Shape-memory implant may keep immobilized muscles from wasting away
When a limb is rendered immobile for long periods of time, its muscles will inevitably begin to atrophy. A new implant could help keep that from happening, however, by mechanically stretching and compressing those muscles.
Developed by scientists at Harvard University, the experimental device is known as MAGENTA, which stands for "mechanically active gel-elastomer-nitinol tissue adhesive."
Running lengthwise through the implant is a spring made of nitinol. The latter is a shape-memory alloy that will temporarily stay at one length after being mechanically stretched to that length, but then return to its default shorter length upon being heated to a certain temperature.
The spring is encased within a rectangular elastomer matrix that provides thermal insulation, and which stretches the spring out when it isn't heated. A biocompatible adhesive on the elastomer allows it to stick to underlying muscle tissue.
The idea is that when a patient's arm or leg becomes immobilized – either through injury or a disease such as multiple sclerosis – a MAGENTA gets surgically implanted on a target muscle within the limb.
A separate (but hardwire-connected) microprocessor/battery implant subsequently delivers an electrical current to the MAGENTA on a regular basis, heating the nitinol spring and causing it to contract. As it does so, the muscle (and elastomer) get contracted along with it. When the current is shut off again, the elastomer stretches the spring – and the muscle – back out.
In lab tests, mice had a tiny version of the device implanted on the calf muscle of one hind leg, after which that leg was immobilized in a cast-like apparatus for up to two weeks. The results of the experiments were promising.
"While untreated muscles and muscles treated with the device but not stimulated significantly wasted away during this period, the actively stimulated muscles showed reduced muscle wasting," said Dr. Sungmin Nam, first author of a paper on the research. "Our approach could also promote the recovery of muscle mass that already had been lost over a three-week period of immobilization, and induce the activation of the major biochemical mechanotransduction pathways known to elicit protein synthesis and muscle growth."
It was additionally found that instead of having to be hardwired to a power source, the MAGENTA could be wirelessly activated by shining laser light onto it through the overlying skin. Taking this approach currently isn't as effective as heating the spring via an electrical current, but it is hoped that this may change once the technology is further developed.
"While the study provides first proof-of-concept that externally provided stretching and contraction movements can prevent atrophy in an animal model, we think that the device’s core design can be broadly adapted to various disease settings where atrophy is a major issue," said senior author Dr. David Mooney.
The paper was recently published in the journal Nature Materials.