# Effects of Hydrophilic Natural Deep Eutectic Solvents on the Rheological, Textural, and Sensory Properties of Carboxymethylcellulose-Based Cosmetic Hydrogels

A Verger, H. Kichou, N. Huang, X Perse, I.-M. Ardeza, C Pradel, R. Goncalves Martins da Conceicao, B. Atanasova, F.-X. Legrand, A. Despres, et al.

► To cite this version:

A Verger, H. Kichou, N. Huang, X Perse, I.-M. Ardeza, et al. Effects of Hydrophilic Natural Deep Eutectic Solvents on the Rheological, Textural, and Sensory Properties of Carboxymethylcellulose-Based Cosmetic Hydrogels. ACS Sustainable Chemistry & Engineering, 2024, 12 (18), pp.7187-7199. 10.1021/acssuschemeng.4c01866. http://dx.doi.org/10.1021/acssuschemeng.4c01866

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Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
Effects of Hydrophilic Natural Deep Eutectic Solvents on
the Rheological, Textural and Sensory Properties of
Carboxymethylcellulose-Based Cosmetic Hydrogels

Verger A.<fnref n="1" />, Kichou H.<fnref n="1" />, Huang N.<fnref n="2" />, Perse X.<fnref n="1" />, Ardeza I-M.<fnref n="1" />,<fnref n="3" />, Pradel C.<fnref n="1" />, Goncalves Martins Da Conceicao R. <fnref n="1" />, Atanasova B.<fnref n="4" />,<fnref n="5" />, Legrand F-X.<fnref n="2" />, Despres A.<fnref n="6" />, Boudesocque-Delaye L.<fnref n="3" /> and Munnier E.<fnref n="1" />*

<footnote n="1">¹UPR CNRS 4301 CBM, département NMNS, Université de Tours, 37200 Tours, France.</footnote>

<footnote n="2">²Université Paris-Saclay, CNRS, Institut Galien Paris-Saclay, 91400 Orsay, France</footnote>

<footnote n="3">³UR 7502 SIMBA, Université de Tours, Faculté de Pharmacie, 37200 Tours, France.</footnote>

<footnote n="4">⁴UMR 1253, IBrain, Université de Tours, Inserm, 37000 Tours, France.</footnote>

<footnote n="5">⁵Département Professionnel Agrosciences, Université de Tours, Faculté des Sciences et
Techniques, 37200 Tours, France.</footnote>

<footnote n="6">⁶RCP-Design Global, 56 Avenue Marcel Dassault, 37200 Tours, France</footnote>
KEYWORDS

Natural deep eutectic solvent; sensory properties; rheology; gels; carboxymethyl cellulose, cosmetic formulation

ABSTRACT

Natural Deep Eutectic Solvents (NaDES), a category of sustainable solvents made from biorefinery ingredients, are an eco-friendly alternative to organic solvents in solubilization of active pharmaceutical or cosmetic ingredients. Biocompatible, NaDES can be introduced in final products but are prone to modify their properties thanks to their hydrogen bonding capacities. The present study focuses on the impact of the incorporation of two hydrophilic NaDES made of betaine and glycerol (BG) or citric acid and glucose (CG), on the properties of a carboxymethylcellulose (CMC)-based hydrogel. Differential scanning calorimetry revealed that NaDES did not affect the endothermic peak of water but eliminated an endothermal peak associated with CMC polymer chain loosening. Rheological analysis displayed shear-thinning behavior, while the addition of 10%wt. NaDES led to a significant increase in viscosity at rest. CG introduction led to a shift from a viscous-dominant behavior to an elastic-dominant behavior, strengthening cohesion in the gel structure. Texture analyses unveiled that NaDES-containing gels exhibit higher hardness and elasticity. Sensory evaluations highlighted differences in five sensory attributes among gels, with NaDES concentrations and types playing significant roles. This research underscores the intricate interplay between NaDES and hydrogel properties, offering insights for the formulation of innovative cosmetic products that achieve both solubility and sensory appeal.
# 1. Introduction

Green chemistry, with its twelve guiding principles aimed at promoting sustainable and environmentally friendly practices, has become a cornerstone for utilizing biodiversity in a mindful manner¹. These principles advocate the reduction of manufacturing waste, the use of renewable resources, and the development of less polluting processes¹. A crucial aspect in achieving these goals lies in the careful selection of solvents, which play a pivotal role in green chemical processes. Organic solvents are often used to extract or solubilize poorly water-soluble active pharmaceutical² or cosmetic ingredients³ (APIs and ACIs, respectively) at different steps of the development and manufacturing of pharmaceutical or cosmetic products in formulation development and manufacturing⁴. n-Hexane, a widely utilized solvent derived from fossil fuels, serves as a notable example and has recently been classified as a potential Category 2 substance with suspected reproductive toxicity under the European Directives and the Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) regulations⁵. In the pursuit of eco-friendly alternatives, two classes of solvents have emerged as promising candidates. Ionic Liquids (ILs), known for their low volatility and chemical inertness, raise concerns about their biotoxicity and biodegradability. Conversely, Deep Eutectic Solvents (DESs), first described by Abbott *et al.* in 2003, are eutectic mixtures of ammonium salts and hydrogen bond donors. They exhibit properties similar to ILs but with improved biodegradability⁶,⁷. Natural Deep Eutectic Solvents (NaDES) form a subcategory of DESs made from biorefinery ingredients, finding applications in cosmetics as eco-friendly extraction solvents⁸,⁹. NaDES are considered as a new generation of ionic liquids, composed of a hydrogen bond acceptor (HBA), usually choline chloride or betaine, and a hydrogen bond donor (HBD), mainly sugars or polyols¹⁰. Their association forms a hydrogen bonds network
resulting in the lowering of the melting point of the solid mixture that becomes liquid at room
temperature<sup>11,12</sup>. NaDES possess desirable physicochemical and sensory characteristics, making
them potential candidates for novel cosmetic formulations. The introduction of Deep Eutectic
Solvents (NaDES) in the cosmetic industry has been garnering increasing interest due to their
potential dual benefits as solubilizing agents for actives and as functional ingredients leveraging
the unique properties of their components<sup>13,14</sup>. Solubilizing ACIs is one of the key challenges in
cosmetic formulations, especially when dealing with hydrophobic or poorly water-soluble
compounds. Conventional solvents used for this purpose may not align with the principles of green
chemistry, emphasizing the need for sustainable alternatives. NaDES present an intriguing
opportunity in this regard, as their diverse compositions can be tailored to suit specific active
ingredients, offering enhanced solubility and stability<sup>15</sup>. NaDES, as an alternative to conventional
solvents, align with the 5th principle of green chemistry by promoting the use of benign solvents
and auxiliaries<sup>16</sup>. Furthermore, all components employed to formulate NaDES could be bio-based,
ensuring they are genuinely renewable and fully biodegradable<sup>17</sup>. This adherence to the 7th
principle, "use of renewable feedstocks," and the 10th principle, "design for degradation,"
establishes NaDES as environmentally conscious<sup>18</sup>. Lastly, if NaDES are composed of nontoxic
compounds, when they are utilized for extraction of active molecules from biomasses, they can
subsequently be incorporated directly into a final product without additional purification or solvent
evaporation. The NaDES extract then can also meet the criteria of the 6th principle, "design for
energy efficiency"<sup>19</sup>. Individual components of NaDES contribute unique functionalities to the
overall solvent system. These properties can be harnessed to create multifunctional cosmetic
ingredients, where NaDES not only solubilize active compounds but also act as functional
ingredients themselves<sup>20</sup>. For example, Al-Akayleh et al. prove an antimicrobial potential of
natural deep eutectic solvents on Gram-positive and negative bacteria²¹. These supplementary activities may require higher concentrations of NaDES in the final product.

