ELASTOMERIC AUXETIC MEMBRANE FOR UROGYNECOLOGICAL AND ABDOMINAL IMPLANTATIONS

Embodiments relate to the use of auxetic geometries to construct the pores of membranes. Auxetic geometries expand in the transverse direction when stretched along the longitudinal direction. This behavior is counterintuitive as most materials contract in the transverse direction when stretched longitudinally. A mesh with pores that are auxetic has the potential to overcome the primary limitation of most prolapse meshes—pore collapse with tensile loading.

FIELD OF THE INVENTION

Embodiments relate to an elastomeric auxetic membrane, and particularly to an elastomeric auxetic membrane for urogynecologic and abdominal implantations.

BACKGROUND OF THE INVENTION

Urogynecologic surgical mesh is used to provide additional support when repairing damaged or weakened tissue. However, the pores of most current urogynecologic meshes contract and/or collapse in response to tensile loads. Pore collapse is problematic for surgical meshes, as meshes with small pores are associated with increased inflammation and fibrosis and have decreased tissue integration into the pores relative to meshes with large pores. Additionally, smaller pores increase the risk of bridging fibrosis (overlapping of the foreign body response to neighboring fibers resulting in a fibrous capsule), a process that can lead to encapsulation and pain. Clinically, pore collapse manifests as mesh contraction or “shrinkage” and is associated with vaginal pain that often does not resolve even with mesh removal resulting in poor patient outcomes. Pore collapse also changes the properties of the material, making it stiffer and resulting in stress shielding, the mechanism underlying mesh exposure. Most commercially available urogynecologic meshes are made from polypropylene, for which the minimal pore diameter for tissue integration has been shown to be 1 mm. Problematic areas for patients experiencing mesh complications are often located in areas where the pores of a mesh have collapsed well below this threshold of 1 mm with tensioning and loading.

Further, additional limitations of current meshes are material stiffness and permanent deformation with loading (i.e., permanent elongation of mesh). Propylene has a material stiffness that is orders magnitude stiffer than vaginal tissue, causing issues such as degeneration, decreased cellular response, and damage to underlying tissue.

Accordingly, there is a need for the development of a device with a stable pore geometry that does not collapse with tensioning and loading. Further, there is a need for a device that can complement the stiffness of native tissue, and a device that can withstand forces, both sudden and repetitive.

The present disclosure is directed toward overcoming one or more of the above mentioned problems, though not necessarily limited to embodiments that do.

SUMMARY OF THE INVENTION

Embodiments relate to the use of auxetic geometries to construct the pores of membranes. Auxetic geometries expand in the transverse direction when stretched along the longitudinal direction. This behavior is counterintuitive, as most materials contract in the transverse direction when stretched longitudinally. A membrane with pores that are auxetic has the potential to overcome the primary limitation of most prolapse meshes—pore collapse with tensile loading.

The disclosed device is referred to as a membrane as opposed to a mesh, as the term “mesh” implies a device manufactured via knitting or weaving. In contrast, the disclosed device is manufactured via molding or 3D printing.

In an exemplary embodiment, an elastomeric membrane for implantation in a human body, comprises a plurality of fibers, comprised of at least one polymer, and a plurality of pores, wherein each pore is defined by the plurality of fibers and has an auxetic shape such that a size of the pores expands in a direction transverse to a longitudinal axis when the membrane is subject to a tensile load along the longitudinal axis.

In some embodiments, the at least one polymer is polycarbonate urethane.

In some embodiments, the plurality of fibers have a material stiffness that is similar to a native tissue to which the membrane is attached.

In some embodiments, the plurality of fibers have a material stiffness of 6 to 35 MPa.

In some embodiments, the at least one polymer is a combination of at least two different types of fibers.

In some embodiments, the at least one polymer is a combination of at least two different grades of a single type of polymer.

In some embodiments, the plurality of fibers have an original length and are configured to return to a second length after tensile loading or unloading at 15 N, wherein the second length is less than or equal to 40% longer than the original length.

In some embodiments, the auxetic shape is a bowtie shape.

