GB2482298A

GB2482298A - Shape memory cast

Info

Publication number: GB2482298A
Application number: GB1012564.9A
Authority: GB
Inventors: Jikui Luo; Mohsen Miraftab; Yongqing Fu
Original assignee: University of Bolton
Current assignee: University of Bolton
Priority date: 2010-07-27
Filing date: 2010-07-27
Publication date: 2012-02-01
Also published as: GB201012564D0

Abstract

A medical cast comprised a shape memory material and preferably an additional substance able to activate the shape memory material upon exposure to an external stimulus by inducing a change in the mechanical properties of the material. The external stimulus is selected from heat, visible light, infrared (IR), ultra violet (UV) light, and alternating magnetic field, RF microwave radiation, chemicals, pH variation, electrical stimulation, and water. The shape memory material maybe a shape memory polymer (SMP).

Description

Medical Cast The present invention relates to a medical cast for aiding in the treatment of an injury to a body part of a human or animal, particularly to a medical cast which is reusable, recyclable, and easy to apply and remove.

Medical casts constitute one of the most commonly used medical devices in hospitals around the world. They are used in the treatment of fractured body parts to enable broken bones to heal more quickly, efficiently and correctly. Plaster of Paris is the most commonly used cast material, with a long history of usage dating back to the 1 800s, and is still continuously widely used across the world. The market size is huge, up to the equivalent of a hundred million US dollars annually in the UK alone and as much as several hundred millions of dollars annually worldwide.

To make the cast, plaster powder is mixed with water and then applied to the injured body part, such as an arm or leg, with a padding underlay. It can easily be smoothened and made to any required shape when the plaster is wet, but it becomes solidified once dried. The dried plaster cast has a high degree of hardness and good mechanical strength such that it can protect the injury and allow the broken bone to heal. However, these conventional plaster casts have a number of drawbacks: *..I * * They can only be used for a single application. Once the plaster is mixed with ****.* * * water, it cannot be reused again as it becomes insoluble in water. This is a *S.* * S S...

costly procedure when new casts have to be applied to every new injury.

*..S.*

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: * Although the plaster cast composition is made of natural materials, : incorporated paddings and fabrics which are necessary for the comfort of the patient make the plaster cast difficult to dispose of. It is therefore not an environmentally friendly product.

* Removal of the cast via a cast saw can be a very traumatic experience and is disliked by most individuals, particularly children. Although the cast saw is specially made with built in safety features, the unpleasant sound and length of time taken to cut the cast can be a daunting experience for the patients.

Furthermore, dust particles generated by the cutting saw can be quite hazardous and irritating despite the normal use of vacuum cleaners associated with the cast saws.

* Application and removal of the cast requires a specially trained nurse or a doctor.

Recently, polyurethane (PU) based casts have been developed with similar properties of fixation. Fibreglass knitted sheets impregnated with a PU-polymer can be wrapped around the injured body part, and a semi-circle shape which is attached to the injury with an additional fixation material such as polymer ribbon or cloth.

Because of its light weight, low cost, good biocompatibility as well as good flexibility to be bent to any required shape, PU polymer casts have started to penetrate the traditional plaster cast market. However, like the plaster cast, the conventional PU-S. * .... plastic casts can only be used once, as well as being relatively weak, which has required the incorporation of fibreglass being knitted into the structures to impart * ** * reinforcement. ** S * * a. *5 S * S

It would therefore be desirable to provide a medical cast which overcomes one or more of the problems listed above. This desire is addressed by the present invention.

According to the present invention, there is provided a medical cast comprising a shape memory material. According to one embodiment, the shape memory material is a shape memory polymer.

According to one embodiment of the invention, the shape memory material also comprises a further additional substance possessing specific properties to be able to activate the shape memory material upon exposure to external stimuli such as, for example, heat, infrared (IR) or ultra-violet (UV) light, alternating magnetic field (AMF), electromagnetic wave radiation, RF microwave radiation, chemicals, pH variation, electrical stimulation, and water. A composite of the shape memory material and the further additional substance is thus formed.

According to one embodiment, the content of the additional substance is typically in the range of from about 0.1 to about 50%, more typically from about 2.0 to about 10%, by weight of the SMP, which is sufficient to control and tailor some properties of the SMPs while maintain the shape memory effect, so that one of the specific external stimuli can be used to activate the SMP composites.

