SOFW Journal 10/18 | Volume 144 | Thannhausen, Germany, October 08, 2018

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New 100% Bio-based Polymer for Effective Odor Neutralization

for a Broad Spectrum against Common Malodors

home care

High SPF Sunscreens that Feel Light on the Skin

Innovative Sunscreen with Cooling Effect for Protection in the VIS and NIR Regions for Asian Skin Type

sun care

Glycolipids – a New Era in Natural CleansingExploring Nature-like Elements for Antimicrobial Preservation Efficacy A Natural Ingredient Meets Current Expectations of the German Skin Care MarketA Multifunctional Solution for Acne Prone Skin with a Single Natural Active Ingredient

natural ingredients

Simple and Effective Particle-size Characterization of Opaque Emulsions

emulsions

The New Dimension of Microcapsules: Plastic-free Encapsulation Technology Using Functional Vegan Silk Polypeptides

microplastics

The New Dimension of Microcapsules: Plastic-free Encapsulation Technology Using Functional Vegan Silk Polypeptides J. Müller, R. Mehrwald, N. Blosl, S. Schlay, K. Schacht

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Encapsulation at a Glance

Encapsulation enables the creation of products and applica-tions with added value for a large variety of industries such as pharma, cosmetics, household, agriculture, chemistry or bio-technology. Thus, microencapsulation has been used in home and personal care products for several decades, particularly for achieving long-lasting freshness, extending the scent of perfume oil or controlled release of substances. The demand from industry and consumers rise steadily, however, innova-tions in the field are rare and many products still have down-sides such as complex encapsulation technologies or the use of non-biodegradable materials. Encapsulated substances are often released after applying mechanical stress, other methods enable the release e.g. by temperature, pH shift or natural biodegradation. Advantag-es of the encapsulation technology include, for example, in-creased stability of active substances in order to ensure the desired effect of controlled and efficiently release at the tar-get destination. Due to the capsule shell, protection from de-composition and controlled release can be achieved. Further, encapsulated volatile substances such as perfume oils are pro-tected during e.g. the laundry processes allowing a sustained and prolonged fragrance release [1]. For some formulations, encapsulation techniques can also provide optical or haptic benefits. Essentially, capsules consist of a protective shell and a core material that is responsible for the functionality of the sys-tem. The core materials may have, for example, anti-aging or antioxidant properties, and are often perfume oils for achieving long-lasting fragrance effects. Capsule shells of current systems are produced from synthetic or natural ma-terials such as polyurethane, acrylate, polyurea, alginate or gelatin. In connection with encapsulation systems, nowadays, the environmental burden of microplastic in cosmetics or home care products is discussed. Solid phase materials are referred

to as microplastic if the particles are not soluble in water and consist of plastics with a particulate size of 5 millimeters or smaller [2]. Studies have shown that microplastics from rinse-off products such as body peelings get into the waste water and enter the aquatic environment, since the filter of waste water treatment plants cannot reduce the particles. In the few years in which plastic particles are used in cosme- tic products, they already accumulated to more than 3.5 % of the primary microplastic found in the ocean [3]. Espe-cially the impact of these tiny particles causes several types of ecological problems. Once arrived in the oceans, for ex-ample algae adhere and accumulate on the surface of the particles, thus entering the marine food chain [4]. In gen-eral, the microplastic particles endanger the ecosystem on a long-term basis, eventually appearing in our seafood and even freshwater. One peeling product can contain up to 2.8 million micro-particles [5]. In a recent study it was estimated that each year several thousand tons of microparticles consisting of polyethylene are produced within the European Union [6]. Meanwhile, the use of synthetic microplastics is already pro-hibited in some countries, and a number of manufacturers have already started to replace those particles in their for-mulations step by step. Alternatives are available, however, the production of plastic-free microcapsules is still difficult and the performance is not as good as those of conventional capsules yet.Now, functional silk polypeptides offer a suitable alternative to plastic based techniques. The polypeptides are produced by a sustainable biotechnological process (fermentation) obtaining 100 % pure vegan silk. The defined polymers can be formed in different kind of morphologies such as pow-ders, gels, fibers, foams or films. Recently, encapsulation of oil- and water-soluble substances such as fragrances, active ingredients or pigments by functional silk polypeptides for

