RESIDUAL STRESS PROPERTIES IN ORGAN MODELS

Description

Field of the Invention

[0001] This invention relates to a simulated tissue structure suitable for use in surgical training tools, and in particular in organ models for teaching and practicing surgical procedures and methods for making them.Background of the Invention

[0002] A highly-skilled operation technique is required of surgeons, in general, and, in particular, for performing laparoscopic surgical procedures. In laparoscopic surgery, several small incisions are made in the abdomen for the insertion of trocars or small cylindrical tubes approximately 5 to 10 millimeters in diameter through which surgical instruments and a laparoscope are placed into the abdominal cavity. The laparoscope illuminates the surgical field and sends a magnified image from inside the body to a video monitor giving the surgeon a close-up view of organs and tissues. The surgeon performs the operation by manipulating the surgical instruments placed through the trocars while watching the live video feed on a monitor. Because the surgeon does not observe the organs and tissues directly with the naked eye, visual information is obtained by a two-dimensional image on a monitor instead of a three-dimensional observation. The loss of information when presenting a three-dimensional environment via a two-dimensional image is substantial. In particular, depth perception is reduced when viewing a two-dimensional image as a guide for manipulating instruments in three dimensions.

[0003] Furthermore, because the trocars are inserted through small incisions and rest against the abdominal wall, the manipulation of instruments is restricted by the abdominal wall which has a fulcrum effect on the instrument. The fulcrum effect defines a point of angulation that constrains the instrument to limited motion. Also, hand motion in one linear direction causes magnified tip motion in the opposite direction. Not only is the instrument motion viewed on the screen in the opposite direction, but also, the magnified tip motion is dependent on the fraction of the instrument length above the abdominal wall. This lever effect not only magnifies motion but also magnifies tool tip forces that are reflected to the user. Hence, the operation of an instrument with a fulcrum requires intentional learning and practice and is not intuitively obvious.

[0004] Also, surgical instruments are placed through ports having seals which induce a stick-slip friction caused by the reversal of tool directions. For example, stick-slip friction may arise from the reversal of tool directions when, for example, quickly changing from pulling to pushing on tissue. During such motion, rubber parts of the seals rub against the tool shaft causing friction or movement of the instrument with the seal before the friction is overcome and the instrument slides relative to the seal. Stick-slip friction, or oil-canning, at the seal and instrument interface creates a nonlinear force.

[0005] Hand-eye coordination skills are necessary and must be practiced in order to correlate hand motion with tool tip motion especially via observation on a video monitor. Also, in laparoscopic surgery, tactile sensation through the tool is diminished. Because haptics are reduced or distorted, the surgeon must develop a set of core haptic skills that underlie proficient laparoscopic surgery. The acquisition of all of these skills is one of the main challenges in laparoscopic training and the present invention is aimed at improving systems and methods for laparoscopic skills training and technique performance.

[0006] Not only do new practitioners have to learn laparoscopic skills, but also, experienced laparoscopic surgeons seek to polish old skills as well as to learn and practice new surgical techniques that are unique to newly introduced surgical procedures. While training can be acquired in the operating room, interest in devising faster and more efficient training methods, preferably outside the operating room has increased. Surgeons that attain a reasonable level of skills outside the operating room are better prepared when they enter the operating room and, thereby, valuable operating room experience can thus be optimized, lowering the risk to patients and reducing costs. To acquaint surgeons with basic surgical skills outside the operating room, various simulators have been devised and tested. An example of a surgical simulator is the SIMSEI ®< laparoscopic trainer manufactured by Applied Medical Resources Corporation in California and described in U.S. Patent No. 8,764,452. The SIMSEI ®< laparoscopic trainer employs three-dimensional live or fake organs inside a simulated abdominal cavity that is obscured from direct observation by the user. Examples of known tissue structures are disclosed in patent documents EP 2400475 A1, US 2012 / 276511 A1, US 2005 / 016548 A1 and WO 99 / 57699 A1.

[0007] Use of a live human or animal organ in a laparoscopic simulator requires freshness for the internal organ. Also, live organs require sanitary arrangements to be made to protect the trainee from being infected by germs and the like. Additional costs are also required for the sanitary management and sterilization of instruments which are used after the exercise of a surgical operation is performed. Also, the used live organ must be properly disposed. Furthermore, the smell of a live organ can be fowl and may distract the trainee from focusing on techniques and skills. Therefore, artificial organs and tissues that simulate live organs and tissues are desirable so that live organs can be replaced in surgical training.

