Sample, testing and analysis variables affecting liver mechanical properties: A review

Mattei, Giorgio; Ahluwalia, Arti

doi:10.1016/j.actbio.2016.08.055

Cited by 59 publications

(53 citation statements)

References 85 publications

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“…Prior to testing, samples were equilibrium swollen in PBS 1X and carefully measured in thickness and diameter with a calliper (0.05 mm resolution), averaging readings from at least three different points. Force and displacement data were acquired starting with the upper plate of the testing device (connected to the load cell) close to but not in contact with the sample, to guarantee a zero pre-stress initial condition and a constant approach velocity [7,10–13]. Samples were partially immersed in PBS 1X while being tested to preserve their hydration during experiments [7,10–12,14].…”

Section: Methodsmentioning

confidence: 99%

On the adhesion-cohesion balance and oxygen consumption characteristics of liver organoids

et al. 2017

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Liver organoids (LOs) are of interest in tissue replacement, hepatotoxicity and pathophysiological studies. However, it is still unclear what triggers LO self-assembly and what the optimal environment is for their culture. Hypothesizing that LO formation occurs as a result of a fine balance between cell-substrate adhesion and cell-cell cohesion, we used 3 cell types (hepatocytes, liver sinusoidal endothelial cells and mesenchymal stem cells) to investigate LO self-assembly on different substrates keeping the culture parameters (e.g. culture media, cell types/number) and substrate stiffness constant. As cellular spheroids may suffer from oxygen depletion in the core, we also sought to identify the optimal culture conditions for LOs in order to guarantee an adequate supply of oxygen during proliferation and differentiation. The oxygen consumption characteristics of LOs were measured using an O2 sensor and used to model the O2 concentration gradient in the organoids. We show that no LO formation occurs on highly adhesive hepatic extra-cellular matrix-based substrates, suggesting that cellular aggregation requires an optimal trade-off between the adhesiveness of a substrate and the cohesive forces between cells and that this balance is modulated by substrate mechanics. Thus, in addition to substrate stiffness, physicochemical properties, which are also critical for cell adhesion, play a role in LO self-assembly.

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Section: Methodsmentioning

confidence: 99%

On the adhesion-cohesion balance and oxygen consumption characteristics of liver organoids

et al. 2017

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“…Preload forces may have some impact on measured viscoelastic properties, especially on softer, biological materials [53]. Strain hardening from preloading can be avoided with strain-rate measurements which negate the use of a trigger force before the measurements.…”

Section: Description Of Viscoelastic Behavior Of Neat Neutralized Anmentioning

confidence: 99%

Viscoelastic Properties of Crosslinked Chitosan Films

2019

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Chitosan films containing citric acid were prepared using a multi-step process called heterogeneous crosslinking. These films were neutralized first, followed by citric acid addition, and then heat treated at 150 • C/0.5 h in order to potentially induce covalent crosslinking. The viscoelastic storage modulus, E , and tanδ were studied using dynamic mechanical analysis, and compared with neat and neutralized films to elucidate possible crosslinking with citric acid. Films were also prepared with various concentrations of a model crosslinker, glutaraldehyde, both homogeneously and heterogeneously. Based on comparisons of neutralized films with films containing citric acid, and between citric acid films either heat treated or not heat treated, it appeared that the interaction between chitosan and citric acid remained ionic without covalent bond formation. No strong evidence of a glass transition from the tanδ plots was observable, with the possible exception of heterogeneously crosslinked glutaraldehyde films at temperatures above 200 • C.Abstract: Chitosan films containing citric acid were prepared using a multi-step process called heterogeneous crosslinking. These films were neutralized first, followed by citric acid addition, and then heat treated at 150 °C/0.5 h in order to potentially induce covalent crosslinking. The viscoelastic storage modulus, E′, and tanδ were studied using dynamic mechanical analysis, and compared with neat and neutralized films to elucidate possible crosslinking with citric acid. Films were also prepared with various concentrations of a model crosslinker, glutaraldehyde, both homogeneously and heterogeneously. Based on comparisons of neutralized films with films containing citric acid, and between citric acid films either heat treated or not heat treated, it appeared that the interaction between chitosan and citric acid remained ionic without covalent bond formation. No strong evidence of a glass transition from the tanδ plots was observable, with the possible exception of heterogeneously crosslinked glutaraldehyde films at temperatures above 200 °C.Processes 2019, 7, 157 2 of 18 While chitosan films have advantages, such as high anti-microbial and low oxygen-permeability properties [3], their high moisture affinity and relatively poorer mechanical properties compared to common plastics, such as polyethylene terephthalate, low density polyethylene, and polypropylene, limit their packaging applications. The water vapor permeability (WVP) of chitosan films is typically a magnitude higher than that of thermoplastics. Their tensile strength (TS) is in the same range as some plastics; however, their elongation capacities and elastic moduli are lower. A comparison of mechanical and barrier properties of chitosan and plastic films is provided in Table 1.Improving mechanical properties and reducing hydrophilicity of chitosan films has been attempted by several methods, including (i) composite formation with fatty acids [6,7] and other polysaccharides [8], (ii) grafting hydrophobic compounds [9,1...

