Self-assembled Membranes Research Articles

Mineral Surface Chemistry and Nanoparticle-aggregation Control Membrane Self-Assembly

The self-assembly of lipid bilayer membranes to enclose functional biomolecules, thus defining a “protocell,” was a seminal moment in the emergence of life on Earth and likely occurred at the micro-environment of the mineral-water interface. Mineral-lipid interactions are also relevant in biomedical, industrial and technological processes. Yet, no structure-activity relationships (SARs) have been identified to predict lipid self-assembly at mineral surfaces. Here we examined the influence of minerals on the self-assembly and survival of vesicles composed of single chain amphiphiles as model protocell membranes. The apparent critical vesicle concentration (CVC) increased in the presence of positively-charged nanoparticulate minerals at high loadings (mg/mL) suggesting unfavorable membrane self-assembly in such situations. Above the CVC, initial vesicle formation rates were faster in the presence of minerals. Rates were correlated with the mineral’s isoelectric point (IEP) and reactive surface area. The IEP depends on the crystal structure, chemical composition and surface hydration. Thus, membrane self-assembly showed rational dependence on fundamental mineral properties. Once formed, membrane permeability (integrity) was unaffected by minerals. Suggesting that, protocells could have survived on rock surfaces. These SARs may help predict the formation and survival of protocell membranes on early Earth and other rocky planets, and amphiphile-mineral interactions in diverse other phenomena.

Versatile self-assembled graphene oxide membranes obtained under ambient conditions by using a water–ethanol suspension

The study reports a low cost and scalable pathway for preparing free-standing GO membranes by a self-assembly process under ambient conditions at an air–liquid interface of an isopycnic sorted GO water–ethanol fraction.

Physicochemical characterization of cellulose nanocrystal and nanoporous self-assembled CNC membrane derived from Ceiba pentandra

This research involves the rare utilisation of the kapok fibre (Ceiba pentandra) as a raw material for the fabrication of cellulose nanocrystal (CNC) and self-assembled CNC membranes. The isolation of CNC from Ceiba pentandra began with the extraction of cellulose via the chemical alkali extraction by using 5wt% NaOH, followed by the typical acidified bleaching method and, finally, the CNC production through acid hydrolysis with 60wt% H2SO4 at the optimum time of 60min. The prepared CNC was then employed for the preparation of self-assembled membrane through the water suspension casting evaporation technique. The obtained CNC membrane was characterised in terms of its composition, crystallinity, thermal stability, as well as, structural and morphological features with the use of several techniques including FTIR, XRD, AFM, TEM, FESEM, and TGA. The FESEM and AFM analyses had illustrated the achievement of a self-assembled CNC membrane with a smooth surface and a well-distributed nano-porous structure, with the porosity of 52.82±7.79%. In addition, the findings proved that the self-assembled CNC membrane displayed good adsorption capability indicated by the recorded efficiency of 79% and 85% for 10mg/L and 5mg/L of methylene blue in an aqueous solution, respectively.

Corrosion resistance and molecular dynamics behavior of the MAO/SAM composite coatings on magnesium alloy

To improve corrosion resistance of magnesium alloy AZ91D, y-Mercaptopropyltrimethoxysilane (MPTS) was assembled on the surface of micro-arc oxidation (MAO) treated magnesium alloy by self-assembly membrane (SAM) technique. The surface morphology and chemical components of the MAO/SAM composite coatings were analyzed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The corrosion resistance of samples was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy and total immersion tests in a 3.5 wt % NaCl solution. The measured EIS data were simulated by an equivalent circuit. Also the molecular dynamic simulation was used to study the adsorption behavior at the molecular level. The results showed that the surface of magnesium alloy was well covered by the MAO/SAM composite coatings with a better corrosion resistance. Chemical adsorption was formed between the organic molecules and the surface of the MAO coating. The approach presented here afforded an effective alternative for surface modification of magnesium-based materials to meet the many aspects of the application requirements.

