New Insight into Agarose Gel Mechanical Properties

Abstract

The current study focuses on the effects of the molecular weight on the mechanical behavior of agarose gels. The small strain rheology and large strain deformation/failure behavior of three different molecular weight agarose gels have been examined, with the results expressed in term of molar concentration. For small deformation strains, the gelation temperature at low concentrations and the critical concentration for gel formation are strongly affected by the molecular weight. In addition, the elasticity of the network is also very sensitive to this parameter. It has been demonstrated that the experimental gelation cure curves can be superimposed on a universal gelation master curve, independent of the cure time. This would indicate self-similarity of the network at different scales, irrespective of concentration. A relationship between the elastic modulus and the molecular weight has been extracted from these results, where the molecular weight dependence exhibits a power law exponent of 2.42. For large deformation strains, the Poisson ratio has been estimated to be 0.5 for each of the agarose types examined, which indicates that these gels are incompressible. The strain at failure is largely dependent on the molecular weight, and is essentially independent of the biopolymer concentration. This result highlights the fact that the strain at failure is sensitive to the connectivity distances in the gel network. However, the failure stress and Young's modulus of agarose gels show a dependence on both concentration and molecular weight. The observations regarding Young's modulus are in good agreement with those found for small deformation strain rheology for the shear modulus. One of the primary advantages of using the lowest molecular weight agarose is that higher molar concentrations can be reached (more molecules per unit volume). However, the mechanical response of agarose gels is very sensitive to the molecular weight at fixed molar concentration, and if the present results are extrapolated to very low molecular weight, it can be suggested that below a limiting molecular weight a percolating network will not be formed, as suggested by the Cascade model (Carbohydr. Polym. 1994, 23, 247-251). This speculation is based on the influence of the "connectivity" at long distances, which influences the strain at failure (when the strain at failure is zero, the system is not connective).

The effect of concentration, thermal history and cell seeding density on the initial mechanical properties of agarose hydrogels

“…A number of reasons for such variations have been proposed (de Freitas et al 2006), including mechanical factors associated with material testing, differences in gel preparation and storage conditions, natural variations in the molecular weight of agarose and water absorption during storage among others. Gel concentration and molecular weight has also been shown to influence the tensile properties of agarose hydrogels (Normand et al 2000), although less is known about the equilibrium tensile modulus. Many of the investigations involving cellular encapsulation utilise agarose type VII as was used in this work.…”

“…However there is significant variation in the reported values for the compressive properties of agarose gel at any given concentration (Buschmann et al 1992;Mauck et al 2000;Normand et al 2000;Gu et al 2003;de Freitas et al 2006;Likhitpanichkul et al 2006). Complete and concise characterisation of the mechanical properties of these hydrogels at different concentrations is necessary to facilitate their use as a scaffold material in cartilage tissue engineering.…”

“…Perhaps more importantly, characterising the mechanical properties of these gels is also necessary to properly interpret the results of cellular mechanotransdution studies that utilise these gels. While factors associated with material testing protocols and differences in molecule weight, gel preparation and storage conditions may be responsible for much of the reported differences (Normand et al 2000;de Freitas et al 2006), little is reported on the influence of factors associated with mixing these hydrogels with cell suspensions on their initial mechanical properties. Depending on the concentration of the agarose and the subsequent stiffness of the hydrogel, the addition of cells into the gel matrix could significantly alter their mechanical properties.…”

Manufacturing of agarose-based chromatographic adsorbents – Effect of ionic strength and cooling conditions on particle structure and mechanical strength

“…The gelation of agarose involves a change from a random coil in solution to a double helix in the initial stages of gelation and then to bundles of double helices in the final stage [3]. The gel is formed when an infinite extensive three-dimensional network of agarose fibres (consisting of helices) develops [4]. At this state the material is characterized by a co-continuous macroporous morphology with polymer-rich regions (fibres) and solvent-rich regions (pores holding water), and therefore the gelation can be interpreted as a phase separation [5].…”

A novel combination of DLS-optical microrheology and low frequency Raman spectroscopy to reveal underlying biopolymer self-assembly and gelation mechanisms

“…In this work, agarose was chosen because its rheological properties have been extensively studied [5][6][7] and it is a model biopolymer system in solution for studying sol-gel transitions because the gelation process can be easily tuned through polymer concentration and thermal conditioning. [8][9][10][11] There have also been studies on the rheological evolution of agarose 10,11 where its rheological changes have been linked with the micro/meso-scale network properties of the gel by analyzing the correlation length or the hydrodynamic mesh size.…”