The development of a safe, effective, and accessible human immunodeficiency virus 1 (HIV-1) vaccine remains a global priority, and nanoparticles (NPs) have emerged as a promising platform for vaccine delivery. However, the efficacy of protein-based NP vaccines is often limited by pre-existing immunity against scaffold components. In this study, we developed a novel HIV-1 vaccine platform by converting self-assembling human papillomavirus (HPV) L1 virus-like particles (VLPs) into immune-stealth biomaterials for focused antigen delivery. Encapsulation of VLPs within a silica shell provided both immune shielding and a surface for site-specific antigen conjugation. The resulting L1-SiO2 NPs were covalently functionalized with HIV-1 Env trimers (L1-SiO2-Env) and characterized for their physicochemical properties and immunogenicity. In vivo, the silica coating effectively masked L1-specific B cell epitopes, reduced anti-scaffold IgG responses and enhanced Env-specific antibody production in mice pre-immunized against HPV. This synthetic strategy offers a versatile platform for overcoming scaffold-directed immunity in nanoparticle vaccines.

The demineralization of tooth enamel is the primary consequence of dental caries, leading to cavities and finally tooth loss. Erosive tooth wear from acidic beverages and food is another factor that degrades enamel. In both cases, an acidic environment leads to etching and the final dissolution of tooth mineral, i.e., hydroxyapatite. Here, this process is discussed from a chemical perspective, taking into account the solubility of calcium phosphate and the presence of the pellicle (protein layer) and plaque (bacterial biofilms), which both affect the dissolution rate. While low pH is definitely decisive, calcium-binding ligands (e.g., acid anions, proteins) contribute to dissolution by removing calcium ions from the equilibrium. This is an important effect in the oral cavity where the concentration of biomolecules is high. The situation is complicated by the fact that the composition of saliva and the oral microbiome vary considerably between individuals. The state of current knowledge on the demineralization of enamel is summarized and discussed, also in the context of approaches to prevent dental caries and erosive tooth wear.

Organoids consisting of primary human cells, i.e., astrocytes, pericytes, and endothelial cells, form a functional blood–brain barrier (BBB) in vitro. The ability of FITC-dextran (70 kDa), calcium phosphate nanoparticles (100 nm), Escherichia coli bacteria (2 µm), and MS2 coliphages (27 nm, a model for viruses) to penetrate the BBB under normoxic and hypoxic conditions (2.5% oxygen) for up to 12 days was assessed by fluorescence microscopy and confocal laser scanning microscopy. All agents were fluorescently labeled to trace them inside the organoids. Under normoxia, FITC-dextran, calcium phosphate nanoparticles, E. coli bacteria and MS2 coliphages did not penetrate the BBB. However, oxygen deficiency (hypoxia) triggered the penetration of the BBB by FITC-dextran and E. coli cells. This was underscored by a strong hypoxic center inside the organoids that developed in the presence of E. coli bacteria.

Three clinically relevant implant metals, i.e., stainless steel (SS316L), pure titanium (grade 4), and the titanium alloy Ti6Al4V (grade 5), were coated with octacalcium phosphate from supersaturated aqueous calcium phosphate solution. Calcium phosphate coatings are frequently applied to enhance the osteoconductivity of metal implants. However, this leads to a higher surface roughness that increases the risk for bacterial adhesion and biofilm formation. The bacterial species Escherichia coli (Gram-negative rods) and Staphylococcus xylosus (Gram-positive cocci) were seeded on the bare metals and the calcium phosphate-coated metals, respectively, and cultivated for up to 72 h to assess the biofilm formation. The efficiency of biofilm production by bacteria was evaluated by the crystal violet assay, scanning electron microscopy, and confocal microscopy. The growth of S. xylosus was always strong, with and without calcium phosphate coating, whereas E. coli proliferated better on calcium phosphate-coated metals. Both bacterial species colonized cavities within the porous calcium phosphate coating as indicated by scanning electron microscopy. The metabolic activity of S. xylosus caused a pH drop to 5.5 that led to corrosion of the calcium phosphate layer by acidic dissolution. In contrast, E. coli led to an increase in pH to about 8.9 that did not affect the coating. Osteoblast-like MG-63 cells adhered and proliferated well on both coated and uncoated metals, underscoring the good osteocompatibility before and after coating.