*.. ..* While the shape memory material may be one of a number of different shape memory materials, such as shape memory alloys, the invention shall generally be m. s * a described herein with reference to shape memory polymers (SMPs) for reasons of ** * convenience. * * * * **

Shape memory materials are able to return to their primary original shapes upon environmental stimuli under no loading. Shape memory alloys, such as TiNi, and SMPs are the two principal shape memory materials. SMPs have a lot of advantages over shape memory alloys, such as low density, light weight, flexibility, large deformation ability up to 1000%, high shape recovery rate, low cost and easy processing.

Polyurethane-and polystyrene-based SMPs are the most intensively studied.

Besides the good properties of general SMPs mentioned above, they have distinctive properties such as high resistance to organic solvents and aqueous solutions, long-term stability against exposure to sunlight, consistent elastic property, and biocompatibility. SMPs have been proposed for a number of medical applications, including catheters, stents and endotrachial devices, surgical staples, intra-arterial catheters, orthopaedic braces and splints, and contact lenses. They have however never been utilised in medical casts.

The principle attraction of SMPs is their ability to remember their original shape once they have undergone a huge transformation in mechanical elasticity upon exposure to an external stimulus (i.e. activation), such as, for example, heat. Like other materials, SMPs have a glass transitional temperature, Tg. Reference is made to * * the graph shown in Figure 1 below. At temperatures lower than Tg, the SMPs are in *** S.. * .

the glassy state with a Young's modulus, B, of over 1 GPa, while at temperatures S... * S *rSS

higher than Tg the Young's modulus drastically decreases to only a few tens of MPa . : once the SMP has undergone its transformation into a rubbery state.

*:*. Therefore, when the temperature is higher than Tg, the SMP can be easily formed into any shape as desired, and the newly formed shape retains the applied force and remains in place once the SMP is cooled down. Upon receiving the stimulus with no load applied, 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 a recovery force. A pure SMP can be used for applications directly, but its recovery force can be relatively small, while composite SMP products also comprising nanoparticles, fibres or fabric matrix reinforcement are much stronger and can provide a much larger recovery force, mechanical strength and stiffness.

Other than the thermally activatable SMPs, various shape memory materials have been developed which can be activated by different external stimuli such as light (including visible, IR and UV), chemicals, pH-values, alternating magnetic field, RF microwaves, and even water. Synthesis of such SMPs typically involves incorporation of one or more molecules, molecular segments andlor nano-or microparticles that are specifically sensitive to a particular stimulus. Also envisaged within the scope of the invention are multi-function SMPs, which contain different materials which respond to different stimuli, such as light and an electrical signal, within a single SMP cast.

For example, SMPs incorporated with ferromagnetic nanoparticles such as Fe- 0, Mg-Fe-U, Ni-Zn-U, and the like, are able to be remotely "heated" by alternating magnetic field, so that the SMP becomes soft with a Young's modulus close to that at * * the rubbery state, so the SMP is sufficiently flexible and malleable to be bent and re-shaped into any desired form. S.

When the sizes of metal nanoparticles such as Au and Ag are smaller than the * wavelength of light, they exhibit strong surface plasmon resonance under light. They *: . absorb light at distinctive wavelength at the UV-to near IR region. Most of the absorbed light is converted into heat with a small part being converted into luminescence. SMPs with incorporated metal nanoparticles are able to be activated by light, particularly IR or UV light, leading to a phase change from the glassy state to the rubbery state, and are sufficiently flexible and malleable to be bent and re-shaped into any desired form. In a similar way, SMPs mixed with photosensitive chemicals such as cinnamic acid and cinnamylidene acetic acid, show the ability to "react" with light, particularly IR or UV light, leading to a phase change from the glassy state to the rubbery state without any significant temperature rise for the polymers, and are sufficiently flexible and malleable to be bent and re-shaped into any desired form.

These have been utilized to form light sensitive SMIPs. Alternative additional substances for light activatable SMPs include, but are not limited to, photoisomerization azobenzenes, and compounds which cause photoinduced ionic dissociation, such as triphenylmethane leuco, as well as any derivatives or combinations thereof.

