GB2470185A

GB2470185A - Medical bandage devices for venous leg ulcer treatments and long distance travelers

Info

Publication number: GB2470185A
Application number: GB0908036A
Authority: GB
Inventors: Jikui Luo; Mohsen Miraftab; Manzoor Ahmed
Original assignee: University of Bolton
Current assignee: University of Bolton
Priority date: 2009-05-11
Filing date: 2009-05-11
Publication date: 2010-11-17
Anticipated expiration: 2029-05-11
Also published as: GB0908036D0; GB2470185B

Abstract

This invention discloses medical bandage devices for venous leg ulcer treatments and long distance travelers on transportations such as trains and planes. The devices utilize the recovery force generated by a shape memory polymer (SMP) or SMP/composite strips to produce a static pressure profile to help blood circulation, hence to speed up the healing process of a venous leg ulcer. The invention discloses the structures of the bandages, which may consist of a single layer or multi-layers, with SMP in sheet or strips form and SMP as a single layer or integrated into fabrics, the structure of the bandage device, and the manufacture methods to produce the SMP-based bandage devices. The stimulus which is used to actuate the SMP may include, but not exclude, heat, UV- or infrared-light, RF microwave, chemical or even water. The SMP may be selected from thermoplastic and thermoset (covalently cross-linked) polymeric materials. Such polymeric materials include polymers based upon polyurethane, polystyrene, polynorbornene, polyethyleneterephthalate, polyethyleneoxide, poly(1,4-butadiene), poly(Tetrahydrofuran) and ABA triblock copolymers made from poly(2-methyl-2-oxazoline)-based SMPs and a biodegradable SMP such as oligo-(&epsi;-caprolactone)diol and crystallisable oligo-(&rgr;-dioxanone)diol.

Description

Pressure Actuator The present invention relates to a pressure actuator which comprises a shape memory polymer (SMP) or a composite comprising SMP. Such a pressure actuator may be of use in, for example, venous leg treatment, where the actuator utilizes the recovery force generated by the SMP or SMP composite to produce a static pressure profile to help blood circulation, and hence speed up the healing process of a venous leg.

Venous leg ulcer is one of the more common illnesses in developed countries. One in several tens of adults aged above 50 years in the UK suffers from venous leg ulcers.

The cost of treatment of venous leg ulcers in the UK alone is well over �600 million a year. Leg ulcers are exacerbated by a lack of physical activities and hence irregularities in blood circulation. This is especially the case for elderly patients. I...

:: : .. For patients with venous disease, the application of graduated external e.

* compression or pressure from the ankle to under the knee can help blood circulation is by forcing fluid from the interstitial spaces back into the vascular and lymphatic S..

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compartments. For this reason, it is a usual practice to ensure an external compression is applied in a graduated fashion, with the highest pressure being applied * at the ankle and a lower pressure being applied at the upper part of the leg. It has been proven that a graduated pressure applied to the leg of a person suffering from a venous leg will rectify blood circulation and enhance the healing process. The optimal value for the degree of pressure required remains a matter of some debate. In practice, the optimum pressure will vary according to a number of factors, including the severity of the condition and the height and limb size of the patient. The need for a range of different levels of compression has been reflected in the current British Standard which recommends a pressure level for stocking type bandage in the range from 14 to 35 nirnHg at the ankle.

There are a number of types of commercial bandages available in the market for venous ulcer treatments, such as lightweight conforming-stretch bandages which offer good elasticity, but produce rather low compression forces. Similarly, light support bandages exert good compression but have rather poor elasticity. There is another group of bandages called compression hosiery. Medical hosiery represents a useful and convenient method of applying a graduated compression to normal legs in order to prevent the development or recurrence of leg ulcers. Compression bandages currently represent the treatment of choice.

However, hosiery and compression bandages are of limited value in the * : treatment of active ulceration, and are difficult to apply over dressings. Importantly, * S *S..

the hosiery and compression bandages lose their mechanical strength, elasticity and * S. stiffness due to breakdown of fibres involved during use. The other drawbacks of these compression bandages are that extreme care needs to be taken to ensure that bandages do not slip or become displaced as this will lead to multiple layers, which in S.*.