Calcium phosphate nanoparticles (CaP NPs) are biocompatible carriers widely studied for drug delivery due to their pH-responsive degradation and controlled release properties. In this study, CaP NPs stabilized with carboxymethyl cellulose (CMC) and coated with a silica layer were designed for gemcitabine (GEM) loading and folate (FA) conjugation, targeting cancer cells overexpressing folate receptor alpha (FRα). GEM was covalently coupled to CMC via an amide bond before CaP precipitation, creating a prodrug system. The NPs exhibited dual pH-responsive release, in which CaP dissolution combined with polymer-drug cleavage through acid-catalyzed hydrolysis of CMC-GEM within endolysosomes ensured intracellular bioavailability of free GEM molecules. FA conjugation by strong covalent bonds via copper-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction enhanced the uptake of CaP NPs in FRα-positive breast cancer cells (MCF-7), whereas both FA-conjugated and nonconjugated NPs exhibited similar uptake in normal human mesenchymal stem cells (hMSCs). GEM-loaded CaP NPs showed high cytotoxicity in FRα-overexpressing cancer cell lines (MCF-7, MDA-MB-231, HeLa), while FA conjugation significantly reduced toxicity in hMSCs without compromising anticancer activity. These findings demonstrate the potential of FA-conjugated and GEM-loaded CaP NPs as a nanoplatform for targeted cancer therapy with reduced toxicity in healthy cells.

Palladium nanoparticles of different sizes and shapes dispersed in water, stabilized by either polyvinylpyrrolidone or glutathione, were studied in both monophasic and biphasic alkyne hydrogenation reactions at 50 bar hydrogen pressure. Spherical nanoparticles of 2 and 5 nm diameter as well as cubic nanoparticles of 18 and 28 nm edge length were investigated. Structural changes in the particles before and after the catalytic reactions were assessed with respect to agglomeration and particle size. The particle size had the strongest effect on the catalytic efficiency, i.e., spherical nanoparticles of 5 nm were the most active and spherical nanoparticles of 2 nm were the least active. The nanocubes had intermediate catalytic activities. Semihydrogenation occurred within minutes at low palladium loadings. The highest turnover frequencies of about 183,000 h-1 were achieved with 5 nm palladium nanoparticles. Mass transport limitations constrained the reaction rates in aqueous biphasic systems with larger nanoparticles.

Gold nanoparticles and calix[n]arenes are well-established platforms for creating multivalent carbohydrate ligands that enhance binding avidity and selectivity toward carbohydrate-recognizing receptors, such as bacterial lectins. In this study, we present a modular synthesis protocol for tailor-made and (multi)functional glycocalix[4]arene derivatives using solid-phase polymer synthesis. A calix[4]arene building block with a single carboxyl group on the lower rim and four nitro groups at the upper rim is introduced. This building block is attached to a solid support using standard solid phase peptide coupling conditions, followed by reduction of the upper rim nitro functionalities to yield four amine groups, that are further functionalized through solid-phase polymer synthesis. Using this modular approach, we access a series of glyco-calix[4]arene structures that are then further conjugated onto ultrasmall gold nanoparticles. Conjugation is promoted either via one or via four alkyne groups on the glycocalixarene structure, providing a handle to tune the overall valency of the final glyco[4]calixarene-gold nanoparticle conjugates. Finally, the glycocalix[4]arene derivatives and conjugates are evaluated for their inhibitory potential against bacterial adhesion showing the importance of multivalent carbohydrate presentation to effectively block Escherichia coli (E. coli) adhesion.