In the embodiment wherein the additional substance is able to activate the shape memory material upon exposure to an infra-red light source, the additional substance may be, for example, selected from metal nanoparticles, such as Au, Ag or Ni, and the like, or nanotubes and nanofibres which are able to absorb infra-red light.

In the embodiment wherein the additional substance is able to activate the

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* shape memory material upon exposure to a UV light source, the additional substance **** **.* 20 may be selected from nano-or microparticles which may be, but not limited to, metal * S.....

* oxide nanoparticles such as Ti02, CeO, ZnO, Ifl2O3, ITO (indium tin oxide) and Si02, which have an absorption edge of <300 tim.

In the embodiment wherein the additional substance is able to activate the shape memory material to form electrical conductive and light-sensitive SMPs, the additional substance may be selected from, but not limited to, carbon nanotubes, short carbon fibres, carbon black, or metallic nanoparticles such as Ni, Au and Ag. The nanoparticles may be, but are not limited to, original surface or coated with other thin materials such as polymers and silica, or surface grafted particles to enhance surface properties.

In the embodiment wherein the additional substance is able to activate the shape memory material to form an SMP which can be activated using an alternating magnetic field, the additional substance may be selected from, for example, ferromagnetic particles, which may be, but not limited to, Fe-O, Fe-Cu-O, Mg-Fe-O, Ni-Zn-Fe-O and Ba-Co-Fe-O and the like.

In the embodiment wherein the additional substance is able to activate the shape memory material to form an SMP which can be activated using electromagnetic waves, the additional substance may be selected from, for example, magnetoelectroelastic (MEE) particles, which may be, but not limited to, Terfenol-D particles, BaTiO3 and CoFe2O4 nanoparticles and the like. S...

* .*. Similarly, specific chemicals which are sensitive to some chemicals and pH-* .* SSS * value changes can be added to modif' the activation mechanisms of the SMPs, **..

* 20 leading to chemical or pH-value driven SMPs. For example, absorbed water will ***.** *:.. affect the bonding strength of N-H andlor C=O bonds of a polyurethane-based SMP, * * leading to a decrease of phase transition at room temperature after immersion in water for a period from a few hours to about a hundred hours. This can form a unique water-activatable SMP. Contact with water leads to the phase change of the SMPs from a glassy state to a rubbery state, allowing them to become sufficiently flexible and malleable to be bent and re-shaped into any desired form. This can be utilized to fabricate water-sensitive SMPs.

Generally, SMPs are insulators with a resistivity larger than about 106 Qcm A new type of conductive SMP has recently been developed by adding conductive nanoparticles such as carbon nanotubes, carbon black and metal nanoparticles. The conductivity of the SMP could be as high as 1 02 S/cm, sufficient to be used as a conductive material to pass electrical current or voltage. This allows for the development of electrically activated SMPs which have the advantages of simple structure and mode of operation over external heating process. The conductivity of the SMP increases with concentration, cB, of carbon black, as aCB) ° ( - The conductivity is initially dominated by hopping conduction, and followed by conduction in percolation fashion, with conductivity levels of up to about 1 02 S/cm obtained. Meanwhile, the Young's modulus and the hardness of the SMP increase with the concentration of the carbon black.

The properties of SMPs can be modified significantly when an amount of S...

nanoparticles and/or chemicals are added into the polymer. This means that the *5*55* * precise properties of the SMPs such as Young's module, hardness, and transitional *..S temperature, can be specifically controlled and tailored to meet the requests for S.....

*:.* specific applications. For example, SMPs with a low Tg value in the range of about * *: 30-50°C, making them particularly suitable for medical devices used in or on human or animal body, have been synthesized. This also allows the development of low transitional temperature SMP composites that can be easily activated by one of the above mentioned stimuli. Therefore, by using such SMP composites incorporated with nanoparticles and/or chemicals, it is possible to fabricate reusable casts which can be applied and removed from the injury by activating either by heat, infrared (IR) or ultra-violet (UV) light, alternating magnetic field, electromagnetic wave radiation, RF microwave radiation, chemicals, pH variation, electrical stimulation, and water, without needing the cast saw. The advantages of the medical casts comprising composite SMPs include: * Reusability (and recyclability): the SMP composite casts can be used many times as the bending motion they are subjected to does not damage the molecular bond and polymer chain structures. The reusability makes the SMP-based composite casts cheap and environmentally friendly.

