The invention relates to the chitosan polymer derivatives of formula I: and pharmaceutically acceptable salts and esters thereof, wherein Y, X1, X4, R1, R2, and n are defined in the detailed description and claims. The chitosan polymer derivatives of formula I bind to or associate with alpha-4-beta-1 (alpha4beta1) and alpha-V-beta-3 (alphaVbeta3) integrin dimers and can be used in delivery formulations to deliver drugs, nucleic acids, or other therapeutic compounds to tissues or cells expressing such integrins.
