Wulin Zhu

Fish scale inspired design of underwater superoleophobic microcone arrays by sucrose solution assisted femtosecond laser irradiation for multifunctional liquid manipulation

The preparation of superhydrophilic/superoleophilic/underwater superoleophobic surfaces is inspired by natural surfaces such as fish scales possessing hierarchical micro/nanostructures. In this paper, we report the assembly of self-organized hierarchical microcone arrays on a nickel surface by sucrose solution-assisted femtosecond laser irradiation. The processed surface is superhydrophilic (13.47°–4.01°), superoleophilic (7.45°–3.73°), and underwater superoleophobic (135.22°–166.16°) which are comparable to those of fish scales. The wettabilities of the processed surfaces are tunable by adjusting the mass ratio of sucrose to water and pulse energy to control the height (1.62–10.34 μm) and size (2.1–2.81 μm) of the microcones. Multifunctional liquid manipulation such as microdroplet transferring, static and dynamic storage, liquid transportation and mixing is demonstrated. Our proposed method features rapidness, simplicity and ease of large-area fabrication, which may find broader applications in many fields such as microfluidic devices, fluid microreactors, biomedicine, biomedical scaffolds, and chemical–biological sensors.

Multifunctional ultrathin aluminum foil: oil/water separation and particle filtration

We present here a kind of novel multifunctional ultrathin aluminum foil which consists of large-area regular micropore arrays covered with nanostructures. These multiscale micro/nanostructures show underwater superoleophobic ability (contact angle > 150°) and oil/water separation function. The novel foils were realized by one-step femtosecond laser irradiation, which is a simple and promising method for preparing special micro/nanostructures due to its high precision, excellent controllability, one-step processing and compatible with various materials. In addition, the micropore arrayed aluminum foil also shows robust filtering performance for particles with different sizes, exhibiting multifunctional applications. This work provides a new way for the construction of aluminum foil-based micropore arrays which can be applied in high-efficiency oil/water separation, particle sorting, and other broader fields.

Three-level cobblestone-like TiO2 micro/nanocones for dual-responsive water/oil reversible wetting without fluorination

In this work, a kind of three-level cobblestone-like anatase TiO2 microcone array was fabricated on titanium sheets by femtosecond laser-induced self-assembly. This three level structure consisted of cobblestone-like features (15–25 μm in height and 20–35 μm in diameter), ∼460 nm ripple-like features, and smaller particles (10–500 nm). The formation of microcone arrays can be ascribed to the interaction of alternant laser beam ablation. TiO2 surfaces display dual-responsive water/oil reversible wetting via heat treatment and selective UV irradiation without fluorination. It is indicated that three-level scale surface roughness can amplify the wetting character of the Ti surface, and the mechanism for reversible switching between extreme wettabilities is caused by the conversion between Ti-OH and Ti-O. Moreover, the double-faced superhydrophobic and double-faced superhydrophilic Ti samples were constructed, which exhibited stable superhydrophobicity and underwater superoleophobicity in water-oil solution, ...

One-step facile fabrication of controllable microcone and micromolar silicon arrays with tunable wettability by liquid-assisted femtosecond laser irradiation

Micro/nanostructured silicon surfaces are attracting more and more research attention because of the wide range of applications in optoelectronic devices, microelectronics, microfluidics, and biomedical devices. Despite numerous efforts for fabricating a variety of micro/nanostructures, a one-step, facile and effective method for preparing diverse, three-dimensional micro/nanostructures is still desired. In this paper, a new approach based on liquid (ethanol and sucrose solution) assisted femtosecond laser irradiation on silicon substrates was proposed for the preparation of controllable microcones and micromolars arrays. Their height can be controlled from 3.3 to 17.6 μm for microcones and 5.9∼33.7 μm for micromolars by adjusting the pulse energy. The processed surfaces are superhydrophilic (25.05∼2.46°), superoleophilic (7.22∼0°), and underwater superoleophobic (124.9∼169.2°). The surfaces further demonstrate many distinct functions such as fog collecting and volatilizing, droplet storage and transportation, and liquid directional transfer. Our proposed method features rapidness, simplicity and easiness of large-area fabrication, which may find enormous potential applications in many fields such as microfluidic devices, fluid microreactors, biomedicine, and chemical–biological sensors.

