Composition and method to crosslink or modify chitosan homogeneously under neutral conditions.

A composition comprising: a) from 0.1 to 10% by weight of chitosan in a clear aqueous and acidic solution of chitosan, the chitosan said has a degree of deacetylation between 70% and 100%; b) 0.1 to 20% by weight of at least one buffering agent having a pKa between 6.0 and 7.6, c) 0.01 to 10% by weight of at least one reagent which reacts with chitosan amino groups, wherein said composition of N-modified chitosan has a pH ranging from 6.8 to 7.2, and said chitosan undergoes a Nmodificacion, N-grafting or N-cross-linking in said composition homogeneous chitosan ; being selected from reagent group consisting of glutaraldehyde, formaldehyde, acetic anhydride, propionic anhydride, butyric anhydride, based on aldehyde bifunctional propionic reagent, a reagent having a reagent selected from the group ester group consisting of ester group sulfosuccinimidyl and N -sulfosuccinimidilo, reagent having an imidoester reactive group selected group consisting of di-metilpimelimidato group, dimethyladipimidate, di-metilsuberimidato, and di-metilpropionimidato, and a reagent having phenyl azide group one, hydrazide, azide or nitrophenyl azide hidrofenilazida wherein said composition comprises an organic solvent.