Within the arena of medical teaching there is a need to provide simulated body tissue for the vast audience of students, trainee doctors and surgeons. There is a demand to practise making incisions and injections, removing tissue using standard wound closure techniques such as, suturing, stapling, use of adhesive appliances and gluing. As an alternative to providing an actual body or part of an animal for practising such techniques there is a need for artificial material whereby they can be practised. Known structures providing simulations of body tissue suffer from the disadvantage that they have an oily surface, are variable in quality and are not always responsive to modern wound closure techniques. One previous attempt to produce just such a simulated body tissue is disclosed in U. K. Patent No. 2 277 826 which discloses the production of simulated body tissue using foam latex rubber bonded to an elastomeric material with silicone sealant and a diluent.

Further, there is a need to provide a spinal model for students, trainee doctors, surgeons and, in particular, junior anaesthetists to practise spinal injection techniques, such as, spinal anaesthesia, spinal tap, lumbar sympathetic block, caudal analgesia, sacral nerve block and epidural anaesthesia.

It is therefore an object of the present invention to provide a simulated body tissue and method of manufacturing same which overcomes the disadvantages of the prior art. In particular, it is an object to provide a simulated body tissue, which can be, utilised with modern wound closure techniques including glues and adhesive strips. It is a further object of the invention to provide a simulated body tissue which is capable of tolerating repeated applications and removals of adhesive appliances and sutures without deterioration. It is a still further object of the invention to provide a simulated body tissue capable of permitting dog-turn or odd sided incisions.

It is a yet further object of the present invention to provide a spinal model incorporating a simulated body tissue which can be used with modern spinal injection techniques. In particular, it is an object to provide a spinal model which is capable of tolerating repeated injections and which is capable of giving both tactile and visual access to the spine.

According to a first aspect of the present invention there is provided a simulated body tissue comprising an upper layer of reinforced polyurethane or thermoplastic gel, a middle layer of thermoplastic gel and a second layer of thermoplastic gel.

Preferably, a reinforcing mesh is positioned between the middle layer and the second layer.

Advantageously, the simulated body tissue comprises two upper layers which sandwich two middle layers and a single common second layer.

The upper layer may be coloured to represent the dermis, the second layer may be coloured yellow to represent the fatty layer and the middle layer may be coloured red to represent the subdermis According to a second aspect of the present invention there is provided a method of making simulated body tissue, the method comprising placing a sheet of reinforced polyurethane or thermoplastic gel on a height adjustable mould bed, heating a second thermoplastic gel and pouring a first portion of the gel into the mould and allowing it to set, subsequently lowering the mould bed and pouring a further quantity of said second thermoplastic gel into the mould.

Preferably, a reinforcing mesh is placed on the first portion of said second thermoplastic gel before the further quantity of said gel is poured into the mould.

Preferably, the sheet of reinforced polyurethane or thermoplastic gel may be coloured to represent the dermis. Furthermore, either or both portions of said second thermoplastic gel may be coloured to represent a particular type of body tissue. Thus, the first portion of the second thermoplastic gel may be coloured red to represent the subdermis and the second portion may be coloured yellow to represent the fatty layer.

In some applications, it is desirable to provide a double sided simulated body tissue having a pair of dermis and subdermis layers separated by a common fatty layer. In which case the method includes the contemporaneous steps of placing a second sheet of reinforced polyurethane or thermoplastic gel on a second mould bed, heating a second thermoplastic gel and pouring a first portion of the second thermoplastic gel into the mould and before it sets completely placing the contents of the mould gel face down onto the contents of the first mould to form a double sided simulated body tissue.

According to a third aspect of the invention there is provided a simulated body tissue formed in accordance with above described method.

According to a fourth aspect of the present invention there is provided a spinal model comprising a base, a plurality of spinal bones supported on said base in a configuration simulating at least a portion of a spinal column, a first section representing the ligamentum flavium and an outer layer of simulated body tissue.

