HPMA-Based Nanoparticles for Fast, Bioorthogonal iEDDA Ligation.

Fast and bioorthogonally reacting nanoparticles are attractive tools for biomedical applications such as tumor pretargeting. In this study, we designed an amphiphilic block copolymer system based on HPMA using different strategies to introduce the highly reactive click units 1,2,4,5-tetrazines (Tz) either at the chain end (Tz-CTA) or statistical into the hydrophobic block. This reactive group undergoes a rapid, bioorthogonal inverse electron-demand Diels-Alder reaction (iEDDA) with trans-cyclooctenes (TCO). Subsequently, this polymer platform was used for the preparation of different Tz-covered nanoparticles, such as micelles and colloids. Thereby it was found that the reactivity of the polymeric micelles is comparable to that of the low molar mass tetrazines. The core-cross-linked micelles can be successfully conjugated at rather low concentrations to large biomacromolecules like antibodies, not only in physiological buffer, but also in human blood plasma, which was confirmed by fluorescence correlation spectroscopy (FCS).

Secondary-Structure-Driven Self-Assembly of Reactive Polypept(o)ides: Controlling Size, Shape, and Function of Core Cross-Linked Nanostructures.

Achieving precise control over the morphology and function of polymeric nanostructures during self-assembly remains a challenge in materials as well as biomedical science, especially when independent control over particle properties is desired. Herein, we report on nanostructures derived from amphiphilic block copolypept(o)ides by secondary-structure-directed self-assembly, presenting a strategy to adjust core polarity and function separately from particle preparation in a bioreversible manner. The peptide-inherent process of secondary-structure formation allows for the synthesis of spherical and worm-like core-cross-linked architectures from the same block copolymer, introducing a simple yet powerful approach to versatile peptide-based core-shell nanostructures.

Polymeric Selectin Ligands Mimicking Complex Carbohydrates: From Selectin Binders to Modifiers of Macrophage Migration.

Novel polymeric cell adhesion inhibitors were developed in which the selectin tetrasaccharide sialyl-LewisX (SLeX ) is multivalently presented on a biocompatible poly(2-hydroxypropyl)methacrylamide (PHPMA) backbone either alone (P1) or in combination with O-sulfated tyramine side chains (P2). For comparison, corresponding polymeric glycomimetics were prepared in which the crucial "single carbohydrate" substructures fucose, galactose, and sialic acid side chains were randomly linked to the PHPMA backbone (P3 or P4 (O-sulfated tyramine)). All polymers have an identical degree of polymerization, as they are derived from the same precursor polymer. Binding assays to selectins, to activated endothelial cells, and to macrophages show that polyHPMA with SLeX is an excellent binder to E-, L-, and P-selectins. However, mimetic P4 can also achieve close to comparable binding affinities in in vitro measurements and surprisingly, it also significantly inhibits the migration of macrophages; this provides new perspectives for the therapy of severe inflammatory diseases.

Degradable cationic nanohydrogel particles for stimuli-responsive release of siRNA.

Well-defined nanogels have become quite attractive as safe and stable carriers for siRNA delivery. However, to avoid nanoparticle accumulation, they need to provide a stimuli-responsive degradation mechanism that can be activated at the payload's site of action. In this work, the synthetic concept for generating well-defined nanohydrogel particles is extended to incorporate disulfide cross-linkers into a cationic nanonetwork for redox-triggered release of oligonucleotide payload as well as nanoparticle degradation under reductive conditions of the cytoplasm. Therefore, a novel disulfide-modified spermine cross-linker is designed that both allows disassembly of the nanogel as well as removal of cationic charge from residual polymer fragments. The degradation process is monitored by scanning electron microscopy (SEM) and fluorescence correlation spectroscopy (FCS). Moreover, siRNA release is analyzed by agarose gel electrophoresis and a fluorescent RNA detection assay. The results exemplify the versatility of the applied nanogel manufacturing process, which allows alternative stimuli-responsive core cross-linkers to be integrated for triggered oligonucleotide release as well as effective biodegradation for reduced nanotoxicity.

Solubilisation of multi walled carbon nanotubes by alpha-pyrene functionalised PMMA and their liquid crystalline self-organisation.

alpha-Pyrene functionalised poly(methyl methacrylate) (PMMA) chains were synthesised by RAFT polymerisation and found to be highly efficient to solubilise and disentangle multi walled carbon nanotubes that can now self-organise as liquid crystalline phases in PMMA and PEG 400 matrices.

Combining Orthogonal Reactive Groups in Block Copolymers for Functional Nanoparticle Synthesis in a Single Step.

We report on the synthesis of polysarcosine-block-poly(S-alkylsulfonyl)-l-cysteine block copolymers, which combine three orthogonal addressable groups enabling site-specific conversion of all reactive entities in a single step. The polymers are readily obtained by ring-opening polymerization (ROP) of corresponding α-amino acid N-carboxyanhydrides (NCAs) combining azide and amine chain ends, with a thiol-reactive S-alkylsulfonyl cysteine. Functional group interconversion of chain ends using strain-promoted azide-alkyne cycloaddition (SPAAC) and activated ester chemistry with NHS- and DBCO-containing fluorescent dyes could be readily performed without affecting the cross-linking reaction between thiols and S-alkylsulfonyl protective groups. Eventually, all three functionalities can be combined in the formation of multifunctional disulfide core cross-linked nanoparticles bearing spatially separated functionalities. The simultaneous attachment of dyes in core and corona during the formation of core-cross-linked nanostructures with controlled morphology is confirmed by fluorescence cross-correlation spectroscopy (FCCS).