Interview with D. Eng. Benjamin Schöps, Managing Director, femtos GmbH
Ever-smaller medical devices with fine structures also necessitate ever more precise production processes. Lasers are used when mechanical machining processes are not precise enough. And manufacturers can cut sharply with ultrashort pulse lasers where conventional lasers are too inaccurate.
At COMPAMED-tradefair.com, D. Eng. Benjamin Schöps talks about the difference between ultrashort and conventional laser pulses, what this means for stent production and the trends in laser use in medical technology manufacturing.
Dr. Schöps, what are so-called ultrashort pulsed lasers?
D. Eng. Benjamin Schöps: Generally speaking, these are pulse lasers with pulse durations in the pico- and femtosecond range. However, on closer inspection, this also depends on the material: the laser pulse needs to be shorter than the response time of the material for the energy transition from electron system to the grid. This is subsequently an ultrashort pulsed laser.
What is the difference compared to continuous laser?
Schöps: Long pulse lasers or cw lasers (continuous wave) can fuse and cut materials. The molten material is subsequently removed from the kerf with process gas. However, the material absorbs a lot of heat energy because the laser dwell time is very long. It is damaged by the heat and this damaged material needs to later be removed. Ultrashort pulsed lasers introduce less and ideally no heat energy into the material.
Where is this process being applied in medical technology manufacturing?
Schöps: This area, in particular, requires very small structures and many components also need an excellent surface quality. The prime example of this are neurovascular stents, but coronary artery stents are also increasingly getting smaller; that is to say, they exhibit reduced strut widths and smaller cross sections. The smaller the structures, the better adapted and specific the laser process needs to become.
What dimensions are we actually talking about here?
Schöps: We are currently working on struts that are 60 micrometers in width. These can also still be produced conventionally. Strut widths of 30 micrometers at a wall thickness of 120 micrometers, however, render a conventional process impossible.
What limitations are there for working with ultrashort pulse lasers?
Schöps: When the wall thickness of the material that needs to be processed is too thick. At this point, one loses the advantages of the femtosecond lasers and this process is no longer justified because it is more expensive than machining with laser pulses in the nanosecond range. Yet I believe this will be secondary if femtosecond lasers become cheaper in the future. The way I see it, the femtosecond laser will become the standard in medical technology manufacturing ten years from now.
The pure cutting process with the femtosecond laser takes up to four times as long as with conventional laser cutting. In turn, there are no rework steps required to remove the damaged material.
What future applications do you see?
Schöps: The trend toward ever smaller structures will continue. At the same time, the ultrashort laser pulses also facilitate processing of the surface because the thickness of removed matter can be well controlled. I am thinking about surface structuring to influence friction and wetting properties for example.