As the demand for eco-friendly and bio-based cosmetic products continues to grow, exploring the potential of NaDES in this industry becomes increasingly relevant²²,²³. The primary objective of this study is to explore the incorporation of NaDES into cosmetic gel formulations, aiming to ascertain whether NaDES, as potential solubilizing agents for key cosmetically active compounds, may influence the rheological characteristics of the resulting formulations. Understanding these potential modifications is essential, as they could have a deep impact on the formulation and manufacturing processes within the cosmetic industry²⁴. Additionally, this research delves into investigating potential interactions between the selected gelling agent and the NaDES of interest.

To address comprehensively the objectives of this research, a sensory analysis component has been integrated, aimed at evaluating whether any observed rheological alteration could translate into perceptible differences in consumer experience and perception.

Polysaccharides, relatively complex carbohydrates, play a key role as gelling agents in cosmetic formulations, notably in the efforts of this industry to replace acrylate or vinyl-based thickening agents in gels and creams by bio-based materials²⁵. These macromolecules consist of numerous monosaccharide units linked by glycosidic bonds, resulting in intricate and often branched molecular structures²⁶. Due to their unique properties, polysaccharides, especially cellulose derivatives such as carboxymethyl cellulose (CMC), have emerged as essential components in various cosmetic and medical applications²⁷,²⁸. CMC, as a well-established thickening agent, plays a key role in these applications by enhancing product consistency, stability, and overall performance, making it a versatile and very interesting ingredient in the formulation of cosmetics and medical products. Moreover, CMC is known for its remarkable resistance to certain solvents,
such as water, which further contributes to its reliability in diverse formulations²⁹. The high
molecular weight of cellulose derivatives, like CMC, ensures effective binding and retention of
moisture, making them valuable additions to skincare products²⁸,³⁰. Their compatibility with
various active cosmetic compounds not only extends their utility but also facilitates the even
dispersion of beneficial ingredients within the gel matrix³¹. This ensures a homogenous
distribution of active compounds, enhancing the overall effectiveness of the cosmetic gel. In the
realm of cosmetics, cellulose derivatives like CMC are widely recognized for their hydrating
properties. Their high molecular weight and hygroscopic nature enable them to effectively bind
and retain moisture, making them valuable additions to skincare products. When incorporated into
cosmetic gels, these polysaccharides enhance the formulation's ability to provide lasting hydration
and maintain skin suppleness. The versatility of cellulose derivatives extends beyond cosmetics,
with their application in medical formulations. The biocompatibility and biodegradability of
polysaccharides, especially cellulose derivatives, make them suitable candidates for drug delivery
systems and tissue engineering. The unique gelation properties of certain polysaccharides have
been harnessed to create controlled-release drug formulations, allowing for precise dosing and
prolonged therapeutic effects. The multifaceted utility of polysaccharides, exemplified by
cellulose derivatives like CMC, underscores their significance in the design and formulation of
cosmetic gels, offering enhanced hydration and improved delivery of ACIs, while also contributing
to advancements in the broader fields of medicine and biotechnology.

This study aims to emphasize the advantages and suitability of hydrophilic NaDES in cosmetic
formulations, focusing on their ability to contribute functional attributes to the product. By
elucidating the interactions between NaDES and cosmetic ingredients, we aim to pave the way for
the development of innovative and sustainable cosmetic formulations in line with the principles of green chemistry. Our investigation specifically delves into the impact of introducing hydrophilic NaDES into a cosmetic gel formulated with carboxymethyl cellulose (CMC). CMC, a widely used cellulose ether, serves as the basis for the gel chassis, and we will examine its properties along with those of the NaDES to determine their compatibility. This investigation involves the analysis of two commonly used hydrophilic NaDES, categorized based on organic acid and amino acid components. The hydrogel chassis formula incorporates NaDES at two mass concentrations: 1% to exemplify the application of NaDES as a solubilizing agent for an active ingredient in the formulation, and 10% when NaDES serves as a functional ingredient, contributing, for instance, to its humectant properties. Rheological properties will be evaluated through flow and viscoelasticity experiments, while Differential Scanning Calorimetry will provide insights into thermal behavior. Additionally, texture analyses of the hydrogels obtained will be carried out. The sensory properties of the cosmetic gel will also undergo assessment by an expert panel, shedding light on the overall performance and suitability of the NaDES-enhanced formulation.
## 2. Materials and methods

### 2.1. Chemicals

Carboxymethylcellulose sodium salt (MW 250 000, DS=0.7) was purchased from Acros Organics. α-D-(+)-glucose (>99%), Betaine (98%), Glycerol (>99%), Citric acid (>99%), Benzyl alcohol and Dehydroacetic acid were obtained from Fisher Scientific (Illkirch, France). Water was purified using a Milli-Q system (Millipore Corporation, Bedford, MA, USA).

### 2.2. NaDES formulation

NaDES Citric acid/Glucose (CG) (1:1, mol/mol) with 20%wt of purified water³² and NaDES Betaine/Glycerol (BG) (1:8, mol/mol)³³ were prepared by mixing components together. The mixture was heated at 80°C and stirred by magnetic stirring for 1h until a colorless liquid was obtained. After returning to room temperature (for about 1h30) the NaDES are stored for a maximum of 7 days at 20°C in an oven. Results from various analyses of NaDES, including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), shear-dependent viscosity at 25°C, constant shear viscosity from 15°C to 60°C, density from 15°C to 40°C, FTIR spectra, refractive index, and conductivity, are provided in the Supplementary Information section of the manuscript.

