Compartmentalized multilayer hydrogel formation using a stimulus-responsive self-assembling polysaccharide

Programmable Electrical Signals Induce Anisotropic Assembly of Multilayer Chitosan Hydrogels

Multilayer hydrogels are widely used in biomedical-related fields due to their complex and variable spatial structures. Various strategies have been developed for preparing multilayer hydrogels, among which electrically induced self-assembly provides a simple and effective method for multilayer hydrogel fabrication. By application of an oscillatory electrical signal sequence, multilayer hydrogels with distinct boundaries can be formed according to the provided programmable signals. In this work, we establish an electrical field in microfluidics combined with polarized light microscopy for in situ visualization of anisotropic construction of multilayer chitosan hydrogel. The noninvasive, real-time birefringence images allow us to monitor the orientation within the hydrogel in response to electrical signals. An increased birefringence was observed from the solution-gel side to the electrode surface side, and a brief electrical signal interruption did not affect the anisotropic assembly process. This understanding of the oscillatory electrical signal-induced hydrogel anisotropy assembly allows us to fabricate chitosan hydrogels with a complex and spatially varying structure.

Treatment of Periodontal Infections, the Possible Role of Hydrogels as Antibiotic Drug-Delivery Systems

With the advancement of biomedical research into antimicrobial treatments for various diseases, the source and delivery of antibiotics have attracted attention. In periodontal diseases, antibiotics are integral in positive treatment outcomes; however, the use of antibiotics is with caution as the potential for the emergence of resistant strains is of concern. Over the years, conventional routes of drug administration have been proven to be effective for the treatment of PD, yet the problem of antibiotic resistance to conventional therapies continues to remain a setback in future treatments. Hydrogels fabricated from natural and synthetic polymers have been extensively applied in biomedical sciences for the delivery of potent biological compounds. These polymeric materials either have intrinsic antibacterial properties or serve as good carriers for the delivery of antibacterial agents. The biocompatibility, low toxicity and biodegradability of some hydrogels have favoured their consideration as prospective carriers for antibacterial drug delivery in PD. This article reviews PD and its antibiotic treatment options, the role of bacteria in PD and the potential of hydrogels as antibacterial agents and for antibiotic drug delivery in PD. Finally, potential challenges and future directions of hydrogels for use in PD treatment and diagnosis are also highlighted.

Electrically induced anisotropic assembly of chitosan with different molecular weights

Anisotropic hydrogel is emerging as an important soft matter in the field of bionics and bioactuators, owing to its outstanding mechanical toughness and strength. Understanding the dynamic construction process of anisotropic hydrogel is beneficial for matching subsequent application. In this work, we establish an electrical field in microfluidics for the in-situ real time visualization of anisotropic assembly of chitosan, an amino polysaccharide. Polarized light microscopy is adopted to observe the dynamic growth of chitosan with different molecular weights. The results demonstrate that electrical signal has a profound influence on anisotropic assembly process of chitosan. It is interesting to notice that high oriented structure can be found in chitosan hydrogel with large molecular weight, which exhibits a dense and compact structure. This work provides a new perspective for predicting and controlling the formation of different molecular weights anisotropic chitosan hydrogels, which permit the rational design of chitosan hydrogels with excellent mechanical properties and specific functions.

Nanoarchitectonics beyond perfect order - not quite perfect but quite useful

Nanoarchitectonics, like architectonics, allows the design and building of structures, but at the nanoscale. Unlike those in architectonics, and even macro-, micro-, and atomic-scale architectonics, the assembled structures at the nanoscale do not always follow the projected design. In fact, they do follow the projected design but only for self-assembly processes producing structures with perfect order. Here, we look at nanoarchitectonics allowing the building of nanostructures without a perfect arrangement of building blocks. Here, fabrication of structures from molecules, polymers, nanoparticles, and nanosheets to polymer brushes, layer-by-layer assembly structures, and hydrogels through self-assembly processes is discussed, where perfect order is not necessarily the aim to be achieved. Both planar substrate and spherical template-based assemblies are discussed, showing the challenging nature of research in this field and the usefulness of such structures for numerous applications, which are also discussed here.

