CONCAVE BIOLOGICAL SURFACES FOR STRONG WET ADHESION

Plant leaves, insects and geckos are masters of adhesion or anti-adhesion by smartly designed refined surface structures with micro- and nano- ＇technologies＇. Understanding the basic principles in the design of the unique surface structures is of great importance in the manufacture or synthesis of micro- and nano- devices in MEMS or NEMS. This study is right inspired by this effort, focusing on the mechanics of wet adhesion between fibers having concave tips and a flat substrate via capillary forces. We show that the concave surface can effectively enhance the wet adhesion by reducing the effective contact angle of the fiber, firmly pinning the liquid bridge at its circumferential edge. A critical contact angle is identified below which the adhesion strength can achieve its maximum, being insensitive to the contact angle between the fiber and liquid. The analytical expression for the critical angle is derived. Then a tentative design for the profile of concave surfaces is proposed, considering the effects of chamfering size, deformation and buckling, etc. The effect of liquid volume on the wet adhesion of multiple-fiber system is also discussed.

Development of wet adhesion of honeybee arolium incorporated polygonal structure with three-phase composite interfaces

Inspired by the dynamic wet adhesive systems in nature,various artificial adhesive surfaces have been developed but still face different challenges.Crucially,the theoretical mechanics of wet adhesives has never been sufficiently revealed.Here,we develop a novel adhesive mechanism for governing wet adhesion and investigate the biological models of honeybee arolium for reproducing the natural wet adhesive systems.Micro-nano structures of honeybee arolium and arolium-prints were observed by Cryogenic scanning electron microscopy(Cryo-SEM),and the air pockets were found in the contact interface notably.Subsequently,the adhesive models with a three-phase composite interface(including air pockets,liquid secretion,and hexagonal frames of arolium),were formed to analyze the wet adhesion of honeybee arolium.The results of theoretical calculations and experiments indicated an enhanced adhesive mechanism of the honeybee by liquid self-sucking effects and air-embolism effects.Under these effects,normal and shear adhesion can be adjusted by controlling the proportion of liquid secretion and air pockets in the contact zone.Notably,the air-embolism effects contribute to the optimal coupling of smaller normal adhesion with greater shear adhesion,which is beneficial for the high stride frequency of honeybees.These works can provide a fresh perspective on the development of bio-inspired wet adhesive surfaces.

Influencing Factors of Fabric-Skin Adhesion Based on Gray Correlation Analysis Method

Fabric-skin adhesion was objectively described by the indices of the maximum adhesion force F_(max) , the maximum separation distance L_(max) ,and adhesion work W as well as the adhesion force-separation distance curve. Firstly,gray correlation analysis method was adopted to investigate the correlation levels between adhesion indices,and secondly the relative importance of fabric structural parameters to fabric-skin adhesion,as well as the correlation levels between skin adhesion, water absorption, and wicking properties of the fabric. The results prove that W exhibits clear correlations with both F_(max) and L_(max) , yet the relevance between F_(max) and L_(max) is weak. Fabric adhesion indices are most associated with fabric mass and least with fabric thickness,whereas fabric wicking and water absorption present closest correlation with fabric thickness. Therefore, it is concluded that the relevance between fabric wicking, water absorption, and skin-adhesion properties are rather comprehensive than straight.

Importance of Metal－Oxide Support Wettingandinteractions on Understanding of Physical and Chemical Behaviours of Supported Metal Catalysts

It has been generally recognised that the metal catalysts supported on oxide ceramic and non-oxide ceramic supports exhibit completely different characteristics as compared with the homogeneous ones. The na-ture of bonding and interactions occurring at the metal / ceramic interfaces are believed to be of importancefor the characteristics of such catalysts. The recently developed microscopic theory of adhesion and wettingin metal/ ceramic systems is briefly presented here with the emphasis on the ionocovalent oxide ceramics.and its consequence on the understanding of the physical and chemical behaviours of supported metal cata-lysts is exploited.

