Abstract
Highly viscous bioinks offer great advantages for the three-dimensional fabrication of cell-laden constructs by microextrusion printing. However, no standardised method of mixing a high viscosity biomaterial ink and a cell suspension has been established so far, leading to non-reproducible printing results. A novel method for the homogeneous and reproducible mixing of the two components using a mixing unit connecting two syringes is developed and investigated. Several static mixing units, based on established mixing designs, were adapted and their functionality was determined by analysing specific features of the resulting bioink. As a model system, we selected a highly viscous ink consisting of fresh frozen human blood plasma, alginate, and methylcellulose, and a cell suspension containing immortalized human mesenchymal stem cells. This bioink is crosslinked after fabrication. A pre-crosslinked gellan gum-based bioink providing a different extrusion behaviour was introduced to validate the conclusions drawn from the model system. For characterisation, bioink from different zones within the mixing device was analysed by measurement of its viscosity, shape fidelity after printing and visual homogeneity. When taking all three parameters into account, a comprehensive and reliable comparison of the mixing quality was possible. In comparison to the established method of manual mixing inside a beaker using a spatula, a significantly higher proportion of viable cells was detected directly after mixing and plotting for both bioinks when the mixing unit was used. A screw-like mixing unit, termed “HighVisc”, was found to result in a homogenous bioink after a low number of mixing cycles while achieving high cell viability rates.
Highlights
Extrusion-based bioprinting is characterized by the continuous release of bioinks through a printing nozzle
Other bioinks of low viscosity take usage of support baths, which are sacrificed during post-processing [5,6]. These technical efforts are limiting the number of processable materials while solutions for challenges such as layer delamination and post-processing of the plotted bioink constructs are still under development. Another application of low viscosity bioinks is their combination with mechanically supporting materials such as poly-ε-caprolactone [7,8] or calcium phosphate cements [9,10], which is often conducted in bone and cartilage tissue engineering research
An easy and reproducible way of mixing cell suspension and biomaterial ink already An easy and reproducible way of mixing cell suspension and biomaterial ink already exists for low viscosity bioinks [26] by having both liquids in separate syringes, merging exists for low viscosity bioinks [26] by having both liquids in separate syringes, merging them by the use of a conventional static mixer comprising several serial helical mixing them by the use of a conventional static mixer comprising several serial helical mixing units
Summary
Extrusion-based bioprinting is characterized by the continuous release of bioinks through a printing nozzle. Other bioinks of low viscosity take usage of support baths, which are sacrificed during post-processing [5,6] These technical efforts are limiting the number of processable materials while solutions for challenges such as layer delamination and post-processing of the plotted bioink constructs are still under development. Another application of low viscosity bioinks is their combination with mechanically supporting materials such as poly-ε-caprolactone [7,8] or calcium phosphate cements [9,10], which is often conducted in bone and cartilage tissue engineering research
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