the invention is based on the discovery that injectable and nucleic acid - compatible polymeric compositions and formulations can be structurally designed to regulate nucleic acid activity or gene expression in vivo , for example , by controlling the bioavailability of the nucleic acid via modulation of the biodegradability and crosslink density of the network formed by the components of the formulation . the polymeric network encases the nucleic acid , not only controlling the release of the dna , but also providing protection from degradation . the invention described herein improves upon prior modes of gene delivery , in that gene expression can be regulated by modulation of a polymeric network formed by combination of at least two water - soluble components capable of reacting with one another . the nucleic acid of interest is incorporated into the network to be released in a sustained manner to achieve level and duration of activity or expression needed .