Functional ingredients (a.a. 2023_24)

HYLURONIC ACID DATA SHIFT:

MW: 1,3 -2,3 MDa

The most used is hyaluronic salt

Cations can react with the negative charge of the hyaluronic salt.

To avoid hyaluronidases degradation:

Oxidation of the hydroxylic group into aldehides, this carboxylic group reacts with ammine (=crosslinking) and the

formation of sodium hyaluronate crosspolymer.

ASSESMENT OF SKIN HYDRATION, LIPID PROFILE AND LIPID ORGANIZATION

By TEWL, water content in the SC

- Epidermis contains 70% of water of which 13% in SC (is drier in respects to epidermis)

- Lipid make the 20% of SC

Water is contained in the corneocytes, but there are layers of water between the shorter lamellae (we have short lipid

lamellae or long based on the length of FFA). The presence of these water layer creates a hydrophilic barrier against

lipophilic molecules that matches the hydrophobic barrier of the lipid lamellae against hydrophilic lamellae.

Strong surfactants can disrupt the lipid phase and destroy the barrier, we have to test if the product can break the skin

barrier!

The barrier retains the TEWL, so we can measure the TEWL to measure the integrity of the skin. 49

TEWL => is the flux of condensed water diffusing through the skin, from inside the body to the surface.

TEWL is a flux density, i.e. a quantity of water per unit area per unit time (see below).

- - -

2 1

The SI units of J are kg x m x s , ie kilograms of water per square meter of skin per second. The practical units is g m

2 -1

h • The measure of TEWL is indirect: TEWL is the diffusion of condensed water through the stratum corneum

(too invasive), whereas TEWL methods measure water vapour flux in the air above the SC.

We can do this in 3 ways:

The first device used was the “open chamber devices”, that was overcame by the “unventilated chamber device”

(closed), then by the “condenser chamber device” that works as 0°C.

• OPEN CHMABER DEVICE: Hollow cylinder with two sensors for measure the flux water in two sites. The

problem is that is very sensitive to T, humidity, air movements etc. It requires standardized conditions.

Relative humidity and temperature of the room should be constant and very strictly checked.

• UNVENTILATED CHAMBER DEVICE: one sensor, not sensitivity. Yet it has not dynamic measurement, as the

humidity saturates the chamber. They have to take off the chamber after every measurement as the

saturation avoid other measuraments=> you can’t have a continuous flux data

• CONDENSER CHAMBER: the chamber is refrigerated to form water condensation (ice) that, then, is removed

by the condenser, avoiding saturation and allowing dynamic measurement

Water vapour from the skin surfaces diffuses through the chamber out the enviroment

Deviation from the values, triangle is open chamber and has big variation of values. The dot is the condenser that has

low variation of values. The high sensitivity of the open chamber gives an high deviation of values. 50

TEWL is related to the integrity of the barrier function. When the barrier is damaged, water can easily escape, and

TEWL increases.

DERMATOLOGICAL APPLICATIONS: Transepidermal water loss (TEWL) is the most widely used objective measurement.

1. Measurement of skin barrier dysfunction, such as atopic dermatitis, contact dermatitis, psoriasis, and

ichthyoses.

The severity of skin disease can be measure by TEWL: (diagnostic device)

Figure 1 (a-c) The levels of transepidermal water loss (TEWL), surface pH and natural moisturizing factors (NMF)

values in healthy controls (Ctrl), non-lesional [atopic dermatitis (AD) NL] and lesional skin (AD L). The carriers of FLG

mutations are presented as black symbols. *P < 0.05, ***P < 0.001, ****P < 0.0001.

- Lesional skin has a major water loss

- pH increases=> microbiota impairment, lactic acid production (?)

- reduction of NMF=> it has demonstrated that people that have atopic dermatitis have a reduction in filaggrin

(protein that binds that keratin filaments in the corneocytes and after hydrolysis in monomers can be

implicated in the formation of NMF. Its deficit can lead to decostructuration of corneoytes and problem with

NMF)

2. To evaluate Skin mildness of cleansing products:

cleansing products containing tensides may cause skin irritation and inflammation or induce a rough

o and dry aspect.

TEWL measurements are therefore valuable tools for the objective comparison of the effect of

o different surfactants on the skin.

Mildness and skin compatibility of cleansing products are frequent claims

o

3. Increase in skin hydration, improvement of moisturizing properties of skin care products: in order to test the

efficiency of a moisturizing cosmetic and to get some information on its mechanism of action, it can be beneficial

to measure not only the effects on SC hydration (by e.g. electrical methods) but also on TEWL. 51

4. Protective effects against UV damage: the main effect of UV radiation is the production of an inflammatory

reaction above the minimal erythemal dose. This goes together with an increase in TEWL. Thus, UV sunscreens can

decrease erythema and inflammatory reactions, thus minimizing TEWL variations.

