Patent Application
20140341871
Not applicable.
1. Field of the Invention
This invention relates generally to the field of tissue matrices for regenerative repair. More particularly, this invention relates to methods for processing tissues for use in regenerative repair of soft tissue defects and the resulting tissue matrices.
2. Description of Related Art
When damage to soft tissue occurs, an inflammatory response is initiated and cells and molecular factors are recruited to the site of injury to begin the healing process. In order for healing to occur, these cells must be able to infiltrate and proliferate into the wounded area.
Cellular proliferation in tissues is controlled by both positive and negative agents present within that tissue. Positive agents are present in tissue to stimulate cellular proliferation (mitogenic agents) and differentiation (morphogenic agents). Negative agents are present in tissue to stop cellular proliferation and/or cellular differentiation. It is this sensitive and balanced approach to regulating cellular activity in tissues that represents what, in certain instances, is a fine line between a non-neoplastic and a neoplastic, or cancerous, state. Regenerative medicine has become an important strategy involving the use of biological materials in the repair of tissue pathologies where the expectation of the regenerative aspects of the repair is to reduce the amounts of fibrous scar tissue formation which may close the pathology, but not further participate in the function of the tissue being regenerated. For instance, U.S. Pat. No. 7,851,447 describes a method for nerve repair comprising one or more chondroitin sulfate proteoglycan (SCPG)-degrading enzymes (for example chondroitinase ABC) that promote axonal penetration into damaged nerve tissue.
Further, U.S. Pat. Nos. 7,008,763, 7,736,845, and 7,687,230 describe methods of treating collagenous connective tissues with the objective of that tissue being “re-habited” or “re-colonized” by host cells without immune rejection and inflammatory reaction. They describe a tissue soaked in cold temperatures with polyglycol, salt, hydrogen peroxide, and phosphate buffer with the objective of permitting ground substances to dissociate such that the collagen fibers remain stable. As a second processing solution, the tissues are soaked in an alcohol and water solution and/or solutions comprising anti-inflammatory and anti-thrombogenic agents.
As another example, many heart attacks are the result of occluded vasculature and the resultant ischemic damage to the cardiomyocytes comprising the contractile component of the heart. Efforts to repair this ischemic damage have been varied, such as efforts involving seeding of cells into the ischemically damaged areas with the objective of restoring functioning cardiomyocytes. For example, U.S. Pat. No. 6,953,466 describes methods for the delivering of therapeutic implants to tissues where the therapeutic agents include vascular endothelial growth factor, fibroblast growth factor, platelet derived growth factor, and angiopoietins. In this particular method, the therapeutic agents are delivered via an elongate catheter and depositing the carrier and therapeutic agent in the tissue. A similar method is described in U.S. Pat. No. 6,749,617; however, the method described in this patent includes the use of a solid or liquid carrier of the therapeutic agents and the therapeutic agents include cells. In this particular method, the carrier constitutes a biocompatible scaffold for the cells which will move from that scaffold into the tissue being repaired. A method for delivery of cellular materials into heart muscle is described in U.S. Pat. No. 7,686,799 wherein the cellular materials are deployed directly into the heart muscle wall. U.S. Pat. No. 7,892,829 specifically describes cardiac muscle regeneration using mesenchymal stem cells. These stem cells can be administered as a liquid injectable or as a preparation of cells in a matrix which is or becomes solid or semisolid.
These efforts to repair damaged heart muscle involve the use of liquid or solid carriers of therapeutic agents and although these therapeutic agents can include cells, these efforts do not depend on the use of a process to prepare the damaged heart muscle to receive cells via a natural ingrowth mechanism wherein the dead cellular remnants from the ischemic damage to the heart have been removed or modified in some manner to expose normally occurring molecular moieties present on a collagenous matrix or tissue matrix. The resultant outcome has mostly been the formation of scar tissue (a repair process) rather than the formation of functional cardiac muscle (a regeneration process). The currently available technologies fail to deal with the presence of agents in the damaged myocardium that will act in a negative manner towards the cells being added such that the cells become directed along a repair pathway leading to scar tissue formation rather than a regenerative pathway leading to restoration of functional cardiac muscle tissue.
There is a considerable body of literature and patents pertaining to a removal of cells from tissues to be used clinically and much of this material falls under a broad category of decellularization of tissues or rendering tissues acellular, and/or avital (lacking a vital cell population). Indeed, one of the earliest patents describing a process for the decellularization of tissues was by Brendel and Duhamel (U.S. Pat. No. 4,801,299) which involved the use of nonionic detergents, hypotonic solutions, anionic detergents, DNAase and RNAase enzymes and protease inhibitors for the removal of cells from tissues. See also U.S. Pat. Nos. 4,539,716; 4,546,500; 4,835,102; 4,776,853; 5,558,875; 5,843,181; 4,776,853; and 5,843,180 for examples of differing strategies for the decellularization of tissues. Most of these decellularization strategies focused on the production of decellularized tissues in which success was evidenced by the lack of visible cellular remnants in histological preparations. Indeed, U.S. Pat. Nos. 5,613,982; 5,632,778; 5,843,182; and 5,899,936 claimed only a partial reduction in extractable nucleic acids in decellularized tissues with little evidence of other changes in lipid, phospholipid and/or proteoglycan compositions. Such tissues were described as having recellularized following implantation into a patient; however, initial outcomes indicated considerable calcification of the tissues without indicating the cause or corrective actions needed with this method for decellularizing tissues.
Similarly, U.S. Pat. Nos. 6,743,574, 6,432,712, and 7,179,287 described decellularization methodologies involving the removal of cell remnants to a level that histologic evidence of cells was not visible in histology preparations. Pulmonary patch grafts processed according to U.S. Pat. No. 6,743,574 have since received clearance based on a pre-market notification to the FDA, and such tissues have been shown to recellularize in situ with little indication of pathologic complications. Thus, specific processing of tissues to remove cellular elements from tissues have been tentatively identified as providing for tissues suitable for repair of soft tissue defects. However, to date such tissues have not been produced which will contribute to a regeneration of soft tissues to produce tissue materials that are functionally equivalent to the native tissue into which they are implanted.
A series of U.S. patents (U.S. Pat. Nos. 6,576,265; 6,893,666; 6,890,564; 6,890,563; 6,890,562; 6,887,495; 6,869,619; 6,861,074; 6,852,339; and 6,849,273) describe a process for producing a devitalized connective tissue for use in tissue repair and regeneration. However, the method used to produce this devitalized tissue is only generally described as involving the use of hypotonic saline and peroxides. Moreover, it is not sufficient to merely decellularize a tissue, nor is sufficient to simply add agents to a processed tissue that act in a positive manner to stimulate cellular proliferation and differentiation.
Thus, the field of regenerative medicine is still in need of a tissue that will be effective in regeneration, rather than repair, of damaged soft tissues, and methods of creating the same. It is not sufficient to just decellularize a tissue, nor is sufficient to just add agents to a processed tissue that act in a positive manner to stimulate cellular proliferation and differentiation.
