A taurine-based hydrogel with the neuroprotective effect and the ability to promote neural stem cell proliferation.

Ischemic stroke, a cerebrovascular disease caused by arterial occlusion in the brain, can lead to brain impairment and even death. Stem cell therapies have shown positive advantages to treat ischemic stroke because of their extended time window, but the cell viability is poor when transplanted into the brain directly. Therefore, a new hydrogel GelMA-T was developed by introducing taurine on GelMA to transplant neural stem cells. The GelMA-T displayed the desired photocuring ability, micropore structure, and cytocompatibility. Its compressive modulus was more similar to neural tissue compared to that of GelMA. The GelMA-T could protect SH-SY5Y cells from injury induced by OGD/R. Furthermore, the NE-4C cells showed better proliferation performance in GelMA-T than that in GelMA during both 2D and 3D cultures. All results demonstrate that GelMA-T possesses a neuroprotective effect for ischemia/reperfusion injury against ischemic stroke and plays a positive role in promoting NSC proliferation. The novel hydrogel is anticipated to function as cell vehicles for the transplantation of neural stem cells into the stroke cavity, aiming to treat ischemic stroke.

A porous micro/nano-structured polyethylene film prepared using a picosecond laser for agricultural passive cooling.

Passive cooling materials, as a promising choice for mitigating the global energy crisis, have limited use as their cooling effects are usually weakened or lost by dust contamination. In this study, a passive cooling polyethylene (PE) film with self-cleaning properties is prepared by picosecond laser ablation. Numerous root-like hierarchical porous micro/nano-structures were obtained on the double side of the PE film. The outside (toward air) shows excellent self-cleaning, corrosion resistance, and anti-friction properties. The inside (towards crops) further reduced the transmittance and water vapor evaporation (keeping the soil moist). Compared with the pristine PE film, the transmittance of the as-prepared double-sided micro/nano-structured PE film decreased by about 40%. In addition, during the crop cultivation experiment, the temperature of the crop leaves was reduced by 2.7-7 °C and showed a higher plant height and greater leaf width under the cover of the laser-treated film. This demonstrates that the passive cooling PE film has an excellent temperature regulation ability and good practical application effects. This study proposes a simple strategy based on a picosecond laser for the preparation of passive cooling materials, which are beneficial for alleviating energy crises and promoting sustainable development.

Optimizing the Production of Hydrogel Microspheres Using Microfluidic Chips: The Influence of Surface Treatment on Droplet Formation Mechanism.

Microfluidic chips have been widely applied in biology and medical research for stably generating uniform droplets that can be solidified into hydrogel microspheres. However, issues such as low microsphere yield, lengthy experimental processes, and susceptibility to environmental interference need to be addressed. In this work, a simple and effective method was developed to modify microfluidic chips at room temperature to improve the production performance of hydrogel microspheres. Numerical simulation-assisted experiments were conducted to comprehensively understand the effect of solution viscosity, hydrophilicity, and flow rate ratio on droplet formation during microsphere production. Chitosan was selected as the main component and combined with poly(ethylene glycol) diacrylate to prepare photocurable hydrogel microspheres as a demonstration. As a result, grafting fluoro-silane (FOTS) increased the contact angle of the channel from 90 to approximately 110°, which led to a 12.2% increase in droplet yield. Additionally, FOTS-modification attenuated the impact of the flow rate ratio on droplet yield by 19.1%. Alternatively, depositing dopamine decreased the channel's contact angle from 90 to 60°, resulting in a 21.4% increase in particle size and enabling the chip to adjust droplet size over a wider range. Further study demonstrates that the obtained hydrogel microspheres can be modified with layers of aldehyde, which can potentially be used for controlled drug release. Overall, this study proposed a facile method for adjusting the yield and droplet size through surface treatment of microfluidic chips while also enhancing the understanding of the synergistic effects of multiple factors in microfluidics-based microsphere production.

Two-step method fabricating a 3D nerve cell model with brain-like mechanical properties and tunable porosity vascular structures via coaxial printing.