In some embodiments, the bowtie shape has horizontal edges and is oriented such that the horizontal edges are perpendicular to an axis of loading.

In some embodiments, the auxetic shape is a chiral hexagon shape.

In some embodiments, each pore has a minimum pore diameter of 0.5 to 5.0 mm.

In some embodiments, the membrane is manufactured using a technique that yields a membrane with no knots or interstices.

In some embodiments, the plurality of fibers have a width between 0.3 and 1 mm in an untensioned state.

In some embodiments, the plurality of fibers have a thickness between 0.3 and 1 mm in an untensioned state.

In some embodiments, the membrane has an effective pore area that does not change in response to a tensile load up to 15 N.

In some embodiments, the at least one polymer is non-biodegradable.

In some embodiments, the at least one polymer is bioresorbable.

In some embodiments, the at least one polymer is configured to interact with a native tissue to enhance tissue integration.

In some embodiments, the membrane comprises a body section and at least one arm section, wherein the at least one arm section extends outwardly from the body section.

In some embodiments, the membrane has a porosity greater than or equal to 75%.

In an exemplary embodiment, a method of implanting a membrane in a human body comprises providing an elastomeric membrane for implantation in the human body. The elastomeric membrane comprises a plurality of fibers, comprised of at least one polymer, and a plurality of pores, wherein each pore is defined by the plurality of fibers and has an auxetic shape such that a size of the pores expands in a direction transverse to a longitudinal axis when the membrane is subject to a tensile load along the longitudinal axis. The method further comprises orienting the plurality of pores to maximize pore expansion when the membrane is subject to the tensile load along the longitudinal axis, and attaching the membrane to human tissue.

In some embodiments, the auxetic shape is a bowtie comprising horizontal edges, and the method further comprises orienting the plurality of pores such that the horizontal edges of the pores are perpendicular to the tensile load along the longitudinal axis.

In some embodiments, the auxetic shape is a bowtie comprising horizontal edges, and the method further comprises orienting the plurality of pores such that the horizontal edges of the pores are aligned with the tensile load along the longitudinal axis.

Additional features, aspects, objects, advantages, and possible applications of the present disclosure will become apparent from a study of the exemplary embodiments and examples described below, in combination with the Figures and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of exemplary embodiments that are presently contemplated for carrying out the present invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles and features of various aspects of the present invention. The scope of the present invention is not limited by this description.

Embodiments relate to an elastomeric auxetic membrane (EAM). The EAM100may be used in urogynecologic procedures including, but not limited to, transabdominal prolapse procedures (sacrocolpopexy) (seeFIGS. 1 and 2A-2B), transvaginal prolapse repairs (seeFIGS. 3-4), and mid-urethral slings. It is contemplated that the EAM100may also be used in other surgical procedures including, but not limited to, abdominal hernia repairs (seeFIG. 5), inguinal hernia repairs (seeFIG. 5), diaphragmatic hernia repairs (seeFIG. 5), and other like surgical procedures.

The EAM100is a three-dimensional porous device that includes a plurality of open spaces (i.e., pores102) that may be defined by polymeric fibers104with no knots (i.e., having no small spaces and interstices that are less than <100 um). As used herein, pores102generally describes102′,102″, and/or102″. It is contemplated that the EAM100is manufactured using 3D printing, molding, or other techniques that adequately yield a membrane with no knots or interstices. The EAM100may be in the form of any shape, and it is contemplated that the shape of the EAM100may complement a particular procedure or native tissue for which the EAM100is being used. In an exemplary embodiment, the EAM100may consist of a body section106only, or may consist of a body section106and either one or more arm sections108or a stem section109, wherein the arm sections108and stem sections109extend outwardly from the body section106. In an exemplary embodiment, the arm sections108may be used to tension the EAM100to ligaments122and other tissue. In another exemplary embodiment, the stem section109may be used to bridge two independent body sections106, one anterior and one posterior, to the sacrum112. For example, one or more arm sections108may be attached to a common body section106in a Y configuration (seeFIGS. 3-4), or a stem section109may connect two body sections106in a Y configuration (seeFIG. 2B). It is further contemplated that the arm sections108or stem section109may have a larger surface area than the body section106. Additionally, the EAM100may have any dimensions, and it is contemplated that the dimensions of the EAM100may complement a particular procedure or native tissue for which the EAM100is being used.

