Team:Aalto-Helsinki/Concept
The Concept
We wanted to create a concept that gathers together the whole project we have been working with. The purpose of the concept is to have a way to communicate with people about the possibilities of synthetic biology. Skin care and acne turned out to be a really good way to do that, because it is part of almost everyone’s daily life in a way or another and with it it was easy to build a bridge between science and people. The concept itself is simple and easy to understand. Our aim was to create purifying skin care product for people suffering from acne. Our primary of importance was to create non-toxic and safe product that does not cause any environmental impacts, is easy to produce and simple to use.
Porifi - Purify Your Pores from Acne Bacteria
Our application for antimicrobial dermcidin is a exfoliating skin care product made out of cellulose hydrogel. Important part of taking care of acne is to remove and exfoliate dead skin gently and purify the skin. Cellulose hydrogel is natural and non-toxic substance that could be ideal for containing dermcidin. By changing content and amounts of water and CMC it was possible to have different viscosities and feelings of hydrogel. By testing different kind of compositions we ended up using the aqueous solution of 3 % CMC with long chain molecules, which we describe in further sections in detail.
Picture on the left: Michal and Maisa making the hydrogel
Picture on the right: Hydrogel sample ready for density measurement
For exfoliating beads ideal material would be cellulose that dissolves in water as time passes but not too fast when product is stored and still under use. Dermcidin could also be bonded with cellulose-based beads. In our product trial we used grinded peach stones.
Picture on the left: Filters for the grinding machine
Picture on the right: Andreas Lindberg helping us with the grinding machine
Smooth as a Peach - The Product
From the survey, meetings with professionals and people suffering from acne we got valuable information what kind of products people in general are willing to use and what kind of effect they expect form the product. We wanted to make our product application as simple and user friendly as possible. Instead of making purifying mask that user should wear for 10 to 20 minutes, we decided to make easy exfoliating gel. User only needs to add it on skin, rub gently on the skin and rinse away.
The efficiency of the product is based on both, antimicrobial dermcidin component which could increase the natural dermcidin balance on the skin and exfoliating the dead skin by rubbing peach stone beads gently on the skin.
Why Cellulose?
Sustainable and environmentally friendly thinking was important part of application design process. We decided to use cellulose together with dermcidin because cellulose-based materials have versatile forms and compositions. Cellulose is also environmental friendly and has a growing importance for Finnish economy.
Cellulose caught our attention because of the posssibility of empowering the dermcidin peptide with cellulose binding domain. Thanks to that, antimicrobial dermcidin could be attached to different kinds of bandages, cotton pads and dressings. Thus, the peptide could be used as an alternative, for example for antimicrobial silver bandages used widely in wound care. Also in skin care, we were first thinking about using cellulose based paper mask or some kind of cotton pads where we could tie up dermcidin. Based on our survey results and discussions with cosmetologists and dermatologists, however, we decided to concentrate more on purifying product with exfoliating properties. A lot of beauty and skin care products contain environmentally harmful ingredients like microplastic beads. We wanted to find substitutes for those and create as pure and natural antimicrobial product as possible. While exploring different cellulose materials, we found and decided to concentrate further on carboxymethyl cellulose-based hydrogel (CMC) because it seemed to be promising base component for our skin-care product. Moreover, CMC hydrogel is safe, non-toxic and easy to experiment with. We got a lot of help from Andreas Lindberg, the doctoral candidate from Aalto University, School of Chemical Engineering.
CMC Hydrogel
Hydrogel pH
We measured the pH of CMC hydrogel to see if it promotes the antimicrobial activity of dermcidin. Using pH test strips, we obtained the pH value of about 6, whereas pH of skin varies from 4.5-5.75 and the theoretical value for dermcidin is about 5.
Hydrogel Viscosity
Viscosity correlates resistance to flow and thickness of a substance. In case of our cosmetic formulation, it affects cleansing efficiency and user perception. It also impacts the way the product should be stored and thus, a packaging choice. Moreover, the high enough viscosity is required to prevent exfoliant from sedimentation at the bottom of the package.
Hydrogel Samples
Carboxymethylcellulose (CMC)-based hydrogel is the base component of our cosmetic formulation. For testing purpose, we used two grades of CMC manufactured by CP Kelco: Cekol 2000 (low modular weight polymer) and Cekol 50000 W (high modular weight polymer).
