Hopping Behavior Mediates the Anomalous Confined Diffusion of Nanoparticles in Porous Hydrogels

Bioinspired bicontinuous adhesive hydrogel for wearable strain sensor with high sensitivity and a wide working range

Conductive hydrogel strain sensors demonstrate extensive potential in artificial robotics, human-computer interaction, and health monitoring, owing to their excellent flexibility and biocompatibility. Wearable strain sensors for real-time monitoring of human activities require hydrogels with self-adhesion, desirable sensitivity, and wide working range. However, balancing the high sensitivity and a wide working range remains a challenge. Herein, a marine coral exoskeleton inspired bicontinuous hydrogel (PAD-iP) for strain sensor was synthesized by in-situ copolymerization of acrylic acid (AA) and dimethylaminpropyl methacrylamide (DMAPMA) in the presence of poly(3, 4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) skeleton, using glycerol as water-retaining agent. Benefiting from the bicontinuous structure composed of electron-transported conductive, tough PEDOT:PSS skeleton and the ion-transported, flexible poly(AA-co-DMAPMA) hydrogel matrix, the strain sensor based on PAD-iP hydrogel struck an optimal balance between ultrahigh sensitivity (gauge factor up to 1049) and a broad sensing range (strain of 0-600 %). The strain sensors could be adhered directly to skin to monitor full-range human activities, physiological activities and physical vibrational signals of the local environment. The strain sensor also exhibited robustness and stable sensing properties across a wide temperature range (-20 ∼ 40 ℃). This work offers a fresh inspiration for preparation of high-performance hydrogel strain sensors.

Super-resolving particle diffusion heterogeneity in porous hydrogels via high-speed 3D active-feedback single-particle tracking microscopy

Nanoparticle diffusion in 3D porous structures is critical to understanding natural and synthetic systems but remains underexplored due to limitations in traditional microscopy methods. Here, we use 3D Single-Molecule Active-feedback Real-time Tracking (3D-SMART) microscopy to resolve nanoparticle dynamics in agarose gels with unprecedented spatiotemporal resolution. We highlight 'hopping diffusion', where particles intermittently escape confinement pockets, providing insights into hydrogel microstructure. Long, highly sampled trajectories enable extraction of kinetic parameters, confinement sizes, and thermodynamic barriers. This study demonstrates 3D-SMART's ability to probe particle-environment interactions at super-resolution (~10 nm in XY and ~30 nm in Z) in 3D, offering new perspectives on nanoparticle diffusion and the structural dynamics of porous materials, with implications for drug delivery, material science, and biological systems.

Supramolecular Crystals based Fast Single Ion Conductor for Long-Cycling Solid Zinc Batteries

The solid polymer electrolytes (SPEs) used in Zn-ion batteries (ZIBs) have low ionic conductivity due to the sluggish dynamics of polymer segments. Thus, only short-range movement of cations is supported, leading to low ionic conductivity and Zn2+ transference (tZn 2+). Zn-based supramolecular crystals (ZMCs) have considerable potential for supporting long-distance Zn2+ transport; however, their efficiency in ZIBs has not been explored. The present study developed a ZMC consisting of succinonitrile (SN) and zinc bis (trifluoromethylsulfonyl) imide (Zn(TFSI)2), with a structural formula identified as Zn(TFSI)2SN3. The ZMC has ordered three-dimensional tunnels in the crystalline lattices for ion conduction, providing high ionic conductivities (6.02×10-4 S cm-1 at 25 °C and 3.26×10-5 S cm-1 at -35 °C) and a high tZn 2+ (0.97). We demonstrated that a Zn‖Zn symmetrical battery with ZMCs has long-term cycling stability (1200 h) and a dendrite-free Zn plating/stripping process, even at a high plating areal density of 3 mAh cm-2. The as-fabricated solid-state Zn battery exhibited excellent performance, including high discharge capacity (1.52 mAh cm-2), long-term cycling stability (83.6 % capacity retention after 70000 cycles (7 months)), wide temperature adaptability (-35 to 50 °C) and fast charging ability. The ZMC differs from SPEs in its structure for transporting Zn2+ ions, significantly improving solid-state ZIBs while maintaining safety, durability, and sustainability.

Effect of polyacrylamide gel elasticity on collagen type II fibril assembly

Collagen type II fibrils provide structural integrity to the articular cartilage extracellular matrix. However, the conditions that control the fibril radial size scale, distribution, and formation inside of dense networks are not well understood. We have investigated how surrounding elastic networks affect fibril formation by observing the structure and dynamics of collagen type II in model polyacrylamide gels of varying moduli. Cryogenic transmission electron microscopy (cryo-TEM) is used to image the fibril structure and is verified qualitatively with optical microscopy of fluorescently-tagged collagen within the gels. Using fluorescence correlation spectroscopy super-resolution optical fluctuation imaging (fcsSOFI), the diffusion dynamics of the collagen in low pH and neutral pH conditions are determined. Overall, the fibril bundle diameter and concentration were found to decrease as a function of gel modulus. The single fibril diameter remains constant at 30 nm within the gels; however, the diameter was found to be smaller when compared to in solution. Additionally, the mode of diffusion of the collagen triple helices changes within gel environments, decreasing the diffusion coefficient. Understanding the intricate relationship between network topology and collagen type II fibril formation is crucial in gaining deeper insights into the transport phenomena within complex acellular tissues that are necessary for the development of future therapeutic materials.

