Laser Drilling Catheters
Laser Drilling holes in single or multi-lumen catheters:
Catheter Drilling Systems are used to drill holes in single or multilumen catheters. The catheter is held by pneumatically-controlled collets and rotated about its circumferential axis by single or dual direct drive rotary stages. The catheter is fed by indexers that incorporate a novel "push-pull" mechanism to direct the catheter to its proper position and orientation. Or the catheter can be held in a vacuum v-groove assembly to support multi-meter length catheters. The catheter tooling fixture is mounted on a XY motion stage with sub micron resolution to give three degrees of freedom (X, Y and theta.)
The laser beam is directed by turning mirrors so that the beam is perpendicular to the longitudinal axis. Depending upon the application, an excimer laser or diode-pumped solid-state laser (DPSS) operating in the deep UV wavelength (193nm, 248nm, 266nm) drill the hole using mask projection, percussion or other direct write techniques.
A mandrel (stainless steel, tungsten or Teflon) is inserted into the central lumen to provide mechanical stability and axis of rotation. For multilumen catheters, mandrels are inserted into the satellite lumens to allow laser drilling of holes through the satellite lumen's outer wall. The mandrel blocks the laser beam from hitting the backside of the satellite lumen.
Hole diameters are typically from 0.001 in. to 0.010 in. with hole diameter tolerances of +/-0.0005 in.. although the optical resolution of the Catheter Drilling systems is much better than 0.0005 in. (more like 0.0001 in.), the material interaction dictates the spread of the hole diameter tolerance.
By controlling three axes of motion (X,Y, theta), the hole can be drilled at any location of the catheter, in both the rotational and longitudinal direction.
To help automate the process, the Catheter Drilling system employs machine vision so that the proper lumen can be selected prior to centering and drilling the hole. To aid the automated machine vision, the catheter can be illuminated axially or from the top, bottom or radially - or a combination of illumination schemes.
The proper laser wavelength is chosen (193nm, 248nm, 266nm, 355nm, femtosecond at 800nm) to ensure excellent hole quality. It is standard practice of every hole having no debris, hanging chads or discoloration that may affect the efficacy of the drilled catheter. In many catheter drilling applications, uniform flow from the proximal to distal end is paramount, necessitating consistently and repeatable hole quality.
Process capability, coupled with In-situ metrology or automated metrology equipment help the quality engineer select the correct quality assurance plan to ensure product is within specifications. For every process, the CpK and standard deviation of critical parameters are recorded and tracked for customer review.
The laser-drilled hole is also used as a conduit for a variety of cardiovascular, peripheral and neurological applications including providing a conduit for drug or saline solution to flow to the lesion. The laser-drilled hole is also used as a conduit for electrical wires for electrophysiology or cardiac rhythm management devices.
Laser Skiving of Catheters
Laser skiving is similar to laser drilling except the machined feature is generally oval not circular and the machining dimensions can be much larger (typically up to 0.5" in length). Skiving is defined as the operation of paring or slicing thin layers of the catheter. The laser replaces the scapel as the instrument to micromachine the catheter.
http://www.resonetics.com/skiving.htm
The oval feature can be machined through the outer wall of the catheter or it can be etched to a specific depth without breaking through the outer wall of the lumen.
Laser skiving is performed on the Catheter Drilling System. In the case of using an excimer laser in a mask projection method, the mask is oval in shape. If a direct write process is used with a Diode-pumped Solid State laser (DPSS), then galvanometers deflect the beam position to follow the outside contour of the skived feature. Laser-skived catheters provide a conduit for electrical wires, drugs or blood for cardiovascular, peripheral, cardiac rhythm management, neuro-stimulation, and diabetes management, among others.
Laser Notching of Catheters
Laser notching is performed on the Catheter Drilling System. Unlike drilling or skiving, a rectangular laser beam is imaged onto the outer diameter of the catheter. By utilizing either an excimer laser or diode-pumped solid-state laser (DPSS), the outer diameter of the catheter is etched layer-by-layer (as small as 0.1 micron per laser pulse) to create a notch or window in the catheter. This notch does not break through the outer wall.
