Nanocomposite microcontainers

Investigating Solvent-Induced Aggregation in Edge-Functionalized Layered Silicates via All-Atom Molecular Dynamics Simulations

Molecular dynamics simulations can provide the means to visualize and understand the role of intermolecular interactions in the mechanisms involved in molecular aggregation. Along these lines, simulations can allow the study of how surface chemical modifications can influence nanomaterial assembly at the molecular level. Layered silicate clays have been of significant interest for some time, particularly with regard to their use in organic/inorganic nanocomposites. However, despite numerous reports on the covalent linkage of organic moieties via silanol condensation, the theoretical understanding of these systems has heretofore been limited to noncovalent interactions, specifically ionic interactions at the charged basal surfaces. Herein, a model for edge-functionalized layered aluminosilicate clay, based on the siloxane linkage, is presented. In addition to reproducing experimentally observed degrees of molecular aggregation of clay-linked perylene diimide derivatives with different terminal functional groups as a function of solvent composition, a molecular-level understanding of the role of van der Waals interactions and hydrogen bonding of the different end-groups on the aggregation state in different water/N,N-dimethylformamide mixtures is obtained. The reported model provides a means to simulate organic moieties covalently bound to the layered silicate edge, which will enable future simulations of nanocomposites and organic/inorganic hybrids based on this system.

Flexible polymeric patch based nanotherapeutics against non-cancer therapy

Flexible polymeric patches find widespread applications in biomedicine because of their biological and tunable features including excellent patient compliance, superior biocompatibility and biodegradation, as well as high loading capability and permeability of drug. Such polymeric patches are classified into microneedles (MNs), hydrogel, microcapsule, microsphere and fiber depending on the formed morphology. The combination of nanomaterials with polymeric patches allows for improved advantages of increased curative efficacy and lowered systemic toxicity, promoting on-demand and regulated drug administration, thus providing the great potential to their clinic translation. In this review, the category of flexible polymeric patches that are utilized to integrate with nanomaterials is briefly presented and their advantages in bioapplications are further discussed. The applications of nanomaterials embedded polymeric patches in non-cancerous diseases were also systematically reviewed, including diabetes therapy, wound healing, dermatological disease therapy, bone regeneration, cardiac repair, hair repair, obesity therapy and some immune disease therapy. Alternatively, the limitations, latest challenges and future perspectives of such biomedical therapeutic devices are addressed.

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The most explored polymeric patches, such as microneedle, hydrogel, microsphere, microcapsule, and fiber are summarized.

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Polymeric patches integrated with a diversity of nanomaterials are systematically overviewed in non-cancer therapy.

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The future prospective for the development of polymeric patch based nanotherapeutics is discussed.

Efficient prediction of temperature-dependent elastic and mechanical properties of 2D materials

An efficient automated toolkit for predicting the mechanical properties of materials can accelerate new materials design and discovery; this process often involves screening large configurational space in high-throughput calculations. Herein, we present the ElasTool toolkit for these applications. In particular, we use the ElasTool to study diversity of 2D materials and heterostructures including their temperature-dependent mechanical properties, and developed a machine learning algorithm for exploring predicted properties.

Green and sustainable cellulose-derived humidity sensors: A review

Cellulose, as the most abundant natural polysaccharide, is an excellent material for developing green humidity sensors, especially due to its humidity responsiveness as a result of its rich hydrophilic groups. In combination with other components including carbon materials and polymers, cellulose and its derivatives can be used to design high-performance humidity sensors that meet various application requirements. This review summarizes the recent advances in the field of various cellulose-derived humidity sensors, with particular attention paid to different sensing mechanisms including resistance, capacitance, colorimetry and gravity, and so on. Furthermore, the roles of cellulose and its derivatives are highlighted. This work may promote the development of cellulose-derived humidity sensors, as well as other cellulose-based intelligent materials.

