Adhesión a dentina parte I: características del sustrato y sistemas adhesivos / Dentin bonding part I: substrate characteristics and bonding systems

La Odontología Restauradora contemporánea no puede concebirse sin la adhesión de los materiales restauradores a las estructuras dentarias. En mu-chos procedimientos restauradores, no sólo el esmal-te sino también la dentina se encuentra involucrada, por lo tanto, la adhesión a esta última juega un rol cla-ve en el éxito clínico. No obstante, todavía supone un gran desafío lograr una adhesión estable y predeci-ble en el tiempo. El propósito del presente artículo es analizar las características principales de la dentina como sustrato adhesivo y describir los sistemas ad-hesivos actuales y sus mecanismos de acción (AU)

Contemporary Restorative Dentistry cannot be conceived without the adhesion of restorative materials to dental structures. In many restorative procedures not only the enamel, but also the dentin is involved, therefore dentin bonding plays a key role in their success. However, it is still a great challenge to achieve stable and predictable dentin bonding over time. The aim of this article is to analyze the main characteristics of dentin as an adhesive substrate and to describe current adhesive systems and their bonding mechanisms (AU)

Principles of Structural Design of Conjugated Polymers Showing Excellent Charge Transport toward Thermoelectrics and Bioelectronics Applications.

Conjugated polymers, especially their second generation with a donor-acceptor alternating structure, have promising properties. These are suitable for two emerging fields, thermoelectrics and bioelectronics, if appropriate structural designs are implemented. This review aims to give a perspective for the potential and challenges of novel conjugated polymers in such applications. In particular, the aspects of synthetic design and the consequences of modifications of the chemical structure on the charge transport in selected second-generation conjugated polymers are reviewed. By understanding the effects of structural motifs on the overall material properties, polymers can be specifically tailored for the respective application. The basics of charge transport measurements are briefly summarized, as the charge transport plays an important role for thermoelectrics as well as for bioelectronics. In particular, the correlation between the reported charge carrier mobility values and the structural design of the polymers is reviewed. Examples of the application of second-generation conducting polymers in thermoelectrics and bioelectronics are shown to demonstrate the current state of research. Finally, the prospect of a purposeful design of new materials for these two emerging fields is discussed.

Identification Performance of Different Types of Handheld Near-Infrared (NIR) Spectrometers for the Recycling of Polymer Commodities.

For sustainable utilization of raw materials and environmental protection, the recycling of the most common polymers-polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polystyrene (PS)-is an extremely important issue. In the present communication, the discrimination performance of the above polymer commodities based on their near-infrared (NIR) spectra measured with four real handheld (<200 g) spectrometers based on different monochromator principles were investigated. From a total of 43 polymer samples, the diffuse reflection spectra were measured with the handheld instruments. After the original spectra were pretreated by second derivative and standard normal variate (SNV), principal component analysis (PCA) was applied and unknown samples were tested by soft independent modeling of class analogies (SIMCA). The results show that the five polymer commodities cluster in the score plots of their first three principal components (PCs) and, furthermore, samples in calibration and test sets can be correctly identified by SICMA. Thus, it was concluded that on the basis of the NIR spectra measured with the handheld spectrometers the SIMCA analysis provides a suitable analytical tool for the correct assignment of the type of polymer. Because the mean distance between clusters in the score plot reflects the discrimination capability for each polymer pair the variation of this parameter for the spectra measured with the different handheld spectrometers was used to rank the identification performance of the five polymer commodities.

Uncertainty in the Life Cycle Greenhouse Gas Emissions from U.S. Production of Three Biobased Polymer Families.

Interest in biobased products has been motivated, in part, by the claim that these products have lower life cycle greenhouse gas (GHG) emissions than their fossil counterparts. This study investigates GHG emissions from U.S. production of three important biobased polymer families: polylactic acid (PLA), polyhydroxybutyrate (PHB) and bioethylene-based plastics. The model incorporates uncertainty into the life cycle emission estimates using Monte Carlo simulation. Results present a range of scenarios for feedstock choice (corn or switchgrass), treatment of coproducts, data sources, end of life assumptions, and displaced fossil polymer. Switchgrass pathways generally have lower emissions than corn pathways, and can even generate negative cradle-to-gate emissions if unfermented residues are used to coproduce energy. PHB (from either feedstock) is unlikely to have lower emissions than fossil polymers once end of life emissions are included. PLA generally has the lowest emissions when compared to high emission fossil polymers, such as polystyrene (mean GHG savings up to 1.4 kg CO2e/kg corn PLA and 2.9 kg CO2e/kg switchgrass PLA). In contrast, bioethylene is likely to achieve the greater emission reduction for ethylene intensive polymers, like polyethylene (mean GHG savings up to 0.60 kg CO2e/kg corn polyethylene and 3.4 kg CO2e/kg switchgrass polyethylene).

