A synthetic mimic of the secretory granule for drug delivery

Design and applications of liposome-in-gel as carriers for cancer therapy

Cancer has long been a hot research topic, and recent years have witnessed the incidence of cancer trending toward younger individuals with great socioeconomic burden. Even with surgery, therapeutic agents serve as the mainstay to combat cancer in the clinic. Intensive research on nanomaterials can overcome the shortcomings of conventional drug delivery approaches, such as the lack of selectivity for targeted regions, poor stability against degradation, and uncontrolled drug release behavior. Over the years, different types of drug carriers have been developed for cancer therapy. One of these is liposome-in-gel (LP-Gel), which has combined the merits of both liposomes and hydrogels, and has emerged as a versatile carrier for cancer therapy. LP-Gel hybrids have addressed the lack of stability of conventional liposomes against pH and ionic strength while displaying higher efficiency of delivery hydrophilic drugs as compared to conventional gels. They can be classified into three types according to their assembled structure, are characterized by their nontoxicity, biodegradability, and flexibility for clinical use, and can be mainly categorized based on their controlled release, transmucosal delivery, and transdermal delivery properties for anticancer therapy. This review covers the recent progress on the applications of LP-Gel hybrids for anticancer therapy.

Effects of Lipid Shape and Interactions on the Conformation, Dynamics, and Curvature of Ultrasound-Responsive Liposomes

We perform coarse-grained molecular dynamics simulations of bilayers composed of various lipids and cholesterol at their different ratios. Simulations show that cholesterol-lipid interactions restrict the lateral dynamics of bilayers but also promote bilayer curvature, indicating that these opposite effects simultaneously occur and thus cannot significantly influence bilayer stability. In contrast, lyso-lipids effectively pack the vacancy in the bilayer composed of cone-shaped lipids and thus reduce bilayer dynamics and curvature, showing that bilayers are more significantly stabilized by lyso-lipids than by cholesterol, in agreement with experiments. In particular, the bilayer composed of cone-shaped lipids shows higher dynamics and curvature than does the bilayer composed of cylindrical-shaped lipids. To mimic ultrasound, a high external pressure was applied in the direction of bilayer normal, showing the formation of small pores that are surrounded by hydrophilic lipid headgroups, which can allow the release of drug molecules encapsulated into the liposome. These findings help to explain experimental observations regarding that liposomes are more significantly stabilized by lyso-lipids than by cholesterol, and that the liposome with cone-shaped lipids more effectively releases drug molecules upon applying ultrasound than does the liposome with cylindrical-shaped lipids.

Multifunctional Silica-Modified Hybrid Microgels Templated from Inverse Pickering Emulsions

Microgels are regarded as soft colloids with environmental responsiveness. However, the majority of reported microgels are inherently hydrophilic, resulting in aqueous dispersions, and only used in water-based applications. Herein, we reported an efficient method for hybridization of poly(N-isopropylacrylamide) microgel by coating hydrophobic silica nanoparticles on their surface. The resultant hybrid microgel had switchable surface wettability and could be dispersed in both aqueous and oil phases. Meanwhile, the coated hydrophobic silica nanoparticles solved the difficulty in redispersing microgels caused by particle aggregation and film formation during the drying process, providing a significant advantage in dried storage. Furthermore, the introduction of hydrophobic silica nanoparticles endowed the hybrid microgel with a variety of applications, including cargo encapsulation, active release induced by emulsion reversion, and trace water absorption.

A self-oscillating gel system with complex dynamic behavior based on a time delay between the oscillations

The time delay existing between the chemical oscillation and mechanical oscillation (C-M delay) in a self-oscillating gel (SOG) system is observable in previous experimental studies. However, how the C-M delay affects the dynamic behavior of a large anisotropic SOG has not been quantified or reported systematically. In this study, we observed that the oscillation period increases with a decrease in the cross-linking density of the anisotropic SOG, and this determined whether regular mechanical oscillation occurs. Unlike before, the disrupted mechanical oscillations interestingly tend to be regular and periodic under visible light, which is an inhibitor for the B-Z reaction incorporating the Ru complex as a catalyst (Ru-BZ reaction). Moreover, the study of the C-M delay at different scales has far-reaching implications for intelligent soft actuators.

