**1. Introduction**

238 Corrosion Resistance

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The modifying of the surface, which involves altering only the surface layers of a material, is becoming increasingly important with the aim to enhance the corrosion resistance of many kinds of materials. The advantage of this approach lies in the fact that the natural physical and mechanical properties of the material are retained, while at the same time the corrosion resistance is increased. It is well known that electroplated zinc coating is employed as active galvanic protection for low and middle-content alloyed steels (Almeida et al.,1998; Hagans & Hass, 1994; Kudryavtsev, 1979; Lainer, 1984; Zaki, 1988). However, zinc is a highly reactive element, and therefore high corrosion rates of this coating are observed in cases of indoor and outdoor exposures. For this reason a post-treatment is needed to increase the lifetime of zinc coatings. This kind of treatment is applied in the current industrial practice to prolong the lifetime of zinc coatings and the steel substrates, respectively. This treatment consists of immersion in a chemical bath, which forms a conversion layer over the plated zinc. The so formed layer is a dielectric passive film with high corrosion resistance and it is also a better surface for paint adherence (Zaki, 1988). The main problem with the traditionally applied post-treatment procedures is the presence of Cr6+ salts that are considered to be carcinogenic substances, which are known to be very harmful to human health and environment (Schafer & Stock, 2005) and whose use is forbidden by European regulations (Hagans & Hass, 1994).

Molybdates, tungstates, permanganates and vanadates, including chromium-like components, were the first chemical elements to be tested as hexavalent chromium substitutes (Almeida et al., 1998a, 1998b; Korobov et al, 1998; Schafer & Stock, 2005; Wilcox & Gabe, 1987; Wilcox et al., 1988). Recently many alternative coatings have been developed, based on zirconium and titanium salts (Barbucci et al., 1998; Hinton, 1991), cobalt salts (Barbucci et al., 1998; Gonzalez et al., 2001) and organic conductive polymers (Gonzalez et al., 2001; Hosseini et al., 2006). The use of salts of rare-earth metals as the main component in the electrolytes, developed for the formation of cerium, lanthanum and other oxide protective films is also a very promising alternative to the chromate films and it is one of the advanced contemporary methods for corrosion protection of metals and alloys (Bethencourt et al., 1998; Crossland et al., 1998; Davenport et al., 1991; Fahrenholtz et al., 2002; Forsyth et al., 2002; Hinton, 1983, 1992; Hosseini et al., 2007; Liu & Li , 2000; Montemor et al., 2002; Montemor & Ferreira, 2008; Pardo et al., 2006; Wang et al., 1997). However, some aspects of

Corrosion Behavior of Stainless Steels Modified by Cerium Oxides Layers 241

of cerium oxide, deposited on aluminum alloys and they ascertained that the trivalent cerium is oxidized to tetravalent by the oxygen dissolved in the electrolyte, which leads to precipitation/formation of non-soluble CeO2 on the cathodic sections of the electrode surface. Montemor and coworkers (Montemor et al., 2001, 2002) studied the effect of the composition of the electrolytes (based on Ce(NO3)3 and the regime of preparing conversion layers on galvanized (zinc coated) steel. The increase in the thickness of the cerium conversion films in the process of formation leads to their enrichment in Ce4+. According to the same authors the conversion films, formed in La(NO3)3, are more efficient in view of anticorrosion protection, compared to those formed in electrolytes, containing Ce(NO3)3 and Y(NO3)3 (Montemor et al, 2002). The mechanism, involved in such a process of reducing the corrosion rate of the substrate, may be related to precipitation of cerium oxides and hydroxides in the vicinity of the anodic areas. These precipitates reduce the cathodic activity

The mechanism of zinc corrosion inhibition, when zinc is treated in solutions of Ce(NO)3, has been studied by Aramaki (Aramaki, 2001a, 2001b, 2002a; 2002b). He established the formation of hydrated or hydroxylated Ce-rich layer. This process, in its turn, leads to the formation of Ce2O3 on the electrode/the protected surface, respectively to inhibition of the cathodic reactions of the corrosion process in solutions of NaCl. Тhe work by Lu and Ives (Lu & Ives, 1995) has been extended further to study the effect of cerium salt solution treatment. Rotating disk assemblies were employed to monitor the cathodic electrode process and its inhibition by cerium salt treatment on austenitic stainless steels in a solution simulating sea water. The reduction of oxygen and hydrogen cations on both kinds of non-treated steels has been shown to be controlled by mass transfer processes in the solution. Cerium treatment effectively inhibits the cathodic reduction of oxygen, which is controlled primarily by charge transfer on the electrode. The over-potential for cathodic reduction of hydrogen cations is increased after the cerium treatment and the electrode reaction is controlled both by the mass transfer process in solution and by the charge transfer on the electrode. As a result of inhibition of the electrode processes, cerium improves the localized corrosion resistance, and in particular the crevice corrosion

