Residual stress features in organ models

Abstract

To provide simulated tissue structures and methods of making the simulated tissue structures.SOLUTION: An elastic first material is placed in tension. An elastic second material is adhered to the first material while the first material is in tension. The adhered second material and the material in tension form a first shape of a simulated tissue structure. Tension on the first material is released. In releasing the tension on the first material, a force is exerted on the adhered second material to bring the combination of the first material and the second material into a second shape. The first shape is maintained by a mold or mandrel, and the second shape is the desired shape of the simulated tissue structure.SELECTED DRAWING: Figure 15

Description

[Technical Field]

[0001] SURGICAL TRAINING TOOLS AND METHODS FOR MANUFACTURE THEREOF FIELD OF THE INVENTION The present invention relates to surgical training tools, and in particular to simulated tissue structure and organ models for teaching and practicing surgical procedures or techniques.

[0002] Description of Related Applications This application claims priority to and benefits from U.S. Provisional Patent Application No. 62 / 327,925, filed April 26, 2016, entitled "Residual stress features in organ models." [Background technology]

[0003] High levels of surgical skill are generally required of surgeons, particularly those performing laparoscopic surgical procedures or techniques. In laparoscopic surgery, several small incisions are made in the abdomen to allow for the insertion of trocars, or small-diameter 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 transmits magnified images from inside the body to a video monitor, which provides the surgeon with a close-up view of organs and tissues. The surgeon performs the surgery by manipulating surgical instruments placed through the trocars while viewing a live video feed on the monitor. Because surgeons do not directly observe organs and tissues with the naked eye, visual information is obtained from two-dimensional images on the monitor rather than from a three-dimensional view. The loss of information when displaying a three-dimensional environment using two-dimensional images is substantial. Depth perception is particularly reduced when viewing two-dimensional images as a guide for manipulating instruments in three dimensions.

[0004] Furthermore, because trocars are inserted through small incisions and placed against the abdominal wall, manipulation of the instruments is limited by the abdominal wall acting as a fulcrum (lever) on the instruments. The fulcrum action defines a point of angulation that constrains the instruments to a limited range of motion. Furthermore, hand movement in one linear direction magnifies tip movement in the opposite direction. Not only is instrument movement observed on the screen in the opposite direction, but the magnified tip movement depends on the extent of the instrument's length above the abdominal wall. This leverage not only magnifies the movement, but also magnifies the tool tip force reflected back to the user. Therefore, manipulation of fulcrum instruments requires deliberate learning and training and is not intuitively obvious.

[0005] Additionally, surgical instruments are placed through ports equipped with seals, which create stick-slip friction caused by tool reversal. For example, stick-slip friction can occur from tool reversal when suddenly changing from pulling to pushing against tissue. During such movement, the rubber components of the seal rub against the tool shaft, creating friction or movement between the surgical instrument and the seal until the friction is overcome and the instrument slides relative to the seal. Stick-slip friction or oil canning at the seal-instrument interface creates non-linear forces.

[0006] Hand-eye coordination skills are required and must be practiced, particularly by correlating hand movements with tool tip movements via observation on a video monitor. Additionally, laparoscopic surgery reduces the sensation received through touching the tool. Because tactile sensation is reduced or distorted, surgeons must develop a core set of tactile skills that underlie skilled laparoscopic surgery. Acquisition of all of these skills represents one of the major challenges in laparoscopic training, and the present invention aims to improve systems and methods for laparoscopic skill training and technique performance.

[0007] Not only must novice surgeons learn laparoscopic skills, but experienced laparoscopic surgeons also strive to hone outdated skills and learn and practice new surgical techniques specific to newly introduced surgical procedures. While training can be acquired in the operating room, there has been growing interest in devising rapid and effective training methods, preferably outside the operating room. Surgeons who achieve a reasonable level of skill outside the operating room are better prepared when they enter the operating room, thereby optimizing their beneficial operating room experience, reducing patient risk and costs. Various simulators have been devised and tested to familiarize surgeons with basic surgical skills outside the operating room. One example of a surgical simulator is the SIMSEI® Laparoscopic Training Device, manufactured by Applied Medical Resources Corporation of California and described in U.S. Patent No. 8,764,452, the entire contents of which are incorporated herein by reference. The SIMSEI® laparoscopic training device employs three-dimensional living or fake organs within a simulated abdominal cavity that are hidden from direct observation by the user.

