Effect of microstructure on anomalous strain-rate-dependent behaviour of bacterial cellulose hydrogel

Abstract

This study is focused on anomalous strain-rate-dependent behaviour of bacterial cellulose (BC) hydrogel that can be strain-rate insensitive, hardening, softening, or strain-rate insensitive in various ranges of strain rate. BC hydrogel consists of randomly distributed nanofibres and a large content of free water; thanks to its ideal biocompatibility, it is suitable for biomedical applications. Motivated by its potential applications in complex loading conditions of body environment, its time-dependent behaviour was studied by means of inaqua uniaxial tension tests at constant temperature of 37°C at various strain rates ranging from 0.0001 s -1 to 0.3 s -1 . Experimental results reflect anomalous strain-rate-dependent behaviour that was not documented before. Micro-morphological observations allowed identification of deformation mechanisms at low and high strain rates in relation to microstructural changes. Unlike strain-rate softening behaviours in other materials, reorientation of nanofibres and kinematics of free-water flow dominate the softening behaviour of BC hydrogel at high strain rates.

Printed hydrogel nanocomposites: fine-tuning nanostructure for anisotropic mechanical and conductive properties

“…According to our previous research [22,23], there is a high likelihood that the mechanical properties of PHEMA-based nanocomposites are viscoelastic or hyperelastic. For a typical viscoelastic material, the phase difference between the stress input and the strain response leads to a hysteresis, known as dissipated energy [24][25][26]. Thus, the stress-strain relationship of the material is sensitive to the loading speed or strain rate [27,28].…”

“…The size of the loop represents the energy dissipated during the cyclic deformation. The degree of viscoelasticity (η) is defined as the ratio of the unloading area (the area under the unloading path) to the loading area (the area under the loading path) [24]. Thus, the more energy dissipated during the cyclic loading, the larger hysteretic loop can be obtained; consequently, the ratio η is farther from the value 1, indicating a larger degree of viscoelasticity.…”

Dry vs. wet: Properties and performance of collagen films. Part I. Mechanical behaviour and strain-rate effect

“…Thus, it may be concluded that while modelling wet or in-vivo collagen specimens, the parameters obtained with the Ogden model should closely reproduced the deformational behaviour of collagen. The collagen films subjected to hydration or in-aqua conditions (submersion) exhibited a similar response to that observed for bacterial cellulose hydrogel (Gao et al, 2016). ε 1 , ε 2 , ε 3 and ε UTS denote the strain magnitude at the end of Stage I, II, III and IV (ultimate tensile strain), respectively.…”

“…11b). The same approach was used to predict the value of m in biomaterials (Gao et al, 2016;Zhao et al, 2017).…”

Assessing stiffness of nanofibres in bacterial cellulose hydrogels: Numerical-experimental framework

“…Motion of water during a process of deformation is involved in the network's response, affecting the measurements of its stiffness [43]. In this study, an initial unloading tangent modulus was used as effective elastic property of bulk specimens based on inelastic behaviour from our previous research [12].…”