Localized corrosion in selective laser melted SS316L in CO2 and H2S brines at elevated temperatures.

In this work, the passivation and localized corrosion of selective laser melted (SLM) stainless steel 316 L when exposed to high pressures of CO2 with the presence of H2S and Cl- at 25 °C and 125 °C were studied. Depletion of Cr/Mo was observed at the cell interiors and melt-pool boundaries (MPBs) compared to the cell boundaries. Volta potential differences obtained from scanning Kelvin probe force microscopy (SKPFM) showed that the MPBs were 8-20 mV lower than the matrix, while the cell interiors were 20-50 mV lower than the cell boundaries. Electrochemical impedance spectroscopy (EIS) and Mott-Schottky tests indicated a more defective passive film at 125 °C, and X-ray photoelectron spectroscopy (XPS) confirmed the formation of a less protective film with an increased S/O ratio at 125 °C than 25 °C. Initiation of localized corrosion was observed at the MPBs and pits formed after a week of immersion were wider by an order of magnitude at 125 °C than 25 °C, with evidence of cell-interior dissolution. While passivity was observed even at elevated temperatures, local chemical heterogeneities compromised the stability of the film and contributed to localized corrosion in SLM SS316L.

Porous Polymer Structures with Tunable Mechanical Properties Using a Water Emulsion Ink.

Recently, the manufacturing of porous polydimethylsiloxane (PDMS) with engineered porosity has gained considerable interest due to its tunable material properties and diverse applications. An innovative approach to control the porosity of PDMS is to use transient liquid phase water to improve its mechanical properties, which has been explored in this work. Adjusting the ratios of deionized water to the PDMS precursor during blending and subsequent curing processes allows for controlled porosity, yielding water emulsion foam with tailored properties. The PDMS-to-water weight ratios were engineered ranging from 100:0 to 10:90, with the 65:35 specimen exhibiting the best mechanical properties with a Young's Modulus of 1.17 MPa, energy absorption of 0.33 MPa, and compressive strength of 3.50 MPa. This led to a porous sample exhibiting a 31.46% increase in the modulus of elasticity over a bulk PDMS sample. Dowsil SE 1700 was then added, improving the storage capabilities of the precursor. The optimal storage temperature was probed, with -60 °C resulting in great pore stability throughout a three-week duration. The possibility of using these water emulsion foams for paste extrusion additive manufacturing (AM) was also analyzed by implementing a rheological modifier, fumed silica. Fumed silica's impact on viscosity was examined, revealing that 9 wt% of silica demonstrates optimal rheological behaviors for AM, bearing a viscosity of 10,290 Pa·s while demonstrating shear-thinning and thixotropic behavior. This study suggests that water can be used as pore-formers for PDMS in conjunction with AM to produce engineered materials and structures for aerospace, medical, and defense industries as sensors, microfluidic devices, and lightweight structures.

Personal Mastery Attenuates the Association between Greater Perceived Discrimination and Lower Amygdala and Anterior Hippocampal Volume in a Diverse Sample of Older Adults.

There is limited research investigating whether perceived discrimination influences brain structures that subserve episodic memory, namely the hippocampus and amygdala. Our rationale for examining these regions build on their known sensitivity to stress and functional differences along the long-axis of the hippocampus, with the anterior hippocampus and amygdala implicated in emotional and stress regulation. We defined perceived discrimination as the unfair treatment of one group by a dominant social group without the agency to respond to the event. A potential moderator of perceived discrimination is personal mastery, which we operationally defined as personal agency. Our primary goals were to determine whether perceived discrimination correlated with amygdala and anterior hippocampal volume, and if personal mastery moderated these relationships. Using FreeSurfer 7.1.0, we processed T1-weighted images to extract bilateral amygdala and hippocampal volumes. Discrimination and personal mastery were assessed via self-report (using the Experiences of Discrimination and Sense of Control questionnaires, respectively). Using multiple regression, greater perceived discrimination correlated with lower bilateral amygdala and anterior hippocampal volume, controlling for current stress, sex, education, age, and intracranial volume. Exploratory subfield analyses showed these associations were localized to the anterior hippocampal CA1 and subiculum. As predicted, using a moderation analysis, personal mastery attenuated the relationship between perceived discrimination and amygdala and anterior hippocampal volume. Here, we extend our knowledge on perceived discrimination as a salient psychosocial stressor with a neurobiological impact on brain systems implicated in stress, memory, and emotional regulation, and provide evidence for personal mastery as a moderating factor of these relationships.

