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In recent years, natural polysaccharides have been widely used in the preparation of drug delivery systems. In this paper, novel polysaccharide-based nanoparticles were prepared by layer-by-layer assembly technology using silica a...
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In recent years, natural polysaccharides have been widely used in the preparation of drug delivery systems. In this paper, novel polysaccharide-based nanoparticles were prepared by layer-by-layer assembly technology using silica as a template. The layers of nanoparticles were constructed based on the electrostatic interaction between a new pectin named NPGP and chitosan (CS). The targeting ability of nanoparticles was formed by grafting the RGD peptide, a tri-peptide motif containing arginine, glycine, and aspartic acid with high affinity to integrin receptors. The layer-by-layer assembly nanoparticles (RGD-(NPGP/CS)3NPGP) exhibited a high encapsulation efficiency (83.23 ± 6.12%), loading capacity (76.51 ± 1.24%), and pH-sensitive release property for doxorubicin. The RGD-(NPGP/CS)3NPGP nanoparticles showed better targeting to HCT-116 cells, the integrin αvβ3 high expression human colonic epithelial tumor cell line with higher uptake efficiency than MCF7 cells, the human breast carcinoma cell line with normal integrin expression. In vitro antitumor activity tests showed that the doxorubicin-loaded nanoparticles could effectively inhibit the proliferation of the HCT-116 cells. In conclusion, RGD-(NPGP/CS)3NPGP nanoparticles have potential as novel anticancer drug carriers because of their good targeting and drug-carrying activity.
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Layer-by-layer (LbL) assemblies have been of great interest due to their versatile functionality and ease of fabrication, but their response to temperature is not completely understood. It has been recently shown that hydrated LbL...
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Layer-by-layer (LbL) assemblies have been of great interest due to their versatile functionality and ease of fabrication, but their response to temperature is not completely understood. It has been recently shown that hydrated LbL assemblies of poly(diallyldimethylammonium chloride) (PDAC) and poly(styrene sulfonate) (PSS) under go a thermal transition much like a "glass-melt" transition. This thermal transition is of great interest because many LbL applications are found in water. Here, we report upon the nature of this thermal transition as probed using electrochemical impedance spectroscopy (EIS) as a function of assembly salt concentration, film thickness, and outermost layer. EIS reveals that the transition is signified by a structural rearrangement of virtual pores, resulting in increased conductivity and decreased surface coverage of the electrode. Two separate thermal transitions are obtained from changes in the film resistance (T_(tr,Rf)) and the charge transfer resistance (T_(tr,Rct)). Only T_(tr,Rct) is strongly dependent on film thickness, salt concentration, and outermost layer, for which values ranging from 50 to 64 ℃ were observed. As the assembly salt concentration increases from 0.5 M to 1.0 M NaCl, T_(tr,Rct) increases by about 10 ℃. Below 20 layers, deviations of T_(tr,Rct) with respect to outermost layer appear, in which PSScapped LbL films tend to show elevated T_(tr,Rct) values. These results suggest that extrinsic charge compensation plays a large role in the value of T_(tr,Rct) in which a large degree of extrinsic charge compensation drives T_(tr,Rct) towards higher values. On the other hand, T_(tr,Rf) is largely unaffected by assembly parameters, and closer in value to prior reports via calorimetry and quartz crystal microbalance with dissipation.
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A three-dimensional (3D) microfluidic network plays an important role in engineering thick organs. However, most of the existing methods are limited to mechanically robust synthetic biomaterials and only planar or simple microflui...
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A three-dimensional (3D) microfluidic network plays an important role in engineering thick organs. However, most of the existing methods are limited to mechanically robust synthetic biomaterials and only planar or simple microfluidic networks have been incorporated into soft natural biopolymers. Here we presented an automatic layer-by-layer micromolding strategy to reproducibly fabricate 3D microfluidic porous scaffolds directly from the aqueous solution of soft natural biopolymers. Process parameters such as the liquid volume for each layer and contact displacement were investigated to produce a structurally stable 3D microfluidic scaffold. Microscopic characterization demonstrated that the microfluidic channels were interconnected in 3D and successfully functioned as a convective pathway to transport a polymer solution. Endothelial cells grew relatively well in the porous microfluidic channels. It is envisioned that this method could provide an alternative way to reproducibly build complex 3D microfluidic networks into extracellular matrix-like scaffolds for the fabrication of soft vascularized organs.
