Stimuli-responsive polymers and nanomaterials for gene delivery and imaging applications.

Multiple extra- and intracellular obstacles, including low stability in blood, poor cellular uptake, and inefficient endosomal escape and disassembly in the cytoplasm, have to be overcome in order to deliver nucleic acids for gene therapy. This review introduces the recent advances in tackling the key challenges in achieving efficient, targeted, and safe nonviral gene delivery using various nucleic acid-containing nanomaterials that are designed to respond to various extra- and intracellular biological stimuli (e.g., pH, redox potential, and enzyme) as well as external artificial triggers (e.g., light and ultrasound). Gene delivery in combination with molecular imaging and targeting enables diagnostic assessment, treatment monitoring and quantification of efficiency, and confirmation of cure, thus fulfilling the great promise of efficient and personalized medicine. Nanomaterials platform for combined imaging and gene therapy, nanotheragnostics, using stimuli-responsive materials is also highlighted in this review. It is clear that developing novel multifunctional nonviral vectors, which transform their physico-chemical properties in response to various stimuli in a timely and spatially controlled manner, is highly desired to translate the promise of gene therapy for the clinical success.