[0008] The use of live human or animal organs in laparoscopic simulators requires freshness of the internal organs. Live organs also require the establishment of sanitation facilities to protect trainees from bacterial and other infections. Additional costs are also required for sanitation and sterilization of instruments used after conducting surgical training. Also, used live organs must be properly disposed of. Furthermore, the odor of live organs can be unpleasant and can distract trainees from their techniques and skills. Therefore, artificial organs and tissues that mimic live organs and tissues are desirable, and thus can replace live organs in surgical training.

[0009] Many artificial organs are used in surgical training to replace live human or animal organs. Typically, these artificial organ models are made of silicone, urethane elastomers, styrene elastomers, etc. These artificial organs must respond appropriately when, for example, cut, manipulated, or sutured, and must provide the same feel and tactile characteristics as in real surgery. However, many artificial organs lack certain characteristics and realism necessary to bridge the gap between artificial and real organs. Furthermore, the degree of realism must be targeted to provide a means of teaching skills specific to laparoscopic skill training. Thus, certain realism may be more important in a laparoscopic environment compared to an open surgical environment. Therefore, there is a need for artificial organs and tissues, and artificial organs and tissues specifically targeted for laparoscopic skill training, that can also be used for non-laparoscopic skill training. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 8,764,452 Summary of the Invention

[0011] According to one aspect of the present invention, a method for fabricating a simulated tissue structure is provided. The method includes providing a mandrel having a first end, a second end, a longitudinal axis, and an outer diameter. The method includes providing at least one elastic ring having a central hole. The at least one elastic ring has a relaxed diameter smaller than the outer diameter of the mandrel. The method includes stretching the at least one elastic ring transversely to the longitudinal axis onto the mandrel to a position where the mandrel is located within the central hole and the at least one ring is expanded around the outer periphery of the mandrel. The method includes applying a layer of uncured silicone to the mandrel and the at least one stretched elastic ring. The method includes curing the layer to adhere the layer to the elastic ring while the elastic ring is expanded. The method includes removing the layer and the elastic ring after performing the step of curing the layer. The method includes allowing the elastic ring to return toward its relaxed diameter.

[0012] According to another aspect of the present invention, there is provided a method for fabricating a simulated tissue structure. The method includes providing at least one elastic strip. The elastic strip has a length and a width, with a relaxed length greater than the width. The method includes stretching the elastic strip to extend its length. The method includes applying a layer of uncured silicone to the elastic strip while the elastic strip is stretched. The method includes curing the layer to attach the layer to the stretched elastic strip. The method includes releasing the elastic strip from the stretched and elongated state after performing the step of curing the layer.

[0013] According to another aspect of the present invention, there is provided a method for fabricating a simulated tissue structure. The method includes providing at least one elastic sheet. The sheet has a length along a longitudinal axis, a width along a transverse axis, and a thickness defined between an upper surface and a lower surface. The method includes stretching the elastic sheet. The method includes applying a layer of uncured silicone to the elastic sheet while stretching. The method includes curing the layer to attach the layer to the stretched elastic strip. The method includes relaxing the stretched elastic strip after performing the step of curing the layer.

[0014] According to another aspect of the present invention, there is provided a method of fabricating a simulated tissue structure. The method includes providing an elastic first material having a relaxed state with an unstretched width and an unstretched length. The method includes stretching the first material. The method includes providing a second material. The method includes attaching the second material to the first material while the first material is stretched and while the first and second materials are held in a first shape. The method includes allowing the first material to return toward its relaxed length to form a simulated tissue structure having a second shape different from the first shape.

