Silver-Sulfamethazine-Conjugated β-Cyclodextrin/Dextran-Coated Magnetic Nanoparticles for Pathogen Inhibition

In the fight against antibiotic resistance, which is rising to dangerously high levels worldwide, new strategies based on antibiotic-conjugated biocompatible polymers bound to magnetic nanoparticles that allow the drug to be manipulated and delivered to a specific target are being proposed. Here, we report the direct surface engineering of nontoxic iron oxide nanoparticles (IONs) using biocompatible dextran (Dex) covalently linked to β-cyclodextrin (β-CD) with the ability to form non-covalent complexes with silver-sulfamethazine (SMT-Ag). To achieve a good interaction of β-CD-modified dextran with the surface of the nanoparticles, it was functionalized with diphosphonic acid (DPA) that provides strong binding to Fe atoms. The synthesized polymers and nanoparticles were characterized by various methods, such as nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectroscopies, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), atomic absorption spectroscopy (AAS), dynamic light scattering (DLS), etc. The resulting magnetic ION@DPA-Dex-β-CD-SMT-Ag nanoparticles were colloidally stable in water and contained 24 μg of antibiotic per mg of the particles. When tested for in vitro antimicrobial activity on Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria and fungi (yeast Candida albicans and mold Aspergillus niger), the particles showed promising potential.

Thiolated poly(2-hydroxyethyl methacrylate) hydrogels as a degradable biocompatible scaffold for tissue engineering

Research of degradable hydrogel polymeric materials exhibiting high water content and mechanical properties resembling tissues is crucial not only in drug delivery systems but also in tissue engineering, medical devices, and biomedical-healthcare sensors. Therefore, we newly offer development of hydrogels based on poly(2-hydroxyethyl methacrylate-co-2-(acetylthio) ethyl methacrylate-co-2-methacryloyloxyethyl phosphorylcholine) [P(HEMA-ATEMA-MPC)] and optimization of their mechanical and in vitro and in vivo degradability. P(HEMA-ATEMA-MPC) hydrogels differed in chemical composition, degree of crosslinking, and starting molar mass of polymers (15, 19, and 30 kDa). Polymer precursors were synthesized by a reversible addition fragmentation chain transfer (RAFT) polymerization using 2-(acetylthio)ethyl methacrylate containing protected thiol groups, which enabled crosslinking and gel formation. Elastic modulus of hydrogels increased with the degree of crosslinking (Slaughter et al., 2009) [1]. In vitro and in vivo controlled degradation was confirmed using glutathione and subcutaneous implantation of hydrogels in rats, respectively. We proved that the hydrogels with higher degree of crosslinking retarded the degradation. Also, albumin, γ-globulin, and fibrinogen adsorption on P(HEMA-ATEMA-MPC) hydrogel surface was tested, to simulate adsorption in living organism. Rat mesenchymal stromal cell adhesion on hydrogels was improved by the presence of RGDS peptide and laminin on the hydrogels. We found that rat mesenchymal stromal cells proliferated better on laminin-coated hydrogels than on RGDS-modified ones.

Poly(N,N-dimethylacrylamide)-coated upconverting NaYF4:Yb,Er@NaYF4:Nd core-shell nanoparticles for fluorescent labeling of carcinoma cells

Upconverting luminescent lanthanide-doped nanoparticles (UCNP) belong to promising new materials that absorb infrared light able to penetrate in the deep tissue level, while emitting photons in the visible or ultraviolet region, which makes them favorable for bioimaging and cell labeling. Here, we have prepared upconverting NaYF4:Yb,Er@NaYF4:Nd core-shell nanoparticles, which were coated with copolymers of N,N-dimethylacrylamide (DMA) and 2-(acryloylamino)-2-methylpropane-1-sulfonic acid (AMPS) or tert-butyl [2-(acryloylamino)ethyl]carbamate (AEC-Boc) with negative or positive charges, respectively. The copolymers were synthesized by a reversible addition-fragmentation chain transfer (RAFT) polymerization, reaching Mn ~ 11 kDa and containing ~ 5 mol% of reactive groups. All copolymers contained bisphosphonate end-groups to be firmly anchored on the surface of NaYF4:Yb,Er@NaYF4:Nd core-shell nanoparticles. To compare properties of polymer coatings, poly(ethylene glycol)-coated and neat UCNP were used as a control. UCNP with various charges were then studied as labels of carcinoma cells, including human hepatocellular carcinoma HepG2, human cervical cancer HeLa, and rat insulinoma INS-1E cells. All the particles proved to be biocompatible (nontoxic); depending on their ξ-potential, the ability to penetrate the cells differed. This ability together with the upconversion luminescence are basic prerequisites for application of particles in photodynamic therapy (PDT) of various tumors, where emission of nanoparticles in visible light range at ~ 650 nm excites photosensitizer.

