Huajian Gao

Brown University · School of Engineering

Biological systems can create materials with intricate structures and specialized functions. In comparison, precise control of structures in human-made materials has been challenging. Here we report on insect cuticle peptides that spontaneously form nanocapsules through a single-step solvent exchange process, where the concentration gradient result...

Liquid‐phase exfoliation (LPE) in aqueous solutions provides a simple, scalable, and green approach to produce 2D materials. By combining atomistic simulations with exfoliation experiments, the interaction between a surfactant and a 2D layer at the molecular scale can be better understood. In this work, two different dyes, corresponding to rhodamin...

The stresses that evolve during plating and stripping in lithium metal electrodes can have a significant impact on battery performance. We have used several different in situ techniques to investigate these stresses, during electrochemical cycling with both liquid and solid electrolytes. Finite element modelling (FEM) was also employed to interpret...

Ceramic and glass electrolytes are a promising replacement for the liquid electrolytes that are commonly used in Li-ion batteries. Their mechanical properties are known to play a critical role not only in practical issues related to safe cell assembly, but also in the battery cell performance. In this talk, inelastic deformation mechanisms in ceram...

The measurement of stress fields around lithium metal dendrites in solid electrolytes in operating conditions is critical for the design of next-generation, dendrite-resistant solid electrolytes. Prior work, both experimental and theoretical, indicates that the developed stresses in the in the electrolyte can be significantly high. However, direct...

Ceramic matrix composites (CMCs) reinforced by two-dimensional (2D) nanomaterials have shown extraordinary load-carrying capacities, even in the harsh environments required by emerging applications. Their exceptional mechanical performance, especially fracture toughness, primarily arises from their heterogeneous microstructures. The deliberate disp...

Regulating the motion of nanoscale objects on a solid surface is vital for a broad range of technologies such as nanotechnology, biotechnology, and mechanotechnology. In spite of impressive advances achieved in the field, there is still a lack of a robust mechanism which can operate under a wide range of situations and in a controllable manner. Her...

Biological systems often create materials with intricate structures to achieve specialized functions. In comparison, precise control of structures in man-made materials has been challenging. Here, we report a serendipitous discovery of insect cuticle peptides (ICPs) spontaneously forming nanocapsules through a single-step solvent exchange process,...

Wide ranging mechanical properties — elasticity, plasticity, fracture, and creep — most relevant to the mechanical reliability of perovskite solar cells (PSCs) are systematically investigated. High quality bulk single-crystals of the commonly studied metal-halide perovskites (MHPs) relevant to PSCs are fabricated and studied: CH3NH3PbBr3 (MAPbBr3)...

Materials displaying negative Poisson’s ratio, referred to as auxeticity, have been found in nature and created in engineering through various structural mechanisms. However, uniting auxeticity with high strength and high stiffness has been challenging. Here, combining in situ nanomechanical testing with microstructure-based modeling, we show that...

The two key interfaces in flexible perovskite solar cells (f‐PSCs) are mechanically reinforced simultaneously: one between the electron transport layer (ETL) and the 3D metal halide perovskite (MHP) thin film using self‐assembled monolayer (SAM), and the other between the 3D‐MHP thin film and the hole transport layer (HTL) using an in situ‐grown lo...

Aside from ultrahigh strength and elasticity, metallic glasses (MGs) possess a number of favorable properties. However, their lack of dislocation based plastic deformation mechanisms in crystalline metals and the resulting loss of ductility have restricted the engineering applications of MGs over the last 60 years. This review aims to provide an ov...

Marine mussels achieve strong underwater adhesion by depositing mussel foot proteins (Mfps) that form coacervates during the protein secretion. However, the molecular mechanisms that govern the phase separation behaviors of the Mfps are still not fully understood. Here, we report that GK-16*, a peptide derived from the primary adhesive protein Mfp-...

Measuring fracture toughness of materials at small scales remains challenging due to limited experimental testing configurations. A recently developed indentation pillar-splitting method has shown promise of improved flexibility in fracture toughness measurements at the microscale, partly due to the occurrence of an unusual fracture instability, i....