[0015] According to another aspect of the present invention, a simulated tissue structure is provided. The simulated tissue structure includes a first layer of elastic material having a length along a longitudinal axis and a width along a transverse axis. The simulated tissue structure includes a second layer of elastic material connected to the first layer, the first layer exerting a compressive force on the second layer along at least one of the longitudinal and transverse axes when in a first shape. The compressive force urges the first and second layers into a second shape defined by the compressive force in equilibrium with the second layer, the second shape being an anatomical shape. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a top perspective view of a mandrel and a plurality of unexpanded silicone rings of the present invention. [Figure 2] FIG. 1 is a top perspective view of a plurality of silicone rings stretched around a mandrel in accordance with the present invention. [Figure 3] FIG. 1 is a top perspective view of a plurality of silicone rings stretched around a mandrel and overlaid with a silicone layer in accordance with the present invention. [Figure 4] FIG. 1 is a top perspective view of a simulated tissue structure of the present invention. [Figure 5] FIG. 1 is a top perspective view of a mandrel and unexpanded silicone ring of the present invention. [Figure 6] FIG. 1 is a top perspective view of a silicone ring stretched around one end of a mandrel in accordance with the present invention. [Figure 7] FIG. 1 is a top perspective view of a silicone ring stretched around a mandrel and overlaid with a silicone layer in accordance with the present invention. [Figure 8] FIG. 1 is a top perspective view of a simulated tissue structure of the present invention. [Figure 9] FIG. 1 is a top perspective view of a silicone ring in an unstretched state positioned adjacent to a mold in accordance with the present invention. [Figure 10] FIG. 1 is a top perspective view of a stretched silicone strip clipped to a mold in accordance with the present invention. [Figure 11] FIG. 1 is a top perspective view of a stretched silicone strip clipped to a mold and overlaid with a silicone layer in accordance with the present invention. [Figure 12] FIG. 1 is a top perspective view of a simulated tissue structure of the present invention. [Figure 13] FIG. 1 is a top perspective view of a mandrel, a plurality of unstretched silicone rings, and an unstretched silicone strip of the present invention. [Figure 14] 1 is a top perspective view of a plurality of silicone rings stretched around a mandrel and a strip stretched alongside the mandrel and overlaid with a silicone layer in accordance with the present invention; FIG. [Figure 15]FIG. 1 is a top perspective view of a simulated tissue structure of the present invention. [Figure 16] FIG. 1 is a top perspective view of a mandrel and unstretched patterned sheet of the present invention. [Figure 17] FIG. 2 is a top perspective view of the mandrel and patterned sheet of the present invention after stretching. [Figure 18] FIG. 2 is a top perspective view of a mandrel partially wrapped with a patterned sheet after stretching in accordance with the present invention. [Figure 19] FIG. 1 is a top perspective view of a mandrel wrapped with a stretched patterned sheet laminated with a silicone layer in accordance with the present invention. [Figure 20] FIG. 1 is a top perspective view of a simulated tissue structure of the present invention. [Figure 21] FIG. 1 is a top perspective view of a strip of elastic material overlaid with a silicone layer in accordance with the present invention. [Figure 22] 1 is a top perspective view of an elongated blood vessel spirally disposed on a strip of elastic material while being stretched in the direction of the arrow in accordance with the present invention; FIG. [Figure 23] FIG. 23 is a top perspective view of the simulated tissue structure of FIG. 22 in an equilibrium state in accordance with the present invention. [Figure 24] 1 is a plan view of a sheet of elastic material with holes in a relaxed state in accordance with the present invention; FIG. [Figure 25] FIG. 1 is a plan view of a sheet in a stretched state in accordance with the present invention, showing the sheet having holes covered with a silicone layer that has been cured and applied to the sheet while it is being stretched. [Figure 26] FIG. 26 is a top perspective view of the simulated tissue structure of FIG. 25 in an equilibrium unstretched state in accordance with the present invention. [Figure 27] FIG. 2 is a plan view of a sheet in a stretched state in accordance with the present invention, showing a silicone layer being cured and applied to the sheet while the sheet is stretched in the direction of the arrows. [Figure 28] FIG. 26 is a top perspective view of the simulated tissue structure of FIG. 25 in an equilibrium unstretched state according to the present invention. [Figure 29] FIG. 1 is a plan view of a layer of mesh material of the present invention. [Figure 30] 1 is a plan view of a plurality of spaced apart strips of mesh material stretched in the direction of the arrows in accordance with the present invention and a layer of silicone cured and applied to the strips. [Figure 31] FIG. 1 is a plan view of a simulated tissue structure of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The following description is provided to enable any person skilled in the art to make and use the surgical tools and practice the methods described herein, and describes the best mode contemplated by the inventors for carrying out their invention. However, various modifications will remain apparent to those skilled in the art. These modifications are intended to fall within the scope of the present invention. Various embodiments or aspects of such embodiments are shown in the various figures and described throughout the specification. It should be noted, however, that although shown or described separately, each embodiment and aspect thereof can be combined with one or more of the other embodiments and aspects thereof, unless expressly specified otherwise. The fact that each combination is not explicitly described is merely to facilitate the readability of the specification.

