Biphasic serum and biomimicry: what are the advantages of a treatment modelled on the skin?

Biphasic serums are distinguished by their simple yet ingenious design, in which two distinct phases – an aqueous phase and an oily phase – coexist, unlike most serums, which are either aqueous or oily. Before each application, these two phases must be shaken to blend briefly, creating a light and unstable emulsion. This duality adheres to a scientific rationale, that of simultaneously supplying the skin with hydration and nourishment. The aqueous phase, often composed of water, plant extracts or water-soluble actives such as hyaluronic acid or glycerine, provides the water required by the upper layers of the epidermis. Conversely, the oily phase contains lipids, such as vegetable oils, esters or squalane, whose role is to strengthen the skin’s lipid barrier and limit water loss.

Unlike traditional water-based serums, which are often lightweight but not very occlusive, biphasic formulations enable prolonged hydration through the inclusion of film-forming agents that slow water evaporation from the stratum corneum. However, this occlusive effect alone is not sufficient to fully protect the skin against dehydration, and the application of a biphasic serum should be followed by a moisturiser. Biphasic serums also differ from pure oil serums, whose texture is sometimes deemed too rich by combination or oily skin. Biphasic serums thus mimic the behaviour of the natural hydrolipidic film: a thin, semi-permeable layer composed of water and lipids.

Biphasic serums are already anticipating the concept of biomimicry.

This approach has recently been confirmed by a clinical study involving a biphasic serum comprising 17.5% plant oils, 61% water, 2% panthenol, 2.7% glycerine and hyaluronic acid. The trial, carried out with eight volunteers over a 14-day period, aimed to measure changes in stratum corneum hydration and transepidermal water loss. Measurements were performed using a corneometer and a tewameter. The results, presented in the table below, showed a significant and rapid improvement in the skin’s barrier function in the group using the biphasic serum, whereas no significant change was observed in the control group.

These results confirm the efficacy of a biphasic serum containing humectants and lipids to enhance skin hydration and fortify its barrier function.

Biomimetics involves drawing inspiration from living organisms to replicate their mechanisms and structures. In cosmetics, a biomimetic formula aims to support the skin while respecting its lipid, aqueous and protein composition. It reproduces the skin’s logic by often drawing inspiration from two elements:

• The hydrolipidic film : This mixture of water, sebum, sweat, free fatty acids and trace elements forms a thin layer on the skin’s surface. It constitutes the primary barrier limiting water loss while protecting the skin from external aggressions (pollution, UV rays, temperature fluctuations…).

• The internal lipid barrier : Composed of intercellular lipids (ceramides, fatty acids, cholesterol…), it ensures cohesion between the corneocytes of the stratum corneum. When tightly interlocked, these cells are less prone to letting water escape or pathogens enter.

These two structures work together to preserve hydration and protect the skin against external aggressors. A biomimetic formulation therefore seeks to mimic both the composition and organisation of these natural elements so as to integrate smoothly with the skin’s own processes. It contains biomimetic active ingredients, such as squalane, phospholipids, ceramides or even NMF-like components (Natural Moisturising Factors), which have a chemical structure very similar to that of the molecules naturally present in the skin. This molecular proximity enhances their biological affinity and tolerance and enables strengthening of the skin’s barrier function.

To understand more concretely how a biomimetic formula works, a recent clinical study analysed the effects of a biomimetic serum combining natural moisturising factors and skin barrier lipids on 44 volunteers with dry skin. The test formulation contained more specifically components of natural moisturising factors (10% urea, amino acids, lactate and PCA) and a biomimetic lipid blend (ceramide NP, cholesterol and sunflower oil enriched with linoleic acid). It was compared with its vehicle, that is, the same cream without the natural moisturising factor components and the biomimetic lipid blend. The results, considered significant by the researchers, are presented in the table below.

The application of the biomimetic formulation thus led to an increase in stratum corneum hydration after just 24 hours, accompanied by a reduction in transepidermal water loss, indicating enhanced barrier function.

In parallel, the researchers had 22 volunteers apply the biomimetic serum daily. After 14 days, they conducted an epidermal transcriptome analysis, which revealed a significant overexpression of 15 genes involved in various skin functions.

• The cohesion of the stratum corneum (FLG, FLG2, IVL, LOR, TGM1, CASP14, CDSN) : These genes encode structural proteins essential for the formation of the stratum corneum. Filaggrin (FLG, FLG2) and involucrin (IVL) participate in keratin aggregation and in the structural integrity of corneocytes. Loricrin (LOR) and transglutaminase 1 (TGM1) mediate the cross-linking of cornified envelope proteins, while caspase 14 (CASP14) contributes to the production of natural moisturising factors (NMF). Together, they ensure a cohesive and resistant skin barrier.

