Here, we have developed a 3D bioprinted microchanneled gelatin hydrogel that promotes human mesenchymal stem cell (hMSC) myocardial commitment and supports native cardiomyocytes (CMs) contractile functionality. Firstly, we studied the effect of bioprinted microchanneled hydrogel on the alignment, elongation, and differentiation of hMSC. Notably, the cells displayed well defined F-actin anisotropy and elongated morphology on the microchanneled hydrogel, hence showing the effects of topographical control over cell behavior. Furthermore, the aligned stem cells showed myocardial lineage commitment, as detected using mature cardiac markers. The fluorescence-activated cell sorting analysis also confirmed a significant increase in the commitment towards myocardial tissue lineage. Moreover, seeded CMs were found to be more aligned and demonstrated synchronized beating on microchanneled hydrogel as compared to the unpatterned hydrogel. Overall, our study proved that microchanneled hydrogel scaffold produced by 3D bioprinting induces myocardial differentiation of stem cells as well as supports CMs growth and contractility. Applications of this approach may be beneficial for generating in vitro cardiac model systems to physiological and cardiotoxicity studies as well as in vivo generating custom designed cell impregnated constructs for tissue engineering and regenerative medicine applications.

The 3D bioprinting of stem cells directly into scaffolds offers great potential for the development of regenerative therapies; in particular for the fabrication of organ and tissue substitutes. For this to be achieved; the lineage fate of bioprinted stem cell must be controllable. Bioprinting can be neutral; allowing culture conditions to trigger differentiation or alternatively; the technique can be designed to be stimulatory. Such factors as the particular bioprinting technique; bioink polymers; polymer cross-linking mechanism; bioink additives; and mechanical properties are considered. In addition; it is discussed that the stimulation of stem cell differentiation by bioprinting may lead to the remodeling and modification of the scaffold over time matching the concept of 4D bioprinting. The ability to tune bioprinting properties as an approach to fabricate stem cell bearing scaffolds and to also harness the benefits of the cells multipotency is of considerable relevance to the field of biomaterials and bioengineering.

Considerable interest has arisen in precision fabrication of cell bearing scaffolds and structures by free form fabrication. Gelatin is an ideal material for creating cell entrapping constructs, yet its application in free form fabrication remains challenging. We demonstrate the use of gelatin, crosslinked with microbial transglutaminase (mTgase), as a material to print cell bearing hydrogels for both 2-dimensional (2-D) precision patterns and 3-dimensional (3-D) constructs. The precision patterning was attained with 3 % gelatin and 2 % high molecular weight poly (ethylene oxide) (PEO) whereas 3-D constructs were obtained using a 5 % gelatin solution. These hydrogels, referred to as “bioinks” supported entrapped cell growth, allowing cell spreading and proliferation for both HEK293 cells and Human Umbilical Vein Endothelial Cells (HUVECs). These bioinks were shown to be dispensable by robotic precision, forming patterns and constructs that were insoluble and of suitable stiffness to endure post gelation handling. The two bioinks were further characterized for fabrication parameters and mechanical properties.

We recently pioneered the cell electrospinning of living cells as viable biological threads and scaffolds. In that study, we demonstrated the process with an immortalized human brain astrocytoma (1321N1, European Collection of Cell Cultures) cell line at a cell concentration of 10(6) cells/ml. The next stage was to demonstrate the ability to cell electrospin primary living cells at cell concentrations of 10(7) cells/ml (the highest-ever cell concentration threaded by any threading methodology). Furthermore, the post-threaded cells needed their viability assessed over a long period of time by way of flow cytometry, which accurately assesses the viable cell populations. In this work, we employ primary porcine vascular and rabbit aorta smooth-muscle cells prepared as cellular suspensions at cell concentrations of 10(7) cells/ml. The cell electrospinning device employs a coaxial needle arrangement that enables the flow of either highly concentrated cellular suspension in the inner needle while the outer needle accommodates the flow of a viscoelasticity medical-grade polydimethylsiloxane medium. Cell viability was assessed over a long timeframe by way of flow cytometry in comparison with controls. The work reported here demonstrates the ability to cell electrospin primary living organisms as highly concentrated cellular suspensions. The viable population of cells post-cell electrospinning are significant and remain viable over both the short and long term, as assessed by flow cytometry. Our work elucidates the ability to cell electrospin primary cells as highly concentrated cellular suspensions. The post-cell electrospun organisms are viable over long periods of time, demonstrating a significant active cell population when compared with controls.