Doxorubicin-Conjugated Iron Oxide Nanoparticles: Surface Engineering and Biomedical Investigation

Development of therapeutic systems to treat glioblastoma, the most common and aggressive brain tumor, belongs to priority tasks in cancer research. We have synthesized colloidally stable magnetic nanoparticles (D_h =336 nm) coated with doxorubicin (Dox) conjugated copolymers of N,N-dimethylacrylamide and either N-acryloylglycine methyl ester or N-acryloylmethyl 6-aminohexanoate. The terminal carboxyl groups of the copolymers were reacted with alendronate by carbodiimide formation. Methyl ester groups were then transferred to hydrazides for binding Dox by a hydrolytically labile hydrazone bond. The polymers were subsequently bound on the magnetic nanoparticles through bisphosphonate terminal groups. Finally, the anticancer effect of the Dox-conjugated particles was investigated using the U-87 glioblastoma cell line in terms of particle internalization and cell viability, which decreased to almost zero at a concentration of 100 μg of particles per ml. These results confirmed that poly(N,N-dimethylacrylamide)-coated magnetic nanoparticles can serve as a solid support for Dox delivery to glioblastoma cells.

Poly(ethylene glycol)-Alendronate-Coated Magnetite Nanoparticles Do Not Alter Cardiovascular Functions and Red Blood Cells' Properties in Hypertensive Rats

In this study, magnetite nanoparticles were prepared and coated with poly(ethylene glycol) terminated by alendronate to ensure firm binding to the iron oxide surface. Magnetic nanoparticles, designated as magnetite coated with poly(ethylene glycol)-alendronate (Fe3O4@PEG-Ale), were characterized in terms of number-average (Dn) and hydrodynamic (Dh) size, ζ-potential, saturation magnetization, and composition. The effect of particles on blood pressure, vascular functions, nitric oxide (NO), and superoxide production in the tissues of spontaneously hypertensive rats, as well as the effect on red blood cell (RBC) parameters, was investigated after intravenous administration (1 mg Fe3O4/kg of body weight). Results showed that Fe3O4@PEG-Ale particles did negatively affect blood pressure, heart rate and RBC deformability, osmotic resistance and NO production. In addition, Fe3O4@PEG-Ale did not alter functions of the femoral arteries. Fe3O4@PEG-Ale induced increase in superoxide production in the kidney and spleen, but not in the left heart ventricle, aorta and liver. NO production was reduced only in the kidney. In conclusion, the results suggest that acute intravenous administration of Fe3O4@PEG-Ale did not produce negative effects on blood pressure regulation, vascular function, and RBCs in hypertensive rats.

Synthesis and modification of uniform PEG-neridronate-modified magnetic nanoparticles determines prolonged blood circulation and biodistribution in a mouse preclinical model

Magnetite (Fe3O4) nanoparticles with uniform sizes of 10, 20, and 31 nm were prepared by thermal decomposition of Fe(III) oleate or mandelate in a high-boiling point solvent (>320 °C). To render the particles with hydrophilic and antifouling properties, their surface was coated with a PEG-containing bisphosphonate anchoring group. The PEGylated particles were characterized by a range of physicochemical methods, including dynamic light scattering, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and magnetization measurements. As the particle size increased from 10 to 31 nm, the amount of PEG coating decreased from 28.5 to 9 wt.%. The PEG formed a dense brush-like shell on the particle surface, which prevented particles from aggregating in water and PBS (pH 7.4) and maximized the circulation time in vivo. Magnetic resonance relaxometry confirmed that the PEG-modified Fe3O4 nanoparticles had high relaxivity, which increased with increasing particle size. In the in vivo experiments in a mouse model, the particles provided visible contrast enhancement in the magnetic resonance images. Almost 70% of administrated 20-nm magnetic nanoparticles still circulated in the blood stream after four hours; however, their retention in the tumor was rather low, which was likely due to the antifouling properties of PEG.