Particle-based simulations of bilayer membranes: self-assembly, structural analysis, and shock-wave damage

We report on the results of particle-based, coarse-grained molecular dynamics simulations of amphiphilic lipid molecules in aqueous environment where the membrane structures at equilibrium are subsequently exposed to strong shock waves, and their damage is analyzed. The lipid molecules self-assemble from unbiased random initial configurations to form stable bilayer membranes, including closed vesicles. During self-assembly of lipid molecules, we observe several stages of clustering, starting with many small clusters of lipids, gradually merging together to finally form one single bilayer membrane. We find that the clustering of lipids sensitively depends on the hydrophobic interaction \(h_\mathrm{c}\) of the lipid tails in our model and on temperature T of the system. The self-assembled bilayer membranes are quantitatively analyzed at equilibrium with respect to their degree of order and their local structure. We also show that—by analyzing the membrane fluctuations and using a linearized theory— we obtain area compression moduli \(K_\mathrm{A}\) and bending stiffnesses \(\kappa _\mathrm{B}\) for our bilayer membranes which are within the experimental range of in vivo and in vitro measurements of biological membranes. We also discuss the density profile and the pair correlation function of our model membranes at equilibrium which has not been done in previous studies of particle-based membrane models. Furthermore, we present a detailed phase diagram of our lipid model that exhibits a sol–gel transition between quasi-solid and fluid domains, and domains where no self-assembly of lipids occurs. In addition, we present in the phase diagram the conditions for temperature T and hydrophobicity \(h_\mathrm{c}\) of the lipid tails of our model to form closed vesicles. The stable bilayer membranes obtained at equilibrium are then subjected to strong shock waves in a shock tube setup, and we investigate the damage in the membranes due to their interaction with shock waves. Here, we find a transition from self-repairing membranes (reducing their damage after impact) and permanent (irreversible) damage, depending on the shock front speed. The here presented idea of using coarse-grained (CG) particle models for soft matter systems in combination with the investigation of shock-wave effects in these systems is a quite new approach.

Nanoscale Control of Polymer Assembly on a Synthetic Catalyst-Bilayer System.

The use of the interior of self-assembled membrane as a template for polymer synthesis and assembly has long attracted the interest of chemists. However, it is difficult to utilize a lipid membrane as a chemical reactor for controlled assembly for polymers because lipid membrane is easily destabilized by loading of extraneous molecules. We found that a several-nanometer-thick bilayer vesicle made by self-assembly of an organic fullerene amphiphile doped with a metathesis catalyst serves as a nanosized chemical reactor in water, where a polymer is synthesized and assembled, depending on the affinity of the growing polymer to the organic groups on the amphiphile. This catalyst-bilayer system can thus control supramolecular assembly of the ester-functionalized polymer product into different nanoscale structures: a nanoparticle made of a single polymer chain and a nanocapsule made of several tens of polymer chains.

Roles of Sterol Derivatives in Regulating the Properties of Phospholipid Bilayer Systems.

Liposomes are considered an ideal biomimetic environment and are potential functional carriers for important molecules such as steroids and sterols. With respect to the regulation of self-assembly via sterol insertion, several pathways such as the sterol biosynthesis pathway are affected by the physicochemical properties of the membranes. However, the behavior of steroid or sterol molecules (except cholesterol (Chl)) in the self-assembled membranes has not been thoroughly investigated. In this study, to analyze the fundamental behavior of steroid molecules in fluid membranes, Chl, lanosterol, and ergosterol were used as representative sterols in order to clarify how they regulate the physicochemical properties of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposomes. Membrane properties such as surface membrane fluidity, hydrophobicity, surface membrane polarity, inner membrane polarity, and inner membrane fluidity were investigated using fluorescent probes, including 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene, 8-anilino-1-naphthalenesulfonic acid, 6-propionyl-2-(dimethylamino) naphthalene, 6-dodecanoyl-2-dimethylaminonaphthalene, and 1,6-diphenyl-1,3,5-hexatriene. The results indicated that each sterol derivative could regulate the membrane properties in different ways. Specifically, Chl successfully increased the packing of the DOPC/Chl membrane proportional to its concentration, and lanosterol and ergosterol showed lower efficiencies in ordering the membrane in hydrophobic regions. Given the different binding positions of the probes in the membranes, the differences in membrane properties reflected the relationship between sterol derivatives and their locations in the membrane.

