Comparison of rheological and texture analysis methods for the assessment of viscoelasticity

The purpose of this work was to analyse and compare dynamic (oscillatory) rheological methods with a novel texture analysis method for the assessment of viscoelastic properties of cosmetic semisolids

Water Resistance vs. Rheology Control: An Exploration

Water resistance is a desirable property across a range of cosmetic product categories, including decorative cosmetics, leave-on hair products, sun protection and skin care (e.g. hand barrier creams). This work has focused on two formulation variables, the type of emulsifier system and the choice of film-forming polymer, both known to change the rheological profiles of semisolid systems. The aim of this study was to assess the effects of these two factors on the rheological and texture profiles, as well as the water resistance characteristics, of semisolid O/W emulsions. A simple O/W emulsion formulation, containing glycerol, mineral oil, water, preservative and emulsifier system was used in this study. The basic emulsifier system consisted of two non-ionic emulsifiers (sorbitan stearate and polysorbate 60) in combination with a co-emulsifier cetearyl alcohol. The alternative emulsifier system had an anionic emulsifier sodium cetearyl sulphate added to the above emulsifier mixture. A range of seven film-forming polymers were used in the study, representing acrylates, silicones, graft copolymers and block copolymers. Two groups of 8 emulsion samples, containing either basic or alternative emulsifier system and including a non-polymer control, were tested. Rheological measurements were carried out in both continuous flow and oscillatory mode and were complemented with texture analysis, performed using a spreadability test. In the absence of universally accepted in vitro water resistance test, a gravimetric method for measuring water resistance was developed and applied to all test samples. The results have shown a variety of rheological profiles, which were both emulsifier- and polymerdependent. The addition of sodium cetearyl sulphate have resulted in softer (lower complex modulus) and more spreadable formulations (lower firmness), which coincided with lower water resistance scores. The block copolymer polyurethane-62 (and) trideceth-6 has produced specific rheological profiles, characterised by high internal resistance and high elasticity. The graft copolymer vinyl pyrrolidone/ eicosene was the best performer in terms of water resistance, showing the lowest weight change of 11.1% after the first 20-min immersion in water and 12.9% after the second immersion. The non-ionic emulsifier mixture based on sorbitan stearate and polysorbate 60 has provided superior performance in comparison to its combination with the ionic emulsifier sodium cetearyl sulphate

Rheological and texture analysis methods for quantifying yield value and level of thixotropy

This study compares different methods for the assessment of yield stress and level of thixotropy in semisolid emulsions, using three instruments: an air-bearing controlled-stress rheometer, a T-bar viscometer and a texture analyser. The following methods were used to assess the yield stress: a low-rotation T-bar test, a shear stress sweep, a shear rate sweep, an oscillatory stress sweep and an immersion/de-immersion test on the texture analyser. The level of thixotropy was assessed by: a hysteresis loop test, a three-step thixotropy test and a repeated immersion/de-immersion test. It has been found that there was good correlation between the two rheological methods for detecting the level of thixotropy, the hysteresis loop and the three-step thixotropy test

Exploring the effect of rheological modifiers and preservatives on the in vitro release of caffeine from gel formulations

It is known that diffusion and partition are the two most important phenomena in the complex process of skin penetration. To start this process, however, the active ingredient has to be released, i.e. it has to diffuse through the formulation and reach the stratum corneum in sufficient quantity. In this study, we have explored two formulation parameters that may influence the diffusion of caffeine through the hydrogel system: the type of gelling agent and the presence of preservative system. The aim was to assess whether and to which extent the changes in rheological properties exerted by the above two parameters affect the in vitro release of caffeine from the hydrogels

Assessing the effects of formulation variables on the water resistance, rheological and texture properties of O/W emulsions

Water resistance is a desirable property across a range of cosmetic product categories, including decorative cosmetics, leave-on hair products, sun protection and skin care (e.g. hand barrier creams). It could be achieved using one or more of the following formulation approaches: high concentration of non-polar emollients, specific combinations of emulsifiers and the inclusion of film-forming polymers. This work has focused on two formulation variables, the type of emulsifier system and the choice of film-forming polymer, both known to change the rheological profiles of semisolid systems. The aim of this study was to assess the effects of these two factors on the rheological and texture profiles, as well as the water resistance characteristics, of semisolid O/W emulsions

Rheological and texture analysis methods for the assessment of viscoelasticity

The purpose of this study was to compare the dynamic (oscillatory) rheological method with a novel texture analysis (TA) method for the assessment of viscoelastic properties of cosmetic semisolids. The instruments used in this study were an air-bearing controlled-stress rheometer (RheoStress RS75, Haake, Germany) and a texture analyser (TA.XT Plus, Stable Micro Systems, UK). The model formulation was a standard semisolid emulsion, containing increasing concentrations of carbomer and xanthan gum, respectively. The rheological methods used were stress sweep (0.5-500 Pa at 1 Hz) and frequency sweep (0.01-10 Hz at 10 Pa). The texture analysis method used was an immersion/de-immersion test with cylindrical probe. The results were analysed for their consistency with theoretical predictions and the presence any correlations between the methods. The analysis revealed consistent trends related to two novel TA parameters, stringiness (which decreased with the increase in thickener concentration) and resilience (which has shown a mild increasing trend). Elastic modulus G’ and viscous modulus G’’ (both at 1 Hz) were positively correlated to resilience and negatively correlated to stringiness, indicating that those TA parameters reflect the viscoelastic status of the sample

Active transport: How rheological modifiers and preservatives impact release

This study explores two formula parameters that could potentially influence the diffusion of an active through a hydrogel: the gelling agent and the preservative system. Here, caffeine was used as the active, along with a range of 12 gelling agents in a simple hydrogel formulation, with and without preservatives

Exploring the use of 3D Printing Technology in the Fabrication of Personalised Lipstick Applicators

This study explores the viability of applying commercially available 3D scanning and printing equipment in the development and manufacture of a personalised lipstick applicator. The shade of a lipstick and its theology are already subject to personalisation. However, the application can be achieved in a more convenient way than using a standardised swivel-up tube. The objective of this project was to examine the possibility of developing a methodology for manufacturing an innovative personalised lipstick applicator using 3D printing technology

Damage limitation: comparing the impact of polymers on bleached hair, when applied within or as post-bleach treatments

Hair bleaching causes undesirable chemical and structural changes to the cortex, the most prominent process being the oxidation of the disulphide bonds of the amino acid cystine and the creation of cysteic acid. It is known that this process affects mostly the Keratin Associated Proteins (KAP) which are amorphous and sulphur-rich. A major secondary effect is the overall destabilisation of the cortex structure within which the crystalline Intermediate Filaments’ (IF) proteins are supported by KAP. An overall decrease in the proportion of ordered protein structure, reduction of mechanical strength and the denaturation temperature of hair have been used to quantify the degree of damage. The cuticle also undergoes oxidative damage during bleaching which causes reduced thickness and increased surface roughness. Mitigating and counteracting these changes in the hair surface and internal structure have been a prime objective of the haircare industry. Such action would be expected to deliver immediate sensory benefits perceivable by the consumer. This project was to compared the impact of three actives said to deliver structural benefits to bleached hair. Their impact was evaluated in two conditions: when applied with the bleaching cream (WB) and after bleaching (AT)