Development of collagen phantoms to investigate collagen specific MR imaging methods

This thesis explores the potential of collagen-based hydrogels as biomimetic materials for biomedical applications, with a dual focus on mechanical characterization and magnetic resonance imaging (MRI) assessment. Collagen is the most abundant structural protein in the human body and a key component of the extracellular matrix, where it provides both mechanical support and biochemical cues essential for cell adhesion, migration, and differentiation. Alterations in collagen concentration, distribution, or organization are strongly associated with pathological processes such as fibrosis and cancer. For instance, in breast cancer, abnormal collagen deposition and stiffening of the surrounding matrix are recognized as hallmarks of tumor progression and metastasis. Being able to detect such changes in a non-invasive and non-destructive way would therefore open new possibilities for early diagnosis and improved disease monitoring. To investigate these aspects, collagen hydrogels at three different concentrations (0.5%, 2.5%, and 4%) were prepared and polymerized in PDMS molds. Their mechanical properties were assessed through uniaxial compression tests in a PBS bath, with the elastic modulus calculated from the final 10% of the linear region of the stress–strain curve. This approach minimized artifacts due to initial machine stabilization and excluded late-stage instabilities such as rupture or leakage. The results confirmed a strong dependence of stiffness on collagen concentration, with moduli ranging at 24 hours approximately from 25 kPa in the lowest concentration to 610 kPa in the highest concentration. The preparation of the hydrogels was successful across all three concentrations, but a key challenge emerged from producing hydrogels composed solely of collagen, without the aid of additional crosslinking agents, which limited long-term stability and indicated that improved formulation strategies could result in more stable and reliable hydrogel systems. The project also comprised the design and fabrication of a custom holder for the hydrogel phantoms, allowing their stable positioning and alignment during MRI scanning. The MRI analysis demonstrated a good alignment of the samples within this setup, confirming the feasibility of using the holder for imaging purposes. However, the presence of air bubbles within the system affected image quality, highlighting the need for further optimization of both the holder design and the choice of materials. Overall, this work contributes to the field of biomaterials and regenerative medicine by clarifying the link between collagen concentration, hydrogel stiffness, and MRI assessment. Furthermore, it provides insights relevant to cancer and fibrotic diseases, where pathological variations in collagen deposition alter tissue mechanics, and where the possibility of an earlier and more accurate diagnosis could play a crucial role in improving patient outcomes. These findings emphasize both the opportunities and current limitations of pure collagen hydrogels, paving the way for more stable, imaging-compatible scaffolds and improved diagnostic tools for future biomedical applications.