Direct cellular organization with ring-shaped composite polymers and glass substrates for urethral sphincter tissue engineering

Although fundamental efforts have been made to engineer circular smooth muscle layers in vitro, engineering structured skeletal muscle tissue equivalents acting as sphincters remains to be investigated. Groove patterned substrates made of homogeneous materials usually lead to cell monolayers instead of patterned cell sheets while patterned matrices failed to generate circular myotubes because cell chirality blocks the end-to-end cellular sequence corresponding to pattern directions. In this paper, we proposed concentric circular and elliptical microgroove patterned substrates with glass substrates as grooves and polymers as ridges to direct ring-shaped myoblast patterns and maximize cell alignment with respect to constraint directions, which are essential for circular myotube generation towards sphincter tissue engineering. Our results showed that our substrates direct myoblasts to proliferate in and orient along the directions of glass grooves, leading to a higher cell alignment degree than homogeneous substrates can achieve. We also found that the cell alignment degree depends on dimensions and parallelism rather than the curvature of the constraint. On the basis of these findings, we proposed finite element models that quantitatively account for our experimental data and emphasized the role of intercellular forces in cell alignment modulation. These results suggest that narrow curved constraints with parallel boundaries can favourably maximize myoblast alignment and facilitate myogenic differentiation regardless of constraint curvature, which will underpin the design of substrates and scaffolds for urethral sphincter or other hollow tissue engineering applications.

A combustion method to synthesize nanoporous graphene

In this paper, we introduce a combustion method which is rapid, low cost, mass-producing and environmentally friendly to produce nanoporous graphene. After loading a graphene oxide aerogel (GOA)/paper (GOP) on a preheated hot plate (as the heat source, with a temperature as low as 200 °C) under an ambient environment, in a few seconds, the GOA/GOP would self-combust and change into reduced graphene oxide (RGO) with nanopores mainly concentrated in the 0.4–2.0 nm range and a large specific surface area of 536 m2 g−1. Supercapacitors fabricated with the synthesized porous RGO (P-RGO) showed a high specific capacitance of 245 F g−1 at 0.1 A g−1, and a retention rate of about 96.9% after 12 000 cycle tests with respect to the initial specific capacitance with a scan rate of 10.0 A g−1. The production yield of this method was as high as 77.0%.

Mechanical-Tunable Capillary-Force-Driven Self-Assembled Hierarchical Structures on Soft Substrate

Capillary-force-driven self-assembly (CFSA) has been combined with many top-down fabrication methods to be alternatives to conventional single micro/nano manufacturing techniques for constructing complicated micro/nanostructures. However, most CFSA structures are fabricated on a rigid substrate, and little attention is paid to the tuning of CFSA, which means that the pattern of structures cannot be regulated once they are manufactured. Here, by combining femtosecond laser direct writing with CFSA, a flexible method is proposed to fabricate self-assembled hierarchical structures on a soft substrate. Then, the tuning of the self-assembly process is realized with a mechanical-stretching strategy. With this method, different patterns of tunable self-assembled structures are obtained before tuning and after release, which is difficult to achieve with other techniques. In addition, as a proof-of-concept application, this mechanical tunable self-assembly of microstructures on a soft substrate is used for smart displays and versatile micro-object trapping.

Stress stiffened silicon nitride micro bridges array as substrate with tunable stiffness for cell culture

Recently, interactions between one-dimensional structural stiffness of physical micro environments and cell biological process have been widely studied. However in previous studies, the influence of structural stiffness on biological process was coupled with the influence of micro fiber curvature. Therefore decoupling the influences of fiber curvature and structural stiffness on cell biological process is of prime importance. In this study, we proposed a novel cell culture substrate comprised of silicon nitride bridges whose structure stiffness can be regulated by altering the axial residual stress without changing material and geometry properties. Both theoretical calculations and finite element simulations were performed to study the influence of residual stress on structure stiffness of bridges. Then multi-positions AFM bending tests were implemented to measure local stiffness of a single micro bridge so as to verify our predictions. NIH/3T3 mouse fibroblast cells were cultured on our substrates to examine the feasibility of the substrate application for investigating cellular response to microenvironment with variable stiffness. The results showed that cells on the edge region near bridge ends were more spread, elongated and better aligned along the bridge axial direction than those on the bridge center region. The results suggest that cells can sense and respond to the differences of stiffness and stiffness gradient between the edge and the center region of the bridges, which makes this kind of substrates can be applied in some biomedical fields, such as cell migration and wound healing.