TECHNICAL FIELD

The present invention relates to a catheter, which comprises a catheter tube everting inside-out during the process of catheterization.

BACKGROUND ART

The term catheter is applied to a generally tubular instrument, which is inserted into a body cavity, for the purpose of drainage, administration of fluids or gases, or accessing the body tissue by surgical instruments in a controlled manner Catheters may perform other tasks depending on the type of catheter.

To date, the most widely used catheter has been the Foley catheter, invented by Dr. Frederick Foley around 1945. The conventional Foley catheter has several drawbacks, for instance, once a conventional catheter, is removed from its sterile package before its application, the exterior surface, which will be in contact with body tissue, is often exposed to non-sterile environment, or it tends to drag bacteria and other debris along the surface of the body cavity as the tube is being pushed in. This increases the likelihood of bacteria spreading along the length of the channel, possibly causing infection, which is probably the most serious health problem arising from the use of conventional catheter.

Apart from that, the insertion of the conventional catheter is slow, difficult, unsecure and painful, because during the catheterization, the body tissue inside the body cavity may be strongly irritated and traumatized. All the drawbacks of the conventional catheter are well described in the U.S. Pat. No. 4,871,358, which discloses a medical catheter using an externally-based inversionary tube, designed to allow the outer surface of the tube, which is adjacent to body tissue, to remain stationary relative to that tissue during advancement and retraction of the catheter. This is ensured by the construction of the tube, the tube being everted onto itself at a fold to define inner and outer tube portions. The inner tube portion resides within said outer tube portion and is slidably moveable into and out of said outer tube portion in an axial direction. When a force is applied by the user onto the inner portion of the catheter tube in the axial direction towards the fold, the force is axially transmitted through the inner portion of the catheter tube to the fold and resolves into radially outward force, which when of sufficient magnitude, transforms the inner portion of the tube into the outer portion of the tube. The relative lengths of said outer and inner tube portions are changed and the position of said fold is shifted further into the body cavity. The problem with this construction is that it does not provide a catheter of sufficient length for a real life usage.

There are several forces acting in the system. First, there is a force applied by the user on the catheter tube in the axial direction of the catheter. This force allows the portion of the catheter tube in its primary position to be pushed through the fold and everted into the everted position. Second, there are counter-forces acting against the force applied by the user. Among the counter-forces, the following forces should be considered. There is a friction between the outer surface of the portion of the tube in its primary position and the inner surface of the portion of the tube in everted position. The friction is primarily caused by a radially acting force created upon everting of the portion of the tube from its primary position into the everted position. Further, upon the deformation of the material during the everting of the tube, there is material resistance against the deformation. Furthermore, the body cavity is primarily closed, or it has a much smaller opening than the actual diameter of the catheter, respectively. When the catheter is inserted, the walls of the cavity are pushed from their natural position by the everting fold. Thus, forces arising from the pressure of the body tissue of the body cavity also need to be overcome. Finally, a pressure inside the cavity, including the curvatures of the cavity may play a role as well. In the end, the above-mentioned forces contribute to the increase of the friction between the outer surface of the portion of the tube in its primary position and the inner surface of the everted portion of the tube.

The basic condition to be fulfilled to make the above-described construction work is that the final counter-force acting against the force applied by the user must be smaller than the force applied by the user. During the catheterization, as the portion of the tube in its primary position is pushed towards the fold, and a portion of the tube is everted into the everted position, the counter-forces acting against the force applied by the user increase with increasing length of the portion of the tube in the everted position. At some point, the force applied by the user and the counter-force are balanced, and further everting of the catheter tube is no longer possible. In the constructions known so far (e.g. U.S. Pat. No. 4,871,358), the length of the everted portion does not exceed a few centimeters (1-2 cm), irrespective of the diameter of the catheter, material or usage of a lubrication layer, before the tube starts to collapse or bend under the axial force, the resistance of the fold, and of the friction between the everted portion and the underlying portion of the tube, which is in the primary position.

As a result, there is no possibility to use such a catheter in real life, which is also a reason, why none of existing solutions has ever been industrially manufactured and marketed. Examples of similar technical solutions may be found e.g. in U.S. Pat. Nos. 3,908,635, 5,902,286, or US 2002/0133127.

DISCLOSURE OF THE INVENTION

The present invention relates to a catheter, which comprises a catheter tube everting inside-out during the process of catheterization. The presented invention overcomes the drawback of the prior art solutions by providing axial reinforcement of the tube by means of longitudinal protrusions, and by providing dilating means that dilate the circumference of the catheter tube in the everted region, while allowing for maintaining a smaller diameter in the portion of the tube which is in the primary position.

