Biomedical Engineering Reference
In-Depth Information
However, incomplete removal of the porogens is sometimes observed due to
incomplete leaching. The mechanical properties and accuracy of 3DP fabricated
scaffolds are other considerations that need to be addressed [
233
] .
Despite the idea of using a water-based ink in order to eliminate a toxic fabrica-
tion environment, and thus creating an opportunity to incorporate biological agents
or even living cells, toxic post-processing of the constructs is often needed to
improve the mechanical properties. Suwanprateeb [
234
] described a double
infiltration technique to increase the mechanical properties of natural polymers fab-
ricated by three-dimensional printing using a water-based binder. The 3DP parts
were porous in nature since the powder bed was only lightly packed during the pro-
cess and only the surface of the powder granules was connected by a binder. Porosity
typically ranged between 50 and 60 %. To enhance the performance of the 3DP
parts based on a mixture of 40 wt.% starch, 15 wt.% cellulose fibre, 25 wt.% sucrose
sugar and 20 wt.% maltodextrin, infiltration by some other material, was performed.
The infiltration material used in this experiment was a heat-cured dental acrylate
prepared by mixing triethylene glycol dimethacrylate, 2,2-bis[4(2-hydroxy-3-
methacryloyloxypropyloxy)-phenyl]propane and a polyurethane dimethacrylate in
a 40:40:20 wt.% proportion. Benzoylperoxide was used as initiator. After infiltration,
the specimen was cured at 105 °C for 30 min. From the results, it was found that
double infiltration and curing of 3DP samples increased the performance of speci-
mens in wet conditions.
P fi ster et al. [
220
] described the fabrication of biodegradable polyurethane scaf-
folds by 3D Printing. In this case, the polyurethane formation is the post-treatment
step. Commercially available powder ZP11 (a powder blend of starch, short cellu-
lose fibres and dextrose as a binder) was processed by the printing of an aqueous
ink, which activates the dextrose binder. The resulting objects were very fragile and
highly water-soluble. Therefore, the authors selected an additional post-treatment
step involving infiltration and partial crosslinking with lysine ethylester diisocya-
nate. The starch polyols react with the isocyanate to form network structures.
The obtained structures exhibited much improved mechanical stability. Because
of the presence of starch incorporated in the network, the structures could swell and
the resulting lysine-based polyurethane networks were biodegradable upon expo-
sure to water and body fluids.
9.4
Preserving the Mechanical Integrity of RP
Processed Hydrogels
As previously mentioned, the mechanical properties of a certain biomaterial play a
partial, although crucial role in its potential success as a scaffolding material. More
specific, it has been generally accepted that in designing a proper scaffold biomate-
rial, one must strive to translate the mechanical characteristic features of the target
tissue into the mechanical features of the fabricated construct. For instance, hard
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