The present invention relates to a biodegradable two-layered matrix for preventing post-surgical adhesions, in particular after soft tissue repair in abdominal surgery, e.g. in hernia repair, within the body of a mammal, as claimed in Claim 1. Further, the invention relates to a method for preparing the biodegradable matrix as defined in Claim 12.
Any trauma to a tissue is usually followed by healing, which is normally accompanied by the formation of collagenous scar tissue. If tissue damage involves two or more tissues that are in close proximity to each other, the scarring process may lead to the formation of an undesirable connection of originally separate tissues. In surgical procedures, multiple tissue trauma has usually occurred beforehand and/or is caused by the incision to reach the surgical site. In consequence, post-surgical adhesions between tissues and/or organs are among the most common complications occurring after any type of surgery. Events such as excessive bleeding and/or inflammation, and intimate contact between tissues substantially increase the probability of adhesion formation at the trauma site. The consequences for the patients are often chronic pain and functional disorders, and in many cases will require re-operation.
While being undesirable in general, the occurrence of post-surgical adhesions is a particular issue in surgical hernia repair. A hernia is the abnormal exit of tissue or an organ, such as the bowel, through the wall of the cavity in which it normally resides. Although hernias can occur in a number of places, most commonly they involve the abdomen, specifically the groin. Groin hernias are mostly of the inguinal type but may also be femoral. Other hernias include hiatus, umbilical, and incisional hernias, the latter being a hernia that pushes through a past surgical incision or operation.
Traditionally, a hernia would be repaired by an open hernioplasty with sutures. During the months following the hernia operation, the repaired site would gradually gather scar tissue, such that the hernia defect becomes closed and reinforced. Unfortunately, this process of scar tissue formation has shown to be impaired in some patients, which results in the formation of a further hernia, i.e. a so-called hernial relapse or recurrence. Therefore, in particular in case of larger hernias or in case of a hernial relapse, mesh implants are nowadays commonly used for the reconstruction and reinforcement of the abdominal wall. The commercially available meshes used in surgical soft tissue repair today are either non-degradable or are fully degraded and absorbed within the patient's body after a certain time.
While helpful to provide additional stability to the repaired hernia area, both non-degradable and biodegradable meshes have shown to cause post-surgical adhesions. In particular when so-called "IPOM" meshes, i.e. "intra-abdominal pre-peritoneal on lay meshes", are used to cover defects in the abdominal wall, the formation of undesirable inflammatory or fibrous bands or collagenous scars connecting the mesh and intra-abdominal structures have shown to be the cause of recurrent pain and small or large bowel obstruction. If the latter is not diagnosed in time, it can cause infarction of the bowel, which generally necessitates larger surgical and high-risk procedures. For that reason, in case of abdominal hernia repair, the formation of post-surgical adhesions can be particularly severe to the patient's well-being.
In order to prevent or at least minimize the formation of post-surgical adhesions, attempts were made to isolate the damaged tissue and separating it from any adjacent tissue with a biocompatible material. As a result, adhesion barriers have been developed, which are nowadays available in the form of physical films, fabrics, gels or other materials that are applied between layers of tissues at the end of a surgery before the incision site is closed. While in place, the adhesion barrier acts as a physical barrier to separate traumatized tissue surfaces so that fibrin formation between the healing surfaces is prevented. Examples of commercially available adhesion barriers for use in surgical procedures include for instance:
- Preclude® is a thin sheet of porous ePTFE (expanded polytetrafluorethylene; also called GoreTex). It provides a non-sticky, microporous insert, which is biocompatible and non-inflammatory. However, it is non-absorbable and non-degradable, so it requires a subsequent operation to remove it. Also, it must be sutured to tissue in place. For this reason, it was not approved for adhesion prevention in the USA.
- Seprafilm® (made by Genzyme) is a clear, sticky film composed of sodium hyaluronic acid with carboxymethyl cellulose (CMC). It sticks to the tissues to which it is applied and is slowly absorbed into the body over a period of seven days. It is approved for use in certain types of pelvic or abdominal surgery.
- Interceed® (made by Johnson & Johnson) is a knitted fabric composed of a modified cellulose that swells and eventually gels after being placed on the injured site, and, like Seprafilm, forms a barrier and then is slowly absorbed over a period of days. It is approved for use in pelvic surgery.
Unfortunately, most of these currently available anti-adhesion barriers are inadequate for use in hernia repair surgery, because in this case it is not enough to prevent the formation of connecting tissues between the healing abdominal wall and the underlying intraabdominal organs. At least as important is to ensure that there is sufficient tissue growth from adjacent tissues into the area of the hernia, such that the gap in the abdominal wall is securely closed. Particularly if biodegradable (temporary) meshes or scaffolds are used to close a hernia it is essential to induce fibrogenesis and scar formation, i.e. the processes involved in wound healing, to form a stable scar plate that prevents recurrent hernia formation. Therefore, successful hernia repair requires means that induce fibrinogenesis and formation of bridging tissue to close the soft tissue defect, yet without provoking adhesions.
The problem solved by the present invention is therefore to provide a biodegradable matrix, which allows for rapid, safe and stable closure of a soft tissue defect, in particular a hernia defect, without promoting adhesion formation. At the same time, the matrix shall be easy and inexpensive to manufacture and allow for its use in conventional open and laparoscopic surgical methods.
This problem is solved by the matrix according to Claim 1. Preferred embodiments are subject of the dependent claims.
In line with the present invention, a biodegradable matrix for preventing post-surgical adhesions in surgical soft-tissue repair, in particular following abdominal surgery, within the body of a mammal is provided. More specifically, the inventive matrix is particularly well suited to cover areas of the peritoneum or abdominal wall that were injured during abdominal surgery or due to a hernia.
