Measuring and inducing mechanical deformation are crucial to applications in healthcare, human-machine interfaces, and soft robotics. However, conventional rigid transducers lack the flexibility, integration, and adaptability required in adaptive soft systems. Integrating sensing and actuation within multimaterial fibers and incorporating them into functional textiles offers a promising route to achieve distributed and autonomous functionality. Yet challenges persist in scalability, material processing, and functional integration.

This thesis addresses these challenges by employing multimaterial thermal drawing to embed magnetically, electrically, thermally, and optically responsive materials into fibers designed for adaptive applications, yielding five key innovations:

(i) High-aspect-ratio magnetic fiber actuators and textiles: Soft magnetic fibers embedding neodymium-iron-cobalt-boron (NdFeCoB) microparticles within thermoplastic elastomers exhibit exceptional stretchability and precise magnetic responsiveness. These fibers enable untethered, complex deformation suited to soft robotics, textile-supported prosthetics, and minimally invasive medical applications.

(ii) Conductive nanocomposite fibers for integrated sensing: A novel sensing framework using fibers composed of carbon nanotubes and carbon-loaded polyethylene composites provides real-time motion tracking via piezoresistive feedback. Integrated into textiles, these fibers support interactive rehabilitation systems, adaptive orthotic devices, and closed-loop control in wearable technologies.

(iii) Soft electromagnetic fiber actuators: Beyond passive actuation, fibers embedding liquid metal conductors and miniaturized electromagnets within magnetic composite cores enable enhanced actuation precision, controllable force modulation, and improved mechanical stability. Detailed electromagnetic mechanical analyses guide optimized designs, significantly boosting dynamic soft robotic performance.

(iv) Heat-responsive liquid crystal elastomer (LCE) fiber actuators: Leveraging the intrinsic anisotropy, reversible deformation, high energy density, and multi-stimuli responsiveness of LCEs, thermally responsive fibers are developed. Tailored polymer chemistries, processing conditions, and rheological modifiers facilitate repeatable thermal deformation. Furthermore, dispersing LCE and LCE-glycerol composites within thermoplastic elastomers provides a scalable pathway to high-performance soft fiber actuators.

(v) Stretchable 1D photonic crystal fibers for mechanical sensing: Expanding the scope of soft, stretchable optical fibers fabricated via thermal drawing, novel photonic crystal fibers with sub-100 nm periodic structures are introduced. Combining structural colors with mechanical resilience, these fibers enable real-time mechanical sensing. Their scalable fabrication promotes integration into interactive textiles for embedded optical signal transduction.

Overall, this thesis establishes multimaterial thermal drawing as a versatile platform for creating soft, functional fibers that integrate magnetic, electrical, thermal, and photonic properties. By incorporating NdFeCoB microparticles, conductive nanocomposites, LCEs, electromagnets, and liquid metal conductors, these fibers offer unprecedented proprioceptive feedback, adaptive actuation, and interactivity, paving the way for advanced biomedical devices, intelligent textiles, and next-generation soft robotic systems.