Atomar aufgelöste Rasterkraftmikroskopie an Luft: Aufbau, Technik, Optimierung und Anwendung auf Graphit, Graphen, Kaliumbromid, Calcit und Molekülfilmen

Diese Arbeit zeigt die Weltneuheit Rasterkraftmikroskopie mit wahrer atomarer Auflösung direkt an Luft und in Flüssigkeiten. Es wurde ein Quarzstimmgabel basierender Sensor -der sogenannte qPlus Sensor- der beliebige Spitzenkristalle tragen kann, verwendet. Wir befassen uns mit dem zugehörigen Aufbau, der Technik und Optimierung, sowie der Anwendung der wahren atomaren Auflösung zur Untersuchung von Graphit, Graphen, Kaliumbromid, Calcit und Molekülfilmen. In diesem Zusammenhang werden einzelne Spitzenmaterialien, wie Silizium, Wolfram, Platin-Iridium, Wolframcarbit und Saphir diskutiert und ihre Eigenschaften und Anwendungen erklärt und demonstriert. Während der Untersuchung von Monolagen- und Bilagengraphen und letztlich Graphit konnte eine selbstorganisierte Streifenstruktur auf den beiden inerteren Oberflächen abgebildet werden. Diese bildet sich scheinbar auf beliebigen, geringreaktiven und mit Graphen bedeckten Substraten an Luft. Die Optimierung der atomaren Auflösung wird mittels eines neu entwickelten Verfahrens, der sogenannten „Q –Spektroskopie“, welche für jede beliebige Spitzen-Proben-Kombination anwendbar ist und die optimalen Abbildungsparameter liefert demonstriert. Das Verfahren wird auf Kaliumbromid in aller Ausführlichkeit gezeigt und schrittweise erarbeitet. Anschließend wird das Verfahren zur Optimierung der Auflösung auf Calcit verwendet und wahre atomare Auflösung an Luft durch das Abbilden von atomaren Fehlstellen im Sauerstoffuntergittern und atomaren Stufen des Kristalles demonstriert. Außer auf Ionenkristallen wird die neue Technik auch auf Graphit und Graphen zur atomaren Auflösung verwendet und in diesem Zusammenhang das Verhalten und die Eigenschaften hydrophiler Siliziumspitzen und hydrophober, neu eingeführter Saphirspitzen gezeigt und diese gegenüber gestellt. Besonderes Augenmerk liegt hierbei auf den stark voneinander abweichenden Abstandsspektren der verschiedenen Spitzentypen. Es wurde entdeckt, dass die neue Technik an Luft und in Flüssigkeiten (z. B. auf Mica) uneingeschränkt anwendbar und auch für hochviskose Flüssigkeiten kein Hindernis darstellt. Durch die Neuerungen in dieser Arbeit werden nicht nur die Untersuchungen von Oberflächen mit höchster Auflösung direkt an Luft und in Flüssigkeiten möglich, sondern auch die Untersuchung von biologischen Proben oder chemischen Reaktionen in natürlichen Bedingungen. In dieser Arbeit wird somit eine revolutionäre Technik für die Studie von einzelnen Atomen und Moleküle, bis hin zu ganzen lebenden Organismen in kleinsten Dimensionen eingeführt

Influence of matrix and filler fraction on biofilm formation on the surface of experimental resin-based composites

The aim of this study was to investigate the impact of resin matrix chemistry and filler fraction on biofilm formation on the surface of experimental resinbased composites (RBCs). Specimens were prepared from eight experimental RBC formulations differing in resin matrix blend (BisGMA/TEGDMA in a 7:3 wt% ratio or UDMA/aliphatic dimethacrylate in a 1:1 wt% ratio) and filler fraction (no fillers; 65 wt% dental glass with an average diameter of 7 or 0.7 lm or 65 wt% SiO2 with an average diameter of 20 nm). Surface roughness, surface free energy, and chemical surface composition were determined; surface topography was visualized using atomic force microscopy. Biofilm formation was simulated under continuous flow conditions for a 48 h period using a monospecies Streptococcus mutans and a multispecies biofilm model. In the monospecies biofilm model, the impact of the filler fraction overruled the influence of the resin matrix, indicating lowest biofilm formation on RBCs with nano-scaled filler particles and those manufactured from the neat resin blends. The multispecies model suggested a more pronounced effect of the resin matrix blend, as significantly higher biofilm formation was identified on RBCs with a UDMA/dimethacrylate matrix blend than on those including a BisGMA/TEGDMA matrix blend but analogous filler fractions. Although significant differences in surface properties between the various materials were identified, correlations between the surface properties and biofilm formation were poor, which highlights the relevance of surface topography and chemistry. These results may help to tailor novel RBC formulations which feature reduced biofilm formation on their surface