* turn may lead to localized areas of unnecessary high pressure on the leg. These compression bandages must therefore be applied by a trained nurse or a doctor who must follow strict application instructions. These two types of bandages also lose their pressure gradually as time passes due to a loss of mechanical strength of the materials used.

For hosiery and compression bandages, uneven pressure applied to the front of the leg due to a non-circular shape of limb may cause irritation or initiate another wound on the bony prominence of the leg. A thick buffer layer or padding is always required between the limb and the compression bandage.

Another type of bandage used for venous ulcer treatment is an air-pressure type bandage, which has multi-chambers to build up a pressure profile or a graduated pressure. In this technique, an air pump is used to inflate and deflate an airtight bag wrapped around the leg. The air-pressure bandage is operated by pumping air into an air-tight bag to increase the pressure to required levels. An air-pressure bandage is a dynamic pressure adjustment, which is suitable for a curing process, but which is not suitable for static pressure application which is important for prevention, or for stopping a recurrence, of venous ulcers after the healing process. It is immobile as it is : : : powered by electricity and can only be operated by an experienced doctor or nurse in *.. . hospitals. It is therefore expensive and difficult to use for untrained, non-medical people.

One patent publication, WO 2008/0203 77, discloses a use of a shape memory *: material (shape memory alloy and shape memory polymer) as a pressure actuator for S.....

* active bandage applications. Heat stimulation by means of a heating element situated between a carrier material and a shape memory material is provided to actuate the shape memory material-based device to generate a dynamic pressure profile exerted on a limb for the leg ulcer treatment. Once again, this device is operated by electricity and therefore consumes a lot of energy. Battery operated versions of these devices are of limited use given their finite life and in any case they are immobile and complicated.

There is therefore a need for a pressure actuator, such as can be used in medical bandage applications and is able to provide a graduated pressure to a person's body part such as a leg, which does not require an inbuilt stimulus to function, which s does not suffer from finite lifetimes due to battery dependence, which is mobile, and which can be used by a non-medically trained people, such as patients themselves.

According to the present invention, there is provided a pressure actuator comprising a carrier material, a shape memory polymer attached to andlor integrated within the carrier material, and an attachment arrangement for attaching the actuator to an object, wherein the shape of the SMP is modified using a stimulus which is independent from the actuator.

The present invention details a pressure actuator comprising a shape memory S...

polymer material which can be used in, for example, medical bandage applications S...

* which are able to exert a static graduated pressure to a patient to treat, for example, a venous leg ulcer when the material is activated by an external stimulation such as mild heating (warm-up) or irradiation by e.g. infrared or ultra-violet light.

*:.E By "shape memory polymer" in the present invention it is meant a polymer which is able to return from a deformed state (temporary shape) to its original (permanent) shape when induced by an external stimulus or trigger, such as e.g. temperature change, irradiation (by UV, IR or electromagnetic radiation such as RF microwaves), pH variation, or chemical stimulus (including by water). This is a commonly accepted term in the art.

Polymers which exhibit a shape memory effect have both a visible, current (temporary) form and a stored (permanent) form. Once the permanent form has been manufactured, the material is then changed into another, temporary, form by processing through e.g. heating, deformation, and fmally, cooling. The polymer maintains this temporary shape until the shape change back into the permanent form is activated by a predetermined external stimulus.

It is the molecular net structure of SMPs which enables this property. The structure contains so-called "switching segments" that have the ability, to soften.

Temperature increase, for example, is one way of activating the switching process.

The rigid switching segments, which are responsible for the temporary shape, soften and the material resumes its original (permanent) form. The SJvlPs are effectively visco-elastic in character. *e..

: Various SMPs have been developed which can be actuated by external stimuli such as heat, infrared and UV lights, chemicals, pH-values, electric field and : 15 electromagnetic waves such as radio frequency (RF) microwaves, and even water.

* Synthesis of such SMPs typically involves incorporation of molecules, molecular *: . segments, nano-or microparticles that are sensitive to heat, infrared and UV light, *.*., * 1 chemicals, pH-values and RF microwaves. Absorption of IR or UV light changes density of cross-linked molecules, making the SMP soft enough to return its original shape, or RF microwave "warms-up" or softens the SMP materials, leading to a phase change from the glassy state to the rubbery state, and the shape of the SMP changes.

