Diels–Alder Click-Based Hydrogels for Direct Spatiotemporal Postpatterning via Photoclick Chemistry

Click chemistry not only has been applied to the design of hydrogel scaffolds for 3D cell culture, but also is an efficient way for hydrogel postfunctionalization and spatiotemporal patterning. To the best of our knowledge, only azide–alkyne cycloaddition (SPAAC) has been exploited by combining photoinitiated thiol–ene click reaction to realize the 3D patterning of hydrogels. In this work, the cyclohexene derivative, which “clicked” by functional groups between furyl and maleimide, were successfully functionalized by thiol-modified molecules or peptides through thiol–ene click reaction. It illustrates a hydrogel that formed via Diels–Alder (DA) click chemistry between furyl-modified hyaluronic acid and bimaleimide functional PEG molecule can be allowed for the directly photoactivated thiol–ene chemistry for hydrogel spatiotemporal patterning. Since the cyclohexene derivatives produced by DA reaction can be employed in all subsequent 3D network patterning by using photoclick reactions, it suggests a new way to design and postfunctionalize all of the DA click-based hydrogels with specific regional bioactive cues

4D Printing of Robust Hydrogels Consisted of Agarose Nanofibers and Polyacrylamide

Hydrogels combined with complex 3D shapes and robust mechanical properties are extremely desired soft platforms in the fields of biomaterials, recently, 4D printing has been developed to be further shaped to form required patterns. On the basis of the excellent thixotropy of Laponite and the thermal-reversible sol–gel transition of agarose and easy formation of nanofibers below 35 °C, a 4D printing hydrogel (4D Gel) was fabricated by in situ polymerizing acrylamide in the agarose matrix containing Laponite. The experimental results demonstrated that Laponite played an important role in the improvement of 4D printing, such as endowing the ink with shear-thinning behavior to extrude easily and excellent shape stability after printing. The mechanical properties of 4D Gel were unexpectedly higher than those of both agarose and polyacrylamide hydrogels. The 4D Gel showed the ability to further transform its shapes, and was used successfully to construct a whalelike hydrogel, which opened mouth and cocked tail by treating with an external force and then cooling, as well as the octopus like hydrogel with waved tentacles to seem to “come alive”. This work opened a new avenue for creating more complex architectures than 3D with excellent properties, which is important in the macromolecule fields for the wide applications

Effective Cell and Particle Sorting and Separation in Screen-Printed Continuous-Flow Microfluidic Devices with 3D Sidewall Electrodes

In recent years, microfluidic dielectrophoresis (DEP) devices, as one of the most promising tools for cell and particle sorting and separation, are facing the bottleneck in the development of practical products due to the high-cost yet low-yield device manufacturing via traditional microelectromechanical systems (MEMS) and the challenge of maintaining the cell viability during DEP treatment. In this paper, we demonstrate a facile, low-cost, and high-throughput method of constructing continuous-flow microfluidic DEP devices via screen-printing technology. The new device configuration and operation strategy not only facilitate cell and particle sorting and separation using 3D electrodes as sidewalls of microchannel but also improve cell viability by reducing the exposure time of cells to high electrical-field gradients. Furthermore, we propose and validate a semiempirical formula with which to simplify the complicated calculation and plotting of DEP spectra. As a consequence, the optimal DEP parameters and crossover frequencies can be obtained directly using our devices instead of typical electrorotation method. To evaluate the performance of a screen-printed continuous flow microfluidic DEP device, a suspension containing polystyrene (PS) microspheres and erythrocytes is used as the biosample. Our results show that a high sorting efficiency (ca. 93%) with a high cell viability (hemolysis ratio of <4.8%) can be achieved, indicating the excellent performance and promising application of such devices for cell and particle sorting and separation

Scatter plot of the modified ERR_{<i>radon</i>, <i>i</i>} versus the original ERR_{<i>radon</i>, <i>i</i>} in each cohort.

<p>Scatter plot of the modified ERR_{<i>radon</i>, <i>i</i>} versus the original ERR_{<i>radon</i>, <i>i</i>} in each cohort.</p

Modified EPA’s estimates of the lifetime lung cancer risks at various indoor radon exposure levels compared to EPA’s original estimate.

<p>Modified EPA’s estimates of the lifetime lung cancer risks at various indoor radon exposure levels compared to EPA’s original estimate.</p

Multifunctional Hydrogel with Good Structure Integrity, Self-Healing, and Tissue-Adhesive Property Formed by Combining Diels–Alder Click Reaction and Acylhydrazone Bond

Hydrogel, as a good cartilage tissue-engineered scaffold, not only has to possess robust mechanical property but also has to have an intrinsic self-healing property to integrate itself or the surrounding host cartilage. In this work a double cross-linked network (DN) was designed and prepared by combining Diels–Alder click reaction and acylhydrazone bond. The DA reaction maintained the hydrogel’s structural integrity and mechanical strength in physiological environment, while the dynamic covalent acylhydrazone bond resulted in hydrogel’s self-healing property and controlled the on–off switch of network cross-link density. At the same time, the aldehyde groups contained in hydrogel further promote good integration of the hydrogel to surrounding tissue based on aldehyde-amine Schiff-base reaction. This kind of hydrogel has good structural integrity, autonomous self-healing, and tissue-adhesive property and simultaneously will have a good application in tissue engineering and tissue repair field

