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Publication Number
US-10426645-B2
Publication Date
2019-10-01
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 invention relates to a polymeric stent comprising a polylactic acid tube in which a pattern is cut on the polylactic acid tube using a second harmonic generator laser. A first wavelength of 940 nm to 1,552 nm is converted to a second wavelength of 470 nm to 776 nm during the cutting of the pattern, and the cutting is performed with an ultra-short pulse width and an associated repetition rate for the second harmonic generator laser.
The method maintains quantitative stability of the polymer after the pattern is cut, as represented by a variation in polydispersity index (PDI). The polymeric stent after the pattern is cut exhibits a variation in PDI of 20% or less, where the variation is defined using PDI before the pattern is cut and PDI after the pattern is cut.
The disclosed approach is also supported by the stability of molecular weight, as represented by variation in average molecular weight. Examples describe that cutting using second harmonic generator laser processing provides cleaner cut surfaces and minimizes changes in molecular-weight/PDI compared with comparative processing that uses a third-harmonic approach or no harmonic conversion.
Claims Coverage
The provided claim set includes one independent claim directed to a polymeric stent defined by second harmonic generator wavelength conversion for cutting a pattern on a polylactic acid tube, specified laser pulse width and repetition rate ranges, and limited variation in polydispersity index (PDI) after cutting. Dependent claims further constrain PDI and molecular-weight variation and narrow the wavelength conversion range.
Cutting a pattern on a polylactic acid tube using a second harmonic generator wavelength conversion
A polymeric stent comprising a polylactic acid tube in which a pattern is cut on the polylactic acid tube using a second harmonic generator laser, wherein a first wavelength of 940 nm to 1,552 nm is converted to a second wavelength of 470 nm to 776 nm.
Ultra-short pulse width and repetition rate for the second harmonic generator laser
The pattern is cut using the second harmonic generator laser with a pulse width of the second harmonic generator laser of 1 fs to 900 fs and wherein a repetition rate of the second harmonic generator laser is 2 kHz to 200 kHz.
Limited polydispersity index variation after cutting
The polymeric stent comprises a variation in polydispersity index (PDI), represented by Equation 1, of 20% or less, where A is a polydispersity index of the polymeric stent before the pattern is cut and B is a polydispersity index of the polymeric stent after the pattern is cut.
Post-cut polydispersity index range
The polymeric stent has a polydispersity index of 1 to 2 after the pattern is cut on the polylactic acid tube.
Limited average molecular-weight variation after cutting
The polymeric stent has a 20% or less variation in its average molecular weight, calculated using Equation 2 from the average molecular weight before the pattern is cut and the average molecular weight after the pattern is cut.
Narrowed second harmonic wavelength conversion band
The cut pattern is formed using a second harmonic generator laser that converts 1000 nm to 1,100 nm light to 500 nm to 550 nm light.
Across the independent claim and dependent refinements, the inventive coverage focuses on forming a cut pattern on a polylactic acid tube using a second harmonic generator laser with specified wavelength conversion, pulse width and repetition rate, while limiting changes in polydispersity index and, in dependent claims, limiting variation in average molecular weight and further narrowing the second harmonic wavelength conversion band.
Stated Advantages
Reduced thermal injury, as supported by example descriptions of cleaner SEM cut surfaces and minimized molecular-weight/PDI changes after second harmonic generator laser processing.
Low degradation at the cut surface, as supported by comparative example descriptions versus third-harmonic (343 nm) or no-harmonic conversion that causes heat/photodegradation and markedly increased PDI and molecular-weight variation.
Documented Applications
Forming a polymeric stent by cutting a pattern on a biodegradable polylactic acid tube using a second harmonic generator laser, including optional downstream features such as forming grooves/holes in struts.
Attaching radiomarkers to the stent with PLA molten at 115–240°C, as described as part of optional downstream features.
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