Bio-ink properties and printability for extrusion printing living cells

Abstract

Additive biofabrication (3D bioprinting) makes it possible to create scaffolds with precise geometries, control over pore interconnectivity and architectures that are not possible with conventional techniques. Inclusion of cells within the ink to form a "bio-ink" presents the potential to print 3D structures that can be implanted into damaged/diseased tissue to promote highly controlled cell-based regeneration and repair. The properties of an 'ink' are defined by its formulation and critically influence the delivery and integrity of structure formed. Importantly, the ink properties need to conform to biological requirements necessary for the cell system that they are intended to support and it is often challenging to find conditions for printing that facilitate this critical aspect of tissue bioengineering. In this study, alginate (Alg) was selected as the major component of the 'bio-ink' formulations for extrusion printing of cells. The rheological properties of alginate-gelatin (AlgGel) blends were compared with pre-crosslinked alginate and alginate solution to establish their printability whilst maintaining their ability to support optimal cell growth. Pre-crosslinked alginate on its own was liquidlike during printing. However, by controlling the temperature, Alg-Gel formulations had higher viscosity, storage modulus and consistency which facilitated higher print resolution/precision. Compression and indentation testing were used to examine the mechanical properties of alginate compared to Alg-Gel. Both types of gels yielded similar results with modulus increasing with alginate concentration. Decay in mechanical properties over time suggests that Alg-Gel slowly degrades in cell culture media with more than 60% decrease in initial modulus over 7 days. The viability of primary myoblasts delivered as a myoblast/Alg-Gel bio-ink was not affected by the printing process, indicating that the Alg-Gel matrix provides a potential means to print 3D constructs that may find application in myoregenerative applications. control over pore interconnectivity and architectures that are not possible with conventional techniques. Inclusion of cells within the ink to form a "bio-ink" presents the potential to print 3D structures that can be implanted into damaged/diseased tissue to promote highly controlled cell-based regeneration and repair. The properties of an 'ink' are defined by its formulation and critically influence the delivery and integrity of structure formed. Importantly, the ink properties need to conform to biological requirements 10 necessary for the cell system that they are intended to support and it is often challenging to find conditions for printing that facilitate this critical aspect of tissue bioengineering. In this study, alginate (Alg) was selected as the major component of the 'bio-ink' formulations for extrusion printing of cells. The rheological properties of alginate-gelatin (Alg-Gel) blends were compared with pre-crosslinked alginate and alginate solution to establish their printability whil...

Rheological study on 3D printability of alginate hydrogel and effect of graphene oxide

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“…During conventional rapid solidification-based extrusion, the printing process has been typically investigated based on the effects of ink rheological properties and homogeneity on the printability and the evaluation of printing resolution and accuracy. For example, Chuang et al [19] reported the filament morphology and diameter are closely dependent on the preprocessing of bioinks and their material properties during extrusion printing different sodium alginate (NaAlg)-based solutions. Kang et al [20] printed various alginate, poly(ethylene glycol) diacrylate (PEGDA), and gelatin bioinks under different printing conditions and found that printing conditions including the nozzle diameter, dispensing pressure, path height (standoff distance), path spacing (feed), and printing speed can affect the printing accuracy and resolution of 3D structures.…”

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“…The printing resolution mainly depends on the device characteristics (e.g., nozzle diameter, flow rate, and printing speed), the material properties (e.g., rheological behaviour, wettability, surface tension) and the cell density. Environmental conditions and crosslinking methods also have a critical role on the achievable resolution [17,31,32,111]. Since extrusion bioprinting involves the deposition of cellular bioinks through a small nozzle, printed cells are subjected to mechanical stresses during the process, which may lead to a loss of cell viability and even to alterations in the phenotype [17].…”

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