Portal pressure and liver stiffness measurements in the prediction of fibrosis regression after sustained virological response in recurrent hepatitis C

Sustained virological response (SVR) improves survival in post-liver transplant (LT) recurrent hepatitis C. However, the impact of SVR on fibrosis regression is not well defined. In addition, the performance of noninvasive methods to evaluate the presence of fibrosis and portal hypertension (PH) post-SVR has been scarcely evaluated. We aimed to investigate the degree of fibrosis regression (decrease ≥1 METAVIR stage) after-SVR and its associated factors in recurrent hepatitis C, as well as the diagnostic capacity of noninvasive methods in the assessment of liver fibrosis and PH after viral clearance. We evaluated 112 hepatitis C virus-infected LT recipients who achieved SVR between 2001 and 2015. A liver biopsy was performed before treatment and 12 months post-SVR. Hepatic venous pressure gradient (HVPG), liver stiffness measurement (LSM), and Enhanced Liver Fibrosis (ELF) score were also determined at the same time points. Sixty-seven percent of the cohort presented fibrosis regression: 43% in recipients with cirrhosis and 72%-85% in the remaining stages (P = 0.002). HVPG, LSM, and ELF significantly decreased post-SVR. Liver function significantly improved, and survival was significantly better in patients achieving fibrosis regression. Baseline HVPG and LSM as well as decompensations before therapy were independent predictors of fibrosis regression. One year post-SVR, LSM had a high diagnostic accuracy to discard the presence of advanced fibrosis (AF) and clinically significant PH (AUROC, 0.902 and 0.888).

CONCLUSION

In conclusion, SVR post-LT induces fibrosis regression in most patients, leading to significant clinical benefits. Pretreatment HVPG and LSM are significant determinants of the likelihood of fibrosis regression. Finally, LSM accurately predicts the presence of AF and PH 1 year after SVR and thus can be used to determine monitoring strategies. (Hepatology 2018;67:1683-1694).

Pilot study of living donor liver transplantation for patients with hepatocellular carcinoma exceeding Milan Criteria (Barcelona Clinic Liver Cancer extended criteria)

A subset of patients with hepatocellular carcinoma (HCC) beyond Milan criteria might obtain acceptable survival outcomes after liver transplantation. Living donor liver transplantation (LDLT) has emerged as a feasible alternative to overcome the paucity of donors. In 2001, we started a protocol for LDLT in Child A-B patients with HCC fulfilling a set of criteria-the Barcelona Clinic Liver Cancer (BCLC) expanded criteria-that expanded the conventional indications of transplantation: 1 tumor ≤ 7 cm, 5 tumors ≤ 3 cm, and 3 tumors ≤ 5 cm without macrovascular invasion or downstaging to Milan after locoregional therapies. We present a prospective cohort of 22 patients with BCLC extended indications based on size/number (n = 17) or downstaging (n = 5) treated with LDLT between 2001 and 2014. Characteristics of the patients were as follows: median age, 57 years old; males/female, n = 20/2; Child-Pugh A/B, n = 16/6; and alpha fetoprotein < 100 ng/mL, n = 21. Twelve patients received neoadjuvant locoregional therapies. At the time of transplantation, 12 patients had HCC staging beyond Milan criteria and 10 within. Pathological reports showed that 50% exceeded BCLC expanded criteria. Perioperative mortality was 0%. After a median follow-up of 81 months, the 1-, 3-, 5-, and 10-year survival was 95.5%, 86.4%, 80.2%, and 66.8%, respectively. Overall, 7 patients recurred (range, 9-108 months), and the 5-year and 10-year actuarial recurrence rates were 23.8% and 44.4%, respectively. In conclusion, a proper selection of candidates for extended indications of LDLT for HCC patients provide survival outcomes comparable to those obtained within the Milan criteria, but these results need confirmation. Liver Transplantation 24 369-379 2018 AASLD.

Mannose-Binding Lectin-Deficient Donors Increase the Risk of Bacterial Infection and Bacterial Infection-Related Mortality After Liver Transplantation

