The present invention relates to a tube-in-tube merger or tube sections merger according to the introductory portion of the independent claim.

In particular, it relates to such a tube-in-tube merger acting to merge separate merging tubes, one merging tube inside the other and also to tube sections that are joined.

Background of the invention

Advanced medical catheters normally have a shaft comprising sections with different material properties. These sections are joined by reflow. The sections are inserted into a shrink tube which is placed in a machine with a circular oven with a centre hole. The shrink tube is placed in the hole and the oven is slid along the entire length of the shrink tube. The shrink tube and shaft is then unloaded and the shrink tube is removed. This is a time consuming and complex procedure and requires advanced and expensive equipment. The same process is also used if an extra layer in form of a tube or a tube in form a plastic strip wrapped around the shaft is added to the shaft.

It would be desirable with a simpler machine that doesn’t need a shrink tube.

GB1161676 discloses a method for merging a tube to a central core. The tube and core are heated to a temperature where they melt together, and uses the difference in coefficient of expansion between the tube and core to compress the two together. The method works only for tubes and cores with such difference in coefficient of expansion, which is disadvantageous.

US4357962 discloses a method for merging a fibrous liner to a tube, the fibrous liner on the outside of side the tube. The method requires the fibrous liner to be precisely fit the outer surface of the tube and generates and still generates a double walled tubular element with an outer diameter that is not precisely controlled, which is disadvantageous.

An object of the invention is therefore to provide a tube-in-tube merger which is more generally applicable than prior art tube-in-tube mergers of plastic tubes.

These and other objects are attained by a tube-in-tube merger according to the characterizing portion of the independent claim.

Summary of the invention

The invention relates to a tube-in-tube merger constituted by an elongated element with a longitudinal axis. The elongated element comprises a rigid outer casing 1, preferably of metal, and an interior expanding substance 2 with a through hole. The through hole is arranged to receive therein at least two separate merging tubes 3, 4, one merging tube 4 inside the other 3. The tube-in-tube merger through hole size at a lower assembly temperature is larger than the outer size of the merging tubes 3, 4, while at a higher merging temperature the tube-in-tube merger through hole size is equal to or smaller than the outer size of the merging tubes 3, 4. Advantageously, the tube-in-tube merger at assembly temperature can the easily receive the merging tubes 3, 4, while it grasps the merging tubes 3, 4 at the merging temperature.

The interior expanding substance 2 has a higher coefficient of thermal expansion than the rigid outer casing 1, causing the size of the through hole to contract at an elevated temperature. The rigid outer casing 1 and the interior expanding substance 2 have melting temperatures higher than the merging temperature, where the merging temperature is equal to or higher than the melting temperature of at least one of the merging tubes 3, 4. By elevating the temperature to the merging temperature, the tube-in-tube merger grasps the merging tubes 3, 4 and melts at least one of them, permanently joining them.

In an advantageous embodiment of the invention the tube-in-tube merger the through hole size varies along the longitudinal axis, advantageously allowing the tube-in-tube merger to receive merging tubes 3, 4 of longitudinally varying sizes.

Brief description of the drawings

Fig. 1 shows a tube-in-tube merger in a passive state in a cross section orthogonal to its longitudinal axis

Fig. 2 shows the tube-in-tube merger in an active state in a cross section orthogonal to its longitudinal axis

Fig. 3 shows a first embodiment of the tube-in-tube merger in a cross section parallel to its longitudinal axis

Fig. 4 shows a second embodiment of the tube-in-tube merger in a cross section parallel to its longitudinal axis

Fig. 5 shows a third embodiment of the tube-in-tube merger in a cross section parallel to its longitudinal axis

Description of preferred embodiments

Fig. 1 shows a tube-in-tube merger according to the invention in a passive state in a cross section orthogonal to its longitudinal axis. The tube-in-tube merger consists of two concentric elements 1, 2 and inside these the two tubes 3, 4 to be merged are arranged. The tube-in-tube merger consists of two concentrically arranged pipe shaped elements 1, 2; an outer tube 1 and a silicon rubber tube 2. The outer diameter of the silicon rubber tube 2 matches the inner diameter of the steel tube 1, such that the two elements form one solid element with no gap between them.

