Porous ceramic structures have long been a subject of investigation as bone sl..bstitute.
Most of these porous structures are typically made by techniques that result .randomly arranged
pores with a wide variety of pore sizes. In recent years, SFF methods are being used for the
fabrication of porous bioceramic implants. Porous ceramic structures have been fabricated using
indirect route where a .polymeric mold is fitst created via fused deposition process. The mold
was then infiltrated with ceramic slurry, dried. and ·then subjected to a binder bum out and
sintering cycle. In this paper, processing of 3D honeycomb porous alumina ceramic structures
and some.initial mechanical properties for bone implants will be discussed.Mechanical Engineerin

Avila, Marisol

Bandyopadhyay, Amit

Bose, Susmita

English

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PROCESSING OF BIOCERAMIC IMPL.t\·NTS-VIA FUSED DEPOSITION PROCESSSusmita Bose, Marisol AvilaandAmit BandyopadhyaySchool of Mechanical and Materials EngineeringWashington State UniversityPullman, WA 99164..2920AbstractPorous ceramic structures have long been a subject of investigation as bone sl..bstitute.Most of these porous structures are typically made by techniques that result .randomly arrangedpores with a wide variety of pore sizes. In recent years, SFF methods are being used for thefabrication of porous bioceramic implants. Porous ceramic structures have been fabricated usingindirect route where a .polymeric mold is fitst created via fused deposition process. The moldwas then infiltrated with ceramic slurry, dried. and ·then subjected to a binder bum out andsintering cycle. In this paper, processing of 3D honeycomb porous alumina ceramic structuresand some.initial mechanical properties for bone implants will be discussed.IntroductionDevelopment of specially designed ceramics and composites for the repair andreconstruction of diseased or damaged parts of the human body have been revolutionized thequality of human life during last five decades [1-5]. A number of different materials have beenutilized for these purposes in various forms. including collagen, metals, metal alloys, ceramics,glasses, carbon based materials and composites of the above materials. Among them, ceramicbased materials are considered the .most suitable artificial graft material [6]. The ceramicmaterials that are used for these purposes are called bioceramics. These bioceramic materialsmay be inert in nature (such as alumina, zirconia, titania), bioactive (such as hydroxyapatite,bioactive glasses or bioactive glass-ceramics) or resorbable (such as tricalcium phosphate,calcium phosphate<salts). Bioceramic implants can again be classified into two categoriesincluding dense bioceramics andmicroporous bioceramics [1]. The potential for ceramics asbiomaterials relies upontheir compatibility with the physiological environment. Bioceramics arecompatible because they are •composed of ions commonly found in physiological environmentand. of. ions showing limited toxicity to body tissues. Moreover, these materials are resistant tomicrobial.attack,pH changes and solvent conditions and stable With. temperature changes [7].Applications of bioceraInic materials. include restoration of material in dentistry, spinal fusion,bonefilling, maxillofacial reconstruction and hip, knee or other bone replac~ments.Among the various bone substitutes that are currently being used that include: (1)autograft (bone from the another location from the body of the same person), (2) allograft(hurnanbone from dead body), (3) genograft{animal bone) and (4) bioceramic implant (artificialbone). Though autograftis probably the mostsuitable one, but it requiresatJeast two operationsand often causes problems with patient body from where the bone is taken (commonly. hip orrib). In both, allograft and genograft, rejection by the patient body and diseases transmitted bythe foreign bone are of serious concern for their applicability. Naturally, applications of artificial629bioceramic implants"",,,,f"11~n,f",,,,,rI nllC'~nt::lC'C' was. over $50Mceramic compositionceramic structures.n""..'"IlA::l<CI';;r,....""'I'V\ ... U..I. ....JL.I..I..I..l.JU,4. ""...,.."' ........ "" nr",.i-'","f''''I'''r\C' consists of three differentdesign, (2) development of(3) binder bum out and sintering cycle development for green......""............. were designed 1650 using filament material.l"idiameter cylindrical molds were designed and fabricated with a (45/-45)and varying the raster gap from 0.010 to 0.030". Top 0.3" had onlyno raster which is> also called lip, to hold excess n ... r'<:1'n"'111'"mold had no raster gap to avoid .I....U..l.lo..I..l.JLjO,from 0.015 to 0.025". Combination ofraster gaps androadpreform. la andb(a) (b)(a) Schematic presentation of polymeric mold design. (b) Optical image of the topview of a polymeric made by FDM 1650 using ICW06 material (scale 0 - 0.5").630Development of Ceramic SliIrryCompositionDevelopment of ceramic slurry work started with different commercially availablealumina powders. Finally most of the work has .been performed with lOD and 30Daluminapowders •doped with 500 ppmofMgO from BaikQwski International Corporation,. N.C. Both10D and 30D powders have. subrilicron sizep~icles (Sedigraphdso for 10D = 0.45. Um and for30D==0.41J.1.m), but specific surface areafor30Dpowderis26.6 m2/gmcomparedto8.6 m2/gmfor lOD. High surface area of the 30D powderisalso evidentfromhigher slurry100--0-- Darvan 1.2%___ Darvan 1.5%-.