[0018] Within the human body, there are numerous anatomical examples where there are valves that can contract, tissue planes that converge and taper, or tissue planes that are in tension under these normal conditions. Additionally, within the human body, there are anatomical structures that preferentially stretch in certain directions, and others that do not. All of these examples are difficult to mimic while creating organ models using current manufacturing techniques.

[0019] According to the present invention, the process for producing such a simulated tissue structure 10 generally involves providing a prefabricated piece or sheet of silicone. The silicone piece is stretched to hold it in place in the stretched form. While the sheet is stretched, uncured silicone liquid is applied to the stretched silicone piece and cured, thereby forming a layer. Once the wet silicone has finished curing, the finished product is removed from the mold or mandrel. The prefabricated stretched silicone relaxes and tends toward its unstretched form, which changes the shape of the final silicone object containing the layer. In an alternative embodiment, a piece or sheet of elastic mesh is employed in place of the prefabricated silicone piece or sheet, and uncured silicone is applied to the stretched elastic mesh piece and cured to form a layer. When mesh is used, the final shape of the simulated tissue structure changes less dramatically than with stretched silicone, as the wet silicone fills the interstices of the mesh, reducing 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 form, instead of applying uncured silicone to the stretched silicone piece or stretched mesh piece, a resting, unstretched piece of cured silicone is adhered to the stretched piece while in place.

[0020] With particular reference to FIGS. 1-4, in one form of this method, a silicone ring-shaped band 12 is placed onto a cylindrical mandrel 14. Prefabricated silicone-shaped bands 12 and mandrel 14 are provided as shown in FIG. 1. The mandrel 14 has an outer diameter greater than the unstressed diameter of the band 12 at rest. Prior to placing the mandrel 14 into a mandrel rotation device, multiple prefabricated, cured silicone bands 12 are stretched onto the mandrel 14 and evenly spaced along their length, as shown in FIG. 2. Next, while the mandrel 14 is rotating, a layer 16 of uncured silicone is applied onto the mandrel 14 and onto the prefabricated stretched silicone rings 12. The silicone layer 16 is allowed to cure. The simulated tissue structure 10 is then removed from the mandrel 14. When multiple bands 12 are stretched onto the mandrel 14 and then removed from the mandrel along with the cured silicone layer 16, the bands 12 attempt to return to their normal, reduced, resting shape and diameter. The outer layer 16 is cured and attached to the bands 12, interconnecting them into a unitary structure 10, as shown in FIG. 4. The resulting unitary simulated tissue structure 10 has multiple locations of reduced diameter 18 at the same locations on the bands 12, as shown in FIG. 4. The simulated tissue structure 10 is substantially cylindrical in shape, with a central lumen extending along its longitudinal axis between an opening at the proximal end and an opening at the distal end. At the reduced diameter locations 18, the simulated tissue structure 10, when removed from the mandrel 14, forms a undulating silicone tube that mimics the look and feel of a natural colon. This method can thus be used, for example, to create a simulated Houston valve within the colon.