The New Dimension of Microcapsules: Plastic-free Encapsulation Technology Using Functional Vegan Silk Polypeptides J. Müller, R. Mehrwald, N. Blosl, S. Schlay, K. Schacht

abstract

Functional vegan silk polypeptides are used in personal care products for protective benefits, such as breathable anti-pollution protection, and as a natural fixator for long-lasting effects. One step further goes the development of the first easy-to-use

functional cosmetic microcapsules without the need of microplastic. This opens up new dimensions for personal care products. Both, lipophilic substances as well as hydrophilic substances (e.g. fragrances, dyes) can be encapsulated by vegan silk, achieving prolonged efficacy and protection of actives.

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plastic-free cosmetic approaches was developed successfully (Fig. 1).

Functional Silk Polypeptides Enable the Encapsulation of Lipophilic Substances

Silk polypeptides are ideally suited to form capsules around actives due to their self-as-sembly properties. Silk polypeptides tend to form stable films on skin, but also around hydrophilic as well as lipophilic liquids. Pre-viously, it was shown that based on this at-tribute, vegan silk can be assembled driv-en by diffusion at an oil/water interface to form microcapsules containing a water-sol-uble substance [7,8]. Now a new, scalable and efficient encapsulation process to also encapsulate lipophilic substances has been established. To produce these oil capsules in a labora-tory environment, a mixture of beta car-otene and perfume oil was added to an aqueous silk polypeptide solution while si-multaneously being treated with a dispers-ing device (Fig. 2). Due to the emerging shear forces, oil droplets were formed in the silk solution. At the water/oil interface of those droplets the silk proteins aligned themselves according to their amphiphilic nature to form a capsule shell. The capsule shell, consisting of silk polypeptides entire-ly surrounds the beta carotene/perfume oil mixture and forms a thin but stable mem-brane. Fig. 2 illustrates the schematic pro-cedure to encapsulate lipophilic substanc-

es with functional silk polypeptides based on beta carotene and perfume oil. The oil capsules produced with this process are particularly un-complicated in handling. Although they can be mechanically destroyed on the skin during application, due to their small size (2 < 100µm) the capsules withstand high shear forces during their incorporation into a cosmetic formulation. In ad-dition, they are easy to extract from the surrounding medium and can be subsequently transferred into other solutions. After production, the silk-encapsulated oil droplets can be stained for instance by a blue dye that specifically colors the capsules’ silk membrane. On one hand the staining makes the otherwise transparent capsule shell visible, on the other hand it allows optical masking of the encapsulated substance. In this case, the blue-colored coating results in an optical im-pression of green color for the otherwise yellowish beta-car-otene capsules. After mechanical force, the capsules break and the yellow color from the capsule interior reappears. This color change effect can be observed very easily for capsules incorporated into a white cream. (Fig. 3).The targeted and controlled color change/release makes the silk based oil capsules especially interesting for color cosmetic applications. They could be used for formulations changing their shade upon application to the skin e.g. by the encapsu-lation of pigments.In principle, the newly developed process enables the man-ufacturing of stable capsules with a homogenous size distri-

Fig. 1 Formulations with functional silk microcapsules. Encapsula-tion of the model substances methylene blue and carmine (E120) with silk polypeptides.

Fig. 2 Schematic procedure for the encapsulation of lipophilic substances with function-al silk polypeptides. To show the encapsulation effect, the silk capsule can optionally be stained with specific dyes.

Fig. 3 Blue-stained beta-carotene silk capsules appear green in a skin cream. Due to the mechanical stress applied during creaming, the capsule shell is destroyed and its contents are released, resulting in a yellow color change.

