The role of silver nanoparticles on skin wound healing, tissue remodeling and their potential cytotoxicity

Abstract

The advance of nanotechnology has made it possible that pure silver can be engineered into nano scale level with less than 100 nm in size. So far many studies have confirmed anti-bacterial and anti-inflammatory efficacy of silver nanoparticles (AgNPs). In our previous study we have revealed that AgNPs could promote wound healing through modulation of cytokines in a burn wound model in mice. Nonetheless, the exact effects mediated by AgNPs on various cell types in skin, including keratinocytes and fibroblasts, during wound healing still remain unknown. Therefore, in the present study we targeted a full-thickness excisional wound model in mice to explore the action and potential toxicity of AgNPs on keratinocytes and fibroblasts.

Immunohistochemistry staining and molecular assay were conducted to explore AgNPs-induced re-epithelization and cell differentiation in both in vivo and in vitro studies. We next targeted the healed skin after AgNPs-mediated wound healing using tensile test to compare their mechanical function. Meanwhile, immunohistochemistry staining and quantitative assay were utilized to further investigate and compare collagen deposition, and scanning electron microscopy (SEM) was used to observe the morphology and distribution of collagen fibrils in healed skin. Moreover, AgNPs of different sizes and doses were studied to investigate the potential toxicity, their influence on cell migration, and extracellular matrix (ECM) production.

Key results:

1. AgNPs could accelerate excisional wound healing in mouse skin when compared with other formats of silver.

2. AgNPs mediated differential cellular response in skin cells. They promoted proliferation and migration of keratinocytes in epidermal layer, through which the re-epithelization process during wound healing was enhanced; while proliferation of fibroblasts in dermal layer was inhibited and they were driven into the differentiation of myofibroblasts, through which wound contraction process was strengthened.

3. AgNPs could suppress the proliferation of human keloid fibroblasts and ECM production including collagen, fibronectin and heat shock protein, which would suggest that AgNPs had anti-fibrosis effect.

4. The AgNPs could stimulate the proliferation of epidermal progenitors and their differentiation into keratinocytes during wound healing. This biological event further contributed to the re-epithelization process.

5. AgNPs-mediated healed skin possessed comparable mechanical function, collagen deposition and fibril alignment to normal skin, which suggested AgNPs could modulate collagen production during skin wound healing.

6. The inhibitory effect on fibroblasts and cytotoxicity mediated by AgNPs showed a dose-dependent and size-dependent manner.

In conclusion, AgNPs not only contribute to healing of infected skin wounds through antibacterial activity, but can also accelerate wound healing through mediating differential cellular responses in different skin cell types and modulate collagen production during wound healing. Furthermore, there should be an optimal concentration and size to exert maximal biological action with minimal toxicity for each specific cell type. Present studies further extended our knowledge of AgNPs and have implications for treatment of wounds in clinical setting.