3D Confinement Research Articles

Mechanobiology of 3D cell confinement and extracellular crowding

AbstractCells and tissues are often under some level of confinement, imposed by the microenvironment and neighboring cells, meaning that there are limitations to cell size, volume changes, and fluid exchanges. 3D cell culture, increasingly used for both single cells and organoids, inherently impose levels of confinement absent in 2D systems. It is thus key to understand how different levels of confinement influences cell survival, cell function, and cell fate. It is well known that the mechanical properties of the microenvironment, such as stiffness and stress relaxation, are important in activating mechanosensitive pathways, and these are responsive to confinement conditions. In this review, we look at how low, intermediate, and high levels of confinement modulate the activation of known mechanobiology pathways, in single cells, organoids, and tumor spheroids, with a specific focus on 3D confinement in microwells, elastic, or viscoelastic scaffolds. In addition, a confining microenvironment can drastically limit cellular communication in both healthy and diseased tissues, due to extracellular crowding. We discuss potential implications of extracellular crowding on molecular transport, extracellular matrix deposition, and fluid transport. Understanding how cells sense and respond to various levels of confinement should inform the design of 3D engineered matrices that recapitulate the physical properties of tissues.

Valley-Hybridized Gate-Tunable 1D Exciton Confinement in MoSe2.

Controlling excitons at the nanoscale in semiconductor materials represents a formidable challenge in the quantum photonics and optoelectronics fields. Monolayers of transition metal dichalcogenides (TMDs) offer inherent 2D confinement and possess significant exciton binding energies, making them promising candidates for achieving electric-field-based confinement of excitons without dissociation. Exploiting the valley degree of freedom associated with these confined states further broadens the prospects for exciton engineering. Here, we show electric control of light polarization emitted from one-dimensional (1D) quantum-confined states in MoSe2. Building on previous reports of tunable trapping potentials and linearly polarized emission, we extend this understanding by demonstrating how nonuniform in-plane electric fields enable in situ control of these effects and highlight the role of gate-tunable valley hybridization in these localized states. Their polarization is entirely engineered through either the 1D confinement potential's geometry or an out-of-plane magnetic field. Controlling nonuniform in-plane electric fields in TMDs enables control of the energy (up to five times its line width), polarization state (from circular to linear), and position of 1D confined excitonic states (5 nm V-1).

Influence of carrier localization on photoluminescence emission from sub-monolayer quantum dot layers

We have investigated the origins of photoluminescence from quantum dot (QD) layers prepared by alternating depositions of sub-monolayers and a few monolayers of size-mismatched species, termed as sub-monolayer (SML) epitaxy, in comparison with their Stranski–Krastanov (SK) QD counterparts. Using measured nanostructure sizes and local In-compositions from local-electrode atom probe tomography as input into self-consistent Schrödinger–Poisson simulations, we compute the 3D confinement energies, probability densities, and photoluminescence (PL) spectra for both InAs/GaAs SML- and SK-QD layers. A comparison of the computed and measured PL spectra suggests one-dimensional electron confinement, with significant 3D hole localization in the SML-QD layers that contribute to their enhanced PL efficiency in comparison to their SK-QD counterparts.

Nuclear deformation and dynamics of migrating cells in 3D confinement reveal adaptation of pulling and pushing forces.

Eukaryotic cells show an astounding ability to remodel their shape and cytoskeleton and to migrate through pores and constrictions smaller than their nuclear diameter. However, the relation of nuclear deformation and migration dynamics in confinement remains unclear. Here, we study the mechanics and dynamics of mesenchymal cancer cell nuclei transitioning through three-dimensional compliant hydrogel channels. We find a biphasic dependence of migration speed and transition frequency on channel width, peaking at widths comparable to the nuclear diameter. Using confocal imaging and hydrogel bead displacement, we determine nuclear deformations and corresponding forces during confined migration. The nucleus deforms reversibly with a reduction in volume during confinement. With decreasing channel width, the nuclear shape during transmigration changes biphasically, concomitant with the transitioning dynamics. Our proposed physical model explains the observed nuclear shapes and transitioning dynamics in terms of the cytoskeletal force generation adapting from purely pulling-based to a combined pulling- and pushing-based mechanism with increasing nuclear confinement.

