Interpenetrating polymer network microspheres based on alginate and thiolated CNF for tumor-triggered localized intratumoral therapy.

Interpenetrating polymer network (IPN) microspheres composed of alginate and thiolated TEMPO-oxidized cellulose nanofibers (Th-TCNF) were developed as reduction-responsive carriers for Mitoxantrone (MIT) delivery. TCNF was thiolated through covalent coupling with cysteamine, as confirmed by H NMR, FT-IR and XPS which successfully verified thiol grafting. Spray-dried microspheres were subsequently cross-linked via Ca2+ coordination and disulfide bond formation, generating a mechanically reinforced IPN structure. Swelling analysis showed significantly reduced equilibrium swelling in the full IPN compared with single-network controls, indicating restricted polymer mobility and enhanced structural stability. SEM revealed progressively denser surfaces with increasing Th-TCNF content, while TGA demonstrated improved thermal resistance. XPS of the microspheres confirmed reduction-induced disulfide cleavage, supporting redox-triggered release. FITC-dextran and MIT release exhibited reduction-dependent, composition-controlled behaviour, and flow cytometry (FACS) showed sustained intracellular MIT accumulation in MDA-MB-231 cells, leading to prolonged cytotoxicity. In vivo intratumoral administration in BALB/c nude mice bearing MDA-MB-231 xenografts produced significant tumor suppression with extensive necrosis and apoptosis, without systemic toxicity, verified by Histological (H&E) and TUNEL staining. Collectively, these findings highlight alginate: Th-TCNF IPN microspheres as a promising localized, reduction-responsive platform for enhancing chemotherapeutic efficacy while minimizing systemic toxicity.