Arrays of Biocompatible and Mechanically Robust Microchambers Made of Protein-Polyphenol-Clay Multilayer Films

There is a growing demand for biocompatible and mechanically robust arrays of microcompartments loaded with minute amounts of active substances for sensing or controlled release applications. Here we report on a novel biocompatible composite material, protein-polyphenol-clay (PPC) multilayer film. The material is shown to be strong enough to make robust microchambers retaining the shape and dimensions of truncated square pyramids. We study the mechanical properties and biocompatibility of the PPC microchambers and compare them to those made of synthetic polyelectrolyte multilayer film, poly(styrenesulfonate)-poly(allylammonium) (PSS-PAH). The mechanical properties of the microchambers were characterized under uniaxial compression using nanoindentation with a flat-punch tip. The effective Young's modulus of PPC microchambers, 166 ± 53 MPa, is found to be lower than that of PSS-PAH microchambers, 245 ± 52 MPa. However, the capacity to elastically absorb the energy of the former, 2.4 ± 1.0 MPa, is marginally higher than of the latter, 2.0 ± 1.3 MPa. Arrays of microchambers were sealed onto a polyethylene film, loaded with a model oil-soluble drug, and their biocompatibility was tested using an ex vivo 3D human skin reconstruct model. We found no evidence for toxicity with the PPC microchambers; however, PSS-PAH microchambers stimulated reduced cell density in the epidermis and significantly affected epidermal-dermal attachment. Both materials do not alter skin cell proliferation but affect skin cell differentiation. We interpret that rather than affecting epidermal barrier function, these data suggest the applied plastic films with microchamber arrays affect transpiration, normoxia, and moisture exchange.

pH dependent degradation properties of lactide based 3D microchamber arrays for sustained cargo release

Encapsulation of small water soluble molecules is important in a large variety of applications, ranging from medical substance releasing implants in the field of medicine over release of catalytically active substances in the field of chemical processing to anti-corrosion agents in industry. In this work polylactic acid (PLA) based hollow-structured microchamber (MC) arrays are fabricated via one-step dip coating of a silicone rubber stamp into PLA solution. These PLA MCs are able to retain small water soluble molecules (Rhodamine B) stably entrapped within aqueous environments. It is shown, that degradation of PLA MCs strongly depends on environmental conditions like surrounding pH and follows first order degradation kinetics. This pH dependent PLA MC degradation can be utilized to control the release kinetics of encapsulated cargo.

Site-specific release of reactive oxygen species from ordered arrays of microchambers based on polylactic acid and carbon nanodots

Illustration of the laser-assisted release of hydrophilic H₂O₂ cargo from free-standing ordered arrays of biopolymer-based microchambers in a highly controlled manner.

A transport model and constitutive equation for oppositely charged polyelectrolyte mixtures with application to layer-by-layer assembly

We develop a general framework for transport of polyions, solvent and salt, with intended application to Layer-by-Layer (LbL) assembly of polyelectrolyte monolayers (PEMs). The formulation for the first time includes electrostatics, chemical potential gradients, and mechanical stress gradients as driving forces for mass transport. The general model allows all species to be mobile throughout the process and avoids the assumptions of stepwise instantaneous equilibrium and/or immobilized structures typical of previous approaches, while reducing to these models in appropriate limits. A simple constitutive equation is derived for a mixture of oppositely charged polyelectrolytes that accounts for network strand dilution and cross-chain ion pairing by appending reactive terms to the Smoluchowski probability diffusion equation for network strand end-to-end vectors. The resulting general framework encompasses the Poisson equation describing the electrostatic potential distribution, an osmotic pressure balance, a stress constitutive equation, and a generalized flux law of polymer transport. The computational domain is split into a PEM phase and an external solution phase with an appropriate boundary condition derived for the interface between the two. The mobile species (water and small salt ions) are taken to be in a state of dynamic equilibrium with their distributions enslaved to the perturbations in the two polyion compositions. The proposed model captures the swelling response of PEM films to external solutions. For the first time, we studied the effects of the temporal evolution of electrostatic and stress distribution on the rate of chain loss and absorption during rinsing and dipping of an idealized and arbitrarily selected and rigid brush layer into external solutions. The temporal evolution provides a kinetic basis for the ability of LbL films to grow under conditions that thermodynamics alone suggests would cause them to be washed away and to account for partial desorption during washing. The proposed transport framework constitutes a solid basis for eventual quantitative modeling of LbL assembly and transport in polyion networks more generally.

