A Methylcellulose Hydrogel as Support for 3D Plotting of Complex Shaped Calcium Phosphate Scaffolds

Abstract

3D plotting is an additive manufacturing technology enabling biofabrication, thus the integration of cells or biologically sensitive proteins or growth factors into the manufacturing process. However, most (bio-)inks developed for 3D plotting were not shown to be processed into clinically relevant geometries comprising critical overhangs and cavities, which would collapse without a sufficient support material. Herein, we have developed a support hydrogel ink based on methylcellulose (mc), which is able to act as support as long as the co-plotted main structure is not stable. Therefore, 6 w/v %, 8 w/v % and 10 w/v % mc were allowed to swell in water, resulting in viscous inks, which were characterized for their rheological and extrusion properties. The successful usage of 10 w/v % mc as support ink was proven by multichannel plotting of the support together with a plottable calcium phosphate cement (CPC) acting as main structure. CPC scaffolds displaying critical overhangs or a large central cavity could be plotted accurately with the newly developed mc support ink. The dissolution properties of mc allowed complete removal of the gel without residuals, once CPC setting was finished. Finally, we fabricated a scaphoid bone model by computed tomography data acquisition and co-extrusion of CPC and the mc support hydrogel.

Methylcellulose – a versatile printing material that enables biofabrication of tissue equivalents with high shape fidelity

“…The temperature-dependent gelation point of mc gels decreases with increasing concentration. 21,41,44 In comparison to 6% and 8%, a 10% mc ink with the lowest gelation point demonstrated best printability, 41 indicating that the printability is improved when mc is processed in sol state near the gelation point. The gelation of mc can be influenced by the presence of diluted salts.…”

“…Due to this reason, commercially available mc usually is characterized by its viscosity (of a 2% solution at 20°C) and the molecular weight is a recalculated value, which does not allow drawing conclusions for the distribution of the molecular weight. We found that most studies [32][33][34][35][36][37][38][39][40][41] used an mc with a given viscosity of 4000 mPa s (M n ≈ 86 kDa); 30 these studies have in common to have achieved printing of multiple layers and only limited collapse of predesigned macropores. Other studies 42,43 reported about the use of mc with a given viscosity of 15 mPa s (M n ≈ 14 kDa) and found significant improvements of the printed shape fidelity in presence of mc compared to mc-free controls, but those structures lacked the evidence of multiple layer stacking.…”

“…40 A similar strategy was investigated for the fabrication of complex scaffold structures. 41 In that work, the printing properties of 6%, 8% and 10% mc sacrificial pastes were investigated and the 10% mc was used as sacrificial ink for 3D extrusion-printing of calcium phosphate cement scaffolds. After setting of the calcium phosphate cement, the mc sacrificial ink was eliminated in a water bath cooled to 4°C.…”

“…After setting of the calcium phosphate cement, the mc sacrificial ink was eliminated in a water bath cooled to 4°C. 41 This allowed the fabrication of real anatomical structures like a scaphoid bone containing a various number of nonprintable overhangs and concave/convex surfaces and cavities (15 × 15 × 15 mm 3 in a 25 × 25 × 25 mm 3 cube) within scaffolds by using extrusion-based printing under mild, cellcompatible conditions. 41 Additionally, a 3D printed 9%-mc/5%-gelatin blend was used as support structure for a casted cell-laden alginate dialdehyde-gelatin (ADA-GEL) hydrogel.…”

“…41 This allowed the fabrication of real anatomical structures like a scaphoid bone containing a various number of nonprintable overhangs and concave/convex surfaces and cavities (15 × 15 × 15 mm 3 in a 25 × 25 × 25 mm 3 cube) within scaffolds by using extrusion-based printing under mild, cellcompatible conditions. 41 Additionally, a 3D printed 9%-mc/5%-gelatin blend was used as support structure for a casted cell-laden alginate dialdehyde-gelatin (ADA-GEL) hydrogel. 45 Latest after 7 d of cell culture, the entire support structure was dissolved without disruption of the ADA-GEL structure, which was obtained as open-porous grid or rings with an outer diameter of 5 mm.…”