News Column

Researchers Submit Patent Application, "Mounting Stents on Stent Delivery Systems", for Approval

September 11, 2014



By a News Reporter-Staff News Editor at Computer Weekly News -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventor Van Sciver, Jason (Los Gatos, CA), filed on April 30, 2014, was made available online on August 28, 2014.

The patent's assignee is Abbott Cardiovascular Systems Inc.

News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to drug-eluting medical devices; more particularly, this invention relates to systems, apparatus and methods for mounting to a delivery balloon a balloon-expandable stent, such as a polymeric stent.

"FIGS. 1A and 1B depict perspective views of a prior art crimping station used to crimp a balloon expandable stent to a deployment balloon of a balloon catheter. The crimping station includes a crimper head 220, an interactive screen 216 for programming a crimping sequence, e.g., diameter reduction, dwell times between successive crimps, temperature control of the crimper jaws, etc. A carriage 242 aligns a catheter 209 with the opening 222 to the crimper head 220 and advances the distal end 209b of the catheter, where a stent 100 and the balloon are located, into the crimper head 220. The crimper head 220 includes three rollers 223, 224 and 225, which place a clean sheet of non-stick polymer material between the crimper jaws and stent 100 to avoid buildup of coating material on the jaws when plural stents having drug-polymer coatings are being crimped to balloon catheters.

"FIG. 1B shows a perspective view of the carriage 242, which includes a slidable block 250 holding catheter 209. The block 250 is used to advance the catheter distal end 209b and stent 100 into and out of the crimper head 220 using knob 274. The catheter 209 is held within a groove 252 formed on the block 250. The catheter 209 shaft is retained in the groove 252 by a pair of cylindrical rods 253, 254 which are rotated down to trap the catheter shaft in the groove 252 before it is advanced into the crimper head 220 via the opening 222. The rods 253, 254 are rotated from the closed position (as shown) to an open position to allow the catheter 209 to be removed from the groove 252 by rotating hinge arms 253a, 254a clockwise (as indicated by A, B). A handle 255 is connected to the hinge arms 253a, 254a and rotated in direction C to move the hinge arms 253a, 254a to the open position. A rail 273 is connected to the block 250 at block extension 250a. The block 250 is displaceable over a distance 'S'. An operator manually moves the distal end 209b and stent 100 towards or away from the crimper head 220 using the knob 274. The rail 273 is received within, and slides over a passage of a support 272, which is mounted to the table of the crimper station. The block 250 is received within, and slides along grooves (not shown) of a support piece 260. An abutment 275 of the support piece 260 serves as a stop to indicate when the catheter distal end 209b is positioned properly within the crimper head 220.

"In operation, the operator manually places the catheter 209 within the groove 252 and holds it in place by rotating the handle clockwise to position the rods 253, 254 into the position shown in FIG. 1B. The operator then manually places the stent 100 over the balloon. Prior to inserting the distal end 209b within the crimper head 220, the operator must ensure that the stent is properly positioned on the balloon, i.e., the operator must ensure that the stent is located between marker bands of the balloon before placing the stent within the crimper head 220, so that when the balloon is inflated, the stent will expand properly within a patient's vasculature. the stent and balloon are then advanced into the crimper head by push the carriage forward until block 250 strikes or abuts the stop 275. When the block 250 hits the stop 275 the stent and balloon are in the desired position within the crimper head.

"Preparing a stent-catheter assembly utilizing equipment such as that described above, and/or production techniques whereby operators dedicated to manually loading a stent on a balloon and ensuring the assembly is positioned/aligned properly so that the stent is properly crimped to the crimping head, is burdensome. In the case of high volume polymer stent--catheter assembly production there can be significantly more time spent properly crimping a polymer stent compared to a metal stent. Moreover, existing procedures for placing and aligning a stent, just prior to crimping has become more problematic and time-consuming as the lengths of deployment balloons have been shortened to about the length of a stent. Since the balloon length is matched more closely to the length of the stent (for purposes of avoiding damage to vascular tissue when the stent is deployed within a body) there is less margin for error by the operator. Given the small sizes for stents and balloons, great care must therefore be exercised by the operator to ensure that the stent is properly located on the balloon before crimping. If the stent is not properly positioned on the balloon before crimping, both the stent and catheter must the discarded.

