Controlled Positioning of Cells in Biomaterials-Approaches Towards 3D Tissue Printing

Abstract

Current tissue engineering techniques have various drawbacks: they often incorporate uncontrolled and imprecise scaffold geometries, whereas the current conventional cell seeding techniques result mostly in random cell placement rather than uniform cell distribution. For the successful reconstruction of deficient tissue, new material engineering approaches have to be considered to overcome current limitations. An emerging method to produce complex biological products including cells or extracellular matrices in a controlled manner is a process called bioprinting or biofabrication, which effectively uses principles of rapid prototyping combined with cell-loaded biomaterials, typically hydrogels. 3D tissue printing is an approach to manufacture functional tissue layer-by-layer that could be transplanted in vivo after production. This method is especially advantageous for stem cells since a controlled environment can be created to influence cell growth and differentiation. Using printed tissue for biotechnological and pharmacological needs like in vitro drug-testing may lead to a revolution in the pharmaceutical industry since animal models could be partially replaced by biofabricated tissues mimicking human physiology and pathology. This would not only be a major advancement concerning rising ethical issues but would also have a measureable impact on economical aspects in this industry of today, where animal studies are very labor-intensive and therefore costly. In this review, current controlled material and cell positioning techniques are introduced highlighting approaches towards 3D tissue printing.

Figure 1

Schematic drawing of the various techniques. (A) During Laser-Guided Direct Write (LGDW) laser light is focused into a suspension of particles and the particles trapped by the light are pulled through the fluid and deposited on a target surface; (B) During MAPLE DW a laser pulse focusing on the absorbing layer evaporates the matrix containing biological material on the lower side of the substrate due to localized heating and thus pushes the material towards the substrate; (C) Inkjet technology ejects material piezoelectric, thermally actuated or electrostatically actuated after receiving a signal and (D) printed cell patterns with 2 different cell types; reprinted from [53] with permission of IEEE (© 2009 IEEE).

Figure 2

Applications of microwell array platforms. (A) Engineering of single cell microenvironments, mimicking the natural 3D milieu for investigating single cell behavior; (B) engineering of multi-cell microenvironments for investigations on cell-cell interactions; and (C) engineering of cellular aggregates into a microwell for investigating cell aggregate behavior. Adapted from [65] and reprinted with permission of RSC.

Figure 3

Alginate/HA scaffold after printing fabricated with a dispensing based technique. (A) Top view; and (B) side view. Reprinted from [81] with permission of IOP.

Figure 4

(A) 3D biofabrication of a tubular structure of 200 μm using inkjet technology. The homogeneously sized alginate precursor beads are deposited in circular patterns layer-by-layer into CaCl₂ crosslinker solution forming a tubular structure due to gelation. Reprinted from [89] with permission of IS&T; (B) LSCM observation of a 3D bioprinted construct consisting of hepatocytes encapsulated in gelatin/chitosan hydrogel after 6 days of culture. Reprinted from [112] with permission of Elsevier.