[0021] In another form of this method, a simulated tissue construct 10 is created having a simulated natural ostium 20 through which a simulated surgical procedure is performed. For example, to create a simulated natural ostium 20, such as a simulated anus, a prefabricated silicone ring-shaped band 12 and mandrel 14 are provided as shown in FIG. 5. The mandrel 14 has an outer diameter greater than the unstretched, resting inner diameter of the band 12 at the desired location along the mandrel 14 where the simulated natural ostium 20 is desired to be formed. The band 12 is stretched around the desired location on the mandrel, in this case around one end of the mandrel 14 as shown in FIG. 6, and a layer of wet silicone 16 is applied to the mandrel 14 and band 12 as shown in FIG. 7. The silicone layer 16 is allowed to cure, and the construct is then removed from the mandrel 14. As a result of layer 16 curing and adhering to the stretched, cured silicone band 12, that portion of the band 12, i.e., the end of the prefabricated silicone band 12, tends to return to its normal, unstretched diameter, thereby creating a reduced-diameter surface area 18 of the simulated tissue structure 10 compared to the outer layer 16 of silicone surrounding it after curing, as shown in FIG. 8. In a variation of this method, the molded, contracted end having a reduced diameter can then be stretched again, in this case over a central peg provided in a transanal adapter mold (not shown). Another layer of silicone is then applied to the stretched end by pouring silicone into the mold, and allowed to adhere to the band and the first layer. Once cured, the prestretched structure is removed from the peg, and the band again contracts back to its original size.

[0022] In another version of this method, a strip 22 of cured silicone having a rest length x is provided, as shown in Figure 9. The silicone strip 22 is stretched to a length y and held in place with length y greater than length x, as shown in Figure 10. The strip 22 is attached by some means, such as clips 26, to a mold 24, or to a mandrel 14, as shown in Figure 10. A layer 16 of wet uncured silicone is applied over and around the stretched strip 22, as shown in Figure 11. The uncured layer of silicone 16 is allowed to cure. Removal of this structure from the mold 24 or mandrel 14 necessarily removes the force holding the strip 22 in its stretched state. As a result, the strip 22 attempts to return to its normal relaxed length x, which moves and contracts the cured silicone layer 16 around it, thereby creating wrinkles and bunching around the strip 22, as shown in Figure 12. When the workpiece is removed from the mold or mandrel, the stretched strips relax and bunch up the new, now cured, silicone layer 16 as shown in FIG.

[0023] 13-15, one or more combinations of methods can be employed. For example, a band 12 can be applied to a mandrel 14 along with a strip 22. One or more bands 12, a mandrel 14, and at least one strip 22 are provided as shown in FIG. 13. The band 12 has a rest inner diameter that is smaller than the outer diameter of the mandrel 14. The strip 22 has a rest length x, which is stretched to a length y and held in place along the mandrel 14 as shown in FIG. 14. A circular, hoop-shaped band 12 is stretched to fit over the strip 22 and mandrel as shown in FIG. 14. Alternatively, the band 12 can be stretched to position itself between the strip 22 and the mandrel 14. An outer layer 16 of uncured wet silicone is applied to the one or more bands 12 and the one or more strips 22 and on the mandrel 14 as shown in FIG. 14 and allowed to cure. Once the outer layer has finished curing, the fabrication is removed from the mandrel 14, and the resulting simulated tissue structure 10 is shown in Figure 15. As can be seen in Figure 15, upon removal of the cured fabrication, the bands 12 attempt to return to their normal rest diameter / configuration, pulling the cured silicone layer 16 inward to form a tubular structure with valleys or a reduced radial dimension at the locations of the rings 12. The stretched strips 22 also attempt to shorten as they return to their normal rest dimension, thereby causing the cured silicone layer 16 to contract along the length of the strips 22, which in some cases gives the resulting tissue structure 10 a natural curvature with depressions in the outer layer 16 at the sides of the strips 22, as shown in Figure 14.

