Modelling and characterization of an airlift-loop bioreactor

An airlift-loop reactor is a bioreactor for aerobic biotechnological processes. The special feature of the ALR is the recirculation of the liquid through a downcomer connecting the top and the bottom of the main bubbling section. Due to the high circulation-flow rate, efficient mixing and oxygen transfer is combined with a controlled liquid flow in the absence of mechanical agitators.Liquid velocities and gas hold-ups in an external-loop airlift reactor (ALR) on different scales were modelled on the basis of a simple pressure balance. The model is adapted for non-isobaric conditions and takes into account nonuniform flow profiles and gas hold-up distributions across the duct. The friction coefficient together with the reactor dimensions are input parameters. It has been shown that the friction coefficient can be obtained from simple one-phase flow calculations based on known data of the seperate reactor parts. The model predicts liquid velocities and local gas hold-ups in an ALR to within 10% and can be applied easily to an internal loop reactor.Mixing in the individual sections of the ALR is determined by a newly developed parameter estimation procedure which has proven to be reliable for the estimation of axial dispersion coefficients in the individual sections of the ALR. From the results it can be concluded, that in an ALR the liquid flow behaves like plug-flow with superimposed dispersion except for the topsection for which it is not reasonable to assume plug-flow. The mixing results simplified the modelling of oxygen transfer in the ALR as it appeared not to be necessary to incorporate the dispersion contribution Into the oxygen model.The non-isobaric plug-flow model, presented in this thesis, predicts dynamic and stationary dissolved oxygen concentration (DOC) profiles in large-scale ALRs and has been applied also to estimate the volumetric oxygen transfer coefficient, k 1 a, in the pertinent ALR. Comparison with the results on the basis of a simple isobaric stirred-tank-reactor model demonstrates, that such a model yields conservative values though for the present situation the underestimation did not exceed a value of 10% relative to the plug-flow model. Therefore, due to its simplicity, it is recommended to use the stirred tank model for a rapid characterization of the overall aeration capacity of laboratory scale and pilot-scale ALRs. Oxygen depletion of the gas phase, even during a fermentation, appeared to be very limited and was fairly well predicted by the plug-flow model. For this reason an ALR is a very suitable reactor for aerobic processes having a high oxygen demand. If necessary, the aeration capacity of the ALR can be enhanced by injection of a small amount of gas at the entrance of the downflow region. This phenomenom is also accurately predicted by the plug-flow model. In the present ALR the aeration capacity of the air-sparger region did not significantly differ from the main aeration process in the upflow region due to its special geometry.The intermediate flow region between the ALR and the bubble-column (BC) flow regime was investigated by gradually closing a butterfly valve at the bottom of the downcomer. When the valve is further shut and thus the friction is enhanced, the liquid velocity will be reduced thereby enlarging the gas hold-up. The maximum value for the gas hold-up is obtained when the ALR is operated as a BC. In the transition flow regime between ALR and BC flow, the liquid velocity was found to be a simple power law function of the gas flow rate. The coefficients of the power law depend on the flow characteristics in the reactor. In the transition flow regime the hydrodynamic calculations based on the plug-flow behaviour of an ALR are only valid up to a certain defined value of the total gas-liquid flow rate. For greater values, the ALR type of flow will change Into a BC type of flow. A simple criterium qualifies the distinction between both flow patterns, determined by the superficial liquid velocity and the liquid circulation velocity.The transition of ALR to BC flow coincides with the decrease of the Bodenstein number which also indicates a less established plug flow. As the dispersion coefficient at a constant gas-flow rate, remained constant for as well the ALR, the BC and the transition flow, the decreased Bodenstein number in the BC-type of flow is mainly attributed to the decreased convective transport as the liquid circulation is impeded. The number of circulations required to achieve complete mixing diminshes when the liquid circulation is impeded and appeared to be proportional to the Bodenstein number.In the transition flow regime, the volumetric oxygen transfer coefficient was estimated by both the stirred-tank model and the plug-flow model. The stirred-tank model yielded reliable results for the entire range of operation while the plug-flow model only appeared to be appropiate for the ALR operation mode. The volumetric oxygen transfer coefficient was found to increase for the BC operation mode and appeared to be a power law function of the ratio of the superficial liquid and gas velocity and the Bodenstein number.Addition of immobilized biocatalysts to the ALR, in our case simulated by neutral buoyant particles with diameters ranging from 2.4-2.7 am, significantly reduces the liquid velocity and the gas hold-up in an ALR. The decrease in liquid velocity is attributed to the decrease in gas hold-up and an increased friction in the ALR. The gas hold-up is reduced mainly because the presence of the particles increases the collision frequency of the air bubbles thereby increasing coalescence due to the diminished flowed area available for the air-water mixture. In comparison to a gas-liquid flow, axial dispersion in the three-phase flow is reduced as the presence of the particles damps the small eddies which are, apart from other mechanisms, responsible for the axial dispersion. Moreover. the increased coalescence also contributes to a decrease in axial dispersion. The presence of the particles negatively influences aeration due to a reduction in the gas-liquid interfacial area as a result of the increased coalescence. The effect of the increase in apparent viscosity in the ALR was not supposed to contribute to the decrease in the aeration process

