Modeling of bioheat equation for skin and a preliminary study on a noninvasive diagnostic method for skin burn wounds

Current and Future Perspectives on Skin Tissue Engineering: Key Features of Biomedical Research, Translational Assessment, and Clinical Application

The skin is responsible for several important physiological functions and has enormous clinical significance in wound healing. Tissue engineered substitutes may be used in patients suffering from skin injuries to support regeneration of the epidermis, dermis, or both. Skin substitutes are also gaining traction in the cosmetics and pharmaceutical industries as alternatives to animal models for product testing. Recent biomedical advances, ranging from cellular-level therapies such as mesenchymal stem cell or growth factor delivery, to large-scale biofabrication techniques including 3D printing, have enabled the implementation of unique strategies and novel biomaterials to recapitulate the biological, architectural, and functional complexity of native skin. This progress report highlights some of the latest approaches to skin regeneration and biofabrication using tissue engineering techniques. Current challenges in fabricating multilayered skin are addressed, and perspectives on efforts and strategies to meet those limitations are provided. Commercially available skin substitute technologies are also examined, and strategies to recapitulate native physiology, the role of regulatory agencies in supporting translation, as well as current clinical needs, are reviewed. By considering each of these perspectives while moving from bench to bedside, tissue engineering may be leveraged to create improved skin substitutes for both in vitro testing and clinical applications.

Heat transfer analysis and resolution quantification of active dynamic thermography through human skin

OBJECTIVES

Active dynamic thermography (ADT) is a non-contact imaging technique that characterizes non-homogeneities in thermal conductance through objects as a response to applied energy stimulus. The aim of this study was to (i) develop a heat transfer model to define the relationship between thermal stimulation and resolution and (ii) empirically quantify the resolution an ADT imaging system can detect through a range of depths of human skin.

MATERIALS AND METHODS

A heat transfer model was developed to describe a thermally non-conductive object below a sheet of skin. The size and depth of the object were varied to simulate wound conditions, while the intensity and duration of thermal stimulation were varied to define stimulation parameters. The model was solved by numerical analysis. For ex vivo experimentation, freshly excised human pannus tissue was cut into sheets of thickness 2.54-6.35 × 10-4  m (0.010-0.025vinches) for a total of 48 grafts from 12 patients. Grafts were placed over a 3D printed resolution target with objects ranging from 0.445-0.125 LP/mm. Stimulation from a 300 W halogen lamp array was applied for 0.5-14 seconds for a total of 480 experiments.

RESULTS

ADT resolved a peak of 0.428 ± 0.025 LP/mm for 2.54 × 10-4  m (0.010 inches) skin thickness, 0.384 ± 0.030 LP/mm for 3.81 × 10-4  m (0.015 inches), 0.325 ± 0.042 LP/mm for 5.08 × 10-4  m (0.020 inches) and 0.249 ± 0.057 LP/mm for 6.35 × 10-4  m (0.025 inches) skin thickness. Additionally, it was determined that the ideal duration of stimulation energy with a 300 W stimulation system was 4 seconds for 2.54 × 10-4  m, 6 seconds for 3.81 × 10-4  m, 8 seconds for 5.08 × 10-4  m, and 14 seconds for 6.35 × 10-4  m skin thickness.

CONCLUSIONS

This study has characterized the correlation between thermal stimulus input and resolvable object size and depth for ADT. Through ex vivo experimentation it has also quantified the functional imaging depth to below the sub-cutis, beyond that of conventional imaging techniques. Lasers Surg. Med. © 2018 Wiley Periodicals, Inc.