Soft and calcified tissue implants   

Abstract: Disclosed herein is processed dermis graft for use in orthopedic surgical procedures. Specifically exemplified herein is a processed dermis graft comprising one or more bone blacks having a groove cut into the surface thereof, wherein said groove is sufficient to accommodate a fixation screw. Also disclosed is a method of processing dermis that results in a dermis derived implant suitable to replace a tendon or ligament in a recipient in need thereof. Other compositions and applications of a dermis derived implant, and methods of manufacture and use, are disclosed.

This application is a continuation of U.S. application Ser. No. 12/260,898, filed Oct. 29, 2008, which is a continuation of U.S. application Ser. No. 11/007,679, filed Dec. 8, 2004, which is a division of U.S. application Ser. No. 09/942,537, filed Aug. 29, 2001, now U.S. Pat. No. 6,893,462, which is a continuation-in-part of copending U.S. application Ser. No. 09/782,594, filed Feb. 12, 2001, and a continuation-in-part of U.S. application Ser. No. 09/750,192, filed Dec. 28, 2000, now abandoned, and a continuation of U.S. application Ser. No. 09/481,319, filed on Jan. 11, 2000, now U.S. Pat. No. 6,497,726. This application also claims priority from U.S. Provisional Application No. 60/181,622, filed Feb. 10, 2000, and U.S. Provisional Application No. 60/296,530, filed Jun. 6, 2001. The foregoing provisional and nonprovisional applications are incorporated by reference herein.

BACKGROUND OF THE INVENTION

Orthopedic medicine is increasingly becoming aware of the vast potential and advantages of using grafts made from allograft bone to treat and repair spinal and common joint injuries, such as Anterior Cruciate Ligament (ACL) or Posterior Cruciate Ligament (PCL) tears. In the case of injuries involves surgically reconnecting the torn portions of a damaged ligament. However, this technique is often not possible, especially when the damage to the ligament is extensive. The recent utilization of bone/tendon grafts has dramatically improved the results of joint repair in cases of severe trauma. Even in cases of extensive damage to the joint ligaments, orthopedic surgeons have been able to achieve 100 percent range of motion and stability using donor bone/tendon grafts.

Despite these realized advantages, there have been some difficulties encountered with utilizing bone/tendon grafts. For example, surgical procedures involving transplantation and fixation of these grafts can be tedious and lengthy. Currently, bone/tendon/bone grafts must be specifically shaped for the recipient during surgery, which can require thirty minutes to over an hour of time. Further, surgeons must establish a means of attaching the graft, which also takes up valuable surgery time.

Another difficulty associated with using allograft implants, such as bone/tendon grafts, is that there is only a limited supply of source tissue. As a result, patients often have to settle for inferior surgical procedures simply based on the lack of availability of tissue. Accordingly, there is a need in the art for the development of implants that implement unrealized sources of tissue.

SUMMARY

One aspect of the subject invention concerns methods of production and compositions for a novel dermis-derived graft (DDG) that facilitates an easier and more efficient surgery for reconstructing ligaments in a joint. While the embodiments herein exemplify the use of dermis tissue, it is understood that other tissue types can be adapted for use in accord with the teachings herein. Specifically, other soft tissues can be used such as ligament, tendon, muscle, dura, pericardium, fascia, and peritoneum, as well as demineralized bone. Tissues can be derived from allogenic, autogenic, or xenogenic sources. Alternatively synthetic materials may be used alone or in combination with natural materials. In one embodiment, the subject invention pertains to a DDG that comprises a section of processed dermis that is rolled to a cylindrical shape, and two bone blocks positioned at opposite ends of the rolled dermis, wherein the bone blocks are preshaped for uniform and consistent alignment into a recipient bone.

In a specific aspect, the subject invention pertains to a dermis derived bone-ended graft useful in orthopedic surgery comprising one or more bone blocks, and processed dermis attached to said one or more bone blocks; wherein said one or more bone blocks is cut to provide a groove sufficient to accommodate a fixation screw. Alternatively, the subject invention pertains to a dermis derived bone-ended graft useful in orthopedic surgery comprising one or more bone blocks and processed dermis attached to said one or more bone blocks, wherein said one or more bone blocks is pre-shaped into a dowel.