Similarly, chemicals and p1-i-value changes may lead to change of phase or shape of the SMP structure. Water can even be used to "soften" some SMPs, leading to shape change and recovery. A new conducting SMP composite has recently been developed by incorporating conductive particles such as carbon nanotubes and metal nanoparticles, and this can be activated by passing electricity through them. By using an SMP and the properties associated with such a material, it is possible to fabricate bandages in accordance with the invention which can be activated by a hand held heat, JR or UV light source, or electromagnetic wave emitter devices ete, where the mode of activation of the SMP is wholly independent from the pressure actuator itself.

SIvIPs return to their primary original shapes upon external stimuli. SMPs have a lot of advantages over shape memory alloys such as their low density, lighter weight, greater degree of flexibility, high shape recovery rate (i.e. up to about 400%), low cost arid easier processing. SMPs differ from shape memory alloys by their glass transition or melting transition from a hard to a soft phase which is responsible for the shape memory effect.

The SMP has a fixed shape once it has been cooled, hence a fixed force is 1:*.* 15 created. This shape remains unchanged as long as the temperature is well below the S..

* transitional temperature, Tg. Therefore, the pressure remains constant during the treatment without deterioration with time, a major problem and shortcoming of *...

* existing stocking and compression-based venous leg ulcer bandages.

One potential application for the pressure actuator of the invention is in medical bandages to provide a graduated pressure to a body part such as a leg, particularly in the treatment of venous leg ulcers, or in preventing their recurrence.

Other potential applications include, but are not limited to, pressure garments or dressings for persons who have suffered from burns, pressure bandages such as to prevent or treat bed sores, varicose veins or thrombosis, massage bandages, massage seats (e.g. in cars or airplanes), touch interactions for mobile devices and/or virtual reality, body contour correcting garments, pressure suits, and more. By modifying the pressure to the low range, the bandage can also be used to help blood circulation to ease discomfort for long distance travelers on a train or a plane and prevent potential cases of deep vein thrombosis.

For the sake of convenience and illustration only, reference will be made to the present invention hereinafter in its use in a medical bandage, particularly in the treatment of venous leg ulcers. However, it will be apparent to a person skilled in the art that this is not limiting upon the scope of the invention.

The pressure actuator of the invention also has the ability to increase the : pressure on a patient locally or wholly, simply by applying mild heat or other * stimulations to the bandage. This pressure increase can be activated by the patient : 15 him-or herself, hence avoiding the need for a nurse or a doctor to be present. The S..

SMP-based bandage can also be reused many times before it loses its functionality.

*. . Therefore, the cost of manufacturing and operating the SMP-based bandage can be * dramatically reduced.

In most instances, localized actuation is sufficient for the pressure adjustment as only minor force is required for the bandage application. The forces or the pressures of the SMP-based bandage can be generated or adjusted by heating, or by infrared or UV-light, or by RF microwave, or even by water, depending on the actuating mechanism of the SMPs used. For heat-sensitive SMPs with a Tg of about 50°C, a household object such as a hair drier or hot towel can be used to stimulate the SMP to produce the required force. For light-sensitive SMPs, IR or U17light sources can be used to produce pressures, for that of RF microwave-sensitive SMP, it can be activated by RF wave source; for a water-aetuatable SMIP, water can be used to activate the SMP. Also the stimulation could be localized, i.e. adjusted, in a particular area or the whole bandage could be loosened or tightened. These sources of external stimuli are all obtainable from common portable and household devices, small in volume and size, and are low cost. Such SMP-based bandages can therefore be applied and adjusted for venous ulcer treatment by patients themselves with no need for an experienced nurse or doctor. The medical device of the present invention has the advantages of low cost, easy to use, reusable and its pressure can be readjusted many times during use by the patient if it becomes loose mechanically, which is one of the major problems with S... existing pressure bandages. *...

According to a further embodiment of the invention, pressure sensors can be integrated with the SMP-based bandage. This can indicate to a person if the pressure *: *. being applied by the bandage has decreased and needs to be adjusted.

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S.....

