Human skin | EPFL Graph Search

The human skin is the outer covering of the body and is the largest organ of the integumentary system. The skin has up to seven layers of ectodermal tissue guarding muscles, bones, ligaments and internal organs. Human skin is similar to most of the other mammals' skin, and it is very similar to pig skin. Though nearly all human skin is covered with hair follicles, it can appear hairless. There are two general types of skin, hairy and glabrous skin (hairless). The adjective cutaneous literally means "of the skin" (from Latin cutis, skin). Skin plays an important immunity role in protecting the body against pathogens and excessive water loss. Its other functions are insulation, temperature regulation, sensation, synthesis of vitamin D, and the protection of vitamin B folates. Severely damaged skin will try to heal by forming scar tissue. This is often discoloured and depigmented. In humans, skin pigmentation (affected by melanin) varies among populations, and skin type can range from dry to non-dry and from oily to non-oily. Such skin variety provides a rich and diverse habitat for bacteria that number roughly 1000 species from 19 phyla, present on the human skin. Human skin shares anatomical, physiological, biochemical and immunological properties with other mammalian lines, especially pig skin. Pig skin shares similar epidermal and dermal thickness ratios to human skin; pig and human skin share similar hair follicle and blood vessel patterns; biochemically the dermal collagen and elastic content is similar in pig and human skin; and pig skin and human skin have similar physical responses to various growth factors. Skin has mesodermal cells, pigmentation, such as melanin provided by melanocytes, which absorb some of the potentially dangerous ultraviolet radiation (UV) in sunlight. It also contains DNA repair enzymes that help reverse UV damage, such that people lacking the genes for these enzymes have high rates of skin cancer. One form predominantly produced by UV light, malignant melanoma, is particularly invasive, causing it to spread quickly, and can often be deadly.

Electronic Skins for Healthcare Monitoring and Smart Prostheses

Stéphanie Lacour, Laurent Mirko Dejace, Haotian Chen

The human skin is a unique organ that embeds multiple functions that no artificial systems can currently replicate. Advances in materials science and engineering are driving the design of electronic skins-large-area sensor arrays that mimic some sensory modalities and have the soft, elastic form of natural skin. Here, we focus on electronic skins designed to be worn on the human body for healthcare monitoring or prosthetic applications. The primary sensing modalities are mechanical, thermal, and electrophysiological. We review key materials and associated designs needed to manufacture electronic devices that can conform to the human body and move along with it. Electronic skins offer exciting opportunities for human-machine interfaces.

ANNUAL REVIEWS2021

Mechanisms and modeling of pathogen fate in pilot scale nutrient recovery reactors

Loïc Decrey, Simon Schindelholz, Manfred Schoger, Ariane Schertenleib, Timothy R. Julian

Due to its high nutrient content, source-separated urine can be processed into marketable liquid or solid fertilizers. The Valorisation of Urine Nutrients in Africa (VUNA) project developed and tested pilot-scale nitrification/distillation and struvite (MgNH4PO4•6H2O) production reactors in Durban, South Africa, where over 80,000 urine diverting dry toilets (UDDTs) are in place in rural and peri-urban communities. Source-separated urine collected from UDDTs at a community scale contains pathogens due to faecal contamination of the urine. The greatest public health threat of urine nutrient recovery in this context thus depends on the fate of pathogens during fertilizer production and potential transmission of pathogens to humans. This work brings together several separate studies to evaluate the fate of bacteria and viral pathogen surrogates through the production of VUNA’s liquid and solid fertilizers. Limited inactivation of hydrophobic viruses was observed during nitrification due to inactivation at the solid-liquid-air interface. Otherwise, conversion of ammonia to nitrate and reduction of pH during nitrification reduces the natural inactivation capacity of urine. High temperature treatment via distillation is thus needed following nitrification. Microbial inactivation during struvite production was correlated with moisture content reduction during product drying. However, initial retention of moisture by drying at elevated humidity enhanced bacterial inactivation, suggesting practical strategies to improve treatment without costly energy input in remote field conditions. Finally, adsorption of viruses to human skin following contact with urine, as well as residual urine on the hands of reactor operators, was evaluated as a potential source of human health risk. A quantitative microbial risk assessment of the struvite production process was conducted to model the transfer of pathogens from urine to skin and the potential for pathogen ingestion during hand-to-mouth contacts.

2017

JewelPUMP (TM) by Debiotech S.A.: Insulin Temperature Measurement Study

Adrien De Muralt

For type 1 Diabetes, insulin injection therapy is the most used treatment today, and insulin pumps are surely the most accurate therapeutic strategy. The insulin use temperature has to not exceed 37°C to prevent unwanted degradation and loss of function. The JewelPUMP (TM) developed by Debiotech S.A., is directly patchable on the skin patient and was the first of its type to integrate a temperature sensor. However, it is unacceptable to place this sensor in direct contact to the insulin, regarding sterility integrity and the actual design of the device. The present study aimed to define how the insulin temperature could be predicted based on the values recorded by this sensor. Two setups were designed to assess the problem in vivo and in vitro: the first includes a patient wearing the pump under different environmental conditions, and the second is based on an electrical thermoregulation system mimicking the human body and its environment by placing it in a climatic chamber. The in vivo setup allowed us to propose a specific Curve Fitting Model (CFM) matching to the real data, based on heat transfer laws and assessing the dynamic of the problem. Two main heat sources were identified: the patient body and the ambient air around the pump. We determined that the insulin restrained in the reservoir reacts more to the body temperature Trbody than to the ambient temperature Trout; inversely, the sensor is more impacted by Trout than by the Trbody. At steady state, the presence of an offset between the sensor and the real insulin temperatures was confirmed. This offset is positive when Trout > Trbody, and negative when Trout < Trbody. Under ideal conditions, if Trout and Trbody are constant, a constant offset was supposed. The behaviour of this offset was investigated with the in vitro setup. The in vitro setup allowed us to monitor accurately the different parameters of the problem. We validated that our thermoregulation system, based on a Peltier system, was able to mimic the thermal behaviour of the human body and the human skin in vitro. Regarding the dynamic, as for in vivo experiments, the proposed CFM matched well to the obtained data. At steady state, the offset was always positive for Tlout > Tlbody, negative for Tlbody > Tlout, and equal to 0 when Tlout=Tlskin corresponding to the equilibrium of our thermal system. The offset after stabilization (Offsetlstab.) was determined as to be a constant exhibiting a dependence on the difference between Tlout and Tlbody. For a fixed Tlbody, the Offsetlstab. increases with Tlout; for a fixed Tlout, the Offsetlstab. increases with Tlbody. This offset ranges between -5°C and +5°C. Based on in vivo and in vitro data analysis, we were able to affirm that it is impossible to predict the real insulin temperature, based only on the single temperature sensor. We identified two main solutions in order to solve this problem. The first consists to placed a different sensor closer to the insulin solution. The second is based on the idea to add a second sensor somewhere else in the JewelPUMP (TM).

2011