In an exemplary embodiment, for a transabdominal prolapse procedure, the EAM100may be a rectangular shape and have overall dimensions of about 5 cm (width) and 15 cm (length). In another exemplary embodiment, for a transvaginal prolapse repair, the EAM100may have arm section108dimensions of about 1 to 3 cm (width) and about 5 to 15 cm (length), and a body section106dimension of about 5 to 7 cm (width) and 5 to 15 cm (length).

The width W and thickness T of the fibers104in an untensioned state may generally range between 0.3 mm and 1 mm (seeFIGS. 8A and 8C). An untensioned state may be defined as a state in which the EAM100has no forces or loading acting upon it. However, as one skilled in the art will appreciate, it is contemplated that the fiber width W and/or fiber thickness T may vary depending on a number of factors including, but not limited to, the severity of the condition (e.g. the degree of prolapse) and/or the body mass index of the individual in whom the EAM100will be placed.

The fibers104may be made from one or more polymers. The polymer(s) may include, but is not limited to, polycarbonate urethane (PCU). It is contemplated that the polymer(s) has a material stiffness that is similar to the native tissue for which the EAM is being used. In an exemplary embodiment, wherein the native tissue is vaginal tissue comprising an estimated tangent modulus or stiffness of 6 to 35 MPa, the material stiffness of the EAM may be similar to (i.e., 6 to 35 MPa), or one that is one or two orders in magnitude stiffer (i.e., 60 to 350 MPa, or 600 to 3,500 MPa), than vaginal tissue. The fibers104may comprise one polymer or of a combination of two or more different polymers, or of a combination of two or more different grades of a single type of polymer. For example, PCU is available in a range of durometers that are typically reported as Shore hardness ranging from 75 A, 85 A, 95 A, and 75D (also referred to as grades), and the fibers104may be comprised of one PCU grade or a combination of PCU grades depending on the application of the EAM100. Any polymer or combination of polymers that provide adequate strength, toughness, and durability while maintaining biocompatibility for soft tissue repairs is suitable.

It is contemplated that the polymer(s) may be non-biodegradable (i.e., permanent). Non-biodegradable may be defined as the ability of the polymer(s) to resist physical and/or chemical changes and to maintain its position within native tissue. It is further contemplated that the polymer(s) may be bioresorbable. Bioresorption may be defined as the ability of the polymer(s) to naturally degrade and/or dissolve over time. It is further contemplated that the polymer(s) may have a combination of both non-biodegradable and bioresorbable properties.

It is contemplated that the polymer(s) may have shape-memory properties (i.e., the polymer(s) may be elastomeric or exhibit elastomeric properties). Shape-memory may be further defined as the ability of the polymer(s) to minimize and potentially eliminate the amount that the EAM100permanently elongates in response to repetitive loading, and the EAM's100ability to return to its original configuration. Specifically, the polymer(s) may deform and return to an initial length with minimal permanent elongation. It is contemplated that a minimal permanent elongation after cyclic loading or unloading of 15 N is less than or equal to a 40% increase in the EAM's100initial length. The shape-memory characteristic mimics native soft tissues.

It is contemplated that the polymer(s) may be modified for the conjugation of proteins and other biomolecules of interest that promote interaction with native tissue to enhance tissue integration. Click chemistry is a popular technique for engineering bioactive polymers due to mild reaction conditions. Thus, motifs such as oximes or dialdehydes that facilitate crosslinking or attachment of peptides may be added. In an exemplary embodiment, the polymer(s) may be modified to provide for an RGD moiety for binding to integrins. In another exemplary embodiment, the one or more polymers may be modified to provide for a VAPG moiety for binding to elastin.