* It is also of note that the time required for actuating SMP is in the order of a few seconds to a few tens of seconds. Therefore any incidence of unintentional heating or water splash on the SMP can be eliminated by simply removing the heat source or wiping off the water before the applied pressure is unintentionally changed.

According to one aspect of the invention, the SMP may be selected from thermoplastic and thermoset (covalently cross-linked) polymeric materials. Non-limiting examples of such polymeric materials include polymers based upon polyurethane-, polystyrene, polynorbornene, polyethyleneterephthalate, polyethyleneoxide, poly(l,4-butadiene), poly(Tetrahydrofuran) and ABA triblock copolymer made from poly(2-methyl-2-oxazoline)-based SMPs, and a biodegradable SMP such as oligo-(c-caprolactone)diol and crystallisable oligo-(p-dioxanone)diol.

Polyurethane-and polystyrene-based SMPs are the most commonly used SMPs for engineering and biomedical applications. Besides the good properties of general SMIPs mentioned above, polyurethane-and polystyrene-based SMPs have distinctive properties, such as a high resistance to organic solvents and aqueous solutions, a long-term stability against exposure to sunlight, a consistent elastic property, and biocompatibility. The transitional temperature of such polyurethane-and polystyrene-based SMPs can be adjusted between about 40°C and about 70°C which enables them * *..

to be stimulated to change shape using a household object such as a hot towel or a hair dryer. Other SMPs which could be used in the pressure actuator of the invention *: will be readily envisaged by a skilled person.

: : According to a further aspect of the invention, the SMP can be combined with a composite material. Such composite SMP products with fibres or fabric matrix reinforcement are even stronger than pure SMPs and can provide a much larger recovery force, mechanical strength and stiffness.

Examples of such fibres or fabrics may include, but are not limited to, polymers, particularly polymer fabrics, such as nylon or polyester, yarns, natural textile fibers, such as cotton or wool fibers, regenerated fibres such as viscose, and synthetic fibres such as polyester, polyamide (nylon) or polyacrylic fibres, polyolefins olypropylene and polyethylene), rubbery substances, leather, or animal skin etc. Typically, the carrier material may be a piece of fabric, a woven, nonwoven or knitted structure, a garment, a compression bandage or even a polymer which has sufficient mechanical elasticity and strength to withstand the force generated by the SMP active material upon external stimuli and provides a graduated pressure on the leg. Typically, nylon or wool based fabrics (knitted or woven) are used.

Typically, the SMP active material is physically attached to the carrier material. Any manner of attaching the material may be used, such as but not limited to embroidering, weaving, sewing and stitching, or gluing by suitable textile glues.

Alternatively, fine strips of SMP could be used as a wefi or an inlay yarn in a woven structure or knitted structure of the carrier material respectively. S... * S S....

A number of attachment fixers are typically used to hold the SMP-based * S. * . S bandage on a person's limb. The fixers are typically physically attached to the carrier S..

material or directly to the SMP active layer. Any manner of attaching the fixers may * be used, such as but not limited to embroidering, sewing, stitching and weaving, or *5***S * gluing using suitable textile glues. The fixers may include, but are not limited to, strings, Velcro�, elastic, elastic bands, a piece of fabric with buttons, mechanical clamping, etc. Other attachment fixers suitable for this use will be readily apparent to a skilled person.

The carrier material may comprise pores for ventilation andlor cooling of a patient's body part, allowing for an exchange of fresh air with the outside of the pressure actuator.

The SM? active material may be a piece of a sheet either with or without pores, or a piece of fishing net-like sheet (i.e. a structure consisting of a carrier material and SMP, intertwined, knitted, braided or woven), or may be a piece of knitted or woven structure comprising strips or yarn of an SM? or an SMP composite.

According to one embodiment, the bandage may be narrower in width at one end than the other. Typically, it is narrower at the lower end which is intended to be positioned nearer a person's anide, as a person's ankle typically has a smaller circumference than a knee or thigh.

