United States Patent c191
`Fink et al.
`
`I lllll llllllll Ill lllll lllll lllll lllll lllll lllll lllll lllll llllll Ill lllll llll
`US005370692A
`5,370,692
`[11] Patent Number:
`[45] Date of Patent:
`Dec. 6, 1994
`
`[54] RAPID, CUSTOMIZED BONE PROSTHESIS
`Inventors: David J. Fink, Marble Cliff; Salvatore
`[7 5]
`T. DiNovo; Thomas J. Ward, both of
`Columbus, all of Ohio
`[73] Assignee: Guild Associates, Inc., Hilliard, Ohio
`[21] Appl. No.: 929,449
`[22] Filed:
`Aug. 14, 1992
`[51]
`Int. CI.> ................................................ A61F 2/28
`[52] U.S. Cl .......................................... 623/16; 623/66
`[58] Field of Search .............................. 623/16, 18, 66
`References Cited
`[56]
`U.S. PATENT DOCUMENTS
`4,936,862 4/1988 Walker et al. ........................ 623/18
`
`OTHER PUBLICATIONS
`C. J. Damien and J. R. Parsons, "Bone Graft and Bone
`Graft Substitutes: A Review of Current Technology
`and Applications", J. Appl. Biomater., vol. 2, 1991, pp.
`187-208.
`R. Z. LeGeros, "Calcium Phosphate Materials in Re(cid:173)
`storative Dentistry: A Review", Adv Dent Res, vol. 2,
`No. 1, Aug. 1988, pp. 164-180.
`R. z. LeGeros et al., "Significance of the Porosity and
`Physical Chemistry of Calcium Phosphate Ceramics
`Biodegradation-Bioresorption", Annals New York
`Academy of Sciences, vol. 523, 1988, pp. 268-271.
`K. DeGroot et al., "Significance of the Porosity and
`·Physical Chemistry of Calcium Phosphate Ceramics
`Dental and Other Head and Neck Uses", Annals New
`York Academy of Sciences, vol. 523, 1988, pp. 272-275.
`J. E. Lemons et al., "Significance of the Porosity and
`Physical Chemistry of Calcium Phosphate Ceramics
`Orthopedic Uses", Annals New York Academy of Sci(cid:173)
`ences, vol. 523, 1988, pp. 278-282.
`K. DeGroot, "Effect of Porosity and Physiochemical
`Properties on the Stability, Resorption, and Strength of
`Calcium Phosphate Ceramics", Annals New York
`Academy of Sciences, vol. 523, 1988, pp. 227-233.
`E. N. Kaplan, "3-D CT Images for Facial Implant
`Design and Maufacture", Clin. Plast. Surg., vol. 14, No.
`4, 1987, pp. 663-676.
`M. J. Cima et al., "Three Dimensional Printing: Form,
`Materials, and Performance'', Quarterly Report 1991,
`
`Proceedings of the Solid Free-form Fabrication Sym(cid:173)
`posium, University of Texas, .1991, pp. 187-194.
`U. Lakshminarayan et al., "Selective Laser Sintering of
`Ceramic Materials", Proceedings of the Solid Freeform
`Fabrication Symposium, University of Texas, 1990, pp.
`16-26.
`J. W. Barlow et al. "Analysis of Selective Laser Sinter-
`ing", 1991, pp. 1-5.
`•
`E. Sachs et al., "Three Dimensional Printing: Ceramic
`Shells and Cores for Casting and Other Applications",
`Proceedings of the Second International Conference on
`Rapid Prototyping, University of Dayton, 1991 pp.
`39-53.
`U. Lakshminarayan et al., "Microstructural and Me(cid:173)
`chanical Properties of AL203/P20s and Ah03/B203
`Composites Fabricated by Selective Laser Sintering",
`Proceedings of the Solid Freeform Fabrication Sympo(cid:173)
`sium, University of Texas, 1991, pp. 205-212.
`"Somatom HiQ-S: Perfecting the Art of CT", Seimens
`Medical Systems, Inc., 1990 sales literature.