Preferably, a second section representing the muscle layer is provided above the first section.

Also preferably, the spinal bones are alternated with synthetic invertebral discs and a synthetic spinal cord placed in the spinal column space. The spinal cord may comprise a neoprene tube filled with fluid.

In order to aid in understanding the invention an embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a portion of simulated body tissue according to the invention; Figure 2 is a perspective view of a variant of the body tissue of Figure 1; Figure 3 is a perspective view of a spinal model according to the fourth aspect of the invention; Figure 4 is a perspective view of the spinal model of Figure 3; Figure 5 is a perspective view of the spinal model of Figures 3 and 4; Figure 6 is a perspective view of the spinal model of Figures 3 to 5; Figure 7 is a perspective view of the spinal model of Figures 3 to 6.

Referring to Figure 1, there is shown a block of simulated body tissue 1. The block 1 comprises an upper layer or dermis of reinforced polyurethane or thermoplastic gel 2 which is tinted to a colour similar to that of human skin, for example, caucasian, negroid or oriental. If the upper layer 2 is of polyurethane, reinforcing material may comprise a weave or cloth backing and if the upper layer 2 is of thermoplastic gel, the reinforcing material may comprise a mesh, preferably of vinyl. By using thermoplastic gel as the upper layer 2, it is possible to create pathologies on the surface of the upper layer by moulding. Beneath the dermis is a middle layer of propriety thermoplastic elastomeric gel or second thermoplastic gel which is dyed to represent a red subdermis layer 3. Finally, a second layer of thermoplastic elastomeric gel or second thermoplastic gel forms the lowermost layer 4 and is dyed yellow to represent fatty tissue. A reinforcing mesh (not shown) of, for example, a two way stretch fabric, may be situated between the subdermis layer 3 and the lowermost layer or fatty layer 4.

Turning to Figure 2, this shows a variant of the block of Figure 1 in which the block is provided with two dermis layers which sandwich two subdermis layers and a single common fatty tissue layer.

The simulated body tissue described with reference to Figure 1 above is formed by first placing a piece of reinforced polyurethane or thermoplastic gel 2 face down onto an industrial mould (not shown) with an adjustable internal tray bed, the tray being perforated and connected to a vacuum pump. The mould tray is set initially to a depth of 2mm and the polyurethane or thermoplastic gel 2 is held in place by a pressure differential established by the vacuum pump which sucks air through the perforations in the tray bed to keep the surface of the polyurethane or thermoplastic gel 2 flat.

A propriety thermoplastic elastomeric gel or second thermoplastic gel is then heated to 180°C and a red dye is added before pouring the liquid onto the flattened cloth surface 2 onto which it adheres immediately. Any bubbles formed in the gel following pouring can be pricked out to maintain an even flatness. The gel is then allowed to cool for one to two minutes so that it sets and forms the subdermis layer 3. A reinforcing mesh (not shown) is then placed onto the subdermis layer 3 and sinks slightly into the gel of the subdermis layer 3.

After the gel has completely set, the mould tray is lowered to the next increment which will be to a total depth of 8mm and a further batch of the same proprietary thermoplastic elastomeric gel or second thermoplastic gel is then heated to 180°C and a yellow dye added before being poured onto the exposed and set surface of the red dyed gel 3 and allowed to set forming a fatty layer 4.

The material may then be removed from the mould to provide a portion of simulated body tissue.

In order to form the variant of Figure 2, the above described steps are taken whilst, contemporaneously, a second piece of reinforced polyurethane or thermoplastic gel 2'is first placed face down onto a second mould (not shown) of the above described type, i. e. with an adjustable internal tray bed, the tray being perforated and connected to a vacuum pump. The mould tray is set to a depth of 2mm and the second piece of polyurethane or thermoplastic gel 2'is held in place by a pressure differential established by the vacuum pump which sucks air through the perforations in the tray bed to keep the surface of the polyurethane or thermoplastic gel 2'flat.

