Abstract
Summary
Silver nanoparticles improve the tensile property of the repaired Achilles tendon by modulating the synthesis and deposition of collagen. This makes silver nanoparticles a potential drug for tendon healing process with less undesirable side effect.
Introduction
Tendon injury is a common injury that usually takes a long time to fully recover and often lead to problems of joint stiffness and re-rupture due to tissue adhesions and scarring on the repaired tendon respectively. Recently, it has been proven that silver nanoparticles (AgNPs) are capable of regenerating skin tissue with minimal scarring and comparable tensile property to normal skin. Hence, it is hypothesised that AgNPs could also improve the healing in tendon injury as both tissues are predominating with fibroblasts. The objective of this study is to look at the in vitro response of primary tenocytes to AgNPs and to investigate the mechanical and histological outcome in vivo.
Methods and Materials
Primary tenocytes were harvested from 4 weeks old Sprague Dawley rat. 1.5×104 cells per cm2 were seeded in triplicate for BrdU incorporation assay and Sirius red/ fast green staining to study the proliferation and collagen synthesis respectively. In vivo rat Achilles tendon injury model was used to investigate the effect of AgNPs to tendon regeneration. Briefly, the Achilles tendon was transected at 0.5cm from its insertion. The wound was either treated with 1mM AgNPs every 5 days or left untreated as the control. Skin incision was done without transecting the tendon in the sham group. The tendons were harvested on day 42 post operation. Tensile test and immunohistological staining on 7μm cryosections were performed to assess the mechanical property and biological events in healing respectively. SHG imaging was used to determine the collagen fibre orientation and abundance.
Results
In vitro BrdU incorporation and Sirius red fast green assay suggested that AgNPs promoted the proliferation and collagen synthesis of tenocytes between 1 to 20μM and 10 to 20μM respectively. Tensile test on in vivo tissue showed that AgNPs-treated samples had significantly better tensile modulus compared to the untreated ones (p<0.05). SHG imaging suggested a better collagen alignment and density in AgNPs-treated samples. Immunohistochemistry demonstrated that AgNPs suppressed tumor necrosis factor (TNF α) whilst promoted fibromodulin (Fmod) and proliferating cell nucleus antigen (PCNA) expression.
Discussion
Collagen is the major component that contributes to the tensile strength of a tendon. Its thickness, abundance and alignment directly affect the strength. In this study, it is found that AgNPs stimulate cell proliferation both in vitro and in vivo which is believed to be the reason of the increase in collagen synthesis. Fmod is an important proteoglycan responsible for collagen fibrillogenesis and TNF α is related to ECM degradation which directly affects collagen integrity. Stimulation of Fmod and alleviation of TNF α therefore promote collagen maturity and integrity which attributes to the improvement in the tensile property of the regenerated tissue. Furthermore, inflammation is known to relate to fibrosis and scarring in healing of many types of tissue. It is therefore postulated that the anti-inflammatory effect of AgNPs is one of the major reasons for this phenomenal healing of tendon. To conclude, this study demonstrates a positive effect of AgNPs to the early events of tendon healing which is important for accelerating the whole healing process and shortening of rehabilitation time.
