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The human body has an organized
hierarchical structure which can be grouped into
various organ systems and organs. These are
comprised of specific tissue types which are
made of multiple cells and matrix elements,
which perform different functions. The body's
functions are ultimately determined by cells.
Thus, understanding the genesis of multicellular
structures and dynamic changes in cellular
activity is of significant importance in a broad
spectrum of medicine including occurrence of
diseases and developmental biology. To
understand cellular activity, concept of in
vitro tissue culture has been developed which
reduces the complexity encountered in studying
the whole body. Cells are cultured outside the
body using tissue culture plastic-ware made of
polystyrene or other polymers but processed to
promote cell adhesion. Serum harvested from
animal sources is also utilized as it contains a
number of essential components that promote
active cell division and exponential growth.
Using in vitro tissue culture technique, variety
of patho/ physiological processes including
embryogenesis, normal tissue development,
cancer, and wound healing have been evaluated.
Extensive studies have shown that dynamic
cell-extracellular matrix (ECM) interactions
orchestrate the morphogenesis of cells; during
the process, cells undergo morphogenesis while
remodeling the ECM. Further, changes in matrix
composition significantly influence cellular
phenotypic characters which in turn alter
assembly of newly synthesized matrix elements.
Although these insights have been helpful in
understanding many concepts, there are many
problems with two-dimensional tissue culture
technique. |
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There are significant discrepancies between the
clinical samples of a disease state to many in
vitro tissue culture analyses. For example,
fibroblasts with actin filaments are increased
in skin autografts and are prominent in open and
burn wounds. However, the role of actin filament
rich fibroblasts in wound healing is still
controversial. The major and persisting problem
for burn survivors is associated with the
problem of scarring, sometimes hypertrophic
which is a detrimental outcome for skin
functionality. However, there are no in vitro
models that mimic hypertropic scar formation,
although 3D porous structures have been used for
skin regeneration and to control hypertrophic
scar formation. Similarly, molecular events
leading to many pathological states are yet to
be clearly understood. Osteoarthritis (OA) is
the most common joint disorder in both men and
women and its etiology is relatively unknown.
Many implantation studies using biocompatible
materials have shown that the microarchitecture
of the materials is the primary determinant in
the foreign body response. Tissue culture
plastic surface offers 2D substrata where
cultured cells are restricted to spread on a
rigid surface. Hence, effects of biophysical
properties of the matrix that provide a spatio-temporal
effect in the body are not part of the effect.
However, biophysical properties significantly
influence cell adhesion and functions in 3D
environment. Some of the recent developments
including our laboratory have shown that cells
respond differently in attachment, morphology,
migration, and proliferation on 3D porous
structures unlike 2D-tissue culture experiments.
For example, 3D cell adhesions appear distinct
from 2D adhesions and are termed as “3D matrix
adhesions” to separate them from 2D
counterparts. There are also significant
differences in many proteins responsible for
cell-matrix interactions. Such differences in
cell adhesion between 2D and 3D structures
trigger different signaling mechanisms. Since
cells exist in 3D spaces in the human body,
developing systems to for the cell colonization
in 3D is necessary.
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The objective
of the project is to develop 3D model systems
that facilitate our understanding of how cells
make healthy tissues. Technologies are developed
mimicking natural matrixes present in the body.
To mimic various matrixes, we develop 3D porous
matrixes (one of them show in the figure) using
a number of polymeric blend systems made of
synthetic polymers and natural polymers. Our
hypothesis is that various matrix elements in
the body contribute different signals to the
cells and they have to be present in an
appropriate composition. If only a single pure
matrix element is present, that may not provide
complete signaling mechanism. These model
studies evaluate the cellular response in
attachment, morphology, differentiation, and
proliferation on a 3D scaffold. Some of the
properties evaluated are the i) surface
roughness of the substrate, ii) surface charge
of the substrate, iii) influence of cell binding
domain in the mixture of polymers that do not
have cell binding domain, iv) mechanical
stiffness of the materials, v) influence of
fiber size, and vi) influence of serum factors.
For example, we have synthesized negatively
charged matrices to understand the influence of
charge on cell adhesion (shown in the figure)
and growth in the 3D environment [Tillman et al,
Biomaterials, 2007]. The knowledge derived from
this project is of broad significance to
medicine and biomedical sciences. Successful
completion of this project will have significant
impact on i) the regeneration and
transplantation of high quality tissues
on-demand, ii) the development of synthetic
surrogates to test disease states (mechanism of
wound healing), iii) for toxicology studies and
to test the effect of pathogens i.e., as real
time sensors for detecting biological agents,
and iv) importantly changes the way cell culture
experiments will be performed in the future
worldwide. |
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