`B. K. Milthorpe, "Three Dimensional Reconstruction
`of Biomaterial Histrological Images", Proceedings of
`(List continued on next page.)
`Primary Examiner-Randy C. Shay
`Attorney, Agent, or Firm-Frank H. Foster
`[57]
`ABSTRACT
`Prosthetic bone implants are fabricated to approxi(cid:173)
`mately replicate a patient's original bone. Medical com(cid:173)
`puter aided imaging techniques are applied to generate
`a data base representing the size and shape of the origi(cid:173)
`nal bone in a three dimensional coordinate system. The
`implantable replica is fabricated using the data base and
`free form manufacturing to sequentially solidify adjoin(cid:173)
`ing, cross-sectional intervals of a fluid material. Appro(cid:173)
`priate fluid .materials include ceramic particles which
`may be selectively bonded by sintering or bonding with
`a polymer, and a monomer which is polymerized at
`selected regions by an incident laser beam.
`
`13 Claims, 2 Drawing Sheets
`
`'
`lWFORT or TRA..~sv.n:o
`FlU: TO :l-0 DATA
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`2-0 RECoc:.mos or
`DATA BY CT UYER TO
`rorui: ARD.
`P£RIW.E:TER(S)
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`>JJCSfll. ORIO."!':E:D.
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`EXPORTE:> F'OR
`RtPROOCCTIOS CREATION
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`BO!'it REPROi'.lt:C'!'lO!ll
`llA."l..TAcn:REP
`BY VENDORS
`
`-1-
`
`Smith & Nephew Ex. 1044
`IPR Petition - USP 9,295,482
`
`

`
`5,370,692
`
`Page 2
`
`. OTHER PUBLICATIONS
`the Fourth World Biomaterials Congress, Berlin, Fed(cid:173)
`eral Republic of Germany, Apr. 1992, p. 564.
`M. Erbe et al., "Geometrically Surface Structured
`Stereolithography Acrylic Resin and Titanium Im(cid:173)
`plants", Proceedings of the Fourth World Biomaterials
`Congress, Berlin, Federal Republic of Germany, Apr.
`1992, p. 165.
`S. J. Bresina, "The Treatment of Bone Defects", Pro(cid:173)
`ceedings of the Fourth World Biomaterials Congress,
`
`Berlin, Federal Republic of Germany, Apr. 1992, p .
`207.
`T. Truby, "Growing a Human Skull'', Med. Equip.
`Designer, Jul. 1992, pp. M8-10.
`M. Burns, "Introduction to Desktop Manufacturing and
`Rapid Prototyping", Rapid Prototyping: System Selec(cid:173)
`tion and Implementation Guide, 1992, pp. 2-6.
`T. Ward et al., "The Evaluation of Component Prototy(cid:173)
`ping and Reverse Engineering Systems", Final Report
`to U.S. Army Chemical Research, Development and
`Engineering Center, Nov. 1990, pp. 1-39.
`
`-2-
`
`

`
`U.S. Patent
`
`Dec. 6, 1994
`
`Sheet 1of2
`
`5,370,692
`
`CREATE CAD FILE
`
`CREATE "SLICED" FILE
`
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`PRINTED
`
`FIG-1
`PRIOR ART
`
`-3-
`
`

`
`U.S. Patent
`
`Dec. 6, 1994
`
`Sheet 2 of 2
`
`5,370,692
`
`2
`
`CT SCAN OF BONE
`
`•
`
`"
`
`~
`
`..,
`
`4
`TRANSLATION OF CT FILE
`TO STANDARD BINARY 4
`OR ASCI FORMAT
`
`r
`
`5
`IMPORT OF TRANSLATED
`FILE TO 3-D DATA
`MANIPULATION PACKAGE
`
`•
`
`7
`6
`AREA PERIMETERS
`2-D RECOGNITION OF
`OPTIMIZED (MANIPULATED 4- DATA BY CT LAYER TO
`FOR SMOOTHNESS,
`FORM AREA
`SIZE, ETC.)
