Axial Back Research Articles

Psoas Muscle Health is Correlated With Time to Achieve MCID in Patients With Predominant Axial Back Pain Following Decompression Surgery: Early Results.

Retrospective cohort study. To determine the impact of psoas muscle health [cross-sectional area (CSA)] on achieving minimal clinically important differences (MCID) in patient-reported outcome measures (PROMs) following laminectomy for patients with predominant back pain (PBP) and leg pain (PLP). Psoas muscle health is linked to postoperative outcomes in decompression patients, with MRI-based grading of psoas CSA correlating with these outcomes. However, evidence on its impact on symptomatic recovery, measured by PROMs, is lacking. One hundred six patients with PBP (VAS back > VAS leg) and 139 patients with PLP (VAS leg > VAS back) who underwent laminectomy from 2017 to 2021 were included. Axial T2 MRI images were analyzed for psoas CSA using a validated method. Based on the lowest-quartile normalized total psoas area (NTPA) thresholds, patients were divided into "good" and "poor" muscle health groups. The correlation analyses were performed between the psoas CSA and changes in PROMs. Kaplan-Meier survival analysis was conducted to determine the probability of achieving MCID as a function of time. Of 106 patients with PBP, 83 (78.3%) had good muscle health, and 23 (21.6%) had poor muscle health. Of 139 patients with PLP, 54 (38.8%) had good muscle health, and 85 (61.1%) had poor muscle health. In the PBP group, older age was associated with poor muscle health (69.70±9.26 vs . 59.92±15.01, P =0.0002). For both cohorts, there were no differences in the rate of MCID achievement for any PROMs between the good and poor muscle health groups. In the PBP group, Kaplan-Meier analysis showed patients with good psoas health achieved MCID-VAS back and Oswestry Disability Index (ODI) in median times of 14 and 42 days ( P =0.045 and 0.015), respectively. Good psoas muscle health is linked to faster attainment of MCID, especially in patients with PBP compared with PLP after decompression surgery. III.

Spinal Cord Stimulation as an Alternative to Opioid for Axial Neck and Back Pain: A Case Series

IntroductionSpinal cord stimulation is emerging as a minimally invasive technique for treatment of persistent spinal pain syndrome (PSPS).MethodsWe describe a case series of 25 individuals with PSPS who underwent implantation of a spinal cord stimulator device between 2017 and 2021.ResultsThere was a significant reduction in mean visual analog scale pain scores in the immediate postoperative phase, (8.61 vs. 2.3, p < 0.001). There were twelve patients who consumed pre-operative opioid, and 75% showed reduction of use with a significantly lower average daily dose (66.8 vs. 26.9 meq/D, p < 0.05). There was a significant reduction in the Oswestry Disability Index during postoperative follow-up visits (p < 0.001). There were no major perioperative or long-term complications from the procedure in follow-up.ConclusionThe analysis of this cohort suggests successful long-term treatment of a diverse set of patients with PSPS who underwent spinal cord stimulation (SCS) and had meaningful improvement in quality of life and reduction in opioid consumption.

Concept of the Number Needed to Treat for the Analysis of Pain Relief Outcomes in Patients Treated with Spinal Cord Stimulation.

In the rapidly evolving field of spinal cord stimulation (SCS), measures of treatment effects are needed to help understand the benefits of new therapies. The present article elaborates the number needed to treat (NNT) concept and applies it to the SCS field. We reviewed the basic theory of the NNT, its calculation method, and its application to historical controlled trials of SCS. We searched the literature for controlled studies with ≥20 implanted SCS patients with chronic axial back and/or leg pain followed for ≥3 months and a reported responder rate defined as ≥50% pain relief. Relevant data necessary to estimate the NNT were extracted from the included articles. In total, 12 of 1616 records were eligible for inclusion. The records reported 10 clinical studies, including 7 randomized controlled trials, 2 randomized crossover trials, and 1 controlled cohort study. The studies investigated traditional SCS and more recently developed SCS modalities, including 10 kHz SCS. In conclusion, the NNT estimate may help SCS stakeholders better understand the effect size difference between compared treatments; however, interpretation of any NNT should take into account its full context. In addition, comparisons across trials of different therapies should be avoided since they are prone to interpretation biases.

Effects of Local Anesthetics With or Without Steroids in High-Volume Transforaminal Epidural Blocks for Lumbar Disc Herniation: A Randomized, Double-Blind, Controlled Trial.