Ultrasmall gold nanoparticles were functionalized with covalently attached DNA strands of 20 or 30 nucleotides. This was achieved via click chemistry with alkyne-terminated DNA and azide-terminated gold nanoparticles. The particles were characterized by high-resolution transmission electron microscopy, UV-Vis spectroscopy, fluorescence spectroscopy, and small-angle X-ray scattering. The DNA strands were fluorescently labelled with either FAM or Cy3, permitting their detection and quantification on the nanoparticle surface. Complementary DNA strands were attached to the nanoparticles via hybridization. The connection of gold nanoparticles by complementary DNA strands was also demonstrated. In-situ fluorescence spectroscopy confirmed the hybridization at ambient temperature and the melting of the DNA strands at elevated temperature. The hybridization was confirmed by fluorescence spectroscopy with the FRET effect. This opens broad possibilities for the noncovalent functionalization of ultrasmall nanoparticles.

Ultrasmall rhenium nanoparticles were prepared by a reduction of rhenium trichloride with sodium borohydride in water capped with the tripeptide glutathione. The particles were approximately spherical with an average diameter of 1.5 nm and had a high degree of internal crystallinity as shown by transmission electron microscopy and X-ray powder diffraction. They were well dispersible in water as differential centrifugal sedimentation (DCS), 1H-NMR DOSY spectroscopy (nuclear magnetic resonance–diffusion-enhanced spectroscopy), and small-angle X-ray scattering (SAXS) showed. 1H-NMR spectroscopy and 13C-NMR spectroscopy confirmed that glutathione was attached to the nanoparticle via the terminal thiol group of cysteine. Upon heating in oxygen, the nanoparticles were converted into dirhenium heptoxide which evaporated above 360 °C.

Dodecylamine-coated ultrasmall palladium nanoparticles were prepared by reduction of dichlorido(1,5-cyclooctadiene)palladium(ii) with tert-butylamine borane in benzene. The synthesis yielded several tens of milligrams per batch. The nature of the metal core as well as the ligand shell was elucidated by a combination of complementary methods. The particles had a diameter of about 2 nm (metallic core; by small-angle X-ray scattering and transmission electron microscopy) and a hydrodynamic diameter of about 5.4 nm (by 1H-NMR DOSY in benzene). They were easily dispersible in organic solvents. The ligand shell was thoroughly investigated by 1H and 13C NMR spectroscopy in dispersion, revealing about 170 ligand molecules on the surface of each 2 nm particle. X-ray powder diffraction (Rietveld refinement) and total-scattering pair distribution function analysis (PDF) showed metallic palladium nanoparticles with a crystallite size of about 2 nm, indicating a mostly single-domain nature of the nanoparticle core. X-ray photoelectron spectroscopy confirmed metallic nanoparticles also but detected oxidized palladium species.

Fluorescent peptides were covalently attached to the surface of ultrasmall gold nanoparticles (2 nm), that is, FITC-AlaCys, FITC-Ala-Ala-Ala-Cys, and Trp-Ala-Cys (WAC). For comparison, the fluorescent dye AlexaFluor-647 was attached to glutathione-coated gold nanoparticles via click chemistry. Each particle carried between 10 and 20 fluorescent ligands, except for WAC where about 60 peptides were attached to each nanoparticle. The photophysical properties of dissolved and nanoparticle-conjugated dyes were assessed by UV-Vis and fluorescence spectroscopy, including measurements of the absolute photoluminescence quantum yields at the same dye concentration. After conjugation to the nanoparticles, the quantum yield decreased by a factor of 10 to 20 in the FITC systems but only by a factor of 1.5 in the AlexaFluor-647 system. The intrinsic fluorescence was almost completely lost for WAC after conjugation to the nanoparticles. The fluorescence intensity at temperatures up to 85 degrees C showed a decrease with temperature in all cases which was stronger for dissolved dyes than for nanoparticle-conjugated dyes. The fluorescence was fully recovered after cooling back to ambient temperature, that is, there was no permanent change of the particles caused by heating.