Dynamics of tissue ingrowth in SIKVAV-modified highly superporous PHEMA scaffolds with oriented pores after bridging a spinal cord transection

While many types of biomaterials have been evaluated in experimental spinal cord injury (SCI) research, little is known about the time-related dynamics of the tissue infiltration of these scaffolds. We analyzed the ingrowth of connective tissue, axons and blood vessels inside the superporous poly (2-hydroxyethyl methacrylate) hydrogel with oriented pores. The hydrogels, either plain or seeded with mesenchymal stem cells (MSCs), were implanted in spinal cord transection at the level of Th8. The animals were sacrificed at days 2, 7, 14, 28, 49 and 6 months after SCI and histologically evaluated. We found that within the first week, the hydrogels were already infiltrated with connective tissue and blood vessels, which remained stable for the next 6 weeks. Axons slowly and gradually infiltrated the hydrogel within the first month, after which the numbers became stable. Six months after SCI we observed rare axons crossing the hydrogel bridge and infiltrating the caudal stump. There was no difference in the tissue infiltration between the plain hydrogels and those seeded with MSCs. We conclude that while connective tissue and blood vessels quickly infiltrate the scaffold within the first week, axons show a rather gradual infiltration over the first month, and this is not facilitated by the presence of MSCs inside the hydrogel pores. Further research which is focused on the permissive micro-environment of the hydrogel scaffold is needed, to promote continuous and long-lasting tissue regeneration across the spinal cord lesion.

Reductively Degradable Poly(2-hydroxyethyl methacrylate) Hydrogels with Oriented Porosity for Tissue Engineering Applications

Degradable poly(2-hydroxyethyl methacrylate) hydrogels were prepared from a linear copolymer (M_w = 49 kDa) of 2-hydroxyethyl methacrylate (HEMA), 2-(acethylthio)ethyl methacrylate (ATEMA), and zwitterionic 2-methacryloyloxyethyl phosphorylcholine (MPC). The deprotection of ATEMA thiol groups by triethylamine followed by their gentle oxidation with 2,2'-dithiodipyridine resulted in the formation of reductively degradable polymers with disulfide bridges. Finally, a hydrogel 3D structure with an oriented porosity was obtained by gelation of the polymer in the presence of needle-like sodium acetate crystals. The pore diameter and porosity of resulting poly(2-hydroxyethyl methacrylate-co-2-(acethylthio)ethyl methacrylate-co-2-methacryloyloxyethyl phosphorylcholine) [P(HEMA-ATEMA-MPC)] hydrogels varied between 59 and 65 μm and between 70 and 79.6 vol % according to Hg porosimetry, and complete degradation of these materials was reached in 86 days in 0.33 mmol solution of l-cysteine/L in phosphate buffer. The cross-linked P(HEMA-ATEMA-MPC) hydrogels were evaluated as a possible support for human mesenchymal stem cells (MSCs). No cytotoxicity was found for the un-cross-linked thiol-containing and protected P(HEMA-ATEMA-MPC) chains up to a concentration of 5 and 1 wt % in α-minimum essential medium, respectively.