Nonlinear optical properties and carrier recombination lifetime of GaN.

Nonlinear optical properties of a selection of gallium nitride samples have been measured using picosecond and nanosecond duration laser pulses at 532 nm. The values of the two-photon absorption coefficient, free carrier absorption cross section, and free carrier refraction cross section are determined along with the recombination lifetime of photogenerated carriers. The effect of hot isostatic pressing on these properties in samples with linear absorption at the band edge due to defects is explored.

Computational analysis of the optical response of ZnSe with d-orbital defects.

The doping of wide band-gap semiconducting ZnSe by transition metal (TM) atoms finds applications from mid-infrared lasing, sensing, photoelectrochemical cells, to nonlinear optics. Yet understanding the response of these materials at the atomic and electronic level is lacking, particularly in comparing a range of TM dopants, which were studied primarily by phenomenological crystal-field theory. In this work, to investigate bulk ZnSe singly doped with first-row TM atoms, specifically Ti through Cu, we applied a first-principles approach and crystal-field theory to explain the origin of the infrared absorption. We show that the use of an appropriate exchange-correlation functional and a HubbardUcorrection to account for electron correlation improved the determination of the electronic transitions in these systems. We outline an approach for the calculation of the crystal-field splitting from first-principles and find it useful in providing a measure of dopant effects, also in qualitative comparison to our experimental characterization for ZnSe doped with Fe, Cr, and Ni. Our calculated absorption spectra indicate absorption signatures in the mid-infrared range, while the absorption in the visible portion of the spectrum is attributed to the ZnSe host. Our calculations will potentially motivate further experimental exploration of TM-doped ZnSe. Finally, the methods used here provide a route towards computational high-throughput screening of TM dopants in III-V materials through a combination of the electronic band structure and crystal-field theory.

In vitro and in vivo assessment of lactic acid-modified chitosan scaffolds for potential treatment of full-thickness burns.

Autologous skin transplantation is today's "gold standard" treatment for full-thickness burns. However, when > 30% of total body surface area is damaged, there is an important shortage of autologous donor sites for skin grafting; then, treatment alternatives become crucial. Such alternatives can be based on polymeric scaffolds capable of functioning as protective covers and cells/factors carriers. Chitosan (CTS) is a natural-derived polymer with relevant biological-related properties but poor mechanical performance. Improved mechanical properties can be achieved through lactic acid grafting (LA-g); nevertheless, LA-g affects the biological response towards the CTS-based materials. In this work, CTS-LA scaffolds with different LA-g percentages were synthesized and evaluated to determine appropriate LA-g degrees for full-thickness burns treatment. In vitro results indicated that the higher the LA-g percentage, the lower the capability of the scaffolds to sustain fibroblasts culture. Scaffolds with LA-g around 28% (CTS-LA28) sustained cell culture and allowed normal cell functionality. Further evaluation of CTS-LA28 as acellular and cellular grafts in a full-thickness burn mouse model showed that at 28 days post-burn, macroscopic characteristic of the reparation tissue were closer to healthy skin when cellular grafts were used for treatment; histological evaluation also showed that dermis cellularity and collagenous fibers structure were similar to those in healthy skin when cellular grafts were used for burns treatment. © 2017 Wiley Periodicals Inc. J Biomed Mater Res Part A: 105A: 2875-2891, 2017.

Adipokines, insulin resistance, and adiposity as a predictors of metabolic syndrome in child survivors of lymphoma and acute lymphoblastic leukemia of a developing country.