Laser notches are used as a platform to support metallic bands, rings, solder or weld forms without the component extending beyond the outer diameter of the catheter.
Laser notches are typically 0.040" (1mm) in length or shorter. The depth of the notch varies but generally the outer wall of the catheter is etched approx. half way. Depth control is very precise as each laser pulse removes a small fraction of materials (as small as 0.1 microns).
Laser Drilling Holes in Angioplasty Balloons
Laser drilling of balloons are performed on polymer stent machines or nine axes systems.
The laser-drilled holes are positioned either on the body or the neck of the balloon. Generally speaking, the balloon is held by an adjustable collet at one end and rotated by a direct drive mechanism. The tooling fixture is mounted on an XY stage to provide three degrees of freedom.
However, unlike laser drilling catheters, balloons may have a non-planar geometry. For example, the neck of the balloon is tapered and is not parallel to the body of the balloon. Therefore the laser beam must be repositioned so that the beam is perpendicular to the neck of the balloon.
The nine axes laser system provides six (6) degrees of freedom (X, Y, theta, Z, yaw and tilt) for the part itself plus three degrees of motion for the mask (X, Y, theta). The versatility and flexibility of the nine axes laser system allows the balloon to be positioned at any angle, ensuring the laser beam to be always perpendicular to the balloon surface, even if the surface geometry is continuously changing in both the radial and longitudinal direction.
Laser-drilled holes in balloons range from 5 microns (0.0002") to 1mm (0.040" in diameter. The hole diameter can be varied from the proximal to distal end by automated mask changers or programmable galvanometer-driven scanners. By utilizing long line optical modules, a large number of rows and holes per row can be drilled at one time to increase throughout and drive down manufacturing costs.
Laser-drilled holes in balloons are used in a variety of drug delivery platforms for cardiovascular, peripheral, ENT, orthopedic and spinal applications.
Laser Drilling Holes in
Embolic Protection Devices
Laser drilling of embolic protection devices utilizes a number of laser micromachining platforms.
Embolic protection devices are filter-based or balloon-based designs. In the former, a large number of holes are drilled to allow blood to flow through the device while capturing the emboli before flowing downstream. The latter blocks the blood flow for a limited time to allow the device to aspirate or remove the emboli.
Drilling a large number of holes in polymer material poses considerable technical issues. As the laser drills more holes, the increased porosity weakens the mechanical integrity of the device Technologies such as glove box systems are used to freeze the material with liquid nitrogen to prevent material from shifting.
For some embolic protection devices, balloon drilling systems such as the nine axes system are used to handle the non-planar geometry. If the geometry varies from part to part, then the system will automatically "map" the surface area, capturing the geometry in 3-D space. Upon completion of the mapping, then the laser system uses the X, Y, Z, theta coordinates to plot the best way to laser drill each hole, keeping the beam perpendicular at all times.
Laser-drilled holes range typically from 5 microns (0.0002") to 200 microns (0.008") in diameter.
Laser Stripping
Laser stripping of plastic insulation from a wire conductor or a metal braid is a classic laser micromachining application. Laser stripping is a selective process. The laser energy density to ablate or remove a polymer insulator is an order magnitude lower than a metal conductor. This means that once the laser beam ablates through the polymer insulator and reaches the underlying metal conductor or braid, the laser beam can continually "hit" the metal layer without any risk of damage. The laser can be tuned to "selectively" remove top layer material without affecting the underlying material.
The laser stripping process removes the polymer insulation layer-by-layer. Each time the laser pulses, a layer as thin as 0.1 micron can be removed.
Laser stripping can be performed as an "end strip" or "mid-span" strip. There is typically a 5 degree taper angle at the transition zone from the insulator to the stripped region.
Typical polymer insulation thickness varies from 0.0002" to 0.040" with the metal conductor or braid thicker than the insulation layer.