A Reversibly Sealed, Easy Access, Modular (SEAM) Microfluidic Architecture to Establish In Vitro Tissue Interfaces.

Microfluidic barrier tissue models have emerged as advanced in vitro tools to explore interactions with external stimuli such as drug candidates, pathogens, or toxins. However, the procedures required to establish and maintain these systems can be challenging to implement for end users, particularly those without significant in-house engineering expertise. Here we present a module-based approach that provides an easy-to-use workflow to establish, maintain, and analyze microscale tissue constructs. Our approach begins with a removable culture insert that is magnetically coupled, decoupled, and transferred between standalone, prefabricated microfluidic modules for simplified cell seeding, culture, and downstream analysis. The modular approach allows several options for perfusion including standard syringe pumps or integration with a self-contained gravity-fed module for simple cell maintenance. As proof of concept, we establish a culture of primary human microvascular endothelial cells (HMVEC) and report combined surface protein imaging and gene expression after controlled apical stimulation with the bacterial endotoxin lipopolysaccharide (LPS). We also demonstrate the feasibility of incorporating hydrated biomaterial interfaces into the microfluidic architecture by integrating an ultra-thin (< 1 μm), self-assembled hyaluronic acid/peptide amphiphile culture membrane with brain-specific Young’s modulus (~ 1kPa). To highlight the importance of including biomimetic interfaces into microscale models we report multi-tiered readouts from primary rat cortical cells cultured on the self-assembled membrane and compare a panel of mRNA targets with primary brain tissue signatures. We anticipate that the modular approach and simplified operational workflows presented here will enable a wide range of research groups to incorporate microfluidic barrier tissue models into their work.

Self-assembled tri-block terpolymer blend membranes reinforced with poly(methyl methacrylate)-coated gold nanoparticles obtained through phase inversion technique

ABSTRACTThe blend membranes of polystyrene-block-polyisoprene-block-polystyrene and polyethylene-block-poly(ethylene glycol)-block-polycaprolactone were designed using the phase inversion technique. The poly(methyl methacrylate)-coated gold nanoparticles are around 40–50 nm in size. The honeycomb-shaped nanopores were uniformly dispersed in polystyrene-block-polyisoprene-block-polystyrene/polyethylene-block-poly(ethylene glycol)-block-polycaprolactone/poly(methyl methacrylate)-coated gold nanoparticles blend membranes. There was a 16% increase in tensile strength and a 33% increase in tensile modulus of polystyrene-block-polyisoprene-block-polystyrene/polyethylene-block-poly(ethylene glycol)-block-polycaprolactone/poly(methyl methacrylate)-coated gold nanoparticles 1 relative to the neat membrane. With 1 wt% nanoparticles, the membrane showed a higher water flux of 59.2 mL cm−2 min−1 and a salt rejection ratio of 25.4%, while the polystyrene-block-polyisoprene-block-polystyrene/polyethylene-block-poly(ethylene glycol)-block-polycaprolactone membrane without poly(methyl methacrylate)-coated gold nanoparticles had lower flux (43.8 mL cm−2 min−1) and salt rejection (18.5%).

A Global Scale Scenario for Prebiotic Chemistry: Silica-Based Self-Assembled Mineral Structures and Formamide.