Classification of stimuli-responsive polymers as anticancer drug delivery systems.

Although several anticancer drugs have been introduced as chemotherapeutic agents, the effective treatment of cancer remains a challenge. Major limitations in the application of anticancer drugs include their nonspecificity, wide biodistribution, short half-life, low concentration in tumor tissue and systemic toxicity. Drug delivery to the tumor site has become feasible in recent years, and recent advances in the development of new drug delivery systems for controlled drug release in tumor tissues with reduced side effects show great promise. In this field, the use of biodegradable polymers as drug carriers has attracted the most attention. However, drug release is still difficult to control even when a polymeric drug carrier is used. The design of pharmaceutical polymers that respond to external stimuli (known as stimuli-responsive polymers) such as temperature, pH, electric or magnetic field, enzymes, ultrasound waves, etc. appears to be a successful approach. In these systems, drug release is triggered by different stimuli. The purpose of this review is to summarize different types of polymeric drug carriers and stimuli, in addition to the combination use of stimuli in order to achieve a better controlled drug release, and it discusses their potential strengths and applications. A survey of the recent literature on various stimuli-responsive drug delivery systems is also provided and perspectives on possible future developments in controlled drug release at tumor site have been discussed.

[Influence of polymer type on the physical properties and the release study of papaverine hydrochloride from tablets]. / Wplyw rodzaju polimeru na wlasciwosci fizyczne i proces uwalniania chlorowodorku papaweryny z tabletek.

BACKGROUND: Polymers are widely used in drug manufacturing. Researchers studied their impact on the bioavailability of active substances or on physical properties of tablets for many years. OBJECTIVES: To study the influence of polymer excipients, such as microcrystalline cellulose (Avicel PH 101, Avicel PH 102), croscarmellose sodium, crospovidone or polyvinylpyrrolidone, on the release profile of papaverine hydrochloride from tablets and on the physical properties of tablets. MATERIAL AND METHODS: Six series of uncoated tablets were prepared by indirect method, with previous wet granulation. Tablets contained papaverine hydrochloride and various excipients. The physical properties of the prepared granules, tablets and the release profile of papaverine hydrochloride from tablets were examined. The content of papaverine hydrochloride from the release study were determined spectrophotometrically. RESULTS: All tablets met the pharmacopoeia requirements during following tests: the disintegration time of tablets, uncoated tablets resistance to abrasion, the weight uniformity and dose formulations, their dimensions, the resistance to crushing of tablets and the drug substance content in the tablet. In four cases more than 80% of papaverine was released up to 2 min, in one formula it was up to 5 min, and in last one up to 10 min. CONCLUSIONS: Tablets containing crospovidone disintegrated faster than tablets with croscarmellose sodium. Adding gelatinized starch to the tablet composition increased the disintegration time, hardness and delayed the release of papaverine. During the wet granulation process, granules containing polyvinylpyrrolidone were characterized by a suitable flow properties and slightly prolonged disintegration time. Tablets containing Avicel PH 102 compared to tablets with Avicel PH 101 had less weight loss during the test of mechanical resistance, improved hardness and faster release profile of papaverine from tablets.

Species of phosphorus in the extracellular polymeric substances of EBPR sludge.

In this study, the species of extracellular phosphorus and their transformation during extracellular polymeric substances (EPS) extraction were explored by using (31)P nuclear magnetic resonance spectroscopy. Results show that the extraction methods had a substantial influence on the phosphorus species in the extracted EPS. Cation exchange resin method was more appropriate for extracting EPS from the enhanced biological phosphorus removal (EBPR) sludge. Orthophosphate, pyrophosphate and polyphosphate were the main species of phosphorus found to be present in the EPS, which together accounted for about 6.6-10.5% of the total phosphorus in the EBPR sludge. The high percentage of extracellular phosphorus and their diverse species might reveal a new insight into the characteristics of the phosphorus in EPS in EBPR system.