Mannose-binding lectin (MBL) is synthesized by the liver and binds to microbes. MBL2 gene polymorphisms produce intermediate/low/null or normal MBL serum levels (MBL-deficient or MBL-sufficient phenotypes, respectively). We aimed to evaluate the incidence and severity of infection, rejection, and survival within 1 year after liver transplantation (LT) according to donor and recipient MBL2 gene polymorphisms. A repeated-event analysis for infection episodes (negative binomial regression, Andersen-Gill model) was performed in 240 LTs. Four hundred twenty-eight infectious episodes (310 bacterial, 15 fungal, 65 cytomegalovirus [CMV]-related, and 38 viral non-CMV-related episodes) and 48 rejection episodes were recorded. The main bacterial infections were urinary (n = 82, 26%) and pneumonia (n = 69, 22%). LT recipients of MBL-deficient livers had a higher risk of bacterial infection (incidence rate ratio [IRR] 1.48 [95% confidence interval 1.04-2.09], p = 0.028), pneumonia (IRR 2.4 [95% confidence interval 1.33-4.33], p = 0.013), and septic shock (IRR 5.62 [95% confidence interval 1.92-16.4], p = 0.002) compared with recipients of MBL-deficient livers. The 1-year bacterial infection-related mortality was higher in recipients of MBL-deficient versus MBL-sufficient livers (65.8% vs. 56.1%, respectively; p = 0.0097). The incidence of rejection, viral, or fungal infection was similar in both groups. Recipient MBL2 genotype did not significantly increase the risk of bacterial infection. LT recipients of MBL-deficient livers have a higher risk of bacterial infection, pneumonia, septic shock, and 1-year bacterial infection-related mortality after LT.

Multimodal character of shear viscosity response in hydrogen bonded liquids

Non-simple viscosity response of 2E1H alcohol forming supramolecular aggregates.

Clinical outcomes of patients undergoing antiviral therapy while awaiting liver transplantation

BACKGROUND & AIMS

Antiviral therapy for the treatment of hepatitis C (HCV) infection has proved to be safe and efficacious in patients with cirrhosis awaiting liver transplantation (LT). However, the information regarding the clinical impact of viral eradication in patients on the waiting list is still limited. The aim of the study was to investigate the probability of delisting in patients who underwent antiviral therapy, and the clinical outcomes of these delisted patients.

METHODS

Observational, multicenter and retrospective analysis was carried out on prospectively collected data from patients positive for HCV, treated with an interferon-free regimen, while awaiting LT in 18 hospitals in Spain.

RESULTS

In total, 238 patients were enrolled in the study. The indication for LT was decompensated cirrhosis (with or without hepatocellular carcinoma [HCC]) in 171 (72%) patients, and HCC in 67 (28%) patients. Sustained virologic response (SVR) rate was significantly higher in patients with compensated cirrhosis and HCC (92% vs. 83% in patients with decompensated cirrhosis with or without HCC, p=0.042). Among 122 patients with decompensated cirrhosis without HCC, 29 (24%) were delisted due to improvement. No patient with baseline MELD score >20 was delisted. After delisting (median follow-up of 88weeks), three patients had clinical decompensations and three had de novo HCC. Only two of the patients with HCC had to be re-admitted onto the waiting list. The remaining 23 patients remained stable, with no indication for LT.

CONCLUSIONS

Antiviral therapy is safe and efficacious in patients awaiting LT. A quarter of patients with decompensated cirrhosis can be delisted asa result of clinical improvement, which appears to be remain stable in most patients. Thus, delisting is a safe strategy that could spare organs and benefit other patients with a more urgent need.

LAY SUMMARY

Antiviral therapy in patients awaiting liver transplantation is safe and efficacious. Viral eradication allows removal from the waiting list of a quarter of treated patients. Delisting because of clinical improvement is a safe strategy that can spare organs for patients in urgent need.

Endoscopic management of bile leaks after liver transplantation: An analysis of two high-volume transplant centers

Background

Bile leak after liver transplantation (LT) is commonly treated with endoscopic retrograde cholangiopancreatography (ERCP); however, there are limited data regarding the optimal treatment strategy.

Objective

We aimed to examine the role of ERCP in LT recipients with bile leaks at two large institutions.

Methods

We reviewed all ERCPs performed in LT recipients with bile leak and duct-to-duct biliary anastomosis at two high-volume transplant centers.

Results

Eighty patients were included. Forty-seven (59%) patients underwent ERCP with plastic stent placement (with or without sphincterotomy) and 33 patients (41%) underwent sphincterotomy alone. Complete resolution was obtained in 94% of the stent group vs. 58% of the sphincterotomy group (p < 0.01). There was no difference in three-month survival among both groups. Percutaneous transhepatic therapy and surgery were required in 4% and 6% in the stent group vs. 12% and 42% in the sphincterotomy group, respectively (p = 0.22 and p < 0.001). The only predictive factor of bile leak resolution was stent placement.

Conclusion

ERCP with plastic stent placement is highly successful and more effective than sphincterotomy alone for post-LT bile leak treatment. These results indicate that ERCP and plastic stent placement should be considered the standard of care for the treatment of bile leaks in LT.

