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Microscale Technologies for Tissue Engineering
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Khademhosseini, A., and Bong Geun Chung. “Microscale
technologies for tissue engineering.” Life Science Systems and
Applications Workshop, 2009. LiSSA 2009. IEEE/NIH. 2009. 5657. © Copyright 2010 IEEE
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Microscale Technologies for Tissue Engineering
Ali Khademhosseini*
Harvard-MIT Division of Health Sciences and
Technology, Harvard Medical School,
Brigham and Women’s Hospital, MA
Bong Geun Chung
Harvard-MIT Division of Health Sciences
and Technology, Harvard Medical School,
Brigham and Women’s Hospital, MA
[email protected]
[email protected]
Abstract—Microscale technologies are emerging as enabling
tools for tissue engineering and biology. Here, we present our
experience in developing microscale technologies to regulate
cell-microenvironment interactions and generate engineered
tissues. Specifically, we will describe the use of microengineered
shape-controlled hydrogels to generate biomimetic 3D tissue
architectures, the utility of surface patterning approaches for
controlling cell-cell interactions and engineered microchannels
for controlling cell-soluble factor interactions.
These shear-protective hydrogel microwell arrays enabled
stable cell patterning. Furthermore, Poly(ethylene glycol)
(PEG) hydrogel microwells have been used to control
homogeneous cell aggregates[4, 6]. It was demonstrated that
cells cultured within PEG hydrogel microwells remained
highly viable, resulting in directed differentiation of stem
In addition to microwell arrays, microfabricated
parylene-C stencils can be fabricated to reversibly seal on a
hydrophobic surface to enable surface patterning[11, 12].
Using this reusable stencil, microscale co-patterns of cells
and proteins were generated on substrates. These
microfabricated parylene-C stencils were used to pattern
co-cultures of cells in static and dynamic conditions.
To study cell-cell contact, patterned co-cultures have been
fabricated by using layer-by-layer deposition of ionic
biopolymers[13]. In this approach, nonbiofouling hyaluronan
polymer was used for micropatterning cells and proteins onto
substrates. The adhesion of a second cell type was
accomplished by switching the cell-repulsive property of the
hyaluronan surface by ionic adsorption of positively charged
poly-L-lysine (PLL). Using this approach, stem cells and
fibroblasts were co-cultured to study cell-cell contacts. These
microfabrication-based surface patterning techniques provide
a useful approach to manipulate cell-cell interactions for
regulating cellular behavior.
Tissue engineering, is an interdisciplinary research field
that aims to generate transplantable tissues that can restore,
maintain, and enhance tissue function[1, 2]. However, despite
significant advances in tissue engineering, a number of
challenges limit the therapeutic applications of tissue
engineering approaches.
Microscale technologies are enabling tools for addressing
the challenges imposed by conventional tissue engineering
methods. Microscale technologies enable the control of
cell-microenvironment interactions, such as cell-cell,
cell-extracellular matrix (ECM), and cell-soluble factor
interactions[3]. One such technique is soft lithography. In
soft lithography, elastomeric poly(dimethylsiloxane)
(PDMS) stamps made from photoresist- patterned silicon
masters can be used to manipulate the topography of a surface
at sub-micron resolution in a rapid and inexpensive manner.
Moreover, microengineering approaches are used to create
tissue scaffolds with enhanced physical, mechanical, and
biological properties. In this paper, we present various
microscale technologies (i.e. surface patterning, microfluidics,
microengineered hydrogel arrays) for tissue engineering
Surface patterning for regulating cell-cell contacts
Microscale surface patterning can be used to control
cell-cell contacts and cellular shapes. Various microscale
technologies, such as microtopography[4-9], microfabricated
stencils[10-12], and layer-by-layer deposition[13], have been
used to pattern cells within geometrically defined substrates.
For example, hyaluronan modified with photoreactive
methacrylates has been used to make microstructures[5].
* This paper was partly supported by the National Institutes of Health (NIH),
US Army Core of Engineers, and the Charles Stark Draper Laboratory.
c 2009 IEEE
978-1-4244-4293-5/09/$25.00 Microfluidics for spatial control of cell-soluble factor
Microfluidic systems are powerful tools for controlling
the spatial and temporal aspects of cell-soluble factor
interactions. Microfluidic systems have been used to control
cell docking[14] and cell-soluble factor interactions. For
example, a multiphenotype cell array inside a microfluidic
channel was fabricated by reversibly sealing a PDMS mold
with the impression of the fluidic channel to a
microwell-containing substrate. Cells and fluids were
selectively delivered to the microwells. This microfluidic
device containing sequentially aligned orthogonal
microchannels is a potentially useful approach for the
high-throughput experimentation.