We prepared several aqueous solutions of different CMC concentrations (5 %, 7 % solutions of Cekol 2000; 1 %, 2 % and 3 % solutions of Cekol 50000 W). This let us initially check how different formulations “feel and look”, and enabled to pick the first candidates for our products.
Viscosity Measurement Setting
We also decided not only to evaluate the hydrogel samples experientially but also to measure their viscosity. We conducted measurements using Brookfield rotational viscometer with RV spindles.
We kept temperature constant at 24-25°C and measured hydrogel viscosity at different spindle speeds (0.1 - 200 RPM). We decided to test the hydrogel samples at broad range of speeds due to its non-newtonian behaviour which means that its viscosity decreases under shear strain (shear-thinning effect). Moreover, assuming that the cosmetic will undergo different shear stress while scooping out from the package, keeping still on fingers, and applying on face by rubbing, we were interested how viscosity would change then. We neglected, however, temperature effect by that.
Measurement Results
The results of our measurements confirmed the non-newtonian behaviour of the CMC-based hydrogel. As it is shown in the graph below, when the shear stress increases the viscosity decreases for all samples. The viscosity changes by one or two orders of magnitude, depending on CMC grade and concentration. However it is also completely and instantaneously reversible and the original viscosity is retained when the shear stops.
According to the CMC information booklet provided by the CP Kelco company [1], the pseudoplastic flow behavior is related to de-entanglement and orientation of the CMC molecules in the direction of the flow. It seems to be seen in our results, where a longer chain molecule (higher molecular weight), as found in 3 % Cekol 50000W CMC, is more "shear thinning" compared to the shorter chain molecule found in 5 % Cekol 2000 CMC at higher spindle speeds.
The viscosity is proportional to the average chain length of the CMC molecule. The average chain length determines the molecular weight of the CMC grade. Thus, the viscosity at low speeds increases more rapidly for long-molecule CMC than short-molecule one with increasing concentration. The higher viscosities can be also obtained for long-molecule CMC despite lower concentration of the solution.
The excel file contains the table of viscosity values with related graphs, as well as more detailed description of the test-bed configuration for particular measurements.
Conclusion
We were looking for the hydrogel composition which would not only remain stable at rest in the package as well as by scooping it with fingers and then applying it on face, but also which would get liquid enough while rubbing and exfoliating dead cells. Based on the perception as well as on the result of the viscosity measurements, the aqueous solution of 3 % CMC with long chain molecules appears to be the good choice. 7 % CMC with short molecules is another option.
Hydrogel with Exfoliant
Cosmetics is one of the major sources for microplastics that end up in the environment. We were critical of microbeads which many cosmetic companies use as exfoliating agents in their products. Microbeads are tiny plastic particles which end up in the oceans, as they cannot be filtered from our waste waters. After, through plankton, they start to accumulate in fish and fish-eating birds [2]. In the beginning of 2017 microplastics were already detectable from table salt. We used natural beads made of peach pits. We grinded them to achieve the beads of different particle sizes: coarse (heavy), medium (mix) and fine. Then, we added them to hydrogel samples to get different compositions. The viscosity also impacts the sedimentation rate of exfoliating beads suspended in the hydrogel.
Exfoliant Sedimentation and User Perception Tests
First, we compared all samples by sensing and realized that the fine exfoliant felt too delicate in all prepared hydrogels. On the other hand, the coarse beads were quite big and had sharp edges. The medium exfoliant seemed to nicely blend with hydrogels and provide good exfoliating effect.
After testing based on perception, we left the samples for several days to see what would happen with the exfoliants. It turned out that the most viscous solutions, 7 % Cekol 2000 and 3 % Cekol 50000 W, remained stable and kept the beads uniformly distributed. However, we also noticed the degradation of cellulose chains in the hydrogels due to microorganism growth, which resulted in severe viscosity reduction.
