First evidence Bond builders actually build bonds

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Is Repair of Lightened Hair Feasible?

Myths and Facts on Different Hair Bonding Treatments T. Förster, T. Hippe, G. Knübel

abstract

W

ith bright blond hair colors becoming more fashionable in recent years, prevention or even repair of hair damage by lightening has become a strong consumer need. Leading edge research of structural changes in keratin caused by strong oxidative stress has led to several approaches how to counteract this oxidative damage by ingredients capable to form bonds between adjacent keratin chains. An overview presents several ingredients used already in market products acting via different mode-of-actions of keratin bonding. For the class of organic di-acids experimental evidence is given, showing protection of keratin during oxidative damage perceivable also by consumers. Results of tensile strength evaluations as well as multiple grooming tests and differential scanning calorimetry (DSC) and finally test salon evaluations support the hypothesis that certain di-acids like maleic acid or succinic acid are able to bridge adjacent keratin chains via ionic interactions and/or hydrogen bonds.

1. Introduction Over the last decade hair lightening has become more and more popular among women all over the world. Blond hair colors are among the most sold shades in the last years. Even grey to white hair has become a trend among young consumers allowing also for fashionable effect shades like temporary pink, red or blue hair colors and strands. Hairdressers and cosmetic hair experts know that strong lightening of hair not only decomposes the melanin pigments but also affects the keratin inside the hair fiber. Lightening of naturally dark hair like brown or even black hair by up to 9 shade levels requires successive bleaching steps with harsh bleaches containing up to 9 % hydrogen peroxide comprising peroxydisulfates as oxidation booster, thus leading to significant oxidation of amino acids, especially cystin (and cysteine) to cysteic acid [1].

Biophysical test methods like tensile strength evaluations [2] as well as multiple grooming tests [3] and differential scanning calorimetry (DSC) [4] allow a quantitative assessment of keratin damage.

Based on in-depth knowledge in hair science, cosmetic formulators have recently developed different innovative keratin bonding products which supposedly are able to mitigate severe keratin damage during the action of strong bleaching agents or are even able to repair keratin damaged by strong oxidative treatments. Henkel e. g. has patented organic di-acids like maleic acid or succinic acid to form bridges between adjacent keratin chains by ionic and/or hydrogen bonds, thereby substituting cleaved cystine bridges [5] (Fig. 1).

Other mechanisms are proposed as well: Hawker and Pressly postulate – among other principles – that the maleic acid derivative bis-aminopropyl diglycol dimaleate forms bridges between keratin chains by a Michael type addition of the maleic acid with cysteine SH-groups [6]. This reaction would lead to

Fig. 1 Schematic representation of a succinate salt bridge linking cationic amino acid side chains of two adjacent keratin chains (as working hypothesis)

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Fig. 2 Schematic representation of the covalent bridge formed by Michael addition of maleic acid groups with cysteine residues of two neighboring keratin chains

an ionic bridge replacing cystine bridges. However, the mechanism seems not entirely plausible under the highly oxidative environment that is transforming free cysteine SH-groups into cysteic acid, which will not act as a nucleophilic agent (Fig. 2).

In this publication we will present experimental results which prove that reduction of keratin damage is feasible by adding organic di-acids to hair lightening products, thus leading to a relevant hair strengthening benefit perceived by consumers as better grooming properties and protection against hair breakage.

2. E-Moduli and Break Stress 2.1 Results Arguably the most important methods for the analysis of mechanical properties of human hair fibers are tensile strength measurements [2]. Several analytical endpoints can be investigated, the most relevant being the E-modulus in the elastic region of the fiber and the break stress in the post-yield region. The measurements are usually done in the wet state. In the experiment conducted here a salon bleaching product (Schwarzkopf BlondMe Premi-

Fig. 3 Change of E-moduli after 2x lightening with BlondMe Premium Lift 9+

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um Lift 9+ / BlondMe Premium Care developer, 9 % H2O2) was spiked with maleic acid or succinic acid. As placebos water and acetic acid were used as additives. The resulting E-moduli changes after bleaching are shown in Fig. 3. It is obvious that only the di-acid bonding agents, in this case succinic acid and maleic acid, exert strengthening of the keratin fiber relative to the decrease of the E-modulus in the bleached hair (blue bar). Placebo treatments like water or equivalent amounts of acetic acid (as a “mono-acid” without linking potential) do not show the desired effect in the same amount.

