Formation of calcium alginate-based macroporous materials comprising chitosan and hydroxyapatite

Abstract

Macroporous alginate hydrogels are prepared by the internal gelation method using crystalline saccharose. For this purpose, a sodium alginate solution containing D-glucono-δ-lactone and dispersed calcium carbonate particles was added to saccharose. Hydrolysis of D-glucono-δ-lactone gives rise to gradual acidification of the solution, which results in the decomposition of CaCO3 with the release of calcium cations; the latter crosslink polysaccharide macromolecules via chelate complexes to cause the formation of a gel. Washing out saccharose with water results in the formation of pores separated by calcium alginate films with a thickness of smaller that 100 nm. It is shown that the proposed method can be applied to produce a composite material containing particles of hydroxyapatite, which is incorporated into implants to accelerate the repair of bone tissues. The particles are entrapped into alginate films. A cationic polysaccharide, chitosan, is additionally incorporated into the alginate materials for their reinforcement; its stabilizing action is achieved via the formation of a polyelectrolyte complex with negatively charged alginate macromolecules. Chitosan is incorporated by a new method, which consists in gradually charging the polysaccharide during the acidification of the solution as a result of D-glucono-δ-lactone hydrolysis. Materials thus prepared are characterized by different methods, including scanning electron microscopy, dynamic mechanical analysis, and porosimetry.