Another aspect of the invention regards a process for calcification of all or part of a dermis implant. Comparative data are provided that show the relative performance of processed dermis implants in laboratory rats, in which dermis implants had been calcified prior to implantation.

Another aspect of the invention regards the calcification of all or part of a tissue selected from: soft tissue; pericardium; fascia; woven soft tissue (as from skeletal muscle); urinary bladder membrane (UBM); and SIS.

Another aspect of the invention is the use of processed dermis as a replacement or as auxiliary support for the Anterior Longitudinal Ligament (ALL), and for use as a Spinal Tension Band (STB) or other type of tension band. For the ALL and STB, the dermis is formed into a shape that spans the anterior of at least two vertebrae (for an ALL support structure) or at least four vertebrae (for an STB), and the ends are affixed to a part of the vertebrae. The preferred attachment points for an STB are at the spinous processes of the adjacent vertebrae. This minimizes movement of (and thereby reduces degradation of) of the vertebrae adjacent to the vertebrae that are being fused. Such adjacent vertebrae are known to undergo excessive wear due to the lack of motion of the adjacent fused vertebrae. The ALL- and STB-type DDGs provide tensioning to help prevent excessive back bending due to the partial or total functional loss of the ALL owing to surgery or traumatic injury. As disclosed herein, the ends of dermis for such use preferably are calcified, and starting materials other than dermis may be used for such applications.

Preferably, the dermis is processed according to a method that preserves the dermis basement membrane. A process known to accomplish this is the subject of U.S. Patent Application Ser. No. 60/296,530, which is incorporated by reference. In yet another aspect, the subject invention pertains to a method of conducting orthopedic surgery on an animal comprising obtaining a dermis derived bone-ended graft, said graft comprising processed dermis having two ends, and one or more bone blocks attached to said processed dermis, wherein at least one of said one or more bone blocks has a groove suitable for accommodating a fixation screw.

An alternative aspect of the invention pertains to an implant comprising a bone block and processed dermis, wherein the bone block comprises a groove for accommodating a fixation screw.

These and other advantageous aspects of the subject invention are described in further detail below.

DETAILED DESCRIPTION

FIG. 1 shows diagrams depicting different shapes and constructions of an implant in accordance with the subject invention. FIG. 1A shows a bone-tendon-bone type implant. FIGS. 1B-E represent an implant comprising a specific assembled bone block.

FIG. 2 is a diagram depicting implant embodiments in accord with the teachings herein.

FIG. 3 depicts a first embodiment FIG. 3A and depicts a second embodiment FIG. 3B of an anterior longitudinal replacement for limiting motion between adjacent vertebrae to be fused.

FIG. 4 depicts a band for limiting the motion and reducing the degradation of vertebrae juxtaposed to vertebrae undergoing spinal fusion (i.e., as a spinal tension band) or for being affixed to any other anatomical structures to minimize motion of such structures in relation to each other.

FIG. 5 shows plan and perspective views of a bone fixation plug that compresses the soft tissue graft component of the implant as the plug is being tightened into a hole.

DISCLOSURE OF THE INVENTION

The present invention uses processed dermis as a material for implants which can be used as replacement or reinforcing tendons, ligaments, and the like. Particular features of the methods and the products of the present invention provide for a dermis-based implant that remodels into a ‘new’ replacement tendon or ligament. The present invention also discloses a process for the calcification of dermis and other tissues, including soft tissue, pericardium, fascia, woven soft tissue (as from skeletal muscle), urinary bladder membrane (UBM), and small intestine submucosa (SIS). These collectively are referred to as “implant material,” and when processed, as “processed implant material.” The bone that is used in this application, for instance to comprise bone blocks, may be selected from cortical, cancellous, cortico-cancellous, or demineralized bone, obtained from human or xenograft sources. Optionally, synthetic material may be incorporated in combination with such bone. Also, bone blocks may be comprised of two or more segments assembled together in a assembled allograft implant. The construction and use of assembled allograft implants is disclosed more fully in U.S. patent application Ser. No. 09/782,594, which is incorporated by reference.

Other features provide for implants fabricated for specific applications, such as to supplement or replace the anterior longitudinal ligament of the spine. Methods of initial preparation and production of dermis implants, and of specific production for use as ALL- and STB-type implants are also disclosed.