Confinement of excited states in two-dimensional, in-plane, quantum heterostructures

Two-dimensional (2D) semiconductors are promising candidates for optoelectronic application and quantum information processes due to their inherent out-of-plane 2D confinement. In addition, they offer the possibility of achieving low-dimensional in-plane exciton confinement, similar to zero-dimensional quantum dots, with intriguing optical and electronic properties via strain or composition engineering. However, realizing such laterally confined 2D monolayers and systematically controlling size-dependent optical properties remain significant challenges. Here, we report the observation of lateral confinement of excitons in epitaxially grown in-plane MoSe2 quantum dots (~15-60 nm wide) inside a continuous matrix of WSe2 monolayer film via a sequential epitaxial growth process. Various optical spectroscopy techniques reveal the size-dependent exciton confinement in the MoSe2 monolayer quantum dots with exciton blue shift (12-40 meV) at a low temperature as compared to continuous monolayer MoSe2. Finally, single-photon emission (g2(0) ~ 0.4) was also observed from the smallest dots at 1.6 K. Our study opens the door to compositionally engineered, tunable, in-plane quantum light sources in 2D semiconductors.

Effects of interlayer spacing and applied pressure on the lanthanide transport in MoS2-based two-dimensional channels

ABSTRACT Rare-earth elements (REEs) are critical to modern industry but difficult to separate due to their subtle and monotonic changes in physicochemical properties. MoS2-based two-dimensional (2D) materials offer novel opportunities for enhancing REE separation, exhibiting a distinct volcano-shaped transport performance distribution that peaks at Sm3+. However, the specific contributions of thermodynamic and kinetic factors to ion transport within 2D confinement remain unclear. In this study, we conducted a series of non-equilibrium all-atom molecular dynamics (MD) simulations to explore the effects of interlayer spacing and external pressure on the transport of lanthanide ions in Å-scale acetate functionalized 2D MoS2 (MoS2-COOH) channels. We examined ion entry and permeation rates, water flux, dehydration, and binding modes. The simulation results reveal that the transport trends of lanthanide ions are jointly driven by the dehydration degree and the relative-binding strengths of ions to water and to the acetate within the 2D channels. Notably, the dehydration pattern of lanthanide ions during permeation is closely linked to kinetic factors. Overall, this study provides a detailed atomistic understanding of the mechanisms underlying lanthanide ion transport under confinement. These findings point to the significant potential for tuning confinement and chemical functionalization within Å-scale channels for more efficient REE separation.

A true triaxial experiment investigation of the mechanical and deformation failure behaviors of flawed granite after exposure to high-temperature treatment

Understanding the mechanical and deformation failure behaviors of heated flawed granite under true triaxial stresses is of great significance for evaluating the wellbore stability in developing hot dry rock resources. In this study, true triaxial experiments are conducted on flawed granite specimens of a varying flaw overlapping length lfo with and without high temperature (HT) treatment, with the emphases on the crack development under true triaxial stresses and its correlations with the strength, plastic anisotropy and failure forecast. Investigations demonstrate that HT, σ2 (intermediate principal stress) and lfo, significantly affect the mechanical properties of flawed granite. Due to strong 3D confinement, the loop crack, the secondary transverse crack and the far-field crack are frequently induced in flawed granite, unlike experiments of uniaxial, biaxial and conventional triaxial compression. When increasing lfo, the rock bridge undergoes the stress amplification which tendentiously drives the internal crack coalescence and typically causes a reduced strength. The PSIRs (Plastic Strain Increments Ratios) analysis, first extended to the true-triaxial experimental data, reveals that the 3D stress-induced extensional/shear fracturing from the flaw tips in σ2-direction is the mechanism of the plastic anisotropy generated. Besides, an attempt to anticipate the failure time in the framework of the time‐reversed Omori’s law suggests a poor predictability by using the acoustic emission but a higher-quality forecast (being more precise and less biased) by using the dissipated energy.

