Abstract:
A medical device having a tabular portion. In the wall of the tabular portion is a row of slots separated by portions of the wall referred to as “ribs”. The device my be folded by forming a longitudinal groove in the tubular portion separating two longitudinal lobes, with a row of alternating ribs and slots located in each lobe. Each rib in one lobe is then inserted into a slot in tie other lobe.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to medical devices and more specifically to such devices having a tubular potion such as a stent or a catheter.  
       BACKGROUND OF THE INVENTION  
       [0002]     Many medical devices that are inserted into the body have a tubular portion. For example, stents are tubular devices that are inserted into body ducts for preventing narrowing of the duct lumen, for tutoring a dilated lumen or for acting as a substrate for tissue growth. As another example, a catheter may have a tubular portion that may serve to transfer a fluid from outside the body to a body cavity, or for draining fluid from a body cavity.  
         [0003]     The tubular portion of a medical device may have a fixed caliber in which it is both delivered and deployed. Alternatively, the tubular portion may be brought into an initial small caliber conformation in which it is inserted into the body and delivered to the site where it is to be deployed. Deployment of the device involves expanding the tubular portion to a final larger caliber. Thus, a stent may be brought into an initial small caliber conformation in which it is inserted into the body and delivered to the site where it is to be deployed, and then expanded.  
         [0004]     Several stents are known in the art that are delivered to the site of their deployment in a small caliber conformation and then deployed in a large caliber conformation. European Patent No. 0382014 discloses a stent made of a flat sheet rolled as a scroll. U.S. Pat. No. 5,151,105 discloses collapsing the coils of a helical stent. U.S. Pat. No. 5,246,445 discloses tightly wrapping the coils of the stent around a catheter. WO 83/000997 discloses making a stent using curved metal wires interwoven into a mesh that is brought into a small caliber conformation by stretching the stent longitudinally. These stents are expanded after delivery either by inflating a balloon positioned in its lumen or by self expansion in the case of an elastic stent material when a constraining mechanism is released, or by a change in temperature in the case of a thermoexpandable stent material. Most stents tend to elongate when brought into the smaller caliber state. This limits the extent to which the caliber may be decreased before the length of the stent becomes too long and difficult to deliver. Stents that elongate when the caliber is decreased subsequently shorten when expanded during deployment. This shortening makes accurate positioning difficult.  
         [0005]     European Patent 0221570 discloses an expandable stent that is a thin-walled tube made from a wire mesh. When a balloon is inflated in the lumen of the stent, a geometrical deformation of the mesh occurs as the stent expands radially. However, this stent may remain rigid, making it difficult to negotiate bends or tortuosities during delivery. Furthermore, the geometrical deformation during expansion may cause multiple weakenings in the wall of the stent thus increasing the possibility of spontaneous breakage.  
         [0006]     U.S. Pat. No. 5,037,427 discloses a stent made from a two-way shape memory alloy. This stent has a transition temperature that is below body temperature in which it changes its diameter from a narrow diameter to a wide diameter. The stent is inserted into the body under a constant flow of cold fluid in order to maintain the stent in the narrow diameter during delivery. Once in the stent has been positioned in the desired location, the flow of the cold fluid is stopped and the stent then expands as it warms up to body temperature. When the stent is to be removed, a flow of cold fluid is again applied to the stent causing the stent to return to the narrow diameter conformation. The flow of cold fluid is maintained until the stent is removed from the body.  
         [0007]     U.S. Pat. No. 6,042,605 discloses a flexible stent that may be folded longitudinally in order to bring the stent into a smaller caliber. The stent may be maintained in the folded, small caliber state by a guidewire that passes through loops formed along both sides of the longitudinal fold. After positioning in the body, the guidewire is removed, and the stent assumes its original large caliber conformation.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention provides a medical device having a tubular portion such as a stent or catheter. In accordance with the invention, the wall of the tubular portion contains at least two rows of slots. The slots may be transverse, parallel or oblique to the longitudinal axis of the tubular portion. Each pair of adjacent slots in a row is separated by a portion of the wall material referred to as a “rib”.  
         [0009]     The tubular portion of the device may be folded into a small caliber, folded configuration by forming one or more longitudinal grooves in the wall of the tubular portion and inserting ribs in one row into slots in another row. The formation of a groove creates two longitudinal lobes in the wall of the tubular portion. In one method of folding the tubular portion, the longitudinal groove is formed so that the each lobe contains a row of slots, with a slot in one row being opposite a rib in the other row. In another method for folding the tubular portion, the longitudinal groove is formed so that one row of slots overlies another row of slots in the groove with each of one or more ribs in one row overlying a slot in the other row. In this case, each of one or more ribs in one or both of the rows is inserted into the juxtaposed slot in the other row. The tubular portion may then be maintained in the folded configuration by means of a rod extending through a lumen that is common to the two lobes.  
