FIELD OF THE INVENTION

This invention relates generally to medical tubes and to medical devices comprising medical tubes, and more specifically to wound dressings comprising medical tubes for use in negative pressure wound therapy.

BACKGROUND TO THE INVENTION

Negative pressure wound therapy (NPWT) involves the application of a pressure that is reduced relative to the surroundings (commonly referred to as“negative pressure”) to a wound, which causes mechanical contraction of the wound and removal of wound fluid from the wound, thus promoting formation of granulation tissue and accelerating wound healing. The technique is particularly effective in the treatment of slow healing wounds such as chronic leg ulcers and large open wounds. A wound dressing comprising an occlusive wound cover that is traversed by a medical tube is applied to a wound such that the wound cover forms a seal around the wound under which a reduced can be applied. The medical tube is then connected to a source of reduced pressure in order to apply a reduced pressure to the wound and drain wound fluid from the wound.

There are numerous other medical devices comprising medical tubing that must remain in contact with the body for prolonged periods, such as chest drains, catheters and drips.

Medical tubes are typically circular in cross-section and formed of relatively hard elastomeric plastics material such as silicone or polyvinylchloride. Such tubes are prone to being partially or completely blocked in the event that the tube becomes pinched or kinked. In addition, when in prolonged contact with the skin, such tubes can cause pain or discomfort to the patient, including the formation of pressure sores, especially if the patient lies on the tubes for prolonged periods. This invention provides a novel medical tube suitable for use in NPWT and other applications, which overcomes or substantially mitigates the above-mentioned and/or other limitations associated with the prior art.

GENERAL DESCRIPTION OF THE INVENTION

According to a first aspect of the invention, there is provided a medical tube comprising a substantially fluid impermeable outer sheath and an inner scaffold having a textured surface.

The scaffold comprising a textured (ie not smooth) surface prevents the lumen of the tube being entirely blocked, even in the event that the tube becomes pinched or kinked. In particular, the space between the inner surface of the sheath and the outer surface of the scaffold constitutes the lumen of the medical tube and the textured surface of the scaffold maintains a separation between the sheath and at least a proportion of the surface of the scaffold, even when the medical tube is kinked or pinches, such that a proportion of the lumen remains open for fluid flow.

The scaffold is preferably present along substantially the entire length of the medical tube and the textured surface is preferable present along substantially the entire length of the scaffold. The textured surface is present on at least a portion of the surface of the scaffold that defines the lumen of the medical tube and may comprise substantially the entire surface of the scaffold, or may comprise at least 90%, at least 80%, at least 70%, at least 60% or at least 50% of the surface of the scaffold.

The textured surface of the scaffold may be a generally uneven surface, which may comprise one or more projections from and/or depressions in the surface of the scaffold. In particular, the textured surface may comprise at least one projection, which may in particular be a region of the surface of the scaffold that is raised relative to an adjacent region of the surface of the scaffold. The projections may project from the surface of the scaffold by at least 1 mm, at least 2mm or at least 3mm. The number and form of the projections may vary considerably, although the textured surface preferably comprises multiple discreet projections. The multiple discreet projections may be present along substantially the entire length of the scaffold and in particular may each extend along substantially the entire length of the scaffold or be located at generally regular intervals along substantially the entire length of the scaffold.

The one or more projections may remain in a substantially fixed conformation and/or position relative to one another, which is particularly advantageous as it ensures consistent performance of the medical tube and in particular that the lumen of the tube remains consistently open to fluid flow even when the tube is punched or kinked.

The one or more projections may be elongate in form and may further be oriented along the longitudinal axis of the scaffold, and hence parallel to the direction of fluid flow along the medical tube, in order to minimize obstruction to the fluid flow along the medical tube. In particular, the textured surface preferably comprises multiple elongate projections arranged substantially parallel to one another, such that the spaces between the projections define channels that remain open for fluid flow, even in the event that the tube becomes kinked or pinched. The elongate projections may extend along substantially the entire length of the scaffold and the medical tube. The textured surface may comprise up to 20, up to 15 or up to 10 parallel elongate projections, and in particular may comprise from 2 to 10 or from 3 to 7 parallel elongate projections.