[0024] Referring now to Figures 16-20, another configuration for fabricating the simulated tissue construct 10 is shown, in which a patterned strip 22 is employed on the mandrel 14. The patterned strip 22 is a piece of cured silicone and / or mesh material cut into the desired pattern / configuration. The mesh, if employed, is a stretchable mesh. In the configuration shown in Figures 16-20, the patterned strip 22 remains in a repeating H-shaped configuration with a longitudinal spine intersecting the transverse strips. The patterned strip 22 is stretched longitudinally along the mandrel 14 in the direction of the arrow in Figure 17. The patterned strip 22 is wrapped around the mandrel 14 while being stretched, as shown in Figure 18, and is affixed in place on the mandrel 14 with an adhesive or other fastener. Next, an uncured silicone layer 16 is applied to the stretched patterned strip 22 and mandrel 14 and allowed to cure. Once the layer 16 is cured, the fabrication is removed from the mandrel 14. The stiffening layer 16 is bonded to the patterned strips 22, and the stretched patterned strips 22 and / or mesh naturally relax back to their stretched equilibrium configuration, resulting in the unique lumen-like simulated tissue structure 10 shown in FIG. 20 having a directional curvature imparted by the patterned strips 22, with bulbous portions formed between the lateral strips and openings formed by the spaces between the lateral strips.

[0025] 21-23, an alternative configuration for forming the simulated tissue construct 10 is shown. A thin strip 22 of cured silicone is stretched along its longitudinal axis, as indicated by the arrow in FIG. 21. In the stretched position, a thin layer 16 of uncured silicone is applied to the surface of the stretched strip 22. While the layer 16 is still wet, a solid or hollow tubular vessel 28 made of silicone is placed on the stretched strip 22. In one configuration, the vessel 28 is placed in a spiral configuration around the stretched strip 22, as shown in FIG. 22. The vessel 28 is wrapped around the stretched strip 22 without tension, and the wet layer 16 of silicone is allowed to cure, adhering to the vessel 28. Upon curing, the final simulated tissue construct 10 is the helical, tortuous vessel shown in FIG. 23.

[0026] Referring now to Figures 24-26, another method for forming the simulated tissue structure 10 is shown. A prefabricated sheet 30 of silicone is provided. Holes 32 are cut from the sheet 30 as shown in Figure 24. The sheet 30 with the holes is uniformly stretched as indicated by the arrows in Figure 25. The holes 32 can be of any size and shape. An uncured silicone layer 16 is applied over the holes 32 in the stretched state and allowed to cure as shown in Figure 25. Alternatively, a prefabricated, cured silicone patch 36, slightly larger and having a complementary shape than the holes 32 in the stretched state, is adhered in place over the holes 32 in the stretched state as shown in Figure 25. In both cases, when the sheet 30 is peeled away from the staging platform, it returns to its unstretched equilibrium position and now bears the dome-shaped feature formed by the cured silicone layer 16 on another flat sheet 30. The dome-shaped feature of the layer 16 extends upward from the flat sheet 30 in its relaxed state as shown in Figure 26.

[0027] 27 and 28, in another form, a flat, cured silicone sheet 30 is void of holes. The void-free sheet 30 is uniformly stretched in the direction of the arrow in FIG. 27, and an uncured silicone layer 16 is applied to one or more areas of the sheet 30. The areas on the sheet 30 where the wet silicone has been applied and cured are rounded away from the newly added silicone layer 16; that is, in the area of ​​the applied silicone layer 16, the sides of the structure bearing the newly applied silicone layer 16 are convex, and the sides of the stretched sheet 30 are concave. This technique is useful for customizing the shape of flat sheets at other points used to create simulated anatomical structures, especially in areas where thin layers connect to other structures.

