 Due to safety concerns with viral vectors , nonviral delivery methods , typically employing lipid @-@ based or polymeric vectors , are also promising candidates . Computational modeling of nonviral siRNA delivery paired with in vitro and in vivo gene knockdown studies elucidated the temporal behavior of RNAi in these systems . The model used an input bolus dose of siRNA and computationally and experimentally showed that knockdown duration was dependent mainly on the doubling time of the cells to which siRNA was delivered , while peak knockdown depended primarily on the delivered dose . Kinetic considerations of RNAi are imperative to safe and effective dosing schedules as nonviral methods of inducing RNAi continue to be developed . 