The present invention is directed to a process of preparing a tissue matrix which is suitable for regenerative repair of soft tissue, as well as being directed to such a tissue matrix and kits therefor. Specifically, the instant process prepares the tissue matrix for optimal use in regenerative repair, by removing or chemically modifying elements present in native tissues that interfere with infiltration, attachment, proliferation and differentiation of cells following in vitro and/or in vivo applications. Specifically, the process includes significantly reducing phospholipids, lipids, nucleic acids, major histocompatibility (MHC) antigens (e.g. I and II), endotoxins, contaminating microorganisms, and less significantly reducing tissue associated proteoglycans without significant changes to the overall structure of the tissue matrix. By removing these tissue elements, the underlying molecular moieties important to cell mediated regenerative repair are exposed and made available to the infiltrating cells. For example, it was observed that transplantation of cryopreserved human heart valves result in such heart valves become avital post implantation and never recellularize. However, by achieving specific reductions in cell associated elements, it becomes possible to produce a tissue which will recellularize post implantation into a recipient or under in vitro cell culture conditions, and which when implanted into a mammalian recipient will not only foster cellular infiltration, but also cellular proliferation and differentiation resulting in the synthesis of new matrix.
The process also includes at least partial acellularization in which directed changes are made to the collagenous structure of the tissue matrix such that cells are capable of physically infiltrating the tissues, by virtue of chemical modifications to specific groups associated with that collagenous structure which infiltrating cells will recognize and respond to via membrane bound receptors. This acellularization may at least partially occur as a result of reducing the proteoglycan content of the tissue matrix.
In at least one embodiment, the present invention is directed to a process for the preparation of a tissue matrix suitable for regenerative repair of tissues which includes steps of isolating a portion of connective tissue for use as the tissue matrix, and contacting the connective tissue with a surfactant and with a disinfectant. This results in reducing the levels of at least one of proteoglycans, lipids, phospholipids, nucleic acids, major histocompatibility (MHC) antigens (e.g., MHC I or MHC II), contaminating microorganisms, and measured endotoxins. While many of these elements are significantly reduced, such as generally up to 90% or 99%, a substantial amount of extractable proteoglycans are generally retained, such as 70% of extractable proteoglycans. The process results in the production of a tissue matrix that facilitates recellularization and regenerative repair in in vitro and in vivo applications.
In some embodiments, the process also includes contacting the connective tissue with a chondroitinase, alcohol, endonuclease, and/or lipase to further reduce certain inhibitory agents from the connective tissue matrix. Moreover, the process may include dehydrating and/or freeze-drying the resultant tissue matrix for storage and/or transport. In some embodiments, the process further includes micronizing the resultant tissue matrix to fragmented pieces measuring in the range of 100-300 microns in size.
In at least one embodiment, the process of the present invention includes contacting an isolated portion of connective tissue with one or more solutions capable of reducing phospholipids, lipids, proteoglycans, nucleic acids, major histocompatibility antigens (MHC) I and II, contaminating microorganisms, and endotoxins. The resultant tissue matrix retains molecular signals appropriate to recellularization in in vitro and in vivo applications.
The present invention is also directed to a tissue matrix as produced by the instant method. In at least one embodiment the tissue matrix of the present invention is suitable for use in regenerative repair of soft tissue. Such tissue matrix includes a scaffold portion structured to provide shape to the tissue matrix, and may be made of structural proteoglycans and have a collagenous structure. The tissue matrix also includes a non-structural portion disposed in interspersed relation through at least a portion of the scaffold or structural portion, and which may include non-structural proteoglycans. The various portions of the tissue matrix are collectively structured to promote cellular infiltration, attachment, and proliferation of host cells into the matrix upon tissue implantation or transplantation into a host. For example, the tissue matrix is reduced in levels of phospholipids, lipids, nucleic acids, major histocompatibility antigens (MHC) I and II, contaminating microorganisms, and endotoxins, and to some degree proteoglycans, and in some embodiments are at least partially acellularized.
The present invention is also directed to kits for regenerative soft tissue repair having at least a tissue matrix as described herein for implantation or use, as well as kits for processing connective tissue to render a resultant tissue matrix suitable for regenerative soft tissue repair, including at least an amount of surfactant and an amount of disinfectant.
The processes, tissue matrices, and kits herein described can be used in connection with pharmaceutical, medical, and veterinary applications, as well as fundamental scientific research and methodologies, as would be identifiable by a skilled person upon reading of the present disclosure. These and other objects, features and advantages of the present invention will become clearer when the drawings as well as the detailed description are taken into consideration.
For a fuller understanding of the nature of the present invention, reference should be had to the following detailed description taken in connection with the accompanying figures in which:
The present invention is directed to processes for treating connective tissue to prepare a tissue matrix suitable for use in regenerative soft tissue repair, as well as such tissue matrix and kits therefor.
Several aspects of the invention are described below, with reference to examples for illustrative purposes only. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the invention. One having ordinary skill in the relevant art, however, will readily recognize that the invention can be practiced without one or more of the specific details or practiced with other methods, protocols, reagents, cell lines and animals. The present invention is not limited by the illustrated ordering of acts or events, as some acts may occur in different orders and/or concurrently with other acts or events. Furthermore, not all illustrated acts, steps or events are required to implement a methodology in accordance with the present invention. Many of the techniques and procedures described, or referenced herein, are well understood and commonly employed using conventional methodology by those skilled in the art.
Unless otherwise defined, all terms of art, notations and other scientific terms or terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this invention pertains. In some cases, terms with commonly understood meanings are defined herein for clarity and/or for ready reference, and the inclusion of such definitions herein should not necessarily be construed to represent a substantial difference over what is generally understood in the art. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and/or as otherwise defined herein.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the indefinite articles “a”, “an” and “the” should be understood to include plural reference unless the context clearly indicates otherwise.
The phrase “and/or,” as used herein, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases.
As used herein, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating a listing of items, “and/or” or “or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number of items, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e., “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.”
As used herein, the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof, are intended to be inclusive similar to the term “comprising.”
As would be understood by those of skill in the art, the processes, tissue matrices, and kits of the present invention are applicable to the regenerative repair of tissues.
The present invention is directed to a process for preparing a tissue matrix suitable for regenerative repair of soft tissue. In at least one embodiment, the process includes isolating a portion of connective tissue for use as the tissue matrix. Any appropriate connective tissue may be used, such as but not limited to dermis, fascia, skin, pericardium, periosteum, tendon, ligament, dura, omentum, cartilage, and combinations thereof. The connective tissue may be allogenic, autogenic or xenogenic, and may be isolated from a cadaver or living donor. Connective tissues to be processed by the methods herein may be first procured or harvested from a human or animal donor and immediately placed in a stabilizing transportation solution which arrests and restricts autolytic and proteolytic degradation, protects against bacterial and fungal contamination, and reduces mechanical damage. The stabilizing solution generally contains an appropriate buffer, one or more antibiotics, and is transported at the temperatures of wet ice. Non-limiting examples of components of a stabilizing solution include a cold solution (generally about 1 to about 10 degrees Celsius) of lactated ringer, sodium bicarbonate and antibiotics (e.g., gentamicin, vancomycin, etc.).
Once isolated, the process includes the steps of contacting the connective tissue with at least one solution capable of significantly reducing molecular elements which are inhibitory to cellular ingrowth and proliferation, which includes at least one component selected from the group consisting of lipids, phospholipids, nucleic acids, major histocompatibility antigens, endotoxins, and contaminating microorganisms. It will also at least partially reduce the proteoglycan content of the connective tissue. In at least one embodiment, the process includes contacting the connective tissue with a surfactant, such as a detergent, as well as contacting the connective tissue with a disinfectant, described in greater detail hereinafter.