`PERIMETER(S)
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`AREA PERIMETERS
`STACKED AND SURFACE
`MODEL FORMED
`
`11
`REPRODUCTION MODEL
`SLICED FOR
`FFM PROCESS
`
`•
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`12
`BONE REPRODUCTION
`MANUFACTURED
`BY VENDORS
`
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`FIG-2
`
`-4-
`
`

`
`1
`
`5,370,692
`
`Endodontic pins:
`
`RAPID, CUSTOMIZED BONE PROSTHESIS
`
`2
`Endosteal-Endosseous implants;
`Orthodontic pins
`Transosseous-Transmandibular
`TECHNICAL FIELD
`Otological Applications
`Ossicular reconstruction
`This invention relates to the fabrication of prosthetic
`Canal wall prostheses
`implants to replace bone and more particularly relates
`to the use of computer based imaging and manufactur-
`ORTHOPEDIC USES
`ing techniques to replicate the hard tissue being re-
`Bone Graft Substitutes
`placed by the prosthesis.
`10 Augmentation-Delayed or failed unions; Arthrode-
`BACKGROUND ART
`sis (fusion of joint); Bone graft donor sites; Me-
`.
`. . .
`chanically stable cystic defects; Revision or pri-
`Wounds of war have alway~ homfied c1viha~ popu-
`mary joint replacement
`lations. Indeed, for all human history, the recogmt1on of
`Replacement-Vertebral body defects; Segmental
`attendant physical mutilation has probably been the 15 bone defects;
`single most effective limitation on the frequency and
`Mechanically unstable subchondral defects (e.g., tib-
`scale of conflicts. It is only within the past century that
`ial plateau fractures and large traumatic defects;
`even crude forms of reconstructive surgery were practi-
`Grafting around prostheses used for mechanical
`cal. However, the parallel revolutions in computer sci-
`fixation
`ence and human-focused biotechnology now open an 20
`Fracture Fixation Materials
`unprecedented opportunity to modern military medi-
`Fracture fixation devices such as plates, screws and
`cine: to make a wounded soldier whole and functional
`rods;
`to a degree that rivals mythology.
`Endoprosthese such as joint replacements
`Coating for Fixation
`CERAMIC IMPLANTS
`Fixation of implant to bone in joint replacement;
`It has been only slightly more than two decades since
`Coated internal fixation devices
`the discovery by Hench and his co-workers that a direct
`Drug Delivery Implants
`chemical bond can form between certain "bioactive"
`Local adjuvant chemotherapy; Local antibiotic ther-
`glass-ceramic materials and bone, thereby potentially
`apy;
`stabilizing dental or orthopaedic implants made from 30
`Local delivery of bone growth factors or osteoinduc-
`these materials. In the meantime, the investigation of
`tive factors
`other chemical formulations (including many ceramics
`HA, the predominant ceramic in bone, and the com-
`and composites), physical forms (e.g., dense or porous
`position of the bond between bioactive ceramics and
`particulates and solids, coatings, and composites), and
`bone, has been assessed to provide the following advan-
`clinical applications have progressed rapidly.
`35 tages in dental implantations: 1. biocompatibility; 2.
`Most research into the use of bioactive materials is
`absence of antigenic response; 3. availability; 4. ability
`to use local anesthesia during implantation; 5. low risk
`now focused on either:
`f · fi
`· k f
`·
`h
`h
`· 7
`6 1
`·
`·
`1·ti·ons
`·1
`o m ect1on;
`. ow ns o permanent yperest es1a;
`.
`I
`1
`1
`. g asses or g ass-ceramic, pnman y c mpos
`1 k f .gnifi
`hi h
`f
`d
`·
`0
`h S·o
`p 0
`C 0 N 0
`t
`8
`ac o s1
`1cant resorption;
`. g
`rate o goo
`re-
`f
`rom .t e 1 2- 2 s- a -:- . a2
`sy~ em,. or
`40 sults; and 9. no need for perfect oral hygiene on the part
`2. ~alc1~ phosphate compositions, primarily /3-
`of the patient. Most of these advantages cart be antici-
`tnc::ic1um phosphat~ (/3-TCP), Ca3(P04)2 :d
`pated in orthopedic applications as well, although the
`calcium h.ydr?xylapatite (HA), Ca10(P04)6(0 )2,
`need for a more rapid rate of resorption has been the
`and combmat1ons of the two.
