Method of fabricating an implantable medical device with biaxially oriented polymers

Abstract

Methods and systems for manufacturing an implantable medical device, such as a stent, from a tube with desirable mechanical properties, such as improved circumferential strength and rigidity, are described herein. Improved circumferential strength and rigidity may be obtained by inducing molecular orientation in materials for use in manufacturing an implantable medical device. Some embodiments may include inducing molecular orientation by expansion of a molten annular polymer film. Other embodiments may include inducing circumferential molecular orientation by inducing circumferential flow in a molten polymer. In certain embodiments, circumferential orientation may be induced by expansion of a polymer tube. Further embodiments may include manufacturing an implantable medical device from a biaxially oriented planar polymer film.

1 . A method of manufacturing an implantable medical device, comprising: 
 introducing a polymer into a forming apparatus comprising a first annular member disposed within a second annular member, wherein the polymer is conveyed through an annular chamber as an annular film between the annular members;    radially expanding the annular film;    forming a tube from the expanded annular film; and    fabricating an implantable medical device from the tube.    
     
     
         2 . The method of  claim 1 , wherein the annular film is expanded after exiting from the apparatus.  
     
     
         3 . The method of  claim 1 , wherein the implantable medical device is a stent.  
     
     
         4 . The method of  claim 1 , wherein the polymer comprises a bioabsorbable polymer.  
     
     
         5 . The method of  claim 1 , wherein the tube is cylindrical or substantially cylindrical.  
     
     
         6 . The method of  claim 1 , wherein the introduced polymer is at a temperature above a melting temperature of the polymer.  
     
     
         7 . The method of  claim 1 , wherein the introduced polymer is at a temperature below a melting temperature of the polymer, and wherein the forming apparatus is configured to melt the polymer.  
     
     
         8 . The method of  claim 1 , wherein the polymer is introduced in a mixture comprising the polymer and a solvent.  
     
     
         9 . The method of  claim 1 , wherein the annular polymer film is at a temperature above a melting temperature of the polymer.  
     
     
         10 . The method of  claim 1 , wherein the forming apparatus comprises an extruder.  
     
     
         11 . The method of  claim 1 , wherein the annular film is expanded with a gas at a selected pressure.  
     
     
         12 . The method of  claim 11 , wherein the gas is conveyed through a second annular chamber within the first annular member.  
     
     
         13 . The method of  claim 11 , further comprising controlling the pressure of the gas to obtain a desired property of the implantable medical device.  
     
     
         14 . The method of  claim 1 , further comprising controlling the temperature of the annular film to obtain a desired property of the implantable medical device.  
     
     
         15 . The method of  claim 1 , wherein the device comprises at least one mechanical property more desirable than an equivalent device fabricated from an equivalent polymer tube formed from an annular film without radial expansion.  
     
     
         16 . The method of  claim 15 , wherein dimensions of the polymer tube are equal to dimensions of the equivalent polymer tube formed from the annular film without radial expansion.  
     
     
         17 . The method of  claim 15 , wherein the fabrication of the equivalent device from the equivalent polymer tube is the same as the fabrication of the device from the polymer tube.  
     
     
         18 . The method of  claim 15 , wherein at least one more desirable mechanical property comprises greater circumferential strength.  
     
     
         19 . The method of  claim 15 , wherein at least one more desirable mechanical property comprises greater modulus or rigidity.  
     
     
         20 . The method of  claim 1 , wherein the temperature of the expanded annular film is greater than the melting temperature of the polymer.  
     
     
         21 . The method of  claim 1 , further comprising drawing the expanded annular film to a desired diameter.  
     
     
         22 . The method of  claim 1 , further comprising cooling the expanded annular film at or substantially at an ambient temperature.  
     
     
         23 . The method of  claim 1 , further comprising cooling the expanded annular film at a temperature less than an ambient temperature.  
     
     
         24 . The method of  claim 1 , wherein the radial expansion of the annular film induces circumferential molecular orientation in the annular film.  
     
     
         25 . The method of  claim 1 , further comprising controlling the radial expansion to obtain a desired property of the implantable medical device.  
     
