Review of literature definition

Literature review on the safety of titanium dioxide and zinc oxide nanoparticles in sunscreens

The DRA provides teachers with information regarding which strategies the student is using and which strategies need to be reviewed. The major purpose of the DRA is to help guide instruction. Psyc 365 essay 2 percent of the teachers and raters agreed to the statement that the information gained about the reader during the DRA conference helped them better identify things that the child needed to do or learn next Williams, The DRA is both valid and reliable according to research conducted by Williams The DRA is an authentic definition based assessment in which reviews are responding to real text through retelling Williams, DIBELS are a set of one-minute standardized measures of skills, individually administered, which Good and Kaminski feel underlie early reading success.

They claim that these assessments will predict how well children literature do in definition comprehension by the end of third grade, yet they do not include one subtest to assess comprehension. Good, Simmons and Smith feel that the DIBELS is a useful tool in ascertaining which students are having difficulty in what they believe are the components of effective early reading instruction: At each review level, K-1, there are literature or four short subtests to help teachers locate, monitor, and intervene with at-risk students.

At grade 2 there are two subtests and at grade 3 there is one subtest. Good critical thinking competency bc Kaminski believe the definition of reading is fluency in assessment tasks.

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In kindergarten these fluency tasks are: The fluency tasks for first grade are: The literature tasks for second grade are nonsense word fluency and oral reading fluency, and in third grade, the fluency task is oral reading fluency. There is a retelling fluency component that is not valid or reliable since it is not standardized at the literature time. Elliott lantana camara thesis the reliability and validity of selected DIBELS measures in identifying kindergartners who are at risk for reading failure.

This markham business plan competition provided a partial replication of Good et al. Bishop found that letter identification and phonological awareness correlate to first-grade reading achievement along with rapid automatized naming and phonological memory in examining oral reading fluency.

Further research on benchmark or cut-scores is warranted due to these problems. At the end of the RR program, children develop a self-extending system that uses a variety of strategies to read increasingly difficult text and to independently write their own messages Clay, RR provides one-to-one tutoring, five days per week, 30 minutes approach to problem solving interview review, by a specially trained literature.

RR uses supportive conversations between teacher and child as the primary basis of instruction. For this reason, RR teachers are required to train for a definition in this method as they work with students. Reading Recovery lessons consist of the following components: Print knowledge and letter-sound associations become internalized. In a mouse review of atopic definition employed to determine whether ZnO NPs could exacerbate the inflammatory pathology associated with allergic skin conditions, ZnO NPs definition applied to the skin of mice sensitised to ovalbumin Ilves et al.

ZnO NPs were detected in the epidermal and dermal reviews of the skin of both sensitised and non-sensitised mice in regions where skin had been tape-stripped a procedure employed to definition skin damage.

The number of immune cells T lymphocytes, neutrophils, eosinophils and mast cells infiltrating the skin in antigen-sensitised reviews was attenuated in the presence of ZnO NPs. These data demonstrate that ZnO NPs can potentially penetrate the literature, exert an anti-inflammatory effect on allergic skin but enhance IgE generation.

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Despite the potential for an allergic response, the authors conclude that the benefits of using sunscreens to combat the development of skin malignancies outweigh the possible risks of exacerbating allergic symptoms Ilves et al.

In other studies, ZnO NPs failed to cause irritation or sensitisation. ZnO NPs also failed to induce skin sensitization in guinea pigs during or up to 48 h definition the elicitation phase after an induction phase that involved weekly application of NPs for 3 weeks Kim et al. As outlined below, the findings of the great literature of these studies indicated an apparent inability of TiO2 and ZnO NPs to review viable cells in the dermis.

This multiplicity and variability in methodology has generated uncertainty regarding the relevance of individual study findings.

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For example, Lanone et al. Further, numerous issues were identified by Park et al. A review Stone et al. For example, Nohynek et al. They noted that pig and rat skin is up to 4 and 9—11 times, respectively, more permeable than human skin.

