Yuan Liu

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.

Preparation of aligned porous gelatin scaffolds by unidirectional freeze-drying method

Porous gelatin scaffolds with microtubule orientation structure were manufactured by unidirectional freeze-drying technology, and their porous structure was characterized by scanning electron microscopy. Scaffolds with tunable pore size and high porosity up to 98% were obtained by adjusting the concentration of the gelatin solution and crosslinking agent during the preparation process. All the porous gelatin scaffolds exhibited oriented microtubule pores, with width and length from 50 to 100 microm and 100 to 500 microm, respectively. Meanwhile, the properties of the scaffolds, such as porosity, water adsorption ability and compressive strength, were studied. In vitro enzymatic degradation results showed that the absolute weight loss of the gelatin scaffolds exhibited an increasing trend from low to high gelatin concentration used to prepare gelatin scaffolds; in vitro cell culture results indicated that the porous gelatin scaffolds were non-toxic to cartilage cells, since the cells spread and grew well.

Injectable Dopamine-Modified Poly(ethylene glycol) Nanocomposite Hydrogel with Enhanced Adhesive Property and Bioactivity

A synthetic mimic of mussel adhesive protein, dopamine-modified four-armed poly(ethylene glycol) (PEG-D4), was combined with a synthetic nanosilicate, Laponite (Na0.7+(Mg5.5Li0.3Si8)O20(OH)4)0.7–), to form an injectable naoncomposite tissue adhesive hydrogel. Incorporation of up to 2 wt % Laponite significantly reduced the cure time while enhancing the bulk mechanical and adhesive properties of the adhesive due to strong interfacial binding between dopamine and Laponite. The addition of Laponite did not alter the degradation rate and cytocompatibility of PEG-D4 adhesive. On the basis of subcutaneous implantation in rat, PEG-D4 nanocomposite hydrogels elicited minimal inflammatory response and exhibited an enhanced level of cellular infiltration as compared to Laponite-free samples. The addition of Laponite is potentially a simple and effective method for promoting bioactivity in a bioinert, synthetic PEG-based adhesive while simultaneously enhancing its mechanical and adhesive properties.

Mesoporous anatase TiO2 nanocups with plasmonic metal decoration for highly active visible-light photocatalysis

This communication describes a method for facile synthesis of mesoporous anatase TiO2 nanocup crystals. The novel cuplike morphology of TiO2 decorated with gold (Au-TiO2) yields remarkably high photocatalytic activity for degradation of methylene blue under visible light irradiation.

Zinc ion uniquely induced triple shape memory effect of dipole-dipole reinforced ultra-high strength hydrogels.

In this study, we demonstrate that dipole-dipole interaction can be employed to not only tremendously enhance the mechanical properties of hydrogel, but also impart the gel to an amazing ability to memorize two temporary shapes. Cross-linked hydrogels synthesized by copolymerization of acrylonitrile, a dipole-dipole containing monomer and hydrophilic comonomer are shown to exhibit triple shape memory (SM) triggered by the dynamic association and dissociation of dipole-dipole pairing between cynao groups uniquely responding to zinc ion species and concentration. This approach contributes to design and fabrication of novel SM hydrogels in a distinct way from conventional SM materials.

Construction of an ultrahigh strength hydrogel with excellent fatigue resistance based on strong dipole-dipole interaction†

A high strength hydrogel was fabricated by one-step copolymerization of dipole–dipole interaction-containing monomer, acrylonitrile, super-hydrophilic comonomer, 2-methacryloyloxyethyl phosphorylcholine and crosslinker, polyethylene glycol diacrylate (Mn = 575, PEGDA575). This dipole–dipole reinforced (DDR) hydrogel demonstrated intriguing combinations of properties such as withstanding several MPa tensile stress, tens of MPa compressive strength, excellent fatigue resistance and no yielding during tensile tests. The equilibrium water content and transparency of DDR hydrogels could be tuned by varying monomer concentration and monomer ratio. The gels exhibited low cytotoxicity and antifouling characteristic. Biodegradable high strength hydrogel could also be constructed by merely replacing PEGDA575 with bioreducible crosslinker. The method reported here offers a general strategy to design biocompatible high-strength hydrogels for tissue engineering scaffolds by copolymerizing monomer containing dipole–dipole pairing with other hydrophilic monomer.

