Dr Ferda Canbaz in the laser laboratory at the Department of Biomedical Engineering, University of Basel. Credit: University of Basel, Christian Flierl.

Researchers have demonstrated a way to cut much deeper and faster with a surgical laser than with previous laser systems.

Lasers cut precisely and without contact – ideal for surgery. The problem is that, in hard tissues such as bone, they are too slow and do not cut deep enough.

Researchers at the University of Basel have now demonstrated a way to cut much deeper and faster than previously.

The saw, chisel and drill are tried-and-true tools in bone surgery. In the future, lasers could be added to this toolbox, especially when it comes to very precise cuts.

Lasers do not exert any mechanical pressure, meaning they can reduce the risk of microcracks and enable more specialised cuts.

This would make it easier to insert joint implants, for example, including custom-made, 3D-printed implants.

Lasers are already used for soft tissue. In the case of bone, however, cuts were previously only possible up to a depth of 2 to 3 centimetres, which is far too shallow for joint implants, for example.

One reason for the insufficient cutting performance is the shape of the laser beam. Researchers led by Dr Ferda Canbaz from the Department of Biomedical Engineering at the University of Basel have now reported a breakthrough.

They achieved cuts down to a depth of 4.5cm by using a different profile of the laser beam, i.e. a different distribution of the energy in the beam. This enabled them to remove the bone material more efficiently and faster.

Canbaz said: “Increasing the energy of the laser beam would not be a good solution. This could char the bone and have a negative impact on the healing process.

“That’s why we changed the shape of the laser, or rather its profile.”

Ferda Canbaz demonstrates the depth of cuts that can be achieved with lasers when the energy profile of the laser beam is adjusted. Credit: University of Basel, Catherine Weyer.

More even distribution

With the usual profile, the beam is strongest in the centre and becomes weaker toward the edge. This is similar to the beam of a flashlight, which is brightest in the centre and runs outward.

The intensity resembles a Gaussian curve with a rounded tip in the middle.

In the new profile the tip is capped, enabling the energy of the laser beam to be distributed more evenly across the entire surface before dropping abruptly at the edge, hence the name ‘top hat’.

Doctoral student and first author Mingyi Liu said:  “Because the energy is transmitted more evenly, the laser cuts more efficiently and faster.”

The team tested the two laser profiles on bovine bones. The bone was cleaned and cooled with compressed air and water to prevent heat damage and keep the cut clear.

The trials showed that, while the laser with the usual Gaussian distribution cut only about 2.6cm deep, the one with the new top hat profile reached 4.4cm.

A key factor for cutting efficiency is the fact that with the conventional laser profile, the walls of the cut absorb part of the energy. At a certain depth, the energy at the bottom of the cut is not sufficient to cut any deeper.

The top hat profile overcomes this problem because the energy in the beam is distributed differently and thus isn’t consumed by the walls of the cut.

Compressed air and water are used to keep the cut surfaces on the bovine bone cool and clear. The laser beam itself is not visible. Credit: University of Basel, Catherine Weyer.

Major progress in cutting depth

The researchers are now working on further optimising the cutting depth and speed of their laser.

The laser-blade is still significantly slower than a metal one: in one second, it can remove around 0.4 cubic millimetres, while a mechanical saw can remove 11 cubic millimetres, more than 20 times as much.

This means that the laser is still too slow, but it approaches the required depth for the first time.

Canbaz said: “As part of the next steps, we will also need to investigate how we can adapt the system to the more complex situation in the body. There, it is also about protecting the surrounding tissue.”

The study is published in Scientific Reports.