[0028] 29-31, another method for forming the simulated tissue construct 10 of the present invention is shown. As described above, when a mesh is employed and stretched, and an uncured silicone layer is applied to the stretched mesh, the wet silicone penetrates the interstices of the mesh, and the resulting quality of the simulated tissue construct 10 due to mesh-related retraction is less pronounced than with non-porous materials. However, a simulated tissue construct 10 utilizing a mesh offers advantageous tactile properties. By providing a mesh layer 38 and stretching it to its elastic limit in only one direction while leaving it relaxed in other directions, a simulated anatomical structure can be formed that stretches preferentially in one direction compared to another. This application of the mesh layer 38 to a simulated tissue construct, characterized by stretching the mesh layer 38 in one direction before application of the uncured silicone layer 16, can be used to fabricate preferentially stretchable sheets or other simulated anatomical structures, such as simulated tendons, that are flexible enough to bend but do not stretch easily. Another example of this is incorporating mesh strips into the sidewall of a simulated intestine, such that when the simulated intestine is insufflated, the simulated intestine expands circumferentially but not longitudinally. The mesh material is an interwoven or intertwined braid or network of interlocking filaments, grouped or ungrouped, thereby forming an open textured structure with small, substantially uniform fenestrations / interstices. The mesh braid is formed such that two interlaced systems of filamentary elements are interwoven, with each filamentary element of one system alternately guided over the filamentary elements of the other system. Such a braid pattern is called a plain weave. The number of intersections within a particular unit length determines the density of the weave; more intersections result in a tighter weave and smaller fenestrations. Due to the weave arrangement and density, the mesh material can stretch along the lateral axis because bands can slide over, under, and relative to each other, thereby increasing the size of the fenestrations. The mesh increases in width when stretched laterally, thereby decreasing in length. The mesh material can also extend along the longitudinal axis of the mesh.The increased length of the mesh when stretched longitudinally reduces the width of the mesh layer. Depending on the weave geometry and orientation, the mesh material can have a dominant or primary stretch direction, in which case the mesh material extends a long distance relative to a minor or secondary stretch direction generally perpendicular to the primary stretch direction. Figure 29 shows a sheet 38 of mesh material having a plurality of filaments forming a weave having a primary, dominant stretch direction 40 and a secondary, minor stretch direction 42. The mesh sheet 38 can be cut into strips 44. The strips 44 are spaced apart and then stretched in the secondary stretch direction 42 to maximize elongation in the secondary stretch direction 42. While the mesh strips 44 are maintained at their maximum elongation, an uncured silicone layer 16 is applied to the mesh strips 44, as shown in Figure 30. The silicone layer 16 is cured while the mesh strips 44 remain in their stretched state. After silicone layer 16 has cured, mesh strip 44 and silicone layer 16 are trimmed as desired. Referring to Figures 29-31, upon release of strip 44, the resulting simulated tissue structure 10 is highly extensible in the primary, dominant stretch direction 42 and resists stretching in the secondary, less dominant stretch direction, which has a negligible small-scale effect on the final shape of structure 10, but has a large-scale effect on tactile qualities, e.g., stretch.

[0029] The above-described method involves carefully combining uncured silicone with prefabricated and stretched silicone or mesh material, resulting in the lifelike feel and appearance of a simulated anatomical structure. The degree of effect achieved by the resulting simulated tissue construct can be controlled by varying the thickness and durometer of both the prefabricated stretched silicone piece and the wet silicone used. The greater the difference in thickness and durometer between the cured silicone and the wet silicone used, the greater and more dramatic the effect on the resulting simulated tissue construct.

[0030] All of these techniques involve intentionally incorporating residual stresses into simulated anatomical structures. There are many examples of the human body that contain structures with residual stresses, and the goal of these techniques is to mimic these real tissue structures in look, feel, and manufacturability.

