Bioprinted Alginate Viability
As a naturally occurring polysaccharide commonly derived from algae or seaweed, sodium alginate’s abundance and low cost make it a popular biomaterial for cellular encapsulation and bioprinting (1). Sodium alginate forms a hydrogel through a sodium-calcium ion exchange. As this crosslinking process occurs very quickly, sodium alginate can be difficult to bioprint on its own. Many studies combine this reagent with other materials to create a hybrid bioink or use complex multi-crosslinking steps to create 3D geometries (2-4). Here, we present a simplified process for printing sodium alginate with the use of Pluronic F127 as a temporary support. This process creates viable 3D structures of cell-laden alginate with repeatible, accurate geometries.
Thin Film Viability
Bioprinted viability was first tested by comparing bioprinted thin films to pipetted thin films. Both 2% and 5% bioprinted thin films had over 85% viability compared to non-bioprinted controls. No statistical differences were found between 2% and 5% groups at each time point.
Figure 1: Live/Dead Images (left) of 2% and 5% bioprinted alginate thin films after 7 days of culture (scale bars = 1 mm). The data was quantified using Image J and viability data for 2% and 5% alginate thin films, normalized to pipetted thin film controls, is shown on the right.
Bioprinted Ring Viability
Ring structures designed with a 300 μm thickness, 400 μm height and an outer diameter of 2.3 mm were printed with 2% cell-laden alginate. Viability of these bioprinted rings were compared to bioprinted and pipetted thin films. Qualitative analysis of live/dead imaging suggests similar viability in the bioprinted ring structures as the bioprinted and pipetted thin films. Line width averages, analyzed with ImageJ software, were 360 ± 80 μm after 1 day of culture.
These results demonstrate the ability of sodium alginate, calcium chloride and Pluronic F127 from BioBots to support viable cultures and create consistent, high resolution 3D geometries when used with a BioBot 1. When used together, these reagents can create cell-laden structures with specific, repeatible 3D geometries. Further, bioprinted thin films and pipetted thin films created in this study can be used as 3D controls for future experiments with these materials.
Primary Human Neonatal Dermal Fibroblasts (HNDFs) obtained from ATCC were cultured in monolayer cultures at 37 °C and 5% of CO2 using Dulbecco’s Modified Eagle Medium (Corning) supplemented with 10% fetal bovine serum (Hyclone) and 1% penicillin-streptomycin-amphotericin (Corning). Passage numbers under 12 were used.
Thin Film Fabrication
HNDFs were mixed with either 2% or 5% (w/v) alginate at a 5 million/ml concentration. Pipetted thin films were created by pipetting 10 μl of solution on transwell plates then submerging the samples in 10 mM Calcium Chloride for 10 – 15 minutes.
2% Bioprinted thin films were created this gcode and suggested print parameters from BioBots. 5% bioprinted thin films, printed with this gcode, were also printed using the suggested print parameters. Volume of extruded bioprinted material was estimated with the volume test. Extrusion time in the printed gcode was set for extrusion of approximately 10 μl. All samples were crosslinked for 10-15 minutes in calcium chloride, then washed three times with phosphate buffered saline (PBS). All samples were bioprinted with a BioBot 1.
Bioprinted Ring Fabrication
First, CAD files of alginate rings and supporting pluronic F127 structure were created with solidworks. Then, these .stl files were loaded into repetier host and sliced with the print parameters suggested by BioBots. 5 ml of Pluronic F127 was loaded into extruder 1 and 2 ml of 2% alginate with a 5 million/ml HNDF concentration was loaded into extruder 2. 30 gauge needles were used for both materials.
Rings were printed into transwell plates, then submerged in 10 mM calcium chloride first at room temperature for 5-10 minutes then on ice for another 5 minutes. After crosslinking, samples were washed with phosphate buffered saline (PBS) three times before adding media. All samples were bioprinted with a BioBot 1.
To assess cell viability, a LIVE/DEAD kit (Life Technologies) was used. Images were taken on a Nikon TE300 Inverted Fluorescent Microscope or a Leica TCS SP5 II Scanning Laser Confocal Microscope. Statistical analysis was performed using an Analysis of Variance (ANOVA) test to determine if differences were present amongst treatment groups. If differences were determined from the ANOVA, a post hoc Tukey’s multiple comparison test was used to determine statistical differences between groups tested. A confidence level of 95% (α=0.05) was used for all analyses. Error bars on graphs represent the standard deviation from the mean.
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