* It is easy for a non-professional person to apply the cast with no requirement for a person who has had extensive medical training. No need is required for smoothening as the cast products can be made with smooth surfaces. This contributes to a lower expenditure for the funding body, such as the UK National Health Service.

* The SMP composite casts can be applied to an injured body part in dry * : conditions with the assistance of external stimuli, so it is much easier and **** * * 20 cleaner. S...

* :** * A wide variety of stimuli are available for the activation of the SMP :: : : composite casts, offering various methods for medical cast developments.

* The casts are waterproof. Other than the specially made water activatable SMP, the SMPs are typically hydrophobic, and therefore naturally waterproof materials. The patient can thus take showers and swim with the cast on.

* Low costs: SMPs based upon PU or polystyrene are cheap and widely available.

According to the present invention, the SMP casts can be provided in the form of a thin sheet and stored as a splint roll or in a tube ready for use. It can be applied to a body part in a similar manner to a medical bandage, or used as a tube which shrinks round the injury once it is activated using one of the activation methods disclosed herein. According to one embodiment, a padding layer may be used under the SMP cast to protect the skin and act as a thermal insulator to prevent direct contact of activated SMP cast with the body part at high temperatures.

To apply the SMP cast to the injury part of a body, one of the above-mentioned external stimuli according to the type of the added material is used to activate and soften the SMP cast, so that it can be applied to the injury either by wrapping or bending it into a semicircle with the optional assistance of another material for fixation. S...

The cast sets into a hard shell around the injury site similar to or stronger than S.....

* conventional plaster casts once the SMPs "cool" and return to their non-activated state S.SS after removal of the external stimulus, but in the shape they were formed into during S.....

*:.* their period of activation. This allows the cast to protect the injured body part as it To remove the cast, the same external stimulus is used to soften the SMP.

When the SMP composite cast is subsequently re-activated once the body part has healed sufficiently for the cast to be removed or for inspection, it becomes soft enough to be unwrapped and removed from the body part like a bandage. The SMP is unwrapped or pulled off as a tube. The removal of the SMP composite cast is therefore very easy and does not need a cast saw to cut the cast. Furthermore, the SMP composite cast does not need to be disposed of after each use as it can be recycled and reused many times. It is thus cheap arid enviromnentally friendly compared with the conventional casts currently available in the market.

According one embodiment of the present invention, the SMP casts may consist of a pure SMP composite sheet, or a hybrid of an SMP composite together with one or more surface protection carrier andlor reinforcement layers to provide extra protection andlor strength for the cast. The surface protection carrier andlor reinforcement layers may include, but are not limited to, a piece of fabric, woven, nonwoven or knitted structure, garment, compression bandage or even polymer which has sufficient flexibility to allow the cast to be wrapped on or inserted into the injured body part to form a fixed solid shell. The carrier structure may be a sheet mesh or a sheet with holes so that it is breathable, allowing for an exchange of fresh air from * outside of the cast for efficient healing. The carrier layers may be affixed to the SMP 20 layer on either side thereof. The carriers layers are typically made of a material which * is flexible without adding additional mechanical strength to the SMP cast, i.e. the hardness and Young's modulus of the cast are determined substantially only by the * * properties of the SMP layer, rather than the carrier layer.

The reinforcement layers may be present in the embodiment where more than one layer of SMP is used in a cast. In this embodiment, a reinforcement layer may be positioned between the layers of SMPs to provide extra tensile strength. If carrier layers are used in conjunction with one or more reinforcement layers in an SMP cast, the carrier layers are typically positioned on the upper and lower surfaces of the overall cast (as depicted in Figure 3 below).

The SMP active material is typically physically attached to the carrier layers and/or reinforcement layers, by laminating, embroidering, weaving, sewing and stitching, or gluing by suitable textile glues, or by any other suitable means which will be readily apparent to the skilled person.