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bution (Fig. 4). Depending on the shear forces applied during manufacturing, capsules made from functional silk polypep-tides differ in their size, ranging from 2 to 100 µm. The higher the introduced shear forces, the smaller (and more robust) the capsule.To assess stability and robustness of the silk capsules against different harsh conditions, various parameters were investi-gated. As mentioned before, introduced shear forces have an influence on the capsule size, but they do not lead to a destruction of the capsules morphology. Even in the tested pH range between 5.5 and 10.6, and at temperatures from -20 °C to 95 °C, no denaturation of the capsules could be de-tected. Furthermore, the stability of the silk capsules in eth-anolic formulations (50 %) was demonstrated (Tab. 1). As a result, the capsules can be efficiently incorporated into gel formulations and emulsions. It has been shown that vegan silk polypeptides fixate ingre-dients to the skin over a longer period of time, thereby pro-longing and enhancing their effectiveness [9,10]. Besides the application in color cosmetics, fragrance fixation and release represents a particularly promising area of application for the encapsulation of lipophilic substances with silk, especially because the protection of perfume oils by this technology allows a prolonged fragrance release (Fig. 5).The encapsulation of lipophilic substanc-es using functional vegan silk polypep-tides provides benefits and opportunities for a variety of applications. In principle, the newly developed silk capsules can be used as carrier, protective shield and/or controlled-release systems for lipophilic active ingredients. Encapsulated actives can act more effective, more targeted

and over longer periods of time, reducing their respective use levels and prolonging the perception of effectiveness for the customer. In addition, encapsulation can influence properties such as color (pigments), skin feel (shea butter) or cooling/warming effects (octadecene, capsaicin) of the formulation.

Encapsulation of Water Soluble Substances Using Functional Silk Polypeptides

In addition to the above-mentioned lipophilic substances, also hy-drophilic ingredients such as green tea extract, caffeine, vitamin A acetate or ascorbic acid are of fundamental importance in cosmet-ics. These active ingredients have anti-oxidant properties reducing reactive oxygen species (ROS) and are therefore particularly well incorporated into anti-aging formulations. A newly developed technology enables the inclusion of such usually sensitive substances into special gel capsules using func-tional silk polypeptides, thus protecting them from premature degradation (Fig. 6). In contrast to the previously method for the encapsulation of water-soluble actives with vegan silk [11,12], it

Tab. 1 Stability parameters for silk capsules.

pH temperature shear forces ethanol (50 %) formulation

optimum range between 5.5 and 10.6

-20 °C to up to 95 °C

workable with dispersing device

no negative effect on morphology

gel and emulsion

Fig. 5 Scent intensity increases upon mechani-cal stress of silk capsules.

Fig. 4 Microscopic image using laser scanning microscopy (LSM) of silk capsules incorpo-rated into an emulsion. The graph illustrates the homogenous size distribution of silk microcapsules with an average diameter of approx. 17 µm. 90 % of the capsules range in size between 10 and 30 µm.

Fig. 6 Schematic composition and laser scanning image (on the right) of hydrophilic silk capsules.

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is now possible to produce extremely stable capsules without us-ing any potentially harmful components (e.g. toxic crosslinker). Basis for the innovative technique again is the peptides ability to self-assemble in water along a water/oil interface. Droplets of hydrophilic actives and the aqueous silk solution solidify in an oil phase to form gel capsules. During the process, the silk peptides first accumulate along the water/oil interface to form a capsule membrane. After a short time, the peptides remaining in the capsule also assemble into a three-dimensional network and stabilize the capsules structure from the inside. The resulting gel capsules shield the bound active ingredient until they are re-leased under mechanical stress.The manufacturing process of the gel capsules is easy to inte-grate into existing production lines and scalable due to its low level of complexity. In a first step, Silkgel, an aqueous, thixotropic silk-polypeptide gel, is ultrasonically liquefied. It can later reas-semble forming the solid core of the capsule. This process step is followed by the addition of the selected water-soluble active substance and an aqueous peptide solution, which ensures the formation of the capsule shell. Next, small droplets of the solu-tion gelate in a continuously stirred oil phase and can be stored as capsules in water after several washing steps (Fig. 7). Depending on their application, capsules with a size between 0.4 and 2 mm can be created. So far, various hydrophilic dyes such as meth-ylene blue and carmine (E120) have been successfully tested (Fig. 1).In analogy to the lipophilic-content capsules already described, the encapsulation of aqueous constituents with functional silk polypeptides enables a multiplicity of different applications. In addition to the protection of the encapsulated substance, the new aqueous capsules offer even more advantages. During production, the whole active ingredient can be encapsulat-ed without any loss. Although the newly developed capsules can be considered an aqueous system, they are insoluble in water and thereby stable, allowing their incorporation into various formulations. Thanks to their versatility, encapsulated water-soluble substances could also be added to oil-based sys-tems, such as lip care products. In addition, the silk capsules are particularly interesting because they can be applied without

