Fungal Ecology in a Tertiary Neonatal Intensive Care Unit after 16 Years of Routine Fluconazole Prophylaxis: No Emergence of Native Fluconazole-Resistant Strains.

OBJECTIVE: We analyzed the fungal ecology of a neonatal intensive care unit (NICU) over a period of 20 consecutive years following the introduction of routine fluconazole prophylaxis for all very low birth weight (VLBW; <1,500 g at birth) preterm babies. The aim was to detect the possible appearance of any ecological shifts toward the emergence of native fluconazole-resistant (NFR) fungal species. STUDY DESIGN: This was a retrospective analysis of clinical and microbiological data of VLBW preterm neonates admitted to a large tertiary NICU in Italy from 1997 to 2016 and surviving more than 3 days. Colonization and infection incidence rates, both for fluconazole-sensitive Candida spp and NFR Candida spp, were calculated for each year. We compared the first 4-year period without prophylaxis (1997-2000) with the last 16-year period with use of routine fluconazole prophylaxis (2000-2016). RESULTS: Overall, the incidence of fungal colonization significantly decreased after the introduction of prophylaxis (from 43.4% to 16.5%) as well as the systemic fungal infection incidence (from 16% to 3.7%). The proportion of colonization and infection by NFR Candida spp, on the other hand, did not increase, remaining stable throughout the 16 years of exposure to fluconazole. During the prophylaxis period, 42 of 1,172 VLBW neonates were colonized by NFR species (3.6%), and of them 11 developed a systemic infection (0.9%). During the preprophylaxis period, colonization by these particular species affected 11 of 285 VLBW neonates (3.8%), and a systemic infection involved 4 neonates (1.4%). CONCLUSION: Fluconazole prophylaxis is effective in decreasing Candida colonization and systemic infections in preterm neonates in NICU and did not cause emergence or shifts toward NFR Candida spp over a 16-year surveillance period.

MEK Inhibition in a Newborn with RAF1-Associated Noonan Syndrome Ameliorates Hypertrophic Cardiomyopathy but Is Insufficient to Revert Pulmonary Vascular Disease.

The RAF1:p.Ser257Leu variant is associated with severe Noonan syndrome (NS), progressive hypertrophic cardiomyopathy (HCM), and pulmonary hypertension. Trametinib, a MEK-inhibitor approved for treatment of RAS/MAPK-mutated cancers, is an emerging treatment option for HCM in NS. We report a patient with NS and HCM, treated with Trametinib and documented by global RNA sequencing before and during treatment to define transcriptional effects of MEK-inhibition. A preterm infant with HCM carrying the RAF1:p.Ser257Leu variant, rapidly developed severe congestive heart failure (CHF) unresponsive to standard treatments. Trametinib was introduced (0.022 mg/kg/day) with prompt clinical improvement and subsequent amelioration of HCM at ultrasound. The appearance of pulmonary artery aneurysm and pulmonary hypertension contributed to a rapid worsening after ventriculoperitoneal shunt device placement for posthemorrhagic hydrocephalus: she deceased for untreatable CHF at 3 months of age. Autopsy showed severe obstructive HCM, pulmonary artery dilation, disarrayed pulmonary vascular anatomy consistent with pulmonary capillary hemangiomatosis. Transcriptome across treatment, highlighted robust transcriptional changes induced by MEK-inhibition. Our findings highlight a previously unappreciated connection between pulmonary vascular disease and the severe outcome already reported in patients with RAF1-associated NS. While MEK-inhibition appears a promising therapeutic option for HCM in RASopathies, it appears insufficient to revert pulmonary hypertension.

[Standardised parenteral nutrition in low birth weight preterm newborns: a case report.] / La nutrizione parenterale standardizzata nei neonati pretermine di basso peso: descrizione di un caso.

The aim of this study is to evaluate the possibility of increasing the use of standardised parenteral nutrition (PN) as a replacement of individualized parenteral nutrition in the neonatal intensive care unit (NICU). The standardisation of the PN formulations has the potential to improve nutrient intakes, quality control, cost effectiveness and reduce prescription errors. In our hospital the individualized PN solutions are made by Chemists for premature babies born during the working days. We have been using standardised PN formulations for about two years for the preterm infants born during the weekend. The use of SPN is currently limited to the weekend, until our Chemists can prepare the IPN.In this study we describe the case of a sick low birth weight baby for whom we used for the first time the bags of a standardised PN "ready to use" since the sixth day of life for thirteen consecutive days. The baby was not a very low birth weight, but he needed parenteral nutrition because he was relatively unstable and he had a poor feeding tolerance. As result of the study, the baby growth was regular and the SPN were well tolerated. No adverse effects were reported.

