BACKGROUND OF THE INVENTION 
     This invention relates to the field of stent deployment devices of the type for delivering and deploying a stent to a treatment site in a vessel of a living organism, more particularly, an animal or human. The device of the present invention includes two balloons, one being compliant and used for stent deployment at a relatively low pressure, and the other being non-compliant and available for post-deployment stent expansion at a relatively high pressure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an overall view of a stent delivery apparatus useful in the practice of the present invention. 
     FIG. 2 is an enlarged view partly in section of detail 2 of FIG. 1 showing the manifold-lumen fluid paths at the proximal end. 
     FIG. 3 is an enlarged section view of a distal end of the apparatus of FIG. 1 showing the lumen-balloon fluid paths with the balloons shown in respective deflated conditions with an outer sleeve and guide wire omitted. 
     FIG. 4 is a section view along line 4--4 of FIG. 3, except with the inner balloon shown inflated and the stent omitted. 
     FIG. 5 is a simplified section view of the distal end of the apparatus of FIG. 3 shown in an initial condition ready for insertion into a vessel with the outer sleeve shown in section and extended over a stent. 
     FIG. 6 is a view similar to FIG. 5 except with the outer sleeve retracted and the outer balloon inflated and in section showing stent deployment. 
     FIG. 7 is a view similar to FIG. 6 except with the inner balloon inflated with parts cut away showing post-deployment stent expansion. 
     FIG. 8 is a simplified section view of a vessel with a stenosis. 
     FIG. 9 is a simplified section view of the vessel and stenosis of FIG. 5 with a stent deployed via inflation of the outer balloon corresponding to FIG. 6. 
     FIG. 10 is a simplified section view of the vessel and stenosis of FIG. 5 with the stent expanded after deployment using the inner balloon corresponding to FIG. 7. 
     FIG. 11 is a graph of the distention characteristics for certain materials suitable for the outer balloon. 
     FIG. 12 is a graph of the distention characteristics for certain materials suitable for the inner balloon. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the Figures, and most particularly to FIGS. 1, 2 and 3, a stent delivery system or medical device 10 may be seen. System or device 10 includes a three lumen catheter 12 preferably formed of a polymer or combination of polymers such as polyamide, polyester, polyimide, or the like and carries a slidable sleeve 14 on the exterior thereof. System 10 also includes a valve body or manifold 16 preferably formed of a relatively rigid conventional polymer material, such as polycarbonate. Manifold 16 is secured to catheter 12 in a conventional fluid-tight manner and has ports 18, 20, and 22 in communication with respective lumens of catheter 12. Port 18 is in fluid communication with lumen 24; port 22 is in fluid communication with lumen 26; and port 20 is in communication with lumen 28, with port 20 and lumen 28 preferably adapted to receive a conventional guide wire 30. As shown in FIG. 1, outer sleeve 14 extends to a region near the proximal end of assembly 10 and is thus retractable by manipulation of the proximal end of sleeve 14, either directly or through the use of an enlarged portion such as a finger loop 15. Sleeve 14 may be formed of a polyolefin such as polyethylene or polypropylene; a fluorinated polymer such as polytetrafluoroethylene or fluoroethylene propylene; a polyamide such as nylon, or other suitable material, as desired, and may be homogeneous or may be formed from more than one kind of polymer. For example, use of more than one kind of polymer allows sleeve 14 to be formed with a distal remainder including the proximal portion having a durometer of about 70 D to about 80 D. 
     Referring now also to FIGS. 3-7, system 10 also includes a first or inner balloon 32, a second or outer balloon 34 and an expandable stent 36. The first, or inner, balloon 32 is preferably formed from a non-compliant material, and the outer balloon 34 is preferably formed from a compliant type material. 
     As use herein, a &#34;non-compliant&#34; material balloon will exhibit a diameter change of about 10 percent or less (preferably 3 to 10 percent) when its internal pressure changes from 4 atmospheres to 13 atmospheres and a &#34;compliant&#34; material balloon will exhibit a diameter change of about 11 percent or more (preferably 11 to 20 percent) when its internal pressure changes from 4 atmospheres to 13 atmospheres. 
     Each of balloons 32, 34 are preferably formed with a &#34;memory&#34; so that when deflated or depressurized, they will return to a rolled or &#34;folded&#34; state (known as &#34;rewrap&#34;) as indicated in the figures. Stent 36 is preferably a non-self deploying or balloon-expandable type stent, such as depicted in U.S. Pat. No. 4,733,665. 