BACKGROUND: There is a growing body of evidence indicating that pediatric survivors of cancer are at a greater risk of developing metabolic syndrome. This study evaluated some probable predictors of metabolic syndrome (MS), such as leptin and adiponectin concentrations, the leptin/adiponectin ratio, insulin resistance, and adiposity, in a sample of child survivors of lymphoma and leukemia in Mexico City. METHODS: Fifty two children (leukemia n = 26, lymphoma n = 26), who were within the first 5 years after cessation of therapy, were considered as eligible to participate in the study. Testing included fasting insulin, glucose, adipokines and lipids; body fat mass was measured by DXA. The MS components were analyzed according to tertiles of adipokines, insulin resistance, and adiposity. Comparisons between continuous variables were performed according to the data distribution. The MS components were analyzed according to tertiles of adipokines, insulin resistance, and adiposity. With the purpose of assessing the risk of a present MS diagnosis, odds ratios (OR) with a 95% confidence interval (95% IC) were obtained using logistic regression analysis according to the various metabolic markers. RESULTS: The median children age was 12.1 years, and the interval time from the completion of therapy to study enrollment was 4 years. Among the MS components, the prevalence of HDL-C low was most common (42%), followed by central obesity (29%). The HOMA-IR (OR 9.0, 95% CI 2.0; 41.1), body fat (OR 5.5, 95% CI 1.6; 19.3), leptin level (OR 5.7, 95% CI 1.6; 20.2) and leptin/adiponectin ratio (OR 9.4, 95% CI 2.0; 49.8) in the highest tertile, were predictive factors of developing MS; whereas the lowest tertile of adiponectin was associated with a protective effect but not significant. CONCLUSIONS: Biomarkers such as HOMA-IR, leptin and leptin/adiponectin are associated with each of the components of the MS and with a heightened risk of suffering MS among children survivors of cancer. Given the close relationship between MS with risk of developing type 2 diabetes and cardiovascular disease, it is imperative to implement prevention measures in this population and especially in developing countries where these pathologies have become the leading cause of death.

Antiphospholipid syndrome: analysis of dilute Russell's viper venom time titer.

To evaluate the characteristic features of the dilute Russell's viper venom time (DRVVT) titer in the antiphospholipid syndrome (APS). The medical record of 3660 consecutive patients with DRVVT orders between 2006 and 2015 were examined for criteria satisfying the diagnosis of APS. DRVVT titer was studied as a function of titer distribution, titer stability, and clinicopathologic features. Twenty-six patients were diagnosed with APS based on a persistently positive DRVVT and a history of arterial or venous thrombosis. DRVVT titer was mostly of low magnitude (65-77% of patients), was of similar value between initial and repeat testing (mean DRVVT titer 1.40 vs. 1.38; P = 0.858; mean time interval 216 days), and was positively associated with anticardiolipin antibodies (IgG and IgM) and antibeta-2-glycoprotein I antibodies (IgG and IgM) (P < 0.020). Low titer and moderate/high titer DRVVT were associated with a triple positive antiphospholipid antibody profile in 0 and 62% of patients, respectively (P < 0.020). DRVVT titer in APS was predominantly low in magnitude, stable over time, and associated with specific antiphospholipid antibody profiles.

Hysterosalpingo-Contrast Sonography With a Saline-Air Device Is Equivalent to Hysterosalpingography Only in the Presence of Tubal Patency.

OBJECTIVES: To compare hysterosalpingo-contrast sonography with a saline-air device to hysterosalpingography for evaluating tubal patency. METHODS: Eighty women undergoing infertility evaluations were recruited for this prospective cohort study. All patients underwent both office-based hysterosalpingo-contrast sonography with a saline-air device and hysterosalpingography as the reference standard, and the fallopian tubes were individually assessed for tubal patency in each procedure. The Cohen κ coefficient was used to assess agreement between each procedure, and the Student t test and χ(2) test were used to compare differences in time, pain, and procedural preference. RESULTS: In total, 75 patients with 148 fallopian tubes were evaluated. Tubal patency on hysterosalpingo-contrast sonography with the saline-air device was noted in 85.8% (n = 127) of tubes compared to 92.5% (n = 137) on hysterosalpingography, with a positive predictive value of 95.2%. Tubal occlusion was noted in 21 tubes (14.2%) on hysterosalpingo-contrast sonography compared to 11 (7.4%) on hysterosalpingography, with a negative predictive value of 23.8% (24 of 28). Overall, hysterosalpingo-contrast sonography agreed with hysterosalpingography in 126 of 148 fallopian tubes (85.1%; κ = 0.47; P < .001). The procedural time and pain scores were significantly greater for hysterosalpingo-contrast sonography compared to hysterosalpingography. CONCLUSIONS: There was a significant degree of agreement between hysterosalpingo-contrast sonography with a saline-air device and hysterosalpingography when the fallopian tube was patent but not when it was occluded. In the absence of patency, further evaluations with hysterosalpingography may be indicated to avoid false-positive results. Although the procedure time and degree of pain appear to be greater, avoidance of radiation exposure by using hysterosalpingo-contrast sonography with a saline-air device may outweigh the drawbacks.