I. Preparation of Dermis Derived Graft Material

For the purposes of this disclosure, the term “tendon”, unless otherwise indicated, is taken to mean flexible fibrous connective tissue that attaches muscle to bone. In the context of bone/tendon/bone grafts, tendon can refer to the fibrous connective tissue that connects the patella to the femur and tibia. The term “ligament” is taken to mean the more general term of any fibrous structure connecting one body part to another, and more particularly to flexible, fibrous connective tissue that connects bone to bone or holds organs in place. Also, the term “processed dermis” is taken to mean dermis that has been processed by the initial processing described herein, or another method of decellularizing dermis, and by the secondary process described herein, in which the initially processed dermis is formed into an implant. A dermis derived graft (DDG) is synonymous with a dermis derived implant, and these terms are defined to indicate a graft or implant substantially comprised of processed dermis.

The term “processed dermis” as used herein is intended in a broad sense and refers to fibrous connective tissue for use in grafts derived from dermis of a donor, or from dermis cultured in vitro. The preferred initial processing is that described in U.S. Patent Application Ser. No. 60/296,530, which is incorporated by reference. The initial processing provides a decellularized dermis sample that retains the structural functionality of the basement membrane. This results in superior structural and functional properties of the final dermis derived implant.

Basic steps of a preferred initial processing method are summarized as follows:

1. Contacting the donor dermis with a viral inactivating agent that includes benzalkonium chloride; and

2. Contacting the dermis with one or more decellularizing agents, for instance about 0.5 percent TWEEN 20 and about 0.5 percent hydrogen peroxide. Additional possible steps include contacting the dermis with calcium hydroxide (to aid in virus inactivation), with a chelating agent, for instance EDTA, sonicating the dermis during such treatments, and drying the dermis, such as by freeze-drying.

Preferably, a method in accordance with U.S. Patent Application No. 60/296,530 is used for initial preparation of the dermis. For example, dermis is selected that is at least 0.7 mm thick, and is free of epidermis, muscle, fat, hair, scars, moles, debris and tattoos. The dermis is cut to a desired size, and is soaked in 1M NaCl. Thereafter the dermis is soaked in a 1% solution of benzalkonium chloride at 2-6 degrees Centigrade for 1-24 hours to reduce microbial load. Then the dermis is immersed in a solution of 1% TWEEN 20 and 0.5% hydrogen peroxide, and is sonicated for approximately 15 minutes at room temperature, stirring at least once per minute. Preferably, microbial load is further reduced by soaking in saturated calcium hydroxide solution while sonicating for approximately 15 minutes. The dermis is rinsed in purified water to remove the calcium hydroxide.

Thereafter the calcium in the dermis is chelated with EDTA by soaking in a 0.1% EDTA solution for about 15 minutes, and stirring or sonicating. After two rinses to remove the EDTA, the dermis pH is neutralized with buffer. Then purified water rinses remove the buffer. Drying is begun with soaking in 70% isopropanol, and is completed with freeze-drying. In general, the volume of solution to dermis is at least tenfold. This or similar initial processing provides dermis ready for further specific processing of the present invention.

In one specific, detailed initial processing procedure, the following steps are used: 1. Wash dermis obtained from donor(s) in sodium monophosphate buffer, pH=7.0, and transfer to a bottle containing a one percent BZK (benzalkonium chloride) solution. Store by freezing. 2. Thaw dermis and transfer to a 1 Molar NaCl solution and incubate overnight at room temperature. This separates the epidermis. 3. Remove the epidermis and rinse dermis in sterile deionized water. Cut into desired sizes as needed. 4. Place dermis into a 0.5% hydrogen peroxide solution and sonicate for 15 minutes at room temperature. All dermis must be covered with the solution during this step. 5. Transfer the dermis to a solution (in excess relative to the dermis sample) of any of the following: 0.5% TWEEN-20; 0.5% sodium dodecyl sulfate; 1.0% TRITON X-100. Then sonicate for 15 minutes at room temperature. 6. Transfer dermis to an excess solution (relative to dermis sample) of saturated, filtered Ca(OH)2. Then sonicate for 15 minutes at room temperature. 7. Rinse-twice with de-ionized water, then transfer to an approximately 0.1% EDTA solution, let soak for 15 minutes, then rinse twice with deionized water. 8. Rinse dermis sample(s) in an excess solution of sodium monophosphate buffer (pH=7.0) three times, for five minutes each time. 9. Rinse dermis sample(s) in sterile deionized water. 10. Transfer dermis sample(s) to an excess of 70% isopropyl alcohol for 15 minutes to dehydrate the dermis (do not sonicate). 11. Package dermis, or cut to size (if not already cut), and package for lyophilization. 12. Lyophilize the sample(s). 13. Treat dermis with a low dose of gamma radiation.

