Introductory experience with haptic/ dermatological research

This spring, I participated in the research project for the purpose of becoming more familiar with the biological mechanisms underlying human sense of touch and the functioning of skin in general. One of my main interests in learning more about dermatology was to better understand the role of haptics in various technologies. Aside from reviewing research papers to gain a baseline familiarity with dermatology, I was also able to become more familiar with the use of basic CAD and 3d printing software. In this article, I would like to summarize some of what I learned over the course of this special research project.

Summary: the role of Epidermal Keratinocytes in effecting haptic sensation.

Epidermal keratinocytes make up 90% of all cells in the epidermis, the topmost layer of human skin. It was initially believed that nerves known as C-fibers were solely responsible for the reception of haptic stimuli such as temperature, humidity, and mechanical stress. However, considering the relative scarcity and wide interspersion of C-fibers in the epidermis which points to the existence of an alternative mechanism, the article “Epidermal keratinocytes as the forefront of the sensory system” (Denda et al.), published in 2007, suggested that responsibility for the initial reception of haptic stimuli in fact falls on the epidermal keratinocytes themselves. According to the researchers, this is supported by the presence, in epidermal keratinocytes (at various levels of the epidermis), of receptors associated with sensory reception, signal transduction, and neurotransmitter reception.

Summary: the role of kelvin’s tetrakaidecahedron in epidermal cell turnover.

Initial theories of the replacement of epidermal cells suggested that they were replaced in vertically independent columns without regard for their neighbors. This conception was challenged by the 2016 article “Epidermal cell turnover across tight junctions based on Kelvin's tetrakaidecahedron cell shape” (Holt et al.), which points out that such a mechanism would inevitably lead to openings in the tight junction which protects the horizontal gaps between epidermal cells. The article suggests an alternative model in which individual epidermal cells in the shape of kelvin’s tetrakaidecahedron are intermeshed, and throughout the process of transitioning epidermal cells to the topmost layer, tight junctions are produced in multiple vertical positions as to prevent any exposure. (I do not understand the experimental method sufficiently to summarize it here.)

Seen below, a 3d-printed model of adjacent epidermal cells, in the interconnected squashed kelvin’s tetrakaidecahedron pattern suggested by the article, shows how their shape might complement their ability to individually “migrate” upwards without compromising tight junctions. (While becoming familiar with CAD and 3d printing, I was also able to experiment with producing objects and regular surfaces of varying haptic characteristics, related to other research interests.)

Sources:

Denda, M., Nakatani, M., Ikeyama, K., Tsutsumi, M., & Denda, S. (2007). Epidermal keratinocytes as the forefront of the sensory system. Experimental dermatology, 16(3), 157–161. https://doi.org/10.1111/j.1600-0625.2006.00529.x

Jesse R Holt, Wei-Zheng Zeng, Elizabeth L Evans, Seung-Hyun Woo, Shang Ma, Hamid Abuwarda, Meaghan Loud, Ardem Patapoutian, Medha M Pathak (2021) Spatiotemporal dynamics of PIEZO1 localization controls keratinocyte migration during wound healing eLife 10:e65415. https://doi.org/10.7554/eLife.65415