EP0250570A1 - Transformation et produits ceramiques - Google Patents

Transformation et produits ceramiques

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Publication number
EP0250570A1
EP0250570A1 EP87900617A EP87900617A EP0250570A1 EP 0250570 A1 EP0250570 A1 EP 0250570A1 EP 87900617 A EP87900617 A EP 87900617A EP 87900617 A EP87900617 A EP 87900617A EP 0250570 A1 EP0250570 A1 EP 0250570A1
Authority
EP
European Patent Office
Prior art keywords
particles
hydroxylapatite
agglomerates
mesh
agglomerate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP87900617A
Other languages
German (de)
English (en)
Inventor
Ronald L. Salsbury
Don J. Henderson
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Orthomatrix Inc
Original Assignee
Orthomatrix Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Orthomatrix Inc filed Critical Orthomatrix Inc
Publication of EP0250570A1 publication Critical patent/EP0250570A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • C04B35/63—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B using additives specially adapted for forming the products, e.g.. binder binders
    • C04B35/632—Organic additives
    • C04B35/634—Polymers
    • C04B35/63404—Polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • C04B35/63416—Polyvinylalcohols [PVA]; Polyvinylacetates
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02—Prostheses implantable into the body
    • A61F2/28—Bones
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
    • A61L27/02—Inorganic materials
    • A61L27/12—Phosphorus-containing materials, e.g. apatite
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/447—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on phosphates, e.g. hydroxyapatite
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • C04B35/63—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B using additives specially adapted for forming the products, e.g.. binder binders
    • C04B35/632—Organic additives
    • C04B35/634—Polymers
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • C04B35/63—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B using additives specially adapted for forming the products, e.g.. binder binders
    • C04B35/632—Organic additives
    • C04B35/634—Polymers
    • C04B35/63404—Polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • C04B35/63444—Nitrogen-containing polymers, e.g. polyacrylamides, polyacrylonitriles, polyvinylpyrrolidone [PVP], polyethylenimine [PEI]
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • C04B35/63—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B using additives specially adapted for forming the products, e.g.. binder binders
    • C04B35/632—Organic additives
    • C04B35/636—Polysaccharides or derivatives thereof
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • C04B35/63—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B using additives specially adapted for forming the products, e.g.. binder binders
    • C04B35/632—Organic additives
    • C04B35/636—Polysaccharides or derivatives thereof
    • C04B35/6365—Cellulose or derivatives thereof
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • C04B35/63—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B using additives specially adapted for forming the products, e.g.. binder binders
    • C04B35/638—Removal thereof
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02—Prostheses implantable into the body
    • A61F2/30—Joints
    • A61F2/3094—Designing or manufacturing processes
    • A61F2002/30968—Sintering
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2310/00—Prostheses classified in A61F2/28 or A61F2/30 - A61F2/44 being constructed from or coated with a particular material
    • A61F2310/00005—The prosthesis being constructed from a particular material
    • A61F2310/00179—Ceramics or ceramic-like structures
    • A61F2310/00293—Ceramics or ceramic-like structures containing a phosphorus-containing compound, e.g. apatite

Definitions

  • the invention disclosed in this application relates to a novel method of processing sinterable powders into sintered ceramic products involving agglomeration of fine particles with a binding agent and extraction of the binding agent from the agglomerates prior to sintering.
  • This application also relates to novel forms of aluminum oxide, hydroxylapatite, and tricalcium phosphate ceramic products prepared in accordance with the method of this invention, as well as novel intermediate products useful to prepare the novel ceramic products of this invention.
  • Bone prostheses are often needed for temporary or permanent use in man or animals.
  • a wide variety of different biocompatible materials have been developed for use as bone prostheses, including, for example, natural or synthetic mineral materials, metals, such as VitalliumTM, stainless steel and chromium alloys, as well as organic resins, such as silicone rubbers.
  • the foregoing materials may be employed, for example to: (1) replace a portion of bone which has been lost due to accident or disease, or (2) reinforce a portion of bone which has atrophied or suffered a reduction in mineral content.
