Research

Melanins are natural biopolymers that have remarkable properties including UV-protection, coloration, and antioxidant activity. Their biosynthesis is regulated both spatially and temporally and involves supramolecular templating and compartmentalization of enzymes and reactants within specialized organelles called melanosomes. In contrast, the laboratory-based bulk synthesis of melanin by tyrosine or dopamine oxidation is a poorly controlled process, resulting in materials with undefined properties. Read More

Functional composite materials that can change their spectral properties in response to external stimuli have a plethora of applications in fields ranging from sensors to biomedical imaging. One of the most promising types of materials used to design spectrally active composites are fluorescent single-walled carbon nanotubes (SWCNTs), noncovalently functionalized by synthetic amphiphilic polymers. Read More

The conductivity of ionic solutions is arguably their most important trait, being widely used in
electrochemical, biochemical, and environmental applications. The Debye-Huckel-Onsager (DHO)
theory successfully predicts the conductivity at very low ionic concentrations of up to a few millimolars, but there is no well-established theory applicable at higher concentrations. Read More

We discuss hydrodynamic forces acting on a two-dimensional liquid domain that moves laterally
within a supported fluid membrane in the presence of odd viscosity. Since active rotating proteins
can accumulate inside the domain, we focus on the difference in odd viscosity between the inside
and outside of the domain. Read More

Living cells respond to mechanical changes in the matrix surrounding them by applying contractile forces that are in turn transmitted to distant cells. We consider simple effective geometries for the spatial arrangement of cells, we calculate the mechanical work that each cell performs in order to deform the matrix, and study how that energy changes when a contracting cell is surrounded by other cells with similar properties and behavior Read More

Mechanical metamaterials present a promising platform for seemingly impossible mechanics. They often require incompatibility of their elementary building blocks, yet a comprehensive understanding of its role remains elusive.  Relying on an analogy to ferromagnetic and antiferromagnetic binary spin interactions, we present a general approach to identify and analyze topological mechanical defects for arbitrary building blocks. Read More

When considering flows in biological membranes, they are usually treated as flat although, more often than not, they are curved surfaces, even extremely curved, as in the case of the endoplasmic reticulum. Here, we study the topological effects of curvature on flows in membranes. Focusing on a system of many point vortical defects, we are able to cast the viscous dynamics of the defects in terms of a geometric Hamiltonian. In contrast to the planar situation, the flows generate additional defects of positive index. Read More

We examine the response of a quasi-two-dimensional colloidal suspension to a localized circular driving
induced by optical tweezers. This approach allows us to resolve over 3 orders of magnitude in the

P´eclet number (Pe) and provide a direct observation of a sharp spatial crossover from far- to near-thermalequilibrium regions of the suspension. Read More

Thin elastic sheets supported on compliant media form wrinkles under lateral compression. Since
the lateral pressure is coupled to the sheet’s deformation, varying it periodically in time creates a parametric excitation. We study the resulting parametric resonance of wrinkling modes in sheets supported on semiinfinite elastic or viscoelastic media, at pressures smaller than the critical pressure of static wrinkling. Read More

The underlying physics governing the diffusion of a tracer particle in a viscoelastic material is a topic of some dispute. The long-term memory in the mechanical response of such materials should induce diffusive motion with a memory kernel, such as fractional Brownian motion (fBM). This is the reason that microrheology is able to provide the shear modulus of polymer networks. Surprisingly, the diffusion of a tracer particle in a network of a purified protein, actin, was found to conform to the continuous time random walk type (CTRW). We set out to resolve this discrepancy by studying the tracer particle diffusion using two different tracer particle sizes, in actin networks of different
mesh sizes. Read More

Periodic organization of cells is required for the function of many organs and tissues. The development of such periodic patterns is typically associated with mechanisms based on intercellular signaling such as lateral inhibition and Turing patterning. Here we show that the transition from disordered to ordered checkerboard-like pattern of hair cells and supporting cells in the mammalian hearing organ, the organ of Corti, is likely based on mechanical forces rather than signaling events. Read More