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“…To investigate whether the E app (ε) fitting method proposed in this study returns viscoelastic constants similar to the originalεM described in Tirella et al (2014), it is essential to maintain all sample, testing and analysis variables unaltered: only then can results be meaningfully compared (Mattei and Ahluwalia 2016). Thus, the same apparent elastic moduli reported in Tirella et al (2014) for both 5% w/v Type A gelatin and PDMS (10:1 base to catalyst) tested in unconfined compression at different constant strain rates (n = 3 replicates per strain rate) were used in this work to obtain two experimental E app vs.ε datasets to analyze with the new E app (ε) fitting method.…”

Section: Resultsmentioning

confidence: 99%

“…To date, different testing and analysis methods are used to derive quantitative mechanical properties for describing intrinsic material behavior and predicting material responses under specific loading conditions (Mattei and Ahluwalia 2016). Although mechanical characterization is often limited to the derivation of elastic properties, many materials, such as soft tissues and hydrogels, are known to exhibit viscoelastic behavior with time-dependent responses (Fung 1993;Mattei et al 2014Mattei et al , 2015bMattei et al , 2017aOyen 2013;Tirella et al 2014;Zhao et al 2010).…”

Section: Introductionmentioning

confidence: 99%

A new analytical method for estimating lumped parameter constants of linear viscoelastic models from strain rate tests

Mattei

Ahluwalia

2018

Mech Time-Depend Mater

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We introduce a new function, the apparent elastic modulus strain-rate spectrum, E app (ε), for the derivation of lumped parameter constants for Generalized Maxwell (GM) linear viscoelastic models from stress-strain data obtained at various compressive strain rates (ε). The E app (ε) function was derived using the tangent modulus function obtained from the GM model stress-strain response to a constantε input. Material viscoelastic parameters can be rapidly derived by fitting experimental E app data obtained at different strain rates to the E app (ε) function. This single-curve fitting returns similar viscoelastic constants as the original epsilon dot method based on a multi-curve global fitting procedure with shared parameters. Its low computational cost permits quick and robust identification of viscoelastic constants even when a large number of strain rates or replicates per strain rate are considered. This method is particularly suited for the analysis of bulk compression and nano-indentation data of soft (bio)materials.

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Sample, testing and analysis variables affecting liver mechanical properties: A review

Cited by 59 publications

References 85 publications

On the adhesion-cohesion balance and oxygen consumption characteristics of liver organoids

On the adhesion-cohesion balance and oxygen consumption characteristics of liver organoids

Viscoelastic Properties of Crosslinked Chitosan Films

A new analytical method for estimating lumped parameter constants of linear viscoelastic models from strain rate tests

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