Engineering hybrid microgels as particulate emulsifiers for reversible Pickering emulsions

Thermo-responsive microgels are unique stabilizers for stimuli-sensitive Pickering emulsions that can be switched between the state of emulsification and demulsification by changing the temperature. However, directly temperature-triggering the phase inversion of microgel-stabilized emulsions remains a great challenge. Here, a hybrid poly(N-isopropylacrylamide)-based microgel has now been successfully fabricated with tunable wettability from hydrophilicity to hydrophobicity in a controlled manner. Engineered microgels are synthesized from an inverse emulsion stabilized with hydrophobic silica nanoparticles, and the swelling-induced feature can make the resultant microgel behave like either hydrophilic or hydrophobic colloids. Remarkably, the phase inversion of such microgel-stabilized Pickering emulsions can be in situ regulated by temperature change. Moreover, the engineered microgels were capable of stabilizing water-in-oil Pickering emulsions and encapsulation of enzymes for interfacial bio-catalysis, as well as rapid cargo release triggered by phase inversion.

Self-Healing of Electrical Damage in Polymers

Polymers are widely used as dielectric components and electrical insulations in modern electronic devices and power systems in the industrial sector, transportation, and large appliances, among others, where electrical damage of the materials is one of the major factors threatening the reliability and service lifetime. Self-healing dielectric polymers, an emerging category of materials capable of recovering dielectric and insulating properties after electrical damage, are of promise to address this issue. This paper aims at summarizing the recent progress in the design and synthesis of self-healing dielectric polymers. The current understanding to the process of electrical degradation and damage in dielectric polymers is first introduced and the critical requirements in the self-healing of electrical damage are proposed. Then the feasibility of using self-healing strategies designed for repairing mechanical damage in the healing of electrical damage is evaluated, based on which the challenges and bottleneck issues are pointed out. The emerging self-healing methods specifically designed for healing electrical damage are highlighted and some useful mechanisms for developing novel self-healing dielectric polymers are proposed. It is concluded by providing a brief outlook and some potential directions in the future development toward practical applications in electronics and the electric power industry.

Particulate Alum via Pickering Emulsion for an Enhanced COVID-19 Vaccine Adjuvant

For rapid response against the prevailing COVID-19 (coronavirus disease 19), it is a global imperative to exploit the immunogenicity of existing formulations for safe and efficient vaccines. As the most accessible adjuvant, aluminum hydroxide (alum) is still the sole employed adjuvant in most countries. However, alum tends to attach on the membrane rather than entering the dendritic cells (DCs), leading to the absence of intracellular transfer and process of the antigens, and thus limits T-cell-mediated immunity. To address this, alum is packed on the squalene/water interphase is packed, forming an alum-stabilized Pickering emulsion (PAPE). "Inheriting" from alum and squalene, PAPE demonstrates a good biosafety profile. Intriguingly, with the dense array of alum on the oil/water interphase, PAPE not only adsorbs large quantities of SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) antigens, but also harbors a higher affinity for DC uptake, which provokes the uptake and cross-presentation of the delivered antigens. Compared with alum-treated groups, more than six times higher antigen-specific antibody titer and three-fold more IFN-γ-secreting T cells are induced, indicating the potent humoral and cellular immune activations. Collectively, the data suggest that PAPE may provide potential insights toward a safe and efficient adjuvant platform for the enhanced COVID-19 vaccinations.

Hydrogel Nanoparticle as a Functional Coating Layer in Biosensing, Tissue Engineering, and Drug Delivery

The development of functional coating materials has resulted in many breakthroughs in the discovery of energy, environmental, and biomedical applications. Responsive polymeric hydrogels are an example of smart coating materials due to their stimuli-responsive characteristics upon changes in their local environment. This review focuses on the introduction of hydrogel nanoparticles and their applications in functional layers as responsive coating materials. Hydrogels are explained by the composition of cross-links and monomers used for preparation. In particular, an important class of responsive hydrogels, that is, nanosized hydrogel particles (nanogels), are described for thee synthesis, modification, and application in assembly of functional coating layers. Finally, nanogel functional layers for biological applications will be discussed with recent advances in biosensing, tissue engineering, and drug delivery.