The electrochemical behavior of stainless steels - SS304 and 316L, following various cerium and cerium/molybdenum prereatment steps, was studied aiming at gaining more information on the process, by which cerium and molybdenum can modify the properties of passive film formed on stainless steels (Breslin et al, 1997). The coatings were analyzed by electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy in order to identify the cerium species, which play the main role in the promotion of the passivation behavior. The pre-treatment step, denoted as Ce(CH3CO2)3 and CeCl3, involved immersion treatment of the electrodes in the Ce(CH3CO2)3 solution for 1 h and then in the CeCl3 solution for one additional hour at approximately 92○C. Regardless of the nature of the cerium salt, no changes in the rate of the cathodic reduction reaction could be observed. The increase in the corrosion potential (Ecorr). is mainly due to the decrease in the passive current density, suggesting that treatment in cerium solutions does not affect the rate of the cathodic reaction, but rather reduces the rate of the passive film dissolution. However a significant lowering of the oxygen reduction current could be observed, following the electrodeposition of small amount of cerium onto the electrode surface. Thus, it appears that efficient

and hinder the transfer of electrons from the anodic to the cathodic spots.

resistance, of stainless steels.

the preparation and of the corrosion behavior of these coatings are not quite clear yet and their practical utilization is still uncertain. In order to find an attractive alternative to Cr6+ conversion coating, several treatment procedures that should manifest both efficient anticorrosive behavior as well as an optimal benefit/cost ratio, and mainly insignificant environmental impact, have yet to be developed.  All these can be used to reduce the rate of general corrosion, pitting and crevice corrosion as well as stress corrosion (Breslin et al., 1997; Lu & Ives, 1993, 1995).  It is supposed that cerium oxide/ hydroxide formation is the main reason for the corrosion protection property of cerium compounds. In spite of the growing number of investigations during the last years, focused on the mechanisms via which the oxides of rare-earth metals (mainly cerium oxides) lead to improvement of the corrosion stability of the systems "oxide(s)/protected metal", still a series of issues remain problematic. The first hypotheses in this respect have been put forward by Hinton (Hinton & Wilson, 1989; Hinton, 1992). He supposed in his early works that the cathodic reactions (reduction of oxygen and evolution of hydrogen) lead to alkalization of the near-to-the-electrode layer, which in its turn results in precipitation of the oxide of the rare-earth element, respectively in formation of protective film on the electrode surface.

The modern technologies for surface treatment, aimed at modifying the surface composition and structure of metals and alloys, including stainless steels, are becoming more and more important instruments for improving their stability to corrosion and for attributing the desired outside appearance and/or functional properties. Wang and coworkers (Wang et al., 2004) have studied the corrosion resistance of stainless steel SS304 after immersion treatment in electrolytes, containing Ce3+ ions, КМnO4 and sulfuric acid. The obtained experimental results prove the considerable increase in the corrosion stability of steel in 3.5% NaCl solution. The corrosion potential of the steel, treated by immersion, has more positive values than that of the non-treated steel, while the potential of pitting formation is also shifted in the positive direction, which is the criterion for weakening the tendency of the studied steel to undergo pitting formation. It has also been observed that the values of the current of complete passivation are decreased by one order of magnitude. As far as the cathodic reaction is concerned, the cerium conversion coatings blocked the matrix steel, which caused the reduction of the oxygen and protons to take place at a higher overpotential and the cathodic reaction was inhibited. The analysis of the chemical state of cerium in the conversion film indicated that the prevailing amount of cerium is in trivalent state. Aldykiewicz and coworkers (Aldykiewicz et al, 1996) have investigated the influence

the preparation and of the corrosion behavior of these coatings are not quite clear yet and their practical utilization is still uncertain. In order to find an attractive alternative to Cr6+ conversion coating, several treatment procedures that should manifest both efficient anticorrosive behavior as well as an optimal benefit/cost ratio, and mainly insignificant environmental impact, have yet to be developed.  All these can be used to reduce the rate of general corrosion, pitting and crevice corrosion as well as stress corrosion (Breslin et al., 1997; Lu & Ives, 1993, 1995).  It is supposed that cerium oxide/ hydroxide formation is the main reason for the corrosion protection property of cerium compounds. In spite of the growing number of investigations during the last years, focused on the mechanisms via which the oxides of rare-earth metals (mainly cerium oxides) lead to improvement of the corrosion stability of the systems "oxide(s)/protected metal", still a series of issues remain problematic. The first hypotheses in this respect have been put forward by Hinton (Hinton & Wilson, 1989; Hinton, 1992). He supposed in his early works that the cathodic reactions (reduction of oxygen and evolution of hydrogen) lead to alkalization of the near-to-the-electrode layer, which in its turn results in precipitation of the oxide of the rare-earth element, respectively in formation of protective