Synthesis and MALDI-ToF characterization of dendronized poly(ethylene glycol)s

Well-defined hybrids of linear poly(ethylene glycol)s (PEGs) and dendritic polyesters were prepared via the dendronization of the alcohol end groups of the mono and difunctional linear PEGs. Though useful for rudimentary product characterization, GPC and NMR could not verify the overall structural purity of these linear-dendritic hybrids. On the other hand, the detailed data provided by MALDI-ToF mass spectrometry enabled confirmation of the high structural purity of the dendronized PEGs at each step of the dendronization procedure. The well-defined number of functionalities on these dendronized PEGs, renders them particularly useful for research in the biomedical sphere where functionality and purity are of the utmost importance. The MALDI-ToF mass spectrometric approach described herein represents a valuable technique for detailed monitoring of these dendronization reactions, as well as a variety of other polymer end group modifications.

Híbridos bem definidos de poli(etilenoglicol) lineares (PEGs) e poliésteres dendriméricos foram preparados via "dendronização" de álcool e grupos de PEGs lineares mono e bifuncionais. Embora úteis para a caracterização rudimentar de produtos, Cromatografia por Permeação em Gel e RMN podem não demonstrar a pureza estrutural global desses híbridos lineares dendríticos. Por outro lado, informações detalhadas provenientes de espectrometria de massas MALDI-ToF permitiram a confirmação de elevada pureza estrutural de PEGs "dendronizados" em cada passo do processo de "dendronização". O número de funcionalidades bem definidas destes PEGs "dendronizados", torna-os particularmente úteis para pesquisa na área biomédica, na qual funcionalidade e pureza são de grande importância. A abordagem de espectrometria de massas MALDI-ToF descrita aqui representa uma técnica valiosa para o monitoramento detalhado destas reações de "dendronização", bem como diversas modificações de outros polímeros e grupos.

Physicochemical and dissolution profile characterization of pellets containing different binders obtained by the extrusion-spheronization process

With the purpose of evaluating the behavior of different polymers employed as binders in small-diameter pellets for oral administration, we prepared formulations containing paracetamol and one of the following polymers: PVP, PEG 1500, hydroxypropylmethylcellulose and methylcellulose, and we evaluated their different binding properties. The pellets were obtained by the extrusion/spheronization process and were subsequently subjected to fluid bed drying. In order to assess drug delivery, the United States Pharmacopeia (USP) apparatus 3 (Bio-Dis) was employed, in conjunction with the method described by the same pharmacopeia for the dissolution of paracetamol tablets (apparatus 1). The pellets were also evaluated for granulometry, friability, true density and drug content. The results indicate that the different binders used are capable of affecting production in different ways, and some of the physicochemical characteristics of the pellets, as well as the dissolution test, revealed that the formulations acted like immediate-release products. The pellets obtained presented favorable release characteristics for orally disintegrating tablets. USP apparatus 3 seems to be more adequate for discriminating among formulations than the basket method.

Com a finalidade de se avaliar o comportamento de diferentes polímeros empregados como aglutinantes em pellets de pequeno diâmetro para uso oral foram preparadas formulações contendo paracetamol e um dos seguintes polímeros: PVP, PEG 1500, hidroxipropilmetilcelulose e metilcelulose por apresentarem diferentes propriedades aglutinantes. Os pellets foram obtidos pelo processo de extrusão/esferonização e secagem em leito fluidizado. Para avaliar a liberação do fármaco, empregou-se o método 3 da Farmacopeia Americana, também conhecido como Bio-Dis e o método preconizado pela mesma farmacopeia para comprimidos de paracetamol. Os pellets foram avaliados, ainda, com relação à granulometria, friabilidade, densidade verdadeira e teor. Os resultados indicaram que os diferentes aglutinantes empregados são capazes de afetar a produção e algumas das características físico-químicas dos pellets e o ensaio de dissolução revelou que as formulações comportam-se como produtos de liberação imediata. Os pellets obtidos apresentaram características de liberação favoráveis para a obtenção de comprimidos de liberação instantânea. O aparato 3 da Farmacopeia Americana demonstrou ser um método com melhor capacidade discriminatória entre as formulações, quando comparado com o método da cesta.

Environmental and health hazard ranking and assessment of plastic polymers based on chemical composition.