Traces of heavy metals found in water resources, due to mining activities and e-waste discharge, pose a global threat. Conventional treatment processes fail to remove toxic heavy metals, such as lead, from drinking water in a resource-efficient manner when their initial concentrations are low. Here, we show that by using the yeast Saccharomyces cer...

Biosurfactant-aided liquid-phase exfoliation (LPE) is emerging as a biocompatible, green, economical, safe, and efficient approach to prepare two-dimensional (2D) materials for biomedical applications. However, relatively little is known about the molecular mechanisms of this process. Herein, we present the first study of how flavin mononucleotide...

Sulfide glasses are emerging as potential electrolytes for solid-state batteries. The mechanical behavior of these materials can significantly impact cell performance, and it is thus imperative to understand their deformation and fracture mechanisms. Previous work mainly reports properties obtained under quasi-static loading conditions, but very li...

Recent studies on nanomechanical devices based on low-dimensional nanomaterials have revealed several different types of thermal fluctuation gradient induced tangential entropic forces (TEFs), including expulsion force, edge force, thermophoretic force, nanodurotaxis force, etc. While all these forces originate from thermal fluctuation gradients, t...

Despite its importance for nanofluidic systems, achieving continuous water flow in long nanochannels remains a major challenge. Here, we propose a general principle to overcome this challenge by introducing a method that involves the building of a series of cascadable driving units, each unit carrying a net thermal gradient force, to maintain conti...

Biological materials have evolved various degrees of robustness against microscopic defects and structural randomness. Of particular interest here is whether and how nacre's brick–mortar microstructure suppresses the adverse effect of microstructural randomness. To this end, a tension–shear–chain (TSC) network model, combined with the virtual inter...

Traces of heavy metals found in water resources, due to mining activities and e-waste discharge, pose a global threat. Conventional treatment processes fail to remove toxic heavy metals, such as lead, from drinking water in a resource-efficient manner when their initial concentrations are low. Here, we show that by using the yeast Saccharomyces cer...

Traces of heavy metals found in water resources, due to mining activities and e-waste discharge, pose a global threat. Conventional treatment processes fail to remove toxic heavy metals, such as lead, from drinking water in a resource-efficient manner when their initial concentrations are low. Here, we show that by using the yeast Saccharomyces cer...

While the interaction between 2D materials and cells is of key importance to the development of nanomedicines and safe applications of nanotechnology, still little is known about the biological interactions of many emerging 2D materials. Here, an investigation of how hexagonal boron nitride (hBN) interacts with the cell membrane is carried out by c...

Significance Data-driven approaches have launched a new paradigm in scientific research that is bound to have an impact on all disciplines of science and engineering. However, at this juncture, the exploration of data-driven techniques in the century-old field of fracture mechanics is highly limited, and there are key challenges including accurate...

Nanostructured alloy‐forming anode materials can resist fracture that is caused by extreme volume changes during cycling. However, the higher surface area per unit mass in nanomaterials increases exposure to the electrolyte reduction reactions that form a solid electrolyte interphase (SEI), which implies that capacity loss will increase as particle...

The potential advantages of lithium (Li) metal anodes have been widely touted (lowest reduction potential, etc.). However, the poor stability of Li metal / liquid electrolyte interfaces leads to chronic problems, such as dendrite formation and capacity loss. The possible impact of mechanical effects on interface stability and dendrite formation is...

Metallic glasses (MGs) are often perceived as quintessential structural materials due to their superior mechanical properties such as high strength and large elastic limit. In practical applications, service conditions that introduce cyclic variations in stresses and strains are inevitably involved. The fatigue of MGs is thus a topic of research an...

Cell division is central for embryonic development, tissue morphogenesis, and tumor growth. Experiments have evidenced that mitotic cell division is manipulated by the intercellular cues such as cell-cell junctions. However, it still remains unclear how these cortical-associated cues mechanically affect the mitotic spindle machinery, which determin...

Metallic nanowires (NWs) with twin boundaries (TBs) running parallel to the NW length direction exhibit unusual plastic strain recovery owing to the interaction of dislocations with TBs. Here, based on in-situ transmission electron microscopy nanomechanical testing and molecular dynamics simulations, we report observation and quantification of disl...