The pathway from simple abiotically made organic compounds to the molecular bricks of life, as we know it, is unknown. The most efficient geological abiotic route to organic compounds results from the aqueous dissolution of olivine, a reaction known as serpentinization (Sleep, N.H., et al. (2004) Proc. Natl. Acad. Sci. USA 101, 12818–12822). In addition to molecular hydrogen and a reducing environment, serpentinization reactions lead to high-pH alkaline brines that can become easily enriched in silica. Under these chemical conditions, the formation of self-assembled nanocrystalline mineral composites, namely silica/carbonate biomorphs and metal silicate hydrate (MSH) tubular membranes (silica gardens), is unavoidable (Kellermeier, M., et al. In Methods in Enzymology, Research Methods in Biomineralization Science (De Yoreo, J., Ed.) Vol. 532, pp 225–256, Academic Press, Burlington, MA). The osmotically driven membranous structures have remarkable catalytic properties that could be operating in the reducing organic-rich chemical pot in which they form. Among one-carbon compounds, formamide (NH2CHO) has been shown to trigger the formation of complex prebiotic molecules under mineral-driven catalytic conditions (Saladino, R., et al. (2001) Biorganic & Medicinal Chemistry, 9, 1249–1253), proton irradiation (Saladino, R., et al. (2015) Proc. Natl. Acad. Sci. USA, 112, 2746–2755), and laser-induced dielectric breakdown (Ferus, M., et al. (2015) Proc Natl Acad Sci USA, 112, 657–662). Here, we show that MSH membranes are catalysts for the condensation of NH2CHO, yielding prebiotically relevant compounds, including carboxylic acids, amino acids, and nucleobases. Membranes formed by the reaction of alkaline (pH 12) sodium silicate solutions with MgSO4 and Fe2(SO4)3·9H2O show the highest efficiency, while reactions with CuCl2·2H2O, ZnCl2, FeCl2·4H2O, and MnCl2·4H2O showed lower reactivities. The collections of compounds forming inside and outside the tubular membrane are clearly specific, demonstrating that the mineral self-assembled membranes at the same time create space compartmentalization and selective catalysis of the synthesis of relevant compounds. Rather than requiring odd local conditions, the prebiotic organic chemistry scenario for the origin of life appears to be common at a universal scale and, most probably, earlier than ever thought for our planet.

Controlling the Formation of Phospholipid Monolayer, Bilayer, and Intact Vesicle Layer on Graphene.

Exciting progress has been made in the use of graphene for bio- and chemical sensing applications. In this regard, interfacing lipid membranes with graphene provides a high-sealing interface that is resistant to nonspecific protein adsorption and suitable for measuring biomembrane-associated interactions. However, a controllable method to form well-defined lipid bilayer coatings remains elusive, and there are varying results in the literature. Herein, we demonstrate how design strategies based on molecular self-assembly and surface chemistry can be employed to coat graphene surface with different classes of lipid membrane architectures. We characterize the self-assembly of lipid membranes on CVD-graphene using quartz crystal microbalance with dissipation, field-effect transistor, and Raman spectroscopy. By employing the solvent-assisted lipid bilayer (SALB) method, a lipid monolayer and bilayer were formed on pristine and oxygen-plasma-treated CVD-graphene, respectively. On these surfaces, vesicle fusion method resulted in formation of a lipid monolayer and intact vesicle layer, respectively. Collectively, these findings provide the basis for improved surface functionalization strategies on graphene toward bioelectronic applications.

Tabas coal preparation plant wastewater treatment with membrane technology

The goal of the present work is the Tabas coal preparation plant wastewater treatment using membrane technology. Polyacrylonitrile membrane was prepared through phase inversion method and then developed by annealing process. Also, high fouling resistance membranes were prepared by the embedding of TiO2 nanoparticles using self-assembling and blending methods. The effect of immersion time and TiO2 nanoparticles concentration was investigated using two techniques. The chemical structure, morphology, hydrophilicity, molecular weight cut-off and antifouling properties of membranes were characterized using energy-dispersive X-ray spectroscopy, scanning electron microscopy, contact angle, polyethylene glycol tracers, and cationic polyacrylamide (C-PAM) filtration, respectively. The optimized self-assembled membrane was shown to have more than 31.2% higher water flux with the best antifouling properties. Improving hydrophilicity leads to excellent antifouling properties for composite membranes and illustrates a promising method for fabrication of high performance membrane for C-PAM separation.