Venous Thrombotic Events After Liver Transplantation

Thromboprophylaxis is not well defined after liver transplantation (LT). The aim of this study was to evaluate the incidence of splanchnic vein thrombosis (SVT) and nonsplanchnic vein thrombosis (NSVT) after LT. Liver transplantations performed between 2009 and 2013 in our institution were reviewed. Demographic, intraoperative, and postoperative data were recorded. Low-molecular-weight heparin was only administered postoperatively if intraoperative thrombectomy was performed or in patients preoperatively anticoagulated. Of a total of 328 patients, 72% were male with a median age of 56 years, score of model for end-stage liver disease 18 (11-23), and 88% had liver cirrhosis. The incidence of postoperative venous thrombotic events was 4.6%: 8 (2.4%) patients had SVT and 7 (2.1%) patients had NSVT. After logistic regression analysis, intraoperative thrombectomy and Child A classification emerged as risk factors for SVT (odds ratio [OR]: 77, 95% confidence interval [95% CI]: 14-421) and NSVT (OR: 20, 95% CI: 3-170), respectively. The incidence of SVT in patients who undergo intraoperative thrombectomy was 33%, whereas the incidence of NSVT in patients grouped as Child A was 7.5%. Our results suggest that thromboprophylaxis should be considered after LT in patients with cirrhosis grouped as Child A and in patients who undergo intraoperative thrombectomy.

Dielectric Susceptibility of Liquid Water: Microscopic Insights from Coherent and Incoherent Neutron Scattering

The analysis of neutron scattering results on H dynamics (H_{2}O) and the dynamic structure factor (D_{2}O) around the intermolecular peak and at intermediate length scales in terms of the susceptibilities reveals three processes (diffusive, local relaxational and vibrational) at frequencies below 3 THz, to which the contributions commonly invoked in dielectric studies can be directly mapped. We achieve a unified description of the results from both techniques, clarifying the nature of the molecular motions involved in the dielectric spectra and their impact on the structural relaxation.

Development of multiorganic calciphylaxis during teriparatide, vitamin D, and calcium treatment

Non-uremic calciphylaxis is a severe rare disorder characterized by ischemic necrosis. Recently, three cases of cutaneous calciphylaxis have been described in the context of teriparatide treatment. We present a 51-year-old woman with alcoholic cirrhosis who developed multiorganic calciphylaxis shortly after starting teriparatide treatment associated with calcium and 25-hydroxyvitamin D supplements for severe osteoporosis. After lengthy care of the infectious complications and treatment with bisphosphonates and sodium thiosulfate progressive improvement was observed over a 3-year period. The time between the initiation of teriparatide and the development of calciphylaxis suggests that this agent may have been the triggering factor of this process. Nevertheless, other non-negligible risk factors for calciphylaxis such as alcoholic liver disease, obesity, and vitamin D treatment must also be considered in this patient. Considering the severity of this extremely rare clinical condition, better knowledge of the risk factors related to calciphylaxis development is mandatory.

Usefulness of liver stiffness measurement during acute cellular rejection in liver transplantation

Liver stiffness measurement (LSM) is a useful method to estimate liver fibrosis and portal hypertension. The inflammatory process that takes place in post-liver transplant acute cellular rejection (ACR) may also increase liver stiffness. We aimed to explore the association between liver stiffness and the severity of ACR, as well as to assess the relationship between liver stiffness and response to rejection treatment in a prospective study that included 27 liver recipients with biopsy-proven ACR, 30 stable recipients with normal liver tests, and 30 hepatitis C virus (HCV)-infected LT recipients with histologically diagnosed HCV recurrence. Patients with rejection were stratified into 2 groups (mild and moderate/severe) according to the severity of rejection evaluated with the Banff score. Routine biomarkers and LSM with FibroScan were performed at the time of liver biopsy (baseline) and at 7, 30, and 90 days in patients with rejection and at baseline in control patients. Median baseline liver stiffness was 5.9 kPa in the mild rejection group, 11 kPa in the moderate/severe group (P = 0.001), 4.2 kPa in stable recipients (P = 0.02 versus mild rejection), and 13.6 kPa in patients with recurrent HCV (P = 0.17 versus moderate/severe rejection). The area under the receiver operator characteristic curve of LSM to discriminate mild versus moderate/severe ACR was 0.924, and a LSM value of 8.5 kPa yielded a positive predictive value of 100% to diagnose moderate/severe rejection. Liver stiffness improved in 7%, 21%, and 64% of patients with moderate/severe rejection at 7, 30, and 90 days. In conclusion, according to the results of this exploratory study, LSM is associated with the severity of ACR in liver transplantation and thus may be of help in its assessment.