  • the alveolar ridge becomes abnormally thin and unable to support either natural or artificial teeth.
  • the support or rebuilding of the alveolar ridge has, therefore, become an important step in the treatment of those individuals suffering from a weakening in the alveolar ridge due to periodontal disease or other causes.
  • Mineral materials of both synthetic and natural origins have been employed for bone restorative purposes in the alveolar ridge and, hence, to prevent tooth loss due to bone loss in the alveolar ridge.
  • Hydroxylapatite is a naturally occurring mineral present in phosphate rock. Hydroxylapatite also constitutes the mineral portion of natural bone and tooth. As such it is highly biocompatible and has a thermal coefficient of expansion quite similar to tooth enamel.
  • fine dry particles of a hydroxylapatite powder are agglomerated with a binding agent into sinterable spheroidal agglomerates.
  • the binding agent is removed from the spheroidal agglomerates and then they are sintered to provide spheroidal ceramic particles of hydroxylapatite having a uniform network of icropores extending throughout the ceramic product.
  • U.S. Patent No. 4,097,935 sets forth a description of a method for preparing a maximally densified, pore-free hydroxylapatite ceramic body.
  • the dense, pore-free ceramic body described therein may be prepared by sintering (under specified conditions) a shaped body or mass prepared from an aqueous gelatinous precipitate of hydroxylapatite.
  • the '935 patent teaches away from the use of both products and processes which employ fine particles of hydroxylapatite as starting materials in the preparation of the dense, pore-free ceramic products described in the '935 patent.
  • the method of this invention employs dry particulate hydroxylapatite as the starting material in a novel method employed to prepare porous hydroxylapatite ceramic particles having a network of micropores extending throughout the ceramic product.
  • the '935 patent also discloses means for introducing pores into the ceramic bodies produced in accordance with the method described in that patent.
  • pores may be introduced by drilling or machining holes in the non-porous ceramic product, or by mixing an organic binder with a body of the gelatinous hydroxylapatite precipitate prior to sintering.
  • the binder is said to volatilize during sintering to produce pores in the ceramic product.
  • the sintered body would then have to be ground, or comminuted in some other way to provide a particulate ceramic product.
  • a binding agent is not added to a gelatinous precipitate of hydroxylapatite, and in producing applicant's final ceramic it is not a sinterable body prepared by adding a binding agent to an aqueous gel which is ultimately sintered.
  • the binding agent is employed to agglomerate together fine dry particles of hydroxylapatite, and it is applicant's novel agglomerate of dry hydroxylapatite particles which is sintered in accordance with the method of the present application. hydroxylapatite particles which is sintered in accordance with the method of the present application.
  • Biocompatible compositions suitable for use as a dental filling material have been prepared by mixing finely divided ceramics such as sintered hydroxylapatite with a hardenable. binder material.
  • finely divided ceramics such as sintered hydroxylapatite
  • moist ceramic particles of hydroxylapatite have been employed as a biocompatible packing material to fill the voids or lesions caused by advanced periodontal diseases.
  • the ceramic particles used have typically been employed in the form of very finely divided ceramic powders made up of particles in the range of about 10 to about 60 mesh.
  • Fine particles of calcium phosphate ceramics suitable for use in such filling or packing compositions may be prepared by grinding larger particles or masses of the ceramic down to fine particles within the desired particle size range.
  • the grinding step may be conducted before or after sintering.
  • particles larger and particles smaller than desired must be separated by sieving or by another particle classification process, from the mass of particles produced by the grinding step.
  • grinding processes typically yield a fraction of ceramic particles which are smaller than the desired particle size range, and which are, often simply discarded as waste.
  • the ceramic particles produced by grinding are typically not uniform in shape, and possess sharp edges or "points" which could lead to local inflammation when placed in contact with tissue.
