1. Emergent epithelial elasticity governed by interfacial surface mechanics and substrate interactionUrška Andrenšek, Matej Krajnc, 2026, izvirni znanstveni članek Povzetek: During the life of animals, epithelial tissues undergo extensive deformations–first to form organs during embryogensis and later to preserve integrity and function in adulthood. To what extent these deformations resemble that of non-living elastic materials is not well understood. We derive an elasticity theory of epithelia, supported by a thin layer of extracellular material and the stroma, in which the mechanics of individual cells are dominated by differential interfacial tensions stemming from cell cortical tension and adhesion. Upon coarse-graining a discrete cell-level mechanics model, we obtain a harmonic deformation energy and derive the critical conditions for the elastic instability, where an initially flat tissue either buckles out of plane or forms wrinkles. Due to the distinct origin of elasticity, the scaling of the critical buckling load and the wrinkling wavelength with layer’s thickness is fundamentally different than in solid plates. The theory also naturally describes reversal of the groove-to-crest thickness-modulation phase–a recently observed epithelial shape feature which cannot be explained by the classical elasticity theory. Our work provides a guideline for understanding the relative role of cell surface tensions and the interaction of tissues with substrates during epithelial morphogenesis.
Ključne besede: tissue mechanics, differential interfacial tension, buckling instability
Objavljeno v DiRROS: 29.04.2026; Ogledov: 2878; Prenosov: 88
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2. Reentrant rigidity transition in planar epithelia with volume and area elasticityTanmoy Sarkar, Matej Krajnc, 2026, izvirni znanstveni članek Povzetek: We find a reentrant columnar-to-squamous rigidity transition in three-dimensional (3D) epithelia, governed by volume and area elasticity. Our model maps to the classic 2D area- and perimeter-elasticity model but, unlike its 2D counterpart, shows compression-induced softening or stiffening, depending on the initial state. The phase diagram reveals floppy states with vanishing shear and in-plane bulk moduli, alongside a lateral-tension-driven discontinuous columnar-to-squamous transition. The critical behavior underlying the emergence of the reentrant transition belongs to the mean-field universality class.
Ključne besede: biophysics, epithelial mechanics, rigidity transition, phase diagram
Objavljeno v DiRROS: 24.02.2026; Ogledov: 323; Prenosov: 143
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3. Modulation of contactless high intensity pulsed electromagnetic field induced electroporation and gene delivery efficacy using various nanoparticlesTamara Polajžer, Matej Krajnc, Slavko Kralj, Maja Caf, Rok Romih, Samo Hudoklin, Vitalij Novickij, Damijan Miklavčič, 2026, izvirni znanstveni članek Povzetek: Introduction: High-intensity pulsed electromagnetic fields (HI-PEMF) can be used to trigger contactless permeabilization of the plasma membrane similar to electroporation (EP). The permeabilization efficiency and gene delivery by HI-PEMF in vitro are currently inferior to EP. It was suggested that the methodology can be improved with conductive gold nanoparticles (AuNPs), which are reported to amplify the induced electric field in close proximity to the cell membrane. Objectives: Therefore, in this work, we have studied different NPs, which varied in material/conductivity (gold and silica), size (10–50+ nm), shape (i.e., round and rods), concentration (50–200 µg/mL), and functionalization (pegylated or not), and combined them with HI-PEMF (6.7 T × 100 pulses, 1 Hz). Methods: The normal Chinese hamster ovary cell line (CHO) and the cancer human urinary bladder’s transitional carcinoma cell line (T24) were used as a model. We have characterized cell membrane permeabilization using propidium iodide (PI) and the efficacy of gene delivery using pEGFP-N1. Results: Larger NPs and higher NP concentrations resulted in up to a 10% increase in membrane permeability. In contrast, semispherical and rod-shaped AuNPs did not further enhance permeabilization efficiency. Gene delivery efficiency increased from 3% in control samples to 6% in the presence of 50 nm AuNPs. Overall, CHO cells were more susceptible to HI-PEMF-induced effects than T24 cells. Conclusions: This study shows the potential to increase gene delivery efficacy by combining HI-PEMF treatment with conductive NPs. However, it was concluded that the HI-PEMF-induced effects are highly dependent on the cell line, NP type, and concentration and therefore require further investigation.
Ključne besede: gene delivery
Objavljeno v DiRROS: 24.02.2026; Ogledov: 317; Prenosov: 200
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4. Graph topological transformations in space-filling cell aggregatesTanmoy Sarkar, Matej Krajnc, 2024, izvirni znanstveni članek Povzetek: Cell rearrangements are fundamental mechanisms driving large-scale deformations of living tissues. In three-dimensional (3D) space-filling cell aggregates, cells rearrange through local topological transitions of the network of cell-cell interfaces, which is most conveniently described by the vertex model. Since these transitions are not yet mathematically properly formulated, the 3D vertex model is generally difficult to implement. The few existing implementations rely on highly customized and complex software-engineering solutions, which cannot be transparently delineated and are thus mostly non-reproducible. To solve this outstanding problem, we propose a reformulation of the vertex model. Our approach, called Graph Vertex Model (GVM), is based on storing the topology of the cell network into a knowledge graph with a particular data structure that allows performing cell-rearrangement events by simple graph transformations. Importantly, when these same transformations are applied to a two-dimensional (2D) polygonal cell aggregate, they reduce to a well-known T1 transition, thereby generalizing cell-rearrangements in 2D and 3D space-filling packings. This result suggests that the GVM’s graph data structure may be the most natural representation of cell aggregates and tissues. We also develop a Python package that implements GVM, relying on a graph-database-management framework Neo4j. We use this package to characterize an order-disorder transition in 3D cell aggregates, driven by active noise and we find aggregates undergoing efficient ordering close to the transition point. In all, our work showcases knowledge graphs as particularly suitable data models for structured storage, analysis, and manipulation of tissue data.
Ključne besede: 3D vertex models, cell, software-engineering
Objavljeno v DiRROS: 03.09.2024; Ogledov: 997; Prenosov: 1819
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