The SMP active material may be pre-stretched to different extensions, e.g. : from about 100% to about 10% at different sections thereof, with a larger extension at Is,, * I * the lower, narrower part of the material, and gradually decreasing towards the upper, *5 wider part which provides a graduated pressure once the SMP is activated, wherein I..

the pressure at the lower part of the material is higher than that at the upper part of the 5, . material. The distributed pressure can push the blood upward from the ankle to the *I.s.* knee, to help blood circulation and hence accelerate the healing process. According to the present invention, the SM? material may be, but not exclusively, substantially 100% shape memory polymers such as polyurethane or polystyrene, or it may be an SMP composite material reinforced with fibre, fabrics or nano-or microparticles, which have a high elasticity and mechanical strength. The fabric/SM? composite may have one, two or more layers of fabric sandwiched by an SMP material, depending upon the requirement for the pressure profile for the bandage application. The process to form an SMP/fabric composite has been developed and used in industry. A typical manufacturing method is as follows: an SMP solution is coated on a base, and a piece of fabric is put on top of it before it dries. Once they are dry, another layer of SMP is coated on the fabric, and is followed by another piece of fabric, which is allowed to dry, and finally the surface SMP is coated.

The degree of stretching possible for a pure SMP is up to about 400%, while the degree of stretching possible for an SMP composite is up to about 100%.

The SMP and the SMP composite must each be sufficiently flexible across its thickness such that it can be wrapped around a limb without difficulty, but also sufficiently strong in a length-wise direction (i.e. along the length of a person's limb) so that it provides sufficient pressure for leg treatment. For simplicity, hereafter the term SMP is used to represent 100% SMP and also an SMP composite reinforced with other materials.

S S..

* According to one embodiment, the width of the strip may vary in a wide range from about 1 mm to up to about 20 mm, and similarly the gap between the strips *5**SS * could be in the range of about 1 mm to about 10 mm, depending upon the requirement for the degree of the venous ulcer leg. Small gaps between the strips are better in assisting blood circulation, and can prevent accumulation of blood in the gaps.

According to a further aspect of the invention, there is provided a method of manufacturing a pressure actuator comprising a carrier material, a shape memory polymer attached to and/or integrated within the carrier material, and an attachment arrangement for attaching the actuator to an object, wherein the shape of the SMP is modified using a stimulus which is independent from the actuator, the method comprising the steps of: a) providing a carrier material; b) attaching and/or integrating a shape memory polymer to or into the carrier material; c) attaching an attachment arrangement for attaching the actuator to an object.

According to a further aspect of the invention, there is provided a method of treating or preventing the occurrence of venous leg ulcers using a pressure actuator o comprising a carrier material, a shape memory polymer attached to andlor integrated within the carrier material, and an attachment arrangement for attaching the actuator to an object, wherein the shape of the SMP is modified using a stimulus which is independent from the actuator.

According to a further aspect of the invention, there is provided a use of a U... * . .

::..: 15 pressure actuator comprising a carrier material, a shape memory polymer attached to S...

.: :* andlor integrated within the carrier material, and an attachment arrangement for attaching the actuator to an object, wherein the shape of the SMP is modified using a *: stimulus which is independent from the actuator in treating or preventing the occurrence of venous leg ulcers.

S..... * U

The invention will now be described further by way of example with reference to the following examples and Figures which are intended to be illustrative only and in no way limiting upon the scope of the invention.

Figure 1 shows a graph depicting variation of an SMP elastic modulus with temperature.

Figure 2 shows a schematic drawing of a bandage strip with an SMPIFabric composite (a) in accordance with the invention and the directions of the acting force when it is used around a leg (b).

Figure 3 shows a graphical relationship between the stress produced and the strain at extensions of 50, 100 and 150% for an SMP/fabric composite strip.

Figure 4 shows a graphical representation of the recovery stress of pre-stretched SMP composite strips with different extensions as a function of temperature.

io Figure 5 shows a schematic drawing of the medical bandage of the invention.

Figure 6 shows a schematic process flow for producing a SMP/fabric composite sheet with two fabric layers for reinforcement.

Figure 7 shows schematic drawings (a) and (b) of the bandage with different SMP/SMP composite strips at a fixed pre-stretched extension (a), and with SMP strips *. 15 with the same length at different extensions (b). S...

Figure 8 shows a schematic representation of the bandage with SMP/SMP * composite strips/yams inserted as weft in a woven structure or as an inlay tape/yarn in * * a knitted structure.

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S.....

