[tt] How bones can be tailor-made

[Arlind Boshnjaku]

http://www.guardian.co.uk/technology/2008/jun/12/8

New software will enable surgeons to create
made-to-measure titanium bone replacements within
hours. 
Mark Zakian reports
The Guardian, Thursday June 12 2008 


The idea of having an irreparably damaged bone
scanned, a titanium copy created in a replicator and
then surgically inserted into our bodies seems more
Star Trek science fiction than modern-day medicine.
But advances in three-dimensional printing and a key
piece of breakthrough software mean that, within a
year, this will be a reality.

It's the vision of engineer Siavash Mahdavi. Mahdavi
was studying robotics at University College London.
Frustrated at being unable to build the robots he
envisioned in his head, he turned to sintering - where
thin layers of powder are laid down in a chamber, then
turned into a three-dimensional object by a laser.

Do the maths

Mahdavi started sintering the materials he needed, but
faced the problem of working out the appropriate
internal structure for these objects. He knew that,
given all the variables, it would take a computer a
lifetime to do the maths. So he designed an artificial
intelligence optimisation engine to develop software
that could do the calculations quickly. In 2005 he
started Complex Matters, a design consultancy that
works with designers and engineers who want to use
this method to make items that exploit the potential
of the software.

Mahdavi's microstructure optimisation software has
arrived at a time when sintering is developing from a
technology for creating rapid prototypes to a fully
fledged manufacturing process. In the past six months,
machines capable of printing in high-quality titanium
have been developed.

One of the first practical applications of the new
sintering software will be to create made-to-measure
orthopaedic implants. "Imagine a hip-bone
replacement," says Mahdavi. "A surgeon will have the
existing bone MRI scanned. This information is passed
via a CAD programme to the 3D printer. By the time the
patient gets to the operating theatre, we will have
printed out a medical-grade titanium bone which is an
identical match to the one being replaced."

But can we be sure they will be as reliable as
existing implants? "Better," insists Mahdavi.
"Firstly, they are much lighter as, like human bone,
they are porous rather than solid. And having an
internal mesh means you can fuse the implant to the
bone, so the natural bone will grow into the holes and
lock itself in. Because it's a porous structure, you
can x-ray the implant and see how the natural bone is
melding with the implant. And, though these
e-manufactured implants are only a quarter of the
weight of solid ones, the laser makes a finer material
than cast metal - so is it is actually stronger than
the current technology."

E-manufacturing implants could have a surprising
number of benefits for the health service. "Firstly
the sintering is cheaper than both custom-made and
off-the-peg prostheses,' says Mahdavi. "It is better
for the environment, as the laser only fuses the
powdered metal that you need; the rest can be
recycled. It should be particularly helpful in
complicated surgical cases, where an expensive
custom-built orthopaedic implant, which currently
takes three weeks to prepare, could be replaced by a
cheaper one made in two hours."

Joint effort

Tanbir Hossain, an orthopaedic surgeon at Heatherwood
and Wexham Park Hospitals 

NHS Trust, is collaborating with Mahdavi on the
development of sintered implants. He is optimistic
that this new technology will offer significant
improvements for patients. "The problems with the
current hip and knee replacements is that, over time,
the contact between the bone and the implant loosens
and the joint wears, due to a less-than-perfect fit.
This can mean further surgery. With the sintering
technology, the bespoke implant will be more securely
attached to the human bone and the custom fitting
should suffer less wear. This would result in fewer
surgical revisions."

"We are also working on sintered titanium spinal
implants," says Hossain. "The first of these should be
used in surgery in January 2009.

"In the long term, 3D printing could replace
traditional implants completely. It can be used for
any bone in the body. The great thing about this
technology is that allows the precise design of
bespoke pieces. So if someone needs a custom-made
prosthetic implant this is a very good solution."

Mahdavi hopes that the bureaucracy of the National
Health Service will move quickly to adopt this new
technology, which has the potential to save the NHS
millions of pounds every year, as well as improving
the outcome for patients.