Synthesis and self-assembly of a DNA molecular brush

Molecular polymer bottlebrushes in nanomedicine: therapeutic and diagnostic applications

Molecular polymer bottlebrushes are densely grafted, individual macromolecules with nanoscale proportions. The last decade has seen an increased focus on this material class, especially in nanomedicine and for biomedical applications. This Feature Article provides an overview of major developments in this area to highlight the many opportunities that these polymer architectures bring to nano-bio research. The article covers aspects of bottlebrush synthesis and summarises their use in drug and gene delivery, imaging, as theranostics and as prototype materials to correlate nanoparticle structure and composition to biological function and behaviour. Areas for future research in this area are discussed.

Triplex Hybridization of siRNA with Bifacial Glycopolymer Nucleic Acid Enables Hepatocyte-Targeted Silencing

Herein, we describe a versatile non-covalent strategy for packaging nucleic acid cargo with targeting modalities, based on triplex hybridization of oligo-uridylate RNA with bifacial polymer nucleic acid (bPoNA). Polyacrylate bPoNA was prepared and side chain-functionalized with N-acetylgalactosamine (GalNAc), which is known to enable delivery to hepatocytes and liver via binding to the asialoglycoprotein receptor (ASGPR). Polymer binding resulted in successful delivery of both native and synthetically modified siRNAs to HepG2 cells in culture, yielding in low nanomolar IC50 silencing of the endogenous ApoB target, in line with observations of expected Dicer processing of the polymer-siRNA targeting complex. Indeed, in vitro Dicer treatment of the polymer complex indicated that triplex hybridization does not impede RNA processing and release from the polymer. The complex itself elicited a quiescent immunostimulation profile relative to free RNA in a cytokine screen, setting the stage for a preliminary in vivo study in a high-calorie-diet mouse model. Gratifyingly, we observed significant ApoB silencing in a preliminary animal study, validating bPoNA as an in vivo carrier platform for systemic siRNA delivery. Thus, this new siRNA carrier platform exhibits generally useful function and is accessible through scalable synthesis. In addition to its utility as a carrier, the triplex-hybridizing synthetic platform could be useful for optimization screens of siRNA sequences using the identical polymer carriers, thus alleviating the need for covalent ligand modification of each RNA substrate.

Surface-Initiated Poly(oligo(2-alkyl-2-oxazoline)methacrylate) Brushes

Polymer brushes are particularly performant antifouling coatings, owing to their high grafting density that prevents unwanted biomacromolecules to diffuse through the coating and adhere to the underlying substrate. In addition to this structural feature, polymer brushes require a relatively high level of hydrophilicity and a globally neutral structure to display ultrahigh protein resistance. Poly(2-alkyl-2-oxaolines) are attractive building blocks for such coatings as they can display relatively high hydrophilicity, owing to their amide repeat units, but can also be side-chain and end-chain functionalized relatively readily. However, poly(2-alkyl-2-oxazolines) have not yet been introduced through a radical-mediated grafting from polymer brush structure that would confer the high level of grafting density that is the hallmark of highly protein resistant brushes. Here, we present the formation of a series of poly(oligo(2-alkyl-2-oxazoline)methacrylate) brushes generated via a grafting from approach, via atom transfer radical polymerization. We characterize the chemical structure of the resulting coatings via ellipsometry, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. We show that allyl end groups can be introduced as a side chain of these brushes to allow functionalization via thiol-ene chemistry. We demonstrate the excellent protein resistance of these coatings in single protein solutions as well as serum solutions at concentration typically used for cell culture. Finally, we demonstrate the feasibility of using these brushes for the micropatterning of cells and the generation of cell-based assays.

Amphiphilic DNA Organic Hybrids: Functional Materials in Nanoscience and Potential Application in Biomedicine

Due to the addressability and programmability, DNA has been applied not merely in constructing static elegant nanostructures such as two dimensional and three dimensional DNA nanostructures but also in designing dynamic nanodevices. Moreover, DNA could combine with hydrophobic organic molecules to be a new amphiphilic building block and then self-assemble into nanomaterials. Of particular note, a recent state-of-the-art research has turned our attention to the amphiphilic DNA organic hybrids including small molecule modified DNA (lipid-DNA, fluorescent molecule-DNA, etc.), DNA block copolymers, and DNA-dendron hybrids. This review focuses mainly on the development of their self-assembly behavior and their potential application in nanomaterial and biomedicine. The potential challenges regarding of the amphiphilic DNA organic hybrids are also briefly discussed, aiming to advance their practical applications in nanoscience and biomedicine.

Gold Nanowire Fabrication with Surface-Attached Lipid Nanotube Templates

A high-throughput approach to fabricate gold nanowires on surfaces with a lipid nanotube template is demonstrated. Streptavidin-coated gold nanoparticles are attached to the biotin-tagged lipid nanotubes. After the chemical fixation, the samples are dried and treated with oxygen plasma to remove the organic template and connect the particles. The created nanowires are characterized by cryo-transmission electron microscopy, atomic force microscopy, and electrical measurements.

Synthetic Polymer Hybridization with DNA and RNA Directs Nanoparticle Loading, Silencing Delivery, and Aptamer Function

We report herein discrete triplex hybridization of DNA and RNA with polyacrylates. Length-monodisperse triazine-derivatized polymers were prepared on gram-scale by reversible addition-fragmentation chain-transfer polymerization. Despite stereoregio backbone heterogeneity, the triazine polymers bind T/U-rich DNA or RNA with nanomolar affinity upon mixing in a 1:1 ratio, as judged by thermal melts, circular dichroism, gel-shift assays, and fluorescence quenching. We call these polyacrylates "bifacial polymer nucleic acids" (bPoNAs). Nucleic acid hybridization with bPoNA enables DNA loading onto polymer nanoparticles, siRNA silencing delivery, and can further serve as an allosteric trigger of RNA aptamer function. Thus, bPoNAs can serve as tools for both non-covalent bioconjugation and structure-function nucleation. It is anticipated that bPoNAs will have utility in both bio- and nanotechnology.

Side-chain cysteine-functionalized poly(2-oxazoline)s for multiple peptide conjugation by native chemical ligation

We prepared statistical copolymers composed of 2-methyl-2-oxazoline (MeOx) in combination with 2-butenyl-2-oxazoline (BuOx) or 2-decenyl-2-oxazoline (DecOx) as a basis for polymer analogous introduction of 1,2-aminothiol moieties at the side chain. MeOx provides hydrophilicity as well as cyto- and hemocompatibility, whereas the alkene groups of BuOx and DecOx serve for functionalization with a thiofunctional thiazolidine by UV-mediated thiol-ene reaction. After deprotection the cysteine content in functionalized poly(2-oxazoline) (POx) is quantified by NMR and a modified trinitrobenzenesulfonic acid assay. The luminescent cell viability assay shows no negative influence of cysteine-functionalized POx (cys-POx) concerning cell viability and cell number. cys-POx was used for multiple chemically orthogonal couplings with thioester-terminated peptides through native chemical ligation (NCL), which was performed and confirmed by NMR and MALDI-ToF measurements.