Internal stimuli-responsive nanocarriers for drug delivery: Design strategies and applications

•Internal stimuli responsive drug delivery systems are presented for tumor targeting or inflammation therapy.•pH-, redox-, enzyme-, temperature-sensitive materials are introduced to compose or modify the nanocarriers including polypeptides, polysaccharides (such as chitosan and glucose) and other multifunctional polymers.•Self-assembled copolymers based micelles or other nanopreparations are introduced in detail.

The design of internal stimuli-responsive nanocarriers has been extensively used for delivery of various active compounds including drugs, peptides and genes. These nanosystems are not only designed for improved solubility, enhanced bioavailability, and prolonged blood circulation time, furthermore, they can be tailored chemically to achieve selective drug release at the desired sites of action, which can enable them to bypass physiological or pathological obstacles and achieve enhanced therapeutic efficacy. This review presents current functional moieties responsive to a variety of internal stimuli, including pH, redox, enzyme, temperature. Their design strategies and biomedical applications are also highlighted in detail. It is expected that this review can provide inspiration and impetus for exploiting more promising internal stimuli-responsive nano-systems for drug delivery.

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