The SMP active material may be a piece of solid sheet with or without holes, a piece of meshed sheet, or may be a piece of knitted or woven structure from SMP yarn. The SMP cast sheet may be made by methods including, but not limited to, casting, injecting molding, spin coating, pressing and rolling of the SMP sheet directly, or by dipping the structured textile/meshed cloth directly into SMP composite resin forming a thin SMP coating.

According to the present invention, the SMP cast is a splint roll which can be a,..

wrapped round the injury once it is activated. The time constant for the SMP *a**ss * composite to stay at its activated state should be in the range of from only a few tens of seconds to about 10 minutes, allowing the cast to be applied to the patient before it sets to become a hard shell. . . a S * a.

*: According to the present invention, the activation mechanism may include, but is not limited to, light (including visible light, JR light and UV light), magnetic field, electromagnetic waves (excluding those harmful to human body), water, chemicals and electrical current or voltage. The light source could be an ordinary light source with specific optical wavelengths of a visible light, or JR or UV-light. The light source can be a specifically made desk-top apparatus, portable or a hand held apparatus such as torch. Similarly, for the alternating magnetic field and electromagnetic wave sensitive SMPs, the sources for the magnetic field and the electromagnetic waves may be an ordinary magnet, or a specifically made apparatus such as solenoid and coils which can generate an alternating magnetic field or transmit electromagnetic waves with sufficient intensity to activate the SMP cast.

In the embodiment where the SMP may be water-activated, when the SMP is pre-made in a splint roll, it requires immersion in water to be activated before application to the injury. Upon removal of the cast once the injury has sufficiently healed, water may be added to the cast either by using a wet towel or cloth, or simply by spraying water on to the surface of the cast. The same unwrapping process can be used to remove the cast as is used for other actuation methods.

In the embodiment where the SMP cast can be made into a conductive SMP with the embedded conductive nanoparticles, the SMP can be activated by applying an electrical current or voltage which should be within the safe range for a human * * ***.* * being or animal being treated. For this conductive type of SMP cast, electrical leads S.., may be attached to the SMP cast, so that electrical current or voltage can be applied to

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*S áI*S * activate the cast before it is applied to or removed from the injury. , I

According to a further embodiment, noble metal nanoparticles such as Ag or Zn may be included in the SMP. These noble metal nanoparticles have an antimicrobial effect. Further, inclusion of such metal nanoparticles in an SMP will have multiple functions: increase mechanical strength while retaining the shape memory effect, enabling the SMP to be activated by light through surface plasmonic resonance absorption, and also imparting an antimicrobial effect to prevent infection of the injured body part being treated.

According to a further embodiment of the invention, the medical cast may comprise a pure SMP, i.e. without any of the activatable substance present. For example, SMPs which are themselves thermally activatable can be used and activated by heating the SMP by using a warm or hot towel, or an apparatus capable of expelling heat, such as a hair dryer or radiator, for application or removal of the cast.

According to a further aspect of the invention, there is provided a method of manufacturing a medical cast as described hereinabove, comprising the steps of: i) providing a shape memory material; and ii) exposing the shape memory material to an external stimulus to induce a change in the mechanical properties of the material in preparation for applying it to a body part. *..� * *

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****** * This method may also include the further step of mixing or at least partially

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embedding one or more additional substances into the shape memory material, the ** **** * * * . : 20 additional substances possessing specific properties to be able to activate the shape * * .: memory material upon exposure to external stimuli such as, for example, heat, infrared or ultra-violet light, electromagnetic wave radiation, RF microwave radiation, chemicals, pH variation, electrical stimulation, and water, thus forming an SMP composite. This step is carried out between steps (i) and (ii) above.

The additional substances may be added and combined with the SMPs using methods such as, but not limited to, mechanical mixing, ultrasonic agitation, physical pressing, and the like, at the process stage for the composites.

According to a further aspect of the invention, there is provided a method of applying a medical cast according to any preceding claim on to an injured body part of a human or animal body, comprising the steps of: i) providing a shape memory material; ii) exposing the shape memory material to an external stimulus to induce a change in the mechanical properties of the material; iii) changing the shape of the shape memory material; iv) applying the shape memory material to the injured body part; and v) removing the external stimulus.

According to one embodiment, the shape memory material is exposed to the S...

* : ** external stimulus for a period of from about 5 seconds to about 30 minutes, typically from about 10 seconds to about 20 minutes, more typically from about 20 seconds to *..

