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 fro

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

Electronic Skins for Healthcare Monitoring and Smart Prostheses

Haotian Chen, Laurent Mirko Dejace, Stéphanie Lacour

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

Understanding engraftment of cultured epidermal stem cells

Nicolas Grasset

The epidermis and its appendages protect our body from environmental hazards. Cells generated in the basal layer continuously replace the terminally differentiated keratinocytes that are shed off the epidermal surface. Long-term renewal depends on specific tissue cells, called stem cells. The epidermis can efficiently repair itself when wounded, thanks to the proliferation, migration and differentiation of the stem cells and their progeny. In extensive full-thickness burns, restoration of the epidermal barrier can only be achieved by means of autologous skin grafts. Cell therapy using cultured epithelium autografts (CEA) has been part of the therapeutic arsenal since the early eighties (Gallico et al., 1984; O'Connor et al., 1981) and it has saved the life of many patients worldwide. Paradoxically, little is known on the behavior of the transplanted stem cells and engraftment has remained variable. Unpublished data from our laboratory have shown that the number of stem cells decrease rapidly in transplanted CEA in humans. This further highlights the necessity to thoroughly comprehend the cellular and molecular mechanisms of stem cell engraftment. Several fundamental questions must be addressed, for example: 1) By which mechanisms do stem cells adjust to the stress of transplantation? 2) How many stem cells are required for long-term renewal of the regenerated epidermis? 3) Can one manipulate the niche? To thoroughly investigate the mechanisms of engraftment, it is critical to develop a predictable animal model since it is difficult to experiment on human. We have chosen the pig as a large animal model because clinical procedures used for CEA transplantation cannot be recapitulated in laboratory animals. Firstly, we have demonstrated that pig and human skin share many features. In particular, the skin of the pig contains keratinocyte stem cells that can be characterized by clonal analysis using the same criteria as in the human (holoclone, meroclone, paraclone). Secondly, we have reproducibly produced CEA, including some made from the progeny of a single EGFP-labeled keratinocyte stem cell. Thirdly, we have recapitulated in the pig all surgical procedures used to transplanting CEA in humans. Fourthly, CEA engraftment has been systematically investigated by histology, immunochemistry and clonal analysis. Fifthly, we have demonstrated that the number of stem cells rapidly decreases following CEA transplantation and that there is little apoptosis in transplanted CEA, which suggests that stem cells are rather lost through terminal differentiation. Collectively our results demonstrate that the pig is the best available model system to investigate the mechanisms that govern stem cell engraftment. Superior engraftment may be achieved by improving the grafting bed, by designing smart matrices to better mimic the niche, or by manipulating stem cell behavior. A better comprehension of stem cell engraftment will certainly benefit patients suffering from large burns and those with disabling skin diseases (e.g. dystrophic epidermolysis bullosa). It will also profit stem cell therapy at large since optimal engraftment is also needed for hematopoïetic, muscle and neural stem cells.

EPFL2008