Interaction of chiral rafts in self-assembled colloidal membranes.

Colloidal membranes are monolayer assemblies of rodlike particles that capture the long-wavelength properties of lipid bilayer membranes on the colloidal scale. Recent experiments on colloidal membranes formed by chiral rodlike viruses showed that introducing a second species of virus with different length and opposite chirality leads to the formation of rafts--micron-sized domains of one virus species floating in a background of the other viruses [Sharma et al., Nature (London) 513, 77 (2014)]. In this article we study the interaction of such rafts using liquid crystal elasticity theory. By numerically minimizing the director elastic free energy, we predict the tilt angle profile for both a single raft and two rafts in a background membrane, and the interaction between two rafts as a function of their separation. We find that the chiral penetration depth in the background membrane sets the scale for the range of the interaction. We compare our results with the experimental data and find good agreement for the strength and range of the interaction. Unlike the experiments, however, we do not observe a complete collapse of the data when rescaled by the tilt angle at the raft edge.

On-chip generation of monodisperse giant unilamellar lipid vesicles containing quantum dots.

Monodispersed lipid vesicles have been used as a drug delivery vehicle and a biochemical reactor. To generate monodispersed lipid vesicles in the nano- to micrometer size range, an extrusion step should be included in conventional hand-shaking method of lipid vesicle synthesis. In addition, lipid vesicles as a drug carrier still need to be improved to effectively encapsulate concentrated biomolecules such as cells, proteins, and target drugs. To overcome these limitations, this paper reports a new microfluidic platform for continuous synthesis of small-sized (∼10 μm) giant unilamellar vesicles (GUVs) containing quantum dots (QDs) as a nanosized model drug. To generate GUVs, we introduced an additional cross-flow to break vesicles into small size. 1,2 - dimyristoyl-sn-glycero - 3 - phosphocholine (DMPC) in an octanol-chloroform mixture was used in the construction of self-assembled membrane. Consequently, we have successfully demonstrated the fabrication of monodispersed GUVs with 7-12 μm diameter containing QDs. The proposed synthesis method of cell-sized GUVs would be highly desirable for applications such as multipurpose drug encapsulation and delivery.

Self and directed assembly: people and molecules.

Self-assembly and directed-assembly are two very important aspects of supramolecular chemistry. As a young postgraduate student working in Canada with Tom Fyles my introduction to Supramolecular Chemistry was through the self-assembly of phospholipid membranes to form vesicles for which we were developing unimolecular and self-assembling transporter molecules. The next stage of my development as a scientist was in Japan with Seiji Shinkai where in a “Eureka” moment, the boronic acid templating unit (directed-assembly) of Wulff was combined with photoinduced electron transfer systems pioneered by De Silva. The result was a turn-on fluorescence sensor for saccharides; this simple result has continued to fuel my research to the present day. Throughout my career as well as assembling molecules, I have enjoyed bringing together researchers in order to develop collaborative networks. This is where molecules meet people resulting in assemblies worth more than the individual “molecule” or “researcher”. My role in developing networks with Japan was rewarded by the award of a Daiwa-Adrian Prize in 2013 and I was recently rewarded for developing networks with China with an Inaugural CASE Prize in 2015.

ChemInform Abstract: Self and Directed Assembly: People and Molecules

AbstractReview: [124 refs.

Spontaneously self-assembled dual-layer mixed matrix membranes containing mass-produced mesoporous TiO2 for CO2 capture