The pores102of the EAM100are in the form of an auxetic shape. An EAM100with auxetic pores102allows for adequate porosity and pore expansion for tissue integration. An auxetic shape expands in the transverse direction when stretched along the longitudinal direction, and is associated with a negative relative lateral contraction, which is analogous to a negative Poisson's ratio which describes deformation in the transverse axis relative to the longitudinal axis. This behavior (i.e., expansion of the pores102when loaded or elongated) is counterintuitive as most materials and shapes contract in the transverse direction when stretched longitudinally. Auxetic shapes that can be used include, but are not limited to bowtie (seeFIGS. 6A-6C), chiral hexagon (seeFIGS. 7A-7C), hexagon, spiral, triangle, square chiral, and square grid (seeFIG. 10). The pores102may have an auxetic shape that is either anisotropic of isotropic. Isotropic auxetic geometry may consist of any combination of polygons including, but not limited to, squares, circles, rectangles, hexagons, etc. Given that the pores102will expand independent of the orientation of the pores102with respect to the direction of loading Lx, the isotropic auxetic pore orientation is often negligible. The direction of loading Lx may be defined as the axis or axes in which force is applied to an object. It is contemplated that the auxetic geometry may be oriented to maximize pore expansion.

In an exemplary embodiment, the auxetic shape of the EAM100′ is defined by fibers104′ as a bowtie pore102′ (seeFIGS. 6A-6C), in which the bowtie pores102′ consist of six sides (seeFIG. 8A) and four congruent internal angles (α1, α2, α3, and α4) (seeFIG. 8B). The internal angles may be between 15° and 70°. The bowtie pores102′ consist of two horizontal edges110opposite of one another, and two bent members122opposite of one another. The bent members122are directed inward toward the center of the bowtie. In use, the bowtie pore102′ geometry will be oriented to maximize pore expansion, such that the horizontal edges110of the bowtie pore102′ are perpendicular (seeFIG. 9A) or aligned (seeFIG. 9B) along the direction of loading Lx. As stated above, the direction of loading Lx may be defined as the axis or axes in which force is applied to an object. In another exemplary embodiment, the auxetic shape of the EAM100″ is defined by fibers104″ as chiral hexagon pores (seeFIGS. 7A-7C), in which the pores consist of a combination of triangles102″ and circles102′″ oriented in a manner to maximize pore expansion.

As a result of the auxetic shape of the pores102′, it is contemplated that the pores102′ may have a minimal diameter D between 0.5 mm and 5.0 mm, with a preferable minimal diameter of 1 mm, regardless of whether the pores102′ are in a tensioned or untensioned state. One skilled in the art will appreciate that the minimal diameter D will increase as the pores102′ expand. However, as one skilled in the art will appreciate, it is contemplated that the minimal diameter D may vary depending on a number of factors including, but not limited to, the severity of the condition (e.g. the degree of prolapse) and/or the body mass index of the individual in whom the EAM100will be placed. An untensioned state may be defined as a state in which the EAM100has no forces or loading acting upon it. Pores102′ of an auxetic shape also result in an EAM100with an increased overall pore area, an increased porosity (i.e., greater than or equal to 75%), and an effective porosity greater than 80% in response to tension and elongation. The effective porosity is defined by the percentage of pores102′ greater than 1 mm in diameter.

In response to tensile loading or elongation, the pores102′ of the EAM100will remain open (i.e. pore size will be greater than or equal to the unloaded pore size) when implanted along the intended direction of loading Lx or irrespective of the orientation with respect to the direction of loading Lx for the isotropic auxetic pore geometry. The EAM100will also experience increased porosity (greater than or equal to 75%) and an effective porosity greater than 80% in response to tension and elongation. It is further contemplated that due to the inherent nature of the auxetic geometry, the polymer(s) used, and the method of manufacture using 3D printing or molded technology (i.e., absence of knots) the EAM100will experience minimal wrinkling in response to tension and elongation.

Moreover, the EAM has an effective pore area that does not change in response to tensile loading or elongation within the physiologic range (i.e., loads up to 15 N). Specifically, in an exemplary embodiment, the effective pore area of an EAM manufactured using polydimethylsiloxane, a relatively weak polymer, did not change in response to tensile loads up to 3 N, and it is contemplated that the effective pore area of an EAM manufactured using a stronger polymer (i.e., PCU), will remain unchanged in response to tensile loads up to 15 N.