### 2.3. Gel formulation

Gels were prepared employing two different methods in triplicate using a bench mixer equipped with a dispersing turbine (Turbotest®, VMI, France); for each method 150g batches were prepared. In the first method, gels were prepared by first mixing water, benzyl alcohol and dehydroacetic acid (antimicrobial agents) and NaDES then the gel-forming agent CMC was added progressively.
For the second method, gel-forming agent and antimicrobial agents were mixed simultaneously in the water slowly and the obtained gel was stored at 20°C for 24 hours. Afterward, NaDES was added in the pre-formed gels. Control samples for each method were done in the same preparation steps except hydrophilic NaDES was replaced by the same weight of water.

The composition of the gels is presented in Table 1. NaDES were introduced at a concentration of 1%wt) and 10%wt, corresponding to their use as active ingredient and functional ingredient respectively in the topical formulations. They were replaced by an equivalent weight of water in the control formulations. After 24h and at 30 days (D30) pH measurement were performed with a suitable pH electrode.

## 2.4. Differential Scanning Calorimetry

The thermal behavior of hydrogels containing NaDES were studied by differential scanning calorimetry (DSC) on a DSC 25 (TA instruments, New Castle, USA). Samples (between 20 and 25 mg) were weighed and placed in hermetical aluminum pans before sealing. With N₂ as the protective gas, samples were heated at a constant rate of 10 °C/min in a temperature range of -10 °C to 80 °C. The thermogram curves were analyzed with a TRIOS software. Calibration was made with a TA instruments water reference's pan.

## 2.5. Rheology

Rheological characterization was conducted using a Kinexus pro+ rheometer (Netzsch, Germany) at a temperature of 25°C. Conducting rheological studies at 25°C aligns with real-world usage conditions of formulation, ensuring the data reflects practical application³⁴. It also assesses product stability, user comfort, and regulatory compliance. All measurements were performed in triplicate,
with a fresh sample loaded for each run. After loading, samples were allowed to relax and acclimatize for a minimum of 2 minutes prior to measurement.

2.5.1. *Shear test.* To assess the flow properties of the hydrogel systems, continuous shear flow tests were conducted using a sanded cone-plate geometry (4° angle, 40 mm diameter). Apparent viscosity values were recorded by subjecting the samples to increasing shear rates ranging from 0.1 to 1000 s⁻¹ for a duration of 150 seconds.

2.5.2. *Oscillation tests.* The deformation sweep experiment was performed at a frequency of 1Hz and a strain ranging from 0.1% to 100%. The frequency sweep experiment was carried out at a strain of 0.5% belonging to the linear regime and the frequency varied from 50 Hz to 0.1 Hz. Viscoelastic modulus results and relaxation times were obtained individually for each replicate using the Rspace software supplied with the rheometer and then averaged using R software.

**2.6. Texture analyses**

Textures properties of the hydrogels were examined at room temperature using a texture analyzer LF plus texture analyzer (Lloyd instruments - AMETEK) equipped with a 5 kg load cell. This device allows up and down vertical displacement at a maximum rate of 40 mm/s. The analysis was performed at a speed of 1 mm/s, 50% of the initial height analyzed and a trigger threshold of 0.05N. A specific compression/stretching test was developed using a cylindrical probe specifically designed for the experiments. 10 measurements were made for each sample. Elasticity (height to which the sample returns between the first and second compression phases), elasticity index (ratio between the height to which the sample returns after the first compression phase and the value of the
maximum deformation) and hardness (maximum force during the compression phase of the test)
were obtained by NEXYGEN software.

**2.7. Molecular analysis of the gels**

Gels with and without NaDES were analyzed by Fourier-Transform-Infrared (FT-IR) using the
Frontier ATR-FT-IR spectrometer (PerkinElmer, Waltham, USA) with the following parameters:
scan range 4400–400 cm⁻¹, number of scans 32, resolution 4.0 cm⁻¹, interval 1.0 cm⁻¹ and unit A.
Hydrogels were also analyzed by proton nuclear magnetic resonance (¹H NMR) spectroscopy
using the Bruker Neo-Avance 400 MHz NMR spectrometer (Bruker, Wissembourg, France).
NMR analyses were conducted on the gel formulation under identical conditions, substituting
water with deuterium oxide. NMR Spectrum treatment were performed TopSpin®. FT-IR Data
analysis was conducted using Matlab® (MathWorks, Natick, MA, USA). The spectra were
trimmed between 500 and 4000 cm⁻¹, and subsequently between 900 and 1900 cm⁻¹ to refine the
analysis to the fingerprint region. After this, a second derivative correction was applied, followed
by a smoothing algorithm (Savitzky-Golay) with a 15-point window, and finally, unit vector
normalization was performed.

**2.8. Sensory analysis**

**2.8.1. Triangular difference test**

For the discriminatory tests carried out, the panel of individuals, defined as a group of subjects
brought together to make a collective judgement on a subject, was recruited internally from the
laboratory's staff. All volunteers were informed of the potential risks and signed a document
attesting of their consent to the experiments. All procedures were in accordance with the Helsinki
Declaration. The number of subjects was 24, aged between 22 and 62, comprising 12 men and 12 women. This number has been established in accordance with the standards (NF EN ISO 4120, α = 0.05, β = 0.05 and pd = 50%). The triangular difference test (NF EN ISO 4120) is used to determine whether there is even a very slight perceptible sensory difference between products. Subjects were presented with a set of three samples, after which they are informed that two of the samples are similar and one is different. Subjects must indicate which of the samples they perceive to be different, even if this choice is only based on a guess, as this is a forced-choice test. There were 6 possible orders of presentation for the samples (AAB, ABA, BAA, BBA, BAB, ABB) so as not to influence the assessor. Once the tests have been carried out, the number of correct answers is counted from all the questionnaires and its significance is determined by reference to a binomial distribution table with a probability of 1/3 (NF EN ISO 4120) For our study, the number of correct answers must be greater than or equal to 13 to consider that two gels are significantly different.

### 2.8.2. Descriptive sensory profiles

Sensory profiles were carried out by a panel of 5 trained subjects (EBI Kit)³⁵ selected based on their sensory skills, their ability to describe a product, their perceptions, their ability to memorize, their motivation and their availability. Six relevant sensory attributes were evaluated for each gel: odor intensity, stickiness, spreadingness, stringiness, pick-up and visual viscosity; and a score was attributed from 0 to 10. Score limits were determined by the references of the EBI kit, except for odor intensity where 0 corresponds to an empty jar and 10 an internal laboratory reference. Pick up was determined with water as a reference with a score of 0 and for limit 10, an internal laboratory reference.
### 3. Results and Discussion

Two preparation methods were tested to prepare NaDES-enriched gels, differing in the moment of introduction of NaDES. Method 1 (M1) consists in the introduction of NaDES at the beginning of the formulation protocol, even before the introduction of the gelling agent (carboxymethylcellulose (CMC) 3%wt.). Method 2 (M2), consists in preparing a suitably overconcentrated CMC before introducing NaDES to obtain a final CMC concentration of 3%wt. The two types of gels were made in triplicates and their physicochemical and sensory characteristics were measured 24h after manufacture (D1) and after one month of accelerated aging in a climatic chamber (40°C, obscurity, and 75% of humidity; D30).