Manufacturing and post-engineering strategies of hydrogel actuators and sensors: From materials to interfaces

Living bodies are made of numerous bio-sensors and actuators for perceiving external stimuli and making movement. Hydrogels have been considered as ideal candidates for manufacturing bio-sensors and actuators because of their excellent biocompatibility, similar mechanical and electrical properties to that of living organs. The key point of manufacturing hydrogel sensors/actuators is that the materials should not only possess excellent mechanical and electrical properties but also form effective interfacial connections with various substrates. Traditional hydrogel normally shows high electrical resistance (~ MΩ•cm) with limited mechanical strength (<1 MPa), and it is prone to fatigue fracture during continuous loading-unloading cycles. Just like iron should be toughened and hardened into steel, manufacturing and post-treatment processes are necessary for modifying hydrogels. Besides, advanced design and manufacturing strategies can build effective interfaces between sensors/actuators and other substrates, thus enhancing the desired mechanical and electrical performances. Although various literatures have reviewed the manufacture or modification of hydrogels, the summary regarding the post-treatment strategies and the creation of effective electrical and mechanically sustainable interfaces are still lacking. This paper aims at providing an overview of the following topics: (i) the manufacturing and post-engineering treatment of hydrogel sensors and actuators; (ii) the processes of creating sensor(actuator)-substrate interfaces; (iii) the development and innovation of hydrogel manufacturing and interface creation. In the first section, the manufacturing processes and the principles for post-engineering treatments are discussed, and some typical examples are also presented. In the second section, the studies of interfaces between hydrogels and various substrates are reviewed. Lastly, we summarize the current manufacturing processes of hydrogels, and provide potential perspectives for hydrogel manufacturing and post-treatment methods.

Smart Hydrogel Formed by Alginate-g-Poly(N-isopropylacrylamide) and Chitosan through Polyelectrolyte Complexation and Its Controlled Release Properties

Smart hydrogels that can respond to external stimuli such as temperature and pH have attracted tremendous interest for biological and biomedical applications. In this work, we synthesized two alginate-graft-poly(N-isopropylacrylamide) (Alg-g-PNIPAAm) copolymers and aimed to prepare smart hydrogels through formation of polyelectrolyte complex (PEC) between the negatively charged Alg-g-PNIPAAm copolymers and the positively charged chitosan (Cts) in aqueous solutions. The hydrogels were expected to be able to respond to both temperature and pH changes due to the nature of Alg-g-PNIPAAm and chitosan. The hydrogel formation was determined by a test tube inverting method and confirmed by the rheological measurements. The rheological measurements showed that the PEC hydrogels formed at room temperature could be further enhanced by increasing temperature over the lower critical solution temperature (LCST) of PNIPAAm, because PNIPAAm would change from hydrophilic to hydrophobic upon increasing temperature over its LCST, and the hydrophobic interaction between the PNIPAAm segments may act as additional physical crosslinking. The controlled release properties of the hydrogels were studied by using the organic dye rhodamine B (RB) as a model drug at different pH. The PEC hydrogels could sustain the RB release more efficiently at neutral pH. Both low pH and high pH weakened the PEC hydrogels, and resulted in less sustained release profiles. The release kinetics data were found to fit well to the Krosmyer-Peppas power law model. The analysis of the release kinetic parameters obtained by the modelling indicates that the release of RB from the PEC hydrogels followed mechanisms combining diffusion and dissolution of the hydrogels, but the release was mainly governed by diffusion with less dissolution at pH 7.4 when the PEC hydrogels were stronger and stabler than those at pH 5.0 and 10.0. Therefore, the PEC hydrogels are a kind of smart hydrogels holding great potential for drug delivery applications.

