Nanomechanical Insights into Versatile Polydopamine Wet Adhesive Interacting with Liquid-Infused and Solid Slippery Surfaces

Molecular Interaction Mechanisms Between Lubricant-Infused Slippery Surfaces and Mussel-Inspired Polydopamine Adhesive and DOPA Moiety

Lubricant-infused slippery surfaces have recently emerged as promising antifouling coatings, showing potential against proteins, cells, and marine mussels. However, a comprehensive understanding of the molecular binding behaviors and interaction strength of foulants to these surfaces is lacking. In this work, mussel-inspired chemistry based on catechol-containing chemicals including 3,4-dihydroxyphenylalanine (DOPA) and polydopamine (PDA) is employed to investigate the antifouling performance and repellence mechanisms of fluorinated-based slippery surface, and the correlated interaction mechanisms are probed using atomic force microscopy (AFM). Intermolecular force measurements and deposition experiments between PDA and the surface reveal the ability of lubricant film to inhibit the contact of PDA particles with the substrate. Moreover, the binding mechanisms and bond dissociation energy between a single DOPA moiety and the lubricant-infused slippery surface are quantitatively investigated employing single-molecule force spectroscopy based on AFM (SM-AFM), which reveal that the infused lubricant layer can remarkably influence the dissociation forces and weaken the binding strength between DOPA and underneath per-fluorinated monolayer surface. This work provides new nanomechanical insights into the fundamental antifouling mechanisms of the lubricant-infused slippery surfaces against mussel-derived adhesive chemicals, with important implications for the design of lubricant-infused materials and other novel antifouling platforms for various bioengineering and engineering applications.

Dual-Protection Inorganic-Protein Coating on Mg-Based Biomaterials through Tooth-Enamel-Inspired Biomineralization

Biocompatible magnesium alloys represent revolutionary implantable materials in dentistry and orthopedics but face challenges due to rapid biocorrosion, necessitating protective coatings to mitigate dysfunction. Directly integrating durable protective coatings onto Mg surfaces is challenging because of intrinsic low coating compactness. Herein, inspired by tooth enamel, a novel highly compact dual-protection inorganic-protein (inorganicPro) coating is in situ constructed on Mg surfaces through bovine serum albumin (BSA) protein-boosted reaction between sodium fluoride (NaF) and Mg substrates. The association of Mg ions and BSA establishes a local hydrophobic domain that lowers the formation enthalpy of NaMgF3 nanoparticles. This process generates finer nanoparticles that function as "bricks," facilitating denser packing, consequently reducing voidage inside coatings by over 50% and reinforcing mechanical durability. Moreover, the incorporation of BSA in and on the coatings plays two synergistic roles: 1) acting as "mortar" to seal residual cracks within coatings, thereby promoting coating compactness and tripling anticorrosion performance, and 2) mitigating fouling-accelerated biocorrosion in complex biosystems via tenfold resistance against biofoulant attachments, including biofluids, proteins, and metabolites. This innovative strategy, leveraging proteins to alter inorganic reactions, benefits the future coating design for Mg-based and other metallic materials with tailored anticorrosion and antifouling performances.

Cellulose-based slippery covalently attached liquid surfaces for synergistic rain and solar energy harvesting

For solar cell-triboelectric nanogenerator (TENG) integration, the design of the solid substrate for the TENG device becomes one of the challenges. The TENG needs to have superior contact electrification properties and be transparent so as to ensure light transmittance. Here, by spontaneous polymerization of dichlorodimethylsilane in the absence of any toxic solvent, we have fabricated a controllable liquid-like polydimethylsiloxane brush, featuring hydrophobicity, long-term stability, robustness, and UV resistance. A drop of liquid slides off at tilt angles below 5° and there is dynamic contact angle hysteresis of no more than 10° that can provide strong self-cleaning ability to the solid substrate. This recipe is also applicable to surfaces composed of hydroxyl group-rich cellulose-based surfaces, such as flexible cellulose acetate film (CAF). Importantly, PDMS@CAF, a flexible, transparent, and self-cleaning TENG device with a light transmission rate of 99% or more, was prepared using a conductive polymer film of PH 1000. The hybrid energy harvesting system formed by the combination of this transparent TENG equipped with solar cells is promising for harvesting energy from the environment in different weather conditions.