Laser Stripping is performed on Laser Stripping Systems which are generally configured with long length optical modules (up to 300mm in length) so that the entire strip length can be machined at one time. The beam is formed as a long thin line where the beam length is the strip length and the beam width is the outer diameter of the wire or mesh assembly. The laser beam is homogenized (guaranteed energy distribution along the entire length of the strip region) to ensure all the organic material is removed, especially at the transition zone between stripped and non-stripped area. Often this transition zone is conical in shape with limited taper. This method offers superior process reliability and consistency than moving a small beam back and forth along the wire length where beam overlap affects the process quality.
The wire can be put on a balloon drilling system where the wire is secured by collets and rotated through the beam. The laser beam can be split by an optical setup so that two (2) beams ablate the wire at 180 degrees orientation. Or the laser beam can be split into three (3) beams so that the angular separation between beams is 120 degrees.
Laser stripping is used in many medical device applications where either an electrical contact is required or the outer jacket needs to be partially removed to provide device flexibility. For high volume applications, the wires are stripped in an automated part handler such as reel-to-reel or reel-to-part. The Laser Stripping system can both strip and cut the wire to length, with in-situ metrology to measure the strip region and wire length.
Applications include Cardiac Rhythm Management leads (pacemakers, ICD, heart failure), electrophysiology ablation devices, embolic protection and guide catheters, among others.
Laser Cutting Bioabsorbable or Polymer Stents
Metal stents represent a significant improvement to combat atherosclerosis, the most common cause of coronary artery blockage. However the implantation of metal-based devices can still result in stent thrombosis and there can be challenges to correctly size the stent inside the artery. The advent of drug-eluting metal stents has reduced restenosis rates but there is evidence of sub acute and late thrombosis
One of the promising technologies to improve in-stenting and to reduce repeat revascularization is the bioabsorbable or polymer stent. Once deployed, the bioabsorbable stent will dissolve back into the bloodstream and leave a healed artery, potentially eliminating late stent thrombosis because the stent is gone.
Laser cutting of bioabsorbable or polymer stents is performed on proprietary Stent Cutting Systems in Class 100,000 clean room(s). Similar to a metal stent cutting system, the polymer tube is held by pneumatic-controlled collets and rotated by direct drive stages in the circumferential direction. The entire tooling is mounted on XY stages to provide three degrees of freedom (X,Y, Theta).
Resonetics provides design guidelines of laser-cut bioabsorbable or polymer stents to help the device engineer. Quality engineers use various metrology tools to help characterize the laser process.
Since the bioabsorbable material is susceptible to moisture and humidity, the raw material is stored in a dry nitrogen box. Precautions are taken during laser cutting to ensure the material is environmentally protected. After laser cutting, the laser-cut bioabsorbable stent is packaged in vacuum-sealed bags with optional desiccant.
Laser Singulation, “kiss” cutting or de-gating
of Polymer-based devices
Laser Cutting, Laser Singulation, “kiss” cutting or de-gating of polymer-based devices is performed on Laser Cutter Systems that deploy diode-pumped solid-stated laser (DPSS) operating at a laser wavelength of 266nm or 355nm.
Traditionally polymer devices are cut into individual devices by dies, mechanical sheers, scalpels or razor blades. The array of polymer devices can be presented in many configurations such as a flexible printed circuit, mold tree, and spun-coated onto a glass substrate. In the case of printed circuits, tight positioning tolerances relative to specific features may require machine vision to singulate the devices precisely. For mold tree, flash or thin polymer webbing may need to be trimmed from the individual device. These flash artifacts will vary from part to part, requiring machine vision to de-gate the devices. If the polymer device is spun-coated on to a glass substrate, then traditional mechanical means will not work as a “Kiss Cut" is required to peel away the polymer device from the underlying substrate.
Lasers are very adapt to perform a “kiss cut” since the laser can be programmed to deliver a prescribed number of pulses to etch through the top layer without damaging the underlying layer. Lasers can be used to not only separate polymer devices from glass but from another adhesive-backed plastic liner. This is common for reel-to-reel applications.