#### 3.1. Gels pH measurements

The pH at D1 and D30 of CMC 3%wt gels with and without NaDES are presented in Table 2A and 2B. The NaDES-free gels (Blank gel) obtained through both manufacturing methods (M1 and M2) have a slightly acidic initial pH, with values ranging from 5.9 to 6.5. On Day 30, the NaDES-free gels maintain their initial pH stable. When 1% NaDES (CG or BG) is added, a slight decrease in pH is observed whatever the NaDES or formulation method, showing a pH around 5.1. This decrease is stable over 30 days, with pH maintained between 5.8 and 4.7. This pH reduction can be attributed to the intrinsic acidity of NaDES components citric acid and betaine, respectively for CG and BG NaDES. Their carboxylic acid function, if not involved in the hydrogen bond network, can be deprotonated in the gel mainly constituted of water, resulting in moderate pH changes. The addition of 10%wt of NaDES CG drops the pH to around 3.5 for both methods at D1. This pH remains stable around 4 over time. These different pH changes should not, however, affect the textural and rheological characteristics of the gel obtained³⁶, as the gelation of CMC is stable in
this pH range. As well, as the skin pH is rather acidic, this range of pH is still tolerated by the skin.

The observed reduction in pH to approximately 3 at D1, induced by the addition of 10%wt BG NaDES, remains consistent regardless of the formulation method. However, after 30 days, the pH appears to have reverted to its initial value of 6, aligning with measurements obtained from control gel samples. Our hypothesis here is that this pH evolution may be attributed to rearrangements within the hydrogen bond network, especially upon interaction between the NaDES components with the water present in the hydrogel³⁷ across the entire gel structure, potentially influencing the ionization of specific formula components³⁸.

## 3.2. Differential Scanning Calorimetry

Differential scanning calorimetry (DSC) measurements were performed to highlight a possible interaction between NaDES and hydrogel components (Fig. 1). The thermograms presented in figure 1 correspond to hydrogels containing 10 %wt NaDES obtained by method 2. They are identical to those obtained by method 1 (data not shown). The addition of NaDES does not appear to modify the endothermic peak of water corresponding to ice melting (between 5°C and 15°C in Fig.1), this was maintained in all conditions. However, without the addition of NaDES, an endothermal peak corresponding to the loosening of CMC polymer chains can be observed at around 40°C³⁹. This peak is not visible following the addition of NaDES to the formulation. In a calorimetric study of CMC, a complete absence of endothermal or exothermal peaks before 100°C/120°C⁴⁰ is generally observed, corresponding to the molecular melting of CMC. However, in the present case, the presence of the peak at around 40°C could indicate partial solubilization of the CMC, which would then be facilitated and increased by the addition of NaDES, causing the peak to disappear. The improved solubility of cellulose derivatives via NaDES has already been
observed for other NaDES. Notably for NaDES choline chloride/malic acid⁴¹, the same type of mechanism could be observed here, with the implementation of a solvent (water) and co-solvent (hydrophilic NaDES) system⁴². This better solubilization of CMC in the NaDES-water mix than in water may lead to an increase in the viscosity and a better stability of the gel³⁰.

### 3.3. Rheology

All combinations of CMC hydrogels had a shear-thinning behavior, that is, viscosity decreased with increasing shear rate (Fig. 2). Shear thinning behavior is a common characteristic observed in a wide range of personal care products, including creams, cream-gels, lotions, emulsions, and similar formulations. This phenomenon refers to the reduction in viscosity as these products are subjected to shear forces during application, such as spreading on the skin. It is a desirable feature as it allows for easy and smooth application, ensuring that the product spreads effortlessly and absorbs effectively, providing a pleasant and user-friendly experience for consumers⁴³,⁴⁴.

Studies on flow properties have led to several observations: firstly, a significant increase (by a factor of 3) in viscosity at low shear rates when using 1% NaDES, whether BG (figure 2-A) or CG (figure 2-B). This increase in the hydrogel's resting viscosity is even greater when NaDES is added up to 10%wt, with a factor of 5 increase for BG NaDES (figure 2-C) and a factor of 20 or 30 for CG NaDES (figure 2-D). This increase at low shear has already been observed in the literature for other NaDES and in the context of other gelling agents⁴⁵. However, despite the increase in viscosity at rest, in the zone corresponding to the spreading zone (between 100 and 1000 s⁻¹), there is no major differences with the control without NaDES. This spreading zone corresponds to the shear rate imposed by the consumer during hydrogel spreading⁴⁶,⁴⁷. It may be noted, however, that when using 10%wt NaDES CG (figure 2-D), the viscosity in this zone is slightly lower than the control without NaDES. The rheological flow studies also show that there are no major differences
between the formulation methods. However, looking at the general trends, method 2 seems to be
slightly more effective in increasing viscosity at low shear rates for BG NaDES (figure 2-A and
2-C) and for 1% CG NaDES (figure 2-B). Conversely, method 1 seems to favor viscosity increase
for CG NaDES when used at 10%wt. In general, the addition of NaDES before or after system
gelation does not appear to be critical to the flow properties of the formulation. Finally, after 30
days of aging at 40°C, the hydrogels undergo an overall decrease in viscosity. The curves obtained
at D30 for all NaDES, whatever the formulation method and whatever the percentage in the
formulation, seem to follow the rheological profiles obtained at D1. This overall loss in viscosity
is relatively consistent with the aging phenomena normally observed with CMC⁴⁸.

To identify the linear viscoelastic region (LVR), strain sweep measurements spanning a range of
0.1 to 100% were conducted at a controlled temperature of 25 °C and a fixed frequency of 1 Hz.
These experiments provided crucial insights into the gel mechanical properties that remain
independent of the applied strain amplitude, relying solely on time or frequency.

Table 3 presents a comprehensive overview of the rheological data obtained from the strain sweep
tests, further illustrating the variations.