A propriety thermoplastic elastomeric gel or second thermoplastic gel is then heated to 180°C and a red dye is added before pouring the liquid onto the flattened cloth surface onto which it adheres immediately. Any bubbles formed in the gel following pouring can be pricked out to maintain an even flatness. The gel is then allowed to cool slightly so that it begins to set. A layer of reinforced mesh (not shown) may be placed onto the layer of red gel 3, which sinks slightly into the layer of red gel 3. This second sheet 2'bearing a single layer of red gel 3'is then placed red gel face down over the yellow gel 4 forming the upper surface of the material in the first mould whilst both are still warm and within their setting time. The result is a double layered portion of simulated body tissue as shown in Figure 2.

Referring to Figures 3 to 7 in which common elements are indicated with the same reference numerals, there is shown a plastic moulded base 5 having a substantially central channel 7 in which is positioned a plurality of spinal bones or vertebrae 8, obviously, synthetically produced spinal bones could be used. The spinal bones 8 are alternated with synthetic invertebral discs 9 and, preferably, the spinal bones 8 and invertebral discs 9 are threaded together and secured at either end, for example, by using wing nuts or any other known technique. Each of the spinal bones 8 has a crest 10 and a hollow section 11, the hollow sections 11 and invertebral discs 9 defining the spinal column space 12.

A spinal cord 13 is positioned in the spinal column space 12, the spinal cord 13 may be of, for example, leather or a synthetic material, for example, a neoprene tube filled with liquid. A first section representing the ligamentum flavium 14 is placed over the crests 10, the first section 14 is of synthetic material being hard and grisely in nature to accurately represent the ligamentum flavium. A second section representing the muscle layer 6 is positioned over the first section 14 and an outer layer of the simulated body tissue 1 is placed on top.

The second section 6 may also comprise simulated body tissue 1. The spinal model 15 is preferably encased in a box 16 removably attached to the base 5 and having a window 17 for access to the model 15.

In use, a trainee, for example a junior anaesthetist, can palpate the simulated body tissue 1 to feel the crests 10 of the spinal bones 8 under the simulated body tissue 1 for correct identification of the precise location for applying a needle 18 attached to a syringe 19. Finger depressions 20 are positioned on the box 16 to identify the illiac crests of the pelvis, the middle finger of either hand acts as a locator while the fore fingers walk up and down the spine. Once the precise position is located the trainee can inject, the needle 18 passes easily through the simulated body tissue 1 and second section representing the muscle layer 6. As the needle 18 travels into the first section representing the ligamentum flavium 14 with a syringe 19 attached to the needle 18 and the plunger fully extended, positive pressure will be experienced when the plunger cannot be made to descend. Only when the needle 18 passes beyond the first section 14 does the needle 18 come into the spinal column space and negative pressure or loss of resistance will again be noticed. It is paramount that the needle 18 be maintained in a perpendicular position and at right-angles to the spinal bones 8, and the model 15 can easily be disassembled to reveal where the needle 18 has been directed. When a tube filled with liquid is used as the spinal cord 13 it is possible to identify whether the needle has correctly reached the spinal column space 12 or spinal cord 13 without disassembling the model 15. Further, it is possible to inject with fluid.

It will be appreciated by those skilled in the art that although the above described embodiments relate to slabs of simulated body tissue through the use of a more complicated mould other shapes and thicknesses of simulated body tissue can be formed. Furthermore, different dyes can be used to simulate other parts of the body including the abdominal wall. Obviously, the base 5 could vary in shape to support the spinal bones 8, and the bones 8 could be set into a gel. Also, further training models, for example, of a human abdomen, may be provided with a cavity which may be filled with simulated, animal or donated organs. These organs may then be operated on through the simulated abdominal wall.

It can also be foreseen that the simulated body tissue of the present invention could be used to form model human breasts for practicing manipulation and aspiration for the detection of tumours.