BackgroundLumbar transforaminal epidural block (TFEB) is an effective treatment modality for radicular pain due to lumbar disc herniation (LDH). The addition of steroids is more effective than local anesthetic alone in TFEBs for patients with LDH. Moreover, the efficacy of TFEBs has been reported to be positively correlated with the volume of injectate. We hypothesized that high-volume TFEBs without steroids effectively alleviate axial back and radicular pain associated with LDH. This study compared the efficacy of high-volume TFEBs with vs. without steroids for the management of the axial and radicular pain caused by LDH.MethodsA total of 54 patients were randomly assigned to either group L or group D. Patients in group L received 8-mL injections of 0.33% lidocaine only. Patients in group D received 8-mL injections of 0.33% lidocaine with 5 mg of dexamethasone. The primary outcomes were pain intensity at baseline and 4 weeks after the procedure. The secondary outcomes included the change of functional disability between baseline and 4 weeks after the procedure, pain scores during injection, and adverse effects.ResultsBoth groups showed a significant reduction in axial and radicular pain and improvement in the functional status at the outpatient visit 4 weeks after TFEB. However, there were no significant differences between the groups in terms of changes in back pain (10.00 [20.00] vs. 10.00 [22.50]; P = 0.896) or radicular pain (5.00 [20.00] vs. 10.00 [12.50]; P = 0.871).ConclusionHigh-volume TFEBs with and without steroid administration yielded similar significant pain reductions and functional improvements among LDH patients 4 weeks after the procedure.

Cooled-radiofrequency neurotomy for the treatment of chronic lumbar facet (zygapophyseal) joint pain: A retrospective study.

Cooled-radiofrequency (CRFA) is a newer technique and may have some theoretical advantages over traditional radiofrequency ablation (TRFA). In this study, we aimed to investigate the efficacy and safety of CRFA for the treatment of lumbar facet joint-mediated pain. In this retrospective study, we evaluated 185 CRFA performed on 105 patients. All patients with axial lower back who received the preliminary diagnosis of lumbar facet joint-mediated pain and refractory to conservative therapy underwent diagnostic medial branch blocks. CRFA was recommended to those patients who responded favorably to two sets of diagnostic medial branch blocks. Pain scores in numeric rating scale (NRS) were recorded pre-treatment and post-treatment at different time-points. The primary outcome measure was to report descriptive NRS score and average % improvement from baseline at each time point. A significant pain relief was determined by a decrease of ≥50% of mean NRS. Secondary outcome measure was the time to repeat treatment with subsequent CRFA. Adverse events were also recorded.Primary outcome measure determined as the improvement in NRS, for at least 50% or more, was achieved in both 1st (4–8 weeks) and 2nd (>2–6 months) follow-up (FU) with 60.5% and 53.6% reduction in NRS respectively. Our subgroup analysis comparing the younger (<50) and older (≥50) age groups showed superior pain relief with CRFA in the older (≥50) age group, both in the 1st (4–8 weeks) and 2nd (>2–6 months) FU time points (63.4% and 58.4% reduction in NRS, respectively). Cooled-radiofrequency ablation is an effective and safe procedure for the treatment of chronic lumbar facet joint related pain. The duration of pain relief was comparable to traditional radiofrequency ablation as reported in the literature.

A new air recirculation system for homogeneous solar drying: Computational fluid dynamics approach

Improvement of air flow distribution, air velocity and temperature inside a mixed greenhouse dryer was numerically investigated using 3D CFD ANSYS FLUENT code. The study was performed considering six different locations of axial fans inside the greenhouse. Additional elements such as a false ceiling and front and back internal walls were included in some configurations to analyze their contribution in improving the air distribution. Numerical simulations were focused on dynamic fluid models in order to select the best configuration to achieve homogeneous air distribution and velocity among the six proposals. Then, the temperature distribution was analyzed considering the contribution of solar energy in the best-selected greenhouse configuration. Additionally, the Discrete Ordinate (DO) model was used to simulate the mechanism of heat transfer from solar radiation to the greenhouse. The results showed that installing an air recirculation system (including: axial fan, false ceiling, back and front walls), into the greenhouse can increase the air velocity in the drying chamber from 0.71 m/s to 1.5 m/s and the temperature from 315 K to 360 K, which represent an increase of approximately 111.26% y 11.11%, respectively, compared with the greenhouse without an air recirculation system. This improvement could result in the reduction of drying time and a homogeneous moisture content in dry products.

