Comparison of the Physical Properties and in vivo Bioactivities of Flatwise-Spun Silk Mats and Cocoon-Derived Silk Mats for Guided Bone Regeneration

Osteoimmunity-Regulating biospun 3D silk scaffold for bone regeneration in critical-size defects

INTRODUCTION

Silk-based biomaterials have received a great deal of attention in tissue engineering research for bone repair. Current silk-based materials are typically derived from silk protein solutions, but the limited solubility and solution stability of silk protein solution, coupled with problems such as high preparation cost and low productivity, which severely restrict the application of silk-based materials.

OBJECTIVE

To address the challenges associated with the complex extraction process and inferior mechanical properties of silk protein or silk fiber-based materials in bone scaffold preparation, flat cocoon silk-based materials were developed to assess their potential for repairing large bone defects.

METHODS

We converted the upper cluster mesh's three-dimensional structure into a two-dimensional flattened plate and controlled the thickness and area of the flattened silkworm cocoons by adjusting the number of mature silkworms and spitting time to match the needs of different sites and bone defect areas. After being hot-pressed, the flattened silkworm cocoons were mixed with PLA to form an excellent tissue engineering scaffold material with a highly porous structure.

RESULTS

The 3D FSC/PLA scaffold demonstrated superior mineralization, mechanical resilience, and biocompatibility. Notably, it promoted anti-inflammatory gene expression, suppressed inflammatory responses through M2 macrophage polarization, and enhanced bone formation and angiogenesis by modulating key pathways, including PI3K-AKT, Wnt, MAPK, and Notch.

CONCLUSIONS

By using silkworm larvae to directly create a scaffold, a three-dimensional matrix with properties similar to extracellular matrix and a gradient structure that closely resembles cortical bone was created. This process effectively modulates the immune balance for fibroin dissolution and regeneration. The targeted infiltration of PLA within the 3D silk matrix enabled precise control over porosity and degradation, fostering optimal cellular adhesion and proliferation. As an osteoimmunity-regulating scaffold, it holds significant promise for enhancing bone regeneration and offers a robust foundation for repairing large-scale bone defects.

Flat silk cocoons: A candidate material for fabricating lightweight and impact-resistant composites

The utilization of silk cocoons in the production of lightweight and tough composites has been gaining increasing attention. However, the limited applications of normal silk cocoons (NSC) are attributed to their small size and irregular shape. To overcome this deficiency, flat silk cocoons (FSC) with a similar structure and controllable size were prepared. Next, we systematically characterized and compared the microstructures, morphologies, compositions, thermal properties, and mechanical properties of FSC with NSC. Subsequently, FSC was successfully utilized to fabricate a novel silk fibroin fiber reinforced sericin matrix composite (HPFSC) using a hot pressing method, followed by the analysis of its microstructure evolution, mechanical properties, failure modes, and theoretical modeling. This composite has outstanding mechanical properties including hardness, modulus, and strength. HPFSC has a relatively low density of ~1.3 g/cm3, whose absorbed impact energy can reach a maximum value of 11.1 J/mm, exceeding that of most engineering materials, such as aluminum alloy, ceramics, glass, and carbon fiber composites. The exceptional performance of HPFSC can be attributed to the reduced porosity, enhanced bonding between silk fibroin fibers facilitated by sericin, and their structural transformation. This study offers valuable guidance for the fabrication of lightweight and impact-resistant composites using flat silk cocoons.

A comparison between anorganic bone and collagen-preserving bone xenografts for alveolar ridge preservation: systematic review and future perspectives

After tooth extraction, dimensional changes affect the alveolar socket, leading to loss in alveolar bone height and width. Histological modifications also occur, with initial formation of a blood clot that is replaced with granulation tissue and subsequently with a provisional connective tissue matrix. Spontaneous healing ends with socket filling with woven bone, which is gradually replaced with lamellar bone and bone marrow. Adequate alveolar ridge dimensions and bone quality are required to assure optimal stability and osseointegration following dental implant placement. When a tooth is extracted, alveolar ridge preservation (ARP) procedures are an effective method to prevent collapse of the post-extraction socket. Heterologous bone is widely chosen by clinicians for ARP, and anorganic bone xenografts (ABXs) made bioinert by heat treatment represents the most used biomaterial in clinical applications. Collagen-preserving bone xenografts (CBXs) made of porcine or equine bone are fabricated by less invasive chemical or enzymatic treatments to remove xenogenic antigens, and these are also effective in preserving post-extraction sites. Clinical differences between anorganic bone substitutes and collagen-preserving materials are not well documented in the literature but understanding these differences could clarify how processing protocols influence biomaterial behavior in situ. This systematic review of the literature compares the dimensional changes and histological features of ABXs versus CBXs in ridge preservation procedures to promote awareness of different bone xenograft efficacies in stimulating the healing of post-extraction sockets.

Silk sericin application increases bone morphogenic protein-2/4 expression via a toll-like receptor-mediated pathway

Bone morphogenic protein-2/4 (BMP-2/4) is an osteoinductive protein that accelerates osteogenesis when administered to bony defects. Sericin is produced by silkworms, and has a biological activity that differs depending on the degumming method used. Our results indicated that the high molecular weight fraction of silk sericin (MW > 30 kDa) obtained via sonication had a more abundant β-sheet structure than the low molecular weight fraction. Administration of the β-sheet structure silk sericin increased BMP-2/4 expression in a dose-dependent manner in RAW264.7 cells and human monocytes. This sericin increased the expression levels of toll-like receptor (TLR)-2, TLR-3, and TLR-4 in RAW264.7 cells. Application of a TLR-2 antibody or TLR pathway blocker decreased BMP-2/4 expression following sericin administration. In the animal model, the bone volume and BMP-2/4 expression were higher in rats treated with a sericin-incorporated gelatin sponge than in rats treated with a gelatin sponge alone or a sponge-incorporated with denatured sericin. In conclusion, sericin with a more abundant β-sheet structure increased BMP-2/4 expression and bone formation better than sericin with a less abundant β-sheet structure.