The term "matrix", as used throughout this application, refers to a three-dimensional support, e.g. a mesh, meaning a scaffold- or sponge-like structure, which is suitable for being colonized by cells. In this sense, the matrix serves as a three-dimensional template which can be colonized by cells or tissue. This colonization can take place in vitro
or in vivo.
Furthermore, the matrix serves, in connection with transplantations, for locating the transplant and also as a place holder for tissue which is gradually formed in vivo.
The expression "biodegradable" refers to a material which can be converted into metabolizable products in living organisms (or body fluids or cell cultures derived from living organisms). Biologically degradable materials include, for example, polymers which are bioresorbable and/or bioerodable. "Bioerodable" denotes the ability to be soluble or suspendable in biological liquids. Bioresorbable means the ability to be able to be taken up by cells, tissues or fluids of a living organism.
In line with the present invention the matrix includes a porous top layer made of a first biocompatible polymer material and a porous bottom layer made of a second biocompatible polymer material. The first polymer material and the second polymer material are both selected from the group consisting of poly(glycolic acid) [PGA], poly(lactic acid) [PLA], poly(glycolic acid-lactic acid) [PLGA], polycaprolactone [PCL], poly(hydroxybutyrate) [PHB] and mixtures or co-polymers thereof. As "biocompatible polymers", the polymers shall be biologically tolerated and not cause rejection when brought into a living organism. For the present invention, biocompatible polymers also encompass polymers which are recognized by a host as being foreign but whose rejection can be suppressed by appropriate immunosuppression. Notably, the term "PLA" encompasses all chiral forms of PLA, i.e. PLLA, PDLA and mixtures (co-polymers) thereof.
With regard to the two layers of the matrix, the term "porous" refers to a structure comprising pores, i.e. cavities or void regions. These pores may have a round shape and/or an angular shape in a 2-dimensional section and/or a canted shape when seen 3-dimensionally. The shape of the pores may also be characterized by extensions such that it can be compared with the shape of nerve cells. As such, the term "pores" also refers to cavities formed by filaments enclosing a void region. These pores or cavities may also be interconnected, meaning that the pore walls between two adjacent pores can comprise holes, forming a connection between said adjacent pores. In this regard, it is to be noted that the pores formed within the top layer and those within the bottom layer may be structurally distinct from one another, e.g. with regard to their shape, size and/or interconnectivity.
One key element of the present invention is that both layers are biodegradable and are in the form of porous scaffolds, whereby the top layer is hydrophilic, having a water contact angle of less than 75°, preferably less than 60°, and the bottom layer is hydrophobic, having a water contact angle of more than 90°.
The term "contact angle" as used in the context of the present application relates to the contact angle of water on a surface, i.e. to the angle formed at the interface where water meets the surface. Thereby, "water" used for the contact angle measurement relates to pure water, specifically ultrapure water. In particular, the contact angle measurement is carried out by the sessile drop method (e.g. by means of a device of the type EasyDrop DSA20E, Kruss GmbH) using a drop size of 0.3 or 0.1 µl. Contact angles are generally calculated by fitting a circular segment function to the contour of the droplet placed on the surface ("Circle Fitting" method).
The term "hydrophilic" or "hydrophilicity" as used in the context of the present invention refers to a water contact angle of a surface area on the matrix being below 75°. The hydrophilic surface can be obtained for example by increasing the content of (poly)lactic acid in the polymer composition and/or by post-processing methods, such as plasma-treatment and/or covering the surface with a natural polymer, such as gelatin. The term "plasma" thereby generally refers to an excited and radicalized gas, i.e. an electrical conducting process gas involving electrons and ions. Plasma is commonly generated by means of electrodes in a vacuum chamber (so-called "RF plasma approach"), but it can also be generated using capacitive or inductive methods, or microwave radiation. More details in this respect are given in the experimental section further below.
On the other hand, the term "hydrophobic" or hydrophobicity shall be understood as a substrate having a surface area with a water contact angle above 90°. With respect to the hydrophobic bottom layer of the inventive matrix, it has preferably a water contact angle above 120°. Hydrophobic properties are generally increased with decreasing content of PLA in the polymer composition and/or by post-processing methods, such as UV-treatment.
The inventive matrix provides multiple beneficial effects: On the one side it has been found that the hydrophilic properties of the matrix' top layer promote tissue ingrowth of e.g. smooth muscle cells and fibroblasts from adjacent tissue into the wound that is to be closed, e.g. a hernia. In addition, the porous nature of the top layer provides a growth-stimulating environment for the cells that help constructing extracellular matrix tissue and various types of collagen fibres, thereby forming a scar plate closing the tissue defect. First, the growing scar plate will establish a firm connection between the degradable (and thus temporary) matrix and the rims of the tissue defect. In case of a hernia, the scar plate will form throughout the matrix to close the gap within the abdominal wall. Over time, while the degradation of the matrix continues, the newly formed scar tissue will gradually take over the necessary support function by creating additional cicatrisation, thereby preventing re-opening of the wound or recurrent hernia formation.
On the other side it was found that the hydrophobic properties of the matrix' bottom layer effectively hinders attachment of most cell types, in particular inflammatory proteins, or hydrophilic fluids to the bottom surface of the matrix - which prevents unwanted tissue adhesion formation. Specifically, when tested in abdominal hernia repair, the hydrophobic properties of the bottom layer of the inventive matrix successfully prevented infiltration of peritoneal or other bodily fluid into the matrix and minimized undesired tissue adhesion formation between the hernia repair and the intra-abdominal structures, in particular the small bowel.
