The spores of Bacillus subtilis will be contained in a compartment which is impermeable to bacteria and liquid, but can still let through volatiles. Metabolites, water, and alanine should be separated from the spores by a breakable membrane. Mixing these compounds will cause germination.
The material we use for our sticker is TPX®, or polymethylpentene. This polymer is available as thin, transparent sheets. The advantage is that it is relatively cheap, strong, and capable of letting through volatiles. The radius of the pores in TPX® is between 1 an 10 nm, which is at least 50x larger than the average badmeat-volatile, but still small enough to keep liquid and bacteria in (see the figure below).
Comparison of the size of the TPX pores, volatiles and Bacillus subtilis.
Design requirements
Material
The material should not break too fast and should resist a human grip strength with a minimum of 40 pounds pinch and pressure.
The product should be made of a material that is light and easy to handle.
The material should be durable and not too expensive.
The volatiles and oxygen should penetrate through the material, while the spores, bacteria and liquid should stay inside.
The material should fit in a meat package.
The should not be toxic or become toxic for the bacteria
The material should be able to cope with a temperature of at least 125 Celsius.
Measurements
Needs a visible feedback for the human eye and should easy to understand for the customer.
The product should keep the visible feedback store in the material.
Appearance
Product should be made of attractive colors and shape.
Safety
The bacteria should not escape from the sticker and or harm the environment. Therefore the product should provide adequate support and be reliable.
Customer comfort
Easy to use the visible feedback device.
The product may provide different degrees of strength depending on the development of the customer strength.
Develop design
For the development of the sticker, the PDCA (Plan Do Check Act) strategy was used to develop a ultimate device that the customer and environment needs is involved in the project design.
The following question where made:
Who is your external customer?
The customer that is against food spoilage and customers that are willing to buy it.
What value do you deliver to that customer?
A replacement for use by date and sell by date and new indicator for when meat is getting spoiled.
Who, in you iGEM group, delivers that value?
The design engineers and cooperation with the biologist to get input for the prototype design.
How do they deliver that value?
To do research and create a new indicator to indicate when meat get spoiled.
Material
Two different materials should be chosen carefully for our final product. In first term, the outer bag should be resistant enough to support the bacteria inside the sticker, strength and pressure that is applied by the customer. Its physical properties and characteristics do not have to be affected when to much pressure or deformation is applied on the sticker. It should be light and small for easy removing and placing in the meat bag.
In second term, the case should be made from a light material and the surface should be flat to avoid any risk for the user.
Taking into account all these characteristics we considered three materials for the sticker: polyetheen (sanwich bag), Polyvinyl chloride (cling film) and Polymethylpentene (PMP) als commonly known as TPX. On the other hand, TPX was considered for the outer bag of the sticker. The reason was that all the requirements was for filled by this material.
In addition, a second material is needed inside the the sticker to separate the medium from the spores: The Polyvinyl chloride was to weak for the outer layer for the sticker. The strength and pressure that will be applied by the customer will break the sticker to fast and the sticker indication liquid will come accidentally come in the environment, what shouldn't happen for safety. For easy to break the inner compartment with medium in the sticker, this material had the best characteristics to full fill our second material needs. Not allot of pressure and strength is needed to break the inner compartment, just to give comfort to the customer when handling the sticker.
Refences
Krentsel B.A., Kissin Y.V., Kleiner V.I., Stotskaya S.S. Polymers and Copolymers of Higher a-Olefins, Hanser Publishers: New York, 1997.
H. C. Raine, J. Appl. Polym. Sci. 11, 39 (1969)
Mitsui Chemicals Co., Properties of Standard TPX Grades, 2004.
FDA CFR Title 21 Sec. 177.1520 Olefin polymers (C) 3.3b for TPX(4-methylpentene-1-based olefin copolymer).
Mathiowetz V, Kashman N, Volland G, Weber K, Dowe M, Rogers S (February 1985). "Grip and pinch strength: normative data for adults". Arch Phys Med Rehabil 66 (2): 69–74. PMID 3970660.
Tools and supply
- Sealboy type: 236 SBSA-2, Serie: 0070133017 to affix the TPX material and cling film in the setting 7.
- Sanyo labo autoclave MLS-3020U (RUG Serial: 4495)to sterilize the TPX material.
- Gas profile 1 SCS, Part: 6.103.000, series: 0213372 to work sterile during fill-up the sticker.
- B-D Plastipak 21G 11/2 40/8 NR2 2ml to fill up the sticker.
- Cling film brand: Folia vershoudfolie, 50m width 29cm, 15 micrometer, oxygen permeability, fat- and waterproof. Inner compartment for the the sticker.
- TPX X-44B#25 and X-44#50, Company: Mitsui Chemicals Co., Brand: TPX to use as outer layer from the sticker.
- Luria Broth Brand: Lenox.
Prototype
The prototype the inner compartment is made with cling film with side affix of 1mm thickness the inner pack was filled with Luria broth and
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