[0008] Many artificial organs have been used in place of live human or animal organs in surgical training. Typically, these artificial organ models are made of silicone, urethane elastomer, styrene elastomer or the like. These artificial organs must respond properly when incised, manipulated or sutured, for example, and provide the same feeling and tactile characteristics as in real life surgery. However, many artificial organs lack certain properties and realism that are necessary to bridge the gap between artificial and real organs. Furthermore, the degree of realism must be targeting to provide means for teaching the skills that are peculiar to laparoscopic skills training. As such, certain realisms may be more important in a laparoscopic environment when compared to an open surgical environment. Therefore, there is a need for artificial organs and tissues and, in particular, for artificial organs and tissues that are targeted for laparoscopic skills training that may also be used for non-laparoscopic skills training.Summary of the Invention

[0009] According to the present invention there is provided a simulated tissue structure as recited in attached claim 1.Brief Description of the Drawings

[0010] FIG. 1 is a top perspective view of a mandrel and a plurality of unstretched silicone rings for producing a tissue structure in accordance with the present invention. FIG. 2 is a top perspective view of the plurality of silicone rings of FIG. 1 stretched around a mandrel. FIG. 3 is a top perspective view of the plurality of silicone rings of FIGs. 1 and 2 stretched around a mandrel and overlaid with a silicone layer. FIG. 4 is a top perspective view of a simulated tissue structure according to the present invention. FIG. 5 is a top perspective view of a mandrel and unstretched silicone ring. FIG. 6 is a top perspective view of a silicone ring stretched around one end of a mandrel. FIG. 7 is a top perspective view of a silicone ring stretched around a mandrel and overlaid with a silicone layer. FIG. 8 is a top perspective view of a simulated tissue structure not in accordance with the present invention. FIG. 9 is a top perspective view of an unstretched silicone strip adjacent to a mold. FIG. 10 is a top perspective view of a stretched silicone strip clipped to a mold. FIG. 11 is a top perspective view of a stretched silicone strip clipped to a mold overlaid with a layer of silicone. FIG. 12 a top perspective view of a simulated tissue structure not in accordance with the present invention. FIG. 13 is a top perspective view of a mandrel, a plurality of unstretched silicone rings, and an unstretched silicone strip for producing a simulated tissue structure in accordance with the present invention and as shown in FIG. 15. FIG. 14 is a top perspective view of the elements of FIG. 13, with the plurality of silicone rings stretched around the mandrel and the strip stretched alongside the mandrel overlaid with a layer of silicone. FIG. 15 is a top perspective view of a simulated tissue structure according to the present invention. FIG. 16 is a top perspective of view of a mandrel and unstretched, patterned sheet for producing the simulated tissue structure in accordance with the present invention of FIG. 20. FIG. 17 is a top perspective view of the mandrel and a stretched, patterned sheet of FIG. 16. FIG. 18 is a top perspective view of the mandrel partially wrapped by the stretched, patterned sheet of FIG. 17. FIG. 19 is a top perspective view of the mandrel wrapped by the stretched, patterned sheet of FIG. 18 overlaid with a layer of silicone. FIG. 20 is a side view of a tissue structure in accordance with the present invention. Detailed Description of the Invention

[0011] The following description is provided to enable any person skilled in the art to make and use the surgical tools and perform the methods described herein and sets forth the best modes contemplated by the inventors of carrying out their inventions. Various modifications, however, will remain apparent to those skilled in the art. Different embodiments or aspects of such embodiments may be shown in various figures and described throughout the specification. However, it should be noted that although shown or described separately each embodiment and aspects thereof may be combined with one or more of the other embodiments and aspects thereof unless expressly stated otherwise. It is merely for easing readability of the specification that each combination is not expressly set forth.

[0012] There are multiple anatomical examples within the human body where there are valves that are able to contract, where tissue planes come together and taper, or tissue planes which are under tension in their normal state. Additionally, there are anatomical structures within the body that stretch preferentially in a certain direction and not another. All of these examples are difficult to simulate while creating organ models using current manufacturing techniques.

