Abstract
Different bioprinting techniques have been used to produce cell-laden alginate hydrogel structures, however these approaches have been limited to 2D or simple three-dimension (3D) structures. In this study, a new extrusion based bioprinting technique was developed to produce more complex alginate hydrogel structures. This was achieved by dividing the alginate hydrogel cross-linking process into three stages: primary calcium ion cross-linking for printability of the gel, secondary calcium cross-linking for rigidity of the alginate hydrogel immediately after printing and tertiary barium ion cross-linking for long-term stability of the alginate hydrogel in culture medium. Simple 3D structures including tubes were first printed to ensure the feasibility of the bioprinting technique and then complex 3D structures such as branched vascular structures were successfully printed. The static stiffness of the alginate hydrogel after printing was 20.18 ± 1.62 KPa which was rigid enough to sustain the integrity of the complex 3D alginate hydrogel structure during the printing. The addition of 60 mM barium chloride was found to significantly extend the stability of the cross-linked alginate hydrogel from 3 d to beyond 11 d without compromising the cellular viability. The results based on cell bioprinting suggested that viability of U87-MG cells was 93 ± 0.9% immediately after bioprinting and cell viability maintained above 88% ± 4.3% in the alginate hydrogel over the period of 11 d.
Highlights
In the past decade, three-dimension (3D) bioprinting as an emerging new technology for tissue engineering has made significant progress towards the regeneration of transplantable tissues [1,2,3] and even organs such as human ear, bones, skins, nose [4,5,6,7] for restoring or repairing the damaged body functions
We present a new bioprinting technique for complex 3D alginate hydrogel structures with living tumour cells in vitro
In order to achieve this balance, we developed here the specified concentrations of the alginate and CaCl2 solutions to form partially cross-linked alginate hydrogel designed to achieve suitable mechanical rigidity with sufficiently low viscosity to avoid high printing shear stresses
Summary
Three-dimension (3D) bioprinting as an emerging new technology for tissue engineering has made significant progress towards the regeneration of transplantable tissues [1,2,3] and even organs such as human ear, bones, skins, nose [4,5,6,7] for restoring or repairing the damaged body functions. As the hydrogel is cross-linked after the cells are extruded from the printing nozzle, this technique is able to significantly reduce the shear stress associated with printing high-viscosity hydrogels and produce sufficiently strong UV cross-linked structures for the regeneration of a clinical-scale human heart valve. The requirement of this approach, though, is the need for photosensitive hydrogel materials and the exposure of live cells to potentially harmful UV radiation and toxic photo-initiators. Lowering the temperature of hydrogels in printing enhances mechanical rigidity before the gels are cross-linked, leading to alginate-gelatin constructs that have shown the ability to support tumour growth [31, 32] and the formation of highly uniform embryonic stem cell culture in 3D [33]
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