In summary, the matrix of the present invention provides a temporary closure of the soft tissue defect - for instance an abdominal hernia - and has the following benefits:
- On the one hand, the hydrophilic top layer facing the hernia promotes ingrowth and proliferation of cells, such as muscle cells and fibroblasts, that will form new scar tissue taking over the continuously decreasing support function of the matrix. In the end, after complete degradation of the matrix (i.e. when the polymeric components of the matrix have been absorbed), no permanent foreign material will be left within the patient's body.
- On the other hand, the hydrophobic properties of the matrix' bottom layer prevents the attachment of inflammatory cells fibrin or debris, to the matrix from the intraperitoneal side (i.e. the side of the matrix facing away from the hernia and towards the abdominal cavity), such that the occurrence of inflammation and the formation of adhesive tissue growth between the matrix or the newly-formed scar plate and the underlying abdominal tissues is avoided.
Although particularly useful in hernia repair, the inventive matrix can be used to aid the healing process after surgical intervention in general. For instance, if abdominal surgery is performed and intraabdominal inflammation is present, it is important to provide a barrier between the inflamed intraabdominal tissue and overlying tissues that have been cut to access the surgical site - irrespective of the wound size, e.g. even if only a small incision is made in a minimally invasive approach. The hydrophobic layer can therefore provide such a barrier and the hydrophilic layer can promote the healing process of the surgical wounds.
Another advantage of the inventive matrix is that both layers are porous, which provides the option to have pharmacologically active agents - such as epidermal growth factor, platelet derived growth factor, transforming growth factor beta, angiogenesis factor, antibiotics, antifungals, spermicidals, hormones, enzymes, and/or enzyme inhibitors - incorporated into the layers, preferably the top layer, to deliver these agents to the wound site and positively affect cell growth, such as collagen types IV and V, fibronectin, laminin, hyaluronic acid and proteoglycans, in and adjacent to the top layer area.
To facilitate cell attachment and growth throughout the top layer it is preferred that the entire top layer has a hydrophilic surface, i.e. a surface having a water contact angle of less than 75°.
Since increasing hydrophilicity has shown to correlate with improved cell attachment and proliferation, the top layer of the matrix has preferably a water contact angle of less than 60°, more preferably less than 45° and even more preferably less than 25°. Most preferably, the water contact angle of the hydrophilic surface on the top layer of the matrix is within the range of 0° to 10°, which means that the top layer is "super-hydrophilic".
The top and the bottom layer may be provided as a one entity structure, i.e. wherein the two layers are integrally formed or firmly connected to one another on multiple locations. Alternatively, the two layers may also be provided as two individual structures that are separate from one another. One example would be that the top layer and bottom layer are both provided in a sheet-like shape and are simply loosely stacked on top of each other.
In a particularly preferred embodiment, the material compositions of the two layers differ from one another. The difference may be either with respect to the polymer type and/or content of a specific polymer in the polymer material. For instance, both layers may consist of the same type of polymers, yet with different polymer ratios. Alternatively, the top layer and the bottom layer may differ with respect to the type of polymers present in the polymer material.
In one preferred embodiment the first polymer material of the top layer consists to at least 70% of polylactic acid (PLA). This means that the top layer may be formed entirely of PLA or it may consist of 70% or more PLA and 30% or less of at least one additional different polymer. If at least one additional polymer is present, the PLA and the other polymer (s) can form a co-polymer or the top layer can be provided as two separate components - e.g. a PLA basic structure with a coating of the other polymer (s). PLA is preferably the main component of the top layer, since it increases the hydrophilic properties and therefore facilitates cell attachment to and ingrowth into the matrix. Pure PLA has, however, the drawback of being less stable, i.e. less strain-resistant, than e.g. PGA. Nevertheless, since the bottom layer may be used to provide additional stability to the matrix, the top layer may also essentially consist of PLA. A specific example of a preferred PLA material is poly(L-lactide) that is commercially available from Sigma Corporation (PLLA catalogue number P1566) with a molecular weight of 85,000-160,000 Da. A suitable alternative is PLLA from Durect Corporation (Lactel® catalogue number B6002-2).
As mentioned, the polymer material of the top layer may be based on PLA, yet combined with one or more other polymer(s) to increase the top layer's more stability. One preferred additional polymer is PGA. Co-polymers of PLA and PGA - so-called "poly-lactide-co-glycolic acid" (abbreviated as PLGA or PLG) can be purchased in different PLA/PGA ratios with well-defined physical properties. By varying the copolymer ratio of PLA to PGA, the different copolymers of PLGA offer a large spectrum of flexibilities and variable degradation rates from a few days to years.
In a preferred embodiment, the second polymer material of the bottom layer of the matrix preferably consists of poly(glycolic acid-lactic acid) [PLGA]. In general, the higher the proportion of PGA in the PLGA composition, the higher the stability and hydrophobicity of the polymer. Again, the bottom layer will generally provide additional stability to the matrix, whereas the top layer provides a hydrophilic, cell-friendly environment that increases the survival and proliferation rate of cells on and within the top layer. As such, the second polymer material of the bottom layer has preferably a higher PGA content than the first polymer material of the top layer (and the first polymer material of the top layer has preferably a higher PLA content than the second polymer material of the bottom layer).