Oxygen Reduction Reaction at Co and Fe MN5 Catalysts. Calculated and Experimental O2-Fe and O2-Co Binding Energy, Activity Indexes, Volcano Correlations

The oxygen reduction reaction (ORR) is a fundamental chemical reaction in industrial processes as well as in living systems, being O2, the final electron (e-) acceptor of many reactions. Since then its importance in the fuel cell technology where energy would be stored in the form of H2 to be oxidized in conjunction with the reduction of the cheap and abundant O2. However, the ORR is a complicated reaction which involves the transfer of 4 electrons and 4 protons and for its nature, it proceeds through the consequent formation of more than one intermediate accounting for the so-called “scaling correlations” [1]. The complexity of the reaction determines the slow kinetics and the difficulties into finding an adequate catalyst for it to proceed without energy losses. The “industrial standard” catalysts for this reaction are based on the very expensive and rare Pt metal. An uncountable number of non-precious metal catalysts (NPMC) have been studied with the purpose to replace Pt. In our research group, we are adopting various strategies to increase the activity and the stability of metal phthalocyanines like the substitution of planar neutral residues with more electron-negative ones, and the addition of axial back ligands [2-5]. In this research work we studied the electrocatalytic activity towards the ORR of a new compound i.e. the iron 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadeca(fluoro) phthalocyanine (16(F)FePc) in the absence and in the presence of a fifth pyridine axial ligand (FeN5). Interesting the 16(F)FePc appears to be the most active among all the FeN4 studied to the moment. The very high redox potential of the active Fe(III)/Fe(II) redox couple (-0.075 V and 0.44 V vs. SCE at pH 13 and at pH 1 respectively) confirms the correlation between the activity of the catalyst vs. redox potential of the active redox couple of the metal in the catalyst. 16(F)FePc was so active towards the ORR that the production of H2O2 measured at rotating ring electrodes was nil at pH 13 and very low at pH 1. In the presence of pyridine axial ligand, the redox potential increased of almost 60 mV and catalytic currents and stability of the catalyst also drastically increased. The catalysts were characterized with electrochemical techniques and by EPR and XPS spectroscopy in the presence and in the absence of O2. We could therefore experimentally evaluate the binding energy of O2 to the Fe metal centre. Ab initio calculations, confirm the experimental data and the importance of the pyridine axial ligand to lower the binding energy of O2 to the Fe metal centre because of decoupling of the Fe from the carbon support and changes in the geometrical and electronic structure.[1] Reactivity Descriptors for the Activity of Molecular MN4 Catalysts for the Oxygen Reduction Reaction. Angew. Chem. Int. Ed., 55 (2016) 14510-14521. J.H. Zagal, M.T.M. Koper.[2] Adsorption of 4,4 ́-dithiodipyridine axially coordinated to Iron(II) phthalocyanine on Au(111) as a new strategy for oxygen reduction electrocatalysis. Chemphyschem, (2018), 19(13), 1599-1604.S. Herrera, F. J. Williams, E. J. Calvo, F. Tasca.[3] Biomimicking vitamin B12. A Co phthalocyanine pyridine axial ligand coordinated catalyst for the oxygen reduction reaction. Electrochimica Acta. (2018), 265, 547-555. J. Riquelme, K. Neira, W. Orellana, P. Hermosilla, J. F. Marco, J. H. Zagal, F. Tasca.[4] Comparison of the Catalytic Activity for the Reduction of O2 of Fe and Co MN4 Complexes Adsorbed on Edge Plane Graphite Electrodes and on Carbon Nanotubes. Physical Chemistry Chemical Physics. (2017), 19(31), 20441-20450. R. Venegas, F. J. Recio, J. Riquelme, K. Neira, J. F. Marco, I. Ponce, J. H. Zagal, F. Tasca.[5] Biomimetic reduction of O2 in acid medium on iron phthalocyanines axially coordinated to pyridine anchored on carbon nanotubes”. Journal of Material Chemistry A. (2017), 5(24), 12054-12059. R. Venegas, F. J. Recio, J. Riquelme, K. Neira, J. F. Marco, I. Ponce, J. H. Zagal, F. Tasca.

A Detailed Analysis of Clinical Features and Outcomes of Patients with Pyogenic Spondylodiscitis Presenting without Axial Back Pain.

