In general, where a fluid is passed through a tube, depending upon the nature of the fluid, there is a risk that matter from the fluid will be deposited on the inner surface of the tube. This is especially the case with biological fluid for example. Where deposition occurs and the flow of fluid continues, the deposition can quickly build up to a point where the tube becomes partially or fully blocked. Much effort is therefore made to filter and clean the fluids that are circulated through tubing or piping to reduce the presence of such matter in the fluid stream and thereby reduce the effects of the deposition of such matter. The problems become acute the smaller the bore of the tubing and thus is of particular concern with micro- tubing that is used in medical and surgical procedures.

To date, other than extracting depositable matter from the fluid stream prior to the circulation of the fluid through such tubing, the only alternatives have been to dispose of the tubing once the deposition becomes too severe or to regularly interrupt the fluid flow and clean the tubing to remove any deposits before they present a partial or total barrier to further fluid flow.

An alternative to these known methods of addressing the problem of deposition that would not attracted the problems currently encountered is desired and in this respect the present invention seeks to provide self- cleaning tubing that is capable of greatly reducing if not eliminating the deposition of matter on its inner walls.

The use of piezo-electric material in tubing to drive flexure of the tubing is already known and an example of a piezo tube is described in US 6,194, 813. However, such piezo tubes are limited in use to producing spatial movements of the entire tubing away from the axis of the tube and involve dividing the wall of the tube circumferentially into four sections.

Furthermore, in DE10109932 a piezoelectric transducer for generating ultrasound particularly for use in ultrasonic cleaning is described. The piezoelectric transducer comprises a vibrating plate for transferring vibrations to a fluid and comprising at least one piezoelectric element for generating ultrasound.

In accordance with the present invention on the other hand there is therefore provided tubing for the passage of a fluid comprising: a resilient tubular support; a plurality of piezo-electric elements, each element being arranged at a respective axial location along the tubular support; and phased drive circuitry connected to the plurality of axial piezo-electric elements, wherein each one of the plurality of axial piezo-electric elements is separately addressable by means of the drive circuitry and the drive circuitry is adapted to issue respective phased driver signals to each one of the plurality of axial piezo-electric elements with the phase of the driver signal for each axial piezo-electric element being dependent upon the axial position of the axial piezo-electric element.

Thus, with the present invention the tubing is adapted to perform a peristaltic action thereby reducing and in many cases preventing the deposition and accumulation of matter on the inner walls of the tubing.

The tubing is particularly suited to use in medicine, for example as a catheter, and also in the food and chemical industries.

An embodiment of the present invention will now be described by way of example with reference to and as shown in the accompanying drawings, in which: Figure 1 is a schematic diagram of self-cleaning micro-tubing in accordance with the present invention; Figure 2a is a diagram of individual control elements and their interconnections in the micro-tubing of Figure 1; Figure 2b illustrates one example of the type of control signals that may be used to induce a peristaltic action in the micro-tubing of Figure 1; Figures 3a to 3d are schematic diagrams of the fabrication process for the micro-tubing of Figure 1; and

Figure 4 illustrates one method of forming, from the planar structure produced according to the method illustrated in Figures 3a to 3d, the micro- tubing of Figure 1.

Figure 1 shows a section of micro-tubing 1 that is suitable for use in a catheter and other medical and surgical equipment and procedures. The device is suitable for tubes with an inner diameter ranging from approximately 1 mm upwards and with a tube wall thickness of approximately 0.5mm upwards. In overview, the micro-tubing 1 has an outer sleeve 2 of the bulk material of the tubing such as a polymer material.

An example for in vivo/medical applications is silicone. For non-medical applications the material could be Teflon. Inside of the outer sleeve 2 is a piezo-electric array 3 that is controlled by drive circuitry 4 which is mounted on a flexible circuit board that is in the form of a tubular support.

Electrical contacts 5 supply power to the piezo-electric array and an antenna 6 may be provided within the outer sleeve 2 to provide remote charging of the power source. In medical applications, for example, the antenna 6 is designed to allow electrical power transmission through the body wall of a patient. This is necessary to eliminate power cables running through the skin and body wall which will increase the probability of infection.

As can be seen more clearly in Figure 2a the piezo-electric array 3 consists of a plurality of separately addressable piezo-electric transducers 7 distributed circumferentially and axially along the tubing. The individual piezo-electric elements of the array are evenly spaced axially along the tubing. Appropriate sequencing of the phased driver signals which actuate the individual piezo-electric transducers 7, by means of the circuit connections 8, can result in a pressure wave tangential to the inner surface being applied to the fluid within the tubing. The driver signals issued to the individual piezo-electric transducers are phased in dependence upon the axial position of the piezo-electric transducer. Optionally, the driver signals may additionally be phased with respect to the circumferential position of individual piezo-electric transducers.

