Papers by Eugene Terentjev
Forces and extensions in semiflexible and rigid polymer chains and filaments
Journal of Physics A: Mathematical and Theoretical, 2007
We present a revised theoretical study of statistical properties of semiflexible filaments. Using... more We present a revised theoretical study of statistical properties of semiflexible filaments. Using a single auxiliary field and mean-field theory, we succeed in obtaining the exact analytical results for force extension relations for a chain with arbitrary stiffness, and compare it with earlier theories and experiment. At a small persistence-to-contour length ratio, lp/L Lt 1 the chain behaves classically, as an entropic spring. However, we find a critical value for L/lp &ap; 3.0 in 3D (or L/lp &ap; 5.4 in 2D) above which the restoring force of the chain becomes negative for the end-to-end distance R_3D/L < \sqrt{1- L/3l_p} (or R_2D/L < \sqrt{1- L/5.4l_p} ). That is, very stiff (or very short) chains and filaments resist an attempt to reduce their preferred end-to-end distance as much as to stretch it.
Soft Matter, 2009
A model for filament buckling at finite temperatures is presented. Starting from the classical wo... more A model for filament buckling at finite temperatures is presented. Starting from the classical worm-like chain model under constant compression, we use a mean-field approach for filament inextensibility to find the complete partition function. We find that there is a simple interpolation formula that describes the free energy of chains or filaments as a function of end-to-end separation, which spans the whole range of filament stiffnesses. Using this formula we study the buckling transition of semiflexible filaments and find that kinetics plays an important role. We propose that the filament buckling is essentially the first order transition governed by the kinetics of escaping a local free energy minimum. A simple model for the kinetics is put forward, which shows the critical buckling force for a filament is reduced by a fraction that has a universal scaling with temperature with an exponent ν = 0.56.
Comparison of the Helmholtz, Gibbs, and collective-modes methods to obtain nonaffine elastic constants
Journal of the Mechanics and Physics of Solids
Bioassemblying Macro-Scale, Lumnized Airway Tubes of Defined Shape via Multi-Organoid Patterning and Fusion
bioRxiv, 2020
Epithelial, stem-cell derived organoids are ideal building blocks for tissue engineering, however... more Epithelial, stem-cell derived organoids are ideal building blocks for tissue engineering, however, scalable and shape-controlled bioassembly of epithelial organoids into larger and anatomical structures has yet to be achieved. Here, a robust organoid engineering approach, Multi-Organoid Patterning and Fusion (MOrPF), is presented to assemble individual airway organoids of different sizes into upscaled, scaffold-free airway tubes with pre-defined shapes. Multi-Organoid Aggregates (MOAs) undergo accelerated fusion in a matrix-depleted, free-floating environment, possess a continuous lumen and maintain prescribed shapes without an exogenous scaffold interface. MOAs in the floating culture exhibit a well-defined three-stage process of inter-organoid surface integration, luminal material clearance and lumina connection. The observed shape stability of patterned MOAs is confirmed by theoretical modelling based on organoid morphology and the physical forces involved in organoid fusion. Imm...
Polymer entanglements lead to complicated topological constraints and interactions between neighb... more Polymer entanglements lead to complicated topological constraints and interactions between neighbouring chains in a dense solution or melt. Entanglements can be treated in a mean eld approach, within the famous reptation model, since they eectiv ely conne each individual chain in a tube-like geometry. In polymer networks, due to crosslinks preventing the reptation constraint release, entanglements acquire a dieren t topological meaning and have a much stronger effect on the resulting mechanical response. We apply the classical ideas of reptation dynamics to calculate the eectiv e rubber-elastic free energy of an entangled rubbery network. We then compare the results with other theoretical approaches and establish a particularly close mapping with the hoop-model, with equally good description of experimental data. The present consistent reptation theory allows further development of dynamic theory of stress relaxation.