`incentive for investigation of mixtures of HA and
`Generally, t?e calcium phosphate cer~cs may be 45 {3-TCP to produce a range of rates.
`somewhat easier t~ produc~ and/?r obtam commer-
`For use in these applications, calcium phosphate ma-
`cially, and ar~ r.ece1vmg 371 mcreasmg ~hare of the re-
`terials are currently produced in a variety of formats,
`search and ~hmcal attention. /3-TCP 1~ normally ob-
`normally by sintering particulate solids:
`served to biodegrade much more rapidly than HA,
`Particulates-range of particle sizes; variable poros-
`which until recently was believed to be non-resorbable. 50
`ity.
`Such bioactive ceramics are generally considered to be
`Moldable Forms-pastes; self-setting slurries or pre-
`osteoconductive (i.e., providing an appropriate scaffol~
`formed shapes.
`that permits ingrowth of vasculature and osteoprogem-
`Block Forms-designed geometries such as rods,
`tor cells), as opposed to osteoinductive, which implies a
`cones, spheres, and discs; variable micro- and mac-
`more active process in which the matrix recruits osteo- 55
`roporosity.
`progenitor cells from the local tissue or circulation.
`Coatings-applied to a preformed substrate by tech-
`Current or potential applications for these materials
`niques such as plasma spraying, flame spraying,
`include:
`electrophoresis, ion beam-radio frequency sput(cid:173)
`tering, dip coating, and frit-slurry enameling.
`DENTAL AND OTHER HEAD AND NECK USES
`Particulate formats were among the first bioactive
`Craniofacial Applications
`ceramics taken to the clinic, but these materials have the
`Augmentation-Ridge; Mandibular; Zygomatic;
`disadvantages 1) they cannot be used where implant
`Chin
`strength is required and 2) particle migration often oc(cid:173)
`Reconstruction-Periodontal; Mandibular; Orthog(cid:173)
`curs in the implant site, decreasing the effectiveness of
`nathy; Bone Grafting; Cranioplasty; Orbital floor;
`65 the material. To minimize the latter problem, many
`Anterior nasal spine
`attempts have been made to use biodegradable materials
`Prosthetic Implants
`to agglomerate and mold the particles during implanta(cid:173)
`Subperiosteal
`tion.
`
`5
`
`25
`
`60
`
`-5-
`
`

`
`5,370,692
`
`3
`4
`In clinical applications in which strength of the ce(cid:173)
`icant constraint when using the composite molding
`ramic implant is a significant factor (e.g., craniofacial
`technique.
`augmentation or reconstruction; bone replacement;
`FREE-FORMING MANUFACTURING
`fracture fixation), block forms of the material are re-
`quired and shaping of the implant becomes more diffi- 5
`The terms free-forming manufacturing (FFM), desk-
`cult.
