Creation of thermo‐responsive ion‐track membranes

Abstract

Worldwide, studies are being devoted to the development of adaptive drug release systems capable of delivering the right amount of drug at the right place and time. Many of these studies use responsive hydrogels capable of adapting reversibly under the influence of environmental conditions such as temperature, pH, concentration of chemical species, or electric charge.A new concept for a mechanically stable drug release system is to combine hydrogels with porous ion-track membranes, which have the advantage of high mechanical strength. Ion-track membranes can be produced with cylindrical pores of controlled pore size and narrow pore size distribution. The result is a responsive microcomposite that can be tailored for specific applications. The membrane consists of a mechanically strong polymer matrix onto which a soft hydrogel is grafted. Due to its symmetric sandwich structure the membrane remains flat and does not expand laterally during thermal cycling.The first component of the microcomposite is an etched ion-track membrane. The technique is based on energetic heavy ions from accelerators. On passing through a polymer each ion releases its energy within a cylinder of -10 nm diameter"] -the latent ion trackcorresponding to a high concentration of active chemical species,[21 which is associated with dramatic changes in molecular structure and properties. The preparation of an etched track membrane, as well as its grafting by a hydrogel, is illustrated in Figure 1. The etched ion-track membrane is characterized by adjustable, highly uniform, pore diameters (adjustable between 10 nm and 100 pm), identical pore length, and uniform pore orientation. The number of ion tracks per cm2 corresponds exactly to the number of impinging ions Intelligent gel Ion track etch techniqueFig. 1. Schematic diagram for the generation of responsive membranes by radiation-grafting of functional monomers onto the surface of ion-track membranes.from the ion accelerator and can be easily varied between lo3 and 10'' ions per cm2. Even individual ion tracks, i.e., one single pore per specimen, can be created.[31 The second component of such a microcomposite is the responsive hydrogel. Recently we found that the acryloylbased polymer with L-proline methyl ester (ProOMe) as a side chain confers an interesting property on the resulting polymer. It undergoes a coil-globule transition at a lower critical solution temperature (LCST) of 14 "C, in connection with the dissociation of structured water molecules surrounding hydrophobic ProOMe groups.[41 The crosslinked polymer is a temperature-responsive hydrogel undergoing a dramatic volume phase transition at 14°C. It swells below this temperature, absorbing water, and shrinks above this temperature, releasingThe volume of swollen hydrogel is approximately 400 times larger than that of the shrunken one. The swelling-shrinking process is reversible.['] Our next goal is thus to synthesize a thermoresponsive ion-track membrane by combining this hydrogel with an ion-track membrane.A 50 pm thick membrane...

Macroporous Membranes with Highly Ordered and Three-Dimensionally Interconnected Spherical Pores

“…Figures 3A and 3B are top-view images of the membrane film. [12] The pores are fully open on both top and bottom surfaces of the film with a diameter of 250 nm; they are packed into an hexagonal array with a surface density as high as~4´10 8 cm ±2 . Figure 3C simultaneously displays the top layer, the bottom layer, and the cross section of the membrane film.…”

“…In addition to their conventional uses as supports in catalysis, [1,2] as filters in separation, [1,3] and as building blocks in tissue engineering, [4] these membrane films also exhibit interesting optical properties such as photonic bandgaps and optical stop-bands due to their spatially periodic structures. [5] A number of methods have been developed for producing such kinds of membranes, including those based on selective etching (electrochemical etching of alumina or silicon, [6] chemical etching of glasses, [7] and ion-track etching of polymers [8] ), those based on self-assembly of block copolymers, [9] and those based on replica molding against various kinds of templates. [10] Methods based on selective etching usually generate straight, one-dimensional channel structures and have been very successful in the manufacture of commercial membrane films.…”

From Particle‐Assisted Wetting to Thin Free‐Standing Porous Membranes

“…However, porous materials can be made in much simpler ways by the selective removal of one component out of structured solids. Such solids can be prepared by ion-bombardment of polymers, [3] spinodal demixing of glasses, [4] self-assembly of block copolymers, [5,6] and embedding of surfactant arrays, emulsion droplets, and colloidal crystals into a continuous matrix. [7][8][9][10][11][12][13][14][15] These structured materials are usually cast onto solid substrates or in a thin layer between two solid plates and have to be separated from these plates if a free-standing membrane is desired.…”

Von partikelassistierter Benetzung zu freitragenden porösen Membranen

“…[1,2] Dünne Membranen mit präzise kontrollierten Poren lassen sich zwar durch konventionelle Photolithographie gewinnen, deutlich einfacher aber können poröse Stoffe durch selektives Herauslösen einer Komponente aus strukturierten Feststoffen hergestellt werden. Beispiele für solche Feststoffe sind strahlengeschädigte Polymere, [3] phasenseparierte Gläser, [4] Block-Copolymere, [5,6] eingebettete Micellen, Emulsionstropfen oder feste Kolloide. [7][8][9][10][11][12][13][14][15] …”