Adhesive cryogel particles for bridging confined and irregular tissue defects

Background Reconstruction of damaged tissues requires both surface hemostasis and tissue bridging.Tissues with damage resulting from physical trauma or surgical treatments may have arbitrary surface topographies,making tissue bridging challenging.Methods This study proposes a tissue adhesive in the form of adhesive cryogel particles(ACPs) made from chitosan,acrylic acid,1-ethyl-3-(3-dimethylaminopropyl) carbodiimide(EDC) and N-hydroxysuccinimide(NHS).The adhesion performance was examined by the 180-degree peel test to a collection of tissues including porcine heart,intestine,liver,muscle,and stomach.Cytotoxicity of ACPs was evaluated by cell proliferation of human normal liver cells(LO2)and human intestinal epithelial cells(Caco-2).The degree of inflammation and biodegradability were examined in dorsal subcutaneous rat models.The ability of ACPs to bridge irregular tissue defects was assessed using porcine heart,liver,and kidney as the ex vivo models.Furthermore,a model of repairing liver rupture in rats and an intestinal anastomosis in rabbits were established to verify the effectiveness,biocompatibility,and applicability in clinical surgery.Results ACPs are applicable to confined and irregular tissue defects,such as deep herringbone grooves in the parenchyma organs and annular sections in the cavernous organs.ACPs formed tough adhesion between tissues[(670.9±50.1) J/m^(2) for the heart,(607.6±30.0) J/m^(2) for the intestine,(473.7±37.0) J/m^(2) for the liver,(186.1±13.3) J/m^(2) for the muscle,and(579.3±32.3) J/m^(2) for the stomach].ACPs showed considerable cytocompatibility in vitro study,with a high level of cell viability for 3 d[(98.8±1.2)%for LO2 and(98.3±1.6)%for Caco-2].It has comparable inflammation repair in a ruptured rat liver(P=0.58 compared with suture closure),the same with intestinal anastomosis in rabbits(P=0.40 compared with suture anastomosis).Additionally,ACP-based intestinal anastomosis(less than 30 s) was remarkably faster than the conventional suturing process(more than 10 min).When ACPs degrade after surgery,the tissues heal across the adhesion interface.Conclusions ACPs are promising as the adhesive for clinical operations and battlefield rescue,with the capability to bridge irregular tissue defects rapidly.

Mechanisms Underlying the Biological WetAdhesion:Coupled Effects of Interstitial Liquid and Contact Geometry

Wet adhesion is widely adopted in biological adhesion systems in nature,and it is beneficial to design new materials with desired properties based on the underlying physics of wet adhesion.The aim of this work is to develop a design criterion to regulate the wet adhesion.The effects of different contact shapes(flat and sphere)and morphologies of the substrate(smooth,microstructure and nanostructure)on the adhesion force are investigated.Combining with the theoretical models,the dominated factors in the separation process and isolating the viscous contributions from the capillary interactions are evaluated.The results demonstrate that the adhesion mechanisms depend significantly on the capillary numbers of the interstitial liquid and the contact geometry,and the ratio of capillary force to viscous force is a key to regulate the wet adhesion mechanism.These findings can not only explain some phenomena of wet adhesion to organisms,but also provide some inspirations to design new adhesion technology for robotic fingers that can grasp objects in wet environments.

Wet-adhesive materials of oral and maxillofacial region:From design to application

Oral and maxillofacial diseases are a group of high-incidence disorders that affect people’s life quality to a great extent,while the wet and highly movable environment of the related regions brings challenges to traditional therapies.Faced with the obstacles of insufficient adhesive strength and ensuing short drug retention time,conventional oral therapeutic agents often have difficulty in achieving their desired efficacy.Oral and maxillofacial wet-adhesive materials have the advantages of excellent wet environment retention,internal stability,plasticity,and clinical potential,thus have become a significant research direction in the field of oral related disorders healing.In the past decade,the development of oral adhesive materials with good wet adhesion has accelerated based on the chemical molecular interaction,physical interlocking,and biological adhesion mechanisms,including biomimetic-inspired materials,naturally derived polymer–based materials and adhesive electrospun fiber films.These fancy wet-adhesive materials can be used for oral mucosal drug delivery,oral vaccination,wound healing,and bone defects treatments.Despite their numerous novel applications,wet-adhesive materials in stomatology still face unresolved challenges from material and biological aspects.Here,advances in designs of oral and maxillofacial wetadhesive materials are reviewed in terms of design backgrounds,attachment mechanisms,and common classifications.Recent demonstrations of wet-adhesive materials for oral and maxillofacial region medical applications from drug delivery to multifunctional tissue treatments are presented.To conclude,current challenges and prospects on potential applications of oral and maxillofacial wet-adhesive materials are also briefly discussed.