This effect is confirmed by the analysis of the break stress of the fibers (Fig. 4). The fibers treated with the bleaching mixture plus di-acids show significantly higher break stress values.

All detected effects of bleach plus maleic acid or succinic acid vs. bleach alone are statistically significant (p < 0,05; ANOVA followed by post-hoc Tukey HSD test).

2.2 Experimental Procedure Tensile Strength 2.2.1 Materials and Apparatus Hair samples: Kerling International (Backnang, Germany), European Natural Hair 7/0 Hair clamps: plastic tabs, code 900.0320 (Dia-Stron Ltd, UK) / hair clamped with liquid epoxy resin Devices: Universal-Dimensions-Measuring-Device UDM 5000A, (Zimmer GmbH, Darmstadt, Germany) Stress-Strain-System MTT 680 with control unit UV 1000 (Dia-Stron Ltd, UK) Software: UvWin 1.32.1000 (Dia-Stron Ltd, UK) 2.2.2 Background The Young's modulus also known as elastic modulus (E-modulus) is defined as the ratio of stress over strain in the Hookean region. Hooke's law of elasticity states that the longitudinal change of a material body (the strain) is linearly related to the

Fig. 4 Break stress after 2x lightening with BlondMe Premium Lift 9+

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force causing the deformation (the stress). For wet hair this region lies between a strain of approximately 0 and 2 %. The Young’s Modulus is a measure for the strength of a fiber (the higher the Young’s Modulus the stronger the fiber) [2].

2.2.3 Treatment 40 single hair fibers (length between clamps 3 cm) were used for each product and for the reference. The bleaching was performed twice on single hair fibers under the following conditions: 30 g of bleaching powder (BlondMe Premium Lift 9+) were mixed with 60 g developer solution (BlondMe Premium Care Developer, 9 % H2O2) and 4 ml of di-acid solution (resp. water or acetic acid as placebo or no additive). The hair was soaked in the bleaching mixture for 45 min at 32 °C. Afterwards the fibers were rinsed with tap water for 120 seconds. Finally, the fibers were blow-dried for 60 minutes. This procedure was repeated once. The treated hair fibers were stored for at least 48 hours before the measurement.

The aequeous acid solutions consisted of • 5.0 % Succinic acid + 15 % sodium succinate hydrate • 5.0 % Maleic acid + 9.0 % potassium maleate • 5.0 % Acetic acid + 9.0 % sodium acetate 2.2.4 Measurement of Hair Thickness At the beginning of the test the mean cross sectional area of each single hair was determined at a temperature of 22 °C and a relative humidity of 50 %. Data thus obtained were used for the stress calculation before and after product application.

2.2.5 Determination of Young’s Modulus before the Application of the Products All the hair fibres were soaked in water for 1 hour before they were stretched with a constant speed rate of 10 mm/min within the elastic phase (0-1.5 % elongation). Afterwards the E-modulus (= Young's Modulus) was calculated with the UvWin software.

2.2.6 Determination of Young’s Modulus and Break Stress after the Application of the Products The hair fibers were soaked in water for at least 1 hour. Afterwards they were stretched with a constant speed rate of 10 mm/min within the elastic phase (0-1.5 % elongation). The E-modulus (= Young's modulus) was calculated. Afterwards they were stretched with a constant speed rate of 10 mm/min up to the break point.

3. Hair Breakage Measurement 3.1 Results After evidence for a hair strengthening effect during bleaching was obtained by biophysical analysis of mechanical strength, hair breakage experiments [4] were performed which are arguably closer to consumer experience and perception. Fig. 5 shows hair breakage results after lightening with BlondMe Premium Lift 9+ in comparison to hair breakage after lightening with BlondMe Premium Lift 9+ containing 6.5 % water (placebo) or 6.5 % keratin bonding fluid with maleic acid (Fibreplex No.1). Hair breakage is not reduced by water as placebo, but reduced by 70 % by addition of Fibreplex No.1 to the lightening mixture. It is worth noting that the lightening/bleaching effect itself is not reduced by the addition of Fibreplex.

Apart from maleic acid, Fibreplex No.1 contains polyvinyl pyrrolidone, monoethanol amine and a small amount of the amino acid arginine.

In real life the consumer will use a whole application regime as described above plus shampoo and conditioner after a bleach. When applying – after a bleach with Fibreplex No.1 – shampoo and afterwards the keratin bonding conditioner (Fibreplex No.2) as the last step the consumer perceivable benefit is even increased to more than 90 % reduction of hair breakage (Fig. 6).