In one embodiment, both layers consist of PLGA, yet with different ratios of PLA to PGA. A preferred polymer material for the top layer is a 85:15 mixture of poly(L-lactid acid) (PLLA) and PGA - i.e. a polymer mixture having a lactic acid (PLA) content of about 85 mol% and a glycolic acid (PGA) content of about 15 mol%. Such a 85:15 mixture can be purchased, for instance, from Evonik Industries AG (Essen, Germany) or from Durect company (Cupertino, CA, USA) under the brand name RESOMER® RG 858 or LACTEL® Absorbable Polymers. The bottom layer poly(D,L-lactide-co-glycolide) may be a 50:50 mixture of PLLA and PLG, e.g. RESOMER® RG 502. Further preferred polymer mixtures for the top and/or bottom layer are poly(D,L-lactide-co-glycolide) 65:35, e.g. RESOMER® RG 653; poly(D,L-lactide-co-glycolide) 75:25, e.g. RESOMER® RG 752; poly(D,L-lactide-co-glycolide).
Preparation methods for preparing porous meshes from the above-mentioned synthetic polymers are well known in the art. One possibility is the use of a salt-leaching technique, as described for instance in EP 2256155
It is preferred that the top layer comprises or is at least partially covered with at least one natural polymer selected from the group consisting of collagen, gelatin, laminin, fibrinogen, albumin, chitin, chitosan, agarose, hyaluronic acidalginate and mixtures thereof, whereby collagen and laminin are preferred. The natural polymer provides the top layer with additional stability, hydrophilicity and facilitates cell proliferation.
In a particularly preferred embodiment, the first polymer material of the bottom layer essentially consists of PLGA or PGA and the second polymer material of the top layer of the matrix essentially consists of PLA alone or in combination with a natural polymer selected from the ones mentioned in the previous paragraph. Of the mentioned natural polymers, collagen is most preferred. This is because collagen is a biomolecule of the extracellular matrix (ECM) and the major component of skin and bone. Thanks to its nano-fibrous architecture it is particularly effective in promoting cell adhesion, growth and differentiated function in tissue cultures. However, it has also been found that the presence of collagen in the first polymer material particularly enhances the hydrophilic properties of the top layer of the matrix.
Notably, the term "collagen" as used in the context of the present invention encompasses naturally derived collagens and synthetically produced collagens as well as collagen derived substances, such as gelatine, which is a hydrolysed form of collagen. Also, the term "collagen" further includes all types of collagen. For instance, the natural polymer may include only one specific type of collagen, e.g. type I, or may consist of a mixture of collagen types, e.g. a mixture of type I collagen and type IV collagen. In the latter case, preference is given to the mixture containing the proteins in approximately equal percentages by weight. Collagen type I is most preferred, since it is one of the main components of natural blood vessels and provides the secondary structure with cellular attachment sites as well as tensile strength. In addition, it is one of the main components of natural blood vessels and provides a natural attachment site for cells involved in the wound healing process. Last but not least, the degradation product of collagen type I to III have also been shown to induce a chemotactic attraction of human fibroblasts, which is particularly beneficial for the intended use of the inventive matrix in surgical soft tissue repair.
In a preferred embodiment, at least one of the top layer and the bottom layer, preferably both layers, has/have a flat sheet-like shape and is/are elastically deformable to allow folding or rolling thereof. In particular, it is preferred that the whole matrix is elastically deformable, such it can be folded or rolled, and it can return to its original shape. This allows insertion of the matrix through a trocar in a laparoscopic procedure.
In general, each layer has preferably a thickness within the range of at least 0.1 mm to 20 mm, more preferably from about 1 mm to about 10 mm, even more preferably from about 1 mm to about 3 mm. It goes without saying that the two layers can also have different thicknesses.
If provided in sheet-like shape, the outer shape (when seen in top view or in longitudinal section) of the matrix can be of any kind, for example rectangular, square, circular, oval, etc., and can also be cut to suit the shape of the soft-tissue defect that is to be repaired. Preferably, the outer shape of the cross-section is circular or oval to avoid any sharp edges.
It is further preferred that the top and bottom layer - and preferably the entire matrix - has a porosity of at least 80%, preferably at least 85%, more preferably at least 90%. This porosity ensures that nutrients can diffuse through the matrix to provide a cell-friendly environment in the hydrophilic top layer that promotes cell proliferation and development. In addition, the porous structure allows incorporation of growth factors or other cell-growth stimulating molecules into the matrix, in particular the top layer.
As regards the degradation time of the matrix within the body - which will usually occur through bio-absorption of its components - it is preferred that the top layer has a faster degradation rate than the bottom layer. In particular, the degradation time of the top layer in the body preferably goes hand in hand with the formation of scar tissue that safely closes the soft tissue defect when the matrix has degraded. In particular in hernia repair it is highly preferred that the bottom layer still provides additional support by the time that the top layer has fully degraded, as this prevents the former hernia from re-opening until the scar plate that is formed over and within the degrading top layer is strong enough to withstand the abdominal pressure. In addition, the hydrophobicity of the bottom layer helps to establish a physical barrier between the scar tissue that is in formation and the underlying abdominal organs. Therefore, during the first few months when that cell growth is most prominent, adhesion formation between the new scar tissue and the intraabdominal organs is effectively prevented by the hydrophobic properties of the bottom layer. By the time that the formation of a stable scar plate that covers the former hernia is completed, the bottom layer will continue to degrade, such that generally after 12 to 24 months after implantation of the matrix, no foreign material will be left within the body.
In a preferred embodiment, the matrix has a total degradation time in a living organism of less than 24 months, with the top layer having a preferred degradation time of less than 6 months, preferably less than 4 months, and the bottom layer having a preferred degradation time of at least 4 months, preferably between 4 and 24 months. As such, the bottom layer will provide an additional support function during the first 4 to 12 months. After 24 months, the bottom layer will generally be more or less full degraded as well.
