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Digital biomanufacturing supporting vascularization in 3D bioprinting

Table 2. Considerations in the development of a bioink and control is in specifically engineered dedicated housing
3DBP culture media immediately surrounding the printer (Advanced Solu-
• Cell-specific metabolites/factors tions, www.advancedsolutionsonline.com). Another
• Printing-specific rheology values approach is to house the entire printing assembly in-
• Application-specific matrix elements side a modular isolator that actively controls such en-
• Specifically control or inhibit apoptosis vironmental parameters as temperature, CO 2 and hu-
• Support or inhibit further differentiation midity. Such equipment also prevents contamination
• Co-culturing and tissue environment effects from both exogenous microbes and aerosols generated
• Address altered cell metabolism rates and flux during the printing process. Randy Yerden, CEO, Bi-
o Existing media formulations are optimized for oSpherix (www.biospherix.com) recently observed,
 rapidly dividing cultures “Modern cytocentric isolators can aseptically and
 low-density culture safely accommodate bioprinters of any dimension, as
o There may be complex gradients well as ancillary equipment — plus control critical
 moving from culture expansion to printing
 moving from 3D culture to in vivo placement cell parameters at optimum CO 2 and O 2 levels during
• Material sourcing, qualification, QA and regulatory printing”.
• Unique matrix and matrix-active component effects 4.3 Many Cellular Requirements
o ECM / glycans / saccharides / polyesters / poloxamers
o Supramolecular chemistry support / control Bioinks may be required to support (for various dura-
o Spontaneous intra- and inter-molecular self-assembly tions) the stable culture of stem cells, co-culture of
 Concentration, ion types, pH diverse differentiated cells, vasculogenesis or other
o Involve multiple linkage types cellular or tissue functions. The cellular requirements
 hydrophobic, SS/disulfide bridge can include primary metabolites/factors optimized to
 Can be assisted the cell populations being printed or unique require-
 Hofmeister series ments due to the nature of the (pre- and post-) printing
o Can be inhibited environment. In some applications, a formulation
 HAPs DTT, carbonate may be required to support 3D high-density culture in
 Must be protected a specialized environment achieved post-printing. This
 bonds are reversible includes post-deposition matrix crosslinking or poly-
o Reported factor sequestration/binding merization forces or chemistries. The type and level of
• Active and passive rheology effects cell growth, attachment and other culture factors
o Additives modulating osmolality and density may be adjusted to accommodate the different de-
o Additives modulating viscosity and surface tension mands or function placed upon the cells post-printing,
o Deposition in plastic flow, rapid elastic response or due to the factor-sequestration by some printing
o Consequences of flow rates, nozzle size and hydrodynamic forces matrices. An increased or different buffering pH che-
• Print matrix-specific stresses mistry may be required due to the pre- and in-
o Unusual light, temperatures and pressures
o Unusual gelling agents, polymerizers, crosslinkers tra-printing ambient gas mixture. Accommodation of
• Serum-free, xeno-free and protein-free ideal such printing-specific stresses as hydrodynamic or
o Can consider FBS and animal protein-based formula dehydration forces are especially important as the
o Regulatory, risk, cost and consistency considerations process progresses from the common product devel-
• Heightened buffering/antioxidant demands opment-supporting serum-containing media to a more
o Variable mass-transfer rates & environment regulatory-friendly serum-free formulation. As the
o Often at high air interface-to-medium ratios types of stresses induced by the printing process are
• High plastic mass-to-medium volume ratio known to induce apoptosis or differentiation in some
o Sorption of lipophilic vitamins/lipids/sterols process cell complements, ingredients known to inhi-
o Heightened leachable and particulates concerns bit these undesired responses may be included. As the
concept of 4D bioprinting progresses, formulations to
also affect the cell’s viability, differentiation, adhesion, either promote or inhibit post-printing differentiation
state, functionality and up- or down-gene regulation. will likely be more strongly considered. Finally, due to
One way of providing some degree of environmental the nature of the disposable bioink storage and print-

22 International Journal of Bioprinting (2017)–Volume 3, Issue 1