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Not all surgical incisions are the same. While some may prefer a typical straight cut, a zigzag path can reduce scar tissue, making it the preferred method for some cosmetic procedures.
Research by researchers at Nanyang Technological University, Singapore (NTU Singapore) found cellular differences between the two methods, which could lead to more effective surgical incisions.
Tracking simulated wound healing in biosynthetic materials for 64 hours found that wavy gaps indeed heal nearly five times faster than straight-edged ones, thanks to distinctions in cell movement pathways.
“Scientists have known for a long time that the way the skin is cut affects how fast it heals,” says mechanical engineer K Jimmy Hsia of NTU Singapore.
“However, not much is known about why this happens and the factors that could affect the rate of healing.”
In addition to scientists’ understanding of processes in wound-healing pathways, Hsia and her team studied how Madin-Darby canine kidney (MDCK) cells close gaps in wounds created by cuts in skin created by from a micropatterned hydrogel.
The epithelial cells they used from the kidneys of dogs are the same type as those from human skin. Epithelial cells form the structural tissue that forms our outer skin and lines our internal organs. Embryonic development, tissue repair, and wound healing depend on the ability of these cells to seal gaps in tissue.
The scientists used a method for measuring fluid motion called particle imaging velocimetry to observe the operation of MDCK cells near slices 30 to 100 micrometers wide.
The wavy cuts had a radius of curvature of 50, 75, or 100 microns. They paid special attention to how the width and curvature of the cuts affected the process.
“The highly non-uniform and rotational movement induced by wavy wounds allowed more opportunities for cells to move, compared to straight wounds,” says biomechanical engineer Xu Hongmei.
Cells near straight wounds moved along the edges, while wavy wounds caused the cells to move in a whirlpool that looked like a vortex.
“This allowed cells to rapidly connect with similar cells at the opposite site of the wound edge, bridging and closing wavy wound spaces faster than straight spaces,” Xu explains.
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The range of curvature did not have a significant effect on the healing speed of rippled wounds, but the width needed to be small enough to form bridging. The experiments showed success with a maximum gap size of 75 micrometers.
The team notes that this upper distance can be different for different cell types, and there could be an effect on bridging and healing speed if the curvatures are smaller or larger than the ranges they used.
However, even in the smallest experimental space of 30 micrometers, cells moved mostly parallel to, and rarely toward, the straight slices. And they did not form bridges.
Hsia and her colleagues considered whether the wavy edges might have aided bridge formation, causing more cells to divide and grow, increasing the number of cells available for healing, but the calculations ruled this out.
“Observations clearly demonstrate that straight and wavy edges provided different geometric confines for cell migration,” they write in their paper, “generating different cell movement patterns…hence, different healing efficiencies.”
Another thing the researchers noted was the position of the cell nucleus. In cells not involved in wound healing, it was roughly in the middle. However, in the cells above the repaired spaces, he was clearly off center, appearing to move closer to the edges of the cells to avoid sitting directly on the space. This was most noticeable in the cells over the corrugated wounds.
They suggest that this indicated that the cells closing the wound spaces were under a lot of mechanical stress, and that the cells near the zigzag wounds were more stretched than those over the straight lacerations.
“This study has revealed the cellular and molecular mechanisms of gap closure, contributing to the scientific understanding of the underlying principles of the wound healing process,” concludes mechanical engineer Huang Changjin.
“Physicians and surgeons can use this knowledge to develop better strategies, such as incision methods, for wound care for patients in the future.”
The research has been published in the journal Proceedings of the National Academy of Sciences.
