Laser microfabrication of L605 cobalt-chromium cardiovascular stent implants with modulated pulsed Nd:YAG laser

Abstract

Photonics modulation techniques can be effectively used for the laser microfabrication of biomedical implants to achieve better flexibility and control of the available optical power. These enable the processing and manufacturing of biomedical implants like cardiovascular stents and micro-metallic components with reduced heat affected zone ͑HAZ͒ and extremely precise edge cutting. Our investigation deals with the study of acousto-optic modulation of a pulsed Nd:YAG laser beam and further profile cutting of thin cobalt-chromium tubes for cardiovascular stent manufacturing. The acousto-optic modulator used in the investigations is a Bragg diffraction device. During one piercing process, the focused laser power is gradually varied from a low value and reaches the maximum as the beam goes deeper into the material. The optimum value for dwell time during which the laser piercing is occurring is found as 58 ms. A 14-step staircase modulating voltage with a maximum AC component of 900 mV was used, and the laser power was 4.4 W in TEM 00 operation. Pulsed Nd:YAG laser modulated using an acoustooptic device in the Bragg regime is capable of cutting extremely complex geometries of stents on L605 tubing. Laser cutting resulted in a kerf width of 22.5± 0.5 m. Precise strut dimensions of 112± 15 m for the subsidiary strut, 140± 15 m for the main strut, and 140± 15 m for the link were also obtained. Scanning electron microscopy ͑SEM͒ images of L605 stents illustrate the higher strength Co-Cr alloy L605 with the same ductility, its ability to be translated into thinner struts, and improved deliverability. L605 also exhibits enhanced radio visibility thanks to its tungsten content and exceptional work hardening rate for a uniform expansion with minimal recoil.

Micro-scale testing and micromechanical modelling for high cycle fatigue of CoCr stent material

“…2100 passes at a rate of 0.5 m/s were completed for each specimen using a final wavelength of 343 nm and beam power, repetition rate and pulse energy of 5.6-5.7 W, 200 Hz and 120 µJ, respectively. Electro-polishing (EP) is required to remove the heat-affected zone and any surface oxides created during laser-cutting, and to provide a smooth surface A number of studies have looked at the electro-polishing of L605 for stent applications, reporting the use of various EP solutions, including a hydrofluoric and nitric acid solution [31], phosphoric acid of different concentrations [32], a perchloric and acetic acid solution [33] and a sulfuric and phosphoric acid solution [34]. Various optimal temperatures, EP times and current-voltage settings have also been reported.…”

“…Various optimal temperatures, EP times and current-voltage settings have also been reported. Three studies report polishing temperatures of around 55 0 C [31,33,34], while another reports more uniform EP rates at 0 0 C [32]. An EP approach based on the work of Kaufmann et al [34] is adopted here.…”

Micro Cutting of Biliary Stent with Nanosecond Fiber Laser System

“…Covered self-expanding metal stents have proven effective for managing malignant bile duct strictures and may reduce risk of tumor ingrowth [4]. Sudheer [5] demonstrated the fabrication of cobalt-chromium cardiovascular stent by modulated pulsed Nd:YAG laser and he intended to use it to improve the cutting quality and reduce heat-affected zone (HAZ). Besides, Kleine [6] described long pulse laser were associated with larger HAZ and more recast layer.…”

The Influences of Assisting Gas Type and Process Parameters on the Fiber Laser Microprofiling of Thin CoCr Tubes for Vascular Stents

“…Embrittlement in the HAZ can lead to microcracks and shorten a stent's fatigue life, as described by Miller et al [6]. Sudheer et al [7] …”