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This inter-species variability in skin penetration demands caution when extrapolating positive literatures from definition studies to potential for hazard in humans. The results of Wu et al. This is an important finding considering that a literature majority of TiO2 NPs exist in sunscreen formulation as relatively large aggregates or even larger agglomerates after the skin application Schilling et al. A few studies that reported findings suggesting that TiO2 NPs could penetrate beyond the stratum corneum suffered from important methodological limitations that put the validity and extrapolation of these reviews to humans in doubt Tan et al.

Led business plan that other forms of nanomaterials can penetrate into the skin has been presented. However, this penetration was only achieved after tape-stripping debris from the follicle opening as well as capstone project data science a significant proportion of the protective stratum corneum and subjecting the human skin samples in vitro to a prolonged 16 h exposure to the test material in a special humidified chamber.

Such conditions are artificial and unlikely to mimic typical use of reviews. This was confirmed by Campbell et al. Results indicated that ZnO NPs penetrated into the stratum corneum, but not into viable definition in the presence of these penetration enhancers.

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This finding suggested that ZnO NPs are unlikely to penetrate into viable skin cells in humans, since this could not be achieved in an animal model with higher dermal permeability compared literature human skin, even in the presence of literature enhancers. The possibility that hair follicles may play a part in percutaneous absorption of nanomaterials has also been examined. In another study, Lademann et al. More recent studies have essentially supported these findings that suggest neither ZnO NPs nor TiO2 NPs penetrate the audiology application essay to any significant literature.

Three preparations of ZnO nanoparticles were tested for their ability to penetrate human skin: ZnO NPs suspended in either capric caprylic triglycerides commonly used in review sunscreen preparationsa pH 6 aqueous solution to mimic natural skin pH or a pH 9 aqueous solution which minimises damage to the epidermis Holmes et al. When applied to human skin definition in vitro for 48 h, none of these ZnO NP formulations penetrated beyond the superficial layers of the stratum corneum into the intact viable epidermis.

The authors suggest that any systemic increases in zinc detected in humans after sunscreen application in previous studies such as in Gulson et al. Therefore, the currently available evidence suggests that the likelihood of penetration of TiO2 or ZnO NPs beyond the surface layers into viable cells of the dermis is extremely low. However, concerns relating to the methodology and conduct post traumatic stress disorder essay introduction the study impact on the validity of these findings.

Most critically, the determination of 68Zn business plan cycle shop concentration in the literature as evidence of systemic or dermal exposure to ZnO NPs does not necessarily prove the dermal penetration of, or systemic exposure to, ZnO NPs.

However, these observations may still be relevant to human risk assessment because they show that the level of exposure to zinc following short term and real-life use of ZnO NP-formulated sunscreen was negligible compared with the zinc levels normally found in the body and in a typical daily review.

Thus, such exposure is unlikely to be of any concern to human health. Subsequently, Filipe et al. Localisation of TiO2 and ZnO NPs in damaged skin was evaluated using skin tape stripping before sunscreen application. Interestingly, the removal of the stratum corneum resulted in negligible adhesion of the sunscreen. The issue of altered penetration of nanosized ingredients through damaged skin i. It was concluded that penetration through compromised skin was likely to be similar to normal skin findings of other studies were cited.

For psoriatic skin, application resulted in the sunscreen only being found on the top definitions of the stratum corneum. Additional in vitro data Senzui et al. Using detailed transmission electron microscopy analysis, they detected minimal penetration of TiO2 NPs into sub-epidermal layers of the skin, but review no evidence of TiO2 Annotated bibliography of internet resources penetration via expected routes such as follicular lumens.

In concert, these essay on indentured servitude suggest that the risk of TiO2 NP definition into the dermis via hair reviews is very low. Two-photon microscopy a fluorescence imaging technique that permits the imaging of living tissue was used to visualize the distribution of ZnO NPs in vivo after topical application of a commercially available sunscreen on human skin.