Generation and manipulation of oil-in-water micro-droplets by confined thermocapillary microvortices

Optofluidic manipulation of droplets is critical in droplet-based microfluidic systems for chemistry, biology, and medicine. Here, we reported a thermocapillary microvortices-based manipulation platform for controlling oil-in-water droplets through integrating a photothermal waveguide into a microfluidic chip. The sizes and shapes of the droplets can be controlled by adjusting optical power or positions of the water-oil interface. Here, teardrop-shaped droplets, which can encapsulate and accumulate mesoscopic matters easily, were generated when the water-oil interface and the channel boundaries approached the photothermal waveguide center simultaneously. The results showed that the thermocapillary microvortices have good controllability of droplet positions, droplet volumes, and encapsulated-particle distribution and thus it will be a powerful droplet manipulation strategy for microreactors and microcapsules.

Transformation of hard pollen into soft matter

Pollen’s practically-indestructible shell structure has long inspired the biomimetic design of organic materials. However, there is limited understanding of how the mechanical, chemical, and adhesion properties of pollen are biologically controlled and whether strategies can be devised to manipulate pollen beyond natural performance limits. Here, we report a facile approach to transform pollen grains into soft microgel by remodeling pollen shells. Marked alterations to the pollen substructures led to environmental stimuli responsiveness, which reveal how the interplay of substructure-specific material properties dictates microgel swelling behavior. Our investigation of pollen grains from across the plant kingdom further showed that microgel formation occurs with tested pollen species from eudicot plants. Collectively, our experimental and computational results offer fundamental insights into how tuning pollen structure can cause dramatic alterations to material properties, and inspire future investigation into understanding how the material science of pollen might influence plant reproductive success.

Pollen is an abundant material; but, currently has limited applications. Here, the authors turn pollen grains into soft microgel by de-esterification of pectin molecules and explore the mechanical and structural changes of the pollen grains using physical and modelling approaches.

Artificial Cells Capable of Long-Lived Protein Synthesis by Using Aptamer Grafted Polymer Hydrogel

Herein we report a new type of artificial cells capable of long-term protein expression and regulation. We constructed the artificial cells by grafting anti-His-tag aptamer into the polymer backbone of the hydrogel particles, and then immobilizing the His-tagged proteinaceous factors of the transcription and translation system into the hydrogel particles. Long-term protein expression for at least 16 days was achieved by continuously flowing feeding buffer through the artificial cells. The effect of various metal ions on the protein expression in the artificial cells was investigated. Utilizing the lac operator-repressor system, we could regulate the expression level of eGFP in the artificial cells by controlling the β-D-1-thiogalatopyranoside (IPTG) concentration in the feeding buffer. The artificial cells based on the aptamer grafted hydrogel provide a useful platform for gene circuit engineering, metabolic engineering, drug delivery, and biosensors.

Liposome-Enveloped Molecular Nanogels

Novel hydrogel@liposome particles were prepared by pH-triggered molecular gel formation inside of liposomes loaded with a low-molecular weight gelator derived from l-valine (1). Liposome formation was carried out using l-α-phosphatidylcholine (PC) and cholesterol as components of the lipid bilayer. Molecular hydrogelator 1 and pyranine, a ratiometric fluorescent pH probe, were entrapped in the liposomes at pH 9 and posterior acidification with d-glucono-1,5-lactone to pH 5-6 provoked intraliposomal gel formation. Removal of the lipid bilayer with sodium dodecyl sulfate yielded naked nanogel particles. The systems were characterized by transmission electron microscopy and dynamic light scattering. The hydrogel@liposomes were loaded with doxorubicin, showing a similar release than that observed for liposomes. The hybrid particles described here are the first case of nonpolymeric hydrogel@liposome systems reported. This type of nanocarriers merges the benefits of liposomal vehicles with the inherent stimuli responsiveness and enhanced biocompatibility of hydrogels formed by low-molecular weight molecules, foretelling a potential use in environmentally sensitive drug release.

Application of radiation for the synthesis of poly(n-vinyl pyrrolidone) nanogels with controlled sizes from aqueous solutions

Controlling of sizes of nanogels is very important for any biomedical application. In the present study we report a facile and reproducible method of preparing biocompatible nanogels of poly(N-vinyl pyrrolidone) (PVP) which were synthesized by using either electron beam (e-beam) (NGEB) or gamma irradiation (NGG) of dilute aqueous solutions. Nanogels with different hydrodynamic sizes were obtained at the variance of the polymer molecular weight, concentration, type of radiation source hence dose rate and total absorbed dose. For the first time a comparative study of gamma and e-beam irradiation was made on the same polymer with the aim of controlling sizes of nanogels in the range of 30-250 nm. Moreover the stability of radiation-synthesized nanogels was followed up to 2 years in refrigerated solution and found to retain their original sizes and distributions enabling their long-term storage and use. The synthesized nanogels were characterized by using dynamic light scattering (DLS), gel permeation chromatography (GPC), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. This work provides a clue to the fundamental question of how to control sizes of nanogels without using any additives which are indispensable with the other techniques. The technique is applicable to any water soluble polymer.