"The art recognizes a variety of factors that affect a polymeric stent's ability to retain its structural integrity when subjected to external loadings, such as crimping and balloon expansion forces. These interactions are complex and the mechanisms of action not fully understand. According to the art, characteristics differentiating a polymeric, bio-absorbable stent of the type expanded to a deployed state by plastic deformation from a similarly functioning metal stent are many and significant. These and related challenges faced in the manufacture and crimping of polymer stents to balloons are discussed in U.S. application Ser. Nos. 12/776,317 (attorney docket no. 62571.398) and 12/772,116 (attorney docket no. 62571.399).

"One aspect of polymer stents, as compared to metal stents, that has presented certain challenges is the procedures required to ensure an acceptable yield when crimping large numbers of polymer stents to balloon catheters, as explained in more detail in applications U.S. application Ser. Nos. 12/776,317 (attorney docket no. 62571.398) and 12/772,116 (attorney docket no. 62571.399), as well as improving efficiency in crimping large numbers of polymer stents to balloons so that production-level polymer stent crimping does not impose unacceptable delays in the manufacturing process. The operation of crimping devices are time consuming when being used to crimp polymer stents and current production yields are less than favorable.

"In view of the foregoing, there is a need to improve upon existing crimping processes, such as in the case of crimping polymer stents to balloon catheters."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventor's summary information for this patent application: "The invention provides an apparatus, system and process for crimping a stent to a balloon catheter. According to one aspect of the disclosure, a stent mounting system includes a crimper head and a pair of stations, located on opposite sides of the crimper head, for positioning first and second stent and catheter assemblies and aligning the first and second stents on their respective balloon catheters prior to crimping the stents to the balloons. The crimper head is adapted for receiving the stent and catheter assemblies from both stations to perform a crimping process at the same time. The system incorporates computer-controlled processes for reducing much of the labor typically required by an operator, e.g., a technician, when preparing a stent and catheter for crimping and monitoring the crimping process. Automated, computer-controlled processes replacing manual pre-crimping processes can increase yield, since there is less likelihood that a stent and catheter will be improperly located within the crimper head, which can result in uneven crimping over the length of a stent, or a stent not properly aligned with a balloon markers prior to crimping. By using automated, computer-controlled process the time required for crimping can be reduced, and production yields increased. Moreover, more operator time is made available, so that multiple crimping sequences can be monitored by the same operator.

"These and other advantages of the invention are particularly worth noting when polymer stents are crimped. In contrast to a metal stent, a polymer stent must be crimped at a much slower rate due to the inherent limitations of the material compared at that of a metal. This slower process can produce significant bottlenecks during stent-catheter production. By automating manual crimping tasks, the overall time needed to crimp a polymer stent can be noticeably reduced. Polymer stents are more sensitive to fracture when crimping produces irregular bending or twisting of struts, since a polymer material suitable for a load-bearing stent, e.g., PLLA, is far more brittle than a metal. Inaccurate crimping within the crimper head, e.g., non-uniform applied forces through the crimper jaws when the stent and catheter are not properly located, or positioned within the crimper head, is therefore more likely to cause fracture in polymer stent struts. Accuracy and repeatability in the crimping process is therefore more critical to increased yield for a polymer stent than a metal stent. According to one aspect of the invention, there is a discovered need for more automation in a crimping process for polymer stents, whereas there is less need for automation when crimping metal stents. A crimping sequence for a polymer stent can be about five times longer than a metal stent. This 5-fold increase in crimping time, when multiplied out by the number of polymer stent-balloon assemblies crimped during a production run, poses unique challenges in planning and resource allocation, which is contrast to the time and resource allocation needed for crimping metal stents. A primary reason for the delay is the need to crimp the polymer material more slowly to reduce instances of crack creation or propagation, and to reduce recoil when the crimping jaws are removed from the stent surface.