Herein, a high performance mixed matrix membrane (MMM) is reported, through control of the solvent evaporation rate based on the spontaneous self-assembly of mesoporous TiO2 (m-TiO2) fillers in a poly(vinyl chloride)-g-poly(oxyethylene methacrylate) (PVC-g-POEM) graft copolymer matrix. In particular, a facile, non-hydrothermal and mass-producible preparation method for m-TiO2 is described. Slow solvent evaporation resulted in the formation of dual-layer MMMs consisting of a top PVC-g-POEM rich layer over a bottom m-TiO2 rich layer, whereas fast evaporation led to the case of single-layer MMMs. Both CO2 permeability and CO2/N2 selectivity increased as the m-TiO2 content increased up to 20wt% for single-layer as well as dual-layer MMMs, due to loose packing structures and increased chain flexibility. However, above 20wt% loading, dual-layer MMMs exhibited much higher CO2 permeabilities and CO2/N2 selectivities than single-layer MMMs, resulting from self-assembled dual-layer architecture as well as better interfacial adhesion properties. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and density measurements revealed that the PVC-g-POEM graft copolymer chains penetrated into the m-TiO2 rich layer to generate web-like interconnected structures, forming proper pore sizes for selective CO2 transport. The dual-layer MMMs exhibited excellent improvements in CO2 permeability of over 3000% from 46.2 to 1430.9 Barrer (1 Barrer = 1×10−10cm3 (STP)cm /cm2scmHg) with a CO2/N2 selectivity of 22.4, which was only slightly below the upper bound (2008).

Membrane-mediated aggregation of anisotropically curved nanoparticles.

Using systematic numerical simulations, we study the self-assembly of elongated curved nanoparticles on lipid vesicles. Our simulations are based on molecular dynamics of a coarse-grained implicit-solvent model of self-assembled lipid membranes with a Langevin thermostat. Here we consider only the case wherein the nanoparticle-nanoparticle interaction is repulsive, only the concave surface of the nanoparticle interacts attractively with the lipid head groups and only the outer surface of the vesicle is exposed to the nanoparticles. Upon their adhesion on the vesicle, the curved nanoparticles generate local curvature on the membrane. The resulting nanoparticle-generated membrane curvature leads in turn to nanoparticle self-assembly into two main types of aggregates corresponding to chain aggregates at low adhesion strengths and aster aggregates at high adhesion strength. The chain-like aggregates are due to the fact that at low values of adhesion strength, the nanoparticles prefer to lie parallel to each other. As the adhesion strength is increased, a splay angle between the nanoparticles is induced with a magnitude that increases with increasing adhesion strength. The origin of the splay angles between the nanoparticles is shown to be saddle-like membrane deformations induced by a tilt of the lipids around the nanoparticles. This phenomenon of membrane mediated self-assembly of anisotropically curved nanoparticles is explored for systems with varying nanoparticle number densities, adhesion strength, and nanoparticle intrinsic curvature.

Immobilization of polymersome in hydrogels via host-guest complexation for triggered drug delivery