         [0010]     The tubular portion of the device may be formed from a resiliently flexible material such as latex or silicone rubber. The tubular portion is in an unstrained state when in the unfolded configuration. The tubular portion may be maintained in the folded configuration by inserting it into a restraining sleeve. After positioning the device in the body, the restraining sleeve is removed and the tubular portion reverts to its initial unfolded and unconstrained configuration. Alternatively, the tubular portion may be maintained in the folded configuration by inserting a longitudinal rod or wire through ribs that have been inserted into slots. After deployment, the wire or rod is withdrawn so as to allow the tubular portion to regain its unfolded configuration. In yet another alternative, the tubular portion may be maintained in the folded configuration by coating the tubular portion with a thin solid coating. After deployment, the coating is mechanically or chemically degraded so as to allow the tubular portion to regain its unfolded configuration.  
         [0011]     The tubular portion may also be made from a metal or a polymeric material that deforms into its plastic zone when folded. The tubular portion is then unfolded by inflating a balloon in the lumen of the tubular portion.  
         [0012]     The tubular portion may also be formed from a super-elastic and/or shape memory alloy such as a nickel-titanium alloy or shape memory polymer. The alloy or polymer is trained to pass from the unfolded configuration to the folded configuration when subjected to a first process such as a temperature change, and to pass from the folded configuration to the unfolded configuration when subjected to a second process. The first process may be, for example, a temporary increase in temperature, and the second process may be a temporary decrease in temperature.  
         [0013]     In its first aspect, the invention thus provides a medical device having at least a tubular portion, the tubular portion containing two or more slots separated by ribs.  
         [0014]     In its second aspect, the invention provides a method for deploying in a body the medical device according to any one of the previous claims comprising: 
        (a) maintaining the device in the folded configuration     (b) positioning the device in the body;     (c) bringing the tubular portion into the unfolded configuration.        
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting exile only, with reference to the accompanying drawings, in which:  
         [0019]      FIG. 1  shows a tubular portion of a medical device in accordance with one embodiment of the invention and a method for folding of the tubular portion from an unfolded configuration to a folded configuration;  
         [0020]      FIG. 2  shows another method for folding the tubular portion of a medical device of the invention; and  
         [0021]      FIG. 3  shows a tubular portion of a medical device in accordance with another embodiment of the invention and a method for holding it. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]      FIG. 1  shows a tubular portion generally indicated by  300  of a medical device, that may be, for example, a stent or catheter. The tubular portion  300  is a thin walled tube. The tubular portion  300  is shown in  FIG. 1   a  in its unfolded configuration in which it is to be deployed in the body. The tubular portion  300  encloses a lumen  320 . In the unfolded configuration shown in  FIG. 1   a , the lumen  320  has a circular cross-section. This is by way of example only, and the device of the invention may have any cross-sectional shape as required in any particular application. For example, a prostatic urethral stent may preferably have a triangular, oval, or hourglass shape. The tubular device may have a cross-sectional shape or size that varies along its length.  
         [0023]     The tubular portion  300  has two rows of slots  330 . This is by way of example only, and the tubular portion may have any number of rows or slots. Two adjacent slots  330  in a row are separated by a portion  338  of the tubular portion  300  referred to as a “rib ”. A slot in one row is in a cross-section with a rib in the other row. A slot in one row and a rib in another row that lie in the same cross-section are referred to herein as being “contiguous” with each other.  
         [0024]      FIG. 1  shows several stages in a first process of bringing the tubular portion  300  into a folded configuration In  FIG. 1   b  the tubular portion  300  is flattened, so as to decrease the cross-sectional area of the lumen  320 . In  FIG. 1   c , a longitudinal groove  240  is introduced in the tubular portion  300 . Formation of the groove  240  separates two longitudinal lobes  350  along the tubular portion  300 . The groove is located between the two rows of slots so that each row of slots  330  is located in a different lobe  350 . In  FIG. 1   d , the lobes  350  are brought near to each other. The ribs in each row are then inserted into contiguous slots in the other row. Inserting the slots  330  into the ribs  338  may be done in such a way so as to create a lumen  360  common to both lobes, as shown in  FIG. 1   e . Alternatively, a lumen common to both lobes is not formed as shown in  FIG. 1   f . The tubular portion may then be maintained in the folded configuration by means of a rod or wire  420  extending through the lumen  360  that is common to the two lobes as shown in  FIG. 1   f.    
         [0025]      FIG. 2  shows several stages in a second process of bringing the tubular portion  300  into the folded configuration. In  FIG. 2   a  the tubular portion  300  is flattened, so as to decrease the cross-sectional area of the lumen  320 . In  FIG. 2   b , a longitudinal groove  450  is introduced in the tubular portion  300 . Formation of the groove  450  separates two longitudinal lobes  455  along the tubular portion  300 . In this method of folding, both rows of slots are located in the groove so that the two rows of slots are juxtaposed, with ribs in one row juxtaposed to slots in the other row. Each of one or more ribs in one of the two rows may then be inserted into a slot in the other lobe as shown in  FIG. 2   c . A lumen  360  is thus formed from the inserted ribs. Alternatively, as shown in  FIG. 2   d , ribs in both rows may be inserted into slots in the other row to form a lumen  360 .  
