Protein-based fibers combine unique mechanical properties with biocompatibility and biodegradability, often outperforming polymer-based fibers. The growing need for sustainable materials has revived interest in natural protein fibers like keratin, collagen, elastin, and silk, which do not require petrochemicals. Bioinspired research aims to mimic natural proteins and their assembly processes to create fibers with properties similar to their natural counterparts. These fibers can mimic natural functions that synthetic polymers cannot achieve, with applications in air/water filtration, energy conversion, smart textiles, and biomedical fields. The challenge of finding sustainable, environmentally friendly materials with excellent performance is significant. Since the early 2000s, issues with plastic waste and microplastics have increased, prompting the exploration of protein-based fibers as alternatives to polymer-based ones. Natural protein fibers, such as silk, collagen, keratin, and elastin, have unique properties and functions. For example, silk fibers are used by spiders for web construction and by silkworms for cocoon formation. Understanding the natural functions and hierarchical structures of these fibers is crucial for developing man-made fibers with similar properties. Silk, produced by spiders and silkworms, has exceptional mechanical properties, with silk fibers reaching lengths of 700–1500 m and strengths up to 1.7 GPa. Spider silk fibers have a hierarchical structure with a skin and core, containing β-sheet-rich nanofibrils. Silk fibroin can exist in two conformational states: Silk I (dissolved) and Silk II (solid). Spider silk proteins, called spidroins, have a central domain with repeated sequence motifs and terminal domains that control self-assembly. Keratins are structural proteins in epithelial cells, forming intermediate filaments. They are found in nails, hair, feathers, horns, and hooves. Keratins have a hierarchical structure with a cortex and cuticle, and can be divided into alpha-keratins (α-helical) and beta-keratins (β-sheets). Keratins can be hard or soft, depending on cysteine content and disulfide bridges. Collagen is a family of ECM proteins with at least one triple helical domain. There are over 50 types of collagen, with fibrillar collagens forming supramolecular assemblies. Collagen is found in tendons, ligaments, skin, organs, and bones. It is a viscoelastic material with high tensile strength and low extensibility. Elastin is a fibrous protein in the ECM, responsible for elasticity and resilience. Elastin forms an insoluble protein network based on its soluble precursor tropoelastin. Natural protein fibers are formed through controlled self-assembly, influenced by protein sequence, concentration, temperature, and ions. Spinning involves storing fibrous proteins in a soluble form until assembly duringProtein-based fibers combine unique mechanical properties with biocompatibility and biodegradability, often outperforming polymer-based fibers. The growing need for sustainable materials has revived interest in natural protein fibers like keratin, collagen, elastin, and silk, which do not require petrochemicals. Bioinspired research aims to mimic natural proteins and their assembly processes to create fibers with properties similar to their natural counterparts. These fibers can mimic natural functions that synthetic polymers cannot achieve, with applications in air/water filtration, energy conversion, smart textiles, and biomedical fields. The challenge of finding sustainable, environmentally friendly materials with excellent performance is significant. Since the early 2000s, issues with plastic waste and microplastics have increased, prompting the exploration of protein-based fibers as alternatives to polymer-based ones. Natural protein fibers, such as silk, collagen, keratin, and elastin, have unique properties and functions. For example, silk fibers are used by spiders for web construction and by silkworms for cocoon formation. Understanding the natural functions and hierarchical structures of these fibers is crucial for developing man-made fibers with similar properties. Silk, produced by spiders and silkworms, has exceptional mechanical properties, with silk fibers reaching lengths of 700–1500 m and strengths up to 1.7 GPa. Spider silk fibers have a hierarchical structure with a skin and core, containing β-sheet-rich nanofibrils. Silk fibroin can exist in two conformational states: Silk I (dissolved) and Silk II (solid). Spider silk proteins, called spidroins, have a central domain with repeated sequence motifs and terminal domains that control self-assembly. Keratins are structural proteins in epithelial cells, forming intermediate filaments. They are found in nails, hair, feathers, horns, and hooves. Keratins have a hierarchical structure with a cortex and cuticle, and can be divided into alpha-keratins (α-helical) and beta-keratins (β-sheets). Keratins can be hard or soft, depending on cysteine content and disulfide bridges. Collagen is a family of ECM proteins with at least one triple helical domain. There are over 50 types of collagen, with fibrillar collagens forming supramolecular assemblies. Collagen is found in tendons, ligaments, skin, organs, and bones. It is a viscoelastic material with high tensile strength and low extensibility. Elastin is a fibrous protein in the ECM, responsible for elasticity and resilience. Elastin forms an insoluble protein network based on its soluble precursor tropoelastin. Natural protein fibers are formed through controlled self-assembly, influenced by protein sequence, concentration, temperature, and ions. Spinning involves storing fibrous proteins in a soluble form until assembly during