Fasceítis necrosante cervicofacial: una infección severa que requiere tratamiento quirúrgico temprano / Cervicofacial necrotizing fasciitis: a rare disease with a high mortality requiring early debridement for survival

Propósito. Revisar la experiencia clínica, el manejo quirúrgico y los resultados del tratamiento de pacientes con fasceítis necrosante cervicofacial (FNC) en nuestras instituciones. Métodos. Un estudio retrospectivo de pacientes con FNC en un periodo de 10 años en 2 instituciones académicas. Resultados. Cinco pacientes con datos completos (clínicos, imágenes, cultivos microbiológicos, tratamiento y seguimiento) fueron identificados. La FNC resultó de una infección polimicrobiana en 4 pacientes y monomicrobiana en un paciente. La etiología de FNC fue odontogénica en 3 pacientes, postraumatismo en un paciente e idiopática en un paciente. Todos los pacientes fueron tratados con tratamiento quirúrgico (desbridamiento) agresivo temprano, antibióticos de amplio espectro y reconstrucción con diferentes tipos de colgajos. Se registró una mortalidad. Conclusiones. El diagnóstico temprano y un tratamiento quirúrgico agresivo son elementos clave en reducir la mortalidad y optimizar los resultados funcionales y cosméticos en los pacientes con FNC (AU)

Purpose. To review the clinical experience, management and outcome of cervicofacial necrotizing fasciitis (CFN) in patients treated in our institution. Methods. A retrospective review of patients with CFN from two large health care institutions completed over a 10-year period. Results. Five patients with complete data were identified. CNF was polymicrobial in 4 and monomicrobial in one patient and occurred as a result of odontogenic infection in 3, trauma in 1, and was idiopathic in one patient. All patients were treated with extensive debridement, broad spectrum antibiotics, and reconstruction with flaps. There was one death. Conclusions. Early diagnosis and rapid aggressive debridement are key elements for reducing mortality and optimizing the cosmetic and functional outcome in patients with CFN (AU)

Mid-IR spectroscopy of Fe:ZnSe quantum dots.

We report spectroscopic characterization of Fe:ZnSe quantum dots (for 2% of Zn/Fe molar ratio) fabricated by microemulsion hydrothermal synthesis. Mid-IR photoluminescence of the 5E↔5T2 transition of Fe2+ ions over 3.5-4.5 µm spectral range was observed in Fe:ZnSe quantum dot samples and kinetics of luminescence have been characterized at temperatures of 30-300 K under direct (2.788 µm) mid-IR excitation and indirect (0.355 µm) photoionization excitation. The radiative lifetime (τrad) was estimated from these measurements to be 48 µs while lifetime at room temperature was measured to be 440 ns. This agrees closely with the behavior of bulk material.

Effects of High-Butterfat Diet on Embryo Implantation in Female Rats Exposed to Bisphenol A.

Bisphenol A (BPA) is an endocrine disruptor associated with poor pregnancy outcomes in human and rodents. The effects of butterfat diets on embryo implantation and whether it modifies BPA's actions are currently unknown. We aimed to determine the effects of butterfat diet on embryo implantation success in female rats exposed to an environmentally relevant dose of BPA. Female Sprague-Dawley rats were exposed to dietary butterfat (10% or 39% kcal/kg body weight [BW]) in the presence or absence of BPA (250 µg/kg BW) or ethinylestradiol (0.1 µg/kg BW) shortly before and during pregnancy to assess embryo implantation potentials by preimplantation development and transport, in vitro blastulation, outgrowth, and implantation. On gestational day (GD) 4.5, rats treated with BPA alone had higher serum total BPA level (2.3-3.7 ng/ml). They had more late-stage preimplantation embryos, whereas those receiving high butterfat (HBF) diet had the most advanced-stage embryos; dams cotreated with HBF and BPA had the most number of advanced embryos. BPA markedly delayed embryo transport to the uterus, but neither amount of butterfat had modifying effects. An in vitro implantation assay showed HBF doubled the outgrowth area, with BPA having no effect. In vivo, BPA reduced the number of implanted embryos on GD8, and cotreatment with HBF eliminated this adverse effect. HBF diet overall resulted in more and larger GD8 embryos. This study reveals the implantation disruptive effects of maternal exposure to an environmentally relevant dose of BPA and identifies HBF diet as a modifier of BPA in promoting early embryonic health.

Large cell neuroendocrine carcinoma: topic review and a unique case of metastasis to the mandible.

