Modelling Hydrogel Mechanics

One of the key engineering challenges in the life science and biomedical sectors is the design and manufacturing of bespoke scaffolds for 3D cell culture, tissue engineering and cell/drug delivery, i.e. cell niches. These cell niches underpin a large and growing sector of biotech and biomed industries, whether they are used in vitro to study cell behaviour, or in vivo to promote regeneration of damaged tissues. Significant efforts have been made to develop novel biomaterials to build such scaffolds. One such class of material, which has attracted significant interest, is hydrogels, as these soft, highly hydrated materials can be engineered to mimic the cell niche. It is important to understand hydrogel mechanics, as a cell's behaviour depends strongly on its mechanical microenvironment.

Hydrogels consist of networks of crosslinked, hydrophilic polymer chains, which, when hydrated, form a soft solid with highly nonlinear, viscoelastic mechanical properties. In this project, we will build a model of how the structure of these networks impacts upon the macroscale mechanics of the hydrogel. At the microscale, we will build a discrete model, whereby each fibre to fibre crosslink defines a node in the network, with the connectivity of the nodes being captured via an adjacency matrix. We will assume that the fibres connecting the nodes resist motion only once taut and will investigate how different assumptions about their constitutive behaviour impacts on the network as a whole. Finally, we will couple the microscale model to a continuum level constitutive equation to describe the macroscale mechanics.

The overarching aim of the project is to understand the relationship between the microscale mechanical properties and network structure of hydrogels and their macroscale mechanical behaviour.
The specific objectives of the project are to:
- Develop a microscale model of the deformation of the polymer networks that make up peptide-based hydrogels, in two dimensions, assuming linear elastic constitutive behaviour for the fibres
- Extend the above model to three dimensions
- Predict the viscoelastic behaviour of the hydrogels by modelling the fibres as linear viscoelastic materials and incorporating fluid flow between the fibres in two dimensions
- Extend the viscoelastic model to three dimensions
- Test the predictions of the models against existing experimental stress-strain data, using mechanical data on individual fibres as the inputs for the models
- Iterate the models based on their agreement, or lack of agreement, with the experimental data
- Determine the optimal fibre mechanical parameters that are required to produce a given macroscale stress-strain curve
- Produce new hydrogels with bespoke mechanical properties that have been designed using the models