Enhancement of Enzymatic Activity Using Microfabricated Poly(ε-caprolactone)/Silica Hybrid Microspheres with Hierarchically Porous Architecture

In this paper, we present a novel and facile microfluidic method to fabricate hierarchically porous poly­(ε-caprolactone)/silica hybrid microspheres and further investigate in detail their performance as enzyme carriers by three famous proteins and enzymes. Because of the synergy effect between sol–gel process and solvent extraction in microdroplets, hierarchically porous architecture can be formed in situ without the use of porogens and templates. More importantly, the surface porosity or the specific surface area of such microspheres can be precisely tuned via adjusting the hydrolysis/condensation rate by ammonia catalyst and thus the competition between the two above-mentioned processes. Fluorescein isothiocyanate-bovine serum albumin, alcohol dehydrogenase, and superoxide dismutase are immobilized via either physical adsorption or covalent binding to evaluate the performance of hierarchically porous microspheres as enzyme carriers. All the qualitative and quantitative data including fluorescence images, enzymatic activity, immobilization yield, and activity yield prove that enzymes covalently immobilized on hierarchically porous microspheres exhibit the optimal immobilization capacity, enzymatic activity, stability, and reusability, which shows very promising application of such microspheres in enzymatic catalysis

Quantitative Evaluation of Biological Reaction Kinetics in Confined Nanospaces

Evaluating the kinetics of biological reaction occurring in confined nanospaces is of great significance in studying the molecular biological processes in vivo. Herein, we developed a nanochannel-based electrochemical reactor and a kinetic model to investigate the immunological reaction in confined nanochannels simply by the electrochemical method. As a result, except for the reaction kinetic constant that was previously studied, more insightful kinetic information such as the moving speed of the antibody and the immunological reaction progress in nanochannels were successfully revealed in a quantitative way for the first time. This study would not only pave the investigation of molecular biological processes in confined nanospaces but also be promising to extend to other fields such as biological detection and clinical diagnosis

Patterning Multi-Nanostructured Poly(l‑lactic acid) Fibrous Matrices to Manipulate Biomolecule Distribution and Functions

Precise manipulation of biomolecule distribution and functions via biomolecule–matrix interaction is very important and challenging for tissue engineering and regenerative medicine. As a well-known biomimetic matrix, electrospun fibers often lack the unique spatial complexity compared to their natural counterparts in vivo and thus cannot deliver fully the regulatory cues to biomolecules. In this paper, we report a facile and reliable method to fabricate micro- and nanostructured poly­(l-lactic acid) (PLLA) fibrous matrices with spatial complexity by a combination of advanced electrospinning and agarose hydrogel stamp-based micropatterning. Specifically, advanced electrospinning is used to construct multi-nanostructures of fibrous matrices while solvent-loaded agarose hydrogel stamps are used to create microstructures. Compared with other methods, our method shows extreme simplicity and flexibility originated from the mono-/multi-spinneret conversion and limitless micropatterns of agarose hydrogel stamps. Three types of PLLA fibrous matrices including patterned nano-Ag/PLLA hybrid fibers, patterned bicompartment polyethylene terephthalate/PLLA fibers, and patterned hollow PLLA fibers are fabricated and their capability to manipulate biomolecule distribution and functions, that is, bacterial distribution and antibacterial performance, cell patterning and adhesion/spreading behaviors, and protein adsorption and delivery, is demonstrated in detail. The method described in our paper provides a powerful tool to restore spatial complexity in biomimetic matrices and would have promising applications in the field of biomedical engineering

miR-29b-Loaded Gold Nanoparticles Targeting to the Endoplasmic Reticulum for Synergistic Promotion of Osteogenic Differentiation

Precise control of stem cells, such as human bone marrow-derived mesenchymal stem cells (hMSCs), is critical for the development of effective cellular therapies for tissue engineering and regeneration medicine. Emerging evidence suggests that several miRNAs act as key regulators of diverse biological processes, including differentiation of various stem cells. In this study, we have described a delivery system for miR-29b using PEI-capped gold nanoparticles (AuNPs) to synergistically promote osteoblastic differentiation. The cell proliferation assay revealed that AuNPs and AuNPs/miR-29b exert negligible cytotoxicity to hMSCs and MC3T3-E1 cells. With the assistance of AuNPs as a delivery vector, miR-29b could efficiently enter the cytoplasm and regulate osteogenesis. AuNPs/miR-29b more effectively promoted osteoblast differentiation and mineralization through induced the expression of osteogenesis genes (RUNX2, OPN, OCN, ALP) for the long-term, compared to the widely used commercial transfection reagent, Lipofectamine. With no obvious cytotoxicity, PEI-capped AuNPs showed great potential as an adequate miRNA vector for osteogenesis differentiation. Interestingly, we observed loading of AuNPs as well as AuNPs/miR-29b into the lumen of the endoplasmic reticulum (ER). Our findings collectively suggest that AuNPs, together with miR-29b, exert a synergistic promotory effect on osteogenic differentiation of hMSCs and MC3T3-E1 cells