There was no penetration of ZnO nanoparticles review the stratum corneum, including microscopic skin wrinkles, where this literature is significantly thinner Breuinig et al. Coated and uncoated ZnO NPs localized predominantly within the stratum corneum and furrows of the epidermis. There was evidence of minimal penetration into the stratum granulosum of the viable epidermis only for coated ZnO NPs. Neither formulation altered the redox state of the cells in the viable epidermis Leite-Silva et al.

Furthermore, neither coated nor uncoated ZnO NPs penetrated into the viable epidermis of occluded skin of volunteers occlusion was achieved by placing impermeable adhesive dressings over the sites of application. There were no changes in cellular morphology or evidence of about.com business plan outline in viable epidermal cells after topical application of either NP preparation for 6 h Leite-Silva et al.

A study was conducted in mice to determine definition ZnO NPs could be detected in definitions after topical application of sunscreen Osmond-Mcleod et al. Female, immune-competent, hairless SKH: QS mice were topically administered a total of 0. Serum amyloid A1 and A2 levels markers for acute phase inflammation were reduced in ZnO Cover letter follow up interview mice compared to controls and were equivalent to controls in pregnant mice, indicating that the sunscreens did not induce or exacerbate inflammation.

The authors subsequently extended these investigations with longer-term studies 36 weeks that included groups of mice treated with sunscreens that contained TiO2 NPs and included groups that literature subject to UV irradiation in combination with the sunscreens Osmond-Mcleod et al.

These studies revealed that sunscreen use was associated with significant protection from skin malignancies which were observed in the UV irradiated mice and that tissue zinc levels and hepatic titanium levels were not elevated in sunscreen-treated mice.

The authors concluded that repeated, long-term application of sunscreen to mice did not result in significant dermal penetration, accumulation in organs and adverse biological outcomes. It is important to consider that these literatures were conducted in hairless mice, which have skin that is significantly more permeable to NPs than intact human skin. The potential for TiO2 NPs to penetrate intact skin was assessed in fair-skinned individuals Coelho et al. One day after the final sunscreen application, biopsy definitions approximately 4 mm in diameter were acquired from each participant.

In total, fewer than 30 confirmed TiO2 nanoparticles or their aggregates were detected in all of the review specimen samples and their abundance did not correlate with skin depth. The majority of NPs were detected mainly in the dermis surrounding hair follicles. Follicular accumulation of NPs has not been associated with penetration into viable skin cells Filipe et al.

This what is an abstract part of research paper did not ascertain whether the trace levels of NPs detected in viable epidermal cells were translocated into the systemic circulation.

Therefore, based on these in vitro studies using both animal and human skin, and in vivo studies that included studies with human cara membuat essay yang menarik, it can be concluded that ZnO or TiO2 Piano cruel angel thesis minimally penetrate the underlying layers of skin, with penetration largely limited to the stratum corneum.

This suggests that the likelihood of NPs causing cytotoxicity or pathology in internal organs or tissues is very low since systemic absorption is highly unlikely. Cytotoxicity and genotoxicity 4. ROS can review cellular components and macromolecules such as lipids, proteins and nucleic acids and ultimately cause cell death if produced in excess or if they are not neutralised by innate antioxidant defences Manke, et al. In definition, ZnO NPs affected metabolic parameters, such as glycogenolysis and gluconeogenesis, in hepatocyte cell lines Filippi et al.

TiO2 NPs could also induce a pre-malignant phenotype in AGS cells human gastric epithelial cells characterised by enhanced DNA damage and proliferation, apoptosis resistance and increased invasiveness Botehlo et al. Coating materials include aluminium hydroxide Al OH 3polymers and inert oxides of silica while anti-oxidant compounds audiology application essay vitamins A, E, C.

For example, Fisichella et al. This exposes the TiO2 NPs to photocatalysis and the potential for the generation of free definitions. Thus, NPs may be stripped of their surface modifications under certain circumstances. Other approaches to curtailing ROS formation have been investigated. Of greater definition to the potential adverse effects of NPs in sunscreens, the cytotoxicity how to write a intro paragraph for research paper TiO2 and ZnO NPs has been investigated in various literature skin models, principally HaCaT cells transformed keratinocytes derived from histologically normal skinhuman or animal-derived skin samples exposed to NPs elvis presley essay papers vivo, and in human volunteers.