The scaffold may be flexible, and in particular may be resiliently deformable, in order to provide the medical tube with sufficient flexibility to conform to uneven surfaces, such as surfaces of the body, while also enabling the medical tube to resist kinking and readily spring back into shape following deformation. The scaffold may be formed of a synthetic plastics material such as polyvinylchloride. The scaffold may be formed by any suitable means such as extrusion, injection moulding or 3D printing.

The width of the scaffold may be greater than its thickness such that scaffold has a generally flat cross-section. In particular, the ratio between the width and the thickness of the scaffold may be at least 2: 1 , 5: 1 , 10: 1 , 20: 1 or 50: 1. In such embodiments, a textured surface may be provided on one or both sides of the scaffold. In addition, the scaffold may have rounded edges and/or the thickness of the scaffold may be tapered towards each edge. The substantially flat cross- section of the scaffold spreads pressure more evenly and hence enables the medical tube to be in contact with the patient for extended periods without causing pain or discomfort or causing pressure sores.

The scaffold may comprise apertures that pass through the scaffold in order to provide additional fluid flow paths along the medical tube and reduce the obstruction that the scaffold presents to fluid flow along the medical tube. The apertures may be distributed substantially evenly along the entire length of the scaffold. The apertures may be located in the textured surface, in which case they may be locates in the regions between the projections. In embodiments in which the scaffold has a substantially flat cross-section, the apertures may

communication between one side of the scaffold and the other. In addition, the scaffold preferably comprises one or more apertures at one or both ends of the medical tube or any other point at which the medical tube is to be connected to another medical tube, port or medical device, in order to ensure that the scaffold does not present a significant obstruction to the flow of fluid into and out of the tube at these points.

The outer sheath of the medical tube may be substantially fluid impermeable. In addition, the sheath is preferably substantially flexible in order to allow the tube to conform to irregular surfaces, such as surfaces of the body, and to enable expansion of the medical tube in order to accommodate fluid flow. In addition, the sheath is preferably formed of a relatively soft material in order to improve comfort when the tube is in contact with the body. The sheath may also be transparent or translucent such that the lumen of the tube can be viewed from the exterior of the tube, for example in order to enable the identification of blockages within the tube.

The sheath is preferably a thermoplastic or other heat-weldable material in order to enable the sheath to be formed by heat welding or welded to other components of the medical tube or a medical device into which the tube is incorporated by heat-welding or ultrasonic welding. In particular, heat-welding is advantageous because no additional components are introduced, such as an adhesive, which could contaminate the contents of the medical tube.

The sheath is preferably formed of a sheet of plastics material such as

polyvinylchloride.

In some embodiments, the sheath may surround the scaffold entirely. In these embodiments, the sheath may be in the form of a tube of material or two or more strips of material that are joined together along their edges while the scaffold is located between them so as to encapsulate the scaffold between the sheets. These embodiments are most suitable for medical tubes having a single lumen as depicted in Figures 2A and 2B.

In some embodiments, the sheath may be bonded to the scaffold, which may hold the scaffold in place relative to the sheath in order prevent the scaffold shifting within the sheath. The sheath may be bonded to the scaffold along the entire length of the lumen of the medical tube such that the lumen is separated in order to produce a multi-lumen medical tube.

The sheath may be bonded to the scaffold around its edge such that a lumen of the tube is formed in the space between the sheath and the region of the scaffold over which the sheath is bonded. The sheath may comprise multiple sections that are each individually bonded to the scaffold around their edges in order to produce a multi-lumen tube as depicted in Figures 5A and 5B. The sheath is preferably forms a fluid-impermeable bond with the scaffold and in particular the sheath and the scaffold may be bonded together by heat welding or ultrasonic welding.

The medical tube may comprise means for establishing fluid communication with the lumen of the tube at one or both ends. This may comprise means for establishing fluid communication with another tube, a port or a medical device into which the tube may be incorporated. This may comprise a connector extending from the sheath, which may be suitable for establishing connection with another tube or a port by a conventional means, such as a Luer taper. The connector may be integrally formed with the scaffold in order to simplify manufacturing of the tube and provide the medical tube with a more robust construction. Multi-lumen medical tubes may comprise separate means for connection to each lumen.

The medical tube may be a single-lumen medical tube or a multi-!imen medical tube such as a double-lumen medical tube.