Within the linear viscoelastic region (LVR), characterized by strain sweep tests, the rheological
behavior of the hydrogels was elucidated. Notably, all blank hydrogels and hydrogels containing
Betaine-Glycerol (BG) primarily exhibited a dominant viscous behavior, where the loss modulus
(G") exceeded the storage modulus (G'). For instance, in the control group, G' was approximately
15.25 ± 0.49 Pa, whereas G" was around 25.61 ± 0.24 Pa. However, a notable transformation in
rheological behavior was observed with the addition of NaDES, specifically Citric Acid-Glucose
(CG). In these cases, there was a significant shift towards an elastic-dominant behavior, indicated
by G' surpassing G". For example, in Gel CG 10%wt, G' reached approximately 38.56 ± 0.14 Pa,
while G'' was approximately 29.01 ± 0.06 Pa. This transition towards elastic behavior was consistent across both formulation methods (method 1 and method 2), even when CG was added while the CMC gel was already formed. The standard deviations obtained are relatively low, showing the homogeneity of the measurements and of the formulations obtained. The results also show a relatively stable and large LVR up to around 20% deformation for all samples (an example is shown in figure 3). This feature of extended LVR is relatively common in CMC hydrogels, and the addition of NaDES does not appear to alter this characteristic³⁶. For formulations (whatever the method) containing 10%wt NaDES CG, a crossover of the G' and G'' moduli can be observed in the measurement range at around 80% deformation (figure 3). This crossover could be the sign of a threshold stress that could lead to a hydrogel flow threshold.

The most intriguing aspect of this observation is the correlated significant decrease in relaxation time ($\tau$), indicating enhanced cohesion within the gel structure. Relaxation times (frequencies for which $G' = G''$ or the curve describing $G'$ reaches a maximum at the same time as $G''$ describes an inflection point) are determined and correspond to the time taken for each interaction to regenerate after the oscillatory disturbance. The shorter the time, the stronger the interaction and the more pronounced the elasticity. Relaxation times obtained from the frequency sweep test were presented in Table 4 and exemplified in Figure 4.

The results show similar relaxation times between control conditions and hydrogels with NaDES BG (at 1 or 10%wt), whatever the formulation method used. The $\tau$ values obtained range from 0.2 to 0.3s. However, with the addition of 1 or 10%wt NaDES CG, whatever the method, $\tau$ values decrease by a factor of 10, from 0.2s to 0.01-0.03s. This variation would indicate an increase in cohesion within the gel structure⁴⁹. Furthermore, with the addition of this NaDES, the $G'$ modulus becomes predominant, denoting the viscoelastic solid character of the formulation. This variation
in rheological profile after frequency sweep is exemplified in figure 4. This shift in the rheological profile is the cause of the substantial differences observed in the flow properties and viscosity at low shear stress and as a result a modification of other texture properties⁵⁰. These modifications of the rheology of the gels cannot be attributed to the only better solubilization of CMC in the NaDES/water system observed on the DSC analysis (see Part 3.2). The main hypothesis of this shift would be a strengthening of the hydrogen bond network within the hydrogel structure, since the increase in the number of hydrogen bonds has been demonstrated statistically correlated with the increase in G' value for polysaccharide or swelling polymer type gelled systems⁵¹. These results highlight the key role of NaDES, particularly Citric Acid-Glucose (CG), in modifying the mechanical behavior of the hydrogel, potentially leading to improved performance in cosmetic formulations. Indeed, increased viscosity can improve the texture of a cosmetic product by making it thicker. A longer relaxation time may mean that the product retains its characteristics longer after application. This can be an advantage for products that need to remain in place for an extended period. Increased viscosity can also contribute to better flow resistance, which is useful for products that need to stay in place without running⁵²,⁵³.

### 3.4. Texture analyses

When examining the gel samples without NaDES, concerning hardness, the results show no significant difference between the two formulation methods, with hardness values for the gels of 0.128 N ± 0.003 N and 0.121 N ± 0.007 N for M1 and M2 respectively. Similarly, elasticity do not seem to be significantly modified by the formulation method, with results for elasticity of 11.757 mm ± 1.851 mm for M1 and 12.251 mm ± 1.536 mm for M2. The elasticity index results are consistent with the elasticity values, with values of 0.714 ± 0.205 for M1 and 0.926 ± 0.294 for
M2. These values are consistent with those found in the literature for 3% CMC hydrogels⁵⁴. This implies that if texture modifications are observed in NaDES-enriched gels, they can be directly linked with this ingredient addition. Concerning the gels with 10%wt BG NaDES, an increase in texture is observed compared to the control gel, particularly in hardness, with values increasing slightly but significantly. The values were 0.135 N ± 0.005 N and 0.140 N ± 0.008 N for M1 and M2 respectively. Similarly, elasticity and elasticity index values are higher for both methods than for control gels, with results for elasticity of 14.155 mm ± 0.739 mm for M1 and 14.540 mm ± 0.934 mm for M2. The elasticity index results are also consistent with the elasticity values, with values of 1.126 ± 0.253 for M1 and 1.236 ± 0.129 for M2. The increase observed for the addition of 10%wt BG NaDES is also found and much more intensely for 10%wt CG NaDES, with a significant increase in hardness for both methods. The values were 0.618 N ± 0.019 N and 0.505 N ± 0.030 N for M1 and M2 respectively. Similarly, elasticity and elasticity index values are higher for both methods than for control gels and close to that observed with the addition of 10%wt BG NaDES, with results for elasticity of 16.247 mm ± 0.392 mm for M1 and 16.026 mm ± 0.396 mm for M2. The elasticity index results are also consistent with the elasticity values, with values of 0.854 ± 0.019 for M1 and 0.841 ± 0.023 for M2. Two critical parameters were modified with the addition of NaDES: hardness and elasticity of the gels. Hardness refers to the resistance a material offers to deformation or penetration by an applied force. It is a critical parameter, as it directly influences how a product feels when applied to the skin. In cosmetic gels, higher hardness values imply a firmer and less yielding texture, which can be perceived by consumers as less spreadable and potentially less comfortable during application. On the other hand, elasticity pertains to the material's ability to return to its original shape after deformation. A higher elasticity index indicates that the material can stretch and then recover its form efficiently. In cosmetics, greater elasticity
often translates to a gel that feels more resilient on the skin, providing a sensation of bounce-back and smoothness during application⁵⁵. These results are consistent with rheology results obtained previously⁵².

### 3.5. Molecular analysis of the gels

In an attempt to comfort our hypothesis of a modification in the hydrogen bond network of the gel following the inclusion of NaDES, the molecular composition of the NaDES-enriched gels was studied by NMR spectroscopy and ATR-FTIR spectroscopy. Using these two methods allows us to observe changes within the gel from two different angles.

