Current Organic Chemistry - Volume 22, Issue 7, 2018

Background: Chitosan thermoresponsive hydrogel is non-covalent crosslinked intelligent hydrogel. The compositions of the hydrogel determine its gelling property associated with particular structure-interaction effects. Simple and mild preparations as well as desirable bioactivities allow chitosan thermoresponsive hydrogels extensively applied in drug delivery and tissue engineering, especially the exciting proceeding in enzyme-free cell harvest and vascular embolic agent. Objective: This paper reviewed the classification of chitosan thermoresponsive hydrogels based on different components, emphasizing their gelling capacities, mechanism and applications in biomedical areas.

Background: Chitosan-based nano-biocomposite has received more and more attentions in the past few years because of the outstanding merits that chitosan is a natural polymer with biodegradable and biocompatible. Objective: The purpose of the present study is to summarize the different preparation methods of chitosan-based nano-biocomposites, such as electrostatic interaction method, preparation of chitosan-based nano-biocomposites from modified chitosan using selfassembly technique, chemical crosslinking approach, metal ions coordination and metal nanoparticles compound methods. In addition, the applications of chitosan-based nanobiocomposites in wound dressing, drug delivery, tissue engineering and biosensors are also discussed. Results: The results show that chitosan-based nano-biocomposites based on nanoparticles or nanohydrogel that can deliver drugs directly to cancer cells at a sustained and controlled rate may provide better efficacy and lower toxicity for the treatment of cancer. Furthermore, chitosan-based nano-biocomposites can enhance the properties of unmodified chitosan and improve the amphipathy, physical and mechanical properties of chitosan and produce new biological functions. Conclusion: It is believed that the rapid development of nano-science and technology must brought broad application prospects for the chitosan-based nano-biocomposites.

Background: Regarded as biofunctional poly- and oligomers having much higher potential than cellulose in many fields, chitosan and its derivatives have become of great interest thanks to the recent progress in chitin chemistry. Chitosan, which is a natural- based polymer obtained by alkaline deacetylation of chitin, is an interesting bioactive polysaccharide composed of many reactive groups. Objectives: This gives huge possibilities of chemical modifications to create new derivatives with a broad range of physico-chemical and biological activities. Method and Results: Special emphasis is given here to quaternized, N-alkyl, N-acyl, oxychitosan derivatives but also depolymerized chitosan. The present review also provides insights into chitosan derivatives and their biological activities. Numerous studies led for twenty years until now have put on track antimicrobial and antioxidant activities of chitosan derivatives. Biomedical applications have also been addressed, such as bioadhesive properties, antitumor activities, adsorption or chelation. Recent progresses of chitosan derivatives chemistry opened the way to new developments in medical and pharmaceutical fields, for example in tissue engineering or drug delivery system. Finally, biodegradability and environmental assessment concepts are reported. Conclusion: This work highlights the need for integral and comprehensive approach to comprehend all the biological potential of chitosan and its derivatives.

Background: Due to poor safety characterstics, viral vectors in gene delivery are usually limited in clinical application. Non-viral vectors have focused on the development of effective gene delivery carriers. As a promising non-viral carrier, chitosan (CS) is advantageous due to its biocompatibility, low toxicity and immunogenicity. Objective: The disadvantages such as low transfection efficiency and lack of celltargeting capability that CS possesses still need to be improved. Method: In this review, we summarized different chemical modifications of CS to overcome the obstacles mentioned before. The latest developments on the modifications of CS as gene delivery carriers will also be the main focus in this article. Results: For chemical modification of CS, the main interest focused on the ease of synthesis with controlled structure and size, biodegradability, high transfection efficiency and cell-targeted ability. Conclusion: Recent technological progress in chemical modification of CS has led to improvements of its transfection efficiency, better targeting specific cells and higher cellular uptake.

Background: Chitosan (CS) is a nontoxic and biocompatible natural polysaccharide with great development potential in the delivery of chemical drugs. However, further applications of CS are limited due to its inherent insolubility in neutral solution. Objective: The chemical modification of CS is of great significance for drug carriers, and the modification would not alter its fundamental skeleton but affords new or improved properties for drug delivery systems. Method: This review is designed to afford an overview of CS and CS derivatives used as drug delivery carriers, with a special stress on chemical modifications of CS to attain specific biomedical purpose. Results: The chemical modification of CS is generally carried out on the primary amine group or on the hydroxyl group. A variety of modifications such as quaternization, acylation, sulfonation, phosphorylation, thiolation, hydrophobization, hydrophilization afford extensive derivatives with improved properties for specific applications in pharmaceutical, biomedical and biotechnological fields. Conclusion: Various drug delivery systems and delivery of different categories of drugs based on CS and CS derivatives have also been illustrated.

Background: Chitosan, a naturally occurring polymer, is a non-toxic, biocompatible, and biodegradable, and has drawn much attention in the recent years for its use as scaffold material either as alone or in a combination with other materials in tissue engineering. In addition, these chitosan-based scaffolds are able to bind bioactive factors, preserve cells phenotype, control gene expression, synthesize and depose tissue-specific extracellular matrix during tissue regeneration. Objective: We hope it will be helpful to the researchers working in the field of tissue engineering and regenerative medicine. Method: In this review, we highlight the properties, modification and fabrication of innovative CS-based scaffolds for TE application. This review also provides an overview of the current status and the most likely directions of CS scaffolds for tissues such as bone, cartilage, nerve, vascular and other applications. Conclusion: Chitosan-based materials have been widely studied as potential scaffolds for bone, cartilage, nerve, vascular tissue and other tissue regeneration, due to the desirable physical, chemical and biological properties. However, more challenges on mechanical properties, fabrication, bioactivity and other performance are still existed.

Background: The microsphere prepared from chitosan, a natural polymeric material, has attracted considerable attentions due to the natural instincts of chitosan and microsphere structure. Objective: In the current review, the recent progress on the preparation and medical applications of chitosan microspheres would be introduced and summarized. Method: The methods for the preparation of CS microspheres were summarized, such as emulsion crosslinking method, coacervation method, precipitation method and polyelectrolyte complexation method, and so on. The tunable chemical properties possessed by CS microsphere, such as easily modified structure, and excellent biological properties including lower cytotoxicity, biocompatibility and biodegradability, would be introduced. Its medical applications based on its amazing properties in the recent years were present in detail with emphasis on the progress and advancement in drug delivery, gene therapy, bone repair, tissue engineering and wound dressing. Conclusion: It was believed that the rapid development of novel preparation technology will bring broader application prospects to CS microspheres.