RGDS- and SIKVAVS-Modified Superporous Poly(2-hydroxyethyl methacrylate) Scaffolds for Tissue Engineering Applications

Three-dimensional hydrogel supports for mesenchymal and neural stem cells (NSCs) are promising materials for tissue engineering applications such as spinal cord repair. This study involves the preparation and characterization of superporous scaffolds based on a copolymer of 2-hydroxyethyl and 2-aminoethyl methacrylate (HEMA and AEMA) crosslinked with ethylene dimethacrylate. Ammonium oxalate is chosen as a suitable porogen because it consists of needle-like crystals, allowing their parallel arrangement in the polymerization mold. The amino group of AEMA is used to immobilize RGDS and SIKVAVS peptide sequences with an N-γ-maleimidobutyryloxy succinimide ester linker. The amount of the peptide on the scaffold is determined using ¹²⁵ I radiolabeled SIKVAVS. Both RGDS- and SIKVAVS-modified poly(2-hydroxyethyl methacrylate) scaffolds serve as supports for culturing human mesenchymal stem cells (MSCs) and human fetal NSCs. The RGDS sequence is found to be better for MSC and NSC proliferation and growth than SIKVAVS.

Silica-coated upconversion lanthanide nanoparticles: The effect of crystal design on morphology, structure and optical properties

NaYF4:Yb(3+)/Er(3+) nanoparticles were synthesized by thermal decomposition of lanthanide trifluoroacetates using oleylamine (OM) as both solvent and surface binding ligand. The effect of reaction temperature and time on the properties of the particles was investigated. The nanoparticles were characterized by transmission electron microscopy (TEM), electron diffraction (ED), energy dispersive spectroscopy (EDX), dynamic light scattering (DLS), thermogravimetric analysis (TGA), elemental analysis and X-ray diffraction (XRD) to determine morphology, size, polydispersity, crystal structure and elemental composition of the nanocrystals. TEM microscopy revealed that the morphology of the nanoparticles could be fine-tuned by modifying of the synthetic conditions. A cubic-to-hexagonal phase transition of the NaYF4:Yb(3+)/Er(3+) nanoparticles at temperatures above 300 °C was confirmed by both ED and XRD. Upconversion luminescence under excitation at 980 nm was observed in the luminescence spectra of OM-NaYF4:Yb(3+)/Er(3+) nanoparticles. Finally, the OM-NaYF4:Yb(3+)/Er(3+) nanoparticles were coated with a silica shell to enable further functionalization and increase biocompatibility and stability in aqueous media, preventing particle aggregation.

Enhanced drought and heat stress tolerance of tobacco plants with ectopically enhanced cytokinin oxidase/dehydrogenase gene expression

Responses to drought, heat, and combined stress were compared in tobacco (Nicotiana tabacum L.) plants ectopically expressing the cytokinin oxidase/dehydrogenase CKX1 gene of Arabidopsis thaliana L. under the control of either the predominantly root-expressed WRKY6 promoter or the constitutive 35S promoter, and in the wild type. WRKY6:CKX1 plants exhibited high CKX activity in the roots under control conditions. Under stress, the activity of the WRKY6 promoter was down-regulated and the concomitantly reduced cytokinin degradation coincided with raised bioactive cytokinin levels during the early phase of the stress response, which might contribute to enhanced stress tolerance of this genotype. Constitutive expression of CKX1 resulted in an enlarged root system, a stunted, dwarf shoot phenotype, and a low basal level of expression of the dehydration marker gene ERD10B. The high drought tolerance of this genotype was associated with a relatively moderate drop in leaf water potential and a significant decrease in leaf osmotic potential. Basal expression of the proline biosynthetic gene P5CSA was raised. Both wild-type and WRKY6:CKX1 plants responded to heat stress by transient elevation of stomatal conductance, which correlated with an enhanced abscisic acid catabolism. 35S:CKX1 transgenic plants exhibited a small and delayed stomatal response. Nevertheless, they maintained a lower leaf temperature than the other genotypes. Heat shock applied to drought-stressed plants exaggerated the negative stress effects, probably due to the additional water loss caused by a transient stimulation of transpiration. The results indicate that modulation of cytokinin levels may positively affect plant responses to abiotic stress through a variety of physiological mechanisms.

