Silver nanoparticles boost collagen maturation in Achilles tendon regeneration

Abstract

BACKGROUND: Rupture Achilles tendon remains a problem in modern medicine. Although the content of the healed tendon should approximate the normal tendon after remodeling, the diameters and cross-linking of the collagen fibrils often remain inferior and are susceptible to tendon creep. The mechanical strength of the healed tendon is dictated by the quality of collagen fibrils and their spatial arrangement produced by the tenocytes during the healing process. Silver nanoparticles (AgNPs) has been shown to express antimicrobial effect, accelerate burn wound healing, reduce wound inflammation, modulate collagen deposition and encourage fibroblast differentiation in skin wound healing. Since both skin and tendon healing share similar pathways, it is hypothesized that AgNPs would enhance the healing of injured tendon. The objective of this study is to 1) investigate the in vitro response of tenocytes to AgNPs in the production of collagen; and 2) study the effect of AgNPs in the regeneration of rat Achilles tendon in vivo by assessing the mechanical strength and collagen maturity. MATERIALS AND METHODS: Primary tenocytes were harvested from the Achilles tendon of 4 weeks-old rats and cultured with AgNPs at different concentration. The collagen content was determined using Sirius red/ fast green staining on day 7 and 14. The collagen to non-collagen ratio was then calculated. In vivo rat Achilles tendon injury model was used to investigate the effect of AgNPs to tendon regeneration. Briefly, the Achilles tendon was transected and was either treated with local AgNPs injection every 5 days or left untreated as control. Skin incision was done without transecting the tendon in the sham group. The tendons were harvested at week 6. Tensile test was performed. The collagen fibrils maturity were assessed by Sirius red staining under the polarized microscope. RESULTS: From the results of the Sirius red/ fast green staining, AgNPs significantly increased collagen production at 10uM and 20uM. Tensile test results showed that the modulus of the AgNPs-treated samples significantly outweighed that of the control (p<0.05) and resembled the modulus of the sham. When viewed under polarized microscope using Sirius Red stain, the collagen fibres were found to be more mature in AgNPs-treated group than the control. DISCUSSION AND CONCLUSION: Collagen fibres constitute the tensile strength of tendon. AgNPs enhanced collagen production (in-vitro), encouraged collagen maturation, and improved tensile property in the regenerated tendon. To conclude, AgNPs remarkably enhance the healing of rupture Achilles tendon.