"Existing systems for crimping a stent to a balloon require an operator to both manually align stents between balloon markers, properly insert the stent and balloon assembly within a crimper head and then verify that the stent is being properly crimped in mid-process. The invention substantially overcomes many of the drawbacks of requiring an operator to perform these tasks by introducing automated processes for positioning and aligning a stent and catheter for crimping.

"According to the disclosure, the system may be configured to automate the following manual tasks:

"Manually positioning a catheter distal end at the entrance of the aperture and then manually advancing the stent and catheter within the crimper head. According to one aspect of the invention, a computer automatically advances the stent and catheter into the crimper head after an operator has verified, e.g., by a laser light identifying the proper location of the catheter's proximal balloon seal relative to a reference point, that the catheter has been properly placed within a carriage that advances the catheter and stent into the crimper head under computer control. A laser positioning system or a camera may be used to locate the proper placement of the catheter relative to the carriage, as well as to signal to a processor controlling the carriage motion forward into the crimper head that the stent-catheter as been positioned properly within the crimper head, once this signal is received, an actuator advances the stent-catheter assembly into the crimper head. The device illustrated in FIGS. 1A-1B, by contrast, utilizes a mechanical stop 275 to indicate to the operator that the stent-catheter assembly is located properly within the crimper head. However, it has been discovered that this manner of positioning the stent-catheter assembly within the crimper head can cause the stent to displace relative to the balloon, thereby throwing the stent out of alignment. The invention recognizes that a mechanical stop, even when found suitable for positioning a metal stent within a crimper head, introduces problems for polymer stents, particularly when the polymer stent has a much larger diameter than the balloon. As a solution to this problem, a servo mechanism is used to advance the stent-catheter assembly into the crimper head at a rate which reduces the chance that the stent will move relative to the balloon.

"Manually aligning the stent between balloon markers. According to one aspect of the invention, an imaging system is used to image the stent and catheter and then determine, e.g., by pattern recognition software, whether the stent is properly aligned. If the stent is not properly aligned, the stent position relative to balloon markers is adjusted using computer-controlled actuators. The actuators may be controlled by servo mechanisms driven by a processor, which processor may utilize a camera or laser alignment system and may incorporate controller logic with or without a feedback loop during the adjustment.

"Manual inspection of the stent on the balloon after an initial, or pre-crimp, to ensure that the stent has not shifted relative to the balloon markers within the crimper. If the stent has shifted, then the operator manually adjusts the stent before placing the stent and catheter back into the crimper. According to another aspect of the invention, the crimping process is under computer control after the stent-catheter assembly is loaded onto a carriage and the operator activates the process. The stent-catheter assembly is placed in the crimper head, a pre-crimp is performed, then the stent-catheter are withdrawn from the crimper head. The imaging system is then activated to verify that the stent is aligned with the balloon markers. After verifying that the stent is between the balloon markers, the stent-catheter assembly is advanced again into the crimper head to perform the final crimp. No operator involvement is necessary.

"Performing the above manual processes, one after another, for a first stent, then a second stent after the first stent has been crimped to a balloon. According to another aspect of the invention, a crimper head is provided for simultaneously crimping first and second stent and catheter assemblies in one crimping sequence. Hence, the automated positioning, aligning, and verification after pre-crimp steps described above can be performed concurrently for two stent and catheter assemblies.

"The invention addresses the need to improve alignment processes for stent-catheter assemblies that demand tighter alignment tolerances. Short balloon tapers and shorter marker bands drive more precise stent positioning. Precise position correction of the stent is difficult to perform manually by an operator and requires special training. Manually positioning can result in stent, coating and/or balloon damage if not done correctly. This positioning task is made more difficult when the stent is manufactured to have a deployed or over-deployed diameter (a large starting diameter is chosen to provide improved mechanical characteristics when the stent is expanded to its deployed diameter). The relatively large annular gap between the stent and folded balloon presents significant positioning challenges.