Small-Scale Biological and Artificial Multidimensional Sensors for 3D Sensing

A vast majority of existing sub-millimeter-scale sensors have a planar, 2D geometry as a result of conventional top-down lithographic procedures. However, 2D sensors often suffer from restricted sensing capability, allowing only partial measurements of 3D quantities. Here, nano/microscale sensors with different geometric (1D, 2D, and 3D) configurations are reviewed to introduce their advantages and limitations when sensing changes in quantities in 3D space. This Review categorizes sensors based on their geometric configuration and sensing capabilities. Among the sensors reviewed here, the 3D configuration sensors defined on polyhedral structures are especially advantageous when sensing spatially distributed 3D quantities. The nano- and microscale vertex configuration forming polyhedral structures enable full 3D spatial sensing due to orthogonally aligned sensing elements. Particularly, the cubic configuration leveraged in 3D sensors offers an array of diverse applications in the field of biosensing for micro-organisms and proteins, optical metamaterials for invisibility cloaking, 3D imaging, and low-power remote sensing of position and angular momentum for use in microbots. Here, various 3D sensors are compared to assess the advantages of their geometry and its impact on sensing mechanisms. 3D biosensors in nature are also explored to provide vital clues for the development of novel 3D sensors.

In-situ NIR-laser mediated bioactive substance delivery to single cell for EGFP expression based on biocompatible microchamber-arrays

Controlled drug delivery and gene expression is required for a large variety of applications including cancer therapy, wound healing, cell migration, cell modification, cell-analysis, reproductive and regenerative medicine. Controlled delivery of precise amounts of drugs to a single cell is especially interesting for cell and tissue engineering as well as therapeutics and has until now required the application of micro-pipettes, precisely placed dispersed drug delivery vehicles, or injections close to or into the cell. Here we present surface bound micro-chamber arrays able to store small hydrophilic molecules for prolonged times in subaqueous conditions supporting spatiotemporal near infrared laser mediated release. The micro-chambers (MCs) are composed of biocompatible and biodegradable polylactic acid (PLA). Biocompatible gold nanoparticles are employed as light harvesting agents to facilitate photothermal MC opening. The degree of photothermal heating is determined by numerical simulations utilizing optical properties of the MC, and confirmed by Brownian motion measurements of laser-irradiated micro-particles exhibiting similar optical properties like the MCs. The amount of bioactive small molecular cargo (doxycycline) from local release is determined by fluorescence spectroscopy and gene expression in isolated C2C12 cells via enhanced green fluorescent protein (EGFP) biosynthesis.

Halloysite Nanotubes: Controlled Access and Release by Smart Gates

Hollow halloysite nanotubes have been used as nanocontainers for loading and for the triggered release of calcium hydroxide for paper preservation. A strategy for placing end-stoppers into the tubular nanocontainer is proposed and the sustained release from the cavity is reported. The incorporation of Ca(OH)₂ into the nanotube lumen, as demonstrated using transmission electron microscopy (TEM) imaging and Energy Dispersive X-ray (EDX) mapping, retards the carbonatation, delaying the reaction with CO₂ gas. This effect can be further controlled by placing the end-stoppers. The obtained material is tested for paper deacidification. We prove that adding halloysite filled with Ca(OH)₂ to paper can reduce the impact of acid exposure on both the mechanical performance and pH alteration. The end-stoppers have a double effect: they preserve the calcium hydroxide from carbonation, and they prevent from the formation of highly basic pH and trigger the response to acid exposure minimizing the pH drop-down. These features are promising for a composite nanoadditive in the smart protection of cellulose-based materials.

