Optical imaging of microfluidic integrated smart hydrogels for research and sensing applications

Smart hydrogels are a versatile class of materials that are attractive for biomedical sensor applications due to their potential biocompatibility and stimuli-responsiveness. However, the integration of these hydrogels into sensors requires development and engineering efforts to optimize the volume phase transition and time response for the respective sensing applications. This work presents an optical evaluation platform for investigating hydrogel swelling properties in a liquid environment with automated flow control. It employs hydrogel features integrated in microfluidic test strips which are easily interchangeable. The evaluation is carried out using an image sensor that records multiple miniaturized hydrogels in parallel. Overall performance is demonstrated by studying the swelling repones of two different hydrogel compositions (based on acrylamide: a polyampholytic glucose-responsive hydrogel as well as a hydrogel optimized for response to ionic strength and temperature) to various external stimuli, which include sodium chloride, temperature, and glucose as well as glucose spiked into serum and blood. The inclusion of relevant body fluids used in diagnostics potentially enables pathways for this sensing platform to be employed at the point-of-care setting. • A compact and automated optical measuring platform with microfluidics and temperature control for hydrogel characterization • No programming knowledge required to implement as an existing ImageJ module is trained to measure the hydrogel dimensions • Microfluidic test strips reduce measurement time significantly by reducing hydrogel dimensions down to ~100 µm • Enabling dynamic and static measurements of the swelling degree of various stimuli-responsive hydrogels