in the soft segment matrix, a segmented structure and thus, microphase separation occur. 2,3 Interactions between the molecules of hard segments increase the phase separation between soft and hard segments and enhance the shape memory properties of polyurethanes. 4 Since soft segments show a thermal transition at transition temperature and they work like a reversible molecular switch point, the molecular weight and the amount of polyol in the polymer are important parameters. The type and the amount of chain extender, which is an indispensable component of the hard segments, are also important parameters, since hard segments are responsible for the original shape.
Photopolymerization kinetics of doxycycline hyclate (DOX)-imprinted hydrogels were monitored by real-time Fourier transform infrared spectroscopy and differential photocalorimetry. 2-Hydroxyethyl methacrylate-based hydrogels were synthesized by using ethylene glycol dimethacrylate as a cross-linker, acrylic acid (AA) as a functional monomer, and 2,2-dimethyl-2-hydroxy acetophenone as a photoinitiator. For imprinting DOX in hydrogels, the molar ratio of template to functional monomer (DOX:AA) was chosen as 1:8 and 1:16. The polymerization was achieved at two different initiator concentrations. The conversion and reaction rate were calculated as a function of the molar ratio of template, and the results were compared to those of nonimprinted ones. In order to reveal the effect of DOX on the photoinduced radical polymerization, thermal polymerization was also performed for imprinted and nonimprinted hydrogels by using 2,2 ′ -azobis(2,4-dimethyl-pentanenitrile) as a thermal initiator. All results showed that there is a significant effect of DOX concentration on the conversion and reaction rate of the photopolymerization reaction. The conversion and reaction rate decreased during photopolymerization when the template concentration increased in the monomer mixture.
The aim of this study is to develop doxycycline imprinted contact lenses that will be used in the treatment of corneal neovascularization, which can eventually cause blindness. For this purpose, doxycycline imprinted contact lenses were first prepared in two different diameters, 5.7 and 5.8 mm, then they were loaded with doxycycline and their in vitro and in vivo performances were determined. In the synthesis of the contact lenses, 2-hydroxyethyl methacrylate was used as a backbone monomer. The functional monomer was selected as itaconic acid using molecular simulations. Doxycycline release profile of the lenses was determined in NaCl solution at 37 °C. Their doxycycline release was reached about 3 µg/mg contact lenses in 6 hours. Higuchi model was fitted better than the others as a kinetic model. Swelling degrees of the contact lenses were determined as 38.8 %. Cytotoxic response of the lenses was investigated on retinal pigment epithelium cells. According to the results the lenses were not cytotoxic to RPE cell line. In vivo experiments in rat models were performed to study the treatment patterns. The rats were sacrificed fifteen days after treatment, and clinical examination under optical microscope was performed to evaluate neovascularization, infiltration of inflammatory cells, and corneal epithelial changes. In conclusion; doxycycline imprinted contact lenses promise as an effective treatment method for corneal neovascularization.
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