Polylactic Acid Sealed Polyelectrolyte Multilayer Microchambers for Entrapment of Salts and Small Hydrophilic Molecules Precipitates

Efficient depot systems for entrapment and storage of small water-soluble molecules are of high demand for wide variety of applications ranging from implant based drug delivery in medicine and catalysis in chemical processes to anticorrosive systems in industry where surface-mediated active component delivery is required on a time and site specific manner. This work reports the fabrication of individually sealed hollow-structured polyelectrolyte multilayer (PEM) microchamber arrays based on layer-by-layer self-assembly as scaffolds and microcontact printing. These PEM chambers are composed out of biocompatible polyelectrolytes and sealed by a monolayer of hydrophobic biocompatible and biodegradable polylactic acid (PLA). Coating the chambers with hydrophobic PLA allows for entrapment of a microair-bubble in each chamber that seals and hence drastically reduces the PEM permeability. PLA@PEM microchambers are proven to enable prolonged subaqueous storage of small hydrophilic salts and molecules such as crystalline NaCl, doxicycline, and fluorescent dye rhodamine B. The presented microchambers are able to entrap air bubbles and demonstrate a novel strategy for entrapment, storage, and protection of micropackaged water-soluble substances in precipitated form. These chambers allow triggered release as demonstrated by ultrasound responsiveness of the chambers. Low-frequency ultrasound exposure is utilized for microchamber opening and payload release.

Self-Assembled Three-Dimensional Graphene-Based Polyhedrons Inducing Volumetric Light Confinement

The ability to transform two-dimensional (2D) materials into a three-dimensional (3D) structure while preserving their unique inherent properties might offer great enticing opportunities in the development of diverse applications for next generation micro/nanodevices. Here, a self-assembly process is introduced for building free-standing 3D, micro/nanoscale, hollow, polyhedral structures configured with a few layers of graphene-based materials: graphene and graphene oxide. The 3D structures have been further modified with surface patterning, realized through the inclusion of metal patterns on their 3D surfaces. The 3D geometry leads to a nontrivial spatial distribution of strong electric fields (volumetric light confinement) induced by 3D plasmon hybridization on the surface of the graphene forming the 3D structures. Due to coupling in all directions, resulting in 3D plasmon hybridization, the 3D closed box graphene generates a highly confined electric field within as well as outside of the cubes. Moreover, since the uniform coupling reduces the decay of the field enhancement away from the surface, the confined electric field inside of the 3D structure shows two orders of magnitude higher than that of 2D graphene before transformation into the 3D structure. Therefore, these structures might be used for detection of target substances (not limited to only the graphene surfaces, but using the entire volume formed by the 3D graphene-based structure) in sensor applications.

Tribological Properties of Water-lubricated Rubber Materials after Modification by MoS2 Nanoparticles

Frictional vibration and noise caused by water-lubricated rubber stern tube bearings, which are generated under extreme conditions, severely threaten underwater vehicles’ survivability and concealment performance. This study investigates the effect of flaky and spherical MoS₂ nanoparticles on tribological properties and damping capacity of water-lubricated rubber materials, with the aim of decreasing frictional noise. A CBZ-1 tribo-tester was used to conduct the sliding tests between rubber ring-discs and ZCuSn₁₀Zn₂ ring-discs with water lubrication. These materials’ typical mechanical properties were analysed and compared. Coefficients of friction (COFs), wear rates, and surface morphologies were evaluated. Frictional noise and critical velocities of generating friction vibration were examined to corroborate above analysis. Results showed that spherical MoS₂ nanoparticles enhanced rubber material’s mechanical and tribological properties and, in turn, reduced the friction noise and critical velocity. Flaky MoS₂ nanoparticles reduced COF but did not enhance their mechanical properties, i.e., the damping capacity, wear resistance property; thus, these nanoparticles did not reduce the critical velocity obviously, even though increased the frictional noise at high load. The knowledge gained in the present work will be useful for optimizing friction pairs under extreme conditions to decrease frictional noise of water-lubricated rubber stern tube bearings.

