Medical device balloons with improved strength properties and processes for producing same

Abstract

A tubular parison for forming a medical device balloon. The parison is formed of a polymeric material, for instance a thermoplastic elastomer. The parison has an elongation at break which is not more than 80% of the elongation of the bulk polymeric material. The elongation of the parison is controlled by altering extrusion conditions. Balloons prepared from the parisons provide higher wall strength and/or higher inflation durability than balloons prepared from conventional parisons of the same material.

Claims

1. An expandable medical balloon, the expandable medical balloon comprising: a balloon wall comprising a thermoplastic elastomer, the balloon having a calculated burst strength of 32,000 psi or greater in a pre-sterilized condition as defined by the following equation:
Strength =(PD/2t) where P = internal pressure when the balloon bursts (kg/cm.sup.2)(1 kg/cm.sup.2=14.2 psi); D is the exterior diameter (mm) of the balloon when a pressure of 6 kg/cm.sup.2 (85.2 psi) is applied; and t is the wall thickness (mm) of the portion of the balloon with the larger exterior diameter.

2. The expandable medical balloon of claim 1 wherein the expandable medical balloon has a calculated burst strength of about 34,000 or greater in a pre-sterilized condition.

3. The expandable medical balloon of claim 1 wherein the expandable medical balloon has a calculated burst strength of about 37,000 or greater in a pre-sterilized condition.

4. The expandable medical balloon of claim 1 wherein the expandable medical balloon has a calculated burst strength of about 32,000 or greater in a post-sterilized condition.

5. The expandable medical balloon of claim 1, the expandable medical balloon comprising poly (ether-block-amide) block copolymer.

6. The expandable medical balloon of claim 1, the expandable medical balloon comprising alternating layers of poly(ether-block-amide) block copolymer.

7. The expandable medical balloon of claim 6 wherein the alternating layers comprise a layer of poly(ether-block-amide) comprising a Shore D hardness of about 70 and a layer of poly(ether-block-amide) comprising a Shore D hardness of about 72.

8. The expandable medical balloon of claim 1, the expandable medical balloon comprising a nominal diameter of about 3 mm at 6 atm.

9. The expandable medical balloon of claim 1 comprising a poly(ether-block-amide) comprising a bulk elongation per ASTM D-638 of about 400%.

10. The expandable medical balloon of claim 1 wherein the thermoplastic elastomer is a poly(ether-block-amide) comprising a Shore D hardness of about 70.

11. The expandable medical balloon of claim 1 wherein the thermoplastic elastomer is a poly (ether-block-amide) comprising a Shore D hardness of about 72.

12. The expandable medical balloon of claim 1 wherein the thermoplastic elastomer is polyester/polyether block copolymer.

13. The expandable medical balloon of claim 1 wherein the thermoplastic elastomer is polyurethane.

14. The expandable medical balloon of claim 1 wherein the thermoplastic elastomer comprises a blend of thermoplastic elastomers.

15. The expandable medical balloon of claim 1 comprising improved resistance to repeat inflation bursts versus a control utilizing the same thermoplastic elastomer extruded to keep a parison elongation at break above 80% of the published elongation of the polymer.

Description

EXAMPLES

(1) In the following examples the following abbreviations are used. Ex Example No. Alphabetic series are comparative, numeric series are invention examples. ID Internal diameter, as extruded. OD Outer diameter, as extruded. Die temp Extruder die zone temperature in degrees Fahrenheit. The extruder barrel was kept at 395 F. in these examples. Line speed Speed in feet/min of the puller. DDR Draw down ratio of the cross-sectional area from extrusion head opening to final tube dimensions. DDR=[(Die ID).sup.2(Tip OD).sup.2]/[(Tubing OD).sup.2(Tubing ID).sup.2] Elong @ break Given as percentage elongation determined on a 3 long extruded tube which is stretched to break. Balloon 2 wall Thickness in inches of the balloon double wall as measured with a micrometer. Hoop Hoop ratio determined as balloon OD (mold diameter)/parison ID (as extruded). Distension The change in diameter as a % of start diameter for the stated ranges of 6:12 (6 atm to 12 atm) and 12:18 (12 atm to 18 atm) inflation pressure. Burst Pressure in psi at which the balloon burst Burst strength Wall strength at burst as calculated by the equation:
T.sub.s=PD/2t where: T.sub.s is the wall tensile strength; P is the balloon burst pressure; D is the nominal diameter of the balloon; and t is the wall thickness.

