title: In situ forming chitosan hydrogels prepared via ionic/covalent co-cross-linking.
abstract: In situ forming chitosan hydrogels have been prepared via coupled ionic and covalent cross-linking. Thus, different amounts of genipin (0.05, 0.10, 0.15, and 0.20% (w/w)), used as a chemical cross-linker, were added to a solution of chitosan that was previously neutralized with a glycerol-phosphate complex (ionic cross-linker). In this way, it was possible to overcome the pH barrier of the chitosan solution, to preserve its thermosensitive character, and to enhance the extent of cross-linking in the matrix simultaneously. To investigate the contributions of the ionic cross-linking and the chemical cross-linking, separately, we prepared the hydrogels without the addition of either genipin or the glycerol-phosphate complex. The addition of genipin to the neutralized solution disturbs the ionic cross-linking process and the chemical cross-linking becomes the dominant process. Moreover, the genipin concentration was used to modulate the network structure and performance. The more promising formulations were fully characterized, in a hydrated state, with respect to any equilibrium swelling, the development of internal structure, the occurrence of in vitro degradability and cytotoxicity, and the creation of in vivo injectability. Each of the hydrogel systems exhibited a notably high equilibrium water content, arising from the fact that their internal structure (examined by conventional SEM, and environmental SEM) was highly porous with interconnecting pores. The porosity and the pore size distribution were quantified by mercury intrusion porosimetry. Although all gels became degraded in the presence of lysozyme, their degradation rate greatly depended on the genipin load. Through in vitro viability tests, the hydrogel-based formulations were shown to be nontoxic. The in vivo injection of a co-cross-linking formulation revealed that the gel was rapidly formed and localized at the injection site, remaining in position for at least 1 week.
authors.affiliation: Departamento de Engenharia Química e Biológica, Instituto Superior de Engenharia de Coimbra, R. Pedro Nunes, 3030-199 Coimbra, Portugal.
authors.forename: M José
authors.initials: MJ
authors.lastname: Moura
authors.forename: H
authors.initials: H
authors.lastname: Faneca
authors.forename: M Pedroso
authors.initials: MP
authors.lastname: Lima
authors.forename: M Helena
authors.initials: MH
authors.lastname: Gil
authors.forename: M Margarida
authors.initials: MM
authors.lastname: Figueiredo
mesh_terms: D000818:Animals; D001672:Biocompatible Materials / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D001673:Biodegradation, Environmental; D001943:Breast Neoplasms / Q000188:drug therapy / Q000473:pathology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D048271:Chitosan / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D003432:Cross-Linking Reagents / Q000737:chemistry; D004337:Drug Carriers / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D055119:Elastic Modulus; D005260:Female; D005990:Glycerol / Q000737:chemistry; D020100:Hydrogels / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007477:Ions; D057889:Iridoid Glycosides / Q000737:chemistry*; D039823:Iridoids; D008297:Male; D051379:Mice; D008855:Microscopy, Electron, Scanning; D009113:Muramidase / Q000378:metabolism; D016062:Porosity; D051381:Rats; D017208:Rats, Wistar; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D001672:Biocompatible Materials; D003432:Cross-Linking Reagents; D004337:Drug Carriers; D020100:Hydrogels; D007477:Ions; D057889:Iridoid Glycosides; D039823:Iridoids; D048271:Chitosan; C007834:genipin; D009113:Muramidase; D005990:Glycerol