The Science of Skin Elasticity and How to Maintain & Promote It

Before we can talk in any great detail about the science of Terproline®, you need to know more about fibroblasts, which are ‘the factory cells which manufacture collagen, elastin, fibronectine and hyaluronic acid. Fibroblasts, when called upon, repair tissue or replace worn out tissue and utilize raw materials to make new collagen, elastin, hyaluronic acid and fibronectine. These are the key functional constituents making up the extracellular (between all the skin cells) fibrous structure of skin. As we age, we make less of these key fibres and hence we start to develop lines and wrinkles. This is due to a lack of raw materials and a slowing down in fibroblast activity.

Terproline can stimulate fibroblasts and provide them with the raw materials to produce new, younger looking skin. Read the associated pages to understand how and see the amazing results that Terproline has shown in clinical studies in Burns Units and in facial resurfacing. Terproline is ideal for skin recovery whether it be from injuries or operations and it is a long term treatment to visibly slow down the aging process and is used to improve the results of anti-aging treatment programme's while at the same time minimizing complications like keloid scarring, pigmentation and erythema.


Skin elasticity can be described as the ability of skin to return to its original position once a deforming force has stopped acting on it. The deforming force can be gravity, muscles causing expressions.

The intensity of the deforming force and the degree of stretching or compression are directly related as long as the material is constant. Skin is not made up of a constant composition so unlike and inert substance like rubber there is no constant to the structure as skin composition changes with time and hence.

In any discussion on elasticity you need also to consider extension. i.e. the skins ability to stretch. Some materials have great extension but poor elasticity. The best example of this would be a ‘slinky’ spring.
Some materials have poor extension but great elasticity like a shock absorber spring or like cartilage.

The skin needs to have both and ideally the skins ability to return to a ‘resting state’ is strong enough to cope with the constant stretching (extension) forces we apply to it all the time.

Certain situations like pregnancy really put this to the test and stretch marks are an example where the elasticity of the skin could not cope with the extension forces.

General Topics - our research dermatology partner - have worked for years to improve skin elastic properties and have investigated the relationships between structural features such as collagen, elastin, fibronectine and hyaluronic acid fibres. Part of the solution is to maintain these structures in the most elastic forma and in the quantities needed to maintain a youthful ‘elastic’ skin. The key raw materials which promote and sustain these fibres need to be available to cells called fibroblasts, which produce new structural fibres when needed, for them to respond to the skins need. Also fibroblasts need to be stimulated to product new material. This gets harder with time as fibroblast activity slows down. 


Collagen is the main structural component of connective tissues and – physiologically - collagen gives the skin toughness and elasticity. Collagens account for approximately 70% of the skin proteins and are differentiated by the different nature of the polypeptide’s chains. In the derma there are collagen fibres of the 1st and 3rd type with a characteristic composition and micro structure.

The synthesis of collagen takes place in the fibroblasts and develops in two distinct phases, one which is intra-cellular and the other one, which is extra-cellular.


Fibronectine is a glycoprotein of considerable biological importance in the tissue repair process and also influences the elastic characteristics of the skin. It is a complex, globular protein characterized by the ability of contracting and extending itself and should be considered as one of the elements which contribute to determine the bio-mechanical characteristics of the skin.

The inter-connective function of fibronectine is enhanced by the property of variation of the tertiary conformation with any variation of pH. This property is due to its globular structure.

When exposed to a high pH, fibronectine tends to expand and acquires greater flexibility, while with a neutral pH or slightly acidic conditions it tends to retract, assuming a greater degree of compactness. Insoluble fibronectine binds mesenchymal cells, collagen, hyaluronic acid and other biological elements together.



Hyaluronic Acid

Hyaluronic Acid (HA) is a chain made of repeating disaccharide (sugar molecules) units of two very important molecules: glucuronic acid and acetyl-glucosamine. It is produced by cells and is mainly secreted into the spaces between cells, where it contributes towards the ‘matrix’ (skeleton) and elastic properties of tissues while also helping to cells to function, through acting as a messaging route between cells and between cell receptors.

Extracellular ‘matrix’ HA is important in development and in the early phases of wound healing, especially in foetuses where the repair process is scar-free. In contrast, its levels become reduced in adult tissues, where wound healing is characterized by scarring, or in keloid's characterized by excessive collagen deposits.

Hyaluronic acid has a huge capacity to bind large quantities of water and this defines a great deal of the extra-cellular matrix. It behaves as an elastic liquid which, in response to varying pressure inputs, frees the water tied to it, and then re-bonds to it when the force stops. This is called solvation.

Solvation of Hyaluronic Acid defines its elastic properties, and enables it to function as a 'reservoir'  which due to natural forces (whereby water molecules move towards more concentrated areas of solution, especially either side of a membrane) this tends to move free water towards the superficial layers of the skin, influencing hydration levels in the derma itself. This process affects the general elasticity of the skin as hydration governed by levels of hyaluronic acid contributes to form and function of other structural fibres in the skin, particularly collagen.

Skin Morphology

The skin is composed of two closely connected layers: The epidermis and the dermis.

The epidermis is a clearly stratified (layered) epithelium, deposited in four layers. New cells at the base are gradually displaced and move towards the surface of the skin, undergoing structural modifications on the way, which leads to the differentiation of cells and eventually, the cells become corneocites(cells which are no longer active).