  • the term "mesh” as used herein refers to particle size as determined on standard sieves and that while there is some variation in the screen size used with different standards those variations are so small, e.g., See, Kirk- Othmer Encyclopedia of Chemical Technology 18:318- 319, 2d ed. (1969), that they are insignificant for purposes of this invention. Accordingly, the mesh sizes may be measured in accordance with e.g., U.S. Bureau of Standards, British Standard, Tyler Standard, or the like.
  • Ground hydroxylapatite particles and other ceramic particles having sharp edges or points can be mechanically treated to render the particles substantially spheroidal in shape and smooth.
  • mechanical procedures involve extensive milling to remove the sharp edges from the ceramic particles. The process itself is very cumbersome, and the yields quite low.
  • the spheroidal ceramic particles produced by the process of this invention are free of sharp edges or ridges capable of producing local irritation when placed in contact with tissue.
  • the spheroidal ceramic particles of this invention are suitable for use as the ceramic component of hardenable binder compositions formulated for use for dental or bone restorative processes.
  • this invention provides a high-yield method for preparing sintered ceramic particles which comprises the steps of binding together fine particles of a sinterable inorganic powder to provide sinterable particulate agglomerates within a desired size range.
  • the fine particles of the sinterable powder are bound together to form the agglomerate with a binding agent, such as polyvinyl alcohol, hydroxypropyl cellulose, polyvinyl pyrrolidone, starch, pregelatinized starch or the like.
  • the binding agent is removed by an extraction step and the agglomerate may then be sintered to provide the final particulate ceramic product.
  • fine particles of sinterable hydroxylapatite and/or whitlockite are agglomerated together with a binding agent to provide sinterable agglomerates which are spheroidal in shape.
  • the agglomerate is subjected to liquid extraction or elevated temperatures in order to substantially eliminate the binder from the agglomerate prior to subjecting the agglomerate to higher temperatures in order to complete the sintering process.
  • the calcium phosphate (e.g. hydroxylapatite and/or tricalcium phosphate) based agglomerate of this invention is sintered at elevated temperatures, the individual inorganic particles which comprise the agglomerate meld together to provide strong, free-flowing, structurally stable ceramic particles.
  • the finally sintered agglomerate will include a network of micropores extending throughout the particles.
  • the microporous structure of the particle provides sites for tissue ingrowth and attachment, while the smooth surface of the particles prevents the inflammatory response noted in connection with the rough and irregular surfaces of untreated ground ceramics.
  • the ceramic particle-forming process of the invention may be conducted such that only a minor amount of the finely powdered ceramic starting material is wasted.
  • agglomerates which are smaller than desired, or any starting ceramic powder which is not agglomerated may be reused in a subsequent agglomerating process.
  • agglomerates which are larger than desired may simply be re-ground and used in a subsequent agglomerating process.
  • sinterable agglomerates are prepared by adhering together fine particles of sinterable powder with a binding agent.
  • the binding agent may be any material which effects adhesion between the particles to be agglomerated, and can be eliminated from the agglomerates without leaving a residue that interferes with the sintering or biological properties of the finished product.
  • Suitable binders include organic polymers, preferably polyvinyl alcohol, polylactic acid, hydroxypropyl cellulose, starch, pregelatinized starch and polyvinyl pyrrolidone.
  • the initial particle size of the fine sinterable powder starting material employed to form the agglomerate is preferably in the range of about 1 to about 75 microns, and most preferably in the range of about 5 to about 50 microns.
  • the fine sinterable powder may be prepared by conventional methods, such as by grinding or milling larger particles or masses of a sinterable material. However, as described in greater detail below, it is preferred to prepare the finely divided ceramic powder by a spray-drying process. Spray-drying is preferred because it provides a better than 90% yield, provides particles within a narrow particle size range, and provides an easy- to-handle, free-flowing powder.
  • the sinterable agglomerate may be prepared by applying the binding agent (or a solution of the binder) to a fluidized bed of the ceramic powder.