Design approaches for 3D cell culture and 3D bioprinting platforms.

The natural habitat of most cells consists of complex and disordered 3D microenvironments with spatiotemporally dynamic material properties. However, prevalent methods of in vitro culture study cells under poorly biomimetic 2D confinement or homogeneous conditions that often neglect critical topographical cues and mechanical stimuli. It has also become increasingly apparent that cells in a 3D conformation exhibit dramatically altered morphological and phenotypical states. In response, efforts toward designing biomaterial platforms for 3D cell culture have taken centerstage over the past few decades. Herein, we present a broad overview of biomaterials for 3D cell culture and 3D bioprinting, spanning both monolithic and granular systems. We first critically evaluate conventional monolithic hydrogel networks, with an emphasis on specific experimental requirements. Building on this, we document the recent emergence of microgel-based 3D growth media as a promising biomaterial platform enabling interrogation of cells within porous and granular scaffolds. We also explore how jammed microgel systems have been leveraged to spatially design and manipulate cellular structures using 3D bioprinting. The advent of these techniques heralds an unprecedented ability to experimentally model complex physiological niches, with important implications for tissue bioengineering and biomedical applications.

Supramolecular structure design of block copolymer by combining 3D confined self-assembly with selective disassembly

3D confined self-assembly (3D-CSA) of block copolymer (BCP) is a significant way to generate polymer microparticles with ordered internal suprastructures. Subsequent selective disassembly of the suprastructures can lead to the formation of unique anisotropic micelles or mesoporous microparticles, which can be hardly achieved by solution self-assembly or disassembly of bulk suprastructures. These micelles or mesoporous microparticles and their composites with functional molecules/nanoparticles have great potential in interfacial compatibilization, catalysis, controlled drug delivery and other fields, thus arising increasing attention in recent years. In this review, we first briefly discuss the influence factors, particularly, packing parameter and interfacial selectivity on morphology of BCP assemblies under 3D confinement. Then, we emphasize recent progress in selective disassembly of BCP microparticles into anisotropic micelles or mesoporous microparticles and derived composites. Finally, the outlook and challenges of this direction are highlighted.

Ultrafast laser inscription of 2D confinement MMI-based beam splitters with tunable splitting ratio in Nd:YAG crystal

The multimode-interference (MMI) devices based on the principle of self-imaging show great potential for applications in different scenarios. The research interest in two-dimensional confinement MMI devices has surged enormously due to the broader areas of applications compared with the one-dimensional confinement MMI devices. In this paper, we report on the characteristics of two-dimensional confinement 2 × 2 output MMI-based beam splitters which were achieved by femtosecond laser direct writing technology in a Nd:YAG crystal. The propagation features with different splitting ratios have been simulated by the beam propagation method. Two splitters with beam division performances of 2 × 2 output have been further demonstrated through an end-face coupling system and investigated with a laser beam at 532 nm wavelength, which have achieved two splitting ratios including 73 %: 12.5 %: 12.5 %: 2 % with a deviation less than 3 %, and 25 %: 25 %: 25 %: 25 % with a deviation less than 5 %. These performances with high consistency manifest that these devices can emerge into kinds of 3D optical applications with the ability of 3D spatial optical signal processing. Moreover, our work further proves that femtosecond laser direct writing technology presents absolute advantages in processing 3D micro-nano devices in transparent materials for on-chip integration.

Anomalously enhanced ion transport and uptake in functionalized angstrom-scale two-dimensional channels.

Emulating angstrom-scale dynamics of the highly selective biological ion channels is a challenging task. Recent work on angstrom-scale artificial channels has expanded our understanding of ion transport and uptake mechanisms under confinement. However, the role of chemical environment in such channels is still not well understood. Here, we report the anomalously enhanced transport and uptake of ions under confined MoS2-based channels that are ~five angstroms in size. The ion uptake preference in the MoS2-based channels can be changed by the selection of surface functional groups and ion uptake sequence due to the interplay between kinetic and thermodynamic factors that depend on whether the ions are mixed or not prior to uptake. Our work offers a holistic picture of ion transport in 2D confinement and highlights ion interplay in this regime.