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Vesicles are dynamic supramolecular structures with a bilayer membrane consisting of lipids or synthetic amphiphiles enclosing an aqueous compartment. Lipid vesicles have often been considered as mimics for biological cells. In th...
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Vesicles are dynamic supramolecular structures with a bilayer membrane consisting of lipids or synthetic amphiphiles enclosing an aqueous compartment. Lipid vesicles have often been considered as mimics for biological cells. In this paper, we present a novel strategy for the preparation of three-dimensional multilayered structures in which vesicles containing amphiphilic β-cyclodextrin are interconnected by proteins using cyclodextrin guests as bifunctional linker molecules. We compared two pairs of adhesion molecules for the immobilization of vesicles: mannose-concanavalin A and biotin-streptavidin. Microcontact printing and thiol-ene click chemistry were used to prepare suitable substrates for the vesicles. Successful immobilization of intact vesicles through the mannose-concanavalin A and biotin-streptavidin motifs was verified by fluorescence microscopy imaging and dynamic light scattering, while the vesicle adlayer was characterized by quartz crystal microbalance with dissipation monitoring. In the case of the biotin-streptavidin motif, up to six layers of intact vesicles could be immobilized in a layer-by-layer fashion using supramolecular interactions. The construction of vesicle multilayers guided by noncovalent vesicle-vesicle junctions can be taken as a minimal model for artificial biological tissue.
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This paper examines K~+/Mg~(2+) selectivities and cation fluxes in diffusion dialysis and electrodialysis through membranes coated with poly(sodium 4-styrenesulfonate) (PSS)/protonated poly(allylamine) (PAH) multilayer films. In b...
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This paper examines K~+/Mg~(2+) selectivities and cation fluxes in diffusion dialysis and electrodialysis through membranes coated with poly(sodium 4-styrenesulfonate) (PSS)/protonated poly(allylamine) (PAH) multilayer films. In both dialysis techniques, K~+/Mg~(2+) selectivities reach values >100, and with (PSS/PAH)5-coated nanofiltration membranes the K~+ flux in electrodialysis is 45-times the flux in diffusion dialysis. Thus, the applied electric current can increase flux without decreasing selectivity. However, the K~+ transference number is at most w0.35 because protons and anions also carry current. Ion fluxes and K~+/Mg~(2+) selectivities depend on the anion of the K~+/Mg~(2+) salts. Sulfate decreases the surface charge on (PSS/PAH)_5-coated membranes and reduces K~+/Mg~(2+) selectivities to ~40 in both diffusion dialysis and electrodialysis through films on porous alumina. Chlorine generated during electrodialysis with chloride salts damages (PSS/PAH)_5-coated membranes, and selectivities decline dramatically after 60 min. Future work should examine selectivities among more valuable ions and methods for increasing stability and the transference numbers for the ions of interest.
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Polymer microcapsules can be used as bioreactors and artificial cells; however, preparation methods for cell-like microcapsules are typically time-consuming, low yielding, and/or involve custom microfluidics. Here, we introduce a ...
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Polymer microcapsules can be used as bioreactors and artificial cells; however, preparation methods for cell-like microcapsules are typically time-consuming, low yielding, and/or involve custom microfluidics. Here, we introduce a rapid (~30 min per batch, eight layers), scalable (up to 500 mg of templates), and efficient (98% yield) microcapsule preparation technique utilizing a fluidized bed for the layerby- layer (LbL) assembly of polymers, and we investigate the parameters that govern the formation of robust capsules. Fluidization in water was possible for particles of comparable diameter to mammalian cells (>5 μm), with the experimental flow rates necessary for fluidization matching well with the theoretical values. Important variables for polymer film deposition and capsule formation were the concentration of polymer solution and the molecular weight of the polymer, while the volume of the polymer solution had a negligible impact. In combination, increasing the polymer molecular weight and polymer solution concentration resulted in improved film deposition and the formation of robust microcapsules. The resultant polymer microcapsules had a thickness of ~5.5 nm per bilayer, which is in close agreement with conventionally prepared (quiescent (nonflow) adsorption/centrifugation/wash) LbL capsules. The technique reported herein provides a new way to rapidly generate microcapsules (approximately 8 times quicker than the conventional means), while being also amenable to scale-up and mass production.
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Molecular self-assembly is usually done at low supersaturation, leading to low rates of growth, in order to allow time for binding mistakes to anneal. However, such conditions can lead to prohibitively long assembly times where gr...
