فهرست مطالب عزیزاله نودهی

During the last decades, an increasing attention has been paid to pharmaceutical and biomedical applications of queous polymeric solutions which respond in accordance to the changes in their environmental conditions i.e., stimuli by turning into in situ forming hydrogels. Of all the stimuli-responsive hydrogels, temperature-responsive solutions have been widely investigated due to their simplicity, applicability and relatively high frequency of temperature-responsiveness, in situ gelling polymeric (natural or synthetic) systems. In contrast with the conventional hydrogels, in situ forming temperature-responsive hydrogels can form under physiological conditions and preserve their morphological integrity for a definite time course. Using the materials makes it easier to formulate pharmaceutical formulations by mixing polymer and drug, and also improve the dissolution of hydrophobic drugs with low molecular weight. Due to the simplicity of the pharmaceutical formulation by simple solution mixing, biocompatibility and convenient usage these materials can be used in biomedical and pharmaceutical fields for tissue engineering, solubilizing of sparingly soluble drug molecules, controlled delivery of drugs and biomacromolecules, such as proteins and genes. In this review, temperature-responsive hydrogels are studied regarding their classification, applications and thermodynamics. Moreover, temperature-responsiveness mechanisms, polymeric gels, recent advances in surface, hydrogel and molecular design and biomedical application are investigated. Also, this review focuses on recent investigation based on the designs of temperature-responsive micelles and intelligent bioconjugates. Finally, limitations and potentials of applications of the temperature-responsive in situ forming hydrogels have been reported. The reported information in this paper are necessary to design and develop a desirable temperature-responsive hydrogels with different characteristics and applications.

Nitrile rubber/clay nanocomposites were prepared via in-situ emulsifier-free emulsion polymerization technique in the presence of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and pristine sodium montmorillonite (Na-MMT). The morphology of the nanocomposites was studied using X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM). The XRD results showed exfoliated morphology for the nanocomposites containing up to 3 wt% nanoclay and exfoliated-intercalated morphology for the nanocomposite containing 5 wt% nanoclay. The basal spacing of the nanocomposite، containing 5 wt% nanoclay، was increased to 1. 8 nm، which was 0. 61 nm wider than that obtained using pristine Na-MMT. Compared to neat rubber، the thermogravimetric analysis (TGA) revealed improvements in the thermal stability of all nanocomposite samples، in which the thermal degradation temperature was increased by increasing the clay content. The maximum increase in the thermal stability of the nanocomposites was obtained for the nanocomposite containing 5 wt% nanoclay with exfoliated-intercalated morphology. The tensile testing results showed remarkable improvements in the mechanical strength of the nanocomposites. In comparison with the neat nitrile rubber، the exfoliated nanocomposite، containing 3 wt% nanoclay، showed 302% and 219% increases in tensile modulus and tensile strength، respectively. The reason for improvementin mechanical properties of a nanocomposite، containing 3 wt% of nanoclay with respect to the nanocomposite containing 5 wt% of nanoclay، was related to the better dispersion of nanoclay platelets in the matrix and formation of exfoliated morphology. In addition، elongation-at-break and hardness were increased in the nanocomposites، when compared with the neat nitrile rubber.