Fabrication and characterization of a toughened spherical chitosan adsorbent only through physical crosslinking based on mechanism of Chain Rearrangement

Chitosan extracted from natural products has gained tremendous attention in the field of adsorption and separation due to its inherent biocompatibility and potential applications. In this research, we synthesized a new type of spherical chitosan adsorbent (SCA) by controlling the mass transfer rate of the entanglement of the polymer chains in the recombination process. This SCA is a highly crystalline polymer material with outstanding mechanical strength, high adsorption capacity, a porous surface and suitable particle size distribution. The value of the sphericity of attrition of this SCA was 89.8%, which is the same as that of the commercial macroporous resin with a polystyrene matrix. The X-ray diffraction (XRD) patterns and differential scanning calorimetry (DSC) curves showed a significant change from powder to spherical structure and confirmed that the SCA is highly ordered and crystalline. Optical microscopy (OM) and scanning electron microscopy (SEM) demonstrated that the SCA was composed of a tightly stacked fiber structure, indicating the homogeneity of the polymerization. The porous structure of the surface provided a channel for mass transfer, which was indicated by a test of the ion exchange capacity and the adsorption performance of the SCA with Cu(ii) as the adsorbed subject. The adsorption capacity was higher than those of all reported non-composite chitosan materials. Therefore, we have successfully synthesized a completely green, nontoxic and environmentally friendly adsorbing resin equipped with excellent mechanical properties and adsorption capacity for future applications in many new fields.

Multicompartment Hydrogels

Hydrogels belong to the most promising materials in polymer and materials science at the moment. As they feature soft and tissue-like character as well as high water-content, a broad range of applications are addressed with hydrogels, e.g. tissue engineering and wound dressings but also soft robotics, drug delivery, actuators and catalysis. Ways to tailor hydrogel properties are crosslinking mechanism, hydrogel shape and reinforcement, but new features can be introduced by variation of hydrogel composition as well, e.g. via monomer choice, functionalization or compartmentalization. Especially, multicompartment hydrogels drive progress towards complex and highly functional soft materials. In the present review the latest developments in multicompartment hydrogels are highlighted with a focus on three types of compartments, i.e. micellar/vesicular, droplets or multi-layers including various sub-categories. Furthermore, several morphologies of compartmentalized hydrogels and applications of multicompartment hydrogels will be discussed as well. Finally, an outlook towards future developments of the field will be given. The further development of multicompartment hydrogels is highly relevant for a broad range of applications and will have a significant impact on biomedicine and organic devices. This article is protected by copyright. All rights reserved.

Ion-responsive chitosan hydrogel actuator inspired by carrotwood seed pod

Inspired by the gradient hygroscopic structure of carrotwood seed pod, patterned anisotropic structure was created in polysaccharide hydrogel by an anodic electrical writing process. Locally released Fe²⁺ was oxidized to Fe³⁺ and chelated with chitosan chains in the written area, resulting in a gradient structure in the hydrogel. The asymmetrical stress generated by the different swelling of the gradient structure enables the hydrogel to bend autonomously. The hydrogel shows opposite bending in deionized water and NaCl solution. The physicochemical properties of the hydrogel are characterized by tensile test, SEM, EDS, XRD, TGA, DTG and FT-IR. SEM and EDS show that the written hydrogel has a structural gradient and a concentration gradient of Fe³⁺ vertically. Moreover, anodic electrical writing increases the flexibility of chitosan hydrogel due to decreased crystallinity. This controllable electrical writing technique is convenient to create patterned anisotropic structure and provide a novel design concept for natural hydrogel actuators.

Research Progress in the Multilayer Hydrogels

Hydrogels have been widely used in many fields including biomedicine and water treatment. Significant achievements have been made in these fields due to the extraordinary properties of hydrogels, such as facile processability and tissue similarity. However, based on the in-depth study of the microstructures of hydrogels, as a result of the enhancement of biomedical requirements in drug delivery, cell encapsulation, cartilage regeneration, and other aspects, it is challenge for conventional homogeneous hydrogels to simultaneously meet different needs. Fortunately, heterogeneous multilayer hydrogels have emerged and become an important branch of hydrogels research. In this review, their main preparation processes and mechanisms as well as their composites from different resources and methods, are introduced. Moreover, the more recent achievements and potential applications are also highlighted, and their future development prospects are clarified and briefly discussed.