Is thrombocytopenia suggestive of organism-specific response in neonatal sepsis?

BACKGROUND: It is controversial whether thrombocytopenia is suggestive of one (or more) causative agents of neonatal sepsis: a low platelet count has been related in turn to Gram-positive, Gram-negative or fungal sepsis. METHODS: A retrospective, cohort study on 514 very low-birthweight (VLBW) neonates admitted over a 9 year period to a large tertiary neonatal intensive care unit (NICU) in Italy was carried out. Through database search, data on platelet counts, sepsis, clinical course, and microbiological culture were collected and analyzed. Statistical analysis was performed to look for significant association between thrombocytopenia and sepsis caused by different (Gram-positive, Gram-negative or fungal) organisms. RESULTS: Sepsis diagnosed on microbiological criteria occurred in 197 of 514 VLBW neonates (38.3%), and thrombocytopenia (at least one finding of platelet count <80,000/mm(3)) was detected in 34 (17.2%) of the 197 septic infants. Thrombocytopenia occurred in 10 of 51 neonates with fungal sepsis (19.6%), and in 24 of 146 with bacterial sepsis (16.4%; P = 0.37). The difference was not significant when clustering for sepsis caused by Gram-positive (nine thrombocytopenic of 51 with Gram-positive sepsis, 17.6%; P = 0.40) and Gram-negative organisms (15/95, 15.7%; P = 0.22), or when considering only coagulase-negative Staphylococcus sepsis (6/37, 16.2%; P = 0.25). CONCLUSIONS: In contrast with previous reports, thrombocytopenia might not be an organism-specific marker of sepsis. Caution should be maintained in relating a low platelet count to any infectious agent (or group of agents) in preterm VLBW neonates.

Routine use of fluconazole prophylaxis in a neonatal intensive care unit does not select natively fluconazole-resistant Candida subspecies.

BACKGROUND: We have previously demonstrated efficacy against fungal colonization and infection of fluconazole prophylaxis that was routinely administered since 2001 in our ICU for preterm infants <1500 g at birth (VLBW). With prolonged use, concerns exist for the emergence of acquired fungal resistance and of Candida subspecies that are natively fluconazole-resistant (NFR), mostly Candida glabrata and Candida krusei. METHODS: We evaluated retrospectively all clinical and surveillance fungal isolates obtained from VLBW infants in our NICU during a 10-year period (1997-2006). Each fungal isolate was speciated, infants colonized or infected with NFR-Candida spp were identified and the incidence rates of colonization and infection by these fungal species were calculated. A comparison was made of the 6-year (2001-2006) prophylaxis period with the 4-year (1997-2000) preprophylaxis period. RESULTS: Overall, colonization by NFR-Candida spp ranged between 2.8% and 6.6% of VLBW infants yearly admitted, without any increasing trend during the study period. There were 18 of 434 (4.1%) neonates colonized by these species. Five episodes of systemic fungal infections caused by NFR-Candida spp occurred (incidence rate, 1.1%). No significant differences were detected when compared with the preprophylaxis period, when 11 of 295 infants (3.7%) were colonized by NFR-Candida spp and 4 episodes of infection occurred (1.4%) (P = 0.84 and 0.76, respectively). CONCLUSIONS: Fluconazole prophylaxis administered to VLBW neonates in 4- to 6-week courses after birth does not lead to the emergence of natively fluconazole-resistant Candida spp.

Deposition of nanosized latex particles onto silica and cellulose surfaces studied by optical reflectometry.

Deposition of positively charged nanosized latex particles onto planar silica and cellulose substrates was studied in monovalent electrolyte solutions at pH 9.5. The deposition was probed in situ with optical reflectometry in a stagnation point flow cell. The surface coverage can be estimated reliably with island film theory as well as with a homogeneous film model, as confirmed with atomic force microscopy (AFM). The deposition kinetics on the bare surface was of first order with respect to the particle concentration, whereby the deposition rate was close to the value expected for a perfect collector. The efficiency coefficient, which was defined as the ratio of the experimental and theoretical deposition rate constants, was in the range from 0.3 to 0.7. Subsequently, the surface saturated and a limiting maximum coverage was attained (i.e., blocking). These trends were in qualitative agreement with predictions of the random sequential absorption (RSA) model, where electrostatic interactions between the particles were included. It was observed, however, that the substrate strongly influenced the maximum coverage, which was substantially higher for silica than for cellulose. The major conclusion of this work was that the nature of the substrate played an important role in a saturated layer of deposited colloidal particles.

