Non-close-packed breath figures via ion-partitioning-mediated self-assembly

We report a one-step method of forming non-close-packed (NCP) pore arrays of micro- and sub-micropores using chloroform-based solutions of polystyrene acidified with hydrogen bromide for breath figure (BF) patterning. As BF patterning takes place, water vapor condenses onto the polystyrene solution, forming water droplets on the solution surface. Concurrently, preferential ion partitioning of hydrogen bromide leads to positively charged water droplets, which experience interdroplet electrostatic repulsion. Self-organization of charged water droplets because of surface flow and subsequent evaporation of the droplet templates result in ordered BF arrays with pore separation/diameter (L/D) ratios of up to 16.5. Evidence from surface potential scans show proof for preferential ion partitioning of HBr. Radial distribution functions and Voronoi polygon analysis of pore arrays show that they possess a high degree of conformational order. Past fabrication methods of NCP structures typically require multi-step processes. In contrast, we have established a new route for facile self-assembly of previously inaccessible patterns, which comprises of only a single operational step

Synthesis and bioactivity of a conjugate composed of green tea catechins and hyaluronic acid

(-)-Epigallocatechin-3-gallate (EGCG) is a green tea polyphenol that has several biological activities, including anti-cancer activity and anti-inflammation. Hyaluronic acid (HA) is a naturally-occurring polysaccharide that is widely used as a biomaterial for drug delivery and tissue engineering due to its viscoelastic, biocompatible and biodegradable properties. By conjugating HA with EGCG, the resulting HA-EGCG conjugate is expected to exhibit not only the inherent properties of HA but also the bioactivities of EGCG. Toward this end, we report the synthesis of an amine-functionalized EGCG as an intermediate compound for conjugation to HA. EGCG was reacted with 2,2-diethoxyethylamine (DA) under acidic conditions, forming ethylamine-bridged EGCG dimers. The EGCG dimers were composed of four isomers, which were characterized by HPLC, high-resolution mass spectrometry and NMR spectroscopy. The amine-functionalized EGCG dimers were conjugated to hyaluronic acid (HA) through the formation of amide bonds. HA-EGCG conjugates demonstrated several bioactivities which were not present in unmodified HA, including resistance to hyaluronidase-mediated degradation, inhibition of cell growth and scavenging of radicals. The potential applications of HA-EGCG conjugates are discussed

Ligation of anti-cancer drugs to self-assembling ultrashort peptides by click chemistry for localized therapy

Self-assembling ultrashort peptides from aliphatic amino acids were functionalized with platinum anti-cancer drugs by click chemistry. Oxaliplatin-derived hybrid peptide hydrogels with up to 40% drug loading were tested for localized breast cancer therapy. Stably injected gels showed significant tumor growth inhibition in mice and a better tolerance compared to the free platinum drug

In situ synthesis of size-controlled, stable silver nanoparticles within ultrashort peptide hydrogels and their anti-bacterial properties

We have developed a silver-releasing biomaterial with promising potential for wound healing applications. The material is made of ultrashort peptides which can self-assemble in water to form hydrogels. Silver nanoparticles (Ag NPs) were synthesized in situ within the biomaterial, using only UV irradiation and no additional chemical reducing agents. The synthetic strategy allows precise control of the nanoparticle size, with the network of peptide fibers preventing aggregation of Ag NPs. The biomaterial shows increased mechanical strength compared to the hydrogel control. We observed a sustained release of Ag NPs over a period of 14 days. This is a crucial prerequisite for effective anti-bacterial therapy. The ability to inhibit bacterial growth was tested using different bacterial strains, namely gram-negative Escherichia coli and Pseudomonas aeruginosa and gram-positive Staphylococcus aureus. Inhibition of bacterial growth was observed for all strains. The best results were obtained for Pseudomonas aeruginosa which is known for exhibiting multidrug resistance. Biocompatibility studies on HDFa cells, using Ag NP-containing hydrogels, did not show any significant influence on cell viability. We propose this silver-releasing hydrogel as an excellent biomaterial with great potential for applications in wound healing due to its low silver content, sustained silver nanoparticle release and biocompatibility

