Shape gradient and classical gradient of curvatures:driving forces on micro/nano curved surfaces

Recent experiments and molecule dynamics simulations have shown that adhesion droplets on conical surfaces may move spontaneously and directionally. Besides, this spontaneous and directional motion is independent of the hydrophilicity and hydrophobicity of the conical surfaces. Aimed at this important phenomenon, a gen- eral theoretical explanation is provided from the viewpoint of the geometrization of micro/nano mechanics on curved surfaces. In the extrinsic mechanics on micro/nano soft curved surfaces, we disclose that the curvatures and their extrinsic gradients form the driving forces on the curved spaces. This paper focuses on the intrinsic mechanics on micro/nano hard curved surfaces and the experiment on the spontaneous and directional motion. Based on the pair potentials of particles, the interactions between an isolated particle and a micro/nano hard curved surface are studied, and the geometric foundation for the interactions between the particle and the hard curved surface is analyzed. The following results are derived： （a） Whatever the exponents in the pair potentials may be, the potential of the particle/hard curved surface is always of the unified curvature form, i.e., the potential is always a unified function of the mean curvature and the Gaussian curvature of the curved surface. （b） On the basis of the curvature-based potential, the geometrization of the micro/nano mechanics on hard curved surfaces may be realized. （c） Similar to the extrinsic mechanics on micro/nano soft curved surfaces, in the intrinsic mechanics on micro/nano hard curved surfaces, the curvatures and their intrinsic gradi- ents form the driving forces on the curved spaces. In other words, either on soft curved surfaces or hard curved surfaces and either in the extrinsic mechanics or the intrinsic mechanics, the curvatures and their gradients are all essential factors for the driving forces on the curved spaces. （d） The direction of the driving force induced by the hard curved surface is independent of the hydrophilieity and hydrophobicity of the curved surface, explaining the experimental phenomenon of the spontaneous and directional motion.

Localized in‑situ deposition:a new dimension to control in fabricating surface micro/nano structures via ultrafast laser ablation

Controllable fabrication of surface micro/nano structures is the key to realizing surface functionalization for various applications.As a versatile approach,ultrafast laser ablation has been widely studied for surface micro/nano structuring.Increasing research eforts in this feld have been devoted to gaining more control over the fabrication processes to meet the increasing need for creation of complex structures.In this paper,we focus on the in-situ deposition process following the plasma formation under ultrafast laser ablation.From an overview perspective,we frstly summarize the diferent roles that plasma plumes,from pulsed laser ablation of solids,play in diferent laser processing approaches.Then,the distinctive in-situ deposition process within surface micro/nano structuring is highlighted.Our experimental work demonstrated that the in-situ deposition during ultrafast laser surface structuring can be controlled as a localized micro-additive process to pile up secondary ordered structures,through which a unique kind of hierarchical structure with fort-like bodies sitting on top of micro cone arrays were fabricated as a showcase.The revealed laser-matter interaction mechanism can be inspiring for the development of new ultrafast laser fabrication approaches,adding a new dimension and more fexibility in controlling the fabrication of functional surface micro/nano structures.

Superhydrophobic Surfaces Produced by Applying a Self- Assembled Monolayer to Silicon Micro/Nano-Textured Surfaces

A novel way of producing superhydrophobic surfaces by applying a self-assembled monolayer(SAM)to silicon micro/nano-textured surfaces is presented in this paper.The micro/nano-textured surfaces on silicon substrates were generated by the aluminum-induced crystallization(AIC)of amorphous silicon(a-Si)technique.Octadecyltrichlorosilane(OTS)SAMs were then applied to the textured surfaces by dip coating.The topography and wetting properties of the resulting surfaces were characterized using scanning electron microscopy(SEM)and a video-based contact angle measurement system.The results show that by introducing OTS SAMs on the silicon micro/nano-textured surfaces,superhydrophobic surfaces with water contact angles(WCAs)of 155°were obtained,as compared to the WCAs of OTS-modified smooth silicon surfaces of about 112°.Surface topography was found to directly influence the WCA as predicted by the Cassie-Baxter model.

