The Biopolymers Texture Triangle

As skin care product formulators, every day we strive to create engaging user experiences that capture the essence of our brands. Through our concoctions, we inspire feelings of beauty, wellbeing and being protected from rigours of the outside world. Historically we have relied heavily on a palette of ingredients such as rheology modifiers based on polyacrylate polymers and sensorial ingredients which utilize silicone- and petroleum-based chemistries.

We have learned to trust these fully-synthetic materials to deliver outstanding sensory, stability and additional performance. In recent years, however, these ingredients have faced increasing scrutiny from consumers, NGOs and the media who communicate avidly online and off-line about which ingredients to choose and which to avoid; with the most recent focus being on questioning the definitions between polymer and non-biodegradable microplastics.¹

Perhaps due to this confusion and negativity, the desire for naturalness, clean label and eco-conscious products has moved from a premium niche to almost a core expectation from consumers. In the lab, we search for “natural” ingredients that offer a formulation experience that either replaces current technology or provides exciting new sensations for consumers. As an industry, we instinctively reach for food grade materials such as xanthan gum, carrageenan gum or simple starches when faced with this challenge, but often feel frustrated when we can’t achieve the premium look, feel and long-term stability that we associate with the fully synthetic ingredients.

To take on this challenge, we consider a simple palette of three readily biodegradable biopolymers with targeted modifications designed to deliver the long-term emulsion and shelf stability of fully-synthetic systems with highly distinct sensory effects: Firstly, potato starch modified (Structure Solanace, an amphoterically stabilized potato starch); secondly, hydroxypropyl starch phosphate (Structure XL, a stabilized and hydrophobically modified corn starch); and thirdly, dehydroxanthan gum (Amaze XT, a xanthan gum that’s received a special heat treatment to convert it to a somewhat hydrophobic film former, with a unique rheology characterized by a high yield value and shear-thinning behavior).  We then assess them individually and in combination to create an array of skin care experiences that can deliver classic market matching and modern disruptive sensorial experiences.

Results and Discussion
We started from a typical European skin care base², Base Low Viscosity Emulsion (formula 1, table 1) and created an additional nine formulations using our biopolymer palette, (formulas 2-10, table 1), to provide a diverse set of user experiences. The sensory experiences were then characterized by a trained descriptive sensory panel and are summarized in the texture triangle (figure 1).

Sensorial Discussion
Potato starch modified was used to create Light Melting Lotion (formula 2, 2.0% biopolymer) and provides a soft pick-up, a lightness and slip during application followed by a sensation of fast absorbance and residue-free finish. Adding more of the polymer as in Bouncy Crème Fraîche (formula 3, 4.0% biopolymer) provides additional viscosity and rebound while maintaining the lightweight user experience.

Hydroxypropyl starch phosphate was used to create Powdery Lotion (formula 4, 1.0% biopolymer) where it brings a soft pick-up as well as a sensation of richness and body during application that gives rise to a palpable powdery finish and caring after-feel. This effect is heightened as the biopolymer level is increased as in Water Gel Cream (formula 5, 3.0% biopolymer) to give a heavier, richer night cream style product.

Dehydroxanthan gum was used to create Milk (formula 6, 0.2% biopolymer) where its strong gelling effect and emulsion stabilization performance is evident even at low inclusion levels. At these lower levels (0.1-0.3%) dehydroxanthan gum is commonly used to provide a priming effect on skin that is particularly relevant in day creams and makeup primers. Increasing the dosage as in Silky Soft Cream (formula 7, 0.7% biopolymer) drives body and viscosity in the formulation and as it is applied the biopolymer creates a flexible hydrophobic film that gives rise to a strong sensation of conditioning and protection of the skin.

Biopolymer Combinations
When we combine potato starch modified with its lightweight sensory and hydroxypropyl starch phosphate which is much richer and adds body to the formulation, we achieve experiences such as Liquid Gel Lotion (formula 8). Combinations of these two biopolymers in particular give the formulator great range to craft experiences that closely mimic classic polyacrylate polymer chemistry; however, with a lower tack and more powder finish.

In the Yogurt Cream example (formula 9), we combine the gelling effect and film-forming performance of dehydroxanthan gum to the slip and softness of potato starch modified. This gives a heavier cream but with a smoother rub-on experience. It is substantive but easily absorbed, drying down to a conditioned and protected after-feel.

When we add singular properties of dehydroxanthan gum to the already rich and powdery feel of hydroxypropyl starch phosphate as in Cream Butter (formula 10) we create a luxurious experience. The result is a heavier cream with very strong sensations of richness, skin conditioning and somewhat occlusive protection. As such this formula is a good starting point for dry skin formulations, winter creams and other products where care and protection are emphasized.

Conclusion
As the paradigm shift continues toward more natural ingredients in cosmetic formulation, eco-conscious, clean label, plant-based and vegan products are becoming our basic materials and inspiration. By using the Biopolymers Texture Triangle as a starting point and introducing new elements and eliminating others, it is possible to identify many more unique and natural sensorial experiences. In this way the art of skin care formulation reminds us very much of perfumery—where one out of place ingredient or note in a formula could be the element that brings another creation to life. Happy formulating! 

References

1. Beat the Microbead Coalition, www.beatthemicrobead.org/guide-to-microplastics/
2. Mintel GNPD research: most common ingredients in skincare base, UK market last 12 months, recorded April 2018)