Magnetic control of MOF crystal orientation and alignment

Most metal-organic frameworks (MOFs) possess anisotropic properties, the full exploitation of which necessitates a general strategy for the controllable orientation of such MOF crystals. Current methods largely rely upon layer-by-layer MOF epitaxy or tuning of MOF crystal growth on appropriate substrates, yielding MOFs with fixed crystal orientations. Here, the dynamic magnetic alignment of different MOF crystals (NH2-MIL-53(Al) and NU-1000) is shown. The MOFs were magnetized by electrostatic adsorption of iron oxide nanoparticles, dispersed in curable polymer resins (Formlabs 1+ clear resin/ Sylgard 184), magnetically oriented, and fixed by resin curing. The importance of crystal orientation on MOF functionality was demonstrated whereby magnetically aligned NU-1000/Sylgard 184 composite was excited with linearly polarized 405 nm light, affording an anisotropic fluorescence response dependent on the polarization angle of the excitation beam relative to NU-1000 crystal orientation

Sequence-complementarity dependent co-assembly of phosphodiester-linked aromatic donor-acceptor trimers.

We have created sequenced phosphoester-linked trimers of aromatic donor/acceptors which participate in charge-transfer interactions. Each sequence displays characteristic self-assembly, and complementary sequences interact with each other to produce new nanostructures and thermochromism. This paves the way towards new functional nanomaterials which make bio-analogous use of sequence to tune structure

Tuning dynamic DNA- and peptide-driven self-assembly in DNA–peptide conjugates

DNA–peptide conjugates offer an opportunity to marry the benefits of both biomolecular classes, combining the high level of programmability found with DNA, with the chemical diversity of peptides. These hybrid systems offer potential in fields such as therapeutics, nanotechnology, and robotics. Using the first DNA–β-turn peptide conjugate, we present three studies investigating the self-assembly of DNA–peptide conjugates over a period of 28 days. Time-course studies, such as these have not been previously conducted for DNA–peptide conjugates, although they are common in pure peptide assembly, for example in amyloid research. By using aging studies to assess the structures produced, we gain insights into the dynamic nature of these systems. The first study explores the influence varying amounts of DNA–peptide conjugates have on the self-assembly of our parent peptide. Study 2 explores how DNA and peptide can work together to change the structures observed during aging. Study 3 investigates the presence of orthogonality within our system by switching the DNA and peptide control on and off independently. These results show that two orthogonal self-assemblies can be combined and operated independently or in tandem within a single macromolecule, with both spatial and temporal effects upon the resultant nanostructures

Stereolithographic 3D printing of extrinsically self-healing composites

We demonstrate for the first time the direct stereolithographic 3D printing of an extrinsically self-healing composite, comprised of commercial photocurable resin modified with anisole and PMMA-filled microcapsules. The composites demonstrate solvent-welding based autonomous self-healing to afford 87% recovery of the initial critical toughness. This work illustrates the potential of stereolithographic printing to fabricate self-healing composites with user-defined structures, avoiding the need for extensive rheological optimization of printing inks, like in direct-write 3D printing. Importantly, this work also demonstrates the inclusion of microcapsules into 3D printing resins to incorporate additional functionality into printed composites, which could be adapted for applications beyond self-healing materials

One-step synthesis and XPS investigations of chiral NHC–Au(0)/Au(i) nanoparticles

Although N-heterocyclic carbenes (NHCs) have been demonstrated as suitable ligands for the stabilisation of gold nanoparticles (AuNPs) through a variety of methods, the manner in which such AuNPs form is yet to be fully elucidated. We report a simple and fast one-step synthesis of uniform chiral (L/D)-histidin-2-ylidene stabilised gold nanoparticles using the organometallic Au(I) complex as a well defined starting material. The resulting nanoparticles have an average size of 2.35 ± 0.43 nm for the L analog whereas an average size of 2.25 ± 0.39 nm was found for the D analog. X-ray photoelectron spectroscopy analyses reveal the presence of Au(I) and Au(0) in all NHC stabilised AuNPs. In contrast, measured X-ray photoelectron spectra of dodecanethiol protected gold nanoparticles showed only the presence of a Au(0) species. This observation leads us to postulate that AuNPs synthesised from organometallic NHC–Au(I) complexes exhibit a monolayer of Au(I) surrounding a Au(0) core. This work highlights the importance of synthetic method choice for NHC-stabilized AuNPs, as this could determine Au oxidation states and resulting AuNP properties such as catalytic activities and stabilities

Optically active histidin-2-ylidene stabilised gold nanoparticles

Drawing from the natural amino acid chiral pool, L and D histidines were utilized as chiral NHC ligands in the synthesis of NHC-stabilized chiroptical gold nanoparticles. Centrifugal size selection afforded monodisperse gold nanoparticles which display mirrored signals in CD spectroscopy