Nature Communications
Nematic liquid crystal elastomers (LCE) exhibit unique mechanical properties, placing them in a c... more Nematic liquid crystal elastomers (LCE) exhibit unique mechanical properties, placing them in a category distinct from other viscoelastic systems. One of their most celebrated properties is the ‘soft elasticity’, leading to a wide plateau of low, nearly-constant stress upon stretching, a characteristically slow stress relaxation, enhanced surface adhesion, and other remarkable effects. The dynamic soft response of LCE to shear deformations leads to the extremely large loss behaviour with the loss factor tanδ approaching unity over a wide temperature and frequency ranges, with clear implications for damping applications. Here we investigate this effect of anomalous damping, optimising the impact and vibration geometries to reach the greatest benefits in vibration isolation and impact damping by accessing internal shear deformation modes. We compare impact energy dissipation in shaped samples and projectiles, with elastic wave transmission and resonance, finding a good correlation bet...
Heliotracking Device using Liquid Crystalline Elastomer Actuators
Advanced Materials Technologies
Nature Communications
Nematic liquid crystal elastomers (N-LCE) exhibit intriguing mechanical properties, such as rever... more Nematic liquid crystal elastomers (N-LCE) exhibit intriguing mechanical properties, such as reversible actuation and soft elasticity, which manifests as a wide plateau of low nearly-constant stress upon stretching. N-LCE also have a characteristically slow stress relaxation, which sometimes prevents their shape recovery. To understand how the inherent nematic order retards and arrests the equilibration, here we examine hysteretic stress-strain characteristics in a series of specifically designed main-chain N-LCE, investigating both macroscopic mechanical properties and the microscopic nematic director distribution under applied strains. The hysteretic features are attributed to the dynamics of thermodynamically unfavoured hairpins, the sharp folds on anisotropic polymer strands, the creation and transition of which are restricted by the nematic order. These findings provide a new avenue for tuning the hysteretic nature of N-LCE at both macro- and microscopic levels via different des...
Journal of Materials Chemistry A
Converting commodity structural thermoplastics into dynamically crosslinked vitrimers.
Bio‐assembling Macro‐Scale, Lumenized Airway Tubes of Defined Shape via Multi‐Organoid Patterning and Fusion
Advanced Science
Abstract Epithelial, stem‐cell derived organoids are ideal building blocks for tissue engineering... more Abstract Epithelial, stem‐cell derived organoids are ideal building blocks for tissue engineering, however, scalable and shape‐controlled bio‐assembly of epithelial organoids into larger and anatomical structures is yet to be achieved. Here, a robust organoid engineering approach, Multi‐Organoid Patterning and Fusion (MOrPF), is presented to assemble individual airway organoids of different sizes into upscaled, scaffold‐free airway tubes with predefined shapes. Multi‐Organoid Aggregates (MOAs) undergo accelerated fusion in a matrix‐depleted, free‐floating environment, possess a continuous lumen, and maintain prescribed shapes without an exogenous scaffold interface. MOAs in the floating culture exhibit a well‐defined three‐stage process of inter‐organoid surface integration, luminal material clearance, and lumina connection. The observed shape stability of patterned MOAs is confirmed by theoretical modelling based on organoid morphology and the physical forces involved in organoid fusion. Immunofluorescent characterization shows that fused MOA tubes possess an unstratified epithelium consisting mainly of tracheal basal stem cells. By generating large, shape‐controllable organ tubes, MOrPF enables upscaled organoid engineering towards integrated organoid devices and structurally complex organ tubes.
Why exercise builds muscles: titin mechanosensing controls skeletal muscle growth under load
Biophysical Journal
ACS Applied Materials & Interfaces
Thermoplastic polyolefins (TPOs) crosslinked by dynamic covalent bonds (xTPOs) have the potential... more Thermoplastic polyolefins (TPOs) crosslinked by dynamic covalent bonds (xTPOs) have the potential to be the most utilized class of polymer in the world, with applications ranging from household and automotive to biomedical devices and additive manufacturing. xTPO combines the benefits of thermoplastics and thermosets in a "single material" and potentially avoids their shortcomings. Here, we describe a new two-stage reaction extrusion strategy of TPOs with a backbone consisting of inert C− C bonds (polypropylene, PP), and thiol-anhydride, to dynamically crosslink PP through thiol-thioester bond exchange. The degree of PP crosslinking determines the rubber plateau modulus above the melting point of the plastic: the modulus at 200°C increases from zero in the melt to 23 kPa at 6% crosslinking, to 60 kPa at 20%, to 105 kPa at 40%. The overall mechanical strength of the solid xTPO plastic is 25% higher compared to the original PP, and the gel fraction of xTPO reaches 55%. Finally, we demonstrate that the crosslinked xTPO material is readily reprocessable (recycled, remolded, rewelded, and 3D printed).