A double-layer hydrogel based on alginate-carboxymethyl cellulose and synthetic polymer as sustained drug delivery system

A new double-layer, pH-sensitive, composite hydrogel sustained-release system based on polysaccharides and synthetic polymers with combined functions of different inner/outer hydrogels was prepared. The polysaccharides inner core based on sodium alginate (SA) and carboxymethyl cellulose (CMC), was formed by physical crosslinking with pH-sensitive property. The synthetic polymer out-layer with enhanced stability was introduced by chemical crosslinking to eliminate the expansion of inner core and the diffusion of inner content. The physicochemical structure of the double-layer hydrogels was characterized. The drug-release results demonstrated that the sustained-release effect of the hydrogels for different model drugs could be regulated by changing the composition or thickness of the hydrogel layer. The significant sustained-release effect for BSA and indomethacin indicated that the bilayer hydrogel can be developed into a novel sustained delivery system for bioactive substance or drugs with potential applications in drugs and functional foods.

Electrochemiluminescence and Photoluminescence of Carbon Quantum Dots Controlled by Aggregation-Induced Emission, Aggregation-Caused Quenching, and Interfacial Reactions

Carbon quantum dots (CQDs) show promise in optoelectronics as a light emitter due to simple synthesis, biocompatibility and strong tunable light emissions. However, CQDs commonly suffer from aggregation caused quenching (ACQ), inhibiting the full potential of these light emitters. Studies into different ideal light emitters have shown enhancements when converting common ACQ effects to aggregation induced emission (AIE) effects. We report CQD synthesis using citric acid and high/low thiourea concentrations, or sample 2/1. These two CQDs exhibited AIE and ACQ PL effects, respectively. CQD characterizations and photoluminescence interrogations of CQD films and solutions revealed that these unique emission mechanisms likely arose from different S incorporations into the CQDs. Furthermore, it was discovered that sample 2 emitted electrochemiluminescence (ECL) more intensely than sample 1 in a homogenous solution with S₂O₈^2- as a coreactant, due to aggregation and interactions of CQD species in solution. Very interestingly, sample 1's CQD film|S₂O₈^2- system achieved an ECL efficiency of 26% and emitted roughly 26 times more efficiently than sample 2 in the same conditions. Predominant interfacial reactions and surface state emission produced intense white light with a correlated color temperature of 2000 K. Spooling ECL spectroscopy was utilized to investigate emission mechanisms. Sample 2's CQD film|TPrA system had four times higher ECL intensity than that of sample 1, most likely due to π-cation interactions leading to a strong CQD^•+ stability, thereby, enhancing ECL. It is anticipated that ECL enhancement of CQD films or solutions by means of AIE will lead to wide CQD optoelectronic applications.

Efficient White Electrochemiluminescent Emission From Carbon Quantum Dot Films

Carbon quantum dots (CQDs) were manufactured from citric acid and urea in a gram-scale synthesis with a controlled size range between 1. 5 and 23.8 nm. The size control was realized by varying volume of the precursor solution in a hydrothermal synthesis method. The prepared CQDs were investigated using electrochemiluminescence (ECL) spectroscopy at interfaces of their electrode films and electrolyte solution containing coreactants rather than conventional optoelectronic tests, providing an in-depth analysis of light-emission mechanisms of the so-called half-cells. ECL from the CQD films with TPrA and K2S2O8 as coreactants provided information on the stability of the CQD radicals in the films. It was discovered that CQD•- has a powerful electron donating nature to sulfate radical to generate ECL at a relative efficiency of 96% to the Ru(bpy)3Cl2/K2S2O8 coreactant system, indicating a strong performance in light emitting applications. The smaller the CQD particle sizes, the higher the ECL efficiency of the film interface, most likely due to the increased presence of surface states per mass of CQDs. Spooling ECL spectroscopy of the system revealed a potential-dependent light emission starting from a deep red color to blue-shifted intensity maximum, cool bright white emission with a correlated color temperature of 3,200 K. This color temperature is appropriate for most indoor lighting applications. The above ECL results provide information on the performance of CQD light emitters in films, permitting preliminary screening for light emitting candidates in optoelectronic applications. This screening has revealed CQD films as a powerful and cost-effective light emitting layer toward lighting devices for indoor applications.