Study design: Retrospective analysis of a single institution prospective, longitudinal database of spinal pyogenic infections. Diagnosis of pyogenic spondylodiscitis (PS) can be challenging. Although presenting symptoms are often non-specific, acute non-remitting axial back pain is the most striking feature. Nevertheless, several authors have reported on the uncommon occurrence of patients with PS without axial back pain. The aim of this study was to characterize presenting symptoms, causative agents, comorbidities, and treatment outcomes of patients presenting with painless pyogenic spondylodiscitis. A total of 214 patients diagnosed with PS were reviewed; patients were divided into two groups: patients presenting with no axial back pain (no pain group, n = 16), and patients presenting with axial back pain (control group, n = 198). Analyzed data comprised general demographics, presenting symptoms, comorbidities, spinal infection location, and amount of spinal involvement. While average age (62.4 vs. 65.0) and sex distribution was similar between the two groups, a significant diagnostic delay was noted in the control group (53 vs. 17 days, p < 0.001). Patients in the no pain group were more likely IV drug abusers or have had liver failure/cirrhosis. Anatomic distribution (i.e., cervical vs thoracolumbar) of the infection did not differ between the two groups, but a higher number of post-surgical infections was noted in the no pain group (37.5 vs. 15.6%, p = 0.026). E. coli and Pseudomonas spp. were more commonly seen in no pain group patients, and mortality was also higher in this group (12.5 vs. 6.0%, p = 0.004).

Percutaneous Peripheral Nerve Stimulation of the Medial Branch Nerves for the Treatment of Chronic Axial Back Pain in Patients After Radiofrequency Ablation.

ObjectiveLumbar radiofrequency ablation is a commonly used intervention for chronic back pain. However, the pain typically returns, and though retreatment may be successful, the procedure involves destruction of the medial branch nerves, which denervates the multifidus. Repeated procedures typically have diminishing returns, which can lead to opioid use, surgery, or implantation of permanent neuromodulation systems. The objective of this report is to demonstrate the potential use of percutaneous peripheral nerve stimulation (PNS) as a minimally invasive, nondestructive, motor-sparing alternative to repeat radiofrequency ablation and more invasive surgical procedures.DesignProspective, multicenter trial.MethodsIndividuals with a return of chronic axial pain after radiofrequency ablation underwent implantation of percutaneous PNS leads targeting the medial branch nerves. Stimulation was delivered for up to 60 days, after which the leads were removed. Participants were followed up to 5 months after the start of PNS. Outcomes included pain intensity, disability, and pain interference.ResultsHighly clinically significant (≥50%) reductions in average pain intensity were reported by a majority of participants (67%, n = 10/15) after 2 months with PNS, and a majority experienced clinically significant improvements in functional outcomes, as measured by disability (87%, n = 13/15) and pain interference (80%, n = 12/15). Five months after PNS, 93% (n = 14/15) reported clinically meaningful improvement in one or more outcome measures, and a majority experienced clinically meaningful improvements in all three outcomes (i.e., pain intensity, disability, and pain interference).ConclusionsPercutaneous PNS has the potential to shift the pain management paradigm by providing an effective, nondestructive, motor-sparing neuromodulation treatment.

Michigan Spine Surgeons are not Overtreating Axial Back Pain Without Radicular Symptoms

Macki, Mohamed MD; Hamilton, Travis; Bazydlo, Michael MS; Schultz, Lonni PhD; Seyfried, Donald M MD; Park, Paul MD; Abdulhak, Muwaffak MD; Chang, Victor W MD; Schwalb, Jason M MD Author Information

Effect of Discharge Energy of Magnetic Pulse Compaction on the Powder Compaction Characteristics and Spring Back Behavior of Copper Compacts

Magnetic pulse compaction (MPC) technology had unique compaction advantages compared to traditional powder compaction methods. In this study, the pure copper compacts have been consolidated by MPC technique. The effect of discharge energy on the microstructures, relative density, micro hardness, strain and stress of copper compacts were analyzed via optical microscopy, scanning electron microscopy, hardness tester and FEM simulation. The relationship between discharge energy and spring back was analyzed by numerical calculation. Results showed that the MPC method had the advantages to refine powder particles. The relative density of copper compacts reached 96% when the discharge energy was 9 kJ. Stress concentration was occurred at the upper edge of the powder body, and propagated to the upper center, lower edge and middle position of the powder body. The powder body could have a uniform strain distribution in a short period of time when the discharge energy was greater than 7 kJ. There was a linear relationship between the relative density and the logarithm of Vickers hardness. The axial and radial spring back both increased with the increase of discharge energy. When the discharge energy was 9 kJ, the axial and radial spring back was 2.36% and 0.42%.

