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Publication Number
US-9510961-B2
Publication Date
2016-12-06
Expiration Date
Abstract
Methods of manufacturing polymeric stents by forming a pattern on a polylactic acid tube using a second harmonic generator laser and polylactic acid polymeric stents having a pattern formed using a second harmonic generator laser.
Core Innovation
The disclosed invention relates to polymeric stents made from a polylactic acid tube by cutting a pattern using a second harmonic generator laser. An initial first laser beam having a first wavelength in the range of 940 to 1,552 nm is passed through a second harmonic generator to create a second laser beam with a second wavelength in the range of 470 to 776 nm, and the polylactic acid tube is contacted with the second laser beam to cut the pattern, thereby generating the polymeric stent.
A pulse width of the second harmonic generator laser is set between 1 fs and 900 fs, and a repetition rate is set between 2 kHz and 200 kHz. The disclosed approach is directed to cutting that yields minimal thermal injury/degradation while limiting changes in polydispersity index and average molecular weight, each variation within 20%. Comparative processing is described in terms of cleaner cuts and substantially reduced changes in number average molecular weight and polydispersity index versus third-harmonic processing and non-SHG processing.
The disclosure further describes integrating additional stent features with the patterned polylactic acid stent while maintaining molecular quality. Examples include forming grooves or holes in struts and attaching a radiomarker, as well as using polylactic acid melt conditions for radiomarker attachment to avoid rapid molecular weight loss. Supporting comparisons use SEM and GPC results to illustrate reduced surface modification and more favorable molecular property retention for SHG-based processing.
Claims Coverage
The independent claim covers a manufacturing method using a first laser beam in a specified near-IR wavelength range, converting it via a second harmonic generator to a second wavelength range, and cutting a pattern on a polylactic acid tube to generate a polymeric stent. The claim includes four core inventive features: SHG wavelength conversion, pattern cutting with the SHG beam, ultra-short pulse width, and limited repetition rate, with additional dependent claims refining wavelengths, laser type, and molecular property retention limits.
Second harmonic generator wavelength conversion for stent cutting
Providing a first laser beam having a first wavelength between 940 nm to 1,552 nm, passing the first laser beam through a second harmonic generator to create a second harmonic generator laser having a second laser beam with a second wavelength between 470 nm to 776 nm.
Contacting the polylactic acid tube with the SHG laser to cut a pattern
Contacting a polylactic acid tube with the second laser beam to cut a pattern on the polylactic acid tube, thereby generating the polymeric stent.
Ultra-short pulse width of the SHG laser
A pulse width of the second harmonic generator laser is 1 fs to 900 fs.
Controlled repetition rate of the SHG laser
A repetition rate of the second harmonic generator laser is 2 kHz to 200 kHz.
Maintaining molecular property variation within 20% using PDI
A variation in polydispersity index between a polylactic acid tube before pattern cutting and a polymeric stent after pattern cutting is 20% or less, as defined by Equation 1.
Groove or hole formation in struts with radiomarker attachment
Forming a groove or a hole in a polymeric stent strut on which a pattern is cut, and affixing a radiomarker to the groove or the hole.
Overall, the claims define manufacturing a polymeric stent by SHG-converting a near-IR first laser beam to a specified second wavelength and using the second harmonic beam to cut a pattern on a polylactic acid tube, with the second harmonic laser limited to an ultra-short pulse width and a controlled repetition rate. Dependent claims further narrow wavelength ranges and laser types, impose a PDI variation constraint of 20% or less, and add groove or hole strut structures with radiomarker attachment.
Stated Advantages
Minimal thermal injury/degradation.
Limiting changes in polydispersity index to a variation of 20% or less.
Limiting changes in average molecular weight to a variation of 20% or less.
Cleaner cuts and reduced surface modification compared with third-harmonic or non-SHG processing.
Lower changes in number average molecular weight and polydispersity index for SHG-based processing compared with comparative examples.
Documented Applications
Manufacturing a polymeric polylactic acid stent by cutting a pattern on a polylactic acid tube using an SHG laser.
Forming additional stent features by making a groove or a hole in a polymeric stent strut on which a pattern is cut and affixing a radiomarker to the groove or the hole.
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