Clinical evaluation of an anatomy-based patient specific quality assurance system

The Delta4DVH Anatomy 3D quality assurance (QA) system (ScandiDos), which converts the measured detector dose into the dose distribution in the patient geometry was evaluated. It allows a direct comparison of the calculated 3D dose with the measured back-projected dose. In total, 16 static and 16 volumetric-modulated arc therapy (VMAT) fields were planned using four different energies. Isocenter dose was measured with a pinpoint chamber in homogeneous phantoms to investigate the dose prediction by the Delta4DVH Anatomy algorithm for static fields. Dose distributions of VMAT fields were measured using GAFCHROMIC film. Gravitational gantry errors up to 10° were introduced into all VMAT plans to study the potential of detecting errors. Additionally, 20 clinical treatment plans were verified. For static fields, the Delta4DVH Anatomy predicted the isocenter dose accurately, with a deviation to the measured phantom dose of 1.1% ± 0.6%. For VMAT fields the predicted Delta4DVH Anatomy dose in the isocenter plane corresponded to the measured dose in the phantom, with an average gamma agreement index (GAI) (3 mm/3%) of 96.9± 0.4%. The Delta4DVH Anatomy detected the induced systematic gantry error of 10° with a relative GAI (3 mm/3%) change of 5.8% ± 1.6%. The conventional Delta4PT QA system detected a GAI change of 4.2%± 2.0%. The conventional Delta4PT GAI (3 mm/3%) was 99.8% ± 0.4% for the clinical treatment plans. The mean body and PTV-GAI (3 mm/5%) for the Delta4DVH Anatomy were 96.4% ± 2.0% and 97.7%± 1.8%; however, this dropped to 90.8%± 3.4% and 87.1% ± 4.1% for passing criteria of 3 mm/3%. The anatomy-based patient specific quality assurance system predicts the dose distribution correctly for a homogeneous case. The limiting factor for the error detection is the large variability in the error-free plans. The dose calculation algorithm is inferior to that used in the TPS (Eclipse)

Stapled coronary anastomosis with minimal intraluminal artifact: The S2 Anastomotic System in the off-pump porcine model

AbstractObjectiveA reliable, easy-to-use, 1-shot anastomotic device will significantly push the barrier for less invasive coronary bypass surgery. The current study was designed to test the safety, efficacy, and early patency of a novel distal anastomotic device.MethodsThe S2 Anastomotic System (iiTech BV, Amsterdam, The Netherlands) was used in 10 consecutive pigs (73 kg) on a mild antiplatelet regimen. In each animal, the device was used to create an internal thoracic artery to left anterior descending bypass on the beating heart. The anastomoses were evaluated intraoperatively (n = 10), at 2 days (n = 2), and at 5 weeks (n = 8) by functional flow measurements, postmortem angiography, and histomorphologic examination.ResultsIn all pigs, the S2Anastomic System rapidly created successful anastomoses at the first attempt (graft loading and coronary ischemia time: 1.2 ± 0.3 minutes and 3.0 ± 0.6 minutes) on target vessels of 1.6 to 2 mm inner diameter. There were no technical failures or anastomotic leaks requiring additional sutures. Both intraoperatively and at the time of death, ischemically induced peak hyperemic flow responses demonstrated widely patent bypasses, which were confirmed by postmortem angiography (FitzGibbon grade A, n = 10) and macroscopic evaluation (anastomotic orifice: 2 mm). Histomorphologic evaluation showed a normal healing response with negligible neointima covering the connector and limited streamlining repair tissue formation between the staple-like elements of the connector.ConclusionsThe S2 Anastomotic System consistently created automated, fast, and reliable internal thoracic to coronary artery anastomoses on the porcine beating heart with excellent graft patency and healing characteristics at the 5-week follow-up