In reference toFIG. 1, in an exemplary method of use, the EAM100is inserted by sacrocolpopexy, a procedure performed via minimally invasive laparoscopy, laparoscopy assisted robotic surgery, or laparotomy. In all 3 approaches, a dissection is carried down to the sacrum112extending to the site of the EAM100attachment and tensioning. The bladder114is dissected off of the anterior vagina116and the rectum118dissected off of the posterior vagina116. A strap of the EAM100(typically 5 by 15 cm) is placed between the bladder114and the vagina116, and a second strap of the same size between the rectum118and the vagina116. The two straps are then pulled up to the longitudinal ligament of the spine120at the level of the sacrum112and attached to it; thereby lifting the vagina116back into its physiological position. For the membrane bridge to the sacrum112, the two straps of EAM100can be attached individually or through a common stem section109in a Y configuration at attachment site121. For an auxetic EAM100, the orientation would be such that when the EAM100is tensioned longitudinally, the pores102open in that direction. Typically, 8 to 10 cm of an arm section108is used posteriorly and 4 to 6 cm anteriorly. The stem section109can range from 3 to 8 cm. For this invention, the amount of material in the body section106of the EAM100in contact with the vagina116may differ from that of the bridge to the sacrum112.

Specifically, in reference toFIG. 2A, sacrocolpopexy EAMs can be configured from two straps of membrane, each containing (i) a body section106that is sutured over the vagina, and (ii) a stem section109from each strap that forms a bridge between the vagina and the sacrum. Alternatively, in reference toFIG. 2B, the EAM can also be configured into a Y in which a posterior body section106″ is attached to an anterior body section106′, which has a stem section109′, at the interface with the stem section109′. In this case, the single stem section109′ forms the bridge between the vagina and the sacrum. The stem section109may have different textile and mechanical properties than the body section.

In reference toFIGS. 3 and 4, in another exemplary method of use, the EAM100is used during transvaginal prolapse repairs. During this procedure, the EAM100is used to reinforce the anterior wall, the vaginal apex or uterus, and the posterior vaginal wall. A full thickness incision is made in the vagina116and the associated organ (i.e., bladder, small bowel, or rectum) dissected away. The dissection is carried down to the sacrospinous ligament or the uterosacral ligament. The membrane is placed over the vaginal wall and then tensioned to the ligaments122via arm sections108or a suture attachment. The amount of material may vary along the EAM's100length. It is contemplated that the arm sections108of the EAM100that insert into the ligaments122may have more material than that the body section106in contact with the vagina116. The pore geometry may be chosen such that the pores102will remain open along the direction of loading. The vaginal incision116will be closed over the EAM100.

In another exemplary method of use, the EAM100is used as a mid-urethral sling. An incision will be made into the vagina116over the mid-urethra and extended laterally toward the ischiopubic ramus. An EAM100with dimensions of 1.5 by 6.25 cm will be placed over the mid-urethra and pulled through the retropubic space, or the transobturator space, or through the fascia overlying the obturator externus. After a cystoscopy to verify that the membrane had not entered the urethra or bladder, the EAM100will be tensioned over the urethra. The vagina116will then be closed over the EAM100.

In another exemplary method of use, the EAM is used for inguinal hernia repair. After incising the skin, subcutaneous tissue, and external oblique aponeurosis, the spermatic cord (males) is elevated from the posterior wall of the inguinal canal. In indirect hernias, the hernial sac is identified, dissected to the internal ring and opened to allow examination of its contents. The sac is ligated and its distal portion is usually excised. In this context, an appropriately sized EAM is prefabricated or trimmed to fit the floor of the inguinal canal. The apex is first sutured to the public tubercle using 3-0 Prolene suture. The same continuous suture is then used to suture the lower border of the membrane to the free edge of the inguinal ligament after an opening is made into its lower edge to accommodate the spermatic cord. The continuous suture extends up just medial to the anterior superior iliac spine. Interrupted Prolene sutures then suture the two cut edges of the membrane together around the spermatic cord. The inferomedial corner of the membrane is then attached while overlapping the pubic tubercle. The membrane is then anchored to the conjoined tendon by metal staples (i.e., titanium) or by interrupted sutures (i.e., Prolene 3-0). The aponeurosis of external oblique is closed using absorbable sutures (i.e., Vicryl No2). The skin is then closed.