     
         26 . The method of  claim 1 , wherein fabricating an implantable medical device from the polymer tube comprises forming a pattern comprising at least two struts on the tube.  
     
     
         27 . An implantable medical device formed by the method of  claim 1 .  
     
     
         28 . A method for fabricating an implantable medical device comprising: 
 radially expanding a tube about a cylindrical axis of the tube from a first diameter to a second diameter, wherein the tube is plastically expanded; and    fabricating an implantable medical device from the expanded tube comprising a second diameter greater than the first diameter.    
     
     
         29 . The method of  claim 28 , wherein the implantable medical device is a stent.  
     
     
         30 . The method of  claim 28 , wherein the tube is cylindrical or substantially cylindrical.  
     
     
         31 . The method of  claim 28 , wherein the tube comprises a polymer.  
     
     
         32 . The method of  claim 28 , wherein the tube comprises a bioabsorbable polymer.  
     
     
         33 . The method of  claim 28 , wherein the tube is expanded radially by applying a radial pressure.  
     
     
         34 . The method of  claim 33 , wherein applying radial pressure comprises conveying a gas at a selected pressure into the tube.  
     
     
         35 . The method of  claim 28 , further comprising applying heat to the tube.  
     
     
         36 . The method of  claim 35 , wherein the application of heat is prior to, contemporaneous with, and/or subsequent to expanding.  
     
     
         37 . The method of  claim 35 , wherein applying heat to the tube comprises conveying a gas at a temperature greater than an ambient temperature on and/or into the tube.  
     
     
         38 . The method of  claim 28 , wherein the tube comprises a polymer, and wherein a temperature of the tube during expansion is greater than or equal to a glass transition temperature of the polymer and less than or equal to the melting temperature of the polymer.  
     
     
         39 . The method of  claim 28 , wherein the tube comprises a polymer, and wherein a temperature of the tube during expansion is less than a glass transition temperature of the polymer.  
     
     
         40 . The method of  claim 28 , wherein the device comprises at least one mechanical property more desirable than an equivalent device fabricated from an equivalent tube formed without radial expansion.  
     
     
         41 . The method of  claim 40 , wherein dimensions of the expanded tube are equal to dimensions of the equivalent tube formed without radial expansion.  
     
     
         42 . The method of  claim 40 , wherein the fabrication of the equivalent device from the equivalent tube is the same as the fabrication of the device from the expanded tube.  
     
     
         43 . The method of  claim 40 , wherein at least one more desirable mechanical property comprises greater circumferential strength.  
     
     
         44 . The method of  claim 40 , wherein at least one more desirable mechanical property comprises greater modulus or rigidity.  
     
     
         45 . The method of  claim 28 , further comprising cooling the expanded tube.  
     
     
         46 . The method of  claim 45 , wherein cooling the expanded tube comprises cooling the expanded tube at a temperature below an ambient temperature.  
     
     
         47 . The method of  claim 45 , wherein cooling the expanded tube comprises cooling the expanded tube at or substantially at an ambient temperature.  
     
     
         48 . The method of  claim 28 , wherein the radial expansion of the tube induces circumferential molecular orientation in the tube.  
     
     
         49 . The method of  claim 28 , further comprising controlling the radial expansion to obtain a desired property of the implantable medical device.  
     
     
         50 . The method of  claim 28 , wherein fabricating an implantable medical device from the expanded tube comprises forming a pattern comprising at least two struts on the expanded tube.  
     
     
         51 . An implantable medical device formed by the method of  claim 28 .  
     
     
         52 . A method of manufacturing an implantable medical device, comprising: 
 stretching a film along a first axis of stretching;    stretching a film along a second axis of stretching; and    fabricating an implantable medical device from the stretched film.    
     
     
         53 . The method of  claim 52 , wherein the implantable medical device is a stent.  
     
     
         54 . The method of  claim 52 , wherein the film comprises a polymer.  
     
     
         55 . The method of  claim 52 , wherein the film comprises a bioabsorbable polymer.  
     
     
         56 . The method of  claim 52 , wherein the film is stretched by application of a tensile force.  
     