Knee adduction moments are not increased in obese knee osteoarthritis patients during stair negotiation

Background: Negotiating stairs is an important activity of daily living that is also associated with large loads on the knee joint. In medial compartment knee osteoarthritis, the knee adduction moment during level walking is considered a marker for disease severity. It could be argued that the discriminative capability of this parameter is even better if tested in a strenuous stair negotiation task. Research question: What is the relation with knee osteoarthritis on the knee adduction moment during the stance phase of both stair ascent and descent in patients with and without obesity? Methods: This case control study included 22 lean controls, 16 lean knee osteoarthritis patients, and 14 obese knee osteoarthritis patients. All subjects ascended and descended a two-step staircase at a self-selected, comfortable speed. Three-dimensional motion analysis was performed to evaluate the knee adduction moment during stair negotiation. Results: Obese knee osteoarthritis patients show a prolonged stance time together with a more flattened knee adduction moment curve during stair ascent. Normalized knee adduction moment impulse, as well as the first and second peaks were not different between groups. During stair descent, a similar increase in stance time was found for both osteoarthritis groups. Significance: The absence of a significant effect of groups on the normalized knee adduction moment during stair negotiation may be explained by a lower ambulatory speed in the obese knee osteoarthritis group, that effectively lowers vertical ground reaction force. Decreasing ambulatory speed may be an effective strategy to lower knee adduction moment during stair negotiation

Diagnosis of diffuse idiopathic skeletal hyperostosis with chest computed tomography:inter-observer agreement

To evaluate and improve the interobserver agreement for the CT-based diagnosis of diffuse idiopathic skeletal hyperostosis (DISH). Six hundred participants of the CT arm of a lung cancer screening trial were randomly divided into two groups. The first 300 CTs were scored by five observers for the presence of DISH based on the original Resnick criteria for radiographs. After analysis of the data a consensus meeting was organised and the criteria were slightly modified regarding the definition of 'contiguous', the definition of 'flowing ossifications' and the viewing plane and window level. Subsequently, the second set of 300 CTs was scored by the same observers. kappa >= 0.61 was considered good agreement. The 600 male participants were on average 63.5 (SD 5.3) years old and had smoked on average 38.0 pack-years. In the first round kappa values ranged from 0.32 to 0.74 and 7 out of 10 values were below 0.61. After the consensus meeting the interobserver agreement ranged from 0.51 to 0.86 and 3 out of 10 values were below 0.61. The agreement improved significantly. This is the first study that reports interobserver agreement for the diagnosis of DISH on chest CT, showing mostly good agreement for modified Resnick criteria. . DISH is diagnosed on fluoroscopic and radiographic examinations using Resnick criteria . Evaluation of DISH on chest CT was modestly reproducible with the Resnick criteria . A consensus meeting and Resnick criteria modification improved inter-rater reliability for DISH . Reproducible CT criteria for DISH aids research into this poorly understood entity

Global probabilistic projections of extreme sea levels show intensification of coastal flood hazard

Global warming is expected to drive increasing extreme sea levels (ESLs) and flood risk along the world’s coastlines. In this work we present probabilistic projections of ESLs for the present century taking into consideration changes in mean sea level, tides, wind-waves, and storm surges. Between the year 2000 and 2100 we project a very likely increase of the global average 100-year ESL of 34–76 cm under a moderate-emission-mitigation-policy scenario and of 58–172 cm under a business as usual scenario. Rising ESLs are mostly driven by thermal expansion, followed by contributions from ice mass-loss from glaciers, and ice-sheets in Greenland and Antarctica. Under these scenarios ESL rise would render a large part of the tropics exposed annually to the present-day 100-year event from 2050. By the end of this century this applies to most coastlines around the world, implying unprecedented flood risk levels unless timely adaptation measures are taken

Interaction between genetic and epigenetic variation defines gene expression patterns at the asthma-associated locus 17q12-q21 in lymphoblastoid cell lines