Soft Matter
The vitrimers based on the epoxy–thiol ‘click’ chemistry are investigated, reporting the role of ... more The vitrimers based on the epoxy–thiol ‘click’ chemistry are investigated, reporting the role of different spacers and substitutes. The correlation between the rubber modulus and the elastic–plastic transition is established.
Journal of Physics: Condensed Matter
Glassy solids may undergo a fluidization (yielding) transition upon deformation whereby the mater... more Glassy solids may undergo a fluidization (yielding) transition upon deformation whereby the material starts to flow plastically. It has been a matter of debate whether this process is controlled by a specific time scale, from among different competing relaxation/kinetic processes. Here, two constitutive models of cage relaxation are examined within the microscopic model of nonaffine elasto-plasticity. One (widely used) constitutive model implies that the overall relaxation rate is dominated by the fastest between the structural (α) relaxation rate and the shearinduced relaxation rate. A different model is formulated here which, instead, assumes that the slowest (global) relaxation process controls the overall relaxation. We show that the first model is not compatible with the existence of finite elastic shear modulus for quasistatic (low-frequency) deformation, while the second model is able to describe all key features of deformation of 'hard' glassy solids, including the yielding transition, the nonaffine-to-affine plateau crossover, and the rate-stiffening of the modulus. The proposed framework provides an operational way to distinguish between 'soft' glasses and 'hard' glasses based on the shear-rate dependence of the structural relaxation time.
Scientific Reports
Liquid crystalline elastomers (LCE) undergo reversible shape changes in response to stimuli, whic... more Liquid crystalline elastomers (LCE) undergo reversible shape changes in response to stimuli, which enables a wide range of smart applications, in soft robotics, adhesive systems or biomedical medical devices. In this study, we introduce a new dynamic covalent chemistry based on siloxane equilibrium exchange into the LCE to enable processing (director alignment, remolding, and welding). Unlike the traditional siloxane based LCE, which were produced by reaction schemes with irreversible bonds (e.g. hydrosilylation), here we use a much more robust reaction (thiol-acrylate/thiol-ene ‘double-click’ chemistry) to obtain highly uniform dynamically crosslinked networks. Combining the siloxane crosslinker with click chemistry produces exchangeable LCE (xLCE) with tunable properties, low glass transition (−30 °C), controllable nematic to isotropic transition (33 to 70 °C), and a very high vitrification temperature (up to 250 °C). Accordingly, this class of dynamically crosslinked xLCE shows u...
The role of rotational molecular motors of the ATP synthase class is integral to the metabolism o... more The role of rotational molecular motors of the ATP synthase class is integral to the metabolism of cells. Yet the function of FliI6-FliJ complex - a homolog of the F1 ATPase motor - within the flagellar export apparatus remains unclear. We use a simple two-state model adapted from studies of linear molecular motors to identify key features of this motor. The two states are the ‘locked’ ground state where the FliJ coiled coil filament experiences fluctuations in an asymmetric torsional potential, and a ‘free’ excited state in which FliJ undergoes rotational diffusion. Michaelis-Menten kinetics was used to treat transitions between these two states, and obtain the average angular velocity of the FliJ filament within the FliI6 stator: ωmax ≈ 9.0 rps. The motor was then studied under external counter torque conditions in order to ascertain its maximal power output: Pmax ≈ 42 kBT/s, and the stall torque: Gstall ≈ 3 kBT/rad. Two modes of action within the flagellar export apparatus are pr...