Fig. 5 Hair breakage after lightening of hair strands with BlondMe

Fig. 6 Hair breakage after lightening of hair strands with BlondMe

Premium Lift 9+ plus Fibreplex No.1

Premium Lift 9+ plus Fibreplex No.1, shampoo and Fibreplex No.2

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The reason for this outstanding efficacy is the additional grooming of the hair surface by the conditioning agents in Fibreplex No.2, which reduce drastically the combing force needed in the experiment, thus resulting in minimized hair breakage.

3.2 Experimental Procedure Hair Breakage 3.2.1 Materials Hair swatches: International Hair Importers (New York), European natural hair 6/0 lot # 05/2015; S 84, length 12 cm tip ends, weight 1 +/-0.05 g Combs: HERCULES Sägemann, fine-toothed hard rubber comb 3.2.2 Pre-treatment of the Hair Strands The hair strands were cleaned with a 3 % aqueous solution of SLES (pH adjusted to pH 6-7) in an ultrasonic bath for 5 minutes. Subsequently the strands were rinsed with tap water while being automatically combed for 5 minutes, then air dried. The pre-treatment was finished at least 48 hours before the application of the products.

3.2.3 Product Application The bleaching was performed under the following conditions on 10 dry hair strands: 20 g of bleaching powder (BlondMe Premium Lift 9+) were mixed with 40 g developer solution (BlondMe Premium Care Developer, 9 % H2O2) and 4 ml of Fibreplex No.1 solution (resp. water as placebo or no addition). The mixtures were applied for 45 min at 32 °C (4 g of mixture per g hair). Afterwards the strands were rinsed under standard conditions (tap water, 32 °C, 0.5 L / min) for 2 minutes. The strands were then stored at 25 °C and 25 % rel. humidity for at least 24 hours and then equilibrated at 25 °C and 50 % rel. humidity for 1 hour prior to the measurement.

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3.2.4 Measurement The tests were carried out at constant temperature and humidity (25 °C, 50 % rel. humidity). The strands treated with product as well as a control series of untreated strands were combed 20,000 times. For each hair strand the broken hair was collected in a box underneath the comb. From the strand 1.5 cm of hair tips are cut off and weighed (app. 100 mg).

The amount of broken hair is weighed, too, and related to the total amount of cut off hair.

4. Differential Scanning Calorimetry (DSC) 4.1 Results The Fibreplex effects were also analyzed by differential scanning calorimetry (DSC). DSC has proven to be a powerful method for analyzing the keratin structure of the inner part of the hair, the cortex [3]. In fact, strong lightening leads to a weakening of the hair keratin, observed as a reduction of the glass transition temperature Tg and a concomitant reduction of denaturation enthalpy delta Hg. Here the addition of maleic acid containing Fibreplex No.1 results in a significant increase in Tg, as well as in Hg, compared to bleach alone (Fig. 7). Statistical significance was shown via ANOVA with post-hoc Tukey HSD test, p < 0.05 . The values for the denaturation enthalpy show the same tendency (Fig. 8), the effects however are not statistically significant.

4.2 Experimental Procedure Differential Scanning Calorimetry (DSC) 4.2.1 Materials and Apparatus Hair sample: Alkinco 6634 (USA), natural dark European hair, A15, #02/2013 Device: Perkin Elmer DSC 8000 Sample Pans: Large volume (60 µl) stainless steel pans, covers and O-ring (24 atm)

Fig. 7 Denaturation temperature of hair after treatment with

Fig. 8 Denaturation enthalpy of hair after treatment with BlondMe

BlondMe Premium Lift 9+

Premium Lift 9+

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GLOBAL INGREDIENTS & FORMULATIONS GUIDE 2017

The Protective Function of Cosmetic Products Today people find themselves exposed to environmental pollution caused by smog, increased radiation from sunlight, electromagnetic radiation, and pollutants in the water.

The personal care industry has developed innovative products to protect the skin from harmful effects of these pollutants. Some of these are able to trigger the body’s own defense system while others serve as protective shield. Another subject is the decontamination of strongly adhering substances from the skin. This book discusses the research results and solutions that have been offered.

Sustainability is still playing a major role, when developing new products in the cosmetic industry. There are many ways to give consideration to this important issue when producing personal care products These and many other new developments will be addressed in this year’s edition of the “Global Ingredients and Formulations Guide 2017”.