All solutions utilized in the process of the invention will reduce “proteoglycan content”. “Proteoglycan content” as used herein refers to structural proteoglycans, soft filler proteoglycans, chondroitins, hyaluronans, proteins, polysaccharides, etc. All processing steps will more readily extract these components residing in the non-structural aspects of the tissue, but steps including disinfectants, such as peracetic acid, will work equally well on proteoglycans in both the structural and non-structural (i.e. soft filler) aspects of the tissue. In other embodiments, however, the process includes contacting a tissue with at least one chondroitinase enzyme, such as but not limited to chondroitinase ABC, to significantly reducing the presence of particular proteoglycans, such as chondroitin sulfate.
Proteoglycans contain covalently linked “chondroitins.” Proteoglycans forming the structural aspect of the tissue are generally not easily extracted by the present invention, but can be chemically modified by the present invention. For proteoglycans not forming the structural aspect of the tissue, the present invention will not only serve to extract, but to chemically modify, by oxidizing, these proteoglycans as well as the non-structural chondroitins, hyluronins, and other smaller molecular weight proteins and polysaccharides and high molecular weight nucleic acids.
Extractable proteoglycans are primarily chondroitins and hyaluronans associated with proteins not yet incorporated into the structural aspects of the tissue (i.e. residing within the “soft filler” aspect of the tissue). Care should be taken not to remove too much proteoglycan content. Allowable ranges of removal of extractable “proteoglycans” (i.e., chondroitins, hyaluronans, proteins, etc.) wherein maximum reductions in extractable “proteoglycans” should not be greater than 50%, nor less than 30%. Sufficient extraction of the extractable “proteoglycans” are necessary to reduce the “soft filler” contained within the structural elements of the tissue such that cells can infiltrate, but not so much as to render the tissue matrix unsuitable to cells entering the tissue matrix. Illustrative of this point, tissue extracellular matrix is normally very viscous and a nominal reduction in this viscosity will aid in cellular movement into the now less viscous environment but still retain a sufficient physical nature that cells will have a solution adjacent to their plasma membranes that will prevent molecules the cells are producing and secreting from diffusing rapidly away from them.
As such, the process may result in retention of a substantial amount of extractable proteoglycans, which help promote cell-cell and cell-matrix interactions. The process results in production of a tissue matrix that facilitates recellularization and regenerative repair in in vitro and in vivo applications. Retention of proteoglycans, matrix proteins such as collagen, laminin and elastin, as well as the glycoprotein vitronectin are all important in cell binding and promote tissue remodeling. The process of preparation of the tissue matrix does reduce many components of the extracellular matrix (ECM) including glycosaminoglycans (GAGs), which are covalently linked to protein to form proteoglycans. GAGs such as hyaluronan, keratin sulfate, and heparin sulfate are an integral component of the ECM and play an important role in cell-cell and cell-matrix interactions, and assist with cell migration and differentiation. Thus, in a preferred embodiment, the tissue matrix retains about 70% of extractable proteoglycans.
As described throughout the specification, the process of the present invention includes steps of contacting the connective tissue with various solutions. As used herein, “contacting” may include application of the solution to only a portion of the connective tissue, but also may include immersion of the connective tissue in the solution, such that the tissue is completely covered thereby. In at least one embodiment, immersion may be static, in which the connective tissue is covered by the solution and is not moved. In other embodiments, immersion is dynamic, which includes covering with a solution as well as includes stirring, rocking, agitation, ultrasonic energy, or other energy or movement being imparted on the connective tissue while it is immersed. Furthermore, the process may include rinsing the connective tissue with one or more rinsing or cleansing solutions, such as saline, buffered saline, or water, to rinse the tissue at various steps in the process to remove any previously used solutions.
The solutions utilized in the process of the present invention include at least a surfactant, such as a detergent, and a disinfectant. Surfactants will break down lipid and phospholipid content, and have also have molecular impacts on endotoxins and MHC antigens to help reduce those as well. Surfactants and detergents may be anionic, nonionic or cationic. Examples of useful surfactants and/or detergents include, but are not limited to, BRIJ 95 detergent, BRIJ 96 detergent, BRIJ 98 detergent, Triton X-100, Tween 20, and combinations thereof.
Disinfectants, and optionally other biocidal agents, are used in the instant process for more than just their microbe killing abilities. Disinfectants are very damaging agents, and will significantly reduce levels of lipids, phospholipids, nucleic acids, MHC antigens, endotoxins, and contaminating microorganisms from the connective tissue being treated. Examples of disinfectants useful in the present process include, but are not limited to: peracetic acid, chlorine dioxide, hydrogen peroxide, polyvinylpyrolidineiodide, formaldehyde, glutaraldehyde, phenoxyethanol, methylparaben, propylparaben, sodium hydroxymethylglycinate, diazolidinyl urea, DMDM hydantoin, iodopropynyl butylcarbamate, propylene glycol, and combinations thereof. In at least one preferred embodiment, peracetic acid is used as a disinfectant. Peracetic acid is a potent antibacterial, antiviral, and antifungal disinfectant.
The disinfectant processing solution, such as peracetic acid, is the most effective solution at reducing nucleic acid content. In the case of peracetic acid, this may be due, at least in part, to the oxidative capacity of the peracetic acid in degrading the size of the nucleic acid polymers rendering them more soluble in aqueous solution and more likely to diffuse from the tissue during processing. Of the optional processing solutions, the endotoxin reducing solutions are the most aggressive for reducing nucleic acid content, and they work by degrading the nucleic acids to their small molecular weight components which will readily diffuse from the tissue during all subsequent processing steps. In some embodiments, the process also includes contacting the connective tissue an endonuclease. An endonuclease(s) may also optionally be used in some embodiments following either the detergent or peracetic acid treatment steps. For example, Benzonase®, OmniCleave™, Pulmozyme® (dornase alfa), and other broad spectrum endonucleases are useful in the present invention to target nucleic acids for destruction.
The disinfectant step of the processes described herein is also the most effective at reducing histocompatibility antigens. For instance, in the case of peracetic acid, the oxidative capacity of the peracetic acid solution accomplishes this result. However, chondroitinases such as chondroitinase ABC are also very effective, by enzymatically degrading the very cell surface polysaccharides of which the MHC I and II antigens are comprised.
Reduction of nucleic acids and major histocompatibility antigens in the steps of the processes of the present invention is useful in the significant reduction of immune responses, and possible tissue rejection, in a host receiving the processed tissue matrix. Nucleic acids that may be reduced include deoxyribonucleic acids, ribonucleic acids, and combinations thereof. Derivatives of both deoxyribonucleic acids and ribonucleic acids may additionally be reduced by the processes involved.
The disinfectant additionally contributes to the disruption of molecular structures and moieties, such as collagen, and also acts as a powerful oxidant of structural elements of the extracellular matrix (ECM) of the connective tissue being treated. Using peracetic acid as an example, the acetic acid component of peracetic acid alters the charge distribution of sulfated polysaccharides, resulting in a disruption of the molecular structures of the non-structural elements (i.e., “soft filler”) (e.g., chondroitin sulfates, dermatin sulfates, hyaluronins, tropocollagens, etc.) and structural elements (e.g., fibrous collagens, elastins, proteoglycans, etc.) of the extracellular matrix of tissues. The oxidative properties of peracetic acid result in oxidation of groups (e.g., alcohol groups to aldehyde groups, amine groups to nitrate groups, etc.) and breakage of covalent bonds. Collectively, such properties of peracetic acid help solubilize the non-structural elements and also alter/solubilize the structural characteristics of the structural elements of tissues.