Effects of heat treatment on the aggregation and charging of Stöber-type silica.

Colloidal silica is known to be stable at high salt concentrations and low pH, where silica is basically uncharged. This observation is in qualitative disagreement with the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO), which predicts rapid aggregation (or coagulation) under these conditions. This study reports a very different behaviour for Stöber-type silica heated at 800 degrees C, as these particles follow DLVO theory quantitatively. Unheated samples behave approximatively according to DLVO theory, but they show systematic deviations, in particular, featuring higher stability at low pH. The heat treatment also substantially modifies the charging properties, as heated particles show titratable surface charge densities in the range expected for the water-silica interface, while much higher charge densities are observed for the unheated samples. The electrophoretic mobilities, on the other hand, are hardly influenced by the heat treatment. We suspect that the suspension stability of the unheated particles is influenced by the presence of a hairy-layer of polysilicilic acid chains on the surface.

CMV infection associated with severe lung involvement and persistent pulmonary hypertension of the newborn (PPHN) in two preterm twin neonates.

The diagnosis of congenital CMV is usually guided by a number of specific symptoms and findings. Unusual presentations may occur and diagnosis is challenging due to uncommon or rare features. Here we report the case of two preterm, extremely low birthweight, 28-week gestational age old twin neonates with CMV infection associated with severe lung involvement and persistent pulmonary hypertension of the newborn (PPHN). They were born to a HIV-positive mother, hence they underwent treatment with zidovudine since birth. Both infants featured severe refractory hypoxemia, requiring high-frequency ventilation, inhaled nitric oxide and inotropic support, with full recovery after 2 months. Treatment with ganciclovir was not feasible due the concomitant treatment with zidovudine and the risk of severe, fatal toxicity. Therefore administration of intravenous hyperimmune anti-CMV immunoglobulin therapy was initiated. Severe lung involvement at birth and subsequent pulmonary hypertension are rarely described in preterm infants as early manifestations of CMV congenital disease. In the two twin siblings here described, the extreme prematurity and the treatment with zidovudine likely worsened immunosuppression and ultimately required a complex management of the CMV-associated lung involvement.

Human milk feeding prevents retinopathy of prematurity (ROP) in preterm VLBW neonates.

BACKGROUND: Retinopathy of prematurity (ROP) is a multifactorial disease, but little is known about its relationships with neonatal nutritional policies. Human, maternal milk is the best possible nutritional option for all premature infants, including those at high risk for severe complications of prematurity, such as ROP. OBJECTIVE: This is a secondary analysis of data collected during two multicenter RCTs performed consecutively (years 2004 through 2008) by a network of eleven tertiary NICUs in Italy. The two trials aimed at assessing effectiveness of fluconazole prophylaxis (Manzoni et al., N Engl J Med 2007 Jun 14;356(24):2483-95), and of bovine lactoferrin supplementation (Manzoni et al., JAMA 2009 Oct 7;302(13):1421-8), in prevention of invasive fungal infection, and of late-onset sepsis in VLBW infants, respectively. We tested the hypothesis that exclusive feeding with fresh maternal milk may prevent ROP of any stage - as defined by the ETROP study - in VLBW neonates, compared to formula feeding. METHODS: We analyzed the database from both trials. Systematic screening for detection of ROP was part of the protocol of both studies. The definition of threshold ROP was as defined by the ETROP study. Univariate analysis was performed to look for significant associations between ROP and several possible associated factors, and among them, the type of milk feeding (maternal milk or formula for preterms). When an association was indicated by p < 0.05, multiple logistic regression was used to determine the factors significantly associated with ROP. RESULTS: In both trials combined, 314 infants received exclusively human maternal milk (group A), and 184 a preterm formula because their mothers were not expected to breastfeed. The clinical, demographical and management characteristics of the neonates did not differ between the two groups, particularly related to the presence of the known risk factors for ROP. Overall, ROP incidence (any stage) was significantly lower in infants fed maternal milk (11 of 314; 3.5%) as compared to formula-fed neonates (29 of 184; 15.8%) (RR 0.14; 95% CI 0.12-0.62; p = 0.004). The same occurred for threshold ROP (1.3% vs. 12.3%, respectively; RR 0.19; 95% CI 0.05-0.69; p = 0.009). At multivariate logistic regression controlling for potentially confounding factors that were significantly associated to ROP (any stage) at univariate analysis (birth weight, gestational age, days on supplemental oxygen, systemic fungal infection, outborn, hyperglycaemia), type of milk feeding retained significance, human maternal milk being protective with p = 0.01. CONCLUSIONS: Exclusive human, maternal milk feeding since birth may prevent ROP of any stage in VLBW infants in the NICU.

