‎3D Bioprinting of Complex Hydrogel ‎Structures by ‎‏‎the Aid of Nanoclay‎-‎Hydrogel ‎Composite ‎Support‎-‎Bath

‎3D Bioprinting of Complex Hydrogel ‎Structures by ‎‏‎the Aid of Nanoclay‎-‎Hydrogel ‎Composite ‎Support‎-‎Bath

Bioprinting created revolutionary perspectives not only limited to fabrication of ‌‎structures geometrically similar to the native tissues, but also in providing biochemically similar ‎complex microenvironment for cells to induce and guide functionalities in tissue regeneration. In this respect, hydrogels showed great potential in ‎providing a favorable ‎microenvironment mimicking the natural three-‎dimensional (3D) extracellular matrix. The challenges arise with bioprinting process for the hydrogel, which needs to ‎have a particular sol-gel transition state without clogging the extrusion nozzle and to keep its ‎shape fidelity after deposition. In addition, it is difficult to keep the structure of such a low ‎mechanical strength of printed biomaterials in overhanging structures.

3D bioprinting in a sacrificial support-bath, is an emerging solution for ‎fabrication of complex hydrogel-based overhanging structures. The support-‎bath material must possess a rigid matrix that yields by a passing nozzle and rapidly ‎recovers itself after nozzle motion. Meanwhile it needs to hold bioprinted structure by providing necessary gelation ‎to the extruded hydrogel before spreading into support-bath and to allow the ‎integration of the subsequent layers without clogging the nozzle. ‎‎A number of materials have been implemented as a sacrificial support-bath in direct free form ‎‎writing of ‎‎hydrogels‎. ‎However, ‎their applications are limited for several reasons including ‎‎ionic sensitivity, ‎‎working temperature range and possible reactions with the extruded ‎‎hydrogel‎. ‎Pluronic (PF) ‎is one of ‎‎the biocompatible materials which has been employed as ‎‏fugitive bioink and support ‎bath due to its ‎‎thermoreversible sol-gel phase transition property. ‎However, due to its mechanical weakness and ‎‎tendency of quick dissolving ‎in physiological ‎‏conditions‎, ‎it might not be able to provide enough support ‎‎required for long‎-‎lasting printing ‎‏processes‎. ‎Moreover‎, ‎pure PF‎ ‎as a sacrificial ‎support-bath, ‎‎did not show promising ‎properties regarding harvesting of the printed structure.

Laponite, a synthetic biocompatible nanoclay mostly known as a rheology-modifier with ‎enhanced ‎thixotropic behavior, has been utilized as a support-bath material. However, ‎instability in the rheological ‎properties does not allow printing of low-viscosity hydrogels in ‎Laponite support bath, which is ‎unfavorable for the encapsulated cells and hence low ‎efficiency. ‎ Despite their unique properties, PF and Laponite RDS have various drawbacks ‎when they are ‎employed as a support bath individually‎. ‎In the work we described in the recent ‏Scientific Reports ‎publication, a blend of PF and nanoclay (Laponite RDS) in ‎the presence of calcium chloride (CaCl2) was utilized with the aim of benefit the distinct characteristics of ‎each, namely the ‎thermoresponsive gelation of PF and the thixotropic behavior of Laponite‎.‎‏ ‏To have optimum rheological properties for printing in a long time printing and recovery ‎process of the structure, various concentrations of PF-Laponite RDS and CaCl2 were evaluated and, an ‎optimum rheological properties were achieved for support-bath. Optimized printing ‎parameters allowed printing of computer aided design (CAD) hollow and overhanging structures ‎from low viscous sodium alginate solution in a long-time process. The homogeneous ‎distribution of cells with high viability revealed a cell friendly bioprinting process and to be ‎further used for various tissue engineering applications. We believe that PF-Laponite RDS composite ‎support-bath will be further modified for other types of hydrogels by providing appropriate ‎crosslinking mechanism.

‎(a and c) CAD models, (b and d) digital images of 3D printed structures after recovery from ‎support-bath for star and nose shape, respectively.(a) Bioprinted tubular cell-laden alginate structure after recovery from support-bath. (b) ‎Confocal microscopy image of live/dead cells of bioprinted structure after 3 days of incubation
(a) Bioprinted tubular cell-laden alginate structure after recovery from support-bath. (b) ‎Confocal microscopy image of live/dead cells of bioprinted structure after 3 days of incubation

Fast forward 3D printing video of a vascular-like structure and the leakage test which a dye passes through its lumen are available here: Fast forward printing demo and Leakage test

You can access the full article from the link below:

Scientific Reports

Members of 3D Bioprinting Lab in Sabanci University (Ferdows Afghah, Dr. Mine Altunbek and Caner Dikyol) have contributed in this research under supervision of Prof. Bahattin Koc.