A catheter of this invention has a tube having two opposite open ends—a first end and a second end, a plurality of longitudinal protrusions extending from the first end through at least a portion of the tube and facing radially inwards, and means for dilating a circumference of the tube upon everting of the first end of the tube.

During the catheterization process, the catheter tube is everted inside-out gradually, starting from the first end. The everting forms a fold which divides the tube into two portions—a non-everted portion which is also referred herein as “primary position” of the tube, and an everted portion which is also referred herein as “everted position” or “everted region”. The everted portion of the tube is folded back over the non-everted portion. The longitudinal protrusions in the non-everted portion face radially inwards, and, in the everted portion, the longitudinal protrusions face radially outwards. The everted region thus may be considered as an outer portion of the catheter tube. The portion of the tube, which is in its primary position, may thus be considered as an inner portion of the catheter tube. The portion of the tube in its primary position is slidably moveable into and out of said everted region in an axial direction, thereby changing the relative length of the portion of the tube in its primary position and the length of the everted region and the position of the fold. During the catheterization process, force is applied by the user onto the portion of the catheter tube, which is in its primary position. The force is applied in the axial direction towards the fold. This force is then axially transmitted to the fold through the portion of the catheter tube in the primary position and results in the radially outward force, which when of sufficient magnitude, transforms a portion of the tube from its primary position into its everted position and shifts the position of the fold on the tube. Thus, the everted region is lengthened, the catheter tube in its primary position is shortened and the position of the fold shifts further into the cavity, into which the catheter is being inserted. As a result, there is no friction between the surface of the catheter tube and the body tissue, because the surface of the tube, which comes into contact with the body tissue, remains stationary relative to that tissue during catheterization. Thus, the irritation of the body tissue, and the resulting pain, is minimized or eliminated at all. As the surface of the catheter tube, which comes into contact with the body tissue, is hidden from manipulation in the interior of the tube before usage, the risks of introducing infection into the body decrease. Moreover, as the catheter is not pushed through the cavity channel (no friction between the catheter tube surface and the body tissue), the bacteria residing the walls of the cavity cannot be dragged deeper into the cavity. Instead, they remain on the walls.

The drawback of the prior art solutions is the impossibility to proceed with the everting for more than a few centimeters before the tube starts to collapse and bend under the axial force and the resistance of the fold and of the friction between the everted portion and the underlying portion of the tube which is in the primary position. This invention overcomes the drawback by providing axial reinforcement of the tube by means of longitudinal protrusions, and by providing dilating means that dilate the circumference of the catheter tube in the everted region, while allowing for maintaining a smaller diameter in the portion of the tube which is in the primary position.

Before the catheterization, the whole catheter tube may be provided in its primary position, in which the longitudinal protrusions are positioned radially inwards. Alternatively, a portion of the tube at the first end of the catheter tube may be pre-folded or pre-everted inside-out, respectively, i.e. everted from its primary position with the longitudinal protrusions positioned radially inwards to its everted position, in which longitudinal protrusions are positioned radially outwards. The provision of this pre-folded portion facilitates the start of the catheterization, there is no need for the medical personnel to deal with the initiation of everting and consequently the safety of the procedure is increased and the hygiene risks are decreased.

The catheter may further comprise a guard that may be located on the pre-everted region to keep the everted region stable and fixed in a position; and/or a gripper that may be positioned on the catheter tube, that may be movable between the everted first end and the second end of the tube and allows for comfortable and smoother pushing of the catheter tube; and/or a connector that may be attached to the tube at the second end of the tube, providing an inflow/outflow connection with a collection bag or with any other medical equipment suitable for the intended use of the catheter.

In a preferred embodiment, the catheter may comprise a gripper, connected with the guard, thus providing a guiding channel for the catheter tube, thus providing for comfortable and smoother pushing of the tube, and for reducing, or even avoiding, the unwanted bending of the tube. The gripper may be equipped with means for moving along the guiding channel and for pushing or pulling the catheter tube. Thus, by pushing or pulling the gripper along the guiding channel, the catheter tube is pushed or pulled in the desired axial direction. The above-mentioned mechanism allows the catheter to be inserted into body cavity as well as to be pull out of the body cavity without irritating or traumatizing the body tissue inside the cavity.