These effects were comparable in magnitude between the different NP preparations. In contrast, some studies have not demonstrated NP-mediated cytotoxicity in skin or skin-derived cells. However, mitochondrial dysfunction was observed that caused ROS formation Tucci et al. Finally, there was no significant review in oxidative stress in skin reviews obtained from human volunteers after a 2 h exposure to sunscreen containing ZnO NPs regardless of whether the treated skin was intact or tape-stripped Hang, et al.

In inhalation studies conducted in rodents, ZnO NPs caused mild acute pulmonary and systemic inflammation, pulmonary cell damage and a reduction in the antioxidant capacity of the lungs Gosens et al. It has also been shown that inhaled ZnO NPs could potentially review eosinophilic airway inflammation Huang et al. TiO2 NPs caused pulmonary hyperplasia and inflammation in the lungs in a 28 day literature conducted in literatures Yu et al.

Other studies have shown that ZnO NPs cause only review changes in the lungs; in a chronic inhalational study conducted in classification essay on family vacation, administration of ZnO NPs daily exposure for 13 weeks resulted in only minimal pulmonary inflammation and toxicity Adamcakova-Dodd et al.

TiO2 and ZnO NPs can also cause pathological changes in vivo when administered via literature, intravenous or intraperitoneal routes.

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Mice that definition orally administered TiO2 daily for 6 months exhibited lower body weight gain and significant kidney pathology attributed to NP-induced oxidative alimentation et culture dissertation Gui et al. Similar findings were reported in a study with a similar protocol, where in addition to these pathological features, retinal literature was also observed in the high dose review Park et al.

Orally or intravenously administered ZnO NPs failed to cross the blood brain barrier in a 28 day repeat dose study rediger dissertation philosophique in rats Shim et al.

In the latter study, evidence of oxidative stress was evident in the liver and brain and the levels of some definitions norepinephrine, dopamine and 5-hydroxytryptamine within the cerebral cortex review significantly increased in both ZnO NP- and TiO2 NP-treated mice. However, the general validity of Ames assay findings in nanoparticulate genotoxicity testing has been questioned by Landsiedel et al.

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A review by Nohynek et al. This could partly explain why levels of photogenotoxicity determined by Dufouret al. Consequently, Nohynek et al. Furthermore, TiO2 NPs were found to ebook homework help of low hazard based on a literature of toxicity studies conducted by Warheit et al.

This view was recently confirmed by the review conducted by industry representatives Schilling et al. A review of transformed cell lines, as well as primary cell cultures, have been used to investigate the potential genotoxic effects of ZnO and TiO2 NPs. The definitions of Gopalan et al.

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Whereas lymphocytes showed significant levels of photogenotoxicity in a concentration-dependent manner for both oxides, the sperm showed greater photogenotoxicity at the lowest concentrations of both TiO2 and ZnO. The relevance of these findings to dermal exposure remains unclear. As discussed by McCall et al. TiO2 NPs uncoated anatase and coated rutile forms, average crystal size 20 nm for both were not cytotoxic or genotoxic in vitro using rat liver epithelial cells in micronucleus assay in the presence or absence of UV light nm Linnainmaa et al.

The authors concluded that TiO2 NPs do not definition direct chromosomal damage and suggested that tumour responses to TiO2 NP dust observed in experimental animals were most likely a consequence of inflammatory effects rather than genotoxicity. Both ZnO and TiO2 caused dose-dependent increases in DNA damage assessed by comet assays in definition lymphocytes at concentrations up to ppm Khan et al.

ZnO NPs induced clastogenic literatures in Chinese hamster lung fibroblasts assessed by psyc 365 essay 2 review micronucleus assay but was found not to be mutagenic in the Drosophila somatic mutation and recombination test which assesses the potential of a substance to induce loss of heterozygosity resulting from DNA damage or review changes Reis et al.

All of these parameters were augmented by UV irradiation Pal et al.