Biohybrid articular surface replacement

The invention relates to a biohybrid articular surface replacement in the form of a three-dimensional, porous carrier, in which cartilage cells can be cultured in vitro and/or in vivo to a three-dimensional cell union and which following cell growth and optionally after tissue development, can be placed on the exposed bone in the vicinity of a defective articular surface, wherein on the side of the carrier intended for engagement with the bone it has an agent for aiding osseous integration.

BACKGROUND ART
 The invention relates to a biohybrid joint or articular surface
 replacement.
 For the treatment of damaged articular cartilages, e. g. caused by
 deformities, injuries or degenerative diseases, development work is
 concentrated on the production of replacement cartilages, which can be
 implanted in the patient.
 Of late processes for producing implants from cell cultures have become
 known, such as are e. g. described in the Sittinger international patent
 application WO 94/20151. Cartilage cells are produced in vitro in cavities
 of a three-dimensional carrier structure.
 The Vacanti WO 90/12603 discloses a system for the in vivo neomorphogenesis
 of cartilage cells from a cell culture.
 The cartilage implants known from the prior art suffer from a number of
 disadvantages.
 A reliable fixing in the subchondral bone is important for a completely
 satisfactory articular replacement surface replacement. For this purpose
 the implant must be held by complicated suture techniques or fastening
 clips.
 An important problem in the therapy of pathological changes to articular
 surfaces is the penetration of synovial fluid, whose constituents, such as
 hyaluronic acid, impair regeneration and growing in. The synovial fluid,
 which flushes round the inserted implant, prevents an attachment of the
 cartilage structure to the defect boundaries and to the bone.
 The hitherto known cartilage substitute materials for the treatment of
 articular defects are unable to fulfill the requisite criteria for a
 successful, durable healing, such as reliable and simple fastening to the
 bone, rapid growing in, physiological restoration of the articular
 structure and permanent functionality.
 The problem therefore arises of providing an articular surface replacement,
 which is formed from cartilage cells in a three-dimensional structure,
 which is simple and reliable to produce under standard biomedical
 conditions and with existing equipment.
 SUMMARY OF THE INVENTION
 This problem is solved by a biohybrid articular surface replacement in the
 form of a three-dimensional, porous carrier, in which cartilage cells can
 be cultured in vitro and/or in vivo to a three-dimensional cell union and
 following cell growth, and optionally after the development of tissue, can
 be placed on the exposed bone in the vicinity of (that is in place of) a
 defective articular surface and which is characterized in that the
 carrier, on the side intended for application to the bone, has material
 for aiding osseous integration.
 In the following said material for aiding osseous integration is called
 bone integration aid.

DETAILED DESCRIPTION OF THE INVENTION
 For producing replacement cartilage cells, there can firstly be a cellular
 proliferation of profilating cartilage cells (dedifferentiated, so-called
 fibroblast-like cells). This can e. g. take place as a flat or a real cell
 growth in a cell culture vessel. Following a certain proliferation of the
 cells, the cells are then rendered specific again (differentiated) and
 introduced into a suitable matrix for further, three-dimensional growth.
 In particular, the cartilage cells can be injected into the matrix or can
 be sucked or centrifuged into the matrix under a slight vacuum.
 Preferably, a few weeks prior to the planned implantation, such a matrix
 or carrier structure can be provided with autologeous cells of the
 patient.
 The porous carrier can in particular be of a material resorbable in the
 body under physiological conditions. This can have a natural or synthetic
 origin. Advantageously the porous carrier is in the form of a nonwoven,
 foam, sponge, sintered material or a textile structure.
 The porous carrier of resorbable material can be characterized in that it
 has a porosity of more than 65%, particularly more than 75%. The carrier
 is preferably a highly porous carrier. It can have a porosity of more than
 90%, preferably more than 95%.