More specifically, the oxidation of molecular moieties by the peracetic acid steps herein (1) alters the antigenic nature of the major histocompatibility antigens by chemically modifying the sugars of the polysaccharide part of the MHC I and II antigens, (2) alters the ionic charge distribution on chondroitins and hyaluronins facilitating their solubilization, (3) alters the structural interactions between the structural proteoglycans (mostly contributing to intra- and intermolecular cross links) rendering the tissues less resorbable post implantation and strengthening them to tensile stress and strain (making them more manageable for handling and clinical application to a wound site). The oxidative reactions also serve to (4) degrade lipids and phospholipids by breaking the bonds at the alcohol/phosphate covalent linkage of glycerol to a phosphotidylacyl (or serine, etc.) group. The oxidative reaction will also (5) break the O-glycosidic linkages which link polysaccharides (chondroitins, hyaluronins, etc.) to proteins (i.e. breaks down proteoglycans). One aspect of this proteoglycan breakdown has to do with reduction of the antigenic components (the polysaccharide part of the MHC I and II antigens in cell membranes) of the major histocompatibility antigens, thus preventing an inflammatory response.
Therefore, one can reduce the viscosity of the soft tissue elements, by improving solubility and by degradation to smaller molecules, through both the disruption of the non-structural elements (i.e., chondroitin sulfates, dermatin sulfates, etc.) and by chemically altering the charge distribution of those molecules not extracted from the tissue. The objective is to reduce this soft tissue element viscosity and to change the molecular structure/nature of non-structural elements, which will change the molecular moieties that interact with cell surface receptors of cells trying to attach, proliferate, and infiltrate into the tissue, whether implanted into the body or in in vitro cell culture conditions.
The degree or extent of oxidation of molecular moieties within the tissue matrix may be quantified as a percentage (or number of oxidizable groups per unit wet/dry weight of the tissue) of the original oxidizable molecular moieties using low concentrations of a peroxide wherein the reduction of peroxide concentration(s) may be accurately determined using standard assays for peroxides. The mechanical properties (for example suture pull out strength) of the tissue matrix may be determined using standard mechanical tensile strength testing methodologies.
Non-limiting examples of some embodiments of concentrations and contacting times are provided below. Peracetic acid may be used for contacting in the processes provided as 0.05%, 0.1%, 0.5% solutions for 8 hours, 4 hours, and 2 hours, respectively. BRIJ 95 may be used for contacting in the processes provided as 0.25%, 0.5%, and 1.0% solutions for 48 hours, 24 hours, and 12 hours, respectively. Triton X-100 could alternatively be used instead of BRIJ 95 as a 0.25%, 0.5%, or 1.0% solution for contacting for 48 hours, 24 hours and 12 hours, respectively. Alcohols may be used for contacting as about 50% to about 85% solutions for about 1-2 hours. Furthermore, when NaCl is utilized, it may be used in contacting solutions at 1M for 48 hours, 1.5M for 24 hours, or 2M for 18 hours.
Tissues may also be aseptically processed through solutions of one or more type of antibiotic, antiviral, antifungal, or combinations thereof to reduce contaminating microorganisms. Examples include detergent, peracetic acid, and/or alcohol. This will render the tissue negative with respect to contaminating microorganisms. The desired times and conditions using the desired concentrations of processing solutions for aseptic treatment are described in more detail hereinafter. Processing solutions may optionally be removed between processing steps using saline, such as phosphate buffered saline (PBS), 1.5M NaCl, and 0.9% NaCl, or water rinsing solutions.
In some embodiments, the process also includes contacting the connective tissue a chondroitinase. Chondroitinase enzymes may optionally be used in some embodiments following the detergent treatment steps, to degrade one or more chondroitin sulfate proteoglycans, which are purported to inhibit axonal growth through a processed allograft nerve being used in the repair of severed or damaged nerves of the peripheral nervous system. One example of a chondroitinase enzyme is chondroitinase ABC, although other chondroitinases are contemplated.
The process may also include contacting the tissue with an endotoxin reducing solution, rendering the resultant tissue negative with respect to tests for endotoxins. In some embodiments, there are two processes that contribute to render the modified matrix negative for detectable endotoxins. The first is the oxidation and degradation of the lipopolysaccharides (LPS) endotoxin. Dilution of the endotoxin through multiple rinsing steps accounts for its further reduction. Such rinsing steps may include one or more of the following: a 0.1% peracetic acid solution, a 1.5M NaCl solution, a 0.5% BRIJ 35 solution, and combinations thereof. Disinfectants such as peracetic acid, as well as lipases, and chondroitinases will also serve to reduce the endotoxin levels mostly by removing the moieties on the endotoxins recognized by assay methods known in the art and in so doing will also reduce the potential for any remaining endotoxins from eliciting an inflammatory response when tissues are implanted.
In some embodiments, the process also includes contacting the connective tissue an alcohol. For instance, alcohols are useful further assisting in the breaking down of proteoglycans, lipids, phospholipids, nucleic acids, MHC antigens, endotoxins, and contaminating microorganisms. Examples of alcohols that may be used include, but are not limited to ethanol, propanol, isopropanol, butanol, glycerol, methanol, pentanol, and combinations thereof. The alcohol treatment step provides for a modest solubilization and extraction of phospholipids and lipids from tissues. It is well established in the art that 70% ethanol/isopropanol is maximally effective in solubilizing lipids. Hence, it is valuable as a disinfectant for Gram negative bacteria, where the lipids present in the bacterial cell walls make such Gram negative microorganisms more resistant to certain antibiotics and biocidal agents. Similarly, lipase enzymes will degrade lipids and chondroitinase (e.g., chondroitinase ABC) will degrade chondroitins, to which lipids and phospholipids may be intimately associated.
Reducible lipids of the processes described herein include nonsaponifiable lipids, or derivatives thereof, including cholesterols, derivatives of cholesterols, and combinations thereof. Reducible phospholipids or derivatives thereof include diacylglycerophosphatides, triacylglycerides and combinations thereof. Lipids and phospholipids tend to form micellar structures in aqueous solutions and thus tend to cover molecular moieties which infiltrating cells will need to “recognize” (via their cell surface receptors); and thus, it is important to remove as much of the lipid/phospholipid content as possible. In some embodiments, the process therefore also includes contacting the connective tissue a lipase, to augment lipid reduction. This may be desired when treating high lipid and phospholipid content connective tissues, such as dermal tissues, and particularly in processing thick dermal tissues.
Once treated, the process includes dehydrating the resultant tissue matrix for storage and/or transport. For example, the tissue matrix may be freeze-dried, such as by lyophilization or other cryogenic method, to reduce the residual moisture content of the tissue matrix to between about 2% and about 6%. Since such tissues may be more brittle than desired, in some embodiments the tissues may first be treated with a 10% to 30% solution of glycerol for a sufficient period of time to allow the preservation or storage solution to replace the water content of the processed tissues, and then freeze-dried to a residual moisture content of between 2% and 6%. Such tissues will be less brittle than similar tissues not being pretreated with glycerol prior to freeze-drying, and such tissues are also better preserved and better protected from any subsequent exposure to gamma irradiation used in some terminal sterilization steps. The tissue matrix may then be stored in a storage solution, which is preferably non-aqueous, such as mineral oil or glycerol.