         [0026]      FIG. 3  shows a tubular portion generally indicated by  500  of a medical device, that may be, for example, a stent or catheter in accordance with another embodiment of the invention. The tubular portion  500  is shown in  FIG. 3   a  in its unfolded configuration in which it is to be deployed in the body. The tubular portion  500  encloses a lumen  520 . In the unfolded configuration shown in  FIG. 3   a , the lumen  520  has a circular cross-section. This is by way of example only, and the device of the invention may have any cross-sectional shape as required in any particular application. For example, a prostatic urethral stent may preferably have a triangular, oval, or hourglass shape. Tie tubular device may have a cross-sectional shape or size that varies along its length.  
         [0027]     The tubular portion  500  has a plurality of ribs, for example, ribs  538   a ,  538   b  and  538   c . The ribs  538  are joined together by bridges, for example, the bridges  525   a ,  525   b  and  525   c . The bridges may be of any shape as required in a particular application. The number of bridges between adjacent ribs may vary, and in the embodiment shown in  FIG. 3 , alternates between 1 and 2. The ribs  538  are separated by slots, for example, the slots  530   a ,  530   b  and  530   c  . The number of slots  530  between adjacent ribs can also vary, and in the embodiment shown in  FIG. 3  alternates between 1 and 2. Thus, for example, the ribs  538   a  and  538   b  are joined by two bridges  525   a  and  525   b  and two slots  530   a  and  530   b . Ribs  538   b  and  538   c  are separated by the bridge  525   c  and the slot  530   c.    
         [0028]      FIG. 3  shows several stages in a first process of bringing the tubular portion  500  into a folded configuration. In  FIG. 3   b  the tubular portion  500  is flattened, so as to decrease the cross-sectional area of the lumen  520 . In  FIG. 3   c , a longitudinal groove  540  is introduced in the tubular portion  500 . Formation of the groove  540  separates two longitudinal lobes  550  along the tubular portion  500 . The groove is formed by pushing the row of single bridges (e.g. the row containing the bridges  525   c ) through the lumen  520  of the tubular portion  500 .  FIG. 3   d  shows the tubular portion in the folded configuration.  
         [0029]     During insertion and delivery of the device in the body, the tubular portion is maintained in the folded configuration. When the tubular portion has been positioned in the body where it is to be deployed, it is made to return to the unfolded configuration. In the case of a tubular portion formed from an elastic material, the tubular portion may be maintained in the unfolded configuration by coating the tubular portion with a polymeric coating. For example, a 2:3 solution of silicone rubber and a solvent may be applied to the tubular portion  300  and allowed to cure. The solution may be applied by any known method such as brushing, dipping or immersion. After positioning in the body, the coating is degraded either mechanically or chemically to allow expansion of the tubular portion. Alternatively, the tubular portion may be maintained in the folded configuration by inserting a wire or rod  420  into a lumen of the folded tubular portion as shown in  FIGS. 1   g ,  2   e  and  3   d . After the device has been positioned in the body, the wire or rod  420  is withdrawn and the tubular portion returns to its unfolded share.  
         [0030]     If the tubular portion is made from a material that deforms into its plastic zone when brought into the folded configuration, the tubular portion can brought back to the unfolded configuration by introducing a balloon into the lumen of the folded configuration, as shown in  FIG. 4   a , and inflating the balloon, as shown in  FIG. 4   b  (not shown).  
         [0031]     The tubular portion may also be made from a one or two way shape memory alloy such as Nitinol. The shape memory alloy is processed by methods known in the art so that when the shape memory alloy is in its superelastic or austenite state, the tubular portion  300  is in the unfolded configuration. The shape memory alloy is further processed so that when it is in its soft or austenite state, the tubular portion  300  is in the folded configuration. The tubular portion is brought into the folded configuration by causing it to undergo a transition from the martensite state to the austenite state. This may be accomplished, for example, by temporarily cooling the tubular portion to a temperature at which this transition occurs. After positioning in the body, the tubular portion is brought into the unfolded configuration by causing it to undergo a transition from the austenite state to the martensite state. This may be accomplished, for example, by temporarily heating the tubular portion to a temperature at which this transition occurs.  
         [0032]     The shape memory alloy preferably has a transition temperature range from the martensite state to the austenite state and a transition temperature range from the state that are near body temperature (around 37° C.). This allows the shape memory alloy to undergo a transformation from one state to the other at temperatures that essentially do not harm the surrounding body tissues.