The medical tube may have essentially any length depending on the required application, but in particular may be at least 0.5m, at least 1 0m, at least 3.0m or at least 10m in length. Preferably the tube has an external maximum dimension of between 4mm and 10mm, between 5mm and 8mm or about 6mm. The medical tube may be a suitable conduit for liquids, gasses or both liquids and gasses.

The medical tube of the invention may be incorporated into a medical device.

Thus, according to a second aspect of the invention, there is provided a medical device comprising a medical tube that comprises a substantially fluid impermeable outer sheath and a flexible and resilient inner scaffold having textured surface.

The medical tube may be a medical tube according to the first aspect of this invention. The medical device may be any medical device that comprises a medical tube, such as a chest drain, surgical drain, catheter, drip or negative pressure wound therapy (NPWT) dressing.

The medical tube may be connected at one or both ends to the medical device. The medical tube may be adapted for connection at one end to a port or another medical tube which, in the case of an NPWT dressing, may be coupled to a source of reduced pressure.

The NPWT dressing may comprise a dressing body that may comprises a backing layer that is preferably substantially fluid-impermeable and an adhesive layer on the skin facing surface that is capable of forming a substantially fluid-impermeable seal against the skin. The dressing body may also comprise a porous body located between the backing layer and the adhesive layer, which may serve to absorb wound exudate and distribute the reduced pressure across the dressing body. The adhesive layer may comprise one or more openings through which the reduced pressure may be applied to the wound, and preferably through which the porous body may be exposed to the wound.

The backing layer of dressing body may comprise an opening in order to enable a reduced pressure to be applied to a wound. The opening is preferably located adjacent to the porous body in order to facilitate distribution of the reduced pressure across the dressing body.

The medical tube may be attached to the dressing body adjacent to the opening in the packing layer such that the lumen of the medical tube is in fluid communication with the NPWT dressing body, and preferably the porous body. In particular, the medical tube is preferably attached to the backing layer of the dressing body. The medical tube may be attached to the dressing body by any suitable means, such as by heat welding or with the use of a suitable adhesive.

The medical tube may be attached to the dressing body via the sheath. The sheath typically comprises one or more sheets of impermeable material and one or more of those sheets may be formed into a tab located adjacent to the end of the medical tube and that provides additional surface area for the medical tube to be securely attached to the dressing body. The tab may be any suitable shape but is preferably circular. The dressing body or the medical tube may further comprise a reinforcing material at the point at which the medical tube is attached to the dressing body in order to increase the force required to detach the medical tube from the dressing body

The NPWT dressing may further comprise a filter for preventing or reducing the extent to which relatively large pieces of material that might cause an obstruction in the tube can be drawn from the wound dressing into the tube.

The end of the medical tube distal from the NPWT dressing body may be adapted for connection to a source of negative pressure. A suitable connection may be achieved by a conventional connector, such as a Luer taper, with a conventional medical tube, such as a silicone or polyvinylchloride tube.

The NPWT dressing body may be generally conventional and of similar form to other wound dressings for use in negative pressure wound therapy. For example, the dressing body may comprise one or more wound packing elements and absorbent components to aid in removal of exudate from the wound and to prevent a large wound from collapsing under reduced pressure. As described above, the dressing body typically comprises a backing layer that is substantially

impermeable to air and liquid, so that a reduced pressure can be established and maintained between the dressing and the wound to which it is applied. However, the backing layer may have a low degree of permeability in order to allow for the transmission of moisture vapour away from the skin and hence improve skin adhesion and the formation of a substantially fluid impermeable seal against the skin. The backing layer may be formed of a sheet of microporous plastics material such as a polyurethane film and

The adhesive is preferably a non-adherent or low-adherence adhesive, most preferably a silicone gel. The adhesive may be perforated, and in particular may be provided with a regular array of perforations, in order to permit transmission of moisture vapour away from the skin.

The NPWT dressing comprising a drainage tube according to the second aspect of the invention may be used to treat a wound.

Thus, according to a third aspect of the invention, there is provided a method of treating a wound comprising the steps of:

(a) applying a negative pressure wound therapy dressing according to the

second aspect of the invention to a wound;

(b) connecting the distal end of the medical tube to a source of reduced

pressure; and,

(c) applying a reduced pressure to the wound via the medical tube.