Use of Single-Photon Emission Computed Tomography Imaging for Hypermetabolic Facet Identification in Diagnosis of Cervical and Axial Back Pain

Few studies have used hybrid single-photon emission computed tomography (SPECT)/computed tomography (CT) scan to identify degenerative facet disease. We aimed to determine the incidence of hypermetabolic facets on SPECT/CT imaging in patients with axial neck or back pain to elucidate the value of SPECT/CT scan in identifying pain generators. A retrospective review of adult patients with axial neck or back pain was conducted. A total of 190 patients underwent high-resolution SPECT/CT imaging using a standardized protocol from January 2010 to April 2018. Facet joints with increased radionuclide uptake on SPECT imaging were characterized as hypermetabolic. Number, level, and laterality of hypermetabolic facets were recorded based on review of imaging and radiologist impressions. The average age of the patients was 58 ± 13 years, and 51% of patients were men. A total of 85 patients (48%) demonstrated zygapophyseal joint hypermetabolism (ZJH) on SPECT imaging. A total of 202 hypermetabolic facets were identified, indicating the average number of facets with ZJH was 2.38 ± 1.91. Of patients with a positive scan, lumbar facets were most commonly affected (69% of ZJH) followed by cervical (24%) and thoracic regions (6%). C1-2 and C2-3 (22% each of cervical ZJH) and L4-5 (32% of lumbar ZJH) were most commonly affected in the cervical and lumbar regions, respectively. Nearly half of all patients with axial neck or back pain demonstrated ZJH on SPECT/CT imaging, supporting ZJH sites as potential pain generators and targets for treatment. Our results support the role for SPECT/CT imaging in the workup of patients with axial neck or back pain, which may reduce invasive diagnostic procedures and aid in treatment planning.

Cervical Interlaminar Epidural Injections In The Treatment Of Cervical Disc Herniation, Post Surgery Syndrome, Or Discogenic Pain: Cost Utility Analysis From Randomized Trials

Background: Neck pain is one of the major conditions attributing to overall disability in the United States. There have been multiple publications assessing clinical and cost effectiveness of multiple modalities of interventions in managing chronic neck pain. Even then, the literature has been considered sparse in relation to cervical interlaminar epidural injections in managing chronic neck pain. In contrast, cost utility studies of lumbar interlaminar injections, caudal epidural injections, cervical and lumbar facet joint nerve blocks, percutaneous adhesiolysis demonstrated costs of less than $3,500 for quality-adjusted life year (QALY). Objectives: To assess the cost utility of cervical interlaminar epidural injections in managing chronic neck and/or upper extremity pain secondary to cervical disc herniation, post-surgery syndrome in neck, and axial or discogenic neck pain. Study Design: Analysis based on 3 previously published randomized trials of the effectiveness of cervical interlaminar epidural injections assessing their role in disc herniation, cervical post-surgery syndrome, and axial or discogenic pain. Setting: A contemporary, private, specialty referral interventional pain management center in the United States. Methods: Cost utility of cervical interlaminar epidural injections with or without steroids in managing cervical disc herniation, cervical post-surgery syndrome, and cervical discogenic or axial neck back pain was conducted with data derived from 3 randomized controlled trials (RCTs) that included a 2-year follow-up, with inclusion of 356 patients. The primary outcome was significant improvement defined as at least 50% in pain reduction and disability status. Direct payment data from all carriers from 2018 was utilized for the assessment of procedural costs. Overall costs, including drug costs, were determined by multiplication of direct procedural payment data by a factor of 1.67 to accommodate for indirect payments respectively for disc herniation, discogenic pain, and cervical post-surgery syndrome. Results: The results of the 3 RCTs showed direct cost utility for one year of QALY of $2,412.31 for axial or discogenic pain without disc herniation, $2,081.07 for disc herniation, and $2,309.20 for post surgery syndrome, with an average cost per one year QALY of $2,267.57, with total estimated overall costs with addition of indirect costs of $3,475.38, $4,028.55, $3,856.36, and $3,785.89 respectively. Limitations: The limitation of this cost utility analysis includes that it is a single center evaluation. Indirect costs were extrapolated. Conclusion: This cost utility analysis of cervical interlaminar epidural injections in patients nonresponsive to conservative management in the treatment of disc herniation, post surgery syndrome and axial or discogenic neck pain shows $2,267.57 for direct costs with a total cost of $3,785.89 per QALY. Key words: Cervical interlaminar epidural injections, chronic neck pain, cervical disc herniation, cervical discogenic pain, post surgery syndrome, cost utility analysis, cost effectiveness analysis, quality-adjusted life years

