Engineering hydrogel-coated surfaces with improved stimulus response for biomedical applications

Poly(N-Isopropylacrylamide) (PNIPAAm)-based hydrogels are well known for their thermoresponsive properties, which make them attractive for applications in smart surfaces, drug delivery, and responsive coatings for biomedical applications. However, conventional PNIPAAm hydrogels coated on surfaces often exhibit restricted thermal response due to their surface attachment, reducing their practical utility. In this study, we developed a hydrogel coating with enhanced thermoresponsive behavior, using PNIPAAm/Poly(methyl methacrylate) (PMMA) electrospun NR (NR) containing Cellulose Nanocrystals (CNCs). These composite NR were incorporated into a crosslinked PNIPAAm hydrogel matrix and aligned using directional blade coating on glass substrates. Since both the composite NR and the hydrogel are composed of PNIPAAm they exhibit a synergistic thermoresponsive behavior, ensuring a coordinated phase transition and volume expansion. The alignment of the NR introduces an anisotropic structure and a synchronous thermal-stimulated volume expansion of both the hydrogel network and the composite NR. Under this matched responsive behavior the coated composite hydrogel shows a higher structural expansion in response to temperature changes. The hydrogels with aligned NR displayed more than 2.5 times higher volume expansion compared both pure hydrogels and hydrogels with non-aligned NR. All hydrogels show cytocompatibility but only the one with aligned NR exhibited a topography that guides skeletal muscle cell alignment, while supporting expression of key muscle differentiation markers. The approach provides an energy-efficient, economical, and scalable method to create highly responsive PNIPAAm-hydrogel coated surfaces. This work opens a new path for functional thermoresponsively activated coatings, soft actuators, and cell-engineering platforms where precise control of surface topography and material volume expansion is critical.