Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

This research project focuses on the characterisation and modelling of the mechanical properties of gelatin and collagen hydrogels. As the most abundant protein in the human body and a main component of the extracellular matrix (ECM), collagen is a promising material for the use in hydrogels for tissue engineering applications. Gelatin, which is denatured collagen, is a inexpensive material which can serve as a surrogate for collagen. Modelling of the ECM can be done by both gelatin and collagen hydrogels through its structural, mechanical and biomechanical properties. Just like the ECM, the hydrogels are fibrous, porous continua with a time-dependent mechanical response. Furthermore, the hydrogels also contain proteins, glycosaminoglycans and proteoglycans. Therefore these gels can provide an easily controllable model for studying cell proliferation, angiogenesis and fibrillogenesis. The characterisation of the hydrogels is done on both macroscale and microscale. Macroscale characterisation is done by unconfined stepwise stress-relaxation compressive tests and atomic force microscopy (AFM). Data analysis of these experiments allows to determine the instantaneous and relaxation Young's moduli of the hydrogels. Through the use of a biphasic poro-viscoelastic (BPVE) model, the hydrogel behaviour is implemented in finite element models of the performed mechanical tests. Using an automated iterative fitting procedure, the results of the finite element analysis (FEA) are fitted to the experimental data. This leads to the automatic determination of the mechanical properties of the solid fibrous constituents of the hydrogels under the assumption of the specific microscale composition as parameterised by the void ratio and hydraulic permeability. The variations in the obtained experimental results are significant. For collagen, the variations are large enough to confound a reliable result. This is probably due to insufficient accuracy of the hydrogel production process and the used testing equipment. The finite element model (FEM) was verified and converged solutions were always found from the fitting procedure. The error between the predicted and the observed time-dependent response for both compression and AFM was at most num{8.12e-4} using the BPVE model. Gelatin fibres were determined to have a higher Young's relaxation modulus and slower time-rate of relaxation than collagen fibres. It is suggested to develop independent measurement methods in order to determine appropriate void ratio and hydraulic permeability values for the fitting procedure. The protocols and procedures developed in this research provide a proof of concept on how to automatically determine and model the mechanical properties of fibrous hydrogels.