Electrochemical behavior of titanium for medical implant in alkaline solutions

Titanium and its alloy have been widely utilized for excellent corrosion-resistance, high melting point, high strength and biocompatibility. However, Ti and Ti alloys are non-bioactive after being implanted in bone. Thus, for further improvement in biocompatibility the various implant surface modifications have been investigated. These surface modifications have included deposition of Ti coating using plasma spraying, and deposition of calcium phosphate or hydroxy-apatite (HA) coating, sandblasting, acid ething, oxidation, ion implantation and alkaline treatment. One of these surface modifications that alkaline solution is formed on Ti in 5 M NaOH solution at 60℃, and it can be converted into an amorphous sodium titanate layer by heat treatment that induces a bone-like apatite formation on its surface in simulated body fluid. Although electrochemical and chemical treatments of Ti have been carried out in alkaline solutions to form surface oxide film for medical application, the detailed electrochemical behavior of titanium in various concentrations of sodium hydroxide has not been reported. In this work, electrochemical behavior of commercially pure titanium in alkaline solution was investigated as a function of NaOH concentration by open-circuit potential transients, cyclic polarization curves, galvanostatic (constant current) method and surface morphological study using SEM and CLSM. Commercially pure titanium specimen (99.6% ASTM grade1) of 1.77 cm2 surface area was used as the working electrode. The specimen was ground successively with silicon carbide papers from 400 to 2000 grit for 30 seconds and then rinsed with ethanol for 30 minutes by using ultra sonic and distilled water. A platinum mesh and saturated calomel electrode (SCE) were used as the counter electrode and the reference electrode, respectively. The open-circuit potential transients of Ti in different concentrations of NaOH were measured. The open-circuit potential showed an increase with time in the solutions lower than 0.1 M NaOH, while it showed a decrease with time in the solutions higher than 0.1 M, which are attributed to the growth and dissolution of surface oxide film, respectively. It is noted that the open-circuit potential value obtained at 2000 seconds of immersion time decreases with increasing concentration of NaOH. This indicates that the dissolution of surface oxide film is easier in more concentrated NaOH solutions. Cyclic polarization curves of Ti were obtained at 5 ㎷/s in different concentrations of NaOH. Current peaks were clearly observed during the positive going scan of potential in concentrated NaOH solutions. The magnitude of the peak current was higher but peak potential became lower with increasing concentration of NaOH. Galvanostatic potential transients obtained form Ti at 0.5 ㎃/㎠ in different concentrations of NaOH. The potential under the anodic current increased with time in the initial stage and then reached a steady-state value in all the concentrations of NaOH. The rate of initial increase and steady-stated value of potential was lowered with increasing concentration of NaOH, which suggest that the dissolution of Ti metal through the anodic oxide film is easier in more concentrated NaOH solutions. Surface morphological observation revealed that the dissolution of Ti is enhanced by the increase of NaOH concentration.1.서론 = 1 2.연구 배경 = 3 2.1임프란트 재료 = 3 2.1.1금속 = 3 2.1.2세라믹 = 6 2.2임프란트 개요 = 7 2.2.1임프란트의 정의 = 7 2.2.2임프란트의 역사 = 7 2.2.3기업체의 임프란트 제조 특징과 발전과정 = 8 2.3타이타늄 표면처리 방법 = 11 2.3.1타이타늄 전처리방법에 따른 종류 = 11 3.실험 방법 = 17 3.1실험 재료 = 17 3.2타이타늄의 전처리 조건 = 18 3.3실험장치 = 18 3.4전기화학적 실험 = 20 3.5표면의 형태관찰 실험 = 21 4.실험결과 및 고찰 = 23 4.1전기화학 실험 결과 = 23 4.1.1OCP 실험 결과 = 23 4.1.2CV 실험 결과 = 27 4.1.3Galvanostatic 실험 결과 = 32 4.2표면의 형태 관찰 실험 결과 = 34 4.2.1LM(Laser Microscopy) 결과 = 34 4.2.2SEM(Scanning Electron Microscopy)결과 = 38 5.결론 = 41 참고문헌 = 4

Urinary angiotensinogen as a marker of elevated blood pressure in patients with chronic kidney disease

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Recalibration and validation of the Charlson Comorbidity Index in acute kidney injury patients underwent continuous renal replacement therapy