The use of hydrophilic poly(N,N-dimethylacrylamide) for promoting engulfment of magnetic gamma-Fe2O3 nanoparticles by mammalian cells

gamma-Fe2O3 nanoparticles obtained by coprecipitation of Fe(II) and Fe(III) chlorides with a base and subsequent oxidation were coated with a shell of hydrophilic biocompatible poly(N,N-dimethylacrylamide) (PDMAAm). Various initiators were attached to the iron oxide surface to enable the use of the "grafting-from" approach for immobilization of PDMAAm. They included 2,2'-azobis(2-methylpropanimidamide) dihydrochloride (AMPA), 2,2'-azobis(N-hydroxy-2-methylpropanimidamide) dihydrochloride (ABHA) and 4-cyano-4-{[1-cyano-3-(N-hydroxycarbamoyl)-1-methylpropyl]azo}pentanoic acid (CCHPA). Engulfment of PDMAAm-coated y-Fe2O3 nanoparticles by murine J774.2 macrophages was investigated. Only some nanoparticles were engulfed by the macrophages. PDMAAm-AMPA-gamma-Fe2O3 and PDMAAm-ABHA-y-Fe2O3 nanoparticles were rapidly engulfed by the cells. In contrast, neat y-Fe2O3 and PDMAAm-CCHPA-gamma-Fe2O3 particles induced formation of transparent vacuoles indicating toxicity of the particles. Thus, PDMAAm-coated AMPA- and ABHA-gamma-Fe2O3 nanoparticles can be recommended as non-toxic labels for mammalian cells.

pH sensitive polymer nanoparticles: effect of hydrophobicity on self-assembly

The influence of hydrophobicity on formation, stability, and size of pH-responsive methacryloylated oligopeptide-based polymer nanoparticles has been studied by dynamic light scattering (DLS), transmission electron microscopy (Cryo-TEM), and NMR. Different polyanions/surfactant systems have been studied at constant polymer concentration and within a broad range of surfactant concentrations. The two newly synthesized pH-sensitive hydrophobic polyanions, poly(N(ω)-methacryloyl glycyl-L-leucine) and poly(N(ω)-methacryloyl glycyl-L-phenylalanyl-L-leucinyl-glycine), and three nonionic surfactants (Brij97, Brij98, and Brij700) have been investigated. The surfactants were different in the length of hydrophilic poly(ethylene oxide) (PEO) chain. In surfactant-free solution at basic pH, the polyanions form hydrophobic domains. In the presence of a surfactant, our results prove the complex formation at high pH between the nonionic surfactant and the polyelectrolyte; a pearl-necklace structure is formed. At low pH below critical pH (pH(tr)), reversible nanoscale structures occur in solutions for all systems. The detailed mechanism of the formation of pH-sensitive nanoparticles from polymer-surfactant complex with varying pH is established. Our results suggest that the polymer hydrophobicity is of primary importance in pretransitional behavior of the complex. Once preliminary nanoparticle nuclei are formed, the hydrophobicity of the polymer plays a minor role on further behavior of formed nanostructures. The subsequent transformation of nanoparticles is determined by the surfactant hydrophilicity, the length of hydrophilic tail that prevents further aggregation due to steric repulsions.

Novel pH-responsive nanoparticles

In this work we report a new type of pH-responsive micelle-like nanoparticle. Reversible nanoscale structures are formed in solutions of a pH-sensitive hydrophobic polyelectrolyte, poly( N-methacryloyl- l-valine) or poly( N-methacryloyl- l-phenylalanine), and nonionic surfactant (Brij 98) in the presence of hydrochloric acid. The influence of composition and pH on particles size and shape was investigated by a variety of methods. An entity's size and polydispersity could be varied in a broad range making them a perspective candidate as a drug carrier. Unlike the case of typical micelles, our results indicate the presence of cavities in the formed particles. A hypothetical model of a nanoparticle and mechanism of formation are proposed.

Preparation and properties of magnetic nano- and microsized particles for biological and environmental separations

The paper presents a critical overview on magnetic nanoparticles and microspheres used as separation media in different fields of chemistry, biochemistry, biology, and environment protection. The preparation of most widely used magnetic iron oxides in appropriate form, their coating or encapsulation in polymer microspheres, and functionalization is discussed in the first part. In the second part, new developments in the main application areas of magnetic composite particles for separation and catalytical purposes are briefly described. They cover separations and isolations of toxic inorganic and organic ions, proteins, and other biopolymers, cells, and microorganisms. Only selected number of relevant papers could be included due to the restricted extent of the review.