15: Review of Smart Materials for Controlled Drug Release

Chapter 15 reviews smart materials for controlled drug release. Systemically-administered controlled release systems allow fine-tuning of drug bioavailability, by regulating the amount and the rate at which the drug reaches the bloodstream, which is critical for the success of the therapy. Some drugs pose important problems in terms of efficacy and safety (e.g., antitumor drugs, antimicrobials) and suffer instability problems in the biological environment (e.g., gene materials), and thus the therapeutic performance of these drugs is improved when they are selectively directed (targeted) from the bloodstream to the site of action (tissues, cells or cellular structures). Both macro-dosage forms and nano-delivery systems may notably benefit from stimuli-responsive materials. Differently to pre-programmed drug release systems, formulations that provide discontinuous release as a function of specific signals (stimuli) are advantageous in many situations. Triggering drug release where, when, and how it is needed requires detailed knowledge of the changes that the illness causes in terms of physiological parameters. These changes can be characterized in terms of biomarkers (e.g., glucose, specific enzymes, or quorum sensing signals in the case of infection) and physicochemical parameters (pH, ions, temperature, glutathione) that may be exploited as internal stimuli. When the physio–pathological changes are too weak or poorly specific, the application of external stimuli may be an alternative. External sources of temperature, ultrasound, light, and magnetic or electric fields may allow for the focal switch on/off of drug release. This chapter provides an overview of the interest in activation-modulated and feedback-regulated controlled release systems, the mechanisms behind them, and some specific examples of responsive materials and their applications.