Hydrogel Degradation
Although CMC has good stability towards degradation, enzymes and oxidants may still degrade it. Enzymes produced by microorganisms may degrade the cellulose chain, and thus, cause serious, irreversible viscosity decreases. [1]
It happened to our samples while keeping them in room temperature and being exposed to light. We were warned about the possible spoilage in the talk with one expert, but despite that, we had neither carefully sterilized the peach pits nor added any preservative before. In result, after one week, two samples (1 % and 2 % Cekol 50000 W with the fine exfoliant) completely turned into cloudy liquids. Some other were affected by mold and the degradation process started too. After another week, the cellulose chains in most of the other samples were either entirely or almost entirely degraded.
Left and middle figures: Severely degraded 3 % Cekol 50000 W with medium exfoliant - hydrogel turned into cloudy liquid after 2 weeks; Right figure: Growing mold in 7 % Cekol 2000 with heavy exfoliant.
An efficient way to stop enzymatic attacks is thus to prevent growth of microorganisms. This can be done by adding preservative. The CMC manufacturer suggest the following preservatives for food, cosmetic and pharmaceutical uses:
- Sodium benzoate
- Sorbates (Na and K salts)
- Sodium propionate
- Methyl parahydroxybenzoate
We also searched for other preservatives which are commonly used in cosmetics. The attachment presents the list of several other preservatives with brief descriptions.
Preservatives
Due to the problem with microorganism growth in the hydrogels, we decided to check the effect of adding a preservative on the solution stability. We picked the benzyl alcohol for a trial, because it is used in a wide variety of cosmetic formulations [3]. According to Cosmetic Ingredient Review, it is safe to use in cosmetic products at concentrations of up to 5 %. However, in the European Union, benzyl alcohol is allowed at maximum concentration of 1 % in ready for use preparation [4].
Benzyl alcohol can be considered as a natural ingredient as many plants, fruits, and teas have it as a component. On the other hand, the cheaper synthetic version usually used in products is produced by mixing benzyl chloride with sodium hydroxide. Other ‘natural’ alternatives are also available and could be also considered in the future.
Benzyl alcohol is a colorless liquid and has a mild, pleasant aromatic scent, so it is used not only as a preservative but also as a fragrance ingredient. We assumed that our cosmetic product should be odorless or with subtle aroma. However, during testing benzyl alcohol as the preservative we got annoyed with its perfumed smell. After mixing the components, the smell was not so irritating anymore, but it is important to consider the influence of preservatives and other additives on the finished product aesthetics such as odor, color and viscosity.
Moreover, the interaction of benzyl alcohol or other preservatives with the dermcidin should be investigated in the future to provide the anti-acne features of our product. The testings we made with benzyl alcohol turned out to be promising and within one week no microorganism growth was found. In the future more test are required and we were also taking into account the possible effect of sterilization of the beads to avoid contamination.
Sterilized peach beads.
Package
In package design we had several potential material candidates: paper, wood, or biodegradable plastics such as polylactic acid (PLA). We decided to go with wooden packages because we had an idea of wood based product packaged inside wooden package. Using wooden packages, we also represented Finnish nature which was an inspiration in the whole design process. The package is made out of flamed birch wood, which has a naturally beautiful structure and outlook. The product label is laser engraved on top of the package and ingredient information can be engraved on the bottom of the package. In actual production process, the wooden package is most probably too expensive, but now we wanted to focus on a show piece, an idea of the beautiful package that can be used after the product has run out. With wooden package we believe to get also more attention in the exhibitions and presentations. In the future, the package could be PLA tube or coated paper tube which is easy to recycle or burn.
Future Work
We considered two possible paths to proceed with the application prototypes within the time frame of iGEM competition. We could either make a looks like product sample using the intended materials and compositions, or a works like prototype with desired functionality. We decided to proceed with the looks like prototype in order to have the product mock-up to show outside and to be able to create a visual concept around. Thanks to that, we could gain more interest and promote our research and product. Next product development steps would be to bring dermcidin and the hydrogel together and testing the antimicrobial activity while defining the cosmetic composition of the final product and checking how it works on skin later.
References
[1] CP Kelco, 2009. The CMC book. Product description. Accessible at: [here].
[2] Haynes G., 2016. Microbeads – tiny objects, massive problem? Article. Accessible at: [here].
[3] Nair B., 2001. Final report on the safety assessment of Benzyl Alcohol, Benzoic Acid, and Sodium Benzoate. Publication. Accessible at: [here].
[4] Benzyl alcohol - CosIng Database. Data sheet. Accessible at: [here].