Role of echinocandins in the management of fungal infections in neonates.

As the incidence rates of neonatal systemic fungal infections (SFI) have been increasing over the last years, research efforts have been addressed towards identifying both effective preventative strategies, and efficacious and well-tolerated antifungal drugs. Historically, the first options in treatment of neonatal SFI have been – and currently are – fluconazole and amphotericin B. However, these two drugs carry limitations both in efficacy and in putative toxicity. Recently, new therapeutic alternatives have drawn the neonatologists' attention. Echinocandins are a new class of antifungal drugs with characteristics that might better meet the needs of this particular population of patients. Caspofungin (CSP), micafungin (MICA), and anidulafungin have inherent good activities both against biofilms, and against natively fluconazole-resistant strains of Candida spp, thus overcoming two of the major weaknesses of the commonly used antifungal drugs in nurseries. CSP and MICA have been recently studied in neonatal populations. The kinetics and appropriate dosing of this agent in premature and term infants have been described, but ongoing further studies are needed to better address this area. Case-report series show clinical efficacy and tolerability in critical neonatal patients given CSP and MICA. In addition, extrapolation of data from randomized trials conducted in pediatric and adult patients showed through a subgroup analysis that both CSP and MICA are effective and well tolerated also in neonates. Further studies properly designed for neonatal populations will better address long-term safety and ecological issues related to echinocandin use in neonates.

Structure of an adsorbed polyelectrolyte monolayer on oppositely charged colloidal particles.

An adsorbed layer of a cationic polyelectrolyte, poly(diallyldimethyl-ammonium) chloride (PDADMAC) on negatively charged colloidal latex particles was investigated by small-angle neutron scattering (SANS) and dynamic light scattering (DLS). SANS gives a layer thickness of 8 +/- 1 A and a polymer volume fraction of 0.31 +/- 0.05 within the film. DLS gives a somewhat larger thickness of 18 +/- 2 A, and the discrepancy is likely due to the inhomogeneous nature of the layer and the existence of polymer tails or loops protruding into solution. These results show that a highly charged polyelectrolyte adsorbs on an oppositely charged colloidal particle in a flat configuration due to the attractive forces acting between the polyelectrolyte and the substrate.

Type and number of sites colonized by fungi and risk of progression to invasive fungal infection in preterm neonates in neonatal intensive care unit.

AIMS: Retrospective cohort study to assess if different patterns of Candida colonization determine different risks of progression to invasive fungal infection (IFI) in preterm neonates in NICU. METHODS: Weekly surveillance cultures from all neonates weighing at birth <1500 g admitted over a 6-year period were reviewed. Infants with available results from at least 3 cultures/week and from at least 4 different sites were enrolled and identified by the number of sites involved [1-2 (low-grade), 3 or more (high-grade)] and type (low-risk, if colonization was recovered from skin, stool, ear canal swab, gastric aspirate, nasopharynx secretions, endotracheal tube; high-risk, from urine, catheter tip, drains, surgical devices). Progression rates from colonization to IFI were calculated for each subgroup. Univariate analysis was performed looking for significant associations between IFI and a number of risk factors, including the different subgroups of colonization. Multiple logistic regression assessed all significantly (P<0.05) associated risk factors. MAIN RESULTS: In the 405 eligible infants, overall colonization rate was 42.9%, IFI rate 9.9%, overall progression rate to IFI 0.23, the latter being significantly higher in high-grade or high-risk than in low-grade or low-risk colonized infants (0.59 vs. 0.18, P=0.001; 0.44 vs. 0.11, P<0.001, respectively). Infants with concomitant high-grade + high-risk colonization had 4-fold higher risk of progression than any other colonized infant, and 7-fold higher risk than infants concomitantly low-grade + low-risk colonized (P<0.001). At multivariate analysis, high-grade and high-risk colonization (P=0.001 for both), birth weight (P=0.02) and presence of central venous line (P=0.04) remained independent predictors of IFI. CONCLUSIONS: Density and severity of fungal colonization condition the progression to IFI in preterm infants in NICU, and certain patterns of colonization are independent predictors of IFI. Increased culture surveillance and prophylactic measures should be addressed to preterm colonized infants in NICU featuring the most risky colonization patterns.

