Page 9 - IJB-3-2

Yi Zhang

the 3D-printed components are made available by and cause developmental malformation and other ad-
adding a functional compound to the 3D-printable verse effects [45] . Although large-chain acrylate poly-
resin. The 3D-printing process embeds the function- mers that form the 3D-printed components are much
al compound in the finished product. The authors have less toxic, a significant amount of acrylate monomers
demonstrated surface-initiated atom transfer radical and short-chain polymers are still present in the
polymerization for post-printing surface modifica- 3D-printed components. These small molecules may
tion by incorporating Br-containing vinyl-terminated leach out and cause damages to biological entities.
initiator [39] . This technique could potentially enable a Post-3D printing modification by additional UV cur-
wide range of chemistry for surface modification of ing could crosslink the small molecules into
3D-printed parts, if 3D-printable materials can be de- long-chain polymer, thereby reducing the cytotoxicity
signed to carry carboxyl group for carbodiimide coup- of 3D-printed components. Future research needs to
ling [40] or other functional groups to conjugate pro- focus on biocompatibility of 3D-printable materi-
teins and other biomolecules to the surface via well- als both before and after printing, and new methods to
established click chemistry [41] with great ease. reduce the toxicity of 3D-printed components also
The post-3D printing modification described above need to be explored.
focuses on in vivo biomedical devices. As a matter of
fact, in vitro biomedical device could also benefit 3. Conclusion
from post-3D printing modification. Many in vitro In conclusion, we have stressed the importance of
assays require functionalization with biologically ac- post-3D printing modification. Because only a limited
tive molecules. The polydopamine chemistry allows selection of 3D-printable materials and techniques are
easy functionalization of microfluidic devices with specifically designed for biomedical applications,
antibodies or other binding agents for immunoassays. post-3D printing modification provides a means to
One may also functionalize 3D-printed devices with achieve desired architectural and functional properties.
silica or nickel for solid phase nucleic acids and re- In this perspective, we have identified structural re-
combinant protein purification.
configuration and surface functionalization as two
1.2.2 Surface Passivation main aspects of post-3D printing modification. We
Compared to surface activation, post-3D printing pa- have discussed techniques that have already been im-
ssivation process has not been paid enough attention. plemented and suggested other potential post-3D
Unlike tissue engineering scaffold, 3D-printed im- printing modification techniques that can be employed
plants are meant to reside permanently in the liv- to close the gap between 3D printing technology and
ing body. Therefore, they are complicated by problems requirements of biomedical application.
such as protein fouling, bacteria fouling and for-
eign body reactions. Many surface modification tech- Conflict of Interest and Funding
niques have been developed to reduce fouling and
foreign body reactions. For example, poly (ethylene No conflict of interest has been reported by the author.
glycol) (PEG) coating effectively prevents protein The author would like to thank the funding support by
adsorption [42] . Silver nanoparticles are embedded in the startup grant from the School of Mechanical and
polymer coatings to form an antimicrobial film that Aerospace Engineering at Nanyang Technological
prevents bacteria fouling [43] . Drug-loaded responsive University.
polymer coating release drugs in a controlled fashion References
to provide long-term protection against foreign body
reaction [44] . These techniques can all be readily ap- 1. Leong K F, Cheah C M, and Chua C K, 2003, Solid
plied to 3D-printed components. The same concept al- freeform fabrication of three-dimensional scaffolds for
so applies to 3D-printed in vitro devices, which could engineering replacement tissues and organs. Biomaterials,
incorporate these passivation techniques to prevent vol.24(13): 2363–2378.
nonspecific adsorption of biomolecules, thereby re- https://dx.doi.org/10.1016/S0142-9612(03)00030-9
ducing undesired background and improving detection 2. Utela B, Storti D, Anderson R, et al., 2008, A review of
sensitivity. process development steps for new material systems in
Many resins used in 3D printing, such as acrylate three dimensional printing (3DP). Journal of Manufac-
and its derivatives, are known to have cytotoxicity turing Processes, vol.10(2): 96–104.

International Journal of Bioprinting (2017)–Volume 3, Issue 2 97