Cell-laden microgel bioinks present a viable pathway to overcome limitations of conventional bulk bioinks in biofabrication such as poor oxygen and nutrient diffusion, as proposed recently by Highley et al [1]. Additionally, microgels can be utilized to improve cell viability by means of protection from exerted shear forces, as well as to provide tailored cell microenvironments. These microgels can be prepared using microfluidics [2]. The time-consuming process of separation, cleanup of the microgels and preparation into the final bioink however has previously been identified as key limitation in establishing microgel bioinks. Here we propose a combination of advanced microfluidic techniques such as on-chip droplet production, in-flow crosslinking and direct bioprinting to accelerate and combine these steps into one single system, capable of the production of cell-containing microgel constructs, which additionally are directly perfusable. The microfluidic devices we developed include innovative features such as double three-dimensional flow focusing, three-dimensional channel contouring and offer precise droplet size control over a wide range (50 to over 230 µm). Polymer crosslinking is done for example via an integrated UV-LED at 385 nm in the outlet tubing, before the microgels are deposited directly by a modified FDM 3D printer, resulting in constructs that are stable enough to be handled by hand. In addition to the perfusion possible through the microgel construct’s intrinsic microporosity, 3D printed vessel-like channels may be included during the preparation of the microgel constructs, allowing directed perfusion via pumps etc. As materials, both poly(2-oxazoline) (UV) and alginate (Ca2+) systems have been successfully utilized to prepare the constructs.

References

[1] C.B. Highley; K.H. Song; J.A. Burdick Adv. Sci, 2019, 1801076.

[2] E. Tumarkin; E. Kumacheva Chem. Soc. Rev, 2009, 38, 2161.