While at work, you notice your gloves changing color, and you know immediately that you've come in contact with dangerous chemicals. Bandages on a patient signal the presence of unseen, drug-resistant microbes. These are ideas that might have once seemed futuristic but are becoming a reality as researchers move forward with technology to use living bacteria in cloth to detect pathogens, pollutants, and particulates that endanger our lives.
Once our greatest foes, bacteria are increasingly being engineered to boost human safety and health. In a study published in the Proceedings of the National Academy of Sciences, researchers from the Massachusetts Institute of Technology created a hydrogel medium to keep bacteria alive, which can form the basis of "interactive genetic circuits and living wearable devices."
By inserting or reorganizing the expression of certain genes in a bacterium, bioengineers can create strains that work as sensors to detect a variety of things, from chemicals to environmental conditions.
While editing bacteria has produced exciting results, real-world application of those bacteria has proved troublesome. For the bacteria to detect a toxin, they must be alive; Keeping them living is a problem that's plagued scientists trying to develop these devices. These wearables must also be cost-effective, flexible, secure, and somewhat reusable, to bring down costs even more.
"The challenge to making living materials is how to maintain those living cells, to make them viable and functional in the device," Timothy Lu, an associate professor and bioengineer at MIT, said in a press release. "They require humidity, nutrients, and some require oxygen. The second challenge is how to prevent them from escaping from the material."
As scientists have tried to integrate these engineered organisms into devices — through freeze drying, embedding in paper sheets, and even seeding cells into flexible films — they've encountered numerous difficulties. As Lu notes, these techniques often fail because the bacteria either leak out or die.
[I]t remains a grand challenge to integrate genetically encoded cells into practical materials that can maintain long-term viability ...
The MIT research team met this challenge head on, proposing and designing a standard unit that combines a secure, flexible structure with a habitable environment for bacteria. The structure has two parts:
- Hydrogel: A biocompatible hydrogel provides a healthy living environment for bacteria. The gel includes molecules that can carry nutrients, water, and (in some cases) oxygen to the bacteria within to ensure they have enough nutrients to grow. By itself, scientists intend to use the flexible, durable hydrogel for applications on — and inside — the body.
- Device: Researchers inserted bacteria into patterned cavities within a rubber-like material called elastomer. The specialized elastomer can be twisted and stretched without breaking or leaking its bacterial contents. After the bacteria is inserted into the compartments, the entire device is soaked in a nutritious medium to make sure the bacteria are well-fed before being sealed. The nutrients absorbed by the device can keep bacteria alive for days. The hydrogel-elastomer material allows diffusion of molecules (signals from the chemicals tested) into the hydrogel, without leaking bacterial cells outward into the environment, even when the material is stretched.
Once the research team solved the problem of combining bacteria with background environment, it set out to test and demonstrate possible uses of the technology. Study authors created rough prototypes of devices including:
- Wearable living patches: Researchers applied a flexible patch loaded with bacteria modified to detect a naturally occurring sugar to skin swabbed with it. The patch immediately glowed in response.
- Gloves: Researchers developed gloves, as seen in the cover image above, designed to detect chemicals. Each fingertip contains a bacterial sensor for a different chemical compound. When tested, each one responded to the chemical it was designed to detect.
- Chemical sensing: Using the flexible elastomer fabric, the team created a sheet of bacterial sensors targeted at different chemicals. As with the glove application, the discrete units on the sheet immediately lit up when exposed to target compounds.
The research group also created a data model to help other researchers develop devices and materials using bacteria and hydrogels.
This proof-of-concept study did not focus on if these glowing gloves could detect minute traces of toxins or bacteria, but instead showed it's possible to create such devices. The researchers didn't compare and contrast this detection method with other techniques, but the approach is promising.
"The model helps us to design living devices more efficiently," co-author Xuanhe Zhao, an associate professor of mechanical engineering at MIT, said in the press release. "It tells you things like the thickness of the hydrogel layer you should use, the distance between channels, how to pattern the channels, and how much bacteria to use."
With future applications in healthcare, industry, and even clothing that senses infection, partnering with genetically-engineered microbes gives new meaning to the phrase "beneficial bacteria."
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