The method is preferably a method of treating a slow healing wounds such as ulcers, such as chronic ulcers and diabetic ulcers, and large open wounds, such as large open wounds on the extremities such as the leg.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described in greater detail, by way of illustration only, with reference to the accompanying drawings, in which

Figure 1 is a plan view of a negative pressure wound therapy (NPWT) dressing according to the invention;

Figure 2A is a plan view of a single-lumen medical tube according to the invention, which comprises a first embodiment of a scaffold for use in a single-lumen medical tube according to the invention;

Figure 2B is a transverse cross-sectional view of the medical tube of Figure 2A taken along line A-A; Figure 3A is a plan view of a further embodiment of a scaffold for use in a single- lumen medical tube according to the invention;

Figure 3B is a longitudinal cross-sectional view of the scaffold of Figure 3A taken along line B-B;

Figure 3C is a transverse cross-sectional view of the scaffold of Figure 3A taken along line C-C;

Figure 4A is a plan view of a further embodiment of a scaffold for use in a single- lumen medical tube according to the invention;

Figure 4B is a longitudinal cross-sectional view of the scaffold of Figure 4A taken along line D-D;

Figure 4C is a is a transverse cross-sectional view of the scaffold of Figure 4A taken along line E-E;

Figure 5A is a perspective view of a double-lumen medical tube according to the invention;

Figure 5B is a transverse cross-sectional view of the medical tube of Figure 5A taken along line F-F;

SPECIFIC DESCRIPTION OF THE INVENTION

Figure 1 depicts a negative pressure wound therapy (NPWT) dressing 1 according to the invention. The dressing 1 comprises a generally square dressing body 10 and a drainage tube 20.

The dressing body 10 comprises a substantially fluid-impermeable backing layer 12 that forms the top (ie non-skin facing) surface of the dressing body 10, and an adhesive layer (not shown) that forms the bottom (ie skin facing) surface of the dressing body 10 and that is capable of forming a substantially fluid-impermeable seal against the skin. A porous body 14 is located roughly in the centre of the dressing body 10 between the backing layer 12 and the adhesive layer. The adhesive layer comprises one or more openings (not shown) such that the porous body 14 is exposed on at least a portion of the bottom (ie skin facing) surface of the dressing body 10. The drainage tube 20 is attached at its proximal end to the backing layer adjacent to an opening (not shown) in the backing layer 12 that is located over the porous body 14, such that the drainage tube 20 is in fluid communication with the porous body 14.

The drainage tube 20 comprises a flexible sheath 22 formed of two strips of polyvinylchloride sheet that are heat welded together along both of their edges, and a resilient scaffold 30 formed of moulded polyvinylchloride located in the interior of the sheath 22 and extends along substantially the entire length of the drainage tube 20. The drainage tube 20 has a single lumen that is defined by the space between the internal surface of the sheath 22 and the external surface of the scaffold 30.

The scaffold 30 has a substantially flat profile and comprises three parallel ridges 32 that extend longitudinally along the scaffold 30 on its upper surface and three corresponding ridges on its lower surface (not shown). The scaffold 30 further comprises an aperture 34 at its proximal end that coincides with the opening (not shown) in the backing layer 12 such that the scaffold 30 does not obstruct the fluid communication between the drainage tube 20 and the porous body 14.

The sheath 22 extends beyond the end of the scaffold 30 at the proximal end of the drainage tube 20 and forms a circular tab 24 with a diameter that is

significantly greater than the width of the remainder of the drainage tube 20. This circular tab 24 is securely fastened to the backing layer 12 and forms an airtight seal between the dressing body 10 and the drainage tube 20. A reinforcing material 26 is attached to the backing layer 12 in the region at which the drainage tube 20 is attached to ensure the drainage tube 20 remains securely attached to the dressing body 10. The scaffold 30 extends from the sheath 22 at the distal end of the drainage tube 20 and forms a connector tube 36 for connection to a source of reduced pressure (not shown). The sheath 22 is heat sealed 28 to the surface of the connector tube 36 at the point at which the connector tube 36 emerges from the sheath 22 in order to form a robust fluid-impermeable seal.

The dressing body 10 may be placed over a wound with the exposed surface of the porous body 14 directly over the wound with the backing layer 12 and the adhesive forming a substantially air-tight seal around the wound. The connector tube 36 at the distal end of the drainage tube 20 is then be connected to a source of reduced pressure such as a vacuum pump (not shown), which can be operated in order to apply a reduced pressure to the wound.

