Hyaluronan Based Biomaterials with Imaging Capacity for Tissue Engineering

Zhang, Y. 2016. Hyaluronan Based Biomaterials with Imaging Capacity for Tissue Engineering. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1402. 60 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-554-9649-4. This thesis presents the preparation of hyaluronan-based biomaterials with imaging capability and their application as scaffolds in tissue engineering. First, we have synthesized HA derivatives functionalized with different chemoselective groups. Then, functional ligands with capacities for hydrophobic drug loading, imaging, and metal ion coordination were chemically conjugated to HA by chemoselective reactions with these groups. An injectable in situ forming HA hydrogel was prepared by hydrazone cross-linking between hybrid iron-oxide nanogel and HA-aldehyde (paper-I). The degradation of this hydrogel could be monitored by MRI and UV-vis spectroscopy since it contained iron oxide as a contrast agent and pyrene as a fluorescent probe. Additionally, this hydrogel has a potential for a delivery of hydrophobic drugs due to its pyrene hydrophobic domains. The degradation study showed that degradability of the hydrogel was correlated with its structure. Based on the obtained results, disulfide crosslinked and fluorescently labeled hydrogels with different HA concentration were established as a model to study the relationship between the structure of the hydrogel and its degradability (paper-II). We demonstrated that disulfide cross-linked HA hydrogel could be tracked noninvasively by fluorescence imaging. It was proved that the in vivo degradation behavior of the hydrogel is predictable basing on its in vitro degradation study. In paper-III, we developed a disulfide cross-linked HA hydrogel for three-dimensional (3D) cell culture. In order to improve cell viability and adhesion to the matrix, HA derivatives were cross-linked in the presence of fibrinogen undergoing polymerization upon the action of thrombin. It led to the formation of an interpenetrating double network (IPN) of HA and fibrin. The results of 3D cell culture experiments revealed that the IPN hydrogel provides the cells with a more stable environment for proliferation. The results of the cellular studies were also supported by in vitro degradation of IPN monitored by fluorescence measurements of the degraded products. In paper-IV, the effect of biomineralization on hydrogel degradation was evaluated in a noninvasive manner in vitro. For this purpose, two types of fluorescently labeled hydrogels with the different ability for biomineralization were prepared. Fluorescence spectroscopy was applied to monitor degradation of the hydrogels in vitro under two different conditions in longitudinal studies. Under the supply of Ca ions, the BP-modified hydrogel showed the tendency to bio-mineralization and reduction of the rate of degradation. Altogether, the performed studies showed the importance of imaging of hydrogel biomaterials in the design of optimized scaffolds for tissue engineering.