27 September 2012

Biodegradable electronics implanted in mice

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Biodegradable electronic implants that can be reabsorbed by the body have been used to administer drugs in mice, a group of international researchers has announced.
Biodegradable electronic circuit

Spot the circuit: scientists have devised a biodegradable electronic circuit that could be
used in biomedical implants and safely reabsorbed by the body. Credit: Beckman Institute, University of Illinois

SYDNEY: Biodegradable electronic implants that can be reabsorbed by the body have been used to administer drugs in mice, a group of international researchers has announced.

In a paper published in U.S. journal Science, the researchers describe how electronic circuits made from silicon, magnesium and silk can be used as medical implants to deliver treatments before degrading into the surrounding environment.

“Many biomedical implants only need to operate for a certain period of time, after which they [could now] dissolve and disappear to eliminate unwanted, and unnecessary, device load on the body,” explained paper co-author John Rogers, a bioengineer and mechanical scientist at the University of Illinois, USA.

Diagnostics, drug delivery and
tissue-engineering scaffolds

The study used implants to deliver an antibacterial drug, which prevents infection, to surgical wound sites in mice. However, the biodegradable electronics could have a number of other applications, said postdoctoral research fellow Katia Bazaka from the electronics materials research group at James Cook University, in Queensland, Australia.

“Biodegradable electronic devices can be used as sensors for rapid diagnostics, as drug-delivery vehicles to enable precisely controlled […] rapid or sustained delivery of drugs or as tissue-engineering scaffolds to support tissue regeneration and healing,” said Bazaka, who was not involved with the study.

With silicon nanomembranes for semiconductors and silk for the substrate and packaging material, the implants reabsorb into the body via subdermal layers and the vascular system.

In this study, reabsorption was triggered by exposure to biofluids and researchers found only faint residues of silk when they examined the implant region in mice three weeks after insertion.

Controllable lifespan

In this study, the electronics worked for 15 days before degrading – to coincide with the critical post-operation period – but the report outlines ways to adjust and control the time between implantation and loss of function in silicon-based electronics.

It suggests the lifespan of the device can be extended by adding silk-encapsulating layers and packaging, or reduced by changing the physical structure of the materials.

Biomedical engineer Rylie Green from the University of New South Wales, Australia, who was not involved in the study, agreed that this approach is effective.

“There are always challenges in developing electronics which can degrade, in that often the ability to pass charge – and remain functional – is lost as soon as the device degradation is initiated,” she said, adding: “The control of degradation through the outer silk layer is a new approach which has the potential to increase the [time] between implantation and loss of function.”

From mice to humans

The report provides a “system level example” of degradable electronic medical implants, and Rogers said the researchers “hope the translation to humans can occur” and are working in that direction.

Reassuringly, the implantations caused no inflammation in the mice, and Rogers said he expects to find the same tolerance in humans.

“The amounts of materials needed for the circuits are extremely small, below both recommended daily allowances as well as naturally occurring physiological levels,” she said.

Green said the study provides a foundation for future research.

“The mouse studies are an important first step which show the potential for these materials, but trials for longer periods in more complex tissues will be required before any substantive claims can be made regarding human tolerance,” she said.

The report outlines possibilities for further research and suggests advances in biodegradable electronics could also give rise to a new generation of biomedical treatments – and even opportunities for electrical waste management.

Dissolution of a transient electronic circuit by falling droplets of water.
Video courtesy of the Beckman Institute, University of Illinois

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