Relation between sensory analysis and rheology of body lotions

Rational Design of Topical Semi-Solid Dosage Forms-How Far Are We?

Specific aspects of semi-solid dosage forms for topical application include the nature of the barrier to be overcome, aspects of susceptibility to physical and chemical instability, and a greater influence of sensory perception. Advances in understanding the driving forces of skin penetration as well as the design principles and inner structure of formulations, provide a good basis for the more rational design of such dosage forms, which still often follow more traditional design approaches. This review analyses the opportunities and constraints of rational formulation design approaches in the industrial development of new topical drugs. As the selection of drug candidates with favorable physicochemical properties increases the speed and probability of success, models for drug selection based on theoretical and experimental approaches are discussed. This paper reviews how progress in the scientific understanding of mechanisms and vehicle-influence of skin penetration can be used for rational formulation design. The characterization of semi-solid formulations is discussed with a special focus on modern rheological approaches and analytical methods for investigating and optimizing the chemical stability of active ingredients in consideration of applicable guidelines. In conclusion, the combination of a good understanding of scientific principles combined with early consideration of regulatory requirements for product quality are enablers for the successful development of innovative and robust semi-solid formulations for topical application.

Study and optimization of oil-in-water emulsions formulated by low- and high-frequency ultrasounds

OBJECTIVE

A combined treatment using both low-frequency (20 kHz) and high-frequency ultrasounds (1.63 MHz) is a promising new process to stabilize emulsions with minimalist formulation. In order to optimize process parameters, a Doehlert experimental design was performed with oil-in-water emulsions, presently used for cosmetic products, composed of water, caprylic/capric triglycerides and oleic acid.

METHODS

Effects of treatment time, oil content and oleic acid content were studied on emulsion properties (droplet size, polydispersity index, ζ-potential and yield of oil incorporation) and on emulsion stability after a 28-day storage (creaming index, Turbiscan stability index (TSI) and oil release).

RESULTS

From experimental data, a model was established that allowed to study effects of each parameter and their interactions on emulsion formation and stability. Oleic acid content had a great impact on emulsion formation: It reduced droplet size, PDI and ζ-potential and increased yield of oil incorporation. However, a critical value could be highlighted, beyond which oleic acid effects reversed. Treatment time had an important beneficial effect on emulsion stability as it decreased creaming index, TSI and oil release after 28 days of storage. Oil content had a negative effect on emulsion formation and on emulsion stability. However, treatment time and oil content often had a beneficial synergistic effect.

CONCLUSION

The optimized conditions for emulsion processing were obtained through a desirability approach. They were experimentally validated.

Design of a Sensorial-Instrumental Correlation Methodology for a Category of Cosmetic Products: O/W Emulsions

The validation of a cosmetic product is performed by physical analyses and sensory assessment. However, the recruitment of panelists takes a long time and is expensive. Moreover, to apply the product on the skin, microbiology analyses and safety are required but may not be not enough to avoid inflammatory reaction on the skin. The solution could be the substitution of sensory evaluation by instrumental measurement to predict the sensory profile before the panel. For the study, thirteen different skin care emulsions based on their composition and texture were carried out simultaneously by 12 expert panelists with a quantitative descriptive sensory evaluation profile and by rheological and textural methods. A statistical methodology was the applied to find correlation trends between both data sets. The methodology confirmed that the correlation between sensory assessment and instrumental parameters is a good solution to save time. The multiple factor analysis (MFA) showed the correlation between firmness with no visual residue attribute and the cohesion with sticky 1 min, which are evident but this methodology could be used for finding more complex correlations not found in literature.

Characterization of Cosmetic Dispersions Based on Friction Dynamics

Frictional properties are one of the most important physical factors in the design of cosmetic dispersions in which solid particles are dispersed in a liquid. The effects of ingredients and formulations on frictional properties have been previously reported. In this study, the frictional properties of 33 cosmetic dispersions were evaluated using a sinusoidal motion friction evaluation system when applied on an artificial skin. A detailed analysis of the velocity dependence of the friction coefficient demonstrated that all cosmetic dispersions exhibited stabile pattern and the friction behavior did not change during the round trip. We analyzed friction-based parameters by principal component analysis and demonstrated that the principal components Z₁ and Z₂ include the static friction coefficient μ_s, kinetic friction coefficient μ_k, delay time δ, and viscosity coefficient C, and that these factors are involved in characterizing friction dynamics. The cluster analysis on Z₁ and Z₂ suggested that these dispersions can be classified in three groups with respect to friction dynamics. These results can help understand the characteristics of cosmetics and control their function and utility.