* S Figure 9 shows a schematic drawing of the bending type SMP bandage in cross sectional view; (a) is the primary shape of the SMP or SMP composite, (b) is pre-opened secondary shape, and (c) is SMP or composite applied on a leg.

The principal attraction of thermoset SMIPs is their ability to remember their original shape once they have undergone a huge transformation in mechanical elasticity when exposed to a temperature higher than its glass transition temperature, Tg, as shown in Figure 1. At temperatures lower than Tg, the SMP is in a glassy state with a Young's modulus, E, of around 1 GPa. The Young's modulus dramatically decreases in the glass transition zone 2 when the SMP is exposed to a temperature higher than Tg, from a few hundreds of KPa to to just a few tens of MPa, such that the SMP is in a rubbery state. Therefore at T> Tg, an SMP can be easily changed to any shape, and the new shape would contain the applied force once it is cooled down.

Upon heating with no load, the molecules or polymer chains return to their original state, leading to recovery of their macro-shape and release of the contained strain in the form of recovery force.

As mentioned, this invention concerns the use of SMP, SMP/fibres and SMP/fabric composite pressure actuators which can be used as medical bandages having a static pressure profile which can thus be used for leg ulcer treatments. Two mechanisms are utilized for the SMP bandage. The principle of the first mechanism is S...

* :* that a recovery force is generated by a pre-stretched SMIP strip or sheet, when it tries *:. to restore its original length upon application of an external stimulation. This force *: * occurs in the directions of the opposing anows x and y above the SMP strip. This *: * 20 axial force can be converted into a required pressure on a leg of a venous ulcer sufferer for treatment or prevention of reoccurrence of the venous ulcer. Figure 2 schematically shows how the axial force is converted into the coaxial pressure on the limb in the directions of the concentric arrows within the SMP/fabric strip A. The pressure generated by the SMP strip can be estimated by P FIarea. The area is the product of strip width and the circumference of the limb, Lg, which is a function of the position of the limb. Lg is small near the ankle, and increases towards the upper leg.

The restoring (shrinking) force of an SMP strip or sheet can be pre-set by the amount of the extension at the pre-stretch stage and be adjusted by stimulation. Figure 3 illustrates load vs. displacement characteristics of three pieces of fabric-reinforced SMP composite strip (5 cm in length) at a fixed temperature with different extensions.

The curve for higher extension ratios fall on the same track as the lower extension ones, and the maximum force required increases with the extension. The result shows a characteristic of a sharp increase in stress (force) initially, and then increases slowly as the extension increases in a linear fashion. The force required for a fixed extension test is high at low temperature, and decreases with increasing temperature.

The stretched SMP strip retains its length once it is cooled down, and remains * : : : : 15 unchanged if the operating/storage temperature is below the transitional temperature, Tg. Once it is stimulated by heat or light etc, it shrinks to restore its original length, and generates a force. The recovery force increases dramatically as the temperature * increases and approaches the transitional temperature, and gradually reduces as the * : .: temperature surpasses Tg. Figure 4 shows a typical recovery force as a function of * : 20 temperature for pre-stretched SMP composite strips with various extensions. At a temperature of >60°C, a small force is generated, and this increases with temperature.

The force is dependent upon the pre-stretched extension of the strip. The recovery force before Tg is suitable for the SMP bandage application. The details of the medical bandage devices are described hereafter: The SMP bandage consists of a carrier material 1 which could be a piece of fabric, garment or medical compression bandage, an SMP active material 2 which is physically attached to the carrier material 1, and a number of fixers 3 which are used to hold the SMP bandage on the limb. The attachment fixers 3 are attached to the carrier material 1 as shown in Figure 5(a). In Figure 5(a) it shows Velcro� type fixers 4 and. 5, with the fixer 5 being situated on the other side of the bandage to fixer 4. The lower part of Figure 5 shows a cross sectional view of the bandage of the invention.

The process to form SMP/fabric composite has been developed and used in industry, and is briefly highlighted in Figure 6 with two pieces of fabrics as an example. An SMP solution is coated on a base (Stage 1), and a piece of fabric is put on top of it before it dries (Stage 2). Once they are dry, another layer of SIVIP is coated on the fabric (Stage 3), and is followed by another piece of fabric (Stage 4), allowed to dry, and finally the surface SMP is coated (Stage 5). The darker lines represent the SIVIP, the lighter lines represent the fabric. *...