NMR analysis gives us information about CMC behavior in the gel in presence of the NaDES. The analyses were performed on the gels prepared with deuterium oxide instead of water to enhance resolution. These conditions eliminate the need to dilute H₂O hydrogels in D₂O, which poses a risk of disrupting the hydrogen bond network. The results, presented in Figure 5, indicate significant insights. In the ¹H spectrum of the gel without NaDES, a multitude of ¹H (H2-H6) resonances from the anhydroglucose units constituting the CMC structure overlap in the narrow region of 4.3–3.0 ppm⁵⁶. Upon incorporating 1 or 10% NaDES into the formulation, a noticeable signal shift occurs, attributed to increased viscosity in the sample⁵⁷. Signals from NaDES CG protons emerge in the region between 3.80 and 3 ppm, particularly those corresponding to glucose⁵⁸. This introduction of additional protons renders the tracking of all CMC protons impossible in this region. However, a discernible disappearance of protons initially present on the blank gel spectra is evident in the range of 4.1 to 3.85 ppm, where no signal from the other components can be found. The disappearance of protons is directly linked to their integration into the three-dimensional structural bonds⁵⁹,⁶⁰. Although attributing these signals precisely to one or more CMC protons is challenging,
the hypothesis of their involvement in new hydrogen bonds with the NaDES components, gains
support.

ATR mode was chosen to analyse directly the samples by FTIR spectroscopy with no sample
dehydration. Raw spectra of the different samples are presented on figure 6A et 6B for CG NaDES
and BG NaDES respectively. The interpretation of these spectra is challenging due to the complex
nature of the samples, the chemical similarities among components with comparable absorption
bands. Notably, there is already a hydrogen bond network present in the gel due to the interactions
between CMC and water in the blank gel. Moreover, the significant presence of 86.7 to 95.7% by
weight of water in the gel samples make it very speculative to analyse the –OH band around 3300-
3500 cm⁻¹ which is commonly used in the literature to illustrate the presence of a hydrogen bond
network. In the present case, it is possible to observe modification of the NaDES intrinsic hydrogen
bond network when CMC NaDES are included in a gel. This is particularly obvious on the second
derivative spectra of the fingerprint region presented on figure 6C and 6D, especially for the 10%
NaDES gels, while the 1% NaDES spectra are less informative due to the low concentrations
involved. The spectral window 1500–950 cm⁻¹ exhibits a number of features, assigned to Csingle
bondC, Csingle bondO stretching and bending modes, which are very sensitive to
conformation⁶¹,⁶². The second derivative of the spectra reveal significant shifts 5 to 6 cm⁻¹ to higher
wavenumbers in the position of absorption bands of NaDES when included at 10% in the gel,
notably bands around 1010 cm⁻¹ and 1170 cm⁻¹ characteristic of glucose (Figure 6C) and band
around 1030 cm⁻¹ characteristic of glycerol (Figure 6D) for CG and BG respectively⁶¹. Such shifts
have been attributed to hydrogen bond network creation or reinforcement in the literature⁶³,⁶⁴. A
specific band of H-O-H scissoring around 1640 cm⁻¹, is also red-shifted for both NaDES. This
band is characteristic of water present in CG NaDES and of glycerol present in BG NaDES⁶¹. The
red-shift of this band has already been described in the literature as a marker of the formation of hydrogen bonds⁶³,⁶⁵. Those modification in the IR spectra seem to demonstrate a modification of the hydrogen bond network of the NaDES when it is included in a gel at 10%wt. Those results do not clearly attest if the NaDES shows molecular interactions with CMC, water or both. However, when they are analyzed in the light of the NMR results, the latter hypothesis appears to be the more serious.

### 3.6. Sensory analysis

The primary objective of the sensory study was to explore the potential impact of incorporating hydrophilic NaDES into a CMC gel formulated for cosmetic purposes on consumer perception. A series of discriminative tests were aimed at discerning even slight alterations in the sensory attributes of the gels resulting from various formulation factors.

In conducting triangle tests for difference, how changes in ingredients or process parameters affected the sensory qualities of the gels was meticulously assessed. Blanks gels prepared by M1 or M2 were first compared and were not differentiated by the panel (P value > 0.3). This finding assures us that any sensory disparities observed subsequently do not stem from the gel manufacturing process by itself but rather from specific components within the formulation.

When the NaDES are introduced at only 1%wt., no significant differences in sensory perception were identified between M1 and M2 (P value > 0.3 for both BG and CG). Furthermore, the panel was unable to differentiate gels containing 1% NaDES from the blank gel, regardless of the NaDES used (P value > 0.5 for both NaDES).

Divergence in sensory perception emerged when NaDES were included in the gels at a concentration of 10%wt. As the difference between the NaDES-enriched gels and the control gel was visible to the naked eye, there was no point in using triangular tests. Nevertheless, they were
useful to bring out that the method of preparation had an impact on the perception of the gel by the consumer (P value < 0.01 for BG NaDES and P value < 0.005 for CG NaDES). These outcomes highlight the potential impact of high NaDES concentrations on the sensory attributes of the product. It was then interesting to continue the sensory analysis to characterize the sensory difference between the control gel and the 10%wt NaDES-enriched gels. Sensory profiles were conducted on the 10%wt NaDES-enriched gels by a trained panel of five experts using the EBI Kit, with each gel subjected to scrutiny across six sensory attributes: odor intensity, visual viscosity, pick-up, stringiness, spreading, and stickiness, each rated on a scale from 0 to 10. Results been shown in Table 5.

The gels with BG (10%wt) and CG (10%wt) NaDES additives exhibited comparable odor intensities, both scoring 4, while the NaDES-free gel also received a score of 4. This suggests that the presence of NaDES did not significantly alter the perceived odor intensity compared to the reference.

Visual viscosity, a critical attribute in cosmetic products, was scored at 3 for the NaDES-free gel, 4 for the BG (10%wt) gel, and notably higher at 9 for the CG (10%wt) gel. This difference in visual viscosity may be attributed to the unique properties of the specific NaDES used, indicating the potential to modulate the product's visual texture through the selection of NaDES components.

These results should also be seen in the context of rheology results, notably the fact that the use of NaDES CG significantly increases viscosity at low shear. On the other hand, despite rheological measurements of the increase in viscosity at low shear with NaDES BG (less than with CG, but significantly greater than the control), the difference does not appear to be perceptible.

Regarding pick-up, the gels with NaDES displayed marked variations. The BG (10%wt) gel scored a perfect 10, indicating high pick-up, while the CG (10%wt) gel scored only 1, signifying low
pick-up. The NaDES-free gel scored 10, indicating high pick-up, which is consistent with the BG (10%wt) gel. This variation suggests that NaDES can influence the ease of product pick-up, with specific NaDES compositions leading to contrasting effects.