Designing Bio-Inspired Wet Adhesives through Tunable Molecular Interactions

Marine organisms, such as mussels and sandcastle worms, can master rapid and robust adhesion in turbulent seawater, becoming leading archetypes for the design of underwater adhesives. The adhesive proteins secreted by the organisms are rich in catecholic amino acids along with ionic and amphiphilic moieties, which mediate the adaptive adhesion mainly through catechol chemistry and coacervation process. Catechol allows a broad range of molecular interactions both at the adhesive-substrate interface and within the adhesive matrix, while coacervation promotes the delivery and surface spreading of the adhesive proteins. These natural design principles have been translated to synthetic systems toward the development of biomimetic adhesives with water-resist adhesion and cohesion. This review provides an overview of the recent progress in bio-inspired wet adhesives, focusing on two aspects: (1) the elucidation of the versatile molecular interactions (e.g., electrostatic interactions, metal coordination, hydrogen bonding, and cation-π/anion-π interactions) used by natural adhesives, mainly through nanomechanical characterizations; and (2) the rational designs of wet adhesives based on these biomimetic strategies, which involve catechol-functionalized, coacervation-induced, and hydrogen bond-based approaches. The emerging applications (e.g., tissue glues, surgical implants, electrode binders) of the developed biomimetic adhesives in biomedical, energy, and environmental fields are also discussed, with future research directions proposed.

Rational Design of a Zr-MOF@Curli-Polyelectrolyte Hybrid Membrane toward Efficient Chemical Protection, Moisture Permeation, and Catalytic Detoxification

Developing high-performance protective materials is important for soldiers and civilians who are exposed to the atmosphere of highly toxic chemical warfare agents (CWAs). Polyelectrolyte membranes are promising candidates with excellent chemical resistance and moisture permeability, but they cannot efficiently degrade CWAs. Here, we design and prepare a hybrid membrane through in situ growth of catalytically active zirconium-based metal-organic frameworks (Zr-MOFs) on a polyelectrolyte membrane mediated by biofilm-inspired curli nanofibers (CNFs). Superior to the bare polyelectrolyte membrane, the prepared MOF-808@CNF-PQ hybrid membrane exhibits improved rejection of the nerve agent simulant dimethyl methyl phosphonate (DMMP) vapor and permeation of the water vapor by 113 and 45%, respectively. The water/DMMP selectivity of the hybrid membrane reaches 498.6, approximately 13 times that of the commercial polyelectrolyte membrane Nafion 117. In addition, the hybrid membrane possesses appreciable catalytic activity for the hydrolysis of the nerve agent simulant dimethyl 4-nitrophenyl phosphate (DMNP) with a half-life of ∼38 min. Nanomechanical characterization results based on atomic force microscopy (AFM) techniques demonstrate the critical role of CNFs in mediating Zr-MOF nucleation and the dominant effect of electrostatic interactions on self-assembly of CNFs on polyelectrolyte base. It is also confirmed that the Zr-MOF toppings serve as the key components in physically adsorbing and chemically degrading the DMNP molecules through multiple strong intermolecular interactions. Our work offers a rational strategy to develop advanced membranes toward efficient chemical protection, moisture permeation, and catalytic detoxification against CWAs.

Multidynamic Osteogenic Differentiation by Effective Polydopamine Micro-Arc Oxide Manipulations

Introduction

The nanostructural modification of the oral implant surface can effectively mimic the morphology of natural bone tissue, allowing osteoblasts to achieve both proliferation and differentiation capabilities at the bone interface of the dental implant. To improve the osteoinductive activity on the surface of titanium implants for rapid osseointegration, we prepared a novel composite coating (MAO-PDA-NC) by micro-arc oxidation technique and immersion method and evaluated the proliferation, adhesion, and osteogenic differentiation of osteoblasts on this coating.

Methods

The coatings were prepared by micro-arc oxidation (MAO) technique and immersion method, and characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) for different coatings; the loading of PDA was examined using Fourier transform infrared spectroscopy (FTIR); the ion release capacity of the coatings was determined by inductively coupled plasma emission spectrometry (ICP-OES); the interfacial bonding of the coatings was examined using nanoscratch experiment strength. The cytotoxicity of the coating was examined by live/dead staining kit; cell proliferation viability was examined by CCK-8 kit; adhesion and osteogenic effect of the coating were examined by immunofluorescence staining and RT-PCR; osteogenic differentiation was examined by alkaline phosphatase staining.