There are few reports of large cell neuroendocrine carcinoma (LCNEC) metastasis to the head and neck region, and no cases reporting LCNEC from lung metastasizing to the mandible. LCNEC is not well reported in the literature due to recent changes in the criteria for diagnosis, revised in 2004 by the world health organization, due to its propensity for rapid growth and low 5 year prognosis. We present a 61 year old female diagnosed with LCNEC of the lung in October, 2007 treated with radiation and chemotherapy. Our patient had a PET scan performed in March, 2009 revealing no sign of metastasis. In July, 2009 she was seen for suspected sialadenitis by another department and referred to our oral and maxillofacial surgery clinic. Her signs and symptoms were consistent with metastatic disease to the mandible confirmed by histologic and immunohistochemical examination which revealed an invasive poorly differentiated non-small cell carcinoma. Palliative care was offered. Our patient died 2 years after initial diagnosis of lung cancer and 3 months after initial finding of metastatic disease. The rapid growth and spread of this cancer was surprising and knowledge of this cancer should be included in a differential diagnosis of expanding mandibular jaw lesions.

Trends in maxillofacial trauma: a comparison of two cohorts of patients at a single institution 20 years apart.

PURPOSE: The purpose of this study was to compare and characterize 2 cohorts of patients with maxillofacial fractures within the same institution over 2 6-year time frames 20 years apart. MATERIALS AND METHODS: A retrospective review of patients with maxillofacial fractures at the authors' institution from 2004 to 2010 was performed, and a comparison was made with the authors' experience from 1984 to 1990. RESULTS: The 1990 study showed 458 maxillofacial fractures (152 midface and 306 mandibular fractures). In the 2010 study, there were 1,731 maxillofacial fractures (1,313 midface and 418 mandibular fractures). There were significant differences in the mechanism of injury between the 1990 and 2010 studies: assaults decreased from 48.8% to 29.7%, motor vehicle collisions decreased from 39.1% to 29.6%, and falls increased from 3.6% to 22.1%. Comparison by age categories showed major changes in the following groups: maxillofacial fractures in patients 21 to 40 years old decreased from 61.7% to 35.3%, those in patients 41 to 65 years old increased from 13.1% to 35.4%, and those in patients at least 66 years old (elderly) increased from 0.2% to 14.5%. All these changes were statistically significant (P < .0001). CONCLUSION: Maxillofacial trauma has changed significantly over the past 2 decades in the authors' institution. A decrease in assault-related injuries in the younger populations and an increase in the incidence of falls in the elderly were the main differences. There was a significant increase in elderly patients with maxillofacial trauma. This change emphasizes the need for adequate prevention programs and appropriate maxillofacial surgery teams to manage these injuries in the older patient.

Orthognathic surgery for correction of patients with mandibular excess: don't forget to assess the gonial angle.

PURPOSE: To evaluate the gonial angle (GA) and associated factors that can contribute to stability after bilateral sagittal split ramus osteotomy setback and Le Fort I advancement osteotomy for the treatment of patients with mandibular excess. MATERIALS AND METHODS: This retrospective study included 42 randomly selected, adult patients. Lateral cephalometric radiographs were obtained before and 1 week and 1 year after surgery. Patients in group 1 (n = 18) had a GA smaller than 125° and those in group 2 (n = 24) had a GA larger than 125°. Data were analyzed by analysis of variance and Pearson correlations. Multivariate linear regression analysis was used to identify factors that influenced postsurgical stability. RESULTS: Mean surgical changes were similar in the 2 groups. The mandible was set back an average of 5.4 mm in group 1 and 6.4 mm in group 2, whereas the maxilla was advanced 2.5 mm in group 1 and 1.7 mm in group 2. Statistically significant postoperative changes were noted for group 1 only. Relapse was found at the innermost point of the contour of the mandible between the incisor tooth and bony chin and the pogonion for the horizontal landmarks; the innermost point of the contour of the maxilla between the anterior nasal spine and incisor tooth and the menton for the vertical landmarks; and the GA, the angle between the sella-nasion line and the innermost point of the contour of the mandible between the incisor tooth and bony chin, and the esthetic plane to the upper lip for the dimensional landmarks. No statistically significant changes were noted for group 2 (GA >125°). CONCLUSION: Patients with a preoperative GA smaller than 125° have a greater risk of relapse after receiving bilateral sagittal split ramus osteotomy setback and Le Fort I advancement for the treatment of mandibular excess. Patients with a preoperative GA larger than 125° appear to have a more predictable procedure.