In a specific embodiment it is preferred that the degradation time for the top layer in the living organism is between 1 and 4 months, preferably about 3 months. For the bottom layer, on the other hand, it is preferred that the degradation time in the living organism is between 6 and 12 months.
Another advantage of the inventive matrix is that it allows incorporation of agents into the matrix, in particular the top layer, that are subsequently delivered to the soft tissue defect. Preferred agents are collagen types IV and V, fibronectin, laminin, hyaluronic acid, and proteoglycans. Similarly, pharmacologically active agents such as growth factors, antibiotics, antifungals, spermicidals, hormones, enzymes, and/or enzyme inhibitors can also be incorporated into the matrix.
To promote scar tissue formation in and around the area of the top layer it is preferred that the top layer further includes growth factors. Growth factors typically act as signalling molecules between cells and often promote cell differentiation and maturation. For example, epidermal growth factor (EGF) enhances osteogenic differentiation, while fibroblast growth factors (FGF) and vascular endothelial growth factors (VEGF) stimulate blood vessel differentiation (angiogenesis). In view of the matrix' use in soft tissue repair, the top layer preferably includes at least one growth factor selected from the group consisting of interleukins, acidic fibroblast growth factor, basic fibroblast growth factor (b-FGF), epidermal growth factor, insulin like growth factor, insulin like growth factor binding protein, platelet-derived growth factor (PDGF), transforming growth factor alpha, transforming growth factor beta, VEGF, and hepatocyte growth factor (HGF). These growth factors are important for regulating cell proliferation and differentiation, protein synthesis and ECM (extracellular matrix) remodelling. In particular, b-FGF, PDGF, VEGF, and HGF have shown to increase granulation, epithelialisation and capillary formation through angiogenic cytokines secretion. They have also proven to inhibit neutrophil and macrophage migration to wound location by secreting factors that inhibit migration and both IL-1α and IL-1β suppression, and to secrete anti-inflammatory factors which prevent apoptosis and improve wound healing.
In a particularly preferred embodiment, the top layer includes growth factors that are added to the matrix, in particular the top layer, in the form of secretome derived from placental mesenchymal cells. The commercially available secretome derived from (or at least comprising) stem cells from human Wharton's Jelly Stem Cell (CM-hWJSC) that were cultured in hypoxia condition was found to be particularly effective in stimulating cell attachment to and cell ingrowth into the top layer of the matrix. This stem cell secretome can be purchased e.g. from Stem Cell and Cancer Institute (PT. Kalbe Farma Tbk.).
For the preparation of the matrix, a method including the following steps can be used:
- a) preparing a first mixture I consisting of salt particulates and a dissolved first polymer material comprising at least one polymer selected from the group consisting of poly(glycolic acid) [PGA], poly(lactic acid) [PLA], poly(glycolic acid-lactic acid) [PLGA], polycaprolactone [PCL], poly(hydroxybutyrate) [PHB] and mixtures thereof, preferably consisting of at least 70% PLA;
- b) spreading the first mixture I on a surface to form a first layer;
- c) preparing a second mixture II consisting of salt particulates and a dissolved second polymer material comprising at least one polymer selected from the group consisting of PGA, PLA, PLGA, PCL, PHB and mixtures thereof;
- d) depositing a layer of the second mixture II of step c) on top of the first layer; and
- e) drying the resulting structure to obtain a two-layered biodegradable matrix with a top layer of first polymer material and a bottom layer of second polymer material.
Instead of the above steps, the matrix of the present invention may also be manufactured using 3D-printing, electro-spinning and other methods known in the art for the preparation of polymeric scaffolds.
The method may further include a step f) in which the top layer of first polymer material is covered with a natural polymer selected from the group of collagen, gelatin, laminin, fibrinogen, albumin, chitin, chitosan, agarose, hyaluronic acidalginate and mixtures thereof, preferably collagen.
In view of its later use as an implant, the matrix of the present invention is then (i.e. after step e) or f)) preferably sterilized. To this end, use is preferably made of a special sterilization technique that has been developed for this purpose. This sterilization technique allows sterilization of heat and/or UV sensitive tissues, in particular polymeric scaffolds, and is therefore not limited to the special matrix described above, but is applicable for all kinds of (heat-sensitive) articles that need to be sterilized.
Nowadays there is no doubt that sterilization is essential for almost any device and article that is used in the medical field, such as instruments, all kinds of implants and any surgical auxiliaries. In theory, numerous sterilization techniques are available, yet they are not all applicable to all substrates. Metal substrates, such as a metal instrument or an implant, for instance, can be subjected to heat sterilization using steam. This technique is typically performed in a steam sterilizer (also referred to as autoclave) using steam typically having a temperature above 120°C under pressure. Heat sterilization is, however, not suitable if the article to be sterilized is heat-sensitive. In addition, the use of steam is unsuitable for components that are biodegradable and therefore to a certain degree soluble in water. Therefore, biodegradable polymeric substrates that comprise a heat-sensitive natural polymer, such as collagen for instance, cannot be sterilized by hot steam without impairing the molecular structure of the substrate.
As an alternative, a substrate can be subjected to ethylene oxide gas sterilization or plasma sterilization. However, in as far as ethylene oxide is used, the technique has the further drawback of requiring relatively strict safety measures due to the high toxicity of the sterilizing agent.
Further sterilization techniques include radiation sterilization, in particular gamma-sterilization or X-ray sterilization. These techniques, on the other hand, have the major drawback that hydrophilic surface characteristics of the substrate are usually lost or at least substantially impaired due to the sterilization treatment.
