Introduction

Laser Micro Manufacturing Technologies and its Impact on Medical Device Manufacturing
Laser micro manufacturing is a compilation of technologies developed to address an ever increasing demand for micro-scale manufacturing in the Medical Device and Advanced Diagnostics Markets. These technologies include laser ablation, laser cutting, laser drilling, and laser welding.

Each technology addresses a common medical device manufacturers’ need to fabricate microscale medical devices in metals or polymers. The advantage of using a laser over traditional mechanical processes includes no part contact, ability for micron scale features and minimal heat-input. These combined advantages are enabling miniaturization to occur across multiple medical device applications with a direct path from prototyping to production.

This article provides details on laser micro manufacturing technologies and applying them to medical devices.

Laser Ablation

Laser ablation is a method of selectively removing material resulting in micron scale features on micro or macro scale metal or polymer components. The material is selectively removed via vaporization resulting from the exposure to a focused laser beam as shown in figure 1. Resonetics employs a variety of laser tools including CO2 diode-pumped solid-state, excimer and ultrafast (picosecond and femtosecond) lasers.

Laser ablation has been a beneficial process for advanced micro manufacturing of medical device applications because it offers a wide range of material compatibility resulting in a diverse scale of products.

Laser Ablation for Medical Devices

Laser ablation continues to gain popularity and demand as R&D engineers understand its benefits in miniaturization of devices.

Example medical device applications:

• Fine wire coating removal
• Single and multi-lumen catheter tip shaping and outside diameter removal
• Balloon surface texturing
• Micro implants
• Micro instruments

Unique Applications

3-D Laser Ablation

As laser ablation technology enables new advancements in the medical device industry, new applications are materializing that push the boundaries of micro manufacturing.

One example is 3-D ablation, which was a process developed to support unmet customer needs in the neurovascular market.

Challenge
A customer required a metal part that was ten times smaller than a Swiss CNC machining process could provide.

Solution

Resonetics developed a micro-scale ablation technique that enabled this neurovascular application through a combination of advanced ultrafast laser technology, motion control and custom software. This technology proved versatile enough to serve additional applications in the ophthalmic and cardiovascular markets.

See figures 2 and 3 for application examples of 3-D ablation.

Wire Stripping

Another unique application of laser ablation is laser wire stripping. This process involves the removal of the outer coating to expose the underlaying layer or the core metal wire.

Challenge
In figure 4, we show cross- sections of an ideal multi-layer coated wire (I) and a real wire with (exaggerated) non-concentricity issues (II). The coating layers are thicker in some locations and thinner in other locations around the wire. If we laser strip the wire in an open-loop process (i.e. delivering the same number of pulses at all rotational locations), then the end result is an uneven, non- uniformly stripped wire with remaining coating layers as well as a possibility of core wire damage at some rotational locations (III, IV).

Solution
To ensure 100% removal of each coating layer and to minimize undesired incursion into the next layer, Resonetics developed and patented a unique closed-loop process control called ASSURE End Point Detection™. By monitoring the plasma plume at the ablation point, whose signature discriminates between materials of subsequent layers and detects presence and type of remaining material, the laser can turn on and off to avoid going too deep in the thinner sections of the wire coating or removing too little in the thicker sections (V, VI).

The major benefit of ASSURE End Point Detection™ is that coated wires can be stripped uniformly and consistently, independent of the inevitable variation of the wire coating from lot to lot or even within the same spool.

Laser Cutting

Laser cutting uses a focused laser beam to melt or ablate material which is removed via a coaxial gas nozzle as shown in figure 5. This process is well-established and used extensively in the manufacturing of medical devices.

Laser cutting typically uses a Nd:YAG or fiber laser. In addition to Resonetics using these lasers, they have also developed ultrafast (picosecond and femtosecond) laser cutting to eliminate heat input which minimizes downstream part processing.

Ultrafast laser cutting can be used for various types of metals and polymers with benefits including; no heat affected zone, clean cut edges and no burrs.

See figures 6 and 7 for application examples of laser cutting.

Example Medical Device Applications:

• Thin walled stents
• Delivery system components
• Pull rings
• Bioresorbable scaffolds

Innovative Cutting Processes

Applications and Advancements for the Medical Device Industry

Resonetics has combined advances in laser and motion control to develop a cost-effective tool for high-volume manufacturing catheter components. This high-speed laser cutting process is called PRIME™ Laser Cut.

The laser cut hypotubes (LCT) from the PRIME™ process have many advantages over traditional catheter manufacturing methods (such as braided coil construction). Below are key benefits of PRIME™ Laser Cut LCT catheter components:

Customization: a key benefit of LCT over traditional catheter construction is the ability to completely customize the part geometry to match the clinical demands of the catheter. For example, if you are designing a catheter with significant stiffness on the proximal end but require uniaxial flexibility on the distal end this can be difficult to achieve with a traditional braiding/coiling technique.

Torque Transfer: LCT typically employs interrupted cutting which enables flexibility but maintains a monolithic connection from proximal to distal ends of the catheter. This direct connection ensures a good torque response when functioning the device in-vivo.

Kink Resistance: an additional advantage of the monolithic aspect is optimized kink resistance. As devices become more flexible they inherently have a higher risk of kinking upon insertion/propagation through the anatomy. The PRIME™ process enables the design of flexibility and optimization of kink resistance without sacrificing functionality.

Ovality: a challenge with braided/coiled catheters is flattening or ovality as they move through difficult anatomy. Since LCT is monolithic it does not collapse as it propagates tortuous anatomy. This is critical when passing additional devices through the inner diameter of the catheter.

Low Profile: LCT based catheters can start with a relatively thin-wall tube (down to <0.0005″) while maintaining the strength requirements of the catheter. Again the monolithic benefits of LCT enable a reduced wall thickness of the catheter which opens up space for larger devices passing through the inner diameter.

Nitinol Cutting

Resonetics has also developed advances in nitinol cutting using ultrafast laser technology. Nitinol is used extensively for the fabrication of catheter components and implants and is sensitive to thermal heat input. Figure 9 below shows an ultrafast laser cut nitinol part. Beyond the elimination of heat input, ultrafast laser cutting also provides a part that is closer to near net shape which minimizes the downstream requirement for electropolishing.

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