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In this work, we present a method to fabricate a hyaluronic acid hydrogel with spatially controlled cell-adhesion properties based on photo-polymerisation cross-linking and functionalisation. The approach utilises the same reaction pathway for both steps meaning that it is user-friendly and allows for adaptation at any stage during the fabrication process. Moreover, the process does not require any additional cross-linkers. The hydrogel is formed by UV initiated radical addition reaction between acrylamide groups on the hyaluronic acid backbone. Cell adhesion is modulated by functionalising the adhesion peptide sequence RGD (arginine-glycine-aspartate) onto the hydrogel surface via radical mediated thiol-ene reaction using the non-reacted acrylamide groups. We show that 10 x 10 µm² squares could be patterned with sharp features and a good resolution. The smallest area that could be patterned resulting in good cell adhesion was 25 x 25 µm² squares, showing single-cell adhesion. Mouse brain endothelial cells adhered and remained in culture for up to 7 days on 100 x 100 µm² square patterns. We see potential for this material combination for future use in novel organ-on-chip models and tissue engineering where the location of the cells is of importance and to further study endothelial cell biology.

Endothelial cells (ECs) line the blood vessel walls and present an elongated characteristic morphology. While the effect of micropatterning on different endothelial cells have been extensively studied, the effects on brain endothelial cells, which are highly specialized cells, have been overlooked [1]. Moreover, it has been shown that brain ECs do not elongate and align in response to shear stress, as e.g. HUVECs do. [2]. Hence, we set out to conclude how brain endothelial cells would behave on micropatterned lines. I We fabricated an RGD micropatterned photocrosslinked hyaluronic acid (HA-am) hydrogel substrate, with lines of controlled dimensions. These substrates were used to study cell elongation and alignment of the cell nuclei when adhering to lines raging from 10 µm to 100 µm in width.

Microfluidic devices are widely used for biomedical applications but there is still a lack of affordable, reliable and user-friendly systems for transferring microfluidic chips from an incubator to a microscope while maintaining physiological conditions when performing microscopy. The presented carrier represents a cost-effective option for sustaining environmental conditions of microfluidic chips in combination with minimizing the device manipulation required for reagent injection, media exchange or sample collection. The carrier, which has the outer dimension of a standard well plate size, contains an integrated perfusion system that can recirculate the media using piezo pumps, operated in either continuous or intermittent modes (50–1000 µl/min). Furthermore, a film resistive heater made from 37 µm-thick copper wires, including temperature feedback control, was used to maintain the microfluidic chip temperature at 37 °C when outside the incubator. The heater characterisation showed a uniform temperature distribution along the chip channel for perfusion flow rates up to 10 µl/min. To demonstrate the feasibility of our platform for long term cell culture monitoring, mouse brain endothelial cells (bEnd.3) were repeatedly monitored for a period of 10 days, demonstrating a system with both the versatility and the potential for long imaging in microphysiological system cell cultures.