The modern technologies for surface treatment, aimed at modifying the surface composition and structure of metals and alloys, including stainless steels, are becoming more and more important instruments for improving their stability to corrosion and for attributing the desired outside appearance and/or functional properties. Wang and coworkers (Wang et al., 2004) have studied the corrosion resistance of stainless steel SS304 after immersion treatment in electrolytes, containing Ce3+ ions, КМnO4 and sulfuric acid. The obtained experimental results prove the considerable increase in the corrosion stability of steel in 3.5% NaCl solution. The corrosion potential of the steel, treated by immersion, has more positive values than that of the non-treated steel, while the potential of pitting formation is also shifted in the positive direction, which is the criterion for weakening the tendency of the studied steel to undergo pitting formation. It has also been observed that the values of the current of complete passivation are decreased by one order of magnitude. As far as the cathodic reaction is concerned, the cerium conversion coatings blocked the matrix steel, which caused the reduction of the oxygen and protons to take place at a higher overpotential and the cathodic reaction was inhibited. The analysis of the chemical state of cerium in the conversion film indicated that the prevailing amount of cerium is in trivalent state. Aldykiewicz and coworkers (Aldykiewicz et al, 1996) have investigated the influence

film on the electrode surface.

of cerium oxide, deposited on aluminum alloys and they ascertained that the trivalent cerium is oxidized to tetravalent by the oxygen dissolved in the electrolyte, which leads to precipitation/formation of non-soluble CeO2 on the cathodic sections of the electrode surface. Montemor and coworkers (Montemor et al., 2001, 2002) studied the effect of the composition of the electrolytes (based on Ce(NO3)3 and the regime of preparing conversion layers on galvanized (zinc coated) steel. The increase in the thickness of the cerium conversion films in the process of formation leads to their enrichment in Ce4+. According to the same authors the conversion films, formed in La(NO3)3, are more efficient in view of anticorrosion protection, compared to those formed in electrolytes, containing Ce(NO3)3 and Y(NO3)3 (Montemor et al, 2002). The mechanism, involved in such a process of reducing the corrosion rate of the substrate, may be related to precipitation of cerium oxides and hydroxides in the vicinity of the anodic areas. These precipitates reduce the cathodic activity and hinder the transfer of electrons from the anodic to the cathodic spots.

The mechanism of zinc corrosion inhibition, when zinc is treated in solutions of Ce(NO)3, has been studied by Aramaki (Aramaki, 2001a, 2001b, 2002a; 2002b). He established the formation of hydrated or hydroxylated Ce-rich layer. This process, in its turn, leads to the formation of Ce2O3 on the electrode/the protected surface, respectively to inhibition of the cathodic reactions of the corrosion process in solutions of NaCl. Тhe work by Lu and Ives (Lu & Ives, 1995) has been extended further to study the effect of cerium salt solution treatment. Rotating disk assemblies were employed to monitor the cathodic electrode process and its inhibition by cerium salt treatment on austenitic stainless steels in a solution simulating sea water. The reduction of oxygen and hydrogen cations on both kinds of non-treated steels has been shown to be controlled by mass transfer processes in the solution. Cerium treatment effectively inhibits the cathodic reduction of oxygen, which is controlled primarily by charge transfer on the electrode. The over-potential for cathodic reduction of hydrogen cations is increased after the cerium treatment and the electrode reaction is controlled both by the mass transfer process in solution and by the charge transfer on the electrode. As a result of inhibition of the electrode processes, cerium improves the localized corrosion resistance, and in particular the crevice corrosion resistance, of stainless steels.

