Surface-immobilized PAMAM-dendrimers modified with cationic or anionic terminal functions: physicochemical surface properties and conformational changes after application of liquid interface stress.

Functionalization of surfaces with highly branched dendrimer molecules has gained attractiveness for various applications because the number of functional groups exceeds those of surfaces functionalized with self-assembled monolayers. So far, little is known about the physicochemical properties of dendrimer functionalized surfaces, especially if the flexibility of dendrimer structure remains after covalent immobilization. Therefore, the purpose of this study was to covalently immobilize polyamidoamine (PAMAM) dendrimer molecules exhibiting terminal amine and carboxyl groups to silicon model surfaces and to explore their properties and structure at the solid-air and solid-liquid interface. Our results show that the surface free energy is higher for PAMAM coatings than for analogously terminated SAMs and also higher for carboxyl than amine functionalized coatings. Furthermore, several findings suggest that conformational freedom of the dendrimers was preserved after surface immobilization. Wet compared to dry PAMAMNH(2) surfaces show reduced hydrophilicity and increased contact angle hysteresis, whereas PAMAMCOOH surfaces become more hydrophilic and showed decreased hysteresis. Streaming current measurements showed an unexpected behavior for PAMAMCOOH surfaces in that they reveal a net positive surface charge over a wide pH range in spite of the carboxylated periphery. All of these results indicate a certain degree of masking, burrowing, back-folding and unfolding of functional groups upon environmental changes.

NCO-sP(EO-stat-PO) coatings on gold sensors--a QCM study of hemocompatibility.

The reliability of implantable blood sensors is often hampered by unspecific adsorption of plasma proteins and blood cells. This not only leads to a loss of sensor signal over time, but can also result in undesired host vs. graft reactions. Within this study we evaluated the hemocompatibility of isocyanate conjugated star shaped polytheylene oxide-polypropylene oxide co-polymers NCO-sP(EO-stat-PO) when applied to gold surfaces as an auspicious coating material for gold sputtered blood contacting sensors. Quartz crystal microbalance (QCM) sensors were coated with ultrathin NCO-sP(EO-stat-PO) films and compared with uncoated gold sensors. Protein resistance was assessed by QCM measurements with fibrinogen solution and platelet poor plasma (PPP), followed by quantification of fibrinogen adsorption. Hemocompatibility was tested by incubation with human platelet rich plasma (PRP). Thrombin antithrombin-III complex (TAT), ß-thromboglobulin (ß-TG) and platelet factor 4 (PF4) were used as coagulation activation markers. Furthermore, scanning electron microscopy (SEM) was used to visualize platelet adhesion to the sensor surfaces. Compared to uncoated gold sensors, NCO-sP(EO-stat-PO) coated sensors revealed significant better resistance against protein adsorption, lower TAT generation and a lower amount of adherent platelets. Moreover, coating with ultrathin NCO-sP(EO-stat-PO) films creates a cell resistant hemocompatible surface on gold that increases the chance of prolonged sensor functionality and can easily be modified with specific receptor molecules.

Wetting behavior of dental implants.

PURPOSE: Hydrophilicity is gaining increasing interest as a factor that might influence the osseointegration of dental implants. Therefore, in this study the dynamic wetting behavior of currently marketed dental titanium implants was analyzed by tensiometry, and its relationship to surface topography was examined. MATERIALS AND METHODS: Nine screw-type implant systems from eight manufacturers were evaluated. Dynamic water contact angles were analyzed by tensiometric multiloop Wilhelmy experiments (10 loops, 10 mm/min immersion speed). The wetted length (perimeter) of the immersed samples was estimated by three-dimensional picture profile measurement of the thread height of the respective implant screws. Wettability was quantified by first advancing contact angles. Additionally, static contact angles were determined using the sessile drop technique. All implant surfaces were characterized by scanning electron microscopy (SEM). Contact angle data were subjected to one-way analysis of variance followed by the Student t test. RESULTS: SEM revealed different types of surface morphology resulting from the different manufacturing processes. The first advancing mean contact angles of all implants ranged from 0 degrees (SLActive) to 138 degrees (OsseoSpeed), demonstrating statistically significant differences between implants. Because of kinetic hysteresis, initially hydrophobic implants became hydrophilic during following immersion loops. CONCLUSIONS: The tensiometric method was used to compare wettability of dental implants. A range from fully wettable/superhydrophilic to virtually unwettable/hydrophobic was observed on the implant surfaces examined.

The impact of dendrimer-grafted modifications to model silicon surfaces on protein adsorption and bacterial adhesion.

In the oral cavity, omnipresent salivary protein films (pellicle) mediate bacterial adhesion and biofilm formation on natural tissues as well as on artificial implant surfaces, which may cause serious infectious diseases like periimplantitis. The purpose of this in vitro study was to investigate the adsorption/desorption behaviour of human saliva on model surfaces grafted with polyamidoamine (PAMAM) dendrimer molecules compared to self-assembled monolayers (SAMs) exhibiting the same terminal functions (-NH(2), -COOH) by two complementary analytical methods. Furthermore, the role of saliva conditioning of PAMAM and analogous SAM modifications on the adhesion of Streptococcus gordonii DL1, an early oral colonizer, was investigated. In contrast to SAMs, PAMAM-grafted surfaces showed reduced streptococcal adherence in the absence of pre-adsorbed saliva similar to the level obtained for poly(ethylene glycol) (PEG) coatings. Moreover, coatings of PAMAM-NH(2) maintained their bacteria-repellent behaviour even after saliva-conditioning. As a general outcome, it was found that lower amounts of protein adsorbed on PAMAM coatings than on analogous SAMs. Since this study demonstrates that covalently bound PAMAM dendrimers can modulate the oral bacterial response, this approach has significant potential for the development of anti-adhesive biomaterial surfaces that are conditioned with proteinaceous films.