`top manufacturing, rapid prototyping, and several oth-
`Perhaps the most important physical properties of
`ers, all describe the new manufacturing processes that
`bioactive ceramics are the volume and size of the pores
`enable the physical fabrication of three-dimensional
`within the material, which strongly influences both the
`computer models with a minimum of human interac-
`tensile and compressive strengths of the material and 10 tion. All of the systems that are on the market or in
`the rate of resorption and cellular colonization. Gener-
`development are based upon mathematically "slicing" a
`ally, pores at least 200-300 micrometers in diameter
`three dimensional Computer Aided Design (CAD)
`(referred to as macroporosity) are believed to be neces-
`model and then sequentially reconstructing the cross
`sary in osteoconductive materials to permit ingrowth of
`sections (slices) of the model on top of one another
`vasculature and osteogenic cells. Microporous ceram- 15 using the manufacturing system's solid medium. One
`ics, on the other hand, with pores only a few microme-
`supplier of FFM systems, 3-D Systems (Valencia,
`ters in diameter, do not permit cellular invasion, and in
`Calif.), markets a "stereolithography" system based
`most cases, are likely to be more difficult to stabilize in
`upon laser-mediated polymerization of photo-sensitive
`the implant site. An example of an implant material
`liquid monomer. Of the FFM processes, only two are
`selected for its consistent macroporosity is the "re- 20 able to work with ceramics: the "Selective Laser Sinter-
`plamineform" calcium phosphate structures derived by
`ing" system marketed by DTM Corporation (Austin,
`chemically transforming a variety of corals (initially
`Tex.) and the "3 Dimensional Printing" system under
`calcium carbonate), which are composed of a network
`development at the Massachusetts Institute Technology
`of interconnecting pores in the range of approximately 25 (Cambridge, Mass.). Both processes can accept the
`200 µ.m diameter. HA materials of this type are mar-
`industry standard STL file format, and both research
`keted by lnterpore Orthopedics, Inc. of Irvine, Calif.
`organizations are working with industry to commercial-
`An alternative approach to the fabrication of custom-
`ize the respective processes.
`ized ceramic implants, involving a CT-integrated com-
`The DTM process is based upon localized sintering
`puterized milling operation to produce molds or im- 30 of ceramic powder material by a scanning laser beam.
`plants, has been clinically tested for facial reconstruc- When the laser beam impinges on the surface powder, it
`tion. Advantages of this prefabricated implant approach melts, and localized bonding between particles take
`were identified as:
`place. By selectively sintering sequential layers, the
`1. Contour (of facial implants) is to the underlying
`shape is built in a matter of hours. The build rate de-
`bone base (as opposed to the surface of the skin by 35 pends on the complexity and size of the part, power
`standard facial moulage techniques);
`output of the laser, the coupling between the laser and
`2. Formamina are localized (implants are designed to
`the material and the rheological properties of the mate-
`avoid nerve foramina);
`rial. Although DTM markets only polymer-based man-
`3. Covered areas are "visible" (no interference in the
`ufacturing at this time, it is currently in the research
`design from hair or dressings);
`40 phase of developing ceramic capabilities. To date, fabri-
`4. Soft-tissue contours can be evaluated;
`cation of ceramics, including alumina/phosphate com-
`5. Pre-existing implants can be evaluated;
`posites, have been demonstrated in the DTM process.
`6. Volume measurements can be obtained;
`The MIT process, which has not been commercial-
`7. Local anatomy can be better visualized;
`ized yet, is based upon selective binding of a powder,
`8. Models are provided for "practice surgery";
`45 using ink-jet techniques to distribute the binding agent,
`9. Templates can be designed for bone graft surgery;
`as illustrated schematically in FIG. 1. Typical devices
`10. An archive can be maintained for clinical re-
`are built from alumina powder bonded with colloidal
`evaluation and academic study;
`silica, to reproduce a typical ceramic shell.
`11. Prefabricated grafts minimize the time for implant
`CT IMAGING
`sculpting in surgery, while the patient is anesthe- 50
`tized, and generally are much more accurate recon(cid:173)
`In 1979 Houndsfield and Cormack were awarded the
`structions of the desired bone than can be accom(cid:173)
`Nobel Prize in Medicine for their contributions to Com(cid:173)
`plished by hand;
`puted Tomography (CT). Since then virtually every
`12. There is no need for a second surgical site, as in
`major hospital in the world has acquired the ability to
`autogenous graft surgery.
`55 perform CT. As opposed to classical x-ray imagining,
`In the CT-integrated milling operation described,
`where a shadow image of a patient volume is created,
`implants can be made directly by milling the solid ce(cid:173)
`CT is a two step process where 1) the patient is imaged
`ramic, or by preparing a "negative" mold of the im(cid:173)
`at multiple angles through the rotation of an x-ray
`plant, then molding the implant using a formable ce(cid:173)
`source, and 2) the image is manipulated in the computer
`ramic composition. Direct milling is difficult with mac- 60
`to create a series of sliced images of the patient.
