Yuyan Weng

Tunable dual-stimuli response of a microgel composite consisting of reduced graphene oxide nanoparticles and poly(N-isopropylacrylamide) hydrogel microspheres

A type of photo- and thermo-responsive composite microsphere composed of reduced graphene oxide nanoparticles and poly(N-isopropylacrylamide) (rGO@pNIPAM) is successfully fabricated by a facile solution mixing method. Due to the high optical absorbance and thermal conduction of rGO, the composite microspheres are endowed with the new property of photo-response, in addition to the intrinsic thermally sensitive property of pNIPAM. This new ability undoubtedly enlarges the scope of applications of the microgel spheres. Furthermore, through controlling the rGO content in the composite, the photo- and thermo-sensitivity of the composite can be effectively modulated. That is, with a lower rGO content (≤32% by weight), the composite microspheres perform only thermally induced changes, such as volume contraction (by ∼45% in diameter) and drug release, when crossing the lower critical solution temperature of pNIPAM. With a higher rGO content (∼47.5%), both temperature and light irradiation can trigger changes in the composite. However, when the rGO content is increased to around 64.5%, the thermo-responsivity of the composite disappears, and the spheres exhibit only photo-induced drug release. With a further increase in rGO content, the environmentally responsive ability of the microspheres vanishes.

Controlled Drug Loading and Release of a Stimuli-Responsive Lipogel Consisting of Poly(N-isopropylacrylamide) Particles and Lipids

Environmentally responsive materials are attractive for advance biomedicine applications such as controlled drug delivery and gene therapies. Recently, we have introduced the fabrication of a novel type of stimuli-sensitive lipogel composite consisting of poly(N-isopropylacrylamide) (pNIPAM) microgel particles and lipids. In this study, we demonstrated the temperature-triggered drug release behavior and the tunable drug loading and release capacities of the lipogel. At room temperature (22 °C), no calcein was released from the lipogel over time. At body temperature (37 °C), the release process was significantly promoted; lipids in the lipogel acted as drug holders on the pNIPAM scaffold carrier and prolonged the calcein release process from 10 min to 2 h. Furthermore, the loading and release of calcein could be effectively controlled by modulating the relative amount of lipids incorporated in the lipogel, which can be realized by the salt-induced lipid release of the lipogel.

Glycopolymer-coated iron oxide nanoparticles: shape-controlled synthesis and cellular uptake

Carbohydrates are involved in different cellular recognition events, and glycopolymers with carbohydrate side chains are currently being applied in many fields, with much potential for disease treatment. The aggregation shape has obvious effects on the nanoparticle-cell interaction and is therefore important for the applications of glycopolymers in biological systems. The synthesis of well-defined glyco-nanoparticles, especially non-spherical ones, is challenging work. Herein, iron oxide nanoparticles with different shapes (spindle and cubic-like) were first obtained and used as a core that was coated with dopamine methacrylamide (DMA) via catecholic chemistry for the introduction of vinyl groups. RAFT-synthesized glycopolymers were then conjugated to the DMA-coated iron oxide nanoparticles via a thiol-ene coupling reaction. By combining the convenience of inorganic nanoparticle shape control, biomimic catecholic chemistry, and efficient thiol-ene reaction, glycopolymer-decorated nanoparticles were easily obtained. Glyco-nanoparticles with variable shapes are stable in serum and exhibit shape-dependent cell uptake behaviors as well as enhanced activity toward specific lectins. The fabrication of biologically active non-spherical nanoparticles will be beneficial for both fundamental research on nanoparticle-cell interaction and related applications for disease treatment.

Guiding the behaviors of human umbilical vein endothelial cells with patterned silk fibroin films.

Silk fibroin is an ideal blood vessel substitute due to its advantageous qualities including variable size, good suture retention, low thrombogenicity, non-toxicity, non-immunogenicity, biocompatibility, and controllable biodegradation. In this study, silk fibroin films with a variety of surface patterns (e.g. square wells, round wells plus square pillars, square pillars, and gratings) were prepared for in vitro characterization of human umbilical vein endothelial cells (HUVEC) response. The affects of biomimetic length-scale topographic cues on the cell orientation/elongation, proliferation, and cell-substrate interactions have been investigated. The density of cells is significantly decreased in response to the grating patterns (70±3nm depth, 600±8nm pitch) and the square pillars (333±42nm gap). Most notably, we observed the contact guidance response of filopodia of cells cultured on the surface of round wells plus square pillars. Overall, our data demonstrates that the patterned silk fibroin films have an impact on the behaviors of human umbilical vein endothelial cells.

Photomechanical bending of linear azobenzene polymer

We firstly report a novel strategy for the preparation of rapid and reversible photo-driven actuators consisting of an active linear azobenzene polymer layer and a passive silk fibroin substrate, avoiding the need for oriented azobenzene liquid crystalline elastomers (LCEs) that have been used until now, just through depositing linear azobenzene polymer on the top of silk fibroin film. The unimorph actuators can show uniquely different bending properties. Moreover, the response speed of the unimorph actuator is on the level of a few hundreds of milliseconds. The bending angle can be well controlled either by changing the UV light intensity or by altering the thickness ratio of the two composed layers. Additionally, complex and attractive arm-like movements are successfully achieved. We believe that the proposed unimorph actuators will pave the way for designing complicated and programmed artificial muscles.