After initial processing, in certain applications the dermis is further processed to form, as described in section III, implant structures suitable for use as a tendon or ligament. Alternately, the dermis is used for other types of implants, including those referred to in section IV below.

The major component of the processed dermis is collagen. A cross linking step may be added in the initial processing, or in the subsequent processing where the implant is being formed or shaped (such as in section Il), to cross link collagen molecules. Cross linking approaches have been described in a previous application for a moldable bone paste, U.S. application Ser. No. 09/750,192, which is incorporated by reference, and is described here for the present application.

Typical chemical cross-linking agents used in accord with this invention include those that contain bifunctional or multifunctional reactive groups, and which react with collagen of the processed dermis. By reacting with multiple functional groups on the same or different collagen molecules, the chemical cross-linking agent increases the mechanical strength of the implant.

The cross-linking step of the subject embodiment involves treatment of the dermis to a treatment sufficient to effectuate chemical linkages between adjacent molecules. Typically, such linkages are between adjacent collagen molecules exposed on the surface of the dermis. Crosslinking conditions include an appropriate pH and temperature, and times ranging from minutes to days, depending upon the level of crosslinking desired, and the activity of the chemical crosslinking agent. Preferably, the implant is then washed to remove all leachable traces of the chemical.

Suitable chemical cross linking agents include mono- and dialdehydes, including glutaraldehyde and formaldehyde; polyepoxy compounds such as glycerol polyglycidyl ethers, polyethylene glycol diglycidyl ethers and other polyepoxy and diepoxy glycidyl ethers; tanning agents including polyvalent metallic oxides such as titanium dioxide, chromium dioxide, aluminum dioxide, zirconium salt, as well as organic tannins and other phenolic oxides derived from plants; chemicals for esterification or carboxyl groups followed by reaction with hydrazide to form activated acyl azide functionalities in the collagen; dicyclohexyl carbodiimide and its derivatives as well as heterobifunctional cros slinking agents; hexamethylene diisocyante; sugars, including glucose, will also cross link collagen.

It is known that certain chemical cross-linking agents, e.g., glutaraldehyde, have a propensity to exceed desired calcification of cross-linked, implanted biomaterials. In order to control this calcification, certain agents can be added into the composition of the subject embodiment, such as dimethyl sulfoxide (DMSO), surfactants, diphosphonates, aminooleic acid, and metallic ions, for example ions of iron and aluminum. The concentrations of these calcification-tempering agents can be determined by routine experimentation by those skilled in the art.

When enzymatic cross-linking treatment is employed, useful enzymes include those known in the art which are capable of catalyzing crosslinking reactions on proteins or peptides, preferably collagen molecules, e.g., transglutaminase as described in Jurgensen et al., The Journal of Bone and Joint Surgery, 79-a(2), 185-193 (1997), herein incorporated by reference.

Formation of chemical linkages can also be accomplished by the application of energy. One way to form chemical linkages by application of energy is to use methods known to form highly reactive oxygen ions generated from atmospheric gas, which in turn, promote oxygen cross links between surface-exposed collagen. Such methods include using energy in the form of ultraviolet light, microwave energy and the like. Another method utilizing the application of energy is a process known as dye-mediated photo-oxidation in which a chemical dye under the action of visible light is used to cross link surface-exposed collagen.

Another method for the formation of chemical linkages is by dehydrothermal treatment which uses combined heat and the slow removal of water, preferably under vacuum, to achieve crosslinking of collagen in the processed dermis. The process involves chemically combining a hydroxy group from a functional group of one collagen molecule and a hydrogen ion from a functional group of another collagen molecule reacting to form water which is then removed resulting in the formation of a bond between the collagen molecules.

