Relationship between perceived softness of bilayered skin models and their mechanical properties measured with a dual-sensor probe

Talk to us about your skin: The relationship between spoken language and haptic exploratory procedures

OBJECTIVE

To enhance satisfaction, the cosmetics industry needs to clearly understand consumers' descriptions of their key tactile preferences. It is difficult for researchers to understand verbal descriptions from people whose native language is different from their own. Previous research has implied that some sensory words with the same lexical meanings have been observed in different haptic exploratory procedures (HEPs). Therefore, our study aims to investigate and understand the key tactile perceptions of people from five different countries based on their descriptions and their HEPs.

METHODS

In Experiment 1, 1545 participants living in the US, Japan, China, Italy, and Thailand described their major tactile perceptions as efficacy in skincare, and we analysed the frequency of each word used in their answers. In Experiment 2, we confirmed the task to observe HEPs for Chinese, Italian, and Thai participants. A total of 24 participants in China, 33 participants in Italy, and 30 participants in Thailand freely explored their faces with their hands and answered which side more closely matched the major tactile adjectives. Experts classified the observed HEPs into six classifications within two categories and three contact area sizes and investigated the cultural differences.

RESULTS

More than 2% of the Chinese, Italian, Thai, US, and Japanese participants described 33, 20, 29, 22, and 18 words, respectively, as efficacy in skincare. Verified words that described the major tactile perceptions in each native language had the same meanings as moistness, firmness, softness, smoothness, and so on. We could confirm the HEPs of these major feelings for the participants from each culture. Chinese and Thai participants' HEPs for moistness or softness were observed with a pressing movement. Conversely, Italian participants' HEPs for moistness or softness were observed with a rubbing movement.

CONCLUSION

This study showed that words with the same lexical meanings evoked different HEPs. The results imply that different HEPs can provide different physical stimuli on the skin. Therefore, it is important to survey both objects and HEPs to better understand the tactile experience.

Skin Sensory Assessors Highly Agree on the Appraisal of Skin Smoothness and Elasticity but Fairly on Softness and Moisturization

We tested the reliability of sensory evaluations of tactile sensation on bare skin and investigated the reliability among evaluation attributes by trained and untrained assessors. Two trained professional panelists and two untrained researchers evaluated skin in terms of several attributes: smooth–rough, elastic–not elastic, soft–hard (surface), soft–hard (base), moisturized–dry. Twenty-two women aged 25–57 years were evaluated, and the sensory evaluation was repeated twice. Correlation coefficients and intraclass correlation coefficients (ICCs) were used to examine intra- and inter-assessor reliability. The sensory evaluation and physical quantities acquired by commercial and non-commercial instruments were moderately correlated. Smooth–rough and elastic–not elastic showed high or moderate inter-assessor reliabilities with mean correlation coefficients between panelists of 0.81 and 0.58, respectively. Further, the ICC (2,1) values were 0.64 and 0.51, respectively, and the ICC (2,2) values were 0.77 and 0.67, respectively. Conversely, the reliabilities of soft–hard (surface), soft–hard (base), and moisturized–dry were low; the mean correlation coefficients between the panelists were 0.36, 0.23, and 0.22; the ICC (2,1) values were 0.27, 0.23, and 0.17; and the ICC (2,2) values were 0.42, 0.29, and 0.26, respectively. Reliability differed between attributes. We found no meaningful differences between the trained and untrained panelists regarding intra- or inter-assessor reliability.

Influence of wall slip, thixotropy, and lubrication regime on the instrumental sensory evaluation of topical formulations

OBJECTIVE

Drawing parallels from rheo-tribology can be used to develop a robust instrumental protocol for non-subjective characterization, product development and design of topical dosage forms with desired sensory attributes. However, instrumental characterization of cosmetic products can be influenced by the measurement protocol, thixotropy, flow anomalies like shear banding or wall slip and nature of the film formed on the skin surface. In this study, we evaluated the influence of above parameters on the instrumental sensory evaluation of twelve topical formulations of different galenic forms.

