Sensors

Researchers Develop Implantable Sensor that Dissolves After Use

16 May 2018

A fully biodegradable and stretchable strain and pressure sensor. a, The sensor can be attached to a tendon for real-time healing assessment, allowing the rehabilitation protocol after a tendon repair to be personalized for each patient. b, Concepts used for strain and pressure sensing. Strain sensing: On application of strain, the two thin-film comb electrodes slide relative to each other, resulting in variation of the capacitance. The range of 0–15% for strain sensing is chosen based on the fact that in vivo the strain exerted on tendons is lower than 10%. Pressure sensing: On application of pressure, variation of the distance between the top and bottom electrodes results in variation of the capacitance. The dielectric layer, made of a thin, highly compressible, regularly microstructured rubber, enables the sensor to have high pressure sensitivity and a fast response time, improving the sensitivity by several orders of magnitude compared to previously published work based on an air gap approach. c, Materials and overall assembly of the fully biodegradable strain and pressure sensor. The biodegradable elastomer PGS (poly(glycerol sebacate)) is used as a dielectric layer for the capacitor constituting the pressure sensor. It is also used in the strain sensor architecture as a stretchable non-sticking layer, allowing the electrodes to slide relative to each other. The biodegradable elastomer POMaC (poly(octamethylene maleate (anhydride) citrate)) is used for the strain sensor and packaging18. POMaC is a soft stretchable biodegradable elastomeric biomaterial synthesized from citric acid, maleic anhydride and 1,8-octanediol, which is able to mimic the mechanical properties of a wide range of soft biological tissues. PLLA is the substrate layer for the magnesium electrodes. d, Picture of the assembled sensor. Source: Nature Electronics (2018). DOI: 10.1038/s41928-018-0071-7 A fully biodegradable and stretchable strain and pressure sensor. a, The sensor can be attached to a tendon for real-time healing assessment, allowing the rehabilitation protocol after a tendon repair to be personalized for each patient. b, Concepts used for strain and pressure sensing. Strain sensing: On application of strain, the two thin-film comb electrodes slide relative to each other, resulting in variation of the capacitance. The range of 0–15% for strain sensing is chosen based on the fact that in vivo the strain exerted on tendons is lower than 10%. Pressure sensing: On application of pressure, variation of the distance between the top and bottom electrodes results in variation of the capacitance. The dielectric layer, made of a thin, highly compressible, regularly microstructured rubber, enables the sensor to have high pressure sensitivity and a fast response time, improving the sensitivity by several orders of magnitude compared to previously published work based on an air gap approach. c, Materials and overall assembly of the fully biodegradable strain and pressure sensor. The biodegradable elastomer PGS (poly(glycerol sebacate)) is used as a dielectric layer for the capacitor constituting the pressure sensor. It is also used in the strain sensor architecture as a stretchable non-sticking layer, allowing the electrodes to slide relative to each other. The biodegradable elastomer POMaC (poly(octamethylene maleate (anhydride) citrate)) is used for the strain sensor and packaging18. POMaC is a soft stretchable biodegradable elastomeric biomaterial synthesized from citric acid, maleic anhydride and 1,8-octanediol, which is able to mimic the mechanical properties of a wide range of soft biological tissues. PLLA is the substrate layer for the magnesium electrodes. d, Picture of the assembled sensor. Source: Nature Electronics (2018). DOI: 10.1038/s41928-018-0071-7 After undergoing orthopedic surgery, patients are typically expected to take part in physical rehabilitation as part of their recovery. Yet, with the untold impact of pressure and strain on the the new components, scientists have long been in search of a better method for measuring such impact. Researchers from Stanford University have developed an implantable sensor designed to both accurately measure strain and pressure and then dissolve once it has outlived its usefulness.

Overcoming both performance and biocompatibility issues, the research team has found a solution that would make a second surgery to remove an implantable sensor wholly unnecessary.

Created by stacking two sensors — one for measuring strain, the other for measuring pressure — the sensor structure consists of two kinds of biodegradable and biocompatible polymers featuring magnesium electrodes.

Once completed, the multi-layer sensor was implanted in the back of a rat where it was capable of measuring strains (as small as 0.4 percent) and pressures (as small as 12 Pa) without interference. Likewise, the sensor worked as intended even during the decomposition phase up until it was no longer of any use.

The team reported that, apart from a minor amount of inflammation at the start, the rat did not experience any negative impact from the implantable sensor.

The research is published in the journal Nature Electronics.

To contact the author of this article, email marie.donlon@ieeeglobalspec.com


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