El colgajo miomucoso de la arteria facial para tratamiento de defectos intraorales. Reporte de 2 Casos / The facial artery myomucosal flap (FAMM) for the management of intraoral defects. Report of 2 cases

El tratamiento de defectos intraorales puede resultar complicado y mórbido cuando se usan colgajos distantes. En determinados casos el uso del colgajo miomucoso de la arteria facial (CMMAF) puede facilitar el cierre de defectos intraorales de tamaño pequeño y mediano. Presentamos 2 casos manejados con CMMAF para cierre de fistulas oronasal y vestíbulo antero inferior mandibular. La técnica es sencilla y no requiere entrenamiento extensivo ya que la anatomía de la zona es muy familiar para todo cirujano oral y maxilofacial. En conclusión el CMMAF debería considerarse como una de las primeras opciones para reconstruir defectos intraorales de cierto tamaño.

The management of intraoral defects can be complicated and carry significant morbidity when using distant flaps. In selected cases the use of a facial artery myomucosal flap (FAMM) facilitates the closure of small and medium size defects. We are reporting 2 cases in which a FAMM flap was used successfully to close an oronasal and orocutaneous fistulaes. The surgical technique is simple and does not require specialized training due to the familiarity with the anatomic region that all oral and maxillofacial surgeons have. In conclusion we believe the FAMM flap should be considered as one of the first reconstruction options for certain size intraoral defects.

Ulipristal acetate as an emergency contraceptive agent.

INTRODUCTION: Emergency contraceptive agents play a crucial role in preventing unplanned pregnancy. These agents and devices have been studied since the 1960s and have had varied results in terms of side effects and efficacy. A new oral tablet for emergency contraception (EC), ulipristal acetate (UPA) , is a selective progesterone receptor modulator and can be used up to 120 h following unprotected intercourse, without an increase in adverse effects or a decrease in efficacy. AREAS COVERED: This article reviews studies that evaluate the pharmacodynamics, pharmacokinetics, clinical efficacy, and safety profile of UPA as an emergency contraceptive agent. EXPERT OPINION: UPA, a selective progesterone receptor modulator, is administered as a single 30 mg dose for EC. This agent provides a comparable, if not better, efficacy and side effect profile than seen with levonorgestrel or mifepristone. Because it has both agonistic and antagonistic effects on the progesterone receptor, ongoing clinical trials are documenting UPA's use for patients with endometriosis and as an extended use contraceptive.

Efficient time-series detection of the strong stochasticity threshold in Fermi-Pasta-Ulam oscillator lattices.

In this work we study the possibility of detecting the so-called strong stochasticity threshold (i.e., the transition between weak and strong chaos as the energy density of the system is increased) in anharmonic oscillator chains by means of the 0-1 test for chaos. We compare the result of the aforementioned methodology with the scaling behavior of the largest Lyapunov exponent computed by means of tangent space dynamics, which has, so far, been the most reliable method available to detect the strong stochasticity threshold. We find that indeed the 0-1 test can perform the detection in the range of energy density values studied. Furthermore, we determined that conventional nonlinear time series analysis methods fail to properly compute the largest Lyapounov exponent even for very large data sets, whereas the computational effort of the 0-1 test remains the same in the whole range of values of the energy density considered with moderate size time series. Therefore, our results show that, for a qualitative probing of phase space, the 0-1 test can be an effective tool if its limitations are properly taken into account.

A high-capacity RNA affinity column for the purification of human IRP1 and IRP2 overexpressed in Pichia pastoris.

Regulated expression of proteins involved in mammalian iron metabolism is achieved in part through the interaction of the iron regulatory proteins IRP1 and IRP2 with highly conserved RNA stem-loop structures, known as iron-responsive elements (IREs), that are located within the 5' or 3' untranslated regions of regulated transcripts. As part of an effort to determine the structures of the IRP-IRE complexes using crystallographic methods, we have developed an efficient process for obtaining functionally pure IRP1 and IRP2 that relies upon the improved overexpression (>10 mg of soluble IRP per liter of culture) of each human IRP in the yeast Pichia pastoris and large-scale purification using RNA affinity chromatography. Despite the utility of RNA affinity chromatography in the isolation of RNA-binding proteins, current methods for preparing RNA affinity matrices produce columns of low capacity and limited stability. To address these limitations, we have devised a simple method for preparing stable, reusable, high-capacity RNA affinity columns. This method utilizes a bifunctional linker to covalently join a 5'-amino tethered RNA with a thiol-modified Sepharose, and can be used to load 150 nmole or more of RNA per milliliter of solid support. We demonstrate here the use of an IRE affinity column in the large-scale purification of IRP1 and IRP2, and suggest that the convenience of this approach will prove attractive in the analysis of other RNA-binding proteins.