Biomaterial-based ink reveals new era in wearable sensing

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Novel silk-based inks can respond to and quantify chemicals released from the body or in the surrounding environment by changing color

Original source: Materials Today

Researchers at Tufts University’s School of Engineering have developed biomaterial-based inks that respond to and quantify chemicals released from the body – in sweat and potentially other biofluids – or in the surrounding environment by changing color. These inks can be screen printed onto textiles such as clothes, shoes or even face masks in complex patterns and at high resolution, providing a detailed map of human response or exposure.

This advance in wearable sensing, reported in a paper in Advanced Materials, could potentially allow conventional garments and uniforms to simultaneously detect and quantify a wide range of biological conditions, molecules and, possibly, pathogens over the surface of the body.

“The use of novel bioactive inks with the very common method of screen printing opens up promising opportunities for the mass-production of soft, wearable fabrics with large numbers of sensors that could be applied to detect a range of conditions,” said Fiorenzo Omenetto, corresponding author of the paper and professor of engineering at Tufts’ School of Engineering. “The fabrics can end up in uniforms for the workplace, sports clothing, or even on furniture and architectural structures.”

Wearable sensing devices have attracted considerable interest for monitoring human performance and health. Many such devices have been invented that incorporate electronics in wearable patches, wristbands and other configurations for monitoring either localized or overall physiological information such as heart rate or blood glucose.

The Tufts team has taken a different but complementary approach based on the non-electronic, colorimetric detection of a theoretically very large number of analytes using sensing garments that can be distributed to cover very large areas – anything from a patch to the entire body, and beyond.

The components that make the sensing garments possible are biologically activated silk-based inks. The soluble silk substrate in these ink formulations can be embedded with various ‘reporter’ molecules – such as pH sensitive indicators, or enzymes like lactate oxidase to indicate levels of lactate in sweat. The former could be an indicator of skin health or dehydration, while the latter could indicate levels of fatigue of the wearer.

Due to the versatility of the silk fibroin protein, many other derivatives of the inks can be created by modifying the protein with active molecules such as chemically sensitive dyes, enzymes, antibodies and more. While the reporter molecules could be unstable on their own, they can become shelf-stable when embedded within the silk fibroin in the ink formulation.

The inks are formulated for screen printing applications by combining them with a thickener (sodium alginate) and a plasticizer (glycerol). The resulting screen printable bio-inks can be used like any ink developed for screen printing. This means they can be applied not just to clothing but also to various surfaces such as wood, plastics and paper to generate patterns ranging from hundreds of microns to tens of meters. While the changes in color presented by the inks can provide a visual cue to the presence or absence of an analyte, more precise information on both quantity and distribution can be gained by using camera imaging analysis to scan the garments or other material.

This technology builds upon earlier work by the same researchers developing bioactive silk inks formulated for inkjet-printing to create petri dishes, paper sensors, and laboratory gloves that could indicate bacterial contamination by changing colors.

“The screen printing approach provides the equivalent of having a large, multiplexed arrangement of sensors covering extensive areas of the body, if worn as a garment, or even on large surfaces such as room interiors,” said Giusy Matzeu, research assistant professor of biomedical engineering at Tufts’ School of Engineering and first author of the paper. “Coupled with image analysis, we can obtain a high-resolution map of color reactions over a large area and gain more insight on overall physiological or environmental state. In theory, we could extend this method to track air quality, or support environmental monitoring for epidemiology.”

The fact that the method uses common printing techniques also opens up avenues in creative applications – something explored by Laia Mogas-Soldevila, architect and recent PhD graduate at Tufts in Omenetto’s SilkLab. Mogas-Soldevila has helped to create beautiful tapestries, displaying them in museums across the US and Europe. These displays are interactive, allowing visitors to spray different, non-toxic chemicals onto the fabric and watch the patterns transform.

“This is really a great example of how art and engineering can gain from and inspire each other,” said Mogas-Soldevila. “The engineered inks open up a new dimension in responsive, interactive tapestries and surfaces, while the 1000-year old art of screen printing has provided a foundation well suited to the need for a modern high resolution, wearable sensing surface.”