"Consistent with these objectives and in view of the foregoing problems and/or needs in the art addressed/met by the invention, the invention provides, in one aspect, a crimper head, a first station and a second station disposed adjacent the crimper head and configured to receive, respectively, a first stent and a first balloon catheter assembly and a second stent and a second balloon catheter assembly, the first station and the second station each include an aligning portion and a positioning portion, and a processor for simultaneously crimping both the first stent to the first balloon catheter and the second stent to the second balloon catheter using the crimper head. When a user command, e.g., start crimping sequence, is received by the processor, the processor, e.g., a local computer, causes (a) the first station to align the first stent with the first balloon catheter and the second station to align the second stent with the second balloon catheter using the respective first and second station aligning portions, (b) the first station to insert the first stent and first balloon catheter into the crimper head and the second station to insert the second stent and second balloon catheter into the crimper head using the respective first and second station positioning portions, and the crimper head to perform a crimping sequence for crimping both the first stent to the first balloon catheter and the second stent to the second balloon catheter.

"According to another aspect of the invention, there is provided machine executable code residing on a machine readable storage medium for performing tasks (a), (b) and . The machine readable code may include code for operating the aligning portion using a control system (with or without a feedback loop).

"The aligning portion may include a camera for obtaining an image of a stent on a balloon, machine readable instructions accessible to the processor for analyzing the image to determine whether the stent is misaligned on the balloon, an actuator for displacing one of the stent and balloon relative to the other of the stent and balloon if a misalignment of the stent relative to the balloon was detected from the analyzed image, and a controller for controlling movement of the actuator for displacing one of the stent and balloon relative to the other using the actuator according to an offset of the stent relative to the balloon.

"According to another aspect of the invention, there is a method for crimping a stent to a balloon of a balloon catheter, the balloon having balloon markers identifying a proper alignment of the stent with the balloon, the method including preparing the balloon catheter for crimping including placing the catheter on a movable carriage; verifying that the stent is aligned with the balloon including collecting at least one image of the stent and balloon and then analyzing the image to verify that the stent is between the balloon markers; after the verifying step, inserting the stent and balloon into a crimper; and crimping the stent to the balloon.

"According to another aspect of the invention, there is a crimping method for a polymer stent including a final crimp followed by a dwelling period. During the dwell period the balloon and stent are maintained at an elevated temperature and a leak test for the balloon is performed while the stent-catheter assembly is being gripped by the crimper jaws.

"According to another aspect of the invention, there is an apparatus for crimping a polymer stent to a balloon catheter, comprising: a crimper head having jaws; an aligning portion; a positioning portion; a processor in communication with the crimper head, aligning portion and the positioning portion; and machine executable code, executable by the processor, for performing a crimping process.

"The machine executable code includes a first code for aligning the polymer stent with the balloon of the balloon catheter and positioning the polymer stent and balloon within the crimper head, and a second code for crimping the polymer stent to the balloon, including setting the crimper jaws at a final crimping diameter followed by a dwell time to allow stress relaxation to occur within the polymer stent and to perform a balloon test including inflating the balloon to a pressure and then measuring the pressure over a time period to detect a leak in the balloon.

"The scope of the methods and apparatus of the invention also encompass processes that crimp a stent as substantially described in US Pub. No. 2010/0004735 and US Pub. No. 2008/0275537. The thickness of the tube from which the stent is formed may have a thickness of between 0.10 mm and 0.18 mm, and more narrowly at or about 0.152 mm. The stent may be made from PLLA. And the stent may be crimped to a PEBAX balloon."

For additional information on this patent application, see: Van Sciver, Jason. Mounting Stents on Stent Delivery Systems. Filed April 30, 2014 and posted August 28, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=7470&p=150&f=G&l=50&d=PG01&S1=20140821.PD.&OS=PD/20140821&RS=PD/20140821

Keywords for this news article include: Abbott Cardiovascular Systems Inc.

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Source: Computer Weekly News


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