Long-term simulation of a full-scale EBPR plant with a novel metabolic-ASM model and its use as a diagnostic tool.

This study evaluates the predictive capacity of the META-ASM model, a new integrated metabolic activated sludge model, in describing the long-term performance of a full-scale enhanced biological phosphorus removal (EBPR) system that suffers from inconsistent performance. In order to elucidate the causes of EBPR upsets and troubleshoot the process accordingly, the META-ASM model was tested as an operational diagnostic tool in a 1336-day long-term dynamic simulation, while its performance was compared with the ASM-inCTRL model, a version based on the Barker & Dold model. Overall, the predictions obtained with the META-ASM without changing default parameters were more reliable and effective at describing the active biomass of polyphosphate accumulating organisms (PAOs) and the dynamics of their storage polymers. The primary causes of the EBPR upsets were the high aerobic hydraulic retention times (HRTs) and low organic loading rates (OLRs) of the plant, which led to periods of starvation. The impact of these factors on EBPR performance were only identified with the META-ASM model. Furthermore, the first signs of process upsets were predicted by variations in the aerobic PAO maintenance rates, suggesting that the META-ASM model has potential to provide an early warning of process upset. The simulation of a new viable operational strategy indicated that troubleshooting the process could be achieved by reducing the aerated volume by switching off air in the first half of the aeration tank. In this new strategy, the META-ASM model predicted a simultaneous improvement in the biological phosphorus (P) and nitrogen (N) removal due to the enhancement of the hydrolysis and fermentation of the mixed liquor sludge in the new unaerated zone, which increased the availability of volatile fatty acids (VFAs) for PAOs. This study demonstrates that the META-ASM model is a powerful operational diagnostic tool for EBPR systems, capable of predicting and mitigating upsets, optimising performance and evaluating new process designs.

A rare complication of a hemodialysis tunneled catheter: Case report of a superior vena cava and right atrium candida endocarditis.

Infections remain an important cause of death among hemodialysis patients. This population have a higher risk of candidemia. Candida endocarditis it´s a rare but frequently fatal complication of candidemia. A 64 year-old female presented with a purulent discharge at the insertion site of a hemodialysis tunneled cuff catheter. A catheter related bloodstream infection was suspected, cultures were obtained and wide-spectrum antibiotic therapy was administered. A multi sensitive Candida albicans was isolated. Transesophageal echocardiography showed a large vegetation located in the superior vena cava, in probable relation with a previous catheter. The first approach was antifungal treatment. Due to non-response, she did a surgical removal of the vegetation. Culture of the vegetation showed the same as the blood cultures. After one year she has no signs of relapse. To improve the prognosis of this high mortality condition a high index of suspicion is necessary for early diagnosis and timely intervention.

Safe Use of Infected Donor Organs in Kidney Transplantation.

INTRODUCTION: Organ availability is limited in the face of the growing number of candidates. Using organs from individuals with an infection at the time of transplantation emerged as a possible but controversial solution. MATERIALS AND METHODS: Retrospective analysis of patients submitted to kidney transplantation in Hospital Garcia de Orta (Almada, Portugal) from January 2008 to March 2019, comparing outcomes between recipients of organs from donors with an active infection and noninfected donors in the referred interval. RESULTS: An active infection in the donor was identified in 55 cases (28.4%) from a total of 194 transplants. The most frequent site of infection was the lung (n = 30), followed by the urinary tract (n = 13); 9 donors (16.4%) had documented bacteremia. None of the identified microorganisms were multidrug-resistant. All recipients from an infected donor received adequate antibiotic prophylaxis (mean duration of 11.1 ± 3.0 days). No significant differences between groups were found regarding patients' demographics, cold ischemia time, duration of hospital stay, delayed graft function, rejection episodes, noninfectious complications, or patient and graft survival. Basiliximab was the preferred induction agent in both groups but was used in a larger proportion of recipients in the infected donor group (87.0% vs 60.6%; P = .001). The rate of infectious complications was significantly lower in the infected donor group (14.5% vs 42.4%; P = .001), and none of the previously isolated agents in the donor was found in the recipient. CONCLUSION: Kidney transplant using infected donors can be performed safely, without worse organ-specific or recipient outcomes, if certain conditions are considered.

Kidney Transplant From Elderly Donors: A Center Experience.