Core-shell particle formation via Co-assembly of AB diblock copolymers and nanoparticles in 3D soft confinement.

Core-shell particle formation via co-assembly of AB diblock copolymers and nanoparticles in 3D soft confinement was studied using a simulated annealing method. Several sequences of soft confinement-induced core-shell particles were predicted as functions of the volume fraction of the nanoparticle to core-shell particles, the incompatibility between blocks, the volume fractions of A-blocks, the chain length of AB diblocks, the eccentricity of the nanoparticle, and the initial concentration of copolymers. Simulation results demonstrate that those factors are able to tune the morphology of the core-shell particles precisely. Calculated data indicate that the copolymer chain was located between a hard confinement wall composed of the nanoparticle and a soft confinement wall composed of solvents, and the arrangement direction of the copolymer chains was in a competitive equilibrium between the two. We anticipate that this work will be helpful and instructive for the preparation of polymer shells with different structures and shapes, as well as the study of self-assembly morphology of copolymers in a complex confinement systems.

Lattice thermal conductivity of ZnO: experimental and theoretical studies.

ZnO has been explored using different approaches such as doping, nanostructuring, 2D confinement, and introduction of interface effects for improving thermoelectric performance and lowering thermal conductivity. Herein, the lattice thermal conductivity (κL) of ZnO determined from Raman thermometry, the 3ω-method and simulation using three-phonon scattering is presented. The average Debye temperature (θD) of A1(TO) and E2(high) modes estimated utilizing bond-order-length-strength correlation with local bond averaging effects is ∼422 K. The average κL of ZnO calculated using the theoretical coefficient of Slack's equation, θD, and Grüneisen parameter (γ) in Slack's equation is 2.75 W m-1 K-1, which is significantly lower than the κL ∼ 50.9 W m-1 K-1 simulated by considering the Perdew-Burke-Ernzerhof functional with Hubbard and non-analytical corrections. The coefficient of Slack's equation is determined from the κL ∼ 31 W m-1 K-1 of ZnO measured using the 3ω-method for the accurate estimation of the κL. The experimental coefficient of Slack's equation with Raman thermometry data yields κL ∼ 50.6 W m-1 K-1, which is higher than the value obtained using the 3ω-method but consistent with the theoretical value. Thus, three-phonon anharmonicity describes the κL of ZnO associated with Raman scattering. The method adopted to calculate κL will help for the in-depth analysis of phonon dynamics and the design of wurtzite-ZnO-related power electronics.

Quantitative Mapping of Transient Thermodynamic States in Ultrafast Laser Nanostructuring of Quartz

Understanding material structural reaction to light is of utmost importance to advance processing resolution in ultrafast laser volume structuring into the nanoscale. Selective thermodynamic pathways are required to quench energy transport in the most rapid manner and to confine the process to nanometer lengths, bypassing optical resolution. Quantifying material dynamics under confinement, with in situ access to transient local temperature and density parameters, thus becomes key in understanding the process. We report in situ reconstruction of thermodynamic states over the entire matter relaxation path in bulk α -quartz irradiated by ultrafast nondiffractive laser beams using time-resolved qualitative and quantitative optical phase microscopy. Thermooptic dynamics indicate rapid spatially confined crystalline-to-amorphous transition to a hot dense fused silica form. Densification exceeds 20% and the matrix temperature rises to more than 2,000 K in the first nanosecond. This structural state relaxes in hundreds of nanoseconds. The dispersion and time design of the optical beam to picosecond durations increases the spatial confinement and triggers an extreme nanostructuring process based on nanocavitation that occurs within the amorphizing material, where the low-viscosity phase lowers the mechanical requirements for the process. Processing feature scales of less than a tenth of the optical wavelength are obtained in the volume. This allows for structural and morphological nanoscale material features under 3D confinement that can engineer optical materials.

Phase behavior of symmetric diblock copolymers under 3D soft confinement

The phase behavior of symmetric diblock copolymers under three-dimensional (3D) soft confinement is investigated using self-consistent field theory.