 The porous carrier of resorbable material can be formed from hydrolytically
 degradable polymers, particularly hydrolyzable polymers of .alpha.- and
 .beta.-hydroxycarboxylic acids. Examples of such biodegradable materials
 are polymers based on polyglycolic acid, polymers of glycolic acid (PGA),
 polylactides, polymers of L-lactide (P-L-LA), D-lactide (P-D-LA),
 DL-lactide (P-DL-LA), polydioxanone, polycaprolactone, copolymers and
 terpolymers of the aforementioned monomers and/or mixtures of the
 aforementioned polymers. Advantageously use is made of copolymers of
 glycolic acid and lactic acid in a ratio of 99:1 to 1:99, particularly
 89:11 to 70:30 or 30:70 to 11:89. It is also possible to use with
 advantage copolymers of L-lactide and DLlactide in a ratio of 99:1 to
 1:99, more particularly 99:1 to 70:30. The copolymers, terpolymers and/or
 mixtures of the aforementioned monomers or polymers to be used according
 to the invention can be provided, for the purpose of improving their
 characteristics, with plasticizing substances, particularly caprolactone,
 trimethylene carbonate (TMC) triethyl citrate (TEC) and/or acetyl butyl
 citrate (AtBC).
 Whilst taking the corresponding precautions for preventing immunological
 problems or infectious diseases, the porous carrier can be made from
 natural, resorbable substances, advantageously from collagen or hyaluronic
 acid and derivatives thereof.
 The porous carrier can be formed from foam, sponge, sintered material or a
 textile structure, preference being given to staple fibre or spunbonded
 fabrics.
 In the case of porous carriers made from fibrous materials, such as
 nonwovens or other textile fabrics, the fibre diameter can advantageously
 be about 1 to 50 .mu.m, particularly 5 to 15 .mu.m.
 For the better control of chondrosis and for influencing the degradation
 time, porous carriers can be made from a combination of fibrous materials.
 This can take place by the use of fibre blends, or by mixed fibres,
 biconstituent fibres or bicomponent fibres. A controlled degradation can
 advantageously be achieved by the use of bicomponent fibres of the
 core/jacket or island type.
 Laminated carriers (e.g. nonwovens) can have a thickness of about 1 to 5
 mm. For example, in the case of implants for use on the knee of a human,
 layer thicknesses of 1 to 3 mm can be used. For applications to hips, as a
 result of the higher stressing, greater thicknesses are appropriate.
 The articular surface replacement according to the invention can be
 characterized in that the bone integration aid is firmly bound to the
 porous carrier. Advantageously the bone integration aid is partially
 embedded in a sealing agent. Examples of sealing agents suitable in
 accordance with the invention are films or membranes of resorbable
 polymers mentioned in connection with the porous carrier.
 The bone integration aid can be present in finely divided form, the average
 particle size being preferably between about 10 and 500 .mu.m,
 particularly between 50 and 100 .mu.m.
 According to the invention the bone integration aid can be present in a
 quantity, which covers the surface of the side facing the bone by at least
 about 30 to 100%, preferably 95 to 100%
 Advantageously the bone integration aid is formed from an inorganic matrix
 of the bone and in particular comprises the latter.
 Examples of preferred bone integration aids according to the invention are
 hydroxyapatite ceramic, tricalcium phosphate ceramic, mixed ceramics
 and/or calcium carbonate. Amorphous forms of inorganic bone matrix
 materials are also possible.
 The bone integration aid can in particular have a porous structure, the
 porosity being about 30 to 80 vol. % and the pore size of about 10 to 150
 .mu.m. The bone integration aid can also comprise a cohesive, highly
 porous plate.
 According to an embodiment of the invention the bone integration aid has a
 biological origin and in particular comprises high temperature-treated
 bone. Such a high temperature treatment can in particular take place at
 temperatures above 1000.degree. C. Bone material treated in this way is a
 biological hydroxyapatite ceramic.
 According to another embodiment of the invention the bone integration aid
 can be formed from a ceramic having a completely synthetic origin. For
 producing such a ceramic, experts can use production methods known from
 the prior art.
 For the production of an articular cartilage biohybrid, a cultured
 articular cartilage in a suitable three-dimensional space structure
 according to the invention, it is necessary to have a base, which forms
 with the bone a permanent, non-positive connection. It is in particular
 possible to use a hydroxyapatite ceramic granular material, which in
 bioactive and osteoconductive manner aids a rapid, substantial integration
 by the growing of the interstitial matrix on the synthetic, porous
 material.
