Analyze This: This material for 3_titanium dioxide safety
2022-05-25 04:52:45

Analyze This! Materials Science

Analyze This: This material for 3-D printing is made by microbes

Engineered bacteria ooze out proteins that link up to make ink

A 3-D printer squirts out a stream of ink made by bacteria. Those bacteria are engineered so that they ooze proteins that link up to form the ink. Scientists have used microbes to make drugs and chemicals for decades. But only recently have they turned bacteria into mini material-making factories.

A.M. Duraj-Thatte et al/Nature Communications 2021 (CC BY 4.0)

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By Carolyn Wilke

Researchers have made inks for 3-D printing from microbes and the goo they exude. Squishy and a bit wet, the inks feel like Jell-O. And some of them are actually alive.

For decades, scientists have put bacteria to use pumping out drugs, chemicals and fuels. But only recently have researchers modified bacteria to turn them into tiny factories for raw materials, says Anna Duraj-Thatte. A bioengineer at Virginia Tech in Blacksburg, she’s part of the team behind the new microbial inks.

Duraj-Thatte and her colleague Avinash Manjula-Basavanna did this work while at Harvard University in Cambridge, Mass. Their team modified a common type of bacteria called E. coli. The scientists tweaked genes in the E. colito modify protein fibers the bacteria make and exude into their environment as a goo. These proteins and other molecules form a structural support for the bacteria — akin to a nest.  

For one group of E. coli, the altered genes added a structure the scientists called “knobs.” In another group, a different modification caused the fibers to have a structure nicknamed “holes.” When both types of modified E. coliwere grown together, both types of fibers were made. The holes acted like sockets for the knobs. And when knobs and holes latched together, the proteins formed a web that made the goo stiffer.

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The team filtered the mix, removing the microbes and the nutrient mix that feeds them. That left a wet gel — a hydrogel — containing the fibers. The team tested this material to see if it would work for 3-D printing. This kind of ink needs to flow like toothpaste when squeezed. They also tested the ink’s rigidity and how much force it took to deform it.

The scientists added microbes back in to some inks. With living cells, those materials could gain new abilities. One ink contained E. coliprogrammed to make a drug for treating cancer. Another had E. colithat can suck up a toxic chemical.

This ink is too squishy for making building materials, says Manjula-Basavanna, who now works at Northeastern University in Boston, Mass. A living materials engineer, he works to mimic the simple processes used in nature to make materials. Microbes could be engineered to make harder, stiffer stuff though. And microbes might be able to help make stuff with less waste or have other advantages the researchers have yet to think up.

Bacterial ink

Researchers engineered two kinds of E. coli. Each kind of bacteria makes protein nanofibers. The CsgA-α bacteria make fibers with features the scientists call “knobs.” The CsgA-γ bacteria make fibers with features called “holes.” When both bacteria are grown together, the mix contains both kinds of fibers. The knobs and holes latch together, forming a structure that is like a web or mesh.

Duraj-Thatte et al/Nature Communications 2021 (CC BY 4.0)

In these bar charts, the researchers tested ink made from only the knob-fiber microbes (CsgA-α), only the hole-fiber microbes (CsgA-γ) or both microbes together (CsgA-αγ). The left graph shows a measure of these inks’ rigidity. The right graph shows the amount of force it takes to permanently stretch or dent the material. That’s a measure of a material’s strength. Both are measured in a unit called Pascals (shortened to Pa).

Data Dive:

  1. Look at Figure A. How much more rigid is CsgA-αγ than CsgA-α? How much more rigid is CsgA-αγ than CsgA-γ?
  2. Think about the structure of CsgA-αγ. Why do you think it is more rigid than the other two inks? (Hint: Reread the fourth paragraph in the story.)
  3. Can you think of other objects or materials that use a similar strategy for strength?
  4. Look at Figure B. The higher the yield stress, the greater the force needed to stretch or dent a material permanently. How does the yield stress for CsgA-α compare with that of CsgA-αγ? How does the yield stress for CsgA-γ compare with that of CsgA-αγ?
  5. Can you imagine ways in which this material could be used? Write down two or three.
  6. Many researchers are working to make materials that are biocompatible. Those materials don’t cause harm when they are placed inside the body. Those are materials that can be safely used in the human body. What are two or three potential uses of very hard, rigid biocompatible materials?
  7. What about materials that are soft and squishy?

Power Words

More About Power Words

3-D: Short for three-dimensional. This term is an adjective for something that has features that can be described in three dimensions — height, width and length. 

3-D printing: A means of producing physical items — including toys, foods and even body parts — using a machine that takes instructions from a computer program. That program tells the machine how and where to lay down successive layers of some raw material (the “ink”) to create a three-dimensional object.

bacteria: (singular: bacterium) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals). Bacteria are one of the three domains of life on Earth.

biocompatible: (adj.) A term for materials that can be used in the body without harming tissues. Such materials often become the basis for surgical and other biomedical implants.

bioengineer: Someone who applies engineering to solve problems in biology or in systems that will use living organisms.

cancer: Any of more than 100 different diseases, each characterized by the rapid, uncontrolled growth of abnormal cells. The development and growth of cancers, also known as malignancies, can lead to tumors, pain and death.

cell: (in biology) The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell. (in telecommunications) A technology that relies on a large number of base stations to relay signals. Each base station covers only a small area, which is known as a cell. Phones that rely on this system are typically referred to as cell phones.

chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

colleague: Someone who works with another; a co-worker or team member.

data: Facts and/or statistics collected together for analysis but not necessarily organized in a way that gives them meaning. For digital information (the type stored by computers), those data typically are numbers stored in a binary code, portrayed as strings of zeros and ones.

E. coli: (short for Escherichia coli) A common bacterium that researchers often harness to study genetics. Some naturally occurring strains of this microbe cause disease, but many others do not.

engineer: A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need. (v.) To perform these tasks, or the name for a person who performs such tasks.

environment: The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).

fiber: Something whose shape resembles a thread or filament. (in nutrition) Components of many fibrous plant-based foods. These so-called non-digestible fibers tend to come from cellulose, lignin, and pectin — all plant constituents that resist breakdown by the body’s digestive enzymes.

force: Some outside influence that can change the motion of a body, hold bodies close to one another, or produce motion or stress in a stationary body.

fuel: Any material that will release energy during a controlled chemical or nuclear reaction. Fossil fuels (coal, natural gas and petroleum) are a common type that liberate their energy through chemical reactions that take place when heated (usually to the point of burning).

gel: A gooey or viscous material that can flow like a thick liquid.

gene: (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

hydrogel: A “smart” material that can change its structure in response to its environment, such as the local temperature, pH, salt or water concentration. The material is made from a polymer — a chain made from links of identical units — that have free, water-attracting ends sticking out. So in the presence of water, it may hold (bond) those water molecules for quite a while. Some hydrogels are used in baby diapers to hold urine, in potting soils to hold water near to plants until they need it and in wound dressings to keep a sore from drying out.

microbe: Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

nutrient: A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.

protein: A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.

strategy: A thoughtful and clever plan for achieving some difficult or challenging goal.

stress: (in physics) Pressure or tension exerted on a material object.

toxic: Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.

waste: Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.

Citations

Journal:A.M Duraj-Thatte​ ​et​ ​al.​ Programmable microbial ink for 3D printing of living materials produced from genetically engineered protein nanofibers.​ Nature Communications.​ ​​Published online November 23. doi:​​ 10.1038/s41467-021-26791-x. 

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