Preoperative Single Photon Emission Computed Tomography Imaging as a Tool for Surgical Planning in Patients With Axial Neck and Back Pain

Abstract INTRODUCTION Single Photon Emission Computed Tomography (SPECT) imaging has recently been employed to identify pain generators in patients with axial neck and back pain, indicating potential sites of degeneration. We describe the largest series to date of patients with axial neck or back who underwent preoperative SPECT imaging for surgical planning. METHODS A retrospective medical and imaging record review was conducted to identify patients who underwent SPECT or SPECT/CT studies between January 2014 and May 2018. Surgical criteria included symptoms of intractable back or neck pain and evidence of degenerative pathology on SPECT imaging. Only those patients who subsequently underwent surgery on a spinal level associated with increased radiotracer uptake were included in the analysis. Patient baseline and demographic information, and data pertaining to SPECT imaging, surgical planning, and postoperative care was collected and analyzed. RESULTS A total of 23 patients with an average age at surgery of 60.0+/−11.0 yr were included. About 15 patients (65%) were male. A total of 53 spinal levels were treated, with an average of 2.30 levels treated per patient. All patients underwent fusion surgery, either lumbar (14) with interbody fusion most commonly employed (64.2%) or cervical (9) with anterior cervical discectomy and fusion (66.6%) most common. Average LOS was 3.45+/−2.32 d. One patient developed a wound infection postoperatively, requiring readmission. At 3-mo follow-up, 18 patients (78.3%) reported clinical improvement in pain. About 11 patients (47.8%) reported complete symptom resolution at 6-mo follow-up. At 1 yr postoperatively, 19 patients (82.6%) reported some relief of their symptoms following surgery. CONCLUSION This is the largest series to date describing patients with axial neck and back pain who underwent preoperative SPECT imaging and subsequent surgical intervention on the affected spinal levels. Our results demonstrate that SPECT imaging may be a useful adjunct to guide surgical planning, resulting in substantial clinical improvement following surgery.

(Invited) Oxygen Reduction Reaction at MN4 and MN5 Catalysts - Calculated and Experimental O2-Fe Binding Energies, Activity Indexes, Volcano Correlations