Stringiness was assessed as 6 for the BG (10%wt) gel, 9 for the CG (10%wt) gel, and 5 for the NaDES-free gel. The CG (10%wt) gel demonstrated higher stringiness, which may be attributed to its distinct NaDES composition. The spreading attribute received a score of 7 for the BG (10%wt) gel, 1 for the CG (10%wt) gel, and 7 for the NaDES-free gel, indicating that the CG (10%wt) gel exhibited lower spreading compared to the others. This result is surprising given that in the rheological observations, viscosity values in the shear zone corresponding to the spreading zone (between 100 and 1000s⁻¹) were lower than for the controls without NaDES. However, as the modulus values G' and G'' were greatly increased (especially with a predominance of G'), the spreading capacity was reduced.

Lastly, stickiness was scored at 4 for the BG (10%wt) gel, 8 for the CG (10%wt) gel, and 4 for the NaDES-free gel, signifying a notable increase in stickiness for the CG (10%wt) gel, likely linked to its unique NaDES composition.

These findings highlight the need for formulators to strike a balance when incorporating NaDES into cosmetic gels. While offering advantages in solubility and performance, NaDES concentration significantly influences sensory experiences. This knowledge can aid formulators in creating innovative products meeting consumer expectations in the cosmetics industry. Overall, the sensory analysis results indicate significant variations in visual viscosity, pick-up, stringiness, spreading, and stickiness, offering the potential to tailor cosmetic properties to specific requirements. Further investigation is required to understand the mechanisms behind these changes and their implications for cosmetic applications.
4. Conclusion

NaDES and NaDES-based extracts emerge as highly promising ingredients for cosmetic products, functioning both as active and functional components, due to their sustainability, robust solubilization power, high tolerance, and intrinsic cosmetic properties such as humectant, antimicrobial, or moisturizing agents. The unique characteristic of these ingredients lies in their hydrogen bond network, achieved through a combination of hydrogen bond donors and acceptors. On this basis, it is expected that these ingredients will exhibit strong interactions with other components commonly found in cosmetic products, such as polysaccharide gelling agents, which, in turn, form a hydrogen network with the water present in the final product. This study specifically focused on two NaDES types commonly used for preparing cosmetic ingredients from biomasses: organic acid-based NaDES and amino acid-based NaDES, incorporating them into a polysaccharide-based gel.

Molecular exploration of the gels using IR and NMR spectroscopies suggests that the initial hydrogen bond networks in the gel and NaDES undergo changes when mixed. Two methods of NaDES inclusion were investigated: before and after gelation. The chosen method exerted a notable impact on the rheological properties of the resulting gels, particularly affecting viscosity "at rest" and the relaxation time. Independently of the method of preparation, these modifications indicated a reinforcement of the gel structure in favor of a rearrangement of the hydrogen bond network within the gel. Fortunately, these rheological modifications did not significantly impede the spreading of the gel.

Further investigation through textural analysis revealed an increase in the hardness of the gels, with more pronounced changes observed when NaDES was included at 10%, a concentration relevant for their use as functional rather than active ingredients, consistent with the rheological
observations and the reinforcement of the hydrogen bond network. It is also at this concentration that NaDES inclusion may influence the consumer's perception of the product. These findings emphasize that NaDES are not conventional ingredients for cosmetic formulas, and their interaction with gelling agents must be considered.

Despite both NaDES types engaging in similar interactions with gel components, significant differences exist between CG NaDES and BG NaDES in terms of their impact on gel structure and properties. Notably, CG has a substantial impact on product viscosity, whereas BG exerts only a moderate influence. CG is identified here as a very efficient viscosity booster, but used with usual concentration of CMC gelling agent, it unfortunately decreases the pick up of the product and increases its stringiness. Adjustments in polysaccharide concentrations may be necessary in products with a high CG concentration, while the use of BG may not require modifications in formulator practices. This underscores the need for further studies on the interaction between NaDES and commonly used cosmetic functional ingredients, aiming to identify their specific properties and to build predictive models to facilitate formulator work and identify the potential of each NaDES as cosmetic ingredients. Such research will contribute to the selection of the most suitable NaDES for various formulations, promoting the incorporation of NaDES-based ingredients in the cosmetic industry in its research toward more sustainability.
<figure><img src="image_2.png" /><figcaption>**Figure.1:** DSC thermograms of CMC hydrogels (without NaDES in black, with CG NaDES in blue and with BG NaDES in green)</figcaption></figure>
<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /><figcaption>**Figure.2:** Flow properties of CMC hydrogels with 1%wt (A and B) and 10%wt (C and D) of hydrophilic NaDES (without NaDES in black, with CG NaDES in blue and with BG NaDES in green, with solid marks for D1 and hollow marks for D30 and also dotted curves for method 1 and solid curves for method 2)</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>**Figure.3:** Oscillatory strain sweep test results of CMC hydrogels by M2 with 10%wt CG NaDES (in blue line) and without NaDES (in black line). G' and G" moduli were represented by solid curves (with circle marks) and dotted curves (with triangle marks) respectively</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>**Figure.4:** Oscillatory frequency sweep test results of CMC hydrogels by M2 with 10%wt CG NaDES (in blue line) and without NaDES (in black line). G' and G'' moduli were represented by solid curves (with circle marks) and dotted curves (with triangle marks) respectively</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>**Figure.5:** ¹H NMR spectra of CMC gels without NaDES (black), with 1% (light blue) and 10% (dark blue) NaDES CG in D₂O. The area of suspected signal loss is indicated by a red rectangle.</figcaption></figure>
<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /><figcaption>**Figure.6:** ATR-IR spectra (mean of n=3, 32 scan per replicate) of NaDES (blue line), control gel (red line) and NaDES-enriched gels with 1% NaDES (yellow line) or 10% NaDES (purple line)</figcaption></figure>

A: CG-samples, B: BG-samples, C: second derivatives for CG-samples (spectra are offset for clarity), D: second derivatives for BG-samples (spectra are offset for clarity).
TABLES.

