May 16, 2025

’Skin is not smooth ... no matter what retouched photos tell you.’

German receives $500K NSF CAREER grant to study human skin

Assistant Professor of Biomedical Engineering Guy German. Assistant Professor of Biomedical Engineering Guy German.
Assistant Professor of Biomedical Engineering Guy German. Image Credit: Jonathan Cohen, Binghamton University.
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Full text of the National Science Foundation Grant

Human skin is the body’s first line of defense, and it’s a robust one.

“Skin acts as a physical, chemical and microbial barrier. It also helps regulate temperature and enables mechanoreception: the ability to sense touch,” said Assistant Professor of Biomedical Engineering Guy German, whose research focuses almost exclusively on the body’s largest organ.

“[There is] a diverse population of microorganisms that naturally reside on your skin. When [skin] becomes ruptured, its barrier function is lost, leaving underlying living tissue exposed to harmful pathogens. These pathogens can cause a variety of diseases and infections,” he said.

German will continue his research into skin with the help of a new, five-year, $500,000 National Science Foundation (NSF) Early Career Development (CAREER) grant. His project — “Understanding the Multi-Scale Failure Mechanics of Human Skin with Age, Ultraviolet Photodamage and Bacterial Growth” — begins in July.

“My first reaction to learning about the award was a combination of happiness that I could support more graduate student research and excitement because the award will enable my lab to explore a new research area that I’m passionate about,” German said. “Overall, this project aims to support up to two graduate students over the five years.”

The fundamental research will explore how aging, ultraviolet light and bacteria weaken skin, cause wrinkles and increase the risk of skin rupture. The results will provide a better understanding of the biomechanical aging process, the onset of skin diseases that could be caused by bacteria in the skin microbiome, and new approaches in skin-based drug delivery in creams and ointments. Some of the results may also be transferable to flexible electronics and energy harvesting units.

Much of the current work in the field focuses on macro-testing equipment and treating skin as a homogenous material, but skin is heterogeneous at many length scales, German said, so he plans to look at the tissue microscopically. Experiments will combine immunostaining, mechanical manipulation, high-speed imaging and traction-force microscopy to show how skin degrades under a variety of conditions.

German’s award comes from the NSF’s CAREER Program, which is among the foundation’s most prestigious awards. CAREER grants support early-career faculty who have the potential to serve as academic role models in research and education while leading advances in their fields.

German explains his experiments firsthand

EDITOR’S NOTE: Guy German took the time to dive deep into each of the areas that he plans to explore thanks, in part, to the $500,000, five-year NSF CAREER grant that begins in July. Though the details of the experiments remain to be finalized, he did speak about what he is looking forward to exploring. Now, Guy German…

“Skin is not smooth and homogeneous no matter what retouched photos in fashion magazines tell you,” German said.

“If you look at the back of your hand, for instance, you will see your skin exhibits a triangular-patterned network of microchannels; canyon-like channels in the skin,” he said.

“Our hypothesis here is that these channels might govern the way skin cracks — just like the way perforations in a notebook allow you to tear a sheet of paper out of the book in a straight line.”

Moreover, at smaller length scales, all tissues are comprised of cells cohesively bonded to their neighbors via intercellular adhesions. German’s work will also examine whether the weakest components of skin are the cells or the cell-cell bonds.

“We’ll perform a number of experiments in this project,” he said. “Essentially, they will be split into two areas: biomechanical studies of skin aging and photoaging (effects of sunlight on skin biomechanics) and studies of the biomechanical impact of bacterial growth on skin.”

Area 1: Aging and photoaging

1. “Macroscopic testing techniques are the current standard for measuring the mechanical properties of tissues. However, they are incapable of measuring heterogeneous responses to stress arising from the tissue’s heterogeneous structure or the underlying mechanics of fracture. Microscale strain energy release rates of propagating cracks report a more reliable energy required to fracture materials. To date, a comparison between these two techniques has not previously been reported for soft heterogeneous tissues. Results are expected to establish, for the first time, whether a meaningful correlation exists between traditional macroscale biomechanical measurements of work of fracture and more representative microscale measurements of strain energy release rate and surface energy.

“As part of this study, we will also assess:

“a. How aging and exposure to UVA and UVB light (which are both contained in sunlight) alter the mechanical properties of the outermost layer of skin, the stratum corneum. This will provide unprecedented insight into a current unknown: whether UVA and UVB light are equally as damaging to the mechanical limits of skin. Approximately 90 percent of solar UV light is UVA. In comparison to UVB light, UVA has lower energy but can penetrate deeper into skin tissue.

“b. Studies of crack formation in skin tissue to unambiguously evaluate whether structural heterogeneities govern crack nucleation and propagation in skin. Results will provide insight into the underlying mechanistic process of fracture in heterogeneous tissues and the ability to predict fracture in soft tissues using noninvasive imaging techniques.

2. “Our studies of dermal rupture will provide a first look at how stretch marks form in skin and will also examine how (and why) age-based skin wrinkles form.

“The dermis layer of skin contains collagen fibers that are aligned in a specific direction (this orientation differs with anatomical site). The fiber alignment means that the skin has different mechanical properties (in particular its stiffness) depending on the direction in which you stretch it. The study aims to measure changes in the anisotropic mechanical properties of skin with age and understand the association between wrinkle and collagen fiber orientations. This fundamental study into the biomechanics of aging will reveal how changes in the skin’s structure and mechanical properties with age lead to the onset of wrinkles,” German said.

Other researchers have proposed a two-layer model of skin wrinkling, and the results of our work will enable empirical evaluation of that model.

Area 2: Bacterial growth

Recent studies have revealed that skin diseases such as atopic dermatitis are associated with increases in Staphylococcus aureus bacteria in the skin microbiome.

“Concurrently, the lipids naturally present on your stratum corneum decrease. This includes ceramides; the most populous type of skin lipid. Ceramides have a fatty acid head and a sphingosine tail,” German said.

“These sphingosine tails have recently been found to exhibit potent antibacterial properties — in particular for S. aureus.

“The aim of our study will be to examine whether a decrease in skin lipids can enable bacterial permeation into and across the stratum corneum barrier.

“Using confocal microscopy of GFP-labeled S. aureus bacteria, we will image bacterial permeation across the barrier and mechanically assess whether bacterial growth on skin under certain conditions can mechanically weaken the tissue.

“If these bacteria can permeate across the tissue or weaken it and cause cracking, then they could invade the underlying living tissue, cause infections and potentially break down the mechanical integrity of the epidermal basal layer, leading to the formation of skin lesions.

“Overall, results of this objective will provide an improved understanding of microbiome-host interactions and bacterial skin disease pathogenesis,” German said.