BACKGROUND: Renal transplantation is the treatment of choice in end-stage renal disease. With the aging of the population and better medical care available, the number of high-risk patients in terms of age and comorbidities on transplant waiting lists is increasing. Due to severe organ shortage, the use of expanded criteria and elderly donors is also increasing. We will review the outcomes of graft function and survival from a series of transplants from elderly deceased donors and compare the characteristics of the organs from donors older and younger than 70 years. METHODS: We collected data from our transplant unit from 1993 until May 2019 and considered 2 groups of donors: donors A (aged ≥70 years) and donors B (aged <70 years). RESULTS: The donors A group had more comorbidities with consequently higher Kidney Donor Profile Index scores than the donors B group, although there was no statistical difference regarding pre-donation serum creatinine level. Among transplant recipients, we also considered 2 groups, according to the age of the organ received: recipients A and recipients B. No difference was found between groups regarding the number of HLA mismatches, incidence of delayed graft function, number of hospitalizations, or incidence of acute rejection. Recipients' age, cold ischemia time, and graft function 1 year after transplant were worse in the recipients A group. CONCLUSIONS: Although kidney graft function was worse in recipients from elderly donors, this difference had no clinical relevance, showing a possible benefit in patient survival compared with permanence in dialysis, so this type of transplant could be considered for older recipients.

Cardiac Progenitor Cells from Stem Cells: Learning from Genetics and Biomaterials.

Cardiac Progenitor Cells (CPCs) show great potential as a cell resource for restoring cardiac function in patients affected by heart disease or heart failure. CPCs are proliferative and committed to cardiac fate, capable of generating cells of all the cardiac lineages. These cells offer a significant shift in paradigm over the use of human induced pluripotent stem cell (iPSC)-derived cardiomyocytes owing to the latter's inability to recapitulate mature features of a native myocardium, limiting their translational applications. The iPSCs and direct reprogramming of somatic cells have been attempted to produce CPCs and, in this process, a variety of chemical and/or genetic factors have been evaluated for their ability to generate, expand, and maintain CPCs in vitro. However, the precise stoichiometry and spatiotemporal activity of these factors and the genetic interplay during embryonic CPC development remain challenging to reproduce in culture, in terms of efficiency, numbers, and translational potential. Recent advances in biomaterials to mimic the native cardiac microenvironment have shown promise to influence CPC regenerative functions, while being capable of integrating with host tissue. This review highlights recent developments and limitations in the generation and use of CPCs from stem cells, and the trends that influence the direction of research to promote better application of CPCs.

Identification of stiffness-induced signalling mechanisms in cells from patent and fused sutures associated with craniosynostosis.

Craniosynostosis is a bone developmental disease where premature ossification of the cranial sutures occurs leading to fused sutures. While biomechanical forces have been implicated in craniosynostosis, evidence of the effect of microenvironmental stiffness changes in the osteogenic commitment of cells from the sutures is lacking. Our aim was to identify the differential genetic expression and osteogenic capability between cells from patent and fused sutures of children with craniosynostosis and whether these differences are driven by changes in the stiffness of the microenvironment. Cells from both sutures demonstrated enhanced mineralisation with increasing substrate stiffness showing that stiffness is a stimulus capable of triggering the accelerated osteogenic commitment of the cells from patent to fused stages. The differences in the mechanoresponse of these cells were further investigated with a PCR array showing stiffness-dependent upregulation of genes mediating growth and bone development (TSHZ2, IGF1), involved in the breakdown of extracellular matrix (MMP9), mediating the activation of inflammation (IL1ß) and controlling osteogenic differentiation (WIF1, BMP6, NOX1) in cells from fused sutures. In summary, this study indicates that stiffer substrates lead to greater osteogenic commitment and accelerated bone formation, suggesting that stiffening of the extracellular environment may trigger the premature ossification of the sutures.

Identification of the mechanisms by which age alters the mechanosensitivity of mesenchymal stromal cells on substrates of differing stiffness: Implications for osteogenesis and angiogenesis.

In order to identify the mechanisms by which skeletal maturity alters the mechanosensitivity of mesenchymal stromal cells (MSCs) and, the implications for osteogenesis and angiogenesis during bone formation, we compared the response of MSCs derived from children and skeletally-mature healthy adults cultured on soft and stiff collagen-coated polyacrylamide substrates. MSCs from children were more mechanosensitive, showing enhanced angiogenesis and osteogenesis on stiff substrates as indicated by increased endothelial tubule formation, PGF production, nuclear-translocation of YAP, ALP activity and mineralisation. To examine these mechanisms in more detail, a customised PCR array identified an age-dependent, stiffness-induced upregulation of NOX1, VEGFR1, VEGFR2, WIF1 and, of particular interest, JNK3 in cells from children compared to adults. When JNK3 activity was inhibited, a reduction in stiffness-induced driven osteogenesis was observed - suggesting that JNK3 might serve as a novel target for recapitulating the enhanced regenerative potential of children in adults suffering from bone degeneration. STATEMENT OF SIGNIFICANCE: We investigated the age-associated changes in the capacity of MSCs for bone regeneration involving the mechanosensitive signalling pathways, which reduce the ability of adult cells to respond to biophysical cues in comparison to cells from children, who are still undergoing bone development. Our results offer new insights into the mechanobiology of MSCs and sheds new light on age-altered mechanosensitivity and, on why children have such an immense capacity to regenerate their skeletal system. We have identified the mechanisms by which skeletal maturity alters the mechanosensitivity of mesenchymal stromal cells and an age-dependent, stiffness-induced upregulation of a number of prominent genes including, most notably, JNK3 in children cells, thus suggesting its potential to promote enhanced bone repair.