     
         57 . The method of  claim 52 , wherein the film is plastically stretched along the first axis of stretching.  
     
     
         58 . The method of  claim 52 , wherein the film is plastically stretched along the second axis of stretching.  
     
     
         59 . The method of  claim 52 , wherein the film is stretched more along the first axis of stretching than the second axis of stretching.  
     
     
         60 . The method of  claim 52 , wherein stretching along the first axis of stretching is equal to or substantially equal to stretching along the second axis of stretching.  
     
     
         61 . The method of  claim 52 , wherein fabricating an implantable medical device from the stretched film comprises forming a tube from the stretched film.  
     
     
         62 . The method of  claim 61 , wherein the tube is cylindrical or substantially cylindrical.  
     
     
         63 . The method of  claim 61 , wherein a cylindrical axis of the tube is parallel, perpendicular, or at an angle between parallel and perpendicular to the first axis of stretching.  
     
     
         64 . The method of  claim 61 , wherein a cylindrical axis of the tube is parallel, perpendicular, or at an angle between parallel and perpendicular to the second axis of stretching.  
     
     
         65 . The method of  claim 52 , wherein fabricating an implantable medical device from the stretched film comprises forming a pattern comprising at least one strut on at least a portion of the stretched film.  
     
     
         66 . The method of  claim 52 , wherein a mechanical property of the device is more desirable than a mechanical property of an equivalent device formed from an unstretched film.  
     
     
         67 . The method of  claim 66 , wherein dimensions of the device are equal to dimensions of the equivalent device formed from the unstretched film.  
     
     
         68 . The method of  claim 66 , wherein fabrication of the equivalent device from the unstretched film is the same as the fabrication of the device formed from the stretched film.  
     
     
         69 . The method of  claim 66 , wherein at least one more desirable mechanical property comprises greater circumferential strength.  
     
     
         70 . The method of  claim 66 , wherein at least one more desirable mechanical property comprises greater modulus or rigidity.  
     
     
         71 . The method of  claim 52 , wherein the film is a polymer, and wherein the film is stretched at a temperature greater than or equal to a glass transition temperature of the polymer and less than or equal to a melting temperature of the polymer.  
     
     
         72 . The method of  claim 52 , wherein the film is a polymer, and wherein the film is stretched at a temperature less than a glass transition temperature of the polymer.  
     
     
         73 . The method of  claim 52 , wherein the stretching of the film along the first axis of stretching induces molecular orientation in the film along the first axis of stretching.  
     
     
         74 . The method of  claim 52 , wherein the stretching of the film along the second axis of stretching induces molecular orientation in the film along the second axis of stretching.  
     
     
         75 . The method of  claim 52 , further comprising controlling the stretching to obtain a mechanical property of the device more desirable than a mechanical property of an equivalent device.  
     
     
         76 . An implantable medical device formed by the method of  claim 52 .  
     
     
         77 . A method of manufacturing an implantable medical device, comprising: 
 introducing a polymer into a forming apparatus comprising a first annular member disposed within a second annular member, wherein the polymer is conveyed through an annular chamber as an annular film between the annular members;    inducing circumferential flow in the annular film;    forming a tube from the annular film; and    fabricating an implantable medical device from the tube.    
     
     
         78 . The method of  claim 77 , wherein the implantable medical device is a stent.  
     
     
         79 . The method of  claim 77 , wherein the polymer comprises a bioabsorbable polymer.  
     
     
         80 . The method of  claim 77 , wherein the tube is cylindrical or substantially cylindrical.  
     
     
         81 . The method of  claim 77 , wherein the introduced polymer is at a temperature above a melting temperature of the polymer.  
     
     
         82 . The method of  claim 77 , wherein the introduced polymer is at a temperature below a melting temperature of the polymer, and wherein the forming apparatus is configured to melt the polymer.  
     
     
         83 . The method of  claim 77 , wherein the polymer is introduced in a mixture comprising the polymer and a solvent.  
     
     
         84 . The method of  claim 77 , wherein the annular film is at a temperature above a melting temperature of the polymer.  
     
     
         85 . The method of  claim 77 , wherein the tube is at a temperature below a melting temperature of the polymer.  
     