Expanding the Palette of SWIR Emitting Nanoparticles Based on Au Nanoclusters for Single-Particle Tracking Microscopy

Single-molecule localization microscopy has proved promising to unravel the dynamics and molecular architecture of thin biological samples down to nanoscales. For applications in complex, thick biological tissues shifting single-particle emission wavelengths to the shortwave infrared (SWIR also called NIR II) region between 900 to 2100 nm, where biological tissues are more transparent is key. To date, mainly single-walled carbon nanotubes (SWCNTs) enable such applications, but they are inherently 1D objects. Here, 0D ultra-small luminescent gold nanoclusters (AuNCs, <3 nm) and ≈25 nm AuNC-loaded-polymeric particles that can be detected at the single-particle level in the SWIR are presented. Thanks to high brightness and excellent photostability, it is shown that the dynamics of the spherical polymeric particles can be followed at the single-particle level in solution at video rates for minutes. We compared single particle tracking of AuNC-loaded-polymeric particles with that of SWCNT diffusing in agarose gels demonstrating the specificity and complementarity of diffusion properties of these SWIR-emitting nano-objects when exploring a complex environment. This extends the library of photostable SWIR emitting nanomaterials to 0D nano-objects of variable size for single-molecule localization microscopy in the second biological window, opening unprecedented possibilities for mapping the structure and dynamics of complex biological systems.

Nonspecific membrane-matrix interactions influence diffusivity of lipid vesicles in hydrogels

The diffusion of extracellular vesicles and liposomes in vivo is affected by different tissue environmental conditions and is of great interest in the development of liposome-based therapeutics and drug-delivery systems. Here, we use a bottom-up biomimetic approach to better isolate and study steric and electrostatic interactions and their influence on the diffusivity of synthetic large unilamellar vesicles in hydrogel environments. Single-particle tracking of these extracellular vesicle-like particles in agarose hydrogels as an extracellular matrix model shows that membrane deformability and surface charge affect the hydrogel pore spaces that vesicles have access to, which determines overall diffusivity. Moreover, we show that passivation of vesicles with PEGylated lipids, as often used in drug-delivery systems, enhances diffusivity, but that this effect cannot be fully explained with electrostatic interactions alone. Finally, we compare our experimental findings with existing computational and theoretical work in the field to help explain the nonspecific interactions between diffusing particles and gel matrix environments.

Temperature-mediated diffusion of nanoparticles in semidilute polymer solutions

The temperature is often a critical factor affecting the diffusion of nanoparticles in complex physiological media, but its specific effects are still to be fully understood. Here, we constructed a temperature-regulated model of semidilute polymer solution and experimentally investigated the temperature-mediated diffusion of nanoparticles using the particle tracking method. By examining the ensemble-averaged mean square displacements (MSDs), we found that the MSD grows gradually as the temperature increases while the transition time from sublinear to linear stage in MSD decreases. Meanwhile, the temperature-dependent measured diffusivity of the nanoparticles shows an exponential growth. We revealed that these temperature-mediated changes are determined by the composite effect of the macroscale property of polymer solution and the microscale dynamics of polymer chain as well as nanoparticles. Furthermore, the measured non-Gaussian displacement probability distributions were found to exhibit non-Gaussian fat tails, and the tailed distribution is enhanced as the temperature increases. The non-Gaussianity was calculated and found to vary in the same trend with the tailed distribution, suggesting the occurrence of hopping events. This temperature-mediated non-Gaussian feature validates the recent theory of thermally induced activated hopping. Our results highlight the temperature-mediated changes in diffusive transport of nanoparticles in polymer solutions and may provide the possible strategy to improve drug delivery in physiological media.

Single-Particle Tracking in Poly(Ethylene Glycol) Diacrylate: Probe Size Effect on the Diffusion Behaviors of Nanoparticles in Unentangled Polymer Solutions

A thorough understanding of the relevant factors governing the transport of nanoparticles in poly(ethylene glycol) diacrylate (PEGDA) is crucial for many applications utilizing this polymer. Here, single-particle tracking (SPT) was used to systematically investigate the role of the probe size (3-200 nm) on the diffusion behaviors of individual fluorescent nanoparticles in semidilute and unentangled PEGDA solutions. The quantitative assessment of the SPT data via the recorded single-particle trajectories and diffusion coefficients (D) not only showed that the observed probe dynamics in PEGDA were temporally and spatially heterogeneous, but more importantly that the measured D were observed to be significantly reduced (vs in solvent) and strongly size-dependent. We explained these results based on a modified multiscale model for particle diffusion, built upon well-established hydrodynamics and obstruction theories. We furthermore showed that the presence of steric interactions and probe confinement effects in highly crowded, unentangled PEGDA microstructures can lead to deviations in the single-particle displacements from the expected Gaussian behavior, as revealed by the van Hove displacement distributions and the associated non-Gaussian parameters. This study has demonstrated the power of SPT methods in offering an advanced characterization of the transport characteristics in complex polymer structures, overcoming challenges posed by traditional characterization techniques.