Dillip Kumar Satapathy

Biopolymer soft actuators capable of programmable, directional motion are essential for the advancement of adaptive soft robotics and intelligent responsive systems. However, existing soft actuators often suffer from weak directional control, poor spatial programmability, limited environmental adaptability, and an inability to operate under confined conditions. Here, we present a sustainable multi-stimuli-responsive soft actuator based on free-standing cassava starch films embedded with plasmonic gold (Au) and silver (Ag) nanoparticles that combines the intrinsic hygroscopicity of starch with plasmonic photothermal actuation. The hybrid films exhibit strong humidity-responsive deformation together with reproducible bending under green and blue laser irradiation. Notably, the nanoparticle-embedded films demonstrate excellent cyclic stability and reproducible light-responsive actuation over 1000 consecutive cycles. We show that laser-induced heating generates localized moisture gradients within the film that serve as the primary driving force for actuation. By engineering an asymmetric structural hierarchy with a polydimethylsiloxane (PDMS) layer, we achieve predictable bending pathways and spatially resolved shape transformations through multispot illumination. Notably, we demonstrate a trilayer Ag–PDMS–Au architecture that exhibits wavelength-selective bidirectional actuation: blue light induces bending toward the source, whereas green light drives bending away. We show that these actuators retain robust performance under confined environments and can be directly integrated into electrical circuits. This chromatically programmable mechanical response, combined with the ability to function in confined spaces, establishes plasmonic starch multilayers as a versatile and sustainable system for programmable soft actuation.

Janus particles provide a powerful platform for studying asymmetric surface functionality and active colloidal matter, yet their broader utilization is hindered by the lack of fabrication strategies that offer quantitative and independent control over patch geometry. Here, we report an interfacial confinement-assisted electroless deposition process that exploits irreversible particle adsorption at the liquid–liquid interface for directed metal deposition. This process enables systematic control over metal patch thickness (5–50 nm) and surface coverage while remaining robust to the deposition of various metals (Au, Ag, Pt, Ni, Cu) and scalable across centimeter-scale interfacial areas (≈ 16 cm2). The generality of the approach is demonstrated by the synthesis of Janus particles with varied shapes (sphere, ellipsoid, peanut, sphero-cylinder, cube) and surface chemistries (hematite, silica, polystyrene, p-NIPAM) at liquid–liquid interfaces formed with different oils. To characterize the activity of particles, we perform experiments in hydrogen peroxide solutions of varying concentrations and demonstrate the influence of the catalytic patch thickness on the self-propulsion of Janus particles. Because the proposed process relies on general principles of colloids and interfacial chemistry, it is readily extendable to diverse systems and provides a versatile chemical route to architected Janus colloids.

PNIPAM microgels, a model soft colloid known to respond to external stimuli such as temperature or pH, show significantly different swelling kinetics at the fluid-fluid interface compared to bulk. When an aqueous dispersion of these microgels dries on a solid substrate, they adsorb onto the air-water interface and undergo significant flattening along the interface. This interfacial rearrangement enables the formation of ordered monolayers, offering a bottom-up route for fabricating colloidal films. Leveraging on their temperature-responsive swelling and surface activity, we investigate how poly(N-isopropylacrylamide) (PNIPAM) microgels can be used to obtain complex deposition patterns by drying sessile aqueous drops containing microgels at different concentrations on hydrophilic substrates maintained at temperatures, below and above the volume phase transition temperature (VPTT) of the microgels. The evaporation dynamics of the drop is monitored using in situ video microscopy and a contact angle goniometer, while the resulting microstructures are characterized using atomic force microscopy (AFM). Our observations reveal a rich diversity in final deposit morphologies, ranging from uniform films to classic coffee-ring and multiring patterns. These deposition outcomes depend on both the initial particle concentration and the substrate temperature. Notably, we find that the average height of the dried microgels increases with the substrate temperature. Moreover, spatial heterogeneity in the height profiles of the microgels across different regions of the deposits suggests that thermally modulated interfacial behavior of the microgels plays a critical role in directing their self-assembly during evaporation.

Fully reversible multi vapor-responsive Cocos nucifera pollen paper exhibits tunable shape morphism.

The composition of polymorphic phases, such as amorphous α-helices, crystalline β-sheets, and other secondary structures, in protein films plays a pivotal role in defining their physical, chemical, and mechanical properties. Bombyx mori silk, which inherently possesses tunable secondary structures, can be easily tailored by processes such as mechanical stretching, water annealing, or exposure to specific solvents. In this work, we investigate the vapor-responsive actuation behavior of silk fibroin films fabricated via a nontoxic, aqueous-based processing route. In particular, we elucidate the influence of the polymorphic phase composition on the water vapor actuation characteristics of the films. The different fractions of secondary structures are achieved by exposing the silk films to various alcohols. We also introduce a novel approach to modulate crystallinity by controlling the ambient humidity during the drying process of the silk aqueous solutions. Our experiments clearly reveal a nonmonotonic dependence of actuation performance on the content of crystalline β-sheets. The actuation characteristics initially improve with increasing β-sheet crystallinity but deteriorate once the fraction exceeds approximately 35%. Furthermore, we demonstrate that the directionality of actuation (bending axis) can be precisely controlled by imprinting periodic microgrooves onto the film surface. As a proof of concept, we present an autonomously actuated "autobreathe" window designed to dynamically regulate humidity levels within a sealed chamber.

Bioinspired three-dimensional shape deformations of smart polymers in response to stimuli such as light, vapor, and external fields have garnered significant attention in the field of soft robotics. Among these stimuli, vapor-induced shape deformation is particularly promising due to its ability to generate substantial deformation in response to minimal vapor input. In this study, we investigated the influence of polymorphic phase fractions of polyvinylidene fluoride (PVDF) films on the actuation behavior upon exposure to acetone vapor. Our findings reveal that the actuation characteristics of PVDF films strongly vary with the polymorphic phase fraction. Notably, maximum actuation is observed at a specific phase ratio of β to α (52:48) in the PVDF film. Finite element analysis was conducted to provide deeper insights into the impact of varying polymorphic phase fractions on the actuation performance of PVDF films, supporting and corroborating the experimental observations.