Long-lived protein expression in hydrogel particles: towards artificial cells

Herein we report a new type of cell-mimic particle capable of long-lived protein expression. We constructed the cell-mimic particles by immobilizing the proteinaceous factors of the cell-free transcription and translation system on the polymer backbone of hydrogel particles and encapsulating the plasmid template and ribosome inside the hydrogel. With the continuous supply of nutrients and energy, the protein expression in the cell-mimic particles remained stable for at least 11 days. We achieved the regulation of protein expression in the cell-mimic particles by the usage of lac operon. The cell-mimic particles quickly responded to the concentration change of isopropyl β-d-1-thiogalactopyranoside (IPTG) in the feeding buffer to regulate the mCherry expression level. We also constructed an in vitro genetic oscillator in the cell-mimic particles. Protein LacI provided a negative feedback to the expression of both LacI itself and eGFP, and the expression level change of eGFP presented an oscillation. We expect the cell-mimic particles to be a useful platform for gene circuit engineering, metabolic engineering, and biosensors.

Manipulating Single Microdroplets of NaCl Solutions: Solvent Dissolution, Microcrystallization, and Crystal Morphology

A new "three-micropipette manipulation technique" for forming, dehydrating, crystallizing, and resolvating nanograms of salt material has been developed to study supersaturated single microdroplets and microcrystals. This is the first report of studies that have measured in situ both supersaturation (as homogeneous nucleation) and saturation (as microcrystal redissolution) for single microdroplets of NaCl solution using the micropipette technique. This work reports a measure of the critical supersaturation concentration for homogeneous nucleation of NaCl (10.3 ± 0.3 M) at a supersaturation fraction of S = 1.9, the saturation concentration of NaCl in aqueous solution as measured with nanograms of material (5.5 ± 0.1 M), the diffusion coefficient for water in octanol, D = (1.96 ± 0.10) × 10^-6 cm²/s, and the effect of the solvent's activity on dissolution kinetics. It is further shown that the same Epstein-Plesset (EP) model, which was originally developed for diffusion-controlled dissolution and uptake of gas, and successfully applied to liquid-in-liquid dissolution, can now also be applied to describe the diffusion-controlled uptake of water from a water-saturated environment using the extended activity-based model of Bitterfield et al. This aspect of the EP model has not previously been tested using single microdroplets. Finally, it is also reported how the water dissolution rate, rate of NaCl concentration change, resulting crystal structure, and the time frame of initial crystal growth are affected by changing the bathing medium from octanol to decane. A much slower loss of water-solvent and concomitant slower up-concentration of the NaCl solute resulted in a lower tendency to nucleate and slower crystal growth because much less excess material was available at the onset of nucleation in the decane system as compared to the octanol system. Thus, the crystal structure is reported to be dendritic for NaCl solution microdroplets dissolving rapidly and nucleating violently in octanol, while they are formed as single cubic crystals in a gentler way for solution-dissolution in decane. These new techniques and analyses can now also be used for any other system where all relevant parameters are known. An example of this is control of drug/hydrogel/emulsion particle size change due to solvent uptake.

Concise Review: Fabrication, Customization, and Application of Cell Mimicking Microparticles in Stem Cell Science

Stem and non-stem cell behavior is heavily influenced by the surrounding microenvironment, which includes other cells, matrix, and potentially biomaterials. Researchers have been successful in developing scaffolds and encapsulation techniques to provide stem cells with mechanical, topographical, and chemical cues to selectively direct them toward a desired differentiation pathway. However, most of these systems fail to present truly physiological replications of the in vivo microenvironments that stem cells are typically exposed to in tissues. Thus, cell mimicking microparticles (CMMPs) have been developed to more accurately recapitulate the properties of surrounding cells while still offering ways to tailor what stimuli are presented. This nascent field holds the promise of reducing, or even eliminating, the need for live cells in select, regenerative medicine therapies, and diagnostic applications. Recent, CMMP-based studies show great promise for the technology, yet only reproduce a small subset of cellular characteristics from among those possible: size, morphology, topography, mechanical properties, surface molecules, and tailored chemical release to name the most prominent. This Review summarizes the strengths, weaknesses, and ideal applications of micro/nanoparticle fabrication and customization methods relevant to cell mimicking and provides an outlook on the future of this technology. Moving forward, researchers should seek to combine multiple techniques to yield CMMPs that replicate as many cellular characteristics as possible, with an emphasis on those that most strongly influence the desired therapeutic effects. The level of flexibility in customizing CMMP properties allows them to substitute for cells in a variety of regenerative medicine, drug delivery, and diagnostic systems. Stem Cells Translational Medicine 2018;7:232-240.