Treatment of type 2 hepatorenal syndrome in patients awaiting transplantation: Effects on kidney function and transplantation outcomes

There is little information on the effects of treatment with vasoconstrictors plus albumin in patients with type 2 hepatorenal syndrome (HRS), particularly those awaiting liver transplantation (LT). This study reports the effects of treatment of type 2 HRS in patients on the waiting list for LT. We included 56 patients with type 2 HRS who were awaiting LT. Out of these 56 patients, 31 were treated with terlipressin and albumin. Nineteen (61%) of these 31 patients had response to therapy, and 11 of them relapsed after treatment withdrawal. There were no differences in mortality on the waiting list between responders and nonresponders. Among the 46 (82%) patients who underwent transplantation, 15 underwent transplantation with reversal of type 2 HRS, whereas the remaining 31 underwent transplantation with type 2 HRS. There were no significant differences in serum creatinine or estimated glomerular filtration rate between the 2 cohorts of patients at 3, 6, and 12 months after transplantation. There were no significant differences regarding development of acute kidney injury, need for renal replacement therapy, frequency of chronic kidney disease 1 year after transplant, length of hospitalization, and survival. In conclusion, treatment of patients with type 2 HRS with terlipressin and albumin does not appear to have beneficial effects either in pretransplantation or in posttransplantation outcomes.

Dynamics of tetrahydrofuran as minority component in a mixture with poly(2-(dimethylamino)ethyl methacrylate): A neutron scattering and dielectric spectroscopy investigation

We have investigated a mixture of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and tetrahydrofuran (THF) (70 wt. % PDMAEMA/30 wt. % THF) by combining dielectric spectroscopy and quasielastic neutron scattering (QENS) on a labelled sample, focusing on the dynamics of the THF molecules. Two independent processes have been identified. The "fast" one has been qualified as due to an internal motion of the THF ring leading to hydrogen displacements of about 3 Å with rather broadly distributed activation energies. The "slow" process is characterized by an Arrhenius-like temperature dependence of the characteristic time which persists over more than 9 orders of magnitude in time. The QENS results evidence the confined nature of this process, determining a size of about 8 Å for the volume within which THF hydrogens' motions are restricted. In a complementary way, we have also investigated the structural features of the sample. This study suggests that THF molecules are well dispersed among side-groups nano-domains in the polymer matrix, ruling out a significant presence of clusters of solvent. Such a good dispersion, together with a rich mobility of the local environment, would prevent cooperativity effects to develop for the structural relaxation of solvent molecules, frustrating thereby the emergence of Vogel-Fulcher-like behavior, at least in the whole temperature interval investigated.

The universal trend of the non-exponential Rouse mode relaxation in polymer systems: a theoretical interpretation based on a generalized Langevin equation

We show that the universal behavior of the Rouse-mode relaxation in polymer systems - which has been recently reported from experimental data [S. Arrese-Igor, et al., Phys. Rev. Lett., 2014, 113, 078302] - can be quantitatively explained in the framework of a theoretical approach based on: (i) a generalized Langevin equation formalism and (ii) a memory function which takes into account the coupling between intra-chain dynamics and collective dynamics. This approach opens the way for generalizing the magnitudes probing chain dynamics in polymer systems.

Dielectric relaxation of 2-ethyl-1-hexanol around the glass transition by thermally stimulated depolarization currents

We explore new routes for characterizing the Debye-like and α relaxation in 2-ethyl-1-hexanol (2E1H) monoalcohol by using low frequency dielectric techniques including thermally stimulated depolarization current (TSDC) techniques and isothermal depolarization current methods. In this way, we have improved the resolution of the overlapped processes making it possible the analysis of the data in terms of a mode composition as expected for a chain-like response. Furthermore the explored ultralow frequencies enabled to study dynamics at relatively low temperatures close to the glass transition (Tg). Results show, on the one hand, that Debye-like and α relaxation timescales dramatically approach to each other upon decreasing temperature to Tg. On the other hand, the analysis of partial polarization TSDC data confirms the single exponential character of the Debye-like relaxation in 2E1H and rules out the presence of Rouse type modes in the scenario of a chain-like response. Finally, on crossing the glass transition, the Debye-like relaxation shows non-equilibrium effects which are further emphasized by aging treatment and would presumably emerge as a result of the arrest of the structural relaxation below Tg.