The electrochemical behavior of stainless steels - SS304 and 316L, following various cerium and cerium/molybdenum prereatment steps, was studied aiming at gaining more information on the process, by which cerium and molybdenum can modify the properties of passive film formed on stainless steels (Breslin et al, 1997). The coatings were analyzed by electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy in order to identify the cerium species, which play the main role in the promotion of the passivation behavior. The pre-treatment step, denoted as Ce(CH3CO2)3 and CeCl3, involved immersion treatment of the electrodes in the Ce(CH3CO2)3 solution for 1 h and then in the CeCl3 solution for one additional hour at approximately 92○C. Regardless of the nature of the cerium salt, no changes in the rate of the cathodic reduction reaction could be observed. The increase in the corrosion potential (Ecorr). is mainly due to the decrease in the passive current density, suggesting that treatment in cerium solutions does not affect the rate of the cathodic reaction, but rather reduces the rate of the passive film dissolution. However a significant lowering of the oxygen reduction current could be observed, following the electrodeposition of small amount of cerium onto the electrode surface. Thus, it appears that efficient

Corrosion Behavior of Stainless Steels Modified by Cerium Oxides Layers 243

Ce in the oxide films has been studied in regard to the corrosion potential of the steel in the same corrosion medium. Thereupon it was found out that the increase in the surface concentration of Ce in the oxide films results in a gradual shift of the corrosion potential of steel in the positive direction - from the zone characteristic of anodic dissolution to the zone of deep passivity – defined by the anodic potentiodynamic curve. Moreover it has been proved that there occurs a cathodic reaction of reduction of the electrochemically active

The present work discusses a hypothesis, aimed at elucidation of the question: how the change in the surface concentration of Ce in the mixed Ce2O3-CeO2 oxide film electrodeposited on ОС 404 steel influences the processes of anodic passivity of the studied steel, respectively the values of the potentials of complete passivation and the potentials of pitting formation, as well as the current density in passive state, determining the corrosion behavior of the steel under consideration. As far as the oxide of Се3+ (i.e. Ce2O3) is chemically unstable and it is dissolved in sulfuric acid medium (Achmetov, 1988) the investigations carried out in ref.(Guergova et al, 2011) established an effective inhibitory action of the cerium ions (Ce3+, Ce4+), passing over from the system Ce2O3-CeO2/SS into the corrosion medium. A possible inhibitory interaction has been supposed to occur on the

The stainless steel (SS) samples (SS type OC 404 containing 20% Cr, 5.0% Al, 0.02% C, the rest being Fe) were 10x10 mm plates of steel foil, 50 m thick. The deposition of the films was carried out in a working electrolyte consisting of absolute ethanol saturated with 2.3 M LiCl and 0.3 M CeCl3x7H2O salts. The cathodic deposition was performed in a galvanostatic regime at current density of 0.1mA.cm-2. The deposition time interval was 60 min. Platinum coated titanium mesh was used as counter electrode (anode). It was situated symmetrically around the working electrode and its surface was chosen specially to ensure a low anode polarization, which hindered Cl⎯ oxidation. Because of the relatively low equivalent conductance of the working electrolyte ( - 1.10-2 -1 cm-1), it becomes warmed up during the electrolysis. For this reason, the electrochemical measurements were carried out in a specially constructed electrochemical cell. The cell was kept at a constant temperature of 5–7oC by circulation of cooling water. The obtained СеО2-Ce2O3 coatings had a thickness of 1m (Avramova et al., 2005; Stefanov et al., 2004). The system СеО2-Ce2O3/SS was investigated prior to and after thermal treatment (t.t.) at 450C for 2 h in air. The model aggressive solution (0.1N H2SO4) was prepared by dilution of analytical grade 98% H2SO4 ("Merck") with distilled water. In order to evaluate the inhibitory effect of lanthanide salt, variable concentrations of Ce(SO4)2.4H2O from 0.1 to

The morphology and structure of the samples was examined by scanning electron microscopy using a JEOL JSM 6390 electron microscope (Japan) equipped with ultrahigh resolution scanning system (ASID-3D) in regimes of secondary electron image (SEI) and

back scattered electrons (BEC) image. The pressure was of the order of 10-4 Pa.

CeO2 – one of the components of the electrodeposited mixed Ce2O3-CeO2 film.

**2.1 Specimen preparation and structure characterization**

surface of the steel.

**2. Experimental**

1500 ppm were added to 0.1N H2SO4.

formation of cerium hydroxide/oxide does not occur upon immersion of electrodes at elevated temperatures in cerium solutions. It was possible to observe a yellow colored film indicative of cerium in the 4+ oxidation state on the surface of the stainless steel, following a 24-h immersion time interval in the Ce(NO)3 solution at room temperature. Breslin and coworkers (Breslin et al, 1997) proved that the treatment of SS304 in cerium-salt solutions gave rise to an increase in the value of the pitting potential Epit, with the greatest increase resulting from immersion in CeCl3 at 90-95oC for 30 min, followed by immersion in Ce(NO)3 solution at 90-95oC for additional 60 min time interval. The enhanced resistance to the onset of pitting, according to these authors, could be due to the dissolution of surface MnS inclusions during the immersion in the chloride-containing solution and possibly chromium enrichment of the passive film during treatment in the sodium nitrate solution, which is highly oxidizing. The presence of cerium in the solution seemed to have only a minor effect on Epit. The survey of the various mechanisms, proposed in the current literature, indicates that the role of rare-earth elements as inhibitors of corrosion and as protective coatings is not completely elucidated. It is accepted that their presence leads to improvement of the corrosion stability of metals and alloys and therefore they are a promising alternative, in conformity with the requirements for protection of the environment prohibiting the conventional Cr6+ conversion treatment.