A current bottleneck in the advance of neurophysics is the lack of reliable methods to quantitatively measure the interactions between neural cells and their microenvironment. Here, we present an experimental technique to probe the fundamental characteristics of neuron adhesion through repeated peeling of well-developed neurite branches on a substr...

Recently, a transition of deformation mechanism from localized dislocation slip to delocalized plasticity via an anomalous tensile detwinning mechanism has been discovered in bitwinned metallic nanowires (NWs) with a single twin boundary (TB) running parallel to the NW length. However, experiments showed that the anomalous tensile detwinning in mos...

Nanotwinned materials have been widely studied as a promising class of nanostructured materials that exhibit an exceptional combination of high strength, good ductility, large fracture toughness, remarkable fatigue resistance, and creep stability. Recently, an apparent controversy has emerged with respect to how the strength of nanotwinned material...

The original version of this Article was incorrectly labelled as a ‘Review Article’. This has now been corrected to ‘Article’ in both the HTML and PDF versions.

Maintaining an electrochemically and mechanically stable solid electrolyte interphase (SEI) is of fundamental importance to the performance of high capacity anode materials such as silicon. In this study, a novel approach is utilized to apply controlled strains to SEI films on patterned Si electrodes. Mechanical failure mechanisms of SEI are invest...

In practical silicon electrodes the coupled mechanical and chemical degradation of the solid electrolyte interphase (SEI) is a critical issue. During electrochemical cycling, the extremely large mechanical strains that are applied to the SEI on Si are a primary factor that limits cycle life. However, the effect of particle size on these strains has...

The potential advantages of lithium metal anodes have received widespread attention (highest capacity, lowest reduction potential, etc). However, the poor stability of Li metal / liquid electrolyte interfaces leads to chronic problems, such as dendrite formation and capacity loss. The possible impact of mechanical effects on interface stability and...

Acellular epicardial patches that treat myocardial infarction by increasing the mechanical integrity of damaged left ventricular tissues exhibit widely scattered therapeutic efficacy. Here, we introduce a viscoelastic adhesive patch, made of an ionically crosslinked transparent hydrogel, that accommodates the cyclic deformation of the myocardium an...

Twinning and dislocation slip are two competitive deformation mechanisms in face-centered cubic (FCC) metals. For FCC metallic nanowires (NWs), the competition between these mechanisms was found to depend on loading direction and material properties. Here, using in situ transmission electron microscopy tensile tests and molecular dynamics simulatio...

History-independent, stable and symmetric cyclic response has been detected in as-deposited bulk polycrystalline Cu with highly oriented nanotwins [Nature 551 (2017) 214–217]. In this study, to deepen the understanding of cyclic deformation in nanotwinned (NT) structures, small levels of tensile pre-strains were applied on NT-Cu, followed by strain...

Although hydrogen embrittlement has been observed and extensively studied in a wide variety of metals and alloys, there still exist controversies over the underlying mechanisms and a fundamental understanding of hydrogen embrittlement in nanostructures is almost non-existent. Here we use metallic nanowires (NWs) as a platform to study hydrogen embr...

Through evolution, spider orb webs have acquired an outstanding ability to capture flying preys. In this work, we aim to understand the robustness of spider adhesion by analyzing the effects of randomness in the adhesion strengths and inter-spacings of glue droplets along a spider orb web capture silk on its load-bearing and energy absorption capac...

Significance Lipid vesicles such as liposomes are widely present in biological systems and drug delivery applications. Numerous studies have focused on their roles in intercellular communication, signaling, and trafficking. Little is known, however, about the correlation between temperature and transport rate of these vesicles in biological media....

The study of structural flaws is of paramount importance in engineering applications. However, the effect of flaws on both the macroscale and nanoscale metallic glasses (MGs) is a debatable topic, drawing from conflicting reports on notch strengthening, notch weakening, and notch insensitivity for MGs. In the present study, molecular dynamics simul...

In their papers, Li et al. proposed an indentation strain stiffening mechanism to explain the experimentally reported ultra-high hardness of nanotwinned (nt-) cBN and nt-diamond at extremely small twin boundary (TB) thicknesses (λ ≤ 5 nm). Here, however, we show that the strain stiffening mechanism proposed by these authors is not exclusive to nt-c...