In some embodiments, the processed tissue may be broken into smaller pieces from the hydrated, the freeze-dried, the preserved hydrated, or the preserved dehydrated state. This breaking into small pieces may be accomplished by standard methods and established means known to those skilled in the art, such as using shear forces in a mechanical blender, impact fragmentation, cryo-fracturing, and/or simple mechanical fragmentation using a mortar and pestle. In at least one embodiment, the tissue matrix is micronized, resulting in a plurality of fragments or pieces measuring in the micron range. For instance, micronized tissue pieces may have a diameter in the range of 100-300 microns, although some fragments may be less than 100 microns in average diameter. This micronized or fragmented tissue matrix may also be provided in a frozen state, a room temperature dehydrated state, a freeze-dried state, or a room temperature hydrated state. This micronized tissue matrix may later be used as an injectable tissue matrix, for subcutaneous regenerative repair, such as for use in cosmetic applications as just one illustrative example.
These above steps result in the modification of the tissue matrix sufficient to promote cellular infiltration and proliferation. For example, the present process involves reducing levels of at least proteoglycans, lipids, phospholipids, nucleic acids, and MHC antigens. As discussed elsewhere in this specification, proteoglycan levels are reduced by a range of 30% to 50%, such that the tissue matrix retains 50% to 70% of extractable proteoglycans. Lipids and phospholipids are reduced by a range of 70% to 95%. Nucleic acids are reduced by a range of 30% to 90%. Major histocompatibility (MHC) antigens I and II are reduced by a range of 85% to 99%. Moreover, endotoxins are essentially eliminated from the tissue matrix.
These results may be assessed by comparing the ability of standard mammalian cells to infiltrate non-processed connective tissues relative to connective tissues processed according to the present invention. Cellular infiltration can be assessed using traditional histological evaluation and/or by extracting nucleic acids from non-processed and processed tissues as a function of time of incubation in the presence of a test population of mammalian cells cultured under standard tissue culture conditions. An increase in extractable nucleic acids over time is indicative of cellular infiltration and proliferation. The Examples given hereinafter demonstrate confirmation by some of these tests.
The present invention is also directed to a tissue matrix suitable for use in regenerative repair of soft tissue, which may be a result of the previously described process in some embodiments. Specifically, the tissue matrix of the present invention comprises a scaffold portion structured to provide shape to the tissue matrix. For example, the scaffold portion may be made of structural or non-extractable proteoglycans. In some embodiments, the matrix is made up of a collagenous structure derived from connective tissues. The collagenous structure is suitable for cellular infiltration, cellular attachment, cellular proliferation, and cellular differentiation in both in vivo and in vitro conditions. The collagenous structure of the tissue matrix may possess hemostatic properties when used in both in vivo and in vitro conditions.
The tissue matrix also includes a non-structural portion disposed in interspersed relation through at least a part of the scaffold portion. For instance, the non-structural portion of the tissue matrix is the extracellular matrix (ECM) component of the tissue. As previously described, it permeates the scaffold and includes cells and molecular factors necessary for cell-cell and cell-matrix interaction that facilitate cellular infiltration, attachment, and proliferation. The non-structural portion of the tissue matrix may also be made up of proteoglycans, such as extractable and non-extractable proteoglycans.
The scaffold portion and non-structural portion of the tissue matrix are collectively structured to promote cellular infiltration, attachment, and proliferation of at least one host cell into the tissue matrix upon implantation or transplantation of the tissue matrix into a host tissue for repair.
Furthermore, the tissue matrix may retain molecular moieties associated with molecules comprising the collagenous structure appropriate to the attachment of mammalian cells. Particularly, the tissue matrix is composed of connective tissue with significant reduction in at least one of lipids, phospholipids, nucleic acids, major histocompatibility antigens, endotoxis, and some proteoglycans. Accordingly, at least part of the tissue matrix, either in the scaffold portion or the non-structural portion, have been at least partially acellularized by the process of removing these components. The tissue matrix nevertheless retains a significant amount of extractable proteoglycans. Preferably, the tissue matrix retains about 70% of extractable proteoglycans.
In some embodiments, the tissue matrix may also retain endogenously derived growth and differentiation factors. Such growth and differentiation factors include, but are not limited to, angiogenic factors, mitogenic factors, morphogenic factors, and combinations thereof. Angiogenic factors include, but are not limited to, one or more factors appropriate for the revascularization of a tissue matrix under in vivo and in vitro conditions. Likewise, mitogenic factors include, but are not limited to, one or more factors appropriate for induction of cells to divide mitotically, thereby proliferating and increasing in numbers. Morphogenic factors include, but are not limited to, one or more factors appropriate for the induction of cells infiltrating the tissue matrix to differentiate into cell phenotypes suitable to the formation of tissues of similar structure and function as the tissues into which the tissue matrix is placed.
Accordingly, the tissue matrix of the present invention meets one or more of the following criteria: (1) it is reduced by at least about 30%, and preferably greater than about 90%, in extractable nucleic acids; (2) it is reduced by about 70% to about 95% in extractable phospholipids; (3) it is reduced by about 70% to about 95% in extractable lipids; (4) it retains about 50% to about 70% of extractable proteoglycans; (5) it presents molecular moieties which have been oxidized; (6) it is reduced by at least about 85% in immunoreactive major histocompatibility antigens; (7) it presents a slightly altered collagenous structure which has been partially dissociated by the organic acid (preferably acetic acid); (8) it is disinfected and is culture negative according to USP Section 71 sterility assessments; (9) it is negative (i.e., not detectable by assay methods utilized by those skilled in the art or within the limits currently allowed by regulatory agencies) with respect to clinically acceptable levels of endotoxins; (10) it retains molecular moieties associated with the collagenous tissue matrix as appropriate to the needs of cells infiltrating the tissue matrix, and (11) it facilitates cellular infiltration, attachment, proliferation, differentiation, and synthesis of matrix materials appropriate to the regenerative repair of soft tissue defects.
The present invention is also directed to kits for regenerative soft tissue repair, which include a tissue matrix of isolated connective tissue as previously described. For instance, such kits include a tissue matrix having reduced levels of at least one of proteoglycans, lipids, phospholipids, nucleic acids, major histocompatibility (MHC) antigens, and endotoxins. The tissue matrix provided by the kit is therefore structured to promote cellular infiltration, attachment and proliferation of host cells therein. Moreover, the kits of the present invention may include tissue matrices of any type of tissue as described herein, such as but not limited to dermis and fascia. The tissue matrix may comprise any appropriate structure and dimension suitable to a particular repair purpose, such as but not limited to a sheet, thick sheet (as is readily understood in the art by those of ordinary skill), fragmented and/or micronized matrix, and which are ready to use in implantation.
In at least one embodiment, the kit further includes an amount of transfer solution, which is to be used in facilitating or assisting in the transfer of the tissue matrix to a host. Such transfer solution may be any appropriate biocompatible solution, such as but not limited to saline, buffered saline, or water. In addition, various instrumentation may be included in some embodiments of the kit to accomplish the transfer or implantation of the tissue matrix to a host. For example, the kit may include a needle and at least one syringe in which the tissue matrix may be loaded for subcutaneous injection into the host. This is particularly useful in connection with micronized tissue matrix, wherein the micronized tissue matrix may be suspended in transfer solution provided in the kit and injected into the host. A plurality of syringes and/or needles may be included in the kit for repeated injections. In some embodiments, the kit is available with the syringe pre-loaded with tissue matrix and transfer solution. In other embodiments, the tissue matrix, transfer solution, and syringe are separate in the kit and must be combined by a user.
