Tailoring Hydrogel Viscoelasticity with Physical and Chemical Crosslinking

Abstract

Biological tissues are viscoelastic, demonstrating a mixture of fluid and solid responses to mechanical strain. Whilst viscoelasticity is critical for native tissue function, it is rarely used as a design criterion in biomaterials science or tissue engineering. We propose that viscoelasticity may be tailored to specific levels through manipulation of the hydrogel type, or more specifically the proportion of physical and chemical crosslinks present in a construct. This theory was assessed by comparing the mechanical properties of various hydrogel blends, comprising elastic, equilibrium, storage and loss moduli, as well as the loss tangent. These properties were also assessed in human articular cartilage explants. It was found that whilst very low in elastic modulus, the physical crosslinks found in gellan gum-only provided the closest approximation of loss tangent levels found in cartilage. Blends of physical and chemical crosslinks (gelatin methacrylamide (GelMA) combined with gellan gum) gave highest values for elastic response. However, a greater proportion of gellan gum to GelMA than investigated may be required to achieve native cartilage viscoelasticity in this case. Human articular chondrocytes encapsulated in hydrogels remained viable over one week of culture. Overall, it was shown that viscoelasticity may be tailored similarly to other mechanical properties and may prove a new criterion to be included in the design of biomaterial structures for tissue engineering.

Formulation and viscoelasticity of mineralised hydrogels for use in bone-cartilage interfacial reconstruction

“…However, the frequency dependent viscoelastic response of hydrogels is often overlooked (Cameron et al, 2011). There is also typically a trade-off between the mechanical suitability of hydrogels and cytocompatibility (Bartnikowski et al, 2015;Mironi-Harpaz et al, 2012). The incorporation of a secondary phase to the hydrogel matrix presents the possibility to add complementary properties (Osmałek et al, 2014), such as mechanical response or enhanced cell adhesion.…”

“…Many synthetic bone mineral analogues have been explored, including calcium phosphates such as hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ; HA) (Danoux et al, 2016;Tamaddon and Czernuszka, 2013). While the advantages for such an approach are clear, the influence of incorporating these secondary phases on the viscoelasticity of hydrogels is currently limited, that is despite the frequency response of these materials being recognised as critical for the intended application (Bartnikowski et al, 2015;Wands et al, 2008).…”

A new light triggered approach to develop a micro porous tough hydrogel

“…The measured moduli values are comparable to that of other chemically-crosslinked tough hydrogels. [42][43][44] Additionally, such mechanical properties are similar to that of human tissue, especially those within the 1-100 kPa compressive modulus range. [45][46][47][48] The compressive toughness of the gels remains within the statistical range of 40-60 kJ m À3 , showing that the altered pore sizes do not change the amount of energy absorbed during deformation.…”

An alternative approach to prepare alginate/acemannan 3D architectures

“…Polysaccharide solutions are viscoelastic materials that exhibit solid and liquid characteristics, where storage (G′) and loss (G″) moduli refer to the elastic and viscous response of a given material, respectively [23]. The results of dynamic frequency sweep tests for ACAL systems are presented in Fig.…”