Methods and apparatus for an adjustable stiffness catheter

Abstract

Apparatus and methods for an endovascular catheter that can be inserted within tortuous body anatomies and then selectively stiffened and fixed in place. In a particular embodiment, this stiffness is reversible. The stiffness or a comparable mechanical characteristic of the catheter assembly may be adjusted to a relatively low value during insertion (so that it easily navigates a guide wire or the like), and then subsequently adjusted to a relatively high value in situ to keep the catheter assembly substantially fixed in place (i.e., during delivery of an interventional device).

What is claimed is: 
     
       1. A catheter apparatus comprising:
 a tubular body having a distal end, a proximal end, and a lumen defined therein, the tubular body having a first state, wherein the tubular body has a first value of a stiffness metric, and a second state, wherein the tubular body has a second value of the stiffness metric that is greater than the first value, the tubular body including:
 at least two fluid impermeable layers defining a pressure-responsive chamber, and 
 an interstitial structure provided within the pressure-responsive chamber and comprising a plurality of layers including a first cylindrical layer of wrapped tape and a second cylindrical layer of wrapped tape coaxial with the first cylindrical layer of wrapped tape, the first and second cylindrical layers extending along an entire length of the pressure-responsive chamber, 
 the pressure responsive chamber configured to increase radial compression of the plurality of layers in response to negative internal pressure in the pressure-responsive chamber and to decrease radial compression of the plurality of layers in response to non-negative internal pressure in the pressure-responsive chamber, 
 the decrease in radial compression corresponding to a decrease in friction between the plurality of layers along of the interstitial structure and a decrease in the stiffness metric and the increase in radial compression of the plurality of layers of the interstitial structure corresponding to an increase in friction between the plurality of layers of the interstitial structure and an increase in the stiffness metric; and 
 
 a controller operatively coupled to the tubular body and configured to cause a change in the internal pressure within the pressure-responsive chamber to actuate the tubular body between the first state and second state. 
 
     
     
       2. The catheter apparatus of  claim 1 , wherein the plurality of layers of the interstitial structure are configured to be substantially slideable slidable with respect to each other during the first state, and be substantially non-slidable with respect to each other during the second state. 
     
     
       3. The catheter apparatus of  claim 2 , wherein the plurality of layers of the interstitial structure each define a substantially cylindrical, helically-wrapped layer. 
     
     
       4. The catheter apparatus of  claim 1 , wherein the first layer of wrapped tape is a helically-wrapped ePTFE tape layer and the second layer of wrapped tape is a helically-wrapped ePTFE layer. 
     
     
       5. A catheter apparatus comprising:
 a tubular body having a distal end, a proximal end, and a lumen defined therein, the tubular body including at least two fluid impermeable layers defining a pressure-responsive chamber and an interstitial structure provided within the pressure-responsive chamber, the interstitial structure comprising a first layer of wrapped tape and a second layer of wrapped tape, the first and second layers of wrapped tape extending along an entire length of the pressure-response chamber; and 
 activation means for selectably causing the tubular body to enter a first state and a second state; 
 wherein, in the first state, the tubular body has a first value of a stiffness metric that is equal to or less than a predetermined navigatibility navigability threshold; 
 wherein, in the second state, the tubular body has a second value of the stiffness metric that is greater than the first value and that is greater than or equal to a predetermined rigidity threshold value; and 
 wherein the activation means includes a controller communicatively coupled to the tubular body and adapted to place the tubular body in the second state by subjecting at least a portion of the tubular body to an increase in radial compression by causing negative pressure within the pressure-responsive chamber thereby causing the collapse of the pressure-responsive chamber. 
 
     
     
       6. The catheter apparatus of  claim 5 , wherein the interstitial structure is adapted to exhibit radial compression in response to a change in internal pressure within the pressure responsive chamber caused by the controller. 
     
     
       7. The catheter apparatus of  claim 6 , wherein the interstitial structure includes a layered structure having a plurality of layers configured to be substantially slideable slidable with respect to each other during the first state, and be substantially nonslideable non-slidable with respect to each other during the second state. 
     
     
       8. The catheter apparatus of  claim 5 , wherein the pressure-responsive chamber is placed under negative pressure in the second state. 
     
     
       9. The catheter apparatus of  claim 5 , wherein the controller is configured to cause the change of state by pneumatic activation. 
     
     
       10. The catheter apparatus of  claim 5 , wherein the controller is a syringe. 
     
     
       11. The catheter apparatus of  claim 5 , further comprising multiple discrete pressure-responsive chambers distributed along a length of catheter, and further wherein the activation means is configured to independently pressurize each of the discrete pressure-responsive chambers. 
     
     
       12. The catheter apparatus of  claim 5 , wherein the first layer of wrapped tape is a helically-wrapped ePTFE tape layer and the second layer of wrapped tape is a helically-wrapped ePTFE layer. 
     