Stronger copper through twin power Materials with structural gradients often have unique combinations of properties. Gradient-structured materials are found in nature and can be engineered. Cheng et al. made a structural gradient by introducing gradients of crystallographic twins into copper. This strategy creates bundles of dislocations in the cry...

Owing to their exquisite geometric structures and excellent mechanical properties, spider orb webs possess an outstanding ability to capture flying prey. In this work, we report a mechanism that enhances the energy absorption ability of spider webs. Through systematic measurements of the mechanical properties of both spiral and radial silks, we fin...

To optimally penetrate biological hydrogels such as mucus and the tumor interstitial matrix, nanoparticles (NPs) require physicochemical properties that would typically preclude cellular uptake, resulting in inefficient drug delivery. Here, we demonstrate that (poly(lactic-co-glycolic acid) (PLGA) core)-(lipid shell) NPs with moderate rigidity disp...

To understand the mechanics of cellular packing of two-dimensional (2D) materials, we perform systematic molecular dynamics simulations and theoretical analysis to investigate the packing of a flexible circular sheet in a spherical vesicle and the 2D packing problem of a strip in a cylindrical vesicle. Depending on the system dimensions and the ben...

Interfacial delamination can be detrimental to the cycle life of solid-state batteries. Here, we investigate a pop-up delamination mechanism by which a delaminated electrode pops up from its underlying current collector against a solid electrolyte. It is shown that the delamination can proceed via the spreading of a single pop-up or multiple pop-up...

It is known that rod-like nanoparticles (NPs) can achieve higher diffusivity than their spherical counterparts in biological porous media such as mucus and tumor interstitial matrix, but the underlying mechanisms still remain elusive. Here, we present a joint experimental and theoretical study to show that the aspect ratio (AR) of NPs and their adh...

Mechanical cues from the microenvironments play a regulating role in many physiological and pathological processes, such as stem cell differentiation and cancer cell metastasis. Experiments showed that cells adhered on a compliant substrate may change orientation with an externally applied strain in the substrate. By accounting for actin polymeriza...

In spite of numerous studies on mechanical behaviors of nanowires (NWs) focusing on the surface effect, there is still a general lack of understanding on how the internal microstructure of NWs influences their deformation mechanisms. Here, using quantitative in situ transmission electron microscopy based nanomechanical testing and molecular dynamic...

Cellular packing of flexible nanofibers, including natural cytoskeletal microtubules, actin filaments, synthetic nanotubes and nanowires, is of fundamental interest to the understanding of a wide range of cell activities, including cell shape control, cell movement, cell division, and nano-cytotoxicity. Here, we perform molecular dynamics simulatio...

The influence of test sample geometry on the fracture toughness measurements of bulk metallic glasses (BMGs) is systematically quantified. Through a combination of thermoplastic forming based toughness measurements and numerical simulations, we investigated the effects of test sample thickness, width, and notch precision on the fracture toughness o...

Nearly 90 per cent of service failures of metallic components and structures are caused by fatigue at cyclic stress amplitudes much lower than the tensile strength of the materials involved. Metals typically suffer from large amounts of cumulative, irreversible damage to microstructure during cyclic deformation, leading to cyclic responses that are...

Cold embrittlement is one of the primary concerns challenging the usage of steels in infrastructures like pipelines and ocean platforms. This challenge is also compounded by the limited selection of materials for application in a cold and corrosive environment. Inspired by recent progresses in developing gradient structured materials with extraordi...

Preventing icing on exposed surfaces is important for life and technology. While suppressing ice nucleation by surface structuring and local confinement is highly desired and yet to be achieved, a realistic roadmap of icephobicity is to live with ice, but with lowest possible ice adhesion. According to fracture mechanics, the key to lower ice adhes...

The dominant deformation behavior of two-dimensional materials (bending) is primarily governed by just two parameters: bending rigidity and the Gaussian modulus. These properties also set the energy scale for various important physical and biological processes such as pore formation, cell fission and generally, any event accompanied by a topologica...

