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. 2020 Sep 18;12(9):2136.
doi: 10.3390/polym12092136.

3D Printed Silicone Meniscus Implants: Influence of the 3D Printing Process on Properties of Silicone Implants

Eric Luis  1 , Houwen Matthew Pan  2 , Anil Kumar Bastola  1 , Ram Bajpai  3 , Swee Leong Sing  1 , Juha Song  2 , Wai Yee Yeong  1
Affiliations

3D Printed Silicone Meniscus Implants: Influence of the 3D Printing Process on Properties of Silicone Implants

Eric Luis et al. Polymers (Basel). .

Abstract

Osteoarthritis of the knee with meniscal pathologies is a severe meniscal pathology suffered by the aging population worldwide. However, conventional meniscal substitutes are not 3D-printable and lack the customizability of 3D printed implants and are not mechanically robust enough for human implantation. Similarly, 3D printed hydrogel scaffolds suffer from drawbacks of being mechanically weak and as a result patients are unable to execute immediate post-surgical weight-bearing ambulation and rehabilitation. To solve this problem, we have developed a 3D silicone meniscus implant which is (1) cytocompatible, (2) resistant to cyclic loading and mechanically similar to native meniscus, and (3) directly 3D printable. The main focus of this study is to determine whether the purity, composition, structure, dimensions and mechanical properties of silicone implants are affected by the use of a custom-made in-house 3D-printer. We have used the phosphate buffer saline (PBS) absorption test, Fourier transform infrared (FTIR) spectroscopy, surface profilometry, thermo-gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) to effectively assess and compare material properties between molded and 3D printed silicone samples.

Keywords: 3D printing; additive manufacturing; meniscus implants; silicone; validation.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
The hydrosilylation reaction of liquid silicone rubbers.
Figure 2
Figure 2
(a) Photographs: (1) motion control platform, (2) discovery extruder, (3) static mixer, (4) printer nozzle head, (5) heated printer bed platform, (6) double-barrel-syringe and (b) simplified schematic of experimental setup for heat-cure extrusion-based printer.
Figure 3
Figure 3
Computer-aided design (CAD) of meniscus implant.
Figure 4
Figure 4
Photograph of the standard and meniscus samples: (A) STD-Eco30 samples (top row) and STD-Eco50 samples (bottom row) and (B) 3DP-Eco30 samples (top row) and 3DP-Eco50 samples (bottom row).
Figure 5
Figure 5
Representative stereomicroscopic images of the core surfaces of silicone meniscus implants. (a) surface of molded implant, (b) surface of 3D printed implant, (c) cross-section of molded implant and (d) cross-section of 3D printed implant (20× magnification).
Figure 6
Figure 6
Representative scanning electron microscope (SEM) pictures (magnification 100×, 400× and 1000×) showing the different surface patterns of (a,c,e) molded silicone and (b,d,f) 3D-printed silicone.
Figure 7
Figure 7
Phosphate buffer absorption test for silicone meniscus implants Ecoflex 50 and 30.
Figure 8
Figure 8
Surface roughness (µm) of the two silicone elastomers (Ecoflex-30 and Ecoflex-50) manufactured by molding and 3D printing.
Figure 9
Figure 9
FTIR absorbance spectra of (a) 3D printed silicone implant and (b) molded silicone sample.
Figure 10
Figure 10
Thermo-gravimetric analysis/differential scanning calorimentry (TGA/DSC) curves of (a) molded and (b) 3D-Printed silicone Ecoflex 50 measured from 30 to 700 °C at a heat rate of 20 K/min. The TGA curve (red) measures the loss of mass and the DSC curve (black) provides information about endothermic and exothermic effects.
Figure 10
Figure 10
Thermo-gravimetric analysis/differential scanning calorimentry (TGA/DSC) curves of (a) molded and (b) 3D-Printed silicone Ecoflex 50 measured from 30 to 700 °C at a heat rate of 20 K/min. The TGA curve (red) measures the loss of mass and the DSC curve (black) provides information about endothermic and exothermic effects.
Figure 11
Figure 11
(a) Cell proliferation of re-seeded L929 cells on printed/casted Eco50/Eco30 substrates after 24, 72, and 120 h culture was quantified based on the WST-8 cell proliferation assay. (b) Fluorescent images of re-seeded L929 cells on printed/casted Eco50/Eco30 substrates after 24, 72, and 120 h culture. Cells were stained with the Live/Dead® cell viability assay. Statistical significance between groups was assessed using two-way analysis of variance (ANOVA) followed by Bonferroni post-tests. ns = p > 0.05 and *** = p < 0.001.
Figure 12
Figure 12
Four-cycle cyclic stress-strain for (a) STD-Eco30 and (b) STD-Eco50 at strain rates of 12, 120, 360, 720, and 1000 mm/min.
Figure 13
Figure 13
1000-cycle cyclic stress-strain for (a) STD-Eco30 and (b) STD-Eco50, at a strain rate of 1000 mm/min.
Figure 14
Figure 14
The 1000-cycle cyclic stress-strain for (a) 3DP-Eco30 and (b) 3DP-Eco50, at a strain rate of 1000 mm/min.
Figure 15
Figure 15
Modulus for Eco30 and Eco50 at different strain rates.
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