`roporous bioceramics, including the coralline HA mate(cid:173)
`Through the use of sophisticated computer algorithms,
`rials. A moldable HA-collagen composite material has,
`the sliced information can be reconstructed to form
`therefore, been clinically tested with good results in
`three dimensional images of the patient's tissue.
`low-strength indications. However, the composite is
`A complexity of the manipulation process to create
`relatively friable, loses strength when moistened, and is 65
`the FFM design file is the isolation of the specific tissue
`not suitable where structural strength is required, for
`of interest from the surrounding tissue, a process (often
`example, for long bone or mandibular reconstructions.
`relatively subjective) termed "segmentation". This se(cid:173)
`In addition, control of implant macroporosity is a signif-
`lection process can be based upon matching grey-scale
`
`-6-
`
`

`
`5,370,692
`
`20
`
`5
`6
`intensities directly from the CT file without operator
`In describing the preferred embodiment of the inven(cid:173)
`interaction.
`tion which is illustrated in the drawings, specific termi(cid:173)
`In the CT process each volume pixel (voxel) in a
`nology will be resorted to for the sake of clarity. How(cid:173)
`patient cross section is assigned a CT number (in
`ever, it is not intended that the invention be limited to
`Houndsfield units) based upon the physical density of 5
`the specific terms so selected and it is to be understood
`the material with respect to water. These numbers are
`that each specific term includes all technical equivalents
`stored in 256X256 or 512X512 square array format.
`which operate in a similar manner to accomplish a simi(cid:173)
`This information is manipulated in the computer to
`lar purpose.
`show corresponding grey or color scales for selected
`DETAILED DESCRIPTION
`tissue on the computer display. This array-formatted 10
`information can also be transferred from the CT scanner
`The invention is a new manufacturing approach that
`into graphic engineering computers for subsequent data
`will provide customized prosthetic devices for hard
`manipulation as demonstrated, for example, by Kaplan
`tissue
`reconstruction. Free-Form Manufacturing
`in the development of the integrated ceramic milling
`(FFM) technology is a valuable new tool for making
`system.
`15 implants that reproduce original tissue size and shape,
`Preliminary investigations, at the Medical College of
`and that maximize the rate of cell-mediated hard tissue
`Ohio, for example, have also demonstrated that rela-
`healing. The concept requires integration of several
`tively crude FFM models of complex anatomical struc-
`independently developing technologies into the FFM
`tures can be prepared from MRI image files by the
`system.
`stereolithography system from 3-D Systems.
`This strategy for reconstruction of traumatic, disease-
`related or surgical loss of hard tissue is based on the
`BRIEF DISCLOSURE OF INVENTION
`hypothesis that therapy will be optimally treated by a
`The invention involves a therapeutic approach that
`prosthesis that:
`will create customized prosthetic devices for hard tissue
`L is matched to the precise anatomical dimensions of
`reconstruction. Rapid manufacturing technology can 25
`the original tissue (or that may be modified to com-
`produce implants that reproduce original tissue size and
`pensate for anticipated healing responses or to pro-
`shape while simultaneously maximizing the rate and
`vide for surgical-assist structures);
`quality of cell-mediated hard tissue healing. This re-
`2. is composed of a ceramic material that exhibits
`quires integration of several independently developing
`properties similar to bone, and that presents physi-
`technologies designed to: provide physical characteris- 30
`cal, chemical and surface properties that facilitate
`tics of the patient's original hard tissue; permit custom-
`bone cell function and production of new bone;
`ized manufacturing by modem techniques; and optimize
`3. is designed to maximize the rate of cellular coloni-
`the rate of healing by incorporating the patient's own
`zation of the ceramic matrix and to direct the pro-
`bone-producing cells into the implant.
`duction of new bone-alternatively, a more active
`Imaging technology is used first to define hard tissue 35
`approach is to optimize the device for seeding by
`characteristics (size, shape, porosity, etc.) before the
`autologous cells derived from the patient.