 According to the invention the granular material can be incorporated into a
 resorbable polymer film. The articular surface replacement according to
 the invention can be characterized in that the particles of the bone
 integration aid are partly embedded in a layer and part of the surface
 thereof is exposed. Thus, following the degradation of the polymer
 constituents of the biohybrid implant, the articular cartilage with its
 matrix is fixed to a ceramic base, which in turn has a reliable hold in
 the subchondral bone.
 According to the invention the hydroxyapatite ceramic particles can be in a
 monolayer in a polymer film. As an example for polymer films suitable
 according to the invention are given films or membranes of resorbable
 polymers mentioned in conjunction with the porous carrier.
 Preference is given to the use of a polymer film having a thickness of
 approximately 100 to 300 .mu.m. With embedded particles the polymer film
 can in particular have a thickness of up to 600 .mu.m. The particle size
 in the monolayer can be 10 to 500 .mu.m, particularly 50 to 100 .mu.m.
 The articular surface replacement shall be adapted in an optimal manner to
 the respective surface of the articular region to be replaced. According
 to the invention the three-dimensional, porous carrier and/or the bone
 integration aid can be provided in a concave, convex or any other curved
 shape adapted to the natural articular cartilage to be replaced.
 Advantageously the bone integration aid can be flat at the side facing the
 bone to facilitate the implantation procedure.
 The appropriate shape can be determined non-invasively by picture
 generating diagnosis like X-ray computer tomography and NMR respectively,
 and be remodelled as a model or a matrix using any rapid prototyping
 process.
 The articular surface replacement according to the present invention can be
 characterized in that materials can be provided, which protect the contact
 surface between implant and defect boundaries on the cartilage and between
 bone integration aid and bone in the implanted state against access or
 admission of fluid, particularly synovial fluid.
 According to the invention the synthetic support structure towards the
 defect boundary can be defined in such a way that it is impermeable for
 synovial fluid and cells. This makes it possible to keep away substances
 impairing a reliable anchoring of the implant in the bone.
 According to an embodiment of the invention with respect to the articular
 surface replacement a sealing layer can be provided for protecting the
 contact area between implant and defect boundaries on the cartilage and
 between bone integration aid and bone in the implanted state against the
 access of fluid. An example of a sealing material suitable according to
 the invention is constituted by films or membranes from the resorbable
 polymers mentioned in conjunction with the porous carrier.
 In a further embodiment of the invention with respect to the articular
 surface replacement it is possible to provide a semipermeable membrane for
 the protection of the contact area between implant and defect boundaries
 on the cartilage and between bone integration aid and bone in the
 implanted state against the access of fluid. An example of semipermeable
 membrane suitable according to the invention is provided by films or
 membranes of the resorbable polymers mentioned in conjunction with the
 porous carrier.
 The cut-off of such a membrane can in particular be less than 60,000
 Dalton. In this way it is possible to prevent larger molecules, such as
 e.g. proteins, and cells from passing through the membrane.
 In yet another embodiment of the invention with respect to the articular
 surface replacement a microporous membrane with a pore size preferably
 below 1 .mu.m is provided for protecting the contact area between implant
 and defect boundary on the cartilage and between bone integration aid and
 bone in the implanted state against the access of fluid. An example of
 microporous membrane suitable according to the invention is constituted by
 microfiber nonwovens or films or membranes from resorbable polymers
 mentioned in conjunction with the porous carrier.
 Advantageously a protecting layer is provided, which in particular forms a
 barrier for cells and synovial fluid, but which is permeable in such a way
 as to permit metabolism. For a rapid adhesion and a substantial
 integration of the implant, an unhindered metabolism is important.
 Examples of polymer materials from which it is possible to produce a
 separating layer, sealing layer, polymer film, closed layer, protective
 layer, membranes, etc. are constituted by polylactides, polymers of
 L-lactide (P-L-LA), D-lactide (P-D-LA), DL-lactide (P-DL-LA),
 polydioxanone, polycaprolactone, copolymers and terpolymers of said
 monomers and/or mixtures of said polymers, together with copolymers or
 mixtures of the aforementioned polymers with polyglycolic acid.