The oxygen reduction reaction (ORR) is a fundamental chemical reaction in industrial processes as well as in living systems, being O2, the final electron (e-) acceptor of many reactions. Since then its importance in the fuel cell technology where energy would be stored in the form of H2 to be oxidized in conjunction with the reduction of the cheap and abundant O2. However, the ORR is a complicated reaction which involves the transfer of 4 electrons and 4 protons and for its nature, it proceeds through the consequent formation of more than one intermediate accounting for the so-called “scaling correlations” [1]. The complexity of the reaction determines the slow kinetics and the difficulties into finding an adequate catalyst for it to proceed without energy losses. The “industrial standard” catalysts for this reaction are based on the very expensive and rare Pt metal. An uncountable number of non-precious metal catalysts (NPMC) have been studied with the purpose to replace Pt. In our research group, we are adopting various strategies to increase the activity and the stability of metal phthalocyanines like the substitution of planar neutral residues with more electron-negative ones, and the addition of axial back ligands [2-5]. In this research work we studied the electrocatalytic activity towards the ORR of a new compound i.e. the iron 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadeca(fluoro) phthalocyanine (16(F)FePc) in the absence and in the presence of a fifth pyridine axial ligand (FeN5). Interesting the 16(F)FePc appears to be the most active among all the FeN4 studied to the moment. The very high redox potential of the active Fe(III)/Fe(II) redox couple (-0.075 V and 0.44 V vs. SCE at pH 13 and at pH 1 respectively) confirms the correlation between the activity of the catalyst vs. redox potential of the active redox couple of the metal in the catalyst. 16(F)FePc was so active towards the ORR that the production of H2O2 measured at rotating ring electrodes was nil at pH 13 and very low at pH 1. In the presence of pyridine axial ligand, the redox potential increased of almost 60 mV and catalytic currents and stability of the catalyst also drastically increased. The catalysts were characterized with electrochemical techniques and by EPR and XPS spectroscopy in the presence and in the absence of O2. We could therefore experimentally evaluate the binding energy of O2 to the Fe metal centre. Ab initio calculations, confirm the experimental data and the importance of the pyridine axial ligand to lower the binding energy of O2 to the Fe metal centre because of decoupling of the Fe from the carbon support and changes in the geometrical and electronic structure. [1] Reactivity Descriptors for the Activity of Molecular MN4 Catalysts for the Oxygen Reduction Reaction. Angew. Chem. Int. Ed., 55 (2016) 14510-14521. J.H. Zagal, M.T.M. Koper. [2] Adsorption of 4,4 ́-dithiodipyridine axially coordinated to Iron(II) phthalocyanine on Au(111) as a new strategy for oxygen reduction electrocatalysis. Chemphyschem, (2018), 19(13), 1599-1604.S. Herrera, F. J. Williams, E. J. Calvo, F. Tasca. [3] Biomimicking vitamin B12. A Co phthalocyanine pyridine axial ligand coordinated catalyst for the oxygen reduction reaction. Electrochimica Acta. (2018), 265, 547-555. J. Riquelme, K. Neira, W. Orellana, P. Hermosilla, J. F. Marco, J. H. Zagal, F. Tasca. [4] Comparison of the Catalytic Activity for the Reduction of O2 of Fe and Co MN4 Complexes Adsorbed on Edge Plane Graphite Electrodes and on Carbon Nanotubes. Physical Chemistry Chemical Physics. (2017), 19(31), 20441-20450. R. Venegas, F. J. Recio, J. Riquelme, K. Neira, J. F. Marco, I. Ponce, J. H. Zagal, F. Tasca. [5] Biomimetic reduction of O2 in acid medium on iron phthalocyanines axially coordinated to pyridine anchored on carbon nanotubes”. Journal of Material Chemistry A. (2017), 5(24), 12054-12059. R. Venegas, F. J. Recio, J. Riquelme, K. Neira, J. F. Marco, I. Ponce, J. H. Zagal, F. Tasca. Acknowledgments F.T thanks Fondeyct project 1181840. J.H.Z thanks the Millennium Project RC120001, Fondecyt 1181037. W.O. thanks Fondecyt 1170480.

(Invited) Climbing over the Volcano Correlation for O2 Reduction By the Effect of a Pyridine Axial Ligand Bound to Co Phthalocyanine Compared to Vitamin B12. 4 Versus 2 Electron Reduction of O2

CoN4 macrocyclic complexes like Co phthalocyanines (CoPc) have been extensively studied as electrocatalysts for the ORR since the discovery by Jasinski [1] but they only promote the 2-e reduction of O2 to give peroxide, this, delivering less energy when used in a fuel cell. Further, they lack the long-term stability required for fuel cell performance. However, they can serve as excellent models for establishing reactivity descriptors and activity correlations that can be very useful for design of more active and stable catalysts such as the Pyrolyzed MNx materials. On the other hand, vitamin B12, a naturally occurring CoN4 macrocyclic molecule has attracted the attention of the scientific community because instead of catalysing the 2 electron reduction of O2 to H2O2 like the other Co macrocyclics in alkaline media it promotes the 4-electron reduction to H2O. In alkaline media vitamin B12 possesses an axial back ligand and this seems to be the reason for its higher activity and selectivity for the 4-e reduction of O2. This is also true for another natural occurring catalyst: FeN4 cytochrome c [2]. To test this hypothesis, we synthesized a CoPc axially coordinated to pyridine anchored to carbon nanotubes (Co-Py-CNT). The Co center becomes then coordinated to 5 nitrogen atoms as in vitamin B12. The modified CoPcPy containing catalytic material was characterized by EPR and XPS spectroscopy. DFT calculations showed that the binding energy of Co to O2 increases dramatically by the presence of the axial ligand (see volcano correlation down below [3]). Koutecky– Levich extrapolation and Tafel plots show the similarities between the 2 complexes (Tafel slopes ca. -RT/F) and reveal insights into the mechanism of action of Co penta-coordinated complexes. According to our results the pyridine back ligand increases the Co-O2 binding energy, making it more similar to VitB12, favouring the splitting of the O-O bond. The back ligand then plays a crucial role in modifying Co-O2 binding energy which is a well know reactivity descriptor [3]. A further evidence eof this dramatic change in reactivity of CoPc by the presence of the "Py" back ligand is that it moves from the weak binding leg of a volcano correlation to the strong leg of the volcano, as illustrated in the Figure down below. This might explain why nature uses a back ligand in cytochrome -c to catalyze the ORR. ACKOWLEDGEMENTS: F.T. thanks for financial support the Fondecyt Iniciación Project 11130167, and Proyecto Basal. J.H.Z thanks the financial support of Millenium Project RC120001, Project Anillo ACT 1412 and Dicyt-USACH. Fondecyt 1140199. REFERENCES: 1. R. Jasinski, Nature, 201 (1964) 1212-1213 2. R. Boulatov, N4 Macrocyclic Metal Complexes (J.H. Zagal, F. Bedioui, J.P. Dodelet Eds.) Springer, Berlin,2006, pp.1-60 3. J.H. Zagal, M.T.M. Koper, Angewandte Chemie Int. Ed., 55 (2016) 14510-14521. Figure 1

