Jianhai Yang

Nano-carrier for gene delivery and bioimaging based on carbon dots with PEI-passivation enhanced fluorescence.

Polyethylenimine (PEI) functionalized carbon dots (CD-PEI) were fabricated by one-step microwave assisted pyrolysis of glycerol and branched PEI25k mixture where the formation of carbon nanoparticles and the surface passivation were accomplished simultaneously. In this hybrid C-dot, PEI molecule played two key roles in the system - as a nitrogen-rich compound to passivate surface to enhance the fluorescence and as a polyelectrolyte to condense DNA. This CD-PEI was shown to be water soluble and emit stable bright multicolor fluorescence relying on excitation wavelength. The DNA condensation capability and cytotoxicity of CD-PEI could be regulated by pyrolysis time possibly due to the somewhat destruction of PEI during the formation of carbon dots. CD-PEI obtained at an appropriate pyrolysis time exhibited lower toxicity, higher or comparable gene expression of plasmid DNA in COS-7 cells and HepG2 cells relative to control PEI25k. Intriguingly, the CD-PEIs internalized into cells displayed tunable fluorescent emission under varying excitation wavelength, suggesting the potential application of CD-PEI in gene delivery and bioimaging.

Strengthening Alginate/Polyacrylamide Hydrogels Using Various Multivalent Cations

We successfully synthesized a family of alginate/polyacrylamide hydrogels using various multivalent cations. These hydrogels exhibit exceptional mechanical properties. In particular, we discovered that the hydrogels cross-linked by trivalent cations are much stronger than those cross-linked by divalent cations. We demonstrate stretchability and toughness of the hydrogels by inflating a hydrogel sheet into a large balloon, and the elasticity by using a hydrogel block as a vibration isolator in a forced vibration test. The excellent mechanical properties of these hydrogels may open up applications for hydrogels.

Tough Al-alginate/Poly(N-isopropylacrylamide) Hydrogel with Tunable LCST for Soft Robotics

Tough Al-alginate/poly(N-isopropylacrylamide) (PNIPAM) hydrogel has been synthesized by introducing an interpenetrating network with hybrid physically cross-linked alginate and chemically cross-linked PNIPAM. Varying the concentration of AlCl3 regulates the mechanical properties of the tough hydrogel and tunes its lower critical solution temperature (LCST) as well. The tough Al-alginate/PNIPAM exhibits 6.3 ± 0.3 MPa of compressive stress and 9.95 of uniaxial stretch. Tunability of LCST is also achieved in a wide range within 22.5-32 °C. A bending beam actuator and a four-arm gripper made of bilayer (Na-alginate/PNIPAM)/(Al-alginate/PNIPAM) hydrogel as prototype of all-hydrogel soft robotics are demonstrated. A finite element (FE) simulation model is developed to simulate the deformation of the soft robotics. The FE simulation not only reproduces the deformation process of performed experiments but also predicts more complicated devices that can be explored in the future. This work broadens the application of temperature-responsive PNIPAM-based hydrogels.

Highly Stretchable and Transparent Ionogels as Nonvolatile Conductors for Dielectric Elastomer Transducers

Large deformation of soft materials is harnessed to provide functions in the nascent field of soft machines. This paper describes a new class of systems enabled by highly stretchable, transparent, stable ionogels. We synthesize an ionogel by polymerizing acrylic acid in ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([C2mim][EtSO4]). The ionogel exhibits desired attributes of adequate conductivity (0.22 S m(-1)), low elastic modulus (∼3 kPa), large rupturing stretch (∼4.6), and negligible hysteresis and degradation after cyclic stretches of large amplitude. Using the ionogel and a dielectric elastomer, we fabricate electromechanical transducers that achieve a voltage-induced areal strain of 140%. The ionogel is somewhat hygroscopic, but the transducers remain stable after a million cycles of excitation in a dry oven and in air. The transparency of the ionogels enable the transducers with conductors placed in the path of light, and the nonvolatility of the ionogels enable the transducers to be used in open air.

Enhanced Therapeutic siRNA to Tumor Cells by a pH-Sensitive Agmatine–Chitosan Bioconjugate

Charge-conversional naturally occurring chitosan-agmatine bioconjugates are prepared by dimethylmaleic anhydride (DMA) modification and the nucleophilic reaction between tosyl of tosylated chitosan and primary amine of agmatine. These bioconjugates (CS-DM-Agm) are shown to condense siRNA into nanocomplexes, which are stable in the presence of serum at physical pH values. Furthermore, the surface charge of complexes can tune from negative to positive while pH is changed to weak acid tumor micromilieu, thus facilitating the target cancer cell internalization in resisting serum adsorption. More importantly, this smart biogenic system shows remarkable gene silencing efficiency and a high apoptotic rate of tumor cells both in vitro and in vivo, indicating its great potential for cancer therapy.

Tough photoluminescent hydrogels doped with lanthanide.