The two tubes 3, 4 to be merged are arranged inside the inner cavity of the silicon rubber tube 2, with the inner merging tube 4 inside the outer merging tube 3. The outer diameter of the outer merging tube 3 is smaller than the inner diameter of the silicon rubber tube 2, leaving a gap between the silicon rubber tube 2 and the merging tubes 3, 4. The two merging tubes 3, 4 can thus easily be pushed into the inner cavity of the silicon rubber tube 2.

The outer diameter of the inner merging tube 4 is smaller than the inner diameter of the outer merging tube 3, leaving a gap between the two merging tubes 3, 4. The inner merging tube 4 can thus easily be pushed into the inner cavity of the outer merging tube 3.

The inner merging tube 4 has been threaded onto a mandrel 5. The outer diameter of the mandrel 5 matches the inner diameter of the inner merging tube 4, such that the two elements form one solid element with no gap between them. The mandrel is of a material with low friction, e.g. Teflon to enable easy threading and removing of the tube 4 on and off the mandrel.

The tube-in-tube merger being in a passive state refers to it being at a lower assembly temperature, where the inner and outer diameters of the elements are as described here. This leaves gaps between the silicon rubber tube 2 and the outer merging tube 3, and between the inner merging tube 4 and the outer merging tube 3. At this lower assembly temperature, the elements can easily be assembled for the proceeding merging step described in association with fig. 2 by threading elements onto elements and inserting elements into each other.

Fig. 2 shows the tube-in-tube merger in an active state in a cross section orthogonal to its longitudinal axis. The tube-in-tube merger being in an active state refers to it being at a merger temperature, higher than the assembly temperature, where the coefficient of expansion changes the inner and outer diameters of the elements to the diameters described here. At the merger temperature the gap between the silicon rubber tube 2 and the outer merging tube 3 has vanished, and the gap between the inner merging tube 4 and the outer merging tube 3 has vanished.

While the elevated temperature would affect all the elements described, the primary effect used is the expansion of the silicon rubber tube 2 forcing it to attain a smaller diameter, making it compress the elements inside of it. While the silicon rubber tube 2 on its own would expand outwardly with temperature elevation, it is held snugly against the inside of outer steel tube 1. While the coefficient of expansion of the steel tube 1 is low, the coefficient of expansion of the silicon rubber tube 2 is higher, forcing the silicon rubber tube 2 to instead expand inwards, shrinking its inner diameter.

As inner diameter of silicon rubber tube 2 shrinks, it reaches the outer merging tube 3 and compresses it inwardly. As inner diameter of silicon rubber tube 2 shrinks further, the outer merging tube 3 reaches the inner merging tube 4 and act to compress both inwardly. As the temperature elevates further, the temperature of the outer merging tube 3 reaches a point where it fully or partially melts, reflows, and merge with the inner merging tube 4.

The temperature of the entire arrangement can now be lowered, such that a gap reforms between the silicon rubber tube 2 and the outer merging tube 3, leaving the outer merging tube 3 merged with the inner merging tube 4. With the lowered temperature the outer merging tube 3 resolidifies, attached to the inner merging tube 4, such that the two merging tubes 3, 4 form a solid element with no gap between them. The mandrel is then removed from the two merged merging tubes 3, 4.

Figs. 3-5 show embodiments of the tube-in-tube merger in a passive state, that is at the lower assembly temperature, where gaps between the silicon rubber tube 2 and the outer merging tube 3, and between the inner merging tube 4 and the outer merging tube 3 appear. The gaps are to scale and are illustrated with sizes typical for a realistic case, so they appear small in the figure. Each of the embodiments is used with a sequence of temperatures, starting at a lower assembly temperature, followed by a higher merger temperature, finally returning to the lower assembly temperature.

Figs. 3-5 show a segment of the tube-in-tube merger, the illustrated length of which is selected such that the diameters of the elements can be properly shown in the figures. The actual length of the tube-in-tube merger is arbitrary.