Streptococcus mutans biofilm formation and release of fluoride from experimental resin-based composites depending on surface treatment and S-PRG filler particle fraction

PURPOSE: To evaluate fluoride release and biofilm formation on resin-based composites (RBCs) including surface pre-reacted glass ionomer (S-PRG) filler particles. MATERIALS AND METHODS: Specimens were prepared from experimental RBCs including different fractions of S-PRG fillers (0/10/30/50/70% w/v). RBCs were light cured against mylar strips (MYL), and 50% of the specimens were additionally polished to a high gloss (POL). Surface roughness (SR), surface free energy (SFE) and fluoride release were determined. Streptococcus mutans biofilm formation (SMBF) was simulated for 48 h and 120 h; adherent viable biomass was assessed using an MTT-based assay. RESULTS: The highest SR was identified for POL specimens manufactured from the RBC with a filler fraction of 70%. For all specimens and surface treatments, polishing caused an increase in surface free energy. For both MYL and POL specimens, increasing the filler fraction coincided with an increased release of fluoride; a higher release of fluoride was identified for POL specimens with filler fractions of 50% and 70% in comparison to their MYL counterparts. Release of fluoride was lower after 120 h than after 48 h. No differences in SMBF were identified between MYL and POL specimens with identical filler fractions after 48 h of biofilm formation; with increasing filler fractions, a tendency towards decreasing SMBF was observed. After 120 h, less SMBF was identified for POL specimens with filler fractions of 30%, 50% and 70% in comparison to corresponding MYL specimens. CONCLUSION: The inclusion of S-PRG fillers and an effective surface treatment may reduce biofilm formation on RBCs

Streptococcus Mutans Biofilm Formation on Resin-based Composites including S-PRG Fillers

Objective: This study aimed to evaluate the release of fluoride and Streptococcus mutans biofilm formation on the surfaces of experimental resin-based composites (RBCs) including different fractions of surface pre-reacted glass ionomer filler particles. Method: Standardized specimens were prepared from five experimental RBCs with an identical BisGMA/TEGDMA matrix blend but different fractions of surface pre-reacted glass-ionomer (S-PRG) fillers (0/10/30/50/70% w/v). The RBCs were light-cured against mylar strips; 50% of the specimens received no further surface treatment (MYL) and the other 50% were polished to high gloss (POL). Surface roughness (SR), surface free energy (SFE) and the release of fluoride from the specimens` surfaces were determined. Streptococcus mutans biofilm formation (SMBF) was simulated for either 48 h or 120 h using a Drip-Flow Reactor; adherent viable biomass was assessed using a MTT-based assay. Statistical analysis was performed using two-way ANOVA and Student\u2019s t-test (p<.05). Result: Significantly highest SR was identified for POL specimens prepared from the RBC with a filler weight of 70% (P=.005). For all specimens and surface treatments, polishing caused an increase in the polar contribution to SFE. For both MYL and POL specimens, increasing the S-PRG filler fraction caused an increased release of fluoride; POL specimens with a filler fraction of 50% and 70% released significantly more fluoride than MYL specimens. After 120 h, less fluoride was released in comparison to the 48 h data. Regarding SMBF, no significant differences were identified between MYL and POL specimens with identical filler fractions after 48 h; however, with increasing filler fractions, a tendency towards decreasing SMBF was observed. After 120 h, less SMBF was identified for POL specimens with a filler fraction of 30%, 50% and 70% in comparison to MYL specimens. Conclusion: High S-PRG filler fraction and surface treatment may positively influence Streptococcus mutans biofilm formation on fluoride-releasing RBCs