In case of the substrate to be sterilized being a two-layered matrix in accordance with the present invention described above, it requires a method that avoids use of heat, i.e. temperatures above 40°C or 50°C, to preserve the three-dimensional polymeric structure of the matrix. In addition, the method must allow for preservation of the high hydrophilicity of the top layer during and after the sterilization procedure.
In consideration of the above, it has also been an additional object of the present invention to provide a simple process that allows thorough sterilization of the matrix without compromising the hydrophilicity of the top layer.
It has been found that the following procedure meets all these requirements and is therefore particularly well suited for the sterilization of sensitive substrates, such as the two-layered matrix of the present invention. The procedure involves the steps of
- I. providing a substrate prepared from a biocompatible and preferably biodegradable material, and
- II. subjecting the substrate to a hydrogen peroxide containing environment at a temperature below 50°C, preferably below 40°C at a reduced pressure within the range of 10-6 to 10-1 bar and for at least 2 hours, preferably at least 6 hours, most preferably about 10 hours.
The hydrogen peroxide containing environment can either be provided by H2
plasma treatment or by placing the substrate to be sterilized into a vacuum chamber, together with a source of (generally liquid) hydrogen peroxide. The plasma treatment preferably involves a low-pressure plasma treatment, in which the matrix is exposed to an ionized gas plasma at a pressure in the range of 10-2
bar and a temperature below 50°, preferably below 40°C, for at least 2 hours. Alternatively, the matrix may be placed inside a vacuum chamber and upon applying a pressure as indicated above, preferably within the range of 10-3
bar, the hydrogen peroxide evaporates, and a hydrogen peroxide-containing atmosphere will be created. Preferred treatment times are between 8 and 12 hours.
As such, this new sterilization method is very simple and straightforward in that no laborious preparation steps are required.
The surprising finding that this low-temperature hydrogen peroxide sterilization achieves a sterile and hydrophilic biodegradable article opens the possibility of a simple process for sterilizing sensitive materials without negatively affecting their hydrophilic properties.
When integrated into the method described above to prepare the inventive two-layered matrix, it is preferred that the matrix obtained in step e) or f) is then sterilized by treating it with H2
, preferably by exposing the matrix to a H2
plasma or a H2
containing atmosphere, at a temperature below 50°C, preferably below 40°C.
The treatment time of the substrate (e.g. the matrix) within the H2
containing atmosphere is preferably at least 1 hour, more preferably at least four hours, even more preferably between 4 and 12 hours. Particularly preferred treatment times are between 8 hours and 12 hours, specifically about 10 hours.
In addition, the negative pressure applied in the vacuum chamber must be sufficient to evaporate the hydrogen peroxide. It is preferably in the range 10-6
, preferably 10-3
bar. Specifically preferred are (negative) pressures of 6 to 12 mbar, , most preferably about 9 mbar.
As initially mentioned, the two-layered matrix of the present invention is particularly useful for application in the field of hernia repair. The present invention therefore also relates to the use of the inventive two-layered matrix in surgical soft-tissue repair in particular in hernia repair. Specifically, the method for hernia repair includes the steps of
- i. providing a biodegradable matrix of the present invention having a hydrophilic top layer and a hydrophobic bottom layer as described in the above sections;
- ii. making an incision through a patient's skin and abdominal tissues to access a hernia in the abdominal wall;
- iii. placing the matrix either above the defect, e.g. the abdominal wall (inguinal hernia repair according to Lichtenstein) or alternatively beneath the muscle layer of the abdominal wall (sub-lay technique) or as an intraperitoneal on lay mesh (IPOM) below the peritoneum;
- iv. closing the incision.
If desired, the matrix may be additionally attached to the abdominal muscles to prevent migration.
Preferred embodiments with respect to the structure of the matrix and its placement within the body of a patient in hernia repair are further illustrated by way of the attached figure, in which
- Fig. 1
- shows a schematic drawing of a section through a soft tissue defect, specifically a hernia, repaired with the aid of a matrix in accordance with the present invention.
The schematic drawing of Fig. 1 shows a defect (gap) 10 in muscle tissue 12 that has been bridged with a matrix 14 of the present invention. Specifically, a biodegradable matrix of the present invention having a porous hydrophilic top layer 16 and a porous hydrophobic bottom layer 18 is provided. The hydrophilic top layer 16 consists of poly(lactic acid) [PLA] and collagen. It has a water contact angle below 10° and is thus super-hydrophilic. The bottom layer 18 of the matrix consists of poly(glycolic acid-lactic acid) [PLGA] and has a water contact angle above 90°. It is thus hydrophobic. The two layers are connected to each other along a common interface 20 and form a single, two-layered matrix unit 14.
In surgical hernia repair, an incision is made through a patient's skin 22 and abdominal tissues 12 to access a hernia 10 in the abdominal wall. Then, the matrix 14 is placed either above the defect, e.g. the abdominal wall (inguinal hernia repair according to Lichtenstein) or alternatively beneath the muscle layer of the abdominal wall (sub-lay technique) or - as in the case shown in Fig. 1 - as an IPOM (intraperitoneal on lay mesh) below the peritoneum 24. The bottom layer 18 will face the intraabdominal organs, in particular the small bowel 26 and the top layer will face the hernia 10. If desired, the matrix 14 may be additionally attached to the abdominal muscles 12 and/or the peritoneum 24 to prevent migration. (Before placing the matrix, the defect in the abdominal wall may also be closed by stitches. The matrix will then be placed above or below the repaired defect to stabilize the suture and help the healing process.) The incision is then closed by closing the overlaying skin 22 by stitches 28.
