IFMBE Proceedings, editors: H.Hutten, P. Krösl, EMBEC’02, Vienna pp172-173

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RAPID PROTOTYPING OF CERAMIC AND POLYMERIC CELLULAR MATERIALS

J. Stampfl1, A. Wöß2, 3, P. Fratzl2 and S. Seidler1

1 TU Wien, Inst. für Werkstoffkunde und Materialprüfung, Favoritenstraße 9-11, A-1040 Wien,

2 Erich Schmid Institut für Materialphysik, Jahnstraße 12, A-8700 Leoben, Austria 3 Austrian Research Centers Seibersdorf, A-2444 Seibersdorf, Austria

Abstract: Cellular structures form the basis of many natural materials (wood, bone, cork, ...). By using solid free-form fabrication techniques, artificial cellular solids are manufactured in order to achieve two goals: (1) By investigating the mechanical response of cellu-lar solids with defined internal and external geome-tries, insight into the mechanical behaviour of natu-ral cellular solids can be gained. (2) Cellular materials are currently used as scaffold-ing material for a wide variety of biomedical applica-tions. By utilizing advanced manufacturing tech-niques like rapid prototyping, new routes for the fabrication of cellular solids for biomedical applica-tions are opened. Keywords: Rapid Prototyping, biomaterials, ceram-ics, cellular materials

Introduction

The mechanical and microstructural properties of

natural cellular materials like wood and bone have been studied [1][2] in great detail. In order to fully under-stand the influence of the cellular architecture on the measured properties, an experimental route for the fab-rication of cellular materials with defined internal ge-ometries is necessary.

Process selection

Rapid prototyping (RP) techniques offer a number of advantages for potential applications based on cellular materials:

• RP can generate parts with very complex arbi-trary geometries

• In combination with appropriate molding proc-esses there is a wide range of materials available, including polymers, metals and ceramics.

• RP processes currently in development (like mi-cro-stereolithography) can achieve feature reso-lutions on a scale which is similar to that occur-ing in natural cellular solids like bone.

Results

In Figure 1 cellular structures made by several RP techniques (stereolithography, selective laser sintering and the Solidscape system) are depicted. For the fabrication of complex structures with extensive

cation of complex structures with extensive overhangs, powder based methods like selective laser sintering offer an advantage since they do not require sacrificial support structures. Nevertheless, stereolithography (SLA) is more likely to become a standard RP technique for biomedical applications, since SLA can fabricate structures with higher resolution and better surface quality.

5mm

Figure 1: Sample RP parts made by stereolithogra-

phy (top) selective laser sintering (middle) and Solid-scape ModelMaker (bottom).

For the fabrication of ceramic cellular materials a

two-step process was chosen: In a first step a polymeric master pattern is fabricated using RP. This master pat-tern is transferred into the final part material by an ap-

IFMBE Proceedings, editors: H.Hutten, P. Krösl, EMBEC’02, Vienna pp172-173

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Tab. 1: Measured strength and stiffness values for cellular structures made by RP. The values for cancellous bone are taken from [1].

Strength RM Stiffness E Density ρ E/ ρ RM/ ρMPa MPa kg/m³ MPa m³/kg Pa m³/g

Cubic primitive 1,8 64,1 170,0 0,4 10,6Cubic body centered 1,5 38,5 170,0 0,2 8,8Gibson Ashby 0,9 20,6 170,0 0,1 5,3Cancellous bone 1-80 50-1200 150- 1000 0,2-2 9-80

propriate molding technique. By using such an ap-proach, it is possible to focus on fabricating a well de-fined geometry in the first step. Materials related issues can be solved independently in the second step.

In Figure 2 two ceramic sample parts are shown,

which were molded using gelcasting [3][4]. The upper part was cast into a mold made by micromachining and illustrates that by using gelcasting small cavities can be filled and a defined replication of the mold can be ob-tained. The lower part in Figure 2 shows a cellular solid out of alumina. The wax-mold for this part has been made with a Solidscape ModelMaker and after filling the mold with aeqeous gelcasting slurry the depicted green part has been obtained.

5mm Figure 2: Ceramic parts made by gelcasting. The up-

per picture shows an SEM image of a micro-turbine out of silicon nitride. The lower picture is a cellular solid

made of alumina.

Tab.1 summarizes the mechanical properties of polymeric cellular solids made by selective laser sinter-ing. All structures were fabricated with the same appar-ent density in order to investigate the influence of the structure on the mechanical properties. The strength and stiffness were measured in compression. Conclusions It could be shown how Rapid Prototyping can be used to fabricate cellular solids with defined internal and exter-nal geometry. The possible materials include polymers and ceramics. The available molding techniques are sufficient for replicating RP patterns with high accuracy and good surface finish. For possible application as scaffolding material, the commercially available RP processes currently do not provide sufficient resolution. But by using processes like micro-stereolithography, it can be expected that cellular solids made of engineering materials (e.g. ceramics) with feature resolutions around 100µm can be fabricated using the techniques described above.

Acknowledgement

We want to thank Dr. A. Ippavitz (Inst. for foundry technology, University of Mining and Metallurgy, Leoben) for providing the Solidscape Modelmaker which was used for the fabrication of wax molds.

REFERENCES [1] L.J. Gibson and M.F. Ashby, "Cellular solids –

structures and properties", 2nd edition, Cambridge University Press, 1997

[2] P. Fratzl, Von Knochen, Holz und Zähnen, Physik Journal vol 1 pp49-55 (2002)

[3] J. Stampfl H.C. Liu, S.W. Nam, K. Sakamoto, H. Tsuru, S. Kang, A. G. Cooper, A. Nickel, F. B. Prinz, Rapid Prototyping and Manufacturing by Gelcasting of Metallic and Ceramic Slurries, Mate-rials Science and Engineering A vol 334 pp 187-192 (2002)

[4] J. Stampfl, H.-C. Liu, S.W. Nam, S. Kang and F.B. Prinz, Rapid prototyping of mesoscopic devices. In: B.Michel (ed.), in: Proceedings MicroMat 2000, Berlin, Germany, pp 1073-1078, Verlag ddp goldenbogen, Dresden, (2000)