Binding of Lysozyme to Spherical Poly(styrenesulfonate) Gels

Polyelectrolyte gels are useful as carriers of proteins and other biomacromolecules in, e.g., drug delivery. The rational design of such systems requires knowledge about how the binding and release are affected by electrostatic and hydrophobic interactions between the components. To this end we have investigated the uptake of lysozyme by weakly crosslinked spherical poly(styrenesulfonate) (PSS) microgels and macrogels by means of micromanipulator assisted light microscopy and small angle X-ray scattering (SAXS) in an aqueous environment. The results show that the binding process is an order of magnitude slower than for cytochrome c and for lysozyme binding to sodium polyacrylate gels under the same conditions. This is attributed to the formation of very dense protein-rich shells in the outer layers of the microgels with low permeability to the protein. The shells in macrogels contain 60 wt % water and nearly charge stoichiometric amounts of lysozyme and PSS in the form of dense complexes of radius 8 nm comprising 30⁻60 lysozyme molecules. With support from kinetic modelling results we propose that the rate of protein binding and the relaxation rate of the microgel are controlled by the protein mass transport through the shell, which is strongly affected by hydrophobic and electrostatic interactions. The mechanism explains, in turn, an observed dependence of the diffusion rate on the apparent degree of crosslinking of the networks.

Mucins as multifunctional building blocks of biomaterials

Mucins glycoproteins are emerging as a multifunctional building block for biomaterials with diverse applications in chemistry and biomedicine.

Characterization of Responsive Hydrogel Nanoparticles upon Polyelectrolyte Complexation

Characterization of responsive hydrogels and their interaction with other molecules have significantly expanded our understanding of the functional materials. We here report on the response of poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAm-co-AAc) nanogels to the addition of the poly(allylamine hydrochloride) (PAH) in aqueous dispersions. We find that the hydrodynamic radius and stability of nanogels are dependent on the PAH/nanogel stoichiometry. If the nanogel solution is titrated with very small aliquots of PAH, the nanogels decrease in radius until the equivalence point, followed by aggregation at suprastoichiometric PAH additions. Conversely, when titrated with large aliquots, the nanogel charge switches rapidly from anionic to cationic, and no aggregation is observed. This behavior correlates well with electrophoretic mobility measurements, which shows the nanogel charge transitioning from negative to positive upon PAH addition. The volume phase transition temperature (VPTT) of the nanogels is also measured to discover the effect of polyelectrolyte complexation on the deswelling thermodynamics. These data show that charge neutralization upon PAH addition decreases the VPTT of the nanogel at pH 6.5. However, if an excess amount of PAH is added to the nanogel solution, the VPTT shifts back to higher temperatures due to the formation of a net positive charge in the nanogel network.

Controlling swelling/deswelling of stimuli-responsive hydrogel nanofilms in electric fields

The swelling/deswelling transition of pH-sensitive, electrode-grafted, hydrogel nanofilms when exposed to electric fields is studied by theoretical analysis. In acidic conditions, the response of these films to changes in pH is dominated by network-surface interactions, while intra-network electrostatic repulsions, which are highly modulated by the adsorption of salt ions, determine material response at a higher pH. Film thickness is a non-monotonic function of solution pH and displays a local maximum, a local minimum or both, depending on the salt concentration and the applied voltage. We suggest the use of these materials in the development of biosensors and control of enzyme activity.

Methods for Generating Hydrogel Particles for Protein Delivery

Proteins represent a major class of therapeutic molecules with vast potential for the treatment of acute and chronic diseases and regenerative medicine applications. Hydrogels have long been investigated for their potential in carrying and delivering proteins. As compared to bulk hydrogels, hydrogel microparticles (microgels) hold promise in improving aspects of delivery owing to their less traumatic route of entry into the body and improved versatility. This review discusses common methods of fabricating microgels, including emulsion polymerization, microfluidic techniques, and lithographic techniques. Microgels synthesized from both natural and synthetic polymers are discussed, as are a series of microgels fashioned from environment-responsive materials.