     FIG. 3 shows the assembly with both balloons deflated, but with the sleeve 14 retracted and with the stent 36 ready for deployment. Lumen 24 is in fluid communication with the interior of inner balloon 32 via a skive 41. Lumen 26 is in fluid communication with the region between inner balloon 32 and the interior of outer balloon 34 via a second skive 43. A first pair of radiopaque marker bands 38, 40 are preferably positioned to indicate the location and extent of first balloon 32 and an anticipated post-deployment location and length of stent 36. A second pair of bands 42, 44 may be used to indicate the location and extent of the second balloon 34 and a predeployed location and length of stent 36. As may be seen in the figures, the first balloon 32 is positioned radially inward of the stent 36 and has a working section 33 having a length 37 substantially equal to the axial length of the stent 36 when the stent is in a deployed condition (as shown in FIGS. 6 and 7) and the second balloon 34 has a working section 35 having a length substantially equal to or greater than the non-deployed length of the stent 36, as indicated most particularly in FIG. 5. It is to be understood that the non-self-deploying stent 36 useful in the practice of the present invention may &#34;shrink&#34; or reduce in axial length by as much as 15 to 20 percent or more (of the non-deployed length) when deployed to the design diameter or condition for the stent. Such axial shrinkage occurs because the filaments or elemental sections of the stent 36 are typically not extensible, but rather move from a generally axial orientation to a more radial (helical) orientation. 
     Because of this property of the stent, it is useful to define a working section for each balloon in relation to the length of the stent when the balloon is disposed within the stent for expansion against the stent. Thus, the working section of the outer balloon will be substantially equal to the length of a collapsed or non-deployed stent, while the working section of the inner balloon will preferably be substantially equal to the length of the post-deployed or expanded stent, after it is enlarged by inflation of the outer balloon, but before any further radial enlargement by the inner balloon. Stated more generally, the working section of a balloon is preferably about equal to the length of the stent as it exists immediately prior to the stent being acted upon (urged radially outward) by that balloon. Making the outer balloon working section equal to the length of the non-deployed stent will ensure that the stent is deployed along its full axial length, while making the working section of the inner balloon equal to the length of the deployed stent will avoid direct contact between the inner balloon and the vessel during post-deployment expansion of the stent and will cause the inner balloon to fully engage the deployed stent for post-deployment &#34;processing&#34; (i.e., &#34;setting&#34; or further enlargement) of the stent. Because of the higher pressures utilized in post-deployment expansion, direct contact between the inner balloon and the vessel could result in over-expansion of the vessel in the regions beyond the axial ends of the stent if the inner balloon were permitted to be longer than the post-deployment length of the stent. Having the inner balloon substantially shorter than the length of the deployed stent may result in an undesirable condition wherein the stent protrudes into the vessel at one or both ends thereof. 
     As an example, and not by way of limitation, the stent may be 20 mm long before deployment and 15.4 mm long after deployment. For such a stent, the present invention will preferably have a working section for the inner balloon of 15.4 mm and a working section for the outer balloon of 20 mm or more. 
     In the practice of the present invention, the stent delivery system is manipulated until the stent is located radially inward of a stenosis in a vessel to be treated, preferably using radiopaque marker bands. The sleeve 14 is then retracted using finger pull 15 until the stent 36 is exposed as shown in FIG. 3. The outer balloon 34 is inflated to deploy the stent, as shown in FIG. 6. The outer balloon 34 is then deflated and the inner or first balloon is then inflated (as shown in FIG. 7) to &#34;set&#34; or fix the stent 36 in place. The inner balloon is then deflated and the stent delivery system (less the stent 36) is removed from the vessel, leaving the stent in place. The outer balloon is preferably of a softer and tougher material than the inner balloon, protecting the inner balloon from damage. 
     The inner balloon, being non-compliant, will also enable a stenosis enlargement procedure, as illustrated by FIGS. 8, 9, and 10. In FIG. 8, a simplified view of a stenosis 46 interior of a vessel 48 is shown. The stent 36 is shown deployed in FIG. 9. However, even after deployment using the outer balloon 34, the stenosis may protrude at least partially radially into the interior bore of the vessel 48. Inflating the inner balloon 32 will urge the stenosis 46 radially outward, substantially restoring the interior diameter of the stenosis to the diameter of the bore of the vessel, as shown in FIG. 10. Using the inner balloon 32 to accomplish this radial enlargement of the stenosis bore typically will entail higher pressures than used to deploy the stent, and thus will utilize the non-compliant character of the inner balloon to hold the diameter more constant over a greater pressure range than would be the case with a compliant inner balloon. It is to be understood that the outer balloon is preferably used to deploy the stent at relatively low inflation pressures and the inner balloon is preferably used to either &#34;set&#34; or shape the stent using relatively high pressures, but without over-enlarging the radial dimension of the deployed stent. It is to be further understood, however, that post-deployment inflation of the inner, non-compliant balloon 32 will typically result in further, limited, expansion of the stent 36, and consequent similar expansion of the vessel region 48 radially outward of the stent 36. In the practice of the present invention, it may be desirable to utilize a laminated balloon construction, particularly for the inner balloon 32. Such a laminated structure may include an exterior nylon layer, for example, and a PET (polyethylene terepthalate) inner layer, combining the puncture resistance and improved rewrap memory of the nylon with the non-compliant high pressure capability of the PET. 
