Advanced solid freeform fabrication (SFF) techniques have been an interest for 
constructing tissue engineered polymeric scaffolds because of its repeatability 
and capability of high accuracy in fabrication resolution at the scaffold macro- 
and microscales. Among many important scaffold applications, hydrogel scaffolds 
have been utilized in tissue engineering as a technique to confide the desired 
proliferation of seeded cells in vitro and in vivo into its architecturally 
porous three-dimensional structures. Such fabrication techniques not only enable 
the reconstruction of scaffolds with accurate anatomical architectures but also 
enable the ability to incorporate bioactive species such as growth factors, 
proteins, and living cells. This paper presents a bioprinting system designed 
for the freeform fabrication of porous alginate scaffolds with encapsulated 
endothelial cells. The bioprinting fabrication system includes a multinozzle 
deposition system that utilizes SFF techniques and a computer-aided modeling 
system capable of creating heterogeneous tissue scaffolds. The manufacturing 
process is biologically compatible and is capable of functioning at room 
temperature and relatively low pressures to reduce the fluidic shear forces that 
could deteriorate biologically active species. The deposition system resolution 
is 10 microm in the three orthogonal directions XYZ and has minimum velocity of 
100 microm/s. The ideal concentrations of sodium alginate and calcium chloride 
were investigated to determine a viable bioprinting process. The results 
indicated that the suitable fabrication parameters were 1.5% (w/v) sodium 
alginate and 0.5% (w/v) calcium chloride. Degradation studies via mechanical 
testing showed a decrease in the elastic modulus by 35% after 3 weeks. Cell 
viability studies were conducted on the cell encapsulated scaffolds for 
validating the bioprinting process and determining cell viability of 83%. This 
work exhibits the potential use of accurate cell placement for engineering 
complex tissue regeneration using computer-aided design systems.