Biophysical characterization of small molecule antiviral-loaded nanolipogels for HIV-1 chemoprophylaxis and topical mucosal application

Nanocarriers are versatile vehicles for drug delivery, and emerging as platforms to formulate and deliver multiple classes of antiretroviral (ARV) drugs in a single system. Here we describe the fabrication of hydrogel-core and lipid-shell nanoparticles (nanolipogels) for the controlled loading and topical, vaginal delivery of maraviroc (MVC) and tenofovir disoproxil fumarate (TDF), two ARV drugs with different mechanisms of action that are used in the treatment of HIV. The nanolipogel platform was used to successfully formulate MVC and TDF, which produced ARV drug-loaded nanolipogels that were characterized for their physical properties and antiviral activity against HIV-1 BaL in cell culture. We also show that administration of these drug carriers topically to the vaginal mucosa in a murine model leads to antiviral activity against HIV-1 BaL in cervicovaginal lavages. Our results suggest that nanolipogel carriers are promising for the encapsulation and delivery of hydrophilic small molecule ARV drugs, and may expand the nanocarrier systems being investigated for HIV prevention or treatment.

STATEMENT OF SIGNIFICANCE

Topical, mucosal intervention of HIV is a leading strategy in the efforts to curb the spread of viral infection. A significant research thrust in the field has been to characterize different dosage forms for formulation of physicochemically diverse antiretroviral drugs. Nanocarriers have been used to formulate and deliver small molecule and protein drugs for a range of applications, including ARV drugs for HIV treatment. The broad significance of our work includes evaluation of lipid-shell, hydrogel-core nanoparticles for formulation and topical, vaginal delivery of two water-soluble antiretroviral drugs. We have characterized these nanocarriers for their physical properties and their biological activity against HIV-1 infection in vitro, and demonstrated the ability to deliver drug-loaded nanocarriers in vivo.

Infrared and fluorescence spectroscopic studies of a phospholipid bilayer supported by a soft cationic hydrogel scaffold

Polarized attenuated total reflection (ATR-IR) spectroscopy and fluorescence microscopy techniques were used to characterize a 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) membrane supported on porous, cationic hydrogel beads. Fluorescence microscopy images showed that the DPhPC coated the external surface of the hydrogel scaffold. In addition, a fluorescence assay of the emission intensity of the Tb(3+)/dipicolinic acid complex demonstrated that the DPhPC coating acted as a barrier to Tb(3+) efflux from the scaffolded vesicle and successfully sealed the porous hydrogel bead. Fluorescence quenching and ATR-IR spectroscopic measurements revealed that the lipid coating has a bilayer structure. The phytanoyl chains were found to exhibit significant trans-gauche isomerization, characteristic of the fluid liquid phase. However, no lipid lateral mobility was observed by fluorescence recovery after photobleaching (FRAP) measurements. The phosphocholine headgroup was found to be well hydrated and oriented such that the cationic choline group tucked in behind the anionic phosphate group, consistent with an electrostatic attraction between the cationic scaffold and zwitterionic lipid. The absence of lipid lateral mobility may be due to the strength of this attraction.

Enzyme-responsive protein/polysaccharide supramolecular nanoparticles

Biocompatible and enzyme-responsive supramolecular assemblies have attracted more and more interest in biomaterial fields, and find many feasible applications especially in the controlled drug release at specific sites where the target enzyme is located. In this work, novel supramolecular nanoparticles were successfully constructed from two biocompatible materials, i.e. a cyclic polysaccharide named sulfato-β-cyclodextrin (SCD) and a protein named protamine, through non-covalent association, and fully characterized by means of atomic force microscopy (AFM) and high-resolution transmission electron microscopy (TEM). Significantly, the disassembly of the resulting nanoparticles can respond especially to trypsin over other enzymes. Owing to their trypsin-triggered disassembly behaviors, these nanoparticles can efficiently release the encapsulated model substrate in a controlled manner. That is, the model substrate can be encapsulated inside the nanoparticles with a high stability and released when treated with trypsin.