Immediately below the epidermis is the "dermis" which is a connective tissue characterized by the presence of cellular elements (fibroblasts, mastocytes and Langherans cells) and fibres (collagen and elastin fibres) all immersed in an universal cellular substance,  made up of proteoglycans, hyaluronic acid and fibronectine.



Hyaluronic acid also determines the conditions of skin elasticity by indirect means, “limiting the conversion of collagen from soluble collagen Type III (which is fluid) to insoluble collagen Type I; the latter being a far more rigid structure and with less elastic properties and defining a major component of the aging process. Older skin collagen has a high percentage of collagen type I.
The amorphous matrix, containing hyaluronic acid and various proteoglycans, along with their ability to bond large quantities of water creates a jelly-like solution in the dermis, in which fibrous macro molecules of collagen and elastin are immersed. This jelly-like mass functions as a "shock absorber” and allows to skin to alter its bio-mechanical properties and facilitate ‘flowability’ (the smooth alterations in skin shape).

In summary hyaluronic acid affects the skin’s elastic properties in the following ways:

1) By directly increasing skin firmness and plumpness due to binding large quantities of water thus improving the skin's plastic qualities

2) By being a hydrating lubricant allowing the structural components of the derma, particularly fibrous ones, to maintain their more fluid ‘youthful’ more elastic forms.

The level of hyaluronic acid available and other factors determines the bio-mechanical characteristics of the skin, including its elasticity. It has been proven that when collagen is produced in the absence of ‘sufficient’ hyaluronic acid, it is much more rigid and less elastic. One can also show an increase in the index of ‘flowability’ of collagen fibres if well lubricated by a sufficient amount of hyaluronic acid.

The Bio mechanical Characteristics of the Skin

  • Elastin fibres - these are responsible for the primary elastic function

  • Collagen - is responsible for skin tone and - in the phase of maturity when the fibres undergo thickening and are less extensible - acts as a limiting factor in skin elasticity.

  • Hyaluronic acid - is a lubricant able to enhance ‘flowability’ in the fibrous component, therefore it is has a direct effect on the elastic parameters of the skin. It also limits the conversion of collagen from soluble (extensible) to insoluble (extremely rigid) thereby promoting elasticity of  the skin.

  • Fibronectine functions as a conjunctive factor between the amorphous and fibrous cellular components of the derma enabling the derma to react as a whole to the force applied and because of its ability to contract and extend if subjected to a deforming force it directly increases the elastic parameters of the skin.  

The elasticity of the skin is therefore directly correlated to the physical and chemical conditions in which the macro molecular structures described above are found.
These characteristics are subject to continual modification on a structural level due to the process of the aging of the skin. 

Qualitative & Quantitative Modifications in the
Fibrous & Amorphous Composition of the Derma During Aging

Ageing of the skin is an extremely complex phenomenon which may be considered as a result of both environmental and genetic events. The fibrous and amorphous components of the derma undergo profound qualitative and quantitative modifications during ageing. For example, collagen in a young person's dermis is structured differently to that in an older person's dermis. The turnover rate of the fibres is slower and the replacement of older fibres seems to take place at a slower rate.

During the ageing process, collagen undergoes a noticeable chemical stabilization whereby there is a significant increase in cross-link bonding, creating a more rigid structure. Also, a percentage of Hyaluronic acid in the dermis is reduced through increased free radical damage and enzymatic breakdown. In addition, the rate of synthesis by the fibroblasts seems to slow. 
There is a decrease in cellular fibronectine beginning from puberty to reach very low levels by maturity. The level of elastin also reduces during ageing.

Older skin is therefore classified by variations in the fibrous composition of the derma with qualitative changes in the collagen component characterized by a thickening of the fibre and greater difficulty in breakdown of collagen by the specific enzymes. This is coupled with a quantitative decrease in structural glycoproteins (fibronectine) and a modification of the amorphous matrix. This change over time is shown in the diagram below.

collagen levels over time

Therefore the aims in any anti-aging regime should be:

  • To promote elastin, collagen and hyaluronic acid manufacture by stimulating fibroblasts to manufacture more.

  • To promote Collagen Type III over Collagen Type I in the skin.

  • To promote Collagen Type III, one should also promote increased hyaluronic acid levels in the skin. This will encourage collagen Type III over collagen Type I.

  • By supplementing the raw materials used to make collagen and elastin (such as proline and glycopeptides respectively) while at the same time stimulating fibroblast activity will lead to increased production of collagen and elastin.

  • Supplementing the skin with the raw materials for making hyaluronic acid at the same time will encourage increased hyaluronic acid production. Hyaluronic acid levels can further be increased by slowing down the destruction of hyaluronic acid by the enzyme hyaluronidase and also reducing the level of oxidative stress (free radicals) which can damage the hyaluronic acid chains.

  • Terproline focuses on supplementing collagen  and elastin raw materials (and some hyaluronic acid) combined with two fibroblast stimulators

Fillast supplements the raw materials of hyaluronic acid while also stimulating fibroblast activity, but also supplies a natural hyaluronidase inhibitor to slow down the destruction of existing hyaluronic acid. It also supplies already formed hyaluronic acid, but as this is a huge molecule, this is only used to supplement the epidermal layer of the skin to increase hydration and water binding at a superficial level while the key increase in hyaluronic acid is developed in the dermis