Are polymers standard glass-forming systems? The role of intramolecular barriers on the glass-transition phenomena of glass-forming polymers

Traditionally, polymer melts have been considered archetypal glass-formers. This has been mainly due to the fact that these systems can easily be obtained as glasses by cooling from the melt, even at low cooling rates. However, the macromolecules, i.e. the structural units of polymer systems in general, are rather different from the standard molecules. They are long objects ('chains') made by repetition of a given chemical motif (monomer) and have intra-macromolecular barriers that limit their flexibility. The influence of these properties on, for instance, the glass-transition temperature of polymers, is a topic that has been widely studied by the polymer community almost from the early times of polymer science. However, in the framework of the glass-community, the relevant influence of intra-macromolecular barriers and chain connectivity on glass-transition phenomena of polymers has started to be recognized only recently. The aim of this review is to give an overview and to critically revise the results reported on this topic over the last years. From these results, it seems to be evident that there are two different mechanisms involved in the dynamic arrest in glass-forming polymers: (i) the intermolecular packing effects, which dominate the dynamic arrest of low molecular weight glass-forming systems; and (ii) the effect of intra-macromolecular barriers combined with chain connectivity. It has also been shown that the mode coupling theory (MCT) is a suitable theoretical framework to discuss these questions. The values found for polymers for the central MCT parameter--the so-called λ-exponent--are of the order of 0.9, clearly higher than the standard values (λ ≈ 0.7) found in systems where the dynamic arrest is mainly driven by packing effects ('standard' glass-formers). Within the MCT, this is a signature of the presence of two competing mechanisms of dynamic arrest, as it has been observed in short-ranged attractive colloids or two component mixtures with dynamic asymmetry. Moreover, recent MD-simulations of a 'bead-spring' polymer model, but including intra-macromolecular potential of different strengths, confirm that the high λ-values found in polymers are due to the effect of intra-macromolecular barriers. Although there are still open questions, these results allow to conclude that there is a fundamental difference between the nature of the glass transition in polymers and in simple (standard) glass-formers.

Chain Dynamics on Crossing the Glass Transition: Nonequilibrium Effects and Recovery of the Temperature Dependence of the Structural Relaxation

In this paper we report thermally stimulated depolarization current results on the chain and segmental dynamics of two monodisperse polyisoprenes accessing both dynamics at ultralow frequency range and exploring the relationship between segmental and chain time scales when crossing the glass transition. In this range, we have recorded experimental evidence of nonequilibrium effects on the slowest chain mode dynamics. The nonequilibrium effects seem to occur simultaneously for both chain and α-relaxation. Moreover, detailed analysis strongly indicates the recovery of an even T-dependence for the chain and α-relaxation dynamics on crossing glass transition and in the glassy state. The obtained results can be understood taking into account the different temperature dependences of the length scales involved in the segmental and chain relaxations.

Use of artificial intelligence as an innovative donor-recipient matching model for liver transplantation: results from a multicenter Spanish study

BACKGROUND & AIMS

There is an increasing discrepancy between the number of potential liver graft recipients and the number of organs available. Organ allocation should follow the concept of benefit of survival, avoiding human-innate subjectivity. The aim of this study is to use artificial-neural-networks (ANNs) for donor-recipient (D-R) matching in liver transplantation (LT) and to compare its accuracy with validated scores (MELD, D-MELD, DRI, P-SOFT, SOFT, and BAR) of graft survival.

METHODS

64 donor and recipient variables from a set of 1003 LTs from a multicenter study including 11 Spanish centres were included. For each D-R pair, common statistics (simple and multiple regression models) and ANN formulae for two non-complementary probability-models of 3-month graft-survival and -loss were calculated: a positive-survival (NN-CCR) and a negative-loss (NN-MS) model. The NN models were obtained by using the Neural Net Evolutionary Programming (NNEP) algorithm. Additionally, receiver-operating-curves (ROC) were performed to validate ANNs against other scores.

RESULTS

Optimal results for NN-CCR and NN-MS models were obtained, with the best performance in predicting the probability of graft-survival (90.79%) and -loss (71.42%) for each D-R pair, significantly improving results from multiple regressions. ROC curves for 3-months graft-survival and -loss predictions were significantly more accurate for ANN than for other scores in both NN-CCR (AUROC-ANN=0.80 vs. -MELD=0.50; -D-MELD=0.54; -P-SOFT=0.54; -SOFT=0.55; -BAR=0.67 and -DRI=0.42) and NN-MS (AUROC-ANN=0.82 vs. -MELD=0.41; -D-MELD=0.47; -P-SOFT=0.43; -SOFT=0.57, -BAR=0.61 and -DRI=0.48).

CONCLUSIONS

ANNs may be considered a powerful decision-making technology for this dataset, optimizing the principles of justice, efficiency and equity. This may be a useful tool for predicting the 3-month outcome and a potential research area for future D-R matching models.

