turning now to the drawings , the present invention relates to devices and methods used to create alterations in a layer of biocompatible material covering or encapsulating a stent . the preferred biocompatible material utilized to cover and encapsulate stents for the present invention is expanded polytetrafluoroethylene ( eptfe ), although a number of different materials are certainly within the scope of this invention , including polytetrafluoroethylene , polyesters , polyurethanes and other covering materials that would be , at a minimum , temporarily deformed from an alteration process such as the one described in the present invention . the term alteration as used herein means a small indentation , crease , dimple or differential density created in the surface of the eptfe or other biocompatible material . referring to fig1 and 2 , a grooved mandrel 10 is illustrated . grooved mandrel 10 is tubular with two distinct diameters , which successively alternate about its circumference . this can best be seen in the cross - sectional view of fig2 where each grooved section 14 set at a first diameter is immediately followed by a raised section 12 set at a second diameter . the importance of the two distinct sections 12 and 14 on the grooved mandrel 10 will be appreciated to one of skill in the art with respect to the creation of the alterations in the covered stents , described in more detail below . [ 0024 ] fig3 illustrates a close - up view of the creation of alterations 122 in the eptfe covering 120 of an esophageal stent - graft 100 . the esophageal stent - graft 100 has a stent 110 that is encapsulated by an eptfe covering 120 . the term encapsulated as used herein means at least one layer of biocompatible material , in this case eptfe , covering each of the luminal and abluminal layers of the stent and adhered to one another through the walls of the stent . ends 104 of the esophageal stent - graft 100 can be left uncovered and flared outward from a central axis of the stent 100 as shown . in a preferred embodiment of the present invention , the esophageal stent - graft 100 is mounted on the grooved mandrel 10 ( see fig4 - 6 for more detail ). pressing comb 20 is positioned to contact the eptfe covering 120 of the esophageal stent - graft 100 at measured equidistant intervals longitudinally along the length of the stent - graft 100 . the grooved mandrel 10 is positioned within the stent - graft 100 such that the grooves 12 of the mandrel 10 are underneath each set of alterations to be fashioned . when contact is made between teeth 24 of the pressing comb 20 and the eptfe covering 120 at each groove 12 of the mandrel 10 , an alteration 122 is created in the eptfe covering 120 . the devices and methods to create alterations in biocompatible layers according to the present invention are especially advantageous to large diameter prostheses such as the esophageal stent - graft 100 illustrated herein . this is due to the presence of increased loading forces acting on a larger diameter prosthesis ( compared to a smaller diameter prosthesis ) when collapsing for loading into a delivery apparatus . however , it should be appreciated that the devices and methods presented herein are equally applicable to biliary stents and other small diameter covered stents as well as grafts or sheaths or other endoluminal prostheses . moreover , the present invention can be used for purposes unrelated to implantable prostheses where alteration techniques can be used advantageously ; for example , where such manipulation of the surface of a material provides increased or facilitated performance of the material or apparatus with which the material is attached or associated in some capacity . ideally , the alterations 122 will be created in the eptfe covering 120 at a mid - point 112 between successive longitudinal articulations 114 in the stent 110 . the term articulation as used herein means a tip or point of a diamond shape in the stent wall . the creation of an alteration 122 at the mid - point 112 between successive longitudinal articulations 114 is accomplished through spacing of the teeth 24 of comb 20 and pre - positioning of the comb 20 prior to the creation of the alterations 122 in accordance with the articulation 114 spacing , so that the teeth 24 correspond to the mid - points 112 . when the comb 20 comes into contact with the eptfe covering 120 , a set of alterations 122 will simultaneously be produced along a longitudinal axis of the esophageal stent - graft 100 . turning now to fig4 - 6 , a preferred embodiment of the present invention is illustrated . fig4 shows a front view of a pressing comb device 40 with esophageal stent - graft 100 mounted thereon . as partially shown in fig3 the grooved mandrel 10 is inserted through the center of esophageal stent - graft 100 . this enables the mounting and stabilization of the esophageal stent - graft 100 for creation of alterations 122 in the eptfe covering 120 . the mandrel 10 is coupled to a main support structure 42 by support pins 54 , which are inserted into the center of the mandrel 10 whereby the mandrel 10 with the esophageal stent - graft 100 mounted is fully rotatable . a stop disk 60 abuts one end