     
         86 . The method of  claim 77 , wherein the forming apparatus comprises an extruder.  
     
     
         87 . The method of  claim 77 , wherein the circumferential flow is induced in the annular film by rotating the first annular member and/or rotating the second annular member.  
     
     
         88 . The method of  claim 87 , wherein the circumferential flow is induced in the annular film by a spiral channel on at least a portion of a surface of the rotating first annular member.  
     
     
         89 . The method of  claim 87 , wherein the circumferential flow is induced in the annular film by a spiral channel on at least a portion of a surface of the rotating second annular member.  
     
     
         90 . The method of  claim 77 , wherein the circumferential flow is induced in the annular film with at least a portion of the annular film external to the apparatus positioned over or within a third annular member that is configured to rotate at least a portion of the annular film.  
     
     
         91 . The method of  claim 77 , wherein the circumferential flow is induced in the annular film by rotating the tube.  
     
     
         92 . The method of  claim 91 , wherein the tube is rotated by positioning the tube over or within a third annular member that is configured to rotate the tube.  
     
     
         93 . The method of  claim 77 , wherein the circumferential flow is induced in the annular film external to the apparatus with at least a portion of the first annular member that is external to the apparatus.  
     
     
         94 . The method of  claim 93 , wherein rotation of the first annular member induces circumferential flow to at least a portion of the annular film external to the apparatus.  
     
     
         95 . The method of  claim 77 , wherein the circumferential flow of the annular film induces circumferential molecular orientation in the annular film.  
     
     
         96 . The method of  claim 77 , further comprising controlling the induced circumferential flow to obtain a desired property of the implantable medical device.  
     
     
         97 . The method of  claim 77 , wherein a mechanical property of the device is more desirable than a mechanical property of an equivalent device formed from a tube formed from an annular film formed without circumferential flow.  
     
     
         98 . The method of  claim 97 , wherein dimensions of the tube are equal to dimensions of the equivalent tube formed from an annular film formed without circumferential flow.  
     
     
         99 . The method of  claim 97 , wherein the fabrication of the equivalent device from the equivalent tube is the same as the fabrication of the device from the tube.  
     
     
         100 . The method of  claim 97 , wherein at least one more desirable mechanical property comprises greater circumferential strength.  
     
     
         101 . The method of  claim 97 , wherein at least one more desirable mechanical property comprises greater modulus or rigidity.  
     
     
         102 . The method of  claim 77 , further comprising drawing the annular film to a desired diameter prior to cooling the annular film.  
     
     
         103 . The method of  claim 77 , further comprising cooling the annular film at or near an ambient temperature.  
     
     
         104 . The method of  claim 77 , further comprising cooling the annular film below an ambient temperature.  
     
     
         105 . The method of  claim 77 , wherein fabricating an implantable medical device from the tube comprises forming a pattern comprising at least two struts on the tube.  
     
     
         106 . An implantable medical device formed by the method of  claim 77   
     
     
         107 . An apparatus for manufacturing an implantable medical device, comprising: 
 (a) a first zone comprising: 
 (i) a first annular member;  
 (ii) a second annular member, the first annular member being disposed within the second annular member so as to provide for an annular chamber between the first and second annular members, the annular chamber configured to receive a material and dispense the material as an annular film to a second zone;  
   (b) the second zone comprising a space for allowing radial pressure to be applied to the annular film to expand the material from a first film diameter to a second, larger film diameter.    
     
     
         108 . The apparatus of  claim 107 , wherein in the second zone, the radial molecular orientation of the film is altered.  
     
     
         109 . The apparatus of  claim 107 , additionally including a third zone for receiving the film and forming a tube from the film.  
     
     
         110 . The apparatus of  claim 109 , wherein the third zone is configured to draw the received film to a desired diameter.  
     
     
         111 . The apparatus of  claim 109 , wherein the third zone is configured to cool the received film.  
     
     
         112 . The apparatus of  claim 107 , additionally including a fourth zone for forming a polymer tube.  
     
     
         113 . The apparatus of  claim 112 , additionally including a fifth zone configured to fabricate an implantable medical device from the polymer tube.