The present invention is also directed to kits for processing connective tissue to render a resultant tissue matrix suitable for regenerative repair. Such kits include an amount of surfactant and an amount of disinfectant. As discussed previously, the surfactant may be a detergent, such as BRIJ 95, BRIJ 96, Tween 20, Triton X100 or others. The disinfectant may be peracetic acid peracetic acid, chlorine dioxide, hydrogen peroxide, polyvinylpyrolidineiodide, formaldehyde, glutaraldehyde, phenoxyethanol, methylparaben, propylparaben, sodium hydroxymethylglycinate, diazolidinyl urea, DMDM hydantoin, iodopropynyl butylcarbamate, propylene glycol, and combinations thereof.
In some embodiments, additional solutions are also included in the kit, such as alcohol, chondroitinase, endonuclease, and lipase, and endotoxin reducing solution, as previously described. The kits may also include a storage solution, preferably a non-aqueous solution such as mineral oil, for storing the resultant tissue matrix. Many embodiments further include instructions of use.
Any of the above-described kits may also include instructions for use of the kit. Moreover, some embodiments of the kits may also include at least one assay reagent for use in detecting regenerative repair and/or instructions for their use. These reagents are structured for use in detecting at least one of cellular infiltration, attachment, proliferation, differentiation, and synthesis of matrix materials appropriate to the regenerative repair of soft tissue defects. Methods of detection may include by conjugation of detectable labels or substrates, such as fluorescent compounds, enzymes, radioisotopes, heavy atoms, reporter genes, luminescent compounds, or antibodies against molecular components of the tissue matrix. As it would be understood by those skilled in the art, additional detection or labeling methodologies may be used in the kits provided.
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following examples are offered by way of illustration, not by way of limitation. While specific examples have been provided, the above description is illustrative and not restrictive. Anyone or more of the features of the previously described embodiments can be combined in any manner with one or more features of any other embodiments in the present invention. Furthermore, many variations of the invention will become apparent to those skilled in the art upon review of the specification.
All publications and patent documents cited in this application are incorporated by reference in pertinent part for all purposes to the same extent as if each individual publication or patent document were so individually denoted. By citation of various references in this document, Applicants do not admit any particular reference is “prior art” to their invention.
The methods and compositions herein described and the related kits are further illustrated in the following examples, which are provided by way of illustration and are not intended to be limiting. It will be appreciated that variations in proportions and alternatives in elements of the components shown will be apparent to those skilled in the art and are within the scope of embodiments of the present invention. Theoretical aspects are presented with the understanding that Applicants do not seek to be bound by the theory presented. All parts or amounts, unless otherwise specified, are by weight.
Freeze-dried dermis samples were prepared by the processing unit using a 10-mm biopsy punch (Acuderm Inc., Ft. Lauderdale). Biocompatibility was assessed by direct contact of L929 and MIAMI cells (a proprietary cell line as identified and described in U.S. Pat. No. 7,807,458) with the dermal matrix samples for various periods of time. Qualitative histology assessment was performed and results collected and documented.
It was hypothesized that tissue samples lacking agents which may be cytotoxic to mammalian cells and which present a matrix structure which at the molecular and macroscopic level provide an environment which is suitable and appropriate for cellular attachment and proliferation were deemed to be biocompatible for cellular attachment and proliferation. When such tissues are tested in this manner and found to be biocompatible there is a strong presumption that such tissue matrices will serve in a regenerative capacity when used clinically in the treatment of pathologies.
Materials and Methods:
All procedures were carried out in a laminar flow hood designed to provide the sterile working environment. Sterile tools and containers were used.
Experimental Procedure:
1) L-929 cells or MIAMI cells were expanded and used before reaching confluency.
2) Each dermal matrix sample was transferred (basement membrane facing down) into individual wells of 24 well plates (Ultra Low Attachment surface, Corning, #3473) containing 500 μL of L-929 or MIAMI cell expansion media.
3) 10×103 or 200×103 L929 or MIAMI cells were harvested and seeded directly onto the surface of the dermal matrix tissue samples in the wells (final volume of media/wells: 1000 μL). Dermal matrix samples without cells were used as negative controls.
4) Plates were incubated at 37° C. and 5% CO2 on a rocker (Rocker II, #260350, Boekel Scientific, 15 oscillations/min) and samples of dermal matrix tissue were collected and placed into formalin (4% CH2O, 1% methanol) for histology preparations at different days to provide an understanding of the behavior of cells after short, medium and long term contact with the dermis.
5) Paraffin embedding, slicing and Hematoxylin/Eosin staining of the samples were performed according to standard histological methodologies.
Results:
Histology preparations were examined and digital images taken of representative sections with the objective of illustrating the adherence of either L-929 or MIAMI cells onto the surfaces of the dermal matrix tissue samplesm as well as any evidence of cellular proliferation.
As illustrated in
Similarly, as illustrated in
Both the cell types were seen to infiltrate the tissue, thereby, indicating the dermal matrix was biocompatible and readily supports cell growth in an in vitro situation.
DNA extraction and quantification from dermal matrix was used to reflect the efficiency of the decellularization process.
Materials and Methods:
DNA was quantified in:
1) Samples of dermis were weighed and approximately 10 mg were transferred to sterile 2 ml microcentrifuge tubes (Eppendorfs®). The exact weight was recorded in the laboratory notebook. For samples that were not washed 1.5 mg was used.
2) The volume of tissue lysis buffer (Buffer ATL) was adjusted per sample according to its weight (360 μl of lysis buffer/5 mg, and 360 μl/1.5 mg).
3) The volume of proteinase K was adjusted per sample according to its weight (40 μl proteinase K/5 mg of sample and same volume for 1.5 mg) was added and mixed by pulse-vortexing for 15 sec.
4) Samples were incubated at 56° C. for 20 hrs until fully lysed.
5) 400 μl of each sample was placed in a new eppendorf tube and 8 μl RNase A (100 mg/ml) was added, mixed by pulse-vortexing for 15 sec, and incubated for 2 min at room temperature.
6) 400 μl lysis buffer (Buffer AL) was added and mixed by pulse-vortexing for 15 sec.
7) Samples were incubated at 70° C. for 10 min.
8) 400 μl ethanol (100%) was added and mixed by pulse-vortexing for 15 sec.
9) Half of the lysates (600 μl) were transferred to the QIAamp MinElute columns.
10) Columns were centrifuged at 6000 g for 1 min.
11) Columns were placed in clean 2 ml collection tubes. Steps 9, 10 and 11 were repeated with the other half of the lysate in the same column.
12) 500 μl washing buffer (Buffer AW1) was added to the columns and centrifuged at 6000 g for 1 min.
13) Columns were placed in clean 2 ml collection tubes.
14) Steps 12 and 13 were repeated.
15) 500 μl washing buffer (Buffer AW2) was added and incubated for 2 min before centrifugation at 18,000 g for 1 min.
16) Columns were placed in clean 2 ml collection tubes.
17) 500 μl washing buffer (Buffer AW2) was added, and incubated for 2 minutes before centrifugation at 18,000 g for 3 min.
18) Columns were placed in clean 2 ml collection tubes.
19) Column was centrifuged at 18,000 g for 1 min to dry the membrane.
20) Columns were placed in clean 2 ml collection tubes.
21) 100 μl TE buffer was applied on the center of the column and incubated at room temperature (15-25° C.) for 5 min.