  • dry and finely ground hydroxylapatite powder may be charged into a Glatt Powder Coater, Model No. GPCG 5-9 (manufactured by Glatt-Air Techniques, Inc. of Ramsey, New Jersey) which fluidizes and agitates the powder particles, while the binder is fed at a controlled rate onto the fluidized bed of particles.
  • the fine powder is fluidized by the introduction of a stream or jet of air into the device which "puffs up" the powder particles and suspends them in air.
  • the powder is agitated in a rotary fashion in the Powder Coater.
  • the binding agent is sprayed onto the rotating, fluidized bed, the powder particles agglomerate into larger and larger sized agglomerates in a snow-ball-like fashion, as the amount of binder added to the bed increases.
  • the resultant agglomerates are substantially spheroidal in shape.
  • the binder may be added as a solid dispersed within the fluidized bed of fine sinterable particles.
  • the fluidized bed of the initially added sinterable particles and binder may be sprayed with a suitable liquid, for example, water or an aqueous or other solution of the binder.
  • hydroxylapatite powder having a particle size in the range of about 1 to about 75 microns, may be agglomerated with an organic binder until agglomerates in about the 10 to about 80, preferably about 20 to about 70 mesh range, are formed.
  • the sintered ceramic is typically somewhat smaller in size than the agglomerate from which it is prepared.
  • the group of particles which are produced by the agglomeration step in order to select agglomerated particles within the appropriate particle size range.
  • the classification of particles may be conducted by sieving, or by any other conventional sorting or particle classification technique.
  • One of the advantages of the process of this invention is that off-sized agglomerates or any non-agglomerated starting material may be recycled. That is, agglomerated particles which are smaller than desired can simply be reused in a later batch, while agglomerates that are too large may be ground to a smaller size, and reused during a subsequent agglomeration process. Thus, there should be little or no waste resulting from the agglomeration process. Moreover, as shown by the following Examples, the sintering process may yield 90% or more of sintered ceramic particles within the desired particle size range.
  • the agglomerated particles produced in the manner described above may be employed as core or seed particles in a second agglomeration process.
  • the previously prepared core particles which is itself an agglomerate, may be coated with additional layers of binder plus additional fine ceramic particles.
  • a sinterable agglomerate made up of a core of one ceramic material, over which a plurality of spheroidal shells or layers of the same or a different ceramic material are formed.
  • a shell or layer may also be applied to the core particle which is made up of an hydroxylapatite having a particle size which is different from the hydroxylapatite particles which make up the core of the sinterable agglomerate.
  • the sinterable agglomerates of this invention preferably are comprised of about 5% to about 25% by weight of the binder, preferably about 10% to about 15% of the binder, while the agglomerate preferably comprises about 75% to about 90%, and preferably about 85% to about 95% by weight of sinterable ceramic particles of hydroxylapatite, and/or whitlockite or aluminum oxide.
  • the bulk density of the agglomerate is preferably about 0.8 to about 1.5 grams/cc, for agglomerates within about the 10 to about 80 mesh range, while for the preferred agglomerates of hydroxylapatite, the bulk density is about 1 to about 1.2 grams/cc for agglomerates in about the 15 to about 30 mesh range.
  • the sinterable powder employed to form the agglomerate may be in the form of irregularly shaped particles which possess microscopic ridges or points.
  • the larger sintered ceramic particle possesses a macroscopically smooth surface.
  • ceramic particles in the 10-80 mesh range prepared, for example, by grinding larger ceramic particles possess larger surface points or ridges. It is the larger ridges or points of the ground ceramic materials which present a danger of local irritation when such ceramics are placed in contact with tissue.
  • the agglomerates of this invention are sintered to provide the finished particulate ceramic product.
  • the temperature and duration employed to sintered the agglomerate may be the same as those one would conventionally employ to sinter the sinterable powder from which the agglomerate was prepared.
  • the binder may advantageously be substantially eliminated before the agglomerate reaches the more elevated sintering temperatures by liquid extraction or heating of the agglomerate to a first temperature that is less than the sintering temperature.