Control of Reversible Self-Bending Behavior in Responsive Janus Microstrips

Here, we demonstrate a simple method to systematically control the responsive self-bending behavior of Janus hydrogel microstrips consisting of a polymeric bilayer with a high modulus contrast. The Janus hydrogel microstrips could be easily fabricated by a simple micromolding technique combined with an initiated chemical vapor deposition (iCVD) coating, providing high flexibility in controlling the physical and chemical properties of the microstrips. The fabricated Janus hydrogel microstrip is composed of a soft, pH-responsive polymer hydrogel layer laminated with a highly cross-linked, rigid thin film, generating a geometric anisotropy at a micron scale. The large difference in the elastic moduli between the two layers of the Janus microstrips leads to a self-bending behavior in response to the pH change. More specifically, the impact of the physical and chemical properties of the microstrip on the self-bending phenomena was systematically investigated by changing the thickness and composition of two layers of the microstrip, which renders high controllability in bending of the microstrips. The curvature of the Janus microstrips, formed by self-bending, highly depends on the applied acidity. A reversible, responsive self-bending/unbending exhibits a perfect resilience pattern with repeated changes in pH for 5 cycles. We envision that the Janus microstrips can be engineered to form complex 3D microstructures applicable to various fields such as soft robotics, scaffolds, and drug delivery. The reliable responsive behaviors obtained from the systematic investigation will provide critical information in bridging the gap between the theoretical mechanical analysis and the chemical properties to achieve micron-scale soft robotics.

Cytokine loaded layer-by-layer ultrathin matrices to deliver single dermal papilla cells for spot-by-spot hair follicle regeneration

Polymer nanocoated dermal papilla cells promoting hair regeneration.

Cellulose Nanocrystal Microcapsules as Tunable Cages for Nano- and Microparticles

We demonstrate the fabrication of highly open spherical cages with large through pores using high aspect ratio cellulose nanocrystals with "haystack" shell morphology. In contrast to traditional ultrathin shell polymer microcapsules with random porous morphology and pore sizes below 10 nm with limited molecular permeability of individual macromolecules, the resilient cage-like microcapsules show a remarkable open network morphology that facilitates across-shell transport of large solid particles with a diameter from 30 to 100 nm. Moreover, the transport properties of solid nanoparticles through these shells can be pH-triggered without disassembly of these shells. Such behavior allows for the controlled loading and unloading of solid nanoparticles with much larger dimensions than molecular objects reported for conventional polymeric microcapsules.

Introducing a high gravity field to enhance infiltration of small molecules into polyelectrolyte multilayers

Loading functional small molecules into nano-thin films is fundamental to various research fields such as membrane separation, molecular imprinting, interfacial reaction, drug delivery etc. Currently, a general demand for enhancing the loading rate without affecting the film structures exists in most infiltration phenomena. To handle this issue, we have introduced a process intensification method of a high gravity technique, which is a versatile energy form of mechanical field well-established in industry, into the investigations on diffusion/infiltration at the molecular level. By taking a polyelectrolyte multilayer as a model thin film and a photo-reactive molecule, 4,4'-diazostilbene-2,2'-disulfonic acid disodium salt (DAS), as a model small functional molecule, we have demonstrated remarkably accelerated adsorption/infiltration of DAS into a poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) multilayer by as high as 20-fold; meanwhile, both the film property of the multilayer and photoresponsive-crosslinking function of DAS were not disturbed. Furthermore, the infiltration of DAS and the surface morphology of the multilayer could be tuned based on their high dependence on the intensity of the high gravity field regarding different rotating speeds. The mechanism of the accelerated adsorption/infiltration under the high gravity field was interpreted by the increased turbulence of the diffusing layer with the thinned laminar boundary layer and the stepwise delivery of the local concentration gradient from the solution to the interior of the multilayer. The introduction of mechanical field provides a simple and versatile strategy to address the paradox of the contradictory loading amount and loading rate, and thus to promote applications of various membrane processes.

Multifunctional inverse opal particles for drug delivery and monitoring

Particle-based delivery systems have a demonstrated value for drug discovery and development. Here, we report a new type of particle-based delivery system that has controllable release and is self-monitoring. The particles were composed of poly(N-isopropylacrylamide) (pNIPAM) hydrogel with an inverse opal structure. The presence of macropores in the particles provides channels for active drug loading and release from the materials.