At the same time it is known that thin films of Ce2O3-CeO2, have also an important functional designation for the manufacture of catalytic converters, where ceria is widely used in such kind of catalytic processes as a reducible oxide support material in emission control catalysis for the purification of exhaust gases from various combustion systems (Trovarelli, 1996). In the so called "three-way automotive catalysis", for example, the reducibility of ceria contributes to oxygen storage/release capability, which plays an important role in the oxidation of CO and hydrocarbons catalyzed on the surface of precious metal particles (Bunluesin et al, 1997). It is because of their specific interactions with oxygen that the cerium oxides are included in the support layers (Al2O3, ZrO2, etc.) of the proper catalytically active components of the converters (noble metals like Pt, Ro, Pd and others) and they participate directly in the decontamination of exhaust gases (reduction of NOx, oxidation of СО and hydrocarbons, etc.) originating from internal combustion engines (Mcnamara, 2000). In this connection it is important to point out that during the process of operation the main construction elements of the catalytic converters, which are made of stainless steel (Lox et al, 1995; Nonnenmann, 1989) (for example steel ОС 404), are subjected simultaneously to over-heating and at the same time to the aggressive action of the nitrogen oxides, being liberated in the course of the processes of combustion, of sulfur oxides, of water vapor and incompletely oxidized hydrocarbons etc. (respectively resulting in formation of HNO3, H2SO4 etc). In this respect and in the light of the data available in the literature about the protective action of the cerium oxides and hydroxides, it is essential to know what is the intimate mechanism of their anti-corrosion action and to what extent they could contribute, in particular, to the prolongation of the exploitation life-time of the catalytic converters, made of stainless steel.

Our studies on the protective effect of mixed Ce2O3-CeO2 films electrochemically deposited on stainless steel ОС 404 (SS) in model media of 0.1N HNO3 and 0.1N H2SO4 (Nikolova et al., 2006a, 2006b, 2008; Stoyanova et al., 2006a, 2006b, 2010), have shown that these films in their nature are in fact cathodic coatings. The influence of the change in the concentration of Ce in the oxide films has been studied in regard to the corrosion potential of the steel in the same corrosion medium. Thereupon it was found out that the increase in the surface concentration of Ce in the oxide films results in a gradual shift of the corrosion potential of steel in the positive direction - from the zone characteristic of anodic dissolution to the zone of deep passivity – defined by the anodic potentiodynamic curve. Moreover it has been proved that there occurs a cathodic reaction of reduction of the electrochemically active CeO2 – one of the components of the electrodeposited mixed Ce2O3-CeO2 film.

The present work discusses a hypothesis, aimed at elucidation of the question: how the change in the surface concentration of Ce in the mixed Ce2O3-CeO2 oxide film electrodeposited on ОС 404 steel influences the processes of anodic passivity of the studied steel, respectively the values of the potentials of complete passivation and the potentials of pitting formation, as well as the current density in passive state, determining the corrosion behavior of the steel under consideration. As far as the oxide of Се3+ (i.e. Ce2O3) is chemically unstable and it is dissolved in sulfuric acid medium (Achmetov, 1988) the investigations carried out in ref.(Guergova et al, 2011) established an effective inhibitory action of the cerium ions (Ce3+, Ce4+), passing over from the system Ce2O3-CeO2/SS into the corrosion medium. A possible inhibitory interaction has been supposed to occur on the surface of the steel.


*4.3. Oncolytic Retrovirus*

Replication-competent retroviruses are a relative newcomer to the OV field. These are single-stranded RNA viruses. Originally, retroviruses were applied in gene therapy approaches, however, it was later shown that replication competence of retroviruses can provide a powerful tool for gene delivery of anticancer agents in tumors [115]. Vocimagene amiretrorepvec (Toca 511) is a replicating γ-retrovirus derived from murine leukemia virus and is engineered to encode a yeast cytosine deaminase (CD) gene [116]. In the presence of the prodrug 5-fluorocytosin (5-FC), CD converts 5-FC to the potent anti-cancer drug 5-fluorouracil (5-FU). The results from a phase I clinical trial for recurrent high-grade gliomas showed that the median survival of the patients (*n* = 53) was 13.6 months with six patients showing complete response [21]. However, in a subsequent phase III study in 403 patients, clinical endpoints were not met [117].