Hyperglycaemia as a possible marker of invasive fungal infection in preterm neonates.

AIM: The incidence of invasive fungal infection in preterm newborns is rising steadily. Early recognition and treatment are imperative, but diagnosis is difficult as data from microbiological investigations are often poor, and clinical and laboratory signs do not help in differentiating bacterial from fungal infections. We evaluated whether glucose intolerance could represent a possible surrogate marker predictor of invasive fungal infection in preterm neonates. METHODS: We performed a case-control study on neonates with birthweight less than 1250 g admitted to our tertiary-level unit during the years 1998-2004 (n = 383), comparing those with invasive fungal infection (n = 45, group A) to matched controls with late-onset sepsis caused by bacterial agents (n = 46, group B). We investigated in both groups the occurrence of hyperglycaemia (serum glycaemia > 215 mg/dl, i.e. 12 mmol/l) in the first month of life, and its temporal relationship with the episodes of sepsis. RESULTS: Hyperglycaemia occurred significantly more often in group A (21/45, 46.6%) than in group B neonates (11/46, 23.9%) (OR 1.95, 95% CI 1.235-4.432, p = 0.008). Moreover, in 19 of 21 (90.4%) neonates with hyperglycaemia in group A, the carbohydrate intolerance episode typically occurred 72 h prior to the onset of invasive fungal infection; in contrast, no temporal relationship was found in neonates with bacterial sepsis (p = 0.002). Correction of hyperglycaemia was successfully achieved in all neonates of both groups, with no significant differences in the number of days of insulin treatment needed to normalize glycaemia (p = 0.15). CONCLUSIONS: Hyperglycaemia is significantly more frequent in neonates who subsequently develop fungal rather than bacterial late-onset sepsis, with a typical 3-d interval. We suggest that a preterm neonate whose birthweight is less than 1250 g in its first month of life should be carefully evaluated for systemic fungal infection whenever signs of carbohydrate intolerance occur.

Heteroaggregation in binary mixtures of oppositely charged colloidal particles.

Heteroaggregation (or heterocoagulation) rate constants have been measured in mixtures of well-characterized colloidal particles of opposite charge with multiangle static and dynamic light scattering. This technique permits routine measurements of absolute heteroaggregation rate constants, also in the presence of homoaggregation. Particularly with multiangle dynamic light scattering, one is able to estimate absolute heteroaggregation rate constants accurately in the fast aggregation regime for the first time. Heteroaggregation rate constants have also been measured over a wide range of parameters, for example, ionic strength and different surface charge densities. Amidine latex particles, sulfate latex particles, and silica particles have been used for these experiments, and they were well characterized with respect to their charging and homoaggregation behavior. It was shown that heteroaggregation rate constants of oppositely charged particles increase slowly with decreasing ionic strength, and provided the surface charge is sufficiently large, the rate constant is largely independent of the surface charge. These trends can be well described with DLVO theory without adjustable parameters.

Risk factors for progression to invasive fungal infection in preterm neonates with fungal colonization.

OBJECTIVE: Colonization by Candida spp is a major risk factor for development of fungal sepsis, but little is known about the variables associated with progression to invasive disease in already colonized neonates. We investigated such variables in a large number of colonized preterm neonates in an NICU. SETTING: This study was conducted in the Department of Neonatology and the NICU at Sant'Anna Hospital in Torino, Italy. DESIGN AND PATIENTS: A database search of clinical charts and weekly surveillance cultures was used to identify all neonates with birth weights < 1500 g (very low birth weight) who were admitted to our NICU during 1998-2005 and were colonized (> or = 1 site) by Candida spp during their stay, as well as infants with invasive fungal infection. The association between a number of factors with progression to invasive fungal infection was evaluated. Those shown to be significantly associated by univariate analysis were cross-checked by logistic regression. RESULTS: Colonization occurred in 201 infants (32.1% of very low birth weight admitted neonates), and invasive fungal infection occurred in 51 (8.1%) of them, with an overall progression rate of 0.25. At univariate analysis, 10 factors (namely low birth weight, low gestational age, use of third-generation cephalosporins, endotracheal intubation, duration of stay in the NICU, bacterial sepsis, colonization of central venous catheter, of endotracheal tube, of gastric aspirate, or in > or = 3 [multiple] sites) were associated with an increased risk of progression, whereas prophylaxis with fluconazole was associated to a decreased risk. After logistic regression, only colonization of central venous catheter and colonization in multiple sites remained significantly associated with invasive fungal infection. Fluconazole prophylaxis remained an independent protective factor. CONCLUSIONS: Central venous catheter colonization and multiple-site colonization are independent risk factors and predictors of progression to fungal sepsis in preterm very low birth weight neonates colonized by Candida spp during their stay in the NICU. Fluconazole prophylaxis is an independent protective factor. These findings can be used to improve the surveillance, prophylaxis, or preemptive measures in neonates at high risk.