Self-(Un)rolling Biopolymer Microstructures: Rings, Tubules, and Helical Tubules from the Same Material

We have demonstrated the facile formation of reversible and fast self-rolling biopolymer microstructures from sandwiched active-passive, silk-on-silk materials. Both experimental and modeling results confirmed that the shape of individual sheets effectively controls biaxial stresses within these sheets, which can self-roll into distinct 3D structures including microscopic rings, tubules, and helical tubules. This is a unique example of tailoring self-rolled 3D geometries through shape design without changing the inner morphology of active bimorph biomaterials. In contrast to traditional organic-soluble synthetic materials, we utilized a biocompatible and biodegradable biopolymer that underwent a facile aqueous layer-by-layer (LbL) assembly process for the fabrication of 2D films. The resulting films can undergo reversible pH-triggered rolling/unrolling, with a variety of 3D structures forming from biopolymer structures that have identical morphology and composition.

Pushing the Limits: 3D Layer-by-Layer-Assembled Composites for Cathodes with 160 C Discharge Rates

Deficiencies of cathode materials severely limit cycling performance and discharge rates of Li batteries. The key problem is that cathode materials must combine multiple properties: high lithium ion intercalation capacity, electrical/ionic conductivity, porosity, and mechanical toughness. Some materials revealed promising characteristics in a subset of these properties, but attaining the entire set of often contrarian characteristics requires new methods of materials engineering. In this paper, we report high surface area 3D composite from reduced graphene oxide loaded with LiFePO4 (LFP) nanoparticles made by layer-by-layer assembly (LBL). High electrical conductivity of the LBL composite is combined with high ionic conductivity, toughness, and low impedance. As a result of such materials properties, reversible lithium storage capacity and Coulombic efficiency were as high as 148 mA h g(-1) and 99%, respectively, after 100 cycles at 1 C. Moreover, these composites enabled unusually high reversible charge-discharge rates up to 160 C with a storage capacity of 56 mA h g(-1), exceeding those of known LFP-based cathodes, some of them by several times while retaining high content of active cathode material. The study demonstrates that LBL-assembled composites enable resolution of difficult materials engineering tasks.

A 3-D multicellular tumor spheroid on ultrathin matrix coated single cancer cells provides a tumor microenvironment model to study epithelial-to-mesenchymal transitions

We report a 3D tumor spheroid model to study epithelial-to-mesenchymal transitions (EMT) using ultra-thin matrix coated single cancer cells.

Active drug release systems: current status, applications and perspectives

Active drug release systems offer an important privilege to manage the dosage, time and sometimes site of drug release after the implantation procedure has been performed. Once developed, they could cover such applications as hormone therapy, implantation surgery, and delivery of immunization boosters. A number of existing approaches towards such systems include arrays of microreservoirs equipped with stimuli-responsive actuators or valves. The very first developed system has reached the stage of in-human trials recently. A breakthrough could happen if microreservoirs themselves are made of responsive material susceptible towards remote triggers. A promising candidate is a material made of Layer-by-Layer assembled films which currently are widely exploited only as passive implantable drug release systems.

Shape-morphing nanocomposite origami

Nature provides a vast array of solid materials that repeatedly and reversibly transform in shape in response to environmental variations. This property is essential, for example, for new energy-saving technologies, efficient collection of solar radiation, and thermal management. Here we report a similar shape-morphing mechanism using differential swelling of hydrophilic polyelectrolyte multilayer inkjets deposited on an LBL carbon nanotube (CNT) composite. The out-of-plane deflection can be precisely controlled, as predicted by theoretical analysis. We also demonstrate a controlled and stimuli-responsive twisting motion on a spiral-shaped LBL nanocomposite. By mimicking the motions achieved in nature, this method offers new opportunities for the design and fabrication of functional stimuli-responsive shape-morphing nanoscale and microscale structures for a variety of applications.