The use of chitosan, a natural polymer, has recently increased due to its antimicrobial and antifungal character, null toxicity, biocompatibility and ability to form biofilms and hydrogels. The areas of application and research include biomedical, pharmaceutical, biomaterials, water treatment and haircare and skincare products. However, the applications of chitosan are limited due to the difficulty associated with modification of its structure and its poor solubility in water. Among the main chemical modifications for functionalising the chitosan structure are the N-substitution, O-substitution (with or without protecting the reactive sites of the chitosan) and cross-linking with other compounds; these chemical modifications allow improvement of its chemical and physical properties. In relation to the current importance of the use of chitosan with chemical modification, the present review attempts to explain in a simple way the main chemical reactions carried out with chitosan and its wide range of applications, and provides a future perspective.

• The chitosan obtained shows physicochemical properties similar to commercials. • The low molecular chitosan for harvesting microalgae shows better results than aluminum sulfate. • The use chitosan for harvesting microalgae reduces the process costs.

The mucilage obtained from cladodes of Opuntia spinulifera has been used in industries and traditional applications. In the present work, the chemical, morphological, thermal and structural features of cladode mucilage from Opuntia spinulifera Salm-Dyck were studied. The 2D ¹H-¹H COSY NMR confirmed ten different residues within the repeating saccharide unit, six with α and four with β configurations. The FTIR showed the presence of galactose and pectins. The XRD detected minerals as calcium salts. The SEM exhibited aggregations and irregular morphology of the particles. The TGA registered the highest mass loss between 246–378°C and the DSC showed the transition state at 55.7°C and at 113.2°C was observed the typical endothermic peak, where it corresponds to the organic compound materials.