-Darvan 2%20 40 60 80Shear Rate (US)(a)1400 ..._----------------,1200-e> 1000-800b.; 6008.~ 400> 2000'---1-_.....11...._......11......._-.1.__.......o10060 80-<>-- Darvan 2.5%___ Darvan 2.8%--Ie- Darvan 3.2%-e--Darvan 3.5%40203000 r=------;=::::::::::::::::~~ 2500~ 2000~.~ 1500- 1000.fQ> 500o 1!!I::I:::==a!i:==:::::.:i~LJoShear Rate (l/S)(b)Figure 2: Effect of dispersant amount on the viscosity of ceramic slurry with (a) lODand(b) 30D powders.viscosity compared to 10D powder at similar solids loading. Brookfield Viscometer was used todetermine ..•the optimum. wt% iQfd.isPt}rsantnt}ed.ed.fortJ1eprt}p~ati()nof ••waterb~edceramicslurry by measuring the viscosity at different shear rates for each solution. I-Butanol (FisherSCientific) was used as anantifoaming agent for this ceramic slurry. Darvah 821 (R.T.Vanderbilt & Co., Norwalk, CTr was used as a dispersant. .. For the lOD alumina powder, 1.5631wt% darvan was found to be optimum and beyond that it increased the viscosity of the slurry alittle bit. Whereas for the 30D alumina powder the optimum dispersant amountwas 3 wt%. Theviscosity vs. shear rate plots at different dispersant wt% for both the powders are shown inFigures 2a and b.Viscosity of lOP and 30Dceratnic slurry compositions at a fixed shear rate of 46 (lIS)were me.asured with· increasing solid loading. The wt% of antifoaming agent and dispersant inthe slurry were kept constant. Figure 3 shows the pl9t of viscosity vs. solids loading for both thepowders. For the IOD powder, up to 63 wt% solid loading could be achieved, but for the 30Dpowder it was only 55 wt%.500_ 4001-:-10 °1~.u...., 300 -ll-30D>......•m 200Qym> 10000 2 4 6 8 10Solids Loading (gms)Figure 3: Effect of solids loading on the viscosity for 10D and 30D alumina ceramic powders.For the present study, 10D and 30D both the powders were used to make water basedceramic slurry. Powder, antifoaming agent and dispersant were added to water and thenmechanically stirred in a polyethylene boat for 10 minutes. The required amount of binder B-1035 (Rohm and Hass) was added to the mixture just before infiltration. Polymeric molds,produced via FDM, were infiltrated with the ceramic slurry using a vacuum oven. The infiltratedmolds were dried at room temperature for 12 hours and then subjected to binder removal andsintering cycles.Binder Removal and Sintering Cycle DevelopmentBinder removal and sintering of dry ceramic powder loaded molds were carried out in amuffle furnace in furnace air environment. Samples were placed on top of a porous zirconiaceramic plate. Figure 4 shows the heating cycle. During the first part of the cycle (by 550°C),polymeric mold material and the bind¥t evaporates. A slower heating rate is necessary up to thispoint to avoid cracking or distortion of the part. At hi~her temperature, densification of aluminaceramic occurs. A final sintering temperature of 1600 C and a hold time of 3 hours was used forall the samples.Physical and Mechanical·CharacterizationThe aim· of this work was to investigate one of the most fundamental and generalquestions regardingbioceramic implants: what are the effects of pore size, pore volume and pore632distribution on the biomechanical properties of porous ceramic implants. During this initial partof the work, porous 3D honeycomb ceramic preforms were fabricated with various pore sizesand pore volumes. The 3D honeycomb structure has unique pore geometry that are inter-180 Minutes1600Temp °c 550RTTime (Minutes)Figure 4: Schematic representation of the binder removal and sintering cycle for green ceramicparts.connected in all three X, Y and Z directions. In this work, two types of ceramic preforms werefabricated. In the first type, the pore size was same in all the three directions or uniform poregeometry sample. But in the second type, pore sizes were different in X and Y compared to Zdirection or non-uniform pore geometry. Similarly, a volume fraction gradient in porosity couldalso be achieved in pore distribution from top to bottom of the preform 'or from side to the centerof the preform.Figure 5: Optical photograph of a polymeric mold (with mold and lip) prepared via FDM and asintered alumina ceramic preform.Shrinkage is one of the most important factors during processing of these porous aluminaceramics. Initial data showed that linear shrinkage for the green to the sintered stage lie between63322 to 25%. Shrinkage data depends on the solids loading of the slurry and the particle sizedistribution of the ceramic powders. Figure 5 shows an optical photograph of a polymeric moldincluding the lip and a sintered ceramic preform fabricated using a similar mold.