Advanced Materials Interfaces
Smart surfaces that reversibly change the interfacial friction coefficients in response to extern... more Smart surfaces that reversibly change the interfacial friction coefficients in response to external stimuli enable a wide range of applications, such as grips, seals, brake pads, packaging films, and fabrics. Here a new concept of such a smart frictional system is reported: a composite film of a plain-weave polyester textile sheet, and a thermo-responsive nematic liquid crystalline elastomer (LCE). The composite is deployed with retractable microundulations of the elastomer inside each weave mesh, enabling dramatic changes of the contact interface with the opposing surface on LCE actuation, which is induced e.g. by a change in temperature (T). At room T, the protruding viscoelastic parts of LCE in the nematic phase make contact with the opposing flat surface, resulting in a very high friction. At an elevated T (~50°C, isotropic phase), the undulations of LCE surface are retracted within the thickness of the textile, and the contacts are limited to small regions around overlapping textile fibers, lowering the friction dramatically. This effect is fully reversible on heating/cooling cycles. The surface undulations are spontaneous, i.e. fabricated without any lithographic or alignment techniques. The present composite opens a new way to practical uses of sheets/films with switchable friction enabled by stimuli-responsive LCEs. Functional flexible polymer films and sheets [1] such as textiles, tapes, and laminating materials, are used in many applications. Their friction against other surfaces in contact [2-4] is one of the most important factors in their practical use, since this affects the force transmission between objects, e.g., in gripping and sliding, and in tactile sensing. In many situations, the ability to switch their friction characteristics on demand [5-9] would be useful. To design such smart contact surfaces, one or more of the parameters governing the friction should be altered through reversible changes in the material components [10,11] .
The Journal of Chemical Physics
Microtubules (MTs) experience an effect called "catastrophe," which is the transition from the MT... more Microtubules (MTs) experience an effect called "catastrophe," which is the transition from the MT growth to a sudden dramatic shrinkage in length. The straight guanosine triphosphate (GTP)-tubulin cap at the filament tip and the intrinsic curvature of guanosine diphosphate (GDP)-tubulins are known to be the key thermodynamic factors that determine MT catastrophe, while the hydrolysis of this GTP-cap acts as the kinetic control of the process. Although several theoretical models have been developed, assuming the catastrophe occurs when the GTPcap shrinks to a minimal stabilizing size, the structural effect of the GTP-cap and GDP-curvature is not explicitly included; thus, their influence on catastrophe kinetics remains less understood. To investigate this structural effect, we apply a single-protofilament model with one GTP-cap while assuming a random hydrolysis mechanism and take the occurrence of a crack in the lateral bonds between neighboring protofilaments as the onset of the catastrophe. Therein, we find the effective potential of the tip along the peel-off direction and formulate the catastrophe kinetics as a mean first-passage time problem, subject to thermal fluctuations. We consider cases with and without a compressive force on the MT tip, both of which give a quadratic effective potential, making MT catastrophe an Ornstein-Uhlenbeck process in our formalism. In the free-standing case, the mean catastrophe time has a sensitive tubulin-concentration dependence, similar to a double-exponential function, and agrees well with the experiment. For a compressed MT, we find a modified exponential function of force that shortens the catastrophe time.
Macromolecules
We develop a continuum model of dynamic-mechanical response of vitrimers, where the elastic energ... more We develop a continuum model of dynamic-mechanical response of vitrimers, where the elastic energy of the material accounts for the conserved number of the crosslinks in the network. We also prepare partial vitrimer networks, which consist of variable fractions of transient network based on boronic ester bond-exchange, and of a permanent polymer network. By fitting the theory to our experimental data on stress relaxation, the bond-exchange rate and the fraction of the permanent elastic network are obtained with a linear relationship between the fraction of the transient polymer network and the ratio between the boronic ester and the flexible spacer among the chain-extending thiols. For a 100% vitrimer undergoing a ramp deformation, the stress of the material first increases and then decreases, where the yield time decreases with the increasing strain rate. A partial vitrimer can behave as a pure elastic material without yielding at low strain rates or show a non-monotonic 'S-shaped' stress-strain relationship at high strain rates.
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Papers by Eugene Terentjev