     Referring now to FIGS. 11 and 12, the distention curves for various materials for certain compliant and non-compliant balloons may be seen. In FIG. 11, two example compliant materials for the outer balloon are shown. Curve 50 illustrates the diameter change versus pressure for a polyethylene polymer, and curve 52 represents nylon 12. In FIG. 12, various example non-compliant materials are illustrated: curve 54 is for a PET material, and curves 56, 58, and 60 show the distention characteristic for PET/PA 12 laminate construction, (where PE is polyethylene, PET is polyethylene terephthalate, PA refers to a polyamide material and PA12 refers specifically to nylon 12). Curve 56 is for a two layer laminate having an internal PET layer laminated to an external PA layer wherein the PET/PA thickness ratio is 75/25; curve 58 is for 50% PET, 50% PA; and curve 60 is for 25% PET, 75% PA. Suitable wall thicknesses for the PET/PA laminated structure are from about 0.00037&#34; to about 0.0008411&#34; overall. Although the curves shown are for layer ratios of 75/25%, 50/50%, and 25/75%, it is to be understood that other layer thickness ratios (such as 60% PET/40% PA) are suitable as well. For illustrative purposes, the following table gives approximate percentage diameter changes over a 4-13 atmosphere pressure range for various representative polymeric materials that are commercially available: 
     
                       TABLE I______________________________________Compliant %         Non-compliant %______________________________________PE        18        PET           7Nylon 12  13        75% PET/25% PA12                             5               50% PET/50% PA12                             8               25% PET/75% PA12                             10______________________________________ 
    
     Generally a variety of polymer types could be used as either the compliant or non compliant material. One skilled in the art could formulate a polymer type so that the polymer would have the right characteristics. Examples of the polymer types that could be used include the below listed materials. Suitable materials for the balloons are as follows. 
     Various nylons (depending upon how they are formulated) can be incorporated into either the compliant or non-compliant balloon (alone or in a blend or in a laminated structure), specifically: Grilamid L25 (available from EMS of Zurich, Switzerland); Vestamide 2101 F or Vestamide 1801 F (available from Huls America Inc. of Piscataway, N.J.). 
     For the non-compliant material, several applicable PET homopolymers are: ICI 5822C (available from ICI Americas, P.O. Box 630, Cardell plant, Fayetteville, N.C., 28302) and Shell Traytuf 1006. 
     For the compliant material, the following are representative of acceptable polymers: 
     
         ______________________________________                 Source______________________________________Thermoplastic Polyether Blockamide                   Elf Atochem7033 Pebax6333 Pebax5533 PebaxRigid Polyurethane      Ashland2510 IsoplastPolyester Elastomer     DuPont72D Hytrel HTR827682D Hytrel HTR828063D Hytrel HTR827945D Hytrel HTR8278Polyurethane            Dow63 D Pellethane55 D75 DPolyethylene            Dow2247A Dowlex2938 Dowlex______________________________________ 
    
     Although a number of materials have been listed above, it is to be understood that the compliant and non-compliant balloons can be prepared from a wide range of thermoplastic and or thermosetting polymer resins having the desired compliant or non-compliant characteristics. 
     A method of using the stent deployment device 10 is as follows. The stent deployment device 10 is inserted into a vessel and manoeuvered to position the distal region at a treatment site. The sheath 14 is then retracted such that the stent 36 is presented to the treatment site. The outer balloon 34 is then inflated to deploy the stent 36 and then deflated to rewrap the outer balloon. The inner balloon is then inflated to expand or &#34;set&#34; the stent in the vessel at the treatment site, after which the inner balloon is deflated to rewrap the inner balloon, and the device 10 is eventually withdrawn from the vessel. 
     The invention is not to be taken as limited to all of the details thereof as modifications and variations thereof may be made without departing from the spirit or scope of the invention.
A stent delivery device having a pair of balloons at a proximal end of a catheter and having separate lumens for selectively inflating the respective balloons. The outer balloon is relatively compliant and the inner balloon is relatively non-compliant. A central lumen is provided for a guide wire. A stent is carried by the delivery device within an axially retractable sheath at the distal end of the catheter and is deployed by retraction of the sheath and inflation of the compliant balloon, and the stent is subsequently expanded by inflation of the non-compliant balloon.