Micro/nano-structured TiO2 surface with dual-functional antibacterial effects for biomedical applications

Implant-associated infections are generally difficult to cure owing to the bacterial antibiotic resistance which is attributed to the widespread usage of antibiotics.Given the global threat and increasing influence of antibiotic resistance,there is an urgent demand to explore novel antibacterial strategies other than using antibiotics.Recently,using a certain surface topography to provide a more persistent antibacterial solution attracts more and more attention.However,the clinical application of biomimetic nano-pillar array is not satisfactory,mainly because its antibacterial ability against Gram-positive strain is not good enough.Thus,the pillar array should be equipped with other antibacterial agents to fulfill the bacteriostatic and bactericidal requirements of clinical application.Here,we designed a novel model substrate which was a combination of periodic micro/nano-pillar array and TiO2 for basically understanding the topographical bacteriostatic effects of periodic micro/nano-pillar array and the photocatalytic bactericidal activity of TiO2.Such innovation may potentially exert the synergistic effects by integrating the persistent topographical antibacterial activity and the non-invasive X-ray induced photocatalytic antibacterial property of TiO2 to combat against antibiotic-resistant implant-associated infections.First,to separately verify the topographical antibacterial activity of TiO2 periodic micro/nano-pillar array,we systematically investigated its effects on bacterial adhesion,growth,proliferation,and viability in the dark without involving the photocatalysis of TiO2.The pillar array with sub-micron motif size can significantly inhibit the adhesion,growth,and proliferation of Staphylococcus aureus(S.aureus)and Escherichia coli(E.coli).Such antibacterial ability is mainly attributed to a spatial confinement size-effect and limited contact area availability generated by the special topography of pillar array.Moreover,the pillar array is not lethal to S.aureus and E.coli in 24 h.Then,the X-ray induced photocatalytic antibacterial property of TiO2 periodic micro/nano-pillar array in vitro and in vivo will be systematically studied in a future work.This study could shed light on the direction of surface topography design for future medical implants to combat against antibiotic-resistant implant-associated infections without using antibiotics.

Hydroxyapatite-modified micro/nanostructured titania surfaces with different crystalline phases for osteoblast regulation

Surface structures and physicochemical properties critically influence osseointegration of titanium(Ti)implants.Previous studies have shown that the surface with both micro-and nanoscale roughness may provide multiple features comparable to cell dimensions and thus efficiently regulate cell-material interaction.However,less attention has been made to further optimize the physicochemical properties(e.g.,crystalline phase)and to further improve the bioactivity of micro/nanostructured surfaces.Herein,micro/nanostructured titania surfaces with different crystalline phases(amorphous,anatase and anatase/rutile)were prepared and hydroxyapatite(HA)nanorods were deposited onto the as-prepared surfaces by a spin-assisted layer-by-layer assembly method without greatly altering the initial multi-scale morphology and wettability.The effects of crystalline phase,chemical composition and wettability on osteoblast response were investigated.It is noted that all the micro/nanostructured surfaces with/without HA modification presented superamphiphilic.The activities of MC3T3-E1 cells suggested that the proliferation trend on the micro/nanostructured surfaces was greatly influenced by different crystalline phases,and the highest proliferation rate was obtained on the anatase/rutile surface,followed by the anatase;but the cell differentiation and extracellular matrix mineralization were almost the same among them.After ultrathin HA modification on the micro/nanostructured surfaces with different crystalline phases,it exhibited similar proliferation trend as the original surfaces;however,the cell differentiation and extracellular matrix mineralization were significantly improved.The results indicate that the introduction of ultrathin HA to the micro/nanostructured surfaces with optimized crystalline phase benefits cell proliferation,differentiation and maturation,which suggests a favorable biomimetic microenvironment and provides the potential for enhanced implant osseointegration in vivo.