Event Abstract Back to Event Immobilization of polymersome in hydrogels via host-guest complexation for triggered drug delivery Meiling Zhu1, Kongchang Wei1 and Liming Bian1 1 the Chinese University of Hong Kong, Department of Mechanical and Automation Engineering, Hong Kong, SAR China Introduction: Stem cell therapy holds promising potential for cartilage repair and regeneration[1]. Controlled delivery of chondrogenic growth factors and small molecues such as TGF (transforming growth factors) and dexamethasone (Dex) is essential to the success of stem cell therapy for cartilage repair and regeneration. Herein, we develop a multifunctional polymersome[2] that is capable of in situ grafting to cartilage for the co-delivery and sustained release of TGF-β3 and Dex to enhance chondrogenic differentiation of hMSCs. Materials and Methods: Polycaprolactone with hydroxyl terminal group (PCL-OH, 5k) was reacted with methylacryloyl chloride and thiolated β-cyclodextrin (βCD-SH) to obtain PCL-βCD (Fig. 1AB). The BSA-FITC and Rhodamine B base were dissloved in distilled water and DMF (H2o:DMF = 2:1, v/v), respectively, and co-loaded into the PCL-βCD polymersome during the self-assembly process. Hydrogels were generated by polymerizing 2.0% methacrylated hyaluronic acid modified with β-CD (MeHA-βCD) and incubated in the drug-loaded polymersome and linker (ADA-PEG4k-ADA) solution for overnight. (Fig. 2A) Then the obtained hydrogels containing immobilized polymersomes were incubated in 1 ml of PBS or 5mg/ml NH3Cl-ADA solution, respectively (Fig. 2B). Figure 1. Synthesis of PCL-βCD. (A) synthesis route of PCL-βCD and structure of βCD-SH. (B) 1H NMR of the PCL-βCD. (C) TEM images of self-assembled PCL-βCD polymersomes. Results and Discussion: The Rh of polymersome (PCL-βCD) is 144nm, and the Rg/Rh is 1.09 based on the dynamic light scattering (DLS) (Rh: hydrodynamic radius, Rg: radius of gyration). This finding supports the assumption (the theoretical value of Rg/Rh = 1) that the scattering objects are vesicles. The vesicle structure is further confirmed by the TEM images, which show the dark rims of the vesicles due to the self-assembled bilayer membrane (Fig. 1C). In both the FITC and Rhodamine channels of the microscope, the HA hydrogels exhibit substantial fluorescence signal, indicating the successful agents loading and immobilization of the polymersomes. In contrast to the hydrogels incubated in PBS, the fluorescence in the hydrogels sharlply decreases after incubation with the competitive free diffusing ADA, which disrupts the host-guest tethering of the polymersome to the hydrogel structure, leading to the release of the polymersomes. This finding shows the successful immoblization of polymeric vesicles into hydrogels via the physical interaction of β-CD and ADA molecules and triggered release of the polymersome and the loaded drugs (Fig. 2C). Significant immobilization of polymersomes on cartilage surface is likely via interacctions between β-CDs of the polymersomes and aromatic groups of the cartilage (Fig. 2 DE). Figure 2. (A) BSA-FITC and rhodamine B base are co-loaded into the PCL-βCD polymersome that are further immobilized in the MeHA-βCD hydrogels. (B-C) Addition of competitive ADA triggers the release of the polymersome and the loaded agents from the hydrogels (dotted line: cutting line of the hydrogel). (D) Quantitative fluorescence analysis of the cartilage coated with polymersomes that are loaded with BSA-FITC and Rhodamine B base (cartilage are treated in the collagenase II for overnight to mimic degenerated cartilage), with free dye solution as the control (***P<0.001, n = 5). (E) Images of porcine cartilage before and after coating trials (Blue line: the cutting site). Conclusion: The self-assembly polymersomes in this study demonstrate the successful drugs loading, immoblization in the hydrogels via host-guest interaction, and in situ controlled drug release in response to a specific triggering signal. The study shows the promising potential of this polymersome for the triggered co-delivery of chondrogenic growth factors and small molecules for cartilage repair. The work described in this paper was supported by an Early Career Scheme grant from the Research Grants Council of HongKong.

Self-assembled particle membranes for in situ concentration and chemostat-like cultivation of microorganisms on a chip.

Recently, microparticles have been used as nanoporous membranes in microfluidic devices, contributing to various bioassays on a chip. Here, we report a self-assembled particle membrane (SAPM) integrated microfluidic device that concentrates particles into an aimed microchamber array by using evaporation-driven capillary forces, and manipulates the chemical environment of the microchamber array by sequentially introducing different solutions. We demonstrate that the SAPM-integrated microchamber array can concentrate microparticles and microbial cells up to 120-fold for 2 h and 35-fold for 1 h, respectively, resulting in remarkably high concentration factors. Additionally, we demonstrate that the microchamber array has high potential as a chemostat-like bioreactor because it can actively manipulate the initial seeding number of bacterial cells and continuously supply and sequentially switch fresh nutrients to them. As an example of various applications, the chemostat-like bioreactor was used as a microbial biosensor platform that enabled microbial sensor cells to respond more efficiently and rapidly to external stimuli, such as heavy metal ions. This was made possible by almost eliminating the initial lag phase that dramatically shortened the whole assay time. Notably, the SAPM-integrated microchamber array not only facilitates various bioassays on a chip but also provides unprecedented experimental platforms to study microorganisms in a simple and convenient manner.