Stage of cirrhosis predicts the risk of liver-related death in patients with low Model for End-Stage Liver Disease scores and cirrhosis awaiting liver transplantation

The Model for End-Stage Liver Disease (MELD) score has reduced predictive ability in patients with cirrhosis and MELD scores ≤ 20. We aimed to assess whether a 5-stage clinical model could identify liver transplantation (LT) candidates with low MELD scores who are at increased risk for death. We conducted a case-control study of subjects with cirrhosis and MELD scores ≤ 20 who were awaiting LT at a single academic medical center between February 2002 and May 2011. Conditional logistic regression was used to evaluate the risk of liver-related death according to the cirrhosis stage. We identified 41 case subjects who died from liver-related causes with MELD scores ≤ 20 within 90 days of death while they were waiting for LT. The cases were matched with up to 3 controls (66 controls in all) on the basis of the listing year, age, sex, liver disease etiology, presence of hepatocellular carcinoma, and MELD score. The cirrhosis stage was assessed for all subjects: (1) no varices or ascites, (2) varices, (3) variceal bleeding, (4) ascites, and (5) ascites and variceal bleeding. The MELD scores were similar for cases and controls. Clinical states contributing to death in cases were: sepsis 49%, spontaneous bacterial peritonitis 15%, variceal bleeding 24%, and hepatorenal syndrome 22%. In a univariate analysis, variceal bleeding [odds ratio (OR) = 5.6, P = 0.003], albumin (OR = 0.5, P = 0.041), an increasing cirrhosis stage (P = 0.003), reaching cirrhosis stage 2, 3, or 4 versus lower stages (OR = 3.6, P = 0.048; OR = 7.4, P < 0.001; and OR = 4.1, P = 0.008), a sodium level < 135 mmol/L (OR = 3.4, P = 0.006), and hepatic encephalopathy (OR = 2.3, P = 0.082) were associated with liver-related death. In a multivariate model including the cirrhosis stage, albumin, sodium, and hepatic encephalopathy, an increasing cirrhosis stage (P = 0.010) was independently associated with liver-related death. In conclusion, assessing the cirrhosis stage in patients with low MELD scores awaiting LT may help to select candidates for more aggressive monitoring or for living or extended criteria donation.

Polymer chain dynamics: evidence of nonexponential mode relaxation using thermally stimulated depolarization current techniques

The slowest (p=1) mode relaxation of several polyisoprenes has been experimentally isolated by thermally stimulated depolarization current techniques. Close to the glass transition the p=1 mode deviates from the exponential behavior assumed by Rouse and tube-reptation theories. This effect is found to be a consequence of the closeness of τ_{p=1} and α-relaxation time scales. The scenario resembles that of broadened fast component dynamics in polymer blends with high dynamic asymmetry and suggests a possible general interpretation in terms of the effect of local density fluctuations (α relaxation) on chain dynamics.

Multi-orthogonal folding of single polymer chains into soft nanoparticles

Efficient folding of single polymer chains is a topic of great interest due, mainly, to the challenging possibility of mimicking and controlling the structure and functionality of natural biomacromolecules (e.g., enzymes, drug delivery vehicles, and catalysts) by means of artificial single chain nano-objects. By performing extensive molecular dynamics simulations we investigate the formation of soft nanoparticles by irreversible intramolecular cross-linking of polymer precursors of different lengths. In order to optimize the folding process and to obtain more compact structures we vary the number of chemical species among the linker groups (orthogonal chemistry) which selectively form the bonds. The use of orthogonal chemistry protocols, by increasing the number of different chemical species of the linkers, leads to nanoparticles that are systematically smaller and more spherical than their homofunctional counterparts. We characterize the conformational properties of the resulting nanoparticles. These are intrinsically polydisperse in size, with a significant fraction of sparse topologies. We discuss the relevance of our results for synthesis protocols in real systems.

Candida norvegensis fungemia in a liver transplant recipient

BACKGROUND

The incidence of candidemia due to non-Candida albicans Candida species has been progressively increasing in recent years. The use of fluconazole as antifungal prophylaxis has been described as a risk factor for the development of infections by fluconazole resistant Candida strains. We report a case of Candida norvegensis bloodstream infection in a liver transplant recipient.

CASE REPORT

A 61-year-old man, who received a third liver allograft and became worse with the onset of ischemic cholangiopathy and recurrent episodes of cholangitis, was admitted to our hospital due to the development of intra-abdominal abscesses. He received multiple antibiotic schemes, and after 3 months he was discharged, maintaining parenteral antibiotic at home. While he was on fluconazole prophylaxis, a breakthrough candidemia due to C. norvegensis occurred. In vitro susceptibilities of the isolate to several antifungal agents were as follows: amphotericin B MIC 0.5 mg/l, flucytosine 64 mg/l, fluconazole 64 mg/l, itraconazole 4 mg/l, voriconazole 0.75 mg/l, and caspofungin 0.047 mg/l. He was treated with anidulafungin with resolution of candidemia.