22) Columns were centrifuged at 6000 g for 1 min.
23) Columns were placed in another clean microcentrifuge tube.
24) Steps 21-23 were repeated twice.
25) The samples were vortexed and then the DNA concentration was determined using a Nanodrop ND-1000 spectrophotometer (Thermo Fisher Scientific). The instrument was initialized using water and blank using TE buffer.
The amount of DNA extracted from each dermal sample was determined, giving the results shown below:
Two fresh, non-processed dermis samples from different donors were analyzed. Both had similar DNA contents (0.83 & 0.66 μg DNA/mg tissue). Samples of dermis were processed according to the process of the present invention, such as described above in Example 1. This dermis sample analyzed had 90% less DNA than the fresh, non-processed sample of the same donor (0.085 & 0.83 μg DNA/mg tissue, respectively). This is shown in Tables 1 and 2 above, and depicted in the graph of
Dermal matrix samples were prepared by the processing unit using a 10-mm biopsy punch (Acuderm inc., Ft. Lauderdale). DNA is quantified in samples taken at pre-detergent processing, post-detergent processing, and post-peracetic acid processing steps. Several donors are analyzed during these 2 steps. Five samples from each single donor are used to average the results:
DNA Extraction Procedure:
1) Samples collected from the processing room were flash-frozen in liquid nitrogen to prevent DNA degradation.
2) Slowly thawed the samples on ice
3) Excess water was removed from the samples by placing them on sterile blotting paper for 2-3 minutes.
Note: all materials coming in contact with the samples are sterile to avoid exogenous DNA contamination.
4) Sub-samples of approximate weight 12.5 mg were excised from every sample and transferred to sterile microcentrifuge tubes (Eppendorf®). The exact weight is recorded in the laboratory notebook.
Note: a DNA extraction kit (QIAamp DNA Mini, Qiagen, #51304) was used according to the manufacturer instructions, with modifications as described in the following. All steps were performed at room temperature.
5) Add 180 μL of tissue lysis buffer (Buffer ATL) to each sample.
6) Fully dissociate the samples by use of micro-scissors.
7) Add 40 μL proteinase K and mix by pulse-vortexing for 15 seconds.
8) Incubate at 56° C. overnight to fully lyse the sample.
10) Add 4 μL RNase A (100 mg/ml), mix by pulse-vortexing for 15 seconds, and incubate for 2 minutes at room temperature.
9) Add 200 μL lysis buffer (Buffer AL) and mix by pulse-vortexing for 15 s.
11) Incubate at 70° C. for 10 minutes.
12) Add 200 μL ethanol (100%) and mix by pulse-vortexing for 15 seconds.
13) Carefully transfer the entire lysate from to the QIAamp MinElute column.
15) Place the QIAamp MinElute column in a clean 2 mL collection tube, and discard the collection tube containing the flow-through.
16) Add 500 μL washing buffer (Buffer AW1) and centrifuge at 6000 g for 1 minute.
17) Place the QIAamp MinElute column in a clean 2 mL collection tube, and discard the collection tube containing the flow-through.
18) Add 500 μL washing buffer (Buffer AW2) and centrifuge at 20000 g for 3 minutes.
19) Place the QIAamp MinElute column in a clean 2 mL collection tube, and discard the collection tube containing the flow-through.
20) Centrifuge at 20,000×g for 1 minute to dry the membrane.
21) Place the QIAamp MinElute column in a clean microcentrifuge tube and discard the collection tube containing the flow-through.
22) Apply 200 μL elution buffer (Buffer AE) and incubate at room temperature (15-25° C.) for 1 minute.
23) Centrifuge at 6000×g for 1 minute.
24) Place the QIAamp MinElute column in another clean microcentrifuge tube and repeat step 22-23.
25) Quantify the double-strand DNA concentration in the samples using a Nanodrop ND-1000 spectrophotometer (Thermo Fisher Scientific). Initialize the instrument using water and blank using elution buffer (buffer AE).
Results:
The amount of DNA present per weight of one sample is calculated from the average amount of the 2 samples of DNA collected in steps 23 and 24 of the protocol. For a single step, the results obtained in five samples are then averaged to give the results presented in the table below:
Conclusion:
On average, experiments performed on 3 donors (5 samples per donor at each step), revealed that 63±15% of DNA are removed between the Pre-BRIJ steps and the Post-PAA steps.
Frozen fascia tissue samples were prepared by the processing unit for use in this study. The fascia tissue samples were only debrided of extrinsic blood elements and were not processed according to the present invention. To assess the cellular inhibition properties of extracts of these tissues, compounds present in the final products were extracted during 24 hours following ISO 10993-5 and ISO 10993-12 guidelines. The extraction media, containing potential inhibitory compounds, were then applied to fibroblast cells in culture (L-929 cell line ATCC #CCL-1). A quantitative assessment of healthy cell density was performed using the CyQUANT® Direct Cell Proliferation Assay while qualitative assessments of cell morphology were performed by microscopic observation.
CyQUANT® Direct Cell Proliferation Assay was chosen for its ability to provide a measure of viable cell density in a single step experiment. Indeed, it combines a DNA-binding dye and a background suppression reagent. The DNA-binding dye is a live-cell permeable reagent that mainly concentrates in the nucleus of metabolically viable mammalian cells, while the suppression dye is impermeable to living (viable) cells and quenches the fluorescence of DNA-binding dye in cells with compromised cell membrane. The combination of these two components results in an assay based on both DNA content and cell membrane integrity.
It was hypothesized that the assessment of cytotoxicity of extracts of materials involves an extraction of potentially toxic agents from materials and subsequent application of these extracts onto a population of metabolically viable mammalian cells. The CyQUANT® Direct Cell Proliferation Assay utilizes a dye which binds to nucleic acids and will bind with DNA of both living and metabolically non-living cells. However, the assay also employs a background suppression reagent which will suppress fluorescence of the dye. In that the background suppression reagent will not penetrate into the interior of a viable cell, any viable cell in the population of cells will fluoresce, but non-living cells will not fluoresce due to the quenching action of the background suppression reagent. This assay is thus a useful tool in determining the percentages of viable versus non-viable cells in a population of cells and any extract of a material which contains extractable agents toxic to a mammalian cell will alter this percentage of viable to non-viable cells and can thus be used to quantitatively determine toxicity of extracts.
Materials and Methods:
All procedures were carried out in an aseptic working environment. The following materials and conditions were adapted from the recommendations described in ISO 10993-12.
Experimental Steps:
1) 1 cm2 square samples of human fascia were dissected and placed in the wells of a low attachment 6 wells plate (total of 21 cm2/wells), 1 wells/donors (Costar, #3471).
2) The total weight of the samples were recorded and 7 mL of extraction media were added to each well (L-929 cell expansion media):
Note: Presence of fetal bovine serum should enable the extraction of polar and non-polar leachable materials. According to the ISO 10993-12, the extraction volume should be of 1 mL for 3 cm2 of samples (thickness >0.5 mm).
2) Samples were then placed on a rocker and incubated for 24 hours at 37° C. in an incubator (>90% humidity and 5% CO2 atmosphere). Media alone was also incubated for L-929 controls and positive (SDS) controls.
3) 20,000 sub-confluent L-929 cells/wells were plated in a black, clear-bottom, 96 well plate (Tissue culture treated, Costar #3904) in a final volume of 100 μL of expansion media. Another black plate was seeded with a density of 10,000 cells/well to ensure the use of subconfluent cells at the time of assay (i.e. day 3).
