The delivery of pulsed electrical field via conductive polymer fabric activates dermal fibroblasts promoting wound healing

Introduction

Conductive polymer materials have been used in delivering electrical stimulation (ES) to activate various types of cells. However these materials are either pure conductive polymers or composites that are less flexible. Flexible conductive fabrics were studied but were rarely used for ES because that its conductivity deteriorates in aqueous environment particularly under continuous electrical current. Wound healing is a complex process since a variety of cell populations taking part in it such as platelets, immune cells, fibroblasts, keratinocytes, endothelial cells etc.. and also due to numerous molecules playing important roles including vascular epithelial growth factor (VEGF), fibroblast growth factor (FGF), transforming growth factor (TGF), matrix metalloproteinases (MMPs), tissue inhibitor of metalloproteinase (TIMP), interleukins (ILs), to mention a few (1,2). Recently we have showed that ES mediated through conductive membranes changed cellular behaviours and improved healing in vitro (3). We also have demonstrated that polyethylene terephthalate (PET) fabric coated with conductive polypyrrole (PPy) (PPy-PET) retained sufficient electrical stability/conductivity when pulsed ES (P-ES) was used. This work is therefore to investigate the effect of P-ES on skin fibroblast behaviours and the significance of such behaviours in wound healing.

Materials and Methods

Four different ES protocols were designed in which two intensities (50, 100 mV/mm) and two types of rectangular pulse (pulse width 300s in cycles of 600s, and pulse width 10s in cycles of 1200s) were used. After ES exposure, fibroblasts were detached from the PPy-PET fabrics and re-cultivated in cell culture plate. As soon as cells reached confluence, wounds were created by a sterile tip, and cell migration or wound repair was photographed and then measured. The expression of fibroblast growth factor 2 (FGF2) was quantified with ELISA assay. To test the contraction of fibroblasts, electrically stimulated fibroblasts were cultivated in collagen gel and the area of the gel sheet was monitored. Also, the expression of alpha-smooth muscle actin (α-SMA) was measured by quantitative polymerase chain reaction (PCR) and immunohistochemistry. The gene expression of matrix metalloproteinases 1 and 3 (MMP1 and MMP3) was underwent quantitative PCR analysis. A t-test was applied for statistical analysis and the difference was considered significant when p value was less than 0.05.

Results

It was found that cell migration was improved marginally after pulsed ES exposure as well as that the expression of FGF2 was up-regulated (Figure 1). In gel contraction experiment an augmented contraction was indicated in the P-ES groups, which was accompanied by an increased expression of α-SMA evidenced by immunohistology stain. Moreover, the expression of MMP1, MMP3 was found changed with a significant increase at 50 mV/mm intensity and a decline at 100 mV/mm intensity. Fabrics are widely used in medicine such as hernia patch and wound dressing. Biodegradable nonwoven fabrics are also used as scaffold in tissue regeneration. Being able to render medical fabrics electrically conductive and to use them as substrate to deliver ES provides a new opportunity for medical fabrics.

Discussion and Conclusion

This work demonstrated that the PPy-coated PET fabric as a flexible textile material retained its electrical stability and successfully delivered four ES protocols to cultured human skin fibroblasts. The P-ES indeed affected the performance of skin fibroblasts such as the synthesis and secretion of growth factors, metalloproteinase and α-SMA, which seemed to contribute to wound healing.

Acknowledgements

This work was supported by The Canadian Institutes of Health Research. Thanks should go to Eric Jacques and Hyunjin Park for their technical assistance.

References

1. Sean E. Gill, William C. Parks. Metalloproteinases and Their Inhibitors: Regulators of Wound Healing. Int J Biochem Cell Biol. 2008; 40(6-7): 1334–1347. 2. Traversa B, Sussman G. The role of growth factors, cytokines and proteases in wound management. Primary Intention. 2001; 9(4):161-167. 3. Rouabhia M, Park H, Meng S, Derbali H, Zhang Z. Electrical stimulation promotes wound healing by enhancing dermal fibroblast activity and promoting myofibroblast transdifferentiation. PLoS One. 2013;8(8):e71660.

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