Abstract
In recent years, the exploration of tumor microenvironment has provided a new approach for tumor treatment. More and more researches are devoted to designing tumor microenvironment-responsive nanogels loaded with therapeutic drugs. Compared with other drug carriers, nanogel has shown great potential in improving the effect of chemotherapy, which is attributed to its stable size, superior hydrophilicity, excellent biocompatibility, and responsiveness to specific environment. This review primarily summarizes the common preparation techniques of nanogels (such as free radical polymerization, covalent cross-linking, and physical self-assembly) and loading ways of drug in nanogels (including physical encapsulation and chemical coupling) as well as the controlled drug release behaviors. Furthermore, the difficulties and prospects of nanogels as drug carriers are also briefly described.
Highlights
The use of nanogels as carriers for drugs and other molecules has been extensively studied over the past 2 decades (Raemdonck et al, 2009; Li Y. et al, 2015; Mohammadi et al, 2020; Zhao et al, 2021)
In order to further explore NG-DDS comprehensively and systematically, this review primarily summarizes the synthetic strategies of nanogels, methods of drug loading as well as stimuli-responsive drug release behaviors
The results showed that the drug release was thermo-dependent with a remarkable increase above the volume phase transition temperature of 32–37°C (Sahle et al, 2017)
Summary
The use of nanogels as carriers for drugs and other molecules has been extensively studied over the past 2 decades (Raemdonck et al, 2009; Li Y. et al, 2015; Mohammadi et al, 2020; Zhao et al, 2021). Nanogels are defined as 3D sub-micron sized hydrophilic polymer networks formed through physical or chemical cross-linking, exhibiting the comprehensive properties of hydrogels and nanoparticles simultaneously. Physical cross-linking mainly includes hydrophobic interactions, electrostatic interactions, hydrogen bonds, and ionic interactions. Chemical method is to produce covalent bonds during the preparation of nanogels (Neamtu et al, 2017). Nanogels are able to absorb a large quantity of water. The cross-linking network of nanogels is considered as a matrix to hold the inner liquid medium, while the absorbed water can be regarded as a filter medium for the diffusion of cargoes. The swelling and shrinking behavior of nanogels is considered as an indispensable feature, which promotes the diffusion of loaded drug (Clegg et al, 2020)
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