Stimuli-Responsive Capsule Membranes for Controlled Release in Pharmaceutical Applications

In conventional drug delivery, the drug concentration in the blood raises once the drug taken, and then peaks and declines. Since each drug has a level above which it is toxic and another level below which it is ineffective, the drug concentration in a patient at a particular time depends on compliance with the prescribed routine.To achieve more effective efficacy and fewer side effects of drugs, the drug carriers with desirable dosing and controllable release property of drugs are highly desired. Stimuli-responsive capsules with smart gating membranes or hydrogel-based membranes as capsule shells are ideal candidates. The smart capsule membranes enable efficient encapsulation of drugs within the large inner volume, and the responsive gating membranes or hydrogel-based membranes could control the release rate of encapsulated drugs in responding to environmental stimuli. The trigger stimuli could be either artificial or natural ones corresponding to specific diseases, such as temperature, pH, glucose concentration, specific ion, light, and magnetic field.This review highlights the recent development in stimuli-responsive capsule membranes for controlled release in pharmaceutical applications, including two types of stimuli-responsive capsule membranes with different architectures for on/off release and burst release, which can achieve potential uses of case-dependent on/off release and burst release.The preponderances of the smart capsule membranes are that the capsules are with controllable inner space for drug vehicles with desired dose and stimuli-responsive membrane as shell to release drugs at a desired site and/or moment. However, the actual difficulties for the stimuli-responsive capsule membrane systems to go before they can be applied widely in the biomedical fields are discussed. The future works should focus on the improvements of biocompatibility, biodegradability and stimuli-responsiveness of the capsule membranes, easy and scalable fabrication techniques with further decrease of the capsule size for more efficient in vivo applications, and the diversification of the multi-compartmental capsule architectures with multi-stimuli-responsive characteristics for controlled release.