  • about 75 to 90 wt. percent or more of the binder is removed from the agglomerate particles by the extraction step prior to sintering.
  • the hydroxylapatite-containing agglomerate is subjected to a preliminary heat treatment, i.e., heat extraction of the binding agent, at a temperature sufficient to eliminate a substantial portion of the binder from the agglomerate leaving at least a sufficient amount of binder so as not to adversely affect the adhering of the particles present in the agglomerate and to provide an agglomerate which may sintered without objectionable coloration by carbonization.
  • This preliminary heat extraction is preferably conducted at temperatures below about 700°C, and more preferably about 500°C or less. Heating is preferably effectuated in an oven at the rate of about 20°C per minute up to the final temperatures set forth above.
  • Results may be improved by enriching the oven air or other atmosphere with oxygen.
  • the actual temperature, heating rate and oven atmosphere employed will be a function of the particular binder selected, air flow in the oven, etc. It has been found that the foregoing heat extraction serves to substantially eliminate the binder while nevertheless providing a structurally-stable agglomerate of hydroxylapatite.
  • the extracted agglomerate of hydroxylapatite particles may then be subjected to elevated sintering temperatures without fear of discolorization due to carbonization of the binder or other adverse effects on the product.
  • the resultant ceramic particle is preferably white, not translucent and biocompatible.
  • the binding agent may be removed from the agglomerates with a liquid extraction technique.
  • Liquid extraction involves washing the agglomerates in a liquid preferably a solvent for the binding agent, e.g., isopropyl alcohol, methylene dichloride, methanol and aqueous solutions thereof.
  • aqueous solutions may contain about 99 to 80% by wt. organic solvent.
  • the presently preferred solvent is 100% isopropyl alcohol.
  • the particular solvent used and extraction conditions employed will depend on the particular binding agent and agglomerate to be treated and enough binding agent should remain in the agglomerate after extraction to prevent disintegration of the agglomerate prior to sintering.
  • the agglomerates may be submerged in the liquid for a sufficient period of time, e.g., about 2 or more hours, to substantially eliminate the binding agent from the agglomerate. Heating or boiling the liquid containing submerged agglomerate may accelerate the extraction process and/or enhance the effectiveness of the extraction.
  • a typical liquid extraction involves charging about 1 liter of isopropyl alcohol into an extraction chamber of a Soxhelt-type extractor. Then about 1.5 kg of agglomerated hydroxylapatite including a polyvinyl pyrrolidone binder prepared as described above is mixed with the aqueous isopropyl alcohol and the mixture is heated to reflux for about 72 hours. Thereafter, the liquid containing extracted binding agent (polyvinyl alcohol) is separated from the agglomerate and the agglomerate is dried to constant weight at about 80-110°C.
  • sufficient binder is preferably removed from the agglomerate to prevent adverse effects on subsequent sintering and/or the physical properties performance and biocompatibility of the finished product. However, if desired an amount of binder may be maintained in the agglomerate to facilitate further processing without undesirable disintegration of the agglomerate particles.
  • agglomerate of hydroxylapatite powder sintering is conducted at a temperature of about 1000°C to 1300°C for about 1 to about 5 hours, most preferably at about 1075°C to 1250°C for about 1 to about 3 hours.
  • Fine sinterable hydroxylapatite powder suitable for agglomeration may be prepared by any conventional granulating and/or particle sorting technique.
  • the fine particulate hydroxylapatite starting material employed herein is prepared by first preparing a gelatinous aqueous precipitate of hydroxylapatite, and then processing the precipitate into a sinterable fine dry powder suitable for use in the agglomeration process.
  • Hayek et al. Inorganic Synthesis. 7, 63 (1963) which is incorporated herein by reference.
