24 September 2020 GloMeca #4 – Skin mechanical behaviour through lifespan

From a biomechanical point of view, ageing is a very complex process that seriously affects the functions of all organs and tissues of the body, and most often has irreversible effects on their mechanical behaviour. The most visible effects of ageing can be observed in the skin, and many studies have been widely realized for dermocosmetic and medical purposes.

Although most of the signs of skin ageing in the epidermis, dermis and subcutaneous layers are linked, changes in mechanical properties are especially interesting as they directly contribute to the development of wrinkles. All the layers of the skin are affected structurally and functionally.

In the lower cutaneous layers, an increase of collagen cross-linking, and a subsequent loss of water result in a decrease of collagen and elastin contents. This is partly due to an imbalance between matrix proteins synthesis and degradation by matrix metalloproteinases.

Skin thickness depends on its anatomical location, the body fluid content and the age.

In skin ageing research, the quantitative biomechanical methods, such as cutaneous elasticity and viscoelasticity measures, are widely used to analyse skin morphology and so to determine the level of changes of the skin with age.

Physiological functions of the skin can be determined by mechanical parameters, subject to change, depending on the density and elastic components of the dermis.

 

Skin elasticity

Some skin thickness measurements, using forces and constraints applied in the skin, clearly revealed that the Young’s modulus increases linearly with age. During ageing process, skin becomes thinner, stiffer, less tense and less flexible. Thickness of the epidermis and dermis of elderly people is also about 0.7 – 0.8 mm smaller than an adult skin.

Cutaneous parameters change with age: skin tension for children is about 21 N/mm², while the result measured for an elderly adult decreases to about 17 N/mm². Furthermore, the child skin elasticity has an average of 70 N/mm², while the elasticity average of elderly people is near 60 N/mm². Studies also show that deformation becomes stiffer with age when an external force is applied on skin.

Strain/deformation characteristics between young and aged skin

 

Characteristics of the skin through 4 ages

1/ Baby

Baby’s skin is nearly 30% thinner than adult skin. It contains the same number of layers as adult skin, but each one is considerably thinner, making it much more delicate and sensitive.

The outermost layer of the epidermis is extremely thin and cells are not as firm as adult skin. Sweat and sebaceous glands are also less active, and so skin’s hydrolipid film is relatively weak. This means that the barrier function is impaired and baby skin is :

  • Less resistant than adult skin
  • Particularly sensitive to external mechanical influences
  • Exposed to drying out.

 

2/ Children (about 6 years old)

  • The skin is thinner and less pigmented than adult skin
  • Activity of the sweat and sebaceous glands is lower.

The structure of skin is slightly more mature, almost corresponding to adult parameters. However, as these self-protection mechanisms are less developed, young skin seems particularly sensitive.

 

3/ Adults (20 and 30 years old)

External environment (genetic factors, lifestyle, or environment), may determine the thinning of the dermis and epidermis. The first signs of ageing can occur from around the age of 25. During the skin thinning process, the skin barrier function and natural protection gradually reduce. Mass and flexibility of the collagen also decrease at a rate of about 1% a year.

 

4/ Aged skin (60 & 70 years old)

  • The skin’s natural ability to produce lipids is reduced, associated with a continuous decrease in production of collagen, resulting in dryness, dehydration and deep wrinkles.
  • Skin regeneration slows down and becomes thinner and thinner, resulting in a loss of elasticity. Wound healing is also impaired.

From the age of 70 onwards, the skin’s immune function declines, making it more vulnerable to potential infections.

 

A and A’: Epidermis

B and B’: Stratum Corneum

C and C’: Dermis

Why AFM?

BioMeca uses Atomic Force Microscopy (AFM) to track any changes in biomechanical properties related to skin ageing and can capture high-resolution topographical images of a local area. AFM allows identifying differences between isolated fibroblasts from healthy skin at 30, 40 or 60 years old. Results obtained by AFM clearly shows that there is a correlation between age of the skin and fibroblast elasticity, highlighting use of cell elasticity as a potential biomarker of skin ageing at the cellular level.

BioMeca suggests the use of AFM to measure mechanical properties of individual cells, which can provide a new alternative cytological method to characterize cell ageing and empower cosmetic ingredients anti-ageing effect.

 

As a fact, skin biomechanical parameters change in a life span. During ageing process, skin becomes thinner, stiffer, less tense and less flexible, reducing its protective functions against mechanical injuries. Skin ageing goes with various epidermal, dermal, and subcutaneous alterations, including changes in volume, skin barrier function and mechanical properties.

Biomechanical studies on human skin make a significant contribution to quantify the efficacy of various dermatological products, detecting skin diseases and planning surgical and dermatological interventions.

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