Krystyna Albrecht

Embedding of Active Proteins and Living Cells in Redox‐Sensitive Hydrogels and Nanogels through Enzymatic Cross‐Linking

Redox-sensitive materials have received dramatically increasing interest over the past years.1 Disulfide cross-linked colloidal networks are particularly appealing, as they are rapidly reduced to thiols under the reductive environment inside cells, allowing the quantitative release of the payload incorporated within the particles.2 Moreover, disulfide cross-linked hydrogels as three-dimensional cell-culture scaffolds can be degraded under cytocompatible mild reductive conditions without affecting the vitality of the embedded cells.3

Structure and properties of urea-crosslinked star poly[(ethylene oxide)-ran-(propylene oxide)] hydrogels.

Isocyanate-terminated six armed star shaped macromers with a statistical copolymer backbone consisting of 80% EO and 20% PO have previously demonstrated excellent protein and cell repellence as nano-layered surfaces. In this study, various macromers are mixed with water and provide a spectrum of materials that range from particles to uniform hydrogels. Due to hydrophobic end groups, 3 kDa molecular weight macromers result in micro and nano-particles, while 18 kDa macromers completely dissolve and consequently uniform, transparent, high water content hydrogels are formed. Oriented channels may be induced into these hydrogels through the controlled freezing of water in the preformed hydrogel.

Mechanically strong hydrogels with reversible behaviour under cyclic compression with MPa loading

Hydrogels are fascinating materials with high water content and low surface friction that can be tailored for numerous applications. However, their practical application is often hampered by an intrinsic mechanical weakness. Strategies for mechanically strong hydrogels have been developed, with double network (DN) hydrogels reaching remarkable compression resistance, although so far with loss of these properties under repeated compression. In this study we present DN hydrogels composed of cross-linked six arm star-shaped poly(ethylene oxide-stat-propylene oxide) (sPEOPO) primary networks and polyacrylamide (PAAm) as secondary network. These hydrogels possess high water content (>90 w/w%) and high compression strength of up to 5.6 MPa. Most importantly, they show a fully reversible behaviour in repeated loading–unloading experiments with 1 MPa maximal stress, which we attribute to the partial healing capacity of the primary network and the overall macroporous morphology of the gels.

Surface Micelles and Surface-Induced Nanopatterns Formed by Block Copolymers

Lateral phase segregation of block copolymers in ultra-thin films results in highly orderedarrays at interfaces. In this brief review we focus on PS-b-P2VPand PS-b-P4VP block copolymers. Selective solvents and polar solidsubstrates lead to a brush surface formed by adsorption of free polymer chains in solution followedby adsorption of whole micelles upon withdrawal of the sample from the solution. These laterallyhighly ordered patterns are obtained by rapid solvent evaporation and are thermodynamically not stable.In the second case presented two-dimensional surface micelles of poly(styrene)-block-poly(N-alkyl-4-vinylpyridinum iodide) are formed by spreading a solutionin a slightly selective solvent mixture onto the water/air interface. The resulting patternmorphology strongly depends on the surface pressure and the length of the alkyl chain used for quaternization.These patterns can be transferred to solid substrates without structural changes. In contrast, polymerdeposition onto mica from nonselective solvents is controlled by the polymer-surface interaction andthe resulting patterns are induced by the surface (Surface-Induced NanoPATterns, SINPATs). The PVPblock adsorbs strongly on mica in a two-dimensional coil whereas the PS block dewets the adsorbedPVP layer forming isolated clusters. These patterns are thermodynamically stable. As one possibleapplication, Ti/SINPAT composites have been successfully used as etch masks allowing the transferof regular structures of nanometer size into substrates.

Nanostructured Ordering of Fluorescent Markers and Single Proteins on Substrates

Highly ordered hexagonal nanopatterns of gold clusters on glass substrates were used as anchoring points for the specifc attachment of fluorescence dyes and proteins labeled with fluorescence dyes. Thiol‐ or disulfide‐containing linker molecules were used for the binding to the gold dots. In order to ensure specific binding on the gold dots only, the surface area in between the dots was protected against unspecific adsorption. For the attachment of polar low‐molecular‐weight fluorescence dyes, an octadecyltrichlorosilane self‐assembled monolayer was prepared on the surface in between the gold dots, whereas a layer prepared from star‐shaped poly(ethylene oxide‐stat‐propylene oxide) prepolymers was used to prevent unspecific adsorption of proteins between the gold dots. Fluorescence microscopy proved the specific binding of the dyes as well as of the proteins. Scanning force microscopy studies show that each gold dot is only capable of binding one protein at a time.