Electrobiofabrication: electrically based fabrication with biologically derived materials

While conventional material fabrication methods focus on form and strength to achieve function, the fabrication of material systems for emerging life science applications will need to satisfy a more subtle set of requirements. A common goal for biofabrication is to recapitulate complex biological contexts (e.g. tissue) for applications that range from animal-on-a-chip to regenerative medicine. In these cases, the material systems will need to: (i) present appropriate surface functionalities over a hierarchy of length scales (e.g. molecular features that enable cell adhesion and topographical features that guide differentiation); (ii) provide a suite of mechanobiological cues that promote the emergence of native-like tissue form and function; and (iii) organize structure to control cellular ingress and molecular transport, to enable the development of an interconnected cellular community that is engaged in cell signaling. And these requirements are not likely to be static but will vary over time and space, which will require capabilities of the material systems to dynamically respond, adapt, heal and reconfigure. Here, we review recent advances in the use of electrically based fabrication methods to build material systems from biological macromolecules (e.g. chitosan, alginate, collagen and silk). Electrical signals are especially convenient for fabrication because they can be controllably imposed to promote the electrophoresis, alignment, self-assembly and functionalization of macromolecules to generate hierarchically organized material systems. Importantly, this electrically based fabrication with biologically derived materials (i.e. electrobiofabrication) is complementary to existing methods (photolithographic and printing), and enables access to the biotechnology toolbox (e.g. enzymatic-assembly and protein engineering, and gene expression) to offer exquisite control of structure and function. We envision that electrobiofabrication will emerge as an important platform technology for organizing soft matter into dynamic material systems that mimic biology's complexity of structure and versatility of function.

Construction of ordered structure in polysaccharide hydrogel: A review

Hydrogels are three-dimensional, hydrophilic, polymeric networks, held together by a variety of physical or chemical crosslinks. Among the numerous polymers that can be employed to fabricate hydrogel, polysaccharides have attracted enormous attention due to their peculiar properties that make them suitable for various applications. Compared with homogeneous hydrogels, hydrogels with ordered structures on various length scales are endowed with excellent properties and promising applications in materials science. In the present review, a wide range of techniques were introduced and discussed, which had been utilized to construct ordered hierarchical structures in polysaccharide hydrogels. These techniques focused on the construction of multi-layered and orientated structure, which are two typical and very important forms of hierarchical structure.

Suppressing inflammation and enhancing osteogenesis using novel CS-EC@Ca microcapsules

The aim of this study was to investigate the suppression of inflammation and enhancement of osteogenesis using chitosan-coated calcium hydroxide-loaded microcapsules (CS-EC@Ca microcapsules) in vivo. Circular defects were created in the mandibular bones of rabbits and filled with Ca(OH)₂ , Bio-oss, or CS-EC@Ca microcapsules, and rabbits without drug implantation served as the controls. Lipopolysaccharides were injected in situ daily in all groups for 7 days. Mandibular bones were investigated at 4 and 12 weeks after surgery using micro-CT, histological observations, and real-time PCR analysis. At the postoperation, there was more substantial nascent bone in the microcapsule and Bio-oss groups than in the control group. The recovery of the rabbits in the Ca(OH)₂ group was slower than the control group, as determined using micro-CT and histological staining. Osteocalcin and collagen type I production was not significantly different between the microcapsule and Bio-oss groups (p > 0.05), but the expression levels of the two molecules were significantly increased compared to the control and Ca(OH)₂ groups at postoperation (p < 0.05). The mRNA transcript levels of inflammatory factors in the microcapsule group had the most reduced expression of IL-6 and TNF-α (p < 0.05). The microcapsules significantly reduced inflammation and promoted osteogenesis in this rabbit model of inflammatory bone destruction. Our findings indicate that CS-EC@Ca microcapsules hold potential for use in apical periodontitis treatment. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 3222-3230, 2018.

Facile Biofabrication of Heterogeneous Multilayer Tubular Hydrogels by Fast Diffusion-Induced Gelation