Photoluminescent hydrogels have emerged as novel soft materials with potential applications in many fields. Although many photoluminescent hydrogels have been fabricated, their scope of usage has been severely limited by their poor mechanical performance. Here, a facile strategy is reported for preparing lanthanide (Ln)-alginate/polyacrylamide (PAAm) hydrogels with both high toughness and photoluminescence, which has been achieved by doping Ln(3+) ions (Ln = Eu, Tb, Eu/Tb) into alginate/PAAm hydrogel networks, where Ln(3+) ions serve as both photoluminescent emitters and physical cross-linkers. The resulting hydrogels exhibit versatile advantages including excellent mechanical properties (∼ MPa strength, ≈ 20 tensile strains, ≈ 10(4) kJ m(-3) energy dissipation), good photoluminescent performance, tunable emission color, excellent processability, and cytocompatibility. The developed tough photoluminescent hydrogels hold great promises for expanding the usage scope of hydrogels.

Exceptionally tough and notch-insensitive magnetic hydrogels

Most existing magnetic hydrogels are weak and brittle. The development of strong and tough magnetic hydrogels would extend their applications into uncultivated areas, such as in actuators for soft machines and guided catheters for magnetic navigation systems, which is still a big challenge. Here a facile and versatile approach to fabricating highly stretchable, exceptionally tough and notch-insensitive magnetic hydrogels, Fe(3)O(4)@Fe-alginate/polyacrylamide (PAAm), is developed, by dispersing alginate-coated Fe(3)O(4) nanoparticles into the interpenetrating polymer networks of alginate and PAAm, with hybrid physical and chemical crosslinks. A cantilever bending beam actuator as well as a proof-of-concept magnetically guided hydrogel catheter is demonstrated. The method proposed in this work can be integrated into other strong and tough magnetic hydrogels for the development of novel hydrogel nanocomposites with both desirable functionality and superior mechanical properties.

ZnO quantum dots-embedded collagen/polyanion composite hydrogels with integrated functions of degradation tracking/inhibition and gene delivery

A collagen/poly(2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt) (collagen/PNaAMPS) interpenetrating polymer network (IPN) hydrogel was prepared by simultaneous reaction of EDC/NHS-mediated crosslinking of concentrated collagen solution and poly(ethylene glycol) diacrylate crosslinking NaAMPS in a sealed syringe. The collagen/PNaAMPS hydrogels were freeze-dried and immersed in an aqueous solution of PDMAEMA-capped ZnO quantum dots (QDs) to construct a ZnO QDs-laden collagen/PNaAMPS IPN hydrogel. The composite hydrogel containing nearly 90% water exhibited light transmission from 85% to 96%. Introducing the PNaAMPS network considerably improved the mechanical strength of the pristine collagen gel, whereas loading ZnO QDs only slightly affected the optical properties, mechanical properties and water absorption. Strikingly, the loaded ZnO QDs were found to serve dual roles – tracking the degradation of collagen by observing directly the reduction of fluorescence intensity in hydrogels; and as a collagenase inhibitor by the proposed interaction with metalloenzyme, an important characteristic which could be used to prolong the degradation time of pure collagen without physical screening of the IPN network. We also demonstrated that anionic PNaAMPS was able to dampen the cytotoxicity of composite hydrogels by neutralizing positive charges of ZnO QDs. The composite hydrogels carrying rabbit corneal anterior stromal fibroblasts and PolyJet™/DNA complexes could achieve the efficient expression of luciferase and EGFP genes. The model composite hydrogels offer an approach to design a novel corneal substitute with integrated functions of real-time degradation tracking, degradation inhibition and gene delivery for the specific treatment of ophthalmic diseases.

Combining magnetic field/temperature dual stimuli to significantly enhance gene transfection of nonviral vectors

Monodisperse magnetic nanoparticles (MNPs) were prepared through an organic phase process, and the obtained MNPs were capped with poly[2-(2-methoxyethoxy)ethyl methacrylate]-b-poly[2-(dimethylamino)ethyl methacrylate] synthesized by surface-initiated atom transfer radical polymerization (ATRP). The MNPs-polymer brushes exhibited both superparamagnetic and thermoresponsive behaviors, and could condense plasmid DNA into nanocomplexes with a size of 100-120 nm at appropriate complexing ratios. Enhanced gene expression in COS-7 cells and HepG-2 cells was achieved under a magnetic field and variable temperature conditions due to magnetic force-facilitated internalization of nanocomplexes, and temporary cooling-triggered intracellular gene unpacking. Amazingly, combining magnetic field and temperature dual stimuli contributed to a 50-100- and 25-45-fold increase of the transfection efficiency in HepG-2 cells compared to conventional protocol and PEI25k, respectively.

Dual-Physical Cross-Linked Tough and Photoluminescent Hydrogels with Good Biocompatibility and Antibacterial Activity

Development of novel photoluminescent hydrogels with toughness, biocompatibility, and antibiosis is important for the applications in biomedical field. Herein, novel tough photoluminescent lanthanide (Ln)-alginate/poly(vinyl alcohol) (PVA) hydrogels with the properties of biocompatibility and antibiosis have been facilely synthesized by introducing hydrogen bonds and coordination bonds into the interpenetrating networks of Na-alginate and PVA, via approaches of frozen-thawing and ion-exchanging. The resultant hydrogels exhibit high mechanical strength (0.6 MPa tensile strength, 5.0 tensile strain, 6.0 MPa compressive strength, and 900 kJ m-3 energy dissipation under 400% stretch), good photoluminescence as well as biocompatibility and antibacterial activity. The design strategy provides a new avenue for the fabrication of multifunctional photoluminescent hydrogels based on biocompatible polymers.