Embodiments of the invention include functionalized polysaccharides and compositions and structures including the same. In an embodiment, the invention includes an active agent delivery composition including a polysaccharide functionalized with a coupling group, wherein the polysaccharide lacks charged groups at a pH of between 6 and 8; and a complex comprising a nucleic acid and a transfection agent. In an embodiment, the invention includes an active agent delivery structure including a matrix comprising a polysaccharide covalently cross-linked through the residue of a coupling group on the polysaccharide, the polysaccharide lacking charged groups at a pH of between 6 and 8; and a nucleic acid delivery complex disposed within the active agent delivery structure. In an embodiment, the invention includes a material for medical applications including glycogen functionalized with coupling groups at a degree of substitution of between about 0.01 and 0.5. Other embodiments are also included herein.