Multilayer (ML) hydrogels are useful to achieve stepwise and heterogeneous control over the organization of biomedical materials and cells. There are numerous challenges in the development of fabrication approaches toward this, including the need for mild processing conditions that maintain the integrity of embedded compounds and the versatility in processing to introduce desired complexity. Here, we report a method to fabricate heterogeneous multilayered hydrogels based on diffusion-induced gelation. This technique uses the quick diffusion of ions and small molecules (i.e., photoinitiators) through gel-sol or gel-gel interfaces to produce hydrogel layers. Specifically, ionically (e.g., alginate-based) and covalently [e.g., gelatin methacryloyl (GelMA-based)] photocross-linked hydrogels are generated in converse directions from the same interface. The ML (e.g., seven layers) ionic hydrogels can be formed within seconds to minutes with thicknesses ranging from tens to hundreds of micrometers. The thicknesses of the covalent hydrogels are determined by the reaction time (or the molecule diffusion time). Multiwalled tubular structures (e.g., mimicking branched multiwalled vessels) are mainly investigated in this study based on a removable gel core, but this method can be generalized to other material patterns. The process is also demonstrated to support the encapsulation of viable cells and is compatible with a range of thermally reversible core materials (e.g., gelatin and Pluronic F127) and covalently cross-linked formulations (e.g., GelMA and methacrylated hyaluronic acid). This biofabrication process enhances our ability to fabricate a range of structures that are useful for biomedical applications.

Bioinspired interconnected hydrogel capsules for enhanced catalysis

Polysaccharide-based hydrogel capsules with cristae-like internal membranes loaded with Ag nanoparticles exhibited effective catalytic activity as micro-reaction systems.

Onion-like multilayered polymer capsules synthesized by a bioinspired inside-out technique

Diverse structures in nature, such as the spinal disc and the onion have many concentric layers, and are created starting from the core and proceeding outwards. Here, we demonstrate an inside-out technique for creating multilayered polymer capsules. First, an initiator-loaded gel core is placed in a solution of monomer 1. The initiator diffuses outward and induces polymerization, leading to a shell of polymer 1. Thereafter, the core-shell structure is loaded with fresh initiator and placed in monomer 2, which causes a concentric shell of polymer 2 to form around the first shell. This process can be repeated to form multiple layers, each of a distinct polymer, and of controlled layer thickness. We show that these multilayered capsules can exhibit remarkable mechanical resilience as well as stimuli-responsive properties. The release of solutes from these capsules can be tailored to follow specific profiles depending on the chemistry and order of adjacent layers.Multiple concentric layers are present in a variety of structures present in nature, including the onion. Here, the authors show an inside-out strategy to synthesize multilayered polymer capsules, with different layers having specific composition and thereby specific responses to stimuli such as pH and temperature.

A Multiple Shape Memory Hydrogel Induced by Reversible Physical Interactions at Ambient Condition

A novel multiple shape memory hydrogel is fabricated based on two reversible physical interactions. The multiple shape memory property is endowed by a simple treatment of soaking in NaOH or NaCl solutions to form chitosan microcrystal or chain-entanglement crosslinks as temporary junctions.

Fusing Sensor Paradigms to Acquire Chemical Information: An Integrative Role for Smart Biopolymeric Hydrogels

The Information Age transformed our lives but it has had surprisingly little impact on the way chemical information (e.g., from our biological world) is acquired, analyzed and communicated. Sensor systems are poised to change this situation by providing rapid access to chemical information. This access will be enabled by technological advances from various fields: biology enables the synthesis, design and discovery of molecular recognition elements as well as the generation of cell-based signal processors; physics and chemistry are providing nano-components that facilitate the transmission and transduction of signals rich with chemical information; microfabrication is yielding sensors capable of receiving these signals through various modalities; and signal processing analysis enhances the extraction of chemical information. The authors contend that integral to the development of functional sensor systems will be materials that (i) enable the integrative and hierarchical assembly of various sensing components (for chemical recognition and signal transduction) and (ii) facilitate meaningful communication across modalities. It is suggested that stimuli-responsive self-assembling biopolymers can perform such integrative functions, and redox provides modality-spanning communication capabilities. Recent progress toward the development of electrochemical sensors to manage schizophrenia is used to illustrate the opportunities and challenges for enlisting sensors for chemical information processing.

A Universal Soaking Strategy to Convert Composite Hydrogels into Extremely Tough and Rapidly Recoverable Double-Network Hydrogels

Soak n' Boost: A universal strategy to manufacture hybrid double-network hydrogels with eminent mechanical properties is developed by postformation of the chitosan microcrystalline and chain-entanglement physical networks via simple treatment of the chitosan composite hydrogels using alkaline and saline solutions. The strategy may open an avenue to fabricate multifarious double-network hydrogels for promising applications in antifouling materials, drug delivery, and tissue engineering.