* ... 20 about 10 minutes. However, of course, it will be readily apparent to the skilled person *: * how long the exposure should be depending upon the particular shape memory * * * material and external stimulus being used. The external stimulus may be removed before or after the step (iv) of applying the shape memory material to the injured body part as desired.

According to a further aspect of the invention, there is provided a method of removing a medical cast according to any preceding claim from a body part of a human or animal body, comprising the steps of: i) exposing the cast to an external stimulus to induce a change in the mechanical properties of the shape memory material; and ii) removing the cast from the body part.

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 typical mechanical behaviour of SMPs upon thermal activation.

Figure 2 shows a 2-dimensional schematic drawing of a composite SMP of the invention.

Figure 3 shows representations of a cross sectional view of a cast layer with no surface protection layer, a cast layer having a single layer structure and a cast layer S...

* : * having a multi-layer structure.

* ** * Figure 4 shows an example of a mesh type SMP cast sheet. **.*

* ... . 20 Figure 5 shows representations of a sheet type of SMP cast being used *: together with a padding layer underneath.

* * * Figure 6 shows representations of an SMP cast made in tubular form both before and after activation by external stimuli.

The graph in Figure 1 depicts the typical thermomechanical behaviour of an SMP. Prior to its exposure to heat, the SMP is a relatively hard material with a Young's modulus (also called elastic modulus), E, of over one GPa at the glassy state at low temperatures. It transforms into a rubbery state once the temperature is above the glass transitional temperature, Tg, with an elastic modulus B value in the range from a few MPa to a few tens of MPa. The SMP is then soft and malleable enough to be formed into different shapes.

Figure 2 depicts a 2-D schematic drawing of a composite SMP 2 containing additional activatable materials 4 embedded or mixed therein. The additional activatable material 4 could be any of a number of specific nano-or microparticles and chemical components, and may be of any shape such as, for example, spheres, tube, rods, wire, or fibres with sizes from a few nanometres to a few hundred micrometres.

Figure 3 shows schematic drawings of an SMP cast having a) a single layer SMP composite 6 without any carrier layer or surface protection layer; b) a single layer SMP composite cast 8 with carrier layers (or surface protection layers) 10 on * *** both sides; and c) a multi-layer SMP composite cast 12 with a re-enforcement layer **** * : * * 14 and surface protection layers 16. The reinforcement and surface protection layers are present to provide extra strength and protection for the cast. ****

* . . 20 Figure 4 shows a schematic drawing of an SMP cast sheet having a mesh **.: structure. The mesh may be any shape, pattern or size. The sheet could be an SMP * composite made simply by pressing or rolling etc, or meshed and woven textile coated with the SMP composite.

When a single layer sheet type SMP composite cast 18 is used on an injured body part, extra leads 20 from the padding layer may be needed which allow the SMP cast to be pulled apart when it is re-activated to remove the cast after the body part has sufficiently healed, as shown in Figure 5.

Figure 6: The SMP could be made in the form of a tube which can then be made to shrink upon activation. Once the tube is activated, it can be shrunk to fit to and secure the injured body part.

According to one embodiment, the SMP composite or hybrid SMP composite/re-enforcement material may be processed into a tube with a diameter smaller than a body part to be treated, but then physically expanded into a large dimensional tube when the SMP is in its activated state, such that the large dimensional tube is suitable to insert the injured body part into. The SMP is then activated and re-shaped so it fits the injured body part in an ideal healing manner before being de-activated and hardened.

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. S... * S ***.

S..... * . * S S...

