Fractures that involve the
separation of the bone into multiple fragments present a problem to medicine. Butterfly
fractures are hard to treat as a small fragment of bone separated from two larger
sections may suffer from delayed re-union. Whereas intramedullary rods can be used
for other breaks, the small triangular fragment of bone is difficult
to incorporate in a conventional system of artificial support. Accidents that
result in multiple fractures are also hard to treat and cerclage wires are sometimes used to hold bones
together while they re-unite. However problems can arise if these wires break
or interrupt the blood supply to the bone.
Although surgical mesh is
currently used in some surgeries for reconstructive work and hernia repair it
would probably only be useful for fractured bone support if it could be made to
contract. In the electronic manufacturing industries
heat-shrinkable plastic is sometimes used to tightly hold together strands of wire
that need to be secured in a bundle. The recent invention of lightweight and operationally simple maser devices could potentially be used to shrink a surgical mesh by
transmitting radio waves from the outside of the skin to the net of specially formulated plastic. The NPL team have
circumvented the need for complicated masers, formerly requiring high intensity
magnetic fields and cryogenic cooling, with the invention of a solid state
device based on a crystal called doped p-terphenyl.
Crucially, if it were
possible to create a shrinkable plastic which responded to a specific radio
frequency instead of heat, a small zone of radio frequency action created by
overlapping masers of different frequencies could sweep the mesh structure and
cause a peristaltic type of contraction thereby gently squeezing the shattered
fragments of bone together. The effective frequency would be generated by
constructive interference only where the maser beams overlap, and the zone
could be made to move in three dimensions, rather like the scanning of electron
beams used to create a picture in an old fashioned cathode-ray television tube.
The movement of the maser beams would need to be computer controlled. Precise
registration of electron beams was achieved in colour televisions before
digital technology was applied, but the concentration of maser radio energy onto
a variable three dimensional structures would need to be controlled with
software. This process might be helped if the beams switched to a radar sensing mode between
radio illumination phases.
The following images illustrate how a mesh of hypothetical plastic material shrinking in response to radio illumination by masers could help to re-establish the correct positions of bone fragments.
A butterfly fracture results
in a triangle of bone separated from two larger pieces of bone.
The mesh of radio-sensitive
plastic surrounds a butterfly fracture.
The mesh is illuminated with
radio frequencies from masers.
The mesh shrinks and pushes
the bone fragments towards each other.
The mesh is illuminated with
radio waves for a second time.
The mesh arrives at its
smallest size.
The mesh dissolves away after
the bone fragments have successfully re-united.
Clearly the type of heat shrinkable plastic currently available would not be suitable for incorporation into the human body as the temperatures required to cause it to shrink would also produce burning of tissue. The challenge for chemists is therefore to create a shrinkable plastic that will respond to the radio frequencies achieved by the newly re-invented maser. If this hypothetical plastic could also be made to dissolve over time this would obviate the need for subsequent surgery to remove it.
Perhaps the most useful medical application for a radio-sensitive shrinkable plastic mesh could be the correction of spinal disc herniation. If it were possible to insert a shrinkable mesh around the bulging nucleus pulposus and a painfully compressed nerve the shrinking mesh might support the spinal column and reduce the pressure on the trapped nerve. Another potential use for a shrinkable mesh could be the treatment of aortic aneurysm or Marfan syndrome.
Another potential application of shrinkable mesh could include 3D forming in conjunction with 3D printing for industrial purposes.
Another potential application of shrinkable mesh could include 3D forming in conjunction with 3D printing for industrial purposes.
Nature
National Physical Laboratory
John Stockton – June 2013
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