  • Hayek et al. disclose the precipitation of hydroxylapatite using phosphate solution, in accordance with the following reaction scheme:
  • the gelatinous precipitate is separated from the mother liquor, and the precipitate is washed to substantially reduce or, if desired, to eliminate the ammonium nitrate present in the gelatinous product. Since ammonium nitrate decomposes into gaseous by ⁇ products at temperatures of about 180°C to about 300°C, the generation of gas from ammonium nitrate during the heating of the agglomerate can lead to a breakup or weakening of the agglomerated hydroxylapatite precipitate by resuspending the precipitate in water, centrifuging the suspension, and then decanting the water.
  • the gelatinous precipitate of hydroxylapatite is next dried and converted into fine particles.
  • Drying techniques which can be used include, for example, tray drying, vacuum drying, etc. If desired, the dried particles may be ground and then classified in order to obtain particles within the desired particle range.
  • Spray drying is the preferred technique for converting the gelatinous precipitate of hydroxylapatite into the fine dry particles suitable for use in the agglomeration process.
  • the gelatinous precipitate may be spray dried by first preparing an aqueous slurry of the precipitate suitable for spray drying.
  • the slurry may have a solids content of about 5% to about 15%, preferably about 7% to about 10% by weight, and the slurry may then be spray dried to provide particles within the desired size range.
  • Spray drying may be conducted at temperatures of less than 400°C, e.g., in a conventional spray dryer employing an air inlet temperature of about 250°C, and an outlet temperature of about 115°C. Under these conditions the spray-dried hydroxylapatite particles are in a substantially anhydrous state, and the hydroxylapatite is no longer gelatinous, but may contain some chemically bound water.
  • the spray-dried product obtained is in the form of dry porous particles of hydroxylapatite which cannot be reconstituted into the gelatinous state by the addition of water.
  • the spray-dried particles of hydroxylapatite are substantially spheroidal in shape.
  • the finally sintered hydroxylapatite agglomerates of this invention preferably have a porosity sufficient to permit the desired degree of tissue ingrowth to ensure proper attachment when the ceramic is employed for prosthetic purposes or as an implant material.
  • the preferred hydroxylapatite ceramic produced in accordance with this invention is substantially spheroidal in shape and has a bulk particle density of about 80% to about 95% of the theoretical maximum density of pure hydroxylapatite.
  • the ceramic hydroxylapatite product includes an extensive network of micropores extending throughout the product, as seen by Scanning Electron Microscopic analysis.
  • the individual pores which form the network are preferably all less than about 40 to about 50 microns (maximum pore diameter) in size. Most preferably, the median pore size is about 1.5 microns as determined by mercury porosimetry, with about 90% of the pores being less than about 0.3 microns.
  • the finely sintered ceramic particles produced by the method of this invention may be combined with an orally compatible binder material and employed as a dental restorative material used to fill lesions caused by periodontal disease, or to augment or restore the alveolar ridge.
  • the dental restorative compositions may also be employed as a tooth filling material, a dental liner, to mold or cast artificial teeth, etc.
  • spheroidal ceramic particles of this invention which employ pure hydroxylapatite are preferred for use in such dental restorative compositions because hydroxylapatite possesses a thermal coefficient of expansion substantially identical to that of natural tooth enamel, the hardness hydroxylapatite is similar to the hardness of natural tooth, and in addition natural tooth and hydroxylapatite stain in a similar way.
  • the preferred dental restorative compositions of this invention are comprised of about 5% up to about 90% by weight of the hydroxylapatite ceramic of this invention dispersed within about 10% to about 95% by weight of an orally compatible secondary binder.
  • Suitable binders for use in the preparation of the dental restorative materials of this invention include secondary binders such as a binder comprised of plaster of paris (calcium sulfate hemihydrate) and water.
  • Secondary binding materials include polymeric or polymerizable materials in combination with the appropriate additives for hardening the binder, e.g., crosslinking agents, polymerization catalysts, diluents, etc.
  • the polymeric or polymerizable secondary binder may be selected from a broad group of known polymeric materials suitable for use in the oral cavity.
  • Such materials include, for example polymethacrylates such as hydroxylethylmethacrylate, poly ethylmethacrylate, as well as other polyacrylic acids or esters, epoxy resins, polyesters, etc.
