IMPLANTABLE DEVICES COMPRISING GRAFT MEMBRANES

Abstract

The invention provides implantable devices and membranes suitable for implantation in a body lumen, as well as methods and processes for their preparation.

Claims

1-55. (canceled)

56. An implantable device for positioning a membrane in a body lumen, the device comprising a frame element and a membrane attached to the frame element, the device having a first, 2-dimensional spatial configuration, and a second, 3-dimensional spatial configuration, the frame element being switchable between the first and second configurations.

57. The device of claim 56, wherein the frame element is a closed-loop wire.

58. The device of claim 56, wherein in the device's first configuration, the frame element has a polygonal, oval or round 2-dimentional shape.

59. The device of claim 56, wherein in the second configuration, the device has a substantially tubular 3-dimentional spatial configuration.

60. The device of claim 56, wherein the device is switchable from said first configuration to said second configuration by folding about a longitudinal symmetry axis.

61. The device of claim 56, wherein in the device's second configuration, the frame is substantially helical.

62. The device of claim 56, wherein the membrane is (i) stretched over at least a portion of the area enclosed by the frame element, or (ii) stretched over the entire area enclosed by the frame element.

63. The device of claim 56, wherein the membrane is an animal or a human tissue graft membrane.

64. The device of claim 63, wherein said animal tissue graft is prepared from prenatal tissue, postnatal tissue, or adult tissue.

65. The device of claim 63, wherein said tissue graft is prepared from a pericardial tissue, a placental tissue, an amniotic membrane and an umbilical-cord tissue.

66. The device of claim 56, wherein said membrane having a secant tensile modulus at 20% elongation (E20) of at most 25 N/mm2, optionally wherein the secant tensile modulus at 20% elongation (E20) is between about 0.5 and 25 N/mm2.

67. A method for obtaining an implantable device of claim 56, comprising attaching a membrane to a frame element when the device is in its first, 2D configuration, such that the membrane is stretched over the entire area enclosed by the frame.

68. The method of claim 67, wherein the membrane is made of an animal tissue graft membrane.

69. The method of claim 68, wherein the attachment of the membrane to the frame element is carried out by gluing, suturing, or mechanical anchoring.

70. The method of claim 68, wherein the membrane is pre-treated by a de-cellularization process.

71. The method of claim 68, wherein the membrane is pre-treated by a process comprising: (a) immersing the tissue graft in an aqueous solution of at least one cross-linking agent; and (b) washing the tissue graft with a 0.9% saline solution and/or distilled water.

72. The method of claim 71, wherein said at least one cross-linking agent is at least one aldehyde.

73. The method of claim 71, wherein (i) said solution of step (a) comprises 0.01-0.4% (v/v) of said cross-linking agent; (ii) the immersion in the cross-linking agent solution is carried out for between about 30 seconds and 30 minutes; and/or (iii) the frame element is pre-treated by polishing, electropolishing, cleaning and/or priming prior to attachment of the membrane.

74. A process of preparing a membrane suitable for implanting into a body lumen, the process comprising: (a) providing an animal or human tissue graft; (b) immersing the tissue graft in an aqueous solution comprising 0.01-0.4% (v/v) of at least one cross-linking agent for between about 30 seconds and 30 minutes, optionally wherein said at least one cross-linking agent is at least one aldehyde optionally selected from glutaraldehyde, formaldehyde, glyceraldehydes, paraformaldehyde, and any combination thereof; and (c) washing the tissue graft with a 0.9% saline solution, thereby obtaining said membrane.

75. The process of claim 74, wherein said animal or human tissue graft is harvested from prenatal tissue, postnatal tissue, or adult tissue, optionally wherein said tissue graft is harvested from a pericardial tissue, a placental tissue, an amniotic membrane and an umbilical-cord tissue.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0075] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0076] FIGS. 1A-1C show various exemplary 3D configurations according to an embodiment of this disclosure, starting from a 2D circular frame.

[0077] FIG. 2 shows an exemplary 3D configuration according to an embodiment of this disclosure, starting from a 2D rectangular frame.

[0078] FIGS. 3A-3D show process steps in the preparation of an implantable device according to an embodiment of this disclosure.

[0079] FIG. 4 shows the implantable device of FIG. 1D, in its deployed position within a simulatory lumen.

[0080] FIGS. 5A-5B show histological sections of H&E-stained porcine pericardial tissue treated by glutaraldehyde full fixation (FIG. 5A) and a process of the invention (FIG. 5B).

[0081] FIG. 6 presents stress-strain tensile test curves for glutaraldehyde fully fixated membrane (gray) and a membrane treated in a process of the invention (black).

[0082] FIG. 7 shows a typical metallic stent covered by a membrane of the invention.

