In a recent article published in the journal Bioactive materialsresearchers have discussed the utility of nano-calcium silicate mineralized fish scale scaffolds in enhancing tendon and bone healing.
Study: Nano-calcium silicate mineralized fish scale scaffolds to enhance tendon and bone healing. Image credit: Imageman/Shutterstock.com
Natural tendons/ligaments, which are attached to bone by unmineralized/mineralized layers of fibrocartilage and transmit stress between bones and between muscle and bone, are known for their excellent toughness and tensile strength.
Tendon grafts/patches have been recommended for several decades as an effective technique to aid in the healing of torn tendons and to reconstruct tendon-bone interfaces, as well as to restore motor function in patients. Current tendon implant materials, on the other hand, are poor: most tendon substitutes do not provide both adequate bioactivity and strong mechanical support.
For the therapeutic treatment of tendon injuries, innovatively designed tendon replacements with good bioactivity, biocompatibility and mechanical qualities capable of accelerating native regeneration of the tendon-bone interface are urgently needed. Surprisingly, several animals have evolved tissues or organs with unique hierarchical microstructures after millennia of development. The most common example is fish scale (FS).
The synergistic action of deformation mechanisms in the microstructure of FS provides exceptional mechanical characteristics. The bioactivity of natural FS, on the other hand, may be limited because its microstructure has remained stable in a liquid environment for a long time.
Diagram summarizing work on the fabrication of calcium silicate (CS)-“bioactivated” fish scale scaffold (CS-FS) by vacuum-induced mineralization, for the repair of tendon defects. In the process of vacuum-induced mineralization, Ca2+ ions can engage in coordinating chelating interactions with carbonyl and carboxyl groups of collagen fibers in fish scales and then combined with SiO32− ions to induce the in situ formation of CS particles. The silicon and calcium ions released from the CS-FS contributed to the regeneration of the tendon-bone interface and the healing of the tendon defect. Image Credit: Han, F et al., Bioactive Materials
About the study
In this study, the authors discussed the utility of FS modified with calcium silicate nanoparticles (CS NP) as a novel biomaterial (CS-FS), inspired by the high-performance exoskeleton of natural creatures. The microstructure and mechanical properties of CS-FS were examined to determine its mechanical qualities.
Researchers performed in vitro investigations to show the ability of silicon and calcium ions to accelerate the regeneration of bone, tendon, and tendon-bone contact, as well as to demonstrate the bioactivity of CS-FS scaffolds. In rabbit and rat rotator cuff tear (RCT) models, the therapeutic effects of CS-FS scaffolds in tendon injury repair and tendon-bone interface healing have been demonstrated, and the biomechanical properties of the regenerated tissue were evaluated.
The team presented a unique bioactivation strategy for the preparation of a calcium silicate bioactivated fish scale scaffold using a vacuum-induced biomineralization method to uniformly mineralize CS NPs on collagen fibers in situ.
Microstructure and morphology of CS-FS scaffolds with different levels of CS mineralization. (A–F) Scanning electron microscope (SEM) images presented the internal microstructure and different levels of mineralization of CS-FS scaffolds in each group. In addition, the attached schematic diagram shows the structural changes of each group. (G) High-resolution transmission electron microscopy (HRTEM) images showed the pattern of deposited CS produced by vacuum-induced mineralization on FS collagen fibers. CS particles that are evenly distributed along the collagen fibers were observed. (H) Energy spectrum analysis confirmed that the particles observed in the HRTEM images were CS. Image Credit: Han, F et al., Bioactive Materials
The ultimate breaking load of 51.65 ± 11.34 N of the 0.5CS-FS group was significantly higher than that of the polyethylene terephthalate (PET) and white groups 12 weeks postoperatively in the failure mode analysis , although there was no difference between the 0FS group and the 0.5CS-FS group.
The ultimate stress of the 0.5CS-FS group was 7.30 ± 1.60 MPa, which was much higher than the other three groups. In addition, the stiffness of 10.88 ± 2.37 N/mm of the 0.5CS-FS group was much higher than that of the PET and white groups, but no significant difference existed between the 0.5CS-FS and 0FS.
Although the biomechanical attributes of the CS-FS group were still not identical to those of a normal rabbit rotator cuff, the 0.5CS-FS group achieved 73.2% of the ultimate breaking load of a conventional rotator cuff. The 0.5CS-FS group achieved 55.3% of normal rotator cuff stiffness. Dense inorganic particles with a diameter of 40.43 nm were attached to the surface of collagen fibers and evenly wrapped around them.
The proposed FS-based scaffolds maintained a good tensile strength of 125.05 MPa and a toughness of 14.16 MJ/m3, which were 1.93 and 2.72 times that of natural tendon, respectively. Moreover, CS-FS exhibited a wide range of bioactivities by stimulating the differentiation and phenotypic maintenance of numerous cell types involved in tendon-bone junction composition. CS-FS played a critical role in tendon-bone interface regeneration and biomechanical function in rat and rabbit RCT models, which could be done via BMP-2/Smad pathway activation /Runx2 in bone marrow mesenchymal stem cells (BMSCs).
CLSM images of specific markers and Q-PCR analysis of specific gene expression for BMSCs, chondrocytes and TSPCs cultured on CS-FS scaffolds in each group. CLSM images showed fluorescence labeled (A) Opn in BMSCs, (B) N-cadh in chondrocytes, and (C) Col 1 in TSPCs. 100 μm bar (D) Expression of genes related to osteogenic differentiation in BMSCs cultured on each CS-FS scaffold. (E) Expression of genes related to chondrocyte phenotype in chondrocytes cultured on each CS-FS scaffold. (F) Expression of genes related to tenogenic differentiation in TSPCs cultured on each CS-FS scaffold. CS deposition enhanced the bioactivity of FS scaffolds that promoted cell differentiation of several tissue cells. Image Credit: Han, F et al., Bioactive Materials
In conclusion, this study proposed that the CS deposited on the FS acts as a “bioactivating factor” to “bioactivate” the FS, allowing it to repair various transitional organs and tissues. Fish scales were chosen as biomaterials for tendon repair. CS-FS was able to significantly stimulate cell differentiation and phenotypic maintenance after being modified by CS NPs for many cell types generated from bone-tendon-interface, chondrocytes, BMSCs and cells tendon stems/progenitors (TSPC). In vivo, CS-FS improved transitional tissue and rotator cuff tendon between bone and tendon healing, demonstrating that inorganic ions, especially the combination of Si and Ca ions, had a more appropriate integrated effect on promoting bone-interface-tendon repair.
According to the results, natural fish scales combined with bioactive ions provide a new class of high-performance biomaterials for repairing complicated tissues. The authors believe that due to their excellent strength and bioactivity, natural fish scale biomaterials are a promising candidate for therapeutic tendon restoration.
Han, F., Li, T., Li, M., et al. Nano-calcium silicate mineralized fish scale scaffolds to enhance tendon and bone healing. Bioactive Materials 20 29-40 (2022). https://www.sciencedirect.com/science/article/pii/S2452199X22002079