PMC

Freeform reversible embedding of suspended hydrogels (FRESH) printing through deposition of sodium alginate precursor ink within thermally reversible gelatin support bath. PANEL A: Dual-layer square construct (10 mm × 10 mm). i) Rendered STL of square, ii) Printed construct embedded within gelatin support bath (24 °C), iii) Printed alginate construct following gelatin dissolving and release of hydrogel (37 °C). PANEL B: Dual-layer grid constructs (20 mm × 10 mm). i) Rendered STL of grid, ii) Printed construct embedded within gelatin support bath (24 °C), iii) Printed alginate construct following gelatin dissolving and release of hydrogel (37 °C). PANEL C: Dual-layer RU construct (25 mm × 18 mm). i) Rendered STL of RU, ii) Printed construct embedded within gelatin support bath (24 °C). Scale bars represent 10 mm. Stereolithography images were drawn and rendered in SketchUp Make (v16.0.1).

Stages of gelatin nanoparticle synthesis. (A) Solution of gelatin and isopropyl alcohol before mixing; (B) incubation of nanoparticles at the water bath; (C) nanoparticle suspension appearance after glutaraldehyde addition; (D) sediment of nanoparticles after centrifugation; (E) combining of washed gelatin nanoparticles prior to final sonication; (F) sonication of gelatin nanoparticles on ice.

Gelatin fiber morphology and analysis using scanning electron microscopy (SEM). a Fibrous gelatin scaffolds (i) produced using three different gelatin concentrations (4%, 10%, and 20% w/w gelatin in DI H₂O) spun into a pure ethanol (EtOH) precipitation bath; scale bars are 20 μm (left panels) and 2 μm (right panel); (ii) scaffolds produced by co-spinning 20% gelatin and a microbial crosslinking agent into 70:30 EtOH:H₂O bath, with subsequent storage in EtOH:H₂O at indicated concentrations (EtOH:H₂O, from left to right: 100:0, 80:20, 60:40, 30:70); scale bar is 20 μm. b Gelatin fibers produced using 20% gelatin spun into EtOH:H₂O precipitation bath at indicated concentrations (EtOH:H₂O, from left to right: 100:0, 80:20, 70:30); scale bar is 50 μm. Data plots for fiber diameter, scaffold porosity, and scaffold coherency (alignment) are N = 3 productions runs for each bath composition. Coherency depicts alignment ranging from 0 (no alignment) to 1 (perfect alignment). Data are presented as box plots, where lower or upper edges of the box represent 25th or 75th percentiles, the middle bar is the median, and whiskers are 5th or 95th percentiles

FRESH printing into a gelatin microparticle support bath. (a) A print container is filled with a yield-stress gelatin microparticle support bath to serve as the embedding medium for bioprinted components. (b) The aqueous phase of the support bath can be tuned to drive cross-linking/gelation of the extruded hydrogel as the microparticles support the print during layer-by-layer deposition. (c) As the needle moves through the support bath, the microparticles yield providing a space for the extruded bioink and subsequently heal behind the needle providing support to the curing bioink.