Silica-Nanopartikel mit speziellen Eigenschaften für die Herstellung dentaler Kompositmaterialien

[no abstract

Nanoporous silica nanoparticles with spherical and anisotropic shape as fillers in dental composite materials

The objective of this study was to test whether nanoporous silica nanoparticles can be employed as fillers in dental composite materials to improve their mechanical properties. These nanoporous silica nanoparticles were synthesized using sol-gel methods, in part modified by silanization, and thoroughly characterized. The nanoporous nanoparticles were added to dental resins to form nanocomposites (resins impregnated with nanoparticles) and hybrid composites (containing in addition conventional microfillers). The incorporation of these nanoporous nanoparticles in dental resins or composites was characterized by investigation of the complex viscosity and double bond conversion as well as by determination of flexural strength and Young's modulus. The dispersion of the nanofillers was examined by SEM and EDX imaging of fracture surfaces. Incorporation of small contents (1-3 wt%) of unmodified nanoporous particles leads to improved mechanical properties. However, the incorporation of larger contents results in particle agglomeration and declining mechanical properties. This effect is less pronounced when the surface of the particles is modified with methacrylate residues, resulting in a lower agglomeration tendency and a more homogeneous filler dispersion. Surface properties and, concomitantly, dispersibility of the nanoparticles have a strong influence on mechanical properties. But the incorporation of nanoporous instead of solid nanoparticles into dental composite materials is indeed a possibility to improve the mechanical behavior. However, modification of the surface is necessary and the key to achieving uniform dispersion and, thereby, improving mechanical properties

PH-responsive release of chlorhexidine from modified nanoporous silica nanoparticles for dental applications

A pH-sensitive stimulus-response system for controlled drug release was prepared by modifying nanoporous silica nanoparticles (NPSNPs) with poly(4-vinylpyridine) using a bismaleimide as linker. At physiological pH values, the polymer serves as gate keeper blocking the pore openings to prevent the release of cargo molecules. At acidic pH values as they can occur during a bacterial infection, the polymer strains become protonated and straighten up due to electrostatic repulsion. The pores are opened and the cargo is released. The drug chlorhexidine was loaded into the pores because of its excellent antibacterial properties and low tendency to form resistances. The release was performed in PBS and diluted hydrochloric acid, respectively. The results showed a considerably higher release in acidic media compared to neutral solvents. Reversibility of this pH-dependent release was established. In vitro tests proved good cytocompatibility of the prepared nanoparticles. Antibacterial activity tests with Streptococcus mutans and Staphylococcus aureus revealed promising perspectives of the release system for biofilm prevention. The developed polymer-modified silica nanoparticles can serve as an efficient controlled drug release system for long-term delivery in biomedical applications, such as in treatment of biofilm-associated infections, and could, for example, be used as medical implant coating or as components in dental composite materials

Effects of ATP7A overexpression in mice on copper transport and metabolism in lactation and gestation

Placentae and mammary epithelial cells are unusual in robustly expressing two copper "pumps", ATP7A and B, raising the question of their individual roles in these tissues in pregnancy and lactation. Confocal microscopic evidence locates ATP7A to the fetal side of syncytiotrophoblasts, suggesting a role in pumping Cu towards the fetus; and to the basolateral (blood) side of lactating mammary epithelial cells, suggesting a role in recycling Cu to the blood. We tested these concepts in wild-type C57BL6 mice and their transgenic counterparts that expressed hATP7A at levels 10-20× those of endogenous mAtp7a. In lactation, overexpression of ATP7A reduced the Cu concentrations of the mammary gland and milk ~50%. Rates of transfer of tracer (64)Cu to the suckling pups were similarly reduced over 30-48 h, as was the total Cu in 10-day -old pups. During the early and middle periods of gestation, the transgenic litters had higher Cu concentrations than the wild-type, placental Cu showing the reverse trend; but this difference was lost by the first postnatal day. The transgenic mice expressed ATP7A in some hepatocytes, so we investigated the possibility that metalation of ceruloplasmin (Cp) might be enhanced. Rates of (64)Cu incorporation into Cp, oxidase activity, and ratios of holo to apoceruloplasmin were unchanged. We conclude that in the lactating mammary gland, the role of ATP7A is to return Cu to the blood, while in the placenta it mediates Cu delivery to the fetus and is the rate-limiting step for fetal Cu nutrition during most of gestation in mice

Antibacterial Silica Nanoparticles with PH-Sensitive Release Properties as Fillers for Dental Composite Materials

Silica nanoparticles with nanopores were used to incorporate antimicrobial agents, like silver nanoparticles or chlorhexidine. By the functionalization of the particles with different organosilanes a controlled drug release is possible. A stimuli-response system was able to react to acidic conditions as caused by an infection and to release the drugs only when necessary. These particles could be incorporated into dental composite materials to prevent infections or periimplantitis.DFG/SFB/59