S S *

Claims

Claims 1. A medical cast comprising a shape memory material.
2. A medical cast according to claim 1, further comprising an additional substance able to activate the shape memory material upon exposure to an external stimulus by inducing a change in the mechanical properties of the material.
3. A medical cast according to claim 2, wherein the external stimulus is selected from heat, visible light, infrared (IR) or ultra-violet (UV). light, an alternating magnetic field, electromagnetic wave radiation, RF microwave radiation, chemicals, pH variation, electrical stimulation, and water.
4. A medical cast according to claim 2 or claim 3, wherein the further substance is present in an amount of from about 0.1% to about 50% by weight of the shape memory material. * * *.e.* :
5. A medical cast according to claim 4, wherein the further substance is present ** ** in an amount of from about 2.0% to about 10% by weight of the shape S...memory material * . . * :*
6. A medical cast according to any of claims 2-5, wherein when the additional substance is able to activate the shape memory material upon exposure to a visible light source, the additional substance is selected from cinnamic acid, cinnamylidene acetic acid, azobenzenes, triphenylmethane leuco, and derivatives and combinations thereof.
7. A medical cast according to any of claims 2-6, wherein when the additional substance is able to activate the shape memory material upon exposure to an infra-red light source, the additional substance is selected from metal nanoparticles, or nanotubes and nanofibres able to absorb infra-red light.
8. A medical cast according to any of claims 2-7, wherein when the additional substance is able to activate the shape memory material upon exposure to an ultra-violet light source, the additional substance is selected from metal oxide nanoparticles which have an absorption edge of <300 nm.
9. A medical cast according to any of claims 2-8, wherein when the additional substance is able to activate the shape memory material upon exposure to an alternating magnetic field and electromagnetic waves, the additional substance is selected from ferromagnetic nanoparticles.S S.. * *10. A medical cast according to claim 9, wherein the ferromagnetic nanoparticles *** *: 20 are selected from Fe-O, Mg-Fe-O, Ni-Zn-O, or magnetoelectroelastic (MEE) *: : particles including Terfenol-D particles, BaTiO3 and CoFe2O4 nanoparticles. S.S S *S11. A medical cast according to any of claims 2-10, wherein when the additional substance is able to form an electrically conductive and light-sensitive shape memory material, the additional substance is selected from carbon nanotubes, short carbon fibers, carbon black, metallic nanoparticles, and combinations thereof.12. A medical cast according to any of claims 2-11, wherein when the additional substance is able to form a water-or pH-sensitive shape memory material, the additional substance is selected from a compound which is sensitive to water or pH-values.13. A medical cast according to any preceding claim, further comprising one or more carrier or surface protection layers.14. A medical cast according to any preceding claim, wherein the cast comprises more than one layer of the shape memory material.15. A medical cast according to claim 14, comprising a layer of a reinforcement material between at least two of the adjacent layers of the shape memory * S...,. * . * .16. A medical cast according to any preceding claim, wherein the cast is in the * form of a solid sheet or a mesh structure. * * . * S. 55. * S.17. A medical cast according to any preceding claim, wherein the cast is reusable and recyclable.18. A medical cast according to any preceding claim, wherein the shape memory material is a shape memory polymer.19. A medical cast according to claim 18, wherein the shape memory material is selected from a polyurethane, a polystyrene, polyethylene terephthalate, polyethyleneoxide, poly( 1,4-butadiene), poly(2-methyl-2-oxazoline) and polytetrahydrofuran-based materials, and combinations thereof.20. A medical cast according to claim 1, wherein the shape memory material is a pure shape memory polymer.21. A method of manufacturing a medical cast according to any of claims 1-19, comprising the steps of: i) providing a shape memory material; and ii) exposing the shape memory material to an external stimulus to * : * induce a change in the mechanical properties of the material in **. *1 preparation for applying it to a body part. S...* 22. A method according to claim 21, further comprising the step of combining the * shape memory material with an additional substance able to activate the shape memory material upon exposure to an external stimulus by inducing a change in the mechanical properties of the material.23. A method of applying a medical cast according to any of claims 1-20 on to an injured body part of a human or animal body, comprising the steps of: i) providing a shape memory material; and ii) exposing the shape memory material to an external stimulus to induce a change in the mechanical properties of the material; iii) changing the shape of the shape memory material; iv) applying the shape memory material to the injured body part; and v) removing the external stimulus.24. A method according to claim 23, wherein the shape memory material is exposed to the external stimulus for a period of from about 5 seconds to about minutes.25. A method of removing a medical cast according to any of claims 1-20 from a body part of a human or animal body, comprising the steps of: S..... * .iii) exposing the cast to, an external stimulus to induce a change in the *5** * :** * 20 mechanical properties of the shape memory material; and iv) removing the cast from the body part.S S S S *S26. A medical cast or method substantially as described herein in the description and drawings.