(2) All values are averages of at least 6 balloons. Balloon blowing conditions used the same times, temperatures and sequences, except where indicated. All data is for balloons having a nominal diameter of 3.0 mm at 6 atm. The balloons were made from PEBAX 7033. The published elongation value for the bulk polymer, per ASTM D-638, is 400%. The balloons were made from conventionally extruded parisons using a very high hoop ratio and a step-wise dipping process similar to that described in Wang et al, Example 3, U.S. Pat. No. 5,714,110. A typical program is as follows:

(3) TABLE-US-00001 Program: bath at 95 C. (1) pressure to 100 psi tension to 50 g dip to D 8 seconds hold at D 6 seconds (2) pressure to 450 psi tension to 20 g dip to C 4 sec hold at C 6 seconds (3) pressure to 550 psi tension to 200 g dip to B 20 sec hold at B 6 seconds
where D, C and B are locations, as described in U.S. Pat. No. 5,714,110. The parison formation conditions and formed balloon results are described in Table 1. Die configuration was not varied between examples. Tank gaps, die temperatures and speeds were varied as needed to obtain parison elongation targets. Extruder pressure was not independently controlled and varied as a result of changing these conditions.

(4) Table 1 provides an example of a balloon formed using conventional tube processing at a high hoop ratio.

(5) TABLE-US-00002 TABLE 1 Control Tube Tube Die Line Elong @ Balloon Distension Distension Burst Ex ID OD Temp Speed DDR break 2X wall Hoop 6:12 12:18 Burst Strength A .0177 .0321 395 24 3.5 367 .00116 6.9 5.6 4.4 301 31056

(6) The elongation at break of this parison corresponds to about 91% of the published value for the bulk polymer.

(7) Table 2 gives the results of the same balloon wall thickness made in accordance with the invention by increasing the DDR. The increased draw down ratio reduced the elongation of this tube to about 48% of the published elongation value.

(8) TABLE-US-00003 TABLE 2 High Draw Down Tube Tube Die Line Elong @ Balloon Distension Distension Burst Ex ID OD Temp Speed DDR break 2X wall Hoop 6:12 12:18 Burst Strength 1 .0176 .0310 395 50 12.1 190 0.00118 6.9 5.4 4.5 331 34411

(9) Table 3 shows extrusion parameters and balloon property results when, after extrusion, the parison was modified by one of the following steps before it was blow-formed into a balloon.

Example 2

(10) A freeze spray process was used to selectively reduce parison cone and waists as per Example 1 of U.S. Pat. No. 5,807,520.

Example 3

(11) Cones and waists were selectively reduced by a grinding and necking process which did not stretch the body-forming portion of the parison. Similar to Example 2, first paragraph of PCT/US01/26140, filed Aug. 22, 2001, attorney docket no S63.3-9928, corresponding to U.S. application Ser. No. 09/672330 filed Sep. 28, 2000.

Example 4

(12) the entire parison was stretched longitudinally at ambient temperature under internal pressurization to maintain ID at the extruded dimension (4%) at a stretch ratio 3 x, where x is starting length. See control in Example 1 of PCT/US01/26140.

(13) TABLE-US-00004 TABLE 3 Parison Modifications Tube Tube Die Line Elong @ Balloon Distension Distension Burst Ex ID OD Temp Speed DDR break 2X wall Hoop 6:12 12:18 Burst Strength 2 0.176 .0290 395 50 12:1 193 .00105 6.9 5.3 4.7 309 36101 3 .0176 .0290 395 50 12:1 193 .00098 6.9 4.8 4.8 297 37423 4 .0176 .0290 395 50 12:1 193 .00097 6.9 4.9 4.7 300 37577

(14) In examples 2-4, the burst pressure in all cases was comparable to the control balloon, but with thinner walls so the wall strength is much improved over the control balloon.

Example 5

(15) Balloons were made using PEBAX 7033 parisons stretched at ambient temperature at a stretch ratio of 1.5 x and a hoop ratio of 7.0. Parisons, extruded to keep the parison elongation at break above 80% of the published elongation of the polymer, were used as controls. Parisons, extruded to provide a parison elongation at break of about 50% or less of the published elongation of the polymer, were prepared as invention examples. The balloons were inflated to 211 psi and deflated repeatedly.

(16) Four balloons were present in each group. The control balloon group, on average, failed at about 80 repeats. All of the balloons of the invention group survived 235 repeats without failure, at which point the test was discontinued.

(17) The above examples and disclosure are intended to be illustrative and not exhaustive. These examples and description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the claims, where the term comprising means including, but not limited to. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims. Further, the particular features presented in the dependent claims can be combined with each other in other manners within the scope of the invention such that the invention should be recognized as also specifically directed to other embodiments having any other possible combination of the features of the dependent claims. For instance, for purposes of claim publication, any dependent claim which follows should be taken as alternatively written in a multiple dependent form from all prior claims which possess all antecedents referenced in such dependent claim if such multiple dependent format is an accepted format within the jurisdiction (e.g. each claim depending directly from claim 1 should be alternatively taken as depending from all previous claims). In jurisdictions where multiple dependent claim formats are restricted, the following dependent claims should each be also taken as alternatively written in each singly dependent claim format which creates a dependency from a prior antecedent-possessing claim other than the specific claim listed in such dependent claim below.