Inkjet printing biomaterials for tissue engineering: bioprinting

Inkjet printing offers controlled placement of both biological and synthetic materials. The precision, control and small working volumes associated with inkjet printing are advantageous where biological materials such as proteins, enzymes and cells can incur high costs. This review is primarily technology focused and divides bioprinting into three categories of interest: proteins, cells and scaffolds and demonstrates that the logistical hurdles and material formulation requirements remain a common denominator to the advancement of the field into commercial applications and three-dimensional (3-D) constructs. A variety of cell types printed using thermal, piezoelectric and electrostatic actuation mechanisms yield 80–95% cell viability. Transient membrane damage is reported for cells printed using a thermal printer. Protein deposition by thermal and piezoelectric printing results in reversible deformation leading to an increased need for the addition of ink modifiers. The fluid characteristics and the drop substrate interactions are identified as crucial with regards to future applications. The current approaches to scaffold matrix selection with regards to the complex criterion require fluid and solid phases and a controlled phase change while maintaining the criterion for printing vary from chemical gelation, physical gelation mechanisms (e.g. thermo reversible gels) and tandem gelation.