4) The extraction media was collected in 15 mL Falcon tubes and centrifuged at 300 g for 10 minutes in order to remove big particles/cells extracted from the Fascia (Fascia being a frozen graft, cells were indeed observed in the extraction media if this step was not performed, resulting in a bias in the following Cyquant® assay).
5) The supernatant of the extraction media was applied to the L-929 cells plated at day 1 (removal of expansion media and addition of 100 μL of extraction media/well). At the same time, negative, positive and blank were performed:
Note: all the following steps were performed avoiding a direct exposure to light.
8) Cyquant® reagent was prepared according to the following recipe (For 12 ml of reagent):
Results:
As can be observed in
As can be seen on
It is important to note that the quantification results obtained with the Cyquan®t test were hardly correlated to the microscopic observations in
Conclusion:
According to the criteria described in the ISO 10993-5, quantification tests resulting in more than 30% of decrease in cell viability is considered as a cytotoxic or cellular inhibition effect. The averaged results obtained in the 5 donors of this experiment were precisely on the borderline of this threshold of 30% (slightly less for one of the fascia processed from donor UBO9084).
The ISO documents also provide directions regarding a qualitative morphological assessment of cell toxicity/inhibition (see Table 4).
According to this table, despite a growth inhibition of approximately 30%, more than 50% of the cells were rounded after exposure to the extraction media, so that we can reasonably conclude that elements present in normal tissue can be inhibitory to cellular infiltration into such tissues and that removal of these inhibitory elements should facilitate a regenerative nature to processed tissues.
The purpose of this experiment is to test and document the biocompatibility of micronized dermis produced by the process of the present invention. Freeze-dried micronized dermis samples were prepared according to the process as described herein to obtain micronized dermis. Biocompatibility was assessed by direct contact of the samples with L-929 cells (ATCC #CCL-1, source: Mus musculus) for two months. Qualitative assessment of cell morphology was performed by microscopic observation. A quantitative assessment of healthy cell density was performed using the CyQUANT® Cell Proliferation Assay.
Note: all procedures were carried out in a laminar flow hood in aseptic conditions. The following materials and conditions have been adapted from the recommendations described in ISO 10993-12 and ISO 10993-xx.
Freeze-dried acellular, micronized dermis samples (Batch 2) were prepared according to the process of the present invention. Micronized dermis from donor BO39698, UBO 0099050202-12, particle size tested 25-300 μm.
The micronized dermis was weighed and then mixed with prepared media, α-MEM Gibco (lot #1045867), with 10% Fetal Bovine Serum, PAA (lot #A20411-7008), and 1% penicillin-streptomycin (Sigma, 051M0853), vortexed and placed on a 6 well, ultra low attachment plate (Corning, Costar #3471, lot #08711003, expiration date Mar. 27, 2014), according to Table 5.
L-929 sub-confluent, P5 culture was split and counted according to standard protocols.
Three of the micronized dermis samples were seeded with 800,000 L-929 cells, two samples were used as control with no cells. The samples were incubated for 2 months at 37° C., 5% CO2, ≧90% humidity (equipment #08-016). Media alone was also placed in the same plate and incubated under the same conditions.
Half the media was changed twice a week. Photographs were taken at days 10, 16 and 30.
L-929 cultures (P6) were harvested and split according to standard protocol and 300,000 cells in 2 ml of freshly prepared media were placed in a centrifuge tube. These cells were later used for a calibration curve. The cells, along with one seeded micronized dermis sample and one control were centrifuged. The supernatant was discarded and the pellets frozen at −80° C.
Two micronized dermis samples and one control were collected, centrifuged, the supernatant discarded and the pellets frozen at −80° C.
A quantitative assessment of healthy cell density was performed using the CyQUANT® Cell Proliferation Assay kit (lot #1050079), C7026.
The samples collected in Day 60 show a larger number of cells then those collected in Day 57, as expected. The L-929 cells proliferated and survived during 60 days attached to the micronized dermis matrix showing that this matrix is biocompatible. See Table 6 below and
The samples were examined microscopically and digital microphotographs were taken of every condition with the objective of illustrating cellular proliferation and adherence of the cells to the dermal matrix. All photomicrographs were taken at 100× unless otherwise noted. Similar microphotographs were taken of micronized dermis samples where no L-929 cells were seeded in order to serve as controls.
At Day 10, shown in
The micronized dermis produced by the process of the present invention has a matrix structure that is biocompatible and provides an environment which is suitable and appropriate for cellular attachment and proliferation.
The purpose of this study was to examine the resorption over four weeks of the micronized dermal matrix product injected subcutaneously on either side of the spine of a nude mouse.
It was hypothesized that the dermal matrix product should not be quickly resorbed in a nude mouse, using a competitive product as a positive control. The size of the injection site should not change significantly. However, this measure is fairly subjective. Histologic evidence of resorption will be examined as well.
Each mouse was injected subcutaneously with test and control article. The injection sites were evaluated by palpation and measurement at termination. Body weights were obtained at injection, daily for the first week, then twice during each week thereafter, with weights collected at termination. Animals were observed cageside daily for signs of general clinical health.
At the end of the scheduled duration, the designated animals were euthanized. The injection sites were palpated and measured and the surrounding tissue was surgically excised. The tissues were placed in formalin for fixation. The samples were then stained with H&E, Alcian blue, trichrome and for elastin.
The mouse is suggested as an appropriate animal model for evaluating biocompatibility by the current ISO testing guidelines. The group size is based on the minimum amount of animals required for biological evaluation. The number of animals was chosen to provide some statistical significance in the results.
The subcutaneous injection route of exposure was selected because it is the intended route of administration to humans. Note: all procedures were carried out in an aseptic working environment. The following materials and conditions were adapted from the recommendations described in ISO 10993-12.
The control article implant was myxoid with sparse cellularity. In the test article implant, collagen is more dense and less cellular.
Both the control article and the test article show the evolution of a subdermal pseudocapsule with mild inflammation. Neither shows a significant inflammatory or giant cell response. The control article consists of loose, vaguely myxoid, fibroconnective tissue. Angiogenesis is more developed in the control article than on the test article. The test article consists of disorganized, more mature collagen with quiescent fibroblasts. Accordingly, the test article is more “active”.
Dermal tissue matrices in the form of tissue grafts were supplied to various clinicians to test whether the grafts could promote regenerative repair of soft tissue in in situ applications to humans. The clinicians followed their own procedures and protocols for applying and/or using the dermal matrix tissue grafts on wounds of their patients. At least two provided data of their results, shown in
Specifically, in
It is to be appreciated that the foregoing Detailed Description section, and not the Abstract section, is intended to be used to interpret the claims. The Abstract section may set forth one or more, but not all, exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, is not intended to limit the present invention and the appended claims in any way.
The foregoing description of the specific embodiments should fully reveal the general nature of the invention so that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Since many modifications, variations and changes in detail can be made to the described preferred embodiment of the invention, it is intended that all matters in the foregoing description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents. Moreover, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should similarly be defined only in accordance with the following claims and their equivalents.
This application claims the benefit of co-pending U.S. Provisional Patent Application having Ser. No. 61/581,803 filed on Dec. 30, 2011, the contents of which are incorporated by reference herein in its entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US12/72027 | 12/28/2012 | WO | 00 | 6/30/2014 |
| Number | Date | Country | |
|---|---|---|---|
| 61581803 | Dec 2011 | US |