CONCLUSIONS

The use of fluconazole for antifungal prophylaxis may lead to the emergence of fluconazole-resistant Candida infections, with C. norvegensis being a possible emerging pathogen in organ transplant recipients.

Bone disease in patients awaiting liver transplantation. Has the situation improved in the last two decades?

In recent years, there has been speculation about the possibility of a reduction in the incidence of fractures after liver transplantation (LT) because of changes in the characteristics of candidates and the use of different immunosuppressive therapies. We analyzed the characteristics of LT candidates (CTC) and compared them with historical data from a group of LT candidate patients (HTC). Data from 60 CTC patients consecutively included in a screening program of metabolic bone disease were compared with data from 60 HTC patients prospectively evaluated between 1992 and 1993. In all patients, we analyzed the clinical and laboratory characteristics, bone mineral density (BMD) dual-energy X-ray absorptiometry, and skeletal fractures. Patients in the CTC group were older than patients in the HTC group. The CTC group had lower femoral neck T scores. No differences were observed between groups in the proportion of patients with osteoporosis (22 vs. 30 %, p = ns) or fractures (36 vs. 33 %, p = ns). The percentage of patients with normal BMD decreased from 38 to 20 %. 25(OH)D values were low in both groups. Only 7.5 % of the CTC patients received calcium and/or vitamin D supplementation. The prevalence of fractures among CTC patients was similar to that seen two decades ago. At present, candidates for LT are older and have lower femoral bone mass. Vitamin D deficiency remains frequent; however, calcium and/or vitamin D supplementation is uncommon.

Applicability of mode-coupling theory to polyisobutylene: a molecular dynamics simulation study

The applicability of Mode Coupling Theory (MCT) to the glass-forming polymer polyisobutylene (PIB) has been explored by using fully atomistic molecular dynamics simulations. MCT predictions for the so-called asymptotic regime have been successfully tested on the dynamic structure factor and the self-correlation function of PIB main-chain carbons calculated from the simulated cell. The factorization theorem and the time-temperature superposition principle are satisfied. A consistent fitting procedure of the simulation data to the MCT asymptotic power-laws predicted for the α-relaxation regime has delivered the dynamic exponents of the theory-in particular, the exponent parameter λ-the critical non-ergodicity parameters, and the critical temperature T(c). The obtained values of λ and T(c) agree, within the uncertainties involved in both studies, with those deduced from depolarized light scattering experiments [A. Kisliuk et al., J. Polym. Sci. Part B: Polym. Phys. 38, 2785 (2000)]. Both, λ and T(c)/T(g) values found for PIB are unusually large with respect to those commonly obtained in low molecular weight systems. Moreover, the high T(c)/T(g) value is compatible with a certain correlation of this parameter with the fragility in Angell's classification. Conversely, the value of λ is close to that reported for real polymers, simulated "realistic" polymers and simple polymer models with intramolecular barriers. In the framework of the MCT, such finding should be the signature of two different mechanisms for the glass-transition in real polymers: intermolecular packing and intramolecular barriers combined with chain connectivity.

Effect of nanoconfinement on polymer dynamics: surface layers and interphases

We present neutron spin echo experiments that address the much debated topic of dynamic phenomena in polymer melts that are induced by interacting with a confining surface. We find an anchored surface layer that internally is highly mobile and not glassy as heavily promoted in the literature. The polymer dynamics in confinement is, rather, determined by two phases, one fully equal to the bulk polymer and another that is partly anchored at the surface. By strong topological interaction, this phase confines further chains with no direct contact to the surface. These form the often invoked interphase, where the full chain relaxation is impeded through the interaction with the anchored chains.

Positron annihilation and relaxation dynamics from dielectric spectroscopy: poly(vinylmethylether)

We report on the temperature dependence of the lifetime of the ortho-positronium (o-Ps), τ(3), annihilation in amorphous polymer poly(vinylmethylether) (PVME) from positron annihilation lifetime spectroscopy (PALS). We show that the behavior of τ(3)(T) can be divided into five regions, each of them having a linear temperature dependence, and that the crossover PALS temperatures situated at T(b1)(G), 0.76T(g)(PALS), T(b1)(L) = 1.14T(g)(PALS) and T(b2)(L) = 1.37T(G)(PALS), and marking the discontinuity in the free volume microstructure are related to various dynamic features from neutron scattering (NS) and broadband dielectric spectroscopy (BDS). First, a slight change in the PALS response in the glassy PVME at T(b1)(G) is related to the onset of the excess wing in an apparent correspondence with the fast secondary β motion from NS. A further slight bend in the liquid state at T(b1)(L) is related to a high-frequency tail of the primary α process as well as to the slow secondary β relaxation from BDS. In addition, it lies also in the vicinity of the crossover temperature, T(B)(βKWW), in the spectral dispersion of the primary α process, indicating a connection of the change in the o-Ps lifetime with the variation in the width of the primary α relaxation times distribution. Finally, the τ(3) value at T(b2)(L) is close to the mean relaxation time of the primary α process, τ(α), in coincidence with the crossover in the secondary effective β process between two regimes in the liquid PVME. All these relationships point to very close connections between the PALS response and the dynamic behavior of PVME, which can be explained in terms of the temperature dependence of the probability function of the liquid-like and the solid-like domains, as obtained from the two-order parameter (TOP) model description of the liquid to glass transition in glass-formers.