After implantation, the following processes will generally occur:
As degradable structure, the matrix provides a temporary support structure for cells to migrate into the matrix, in particular the top layer of the matrix, from adjacent tissues and to proliferate. The hydrophilic properties of the top layer facing the hernia promotes ingrowth and proliferation of cells, such as muscle cells and fibroblasts, that will form new scar tissue taking over the continuously decreasing support function of the matrix. The hydrophobic properties of the bottom layer, on the other hand, does the opposite: it prevents the attachment of cells, such as inter alia inflammatory cells, fibrin or debris, to the matrix from the intraperitoneal side, i.e. the side of the matrix facing away from the hernia and towards the abdominal cavity, such that the occurrence of inflammation and the formation of adhesive tissue growth between the matrix or the newly-formed scar plate and the underlying abdominal tissues is avoided.
The top layer has a faster degradation rate than the bottom layer. The degradation of the top layer takes about 3 to 6 months and goes hand in hand with the formation of scar tissue that safely connects the rims of the former hernia with the abdominal wall. By the time that the top layer has fully degraded, the bottom layer still continues to provide additional support against the abdominal pressure and also provides a physical barrier between the newly formed scar tissue and the underlying abdominal organs. Therefore, at the time that cell growth is most prominent, adhesion formation between the scar tissue and the intraabdominal organs is effectively prevented by the hydrophobic properties of the bottom layer. In addition, if intraabdominal inflammation is present, said physical barrier also separates the inflamed tissues from the surgical wound. After about 12 months, when the formation of a stable scar plate covering the former hernia is completed, the bottom layer will generally also be essentially fully degraded and no foreign material is left within the body.
The matrix may be simply placed over the defect or additionally secured in place by stitches or other measures to prevent displacement of the matrix.
Over the days and weeks after insertion of the matrix, cells from adjacent tissues, in particular smooth muscle cells and fibroblasts, will continue to proliferate and build up scar tissue that firmly closes the hernia. Said scar tissue will safely close the hernia at the time that both layers of the matrix have fully degraded.
To prove the above-described effects, the inventive matrix has been tested in vivo
by being implanted into rats. Specifically, an experimental abdominal wall hernia in a rat was repaired with the aid of a two-layered matrix in accordance with the present invention. In this experiment, the matrix was placed below the peritoneum as shown in Fig. 1. To keep the implanted matrix in place, the matrix was attached to the muscle tissue by few stitches before closing the skin by stitches. After a healing time of six weeks, the implantation site was re-opened. It was found that no adhesions had formed between the matrix and the underlying small bowel. On the other hand, in an area that was not covered by the matrix, formation of an adhesion band from the liver rim to the abdominal wall was observed. Therefore, the in vivo
experiment confirmed that the inventive matrix successfully prevents the formation of post-surgical adhesions.
In the following sections, specific examples of ways to prepare the inventive matrix will be described in detail.
Preparation of the matrix
Sodium chloride (NaCl) particulates were ground using mortar and pestle before being sieved to obtain NaCl particulates ranging from 355 to 425 µm. 9 g NaCl particulates were put in a centrifuge tube and dried in a desiccator. The NaCl particulates were then put into an aluminium pan and a PLLA solution prepared of 1 g of PLLA pellets in 5 ml of chloroform was poured onto the NaCl particulates. The PLLA solution was mixed with the NaCl particulates and the mixture was then spread evenly in the aluminium pan to form a flat PLLA layer.
Optional Collagen Post-processing
Some matrices were also provided with a collagen coating on the PLLA layer (which will later form the top layer). To this end, the prepared PLLA layer was dried and detached from the aluminum pan. Then, a collagen solution (Collagen Type I Solution; Wako) was poured in a petri dish. The concentration of the collagen solution was chosen within the range from 0.1 to 5.0 (w/v)%, preferably 1% (w/v). The PLLA layer was immersed in the collagen solution before being placed in another petri dish and frozen in a deep freezer at -80°C for several hours before freeze-drying (also known as lyophilisation) under a vacuum of < 5 mbar (at a temperature between -50 °C and -80 °C) for at least 24 h.
To form the hydrophobic PLGA layer (which will later form the bottom layer), 9.0 g of NaCl particulates were put into a second aluminium pan and a PLGA solution of 1 g of PLGA pellets in 5 ml of chloroform was prepared. The PLGA solution was mixed with the NaCl particulates. Then the PLGA/NaCl-mixture was poured on top of the PLLA layer (either with or without collagen coating) provided in the first aluminium pan and spread evenly to form a matrix with a PLGA layer on top of the PLLA layer.
The PLLA/PLGA-NaCl matrix was detached from the aluminum pan and dried in a vacuum chamber under -0.1 MPa for 3-4 days.
The resulting dried PLLA/PLGA-NaCl matrices were put in a beaker, immersed in ddH2
O (twice deionized water) and kept in a linear shaking bath at 25°C (room temperature), at 60 rpm for 48 hours to leach/wash out the NaCl particulates. The water in the beaker was exchanged every 1-2 hours. The two-layered PLLA/PLGA matrices were removed from the beaker and dried in the fume hood overnight.
The matrices were prepared with pores having a diameter within the range of 355 - 425 micrometers.
Either with collagen coating or without, the matrices were subsequently sterilized by placing them in a H2
-containing environment at a temperature below 40° for about 10 hours. The H2
-containing environment was created within a vacuum chamber, by placing the matrix into the chamber, together with an open flask or dish containing a H2
solution and by subsequently evacuating the chamber to evaporate the H2
O2. The H2
solution comprises H2
in an amount of 30% by volume or less. The treatment time depends highly on the pressure within the chamber and the concentration of the H2
solution. The pressure within the chamber is such, that evaporation of the hydrogen peroxide occurs. Preferred (negative) pressures are in the range of 10-2
bar. Preferred treatment times are between 8 and 12 hours, most preferably about 10 hours.
