Microfluidic Production of Cell-Laden Microspheroidal Hydrogels with Different Geometric Shapes.

Providing control over the geometric shape of cell-laden hydrogel microspheroids, such as diameter and axial ratio, is critical for their use in biomedical applications. Building on our previous work establishing a microfluidic platform for production of large cell-laden microspheres, here we establish the ability to produce microspheroids with varying axial ratio (microrods) and elucidate the mechanisms controlling microspheroidal geometry. Microspheroids with radial diameters ranging from 300 to over 1000 μm and axial ratios from 1.3 to 3.6 were produced. Although for microfluidic devices with small channel sizes (typically <500 μm) the mechanisms governing geometric control have been investigated, these relationships were not directly translatable to production of larger microspheroids (radial diameter 102 - 103 μm) in microfluidic devices with larger channel sizes (up to 1000 μm). In particular as channel size was increased, fluid density differences became more influential in geometric control. We found that two parameters, narrowing ratio (junction diameter over outlet diameter) and flow fraction (discrete phase flow rate over total flow rate), were critical in adjusting the capillary number, modulation of which has been previously shown to enable control over microspheroid diameter and axial ratio. By changing the device design and the experimental conditions, we exploited the relationship between these parameters to predictably modulate microspheroid geometric shape. Finally, we demonstrated the applicability to tissue engineering through encapsulation of fibroblasts and endothelial colony forming cells (ECFCs) in hydrogel microspheroids with different axial ratios and negligible loss of cell viability. This study advances microfluidic production of large cell-laden microspheroids (microspheres and microrods) with controllable size and geometry, opening the door for further investigation of geometric shape-related biomedical applications such as engineered tissue formation.