Abstract
Polymers that can change their properties in response to an external or internal stimulus have become an interesting platform for drug delivery systems. Polymeric nanoparticles can be used to decrease the toxicity of drugs, improve the circulation of hydrophobic drugs, and increase a drug’s efficacy. Furthermore, polymers that are sensitive to specific stimuli can be used to achieve controlled release of drugs into specific areas of the body. This review discusses the different stimuli that can be used for controlled drug delivery based on internal and external stimuli. Internal stimuli have been defined as events that evoke changes in different characteristics, inside the body, such as changes in pH, redox potential, and temperature. External stimuli have been defined as the use of an external source such as light and ultrasound to implement such changes. Special attention has been paid to the particular chemical structures that need to be incorporated into polymers to achieve the desired stimuli response. A current trend in this field is the incorporation of several stimuli in a single polymer to achieve higher specificity. Therefore, to access the most recent advances in stimuli-responsive polymers, the focus of this review is to combine several stimuli. The combination of different stimuli is discussed along with the chemical structures that can produce it.
Highlights
Academic Editors: Valentina OnestoControlled release of drugs is a growing field with many challenges to overcome.Many drugs are hydrophobic, which limits their bioavailability
Temperature-sensitive polymers are one of the most well-known materials. These polymers change their structure from a shrunken to a swollen form, in response to temperature change. The characterization of these polymers is made by the upper critical solution temperature (UCST) or the lower critical solution temperature (LCST) [59,68,69,70]
Stimuli-responsive polymer particles have become a trend in the drug delivery field
Summary
Controlled release of drugs is a growing field with many challenges to overcome. Many drugs are hydrophobic, which limits their bioavailability. While there are reviews focus- as particles for ing on the use of stimuli-responsive for targeting or imaging purposes [9,10,11,12,13], controlled drug release, with apolymers focus on the recent advances in the field. As there are this review will summarize the progress stimuli-responsive already several recent reviews discussing theinrole of hydrogelspolymers in drugasdelivery [14,15,16,17,18,19], particles for controlled drug release, with a focus on the recent advances in the field. Table presentsofathe brief summary of the different stimuli thatthe we will discuss in review with some1examples active parts needed within a polymer to achieve desired stimuli response. Hyaluronic acid-methoxy Poly(ethylene-glycol) amine (Di)methyl maleate bond: PDLLA-PEG
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