Three-dimensional (3D) nerve cell models have been widely developed to understand the mechanisms and discover treatment methods of ischemic stroke and neurodegenerative disease. However, there is a contradiction in the production of 3D models that they should possess high modulus to ensure mechanical stability while low modulus to provide mechanical stimuli for nerve cells. In addition, it is challenging to maintain the long-term viability of 3D models when lacking vascular structures. Here, a 3D nerve cell model with brain-like mechanical properties and tunable porosity vascular structures has been fabricated. The matrix materials with brain-like low mechanical properties were favorable for promoting HT22 proliferation. The nerve cells could exchange nutrients and waste with the cultural environment through vascular structures. The vascular structures also played a supporting role, and model stability was enhanced by combining matrix materials with vascular structures. Furthermore, the porosity of vascular structure walls was adjusted by adding sacrificial materials to the tube walls during 3D coaxial printing and removing them after preparation, resulting in tunable porosity vascular structures. Finally, HT22 cells showed better cell viability and proliferation performance after culturing 7 days in the 3D models with vascular structures than in the 3D models with solid structures. All these results suggest that this 3D nerve cell model possesses good mechanical stability and long-term viability, which is expected to be used in pathological studies and drug screening for ischemic stroke and neurodegenerative diseases.

Ferroferric oxide loaded near-infrared triggered photothermal microneedle patch for controlled drug release.

HYPOTHESIS: The drug release efficiency of microneedle is usually slower than that of oral delivery or hypodermic injection, which severely restricts its widespread use. Herein, a Fe3O4-loaded photothermal microneedle (Fe3O4@MN) patch is developed for controlled drug delivery. Under near infrared (NIR) irradiation, the drug loaded on Fe3O4@MN can be quickly released, achieving an enhanced drug release efficiency. EXPERIMENTS: The mechanical property and characterization of Fe3O4@MN were systematically investigated, and the photothermal performance of Fe3O4@MN was also conducted. Moreover, the model-drug-releasing tests and doxycycline hydrochloride releasing tests were carried out to evaluate the drug release performance of Fe3O4@MN under NIR irradiation. FINDINGS: Fe3O4@MN has enough mechanical strength to pierce into skins, and the temperature of Fe3O4@MN patch could rapidly increase by 40 â„ƒ in 1 min under NIR irradiation. In vitro experiment, the release rate of model drug in Fe3O4@MN reached âˆ¼ 80 % in 20 min and the doxycycline hydrochloride release rate of Fe3O4@MN reached âˆ¼ 70 % after 20 min of NIR irradiation, indicating the potential application of the synthesized microneedle patch for transdermal drug delivery. Further penetration test showed that the penetration depth of model drugs carried by Fe3O4@MN patch on the porcine skin under NIR irradiation was 150 - 200 µm longer than that of the patch without Fe3O4 nanoparticles.

An ultra-stretchable glycerol-ionic hybrid hydrogel with reversible gelid adhesion.

Functional hydrogels have attracted enormous interest as wet adhesives for biomedical research and engineering applications. However, reversible hydrogel adhesives that can be used for gelid conditions were rarely reported. In this work, we have developed a freezing-tolerant (freezing temperature < -50 °C), ultra-stretchable (stretch strain > 30000% at 25 °C) glycerol-ionic hydrogel via the ultraviolet curing of acrylamide monomer and hyper-branched polyethylenimine polymer in CaCl2-water-glycerol solution. The fabricated hydrogel exhibited reversible gelid adhesion, rapid self-healing (recover in 3 s) and weight-retaining (>2 weeks) properties. The hydrogel allows two iron substrates to adhere together at -40 °C with the lap-shear adhesion strength as high as ~1 MPa. Such strong adhesion measured was reversible, specifically achieving ~100% of initial adhesion strength at 25 °C and ~36% at -40 °C. Additionally, decreasing the testing temperature significantly improved the tensile strength but decreased the fracture strain of the hydrogel. Interestingly, lap-shear adhesion tests suggested that the gelid adhesion strength was enhanced by 130 times as the testing temperature decreased from 25 °C to -40 °C, which was mainly attributed to the enhanced mechanical strength of the bulk hydrogel as well as the increased surface interaction at gel-substrate interfaces. More importantly, the adhesion failure gradually changed from cohesive failure to adhesive failure as the temperature decreased. This work provides new practical and fundamental insights into developing multifunctional freezing-tolerant hydrogel adhesive for gelid conditions.

Modulation of Ionic Current Rectification in Ultrashort Conical Nanopores.

