Cells are able to recognise their external environment. Cellular mechanotransduction pathways are regulated, for instance, by the cell dependency on the rigidity of extracellular matrix. Thus, changes can influence cell fate (survival, pluripotency, differentiation) and dysregulation can also result in different types of diseases [1]. To culture cells in a more in vivo-like environment it is necessary to choose a surrounding which can be adjusted related to mechanical properties like roughness, topography, stiffness as well as biological properties like adherence factors or biodegradability. In general, hydrogels are used as scaffolds to mimic the physiological in-vivo environment to generate meaningful cell-based models for disease modelling, drug studies and cytotoxicity analyses. There are natural and synthetic hydrogel materials, each with different properties (e.g., porosity, density) and crosslinking principles (e.g., ionic, photo-based, enzymatic). All these properties can affect the hydrogel’s properties and thus the cell environment in cell cultures.

Alginate is one of the most common hydrogels in tissue engineering, due to its high biocompatibility and adjustable properties. Typically, the polysaccharides are extracted from brown algae, are non-toxic and xenofree after sophisticated purification. In addition, it is modifiable in terms of adhesion factors. Generally, parameters like stiffness, swell behaviour and topography are crucial for the cell to grow on or in the hydrogel material. In this work, we focus on the characterisation of UHV alginate, as this class of alginate overcomes the typical drawbacks such as low molecular weight, high inorganic and organic impurities [2, 3]. UHV-alginate consists out of two different algae species, Lessonia trabeculata (LT) and Lessonia nigrescens (LN), differing in molecular properties (monomer composition and sequence) which are responsible for, e.g., the strength of the resulting hydrogel.

In order to design cell-specific environment, one first step is the generation of alginate scaffolds with different stiffnesses. In this work, we established the first steps towards a screening platform of alginate hydrogels by using a commercial nanoindenter system to evaluate hydrogel stiffnesses. Using distinct formulations of alginates and cross-linking protocols, low hydrogel stiffness around 2 kPa for the cultivation of neurons can be generated. On the same time, it is also possible to increase the hydrogel stiffness up to 12 kPa suitable for the cultivation of cardiac cells. In addition, the crosslinking process itself can be used as a tool to generate specific hydrogel stiffnesses by maintaining a particular LT/LN ratio. We will present the results of the screening by analysing different alginate hydrogels (beads and membranes) and will discuss correlations of alginate formulation and cross-linking procedures.

References

[1] D.E. Discher, Science (New York, N.Y.), 2005, 310, 1139-1143.

[2] E.M. Sánche, Frontiers in Bioengineering and Biotechnology, 2020, 8, 776.

[3] H. Storz, Carbohydrate research, 2009, 8, 985-995.