  • the ceramic particles produced in accordance with this invention may be admixed with a biocompatible inorganic or organic secondary binder, and then cast or molded into the form of a tooth, bone, a portion of a bone, etc. Bone prostheses prepared in this manner may then be surgically implanted employing conventional surgical techniques.
  • the spheroidal ceramic hydroxylapatite of this invention is also particularly well suited for use as a surgical implant material.
  • moist spheroidal particles of the hydroxylapatite ceramic in the size range of about 10 to 60 mesh may be used to fill properly prepared lesions caused by periodontal diseases.
  • the moist hydroxylapatite is packed into the lesion following known periodontal procedures.
  • the ceramic hydroxylapatite ceramic of this invention may be diluted with a biocompatible diluent such as saline solutions or even blood, and injected into or about the alveolar ridge in order to augment or restore portions of that ridge, in accordance with known surgical procedures.
  • the spheroidal hydroxylapatite ceramic is preferably in about the 10 to about 60 mesh range.
  • the ceramic filling substantially retains its original volume with little or no reduction in the volume of the filling material due to the settling of the particles in the void.
  • irregularly shaped non-spheroidal particles tend to settle in a void causing an undesired reduction in the volume of the filling material.
  • the crush strength, i.e., friability, of the ceramic particles produced in accordance with the present invention was measured by crushing 5 to 10 uniformly shaped particles (one at a time) of 20-40 mesh hydroxylapatite agglomerate in a Chatillon Model 1750B die shear tester.
  • the average friability values presented in the following examples are given in pounds as read directly from the scale on the Chatillon tester.
  • EXAMPLE 1 45.4 kg of calcium nitrate tetrahydrate was dissolved in 265 liters of deionized water and 62 kg of 26% ammonia water was added.
  • EXAMPLE 2 45.4 kg of the calcium nitrate was precipitated with ammonium phosphate exactly as described in Example 1. The precipitate was centrifuged and twice redispersed in 500 liters of D.I. water and centrifuged again. The gelatinous solid was dispersed in D.I. water again to produce a slurry with 8.3% of solids which was then spray dried using a Bowen spray dryer. air inlet temperature: 250°C air outlet temperature: 115°C The product obtained was a white powder having a particle size of about 20-40 microns in the main fraction. Yield: 17.60 kg of Ca 5 (OH) (P0 4 ) 3 - 91.1%
  • EXAMPLE 3 4.0 kg of hydroxylapatite powder prepared as described in Example 1 was charged into Glatt powder coater/granulator GPCT 5-9. 400 g of pregelatinized starch was dissolved in 4600 g of D.I. water.
  • the rotor was turned on and speed adjusted at 400 rpm, the air let temperature was 70°C and a starch solution was sprayed-in initially at 120 g/min. , and later at 40 g/min. High initial flow rate is necessary to prevent loss of the dry fine powder. Agglomeration was monitored by sieving samples taken in approximately 5 min. intervals. Feeding of the starch solution was discontinued when the desired particle size was reached (approx. 60 min.); material was dried, discharged and sieved.
  • PVP polyvinylpyrrolidone
  • the rotor was turned on at 400 rpm speed, starch solution was fed in at 80 g/min. and the powder injection was set for 8.0 kg/hr. Agglomeration of particles 40-60 mesh and coating of this preagglomerate took place simultaneously. The particle size 14-25 mesh was reached within 54 minutes. At this point the speed of the rotor was increased to 900 rpm feeding of the powder and the starch was discontinued, heating was stopped and material was sprayed with D.I. water for 10 minutes. Higher speed compacted the particles and increased their density and the particle size shrunk to the desired 16-30 mesh. The rotor speed was brought down to 400 rpm, water spraying was discontinued and material was dried.
  • Rotor was turned on at 400 rpm speed and starch feeding started at 80 g/min. Agglomeration began within 10 minutes and the desired particle size 16-30 mesh was reached in 35 minutes. Faster response was due to the starch content in the starting material. The material was dried and discharged.