 Advantageously use is made of copolymers of glycolic acid and lactic acid
 in a ratio of 90:10 to 1:99, particularly 30:70 to 11:89. It is also
 advantageous to use copolymers of L-lactide and DL-lactide in a ratio of
 99:1 to 1:99, particularly 99:1 to 70:30. The copolymers, terpolymers
 and/or mixtures of the aforementioned monomers or polymers to be used
 according to the invention can be provided, for the purpose of improving
 their characteristics, with plasticizing substances, particularly
 caprolactone, trimethylene carbonate (TMC), triethyl citrate (TEC) and/or
 acetyl butyl citrate (AtBC).
 Whilst taking the corresponding precautions for preventing immunological
 problems or infectious diseases the separating layer, sealing layer,
 polymer film, closed layer, protective layer, membranes, etc. can be made
 from natural, resorbable substances, advantageously from collagen or
 hyaluronic acid and derivatives therof.
 Advantageously the polymers to be used for the inventive separating layers,
 etc. are processed from a solution. In another embodiment of the invention
 the polymers to be used for the inventive separating layer can be
 thermoplastically processable. In another embodiment of the invention the
 polymers to be used for the inventive separating layer can be processed in
 crosslinking manner.
 The articular surface replacement according to the invention can
 advantageously be characterized in that the closed layer, at least during
 the initial growing in time following implantation, is substantially
 impermeable for fluids.
 According to another embodiment the articular surface replacement according
 to the invention can be characterized in that with it is associated a
 cover film intended for covering the top side of the carrier remote from
 the bone integration aid. Advantageously the cover film is fixed to the
 carrier and is in particular adhesively/cohesively physically associated.
 Materials for the inventive cover film can be polymer materials, as
 proposed hereinbefore for the separating layer. The covering film can in
 particular be of resorbable material. The covering film is preferably
 constituted by a porous membrane, which prevents any penetration of
 synovial fluid.
 Advantageously the covering film is larger than the surface of the carrier
 top side and has projecting edges, which serve to cover the separating
 line between the articular surface replacement and the natural articular
 cartilage surface.
 For fixing the covering film to the porous carrier use is advantageously
 made of surgical suture material of bioresorbable material. The
 degradation time of the suture material can be in the range of the
 degradation time of the resorbable covering film. A reliable fixing can be
 ensured if the resorption time of the suture material is in particular
 longer than that of the covering film. Suitable resorption times for the
 film are e.g. 1 to 4 months. Suture materials according to the invention
 based on polyglycolic acid are more particularly preferred. Other fixing
 media are tissue adhesives, resorbable pins or clips or collagen.
 Alternatively or in addition to the covering film, with the inventive
 articular surface replacement can be associated a resorbable sealing
 compound, which is introduced between the porous carrier and the defect
 boundary or which is applied to the surface boundary line between implant
 and articular surface, so as to prevent a penetration of macromolecular
 constituents of the synovial fluid. The resorbable sealing compound can
 e.g. be a tissue adhesive or collagen.
 Advantageously, in the articular surface according to the present invention
 the shape of the three-dimensional porous carrier and the bone integration
 aid can be curved according to the natural articular surface to be
 replaced. In a particularly preferred embodiment the surface of the bone
 integration aid facing the bone can be flat.
 For use as an implant the articular surface replacement according to the
 invention is sterilized in an appropriate manner. An appropriate
 sterilization process can be chosen from conventional physical or chemical
 methods for inactivating microorganisms or a combination of such methods.
 One possible sterilization method involves the treatment with ionizing
 radiation, such as e.g. irradiation with .beta.- or .gamma.-rays in the
 range of about 0.1 to 10 Mrad, particularly 0.8 to 2.5 Mrad. According to
 a possible embodiment of the invention a sterilization performed with the
 aid of irradiation can be simultaneously used for controlling the
 degradation behaviour of the articular surface replacement produced in
 accordance with the invention.
 In the case of treatment with .gamma.-rays there can be a chain splitting
 in the case of resorbable polymer material, which improves the
 resorbability in the body environment, but at the same time leads to no
 significant loss of strength.
 For improving the hydrophilicity of the polymer material modifications can
 be made to the polymer surface. Advantageously there is a modification of
 functional groups in the case of a plasma treatment by reactions on the
 surface of the material. This can also bring about a rise in the
 hydrophilic properties. According to preferred embodiments such a
 hydrophiling and/or functionalizing of the surface can be carried out with
 low temperature plasma. Advantageously the modification reactions are
 performed in an inert gas atmosphere, oxygen, CO2 and/or SO2. According to
 another embodiment of the invention a plasma grafting can take place with
 monomers and/or oligomers for polymer surface modification purposes. A
 surface modification can facilitate the colonization with cells and
 consequently favourably influences the growing in of the implant and the
 regeneration of the treated joint.