The catheter tube comprises a plurality of longitudinal protrusions. The longitudinal protrusions may be parallel to the longitudinal axis of the tube or they may be inclined with respect to the longitudinal axis, forming a spiral. A spiral shall be understood as a three-dimensional curve that turns around the longitudinal axis of the tube, the diameter of the spiral remaining constant. The inclination angle of the longitudinal protrusions vis-a-vis the longitudinal axis of the catheter tube may range from 0 degrees for parallel protrusions up to 45 degrees, preferably 0 degrees to 30 degrees, more preferably 0 degrees to 20 degrees, even more preferably 5 degrees to 15 degrees, and even more preferably 5 degrees to 10 degrees.

The longitudinal protrusions provide an axial reinforcement of the tube, i.e. a stabilization of the tube in the axial direction, thus preventing the catheter tube from bending under the axial force exerted by the user during the process of catheterization. Moreover, the spiral structure of the protrusions allows reducing stresses arising at the fold of the catheter tube, especially when passing through curved trajectories.

The longitudinal protrusions extend from the first end of the tube through at least a portion of the catheter tube. The length of the portion of the tube comprising the longitudinal protrusions may extend through the full length of the catheter tube, it may extend to the half of the length of the catheter tube, or it may extend to any length, which may be at least 1 cm, or at least 2 cm, or at least 3 cm, or at least 4 cm, or at least 5 cm, or at least 6 cm, or at least 7 cm, or at least 8 cm, or at least 9 cm, or at least 10 cm.

The primary outer surface, which is the outer surface of the portion of the catheter tube which is in the primary position, may also have a structure. Preferably, the structure may have a form of protrusions extending in the longitudinal direction—tips. The tips may be narrower and smaller than the longitudinal protrusions and the may be of the same length as the longitudinal protrusions.

The catheter tube may be formed of one or more tubular elements, preferably of one or two tubular elements. The tubular elements may be attached to one another by any means suitable for medical instruments, e.g. by adhesive means or by welding. A combination of tubular elements provides for more design freedom in respect of materials, which may be used to manufacture the tube. In general, the first tubular element containing the first end, which is the tubular element to be everted, should be more flexible (though still stiff enough not to collapse) than the second or further tubular elements, onto which the axial force will be applied by the user during the everting. Thus, the second and further tubular elements should preferably be stiffer than the first tubular element to prevent their bending and to provide a smoother application of the catheter. The first tubular element needs to contain longitudinal protrusions, as it needs to combine sufficient flexibility for everting with sufficient axial strength (due to the longitudinal protrusions) in order to not bend under the axial force exerted by the user. Therefore, the length of the first tubular element corresponds to the length of the protrusions, which may be at least 1 cm, or at least 2 cm, or at least 3 cm, or at least 4 cm, or at least 5 cm, or at least 6 cm, or at least 7 cm, or at least 8 cm, or at least 9 cm, or at least 10 cm. The second and further tubular elements are not everted, they form the part of the tube which remains in its primary position during the catheterization process, and thus they can be made of a material stiff enough to resist to the axial force exerted by the user without the need for the presence of the longitudinal protrusions.

When the tube is made of one tubular element, often the longitudinal protrusions will be present over the whole length of the tube. In any case, the longitudinal protrusions need to be present in at least a portion of the length of the catheter tube, starting from the first end of the tube. The remaining portion of the tube may comprise longitudinal protrusions and/or other means for increasing the stiffness and resistance to the axial force exerted by the user—such as an increased thickness of the wall of the tube or a layer of a material, which is stiffer than the material of the tube.

In a preferred embodiment, the tube may be provided with the longitudinal protrusions over the whole length of the tube. Subsequently, the non-everting portion of the tube undergoes a heat treatment, such that the longitudinal protrusions are “welded” together to form the stiffened part of tube. Advantageously, due to the heat treatment, the tube is stiffer in comparison to other stiffening methods.

The everting of the catheter tube inside-out is possible only if the final force acting against the force applied by the user is smaller than the force applied by the user. This is the basic condition to be fulfilled in order to successfully apply the catheter. The counter-force acting against the force applied by the user is primarily determined by the radially acting force created upon everting of the tube, the material resistance against the material deformation arising at the fold, and by the friction arising between the touching surfaces—the outer surface of the tube in its primary position and the inner surface of the everted region, and increases with the increasing length of the everted region. In order to evert the tube without creating the counter-forces that would be too large to overcome, it is necessary to increase the diameter—and so the circumference—of the tube upon everting. Therefore, dilating means must be present at least in the portion of the tube, which is to be everted, i.e., in a portion of the length of at least 1 cm, or at least 2 cm, or at least 3 cm, or at least 4 cm, or at least 5 cm, or at least 6 cm, or at least 7 cm, or at least 8 cm, or at least 9 cm, or at least 10 cm, always extending from the first end of the tube. In the present invention, several examples are provided of suitable dilating means which allow the catheter tube to dilate its diameter upon everting. The dilating means may consist in various configurations of the longitudinal protrusions, such as unevenly distributed protrusions and/or dilatable protrusions, and/or a layer of flexible material forming the tube and supporting the longitudinal protrusion.

