Hydrogen bonding impact on chitosan plasticization

Strategy to design a smart photocleavable and pH sensitive chitosan based hydrogel through a novel crosslinker: a potential vehicle for controlled drug delivery

We report herein the synthesis of a novel photocleavable crosslinker, 4-formylphenyl 4-((4-formylphenoxy)methyl)-3-nitrobenzoate (CHO-ONB-CHO) and its joining with amine-based polysaccharides, viz. chitosan, resulting in the formation of a dual stimuli-responsive (ONB-chitosan) hydrogel having UV- and pH-responsive sites. The detailed mechanism for the formation of CHO-ONB-CHO and ONB-chitosan hydrogel is proposed. The (CHO-ONB-CHO) crosslinker was characterized using 1H-NMR, LCMS and UV-visible spectroscopy. The dual responsive hydrogel is characterized by FTIR, SEM, XRD, DSC and TGA. The crosslinked hydrogel displayed mechanical robustness with a storage modulus of about 1741 pa. The pH-responsiveness of the hydrogel was studied via equilibrium swelling studies in various pH media at 37 °C. The photocleavable behavior of the crosslinker was observed in the UV-absorption range of 310-340 nm and the hydrogel exhibited maximum swelling at pH 5.7. The higher swelling of the hydrogel in acidic conditions and its photo-responsiveness can be exploited for the controlled, temporal and spatial release of therapeutic drugs at any inflammatory areas with acidic environments. It was observed that the hydrogel exhibited higher drug release at pH 5.7 than at pH 7.4.

Effect of an ionic liquid on the physicochemical properties of chitosan/poly(vinyl alcohol) mixtures

Mixtures containing two polymers, chitosan (Ch) and poly(vinyl alcohol) (PVA) as well as mixtures with addition of an ionic liquid (IL) 1-butyl-3-methyl-imidazolium chloride (BMIM⁺Cl^-) were prepared via casting from aqueous solutions. The morphology, mechanical and surface properties of Ch/PVA mixture films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA), infrared spectroscopy (ATR-FTIR), contact angle measurements and tensile tests. Rheological studies were performed via solutions of pure polymers and their mixtures with and without the addition of an ionic liquid. The viscosity curves of mixtures were found to lie between those of pure components over the entire compositional range. The non-Newtonian index (n) of these mixtures were determined by the power law model indicating shear-thinning behavior with pseudoplasticity increasing with an increasing weight fraction of chitosan. Results obtained from SEM, AFM, contact angle measurements, TGA and infrared spectroscopy (ATR-FTIR) were compared and showed that the addition of an ionic liquid is beneficial to the formation of intermolecular forces and the network structure between the polymer and mixture films, which leads to an improvement in the properties of these materials.

The thiolated chitosan: Synthesis, gelling and antibacterial capability

Chitosan-1-(mercaptomethyl)-cyclopropane acetic acid (CS-MCA) copolymer was synthesized by amino linkage. The obtained copolymer was characterized by FTIR, ¹H NMR, XRD, TGA and SEM. Porous and reticulate morphologies were found on the CS-MCA surface. The effects of pH on the rheological properties of CS-MCA were investigated. On the one hand, the apparent viscosity of CS-MCA indicated a shear-thinning behavior. The graft of MCA enhanced the moduli and the maximum elastic properties were observed at pH = 7.00. The addition of dithiothreitol reduced the viscosity and modulus of CS-MCA hydrogel, and the gelation time, temperature and frequency were obtained in dynamic oscillatory tests. The antibacterial effect of CS-MCA against E. coli was investigated for the inhibition zone and bacterial growth curve. These results showed that CS-MCA had better antibacterial ability than chitosan without modification. Therefore, the rheological behavior and functional activities can be applied for the hydrocolloid gels in food and pharmaceutical applications.