To most closely mimic the conventional peristaltic action, a plurality of piezo-electric transducers having a common axial position along the tubing 1 are actuated together. In Figure 2b an example of a sequence of driving pulses for three series of piezo-electric transducers A, B and C at three different but adjacent axial positions along the tubing is illustrated.

Thus, the A series of transducers is actuated first and subsequently series B and then series C are actuated in turn with a partial overlap in the driving signals supplied to each transducer series. This produces the effect on the fluid within the tube of a travelling pressure wave which is particularly effective at preventing the deposition of matter on the walls of the tubing.

Preferably, the individual piezo-electric transducers 7, which can be single slab piezo transducer or bi-morph (dual slab) transducers are distributed evenly around the circumference of the tubing with the axial spacing between the piezo-electric elements preferably differing from the circumferential spacing of the piezo-electric elements. Phased electrical driving signals ensure that the inner surface of the tube is repeatedly agitated. The segmented transducer system allows a combination of axial and circumferential pressure waves to be applied to the fluid in the tube.

In Figures 3a to 3d one method of fabrication the micro-tubing described above is illustrated. The fabrication process begins (Figure 3a) with a flexible circuit board 4 consisting of, for example, a polyimide film 9 such as that available from DuPont under the trade name KaptonTM on which the necessary control and power circuitry 10 for driving the piezo- electric transducers is written along with a power supply line 11. A layer of conductive adhesive 12 such as Ablebond 84-1 TM is applied to the upper surface of the circuit board 9 and is used to adhere a PZT (lead zirconate titanate) thin film layer 13 on which sintered contacts 14 such as copper contacts are already established. A blast resistant mask 15 is then applied and patterned so as to define the structure of the desired piezo-electric transducers 7.

As illustrated in Figure 3c, the piezo-electric layer 13 is then powder blasted through the blast resistant mask 15 to define the transducer

structure. The etching of the PZT film is controlled to achieve a desired angle 6 which is the angle of the side walls of each transducer element with respect to the perpendicular. The angle 9 is significant because later in the fabrication procedure the circuit board will be curved to describe a cylinder and it is important to ensure that the edges of adjacent transducers do not contact one another. The range of angle is dependent on the tube diameter and the number of segments around the circumference.

Turning now to Figure 3d, once the individual transducer structures are formed, the blast resistance mask 15 is removed and the upper surface of the circuit board and the transducers is spray coated with a photo- imageable insulator 16 such as polyimide BLB etc. A mask is applied over the insulator 16 so that it may be etched to expose a selected region of the upper contact of each transducer. Thereafter, a common electrode 17 is deposited over the insulator and the exposed regions of the transducers using for example a conventional vacuum coating deposition process.

Finally the common electrode 17 is patterned using conventional lithographic and etching techniques.

The underside of the flexible circuit board 4 is cut 18 at regular intervals by means of laser ablation so as to further improve the flexibility of the structure and then the structure is sliced into a series of long strips with each strip intended to from a single tube.

The long sides of each strip are then rolled together to form the tube and the inner surface of the tube is preferably coated with a planarising polymer solution which may additionally contain an anti-bacterial agent.

This inner layer may be introduced by passing the polymer solution through the tube. External electrodes are attached to provide the power connection and finally the outer surface of the tube is coated with the bulk polymer material 2. The antenna 6 may also be incorporated into the structure at this stage in the fabrication process. The antenna could be a simple loop antenna consisting of electrical wire. This is incorporated into the outer sheath.

As illustrated in Figure 4, the strip may be rolled into a tube structure

using a jig (not illustrated) which gradually urges the long sides of the strip towards one another. With this process each of the long edges of the strip has a dry curable adhesive applied 19 so that when the long edges contact one another the adhesive may be activated to secure the edges together.

Alternatively, a cylindrical former 20 may be used to shape the tube.

The present invention is not limited to the above described micro- tube and alternative and additional features are envisaged without departing from the scope of the appended claims. For example, instead of Kapton an alternative material for the circuit board substrate may be used and to provide added flexibility an elastic substrate may be chosen.

Although not illustrated, the layout of the microstructures may be chosen to accommodate greater flexibility and achieve a smaller minimum radius through a greater use of laser ablation of the circuit board substrate in selected regions. For example, a meandering electrical trace may be defined between adjacent common addressing pads. Such a meander allows the Kapton to extend and compress, when the tube is flexed. These and other features are encompassed by the present invention.