Cell and Tissue Mechanics:
Most cell types in human body stick to other
cells or to the extracellular matrix in order to communicate and
maintain structural integrity. At the same time, they respond
quickly to changes in their environment. This corresponds to a
continuous remodeling of cell-cell and cell-matrix contacts and
the structures they are attached to. We focus at developing a
quantitative modeling framework to deal with the structural
aspects of cell adhesion. Such a framework has to integrate the
cytoskeletal dynamics, adhesion cluster dynamics, and the
|Mitotic cell division generates two
identical daughter cells from a single cell using a complex
machinery called "mitotic spindle" which essentially helps the
chromosomes to segregate properly. Dynamic filaments known as
Microtubules (MT), "Search and Capture" the chromosomes to
assemble the "Mitotic spindle". In order to proceed through the
mitosis MTs should be properly "attached" to the chromosomes -
failing to which causes cell death and even cancer. Our "Search
and Capture" model can predict the probability of erroneous
attachments and test the effectivness of different error
|Percolation in tumor vasculature:
|Tumor induced angiogenesis is the
formation of new blood vessels around the tumor from
pre-existing capillaries in a hypoxic (O2 depleted)
microenvironment. Hypoxia induces growth factor synthesis and
release from tumor cells which act on endothelial cells or
nearby blood vessels. Angiogenic sprouting, new vessel formation
and vessel dilation is the result of this interaction leading to
favorable tumor growth conditions. We introduce a stochastic
model to describe
vascularization and necrotic regions develops outside and inside
the tumor respectively. A percolation transition is found for
vessel collapse inside the tumor as a function of angiogenic
probability. Applying blood flow one finds a completely
different evolution morphology of the tumor-vascular system and
the results resembles to the experimental observations.
|Coarsening in disordered media:
|A homogeneous binary mixture becomes
thermodynamically unstable if it is rapidly quenched below the
coexistence curve. The subsequent far-from-equilibrium evolution
of the system is characterized by the emergence and growth of
domains enriched in the new equilibrium phases. There is a good
understanding of domain-growth kinetics in pure and isotropic
systems. In our research, we focus on domain growth in
ferromagnets and binary alloys with quenched disorder in the
form of random exchange interactions as well as site dilution.
At early times, domain coarsening is not affected by disorder.
Then, there is a crossover to a disorder-affected regime, which
occurs earlier for higher disorder amplitudes. Kinetics is
slowed down due to the effect of random bonds or non-magnetic
atoms, since both these factor reduces the driving force
responsible for domain growth. Near the percolation threshold,
this effect is quite large. However in all cases domain
evolutions are consistent with power-law growth with a variable
exponent. These results are interpreted in the context of
disorder barriers with a logarithmic dependence on the domain
Dr. Raja Paul
Department of Solid State Physics
Indian Association for the Cultivation of Science
Jadavpur, Kolkata 700 032, India
E-mail: ssprp [ AT ] iacs.res.in
Phone: +91-33-24734971 (Ext. 1310 (Office), 2114 (Lab))
|| Vinogradova T, R. Paul, Grimaldi AD, Loncarek J, Miller PM, Yampolsky D,
Magidson V, Khodjakov A, Mogilner A, Kaverina I., Concerted effort of
centrosomal and Golgi-derived microtubules is required for proper Golgi
complex assembly but not maintenance,
Mol. Biol. Cell, 23: 820-833 (2012).
|| William T. Silkworth, Isaac K. Nardi, R. Paul, Alex Mogilner, Daniela
Cimini, Timing of centrosome separation is important for accurate
Mol. Biol. Cell, 23: 401-411 (2012).
||Valentin Magidson, Christopher B. O'Connell, R. Paul, Jadranka Loncarek,
Alex Mogilner and Alexey Khodjakov, Spatial arrangement of chromosomes
during prometaphase accelerates spindle assembly, Cell, 146: 555-567
|| R. Paul, Modeling Biological Cells, Chem. Modell., 9, 61-91 (2012)
|| R. Paul, R. Wollman, W.
T. Silkworth, I. K. Nardi, D. Cimini, A. Mogilner, Computer simulations predict that chromosome movements and
rotations accelerate mitotic spindle assembly without
compromising accuracy, PNAS, 106:
||N. P. Ferenz, R. Paul, C.
Fagerstrom, A. Mogilner, P. Wadsworth, Eg5/Dynein antagonism during
bipolar spindle assembly formation requires overlapping
Current Biol., 19 : 1833-1838 (2009)
||R. Paul, Flow-correlated dilution of a regular network leads to a percolating network during tumor induced angiogenesis,
Eur. Phys. J. E 30, 101-114 (2009)
||R. Paul and U.S. Schwarz. Pattern formation and force generation by cell ensembles in a filamentous matrix. Proceedings of the IUTAM Symposium on Cellular, Molecular and Tissue Mechanics, in press, Springer (2009).
||R. Paul, P. Heil, U. Schwarz and J. Spatz,
Propagation of mechanical stress through the actin cytoskeleton towards focal adhesions: model and experiment,
Biophys. J. , 94:1470-1482, (2008).
J.-D. Noh, G. Schehr, H. Rieger,
Computer simulations of phase transitions and dynamics in confined systems,
Z. Phys. Chem., 222, 433 (2008)
||R. Paul, A. Gambassi and G. Schehr,
Dynamic crossover in the global persistence at criticality,
Europhys. Lett. 78, 10007 (2007).
||R. Paul, G. Schehr and H. Rieger,
Super-Aging in two-dimensional random ferromagnets,
Phys. Rev. E 75, 030104(R) (2007).
||G. Schehr and R. Paul, Non-equilibrium critical dynamics in disordered ferromagnets,
J. Phys: Conf. Series 40 27-35 (2006).
||R. Paul and G. Schehr, Non Markovian persistence in the diluted Ising model at criticality,
Europhys. Lett. 72(5), 719 (2005).
||R. Paul and H. Rieger, Condensation Phenomena in Nanopores - a Monte Carlo Study,
J. Chem. Phys. 123, 024708 (2005).
S. Puri and H. Rieger, Domain Growth in Ising Systems with Quenched Disorder,
Phys. Rev. E 71, 061109 (2005).
||G. Schehr and R. Paul, Universal aging properties at a disordered critical point,
Phys. Rev. E 72, 016105 (2005).
||G. Schehr, R. Paul, H. Rieger,
Growing length scales in 2d disordered systems,
Prog. Theor. Phys. Suppl., 157, 111 (2005)
S. Puri and H. Rieger, Domain growth in random magnets,
Europhys. Lett. 68(6), 881 (2004).
||R. Paul, M. Alava and H. Rieger,
Low temperature properties of the random field Potts chain,
Eur. Phys. J. B 30, 357 (2002).