Nano- and Microgels Through Addition Reactions of Functional Oligomers and Polymers

Nano- and Microgels are predominantly prepared using radical polymerization techniques. This chapter reviews alternative approaches to microgel preparation based on addition reactions of functional oligomers and polymers. This allows preparation of microgels under physiological conditions and in the presence of biologically active molecules without affecting their function. This method is therefore predominantly used to synthesize microgels for biomedical applications. Different crosslinking chemistries that have been used in this context are presented and discussed with regard to reaction conditions and stability of the reaction product. Microgels that have been prepared by these techniques are divided into two groups. Natural polymers used for the preparation of microgels are described first, followed by artificial prepolymers that are suitable for the preparation of microgels. The different preparation methods as well as the resulting microgels and their properties are presented and discussed.

Mild Oxidation of Thiofunctional Polymers to Cytocompatible and Stimuli-Sensitive Hydrogels and Nanogels

Nanogels consist of three dimensionally cross-linked hydrophilic polymer chains and can thus be easily modified through functionalization of the polymeric building blocks, for example to yield stimuli-sensitive materials. For drug transport and intracellular release, redox-sensitive systems are especially of interest, as the intracellular space is reductive. In this study, parameters that allow preparation of nanogels with tunable size between 150 and 350 nm are systematically evaluated and identified. Most importantly, a new and mild oxidation catalyst, alloxan, is introduced for the preparation of the nanogels. This broadens the range of possible payloads to more-sensitive molecules. Particle stability, degradation in cytosolic conditions, and cytocompatibility in concentrations up to 10 mg · mL(-1) are demonstrated.

Reactive amphiphilic block copolymers for the preparation of hybrid organic/inorganic materials with covalent interactions

The preparation of micelles based on polystyrene-block-polyglycidol (PS-b-PG) in a selective solvent and their loading with titanium(IV)-isopropoxide, a precursor for titanium dioxide, nanoparticles is described. The formation of micelles was studied with scanning force microscopy (SFM) and transmission electron microscopy (TEM), before and after loading with the titanium alcoholate. Interaction of the hydroxyl groups of the polyglycidol side chains with titanium(IV)-isopropoxide leads to covalent cross-linking of the micellar core. Formation of micelles with frozen cores was verified by dynamic light scattering. The cross-linked micelles were coated onto a substrate and treated with plasma to achieve hexagonally ordered titanium dioxide nanoparticles.

DNA Nanogels To Snare Carcinogens: A Bioinspired Generic Approach with High Efficiency.

Polycyclic aromatic hydrocarbons (PAHs) are combustion-related pollutants and are ubiquitous in the environment, including in sources of drinking water. Upon contact with DNA, stable PAH-DNA adducts form rapidly as the first step towards their toxic effects. In this work, we prepared hydrophilic DNA nanogels to exploit this generic complexation process as a biomimetic scavenging method. This approach relies on interaction between PAHs and the complete network that constitutes the water-swollen nanogels, and is not restricted to interfacial adsorption. Up to 720 μg of PAH per gram of DNA nanogel are taken up, meaning that 1 mg of DNA nanogel is sufficient to purify a liter of water containing the critical PAH concentration for cancer risk (600 ng L(-1) ). As a result of short diffusion pathways, PAH uptake is rapid, reaching 50 % loading after 15 minutes. Beyond PAHs, DNA nanogels may be useful for the generic detoxification of water containing genotoxins, since most known molecules that strongly associate with DNA are mutagenic.

An in vitro and in vivo study of peptide-functionalized nanoparticles for brain targeting: The importance of selective blood???brain barrier uptake

Targeted delivery of drugs across endothelial barriers remains a formidable challenge, especially in the case of the brain, where the blood-brain barrier severely limits entry of drugs into the central nervous system. Nanoparticle-mediated transport of peptide/protein-based drugs across endothelial barriers shows great potential as a therapeutic strategy in a wide variety of diseases. Functionalizing nanoparticles with peptides allows for more efficient targeting to specific organs. We have evaluated the hemocompatibilty, cytotoxicity, endothelial uptake, efficacy of delivery and safety of liposome, hyperbranched polyester, poly(glycidol) and acrylamide-based nanoparticles functionalized with peptides targeting brain endothelial receptors, in vitro and in vivo. We used an ELISA-based method for the detection of nanoparticles in biological fluids, investigating the blood clearance rate and in vivo biodistribution of labeled nanoparticles in the brain after intravenous injection in Wistar rats. Herein, we provide a detailed report of in vitro and in vivo observations.