High-entropy prussian blue analogs with 3D confinement effect for long-life sodium-ion batteries

By combining the benefits of high entropy (HE) and carbon wrapping (CW), HEPBAs@0.1C achieves excellent electrochemical performance and unprecedented stability in the ambient environment.

Electrodeposition of Au and AgAu Nanoparticles from Reverse Micelles – Tuning Particle Properties and Understanding Solvent and Confinement Effects by Ensemble and Single Entity Approaches

The synthesis and reactivity of nanoparticles (NPs) has vastly been studied for years,[1-3] yet still there are several open questions about how a synthesis method and its parameters influence the final properties of the obtained NPs. In the classical wet-chemical synthesis, capping agents are widely used to adjust the morphology and size, preventing further growth of NPs. However, their presence can be disadvantageous for some applications, e.g. electrocatalysis, where they decrease reaction kinetics. To overcome this issue, we use electrodeposition as synthetic route, and the size of the obtained NP is tuned by the amount of precursor that is loaded inside a reverse micelle. The NP formation is induced by applying a suitable potential to reduce the entrapped precursor at the electrode. This deposition can be done by ensemble or single entity approaches.Experimentally speaking, both approaches consist of an electrode immersed in a media with suspended precursor-loaded reverse micelles. However, for ensemble electrodeposition a macroelectrode is used, a standard chronoamperometry is recorded and average information about the system is provided. On the other hand, single entity approach relies on random collision of reverse micelles at a micro- or nanoelectrode, which appears as spikes on the chronoamperometric response, and data can be determined based on statistical analysis of single particle events.[4,5] It has been used to characterize different types of NPs, their size, composition and kinetic reaction parameters.[6,7] Focusing on the electrosynthesis, this work investigates the formation of Au and AgAu NPs by both ensemble and single entity approaches. Besides the synthesis method, the effect of the solvent and the 0D confinement is also under evaluation to better understand how one can tune NPs’ shape and structure, i.e. core-shell vs alloy arrangements. The solvent effect is investigated by using room temperature ionic liquid or organic solvents during electrodeposition. The reverse micelles act as a nanoreactor cage, confining the precursors, and therefore changing the type of this cage helps us to understand the influence of the 0D confinement. For this, reverse micelles of two different materials were used: SDS (sodium dodecyl sulphate) and PS-P2VP (polystyrene-b-poly(2-vinylpyridine)), with the former forming nanodroplets of an aqueous phase protected by a thin wall, and the latter assembling to a sphere with a polymeric core, completely binding the precursor.The resulting NPs were imaged by AFM, SEM and TEM and their composition resolved by EDX. Initial catalytic CV and LSV measurements towards hydrogen evolution reaction were done to provide further insights about the NPs’ properties. From these characterizations of the NPs, it has been demonstrated that the synthesis approach, the applied potential, the solvent, and the type of RM influence the final NPs’ properties. Hence, the size, composition, structure and catalytic activity of the resulting NPs can by tuned by electrochemical parameters, avoiding the necessity to select different capping and reducing agents as done in wet-chemical synthesis.[1] D. V. Talapin, E. V. Shevchenko. Chem. Rev. 2016, 116, 18, 10343–10345. doi: 10.1021/acs.chemrev.6b00566.[2] H. Duan, D. Wang, Y. Li. Chem. Soc. Rev., 2015, 44, 5778-5792. doi: 10.1039/C4CS00363B.[3] M. Grzelczak, J. Pérez-Juste, P. Mulvaney, L. M. Liz-Marzán. Chem. Soc. Rev., 2008, 37, 1783-1791. doi: 10.1039/B711490G[4] K. J. Stevenson, K. Tschulik. Curr. Opin. Electrochem. 2017, 6, 38–45. doi:10.1016/j.coelec.2017.07.009.[5] M. V. Evers, M. Bernal, B. Roldán Cuenya, K. Tschulik. Angew. Chem. 2019, 58, 8221-8225. doi: 10.1002/anie.201813993[6] E. N. Saw, M. Kratz, K. Tschulik. Nano Res. 2017, 10, 3680–3689. doi:10.1007/s12274-017-1578-3.[7] K. Shimizu, K. Tschulik, R. G. Compton. Chem. Sci. 2016, 7, 1408–1414. doi:10.1039/C5SC03678J.