Results

The surface morphology of titanium implants was modified by micro-arc oxidation technology, and a new MAO-PDA-NC composite coating was successfully prepared. The results showed that the MAO-PDA-NC coating not only optimized the physical and chemical properties of the titanium implant surface but also significantly stimulated the biological properties of osteoblast adhesion, proliferation, and osteogenic differentiation on the coating surface.

Conclusion

These results show that MAO-PDA-NC composite coating can significantly improve the surface properties of titanium implants and achieve a stable bond between implant and bone tissue, thus accelerating early osseointegration.

Metal organic frameworks (MOFs) as multifunctional nanoplatform for anticorrosion surfaces and coatings

Corrosion of metallic materials is a long-standing problem in many engineering fields. Various organic coatings have been widely applied in anticorrosion of metallic materials over the past decades. However, the protective performance of many organic coatings is limited due to the undesirable local failure of the coatings caused by micro-pores and cracks in the coating matrix. Recently, metal organic frameworks (MOFs)-based surfaces and coatings (MOFBSCs) have exhibited great potential in constructing protective materials on metallic substrates with efficient and durable anticorrosion performance. The tailorable porous structure, flexible composition, numerous active sites, and controllable release properties of MOFs make them an ideal platform for developing various protective functionalities, such as self-healing property, superhydrophobicity, and physical barrier against corrosion media. MOFs-based anticorrosion surfaces and coatings can be divided into two categories: the composite surfaces/coatings using MOFs-based passive/active nanofillers and the surfaces/coatings using MOFs as functional substrate support. In this work, the state-of-the-art fabrication strategies of the MOFBSCs are systematically reviewed. The anticorrosion mechanisms of MOFBSCs and functions of the MOFs in the coating matrix are discussed accordingly. Additionally, we highlight both traditional and emerging electrochemical techniques for probing protective performances and mechanisms of MOFBSCs. The remaining challenging issues and perspectives are also discussed.

Surface interaction mechanisms in mineral flotation: Fundamentals, measurements, and perspectives

As non-renewable natural resources, minerals are essential in a broad range of biological and technological applications. The surface interactions of mineral particles with other objects (e.g., solids, bubbles, reagents) in aqueous suspensions play a critical role in mediating many interfacial phenomena involved in mineral flotation. In this work, we have reviewed the fundamentals of surface forces and quantitative surface property-force relationship of minerals, and the advances in the quantitative measurements of interaction forces of mineral-mineral, bubble-mineral and mineral-reagent using nanomechanical tools such as surface forces apparatus (SFA) and atomic force microscope (AFM). The quantitative correlation between surface properties of minerals at the solid/water interface and their surface interaction mechanisms with other objects in complex aqueous media at the nanoscale has been established. The existing challenges in mineral flotation such as characterization of anisotropic crystal plane or heterogeneous surface, low recovery of fine particle flotation, and in-situ electrochemical characterization of collectorless flotation as well as the future work to resolve the challenges based on the understanding and modulation of surface forces of minerals have also been discussed. This review provides useful insights into the fundamental understanding of the intermolecular and surface interaction mechanisms involved in mineral processing, with implications for precisely modulating related interfacial interactions towards the development of highly efficient industrial processes and chemical additives.

Atomic Force Microscopy Nanomechanics of Hard Nanometer-Thick Films on Soft Substrates: Insights into Stretchable Conductors

The nanomechanical properties of ultrathin and nanostructured films of rigid electronic materials on soft substrates are of crucial relevance to realize materials and devices for stretchable electronics. Of particular interest are bending deformations in buckled nanometer-thick films or patterned networks of rigid materials as they can be exploited to compensate for the missing tensile elasticity. Here, we perform atomic force microscopy indentation experiments and electrical measurements to characterize the nanomechanics of ultrathin gold films on a polydimethylsiloxane (PDMS) elastomer. The measured force-indentation data can be analyzed in terms of a simple analytical model describing a bending plate on a semi-infinite soft substrate. The resulting method enables us to quantify the local Young's modulus of elasticity of the nanometer-thick film. Systematic variation of the gold layer thickness reveals the presence of a diffuse interface between the metal film and the elastomer substrate that does not contribute to the bending stiffness. The effect is associated with gold clusters that penetrate the silicone and are not directly connected to the ultrathin film. Only above a critical layer thickness, percolation of the metallic thin film happens, causing a linear increase in bending stiffness and electrical conductivity.