New results from the earlier phase I clinical trial (NCT01470794) were recently published demonstrating that 86% of the patients that lived >2 years had neoantigens deriving from IDH1, PI3K3CA, EGFR, SYNE1 genes. Interestingly, only 26% of the patients with <2 years survival had neoantigens arising from these genes, suggesting that neoantigens arising from driver genes may support Toca+5-FC therapy response. Moreover, the numbers of M0 macrophages and NK cells at the tumor site at the time of treatment were associated with poor response [118]. It is conceivable that these cells contributed to clearance of the virus before its therapeutic effect could take place. Further investigation is needed to establish if the immune composition could serve as a predictive marker and whether this is also the case for other oncolytic viruses.


**6.4 Vacuum control**

Proper control of vacuum pressure is paramount in countergravity casting. Too much vacuum will result in splatter of melt inside the moulding flask due to over-filling of the mould cavity. Loss of vacuum during casting is also a real problem for countergravity technique. This may be caused by improperly closed lid, damage to or cracks in the moulding flask, or a poor seal between the recess of the lock-nut and the conical connection

Aluminium Countergravity Casting – Potentials and Challenges 15

The possibility of more economical use of the melt is good for the bottom line of foundry operation and was actually the original goal of the countergravity technique. This has

The combination of precision near net shape and strength has resulted in countergravity die casting being used to produce parts formerly made of steel that required a significant

Net shape casting, particularly for thin sections is easily achievable in countergravity casting. Countergravity cast part may have walls as thin as 0.5 mm (National Institute of

In order to make the benefits of this casting technique more accessible, low-cost countergravity equipment have been developed. A low-cost design developed by the

The design utilizes a simplified vacuum control system and manual positioning of mould and moulding flask. Such low cost alternatives would be invaluable for small scale

Size restrictions have been tackled by many recent designs. Jie *et al* (2009) reported a system using compressed air to assist the up-flow of melt for large-sized castings. The Check Valve (CV) process is has been developed Hitchiner for larger sized casting. This allows for

motivated a growing list of companies and industrial sector to adopt the technology.

amount of secondary machining (Aurora Metals LLC, 2009).

Fig. 13. A low-cost machine for countergravity casting

Industrial Research, 2005).

operations.

authors is presented in figure 13.

point of the sprue on the mould. These non-ideal, but very real instances may require a more interactive vacuum system, wherein pressure feedback is used to constantly adjust the flask vacuum pressure.


4. vWF-related antithrombotic treatment strategies

Despite recent major advances in the vascular biology of thrombosis, we face unmet treatment needs which warrant search for novel antithrombotic medication. Inhibition of vWF secretion constitutes an attractive therapeutic strategy to counteract thrombus initiation and propagation as the plasma concentration of vWF increases in high risk populations and predicts cardiovascular disease outcome. In this section, we review the drugs with the potential of vWF antagonism, illustrating how they might become an option to overcome current limitations of antithrombotic therapy.

activation is sepsis-induced elevation of plasma vWF levels [121, 129, 163, 179]. Sepsis can promote DIC, which is common in critically ill patients. When unfolded, highly multimeric sepsis-induced vWF interacts with platelets [26] and generates small clots in the microvasculature [45, 124]. Microvascular thrombosis appears to be a major pathological mechanism in sepsis pathology resulting in multi-organ dysfunction syndrome (MODS) [124]. Hence, sepsisinduced vWF secretion in excess in DIC and MODS are inevitably linked. In addition, sepsisinduced ultra-large high molecular weight multimeric vWF permits complement activation,

In murine model of sepsis, mice subjected to cecal ligation and puncture (CLP) have increased circulating levels of vWF that promote a procoagulant phenotype and poor outcome [29]. vWF-deficient mice subjected to the CLP model of sepsis exhibit increased survival [180]. For the purpose of testing whether Gα12 modulates vWF secretion in sepsis pathological setting, we subjected Gα12/ mice and WT control mice to the CLP model of polymicrobial sepsis and monitored survival [181]. Our preliminary results indicate that 80% of the Gα12/ mice survived, while all WT mice succumbed in the first 96 h [182]. To further determine whether decreased vWF was responsible for the protective effect of G12 deficiency, we restored circulating vWF level in Gα12/ mice, by intravenous administration of purified vWF [10], to the level observed in WT mice. This procedure resulted in the loss of the protective effect of G12 deletion [182]. Furthermore, we employed a pharmacological G12 inhibition approach to prove G12 involvement in sepsis-induced vWF secretion [183]. We hypothesized that a synthetic peptide derived from Gα12 would inhibit α-SNAP-dependent WPB priming and fusion with the plasma membrane [89, 182], thereby inhibiting vWF secretion from activated ECs,