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4.2.2 Pre-treatment of the Hair Strands The hair strands were cleaned with a 3 % aqueous solution of SLES (pH adjusted to pH 6-7) in an ultrasonic bath for 5 minutes. Subsequently the strands were rinsed with tap water while being automatically combed for 5 minutes, then air dried. The pre-treatment was finished at least 48 hours before the application of the products.

4.2.3 Application of the Products The bleaching was performed under the following conditions on dry hair: Mixing ratio: 1 : 2 : 0.2 (BlondMe Premium Lift 9+ / BlondMe Premium Care Developer, 9 % H2O2 / additive) Application ratio: 4 g of coloration mixture per g of hair Exposure time: 45 minutes at 32 °C Afterwards the strands were rinsed thoroughly with lukewarm tap water for 1 minute and finally air-dried. The measurement was carried out after a resting period of 48 h.

4.2.4 Background DSC Hair is a keratin material which exhibits a complex morphological fine structure. For mechanical or thermal investigations

4.2.5 Test Procedure All the strands were cut into snippets of app. 1 mm in length.

12 samples per product (app. 6-8 mg each) and per reference were placed into the DSC-pans. After adding 50 µl of deionised water each pan was sealed. The measurement was conducted in a temperature range of 100-200 °C with a heating rate of 10 K/min . The denaturation temperature (peak apex [°C]) and the specific enthalpy [J/g] were determined.

5. Test Salon Evaluation A benchmark bleaching product was tested against an identical formula with added Fibreplex No.1 (Fig. 9).

Here 10 volunteers were investigated in a halfside test design. The following hair properties were then evaluated by a panel of six professional evaluators on a scale of 1-6 (6 being the best rating): feel of wet hair, combing ease of wet hair, feel of dry hair, combing ease of dry hair, level of lift. For each parameter the ranks of the professional evaluation were used for statistical evaluation (pairwise Wilcoxon rank sum test, p < 0.05): • No significant difference in lightening performance was observed which indicates that the products perform on the same level • The Fibreplex No.1 containing product performed better in all other categories.

However, due to the scatter of the data and the small panel size statistical significance could only be obtained for better combing ease of wet hair.

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March 15, 2018

Fig. 9 Performance evaluation in the test salon

the structure can be simplified as a two-phase filament/matrix composite [7], in which α-helical filaments are embedded in an amorphous matrix [8]. These two dominant compounds largely determine the mechanical properties of human hair and play specific roles in the performance and effects of hair cosmetic treatments [9]. The values of the peak temperature indicate the damaging or integrity of both the matrix and the α-helix. The looser (less cross linked) the matrix or the smaller the crystals of the α-helical phase, the lower the peak temperature [10].

The value of the enthalpy is a measure of the amount of crystalline α-helical filaments.

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6. Conclusion It was demonstrated through tensile strength investigations that the addition of organic di-acids like maleic acid or succinic acid during bleaching processes offers fiber protective properties compared to the bleaching mixture alone or compared to bleach plus placebos. The mechanism of this protective effect is not yet fully elucidated and understood; as a working hypothesis we propose the absorption by the hair cortex and the formation of salt bridges and/or bridges with hydrogen bond interactions.

Furthermore it was shown in biophysical tests and test salon studies that the use of products like e.g. Fibreplex No.1 (which contain high concentrations of di-acids) offer considerable, consumer perceivable benefits (like e. g. reduced hair breakage) when applied together with bleaches.

References [1] C. Robbins, Chemical and Physical Behavior of Human Hair, Springer (2012) 272 [2] T. Evans, Measuring Hair Strength – Part 1: Stress-Strain-Curves, Cosm. Toil.

128 (2013) 590 [3] C. Gummer and C. Popescu; DSC of human hair: a tool for claim support or incorrect data analysis, Int. J. Cosmet. Sci. 38 (2016) 433-439 [4] H. M. Haake, W. Eisfeld, S. Marten, W. Seipel, Hair breakage – How to measure and counteract, J. Cosmet. Sci. 60 (2009) 143 [5] EP1326577B2 [6] US 2015/0034117A1 [7] M. Feughelmann, Text. Res. J. 29 (1959) 223 [8] D. A. D. Parry, P. Steinert, Quarterly Rev. Biophys. 32, (1999) 99 [9] F.-J. Wortmann, J. Souren, J. Soc. Cosmet. Chem. 38 (1987) 125-150 [10] C. Popescu and F.-J. Wortmann, Rev. Roumaine de Chimie 48 (2003) 981

contact Thomas Förster | (corresponding author) Thomas.Foerster@henkel.com Thomas Hippe Georg Knübel

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