Background: Comorbid conditions impact the survival of patients with severe acute kidney injury (AKI) who require continuous renal replacement therapy (CRRT). The weights assigned to comorbidities in predicting survival vary based on type of index, disease, and advances in management of comorbidities. We developed a modified Charlson Comorbidity Index (CCI) for use in patients with AKI requiring CRRT (mCCI-CRRT) and improved the accuracy of risk stratification for mortality. Methods: A total of 828 patients who received CRRT between 2008 and 2013, from three university hospital cohorts was included to develop the comorbidity score. The weights of the comorbidities were recalibrated using a Cox proportional hazards model adjusted for demographic and clinical information. The modified index was validated in a university hospital cohort (n = 919) using the data of patients treated from 2009 to 2015. Results: Weights for dementia, peptic ulcer disease, any tumor, and metastatic solid tumor were used to recalibrate the mCCI-CRRT. Use of these calibrated weights achieved a 35.4% (95% confidence interval [CI], 22.1%-48.1%) higher performance than unadjusted CCI in reclassification based on continuous net reclassification improvement in logistic regression adjusted for age and sex. After additionally adjusting for hemoglobin and albumin, consistent results were found in risk reclassification, which improved by 35.9% (95% CI, 23.3%-48.5%). Conclusion: The mCCI-CRRT stratifies risk of mortality in AKI patients who require CRRT more accurately than does the original CCI, suggesting that it could serve as a preferred index for use in clinical practice.ope

Pathophysiologic Mechanisms and Potential Biomarkers in Diabetic Kidney Disease

Although diabetic kidney disease (DKD) remains the leading cause of end-stage kidney disease eventually requiring chronic kidney replacement therapy, the prevalence of DKD has failed to decline over the past 30 years. In order to reduce disease prevalence, extensive research has been ongoing to improve prediction of DKD onset and progression. Although the most commonly used markers of DKD are albuminuria and estimated glomerular filtration rate, their limitations have encouraged researchers to search for novel biomarkers that could improve risk stratification. Considering that DKD is a complex disease process that involves several pathophysiologic mechanisms such as hyperglycemia induced inflammation, oxidative stress, tubular damage, eventually leading to kidney damage and fibrosis, many novel biomarkers that capture one specific mechanism of the disease have been developed. Moreover, the increasing use of high-throughput omic approaches to analyze biological samples that include proteomics, metabolomics, and transcriptomics has emerged as a strong tool in biomarker discovery. This review will first describe recent advances in the understanding of the pathophysiology of DKD, and second, describe the current clinical biomarkers for DKD, as well as the current status of multiple potential novel biomarkers with respect to protein biomarkers, proteomics, metabolomics, and transcriptomics.ope

Novel biomarkers for diabetic kidney disease

Although diabetic kidney disease (DKD) remains one of the leading causes of reduced lifespan in patients with diabetes mellitus; its prevalence has failed to decline over the past 30 years. To identify those at high risk of developing DKD and disease progression at an early stage, extensive research has been ongoing in the search for prognostic and surrogate endpoint biomarkers for DKD. Although biomarkers are not used routinely in clinical practice or prospective clinical trials, many biomarkers have been developed to improve the early identification and prognostication of patients with DKD. Novel biomarkers that capture one specific mechanism of the DKD disease process have been developed, and studies have evaluated the prognostic value of assay-based biomarkers either in small sets or in combinations involving multiple biomarkers. More recently, several studies have assessed the prognostic value of omics- based biomarkers that include proteomics, metabolomics, and transcriptomics. This review will first describe the biomarkers used in current practice and their limitations, and then summarize the current status of novel biomarkers for DKD with respect to assay- based protein biomarkers, proteomics, metabolomics, and transcriptomics.ope

Creatinine-cystatin C ratio and mortality in cancer patients: a retrospective cohort study

Background: Muscle wasting is prevalent in cancer patients, and early recognition of this phenomenon is important for risk stratification. Recent studies have suggested that the creatinine-cystatin C ratio may correlate with muscle mass in several patient populations. The association between creatinine-cystatin C ratio and survival was assessed in cancer patients. Methods: A total of 3060 patients who were evaluated for serum creatinine and cystatin C levels at the time of cancer diagnosis were included. The primary outcome was 6-month mortality. The 1-year mortality, and length of intensive care unit (ICU) and hospital stay were also evaluated. Results: The mean age was 61.6 ± 13.5 years, and 1409 patients (46.0%) were female. The median creatinine and cystatin C levels were 0.9 (interquartile range [IQR], 0.6-1.3) mg/dL and 1.0 (IQR, 0.8-1.5) mg/L, respectively, with a creatinine-cystatin C ratio range of 0.12-12.54. In the Cox proportional hazards analysis, an increase in the creatinine-cystatin C ratio was associated with a significant decrease in the 6-month mortality (per 1 creatinine-cystatin C ratio, hazard ratio [HR] 0.35; 95% confidence interval [CI], 0.28-0.44). When stratified into quartiles, the risk of 6-month mortality was significantly lower in the highest quartile (HR 0.30; 95% CI, 0.24-0.37) than in the lowest quartile. Analysis of 1-year mortality outcomes revealed similar findings. These associations were independent of confounding factors. The highest quartile was also associated with shorter lengths of ICU and hospital stay (both P < 0.001). Conclusions: The creatinine-cystatin C ratio at the time of cancer diagnosis significantly associates with survival and hospitalization in cancer patients.ope