Tight coupling of metabolic oscillations and intracellular water dynamics in Saccharomyces cerevisiae

We detected very strong coupling between the oscillating concentration of ATP and the dynamics of intracellular water during glycolysis in Saccharomyces cerevisiae. Our results indicate that: i) dipolar relaxation of intracellular water is heterogeneous within the cell and different from dilute conditions, ii) water dipolar relaxation oscillates with glycolysis and in phase with ATP concentration, iii) this phenomenon is scale-invariant from the subcellular to the ensemble of synchronized cells and, iv) the periodicity of both glycolytic oscillations and dipolar relaxation are equally affected by D₂O in a dose-dependent manner. These results offer a new insight into the coupling of an emergent intensive physicochemical property of the cell, i.e. cell-wide water dipolar relaxation, and a central metabolite (ATP) produced by a robustly oscillating metabolic process.

Strong anionic polyelectrolyte microgels

We report a facile synthesis of highly uniform poly(styrene sulfonic acid) microgels, which carry a strong polyelectrolyte group at every repeating unit.

Spectroscopic and permeation studies of phospholipid bilayers supported by a soft hydrogel scaffold

Polarized attenuated total reflection infrared (ATR-IR) spectroscopy, fluorescence microscopy, and fluorescence spectroscopy were used to characterize a lipid coating composed of 70 mol % 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 30 mol % cholesterol, supported on a spherical hydrogel scaffold. The fluorescence microscopy images show an association between the lipid coating and the hydrogel scaffold. Fluorescence permeability measurements revealed that the phospholipid coating acts as a permeability barrier, exhibiting characteristics of a lamellar bilayer coating structure. Variable evanescent wave penetration depth ATR-IR spectroscopy studies validated the determination of quantitative molecular orientation information for a lipid coating supported on a spherical scaffold. These polarized ATR-IR studies measured an average DMPC acyl chain tilt angle of ∼21-25°, with respect to the surface normal.

Molecular composition, grafting density and film area affect the swelling-induced Au-S bond breakage

In previous studies, we reported the first observation of the Au-S bond breakage induced mechanically by the swelling of the surface-tethered weak polyelectrolyte brushes in phosphate buffered saline (PBS), a phenomenon with broad applications in the fields of biosensors and functional surfaces. In this study, three factors, namely the molecular composition, grafting density and film area of the weak polyelectrolyte, carboxylated poly(oligo(ethylene glycol) methacrylate-random-2-hydroxyethyl methacrylate) (poly(OEGMA-r-HEMA)), were studied systematically on how they affected the swelling-induced Au-S bond breakage (ABB). The results showed that, first, the swelling-induced ABB is applicable to a range of molecular compositions and grafting densities; but the critical thickness (Tcritical,dry) varied with both of the two factors. An analysis on the swelling ratio further revealed that the difference in the Tcritical,dry arose from the difference in the swelling ability. A film needed to swell to ∼250 nm to induce ABB regardless of its composition or structure, thus a higher swelling ratio would lead to a lower Tcritical,dry value. Then, the impact of the film area was studied in micrometer- and sub-micrometer-scale brush patterns, which showed that only partial, rather than complete ABB was induced in these microscopic films, resulting in buckling instead of film detaching. These results demonstrated that the ABB is suitable to be used in the design of biosensors, stimulus-responsive materials and mechanochemical devices. Although the >160 μm(2) required area for uniform ABB hinders the application of ABB in nanolithography, the irreversible buckling provides a facile method of generating rough surfaces.

Micro hydrogels: preparation, properties, and applications

A micro hydro-gel is a submicron- or micron-sized network polymer particle that is insoluble in water but highly swellable. This review presents the following topics: preparation, properties, and applications of micro hydrogels. First, two types of preparation methods for micro hydrogels are presented: (i) particle-forming polymerization and (ii) molecular assembly of polymer chains dissolved in water. Next, the characteristic properties of micro hydrogels are discussed. Finally, the applications of micro hydrogels are reviewed, with special emphasis on environmentally sensitive optical/photonic, biological/biomedical, and chemical applications. This review is not comprehensive, but is rather a "mini-review" primarily focused on results obtained in the author's laboratories.