Measurement of heteroaggregation rate constants by simultaneous static and dynamic light scattering.

The early stages of the heteroaggregation (or heterocoagulation) of latex particles were probed by time resolved simultaneous static and dynamic light scattering (SSDLS). We show that the heteroaggregation rate constant and the apparent hydrodynamic radius of the dimer can be obtained by analyzing the SSDLS data without the need to invoke the optical form factors for the doublets. A similar approach was proposed earlier for homoaggregation. The validity of the present approach was tested by investigating heteroaggregation between sulfate and amidine latex particles of different size, and similar data for smaller particles, which were previously analyzed in terms of the Rayleigh-Debye-Gans (RDG) theory. In this case, the presently obtained rate constants were found to be in excellent agreement with the results based on RDG. The present technique is particularly interesting for larger particles, where RDG cannot be applied, or to particles of more complex shapes, where the optical form factor cannot be easily evaluated.

Light-scattering form factors of asymmetric particle dimers from heteroaggregation experiments.

Measurements of form factors of asymmetric particle dimers composed of oppositely charged polystyrene latex particles are presented. These measurements are based on time-resolved static and dynamic light scattering on dilute aggregating aqueous suspensions. The experimental form factors are compared with independent calculations based on the superposition T-matrix method and Rayleigh-Debye-Gans (RDG) approximation. While the RDG approximation is found to be reliable only up to particle diameters of about 250 nm, the superposition T-matrix method is very accurate for all types of dimers investigated. The present results show clearly the appropriateness of the superposition T-matrix method to estimate the optical properties of colloidal particles in the micrometer range reliably.

Aggregation and charging of colloidal silica particles: effect of particle size.

We studied systematically aqueous suspensions of amorphous well-characterized silica particles by potentiometric titration, electrophoretic mobility, and time-resolved light scattering. Their charging behavior and aggregation rate constants were measured as a function of pH and ionic strength in KCl electrolytes for three types of particles of approximately 30, 50, and 80 nm in diameter. The charging behavior was consistent with the basic Stern model; the silica particles carry a negative charge, and its magnitude gradually increases with increasing pH and ionic strength. On the other hand, their early-stage aggregation (or coagulation) behavior is complex. The aggregation of the largest particles shows features resembling predictions of the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory. On one hand, the rate constant decreases sharply with increasing pH at low ionic strengths and attains fast aggregation conditions at high ionic strengths. On the other hand, we observe a characteristic slowing down of the aggregation at low pH and high ionic strengths. This feature becomes very pronounced for the medium and the small particles, leading to a complete stabilization at low pH for the latter. Stabilization is also observed at higher pH for the medium and the small particles. From these aggregation measurements we infer the existence of an additional repulsive force. Its origin is tentatively explained by postulating hairy layers of consisting of poly(silicilic acid) chains on the particle surface.

Charging and aggregation of latex particles by oppositely charged dendrimers.

Poly(amidoamine) (PAMAM) dendrimers were shown to adsorb strongly on negatively charged latex particles, and their effect on the particle charge and aggregation behavior was investigated by light scattering and electrophoretic mobility measurements. Time-resolved simultaneous static and dynamic light scattering was used to measure absolute aggregation rate constants. With increasing dendrimer dose, the overall charge could be tuned from negative to positive values through the isoelectric point (IEP). The aggregation is fast near the IEP and slows down further away. With decreasing ionic strength, the region of fast aggregation narrows and the dependence of the aggregation rate on the dendrimer dose is more pronounced. Surface charge heterogeneities become important for higher dendrimer generations. They widen the fast aggregation region, reduce the dependence of the aggregation rate on the dendrimer dose, and lead to an acceleration of the rate in the fast aggregation regime near the IEP. The ratio of the dendrimer charge and the particle charge exceeds the stoichiometric ratio of unity substantially and further increases with increasing generation. The tentative interpretation of such superstoichiometric charge neutralization involves coadsorption of anions and the finite thickness of the adsorbed dendrimer layer.