Nationwide Implementation of Nonpharmaceutical Interventions During the Coronavirus Disease 2019 Pandemic Is Associated With Decreased Incidence of Pneumocystis jirovecii Pneumonia in Kidney Transplant Recipients

This study aimed to investigate the impact of nationwide nonpharmaceutical interventions against coronavirus disease 2019 (COVID-19) on the incidence of Pneumocystis jirovecii pneumonia (PCP) in kidney transplant recipients. The monthly incidence of PCP during the COVID-19 period decreased significantly compared to that of the pre-COVID-19 period in kidney transplant recipients.ope

Proteinuria Modifies the Relationship Between Urinary Sodium Excretion and Adverse Kidney Outcomes: Findings From KNOW-CKD

Introduction: High sodium intake is associated with increased proteinuria. Herein, we investigated whether proteinuria could modify the association between urinary sodium excretion and adverse kidney outcomes in patients with chronic kidney disease (CKD). Methods: In this prospective observational cohort study, we included 967 participants with CKD stages G1 to G5 between 2011 and 2016, who measured 24-hour urinary sodium and protein excretion at baseline. The main predictors were urinary sodium and protein excretion levels. The primary outcome was CKD progression, which was defined as a $50 Results: During a median follow-up period of 4.1 years, the primary outcome events occurred in 287 participants (29.7$0.5 g/d, a 1.0 g/d increase in sodium excretion was associated with a 29% higher risk of adverse kidney outcomes. Moreover, in patients with proteinuria of $0.5 g/d, the hazard ratios (HRs) (95$3.4 g/d were 2.32 (1.50–3.58) and 5.71 (3.58–9.11), respectively, compared with HRs for patients with proteinuria of <0.5 g/d and sodium excretion of <3.4 g/d. In sensitivity analysis with 2 averaged values of sodium and protein excretion at baseline and third year, the results were similar. Conclusion: Higher urinary sodium excretion was more strongly associated with an increased risk of adverse kidney outcomes in patients with higher proteinuria levels.ope

능동 데이타베이스에서 릴레이션간의 관계를 고려한 분산 규칙 리

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밀폐형 연소기에서 난류 예혼합 보염기 화염의 동적 특성