of the esophageal stent - graft 100 to prevent the esophageal stent - graft 100 from migrating , and a detent disk 50 is coupled to the mandrel 10 via one of the pins 54 to control the rotation of the esophageal stent - graft 100 . the control of the esophageal stent - graft 100 is further accomplished through the use of a locking pin 52 , which is utilized to lock the detent disk 50 in each axial position for creation of alterations on the esophageal stent - graft 100 . the locking action of pin 52 can best be seen in fig5 where an end view of the pressing comb device 40 is shown . the detent disk 50 has several pin holes 56 therein , each associated with an axial position of the esophageal stent - graft 100 where a set of alterations is desired . certainly , depending on the prosthesis or material to be manipulated by the pressing comb device 40 , these pin holes 56 can be more or less numerous . a linear slide 30 is mounted atop the main support 42 . the linear slide 30 is controlled mechanically to move in a vertical direction a desired predetermined distance . pressing comb 20 is attached to the base of the linear slide 30 via screws 28 that slide into a pressing comb body 22 through a comb mounting plate 26 . the features of the pressing comb device 40 can alternatively be viewed from above in fig6 . from this overhead view the esophageal stent - graft 100 can be seen more clearly . once completely mounted on the pressing comb device 40 , the esophageal stent - graft 100 can be acted on by the pressing comb 20 , where each pass of the pressing comb 20 downward , contacting the esophageal stent - graft 100 , creates a longitudinal set of alterations 122 along the eptfe covering 120 of the esophageal stent 100 . referring now to fig7 an alternate preferred embodiment is depicted . in this embodiment , the alterations are created in the eptfe covering 120 of the esophageal stent - graft 100 through the use of a marking wheel device 90 . the marking wheel device 90 includes a marking wheel 92 and a shaft 96 . the shaft 96 is positioned through the center of the marking wheel 92 for smooth and steady movement thereof . the marking wheel device 90 may have teeth around the circumference of the marking wheel 92 to produce alternating dimples in the eptfe covering 120 . in the absence of teeth , alterations can be formed by the wheel 92 itself in the form of grooves along the length of the eptfe covering 120 . in preferred embodiments , a coupling apparatus will be attached to the shaft 96 to ensure uniform movement and pressure of the wheel 92 along the eptfe covering 120 . in alternate preferred embodiments of the present invention , rather than a set of alterations being created along a longitudinal axis of a prosthesis as described above , different sets of alterations or a series of single alterations could be produced . for example , a circumferential set of alterations could be produced along a circumferential axis of the prosthesis by a disc - like device fashioned to fit around the circumference of the prosthesis . teeth or other alteration - forming units could be on the inside of the disc - like device and the disc could contract at once or in intervals to cause alterations on the outside of the prosthesis . similarly , the teeth on the disc - like device could be placed around the outside of the disc , similar to the marking wheel 92 in fig7 and the device could be placed within the prosthesis to be expanded outward to cause alterations on the inside of the prosthesis along a circumferential axis . in addition , circumferential alterations and longitudinal alterations could be made in concert by different types of devices , or sets of alterations could be made on different axes simultaneously . it should also be noted that while examples have been provided herein with regard to collapse of prostheses from a large to a small diameter , the scope of the present invention extends to the creation of alterations in the prosthesis to effectuate other forms of collapse as well . thus , for example , alterations could be produced in a prosthesis to facilitate an accordion - like collapse thereof . finally , many modifications may be made by those having ordinary skill in the art without departing from the scope of the present invention . in particular , it should be understood that the invention can be carried out by specifically different equipment and devices , and that various modifications , both as to the equipment details and procedures , can be accomplished without departing from the spirit and scope of the invention . the spirit and the scope of the claims should not , therefore , be limited to the description of the preferred embodiments contained herein .
a device and method to ensure the uniform collapse and diminished loading forces of a prosthesis , the prosthesis having at least one layer of biocompatible material . the device includes a way to stabilize the prosthesis , wherein the prosthesis can be incrementally axially rotated , and a way to manipulate the layer of biocompatible material simultaneously at several distinct points along an axis of the prosthesis so that a set of alterations is formed in the biocompatible layer .