58 R. Tran et al.
to cells deeply embedded in the substrate has proven to be a formidable task.
100
The development of an established vasculature system to provide oxygen, nutri-
ents, and waste removal is critical in the survival of tissue engineered organs.
107
From this limitation, current engineered tissue is limited to 150–200 micron thick-
nesses due to oxygen diffusion limitations.
108
Fidkowski et al. have used BioMEMS to build capillary networks onto syn-
thetic substrates. Using standard soft photolithography techniques, the research
group patterned intricate capillary networks 10 microns in size onto PGS using
silicon wafers as molds. Human umbilical vein endothelial cells (HUVECs) were
seeded onto the PGS substrates and perfused under flow conditions to create
confluent endothelialized two–dimensional cell layers. The HUVECs could be
lifted from the PGS substrate and incorporated into other devices. Thus, this study
showed the potential for using PGS in combination with BioMEMS techniques to
create microvasculature in vitro towards the fabrication of vascularized organs.
107
3.6 OUTLOOK
Many of the tissues in the body are soft and elastic. Much attention has been paid
in using biodegradable soft and elastic scaffolds for tissue engineering soft tissues
such as skin, blood vessel, tendon, ligament, cartilage, bladder etc. The roles of
biodegradable elastomeric materials in tissue engineering have been increasingly
emphasized as the evolving progress in understanding the cell/materials/host
interactions. Soft and elastic scaffolds made of biodegradable elastomeric scaffolds
not only provide a substrate for cells to adhere and proliferation, but also minimize
the compliance mismatch with surround tissues and provide cues and signals to
promote tissue development and functional integration with the host.
The design and synthesis of biodegradable elastomers will continuously
evolve owing to the more stringent material requirements in personalized tissue
regeneration. Despite the recognized importance of the mechanical properties of
tissue engineering scaffolds on the tissue development, there has been a dearth
on fundamental understanding on how the soft and elastic scaffolds affect the
inflammatory response of the host and the tissue/graft integration.
The application of BioMEMS in tissue engineering has resulted in more un-
derstanding on how cells respond to micro/nano structure created by BioMEMS.
Constructing vasculature with the aid of BioMEMS on biodegradable elastomeric
scaffolds for tissue engineering is still in its infancy. The current studies lie on fab-
ricating channels on two-dimensional films, and then stacking them into 3D chan-
nels on elastomers, mostly on PDMS. More studies should be focused on using
biodegradable elastomeric substrates. More importantly, the vasculature should
be built up within 3D porous scaffolds instead of just in between two-dimensional
solid films. Our recent studies have resulted in 3D scaffolds with vasculature-like
channels built using our recently developed CUPE polymers via the scaffold-sheet
tissue engineering strategy combined with BioMEMS technology.
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