Download Living cells can sense their physical

Living cells can sense their physical microenvironment and respond to mechanical and biochemical cues with changes in their morphology, migration, division, and gene expression.
We are trying to engineer this micro-environment by controllably varying the stiffness,
geometry, ligand density and dimensionality to control the fate of primary cells and stem
cells. By modulating the stiffness of the substrate, embryonic chicken cardiac cells responded
with changes in their cytoskeletal structure, force of contraction and beating rate.[1]
Furthermore, by culturing these cells on very soft substrates (0.5 – 1 kPa), we were able to
stimulate quiescent (non-beating) cardiac cells by application of a local cyclic stretch to the
substrate and make the cells beat periodically even after the removal of the cyclic stretch. [2]
By using soft lithography and micro-contact printing, we were able to control the
differentiation of mouse skeletal myoblasts. When these cells were cultured on fibronectin
islands of hybrid shapes (combined linear and circular regions) they showed highest fusion
index, degree of maturation, alignment, and best response to electrical pulse stimulation.[3]
Thus by geometrical constraints we were able to modulate the process of myogenesis. Now,
we are combining these different mechanical cues and encapsulating pluripotent embryonic
stem cells (ESCs) in poly ethylene glycol diacrylate (PEGDA) hydrogels. These hydrogels
are being fabricated using a three dimensional printer - stereolithography apparatus (SLA).
SLA offers several advantages like multi-cell, multi-material fabrication and capability to
encapsulate cells during the process of fabrication of the structure. Also, unlike other photopolymerization techniques which require a physical mask, SLA is a maskless computer aided
design (CAD) based rapid prototyping (RP) technology. Thus by changing the molecular
weight of the polymer we hypothesize that it will modulate the mechanical microenvironment and we will be able to control the differentiation of ESCs to different lineages.
This platform can thus be used to create hydrogels of physiologically relevant stiffness and
can have applications in tissue engineering, regenerative medicine and stem cell biology.
[1]
[2]
[3]
P. Bajaj, X. Tang, T. A. Saif, R. Bashir, Journal of Biomedical Materials Research Part
A 2010, 95A, 1261.
X. Tang, P. Bajaj, R. Bashir, T. A. Saif, Soft Matter 2011, 7, 6151.
P. Bajaj, B. Reddy, L. Millet, C. Wei, P. Zorlutuna, G. Bao, R. Bashir, Integrative
Biology 2011, 3, 897.
Figure: (A) Embryonic chicken cardiac cells on polyacrylamide hydrogels of different stiffness
(B) C2C12 skeletal myoblasts patterned on fibronectin protein islands (C) Cells (red) and
polystyrene beads (green) patterned by dielectrophoresis in 3D PEGDA 700 hydrogels (D)
Mouse embryonic stem cells after 24 hours in AggreWellTM plates forming mouse embryoid
bodies (E) C2C12 cells with IGF on graphene chips.