Static contact angle measurements, sessile drop method
Contact angle measurements were performed in order to determine the degree of hydrophilicity or hydrophobicity. Usually, the contact angles of the top and bottom layers of the matrix were determined by static contact angle measurements, using a sessile drop test with ultrapure water (EasyDrop DSA20E, Kruss GmbH). The droplet size for the contact angle measurements was set to 0.1 µl. Contact angles were calculated by fitting a circular segment function to the contour of the droplet placed on the surface (circle fitting procedure).
1. Biodegradable matrix (14) for preventing post-surgical adhesions, in particular after soft tissue repair following abdominal surgery, within the body of a mammal, the matrix including
a top layer (16) made of a first biocompatible polymer material and
a bottom layer (18) made of a second biocompatible polymer material,
the first polymer material and the second polymer material both comprising at least one polymer selected from the group consisting of poly(glycolic acid), poly(lactic acid), poly(glycolic acid-lactic acid), polycaprolactone, poly(hydroxybutyrate) and mixtures thereof;
wherein both layers (16, 18) are formed as porous scaffolds,
the top layer (16) being hydrophilic, having a water contact angle of less than 75° and
the bottom layer (18) being hydrophobic, having a water contact angle of more than 90°.
2. Matrix as claimed in Claim 1, wherein the top layer (16) having a water contact angle of less than 60°, preferably less than 45°, more preferably less than 25°, even more preferably less than 15°, most preferably within the range of 0° to 10°.
3. Matrix as claimed in Claim 1 or 2, wherein the two layers (16, 18) are either integrally formed or firmly connected with one another along a common interface 20.
4. Matrix as claimed in Claim 1 or 2, wherein the two layers (16, 18) are provided as two individual structures that are separate from one another.
5. Matrix as claimed in one of Claims 1 to 4, wherein the first polymer material of the top layer (16) has a material composition that is different from the one of the second polymer material of the bottom layer (18) .
6. Matrix as claimed in Claim 5, wherein the first polymer material consists to at least 70%, preferably at least 85%, of poly (lactic acid), and more preferably essentially consists of poly(lactic acid).
7. Matrix as claimed in one of Claims 1 to 6, wherein at least one, preferably each, of the two layers (16, 18) has a flat sheet-like shape and is elastically deformable to allow folding or rolling thereof.
8. Matrix as claimed in one of Claims 1 to 7, having a total degradation time in the living organism of less than 24 months, with the top layer having a preferred degradation time of less than 6 months, preferably less than 4 months, and the bottom layer having a preferred degradation time of more than 4 months, preferably between 4 and 12 months.
9. Matrix as claimed in one of Claims 1 to 8, wherein one of the two layers (16, 18), preferably the top layer (16), has a faster degradation rate than the other layer.
10. Matrix as claimed in one of Claims 1 to 9, wherein the top layer (16) comprises or is covered with at least one natural polymer selected from the group consisting of collagen, gelatin, laminin, fibrinogen, albumin, chitin, chitosan, agarose, hyaluronic acidalginate and mixtures thereof, whereby collagen and laminin are preferred.
11. Matrix as claimed in one of Claims 1 to 10, wherein the top layer (16) further comprises growth factors, preferably selected from the group consisting of interleukins, acidic fibroblast growth factor, basic fibroblast growth factor, epidermal growth factor, insulin like growth factor, insulin like growth factor binding protein, platelet-derived growth factor, transforming growth factor alpha, transforming growth factor beta, vascular epithelial growth factor, and hepatocyte growth factor .
Method for preparing a matrix according to Claim 1 to 11, by
a) preparing a first mixture I of salt particulates and a dissolved first polymer material comprising at least one polymer selected from the group consisting of poly(glycolic acid), poly(lactic acid), poly(glycolic acid-lactic acid), polycaprolactone, poly(hydroxybutyrate) and mixtures thereof, preferably poly(lactic acid);
b) spreading the first mixture I on a surface to form a first layer;
c) preparing a second mixture II of salt particulates and a dissolved second polymer material comprising at least one polymer selected from the group consisting of poly(glycolic acid), poly(lactic acid), poly(glycolic acid-lactic acid), polycaprolactone, poly(hydroxybutyrate) and mixtures thereof, preferably poly(glycolic acid) and/or poly(glycolic acid-lactic acid);
d) depositing a layer of the second mixture II of step c) on top of the first layer of step b); and
e) drying the resulting structure to obtain a two-layered biodegradable matrix (14) with a bottom layer (18) of second polymer material and a top layer (16) of first polymer material.
13. Method as claimed in Claim 12, further including a step d2) of covering the top layer (16) of the matrix (14) obtained in step d) with a natural polymer selected from the group of collagen, gelatin, laminin, fibrinogen, albumin, chitin, chitosan, agarose, hyaluronic acidalginate and mixtures thereof, preferably collagen.
14. Method as claimed in Claim 12 or 13, further including a step f) of sterilizing the resulting matrix (14) by treating it with hydrogen peroxide.
15. Method as claimed in Claim 14, wherein the hydrogen peroxide treatment in step f) is conducted by exposing the matrix (14) to a H2O2 plasma or a H2O2 containing atmosphere, under reduced pressure, preferably in the range of 10-3 to 10-2 bar, and for at least 2 hours, preferably at least 6 hours, more preferably at least 8 hours, most preferably for about 10 hours.