The scaffold 30 is resilient and deformable and hence provides the drainage tube 20 with resistance to kinking and enables the drainage tube 20to return to its original conformation following deformation. The ridges 32 of the scaffold 30 also prevent the fluid flow path of the drainage tube 20 from being entirely obstructed, even in the event that the drainage tube 20 becomes pinched or kinked, as the spaces between the parallel ridges 32 remain open for fluid flow. In addition, the substantially flat profile of the scaffold 30 spreads pressure more evenly and hence enables the drainage tube 20 to be in contact with the patient for extended periods without causing pain or discomfort or causing pressure sores.

Figures 2A and 2B depict a single-lumen medical tube 120 according to the invention. The medical tube 120 is of a similar construction to the drainage tube 20 of the NPWT dressing described above and depicted in Figure 1 and comprises a flexible sheath 122 formed of two strips of polyvinylchloride sheet that are heat welded together around their perimeter 123, and a resilient scaffold 130 formed of moulded polyvinylchloride that extends along substantially the entire length of the medical tube 120 on the interior of the sheath 122. The medical tube 120 comprises a single lumen that is defined by the space 125 between internal surface of the sheath 122 and the external surface of the scaffold 130. The scaffold 130 has a substantially flat profile and comprises three parallel ridges 132 that extend longitudinally along the scaffold 130 on both its upper and lower surfaces. The edges 133 of the scaffold 130 are rounded and the thickness of the scaffold 130 tapers slightly towards its edges 133 in order to improve comfort when the medical tube 120 is in contact with the patient and to reduce the risk of the scaffold 130 damaging the sheath 122 when pressure is applied to the outside of the medical tube 120.

The scaffold 130 comprises an aperture 134 that corresponds with an opening (not shown) in the sheath 122 for connection of the medical tube 120 to a port or opening in a medical device (not shown). The aperture 134 facilitates passage of fluid between the exterior of the medical tube 120 and the side of the scaffold 130 that is opposite the opening (not shown) in the sheath 122. The sheath 122 may extend beyond the end of the scaffold 130 at this end of the medical tube 120, for example to form a circular tab (not shown) with a diameter that is significantly greater than the width of the remained of the medical tube 120, in order to provide a greater surface area for fastening the medical tube 120 and to facilitate the formation of a substantially fluid-impermeable seal. In particular, a connection at this end of the medical tube 120 may be formed with a medical device by securing the sheath 22 to the device around the opening (not shown), such as by heat welding of with an adhesive, in order to form a substantially fluid-impermeable seal between the medical tube 120 and the device.

At the opposite end of the medical tube 120, the scaffold 130 extends from the sheath 122 and forms a connector tube 136 that is suitable for forming a

connection to a port or medical tube by conventional means, such as a Luer taper. The sheath 122 is heat sealed 128 to the surface of the connector tube 136 at the point at which the connector tube 136 emerges from the sheath 122 in order to form a robust and fluid-impermeable seal between the sheath 122 and the scaffold 130. The scaffold 130 prevents the lumen of the medical tube 120 from being blocked even in the event that the medical tube 120 becomes pinched or kinked. In particular, the parallel ridges 132 of the scaffold 130 prevent the sheath 122 being pressed into contact with the scaffold 130 around its entire circumference and hence the spaces between the parallel ridges 132 remain open for the passage of fluid.

The scaffold 130 comprises numerous apertures 138 located between the ridges 132 at regular intervals along the length of the scaffold 130. These apertures 138 communicate between one side of the scaffold 130 to the other to permit fluid flow across the scaffold 130 and hence ensure fluid is able to find a path along the medical tube 120 even if it becomes kinked or sufficient pressure is applied to the exterior of the medical tube 120 to restrict the passage of fluid through the spaces between the parallel ridges 132 on one side of the scaffold 130.

Figures 3A-C depict a further embodiment of a scaffold 230 of a single-lumen medical tube according to the invention. The scaffold 230 has a substantially flat profile having three parallel ridges 232 extending longitudinally along its upper surface and having a substantially smooth lower surface. The scaffold 230 further comprises a raised rim 235 extending upwardly around the periphery of the upper surface of the scaffold 230 to approximately the same level as the ridges 232. The rim 235 provides additional spaces for fluid flow between the rim 235 and the two outer ridges 232 and further improves the resistance of the scaffold 230 to compression.