The unevenly distributed protrusions allow the diameter of the tube in its primary position to be reduced by deforming its otherwise spherical circumference. Upon everting, the deformation ceases to exist and the tube may be fully stretched out in its circumference, thereby dilating it. The dilatable protrusions have dilatable frames, which may be stretched out upon everting of the catheter tube, thus allowing the catheter tube to be fully stretched out in its circumference, thereby dilating it. The layer of flexible material allows the dilatation of the diameter of the catheter tube upon everting; therefore, the term “flexible” should be understood as flexible and extensible.

The friction between the two touching surfaces may further be reduced by application of a lubrication coating, or by the tips of the primary outer surface. The tips may be provided on the primary outer surface and the everted inner surface, thus crossing each other, which reduces the contact area of the two surfaces and so the friction between the two surfaces, allowing for a smoother sliding.

These dilating means may be provided separately or in combinations.

In a preferred embodiment, the longitudinal protrusions and dilatable protrusions may be alternating along the circumference of the tube, such that a dilatable protrusion is always positioned between two adjacent longitudinal protrusions. The even distribution of dilating protrusions provides the dilatation of the circumference of the catheter tube upon everting, as well as reduction of the deformation of the circular shape of the tube and of the free passage channel.

In further preferred embodiment, the longitudinal protrusions of any of the above-mentioned configurations may be provided in a “shutter” structure, such that the longitudinal protrusions are folded or inclined with respect to their normal.

In another preferred embodiment, the dilating means of any of the above-mentioned configurations may also be provided in combination with a tapered shape of the tube.

The tapered shape of the catheter tube is provided by continuous change of the diameter of the tube (both the inner diameter and the outer diameter) such that the diameter of the first end of the catheter tube—the end to be everted—is larger than the diameter of the second end of the catheter tube and so the everted portion of the tube has larger diameter than the on-everted portion. Thus, while the force is applied onto the non-everted portion in the axial direction, and the everted portion is being folded back over the non-everted portion, the difference of diameters is continuously increasing, thereby further reducing the friction between the outer surface of the tube in its primary position and the inner surface of the everted region. The difference of the diameters may range from 0.1 mm up to 3 mm, preferably it may range from 0.1 mm up to 2 mm, more preferably from 0.1 mm to 1 mm, more preferably from 0.2 mm to 1 mm, more preferably from 0.3 mm to 1 mm, even more preferably from 0.4 mm to 1 mm and even more preferably from 0.5 mm to 1 mm. This difference is independent of the length of the catheter tube, e.g. the difference of 1 mm may apply to any length catheter tube.

In another preferred embodiment, the longitudinal protrusions may be pre-formed during manufacture of the catheter tube and expanded upon everting the catheter tube inside-out.

The pre-formation of the longitudinal protrusions may be provided by radially cutting or perforating the catheter tube. In the following, perforations will be used as an example, but it is to be understood that other suitable means for pre-forming the longitudinal protrusions may be provided. The perforations are provided between the primary inner surface and the primary outer surface of the tube, such that the perforations extend from the primary inner surface of the catheter tube towards the primary outer surface and/or from the primary outer surface of the catheter tube towards the primary inner surface of the tube, depending on whether protrusions or dilatable protrusions are to be provided. In the case of longitudinal protrusions, the primary outer surface shall not be perforated in order to provide the movable connection joints between adjacent protrusions. In the case of dilatable protrusions, the primary inner surface shall not be perforated in order to provide the dilatable frames of the dilatable protrusions.

The perforations extend from the first end of the tube through at least part of the catheter tube in its longitudinal direction. In a preferred embodiment, the length of perforations corresponds to at least the part of the tube that is to be everted.

The perforations are provided at several places on the circumference of the catheter tube, the distance between the perforations determining the width of the longitudinal protrusion and the number of the perforations determining the number of longitudinal protrusions. The number of perforations corresponds to the number of protrusions, i.e. four perforations shall be provided for four longitudinal protrusions, twelve perforations shall be provided for twelve longitudinal protrusions, etc.