`trauma occurs ("pre-trauma" file) by archival use of Manufacturing steps in the process will include:
`available imaging techniques (CT, MRI, etc.). The loss
`1. specification of the physical properties of the cus-
`of hard tissue is determined by imaging in the locale of
`tomized prosthetic device by use of available com-
`the affected tissue after the injury ("post-trauma" file). 40
`puterized imaging techniques (for example, Com-
`Then the physical properties of the customized pros-
`puterized Tomography, CT, or Magnetic Reso-
`thetic device is specified by comparison of the pre-
`nance Imaging, MRI) to produce a solid model
`trauma and post-trauma files to produce a solid model
`"design file" or CAD file. This specification may
`"design" file. This specification may also involve sec-
`also involve secondary manipulation of the files to
`ondary manipulation of the files to assist in surgical 45
`assist in surgical implantation and/or to compen-
`implantation and to compensate for anticipated healing
`sate for, or optimize, anticipated healing processes;
`process. The design file is mathematically processed to
`2. development of a mathematically processed design
`produce a "sliced file" that is then used to direct a
`file to produce a "sliced file" suitable for directing
`"rapid manufacturing" system to construct a precise
`an FFM process;
`replica of the design file in a resorbable ceramic mate- 50
`3. construction of a precise replica of the sliced file by
`rial to produce the implant. The unique porosity charac-
`FFM in an appropriate ceramic material to pro-
`teristics (potentially adaptable to specific patients) of
`duce the implant.
`the missing hard tissue structures may then be repro-
`This is an integrated system for imaging hard tissue,
`duced. Autologous cells, derived from the patient's manipulating the image file to produce the design file,
`post-trauma tissue, are cultured and then used to "seed" 55 processing the design file to drive the FFM system and
`the cells onto the ceramic matrix under conditions ap-
`produce the implant, and optimizing the surgical im-
`propriate to maximize cell attachment and function.
`plantation and performance of such devices. It provides
`The implanted cells will rapidly begin producing new
`a method for fabricating customized medical implant
`bone while other natural process slowly degrade and
`devices. This technology will be used by the general
`remove the specialized ceramic matrix. The cell-seeded 60 orthopedic and dental communities as a specialized
`prosthesis is then implanted at the trauma site and ap-
`service.
`propriate rehabilitation therapy is begun.
`The glass, glass-ceramic or calcium phosphate mate-
`rials described above in the Background Art may be
`BRIEF DESCRIPTION OF DRAWINGS
`used. Additionally, implant devices may also be con(cid:173)
`FIG. 1 is a diagram illustrating the MIT powder 65 structed from calcium carbonate, a resorbable ceramic,
`process.
`alumina or other biocompatible ceramics. Unique ce(cid:173)
`FIG. 2 is a flow chart illustrating the method of the
`ramic processing may be required for each specific
`present invention.
`approach. In the A}i03/NH4ff2P04 system, for exam-
`
`-7-
`
`

`
`5,370,692
`
`7
`pie, alumina has a melting point of 2045° C., while
`N!Wf 2P04 has a melting point of 190° C. Crystalline
`materials like ammonium phosphate and boron oxide
`show a definite melting point which the viscosity drops
`sharply. When the alumina/ammonium phosphate
`blend is processed with the DTM laser, the lower-melt(cid:173)
`ing-point phosphate melts to form a glassy material and
`bonds the alumina particles. A secondary heat treat(cid:173)
`ment is necessary to develop the full strength of the
`material. During heat treatment at 850° C., the follow- 10
`ing net reaction takes place.
`
`8
`to hydroxyapatite by conventional processing tech(cid:173)
`niques.
`While certain preferred embodiments of the present
`invention have been disclosed in detail, it is to be under-
`5 stood that various modifications may be adopted with(cid:173)
`out departing from the spirit of the invention or scope
`of the following claims.
`We claim:
`1. A method for fabricating an implantable device,
`the method comprising:
`fabricating an approximate replica of bone by sequen(cid:173)
`tially solidifying adjoining, cross-sectional inter(cid:173)
`vals of a fluid material along an axis.