Supplementary Information--- Determining the Gaussian modulus and edge properties of 2D materials: from graphene to lipid bilayers

Solid electrolytes in batteries are inevitably subjected to mechanical strains when the active materials undergo chemically induced volume changes. It is difficult to probe these effects in complex battery structures. Thus we developed a new in situ method to monitor mechanical deformation during electrochemical cycling, using simplified thin film...

2D Si nanomaterials have attracted tremendous attention due to their novel properties and a wide range of potential applications from electronic devices to energy storage and conversion. However, high-quality and large-scale fabrication of 2D Si remains challenging. This study reports a room-temperature and one-step synthesis technique that leads t...

On-demand, ultra-high precision delivery of molecules and cells is of great importance in the field of controlled release. In article number 1600410, inspired by sea sponges, Lei Yang, Yuekun Lai, and co-workers design and fabricate a biomimetic macroporous ceramic composite sponge which reveals unique precise AND logic release behaviors of molecul...

Penta-twinned Ag nanowires (pt-AgNWs) have recently attracted much attention due to their interesting mechanical and physical properties. Here we perform large-scale atomistic simulations to investigate the influence of sample size and strain rate on the tensile strength of pt-AgNWs. The simulation results show an apparent size effect in that the n...

Penta-graphene (PG), a newly proposed two-dimensional material composed entirely of carbon pentagons, is believed to possess much lower failure stress and strain than those of graphene. An open question is whether and how these properties can be enhanced. Herein using molecular dynamics simulations, we examine the deformation and failure processes...

Ultralight and resilient porous nanostructures have been fabricated in various material forms, including carbon, polymers, and metals. However, the development of ultralight and high-temperature resilient structures still remains extremely challenging. Ceramics exhibit good mechanical and chemical stability at high temperatures, but their brittlene...

Recent experiments have revealed that external bending breaks the symmetry of lithiation in germanium nanowires. However, the effects of external stress on lithiation in silicon and the associated underlying mechanisms remain unclear. Here, we have performed a series of large-scale atomistic simulations based on a newly developed reactive force fie...

While many experiments and simulations on metallic glasses (MGs) have focused on their tensile ductility under monotonic loading, the fatigue mechanisms of MGs under cyclic loading still remain largely elusive. Here we perform molecular dynamics (MD) and finite element simulations of tension-compression fatigue tests in MGs to elucidate their fatig...

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While many experiments and simulations on metallic glasses (MGs) have focused on their tensile ductility under monotonic loading, the fatigue mechanisms of MGs under cyclic loading still remain largely elusive. Here we perform molecular dynamics (MD) and finite element simulations of tension-compression fatigue tests in MGs to elucidate their fatig...

The extracellular matrix (ECM) of a solid tumor not only affords scaffolding to support tumor architecture and integrity but also plays an essential role in tumor growth, invasion, metastasis, and therapeutics. In this paper, a non-equilibrium thermodynamic theory is established to study the chemo-mechanical behaviors of tumor ECM, which is modeled...

The adhesion of two-dimensional (2D) materials to other surfaces is so far believed to be a solid-solid mechanical contact. Here, we conduct both atomistic simulations and theoretical modeling to show that there exists a reversible conversion of energy between thermal and mechanical work in the attachment/detachment of 2D materials on/off a surface...

Measuring fracture toughness of metallic glasses (MGs) is challenging, and a large scatter has been observed which has been at least partially attributed to varying processing conditions. Here, we investigated the influence of main processing conditions, cooling rate and processing environment, on the fracture toughness of MGs. Through a thermoplas...

The application of silicon as ultrahigh capacity electrodes in lithium-ion batteries has been limited by a number of mechanical degradation mechanisms including fracture, delamination and plastic ratcheting, as a result of its large volumetric change during lithiation and delithiation. Graphene coating is one feasible technique to mitigate the mech...

On-demand, ultrahigh precision delivery of molecules and cells assisted by scaffold is a pivotal theme in the field of controlled release, but it remains extremely challenging for ceramic-based macroporous scaffolds that are prevalently used in regenerative medicine. Sea sponges (Phylum Porifera), whose bodies possess hierarchical pores or channels...