Amino groups were covalently introduced onto a polycaprolactone (PCL) surface by the reaction between 1,6-hexanediamine and the ester groups of PCL. The occurrence of the aminolysis and the introduction of free NH(2) groups were verified qualitatively by fluorescence spectroscopy, where rhodamine B isothiocyanate was employed to label NH(2) groups, and quantitatively by absorbance spectroscopy, where ninhydrin was used to react with NH(2) to generate a blue product. Due to the presence of deep pores on the PCL membrane, the aminolysis reaction could penetrate as deep as 50 microm to yield NH(2) density as high as 2 x 10(-7) mol/cm(2). By use of the NH(2) groups as active sites, biocompatible macromolecules such as gelatin, chitosan, or collagen were further immobilized on the aminolyzed PCL membrane via a cross-linking agent, glutaraldehyde. X-ray photoelectron spectroscopy (XPS) and surface wettability measurements confirmed the coupling of the biomacromolecules. The endothelial cell culture proved that the cytocompatibility of the aminolyzed PCL was improved slightly regardless of the NH(2) amount on the surface. After immobilization of the biomacromolecules, however, the cell attachment and proliferation ratios were obviously improved and the cells showed a similar morphology to those on tissue culture polystyrene. Measurement of the von Willebrand factor (vWF) secreted by these endothelial cells (ECs) verified the endothelial function. Hence, a better EC-compatible PCL was produced.

Osmotically induced deformations (invaginations) of polyelectrolyte capsules were observed in poly(styrene sulfonate, sodium salt) (PSS) solution since PSS of Mw 70 000 is excluded from the capsule interior. It was found that there is a critical osmotic pressure difference at which the initial spherical capsule shape becomes unstable and invaginations are formed. This critical osmotic pressure was obtained as a function of the wall thickness and the capsule size. A theoretical model is provided which describes the relationship between the critical osmotic pressure, the elasticity modulus, the capsule wall thickness, and the capsule radius. The model was verified by measuring the invagination onset as a function of particle radius and wall thickness. The elasticity modulus of the PSS/PAH (polyallylamine hydrochloride) polyelectrolyte multilayer was measured as a function of wall thickness and capsule diameter. The modulus ranges between 500 and 750 MPa, which indicates a relatively strongly interconnected polyelectrolyte multilayer structure. With higher molecular weight PAH the elasticity modulus of the PSS/PAH multilayer was slightly enhanced.PACS. 46.32.+x Static buckling and instability -68.60.Bs Mechanical and acoustical properties

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Nanoengineered multifunctional capsules with tailored structures and properties are of particular interest due to their multifunctions and potential applications as new colloidal structures in diverse fields. Among the available fabrication methods, the layer-by-layer (LbL) assembly of multilayer films onto colloidal particles followed by selective template removal has attracted extensive attention due to its advantages of precise control over the size, shape, composition, wall thickness and functions of the obtained capsules. The past decade has witnessed a rapid increase of research concerning the new fabrication strategies, functionalization and applications of this kind of capsules, particularly in the biomedical fields such as drug delivery, biosensors and bioreactors. In this critical review, the very recent progress of the multilayer capsules is summarized. First, the advances in assembly of capsules by the LbL technique are introduced with focus on tailoring the properties of hydrogen-bonded multilayer capsules by cross-linking, and fabrication of capsules based on covalent bonding and bio-specific interactions. Then the fabrication strategies which can speed up capsule fabrication are reviewed. In the following sections, the multi-compartmental capsules and the capsules that can transform their shape under stimulus are presented. Finally, the biomedical applications of multilayer capsules with particular emphasis on drug carriers, biosensors and bioreactors are described (306 references).

The complexation between a water-soluble pillar[6]arene (WP6) and paraquat (G1) in water was investigated. They could form a stable 1:1 [2]pseudorotaxane with an extremely high association constant of (1.02 ± 0.10) × 10(8) M(-1) mainly driven by electrostatic interactions, hydrophobic interactions, and π-π stacking interactions. This molecular recognition has not only high binding strength but also pH-responsiveness. The threading and dethreading processes of this [2]pseudorotaxane could be reversibly controlled by changing the solution pH. This novel recognition motif was further used to control the aggregation of a complex between WP6 and an amphiphilic paraquat derivative (G2) in water. The reversible transformations between micelles based on G2 and vesicles based on WP6⊃G2 were realized by adjusting the solution pH due to the pH-responsiveness of WP6. The controlled release of water-soluble dye molecules from the vesicles could be achieved by the collapse of the vesicles into the micelles upon changing the solution pH to acidity. Additionally, the high binding affinity between WP6 and paraquat could be utilized to efficiently reduce the toxicity of paraquat. After the formation of a stable host-guest complex between WP6 and paraquat, less opportunity was available for paraquat to interact with the reducing agents in the cell, which made the generation of its radical cation more difficult, resulting in the efficient reduction of paraquat toxicity.