Quasielastic neutron scattering study of hydrogen motions in an aqueous poly(vinyl methyl ether) solution

We present a quasielastic neutron scattering (QENS) investigation of the component dynamics in an aqueous Poly(vinyl methyl ether) (PVME) solution (30% water content in weight). In the glassy state, an important shift in the Boson peak of PVME is found upon hydration. At higher temperatures, the diffusive-like motions of the components take place with very different characteristic times, revealing a strong dynamic asymmetry that increases with decreasing T. For both components, we observe stretching of the scattering functions with respect to those in the bulk and non-Gaussian behavior in the whole momentum transfer range investigated. To explain these observations we invoke a distribution of mobilities for both components, probably originated from structural heterogeneities. The diffusive-like motion of PVME in solution takes place faster and apparently in a more continuous way than in bulk. We find that the T-dependence of the characteristic relaxation time of water changes at T ≲ 225 K, near the temperature where a crossover from a low temperature Arrhenius to a high temperature cooperative behavior has been observed by broadband dielectric spectroscopy (BDS) [S. Cerveny, J. Colmenero and A. Alegría, Macromolecules, 38, 7056 (2005)]. This observation might be a signature of the onset of confined dynamics of water due to the freezing of the PVME dynamics, that has been selectively followed by these QENS experiments. On the other hand, revisiting the BDS results on this system we could identify an additional "fast" process that can be attributed to water motions coupled with PVME local relaxations that could strongly affect the QENS results. Both kinds of interpretations, confinement effects due to the increasing dynamic asymmetry and influence of localized motions, could provide alternative scenarios to the invoked "strong-to-fragile" transition.

Contrast inversion in electrostatic force microscopy imaging of trapped charges: tip-sample distance and dielectric constant dependence

We present a numerical and analytical study of the behavior of both electrostatic force and force gradient created by a charge trapped below the surface of a dielectric on an atomic force microscope tip as a function of the dielectric constant and tip-sample distance. As expected, the force decreases monotonously when the dielectric constant increases. However, a maximum in the dielectric constant dependence of the force gradient is found. This maximum occurs in the typical experimental parameters' range and depends on the tip-sample distance and the sample thickness. The analytical study permits us to understand the physical origin of this phenomenon and is in good agreement with the numerical simulation for small tip-sample distances. We also report a study exemplifying a possible contrast inversion in electrostatic force microscopy (EFM) signals while scanning, at different heights, two charges trapped in a sample having heterogeneous dielectric domains. In addition to this particular contrast inversion effect, this study can be considered as a way to gain insight into the mechanisms of EFM image formation as a function of the dielectric constant and tip-sample.

Numerical study of the lateral resolution in electrostatic force microscopy for dielectric samples

We present a study of the lateral resolution in electrostatic force microscopy for dielectric samples in both force and gradient modes. Whereas previous studies have reported expressions for metallic surfaces having potential heterogeneities (Kelvin probe force microscopy), in this work we take into account the presence of a dielectric medium. We introduce a definition of the lateral resolution based on the force due to a test particle being either a point charge or a polarizable particle on the dielectric surface. The behaviour has been studied over a wide range of typical experimental parameters: tip-sample distance (1-20) nm, sample thickness (0-5) µm and dielectric constant (1-20), using the numerical simulation of the equivalent charge method. For potential heterogeneities on metallic surfaces expressions are in agreement with the bibliography. The lateral resolution of samples having a dielectric constant of more than 10 tends to metallic behaviour. We found a characteristic thickness of 100 nm, above which the lateral resolution measured on the dielectric surface is close to that of an infinite medium. As previously reported, the lateral resolution is better in the gradient mode than in the force mode. Finally, we showed that for the same experimental conditions, the lateral resolution is better for a polarizable particle than for a charge, i.e. dielectric heterogeneities should always look 'sharper' (better resolved) than inhomogeneous charge distributions. This fact should be taken into account when interpreting images of heterogeneous samples.