Influence of surface chemistry on particle internalization into giant unilamellar vesicles

Cellular uptake of materials plays a key role in their biomedical applications. In this work, based on the cell-mimic giant unilamellar vesicles (GUVs) and a novel type of microscale materials consisting of stimuli-responsive poly(N-isopropylacrylamide) microgel particles and the incorporated lipids, the influence of particle surface chemistry, including hydrophobic/hydrophilic property and lipid decorations, on the adsorption and consequent internalization of particles into GUVs was investigated. It is found that the decoration of particle surface with lipids facilitates the adsorption of particles on GUV membrane. After that, the hydrophobic property of particle surface further triggers the internalization of particles into GUVs. These results demonstrate the importance of surface properties of particles on their interactions with lipid membranes and are helpful to the understanding of cellular uptake mechanism.

Controlled synthesis and self-assembly of dopamine-containing copolymer for honeycomb-like porous hybrid particles.

Dopamine-containing monomers, N-3,4-dihydroxybenzenethyl methacrylamide (DMA) and dimethylaminoethyl methacrylate (DMAEMA), are successfully copolymerized in a well-controlled manner via ambient temperature single-electron transfer initiation and propagation through the radical addition fragmentation chain transfer (SET-RAFT) method. The controlled behaviors of the copolymerization are confirmed by the first-order kinetic plots, the linear relationships between molecular weights, and the monomer conversions while keeping relatively narrow molecular weight distribution (Mw/Mn ≤ 1.45). Moreover, biomimetic self-assembly of poly(N-3,4-dihydroxybenzenethyl methacrylamide-co-dimethylaminoethyl methacrylate) PDMA-co-PDMAEMA and inorganic particles are employed to prepare tunable honeycomb-like porous hybrid particles (HPHPs) by regulating the predesigned chemical composition. In addition, the inorganic sacrificial templates are successfully selective etched for the formation of porous organic materials.

Photoresponsive superhydrophobic surfaces from one-pot solution spin coating mediated by polydopamine

Smart stimuli-responsive superhydrophobic surfaces with reversibly switchable wettability have received considerable attention due to their various potential applications. We demonstrate here a new but versatile approach for preparing photoresponsive superhydrophobic surfaces. Fluorinated azobenzene derivatives or polymers are immobilized onto silica surface by taking advantage of the remarkable adhesive ability of polydopamine. By simply spin coating the silica particles onto silicon wafer, superhydrophobic surfaces can be obtained with a water contact angle greater than 150° and low contact angle hysteresis (<10°). In addition, reversible change water contact angles on the surfaces can occur upon irradiation with alternate UV and visible light.

Reduced graphene oxide directed self-assembly of phospholipid monolayers in liquid and gel phases.

The response of cell membranes to the local physical environment significantly determines many biological processes and the practical applications of biomaterials. A better understanding of the dynamic assembly and environmental response of lipid membranes can help understand these processes and design novel nanomaterials for biomedical applications. The present work demonstrates the directed assembly of lipid monolayers, in both liquid and gel phases, on the surface of a monolayered reduced graphene oxide (rGO). The results from atomic force microscopy indicate that the hydrophobic aromatic plane and the defect holes due to reduction of GO sheets, along with the phase state and planar surface pressure of lipids, corporately determine the morphology and lateral structure of the assembled lipid monolayers. The DOPC molecules, in liquid phase, probably spread over the rGO surface with their tails associating closely with the hydrophobic aromatic plane, and accumulate to form circles of high area surrounding the defect holes on rGO sheets. However, the DPPC molecules, in gel phase, prefer to form a layer of continuous membrane covering the whole rGO sheet including defect holes. The strong association between rGO sheets and lipid tails further influences the melting behavior of lipids. This work reveals a dramatic effect of the local structure and surface property of rGO sheets on the substrate-directed assembly and subsequent phase behavior of the supported lipid membranes.

Encapsulation of Hydrophobic Phthalocyanine with Poly(N-isopropylacrylamide)/Lipid Composite Microspheres for Thermo-Responsive Release and Photodynamic Therapy

Phthalocyanine (Pc) is a type of promising sensitizer molecules for photodynamic therapy (PDT), but its hydrophobicity substantially prevents its applications. In this study, we efficiently encapsulate Pc into poly(N-isopropylacrylamide) (pNIPAM) microgel particles, without or with lipid decoration (i.e., Pc@pNIPAM or Pc@pNIPAM/lipid), to improve its water solubility and prevent aggregation in aqueous medium. The incorporation of lipid molecules significantly enhances the Pc loading efficiency of pNIPAM. These Pc@pNIPAM and Pc@pNIPAM/lipid composite microspheres show thermo-triggered release of Pc and/or lipid due to the phase transition of pNIPAM. Furthermore, in the in vitro experiments, these composite particles work as drug carriers for the hydrophobic Pc to be internalized into HeLa cells. After internalization, the particles show efficient fluorescent imaging and PDT effect. Our work demonstrates promising candidates in promoting the use of hydrophobic drugs including photosensitizers in tumor therapies.