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Biomechanics

Biomechanics - Poster Session E

Poster D9 - Soft Silicone Stiffness Modulation with Deep UV and Characterization with Nanoindentation

Saturday, October 26, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  The stiffness of the extracellular matrix (ECM) greatly influences cellular function. Various soft substrates such as polyacrylamide gels and soft silicones have been used to mimic the ECM. Soft silicones are particularly advantageous for mechanobiology studies, but there are not any known straightforward methods to alter their mechanical properties. In this study, we use nanoindentation to investigate if deep UV exposure can alter the stiffness of soft silicones.

Materials and

Methods:  The two soft silicones used in this study were GEL-8100 1:1, 0.5% Sylgard (GEL-8100/Syl) and Qgel 1:2.2 (Qgel). 4-5 drops of silicone were spread on top of a 22 mm x 22 mm glass coverslip and then cured (in an oven at 70 deg C for 2.5 hrs for GEL-8100/Syl and on a hotplate at 100 deg C for 1 hr for Qgel). Half of the silicone samples were then treated with deep UV for 30 min and the Young’s modulus of elasticity of each sample was measured using a nanoindenter (Chiaro, Optics11 Life) with a probe of stiffness 0.47N/m and tip radius 26.5μm. Measurements were taken in Phosphate-Buffered Saline (PBS) or in 1% (w/w) sodium dodecyl sulfate (SDS) in PBS. Measurements were made with a piezo-induced cantilever downward speed of 10,000 nm/s, to reduce noise which increases at lower speeds, as well as to limit adhesion which increases at higher speeds. We made 6 coverslips of each silicone type and treated 3 of each with deep UV. Each silicone sample was indented six times with indentations 1000 μm apart along x/y.

Results, Conclusions, and Discussions: When using the nanoindenter to measure our soft silicone samples, we found that there was a very high amount of adhesion between the surface of the silicone and the tip of the probe (Fig. 1). Based on a previous report (Zhang et al (2021) Acta Mech. Sin. 37, 554), we hypothesized that using a surfactant such as 1% sodium dodecyl sulfate (SDS) would reduce the adhesion between our soft silicones and glass probes as well. By adding SDS to our PBS solution, we were able to eliminate almost all of the adhesion (Fig 2.)
Young’s Moduli was obtained from the indentations using a fit of the loading curve with Hertz model for elastic materials. The Young’s modulus for Qgel was 27.95 ± 3.07 kPa and the Young's modulus for GEL-8100/Syl was 6.77 ± 0.56 kPa. After 30 min of deep UV exposure, the Young’s modulus for Qgel was 46.24 ± 6.86 kPa and for GEL-8100/Syl was 7.91 ± 1.03 kPa. This reveals a ~65% increase in stiffness for Qgel and a ~17% increase in stiffness for GEL-8100/Syl. It is also evident from Fig. 2 and 3 that the slope of the load indentation curves increases after deep UV exposure, and that deep UV exposure has a much greater effect on the Qgel than the GEL-8100/Syl.
Determination of soft silicone substrate stiffness using nanoindentation enabled us to particularly assess topical changes in the Young’s modulus. Use of multiple soft silicones also indicates the general applicability of our approach. We have thus demonstrated a physical method to alter the stiffness of soft silicones. We propose that this approach can be used to assess the effect of substrate stiffness on cell behavior in mechanobiological studies.

Acknowledgements (Optional):