A LIGHTWEIGHT foam designed for protecting radio antennas on F-18 fighter
jets is also being developed to do something entirely different: mend broken
bones. Strong and sturdy enough to replace bone, the foam might be able to
actively help healing by attracting bone-forming cells, its developers say.
Orthopaedic surgeons need bone-like materials to replace bone destroyed by
disease or injury. Grafts from other parts of the body are not necessarily
suitable, because they don鈥檛 always match the needs of the bone being replaced,
and titanium implants lack the elasticity of bone and can be dislodged. The
ideal implant is a scaffold on which bone-forming cells can settle and
grow鈥攂ut many of today鈥檚 scaffold materials are not strong enough for the
task.
快猫短视频s at Boeing鈥檚 Phantom Works in La Mesa, California, had none of
these concerns in mind when they invented the aerospace foam. They were after a
material that could be used to surround aircraft antennas and protect them from
damage without disrupting the signals they receive. The final foam was a
solidified mixture of hollow silica spheres, each 90-micrometres in diameter.
These 鈥渕icro-balloons鈥� were glued together using a polymer, allowing air to
permeate the spaces between the spheres.
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The Boeing scientists found that adjusting the ratios of microballoons to
polymer made a big difference to the strength, density and porosity of the foam.
And one recipe closely matched the properties of natural bone. They were able to
implant the foam into rabbits鈥� bones without it being rejected. Even better,
when they removed the implants they found that new bone cells and blood vessels
had grown in the foam鈥檚 airy spaces.
Bone cells use electrical signals to communicate, and one known method of
attracting bone-forming cells is to apply an electric field. The same property
that lets electromagnetic signals flow unimpeded through the foam may allow
electrical signals from existing bone cells to recruit bone-forming cells into
the foam.
Only when heated to about 350 掳C can the foam be moulded into shapes. 鈥淪o
you won鈥檛 get into a hot tub and have your leg melt,鈥� Charles Cruit, a Boeing
technology manager, assured 快猫短视频.
The University of Pennsylvania is now developing Boeing鈥檚 biofoam in
collaboration with orthopaedic surgeon Carl Brighton, who has pioneered the use
of electrical stimulation to promote bone growth. 鈥淭his foam could provide a
longer lasting implant or work as a transitional interface between the bone and
implant,鈥� says Thomas Fitzsimons, a member of the Pennsylvania team.