Electro-molecular Assembly: Electrical Writing of Information into an Erasable Polysaccharide Medium

We report that information can be written into an erasable hydrogel medium by precisely imposing controlled electrical signals that trigger supramolecular self-assembly. We prepare the medium from a blend of two stimuli-responsive self-assembling polysaccharides agarose (thermally responsive) and chitosan (pH-responsive). Upon cooling the blend, agarose forms the hydrogel medium while the embedded chitosan chains can be induced to self-assemble in response to imposed pH cues. Importantly, these triggering pH-cues can be imposed electrically (by inserted electrodes) enabling complex messages (e.g., self-assembled multilayers) to be written within the hydrogel medium. The reversibility of these self-assembly mechanisms allow the written information, and the medium itself, to be erased. These physicochemical properties enable this dual responsive medium to encrypt information, while the responsiveness of this structural information and the biocompatibility of the medium suggest uses for accessing/reporting information in diverse life science applications, such as foods, cosmetics, medicine, and the environment.

Biocompatible Double-Membrane Hydrogels from Cationic Cellulose Nanocrystals and Anionic Alginate as Complexing Drugs Codelivery

A biocompatible hydrogel with a double-membrane structure is developed from cationic cellulose nanocrystals (CNC) and anionic alginate. The architecture of the double-membrane hydrogel involves an external membrane composed of neat alginate, and an internal composite hydrogel consolidates by electrostatic interactions between cationic CNC and anionic alginate. The thickness of the outer layer can be regulated by the adsorption duration of neat alginate, and the shape of the inner layer can directly determine the morphology and dimensions of the double-membrane hydrogel (microsphere, capsule, and filmlike shapes). Two drugs are introduced into the different membranes of the hydrogel, which will ensure the complexing drugs codelivery and the varied drugs release behaviors from two membranes (rapid drug release of the outer hydrogel, and prolonged drug release of the inner hydrogel). The double-membrane hydrogel containing the chemically modified cellulose nanocrystals (CCNC) in the inner membrane hydrogel can provide the sustained drug release ascribed to the "nano-obstruction effect" and "nanolocking effect" induced by the presence of CCNC components in the hydrogels. Derived from natural polysaccharides (cellulose and alginate), the novel double-membrane structure hydrogel material developed in this study is biocompatible and can realize the complexing drugs release with the first quick release of one drug and the successively slow release of another drug, which is expected to achieve the synergistic release effects or potentially provide the solution to drug resistance in biomedical application.

pH-Responsive Self-Assembly of Polysaccharide through a Rugged Energy Landscape

Self-assembling polysaccharides can form complex networks with structures and properties highly dependent on the sequence of triggering cues. Controlling the emergence of such networks provides an opportunity to create soft matter with unique features; however, it requires a detailed understanding of the subtle balance between the attractive and repulsive forces that drives the stimuli-induced self-assembly. Here we employ all-atom molecular dynamics simulations on the order of 100 ns to study the mechanisms of the pH-responsive gelation of the weakly basic aminopolysaccharide chitosan. We find that low pH induces a sharp transition from gel to soluble state, analogous to pH-dependent folding of proteins, while at neutral and high pH self-assembly occurs via a rugged energy landscape, reminiscent of RNA folding. A surprising role of salt is to lubricate the conformational search for the thermodynamically stable states. Although our simulations represent the early events in the self-assembly process of chitosan, which may take seconds or minutes to complete, the atomically detailed insights are consistent with recent experimental observations and provide a basis for understanding how environmental conditions modulate the structure and mechanical properties of the self-assembled polysaccharide systems. The ability to control structure and properties via modification of process conditions will aid in the technological efforts to create complex soft matter with applications ranging from bioelectronics to regenerative medicine.