  • Rotor was turned on at 400 rpm speed and the fluidized powder was sprayed with D.I. water at the rate of 80 g/min. initially and at 40 g/min. rate later. Powder was gradually agglomerized and the spray of the water was discontinued when the main fraction reached the size 16-30 mesh. Material was dried and discharged.
  • EXAMPLE 9 5.0 kg of the agglomerated hydroxylapatite of the particle size 20-30 mesh was charged into the Glatt GPCG 5-9 granulator with a Wurster column insert.
  • Sludge of the hydroxylapatite was prepared as described in Example 2, redispersed in D.I. water and centrifuged again twice and diluted with D.I. water to contain 7% solids.
  • EXAMPLE 10 12-60 mesh hydroxylapatite was agglomerated with polyvinyl pyrrolidone (PVP) binder generally following the agglomeration procedures set forth in the preceding Examples.
  • PVP polyvinyl pyrrolidone
  • the binder was extracted as follows: 20 g of the PVA agglomerated hydroxylapatite was added to a solution of 2 ml isopropyl alcohol and 100 ml D.I. water heated to a boil, allowed to cool for 2 hrs., decanted, dried at 110°C to substantially constant weight and fired at 1200°C for 2 hours.
  • Example 11 The procedure of Example 9 was repeated except that the binder extraction step was carried out in 2 mis ammonium hydroxide and 100 ml D.I. water.
  • EXAMPLE 12 Four different batches of hydroxy ⁇ lapatite agglomerated with polyvinylpyrolidone (PVP) binder were prepared generally following the procedure of Example 5.
  • PVP polyvinylpyrolidone
  • the PVP binder was extracted from a sample of each batch of PVP agglomerated hydroxylapatite as follows: lOg of the PVP agglomerated hydroxy ⁇ lapatite was added to 40 ml isopropyl alcohol (IPA) , boiled, cooled for 2 hours, decanted, dried at 90°C to substantially constant weight and sintered at 1200°C for 2 hrs.
  • IPA isopropyl alcohol
  • Samples from each batch of the hydroxylapatite agglomerates were placed in an oven having an oxygen atmosphere and heated at the rate of 20°C per min. to 500°C each producing white material which produced acceptable ceramics, i.e. Friability greater than about 3.0, and an unchanged X-ray diffraction pattern (approximately 100% hydroxylapatite) .

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Abstract

Un nouveau procédé de transformation de poudres frittables en produits céramiques frittés en composés de phosphate de calcium, tels que h'hydroxylapatite, comprend l'agglomération de fines particules avec un liant et l'extraction du liant contenu dans les particules agglomérées avant le frittage. La porosité des agglomérés, la taille et la forme sphérique des particules qui les composent, permettent d'obtenir une combinaison unique de propriétés favorables lors de leur utilisation comme matériau d'implants.
EP87900617A 1985-12-31 1986-12-30 Transformation et produits ceramiques Withdrawn EP0250570A1 (fr)

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DE4033343A1 (de) * 1990-10-19 1992-04-23 Draenert Klaus Werkstoff als ausgangsmaterial zur herstellung von knochenzement und verfahren zu seiner herstellung
US7968110B2 (en) 1992-02-11 2011-06-28 Merz Aesthetics, Inc. Tissue augmentation material and method
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JP3679570B2 (ja) 1997-03-14 2005-08-03 ペンタックス株式会社 骨補填材及びその製造方法
FR2850282B1 (fr) 2003-01-27 2007-04-06 Jerome Asius Implant injectable a base de ceramique pour le comblement de rides, depressions cutanees et cicatrices, et sa preparation
US20070184087A1 (en) 2006-02-06 2007-08-09 Bioform Medical, Inc. Polysaccharide compositions for use in tissue augmentation
CA2702997A1 (fr) * 2007-10-19 2009-04-23 Metafoam Technologies Inc. Dispositif de gestion thermique utilisant de la mousse inorganique
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