Plastics constitute a large material group with a global annual production that has doubled in 15 years (245 million tonnes in 2008). Plastics are present everywhere in society and the environment, especially the marine environment, where large amounts of plastic waste accumulate. The knowledge of human and environmental hazards and risks from chemicals associated with the diversity of plastic products is very limited. Most chemicals used for producing plastic polymers are derived from non-renewable crude oil, and several are hazardous. These may be released during the production, use and disposal of the plastic product. In this study the environmental and health hazards of chemicals used in 55 thermoplastic and thermosetting polymers were identified and compiled. A hazard ranking model was developed for the hazard classes and categories in the EU classification and labelling (CLP) regulation which is based on the UN Globally Harmonized System. The polymers were ranked based on monomer hazard classifications, and initial assessments were made. The polymers that ranked as most hazardous are made of monomers classified as mutagenic and/or carcinogenic (category 1A or 1B). These belong to the polymer families of polyurethanes, polyacrylonitriles, polyvinyl chloride, epoxy resins, and styrenic copolymers. All have a large global annual production (1-37 million tonnes). A considerable number of polymers (31 out of 55) are made of monomers that belong to the two worst of the ranking model's five hazard levels, i.e. levels IV-V. The polymers that are made of level IV monomers and have a large global annual production (1-5 million tonnes) are phenol formaldehyde resins, unsaturated polyesters, polycarbonate, polymethyl methacrylate, and urea-formaldehyde resins. This study has identified hazardous substances used in polymer production for which the risks should be evaluated for decisions on the need for risk reduction measures, substitution, or even phase out.

Zooxanthellamide D, a polyhydroxy polyene amide from a marine dinoflagellate, and chemotaxonomic perspective of the Symbiodinium polyols.

A long-chain polyhydroxy polyene amide, zooxanthellamide D (ZAD-D, 1, C54H83NO19), was isolated from a cultured marine dinoflagellate of the genus Symbiodinium. ZAD-D (1) is a polyhydroxy amide consisting of a C22-acid part and a C32-amine part and furnishes three tetrahydropyran rings and six isolated butadiene chromophores. The relative stereochemistry of the tetrahydropyran ring systems was elucidated by NMR techniques. This metabolite showed moderate cytotoxicity against two human tumor cell lines. A phylogenetic tree of Symbiodinium has been updated and compared with the structures of the hitherto isolated polyols of Symbiodinium, zooxanthellatoxins and zooxanthellamides, providing a promising chemotaxonomic perspective for the classification of this morphologically indistinguishable dinoflagellate.

Preparation of redispersible dry nanocapsules by means of spray-drying: development and characterisation.

Nanoparticles suspensions very often present a physicochemical instability during their storage. In order to overcome this lack of stability and facilitate the handling of these colloidal systems, the water elimination from the aqueous dispersions to obtain a dry solid form appears as the most promising strategy. The present paper reports the use of the spray-drying technique for the nanocapsules (NC) suspensions conversion into redispersible dried solid particles in presence of different water-soluble excipients as drying auxiliaries. Following the combination of additives solutions with NC suspension, the final dispersion homogeneity was favoured, avoiding phase separations. According to the size measurement after a simple atomisation experiment, the NC, which have a thin and fragile shell structure can withstand the shear forces developed for the feed disintegration in droplets. During drying, certain additives molecules are able to act as NC protectors. The physicochemical characterization of the spray-dried powders included an investigation of their properties, such as residual moisture content, particulate density, morphology and redispersion in water. Using a NC concentration of 1% (w/v), the best result was obtained with the preparation containing 10% (w/v) of lactose which led to more desirable powder morphology and favouring NC suspension reconstitution with only approximately 2% of the size distribution in the micrometer range. The spray-drying technique is an attractive method to improve the NC conservation and facilitate future handling.

Pattern recognition for the analysis of polymeric materials.