Self-assembly with orthogonal-imposed stimuli to impart structure and confer magnetic function to electrodeposited hydrogels

A magnetic nanocomposite film with the capability of reversibly collecting functionalized magnetic particles was fabricated by simultaneously imposing two orthogonal stimuli (electrical and magnetic). We demonstrate that cathodic codeposition of chitosan and Fe3O4 nanoparticles while simultaneously applying a magnetic field during codeposition can (i) organize structure, (ii) confer magnetic properties, and (iii) yield magnetic films that can perform reversible collection/assembly functions. The magnetic field triggered the self-assembly of Fe3O4 nanoparticles into hierarchical "chains" and "fibers" in the chitosan film. For controlled magnetic properties, the Fe3O4-chitosan film was electrodeposited in the presence of various strength magnetic fields and different deposition times. The magnetic properties of the resulting films should enable broad applications in complex devices. As a proof of concept, we demonstrate the reversible capture and release of green fluorescent protein (EGFP)-conjugated magnetic microparticles by the magnetic chitosan film. Moreover, antibody-functionalized magnetic microparticles were applied to capture cells from a sample, and these cells were collected, analyzed, and released by the magnetic chitosan film, paving the way for applications such as reusable biosensor interfaces (e.g., for pathogen detection). To our knowledge, this is the first report to apply a magnetic field during the electrodeposition of a hydrogel to generate magnetic soft matter. Importantly, the simple, rapid, and reagentless fabrication methodologies demonstrated here are valuable features for creating a magnetic device interface.

Vaccine self-assembling immune matrix is a new delivery platform that enhances immune responses to recombinant HBsAg in mice

Vaccination remains the most effective public health tool to prevent infectious diseases. Many vaccines are marginally effective and need enhancement for immunocompromised, elderly, and very young populations. To enhance immunogenicity, we exploited the biphasic property of the (RADA)4 synthetic oligopeptide to create VacSIM (vaccine self-assembling immune matrix), a new delivery method. VacSIM solution can easily be mixed with antigens, organisms, and adjuvants for injection. Postinjection, the peptides self-assemble into hydrated nanofiber gel matrices, forming a depot with antigens and adjuvants in the aqueous phase. We believe the depot provides slow release of immunogens, leading to increased activation of antigen-presenting cells that then drive enhanced immunogenicity. Using recombinant hepatitis B virus surface antigen (rHBsAg) as a model immunogen, we compared VacSIM delivery to delivery in alum or complete Freund's adjuvant (CFA). Delivery of the rHBsAg antigen to mice via VacSIM without adjuvant elicited higher specific IgG responses than when rHBsAg was delivered in alum or CFA. Evaluating IgG subtypes showed a mixed Th1/Th2 type response following immunization with VacSIM, which was driven further toward Th1 with addition of CpG as the adjuvant. Increased specific IgG endpoint titers were observed in both C57BL/6 and BALB/c mice, representative of Th1 and Th2 environments, respectively. Restimulation of splenocytes suggests that VacSIM does not cause an immediate proinflammatory response in the host. Overall, these results suggest that VacSIM, as a new delivery method, has the potential to enhance immunogenicity and efficacy of numerous vaccines.

Chitosan-decorated calcium hydroxide microcapsules with pH-triggered release for endodontic applications

The treatment of apical periodontitis (AP) remains challenging because traditional root canal therapy (RCT) outcomes are limited by the complexity of the root canal system, drug toxicity, and host immune factors.

Design of chitosan and its water soluble derivatives-based drug carriers with polyelectrolyte complexes

Chitosan, the cationic polysaccharide derived from the natural polysaccharide chitin, has been studied as a biomaterial for more than two decades. As a polycationic polymer with favorable properties, it has been widely used to form polyelectrolyte complexes with polyanions for various applications in drug delivery fields. In recent years, a growing number of studies have been focused on the preparation of polyelectrolyte complexes based on chitosan and its water soluble derivatives. They have been considered well-suited as biomaterials for a number of vital drug carriers with targeted/controlled release profiles, e.g., films, capsules, microcapsules. In this work, an overview highlights not only the favorable properties of chitosan and its water soluble derivatives but also the good performance of the polyelectrolyte complexes produced based on chitosan. Their various types of applications as drug carriers are reviewed in detail.

Assembly, postsynthetic modification and hepatocyte targeting by multiantennary, galactosylated soft structures

Enzyme modifiable, hollow self-assembled structures offer an excellent scope for multiantennary delivery vectors.