Nanopores that exhibit ionic current rectification (ICR) behave like diodes such that they transport ions more efficiently in one direction than in the other. Conical nanopores have been shown to rectify ionic current, but only those with at least 500 nm in length exhibit significant ICR. Here, through the finite element method, we show how ICR of conical nanopores with lengths below 200 nm can be tuned by controlling individual charged surfaces, that is, the inner pore surface (surfaceinner) and exterior pore surfaces on the tip and base side (surfacetip and surfacebase). The charged surfaceinner and surfacetip can induce obvious ICR individually, while the effects of the charged surfacebase on ICR can be ignored. The fully charged surfaceinner alone could render the nanopore counterion-selective and induces significant ion concentration polarization in the tip region, which causes reverse ICR compared to nanopores with all surfaces charged. In addition, the direction and degree of rectification can be further tuned by the depth of the charged surfaceinner. When considering the exterior membrane surface only, the charged surfacetip causes intrapore ionic enrichment and depletion under opposite biases, which results in significant ICR. Its effective region is within ∼40 nm beyond the tip orifice. We also found that individual charged parts of the pore system contributed to ICR in an additive way because of the additive effect on the ion concentration regulation along the pore axis. With various combinations of fully/partially charged surfaceinner and surfacetip, diverse ICR ratios from ∼2 to ∼170 can be achieved. Our findings shed light on the mechanism of ICR in ultrashort conical nanopores and provide a useful guide to the design and modification of ultrashort conical nanopores in ionic circuits and nanofluidic sensors.

Probing the Self-Assembly and Nonlinear Friction Behavior of Confined Gold Nano-Particles.

For the wide application of nanoparticles (NPs) (e.g., in nanotribology), it is of fundamental and practical importance to understand the self-assembly and lubrication behavior of confined NPs. In this work, a systematic study was conducted to probe the assembly and associated surface forces of spherical gold nanoparticles (Au NPs, diameter ∼5 nm) confined between pairs of mica (negatively charged) and (3-aminopropyl)triethoxysilane modified mica (APTES-mica, positively charged) surfaces using a surface forces apparatus (SFA) under aqueous conditions. It is observed that Au NPs were squeezed out of the confined gap between two mica surfaces during the loading process, resulting from the repulsive electric-double layer force. In contrast, multilayers of Au NPs were confined between two APTES-mica surfaces because of the attractive double-layer force between oppositely charged Au NPs and APTES-mica. Interestingly, the interaction between Au NPs and APTES-mica is stronger than the interactions between Au NPs, resulting in the rearrangement of the confined Au NPs under shearing. Importantly, a large friction coefficient (µ > 0.7) with unexpected nonlinear stick-slip friction was observed when sliding two APTES-mica surfaces with thin layers of Au NPs (∼20 nm) confined in between. The observed stick-slip motion could be explained by the velocity-dependent friction model where a critical shear velocity was required for transiting from stick-slip to smooth sliding. Our study provides useful information on the assembly and interaction forces of confined nanoparticles on charged surfaces, with implications for predicting the behaviors of NPs under confinement in various engineering applications.

A study on biosafety of HAP ceramic prepared by SLA-3D printing technology directly.

Hydroxyapatite powder was mixed into photosensitive resin to form complex shape scaffold using SLA-3D printing technology, and then the final entity was obtained successively by debinding and sintering. It is crucial to confirm whether the prepared hydroxyapatite scaffold have the toxic effects after our designed printing, debinding, and sintering processes because the photosensitive resin in the starting printing paste is poisonous to cells. To investigate these issues in details, thermogravimetric analysis (TG), differential scanning calorimetry (DSC), in vitro cytotoxicity test, and implantation pre-experiment in the rabbit parietal were performed, aiming to develop the SLA-3D prepared hydroxyapatite scaffold. Through thermal analysis, it was proved that photosensitive resin would be completely pyrolyzed at temperature ranging from 350 °C to 580 °C, corresponding to a secondary chemical reaction mechanism. Combined with cytotoxicity test results, it is unquestionable that the toxic substances would be totally decomposed after debinding process and a good biocompatible HAP samples could be obtained. The finally prepared HAP samples with micro-holes showed good biosafety in pre-experiment of the rabbit parietal implantation.