Skin Biomechanics

Overview

Human skin is a complex, multifunctional composite biomaterial of extreme importance to our everyday lives.  As the largest and outermost organ of the human body, it serves a variety of protective and structural roles.  For instance, the top layer of skin serves as a physical barrier against environmental damage and microbial infection, while also regulating our tactile perception of the world around us.  Using a combination of in vitro, in silico, and in vivo techniques, we assess changes in the structure-property-function relationships of skin in response to a wide-range of environmental and physiological conditions including UV exposure, skin-care treatments, wearables, and projectile impact.

Group Members ("Skin Squad")

• Sebastian Hendrickx-Rodriguez
• Chrystalen Jade Stambaugh
• Saehui Hwang
• Ashley David

 Understanding the Perception of Skin Tightness

• Harsh environmental conditions result in unwanted feelings of skin tightness
• Using in vivo and in silico techniques, we show this perception arises from contraction of the top layer of human skin, the stratum corneum, as it loses water
• We develop a neurological model predicting firing rates of cutaneous mechanoreceptors, and relate this to tightness scores reported by consumers during in vivo studies
• We show that cleansers can exacerbate this feeling of discomfort, while moisturizers alleviate skin tightness

Project Members: Sebastian Hendrickx-Rodriguez, Saehui Hwang, Ashley David, Chrystalen Jade Stambaugh
Past Project Members: Joseph Pace, Omar Elsafty, Jonathan Sepulveda

Measuring and Predicting Cosmetic Formulation Effects on Human Stratum Corneum

• Using thin-film substrate curvature techniques, we measure stresses that develop in the top layer of human skin, known as the stratum corneum (SC)
• As the SC tries to contract during drying, tensile film stresses develop
• Cleansers can accelerate and accentuate this stress development
• Moisturizing emollients penetrate into the SC, replacing lost water volume and reducing film stresses

Project Members: Sebastian Hendrickx-Rodriguez, Chrystalen Jade Stambaugh 
Past Project Members: Christopher Berkey, Maria Isabel Sanchez

Design and Fabrication of Protective Appliques

• Cutaneous injuries on the face and joints can have significant implications for the wounded.
• Since joint regions have high mobility, and facial regions are necessary for identification purposes, protective wearables for these body locations must be light, stretchable, and flexible.
• Using computational modeling and rapid prototyping, we design and manufacture protective thin film appliques that reduce and/or prevent cutaneous injuries caused by blast debris while allowing full natural motion of the protected regions.

Project Members: Sebastian Hendrickx-Rodriguez
Past Project Members: Christopher Berkey, Omar Elsafty

Past Project: Analysis of Partial-Thickness Skin Injuries from Non-Lethal High-Rate Impact

• Partial-thickness cutaneous injuries can cause mortality due to wound infection, and a decline in a person’s wellbeing due to scar formation which can have long lasting functional, aesthetic, and psychological effects on the wounded.
• The damage processes involved in this impact sequence remain unclear.
• We quantitatively characterize the damage mechanisms involved in partial-thickness cutaneous injuries and develop a three-dimensional multi-layered full-thickness cutaneous finite element (FE) damage model to accurately predict injuries at highly dynamic impact conditions.
• We quantify the effect of impact conditions such as energy density at impact, and the angle of impact.
• We analyze the influence of projectile attributes, including as shape, size, friction behavior, and orientation at impact on injury severity.
• We explore the effects of biological parameters such as hydration, skin layer thickness, age, and sex at birth on wound area, depth, and shape.

Past Project Members: Christopher Berkey, Omar Elsafty

Past Project: Multi-Method Approaches for Assessing Full-Body Distributed Injuries

• Finite element models have helped understand the damage mechanisms of single projectile impact, but are too computationally costly to use in full-body multi-impact analysis of blast debris.
• We develop a multi-method approach for assessing full-body distributed impact injuries using machine learning algorithms coupled with physics-based analysis and computer graphics tools.
• The machine learning algorithms are trained with computational and experimental results generated in our lab.
• The multi-method model is used to analyze the effect of distance, body orientation, alignment, and blast source shape and size on the predicted injury severity.
• The model explores the frequency of impact and injury types on body locations to guide the design process for protective wearables.

Past Project Members: Ross Bennett-Kennett, Jacob Bow, David Kanno, Omar Elsafty