`2. A method in accordance with claim 1 wherein a
`15 design data base is first generated by scanning at least a
`The reaction results in an A1203/ AlP04 composite
`portion of an animal's body using imaging techniques to
`where aluminum phosphate forms a thin layer around
`generate a design data base of measurement data repre-
`the alumina particles. The AlP04 volume fraction de-
`senting size and shape of the bone in a three dimensional
`pends on the initial composition.
`coordinate system and then fabricating said replica in
`FFM technology presents a unique capability to in- 20 correspondence with the data in said design data base.
`troduce a defined porosity into ceramic devices formed
`3. A method in accordance with claim 2 wherein the
`by aggregation (sintering) of particulate substrates. For
`step of solidifying a fluid material comprises bonding
`example, the porosity might be introduced or modified:
`ceramic particles.
`1. by direct reproduction of a "porous" CT file; 2. by
`4. A method in accordance with claim 2 wherein the
`varying the particle size distribution of the base ce- 25 scanning step comprises generating the data base by
`ramie; or 3. by post-treatment of formed devices to
`scanning a body part of a healthy individual animal and
`remove specific agents included in the original mixed-
`archiving the data base for subsequent use.
`particulate bed (e.g., by differential solubility). These
`5. A method in accordance with claim 4 wherein the
`processes offer a range of porosities available to tailor
`method further comprises modifying the data base to
`FFM devices to specific applications.
`30 make selected changes in the size and shape of the bone
`The transformation of a CT bone image to a poly-
`represented by the data base.
`meric FFM reproduction may also be done using photo-
`6. A method in accordance with claim 1 wherein the
`active polymer techniques. In such a technique a mono-
`step of solidifying a fluid material comprises bonding a
`mer is polymerized at selected regions by an incident
`photo-active polymeric material.
`laser beam to create a solid polymeric model. The ap- 35
`7. A method in accordance with claim 1 wherein the
`proach for the fabrication of ceramic devices is outlined
`step of solidifying a fluid material comprises sintering
`in FIG. 2. Thus, fluid materials, either liquids or masses
`ceramic particles.
`of particles, are used to fabricate the replica of the bone.
`8. A method in accordance with claim 1 wherein the
`One key aspect of this manufacturing technique is the
`step of solidifying a fluid material comprises bonding
`segmentation process, in which the "bone" is recog- 40 particles a first ceramic material together with particles
`nized and separated from the other tissues in the image,
`of a second ceramic material.
`and the reproduction of a smooth bone surface, which
`9. A method in accordance with claim 1 wherein the
`entails the manipulation of the data after segmentation.
`step of solidifying fluid material comprises cementing
`The fluid materials may be ceramic particles which
`particles together with a polymer.
`are sintered to form the solidified replica using a DTM 45
`10. A method in accordance with claim 1 wherein the
`process. Ceramic particles may be cemented together
`fluid material comprises ceramic particles suspended in
`with a second type of ceramic particles or with a poly-
`a liquid monomer and wherein the monomer is poly-
`meric phase. The replica may be formed by a laser
`merized to form a solid polymer network and wherein
`photo polymerization process (e.g. 3 D systems) in
`at least a part of the polymer is then removed.
`which ceramic particles are suspended in a liquid mono- 50
`11. A method in accordance with claim 1 wherein the
`mer and then became trapped in the liquid polymer
`fluid material comprises ceramic particles and wherein
`after polymerization. Thereafter, a part or all of the
`the solidified replica is then reacted with an agent to
`polymer may be removed. In addition, with the above
`change its composition.
`processes in which the precursors of the final ceramic
`12. A customized implantable device prepared by the
`product are formed by FFM methods, the resulting 55 method of claim 1.
`solid replica may be converted to a desired composi-
`13. A customized implantable device prepared by the
`tion. For example, the replica may be formed of calcium method of claim 2.
`carbonate or tricalcium phosphate and then converted
`
`* * * * *
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`60
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`65
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