A new method of polymer classification is described involving dynamic mechanical analysis of polymer properties as temperature is changed. The method is based on the chemometric analysis of the damping factor (tan delta) as a function of temperature. In this study four polymer groups, namely, polypropylene, low density polyethylene, polystyrene and acrylonitrile-butadiene-styrene, each characterised by different grades, were studied. The aim is to distinguish polymer groups from each other. The polymers were studied over a temperature range of -50 degrees C until the minimum stiffness was reached, tan delta values were recorded approximately every 1.5 degrees . Principal components analysis was performed to visualise groupings and also for feature reduction prior to classification and clustering. Several clustering and classification methods were compared including k-means clustering, hierarchical cluster analysis, linear discriminant analysis, k-nearest neighbours, and class distances using both Euclidean and Mahalanobis measures. It is demonstrated that thermal analysis together with chemometrics provides excellent discrimination, representing a new approach for characterisation of polymers.

Influência do agente de união na resistência ao cisalhamento da interface titânio/polímero de vidro / Bonding agent influence on shear bond strength of titanium/polyglass interface

Há poucas informações em relação à efetividade da união entre compósitos e superfícies metálicas. Este estudo avaliou a influência de dois agentes de união na resistência ao cisalhamento da interface formada pelo titânio comercialmente puro (Ti cp) e um compósito (Artglass/ Heraeus Kulzer). Vinte estruturas metálicas (4mm de diâmetro e 5mm de altura) de titânio grau 1 foram fundidas, jateadas com partículas de óxido de alumínio (250µm) e separadas em dois grupos. Para cada grupo foi utilizado um agente de união (Sistema Siloc-Pre ou Retention Flow) como procedimento anterior à aplicação do material opaco. Sobre este foram aplicados camadas do polímero referente à dentina com o auxílio de uma matriz de teflon. A manipulação e polimerização foram realizadas de acordo com as recomendações do fabricante. Os corpos-de-prova foram armazenados em água destilada por 24 horas à 37ºC e termociclados (5º e 55ºC/ 500ciclos). O teste de resistência ao cisalhamento foi realizado em uma máquina de ensaios universal (Instron) com velocidade de 5mm/min. Os dados foram tratados estatisticamente pela Análise de Variância one-way (a=0,5). Os resultados indicaram que o sistema adesivo Retention Flow foi estatisticamente melhor do que o Siloc, com médias de 20,74MPa e 11,65MPa, respectivamente. Foi possível concluir que o sistema de união influenciou na adesão entre o titânio grau I e o polímero de vidro estudado.

Evaluation of the anti-oxidative effect (in vitro) of tea polyphenols.

Forty-three polyphenols from tea leaves were evaluated for their anti-oxidative effect against lipid peroxidation by the ferric thiocyanate method in vitro. Among these, 1,4,6-tri-O-galloyl-beta-D-glucose (hydrolyzable tannin) showed the highest anti-oxidative activity against lipid peroxidation, even stronger than that of 3-tert.-butyl-4-hydroxyanisole (BHA). The assay demonstrates that tea polyphenols, except for desgalloylated dimeric proanthocyanidins that possess a catechin structure in the upper unit and desgalloylated flavan-3-ols, and excepting theaflavin 3,3'-di-O-gallate, had more anti-oxidative activity than that of alpha-tocopherol. The chemical structure-activity relationship shows that the anti-oxidative action advanced with the condensation of two molecules of flavan-3-ols as well as with 3-O-acylation in the flavan skeleton such as that by galloyl, (3'-O-methyl)-galloyl, and p-coumaroyl groups.

Inherently conducting polymer nanostructures.

Inherently conducting polymers (ICPs) have been an area of intense interest over the past 30 years, culminating with the award of the 2000 Nobel Prize in Chemistry to MacDiarmid, Heeger and Shirakawa. More recently the unique properties of these materials (e.g., higher conductivity, more rapid discrete electrochemical switching processes) apparent at the nanodimension have become accessible. Significant breakthroughs in synthesis and fabrication of inherently conducting polymers with nanodimensional control have made this possible. This review aims to discuss some of the synthetic approaches researchers have made in an attempt to probe the nano domain as well as some of the property enhancements afforded to these structures.

Compómero: ¿vidrio ionomérico modificado con resina o resina modificada con vidrio ionomérico?: revisión de la literatura / Compomer: resin-modified glass ionomer or glass ionomer-modified composite resin?

