Page 276 - IJB-10-4

International Journal of Bioprinting 3D printing prosthesis for palatal fistula

were recorded before curing, and then, the samples were 2.5.7. Shore hardness determination of PU elastomers
cured using a light curing lamp. Subsequently, the FT-IR Shore-A hardness of each light-curable PU elastomer
absorption spectra of the cured samples were immediately was determined according to the standard, ISO
measured. The absorbance change (A) of the C=C double 10139-2-2016-compliant method for testing the shore
bond at 1638 cm was calculated using the absorption peak hardness of soft denture lining materials for long-term use.
-1
of C=O (1720 cm ) as an internal standard. The calculation We performed hardness measurements on each sample
-1
formula is as follows: C=C bond conversion rate (%) = [1 – with a thickness of 1.0 cm using a Shore-A durometer.
(A1638 cm /A1720 cm after curing)/(A1638 cm /A1720 Readings were taken 5 s after indentation and recorded as
-1
-1
-1
cm before curing)] × 100%. hardness values for the materials.
-1
2.5.4. Curing shrinkage test of photocurable PU 2.5.8. Observation via atomic force microscope
The uncured printing ink was added to the rigid mold, The surface roughness of the NPP composites at nano
which had a depth of 3 mm and an inner diameter of 10 level was measured by means of atomic force microscopy
mm, until it reached its maximum capacity. Subsequently, (AFM; Bruker MultiMode 8, Germany). Image analysis
the sample was exposed to UV irradiation for 60 s to was performed using Gwyddion software.
ensure complete curing, after which the height variation
was measured using a displacement meter. The curing 2.5.9. Friction coefficient test of PU elastomers
shrinkage of PU (A ) from the start to the end is defined The friction coefficient test of the PU elastomers was
D
by the formula: A = (V - V )/V × 100%, where V refers performed with a UMT-2MT Tribological Tester (UMT-
D
0
0
0
D
to the volume before curing, and V refers to the volume 2MT, CETR Corporation Ltd, USA). The counterpart ball
D
after curing. The experiment was repeated three times. was made of grade 440C steel with an HRC62 hard value
and cleaned ultrasonically in acetone for 20 min. Friction
2.5.5. Hydrophilicity of PU elastomers and wear tests were performed under wet friction, with a
We evaluated the surface hydrophilicity of the PU sliding speed of 40 mm/s and a normal load of 5 N, for a
elastomers and MDX-4210 silicone rubber by measuring duration of 20 min.
the static aqueous contact angles using a contact angle
measurement instrument (SL250, USA) (n = 5). 2.5.10. Tensile property and compressive property
tests of light-curable PU elastomers
2.5.6. Water sorption value and water solubility value We utilized a universal testing machine (UTM4204, China)
of light-curable PU elastomers to assess the tensile and compressive properties. For the
The specimens used for testing were prepared according tensile properties, we followed ASTM D412 standard to
to the standard (ISO 10139-2-2016). The samples with a create dumbbell-shaped samples symmetrically loaded
50 ± 0.1 mm diameter and a 0.5 ± 0.05 mm thickness were into the testing machine fixture. The test speed was
wholly immersed in water for 7 days. The water used was maintained at 500 ± 50 mm/min, and if the sample’s
of grade 2 according to ISO 3696. The specimens were yield point was below 20% elongation, the test speed was
placed in a desiccator with silica gel, transferred to an reduced to 50 ± 5 mm/min. Test results, representing the
oven at 37°C, and repeatedly weighed on an electronic median values, were tabulated based on three consecutive
analytical balance at 24-h intervals until a constant independent samples.
mass (M1) was obtained. The thickness and diameter of Compression mechanical tests for light-curable PU
the specimens were measured to the nearest 0.01 mm elastomer samples (measurement range: 0–10 kN) were
using an electronic digital caliper. We calculated each conducted on a universal testing machine (WDW-5,
specimen’s volume (V) in cubic millimeters (mm ). Hualong, Shanghai, China). Each sample underwent
3
These specimens were individually stored in sealed glass 50% compression (4 mm) at a rate of 1.2 mm/min at
vials containing 20 mL of deionized water (pH 7.2) at room temperature, following the ISO 604:2002 standard.
37°C for 7 days and then washed in running deionized Engineering stress–strain curves of light-curable PU
water. The surface water was gently wiped with absorbent elastomers were obtained post-compression.
paper and weighed on an analytical balance for M2
determination. As previously described, the specimens 2.5.11. Prosthesis made by 3D printing
were re-dried in a desiccator and weighed daily until a LCD printer (Creality, Shenzhen, China) was used to
dried constant mass (M3) was obtained. Water sorption fabricate all the 3D-printed structures. All the printing ink
value (WSP) and water solubility value (WSL) were was poured into an amber bottle and stirred for more than
calculated after 7 days of keeping the specimens in water 1 h to ensure its homogeneity. The model of the speech aid
using the following formulas: WSP = (M2 - M3)/V; WSL prosthesis was loaded into the slicing software (CHITU8.0,
= (M1 - M3)/V. Shenzhen, China) to set the basic parameters. We added

Volume 10 Issue 4 (2024) 268 doi: 10.36922/ijb.2516