Primary cilia mechanics affects cell mechanosensation: A computational study.

Primary cilia (PC) are mechanical cell structures linked to the cytoskeleton and are central to how cells sense biomechanical signals from their environment. However, it is unclear exactly how PC mechanics influences cell mechanosensation. In this study we investigate how the PC mechanical characteristics are involved in the mechanotransduction process whereby cilium deflection under fluid flow induces strains on the internal cell components that regulate the cell׳s mechanosensitive response. Our investigation employs a computational approach in which a finite element model of a cell consisting of a nucleus, cytoplasm, cortex, microtubules, actin bundles and a primary cilium was used together with a finite element representation of a flow chamber. Fluid-structure interaction analysis was performed by simulating perfusion flow of 1mm/s on the cell model. Simulations of cells with different PC mechanical characteristics, showed that the length and the stiffness of PC are responsible for the transmission of mechanical stimuli to the cytoskeleton. Fluid flow deflects the cilium, with the highest strains found at the base of the PC and in the cytoplasm. The PC deflection created further strains on the cell nucleus but did not influence microtubules and actin bundles significantly. Our results indicate that PC deflection under fluid flow stimulation transmits mechanical strain primarily to other essential organelles in the cytoplasm, such as the Golgi complex, that regulate cells' mechanoresponse. The simulations further suggest that cell mechanosensitivity can be altered by targeting PC length and rigidity.

Structural finite element analysis to explain cell mechanics variability.

The ability to model the mechanical responses of different cell types presents many opportunities to tissue engineering research to further identify changes from physiological conditions to disease. Using a previously validated finite element cell model we aim to show how variation of the material properties of the intracellular components affects cell response after compression and shearing. A parametric study was performed to understand the key mechanical features from different cell types, focussing on specific cytoskeleton components and prestress. Results show that actin cortex does not have a mechanical role in resisting shearing loading conditions. The sensitivity analysis predicted that cell force to compression and shearing is highly affected by changes in cortex thickness, cortex Young's modulus and rigidity of the remaining cytoplasm. Variation of prestress affects mainly the response of cells under shear loads and the model defines a relationship between cell force and prestress depending on the specific loading conditions, which is in good agreement with in vitro experiments. The results are used to make predictions that can relate mechanical properties with cell phenotype to be used as guidelines for individual cytoskeletal structures for future modelling efforts of the structure-function relationships of living cells.

A multi-structural single cell model of force-induced interactions of cytoskeletal components.

Several computational models based on experimental techniques and theories have been proposed to describe cytoskeleton (CSK) mechanics. Tensegrity is a prominent model for force generation, but it cannot predict mechanics of individual CSK components, nor explain the discrepancies from the different single cell stimulating techniques studies combined with cytoskeleton-disruptors. A new numerical concept that defines a multi-structural 3D finite element (FE) model of a single-adherent cell is proposed to investigate the biophysical and biochemical differences of the mechanical role of each cytoskeleton component under loading. The model includes prestressed actin bundles and microtubule within cytoplasm and nucleus surrounded by the actin cortex. We performed numerical simulations of atomic force microscopy (AFM) experiments by subjecting the cell model to compressive loads. The numerical role of the CSK components was corroborated with AFM force measurements on U2OS-osteosarcoma cells and NIH-3T3 fibroblasts exposed to different cytoskeleton-disrupting drugs. Computational simulation showed that actin cortex and microtubules are the major components targeted in resisting compression. This is a new numerical tool that explains the specific role of the cortex and overcomes the difficulty of isolating this component from other networks in vitro. This illustrates that a combination of cytoskeletal structures with their own properties is necessary for a complete description of cellular mechanics.

The influence of the pelvic bone on the computational results of the acetabular component of a total hip prosthesis.

The computational models developed to evaluate the hip joint performance usually neglect the presence of the pelvic bone. However, deformation depends on the stiffness of the underlying bone, and thus, the inclusion of the pelvic bone in the model influences the computed contact pressure and wear. This work discusses the influence of the pelvic bone, and how it depends on the acetabular component stiffness. It was modeled as two different polyethylene acetabular cups, considering or not a metal-backing for both 28 mm and 32 mm diametric cups. Two finite element models are developed, considering either the acetabular component rigidly fixed or attached to the deformable bone. Results present 28% and 42% difference on the contact pressure for a polyethylene cup without metal-backing when the support conditions are changed, for the 28 mm and 32 mm cups, respectively. Linear wear results present 21% and 31% difference for the same type of cups of 28 mm and 32 mm, correspondingly. The numerical results obtained in the present work show that to model the pelvic bone of the patient with a metal-backed cup did not greatly affect contact pressures and linear wear. However, when a total hip replacement is performed with an all-polyethylene acetabular cup, the presence of the pelvic bone in the model has a major influence.