Wearable hydrogel-integrated microfluidic platforms for controlled cutaneous and transdermal drug delivery: engineering design, stimuli-responsive release, and computational modeling.

Wearable microfluidic systems that integrate stimuli-responsive hydrogel reservoirs with flexible, skin-conformal architectures can support several distinct delivery routes, including topical or dermal treatment, wound-bed delivery, microneedle-assisted intradermal or transdermal administration, and electrically enhanced transdermal delivery. This critical narrative review evaluates hydrogel materials, loading and release mechanisms, route-specific interfaces, empirical release kinetics, mechanistic transport, and COMSOL Multiphysics-based numerical modeling. Drug liberation from a reservoir is distinguished from device output, skin partitioning, permeation, tissue deposition, systemic absorption, and therapeutic response. PNIPAM behavior is interpreted temporally: heating above the LCST may produce a short deswelling-driven expulsion phase followed by reduced sustained diffusion through the collapsed network. Computational models are positioned as tools for design-space exploration, sensitivity analysis, and reduction-not elimination-of experimental iterations. Cross-cutting translation requirements include dehydration control, mechanical and adhesive reliability, payload stability, manufacturing reproducibility, biocompatibility, human factors, and jurisdiction-dependent regulation. Qualitative Technology Readiness Level estimates are used only as comparative evidence-maturity indicators and not as formal regulatory determinations.