Dextran of the following general formula I: is described, wherein R represents a chain containing from 1 to 15 carbon atoms and having at least one acid functional group prior to attachment to AA, the chain optionally being branched and/or unsaturated and containing one or more heteroatoms, such as O, N or/and S, F represents an ester, a carbamate or an ether, AA represents a hydrophobic amino acid radical, L or D, derived from a coupling between an amine of an amino acid and at least one acid functional group of R; the amino acid, prior to attachment to R, being selected from the group consisting of tryptophan, phenylalanine, leucine, isoleucine, alanine and valine, and alcohol, amide or decarboxylated derivatives thereof, and alkaline cation salts thereof, i represents the molar fraction of substituent F—R-[AA]n per glycosidic unit and is from 0.1 to 2, n represents the molar fraction of R groups substituted by AA and is from 0.05 to 1, and wherein for R groups not substituted by AA, the acid(s) of the group R are alkaline cation carboxylates such as Na or K.