Tunable porosity of covalently crosslinked alginate-based hydrogels and its significance in drug release behavior.

Task-specific drug release is essential in the development of hydrogels as drug delivery systems. The aim of the study is to report the effect of porosity on alginate hydrogels, which may be controlled by the design of crosslinkers, on drug release behavior. Two alginate-based hydrogels were prepared: alginate-norbornene (Alg-Nb) crosslinked by disulfide-tetrazine (S-Tz; hydrogel A) and alginate-furfuryl amine (Alg-FA) crosslinked by disulfide-maleimide (S-Ma; hydrogel B). Results showed the porosity of hydrogel A was controllable by adjusting the amount of S-Tz. Gel formation was facilitated by a "click" reaction between Alg-Nb and S-Tz, producing nitrogen gas, which, in turn, acted as an in-situ pore generator. Hydrogel B showed a non-porous morphology, as gelation was processed via addition reaction between Alg-FA and S-Ma, which produced no by-product. The study showed that crosslinker proportion and porosity were significant factors influencing drug release behavior of the alginate hydrogels. The presence of a porous structure increased the drug release while non-porous hydrogels led to a very slow release. In addition, the porous alginate hydrogels could sustainably release doxorubicin for 35 days.

Diselenide Core Cross-Linked Micelles of Poly(Ethylene Oxide)-b-Poly(Glycidyl Methacrylate) Prepared through Alkyne-Azide Click Chemistry as a Near-Infrared Controlled Drug Delivery System.

In this article, a drug delivery system with a near-infrared (NIR) light-responsive feature was successfully prepared using a block copolymer poly(ethylene oxide)-b-poly(glycidyl methacrylate)-azide (PEO-b-PGMA-N3) and a cross-linker containing a Se-Se bond through "click" chemistry. Doxorubicin (DOX) was loaded into the core-cross-linked (CCL) micelles of the block copolymer along with indocyanine green (ICG) as a generator of reactive oxygen species (ROS). During NIR light exposure, ROS were generated by ICG and attacked the Se-Se bond of the cross-linker, leading to de-crosslinking of the CCL micelles. After NIR irradiation, the CCL micelles were continuously disrupted, which can be a good indication for effective drug release. Photothermal analysis showed that the temperature elevation during NIR exposure was negligible, thus safe for normal cells. In vitro drug release tests demonstrated that the drug release from diselenide CCL micelles could be controlled by NIR irradiation and affected by the acidity of the environment.