Transient elevations of plasma vWF level were also observed after epinephrine infusion [184], and chronic elevation of circulating vWF (2–3-fold) was reported in hyperthyroidism, which is thought to be due to β-adrenergic receptor stimulation. In contrast, hypothyroidism is associated with a 15% decrease in vWF level, although this is reversible with appropriate treatment [185]. vWF secretion from ECs might play a role in sickle cell disease pathogenesis [186, 187]. Erythrocytes bind specifically to vWF [186] and stasis, or the reduction of blood flow and shear, promotes binding of erythrocytes to vWF which form fibrin-rich regions in venous thrombi [186].

Despite recent major advances in the vascular biology of thrombosis, we face unmet treatment needs which warrant search for novel antithrombotic medication. Inhibition of vWF secretion constitutes an attractive therapeutic strategy to counteract thrombus initiation and propagation as the plasma concentration of vWF increases in high risk populations and predicts cardiovascular disease outcome. In this section, we review the drugs with the potential of

[121] leading to a positive feedback cycle of inflammation and thrombosis.

and reducing the risk of thrombotic microangiopathy during sepsis [182].

4. vWF-related antithrombotic treatment strategies

3.5. vWF role in other inflammatory diseases

160 Endothelial Dysfunction - Old Concepts and New Challenges

Most of the studies involving anti-vWF antibodies were conducted in animal models. Monoclonal antibodies have been widely tested in murine, monkey and rabbit models of cardiovascular disease, including coronary thrombosis, stroke and in-stent stenosis: GPG-290, 6B4-Fab, AJW200, 82D6A6 and SZ-123 [188, 189]. These are all agents with antithrombotic and antiinflammatory effects which do not prolong bleeding time and do not provoke thrombocytopenia. However, to date, none of these have made it into clinical trials. Hillgruber and colleagues recently published a study that found a massive accumulation of vWF in skin biopsies of patients suffering from leukocytoclastic vasculitis, an immune complex (IC)-mediated vasculitis (ICV) frequently encountered in dermatology that is caused by IC precipitation in the vessel wall followed by recruitment of neutrophils [28]. These results were confirmed in a murine model of vasculitis [28], and importantly, they identified ICs as possible vWF secretagogues. Of note, polyclonal anti-vWF blocking antibodies had an anti-inflammatory effect, reducing leukocyte recruitment and edema formation in a murine model of vascular inflammation [28]. Although the physiological implications of elevated vWF levels (increasing up to 400% of the normal level in various conditions [190, 191]) require additional investigation, it is currently believed that plasma vWF level is a surrogate marker of increased risk of vascular complications in septic patients and in those with vascular disease, which makes vWF antagonism a promising therapeutic target in thrombosis and inflammation.

Aptamers and nanobodies have been demonstrated to directly interfere with the vWF pathway, suggesting their powerful antithrombotic properties and acceptable level of safety may prove to be useful strategies. Aptamers are oligonucleotides that have similar characteristics with monoclonal antibodies and with small molecules. ARC1779 is an aptamer that binds to the A1 domain of vWF, blocking its interaction with GpIb and thereby inhibiting vWFdependent platelet function. Clinical trials with ARC1779 were conducted and completed, but until truly meaningful clinical endpoints can be obtained that indicate effective inhibition of thrombosis without increasing bleeding, the utility of aptamers will remain unclear. Before the clinical trial was prematurely closed by the sponsor, the clinical and laboratory data after 14 days of dosing in nine patients with TTP aged 18–75 were very promising, and the authors optimistically proposed the study continuation (www.clinicaltrials.com; [192]) suggesting further development may be in order.

Nanobodies have the advantage of being highly specific therapeutic agents. Caplacizumab (ALX-0081) is an anti-vWF humanized nanobody that selectively targets vWF A1 domain, locking platelets launching on VWF A1 domain via interaction with their receptor GPIb. TITAN phase II trial concluded that caplacizumab administration in 75 patients with acquired TTP lead to a rapid resolution of the acute TTP episode, but it was adversely seconded by mild bleeding when compared to placebo group [193–195].