METHODS

Oscillatory strain sweep measurements (SAOS and LAOS) were performed to investigate the influence of frequency and wall slip on the material parameters. The textural attributes at different consumer touch points were evaluated by accounting time dependent simulation of visco-elastic flow. Further, the influence of film thickness and sample drying on the tactile properties of the topical formulations were studied on a non-biological skin model using a sliding probe tribometer.

RESULTS

The study shows that the flow properties of the semi-solid formulations depend on the time scale of the problem. A few formulations exhibited wall slip to varying degrees in the linear visco-elastic regime where the behaviour was found not to be characteristic of a particular topical dosage form. The material functions obtained from the Lissajous plots suggest that the non-linear flow behavior of different galenic forms is least influenced by the boundary conditions imposed by the measurement geometry. The results were statistically analyzed using principal component analysis where the attributes used for discriminating skin creams during pick-up and rub out are found to be closely associated with non-linear rheology. The friction coefficient exhibited speed dependence where it formed different parametric group with rheological data depending on the lubrication regime.

CONCLUSION

The study highlights that correlations are possible among rheological, tribological, and instrumental textural analysis data, which can act an impetus for the development of models to predict attributes that drive perception at different consumer touch points. However, the choice of instrumental settings, anomalies associated with rheological measurements and friction dependence on a number of parameters can influence the model prediction.

Sensory words may facilitate certain haptic exploratory procedures in facial cosmetics

OBJECTIVE

Many people want to have healthy facial skin. They tend to check their skin's condition by touching their face with their hands. In the cosmetic industry, we need to understand what consumers are perceiving in a tactile sense when touching their own facial skin. The purpose of this study was to investigate these observation methods in order to systematically understand people's haptic exploratory procedures (HEPs).

METHODS

Thirty-four participants living in the United States and twenty-two participants living in Japan freely explored their faces and answered which side felt more closely related to the six tactile adjectives. A new analysis was applied to classify the observed HEPs into six classifications within two categories and three sizes of contact area by experts.

RESULT

It was confirmed that the new task was useful to observe the HEPs for participants from United States and Japan. The US participants' HEPs for 'moisturized' were mainly a middle-sized contact area using a stroking motion. On the other hand, Japanese participants' HEPs for 'moisturized' ('shittori' in Japanese) mainly used a pushing movement. Moreover, the US participants' HEPs for 'soft' included both pushing and stroking, but Japanese participants HEPs for 'soft' ('yawarakai' in Japanese) were again mainly pushing.

CONCLUSION

This study suggests that the proposed analysis method enables the systematic understanding of HEPs when checking the skin, along with the cross-cultural differences affecting those procedures. These systematic findings could allow cosmetic formulators to have a better understanding of the tactile sensations consumers themselves are feeling in a variety of different global markets.

Visualizing Individual Perceptual Differences Using Intuitive Word-Based Input

Numerous studies have investigated the fundamental dimensions of human tactile perceptual space using a wide range of materials. Participants generally touch materials and quantitatively evaluate variations in tactile sensations for pairs of adjectives pertaining to the material properties, such as smooth—rough and soft—hard. Thus, observers evaluate their perceptual experiences one by one in terms of adjective pairs. We previously proposed an alternative method of qualitative evaluation of tactile sensations. Our system can automatically estimate ratings of fundamental tactile properties from single sound-symbolic words. We were able to construct a word-based perceptual space by collecting words that express tactile sensations and applying them to the system. However, to explore individual differences in perceptual spaces, different databases for converting words into ratings of adjective pairs are required for each individual. To address this, in the present study we created an application that can automatically generate an individualized perceptual space by moving only a few words in the initial word-based perceptual space. In addition, we evaluated the efficacy of the application by comparing the tactile perceptual space before and after use.