The perforations allow pre-forming of the longitudinal protrusions. When the catheter is to be used, and the first end of the catheter tube is everted, the perforations tear up under the tension acting at the fold of the tube upon everting and the longitudinal protrusions expand, such that the inter-protrusional space is formed between the adjacent protrusions and, in case of dilatable protrusions, the inner space embodied by the dilatable frame is created, thus dilating the circumference of the catheter tube.

In a preferred embodiment, the protrusions inclined with respect to the longitudinal axis of the catheter tube may be pre-formed in a way similar to the way described above, preferably by providing cuts or perforations inclined with respect to the longitudinal axis of the catheter tube.

The materials used for manufacture of individual components of the catheter include silicon, thermoplastic elastomers (TPE), or thermoplastic polyurethane (TPU). The materials must be suitable for medical instruments, thus being of a medical grade quality. The materials should preferably have a hardness is the range of Shore A 50 to Shore A 90, depending on the component.

In a preferred embodiment, the dilating means of any of the above-mentioned configurations may also be provided in combination with the application of an active material and/or with application of different materials for different parts of the tube.

The active material allows altering its shape in a controllable manner, i.e. usually in reaction to changes in external conditions, such as pressure, temperature, pH, etc., while this kind of change may or may not be reversible.

In a preferred embodiment, the active material may recognize the tension at the fold upon everting the portion of the catheter tube, or it may recognize changes in temperature or pH of the environment. In reaction to such a change of external conditions, it may change its structure, e.g. by tearing apart the material bonds, such that a dilated circumference of the catheter tube upon everting is provided. The other properties of the material, such as elasticity or strength may or may not remain unchanged. It is preferred that the material loses its properties upon everting, e.g. when the elasticity of the material is lost, the friction between the inner surface of the everted region and the outer surface of the non-everted portion and so the overall counterforce is reduced. The person skilled in the field of materials is aware of the properties and types of active materials and would be able to select a suitable active material based on his knowledge.

In a preferred embodiment, the active material may also be provided in combination with other material or materials in order to reduce the manufacture costs. For example, a first, stiffer, material may be used for the longitudinal protrusions, while an active material is used for the movable contact joints between the adjacent protrusions. Alternatively, catheter tube may be made of a material that can be modified for the manufacture of the movable contact joints between the adjacent protrusions, e.g. by some suitable additives, in such a way that the longitudinal protrusions are stiffer than the movable contact joints between the adjacent protrusions. The desired properties may even be achieved by providing one single material, adjusting its properties in one step directly by the manufacture, e.g. by varying thickness of the tube. Different materials or various modifications of material may also be applied in one step directly by the manufacture of the tube. This simpler and cheaper manufacture reduces the number of components to be assembled and requires less manipulation with the tube, thereby reducing number of defective pieces as well as potential failures during application.

A catheter tube of the invention may be extruded, injection molded or 3D printed—directly so that the longitudinal protrusions face radially inwards. As an alternative to the injection molding, the catheter tube may also be dip molded or vacuum formed. The person skilled in the field of medical instruments and their manufacture is aware of the aforementioned and other available manufacture methods and would be able to select a method suitable for manufacture of a particular catheter type.

Alternatively, the catheter tube may be produced so that in a first step, it is extruded in a position “inside-out”, i.e., so that the longitudinal protrusions face radially outwards, and in a second step, the extruded tube is everted in its full length so that the longitudinal protrusions face radially inwards. Following these two manufacture steps, the stresses arising at the fold upon everting of the tube are reduced, because during the catheterization process the tube is in fact everted back into its natural position. In one preferred embodiment, in the second step, the extruded tube is everted in part of its length (in majority of its length, preferably in at least 90% of its length), but a portion of the tube is left in the position where the longitudinal protrusions face radially outwards—thereby forming a pre-folded region at the first end of the tube.

The method of manufacture providing the longitudinal protrusions radially inwards is especially advantageous for the catheter tube made of active material or in a combination with the active material, because in this embodiment, the main advantage of the double everted catheter tube, i.e. the reduction of stresses arising at the fold upon everting of the tube because of everting the tube back into its natural position, is achieved by the active material.

In the preferred embodiment with the shutter structure, the inclined longitudinal protrusions may be manufactured in the same way as the non-inclined longitudinal protrusions, or, alternatively, the catheter tube may initially be manufactured as a smooth tube and the protrusions may be subsequently provided by folding the tube along its circumference. The folded protrusions may extend over the whole length of the tube, or they may extend from the first end of the catheter tube through at least a portion of the catheter tube, which is to be everted—which is especially advantageous in combination with a tapered shape of the tube.

