Synthesis of thermoresponsive hyaluronic acid functionalized microgels for the control of cell adhesion

One of the major difficulties in the treatment of cancer is the formation of metastases. Since metastases are often caused by circulating tumor cells (CTCs), their early detection is of great importance. Strategies to isolate and detect CTC include specific targeting via ligand-receptor interactions, e.g. by using cancer-related receptors like CD44 and their natural ligand hyaluronic acid (HA). Our aim was to create a gentle isolation method for CTCs with HA-functionalized switchable microgels.
For this purpose, HA-functionalized thermoresponsive microgels based on poly-(N-isopropylacrylamide) were prepared and coated on glass surfaces. The prepared microgels were examined for size, swelling degree, surface charge and ligand functionalization. We expected that by increasing the temperature above the lower critical solution temperature (LCST) at 32°C the cells would show enhanced binding to the microgels, because the ligand density at the microgel surface is increased and by decreasing the temperature below the LCST the cells would detach due to decreasing the ligand density and brush-like conformation of the microgels. Therefore, extensive cell-adhesion studies were performed on the microgel surfaces, 37°C and 20°C via microscopy and automated cell counting. Overall, moderately selective adhesion of the cells to HA-functionalized microgels was observed and detachment of the cells below the LCST could be shown as intended.

Schematic representation of the temperature-dependent binding of CD44 receptors to hyaluronic acid-functionalized PNIPAm microgels below (left) and above (right) the LCST. The microgels were coated on a glass plate. Above the LCST, the microgels are collapsed and become hydrophobic, which leads to an increase in hyaluronic acid density at the microgel surface. As a result, the CD44 receptor can bind specifically better to this ligand.