Notch signaling is the primary juxtacrine signaling pathway used for direct cell-to-cell communication
between neighboring cells during development. At its core, theNotch pathway is a mechanotransduction pathway involving the direct interaction between receptors and ligands that conveys information between adjacent sender and receiver cells. Read More

A major risk factor for Gaucher’s disease is loss of function mutations in the GBA1 gene that encodes lysosomal β- glucocerebrosidase, resulting in accumulation of glucosylceramide (GlcCer), a key lysosomal sphingolipid. GBA1 mutations also enhance the risk for Parkinson’s disease, whose hallmark is the aggregation of α-synuclein (αSyn). Read More

The human proteome is enriched in proteins that do not fold into a stable 3D structure. These
intrinsically disordered proteins (IDPs) spontaneously fluctuate between a large number of
configurations in their native form. Remarkably, the disorder does not lead to dysfunction as with
denatured folded proteins. Read More

Amphiphilic molecules and their self-assembled structures have long been the target of extensive research due to their potential applications in fields ranging from materials design to biomedical and cosmetic applications. Increasing demands for functional complexity have been met with challenges in biochemical engineering, driving researchers to innovate in the design of new amphiphiles. Read More

Mechanical metamaterials present a promising platform for seemingly impossible mechanics. They often require incompatibility of their elementary building blocks, yet a comprehensive understanding of its role remains elusive. Relying on an analogy to ferromagnetic and antiferromagnetic binary spin interactions, we present a universal approach to identify and analyze topological mechanical defects for arbitrary building blocks. Read More

Pushing and pulling on a material’s surface in a steady, periodic way is a common test for characterizing that material’s mechanical properties. Simple materials typically exhibit a single steady state response to a given way of forcing. We proposed a metamaterial made of mechanically bistable elements, which responds with a wide variety of distinct steady state cycles in response to just a single, persistently applied periodic force. Read More

We study the Brownian motion of an assembly of mobile inclusions embedded in a fluid membrane. The motion includes the dispersal of the assembly, accompanied by the diffusion of its center of mass. Usually, the former process is much faster than the latter because the diffusion coefficient of the center of mass is inversely proportional to the number of particles. Read More

Two identical particles driven by the same steady force through a viscous fluid may move relative to one another due to hydrodynamic interactions. The presence or absence of this relative translation has a profound effect on the dynamics of a driven suspension consisting of many particles. We consider a pair of particles which, to linear order in the force, do not interact hydrodynamically. Read More

Melanin and related polyphenolic pigments are versatile functional polymers that serve diverse aesthetic and protective roles across the living world. These polymeric pigments continue to inspire the development of adhesive, photonic, electronic and radiation‐protective materials and coatings.
Read More

Tuning the enzymatic degradation and disassembly rates of polymeric amphiphiles and their assemblies is crucial for designing enzyme-responsive nanocarriers for controlled drug delivery applications. The common methods to control the enzymatic degradation of amphiphilic polymers are to tune the molecular weights and ratios of the hydrophilic and hydrophobic blocks. Read More

Characterizing the entropy of a system is a crucial, and often computationally costly, step in understanding its thermodynamics. It plays a key role in the study of phase transitions, pattern formation, protein folding, and more. Current methods for entropy estimation suffer from a high computational cost, lack of generality, or inaccuracy and inability to treat complex, strongly interacting systems. Read More

We use a lattice model to study first-passage time distributions of target finding events through complex environments with elongated fibers distributed with different anisotropies and volume occupation fractions. For isotropic systems and for low densities of aligned fibers, the three-dimensional search is a Poisson process with the first-passage time exponentially distributed with the most probable finding time at zero. Read More

Stochastic resetting is prevalent in natural and man-made systems, giving rise to a long series of nonequilibrium phenomena. Diffusion with stochastic resetting serves as a paradigmatic model to study these phenomena, but the lack of a well-controlled platform by which this process can be studied experimentally has been a major impediment to research in the field. Read More

Metastable states in first-order phase-transitions have been traditionally described by classical nucleation theory (CNT). However, recently an increasing number of systems displaying such a transition have not been successfully modelled by CNT. The delayed crystallization of phospholipids upon super-cooling is an interesting case, since the extended timescales allow access into the dynamics. Read More