Fig. 3 shows a first embodiment of the tube-in-tube merger in a cross section parallel to its longitudinal axis. Here, as in figs. 1-2, the outer steel tube 1 holds inside it the silicon rubber tube 2, with the outer merging tube 3 inside the silicon rubber tube 2, the inner merging tube 4 inside the outer merging tube 3 and finally the mandrel 5 inside the inner merging tube 4.

The diameter of each of these elements remain constant throughout the entire length of the arrangement. After temperature sequencing, the end result is a homogenous inner and outer diameter element merged tube pair, comprising the inner merging tube 4 and the outer merging tube 3 merged together.

Fig. 4 shows a second embodiment of the tube-in-tube merger in a cross section parallel to its longitudinal axis. The elements are here arranged in the same way as in figs. 1-3, but with the inner merging tube 4a-c having varying wall thickness along its length. The inner merging tube 4a-c comprises three consecutive segments, a first segment 4a with the smallest wall thickness, followed by a second segment 4b with an intermediate wall thickness and finally a third segment 4c with the largest wall thickness.

In order to be able to fit the outer merging tube 3 onto the inner merging tube 4a-c, the outer merging tube 3 diameter varies in a corresponding fashion. The outer merging tube 3 comprises three consecutive segments, a first segment with the largest diameter, followed by a second segment with an intermediate diameter and finally a third segment with the smallest diameter. The outer merging tube 3 is illustrated as a single element, but alternatively, three consecutive outer merging tube 3 segments may be constituted by separate elements.

In order to fit the inner merging tube 4a-c and outer merging tube 3 into the silicon rubber tube 2a-c with a snug fit, the inner diameter of silicon rubber tube 2a-c varies in a corresponding fashion. The silicon rubber tube 2a-c comprises three consecutive segments, a first segment 2a with the largest wall thickness, followed by a second segment 2b with an intermediate wall thickness and finally a third segment 2c with the smallest wall thickness. If the variation of the diameters is big it may be necessary to also have varying diameters of the metal tube.

After temperature sequencing, the end result is a merged tube pair with a homogenous inner diameter and varying outer diameter, comprising the inner merging tube 4 and the outer merging tube 3 merged together.

Fig. 5 shows a third embodiment of the tube-in-tube merger in a cross section parallel to its longitudinal axis. The elements are here arranged in the same way as in figs. 1-3, but with the outer merging tube 3 extending only a portion of the length of the inner merging tube 4a-b.

In order to fit the inner merging tube 4a-b and outer merging tube 3 into the silicon rubber tube 2a-b with a snug fit, the inner diameter of silicon rubber tube 2a-b varies in a corresponding fashion. The silicon rubber tube 2a-b comprises two consecutive segments, a first segment 2a with the largest wall thickness and a second segment 2b with the smallest wall thickness.

After temperature sequencing, the end result is a merged tube pair with a homogenous inner diameter and varying outer diameter, comprising the inner merging tube 4 and the outer merging tube 3 merged together, where the outer merging tube 3 extends only a portion of the length of inner merging tube 4.

Alternative embodiments

During temperature cycling the temperature of the entire tube-in-tube merger with merging tubes 3, 4 can have time to equalize. The melting point of the outer merging tube 3 is below the merging temperature, so that it fully or partially melts, reflows, and merge with the inner merging tube 4. The melting point of the inner merging tube 4 should preferably be above the merging temperature. The melting point of the silicon rubber tube 2a-b must be above the merging temperature, and that is one of the reasons silicon rubber is suggested, as it has a high melting temperature. Silicon rubber also has low surface friction, which facilitates introducing the merging tubes 3, 4 into the silicon rubber tube 2a-b.

Obviously, the silicon rubber tube 2a-b may be made from other substances with suitable coefficient of expansion, sufficiently high melting point and preferably low surface friction.

In the illustrated embodiments the silicon rubber tube 2 does - during a temperature increase - act against a steel tube 1, forcing the inner diameter of the silicon rubber tube 2 to shrink. The tube 1 may be made from any other substance with a low coefficient of expansion or at least coefficient of expansion lower than that of the silicon rubber tube 2. This could for example be copper or glass. It is however advantageous to have a big difference since it is easier to calculate the diameters needed for the metal tube and the hole in silicon rubber. The expansion coefficient of silicon rubber is approximately 10 times higher than for steel which means that for most cases the expansion of the steel tube expansion can be neglected when doing this calculation.