[0013] A process of manufacturing a simulated tissue structure 10, which tissue structure is in accordance with the present invention, may generally include providing a pre-made silicone piece. The simulated tissue structure 10 may be made by the piece being stretched and held in place in the stretched configuration on a mandrel. While the piece is stretched, uncured silicone liquid may be applied over the stretched piece and allowed to cure to create a layer. When the wet silicone is finished curing, the final product is removed from the mandrel. The premade stretched piece relaxes, tending toward its unstretched configuration which changes the shape of the final simulated tissue structure 10 including the formed layer of silicone. In an alternative variation, a piece or sheet of elastic mesh is employed instead of pre-made piece or sheet of silicone and uncured silicone is applied over the stretched piece of elastic mesh and allowed to cure to create a layer. When mesh is used, the final shape of the simulated tissue structure is less dramatic compared to the stretched silicone as wet silicone fills the interstices of the mesh reducing the degree of retraction. However, the stretch characteristics resulting in the final simulated tissue structure can be advantageously tailored to limit stretch in one direction while allowing full stretch in another direction. In yet another variation, instead of applying uncured silicone to the stretched piece of silicone or stretched piece of mesh, a piece of cured silicone that is at rest and not stretched is glued in place to the stretched piece.

[0014] With particular reference to FIGs. 1-4, in one variation of this method, silicone ring-shaped bands 12 are placed on a cylindrical mandrel 14. The pre-made, silicone ring-shaped bands 12 and mandrel 14 are provided as shown in FIG. 1. The mandrel 14 has an outer diameter that is larger than the resting, unstressed diameter of the bands 12. Before the mandrel 14 is placed in the mandrel-turning device, a number of pre-made, cured, silicone bands 12 are stretched over the mandrel 14 and spread out evenly along its length as shown in FIG. 2. Then, a layer of uncured silicone 16 is painted on the mandrel 14 and over the premade stretched silicone rings 12 as shown in FIG. 3 while the mandrel 14 is rotating. The silicone layer 16 is allowed to cure. Afterwards, the simulated tissue structure 10 is removed from the mandrel 14. When multiple bands 12 are stretched over a mandrel 14 and then removed from the mandrel 14 along with the cured silicone layer 16, the bands 12 will tend to return to their normal, reduced resting shape and diameter. The outer layer 16 is cured to the bands 12 interconnecting them into a unitary structure 10 as shown in FIG. 4. This results in a unitary simulated tissue structure 10 in accordance with the present invention, which has a plurality of locations 18 of reduced diameter in the same locations of the bands 12 as shown in FIG. 4. The simulated tissue structure 10 will be substantially cylindrical, tubular in shape with a central lumen extending along a longitudinal axis between an opening at the proximal end and an opening at the distal end. The simulated tissue structure 10 in the reduced-diameter locations 18 forms an undulating silicone tube when removed from the mandrel 14 that simulates the look and feel of a real colon. In this way, this method can be used for creating simulated valves of Houston, for example, within the colon.

[0015] In another variation of this method, simulated tissue structures 10 not in accordance with the present invention having simulated natural orifices 20 through which simulated surgery is practiced are created. For example, to make a simulated natural orifice 20, such as a simulated anus, a premade silicone ring-shaped band 12 and mandrel 14 are provided as shown in FIG. 5. The mandrel 14 has an outer diameter that is greater than the unstretched, resting inner diameter of the band 12 in the desired location along the mandrel 14 where the simulated natural orifice 20 is desired to be created. The band 12 is stretched around that desired location of the mandrel, in this case, around one end of a mandrel 14 as shown in FIG. 6, and a layer 16 of wet silicone is painted onto the mandrel 14 and band 12 as shown in FIG. 7. The silicone layer 16 is allowed to cure and then the construct is removed from the mandrel 14. As a result of the layer 16 curing onto the stretched cured silicone band 12, the location of the band 12, the end with the premade silicone band 12 tends to return to its normal unstretched diameter creating an area location 18 of reduced diameter of the simulated tissue structure 10 compared to the surrounding outer layer 16 of cured silicone as shown in FIG. 8. In a variation of this method, the formed shrunken end with a reduced diameter may then be stretched again, this time, over a central peg on a trans-anal adapter mold (not shown). Another layer of silicone is then applied to the stretched end by pouring silicone into the mold and allowed to attach to the band and first layer. Once cured, the pre-stretched construct is removed from the peg and the band again shrinks back to its original size.