Skin surface physico-chemistry: Characteristics, methods of measurement, influencing factors and future developments

Physico-chemical properties such as surface free energy, polarity or hydrophobicity of solid surfaces have been largely studied in literature because they are involved in many physical phenomena: adhesion, friction, wetting … Nowadays, the study of biointerfaces is of great interest for the medical, the pharmaceutical or the cosmetic field but also for material design researches, especially for the development of biomimetic surfaces. The present paper focuses on a particular biointerface, namely skin, which is the most extended organ of the human body. The different ways for the study of skin physico-chemistry are first reviewed, followed by their practical uses, from pharmaceutical to cosmetic science. Those properties depict the ways skin interacts with topical products, its lipid composition but also its hydration state. In addition, this article aims to present recent approaches using original model materials in order to mimic human skin; indeed, in vivo experiments are often limited by the inter and intra individual variability, the safety regulation and above all the time and the cost of such studies. Finally, further data clearly highlight the importance of skin surface properties for dermatological and pharmaceutical researches.

Bouba/Kiki in Touch: Associations Between Tactile Perceptual Qualities and Japanese Phonemes

Several studies have shown cross-modal associations between sounds and vision or gustation by asking participants to match pre-defined sound-symbolic words (SSWs), such as “bouba” or “kiki,” with visual or gustatory materials. Here, we conducted an explorative study on cross-modal associations of tactile sensations using spontaneous production of Japanese SSWs and semantic ratings. The Japanese language was selected, because it has a large number of SSWs that can represent a wide range of tactile perceptual spaces with fine resolution, and it shows strong associations between sound and touch. In the experiment, we used 120 everyday materials to cover basic material categories that could be associated with fundamental dimensions of tactile perception. Upon contact with these materials, participants expressed their tactile sensations by using Japanese SSWs, and at the same time, evaluated the tactile sensations by semantic differential scales using adjective pairs. Thanks to the variety of testing materials, we were able to demonstrate the existence of systematic associations between sounds and tactile fundamental perceptual dimensions in a more detailed and comprehensive way than ever done so before. In particular, we found that for vowels, positive tactile ratings were associated with the back vowel (/u/), while negative ratings were associated with the front vowels (/i/ and /e/). The central vowels (/o/ and /a/) were mainly associated with rough, hard, and dry feelings. Consonants were categorized based on vocal features and articulation. The category of the voiced consonants (e.g., /dz/ and /g/) corresponded to feelings of roughness, while that of voiceless consonants (e.g., /ʦ/, and /s/) corresponded to feelings of smoothness. The categories of the bilabial plosive (/p/ and /b/) and voiced alveolar nasal (/n/) consonants were mainly related to soft, sticky and wet feelings, while that of voiceless alveolar affricate (/ʦ/) and voiceless velar plosive (/k/) consonants were related to hard, slippery and dry feelings.

Exploring Tactile Perceptual Dimensions Using Materials Associated with Sensory Vocabulary

Considering tactile sensation when designing products is important because the decision to purchase often depends on how products feel. Numerous psychophysical studies have attempted to identify important factors that describe tactile perceptions. However, the numbers and types of major tactile dimensions reported in previous studies have varied because of differences in materials used across experiments. To obtain a more complete picture of perceptual space with regard to touch, our study focuses on using vocabulary that expresses tactile sensations as a guiding principle for collecting material samples because these types of words are expected to cover all the basic categories within tactile perceptual space. We collected 120 materials based on a variety of Japanese sound-symbolic words for tactile sensations, and used the materials to examine tactile perceptual dimensions and their associations with affective evaluations. Analysis revealed six major dimensions: "Affective evaluation and Friction," "Compliance," "Surface," "Volume," "Temperature," and "Naturalness." These dimensions include four factors that previous studies have regarded as fundamental, as well as two new factors: "Volume" and "Naturalness." Additionally, we showed that "Affective evaluation" is more closely related to the "Friction" component (slipperiness and dryness) than to other tactile perceptual features. Our study demonstrates that using vocabulary could be an effective method for selecting material samples to explore tactile perceptual space.