Anisotropic and High‐Mobility Electronic Transport in a Quasi 2D Antiferromagnet NdSb2

AbstractAdvancements in low‐dimensional functional device technology heavily rely on the discovery of suitable materials which have interesting physical properties as well as can be exfoliated down to the 2D limit. Exfoliable high‐mobility magnets are one such class of materials that, not due to lack of effort, has been limited to only a handful of options. So far, most of the attention has been focused on the van der Waals (vdW) systems. However, even within the non‐vdW, layered materials, it is possible to find all these desirable features. Using chemical reasoning, it is found that NdSb2 is an ideal example. Even with a relatively small interlayer distance, this material can be exfoliated down to few layers. NdSb2 has an antiferromagnetic ground state with a quasi 2D spin arrangement. The bulk crystals show a very large, non‐saturating magnetoresistance along with highly anisotropic electronic transport properties. It is confirmed that this anisotropy originates from the 2D Fermi pockets which also imply a rather quasi 2D confinement of the charge carrier density. Both electron and hole‐type carriers show very high mobilities. The possible non‐collinear spin arrangement also results in an anomalous Hall effect.

Molecular dipole regulated surface potential and ferroelectric characteristics in nanoconfined P(VDF-TrFE) architectures

Molecular dipole orientation is crucial to efficiently utilize the piezo- and ferroelectric polarization in polymers. Modern electronic applications of these polymer demand switching of dipoles with low voltage, which requires the dipole orientation to be perpendicular to the substrate (edge-on) rather than parallel (face-on). The 0D, 1D and 2D confinement of polymer architectures into nanoparticles, nanofibers, and thin films is a vital approach to control dipole orientation in ferroelectrics. Our findings show that for 1D (d33 ∼ 18 ± 2.2 pm/V) and 2D nanostructures (d33 ∼ 15 ± 1.5 pm/V) of poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)), the molecular dipoles are edge-on, whereas for 0D, the dipoles are face-on, which would govern the ferroelectric and piezoelectric behaviour of these confined structures. The subsequent observation concludes that altering the dipole orientation allows precise modulation of surface potential and work function. The work functions of the 0D, 1D and 2D nanostructures are 4.56 ± 0.03 eV, 4.93 ± 0.51 eV and 4.68 ± 0.18 eV, respectively. The tunability of surface potential opens up the possibility of utilizing these nanostructures in single-material triboelectric series. Density functional theory (DFT)-based computations substantially support these experimental findings. This study provides a thorough understanding of the effect of molecule dipole orientation on piezo- and ferroelectric properties of P(VDF-TrFE) nanostructures.

Effect of Film Thickness on the Self-Assembly of CBABC Symmetric Pentablock Terpolymer Melts under 1D Confinement: A Dissipative Particle Dynamic Study.

The study investigates the impact of film thickness on the phase behavior of pentablock terpolymers, denoted as C3B3A6B3C3, when subjected to wall confinement by utilizing the dissipative particle dynamics method. Phase diagrams were constructed to elucidate how factors such as block-block interaction strength, film thickness, and wall properties affect the self-assembly structures. In cases where the wall exhibits no preference for any of the blocks, lamellae phases with orientations perpendicular to the wall are observed. The order-disorder transition (ODT) temperature is found to be influenced by the interaction between the polymer and the wall in thin confinement scenarios. When the wall displays a preference for specific blocks, the orientation of lamellae structures undergoes variations. Lamellae tend to align parallel to the wall when the wall favors A or C blocks, and they orient perpendicularly when B blocks are favored. Furthermore, the mechanical properties of the lamellae structures are related to the conformations of the polymer chains. Structures where chains predominantly adopt a loop conformation exhibit enhanced elastic properties. The ratio of looping to bridging conformations can be adjusted by altering the film thickness and wall selectivity.