• Cellular permeability and cohesion (OCLN, CLDN1) : The genes OCLN and CLDN1 encode occludin and claudin-1 respectively, two key proteins of the tight junctions linking keratinocytes. These structures control the passage of molecules between cells, regulate skin permeability and maintain barrier integrity. Their proper functioning prevents water loss and entry of irritating or pathogenic substances.

• Corneocyte renewal (KLK5, KLK7) : Kallikrein 5 and 7 are proteolytic enzymes involved in the controlled shedding of corneocytes. They degrade adhesion proteins between dead cells, allowing their gradual removal. Proper desquamation is essential to prevent thickening of the stratum corneum, which would compromise the skin barrier.

• Hydration and water transport (AQP3, AQP9) : Aquaporins 3 and 9 are membrane channels that facilitate the passage of water and glycerol between epidermal cells. AQP3 is particularly abundant in the basal layers and plays a major role in skin suppleness and plasticity. Their activation promotes optimal hydration and supports barrier function by maintaining the skin’s water balance.

• Epidermal lipid metabolism (ELOVL4, SMPD1, HMGCR) : These genes are involved in the synthesis and remodelling of the lipids that constitute the intercellular cement. ELOVL4 elongates fatty acid chains, SMPD1 participates in sphingolipid metabolism, and HMGCR regulates cholesterol production. These lipids form an impermeable matrix that prevents water loss and shields the skin against external aggressors.

Other clinical studies have sought to determine whether biomimetic formulations can outperform traditional occlusive-based formulas, especially in mature skin, where the hydrolipidic film and intercellular lipid cohesion are often compromised with age. One study thus evaluated the efficacy of a biomimetic cream containing 2.5% lipids (ceramides, cholesterol and long-chain fatty acids) incorporated into a standardised emulsified base with glycerine, compared with a conventional emulsion on the skin of 20 participants aged over 60. These individuals applied one or the other formulation for two weeks.

The results show that, on the hands, application of the biomimetic cream induced a significant increase in hydration that was maintained after the study, unlike the control cream. A similar observation was made on the legs. One may infer that the biomimetic treatment encouraged prolonged hydration by stimulating the maturation of epidermal lamellar bodies, those minute structures within the cells of the stratum corneum that release lipids essential to skin cohesion. This process supports the restoration of the lipid cement and limits water loss. Conversely, the traditional cream, although effective in the short term, failed to sustain the physiological mechanisms underlying skin barrier regeneration.

Combining biomimicry with a biphasic formula amounts to drawing direct inspiration from the functioning of the hydrolipidic film, composed of an aqueous phase and a lipid phase. By replicating this organisation, a biphasic serum can more faithfully restore the balance between water supply and lipid reinforcement, two essential aspects of skin barrier integrity.

Biomimetic supplementation involves selecting molecules similar to those naturally present in the epidermis: essential fatty acids, ceramides, cholesterol and natural moisturising factors. This structural affinity promotes their integration into the skin’s superficial layers and minimises the risk of irritation. It is for this reason that biomimetic formulations often display improved skin tolerance, particularly on sensitive skin.

However, it is important to emphasise that the chemical structures of the molecules used in cosmetics are not always perfectly identical to those naturally found in the skin, although they are similar. This difference can influence their biological behaviour, and further studies are still needed to confirm their ability to replicate exactly the same functions. Furthermore, the stratum corneum, the outermost layer of the skin, constitutes a physical and selective barrier: not all biomimetic molecules are absorbed or utilised in the same way. Parameters such as molecular size, lipophilicity and formulation are critical to their penetration and effectiveness.

Thus, even though biomimicry increases skin compatibility and the likelihood of integration, the efficacy of these molecules depends both on their chemical structure and on their ability to penetrate the skin.

Formulated with a complex mimicking natural skin factors (NGF), squalane and hyaluronic acid, our bi-phase repair serum repairs the skin barrier of sensitive, atopic and rosacea-prone skin to soothe redness and discomfort. Developed in collaboration with a dermatologist, this 99% natural origin treatment has a two-phase formula that is directly inspired by the composition of the skin, in order to ensure optimal effectiveness while offering excellent skin tolerance. Application after application, it reconstructs the hydrolipidic film and relieves the most sensitive skin.

• SLOBODANKA T. & al. An in vivo comparative study on ageing skin: A biomimetic versus a traditional approach to skin moisturisation. University of Applied Sciences (2015).

• KUREK-GORECKA A. & al. Assessment of the moisturizing potential of a two-phase topical care product containing vegetable oils, glycerin, panthenol, and sodium hyaluronate – A preliminary studies. Acta Poloniae Pharmaceutica (2022).

• GRÖNNIGERA E. & al. A biomimetic combination of actives enhances skin hydration and barrier function via modulation of gene expression: Results of two double-blind, vehicle-controlled clinical studies. Skin Pharmacology and Physiology (2022).