Microfluidics has also been used to create stable hydrogel
gradients and generate cell-laden hydrogel scaffolds. These
microfluidic devices can address several challenges
associated with current scaffolds, such as the inability to
control the complex cellular interactions in the scaffolds and
the lack of vascularization. Microfluidic systems can be used
to synthesize microengineered scaffolds that can overcome
these limitations[15]. To generate hydrogel scaffolds with
gradients, materials can be generated with embedded
gradients by using a microfluidic device[16]. By creating
gradients of adhesive peptides conjugated within hydrogels,
the attachment of endothelial cells along the material can be
Microfluidic devices have also been shown as a promising
tool to facilitate the exchange of nutrients and oxygen in 3D
tissue constructs. We have recently developed cell-laden
hydrogel microfluidic channels and demonstrated that (just
like in real tissues) only cells near microfluidic channels
remained viable after three days in vitro [17]. These
cell-laden hydrogel microfluidic devices can be scaled up by
stacking the vascular patterns to create biomimetic
multi-layer vascularization. Therefore, microfluidic devices
are powerful tools for controlling cell-soluble factor
interactions and are increasingly used by biologists and tissue
engineers to study cell behavior and create tissue constructs.
Microengineered hydrogel arrays for tissue engineering
Recently the merger of microengineered hydrogels and
microscale techniques has been used to develop new
approaches to create 3D tissue constructs. We have
developed bottom-up tissue engineering technique that use
directed assembly of hydrogels. In this approach,
tissue-mimetic building blocks are generated and
subsequently assembled to create larger structures. The shape
of the individual pieces can be controlled to enable their
assembly by using directed self-assembly[18, 19] or
stop-flow lithography in a microfluidic device[20].
Therefore, the modular design and assembly of these
approaches can influence many areas of tissue engineering.
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Biomaterials, vol. 29, 2008, pp. 752-763.
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[12] D. Wright, B. Rajalingam, S. Selvarasah and A. Khademhosseini, M.R.
Dokmeci, Generation of static and dynamic patterned co-cultures using
microfabricated parylene-C stencils, Lab Chip, vol. 7, 2007, pp. 1272-1279.
[13] A. Khademhosseini, K.Y. Suh, J.M. Yang and J. Yeh, G. Eng, S.
Levenberg, et al., Layer-by-layer deposition of hyaluronic acid and
poly-L-lysine for patterned cell co-cultures, Biomaterials, vol. 25, 2004, pp.
[14] A. Khademhosseini, J. Yeh, G. Eng, J.M. Karp, and J. Borenstein, et
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in biology and medicine: From molecular principles to bionanotechnology,
Advanced Materials, vol. 18, 2006, pp. 1345-1360.
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gradient hydrogels using a microfluidics/photopolymerization process,
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[17] Y. Ling, J. Rubin, Y. Deng, C. Huang, U. Demirci, J.M. Karp and A.
Khademhosseini, A cell-laden microfluidic hydrogel, Lab Chip, vol. 7, 2007,
pp. 756-762.
[18] J. Yeh, Y. Ling, J.M. Karp, J. Gantz, A. Chandawarkar, G. Eng, J.
Blumling 3rd, R. Langer and A. Khademhosseini, Micromolding of
shape-controlled, harvestable cell-laden hydrogels, Biomaterials, vol. 27,
2006, pp. 5391-5398.
[19] Y. Du, E. Lo, S. Ali and A. Khademhosseini, Directed assembly of
cell-laden microgels for fabrication of 3D tissue constructs, Proc Natl Acad
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[20] P. Panda, S. Ali, E. Lo, B.G. Chung, T.A. Hatton, A. Khademhosseini
and P.S. Doyle, Stop-flow lithography to generate cell-laden microgel
particles, Lab Chip, vol. 8, 2008, pp. 1056-1061.
The merger of microscale technologies and hydrogels
offers new opportunities to address the challenges imposed
by existing technologies to create 3D tissue scaffolds and
control cellular behavior.
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2009 IEEE/NIH Life Science Systems and Applications Workshop (LiSSA 2009)
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