While the illustrated embodiments do not show how the temperature cycling is done, it could be done by supplying heat to the steel tube 1. To increase the speed of the cycling the steel tube 1 could be replaced by a tube made from a substance with a degree of higher heat conductivity, such as copper or aluminum. Alternatively, heat could be supplied using radiation, in which case metals would be disadvantageous, and steel tube 1 replaced by a glass tube. A simple way to manufacture the device is to place a Teflon tube in the center of the steel tube, fill the free space with silicone rubber, let the silicon rubber cure and remove the Teflon tube

In the illustrated embodiments the outer diameter of the silicon rubber tube 2 matches the inner diameter of the steel tube 1. The silicon rubber tube 2 may adhesively adhere to the inner diameter of the steel tube 1, firmly holding the two elements together. Alternatively, the outer diameter of the silicon rubber tube 2 in its uncompressed state may be slightly larger the inner diameter of the steel tube 1 and held in place by it pressing against the inner diameter of the steel tube 1.

In the illustrated embodiments two merging tubes 3, 4 are merged together, but obviously any number of merging tubes may be merged together, each inside a larger one. In the illustrated embodiments the inner merging tube 4 has been threaded onto a mandrel 5. If the innermost merging tube is sufficiently sturdy, no such mandrel is necessary. While the innermost merging tube is denoted tube, it could have a more complex shape than a simple tube, with varying inner and outer diameter, having more than one lumen or lack lumens, that is it constitutes a solid element. The denotation tube is here used meaning any such element.

In a typical application, the inner merging tube 4 is constituted by a catheter shaft. The outer merging tube 3 may then for example be constituted by a flexible and stretchable PCB, an FPC, wrapped around the catheter shaft. While the FPC in itself is a flat element, it is here formed into a tubular element with a longitudinally extending gap. The outer merging tube 3, although denoted tube, may attain a number of different shapes, such as such a split tube, one with varying inner and/or outer diameter and still here be denoted tube.

A preferred embodiment would have a coil outside and around the steel tube, the coil used to inductively heat the steel tube. The coil could also be split into several coils along the length of the device which would allow the use of different temperatures for reflow. This could be an advantage if the shaft and the tube comprise sections with different material properties.

In prior art EP catheters the lumens are used for conductor wires from electrodes to a proximal connector and/or possible steering wires to a handle. These conductor wires and electrodes are elements separate from the catheter main body, contrary to the situation with a catheter according to the invention. In a catheter according to the invention, the conductor wires and electrodes are solidly fixed to the FCB, which is reflowed into a tubular shape which with the exception of a centre cavity, after reflowing forms a single continuous solid element. If the FCB with conductor wires and electrodes are instead wrapped around a core element and reflowed onto it, it does in its entirety form a single continuous solid element. Since the conductor traces and electrodes for a catheter according to the invention are integrated with the catheter body the lumen or lumens are free to use for other purposes at least for pre-shaped catheters.

In one embodiment taking advantage of the advantage mentioned above, a pressure sensor or thermistor can easily be inserted, fixed and thermally contacted to the catheter body near the proximal end, close to the electrodes. The conductor traces are placed in the lumen and drawn to the proximal connector. Continuous measurement of temperature during ablation improves the safety of the procedure.

In another embodiment taking advantage of the advantage mentioned above, an alternative temperature sensor is based on optical measurement and in this case the temperature information is transmitted by an optical fiber. The sensor is integrated with the tip of the fiber so in this case the sensor/fiber is aligned with the proximal end of the catheter.

In yet another embodiment taking advantage of the advantage mentioned above, a device that can give a visible overview of the inside of the heart, placed on the distal end of the catheter and using the lumen for data transmission either by a fiber or a data bus depending on the sensor type and the electronics used for transforming sensor information to digital format. Two sensor options are constituted by an ultrasound transceiver or alternatively an infrared sensitive camera (e.g. Omnivision OV6948 or similar) with an associated LED. Visible orientation is valuable at catheterization inside the heart and would be particularly useful when a lasso catheter is positioned for pulmonary vein isolation.