Introduction

Silk fibroin, a protein derived from the cocoon of the silkworm Bombyx mori and other arthropods, has emerged as a multifunctional biomaterial with significant applications across various fields, including medicine, textiles, electronics, and particularly dentistry. Historically, silk has been prized for its mechanical strength, softness, and smoothness, qualities that rendered it invaluable in the textile industry for over 4000 years. However, it is the remarkable physicochemical properties of silk fibroin-namely, its biocompatibility, controlled biodegradability, and mechanical robustness—that have catapulted it to the forefront of biomedical research, offering promising solutions for medical issues, including tissue regeneration and drug delivery.

Recent advancements in nanotechnology have further extended the applications of silk fibroin, particularly with the creation of nanoparticles and hydrogels capable of cellular and drug delivery. With the healthcare system under substantial pressure due to a global rise in demand for tissue substitutes, silk fibroin offers an appealing and multifaceted alternative to traditional autografts and allografts, especially in dentistry. This article delves into the structure, properties, processing methods, and burgeoning applications of silk fibroin in dental science and engineering.

Structure and Properties of Silk Fibroin

Composition and Molecular Structure

Silk fibroin (SF) comprises a significant portion of silkworm silk, typically accounting for 70–80%, with sericin, waxes, inorganic substances, and pigments making up the remainder. Silk fibroin (SF) consists of a heavy chain (Hc) of about 350 kDa and a light chain (Lc) of 25 kDa, linked by a disulfide bond to form the (H-L) complex. This complex is associated with a 27 kDa glycoprotein, P25, in a 6:6:1 ratio, crucial for SF secretion and fiber formation. The Lc prevents excessive crystallization, while the Hc stabilizes the structure. P25 maintains the stability of the (H-L) complex and may function as a molecular chaperone. The Hc is primarily composed of glycine, alanine, serine, and tyrosine, with highly repetitive sequences forming crystalline and semicrystalline regions, interspersed with hydrophilic, non-repetitive linker regions. These structural elements are essential for the mechanical and biological functions of silk fibroin.

Fig. 1 Structure of silk fibroin (De Giorgio G.; et al. 2024).

Mechanical and Biocompatibility Traits

Silk fibroin is acclaimed for its mechanical strength and flexibility, traits that arise from its nano-fibrillar structure that balances crystalline and amorphous regions. This structure ensures a remarkable density-to-strength ratio, critical for applications demanding high tensile strength and elasticity, such as sutures and tissue scaffolding.

The biocompatibility of SF is further underscored by its minimal immunogenicity and degradability by proteolytic enzymes into non-toxic by-products. This makes SF suitable for prolonged medical applications involving implantation without eliciting significant immune responses.

Applications in Dentistry

Silk fibroin is a prime candidate for a wide range of dental applications, from tissue engineering and drug delivery to implantable devices. Several key areas where silk fibroin excels in dentistry are outlined below.

Tissue Engineering

Bone and Periodontal Regeneration

Bone defects and periodontal diseases pose significant challenges in dental health, often necessitating complex grafting procedures. Silk fibroin scaffolds have shown great promise in bone tissue engineering due to their osteoconductive properties, mechanical strength, and compatibility with bone morphogenetic proteins (BMPs). In a typical application, SF scaffolds loaded with nano-hydroxyapatite (n-HAp) support osteoblast adhesion, proliferation, and differentiation, essential for effective bone regeneration.

Additionally, periodontal regeneration benefits significantly from SF scaffolds. Studies involving human stem cells derived from teeth have demonstrated that these cells proliferate effectively on SF matrices, laying the groundwork for regenerating tooth-supporting structures.

Cartilage and Soft Tissue Regeneration

The versatility of silk fibroin extends to the regeneration of soft tissues, including cartilage, which is crucial for the function and aesthetics of maxillofacial structures. SF scaffolds, often combined with other biocompatible materials like collagen, have been employed to support chondrocyte proliferation and ECM production. Moreover, SF's favorable mechanical properties and bioactivity facilitate the repair and regeneration of other soft tissues around the oral cavity.

Drug Delivery Systems

Effective drug delivery within the oral and maxillofacial regions requires biocompatible carriers capable of controlled release. Silk fibroin nanoparticles and microspheres offer a potent solution, demonstrating high loading capacities, and adjustable release profiles. For instance, SF-coated liposomes significantly retard the release of encapsulated drugs, enhancing the therapeutic efficacy of localized treatments.

One compelling example involves the delivery of anti-tumor agents using SF nanoparticles. Such systems ensure the gradual release of drugs like Emodin, maximizing their impact while minimizing systemic side effects. SF's ability to encapsulate antibiotics and anti-inflammatory agents is also being leveraged to fight periodontal and post-surgical infections.

Dental Implants and Prosthetics

Biocompatibility and Integration

The integration of dental implants into bone tissue is crucial for their success. Silk fibroin enhances the bio-activity of titanium implants by promoting cell adhesion and differentiation, thereby improving osseointegration. SF coatings on implant surfaces have been shown to positively interact with bone marrow stromal cells, facilitating new bone growth and implant stabilization.

Customized Implants and Scaffolds

With advancements in 3D printing and electrospinning, custom SF-based scaffolds and implants are becoming feasible. These technologies allow for the design of implants tailored to the patient's specific anatomical needs, improving fit and function while reducing the risk of rejection and infection. The development of hybrid scaffolds combining SF with other biomaterials, such as hydroxyapatite or bioactive glass, further enhances their mechanical properties and biological activity.

Wound Healing and Tissue Repair

Accelerated Healing

SF-based dressings and scaffolds have demonstrated the ability to accelerate wound healing, an essential aspect of post-extraction and surgical recovery in dental procedures. By promoting cell migration, proliferation, and matrix deposition, SF dressings aid in the faster closure of wounds and regeneration of oral tissues.

Preventing Infections

The antimicrobial properties of SF, especially when combined with silver or gold nanoparticles, offer a robust solution for preventing infections in dental wounds. SF's biocompatibility ensures that these advanced dressings do not provoke adverse reactions while providing an effective barrier against pathogens.

Conclusion

Silk fibroin stands out as a versatile and biocompatible material with extensive applications in dentistry. Its unique properties, including mechanical strength, biocompatibility, and degradability, make it an ideal candidate for various applications ranging from tissue engineering and drug delivery to dental implants and wound healing. As research continues to evolve, silk fibroin is poised to play a pivotal role in advancing dental science and improving patient outcomes, offering innovative solutions to some of the most challenging issues in dental care.