학위논문 (박사)-- 서울대학교 대학원 : 기계항공공학부, 2017. 2. 윤영빈.The dynamic characteristics and the combustion instability phenomenon of a premixed bluff body flame were investigated in a confined duct combustor. When the lean blowoff occurred due to the decrease of the equivalence ratio from the stable flame condition, the characteristics of the lean blowoff was compared and analyzed according to acoustic excitation to consider the external disturbance. Meanwhile, self-excited combustion instability that occur when the equivalence ratio increase from the stable flame conditon and the flashback phenomenon coupled with self-excited combustion instability was investigated. The blowoff equivalence ratio increases with the Reynolds number and changes depending on the extent of the recirculation zone. Using the relation between the Damköhler number and the Reynolds number, it was confirmed that the flow velocity at the downstream tip of the bluff body and the laminar flame speed are decisive blowoff factors. Although a periodic flame hole appeared far from the blowoff only with acoustic excitation, the blowoff observed by OH radical chemiluminescence occurred using a similar process regardless of the excitation. The recirculation zone collapses and the flame becomes small when it is close to the blowoff. Then, the flame is locally extinguished downstream from the bluff body and the recirculation zone completely collapses. Eventually, the unburned gas does not ignite and the flame is extinguished. The blowoff equivalence ratio rapidly increases at specific acoustic excitation frequencies. This was investigated using proper orthogonal decomposition analysis, the two-microphone method, and phaselock particle imaging velocimetry measurement. Resonance occurs when the excitation frequency approaches the harmonic frequency of the combustor and it increases the velocity fluctuation in the combustor and the infiltration velocity of the unburned gas in the shear layer of the recirculation zone. Consequently, because the burning velocity must have a larger value corresponding to the enhanced mixture velocity for a sustained flame, the blowoff occurs at a higher equivalence ratio. In addition, the size of the recircualtion zone was changed according to the phase of the excitation frequency occuring the resonance and it was considered as the cause of attenuation for flame stability. Previous studies investigating flashback in a bluff body have found that the flame moves back and forth around the trailing edge of the bluff bodyhowever, the phenomenon in which the flame propagates beyond the bluff body has not been sufficiently studied. Therefore, it was necessary to understand a strong flashback, which can damage the upper section of a combustor and which is vulnerable to heat due to flame propagation over the front of the bluff body. The combustion instability frequency resulting from changes in the combustion length occurred within the range of the resonance frequency of the combustor, thereby confirming that thermal-acoustic combustion instability occurred in the combustor. In order to examine the flame structure at the moment of flashback, high-speed OH-PLIF and pressure fluctuation measurement were simultaneously conducted and the phase-locked PIV technique was applied. When the strong flashback occurs, an instantaneous adverse pressure gradient is formed within a combustion instability cycle. Consequently, the generated reverse flow pushed the flame attached at the trailing edge of the bluff body to the upstream from the bluff body. The flame propagated rapidly along the side of the bluff body by the influence of the boundary layer flow and the decreased quenching distance. This propagated flame became the ignition source at the front tip of the bluff body and generated the flame surface that propagated in all directionsthus, it was found to be the primary cause of the increase in the flashback distance. The flame flashback distance also varied depending on the combustor length and the initial flow condition. An attempt was made to concentrate the measured data of flashback distance under various conditions into a single line, and turbulence intensity and combustion instability frequency were the dominant factors that impacted the flashback distance. Additionally, in order to confirm the applicability of the research results of flashback under more practical conditions, an experiment was conducted using the hydrogen to fuel ratio, the blockage ratio of the perforated plate, and the reactant temperature as variables. The addition of hydrogen increases the flame speed and flashback distance compared to the methane flame. However, when the proportion of hydrogen exceeds 50%, a flashback proceeds to the fuel injector and the condition for which a flashback distance measurement is meaningless, easily occurs. The increase in the blockage ratio of the perforated plate attenuates the turbulence intensity flow in a non-reacting condition. This property decreases the pressure fluctuation, when combustion instability occurs and also the flashback distance. A rise in the reactant temperature increases the flame stability as well as the flame speed, and a flashback does not occur at a high reactant temperature. As the data gathered with the turbulence intensity and the instability frequency only is incomplete, a modification of the parameters is necessary. The pressure fluctuation data near the orifice is used to represent the pressure fluctuation characteristics of the combustion instability instead of the data at the position of the bluff body. Additionally, the turbulent flame speed is considered to represent the laminar flame speed and the turbulence intensity in each condition. Consequently, using the modified parameters, the relationship amongst the velocity fluctuation, turbulent flame speed, mean velocity, and the combustion instability frequency, and the factors affecting the flashback are confirmed by effectively collecting the experimental results obtained for various cases, including the methane flame condition.CHAPTER 1 INTRODUCTION 1 CHAPTER 2 EXPERIMENT AND MEASUREMENT SYSTEMS 9 2.1 Combustor 9 2.2 Flame Imaging 11 2.2.1 Chemiluminescence Spectroscopy 11 2.2.2 OH PLIF Measurements 13 2.2.3 PIV Measurements 18 CHAPTER 3 EFFECT OF ACOUSTIC EXCITATION ON LEAN BLOWOFF IN TURBULENT PREMIXED BLUFF BODY FLAEMS 21 3.1 Background and Objectives 21 3.2 Experimental Methods 22 3.3 Characteristics of Lean Blowoff under Stable Flame Conditions 27 3.4 Characteristics of Lean Blowoff with Acoustic Excitation 34 3.5 Hypothesis of the Blowoff Mechanism 40 CHAPTER 4 FLASHBACK CHARACTERISTICS COUPLED WITH COMBUSTION INSTABILITY IN TURBULENT PREMIXED BLUFF BODY FLAMES 50 4.1 Background and Objectives 50 4.2 Experimental Methods 51 4.3 Comparison of One Cycle of the Flashback with Different Conditions 53 4.4 Combustion Instability Characteristics with Flashback 55 4.5 Characteristics of the Strong Flashback Phenomenon 57 4.6 Factors Affecting the Flashback Distance 68 CHAPTER 5 EFFECT OF HYDROGEN/PERFORATED PLATE/REACTANT TEMPERATURE ON THE FLAHSBACK IN BLUFF BODY FLAMES 66 5.1 Background and Objectives 66 5.2 Experimental Methods 68 5.2.1 Experimental Apparatus 68 5.2.2 Experimental Conditions 69 5.3 Effect of Hydrogen/Methane Fuel on the Flashback 71 5.4 Effect of Perforated Plate on the Flashback 74 5.5 Effect of the Reactant Temperature on the Flashback 78 5.6 Relationship between the Experimental Conditions and Flashback Distance 80 CHAPTER 6 CONCLUSION 85 APPENDIX A. VOLATGE ADJUSTMENT 89 APPENDIX B. SOUND PRESSURE LEVEL 91 REFERENCES 92 ABSTRACT IN KOREAN 102Docto