In another exemplary method of use, the EAM is used for abdominal wall or ventral hernia repair. Surgical repair technique can be performed minimally invasively or open. In some instances, an EAM can be placed over a suture repair of the fascial defect while in others in which a suture repair is not possible, the EAM is used to cover the defect and fixed in place by sutures or alternatively via a tack device. Typically, the EAM is placed over a fascial defect such that 5 cm of the membrane spans all sides of the defect.

In another exemplary method of use, the EAM is used for hiatal or diaphragmatic hernia repairs. Hiatal hernias can effectively be repaired via a transabdominal or transthoracic approach. More recently, a laparoscopic approach has gained popularity as it is markedly less morbid than an open approach. The use of surgical mesh for reinforcement of large hiatal hernia repairs has been shown to lead to decreased recurrence rates. Surgical repair may be a primary suture closure reinforced by the EAM or an EAM closure alone (larger defects). In both cases, the defect of the diaphragm is closed by placing the EAM over the space between the diaphragm and the esophagus after reduction of the herniated contents.

EXAMPLES

The following examples serve to illustrate certain aspects of the disclosure and are not intended to limit the disclosure.

Computational models of membranes with different auxetic geometries intended for use via a sacrocolpopexy, in which the forces along the membrane in vivo are predominantly uniaxial, were constructed. The deformation of the models was assessed via simulated uniaxial tensile tests using finite element analysis (FEA). A simulated load of 3 N was applied along the longitudinal axis of the models. The pore geometries for the auxetic models included (1) bowtie, (2) chiral hexagon, (3) hexagon(b), (4) spiral, (5) triangle, (6) square chiral(a), (7) square chiral(b), and (8) square grid (seeFIG. 10). For comparison purposes, computational models with standard pore geometries mimicking current commercially available prolapse meshes were also created. The standard models included (1) square, (2) diamond, and (3) hexagon(a) (seeFIG. 11). Quantitative measurements of the following parameters were used to characterize the deformation of the pore geometries and models overall: minimal pore diameter, effective pore area (defined by the area of the pores with widths greater than 1 mm), porosity (defined by the amount of pore space within the mesh), effective porosity (defined by the amount of void space within the membrane from the pores that are greater than 1 mm), and relative lateral contraction (representative of the degree of contraction of the model with a positive value indicating model contraction (i.e., pore collapse) and a negative value indicating expansion (i.e., pores remaining open/enlarging)).

Regarding effective pore area, the effective pore area for all models was 100%. No change means that the effective pore area at 3 N was maintained at 100%. Regarding effective porosity, no change means that the effective porosity before (0 N) and after loading (3 N) are the same. Regarding relative lateral contraction, a positive value indicates model contraction and a negative value indicates model expansion/pore expansion.

As seen in Table 1, the results show that, generally, auxetic pore geometries expand in response to uniaxial loading. As anticipated, the models with standard pore geometries contracted and/or their pores collapsed with loading consistent with ex vivo testing of commercial polypropylene meshes with similar pore geometries.

Computational models of membranes with different auxetic geometries intended for use via transvaginal prolapse repairs, in which the forces along the membrane are oriented in a variety of directions, were constructed. For transvaginal membranes, it was important to assess how pore orientation impacts the ability of auxetic pores to expand in multiple directions. Accordingly, the deformation of the models was assessed via simulated tensile tests FEA with the auxetic pores rotated 45° (seeFIG. 12) and 90° (seeFIG. 13) with respect to the longitudinal axis of the membranes. A simulated load of 3 N was applied along the longitudinal axis of the models. For 3 of the 8 auxetic geometries, a 90° rotation resulted in the same pore orientation as the respective model created in the previously mentioned FEA study; hence, there were only five models with the pores rotated 90°: (1) bowtie, (2) triangle, (3) chiral hexagon, (4) hexagon (b), and (5) square chiral (b). All of the auxetic geometries were tested with a 45° degree rotation.