<table><caption>**Table 1:** Gels composition</caption><thead><tr><th rowspan="2">Ingredients</th><th rowspan="2">function</th><th colspan="2">%wt in the samples</th></tr><tr><th>Control</th><th>NaDES gels</th></tr></thead><tbody><tr><td>NaDES (%wt.)</td><td>Solvent</td><td>0</td><td>1 or 10</td></tr><tr><td>CMC (%wt.)</td><td>Gelling agent</td><td>3</td><td>3</td></tr><tr><td>Dehydroacetic acid/ benzyl alcohol mix (%wt.)</td><td>Antimicrobial agents</td><td>0.3</td><td>0.3</td></tr><tr><td>Water (%wt.)</td><td>Solvent</td><td>q.s 100</td><td></td></tr></tbody></table>

<table><caption>**Table 2A:** pH of hydrogels with or without 1% NaDES. Data represent the mean ± SD.</caption><thead><tr><th></th><th>Blank gel M1</th><th>Blank gel M2</th><th>CG gel M1</th><th>CG gel M2</th><th>BG gel M1</th><th>BG gel M2</th></tr></thead><tbody><tr><td>pH at D1</td><td>6.2 ± 0.4</td><td>5.9 ± 0.3</td><td>5.2 ± 0.5</td><td>5.3 ± 0.6</td><td>5.1 ± 0.2</td><td>5.2 ± 0.4</td></tr><tr><td>pH at D30</td><td>6.4 ± 0.5</td><td>5.8 ± 0.3</td><td>5.8 ± 0.3</td><td>5.5 ± 0.6</td><td>4.7 ± 0.3</td><td>5.4 ± 0.3</td></tr></tbody></table>

<table><caption>**Table 2B:** pH of hydrogels with or without 10%wt NaDES obtained. Data represent the mean ± SD.</caption><thead><tr><th></th><th>Blank gel M1</th><th>Blank gel M2</th><th>CG gel M1</th><th>CG gel M2</th><th>BG gel M1</th><th>BG gel M2</th></tr></thead><tbody><tr><td>pH at D1</td><td>6.2 ± 0.3</td><td>5.9 ± 0.2</td><td>3.9 ± 0.3</td><td>3.3 ± 0.4</td><td>3.7 ± 0.7</td><td>3.2 ± 0.8</td></tr><tr><td>pH at D30</td><td>6.5 ± 0.5</td><td>5.8 ± 0.1</td><td>4.3 ± 0.1</td><td>3.8 ± 0.4</td><td>5.9 ± 0.4</td><td>5.8 ± 0.5</td></tr></tbody></table>
<table><caption>**Table 3.** Rheological data (means ± SD) obtained from the strain sweep tests. The values of G' and G'' correspond to the linear viscoelastic region.</caption><thead><tr><th>Method</th><th>Formulations</th><th>G' (Pa)</th><th>G'' (Pa)</th></tr></thead><tbody><tr><td rowspan="5">1</td><td>Control</td><td>15.25 ± 0.49</td><td>19.39 ± 0.24</td></tr><tr><td>Gel BG 1%wt</td><td>19.06 ± 0.01</td><td>23.97 ± 0.08</td></tr><tr><td>Gel BG 10%wt</td><td>25.00 ± 0.09</td><td>33.07 ± 0.03</td></tr><tr><td>Gel CG 1%wt</td><td>28.33 ± 0.21</td><td>15.39 ± 0.05</td></tr><tr><td>Gel CG 10%wt</td><td>40.12 ± 0.42</td><td>32.88 ± 0.17</td></tr><tr><td rowspan="5">2</td><td>Control</td><td>12.57 ± 0.12</td><td>13.98 ± 0.09</td></tr><tr><td>Gel BG 1%wt</td><td>18.85 ± 0.13</td><td>23.61 ± 0.06</td></tr><tr><td>Gel BG 10%wt</td><td>22.64 ± 0.27</td><td>32.74 ± 0.15</td></tr><tr><td>Gel CG 1%wt</td><td>22.33 ± 0.21</td><td>11.39 ± 0.05</td></tr><tr><td>Gel CG 10%wt</td><td>38.56 ± 0.14</td><td>29.01 ± 0.06</td></tr></tbody></table>

<table><caption>**Table 4.** Relaxation times (means ± SD) obtained from the frequency sweep tests.</caption><thead><tr><th>Method</th><th>Formulations</th><th>τ (s)</th></tr></thead><tbody><tr><td rowspan="5">1</td><td>Control</td><td>0.20 ± 0.01</td></tr><tr><td>Gel BG 1%wt</td><td>0.30 ± 0.07</td></tr><tr><td>Gel BG 10%wt</td><td>0.20 ± 0.09</td></tr><tr><td>Gel CG 1%wt</td><td>0.03 ± 0.01</td></tr><tr><td>Gel CG 10%wt</td><td>0.02 ± 0.02</td></tr><tr><td rowspan="5">2</td><td>Control</td><td>0.20 ± 0.03</td></tr><tr><td>Gel BG 1%wt</td><td>0.30 ± 0.02</td></tr><tr><td>Gel BG 10%wt</td><td>0.20 ± 0.08</td></tr><tr><td>Gel CG 1%wt</td><td>0.01 ± 0.04</td></tr><tr><td>Gel CG 10%wt</td><td>0.03 ± 0.01</td></tr></tbody></table>
<table><caption>**Table 5.** Results from descriptive sensory profiles (average results after consensuses)</caption><thead><tr><th></th><th>Odor intensity</th><th>Visual viscosity</th><th>Pick up</th><th>Stringiness</th><th>Spreading</th><th>Sticky</th></tr></thead><tbody><tr><td>Gel with BG 10%wt</td><td>4</td><td>4</td><td>10</td><td>6</td><td>7</td><td>4</td></tr><tr><td>Gel with CG 10%wt</td><td>4</td><td>9</td><td>1</td><td>9</td><td>1</td><td>8</td></tr><tr><td>Blank Gel</td><td>4</td><td>3</td><td>10</td><td>5</td><td>7</td><td>4</td></tr></tbody></table>
# AUTHOR INFORMATION

## Corresponding Author

* Pr. Emilie Munnier

¹UPR CNRS 4301 CBM, département NMNS

Faculté de Pharmacie

31 Avenue Monge, 37200 Tours, France.

Tel: +33 2 47 36 72 01

Email: emilie.munnier@univ-tours.fr

## Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

## ACKNOWLEDGMENT

Dr. Marian Amela-Cortes is acknowledged for differential scanning calorimetry experiments at Solid State Chemistry and Materials (CSM) in the Rennes Institute of Chemical Sciences (ISCR - UMR CNRS 6226). Acknowledgements for Florence Dardaud from Département professionnel Agrosciences – filière Sensoriel et Innovation UFR de Sciences et Techniques. Pr Marie-Claude Viaud-Massuard and Dr. Cécile Croix are acknowledged for NRM experiment at UMR INSERM U 1100 - Centre d'Etudes des Pathologies Respiratoires.

Authors particularly thank Conseil Régional Centre Val de Loire (ARD CVL Cosmétosciences 2020-00141275) and Agence Nationale de la Recherche (DES4Skin project ANR-22-CE43-0006-04). Graphical abstract was created with BioRender.com.
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ABSTRACT GRAPHIC

<figure><img src="image_14.png" /></figure>

NONTECHNICAL SYNOPSIS

Research exploring NaDES impact on CMC hydrogel promotes sustainable cosmetic innovation, supporting eco-friendly solvent use.