Since the force generated by an SMP strip can be adjusted by pre-stretch L: :* extension and the external stimulus, the pressure profile of the bandage can be generated by a number of SMP strips rather than a single piece. Another embodiment * of the present invention includes use of SMP strips 2 on a carrier material I as shown *....* in Figure 7(a), wherein a number of SMP or SMP composite strips 2 of different lengths with a fixed pre-stretched extension are used for the bandage. The recovery force was found to decrease with an increase of the SMP strip length at a fixed extension, hence the SMP strips at the lower part of Figure 7(a) generate a larger force than those at the top, and gradually decrease going upwards, providing a graduated pressure. Figure 7(b) shows another embodiment of the invention, wherein a number of SMP or SMP composite strips 2 of the same length with different pre-stretched extensions are used on a carrier material 1. The SMP strips 2 at the lower part are pre-stretched to a larger extension, e.g. about 50%, more than those used at the upper part, which can be e.g. about 20%. Upon external stimulation, the SMP strips generate a larger force at the lower part than that at the upper part, generating a pressure profile suitable for leg ulcer treatment. These two strip type SM1Ps are to be attached to the carrier material I as shown in Figure 5. These two designs have the advantages of better flexibility and permeability owing to the gaps between the strips 2. It is therefore better for mobility, and is also easy to be fabricated at low cost as less SMP material is used. The width of the strip could vary in a wide range from 1 mm to up to nmi, and similarly the gap between the strips could be in the range of 1 mm to 10 mm, depending on the requirement for the degree of pressure for the venous ulcer leg.

Small gaps between the strips are better in assisting blood circulation, and can prevent

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accumulation of blood in the gaps. In Figure 7, string type fixers 3 are shown as an

* example. ***

* Similarly, fine strips/tapes or yam of SMP/SMIP composite strips 2 could be * :.: 20 integrated within the carrier material 1, i.e. in a woven structure. The strips/tapes or yams could be inserted as wells/warps or in the case of a knitted structure, the same could be inserted as inlay strips/tapes or yams. A bandage using the SMP knitted structure is shown in Figure 8.

The second actuation mechanism used for the SMP bandage is to utilize bending force, rather the shrinking force, generated during the shape recovery of a SMP or SMSP composite upon stimulus. Figure 9 schematically shows the principle of the operation of this bending type SMP bandage. A SMP or SMP composite 2 with a primary semicircular shape (a) is forced to fonn a widely opened shape (b) prior to use. When applied to a leg 10, it returns to its original shape (c) with a smaller circumference upon external stimulation, creating a co-axial type force F on the leg in the direction of the arrows. An advantage of this type of bandage is that the front, bony part 12 of the leg 10 is not covered by the SMP 2; the generated pressure around the limb is hence minimal in these areas. Excessive pressure at front or bony part 12 of the leg 10 when using conventional bandages can lead to unnecessary and avoidable pressure wounds; this is avoided here. However, the bending force is relatively small when recovering its shape. Therefore the SMP or SMP composite sheets 2 of relatively thick types are to be used in this design to generate sufficient force for leg ulcer treatment. In a similar manner to what is discussed above, the :::. * forces required at different sections are different, the bandage is so designed that the * lower sections of this bandage has a larger bending force, and gradually decreases towards the upper part of the limb, and also the sheet type and the strip type of SMP *** * *: or SMP composite can be used for the bending type SMP bandage. For this bending * 20 type SMP bandage, fixers can still be used, but they are only used to hold the SMP *.*..* * . bandage in position, not to provide a mechanism to generate a co-axial force.

It is of course to be understood that the present invention is not intended to be restricted to the foregoing examples which are described by way of example only.

