1. Stereolithographic
layer-by-layer
printing
Debinding
Sintering
Lithography-based Additive Manufacturing
of Bioactive Glass Ceramics
Robert Gmeiner1*, Ileana Panaitescu1, Gerald Mitteramskogler1, Jakub Wojak1,
Aldo R. Boccaccini2, Jürgen Stampfl1
1Institute of Materials Science and Technology, Vienna University of Technology, Favoritenstraße 9-11/E308, A-1040 Vienna, Austria
2Institute for Biomaterials, University of Erlangen-Nuremberg, Cauerstrasse 6, 91058 Erlangen, Germany
*Corresponding author: robert.gmeiner@tuwien.ac.at (R. Gmeiner)
Introduction
1. Light source
2. DMD-chip (dynamic mask)
3. Optic
4. Material vat
5. Coating blade
6. Back light
7. Building platform
8. Load cell
9. Manufactured part
DLP-based Lithography
The additive manufacturing system used for this study is
based on the DLP (Digital Light Processing) technology
(see Figure 1). A Digital Mirror Device (DMD) chip acts as
an dynamic mask to expose a well defined area on the
bottom of a transparent material vat above an optical
system. The so generated pictures enable layer-by-layer
polymerization of a photosensitive resin resulting in 3-
dimensional objects. Curing takes place at wavelengths
around 460nm which means blue visible light. The
system used combines high optical resolution, allowing
voxel geometries of 25x25x25µm3, in a building area the
size of a coffee cup.
[1] R. Gmeiner, G. Mitteramskogler, A.R. Boccaccini, and J. Stampfl, “Stereolithographic Ceramic Manufacturing of High Strength Bioactive Glass”; Int. J. Appl. Ceram. Tec. 2014, DOI:10.1111/ijac.12325
[2] P. Tesavibul, R. Felzmann, S. Gruber, R. Liska, I. Thompson, A.R. Boccaccini, and J. Stampfl, “Processing of 45S5 Bioglass® by lithography-based additive manufacturing,” Mater. Lett., 74 81–84 (2012).
[3] L.L. Hench and T. Kokubo, “Properties of bioactive glasses and glass-ceramics”; pp. 355–363 in Handb. Biomater. Prop. Edited by J. Black and G. Hastings. Springer US, 1998.
Bioactive glasses and glass ceramics like the 45S5 formulation have been studied towards biocompatibility and –degradability for years. Nevertheless clinical applications as bone substitute or scaffold material are
highly limited because of their often poor mechanical behaviour. In this study we are able to provide a new production alternative for 45S5 bioactive glass structures resulting in parts with high density and
strength. By using the Stereolithographic Ceramic Manufacturing (SLCM) process it is possible to additively produce solid bulk glass ceramics as well as delicate scaffold structures. Recent developments in SLCM
slurry preparation together with an appropriate selection of raw materials led to 3D-parts with a very homogeneous microstructure and a density of about 2,7g/cm³. Due to the low number and small size of
defects, a high biaxial bending strength of 124MPa was achieved. Weibull distribution also underlines good process control showing a Weibull modulus of 8.6 and a characteristic strength of 131MPa for the
samples tested here. By reaching bending strength values of natural cortical bone, bioactive glasses processed with SLCM could eventually advance to be an interesting bone substitute material even in load
bearing applications.[1]
0,00
20,00
40,00
60,00
80,00
100,00
120,00
140,00
160,00
Bioactive glass
(Vitryxx®)
Biaxialbendingstrength[MPa]
y = 8,6205x - 42,033
-5
-4
-3
-2
-1
0
1
2
3
4,5 4,6 4,7 4,8 4,9 5 5,1 5,2
lnln(1/1-Pf)
ln(σ) [MPa]
Name [weight %]
SiO2 45,50
CaO 24,25
Na2O 24,25
P2O5 6,00
Table 1: Composition of the ‘bioactive
glass powder’ used (Vitryxx, Schott
AG, Mainz, Germany)
The 45S5 bioactive glass formulation is well known for its biocompatible and biodegradable
properties. The bioactive glass ceramic filling material used in this study is comparable to the 45S5
formulation (see Table 1) and available under its commercial name Vitryxx® (Schott AG, Mainz,
Germany). By using small grained powder we have been able to generate homogenious slurries
without perturbing agglomerates, thus enabling smooth and defect free green part production.
Stereolithographic green part generation is subsequently followed by a debinding cycle, eliminating
the organic binder compounds. Dense glass ceramic parts can be manufactured using a final
sintering step, completing the SLCM process.
Mechanical characterization of the resulting
bioactive glass ceramics included density
measurements, biaxial bending tests, EDX
analysis and SEM fracture inverstigations.
Tested specimens show suprisingly high biaxial
bending strength (124 MPa) compared to other
production techniques known in literature (see
Table 2). This is understood to be related to the
high density found for the glass ceramic parts.
SEM images confirm the homogenious
microstructure of the generated parts, showing
only a few minor defects on fracture surfaces
(see Figure 3). Weibull statistics reveal good
process control, resulting in a Weibull modulus
of 8.6 for biaxial beding test specimen.
SLCM enables high feature resolution as well as outstanding material properties and can therefore be considered as a
possible key technology for manufacturing delicate bioactive scaffolds or patient specific bone restorations out of
bioactive glass ceramics like the 45S5 formulation (see Figure 4). The technology could assist bone cancer treatment or
pioneer new approaches in maxillofacial surgery, valuing the huge efforts undertaken to understand bioactive glass
ceramic behaviour.
Bioactive glass 45S5
Density of sintered samples [g/cm³] 2,701
Biaxial bending strength [MPa] 124 ±17
Biaxial bending strength in literature [MPa] 422, 403
Weibull modulus [ - ] 8.6
Weibull characteristic strength [MPa] 131
Table 2: Material properties of 45S5 bioactive glass ceramic
manufactured by SLCM-technology
Figure 2: Biaxial bending strength and Weibull modulus of 45S5 bioactive glass used in the
stereolithographic ceramic manufacturing process (accord. to ISO 6872)
Figure 3: SEM images of fracture surfaces of 45S5 test specimen are showing high density and
only a few, minor defects in the microstructure of the bioactive glass ceramic
Bioactive Glass
Material Properties
Conclusion
Figure 1: DLP-based stereolithographic printing process
Figure 4: Bioactive glass ceramic scaffold based on µCT data of human femoral bone
(spongiosa), manufactured by SLCM process