[0083] FIGS. 8A-8C present 3-point bending test results for the stent of FIG. 7, covered by a glutaraldehyde fully fixated membrane (gray, FFG) and a membrane treated in a process of the invention (black, pGlut)—% relative applied force (FIG. 8A), % relative curvature upon application of 1N force (FIG. 8B), and % relative curvature upon application of 1.5 N force (FIG. 8C).

[0084] FIGS. 9A-9D show host-response to implanted membranes for glutaraldehyde fully fixated membrane (FIGS. 9A-9B) and membranes produced according to a process of the invention (FIGS. 9C-9D).

DETAILED DESCRIPTION OF EMBODIMENTS

[0085] Exemplary Devices

[0086] The implantable devices of this disclosure assume at least 2 spatial configurations: a flat, planar 2D configuration and a deployable 3D, voluminous configuration. Examples of such configurations are provided in FIGS. 1A-2.

[0087] FIGS. 1A-1C demonstrate various 3D configurations of the implantable device, all starting from a 2D circular frame. These 3D configurations vary in their degree of overlap between sections of the frame, thereby enabling to control the diameter of the tubular 3D configuration. For example, the same 2D disc configuration may be folded to various degrees of overlap of the membrane and frame, thereby resulting in implantable device of the approximately the same length (H), determined by the diameter of the 2D disc, but having different diameters (d1>d2>d3). Such variability enables to insert the device into the lumen when the device has a significantly smaller diameter than the diameter of the lumen (for example in the configuration presented in FIG. 1C), and once positioned in the desired location, the device is allowed to assume a larger diameter (such as that shown in FIG. 1A or 1B).

[0088] In addition, the flexibility of the frame allows for variability of the diameter along the tubular device, such that differences in diameters may be obtained along the longitudinal axis of the 3D tubular device. This permits adjustment of the device dimensions to the dimensions of the treated lumen.

[0089] FIG. 2 presents a tubular 3D configuration of the device starting from a rectangular 2D planar configuration, thus resulting in a tubular device having a height (H) identical to that of the corresponding 2D planar configuration.

[0090] It is of note that the extent of overlap between portions of the device (x) and the distance between the frame edges (X) when the device's edges are not in contact with one another, may be calculated according to the following formula (w is the thickness or diameter of the wire constituting the frame element):

[00001]$\frac{H-x}{\pi }=d_i-2.Math.w$$\frac{H+X}{\pi }=d_i-2.Math.w$

[0091] The extent of overlap x and/or the distance X has an impact on the radial force exerted by the device onto the surrounding lumen, once implanted. Namely, the greater the value of x (and smaller value of X, similarly), the greater the radial force applied by the device onto the lumen. Such variation allows the design and control of the force maintaining the device in position, once implanted, as well as controlling the force applied onto the lumen's tissue that comes into contact with the device.

[0092] Preparation of an exemplary implantable device according to a method of the present disclosure is demonstrated in FIGS. 3A-3D. A membrane, which may be synthetic or of a biological source (treated or untreated by a process of this disclosure) is placed beneath a circular frame element (as shown in FIGS. 3A-3B). In the exemplary method, the membrane is a human amniotic tissue graft, treated by a process of this disclosure, placed over a stainless steel wire circular frame.

[0093] The membrane is then trimmed to the desired dimension and attached to the frame. In this non-limiting example, the membrane is trimmed to form several circumferential flaps (FIG. 3C), which are then folded about the frame element and glued in position by a surgical adhesive (FIG. 3D). Such trimming enables full coverage of the frame element by the membrane without any overlapping or stacking of membrane, as well as application of adhesive only onto the flaps, thereby bonding the membrane flaps to the membrane surface about the frame element to increase bonding strength.

[0094] For implantation, the 2D configuration is switched to the 3D configuration by application of mechanical load or heat, whereby the device assumes its permanent 3D configuration, as seen in FIG. 4.

[0095] Membrane Preparation

[0096] As noted above, it is desired that the membrane used in implantable devices of this disclosure have certain mechanical properties, and preferably have an elastomeric behavior. Due to the inherent non-homogeneity of biological tissues, the inventors have developed a unique pre-treatment process, involving short immersion in low concentration fixative solution, which enables tailoring of the mechanical properties of the graft tissue from which the membrane is prepared, while substantially maintaining its natural structure.

[0097] In an exemplary process, porcine pericardial tissue was harvested and thinned to a thickness of 60 μm. The tissue was then treated by immersing the tissue graft in a 0.25% (v/v) aqueous solution of glutaraldehyde for 60 seconds. The tissue was then immediately washed with 0.9% saline (physiological water) and distilled water.

[0098] In comparison, a porcine pericardial tissue was treated by a traditional fixation process involving immersing the tissue in a 0.5% (v/v) aqueous solution of glutaraldehyde for 24 hours, and then rinsed with distilled water.

