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Inadequate supply
of transplantable organs/tissues severely limits
the effective treatment of malignant diseases.
Apart from the shortage of available donors, the
disadvantages of autografts, increased risk
associated with allografts, induction of
hyperacute rejection due to potential mismatch
of xenografts and the possible transmission of
zoonoses due to xenografts have necessitated the
need for alternative repair options. But,
synthetic/semi-synthetic alternatives such as
bioinert or bioprosthetic substitutes have
performed poorly in clinical settings. There is
a need for alternative approaches to obtain
transplantable tissue/body parts. Tissue
engineering provides an approach to replace,
restore tissue functions by growing cells on
three-dimensional (3D) matrices. Porous
structures are molded into the desired shape of
the tissue and are used to support/guide cells
to colonize, organize and produce their own
extracellular matrix elements. Regenerating the
tissue outside the body is necessary in
transplantations where functionality of a tissue
is critical to the survival of a patient. |
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Tissue regeneration outside the body requires
seeding appropriate cells on to porous
structures to establish cell-composite grafts.
Seeding immono-compatible cells to colonize the
scaffolds is necessary to circumvent immune
rejection of the transplanted graft. Current
practice is to retrieve cells from a patient
(possible for skin), populate using tissue
culture techniques and transplant the
cell-seeded scaffold back to the patient. This
procedure is not applicable for less abundant
tissues which cannot be accessed without a
surgical procedure. Further, there are
complications associated with the pathology of
the disease and time constraints. Significant
developments in stem cell differentiation and
proliferation have offered a useful solution.
Recent understanding of the components required
to proliferate human embryonic stem cells in
two-dimension without lineage commitment, has
opened a new window of opportunity. Furthermore,
the plastic nature of adult stem cells to
restore the functionality of a needed cell type
after localizing into a microenvironment has
added another driving force in regenerative
medicine. However, transforming these concepts
into useful applications is currently limited
due to the complexity of interactions that
affect the differentiation and proliferation of
stem cells. Standard practice of culturing stem
cells on a pre-formed feeder layer of accessory
cells has severe limitations such as i)
optimization problem due to the presence of
multiple components with un-defined role(s) and
ii) restriction in scale-up to two dimensions
due to the necessary contact of stem cells with
the feeder layer. Further, evaluating 3D
configurations are critical a) to understand the
spatio-temporal effects, b) to evaluate the
reorganization of various compartments and organ
formation, and c) to develop devices that can be
used in clinical applications.Thus, exploring
the possibility of differentiating cells in
porous structures will significantly help as an
alternative cell source in tissue regeneration. |
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TThe goal of this
project is two-fold: i) understand the influence
of structural features, chemical signals, and
mechanical signal on the proliferation and
differentiation of stem cells from various
sources which leads to the development of a 3D
stem cell culture system and ii) to use these
conditions in regenerating tissue of interest.
We use 3-D porous matrices formed from routinely
used 2-D substrates (gelatin, shown in the
picture above and collagen). To better
understand the interplay between structural
features, chemical signals and mechanical
signals, we study the interactions at two levels
a) microscale (histology figure shown above) and
b) nanoscale using novel technologies. Since
secretion and assembly of extracellular matrix
turnover (deposition and degradation)
significantly influences quality of the
regenerated tissue and cellular phenotypic
characters, we evaluate the secretion and
assembly of matrix elements. For example,
collagen provides tensile strength to bladder
while proteoglycans fills the extracellular
space, creating a space for the tissue
regulation of growth factors and other
interactions. The elasticity of soft tissues
subjected to repeated deformation, is provided
by the presence of elastic fibers in the
extracellular matrix. Several disorders in
humans have been found to involve the
disorganization of elastin fibers. Unlike many
components of the extracellular matrix, elastic
fibers are formed only in developing tissues,
with little or no synthesis in adults; impaired
functioning of elastic fibers results
age-related phenotypes such as skin wrinkling,
emphysema, and arteriosclerosis. Hence, assembly
and maturation of these matrix elements in
tissue regeneration play a significant role in
determining the biomechanics and the quality of
the regenerated tissue. We utilize adult cells
from different tissues of interest and evaluate
the regeneration patterns and compare how stem
cells would perform under the same settings. |
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