arXiv subjects

Boris Rubinsky

Publications and source records attributed to Boris Rubinsky.

7 recordsLinked to original sources

arXiv2026

A Thermodynamic Analysis of Enhanced Metastability in Isochoric Supercooled Liquids

Experiments show that isochoric (constant-volume) conditions enhance supercooling stability relative to isobaric (constant-pressure) conditions. Here, combining Helmholtz equilibrium thermodynamics with a first-order perturbation methodology, we derive an inequality governing nucleation stability under volumetric constraint. The derivation provides a general thermodynamic proof that for any substance undergoing phase transformation in which the solid is less dense than the liquid, the Helmholtz driving force for solidification in isochoric systems is smaller than the Gibbs driving force in isobaric systems. Since nucleation rates depend exponentially on the inverse square of the driving force, this provides a thermodynamic basis for the observed suppression of nucleation rates. While a full stochastic treatment is beyond the scope of this work, the reduction in driving force implies a weakening of the bias toward growth of pre-critical fluctuations, increasing their probability of thermal dissolution. The analysis yields a dimensionless isochoric stability number. This number is computable from bulk thermodynamic data alone and provides a geometry-independent criterion for comparing metastable liquid stability across materials and conditions.

cond-mat.soft↗

arXiv2026

Time-Resolved Multi-Spectral X-ray Computed Tomography of Cryoprotectant Diffusion Into Biomimetic Material

Cryopreservation via vitrification requires loading cryoprotective cocktails. Insufficient loading may lead to freezing, precluding successful recovery; overloading is toxic. Yet, existing in situ measurements of cryoprotectant permeation remain largely unvalidated and do not resolve individual cryoprotectant concentrations. We introduce multi-spectral X-ray computed tomography (MSCT) to noninvasively quantify the spatiotemporal distribution of cryoprotectants diffusing into a tissue mimicking phantom. A developed photon-energy bin selection algorithm achieves sensitivity to low contrast cryoprotectants without contrast agents or fluorescence edges. The technique is validated with a dimethyl sulfoxide, glycerol, and water solution, resolving cryoprotectant volume fractions to within 5% accuracy. We observe heterogeneous diffusion of the cryoprotectants into the tissue mimicking hydrogel, a phenomenon not observable with conventional techniques. MSCT improves upon existing X ray CT methods because it is not underdetermined for multicomponent solutions and does not implicitly assume homogeneous diffusion. These advancements enable the systematic development of cryoprotectant loading protocols and provide diagnostics to assess vitrifiability before cryopreservation.

physics.med-ph↗

arXiv2026

The thermodynamics of pressure activated assembly of supramolecules in isochoric and isobaric systems

The efficacy of cryopreservation is constrained by the difficulty of achieving sufficiently high intracellular concentrations of cryoprotective solutes without inducing osmotic injury or chemical toxicity during loading. This thermodynamic study introduces a new conceptual mechanism for cryoprotectant delivery into cells directly or through vascular perfusion. In this framework, effective cryoprotection could be achieved through the in situ generation of high intracellular concentrations of cryoprotective solutes via pressure-activated disassembly of membrane-permeant supramolecular assemblies composed of cryoprotectant monomers or oligomers. These supramolecules, present initially at low concentrations, are envisioned to enter cells through passive partitioning or endocytosis with minimal osmotic effect, and subsequently transform into a high intracellular concentration of cryoprotectants upon disassembly. We propose that elevated hydrostatic pressure, generated intrinsically during isochoric (constant-volume) freezing or applied externally under isobaric (constant-pressure) conditions, can destabilize supramolecular assemblies whose dissociated state occupies a smaller molar volume than the assembled state. Under isochoric freezing, ice formation within a fixed volume produces a substantial pressure increase as a thermodynamic consequence of phase change, rendering pressure a dependent variable governed by the Helmholtz free energy. Under isobaric conditions, pressure acts as an externally controlled variable through the Gibbs free energy. In both formulations, pressure-activated disassembly decouples membrane transport from cryoprotectant availability and enables synchronized solute generation precisely during cooling or freezing, without pre-loading of osmotically active solutes.

cond-mat.soft↗

arXiv2025

A Wrist-Worn Multimodal Reaction Time Monitoring Device for Ecologically-Valid Cognitive Assessment

