Tissue engineering combines the fields of medicine and engineering to build replacement tissue capable of restoring, maintaining, or improving damaged tissue. Researchers have recently developed techniques to fabricate tissue in which both the cells and matrix have a carefully defined architecture. This report details studies evaluating the use of a direct-write, 3-dimensional (3D) bioassembly tool (BAT) capable of extruding cells and matrix into spatially organized, 3D constructs. This system has been characterized by its ability to fabricate viable 2-dimensional and 3D constructs containing up to 2 separate cellular solutions suspended in type I collagen. The effects of various environmental factors, such as extrusion pressure, humidity, and stage heating, were examined with respect to the viability of the extruded cells. The data indicate that the system parameters required to extrude cells suspended in collagen do not adversely affect the viability of those cells. Maintaining a high humidity, especially when stage heat was applied, is critical in maintaining the viability of the printed cells. These results demonstrate that the BAT is capable of spatially organizing separate cellular solutions into a defined architecture; however, when cells were extruded in a supporting matrix of 3.0 mg/mL type I collagen, it was not possible to consistently generate adjacent, touching, but nonoverlapping lines of separate solutions. Thus, when a fabrication system such as BAT is used to generate complex, 3D viable constructs, the supporting matrix for the cells should be carefully chosen on the basis of such characteristics as its rate of polymerization and stiffness.