Calcium phosphate is the inorganic component (biomineral) of hard tissue, i.e., bone and teeth, of many higher organisms, including humans. Calcium phosphate is also synthetically prepared for biomedical application, usually as calcium phosphate ceramics for bone substitution and as calcium phosphate nanoparticles for drug delivery and imaging. Finally, hydroxyapatite occurs as a mineral in geology, sometimes in cm-sized single crystals. Two types of nanocrystalline biological apatite (human tooth enamel and shark tooth enameloid), one single-crystalline geological apatite, one sintered hydroxyapatite, and four different types of calcium phosphate nanoparticles are analyzed in-depth for their external and internal structure. Particle size, crystallinity, and crystallite size determine the materials properties, like the solubility under biological conditions, e.g., during resorption by osteoclasts in bone defects or inside cells after uptake by endocytosis. The structure-sensitive methods electron microscopy (scanning electron microscopy; SEM; and transmission electron microscopy; TEM), X-ray powder diffraction (XRD; including Rietveld refinement) and total scattering analysis (pair-distribution function, PDF) are applied. In addition, the sample composition is assessed by elemental analysis, infrared spectroscopy, and thermogravimetry. XRD and PDF showed that all samples consisted of crystallites that are smaller than their overall particle size as determined by electron microscopy.

Ultrasmall gold nanoparticles (2 nm) were surface-coated with photoswitchable 3-azopyridine ligands by ligand exchange with n-dodecanethiol-stabilized gold nanoparticles. Each gold nanoparticle carried about 66 dodecanethiol (DDT) ligands and 49 azo ligands. The azo ligands were reversibly switchable between the stable E- and the metastable Z-isomer by UV and green light irradiation as shown by UV-Vis and NMR spectroscopy. The photoswitching was not significantly affected by the conjugation of the azo ligand to the nanoparticle surface, despite the high density of ligands on the particle surface. This offers a pathway for photoswitchable systems on the nanoscale, for example, to manipulate supramolecular systems. The introduction of 0.5 wt% of the nanoparticles into a liquid crystalline host yielded a photoresponsive material which showed a reversible nematic-to-isotropic phase transition upon irradiation.

The rapid expansion and application of nanoparticles in medicine has meanwhile contributed to a large number of experimental and clinical studies, especially in cancer research. Numerous different fields within nanomedicine have now become established more clearly. These are based on the one hand on the properties of different types of nanoparticles (chemical, physical, and biological) and on the other hand on the possible specific applications such as drug carrier, radioenhancer, in vivo monitoring of drug distribution within the tumor, or tumor-specific immune-modulating effects. Nanoparticles can also be functionalized by multiple properties potentiating their intrinsic antitumoral effects, such as coupling of antibodies to address target tissue or coupling to chemotherapeutic agents. In this work, an up-to-date overview of the developments and applications related to nanoparticles in head and neck cancer is given.

Die rasante Verbreitung und Anwendung von Nanopartikeln in der Medizin haben zu einer Vielzahl von experimentellen und klinischen Studien insbesondere in der onkologischen Forschung beigetragen. Innerhalb dieser sog. Nanomedizin haben sich unterschiedliche Schwerpunkte etabliert. Diese orientieren sich zum einen an den chemischen, physikalischen und biologischen Eigenschaften unterschiedlichster Nanopartikel und zum anderen an den möglichen spezifischen Anwendungen wie beispielsweise Medikamententransport, Strahlentherapie, In-vivo-Monitoring von Wirkstoffen im Tumor oder auch immunmodulierende Wirkungen. Nanopartikel können zudem funktionalisiert werden, indem bestimmte Faktoren wie Antikörper zur spezifischen Adressierung eines Zielgewebes oder die Kopplung von Chemotherapeutika die intrinsische antitumorale Wirkung von Nanopartikeln potenzieren. In der vorliegenden Arbeit wird ein aktueller Überblick über die Entwicklungen und Anwendungen von Nanopartikeln in der Kopf-Hals-Onkologie gegeben.