[0016] In another variation of this method, a strip 22 of cured silicone having a resting length x is provided as shown in FIG. 9. The strip 22 of silicone is stretched to length y and held in place at length y which is greater than length x as shown in FIG. 10. The strip 22 can be attached to a mold 24, for example, or on a mandrel 14 by some means such as clips 26 as shown in FIG. 10. A layer 16 of wet, uncured silicone is applied over and around the stretched strip 22 as shown in FIG. 11. The uncured silicone layer 16 is allowed to cure. Removing the construct from the mold 24 or mandrel 14 entails releasing the force keeping the strip 22 stretched. As a result, the strip 22 will tend to return toward its normal relaxed length, x, moving, contracting the cured layer 16 of silicone surrounding it creating wrinkles and bunching around the strip 22 as shown in FIG. 12. When the work-piece is removed from the mold or mandrel, the stretched strip will relax, causing bunching of the newer, now cured silicone layer 16 as shown in FIG. 12.

[0017] Turning now to FIGs. 13-15, a combination of one or more methods may be employed. For example, bands 12 together with a strip 22 may be employed over a mandrel 14 to form a simulated tissue structure in accordance with the present invention. One or more bands 12, a mandrel 14 and at least one strip 22 are provided as shown in FIG. 13. The bands 12 have a resting inner diameter that is smaller than the outer diameter of the mandrel 14. The strip 22 has a resting length, x, and is stretched to length, y, and held in place along the mandrel 14 as shown in FIG. 14. The circular, hoop-shaped bands 12 are stretched and placed over the strip 22 and mandrel as shown in FIG. 14. Alternatively, the bands 12 are stretched and placed between the strip 22 and mandrel 14. An outer layer 16 of uncured, wet silicone is applied to the one or more bands 12, one or more strip 22 and onto the mandrel 14 as shown in FIG. 14 and allowed to cure. When the outer layer has finished curing, the construct is removed from the mandrel 14 and the resulting simulated tissue structure 10 in accordance with the present invention is shown in FIG. 15. As can be seen in FIG. 15, when the cured construct is removed, the bands 12 will tend to return to their resting, normal diameter / configuration pulling the cured silicone layer 16 inwardly to create a tubular structure with valleys or a tubular structure with reduced radial dimensions in the location of the rings 12. Also, the stretched strip 22 will tend to return to its normal resting dimension and shorten, bringing the cured silicone layer 16 into contraction along the length of the strip 22, thereby as show in FIG. 15, imparting the resulting tissue structure 10 with a natural curvature having a concavity in the outer layer 16 on the side with the strip 22.

[0018] Turning now to FIGs 16-20, here there is shown another variation of making a simulated tissue structure 10 equivalent to that of FIG. 15. Here a patterned strip 23 is employed over a mandrel 14. The patterned strip 23 is a piece of cured silicone and / or mesh material that is cut into a desired pattern / shape. The mesh if employed is stretchable mesh. The pattern strip 23 has a repeating H-like shape having a longitudinal spine intersected by lateral strips. The pattern strip 23 is stretched longitudinally along the mandrel 14 in the direction of the arrows in FIG. 17. The pattern strip 23 is wrapped around the mandrel 14 while stretched as shown in FIG. 18 and adhered in position on the mandrel 14 with adhesive or other fastener to form a structure equivalent to both the plurality of rings 12 and strip 22 of FIG. 13, from the one pattern strip 23. Then a layer 16 of uncured silicone is applied over the stretched pattern strip 23 and over the mandrel 14 and allowed to cure. When the layer 16 is cured, the construct is removed from the mandrel 14. The cured layer 16 is bonded to the pattern strip 22 and the stretched pattern strip 22 and / or mesh naturally relaxes and returns to an unstretched, equilibrium configuration resulting in the unique luminal simulated tissue structure 10, in accordance with the present invention, as shown in FIG. 20 having a directional curvature imparted by the spine of the pattern strip 16 with bulbous portions formed between the lateral strips where openings were formed by the spaces between the lateral strips.

[0019] The above-mentioned methods involve carefully combining uncured silicone with pre-made and stretched silicone, which results in a more lifelike feel and appearance of the simulated anatomy. The degree of the effects produced by the resultant simulated tissue structure can be controlled by altering the thickness and durometer of both the pre-made stretched silicone pieces and the wet silicone being used. The larger the difference in thickness and durometer between the cured and wet silicone being use, the greater and more dramatic the effects will be in the resulting simulated tissue structure.