In response to 3 N, the pores of all of the models with the pores rotated at 45° contracted and only two of the auxetic geometries were able to maintain its ability to expand when rotated 90°, the bowtie and triangle. Collectively, these results suggest that, in addition to load dependence, the ability of an auxetic geometry to expand is also dependent on the orientation of the auxetic geometry with respect to the direction of loading. The chiral hexagon geometry demonstrated the least sensitivity to pore orientation relative to the other auxetic geometries.

Synthetic membranes with the bowtie and chiral hexagon pore geometries at 0°, 45°, and 90° were manufactured (seeFIGS. 14-15). Membranes were manufactured from polydimethylsiloxane (PDMS), an elastomer with a material stiffness (9.9 MPa) similar to that of a vagina. 3 N of force were applied along the longitudinal axis of the membranes. Quantitative measurements of the following parameters were used: minimal pore diameter, effective pore area (defined by the area of the pores with widths greater than 1 mm), porosity (defined by the amount of pore space within the membrane), effective porosity (defined by the amount of void space within the mesh from the pores that are greater than 1 mm), and relative lateral contraction (representative of the degree of contraction of the model with a positive value indicating model contraction (i.e., pore collapse) and a negative value indicating expansion (i.e., pores remaining open/enlarging)).

Regarding effective pore area, the effective pore area for all models was 100%. No change means that the effective pore area at 3 N was maintained at 100%. Regarding a result of “N/A,” a parameter was not calculated.

As seen in Table 2 andFIG. 14, the minimal pore diameter, porosity, and effective porosity all increased for the bowtie 0° membranes while mesh burden decreased. There was no change in the effective pore area (i.e. the minimal pore diameter of pores was >1 mm). These results are similar to the results for bowtie 90° membranes in which the minimal pore diameter, porosity, and effective porosity all increased while mesh burden decreased and the effective pore area was unchanged. The observed pore collapse with the bowtie 45° membranes was associated with a decrease in the minimal pore diameter and porosity, and there was a complete loss (i.e. 100% decrease) in the effective pore area and effective porosity. Mesh burden however was increased for the bowtie 45° membranes, and this result was anticipated given that pore collapse results in an increased amount of material.

As seen in Table 2 andFIG. 15, the minimal pore diameter decreased for the chiral hexagon 0° and 45° membranes while it increased for the 90° membranes. The porosity for all of the chiral hexagon membranes increased while mesh burden decreased for all of them. The effective pore area and effective porosity was not calculated for the chiral hexagon membranes given that the minimal pore diameter for all pores within these membranes was less than 1 mm prior to the application of loading (this was a result of our manufacturing process). Thus, calculations of these two parameters would not accurately reflect how the effective pore area and effective porosity changes with loading and we therefore did not analyze these two parameters for the chiral hexagon membranes.

Collectively the results from this mechanical testing of the bowtie and chiral hexagon 0°, 45°, and 90° membranes demonstrate that auxetic pores have the ability to expand; however, expansion is dependent on the orientation of the pore with respect to the direction of loading.

It should be understood that modifications to the embodiments disclosed herein can be made to meet a particular set of design criteria. For instance, the number of or configuration of components or parameters may be used to meet a particular objective.

It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternative embodiments may include some or all of the features of the various embodiments disclosed herein. For instance, it is contemplated that a particular feature described, either individually or as part of an embodiment, can be combined with other individually described features, or parts of other embodiments. The elements and acts of the various embodiments described herein can therefore be combined to provide further embodiments.

It is the intent to cover all such modifications and alternative embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof. Additionally, the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points. Thus, while certain exemplary embodiments of the device and methods of making and using the same have been discussed and illustrated herein, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims, which is to be given the full breath thereof.