Diode-pumped solid-state lasers operating in the deep UV (ultra-violet spectrum) are suitable laser sources because they are high repetition rate lasers that direct write a small spot (typically as small as 10 to 15 microns in diameter). The laser beam follows the path of the cut out, much like a die cut except there is no tool wear. By operating at laser wavelength of 266nm or 355nm, the polymer devices is “ablated” or vaporized, with little melting or debris resulting from the cut.
The Laser Cutter systems deploy galvos (spinning XY mirrors) to deflect the laser beam at high speeds, using XY motions stages to index the device array. Machine Vision and through-the-lens camera system help to provide both global and individual part alignment.
For certain medical applications involving ETFE, fabric, silicone rubber, laser singulation is accomplished using a CO2 Router System. Unlike the Laser Cutter System that ablates material, the Router deploys a thermal process using a short pulse CO2 laser. The laser liquefies the material and forces the material out the back side using gas assist.
Laser singulation, kiss-cutting or degating of polymer devices is used in a wide variety of applications, ranging from cardiac rhythm management, electrophysiology, diabetes management, medical electronics and bioabsorbable implants, among others.
Laser Texturing of Metal Stents,
Implants or Catheters
A novel application of lasers involves texturing of metals, polymers and ceramics with tiny mesas or sinusoidal patterns to improve a device performance such as surface adhesion, increased contact area, promotion of tissue growth or machining tiny drug/gene reservoirs.
Utilizing a dielectric mask (aluminum deposited on a quartz substrate), an excimer laser can project a complex mesa pattern on to the part. The laser etches away minute portions of material (ie; the material surrounding the mesa), leaving free-standing raised structures that can be a few microns high and few microns square. The cross-section and height of the mesa can be varied by changing the mask or the number of laser pulses.
For every material, there is an ablation threshold which is defined as the energy density (measured in J/cm2) where the material ablates or vaporizes. If a UV laser (excimer or diode-pumped solid-state laser) etches a material at this ablation threshold, then surface modification takes place. This surface modification can result in a “smoother” surface or a “rougher” surface, depending upon the material and fluence.
Laser texturing of medical devices can be found in applications involving coronary stents, dental implants, peripheral arterial disease and orthopedics, among others.
Laser Micromachining 3-D Devices
MEMs and nanotechnology have led to the development of smart implantable medical device technologies that contain both passive and active components. Active sensors and closed loop feedback systems can greatly improve the efficacy of biomedical devices. In the early days, biomedical devices were simply mechanical inventions but today, the proliferation of drug and gene therapy, coupled with sensor technology has resulted in devices migrating into more complex 3-D geometries.
To address this growing market, Resonetics has developed 9 axes laser micromachining technology and software-intensive auto-mapping to permit the laser micromachining of complex, non-planar 3-D polymer-based devices. One of the most difficult technical challenges lies in non-planar geometry where the device is conical or hemispherical in shape, meaning the surface curvature is continuously changing in the axial direction. Moreover the surface curvature or cone angle is not constant so simple fixturing techniques are not applicable.
Prior to machining the 3-D device, the Resonetics 9 axes system will map the geometry with sophisticated pre-processing software-intensive mapping techniques to capture the device in X,Y,Z coordinates. Pre-processing is critical because the geometries of 3-D non-planar devices will vary (OD, cone angle, radius of curvature). By capturing the geometrics, the laser system can use auto focus techniques to adjust the focus on-the-fly to accurately and consistently machine features with micron precision.
In terms of actual machining, the device is mounted on a six (6) axes tooling fixture (x,y,z, theta, yaw and tilt) to allow manipulation in multiple directions. However this is not adequate as sophisticated scanning techniques are required to ensure stitchless, seamless machined features on the non-planar surface. This is accomplished by an additional three axes of motion in the mask plane (X,Y,Theta) where the beam is scanned in an angular fashion. Recall that features of non-planar devices look different in a planar format so angular compensation is required.
