Speaker
Description
The major challenges in new drug development are the low translational efficiency (<10%), soaring costs (>$5 billion/drug) and ethical concerns regarding animal welfare. The emergence of a novel research field with bioengineering promises to offer new strategies to create non-animal models using human cell lines to address these shortcomings. Absence of vascularisation is one of the main bottlenecks to obtaining fully functional bioengineered tissues. The passive diffusion limit for oxygen and nutrients in biological tissues is ~200 µm. Providing a dense and functional microvascular network is key to the formation of larger healthy constructs. The current microfabrication technologies only allow to engineer passive tubular networks in hydrogel matrices, but they lack the biological/cellular components and the dynamic functionality of in vivo capillaries. If angiogenic biochemical cues and their gradients’ impact on microvascular tubule self-assembly have been thoroughly investigated, the importance of local mechanical properties in scaffolds has often been overlooked in the development of functional bioengineered tissues. Exploring the impact of local mechanical properties in 3D matrices is one of the next main axes of progress for the field of tissue engineering and being able to intertwine engineering and biological-based knowledge and techniques will be crucial.
Angiogenesis is a very complex and sensitive process, and multiple environmental cues have been extensively studied in 2D systems. In this study, we use a simple, non-inflammatory collagen-based 3D system to study the impact of local mechanical property gradients on HUVECs’ self-assembly and lumenisation. This study focused on cross-validating imaging-based observations on properties of the tubules across the system, like morphology or cytoskeleton distribution with biomechanical data obtained through rheological measurements, nano-indentation and optical micro rheology to depict a comprehensive and robust picture of angiogenic behaviours in mechanically heterogeneous matrices, by comparison to homogeneous matrices.
Methods
HUVECs are seeded in different concentrations of 3D Collagen Type I hydrogels and submitted to a constant stimulus of 50ng/mL VEGF via the culture medium. The endothelial cells self-assemble into microvascular networks. The impact of growth factors on the tubule formation has been studied and a reproducible microvascular network formation protocol was established. The microvascular networks were stained and imaged, and automated analysis of morphological (average lumenised tubule length, number of branches, tubule diameter…), cellular (cytoskeleton organisation) and expression profiles were acquired. These biological profiles were put in parallel with bulk and local micromechanical ones.
Results & Future Work
Lumen-presenting microvascular networks have been obtained in a static environment. Exploration of mechanical property gradients have allowed us to highlight the importance of local mechanical property gradients over bulk material properties and to validate the use of different mechanical property measurements’ methods for the exploration of soft 3D hydrogels. Perfusion tests will allow to paint a complete picture of the tubular formation and further optimise the protocol before the functional validation of the microvessels, paving the way to larger, physiologically relevant bioengineered constructs.
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