II. Preparation of Calcified Dermis Derived Implant

It has been learned that the ends, other sections of, or an entire piece of the processed dermis, may be calcified by the following process. By modifying the twelve step method shown above, such that the contacting with calcium hydroxide solution is followed immediately by the phosphate buffer solution, calcium is deposited onto (or precipitates onto) the dermis. Approaches to calcifying the dermis sample include contacting with the phosphate buffer slowly, as by changing out the solution in which the dermis section is held, or rapidly, as by moving the dermis section from a vessel containing the calcium hydroxide to a vessel containing phosphate buffer. The preferred pH of the phosphate buffer is in the range of 6.8 to 7.2 pH units. While not being bound to a particular theory, the change in pH is believed to cause a precipitation of calcium onto the processed dermis. The deposited calcium adds rigidity to the section. It has been observed that calcification will not occur appreciably if the EDTA solution is used between the calcium hydroxide step and the phosphate buffer step. The following evaluation illustrates one use of calcified dermis prepared according to this invention.

Evaluation of Initially Prepared Dermis in Animal Model

Samples of dermis were prepared using the twelve-step method described in section I, varying the type and amount of detergent agent, as shown in the table of results.

Thereafter, the dermis so prepared was implanted and evaluated as described below.

1.) Lyophilized dermis was cut (aseptically) into approximately I×1 cm implants, weighed before hydration (pre-implantation dry weight), and rehydrated with sterile saline containing antibiotics. 2.) Samples were implanted (4 per rat) into Athymic nude rat model following SOP# with modification: only one suture was used to hold the implant in place. 3.) Implants were recovered at 3, 6, and 12 week post-implantation (2 week samples per donor/per treatment/per time point—total of 6 for each treatment/time point) 1-2 were kept for historical analysis and 4-5 were removed, lyophilized to determine dry-weight post-implantation (to determine percent loss of tissue after in vivo exposure).

1.) Surgeries were performed as follows: Animals were anesthetized via intramuscular injection (thigh or gluteus muscle) of ketamine (100 mg/k) and Xylazine (15 mg/kg). Sterile technique was used and surgery was performed in a class 100 hood. Alcohol and providone iodine were applied to the abdomen of the animal. An incision was made parallel to the midline of the abdomen from just below the tip of the sternum to just above the navel. The skin is dissected away from the underlying muscle on either side of the abdomen. The muscle is isolated and a 0.5×0.5 cm area of fascia was scored from the muscle until the muscle bled, one are in each quadrant of the abdomen. A 1×1 cm piece of dermis was sutured to the muscle over the area that was previously scored, with two corners of the dermis sutured in to place with non-absorbable 3-O prolyene suture. The skin was closed with wound clips in a continuous line. Providone iodine is reapplied to the wound and the animal is returned to its\' cage. according to (Rat Assay Osteoinductivity Surgery) with the following exceptions: 2.) At 3, 6, and 12 weeks, animals were sacrificed according to a humane procedure. 3.) The skin was shaved on the stomach using a disposable razor or hair clippers. 4.) The muscle flap with the overlying skin was removed. 5.) The entire muscle flap was photographed for macroscopic observation. 6.) Implant material was removed (6 per time point for each test sample), and placed in labeled sterile petri dishes for drying. If implants were difficult to remove, the entire muscle flap was removed and the implant was carefully excised using scalpels in the lab. Before dissection, each implant site was photographed for documentation purposes. 7.) 3 implants of each sample at each time point was prepared for histological processing. (H&E staining)

Dry Implant Group Implant Weight Dry Explant Weight % Change 1Fa 40 SDS .0225 .0542 +140.9% 1Ed .0218 .0469 +115.1% 1Bd .0236 .0259  +9.7% 1Gd 40 TRITON .0121 .0352 +190.9% 1He .0126 .0404 +220.6% 2Ad .0086 .0271 +215.1% 1Db 40 TWEEN .0073 .0231 +216.4% 2Fe .0091 .0309 +239.6% 1Fe .0073 .0289 +295.9% 2Eb 41 SDS .0148 .0370   +150% 1Eb .0107 .0342 +219.6% 1Cb .0104 .0342 +228.8% 2Ee 41 TRITON .0068 .0272   +300% 1Gb .0080 .0282 +243.9% 2Be .0077 .0304 +294.8% 2Da 41 TWEEN .0075 .0239 +218.7% 2Ca .0071 .0241 +239.4%

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