Ultrasmall gold nanoparticles were functionalized with peptides of two to seven amino acids that contained one cysteine molecule as anchor via a thiol-gold bond and a number of alanine residues as nonbinding amino acid. The cysteine was located either in the center of the molecule or at the end (C-terminus). For comparison, gold nanoparticles were also functionalized with cysteine alone. The particles were characterized by UV spectroscopy, differential centrifugal sedimentation (DCS), high-resolution transmission electron microscopy (HRTEM), and small-angle X-ray scattering (SAXS). This confirmed the uniform metal core (2 nm diameter). The hydrodynamic diameter was probed by 1H-DOSY NMR spectroscopy and showed an increase in thickness of the hydrated peptide layer with increasing peptide size (up to 1.4 nm for heptapeptides; 0.20 nm per amino acid in the peptide). 1H NMR spectroscopy of water-dispersed nanoparticles showed the integrity of the peptides and the effect of the metal core on the peptide. Notably, the NMR signals were very broad near the metal surface and became increasingly narrow in a distance. In particular, the methyl groups of alanine can be used as probe for the resolution of the NMR spectra. The number of peptide ligands on each nanoparticle was determined using quantitative 1H NMR spectroscopy. It decreased with increasing peptide length from about 100 for a dipeptide to about 12 for a heptapeptide, resulting in an increase of the molecular footprint from about 0.1 to 1.1 nm2.

AbstractThe clinical need for bone adhesives as an alternative to osteosynthesis is evident. However, this is a challenging problem due to the moist environment in surgical sites with bone surfaces covered with blood and biomolecules like lipids or proteins. A nanoparticle-loaded hydrogel that is based on a freeze-dried powder of silica-coated calcium phosphate/carboxymethyl cellulose nanoparticles (CaP/CMC/SiO2) and an aqueous solution of sodium alginate (2 wt%) was developed and optimized with respect to the gluing ability in air and in water. The final paste was crosslinked within about one minute by calcium ions released from the calcium phosphate nanoparticles and contained about 20 wt% nanoparticles and 80 wt% water. The mechanical properties of the hydrogel were determined by extensive rheological tests. The thixotropic pasty hydrogel can be applied with a syringe. The adhesion strength was about 84 kPa between moist bone fragments in air. The hydrogel kept fragments of cortical bone well connected for >3 months during complete submersion in water. Besides water, the material consists only of biocompatible and biodegradable components (calcium phosphate, CMC, alginate). It carries only a very low dose of these materials into the bone site (mainly calcium phosphate nanoparticles). In-vitro cell culture with hMSCs that differentiated to osteoblasts confirmed a good biocompatibility of the bone adhesive formulation. Graphical Abstract

Ultrasmall nanoparticles have a diameter between 1 and 3 nm at the border between nanoparticles and large molecules. Usually, their core consists of a metal, and the shell of a capping ligand with sulfur or phosphorus as binding atoms. While the core structure can be probed by electron microscopy, electron and powder diffraction, and single-crystal structure analysis for atom-sharp clusters, it is more difficult to analyze the ligand shell. In contrast to larger nanoparticles, ultrasmall nanoparticles cause only a moderate distortion of the NMR signal, making NMR spectroscopy a qualitative as well as a quantitative probe to assess the nature of the ligand shell. The application of isotope-labelled ligands and of two-dimensional NMR techniques can give deeper insight into ligand-nanoparticle interactions. Applications of one- and two-dimensional NMR spectroscopy to analyze ultrasmall nanoparticles are presented with suitable examples, including a critical discussion of the limitations of NMR spectroscopy on nanoparticles.