     
       13. A catheter comprising:
 a catheter body having an outer body layer and an inner body layer disposed within the outer body layer to define an air-impermeable chamber there between, at least one of the inner and outer body layers comprising a flexible polymeric material that is at least partially collapsible upon a reduction of an internal pressure of the air-impermeable chamber; and   an interstitial component (IC) disposed within the air-impermeable chamber, the interstitial component having at least two opposing portions including a first cylindrical layer and a second cylindrical layer coaxial with the first cylindrical layer and extending along an entire length of the air-impermeable chamber, the at least two opposing portions disposed between the inner and outer body layers and positioned to define a first state where the opposing portions are disposed such that the opposing portions slide across each other with minimal friction and to define a second state where the opposing portions abut each other such that layer-to-layer friction limits the opposing portions to slide with respect to each other, the first state defining a slidable engagement having a first state stiffness metric, the second state defining a non-slidable engagement having a second state stiffness metric,   wherein a reversible transition from the first state to the second state is defined by the reduction of the internal pressure driving a collapse of the air-impermeable chamber during which at least one of the inner and outer body layers move towards the other to impart a radial force on the interstitial component, and   wherein the reversible transition is further defined by a passive reversal of the collapse of the air-impermeable chamber to at least partially restore the first state during which the inner and outer body layers at least partially move away from each other to reestablish the space between the at least two opposing portions.    
     
     
       14. The catheter of claim 13, wherein the first cylindrical layer of the interstitial component has a first surface disposed to face a second surface of the second cylindrical layer of the interstitial component.  
     
     
       15. The catheter of claim 13, wherein bending of the body causes the first and second cylindrical layers of the interstitial component to slide across one another in the first state.  
     
     
       16. The catheter of claim 13, wherein the first and second cylindrical layers of the interstitial component are configured to radially compress in response to application of the radial force.  
     
     
       17. The catheter of claim 16, wherein the radial force increases a stiffness metric of the interstitial component from the first state stiffness metric to the second state stiffness metric.  
     
     
       18. The catheter of claim 13, wherein the first and second cylindrical layers of the interstitial component are configured to radially compress in response to application of a negative pressure in the air-impermeable chamber.  
     
     
       19. The catheter of claim 18, wherein the first and second cylindrical layers of the interstitial component are configured to exhibit radial compression in response to the negative change in internal pressure in the air-impermeable chamber.  
     
     
       20. The catheter of claim 13, wherein the first and second cylindrical layers of the interstitial component are formed by at least one of tape wrapping, braiding, serving, coiling, and manual layup.  
     
     
       21. The catheter of claim 13, wherein the inner and outer body layers are configured to move towards one another in response to collapse of the air-impermeable chamber.  
     
     
       22. The catheter of claim 13, wherein both of the inner and outer layers forming the air-impermeable chamber are formed of flexible polymer material configured to be non-permeable in a human blood stream.  
     
     
       23. The catheter of claim 13, wherein the first state is at a first state pressure approximately equal to atmospheric pressure and the second state is at a second state pressure less than atmospheric pressure.  
     
     
       24. A catheter comprising:
 a catheter body having an outer tubular body and an inner tubular body disposed within the outer tubular body to define a pressure chamber between the inner and outer tubular bodies; and   an interstitial structure comprising a first layer and a second layer coaxial with the first layer disposed within the pressure chamber and extending along an entire length of the pressure chamber, the first layer disposed proximate to an inner surface of the outer tubular body and the second layer disposed proximate to an outer surface of the inner tubular body,   wherein the catheter comprises a first state defining a first state stiffness metric and a slidable engagement between the first and second layers,   wherein the catheter further comprises a second state defining a second state stiffness metric and a non-slidable engagement between the first and second layers,   wherein a first transition from the first state stiffness metric to the second state stiffness metric is defined by a collapse of the pressure chamber in response to a reduction in a pressure in the pressure chamber during which at least one of the inner and outer tubular bodies move towards the other, and   wherein a second transition from the second state stiffness metric towards the first state stiffness metric is defined by a passive expansion of the pressure chamber during which the inner and outer tubular bodies move away from each other to at least partially reverse the first transition.    
     
     
       25. The catheter of claim 24, wherein the first layer and the second layer are configured to slide across each other in the first state and are substantially non-slidable in the second state.  
     
     
       26. The catheter of claim 24, wherein bending of the body causes the first layer and the second layer to slide across one another in the first state.  
     
     
       27. The catheter of claim 24, wherein the catheter is configured to transition from the first state stiffness metric to the second state stiffness metric in response to application of a radial force.  
     
     
       28. The catheter of claim 24, wherein the catheter is configured to transition from the first state stiffness metric to the second state stiffness metric to response to reduction of a pressure.  
     