Phenotypic variation results from variation in gene expression, which is modulated by genetic and/or epigenetic factors. To understand the molecular basis of human disease, interaction between genetic and epigenetic factors needs to be taken into account. The asthma-associated region 17q12-q21 harbors three genes, the zona pellucida binding protein 2 (ZPBP2), gasdermin B (GSDMB) and ORM1-like 3 (ORMDL3), that show allele-specific differences in expression levels in lymphoblastoid cell lines (LCLs) and CD4+ T cells. Here, we report a molecular dissection of allele-specific transcriptional regulation of the genes within the chromosomal region 17q12-q21 combining in vitro transfection, formaldehyde-assisted isolation of regulatory elements, chromatin immunoprecipitation and DNA methylation assays in LCLs. We found that a single nucleotide polymorphism rs4795397 influences the activity of ZPBP2 promoter in vitro in an allele-dependent fashion, and also leads to nucleosome repositioning on the asthma-associated allele. However, variable methylation of exon 1 of ZPBP2 masks the strong genetic effect on ZPBP2 promoter activity in LCLs. In contrast, the ORMDL3 promoter is fully unmethylated, which allows detection of genetic effects on its transcription. We conclude that the cis-regulatory effects on 17q12-q21 gene expression result from interaction between several regulatory polymorphisms and epigenetic factors within the cis-regulatory haplotype region

Developing new classification criteria for diffuse idiopathic skeletal hyperostosis : back to square one

Objective. To revise the definition of DISH and suggest a classification that may better represent our current knowledge of this entity allowing earlier diagnosis.Methods. Seven rheumatologists and an orthopaedic surgeon suggested a list of 63 parameters that might be included in a future classification of DISH. Participants rated their level of agreement with each item, expressed in percentages. In a second session, participants discussed each item again and re-rated all parameters. Thirty items that were granted 6550% support on average were considered valid for a third round. A questionnaire listing these 30 items was mailed to 39 rheumatologists and orthopaedic surgeons worldwide with a request to answer categorically if they agreed on an item to be included as a criterion for a future classification of DISH. Items were regarded as perfect consensus when at least 95% of the respondents agreed and were regarded as consensus when at least 80% agreed.Results. There was perfect consensus for 2 (6.7%) of the 30 parameters and consensus for another 2 parameters. These items were ossification and bridging osteophytes in each of the three segments of the spine and exuberant bone formation of bone margins.Conclusion. At present there is no agreement about the inclusion of extraspinal, constitutional and metabolic manifestations in a new classification of DISH. Investigators with an interest in this condition should be encouraged to restructure the term DISH in an attempt to establish a more sophisticated definition

HDMX-L is expressed from a functional P53-responsive promoter in the first intron of the HDMX gene, and participates in an auto-regulatory feedback loop to control P53 activity.

The p53 regulatory network is critically involved in preventing the initiation of cancer. In unstressed cells p53 is maintained at low levels and is largely inactive, mainly through the action of its two essential negative regulators, HDM2 and HDMX. p53 abundance and activity are upregulated in response to various stresses including DNA damage and oncogene activation. Active p53 initiates transcriptional and transcription-independent programs that result in cell cycle arrest, cellular senescence or apoptosis. p53 also activates transcription of HDM2, which initially leads to the degradation of HDMX, creating a positive feedback loop to obtain maximal activation of p53. Subsequently, when stress-induced post-translational modifications start to decline, HDM2 becomes effective in targeting p53 for degradation, thus attenuating the p53 response. To date, no clear function for HDMX in this critical attenuation phase has been demonstrated experimentally. Like HDM2, the HDMX gene contains a promoter (P2) in its first intron that is potentially inducible by p53. We show that p53 activation in response to a plethora of p53-activating agents induces the transcription of a novel HDMX mRNA transcript from the HDMX-P2 promoter. This mRNA is more efficiently translated than that expressed from the constitutive HDMX-P1 promoter, and it encodes a long form of HDMX protein, HDMX-L. Importantly, we demonstrate that HDMX-L cooperates with HDM2 to promote the ubiquitination of p53, and that p53-induced HDMX transcription from the P2 promoter can play a key role in the attenuation phase of the p53-response, to effectively diminish p53 abundance as cells recover from stress