On elastocapillarity:A review

Elastocapillary phenomena involving elastic deformation of solid structures coupled with capillary effects of liquid droplets/films can be observed in a diversity of fields, e.g., biology and microelectromechanical systems （MEMS）. Understanding the physical mechanisms underlying these phenomena is of great interest for the design of new materials and devices by utilizing the effects of surface tension at micro and nano scales. In this paper, some recent developments in the investigations on elastocapillary phenomena are briefly reviewed. Especially, we consider the deformation, adhesion, self-assembly, buckling and wrinkling of ma- terials and devices induced by surface tensions or capillary forces. The main attention is paid to the experimental results of these phenomena and the theoretical analysis meth- ods based on continuum mechanics. Additionally, the applications of these studies in the fields of MEMS, micro/nanometrology, and biomimetic design of advanced materials and devices are discussed.

Role of the Bandgaps on Some Interfacial Phenomena with Ionocovalent Oxides

Many ionocovalent oxide materials are either semiconducting or insulating in nature.One of the most im- portant quantities characterising these materials,therefore,is the bandgap energy.The thermodynamic ap- proaches to the bandgaps of oxides are briefly described and some interracial phenomena with oxides are pres- ented.The standard electrode potentials of oxide electrodes and the heterogeneous catalytic behaviours of the oxides as well as the wetting and adhesion in liquid metal/oxide systems can be closely related to the bandgap energies of the oxides.The interfacial phenomena involving the ionocovalent oxides are associated with the electronic processes.

Wet adhesive hydrogel cardiac patch loaded with anti-oxidative,autophagy-regulating molecule capsules and MSCs for restoring infarcted myocardium

Hydrogel patch-based stem cell transplantation and microenvironment-regulating drug delivery strategy is promising for the treatment of myocardial infarction(MI).However,the low retention of cells and drugs limits their therapeutic efficacies.Here,we propose a prefixed sponge carpet strategy,that is,aldehyde-dextran sponge(ODS)loading anti-oxidative/autophagy-regulating molecular capsules of 2-hydroxy-β-cyclodextrin@resveratrol(HP-β-CD@Res)is first bonded to the rat’s heart via capillary removal of interfacial water from the tissue surface,and the subsequent Schiff base reaction between the aldehyde groups on ODS and amino groups on myocardium tissue.Then,an aqueous biocompatible hydrazided hyaluronic acid(HHA)solution encapsulating mesenchymal stem cells(MSCs)is impregnated into the anchored carpet to form HHA@ODS@HP-β-CD@Res hydrogel in situ via click reaction,thus prolonging the in vivo retention time of therapeutic drug and cells.Importantly,the HHA added to outer surface consumes the remaining aldehydes to contribute to nonsticky top surface,avoiding adhesion to other tissues.The embedded HP-β-CD@Res molecular capsules with antioxidant and autophagy regulation bioactivities can considerably improve cardiac microenvironment,reduce cardiomyocyte apoptosis,and enhance the survival of transplanted MSCs,thereby promoting cardiac repair by facilitating angiogenesis and reducing cardiac fibrosis.

Bioactive citrate-based polyurethane tissue adhesive for fast sealing and promoted wound healing

As a superior alternative to sutures,tissue adhesives have been developed significantly in recent years.However,existing tissue adhesives struggle to form fast and stable adhesion between tissue interfaces,bond weakly in wet environments and lack bioactivity.In this study,a degradable and bioactive citrate-based polyurethane adhesive is constructed to achieve rapid and strong tissue adhesion.The hydrophobic layer was created with polycaprolactone to overcome the bonding failure between tissue and adhesion layer in wet environments,which can effectively improve the wet bonding strength.This citrate-based polyurethane adhesive provides rapid,non-invasive,liquid-tight and seamless closure of skin incisions,overcoming the limitations of sutures and commercial tissue adhesives.In addition,it exhibits biocompatibility,biodegradability and hemostatic properties.The degradation product citrate could promote the process of angiogenesis and accelerate wound healing.This study provides a novel approach to the development of a fast-adhering wet tissue adhesive and provides a valuable contribution to the development of polyurethane-based tissue adhesives.