Reaction time (RT) is a fundamental measure in cognitive and neurophysiological assessment, yet most existing RT systems require active user engagement and controlled environments, limiting their use in real-world settings. This paper introduces a low cost wrist-worn instrumentation platform designed to capture human reaction times (RT) across auditory, visual, and haptic modalities with millisecond latency in real-world conditions. The device integrates synchronized stimulus delivery and event detection within a compact microcontroller-based system, eliminating the need for user focus or examiner supervision. Emphasizing measurement fidelity, we detail the hardware architecture, timing control algorithms, and calibration methodology used to ensure consistent latency handling across modalities. A proof-of-concept study with six adult participants compares this system against a benchmark computer-based RT tool across five experimental conditions. The results confirm that the device achieves statistically comparable RT measurements with strong modality consistency, supporting its potential as a novel tool for non-obtrusive cognitive monitoring. Contributions include a validated design for time-critical behavioral measurement and a demonstration of its robustness in unconstrained, ambient-noise environments. It offers a powerful new tool for continuous, real-world cognitive monitoring and has significant potential for both research and clinical applications.

q-bio.QM↗

arXiv2023

Direct Comparison of Isobaric and Isochoric Vitrification of Two Aqueous Solutions with Photon Counting X-Ray Computed Tomography

Vitrification is a promising approach for ice-free cryopreservation of biological material, but progress is hindered by the limited set of experimental tools for studying processes in the interior of the vitrified matter. Isochoric cryopreservation chambers are often metallic, and their opacity prevents direct visual observation. In this study, we introduce photon counting X-ray computed tomography (CT) to compare the effects of rigid isochoric and unconfined isobaric conditions on vitrification and ice formation during cooling of two aqueous solutions: 50 wt% DMSO and a coral vitrification solution, CVS1. Previous studies have only compared vitrification in isochoric systems with isobaric systems that have an exposed air-liquid interface. We use a movable piston to replicate the surface and thermal boundary conditions of the isochoric system yet maintain isobaric conditions. When controlling for the boundary conditions we find that similar ice and vapor volume fractions form during cooling in isochoric and isobaric conditions. Interestingly, we observe distinct ice and vapor cavity morphology in the isochoric systems, possibly due to vapor outgassing or cavitation as rapid cooling causes the pressure to drop in the confined systems. These observations highlight the array of thermo-fluidic processes that occur during vitrification in confined aqueous systems and motivate the further application of imaging techniques such as photon counting X-ray CT in fundamental studies of vitrification.

physics.med-ph↗

arXiv2023

An extreme value statistics model of heterogeneous ice nucleation for quantifying the stability of supercooled aqueous systems

The propensity of water to remain in a metastable liquid state at temperatures below its equilibrium melting point holds significant potential for cryopreserving biological material such as tissues and organs. The benefits conferred are a direct result of progressively reducing metabolic expenditure due to colder temperatures while simultaneously avoiding the irreversible damage caused by the crystallization of ice. Unfortunately, the freezing of water in bulk systems of clinical relevance is dominated by random heterogeneous nucleation initiated by uncharacterized trace impurities, and the marked unpredictability of this behavior has prevented implementation of supercooling outside of controlled laboratory settings and in volumes larger than a few milliliters. Here, we develop a statistical model that jointly captures both the inherent stochastic nature of nucleation using conventional Poisson statistics as well as the random variability of heterogeneous nucleation catalysis through bivariate extreme value statistics. Individually, these two classes of models cannot account for both the time-dependent nature of nucleation and the sample-to-sample variability associated with heterogeneous catalysis, and traditional extreme value models have only considered variation of the characteristic nucleation temperature. We conduct a series of constant cooling rate and isothermal nucleation experiments with physiological saline solutions and leverage the statistical model to evaluate the natural variability of kinetic and thermodynamic nucleation parameters. By quantifying freezing probability as a function of temperature, supercooled duration, and system volume, while accounting for nucleation site variability, this study also provides a basis for the rational design of stable supercooled biopreservation protocols.

cond-mat.mtrl-sci↗

arXiv2021

Methods to stabilize aqueous supercooling identified by use of an isochoric nucleation detection (INDe) device

Stable aqueous supercooling has shown significant potential as a technique for human tissue preservation, food cold storage, conservation biology, and beyond, but its stochastic nature has made its translation outside the laboratory difficult. In this work, we present an isochoric nucleation detection (INDe) platform for automated, high-throughput characterization of aqueous supercooling at >1 mL volumes, which enables statistically-powerful determination of the temperatures and time periods for which supercooling in a given aqueous system will remain stable. We employ the INDe to investigate the effects of thermodynamic, surface, and chemical parameters on aqueous supercooling, and demonstrate that various simple system modifications can significantly enhance supercooling stability, including isochoric (constant-volume) confinement, hydrophobic container walls, and the addition of even mild concentrations of solute. Finally, in order to enable informed design of stable supercooled biopreservation protocols, we apply a statistical model to estimate stable supercooling durations as a function of temperature and solution chemistry, producing first-in-field supercooling stability maps for four common cryoprotective solutes.

cond-mat.mtrl-sci↗