[0099] Histological sections were cropped from both samples, stained by hematoxylin and eosin (H&E) stains and visualized. As can be clearly seen from FIGS. 5A-5B, deterioration and cross-linking of the extracellular matrix (mainly collagen and elastin fibers) result in bulky clusters in the traditionally treated tissue (FIG. 5A), while the structure and integrity of the elastin fibers is clearly maintained in the tissue treated by the gentle fixation process of the invention (FIG. 5B). As evident by the results, the treatment process of the invention has no significant effect on the structure of the tissue, however provides sufficient fixation to prevent the undesired side effects associated with the traditional fixation process, as will also be shown below.

[0100] The effect of the fixation process on the mechanical properties of the membrane was assessed by a uni-axial tensile test, in which 15×20 mm samples of the membranes were clamped by suitable metal clamps and subjected to tensile force at a strain rate of 0.5-1 mm/sec. The secant modulus at 20% elongation (E.sub.20) was calculated from the stress-strain curves shown in FIG. 6.

[0101] As clearly shown in FIG. 6, tissue samples treated by the gentle fixation process showed elastomeric-like mechanical behavior and relatively high elongation to break (at least 50% elongation), while tissues treated by the traditional fixation process failed at significantly lower elongations and demonstrated a stiffer behavior (higher modulus). Some traditionally treated tissues failed well before reaching 20% elongation, and for such, E.sub.20 values could not be calculated.

[0102] Effect of Membrane Treatment Process on Stent Properties

[0103] In order to estimate the effect of the membrane on the flexibility of a covered stent, a traditionally-treated membrane (marked “FFG”) and a membrane obtained by a process of the invention (marked “pGlut”), where used to fully cover a metallic stent, as shown in FIG. 7, such that the membrane formed an outer tubular casing of the metallic stent scaffold. The dimensions of the stents were 3×27 mm The thickness of the membranes was 50-60 μm.

[0104] The covered stents were subjected to 3-point bending test, in which the stents were positioned horizontally on support legs (distance between the support legs: 11 mm). A force, normal to the stent, is then applied at the midpoint between the supporting legs, thereby bending the sample.

[0105] FIG. 8A shows the force required to obtain a 2 mm vertical displacement of the stent at the force-application point. The results are shown relative to the stent covered by the membrane of the invention (i.e. pGlut=100%). As is evident from the results, the force required to obtain a 2 mm displacement for the stent covered by the traditionally-treated membrane is 38% larger than the force required to obtain the same displacement in a stent covered by a membrane of the gentle-fixation process.

[0106] Further, the bending radius (curvature) of the covered stents was measured upon application of a constant force. The results shown in FIGS. 8B and 8C show % relative curvature obtained for applied constant force of 1N and 1.5N, respectively, normalized to the curvature of the stent covered with traditionally-treated membrane (i.e. FGG=100%). In both cases, the stents covered with the gentle-fixated membrane enabled obtaining higher curvature (38% and 50% respectively).

[0107] The 3-point bending test results clearly indicate that stents covered by membranes of the gentle-fixation process show significantly improved flexibility as compared to the stents covered by traditionally-fixated membranes. This may enable easier implantation and higher structural adaptability to the structure of the lumen in which the stents are to be implanted.

[0108] In Vivo Tissue Healing Effect

[0109] Assessment of the effect the membrane treatment process is expected to have in vivo, porcine pericardial tissue graft membranes, treated by either the traditional process or the gentle-fixation process, were implanted in healthy mice.

[0110] 8×8 mm membrane samples prepared in both preparation methods were washed 3 times with saline, and preserved in 0.9% saline and penicillin/streptomycin solution until implantation.

[0111] ICR mice were anesthetized and a membrane sample was subcutaneously ectopically implanted into a pocket artificially formed in the dorsal area of the mouse. Each mouse was implanted with both types of membrane samples. After 4 weeks, the mice were humanely euthanized and the tissue-response to the implanted membrane samples was assessed.

[0112] In all mice, a clear and robust inflammatory reaction was observed at and in the vicinity of the traditionally-treated membrane sample, while minimal inflammation was observed at and in the vicinity of the gentle-fixated membrane samples. As is shown is FIGS. 9A-9D, which are cross-sections of the implantation areas, no healing of the pocket tissue was observed in the area in which the traditionally-treated membrane sample was implanted (FIGS. 9A-9B). In comparison, closure of the pocket and tissue healing response was clearly observed in the area into which the gentle-fixated membrane was implanted (FIGS. 9C-9D). Thus, in addition to prevention of host-vs.-graft symptoms, membranes treated in the gentle-fixation of the invention showed the potential of promoting tissue healing in the implantation area. Without wishing to be bound by theory, this may result from the structure of the treated membrane, which remains substantially in its natural (i.e. pre-processed) structure, enabling improved cell adhesion and growth once implanted.