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Molecular self-assembly is usually done at low supersaturation, leading to low rates of growth, in order to allow time for binding mistakes to anneal. However, such conditions can lead to prohibitively long assembly times where growth proceeds by the slow nucleation of successive layers. Here we use a lattice model of molecular self-assembly to show that growth in this regime can be sped up by impurities, which lower the free-energy cost of layer nucleation. Under certain conditions impurities behave almost as a catalyst in that they are present at high concentration at the surface of the assembling structure, but at low concentration in the bulk of the assembled structure. Extrapolation of our numerics using simple analytic arguments suggests that this mechanism can reduce growth times by orders of magnitude in parameter regimes applicable to molecular systems.
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Polyelectrolyte multilayer films were fabricated via layer-by-layer deposition using polyallylamine hydrochloride lightly functionalized (～1%) with a covalently bound polypyridyl Ru(II) chromophore dye (RuPAH) and polystyrenesulf...
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Polyelectrolyte multilayer films were fabricated via layer-by-layer deposition using polyallylamine hydrochloride lightly functionalized (～1%) with a covalently bound polypyridyl Ru(II) chromophore dye (RuPAH) and polystyrenesulfonate (PSS). Absorbance oscillations were noted in the UV-visible spectra of these films as functions of the number of PSS/RuPAH bilayers and identified as optical interference effects. The interference effects were modeled according to a Fabry-Pérot cavity and a powerful conversion methodology was developed capable of correcting many spectra from relatively few fits. It is recommended that this method be applied as a standard to enable accurate analysis of absorbance spectra in thin films containing chromophores.
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We have developed a new method to fabricate multilayer films, which uses prepared thin films as modular blocks and transfer as operation mode to build up multilayer structures. In order to distinguish it from the in situ fabricati...
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We have developed a new method to fabricate multilayer films, which uses prepared thin films as modular blocks and transfer as operation mode to build up multilayer structures. In order to distinguish it from the in situ fabrication manner, this method is called modular assembly in this study. On the basis of such concept, we have fabricated a multilayer film using the silver mirror film as the modular block and poly(lactic acid) as the transfer tool. Due to the special double-layer structure of the silver mirror film, the resulting multilayer film had a well-defined stratified architecture with alternate porous/compact layers. As a consequence of the distinct structure, the interaction between the adjacent layers was so weak that the multilayer film could be layer-by-layer stripped. In addition, the top layer in the film could provide an effective protection on the morphology and surface property of the underlying layers. This suggests that if the surface of the film was deteriorated, the top layer could be peeled off and the freshly exposed surface would still maintain the original function. The successful preparation of the layer-by-layer strippable silver multilayer demonstrates that modular assembly is a feasible and effective method to build up multilayer films capable of creating novel and attractive micro/nanostructures, having great potential in the fabrication of nanodevices and coatings.
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Charges generated by contact of solid surfaces (contact electrification) can be hazardous or useful depending on the circumstance. This paper describes a process to design a solid surface rationally to either induce or prevent cha...
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Charges generated by contact of solid surfaces (contact electrification) can be hazardous or useful depending on the circumstance. This paper describes a process to design a solid surface rationally to either induce or prevent charging during contact electrification; this process coats the surface with polyelectrolytes. It is observed experimentally that a surface coated with a layer of a polymer having multiple, covalently attached positive charges (a "polycation") develops a positive charge after contacting another surface; a surface coated with a layer of polymer having negative charges (a "polyanion") develops a negative charge. By coating the surface using layer-by-layer (LBL) deposition, the tendency of the surface to charge either positively or negatively can be switched: adding a layer of polyelectrolyte with charge opposite to the charge on the surface switches the polarity of the surface. Through microcontact printing (μCP), the surface can be stamped to create a mosaic pattern of polycation and polyanion - and importantly, the fraction of the surface area covered with polycation and polyanion can be tuned by using stamps of different patterns. Using poly(diallyldimethylammonium chloride) (PDDA) as the polycation and poly(sodium 4-styrenesulfonate) (PSS) as the polyanion, it is found that for a surface with >75% PSS, the surface charges negatively; with <75% PSS, the surface charges positively. At ～75% PSS, the surface becomes non-charging. The patterns on the surface can, subsequently, be erased through coating the surface with a uniform layer of polyelectrolyte. After erasing, the surface is rewritable by depositing or patterning the surface with a desired polyelectrolyte.
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