5. Development of novel cosmetic ingredients and products: TEWL measurements can help in the development

of novel cosmetic ingredients effective on barrier function. Specific lipids and in particular barrier lipids in

cosmetics may affect the repair of sodium lauryl-sulphate-damaged skin, tape stripped skin and aged skin.

ASSESMENT OF SKIN HYDRATION

• The skin possesses electrical properties that relate to SC hydration

• Dry stratum corneum has weak electrical conduction, whereas hydrated stratum corneum is more sensitive

to the electric field, inducing an increase of dielectric constant.

• The dielectric constant of a substance is a measure of its ability to store electrical energy. It is an expression

of the extent to which a material holds or concentrates electric flux.

• An increase in the dielectric constant leads to a decrease in IMPEDANCE and increased CONDUCTANCE and

CAPACITANCE (capability of a material object or device to store electric charge).

• water has a higher dielectric constant (81) than most other substances (mainly < 7) and this impacts the

conductivity and the capacity (ability of a material to concentrate the electric flux) that are increased.

There are three main methods used to evaluate skin moisture using non-invasive instruments:

CAPACITANCE- CONDUCTANCE - IMPEDANCE.

1. CAPACITANCE (corneometer) => ability of the skin to maintain the electricity within the skin .

High HOH=> High k => high CAPACITANCE

• This principle is based on the classical operation of a capacitor, whose main role is to store electrical charge

induced by a charged field

• The capacitor is comprised of at least two electrical conductors separated by an insulating material acting as

a dielectric (SC).

• When the skin has high water content the dielectric constant is high and increase the capacity of the

capacitor

• The measurement is based on the very different dielectric constant of water (81) and other substances

(mostly <7).

• This means that most materials increase the capacity of a capacitor by a factor of 7, whereas water increases

the capacity by a factor of around 81.

• this means that the capacitance is directly proportional to the moisture content of the samples: the higher

the moisture, the higher the capacitance.

2. CONDUCTANCE

High HOH=> high k=> high CONDUCTIVITY

• Skin conductance is an alternative approach for measurement of skin moisture derived from alterations in

the electrical properties of the SC.

• A layer of SC with high water content produces stronger and more sensitive electrical conductivity than

dehydrated SC, and increases the induction of the dielectric constant

3. IMPEDANCE

High HOH => high k=> low IMPEDANCE

• Opposite to capacitance and conductance, skin impedance evaluates the resistance of skin, which increases

with dehydration of the SC layer and is influenced by the composition and metabolic activity of skin. 52

The active (blue) is effective as it better the TEWL in 4 weeks. The error in the barrier is not mentioned the

statistical significance. By using T test.

CONFOCAL RAMAN SPECTROSCOPY: INFORMATION ABOUT STRUCTURE E PROPERTIES OF MOLECULES

Similar to infrared spectroscopy. Spectroscopic method, it permits to evaluate the water content (hydration), and it is

confocal, which means it allows to measure hydration at different level, at different depth of the skin, from the SC to

the epidermis.

We can select at which depth measuring the water content.

The water content is evaluated as a percentage and is calculated from the ratio of integrated Raman signals for water

and protein (keratin). So, it evaluates the quantity of water to the respect of proteins.

RAMAN SPECTRUM OF WATER (x= raman shift, y= intensity):

(A) Raman spectrum of freeze-dried stratum corneum. (B) Raman spectrum of water. The gray areas highlight the

spectral intervals that are used in the calculation of water content in the skin.

- For proteins (keratin) we consider the CH3 band (the NH has very low signal)

- For water content the intensity of the band of OH is calculated. 53

No interference between the bands. Formula to calculate the water content:

W and P are the integrated peak intensities of water and keratin (the intensity of the bands), respectively, and R is an

empirical constant

Expensive instrument. Quite complex. There is a spectrometer, detector, laser source, computer.

As we increase the depth of the SC we increase the hydration-> because the evaporation is decreased.

The water increases up to a plateau. This is the typical distribution of water.

.

The depth of the stratum corneum can also be estimated by the intersection of the two straight lines.

We can evaluate the efficacy of a product formulated using this technique.

We can evaluate the quantity of ceramides, as lipids give a typical spectrum and it is possible to distinguish the

wavelength of lipids from those of water and proteins. So, if we measure the wavelengths of lipids (if there is not

interference) we can evaluate the percentage of lipids and of ceramides:

So we can evaluate water, protein and lipid content at different depth. We can also evaluate the lesion and non-lesion

regions.

If we consider an healthy skin: we have up to 70% of water in the epidermis. The water content increases as the depth

increases, whereas lipid (5% in SC) and protein (60%) contents decrease, 54

ANALYSIS OF PENETRATION WITH RAMAN (OF DEXPANTHENOL): we can use this instrument to assess the permeability

of a molecule in the skin=> at the depth of 20-25 µ there is no compound. It reaches up to 10 microns. This technique

can be applied to other molecules such as HA.

These studies are done on volunteers.

SKIN THICKNESS TECHNIQUE: It evaluates the thickness of different layers. -> (questa technique non la vuole in details).

You can see the distribution of thickness of the strata accord