Bio-sourced polymers in cosmetic emulsions: a hidden potential of the alginates as thickeners and gelling agents

OBJECTIVE

The present work aims to investigate the impact of the alginates on the texture properties of cosmetic emulsions. For this purpose, five systems were selected: a classical emulsion without polymer and four emulsions containing polymers, as texture modifiers, at the level of 1%. Two different grades of alginates were chosen: one rich in mannuronic acid and one rich in guluronic acid. The objective was also to evaluate the potential of in-situ gelation during formulation. The guluronic rich sample was gelled to evaluate the effect on the texture properties. Finally, alginates-based systems were compared to the xanthan gum as a bio-sourced polymer reference.

METHODS

The sensory profile of the systems was established through a combination of prediction models and sensory analysis. The emulsion residual films obtained with natural polymers, Alginates and Xanthan Gum used as thickeners, as well as with the gelled version, were similar. However, the structural differences between polymers intervene during the characterisation of the sensory properties "before" and "during" application. A multi-scale physicochemical analysis was used to explain these differences.

RESULTS

Due to a controlled formulation process, the use of the polymers did not affect the microstructure of the emulsion which remained similar to the control one. The main impact of the polymers was observed on the macroscopic level: both alginates showed their unique textural signature, different from the classical Xanthan Gum. Due to weak structural differences, mechanical and textural properties were very close between the mannuronic rich and guluronic rich samples, when not gelled, compared to other emulsions. However, the molar mass and the mannuronic/guluronic acids ratio were proved to be crucial for the stretching and consistency properties, showing that this structural difference may have an impact when products are handled in traction and compression.

CONCLUSION

Meanwhile, the viscoelastic properties and the dynamic viscosity were greatly increased for the emulsion containing the gelled version of the alginate when compared to the classical polymers. The emulsion was also more consistent as proved by the textural analysis, pointing at better stability and suspension potential of the gelled emulsion versus the classical one containing the usual natural thickening agents.

Rheology of α-Gel Formed by Amino Acid-Based Surfactant with Long-Chain Alcohol: Effects of Inorganic Salt Concentration

Mixtures of surfactants, long-chain alcohols, and water sometimes yield lamellar gels with hexagonally packed alkyl chains. This assembly is called "α-gel" or "α-form hydrated crystal." In this study, we characterized the rheological properties of α-gel prepared using disodium N-dodecanoylglutamate (C12Glu-2Na), 1-hexadecanol (C16OH), and water at different NaCl concentrations. The α-gel structure was assessed using small- and wide-angle X-ray scattering (SWAXS). The SWAXS measurements revealed that an increased NaCl concentration (0-200 mmol dm^-3) resulted in a decreased d-spacing caused by the screening of electrostatic repulsion between lamellar bilayers. This led to an increased amount of excess water (i.e., the water present between the α-gel domains), and hence, the viscosity of the α-gel decreased in the range of the NaCl concentration. A further increase in the NaCl concentration (200-1000 mmol dm^-3) resulted in decreased electrostatic repulsion between the α-gel domains and/or an increased number of α-gel domains (multilamellar vesicles). These effects increased the domain-to-domain interactions, leading to increased viscosity. Therefore, we concluded that the viscosity of the α-gel was controlled by the amount of excess water and the domain-to-domain interactions. Once the network structure collapsed under the strain, it was difficult to recover the original network structure. The low recoverability resulted from increased cohesion between the domains at high NaCl concentrations.

The Quality of Emulsions with New Synthetized Lipids Stabilized by Xanthan Gum

The study investigated the quality of emulsions containing rabbit fat modified with vegetable oil. The modification of the fat and introducing it as a fatty base into the emulsion was dictated by consumer preferences. Emulsion systems containing various fatty bases and viscosity modifier contents were evaluated in the terms of their stability (by means of Turbiscan test), texture properties, color, and viscosity. Moreover, the emulsions were assessed by a sensory panel in the context of the intensity of the following parameters: color, fragrance, consistency, greasiness, and hydration. The same characteristics were also subject to consumer evaluation. The results of the sensory assessment showed the sensory panel attributed higher scores to consistency and skin hydration to the emulsions formed with modified fats; these systems were more appreciated by consumers as well. The results confirmed a major role of sensory determinations in the development of new emulsion products. They also provide knowledge on modifications to product characteristics that would lead to the best possible quality and consumer acceptance. This research has also reaffirmed that looking for new fats among waste fats is becoming a solution to finding new fatty bases for emulsions. The natural origin of these components, and thus their agreeability with the human body, appear noteworthy as well. Enrichment with unsaturated fatty acids is an added advantage of the enzymatic modification of rabbit fat with pumpkin seed oil and can be applied not only for food but also for skin applications.

