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Advanced development of chitosan hydrogels has led to new drug delivery systems that can release their active ingredients in response to environmental stimuli. This review considers more recent investigation of chitosan hydrogel preparations and the application of these preparations for drug delivery in wound dressings. Applications and structural characteristics of different types of active ingredients, such as growth factors, nanoparticles, nanostructures, and drug loaded chitosan hydrogels are summarized., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Wound healing is a complicated process requiring appropriate environment to accelerate healing process. In the recent years, many wound dressings have been developed for treating various kinds of wounds. In this study, we aimed to develop a novel dressing with high ability of burn wound healing and minimum side effects. Carboxymethyl cellulose (CMC) based hydrogels containing Hypericum perforatum were developed by grafting methacrylic acid and acrylamide onto CMC to produce a good mechanical strength dressing. Covalent crosslinking, which is responsible for stable mechanical structure, led to a 3D structure with appropriate water vapor transmission rate (2950 g/m2/day), controlled drug release (33% in 78 h), and great burn healing ability (almost complete healing in 10 day). The hydrogel has proper antimicrobial activity against the tested microorganisms. Zone of inhibition against E.coli was the higher in comparison with S. aureus and Candida. Minimum inhibitory concentration (MIC) for C. albicans, S. aureus, and E. coli were as 6, 4, and 5 mg/ml of H. perforatum. In vivo experiments on rats revealed that wound healing process by loaded hydrogels was faster in comparison with control group. All the results indicated that prepared hydrogel has the capability to accelerate burn wound healing process. [ABSTRACT FROM AUTHOR]

Chitosan‐based hydrogels involving γ‐cyclodextrin inclusion compounds of thyme oil were prepared by freeze–thaw cycling method. Clinoptilolite as a natural zeolite was added to investigate its effects on the structural, mechanical, and drug release behaviors of the hydrogels. Zeolite compressed the structure and improved mechanical properties, which decreased swelling values. Release of thyme oil in prepared hydrogels were investigated by UV spectroscopy and drug release mechanism was evaluated by applying various mathematical methods. Rates of water vapor transmission of the samples were calculated as 2247–2998 g m−2 day−1 which are all in the range of an ideal wound dressing. Hydrogels with clinoptilolite had slower drug release (from 56% to 24% for hydrogels containing zeolite 1%) in comparison with that of without zeolite. Based on MTT assay, samples were low‐toxic. Obtained results suggest that drug loaded hydrogels can be applied in biomedical field including drug delivery systems and wound dressings. [ABSTRACT FROM AUTHOR]

Hydrogels derived from natural polysaccharides are ideal scaffolds for use in biomedical applications. pH‐sensitive polyvinyl alcohol and chitosan hydrogels containing inclusion compounds of thyme oil (TM) with host methyl‐β‐cyclodextrin (MβCD) and hydroxypropyl‐β‐cyclodextrin (HβCD) and TM nanoemulsion (TM‐nano) were prepared via controlled, biocompatible and low cost freeze–thaw method. The structure of the hydrogels was characterized by Fourier transform IR spectroscopy and optical and scanning electron microscopy. The physicochemical properties of the hydrogels such as gel fraction, swelling ratio and tensile properties were measured. The water vapor transmission rate of the hydrogels indicated that they can maintain a moist environment over the wound bed. Encapsulation and release of antibacterial TM from the hydrogels were determined by UV spectroscopy. In all cases, hydrogels with lower amounts of TM evidenced slower and more controlled release. Different kinetic models were applied for evaluating the drug release mechanism. The antibacterial activity of the samples was studied by counting the number of both Gram‐negative and Gram‐positive bacteria surviving in a broth medium and the results proved the antibacterial activity of all prepared hydrogels. The results of an MTT (3‐(4,5‐dimethylthiazol‐2yl)‐2,5‐diphenyltetrazolium bromide) assay indicated more cell viability of TM‐nano hydrogels in comparison with those of TM‐βCD inclusion compounds. Cell attachment observations also showed great biocompatibility of TM‐nano hydrogels. The prepared hydrogels, especially those containing TM‐nano, might be used as potential wound dressings to improve the wound healing process. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

• pH sensitive polyvinyl alcohol and chitosan hydrogel wound dressings containing cyclodextrin inclusion compounds (CD-ICs) were developed by freeze-thaw method. • The structures of the hydrogels were characterized by FTIR, optical and scanning electron microscopy. • The MTT assay indicated low-toxicity of the prepared hydrogels and the in vitro test showed antibacterial activity of all prepared hydrogels against E. coli and S. aurous. • Different mathematical models were applied for evaluating drug release mechanism and kinetic. • The prepared hydrogels might be used as potential wound dressings to improve wound healing. Hydrogels, based on polysaccharides such as chitosan have found various applications as drug delivery carriers. Three different preparations of pH sensitive chitosan/polyvinyl alcohol hydrogels containing inclusion compounds of thyme oil with methyl-β-, hydroxypropyl-β- and γ-cyclodextrin were developed by using a controlled, bio-compatible and low cost method based on freeze-thaw cycling. The structures and morphology of the hydrogels were characterized by FTIR, optical and scanning electron microscopy. Stable hydrogels of chitosan and polyvinyl alcohol had good mechanical properties and swelling ratios. The water vapor transmission rates of the hydrogels were all in the range of an ideal wound dressing. Encapsulation and release of thyme oil-cyclodextrin inclusion compounds (TM-CD-ICs) in the hydrogels were detected and followed by UV spectroscopy and different mathematical models were applied for evaluating the drug release mechanisms. Hydrogels loaded with TM-CD-ICs had slower and more controlled drug release. The antibacterial activity of the samples was studied by counting the number of surviving both gram-negative and gram-positive bacteria in a broth medium and the results showed antibacterial activity of all prepared hydrogels, especially those containing TM-γCD-ICs. The MTT assay indicated more cell viability of TM-γCD-ICs hydrogels in comparison with those containing β-cyclodextrin inclusion compounds (TM-βCD-ICs hydrogels). Cell attachment study showed great biocompatibility of TM-γCD-ICs hydrogels. Finally, the modified hydrogels can be used in different biomedical applications, such as wound dressings for improving the wound healing process and in drug delivery systems. [ABSTRACT FROM AUTHOR]