Claims

Claims 1. A pressure actuator comprising a carrier material, a shape memory polymer (SMP) attached to and/or integrated within the carrier material, and an attachment arrangement for attaching the actuator to an object, wherein the shape of the SMP is modified using a stimulus which is independent from the actuator.
2. A pressure actuator according to claim I, wherein the stimulus is selected from temperature change, irradiation, pH variation, or chemical stimulus.
3. A pressure actuator according to claim 2, wherein the irradiation stimulus is selected from ultra-violet (T.JV), infra-red (IR) or electromagnetic radiation.
4. A pressure actuator according to any preceding claim, wherein the carrier material is a piece of fabric, woven, nonwoven or knitted material, or a polymer.
5. A pressure actuator according to any preceding claim, wherein the shape memory polymer is physically attached to the carrier material by embroidering, sewing, stitching, weaving, knitting, gluing or by chemical bonding.*::: :* 15
6. A pressure actuator according to any preceding claim, wherein the material used for the SMP may be a pure SMP, or a composite material comprsing an SMP.:
7. A pressure actuator according to any preceding claim, wherein the SMP or SMP * composite material comprises a piece of sheet, or a piece of net which has been

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S.....pre-stretched, the degree of stretching being greater at one end of the sheet or net than at another.
8. A pressure actuator according to claim 7, wherein the degree of stretching is greater at one end than at the other end.
9. A pressure actuator according to claim 8, wherein the degree of stretching is about 40% at one end and about 20% at the other end.
10. A pressure actuator according to claims 1-9, wherein the SMP or SMP composite is inserted as a weft or warp in the carrier material.
11. A pressure actuator according to any preceding claim, wherein the SMP or SMP composite may be a number of SMP or SMP composite strips with different lengths, wherein the SMP or SMP composite strips have been pre-stretched at fixed extensions.
12. A pressure actuator according to claims 1-10, wherein a plurality of SMP or SMIP composite strips of approximately the same length are used, which strips are pre-stretched at the different degrees of extension.
13. A pressure actuator according to claims any preceding claim, wherein the SMP or SMP composite is able to return to substantially its original length to generate a co-axial pressure profile exerting on the object with a high pressure near one *: :: : 15 end of the object, the pressure gradually decreasing towards the other end. * .
14. A pressure actuator according to any preceding claim, wherein the SMP or SMP * composite strips or sheet have a primary semicircular shape, and are pre-formed to a widely opened secondary shape with different bending forces at different ** * * * * sections thereof * ** * * 20
15. A pressure actuator according to any preceding claim, wherein the length of the SMP or SMP composite is such that the actuator does not completely surround the object it is applied to.
16. A pressure actuator according to any preceding claim, wherein the SMP is selected from a polyurethane-based or polystyrene-based polymer having a glass transition temperature (Tg) of between about 40 and about 100°C.
17. A pressure actuator according to any preceding claim, wherein the SMP is reinforced by fibres or one or more fabrics.
18. A pressure actuator according to claim 17, wherein the fibres or one or more fabrics are selected from polymers, yams, natural textile fibres, regenerated fibres, and synthetic fibres, rubbery substances, leather, or animal skin.
19. A pressure actuator according to claim 18, wherein the polymers comprise nylon or polyester, the natural textile fibres comprise cotton or wool fibres, the regenerated fibres comprise viscose, and the synthetic fibres comprise polyester, polyamide (nylon), polyolefms, or polyacrylic fibres.
20. A pressure actuator according to any preceding claim, wherein the SMP is incorporated with nano-or microparticles or molecular segments which are sensitive to infrared or UV-light, or to an electric field, microwaves or water.
21. A pressure actuator according to any preceding claim, further comprising one or * more pressure sensors. *22. A pressure actuator according to any preceding claim, wherein the attachment arrangement comprises strings, elastic, elastic bands, Velcro�, buttons, or a mechanical clamp.23. A pressure actuator according to any preceding claim, wherein the actuator is porous. q24. A pressure actuator according to any preceding claim, wherein the actuator is a medical bandage.25. A method of treating or prevention of venous leg ulcer using a pressure actuator according to any preceding claim.26. Use of a pressure actuator according to any of claims 1-24 in the treatment or prevention of venous leg ulcer.27. A method of manufacturing a pressure actuator according to any of claims 1-24 comprising the steps of: a) providing a carrier material; b) attaching and/or integrating a shape memory polymer to or into the carrier material; c) attaching an attachment arrangement for attaching the actuator to an object.28. A pressure actuator or method substantially as described herein in the description : and drawings. * * **** * ** * * 3 *** * *** S. * * . . * ****.*.* * .