Quantitative optical microscopy and micromanipulation studies on the lipid bilayer membranes of giant unilamellar vesicles

This manuscript discusses basic methodological aspects of optical microscopy and micromanipulation methods to study membranes and reviews methods to generate giant unilamellar vesicles (GUVs). In particular, we focus on the use of fluorescence microscopy and micropipet manipulation techniques to study composition-structure-property materials relationships of free-standing lipid bilayer membranes. Because their size (∼5-100 μm diameter) that is well above the resolution limit of regular light microscopes, GUVs are suitable membrane models for optical microscopy and micromanipulation experimentation. For instance, using different fluorescent reporters, fluorescence microscopy allows strategies to study membrane lateral structure/dynamics at the level of single vesicles of diverse compositions. The micropipet manipulation technique on the other hand, uses Hoffman modulation contrast microscopy and allows studies on the mechanical, thermal, molecular exchange and adhesive-interactive properties of compositionally different membranes under controlled environmental conditions. The goal of this review is to (i) provide a historical perspective for both techniques; (ii) present and discuss some of their most important contributions to our understanding of lipid bilayer membranes; and (iii) outline studies that would utilize both techniques simultaneously on the same vesicle thus bringing the ability to characterize structure and strain responses together with the direct application of well-defined stresses to a single membrane or observe the effects of adhesive spreading. Knowledge gained by these studies has informed several applications of lipid membranes including their use as lung surfactants and drug delivery systems for cancer.

Tunable adsorption of soft colloids on model biomembranes

A simple procedure is developed to probe in situ the association between lipid bilayers and colloidal particles. Here, a one-step method is applied to generate giant unilamellar 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) vesicles (GUVs) by application of an alternating electric field directly in the presence of thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) microgels. We demonstrate that the soft PNIPAM microgel particles act as switchable stabilizers for lipid membranes. The change of the particle conformation from the swollen to the collapsed state enables the reversible control of the microgel adsorption as a function of temperature. At 20 °C, the swollen and hydrophilic soft microgel particles adsorb evenly and densely pack in 2D hexagonal arrays at the DOPC GUV surfaces. In contrast, at 40 °C, that is, above the volume phase transition temperature (TVPT = 32 °C) of the PNIPAM microgels, the collapsed and more hydrophobic particles partially desorb and self-organize into domains at the GUV/GUV interfaces. This study shows that thermoresponsive PNIPAM microgels can be used to increase and control the stability of lipid vesicles where the softness and deformability of these types of particles play a major role. The observed self-assembly, where the organization and position of the particles on the GUV surface can be controlled "on demand", opens new routes for the design of nanostructured materials.

A novel pulsatile drug delivery system based on the physiochemical reaction between acrylic copolymer and organic acid: in vitro and in vivo evaluation

Multilayer-coating technology is the traditional method to achieve pulsatile drug release with the drawbacks of time consuming, more materials demanding and lack of efficiency. The purpose of this study was to design a novel pulsatile drug delivery system based on the physiochemical interaction between acrylic copolymer and organic acid with relatively simpler formulation and manufacturing process. The Enalapril Maleate (EM) pulsatile release pellets were prepared using extruding granulation, spheronization and fluid-bed coating technology. The ion-exchange experiment, hydration study and determination of glass transition temperature were conducted to explore the related drug release mechanism. Bioavailability experiment was carried out by administering the pulsatile release pellets to rats compared with marketed rapid release tablets Yisu. An obvious 4h lag time period and rapid drug release was observed from in vitro dissolution profiles. The release mechanism was a combination of both disassociated and undisassociated forms of succinic acid physiochemically interacting with Eudragit RS. The AUC0-τ of the EM pulsatile pellets and the market tablets was 702.384 ± 96.89 1 hn g/mL and 810.817 ± 67.712 h ng/mL, while the relative bioavailability was 86.62%. These studies demonstrate this novel pulsatile release concept may be a promising strategy for oral pulsatile delivery system.

Smart Nanoscale Drug Delivery Platforms from Stimuli-Responsive Polymers and Liposomes

Since the 1960's, stimuli-responsive polymers have been utilized as functional soft materials for biological applications such as the triggered-release delivery of biologically active cargos. Over the same period, liposomes have been explored as an alternative drug delivery system with potentials to decrease the toxic side effects often associated with conventional small-molecule drugs. However, the lack of drug-release triggers and the instability of bare liposomes often limit their practical applications, causing short circulation time and low therapeutic efficacy. This perspective article highlights recent work in integrating these two materials together to achieve a targetable, triggerable nanoscale platform that fulfills all the characteristics of a near-ideal drug delivery system. Through a drop-in, post-synthesis modification strategy, a network of stimuli-responsive polymers can be integrated onto the surface of liposomes to form polymer-caged nanobins, a multifunctional nanoscale delivery platform that allows for multi-drug loading, targeted delivery, triggered drug-release, and theranostic capabilities.