Liquid-like Solids Support Cells in 3D

Abstract

The demands of tissue engineering have driven a tremendous amount of research effort in 3D tissue culture technology and, more recently, in 3D printing. The need to use 3D tissue culture techniques more broadly in all of cell biology is well-recognized, but the transition to 3D has been impeded by the convenience, effectiveness, and ubiquity of 2D culture materials, assays, and protocols, as well as the lack of 3D counterparts of these tools. Interestingly, progress and discoveries in 3D bioprinting research may provide the technical support needed to grow the practice of 3D culture. Here we investigate an integrated approach for 3D printing multicellular structures while using the same platform for 3D cell culture, experimentation, and assay development. We employ a liquid-like solid (LLS) material made from packed granular-scale microgels, which locally and temporarily fluidizes under the focused application of stress and spontaneously solidifies after the applied stress is removed. These rheological properties enable 3D printing of multicellular structures as well as the growth and expansion of cellular structures or dispersed cells. The transport properties of LLS allow molecular diffusion for the delivery of nutrients or small molecules for fluorescence-based assays. Here, we measure viability of 11 different cell types in the LLS medium, we 3D print numerous structures using several of these cell types, and we explore the transport properties in molecular time-release assays.

Quantitative criteria to benchmark new and existing bio-inks for cell compatibility

“…Together, our data demonstrate that as the bioprinting community begins to scale-up this technology to print larger constructs, we will either need to dramatically reduce the overall print time or develop printing techniques that prevent cell dehydration. Alternative techniques to prevent construct dehydration have been explored by groups printing into either colloidal slurries [32, 34] or into a shear-thinning gel bath [33]. Additionally, one could design a humidified print chamber or hygroscopic bio-inks to help offset the effects of dehydration during curing.…”

From Shape to Function: The Next Step in Bioprinting

“…This enables a rapid stabilization of the microparticles after a sudden change in applied shear stress exceeding or undershooting the yield point . Carbopol concentrations between 0.2 and 0.9 wt% did not impede cell migration and proliferation . Although demonstrated in a cell‐free approach, Carbopol‐based support bath printing (Figure C) showed the potential to generate constructs composed of strands with diameters as small as 35–50 µm.…”

“…This revealed the possibilities offered by the support bath approach and enabled printing of highly complicated structures (Figure C) . Printing cell containing materials into Carbopol allowed the fabrication of objects with a resolution between 100 and 200 µm . A layer thickness of 100 µm could be achieved and even a single‐cell ejection along the printing direction by increasing translation speed was possible.…”

Aspiration-assisted Freeform Bioprinting of Tissue Spheroids in a Yield-stress Gel

“…In most cases of bioprinting in a granular gel, cells are bioprinted while encapsulated within a hydrogel formulation, resulting in limited cell densities. 13 Hence, cellular aggregates, such as tissue spheroids, possess greater promise due to their favorable properties in building native-like tissues [14][15][16] .Bioprinting of spheroids is an attractive approach, in which spheroids are used as building blocks for fabrication of tissues that mimic the native counterparts in terms of histology and physiology 14,16,17 . Several spheroid bioprinting techniques have been reported.…”

“…In most cases of bioprinting in a granular gel, cells are bioprinted while encapsulated within a hydrogel formulation, resulting in limited cell densities. 13 Hence, cellular aggregates, such as tissue spheroids, possess greater promise due to their favorable properties in building native-like tissues [14][15][16] .…”