Effect of pH on the Rate of Curing and Bioadhesive Properties of Dopamine Functionalized Poly(ethylene glycol) Hydrogels

The remarkable underwater adhesion strategy employed by mussels has inspired bioadhesives that have demonstrated promise in connective tissue repair, wound closure, and local delivery of therapeutic cells and drugs. While the pH of oxygenated blood and internal tissues is typically around 7.4, skin and tumor tissues are significantly more acidic. Additionally, blood loss during surgery and ischemia can lead to dysoxia, which lowers pH levels of internal tissues and organs. Using 4-armed PEG end-capped with dopamine (PEG-D) as a model adhesive polymer, the effect of pH on the rate of intermolecular cross-linking and adhesion to biological substrates of catechol-containing adhesives was determined. Adhesive formulated at an acidic pH (pH 5.7–6.7) demonstrated reduced curing rate, mechanical properties, and adhesive performance to pericardium tissues. Although a faster curing rate was observed at pH 8, these adhesives also demonstrated reduced mechanical and bioadhesive properties when compared to adhesives buffered at pH 7.4. Adhesives formulated at pH 7.4 demonstrated a good balance of fast curing rate, elevated mechanical properties and interfacial binding ability. UV–vis spectroscopy evaluation revealed that the stability of the transient oxidation intermediate of dopamine was increased under acidic conditions, which likely reduced the rate of intermolecular cross-linking and bulk cohesive properties for hydrogels formulated at these pH levels. At pH 8, competing cross-linking reaction mechanisms and reduced concentration of dopamine catechol due to auto-oxidation likely reduced the degree of dopamine polymerization and adhesive strength for these hydrogels. pH plays an important role in the adhesive performance of mussel-inspired bioadhesives and the pH of the adhesive formulation needs to be adjusted for the intended application.

Fibrin Gel as an Injectable Biodegradable Scaffold and Cell Carrier for Tissue Engineering

Due to the increasing needs for organ transplantation and a universal shortage of donated tissues, tissue engineering emerges as a useful approach to engineer functional tissues. Although different synthetic materials have been used to fabricate tissue engineering scaffolds, they have many limitations such as the biocompatibility concerns, the inability to support cell attachment, and undesirable degradation rate. Fibrin gel, a biopolymeric material, provides numerous advantages over synthetic materials in functioning as a tissue engineering scaffold and a cell carrier. Fibrin gel exhibits excellent biocompatibility, promotes cell attachment, and can degrade in a controllable manner. Additionally, fibrin gel mimics the natural blood-clotting process and self-assembles into a polymer network. The ability for fibrin to cure in situ has been exploited to develop injectable scaffolds for the repair of damaged cardiac and cartilage tissues. Additionally, fibrin gel has been utilized as a cell carrier to protect cells from the forces during the application and cell delivery processes while enhancing the cell viability and tissue regeneration. Here, we review the recent advancement in developing fibrin-based biomaterials for the development of injectable tissue engineering scaffold and cell carriers.

The biocompatibility of fatty acid modified dextran-agmatine bioconjugate gene delivery vector

A lauric acid modified dextran-agmatine bioconjugate (Dex-L-Agm) was prepared by 1,1-carbonyldiimidazole (CDI) activation and the nucleophilic reaction between tosyl of tosylated dextran and primary amine of agmatine. Dextran-agmatine bioconjugates (Dex-Agm) were capable of condensing DNA into nanocomplexes, and combining lauric acid promoted the complexation with DNA supposedly due to the cooperative binding effect attributed to hydrophobic interaction. Higher degree substitution of agmatine and hydrophobic grafting resulted in increased luciferase activities expressed in COS-7 and HEK293 cells; Semiquantitative assay of GFP expression by flow cytometry in COS-7, HEK293 and CHOK1 cells further demonstrated that conjugation of fatty acid could remarkably increase gene transfection of Dex-Agm in spite of 1.1-2.3-fold lower efficiency compared to Exgen 500. The biocompatibilities of Dex-Agm and Dex-L-Agm were assessed in detail by hemolytic activity determination, red blood cell aggregation assay as well as MTT evaluation of degraded products. Dex-Agm and Dex-L-Agm were shown to be highly cytocompatible without causing hemolysis and red blood cell aggregation presumably owing to the bidentate hydrogen bonding of guanidine with the constituents present in cell membrane rather than electrostatic interactions alone which could cause cell damage. Importantly, cells cultured with the degraded products of Dex-Agm and Dex-L-Agm retained more than 80% viability, suggest their potential application as a gene delivery vector.

N-doped Ag/TiO2 hollow spheres for highly efficient photocatalysis under visible-light irradiation

This paper describes the synthesis of TiO2 hollow spheres (HSs) modified via nitrogen doping and silver loading (Ag–N–TiO2) with particle diameters of ~100 nm. The specific surface area of the Ag–N–TiO2 was up to 147 m2 g−1 and this structure is stable upon high temperature treatment. Ag–N–TiO2 exhibited excellent photocatalytic activity for the degradation of dye compounds under visible light irradiation (≥410 nm) due to their larger surface area and controlled morphology compared with previously reported N-doped TiO2 fine particles (e.g. N–P25).