Chemical and physical modifications of alginate to improve its use as carriers for delivery systems

Abstract

Alginate is a biopolymer of anionic nature with numerous applications as a biomaterial and in biomedical science owing to its advantageous properties, the main ones being biocompatibility, biodegradability, low toxicity and ease of gelation. To date alginate polymers and derivatives have had particular attraction in wound healing, drug delivery and tissue engineering applications.It is known that drug molecules, from small chemical drugs to macromolecular proteins, can be released from alginate gels in a controlled manner, depending on the specific characteristics of the network. In order to understand how alginates can be optimized as a useful delivery system for therapeutic applications, however, it is necessary to know more about the various factors affecting drug release from alginate matrices, such as network porosity, pH effect, composition, and modification of the functional groups in alginates; these can then be controlled through their structure/property relationships, which closely dependent on the type of cross-linker and cross-linking methods. Several synthetic strategies have been employed to improve the behavior of alginates, including covalent and non-covalent bonds. In this chapter we present the different methodologies for the formation of networks: ionic interaction, covalent cross-linking, grafting reactions, interpenetrating and semi-interpenetrating polymer networks and amphiphilic structures formed by association or conjugation. In each case we show their advantages and main applications deriving from the synthetic pathway employed. In summary, this chapter provides a comprehensive overview of synthetic ways to improve the physical-chemical properties of alginate hydrogels in relation to their biomedical applications as alginate carriers in delivery systems.Lastly, we present the advantages and preparation of alginate nanogels and their potential application in nanomedicine.