Measurements meet perceptions: rheology-texture-sensory relations when using green, bio-derived emollients in cosmetic emulsions

OBJECTIVE

Product aesthetics and sensory performance can strongly influence a cosmetic product's acceptance by consumers. However, classic sensory analysis is time-consuming, expensive and does not provide information on the target group's preference. In the previous phase of this project, we had untrained consumers evaluate six cosmetic emulsions based on their aesthetics using a check-all-that-apply (CATA) survey. In this project, our goals were to quantitatively characterize the rheology and textural properties of the six cosmetic emulsions containing green, bio-derived emollients and identify statistical relationships between the consumers' description of products and the instrumental measurements.

METHODS

Six emulsions were prepared-three with olive oil and three with heptyl undecylenate as an emollient. Four sensory-like attributes, namely firmness, work of shear, stickiness and adhesiveness, were tested using a texture analyser. Rheological characterization included continuous flow testing and oscillatory measurements. Droplet size and stability were also evaluated. Statistical relationships were quantified between measurements in this study and sensory survey results published previously.

RESULTS

The textural and rheological results indicated that the emulsions were different-as designed. The texture and rheology measurements had analogous grouping outcomes to the consumers' discrimination. Emulsions 1 and 2 were the firmest, hardest to spread, stickiest and had the highest viscosity, while Emulsions 5 and 6 were the least firm, easiest to spread, less sticky than Emulsions 1 and 2, and had the lowest viscosity. Emulsions 3 and 4 fell in between the other two groups. Using olive oil instead of heptyl undecylenate as an emollient increased firmness, spreading, stickiness, viscosity and droplet size of the emulsions in every case-when comparing emulsions within each pair. All six emulsions had a shear-thinning behaviour. Viscosity and firmness directly correlated for the emulsions. Emulsions were visually stable at room temperature over the course of 6 months and viscosity remained relatively constant over this period also.

CONCLUSION

Certain sensory attributes can be reliably predicted with instrumental measurements. Identifying and quantifying sensory-texture-rheology relationships can contribute to achieving appropriate product characteristics tailored to suit market needs.

Influence of the emollient on emulsions containing lamellar liquid crystals: from molecular organization towards applicative properties

OBJECTIVE

The sensory perception of cosmetic emulsions is complex as it is governed by an important number of parameters like the choice of raw materials, their interactions, the structural organisation of the system, etc. The aim of the present work was to go further in the interpretation of the emollient-surfactant interactions, towards the emulsions applicative properties. For this purpose, two systems containing liquid crystals of the lamellar type were formulated, differing only in the selected emollient.

METHODS

First, the liquid crystals types were checked using different tools like the optical microscopy under the bright and polarized light, the wide-angle X rays diffraction and, finally, thermogravimetric analysis. Next, two sensory attributes, namely compression force and difficulty of spreading, were evaluated by a sensory panel. In addition to that, complementary instrumental characterizations (flow tests, textural analysis and contact angle measurements) were performed in order to understand how the panel could discriminate the products.

RESULTS

The results showed that isohexadecane emollient induces the α-gel structures, while caprylic capric triglycerides favour the formation of the lamellar liquid crystals near to α-gel. For the compression force, the results point out that there is no direct interaction between the oil phase and the skin. For this attribute, depending on its chemical structure, emollient impacts the human perception only by changing the lamellar phase type. Concerning the difficulty of spreading, both the emulsion structure and the emollient properties should be considered. Immediate perception is impacted by the emulsions destruction, making the droplet roll one on each other. Then, once the droplets monolayer is disrupted, the emollient comes into direct contact with the skin. In this case, the perception is governed by the direct affinity of the emollient with the skin, nonpolar emollients being easier to spread if compared to polar ones.

CONCLUSION

The sensory perception is guided not only by the choice of the raw materials but also by their interactions. It was shown that the chemical structure of the emollients affected the molecular organization of liquid crystals present in the emulsion and, consequently, directly or indirectly its sensory perception.

Rheological and physical parameters correlations in formulations with pinhão derivatives stability study: building up an analytical route

This study focuses on the correlation investigation between rheological and physical parameters and how it can contribute to optimize the topical formulations development. A gel and an emulgel containing pinhão derivatives, and their respective controls, were analyzed along six months of storage. A flowchart of analyses was proposed to use in topical formulation development when a benchmark is the goal or when it is necessary to change some raw material. All formulations were stable over the storage time and the formulations containing pinhão starch and coat extract presented similar properties to those of the control formulations. Correlations between rheological and physical data, as moisture content and particle size, were determined using Pearson's correlation coefficient. A moderate positive correlation was verified between particle size distribution and flow index, and a strong positive correlation between particle size and flow index. It was also found that the higher the moisture content, the higher the consistency index, quality factor, and apparent viscosity. The correlation analyses applied in this study contributed to build up an analytical route for topical formulation development, saving time and costs.