Unlike the vWF aptamer or antibodies, a pharmacological inhibitor of vWF secretion would have the advantage of acting from the inside of ECs, thereby limiting the amount of vWF available to support binding of platelets and thrombus formation. Studies thus far from our group suggest inhibition of Gα12-dependent activation of vWF secretion from WPBs may in fact be one such option [89, 90, 181, 182, 196]. Ongoing studies are demonstrating that inhibition of vWF secretion from ECs, using a novel peptide inhibitor to block Gα12/α-SNAP-dependent WPB exocytosis [89], reduces DIC and mortality in septic mice [89, 90, 182, 183, 196].

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**2.1 Participants**

The present work is a cross-sectional study conducted in a sample of 602 individuals from ages 3.1 to 15.4 years after the completion of a clinical examination and blood testing in the period January 2014 to December 2014. Tests were carried out in the Pediatric Endocrinology Unit of our hospital. Tanner's criteria were evaluated in every individual and were used in the assignment of individuals in two different groups: school group (Tanner stage I) and adolescent group (Tanner stages II–V). The characteristics of the place of residence were recorded as urban or rural (< or > 10,000 inhabitants, respectively).

All individuals were healthy Caucasian children living in Navarra, Spain. They were selected from the external consultations of the different pediatric subspecialties and were not affected by any chronic pathology with potential interference in growth, body composition, food ingestion, or physical activity. Any participant under treatment with concrete medications (antiepileptic drugs or glucocorticoids), vitamin D, or calcium supplements was put aside from our sample.


**5.4. Prenatal management**

The presence of bronchogenic cysts does not cause the death of the fetus in utero [25, 26]. It is not recommended to perform karyotyping because the risk of associated chromosomal abnormalities is extremely low. There is, however, the risk of an emergency intubation at birth, so birth is recommended to take place in a tertiary center.


**9. Conclusions**

230 International Perspectives of Distance Learning in Higher Education

Whether or not an overview was required at that point in the respective annotations, it would appear that detailed information had been suppressed and students were resorting to vague, non-specific utterances that were largely devoid of the core essence of the content of

A third area of interest emerged in what appeared to be a strategy to ensure the relevancy of the content of the annotation. It can be argued that some students seemed to be making a conscious effort to ensure that their output was consistent with the requirements of the essay topic. In short, they wanted to ensure that they were 'answering the question'. As noted earlier, this sometimes meant the direct transfer of key terms from the essay topic into the annotation, as reflected in the items included in the category defined earlier as 'superimposition'. This superficial approach meant that the annotation itself was not able to

A fourth area of interest was the use of assertions by some students in which they appeared to be advancing propositions as if they (the propositions) were emanating from the source material. One wonders whether this resort to what was essentially a personal position, through the use of the 'grand statement', derived from an inability to accommodate openended thought and the need to remain in the comfort zone of clearly-defined factual

The use of assertions may have also been propelled by an orientation towards more prescriptive rather than analytical modes of thinking, as implied in the tendency towards providing a solution in MP148 and MP149. Overall, what appears to be the case here is a need to define knowledge within firm boundary lines and it can be argued that the assertion

Finally, the data analysed appeared to reveal a likely weakness in students' capacity to engage in relational thinking that was able to observe and deal with elements of a body of knowledge in a manner that allowed a focus on the elements in interaction with one another rather than singly and sequentially. Such an approach to thinking would demonstrate an appreciation of the Gestalt principle of the whole being greater than the sum of its parts and conversely, the significance of viewing the parts in the context of the whole. As noted earlier a large proportion of the meaning units analyzed were focused on the mobile phone only. Even when the focus extended to include the landline phone, the context in which the two

Additionally, when the use of these technologies was shown as impacting life style changes, it was the impact of the mobile phone only that was focused on. For example, even though

were being discussed bore little relation to that espoused in the essay topic.

reflect the essence of the source material on which it was based.

provided the required mechanism for doing so.

MP84 The focus was on three research questions which sought to examine the influences of generation and lifestyle factors to mobile phone. MP143 This document explains the impact telephones had on the lives of people in

The following are to be noted in this regard:

**Data Meaning Unit**

the source material.

information.

earlier times.

One of the main factors that influenced the decision to undertake this study was the perception that the outcome-oriented task-focused approach to providing guidelines for assisting students in developing information literacy skills, may not be sufficient to address the fundamental process skills that students need to apply in order to achieve the intended outcome. This view was also shared by the two library information specialists cited. In particular, one recalls Kavanagh's (2011) discussion about the research strategy log. This view also resonates with Ally's (2004) assertion that the developer of online materials must select learning strategies that, inter alia, promote meaningful learning and provide support during the learning process. It is envisaged that the findings of this study can provide a useful starting point for taking the design of information literacy instruction for online graduate students beyond the level of task-identification.