Regenerative medicine seeks to repair or replace dysfunctional tissues with 
engineered biological or biohybrid systems. Current clinical regenerative models 
utilize simple uniform tissue constructs formed with cells cultured onto 
biocompatible scaffolds. Future regenerative therapies will require the 
fabrication of complex three-dimensional constructs containing multiple cell 
types and extracellular matrices. We believe bioprinting technologies will 
provide a key role in the design and construction of future engineered tissues 
for cell-based and regenerative therapies. This review describes the current 
state-of-the-art bioprinting technologies, focusing on direct-write bioprinting. 
We describe a number of process and device considerations for successful 
bioprinting of composite biohybrid constructs. In addition, we have provided 
baseline direct-write printing parameters for a hydrogel system (Pluronic F127) 
often used in cardiovascular applications. Direct-write dispensed lines (gels 
with viscosities ranging from 30 mPa s to greater than 600 × 10⁶ mPa s) were 
measured following mechanical and pneumatic printing via three commercially 
available needle sizes (20 ga, 25 ga, and 30 ga). Example patterns containing 
microvascular cells and isolated microvessel fragments were also bioprinted into 
composite 3D structures. Cells and vessel fragments remained viable and 
maintained in vitro behavior after incorporation into biohybrid structures. 
Direct-write bioprinting of biologicals provides a unique method to design and 
fabricate complex, multicomponent 3D structures for experimental use. We hope 
our design insights and baseline parameter descriptions of direct-write 
bioprinting will provide a useful foundation for colleagues to incorporate this 
3D fabrication method into future regenerative therapies.