(a) (b)(c)Figure 6: Optical and SEM micrographs of the sintered alumina ceramic preforms. (a) Top viewof a cylindrical sample·(-0.6" diameter). (b) Top view of a ceramic preform with uniform poresizes in X, Y and Z directions (- 300J.!m diameter). (c) Side view of a ceramic preform withnon-uniform pore sizes in X, Y and Z directions (- 300J.!m dia.meter in X and Y and 750J.!m inZ).Figure 6 shows the optical a.nd scanning electronrnigrographs of samples with uniformand non-uniform pore sizes. 3D>honeycomb structures with 33% to 50% total pore volumeswere fabricated with pore sizes varying from 300 J.!m to 750 J.!m. Figure 6 (b) shows the SEMmicrograph of the uniform pore size sample where -300 J.!m diameter pores are interconnected inX, Y and Z directions. Figure 6 (c) shows another structure where pore sizes in Z direction is-750 IJ.m and -300 J.!m in X and Y directions.634Initial compression tests were performed with some of these samples having 33% porevolume and uniform pore sizes using an MTS servo hydraulic machine. The compression testdata is shown in Figure 7. These tests were performed with.samples having a diameter vs. heightratio 1: 1. The load vs. displacement curve showed a stepwise increase due to the failure of someof the pore walls during testing. The final fracture ofthese test samples occurred longitudinallywith a multifaceted fracture surface. Final fracture stress varied between 2000 to 2500 MPa forsamples with 33 volume% of porosity with pore .sizes varying from 300 to 400 J.Lm. Furthercompression tests and four point flexural tests of these samples are currently under investigation.2500-2000~~:g 1500'-'fI.l 1000fI.lf.... 5000000 0.5 1 1.5 2Displacement (mm)Figure 7: Displacement vs. stress plot for the 3-D honeycomb porous alumina ceramic preformshaving 33% porosity.Conclusions3D honeycomb porous alumina ceramic preforms were fabricated using indirect SFFroute. Polymeric molds were fabricated using FDM 1650 with ICW06 filaments and theninfiltrated with ceramic slurry and then dried. Dry molds were subjected to a binder bum out andsintering cycle. Structures with uniform and non-uniform pore sizes were fabricated via thismethod. Initial compression tests of 33 volume % porous structures showed that ultimate failurestress varied in the range of 2000 to 2500 MPa. Detailed mechanical characterization of thesesamples is currently under investigation.AcknowledgementsThe authors would like to acknowledge John Merlino, Rubiela Diaz, Shinichi Sugiuraand Sudharshan Rangaraj of the School of Mechanical and Materials Engineering at WSU fortheir help in SEM, and other materials processing work.635References1. L. L. Hench, "Bioceramics: From Concept to Clinic," J. Amer. Ceram. Soc., 74[7], pp 1487-510 (1991).2. L. L.Hench, "Bioceramics," J. Amer.Ceram. Soc., 81[7], pp 1705..28 (1998).3. L. Hench and J. Wilson, "An Introduction to Bioceramics," World Scientific (1993).4. A. Ravaglioli and A. Krajewski, "Bioceramics: Materials, Properties, Applications,"Chapman and Hall,·London, (1992).5. K. deGroot, "Clinical Applications of Calcium Phosphate Biomaterials: A Review,"Ceramics International, 19, pp 363-66 (1993).6. H. Alexander, J. R. Parsons, J. L. Ricci, P. K. Bajpai and A. B. Weiss, "Calcium BasedCeramics and Composites in Bone Reconstruction," CRC Critical Reviews inBiocompatibility, 4 [1], pp 44 (1987).7. L. L. Hench and E. C. Ethridge, "Biomaterials: An Interfacial Approach," Academic Press,New York, (1982).8. G. Lee and J .. W. Barlow, "Selective Laser Sintering of Calcium Phosphate Powders,"Proceedings of the Solid Freeforrn Fabrications 1993, The University of Texas at Austin, TX,pp 191-97 (1993).9. G. Lee, J. W. Barlow, W. C. Fox and T. B. Aufdermorte, "Biocompatibility of SLS formedCalcium Phosphate Implants," Proceedings of the Solid Freeform Fabrications 1996, TheUniversity of Texas at Austin, TX, pp 15-21 (1996).10. US patent 5,518,680.11. US patent 5,490,962.12. T. M. Chu and J. W. Halloran, "Hydroxyapatite Scaffolds with Controlled Porosity,"presented at the Bioceramics: Materials and Applications Symposium at 100th AnnualAmerican Ceramic Society Meeting, Cincinnati, OH, May 2-6, 1998.13. R. Garg, R. K. Prud' homme and I. A. .Aksay, "Orthopaedic Implants by CeramicStereolithography," presented at the Bioceramics: Materials and Applications Symposium at100th Annual American Ceramic Society Meeting, Cincinnati, Ohio, May 2-6, 1998.14. P. Teung, R. K. Panda, S. C. Danforth and A. Safari, "Fabrication of Porous HydroxyapatiteCeramics by Solid Freeform Fabrication Technique," presented at the Bioceramics: Materialsand Applications Symposium at 100th Annual American Ceramic Society Meeting,Cincinnati, OH, May 2-6, 1998.636

Processing of Bioceramic Implants Via Fused Deposition Process

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Processing of Bioceramic Implants Via Fused Deposition Process

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