[0020] All of these techniques are ways of intentionally incorporating residual stress into simulated anatomy. There are many examples in the human body with structures that contain residual stress, and these techniques aim to mimic these real tissue structures in terms of look, feel, and manufacturability.

[0021] Currently, many organ structures are made in several pieces in order to reduce the complexity of the molding. These pieces are then glued together in order to get a desired curved shape. Advantageously, through the use of pre-stretched pieces in order to create residual stresses in a simulated tissue structure according to the present invention, less complex molds can be used. Additionally, in order to create curved simulated intestines, a straight tube is currently "kinked" in order to take the desired path. Advantageously, residual stresses in a simulated tissue structure of the present invention can help create more realistic curves without collapsing tubes through kinking and still allow for easy demolding.

[0022] It is understood that various modifications may be made to the embodiments disclosed herein. Therefore, the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. Those skilled in the art will envision other modifications within the scope of the following claims.

Claims

1. A simulated tissue structure comprising: a plurality of elastic rings (12), the plurality of elastic rings (12) each having a central aperture; and an outer layer (16) of cured silicone, wherein the outer layer (16) forms a cylindrical, tubular shape with a central lumen extending along a longitudinal axis between a proximal opening located at a first end and a distal opening located at a second end, characterized in that: each of the plurality of elastic rings (12) is located within the central lumen formed by the outer layer (16), with the outer layer (16) cured or glued to each of the plurality of elastic rings (12), wherein the simulated tissue structure generally has a first diameter but with a reduced diameter compared to the first diameter at a plurality of locations along the longitudinal axis of the simulated tissue structure where the outer layer (16) is cured or glued to each of the plurality of elastic rings (12), with the reduced diameter locations resulting from the elastic rings (12) tending to return to their normal reduced resting shape.

2. The simulated tissue structure of claim 1, wherein the plurality of locations of reduced diameter provides an undulating silicone tube that resembles a colon.

3. The simulated tissue structure of any one of the previous claims claim, further comprising an elastic strip (22), the elastic strip (22) disposed in the lumen between the outer layer (16) and the plurality of elastic rings (12) or disposed in the lumen with the plurality of elastic rings disposed between the outer layer (16) and the elastic strip (22), wherein the elastic strip (22) is positioned to cause contraction in the longitudinal direction of one side of the lumen, so as to cause the lumen and simulated tissue structure to bend towards the side where the elastic strip (22) is located.

4. The simulated tissue structure of claim 3, wherein the elastic strip (22) comprises a stretchable mesh.

5. The simulated tissue structure of any one of the previous claims, wherein the plurality of elastic rings (12) are comprised of silicone.

6. The simulated tissue structure of claim 3 comprising a patterned strip (23) which is in the form of a piece of cured silicone or stretchable mesh patterned with a repeating H-like shape having a longitudinal spine intersected by lateral strips, wherein each lateral strip is joined to itself to form a respective one of the elastic rings (12) and the longitudinal spine forms the elastic strip and causes the simulated tissue structure (10) to bend by causing contraction of the lumen, in the longitudinal direction, on the side where the longitudinal spine is located.

7. The simulated tissue structure of claim 6, wherein the patterned strip (23) is a piece of stretchable mesh.

8. The simulated tissue structure of any one of claims 4 or 7, wherein the outer layer (16) of silicone is cured to the stretchable mesh.

9. The simulated tissue structure of claim 8 wherein the outer layer (16) of cured silicone has been applied uncured over the stretchable mesh in a stretched state.

10. The simulated tissue structure of claim 4, 7, 8 or 9, wherein the stretchable mesh is configured to limit stretching in one direction.

11. The simulated tissue structure of claim 10, wherein the stretchable mesh is configured to limit stretching in a lateral direction but allow a full stretch in a longitudinal direction.

12. The simulated tissue structure of any one of claims 4, 7, 8, 9 10 or 11, wherein a degree by which the stretchable mesh can stretch in one direction is based on a number of intersections within a unit length of measure associated with the stretchable mesh, wherein the number of intersections within the unit length of measure corresponds to weave density and window size of the stretchable mesh.

13. The simulated tissue structure of Claim 1, wherein the outer layer (16) has been applied uncured to the plurality of elastic ring, and wherein an extent of changes to the simulated tissue structure is based on a difference in thickness and durometer of the cured silicone associated with the plurality of elastic rings and the uncured silicone associated with the outer layer (16).