[0031] Currently, many organ constructs are made in several pieces to reduce molding complexity. These pieces are then glued together to achieve the desired curved shape. Advantageously, by using pre-stretched pieces to create residual stresses in accordance with the present invention, less complex molds can be used. Additionally, to create curved simulated intestines, straight tubes are currently "kinked" to achieve the desired path. Advantageously, the residual stresses of the present invention can help create more realistic curves without collapsing the tube due to the kinks, and also allow for easier demolding.

[0032] It will be appreciated that various modifications can be made to the embodiments disclosed herein. Accordingly, the above description should not be construed as limiting the invention, but merely as exemplifications of preferred embodiments. Those skilled in the art will envision other modifications that are within the scope and spirit of the invention.

Claims

1. A simulated tissue structure, a strip having an extended state and a relaxed state; an outer layer of silicone disposed on the strip as it attempts to return from the stretched state to the relaxed state.

2. The simulated tissue structure of claim 1 , wherein the strip is a cured silicone strip.

3. 3. The simulated tissue structure of claim 2, wherein the outer layer of silicone wrinkles or bunches around the cured silicone strip as the cured silicone strip returns from the stretched state to the relaxed state.

4. The simulated tissue structure of claim 1 , wherein the strip is a patterned strip.

5. The simulated tissue structure of claim 4 , wherein the patterned strips are cured silicone.

6. 6. The simulated tissue structure of claim 4 or 5, wherein the patterned strip is a mesh material.

7. 7. The simulated tissue structure of claim 6, wherein the patterned strip has a repeating H-shaped configuration having a plurality of spaced-apart lateral strips and longitudinal spines intersecting the lateral strips.

8. 8. The simulated tissue construct of claim 7, wherein the outer layer of silicone and the patterned strips have an equilibrium configuration that results in a lumenal simulated tissue construct.

9. The simulated tissue structure of claim 7 , wherein the outer layer of silicone and the patterned strips have a directional curvature imparted by relaxation of the longitudinal spines.

10. 10. The simulated tissue structure of claim 9, further comprising bulbous portions formed between said transverse strips, said openings being defined by spaces between said transverse strips.

11. The simulated tissue structure of claim 1 , further comprising a tubular blood vessel disposed on said strip.

12. The simulated tissue structure of claim 1 , further comprising a tubular blood vessel spirally disposed around said strip.

13. 10. The simulated tissue structure of claim 1, further comprising a tubular blood vessel wrapped around said strip without tension.

14. 10. The simulated tissue structure of claim 1, wherein the strip comprises a plurality of strips of a sheet of mesh material, the sheet of mesh material having a plurality of filaments forming a weave having a primary, predominant direction of stretch and a secondary, minor direction of stretch.

15. 15. The simulated tissue structure of claim 14, wherein the plurality of strips are spaced apart from one another, and in the stretched state, each of the plurality of strips is stretched in the secondary, minor stretch direction to a maximum elongation in the secondary, minor stretch direction.

16. 16. The simulated tissue structure of claim 15, wherein in the relaxed state of the plurality of strips, the simulated tissue structure is stretchable in the primary, predominant direction of stretch and resists stretching in the secondary, minor direction of stretch.

17. 17. The simulated tissue structure of claim 14, 15 or 16, wherein the mesh material is woven with interlocking filaments to form an open textured structure with uniform interstices.

18. 17. The simulated tissue structure of claim 14, 15 or 16, wherein the primary predominant direction of extension of the mesh material is based on the shape and direction of the weave of the mesh material.

19. 2. The simulated tissue structure of claim 1, wherein the strip is a mesh strip incorporated into the side wall of the simulated intestine, and when the simulated intestine is insufflated, the simulated intestine expands circumferentially but not longitudinally.

20. The simulated tissue structure of any one of claims 1 to 5 and 11 to 16, wherein the outer layer of silicone is cured into the strip in the stretched state.

Images