In the fields of tissue engineering and regenerative medicine, many researchers and companies alike are investigating the utility of concentrated mesenchymal stem cell suspensions as therapeutic injectables, with the hope of regenerating the damaged tissue site. These cells are seldom used alone, being instead combined with synthetic biomacromolecules, such as branched poly(ethylene glycol) (PEG) polymers, in order to form cross-linked hydrogels postinjection. In this article, we present the results of a detailed experimental and analytical investigation into the impacts of a range of eight-arm PEG polymers, each presenting functional end groups, on the rheological properties of concentrated living cells of mesenchymal origin. Using two-photon confocal microscopy, we confirmed that the aggregates formed by the cells are fractal structures, the dimension of which changed with PEG polymer type addition. From these results and the observed substantial variation in rheological footprint with increasing volume fraction and different PEG polymer type, we propose a number of mechanisms driving such structural changes. Lastly, we derived a modified Krieger-Dougherty model to produce a master curve for the relative viscosity as a function of volume fraction over the range of conditions investigated (including shear stress and PEG polymer type), from which we extract the adhesion force between individual cells within these concentrated suspensions. The outcomes of this study provide new insights into the complex interactions occurring in concentrated mesenchymal cell suspensions when combined with synthetic biomacromolecules commonly used as precursors in tissue engineering hydrogels, highlighting their substantial impacts on the resultant rheological footprint.

With the rise of microfluidics for the past decade, there has come an ever more pressing need for a low-cost and rapid prototyping technology, especially for research and education purposes. In this article, we report a rapid prototyping process of chromed masks for various microfluidic applications. The process takes place out of a clean room, uses a commercially available video-projector, and can be completed in less than half an hour. We quantify the ranges of fields of view and of resolutions accessible through this video-projection system and report the fabrication of critical microfluidic components (junctions, straight channels, and curved channels). To exemplify the process, three common devices are produced using this method: a droplet generation device, a gradient generation device, and a neuro-engineering oriented device. The neuro-engineering oriented device is a compartmentalized microfluidic chip, and therefore, required the production and the precise alignment of two different masks.