leaving any unwanted residues on skin, while additionally pro-viding the positive effects generally associated with functional silk, such as the formation of a thin protective layer.

Conclusion

Functional silk peptides can be processed into microcapsules in order to either encapsulate lipophilic or hydrophilic substances. Afterwards, the obtained silk capsules can easily be integrated in cosmetic formulations and are suitable especially for plas-tic-free cosmetic applications. The vegan silk capsules protect the core material from early release and improve the stability of the encapsulated substance. Additionally, the capsules’ silk can protect skin and hair due to its film forming, breathable properties. The functional silk encapsulation is particularly suit-able for the protection of anti-aging ingredients, vitamins, pig-ments, antioxidants and further active substances and can help to realize new high-performance products. Yet, the innovative silk capsule technology offers a sustainable and biodegradable solution for the personal care industry.

References[1] Casanova F, Santos L: Encapsulation of cosmetic active ingredients for topical

application – A Review. Journal of Microencapsulation; 2016, 33(1), 1-17

[2] Leslie H A: Plastic in Cosmetics. United Nations Publications; 2017

[3] Eunomia Research & Consulting Ltd: Plastics in the Marine Environment; 2016

[4+5] Grammes F: Mikroplastik Studie 2016. codecheck.info; 2016

[6] Umwelt Bundesamt: Quellen für Mikroplastik mit Relevanz für den Meeres-schutz in Deutschland; 63/2015

[7] Blüm C, Nichtl A, Scheibel T: Spider Silk Capsules as Protective Reaction Con-tainers for Enzymes. Advanced Functional Materials; 2013, 24(6):763-768

[8] Hermanson K, Huemmerich D, Scheibel T, Bausch A: Engineered Microcapsules Fabri-cated from Reconstituted Spider Silk. Advanced Materials; 2007, 19(14):1810 – 1815

[9] Mehlhorn H: Gentle Protection from Bloodsuckers – Icaridin/Saltidin and Veg-an Silk. SofwJournal; 2016; 142(7); 30-33

[10] Mehlhorn H: Bloodsuckers are not Fussy! Reliable Protection is Essential. Sof-wJournal; 2017; 143(12); 44-47

[11] Blüm C, Nichtl A, Scheibel T: Spider Silk Capsules as Protective Reaction Con-tainers for Enzymes. Advanced Functional Materials; 2013, 24(6):763-768

[12] Hermanson K, Huemmerich D, Scheibel T, Bausch A: Engineered Microcapsu-les Fabricated from Reconstituted Spider Silk. Advanced Materials; 2007, 19(14):1810 - 1815

Joachim Müller, Ralf Mehrwald, Natalie Blosl,Sabine Schlay, Dr. Kristin Schacht

AMSilk GmbHAm Klopferspitz 19 im IZB

82152 Planegg/Munich | Germany

contact

Fig. 7 Manufacturing process of silk capsules containing water soluble substances. The encap-sulation solution, consisting of liquefied Silkgel, liquid silk solution and the substance to be en-capsulated, is transformed into an oil phase in single droplets. After solidification and washing, capsules are ready for the incorporation into cosmetic products.