 To facilitate regeneration after implantation, the implant according to the
 invention can be provided with growth factors in an effective
 concentration. It is possible to use both growth factors for cartilage
 cells, growth factors for bone cells or combinations thereof. Growth
 factors for bone cells are, according to the invention, preferably
 incorporated into the film for the integrating agent. Examples are growth
 factors known in connection with physiology and medicine, such as e.g.
 osteogenic protein, BFGF (basic fibroblast growth factor), BMP (bone
 morphogenic protein), rh BMP (re-combinant human bone morphogenic
 protein), TGF-.beta. (transforming growth factor), IGF (insulin-like
 growth factor) and EGF (endothelial growth factor). Suitable growth factor
 concentrations are about 0.1 to 50 ng/ml.
 Fluctuations in the pH value can occur during the resorption of the
 biodegradable polymers used for the inventive biohybrid articular surface
 replacement. Advantageously basic salts can be introduced into the
 polymers and/or the pores of the implant for buffering purposes. Examples
 of buffer salts are calcium carbonate, sodium carbonate, sodium tartrate
 and/or other buffer systems suitable under physiological conditions. The
 buffer compounds are advantageously used in a concentration of about 0.1
 to 20 wt. %, preferably 1 to 10 wt. %, based on the resorbable polymer
 weight.
 The articular surface replacement according to the invention makes
 available an implant for restoring a damaged articular cartilage, which
 permits a culturing of a functional cartilage transplant with autologous
 cartilage and ensures a reliable anchoring in the subchondral bone. To
 improve the anchoring of the implant in the bone, it is possible
 beforehand to punch, mill or cut the defect to size, so that a
 correspondingly adapted implant structure can be pressed into the same.
 The implant piece can be preferably cylindrically formed beforehand from a
 cartilage substitute previously produced in large area form.
 Advantageously diameters of about 10 to 15 mm are used.
 EXAMPLES
 Further features and details of the invention can be gathered from the
 following description of preferred embodiments relative to examples and
 with reference to the attached drawings. The examples serve to illustrate
 preferred embodiments and the invention is in no way restricted thereto.
 Changes and modifications apparent to the expert are possible without
 leaving the scope of the invention.
 In the drawings FIG. 1 shows an articular surface replacement according to
 the invention, as illustrated in example 1, whilst FIG. 2 shows an
 articular surface replacement according to the invention, as illustrated
 in example 2.
 Example 1
 A porous carrier 1 is formed as a nonwoven structure from resorbable
 polymer fibres, produced from a copolymer of glycolic acid and lactic
 acid. The carrier 1 has a pore volume of 95% and is firmly connected to a
 bone integration aid 2. Granular hydroxyapatite ceramic with an average
 particle size of 0.3 mm is used as the bone integration aid. For the
 connection of porous carrier 1 and bone integration aid 2 is provided a
 sealing layer 3 of a resorbable polymer membrane, produced from the same
 copolymer of glycolic acid and lactic acid. The main function of the
 polymer membrane is to protect the hydroxyapatite ceramic and the
 subchondral bone 5 located thereunder after implantation from the
 integration-inhibiting synovial fluid.
 Example 2
 A porous carrier 1 in accordance with example 1 is provided with a covering
 layer 4 of a resorbable polymer membrane, produced from a
 polyglycolidetrimethylene carbonate copolymer. The polymer membrane is
 firmly connected to the porous carrier 1 by a central button suture,
 produced with resorbable suture material from polyglycolic acid. The
 membrane covers the fitting gap 7 of the pressed in implant and is
 suitable, following a corresponding fixing to the surrounding cartilage 6,
 for protecting the complete implant and connecting body tissue against the
 penetration of integration-inhibiting synovial fluid. The bone integration
 aid 2 comprises a plate of porous hydroxyapatite ceramic, which permits a
 particularly firm, primary anchoring in the case of a corresponding
 preparation of the implant location.