Structural Peptides intermediate
Silk Fibroin
The main structural protein of silk, composed of repetitive GAGAGS sequences that form beta-sheet crystalline structures, with applications in biomedical engineering and drug delivery.
By Encyclopeptide Editorial | 3 min read
silk fibroin structural-protein biomaterial drug-delivery
Chemical Identity
| Property | Value |
|---|---|
| Name | Silk Fibroin |
| Source | Bombyx mori (domesticated silkworm) |
| Heavy chain | ~391 kDa (5,263 residues) |
| Light chain | ~26 kDa (262 residues) |
| P25 glycoprotein | ~30 kDa (assembles with heavy/light chains) |
| Repeating motif | (GAGAGS)ₙ |
| MW of repeating unit | 452.5 Da |
Structure
Silk fibroin is a semicrystalline protein with two distinct structural regions:
Crystalline β-Sheet Regions
- Sequence: (GAGAGS)ₙ repeats
- Structure: Antiparallel β-sheets
- Hydrogen bonding: Inter-chain H-bonds between Gly NH and Ser C=O
- Properties: High tensile strength, chemical resistance
Amorphous Regions
- Sequence: Non-repetitive sequences with bulky side chains
- Structure: Random coil, α-helical
- Properties: Elasticity, flexibility
Structural Hierarchy
| Level | Structure | Feature |
|---|---|---|
| Primary | GAGAGS repeats | Silk sequence |
| Secondary | β-sheets + random coil | Crystalline + amorphous |
| Tertiary | Microfibrils | ~10 nm diameter |
| Quaternary | Fiber bundles | 10-15 μm diameter |
Properties
Mechanical Properties
| Property | Value |
|---|---|
| Tensile strength | 500-600 MPa |
| Elongation | 15-25% |
| Young’s modulus | 5-17 GPa |
| Toughness | 70 MJ/m³ |
Biological Properties
| Property | Value |
|---|---|
| Biocompatibility | Excellent |
| Biodegradability | Slow (months to years) |
| Cell adhesion | Moderate (enhanced by RGD modification) |
| Immunogenicity | Low |
Biomedical Applications
Tissue Engineering
- Scaffolds: 3D-printed silk scaffolds for bone, cartilage, and ligament
- Wound healing: Silk fibroin dressings promote healing
- Nerve regeneration: Aligned silk fibers guide axon growth
Drug Delivery
- Microparticles: Silk fibroin microspheres for sustained release
- Nanoparticles: Silk nanoparticles for targeted delivery
- Hydrogels: Injectable silk hydrogels for local delivery
- Implants: Silk fibroin implants with embedded drugs
Other Applications
- Sutures: Silk sutures (surgical grade)
- Optics: Silk fibroin films for optical devices
- Electronics: Silk-based flexible electronics
- Cosmetics: Silk proteins in skincare
Manufacturing
Extraction Process
- Degumming: Remove sericin (gummy coating) with soap/NaOH
- Dissolution: Dissolve in LiBr or ionic liquids
- Filtration: Remove impurities
- Dialysis: Remove salts
- Casting/electrospinning: Form films, fibers, or scaffolds
Processing Methods
| Method | Product | Application |
|---|---|---|
| Casting | Films | Wound dressings, optics |
| Electrospinning | Nanofibers | Tissue engineering |
| 3D printing | Scaffolds | Bone/cartilage |
| Hydrogel formation | Hydrogels | Drug delivery |
| Fiber spinning | Fibers | Sutures, textiles |
Silk vs. Spider Silk
| Property | Bombyx mori silk | Spider silk |
|---|---|---|
| Tensile strength | 500-600 MPa | 1-2 GPa |
| Elongation | 15-25% | 30-40% |
| Toughness | 70 MJ/m³ | 160 MJ/m³ |
| Production | Farmed (silkworms) | Recombinant |
| Cost | Low | High |
References
- Bhardwaj N, Kundu SC. “Silk fibroin: a versatile biopolymer.” Advanced Drug Delivery Reviews 62:1361-1384, 2010. doi:10.1016/j.addr.2013.04.001
- Rockwood DN, et al. “Materials fabrication from Bombyx mori silk fibroin.” Nature Protocols 6:1612-1631, 2011. doi:10.1038/nprot.2011.352
- Omenetto FG, Kaplan DL. “New opportunities for an ancient material.” Science 329:528-531, 2010. doi:10.1126/science.1188936
- Jin HJ, et al. “Human fibroin: a new biocompatible protein for tissue engineering.” Biomacromolecules 6:2557-2564, 2005.
- Meinel L, et al. “Engineering silk-based tissue and organ replacements.” Advanced Drug Delivery Reviews 60:1493-1506, 2008.
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