     
       29. A catheter comprising:
 a catheter body defining a catheter axis and having an outer body layer and an inner body layer disposed within the outer body layer to define a pressure chamber between the inner and outer body layers, at least one of the inner body layer and the outer body layer comprising a flexible polymeric material such that the pressure chamber is configured to collapse upon the application of a reduced pressure within the pressure chamber, the catheter having a first state in which the air chamber is in a non-collapsed orientation prior to the application of the reduced pressure and having a second state in which the air chamber is in a collapsed orientation after the application of the reduced pressure, the inner and outer body layers in the first state each having a smooth surface along an axial length of the respective body layer defining a slidable operation of the catheter in the first state; and   an interstitial component including a first component and a second component coaxial with the first component disposed within the air chamber between the inner and outer body layers and extending along the entire length of the air chamber,   wherein in the second state at least one of the inner and outer body layers at least in part deforms along the axial length of the respective body layer in response to a normal force defining a rigid non-slidable operation of the catheter in the second state, and   wherein in the second state at least one of the first and second components are repositioned by the normal force to permit engagement between the first component and the second component further defining the rigid non-slidable operation of the catheter in the second state.    
     
     
       30. The catheter of claim 29, wherein the first and second components are configured to move toward one another to transition between a first state stiffness metric and a second state stiffness metric.  
     
     
       31. The catheter of claim 29, wherein the first and second components move towards one another in response to application of a vacuum to the pressure chamber.  
     
     
       32. The catheter of claim 29, wherein the interstitial component is configured to transition between a navigable configuration corresponding to the first state and a rigid configuration corresponding to the second state.  
     
     
       33. The catheter of claim 32, wherein the interstitial component includes non-axial surfaces in the navigable configuration and axial surfaces in the rigid configuration.  
     
     
       34. The catheter of claim 32, wherein the pressure chamber is configured to collapse to result in the body having a first stiffness metric along a first curvature axis and a second stiffness metric along a second curvature axis.  
     
     
       35. The catheter of claim 34, wherein the second curvature axis is orthogonal to the first curvature axis.  
     
     
       36. The catheter of the claim 35, wherein the inner and outer body layers are configured to move toward one another to result in the body having the first and second stiffness metrics.  
     
     
       37. The catheter of claim 36, wherein at least one of inner and outer body layers are configured to warp from an axially aligned state to a non-axially aligned state in response to application of a vacuum to the pressure chamber.  
     
     
       38. The catheter of claim 37, wherein the interstitial component includes non-axially aligned surfaces in the navigable configuration and substantially axially aligned surfaces in the rigid configuration and the vacuum is configured to transition the interstitial component between the navigable configuration and the rigid configuration.  
     
     
       39. The catheter of claim 37, wherein axial movement between the inner and outer body layers is opposed in the rigid configuration.  
     
     
       40. The catheter of claim 39, wherein the inner and outer body layers collapse toward one another to arrest movement between the inner and outer body layers in the rigid configuration.  
     
     
       41. The catheter of claim 29, wherein the catheter body includes a plurality of segments defining non-axial surfaces.  
     
     
       42. The catheter of claim 29, wherein the catheter body includes two or more zones, and each of the two or more zones include a zone stiffness metric.  
     
     
       43. The catheter of claim 42, wherein the zone stiffness metric of each of the two or more zones is variable between the two or more zones.  
     
     
       44. A method of increasing a stiffness metric of a catheter from a first state having a flexible orientation to a second state having a comparatively rigid orientation, the method comprising:
 reducing pressure in a pressure chamber within a catheter body of the catheter to apply an inwardly radial force;   advancing a first interstitial component within the pressure chamber towards a second interstitial component within the pressure chamber to engage irregular surfaces of the first and second interstitial components to defining a non-sliding engagement between the first and second components in the second state   wherein the first interstitial component and the second interstitial component are coaxial layers that extend along the entire length of the pressure chamber.    
     
     
       45. The method of claim 44, wherein advancing the first interstitial component within the pressure chamber towards the second interstitial component includes sliding the first interstitial component relative to the second interstitial component to transition between the first state stiffness metric in the first state and the second state stiffness metric in the second state.  
     
     
       46. The method of claim 44, wherein the catheter body includes an outer body layer and an inner body layer to define the pressure chamber, and reducing pressure in the pressure chamber includes applying a vacuum to the pressure chamber to move the outer body layer and the inner body layer toward one another to transition between the first state stiffness metric and the second state stiffness metric.  
     
     
       47. The method of claim 46, wherein applying the vacuum to the pressure chamber includes warping at least one of the outer body layer and the inner body layer from an axially aligned state to a non-axially aligned state.  
     
     
       48. The method of claim 47, wherein applying the vacuum includes transitioning the body between a navigable configuration corresponding to the first state and a rigid configuration corresponding to the second state.  
     
     
       49. The method of claim 48, wherein the catheter body includes non-axially aligned surfaces in the navigable configuration and substantially axially aligned surfaces in the rigid configuration and applying the vacuum to the pressure chamber transitions the layered structured between the navigable configuration and the rigid configuration.  
     
     
       50. The method of claim 44, wherein the catheter body includes two or more zones, and each of the two or more zones include a zone stiffness metric and the zone stiffness metric of each of the two or more zones is variable between the two or more zones.  
     
     
       51. The method of claim 44, wherein reducing pressure in the pressure chamber includes collapsing the pressure chamber to place the catheter body in the first stiffness metric along a first curvature axis and the second stiffness metric along a second curvature axis that is orthogonal to the first curvature axis.