Microfluidic engineering of triple-responsive cystine-crosslinked microgels for mild-redox-triggered chemotherapy

Stimuli-responsive microgels promise site-directed chemotherapy, yet most redox-sensitive carriers depend on poorly soluble disulfide crosslinkers and require intracellular glutathione (≥10 mM) to trigger release. In contrast, we introduce the water-soluble cystine derivative N,N'-diacryloyl-L-cystine disodium salt (DACS) as a crosslinker that enables one-step microfluidic synthesis of poly(acrylamide) microgels with in-process doxorubicin encapsulation. Flow-focusing devices with junctions 100 × 100 μm and 24 × 24 μm yielded two monodisperse fractions (μG100 with mean diameters ≈ 412 μm and μG24 with mean diameters ≈ 82 μm) of microgels - with encapsulation efficiencies of 98 % (μG100) and 87 % (μG24). The microgels are triple-responsive: they swell with increase of pH, shrink with increase of ionic strength, and degrade in redox conditions. Critically, DACS-crosslinked microgels achieve enhanced release under tumor-relevant conditions - at pH 6.5 and at only 100 μM glutathione, near extracellular tumor levels - while 10 mM GSH induces complete network disintegration. Particles remain morphologically stable for 90 days at pH 7.4 and exhibit selective cytotoxicity toward cancer cells under in vitro conditions. DACS-crosslinked microgels thus offer mild redox-triggered delivery combined with a scalable, in-process encapsulation strategy, providing a potential versatile platform for future applications in localized chemotherapy and other biomedical payloads. In vitro, drug-free microgels were non-cytotoxic to WJ and to MCF-7 cells, whereas DOX-loaded microgels retained anticancer activity with reduced effects on WJ relative to free drug, with morphological changes in MCF-7 consistent with apoptotic-like features at effective doses. Time-resolved assays indicated that size modulates performance: μG100 appeared more potent against MCF-7, while μG24 provided a wider safety margin for WJ. Together, DACS-crosslinked microgels constitute a water-processable, redox-triggered delivery platform that couples single-step encapsulation with size tuning to balance efficacy and healthy-cell sparing for localized chemotherapy.