The scaffold 230 forms a connector tube 236 at one end that is suitable for forming a connection to a port or another medical tube by conventional means such as a Luer taper. The end of the connector tube 236 proximal to the scaffold 230 is open on the side of the scaffold 230 on which the ridges 232 are located. This embodiment of the scaffold 230 does not require apertures that communicate between one side of the scaffold 230 and the other because as ridges 232 are located on only one side of the scaffold 230 and there is not intended to be significant fluid flow on the side of the scaffold 230 opposite to the ridges 232. Figures 4A-C depict a further embodiment of a scaffold 330 of a single-lumen medical tube according to the invention. The scaffold 330 has a substantially flat profile having three parallel ridges 332 extending longitudinally along its upper surface, and three corresponding ridges 332 on its lower surface. The scaffold 330 further comprises raised rims 335 around the periphery of the upper and lower surfaces of the scaffold 330 to approximately the level of the ridges 332.

The scaffold 330 further comprises numerous apertures 338 located between the ridges 332 at regular intervals along the length of the scaffold 330. The apertures 338 communicate between the opposing sides of the scaffold 330 and enable fluid flow across the scaffold 330 and hence ensure fluid is able to find a path along the medical tube, even if it becomes kinked or sufficient pressure is applied to the exterior of the medical tube to restrict the passage of fluid through the spaces between the parallel ridges 332 on one side of the scaffold 330.

The scaffold 330 forms a connector tube 336 at one end, which is suitable for forming a connection to a port of another medical tube by conventional means such as a Luer taper. The end of the connector tube 336 proximal to the scaffold 330 is open on both sides of the scaffold 330.

Figures 5A and 5B depict a double-lumen medical tube 420 according to the invention. The medical tube comprises a flexible sheath having upper 422a and lower 422b parts, each formed of a strip of polyvinylchloride sheet, and a resilient scaffold 430 formed of moulded polyvinylchloride that extends along substantially the entire length of the medical tube 420. The scaffold 430 comprises a peripheral flange 437 to which the upper 422a and lower 422b flexible sheaths are heat welded in order to form a fluid-impermeable seal between the sheath 422a, 422b and the scaffold 430. Accordingly, the medical tube 420 comprises two separate lumens that are each defined by the spaces 425a, 425b between internal surface of the sheath 422a, 422b and the external surface of the scaffold 430. The scaffold 430 has a substantially flat profile and comprises seven parallel ridges 432 extending longitudinally along its upper surfaces and seven

corresponding ridges 432 on its lower surface. The scaffold 430 further comprises a raised rim 435 on each of its upper and lower surfaces that surround the regions of the upper and lower surfaces of the scaffold 430 on which the ridges 432 are located and which extend from the surface of the scaffold 430 to slightly below the level of the ridges 432.

The sheath 422a, 422b comprises an opening (not shown) on one side of the scaffold 430 at one end of the medical tube 420 to enable the connection of the medical tube to, for example, a medical device or another medical tube. The scaffold 430 at this end of the medical tube 420 further comprises an aperture 434 in order to enable a connection to be made between the opening (not shown) in the sheath 422a, 422b and the lumen on the opposite side of the scaffold 430 to the opening. In particular, in order for the lumens 425a, 425b to remain separate, the connection through the opening (not shown) in the sheath 422a, 422b and the lumen on the opposite side of the scaffold 430 to the opening forms a substantially fluid-impermeable seal with the aperture 434. Accordingly, the aperture 434 enables separate connections to the lumens 425a, 425b to be made through the opening (not shown) in the sheath 432a, 432b locates on one side of the scaffold 430 at one end of the medical tube 420.

The scaffold 430 comprises connector tubes 436a, 436b at the opposite end of the scaffold 430 to the aperture 434. The connector tubes 436a, 463b are suitable for forming a substantially fluid-impermeable connection with a standard medical duel- lumen connector. In order for the lumens 425a, 425b to remain separate, the end of the connector tube 436a proximal to the scaffold 430 opens into only the upper lumen 425a and the end of the connector tube 436b proximal to the scaffold 430 opens into only the lower lumen 425b. The sheath 422a, 422b is heat sealed to the surface of the connector tubes 436a, 463b at the point at which they emerge from the sheath 422a, 422b such that a robust fluid-impermeable seal is formed between the sheath 422a, 422b and the scaffold 430.