Hydrogel mechanical properties in altered gravity

Abstract

Exposure to altered gravity influences cellular behaviour in cell cultures. Hydrogels are amongst the most common materials used to produce tissue-engineering scaffolds, and their mechanical properties play a crucial role in cell-matrix interaction. However, little is known about the influence of altered gravity on hydrogel properties. Here we study the mechanical properties of Poly (ethylene glycol) diacrylate (PEGDA) and PEGDA incorporated with graphene oxide (GO) by performing tensile tests in micro and hypergravity during a Parabolic flight campaign, and by comparing them to the same tests performed in Earth gravity. We show that gravity levels do not result in a statistically significant difference in Young's modulus.

Fig. 1. Parabolic flight manoeuvre.

a Typical path of the aircraft during a single parabola. Adapted from ref. . b Parabolic flight z-axis acceleration data taken by the accelerometer inside the experimental test rig. c Timeline of the standard testing procedures registered during the flight.

Fig. 2. Schematic tensile system.

a Sample in Position 1 for the tensile test, b sample in position 2 for spraying. c Experimental setup inside a protective box. i–ii detailed views of i spraying loop and ii tensile system.

Fig. 3. Force–displacement curves.

a PEGDA curves; (b) PEGDA-GO in hyperg-, micro-, and Earth gravity curves; (c) E changes during 5 cycles in hyper- and microgravity; (d) Stress–strain curve in the 5th parabola, during hyper- and microgravity, including the transition between two gravities (red box). The test is stopped when a maximum force of ~6.5 N is reached.

Fig. 4. Force displacement curves.

a Comparison between two hydrogels with 0%SR of the same size, tested on flight and on ground following the same procedure. b Same samples after the setup offset is calculated and applied to the ground data.

Fig. 5. Mechanical properties of hydrogels under altered gravity conditions.

E modulus (a) PEGDA and (b) PEGDA-GO hydrogels with different PBS content, comparing ground and flight data. The error bars indicate the minimum and maximum values. The line in the middle presents the median value. Outliners (anything higher or lower than 1.5 times the interquartile range) are presented with a diamond shape. *p < 0.05, n.s. = not significant (p > 0.05); Stress–strain curve of swollen (c) PEGDA and (d) PEGDAGO hydrogels. Comparison between ground and flight after the 4th spray. The test is stopped at a maximum force of ~6.5 N.