Quizás ningún otro material ha experimentado tantas modificaciones desde su presentación como el vidrio ionomérico. Este cemento ha presentado modificaciones no sólo en su composición y estructura original, sino también en sus indicaiciones y sus aplicaciones clínicas, lo que ha traído como consecuencia confusión cuando se habla de vidrio ionomérico, compómero o de cualquiera otra modificación realizada a dicho material. El cemento de vidrio ionomérico es un cemento de reacción ácido-base, siendo el ácido un homopolímero o copolímero de ácidos alquenoicos. El componente básico es un aluminio silicato de vidrio que contiene flúor. La introducción de las versiones modificadas con resina representan un intento más reciente de obtener algunas mejoras sobre las desventajas de los vidrios ionoméricos convencionales. La modificación implica grupos acrilatos en la parte poliácida del cemento convencional. La reacción de establecimiento ácido-base del cemento de vidrio ionomérico es suplementada por una reacción de polimerización de la resina de los monómeros como el HEMA y el bis-GMA o de cadenas sobre la molécula de poliácidos iniciada por la luz visible. El primer compómero comercialmente disponible estaba combinado con un imprimador de autograbado, que contenía un promotor de adhesión basado en la acetona con un componente activo PENTA (ácido ésterdipentaericitol pentacrilato fosfórico) y monómeros dimetacrilatos elastoméricos e iniciadores. El contenido restaurativo polimerizable ácido y otros monómeros como UDMA y resina TCB (un biéster de 2 HEMA y ácido tetracarboxílico butano) y vidrio de sodiofluorurosilicato de aluminio estroncio. En consecuencia, los compómeros constituyen un grupo de materiales sin relación con los vidrios ionoméricos; los compómeros no son vidrios ionoméricos, sino resinas reforzadas fotopolimerizables con algunas diferencias respecto a las resinas tradicionales. La terminología de algunas de las combinaciones de vidrio ionomérico/resina más nuevas es muy contradictoria y confusa. En esta revisión se han conseguido términos diferentes para agentes de cementación y materiales restauradores con una combinación de vidrio ionomérico y la química de la resina entre los cuales se incluye al compómero

Dietary intake and bioavailability of polyphenols.

The main dietary sources of polyphenols are reviewed, and the daily intake is calculated for a given diet containing some common fruits, vegetables and beverages. Phenolic acids account for about one third of the total intake and flavonoids account for the remaining two thirds. The most abundant flavonoids in the diet are flavanols (catechins plus proanthocyanidins), anthocyanins and their oxidation products. The main polyphenol dietary sources are fruit and beverages (fruit juice, wine, tea, coffee, chocolate and beer) and, to a lesser extent vegetables, dry legumes and cereals. The total intake is approximately 1 g/d. Large uncertainties remain due to the lack of comprehensive data on the content of some of the main polyphenol classes in food. Bioavailability studies in humans are discussed. The maximum concentration in plasma rarely exceeds 1 microM after the consumption of 10-100 mg of a single phenolic compound. However, the total plasma phenol concentration is probably higher due to the presence of metabolites formed in the body's tissues or by the colonic microflora. These metabolites are still largely unknown and not accounted for. Both chemical and biochemical factors that affect the absorption and metabolism of polyphenols are reviewed, with particular emphasis on flavonoid glycosides. A better understanding of these factors is essential to explain the large variations in bioavailability observed among polyphenols and among individuals.

Biochemical changes associated with the adaptive response of human keratinocytes to N-methyl-N'-nitro-N-nitrosoguanidine.

Exposure of cells to low doses of radiation or chemicals renders them more resistant to higher doses of these agents. This phenomenon, termed adaptive response, was studied in quiescent human keratinocytes exposed to the alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). The cells were adapted with 2.5 nM MNNG for 60 min and challenged immediately thereafter with 2.5 microM MNNG for 30, 45 or 60 min. Clonogenic survival studies revealed that adapted cells were more resistant to the subsequent challenge treatment (up to 30% higher survival) than unadapted cells. In addition, formation of DNA strand breaks was lower in adapted cells. We monitored poly-ADP-ribosylation activity during expression of the adaptive response both at the substrate as well as the product level. NAD+ utilization in adapted and non-adapted cells exposed to the high dose of MNNG was similar, but recovery from NAD+ depletion was faster in low-dose pretreated cells. Induction of poly(ADP-ribose) formation was more than 2 times higher in low-dose adapted cells and this was associated with the formation of a distinct class of ADP-ribose polymers, i.e., branched polymers. These polymers exhibit a very high binding affinity for histones and can displace them from DNA. Elevated levels of poly(ADP-ribose) and, particularly, synthesis of branched polymers may play a critical role in low-dose adaptation.