(Invited) Climbing over the Activity Volcano Correlation by Biomimicking Vitamin B12: A Co Phthalocyanine Pyridine Axial Ligand Coordinated Catalyst for the Reduction of Molecular Oxygen

CoN4 macrocyclic complexes like Co phthalocyanines (CoPc) have been extensively studied as electrocatalysts for the ORR but they preferentially promote the 2-e reduction of O2 to give peroxide. In contrast, vitamin B12, a naturally occurring CoN4 macrocyclic molecule alkaline media promotes the 4-electron reduction of O2 to H2O. Vitamin B12 possesses an imidazole axial back ligand and this seems to be the reason for its higher activity and selectivity for the 4-e reduction of O2. To test this hypothesis, we synthesized a CoPc axially coordinated to pyridine anchored to carbon nanotubes (Co-Py-CNT). The Co center is therefore coordinated to 5 nitrogens as in vitamin B12. The modified CoPcPy containing catalytic material was characterized by EPR and XPS spectroscopy. DFT calculations. According to our results the pyridine back ligand increases the Co-O2 binding energy, making it more similar to VitB12, favoring the splitting of the O-O bond. The back ligand then plays a crucial role in modifying Co-O2 binding energy which is a well know reactivity descriptor. A further evidence of this dramatic change in reactivity of CoPc by the presence of the "Py" back ligand is that it moves from the weak binding leg of a volcano correlation to the strong leg of the volcano. This might explain why nature uses a back ligand in cytochrome c to catalyze the ORR.

Study of the die compaction of powders to high relative densities using the discrete element method

The mechanical behavior of powders during die compaction was investigated using the discrete element method (DEM), in which powders are modeled as discrete particles with elastoplastic material behavior. A new adhesive elastoplastic contact model that describes the force displacement behavior of contacting particles subjected to high confining conditions was introduced and implemented in DEM simulations of die compaction and uniaxial tension. The objectives of these simulations were: (1) to investigate the micromechanical behaviors of powder systems during die compaction; (2) to understand the influence of model parameters on the macroscopic behavior; and (3) to develop a methodology for the calibration of the model parameters from macroscopic experimental results. The methodology developed for the calibration of the model parameters was carried out by a combination of statistical design of experiments (DOE) and optimization techniques. The calibration methodology provided simulation results that were in good agreement with experimental results conducted on hot melt extruded (HME) copovidone powder. One of the key advantages of the calibration procedure is the need for only two experimental techniques – die compaction, and diametric compression strength tests. Furthermore, examination of the microscale behavior from simulated results revealed a connection between the level of interparticle cohesion and the corresponding level of residual wall stress of powder compacts after complete unloading in die compaction. It was found that lower levels of interparticle cohesion resulted in decreased residual wall stresses and an increase in the axial spring back from the minimum compact height at the end of compaction. These results suggest that the decrease in residual wall stress and the increase in axial spring back with lower levels of interparticle cohesion depend not only on the elastic properties of the constituent particles during unloading, but also depend on the decohesion of particle-particle contacts.

Biomimicking vitamin B12. A Co phthalocyanine pyridine axial ligand coordinated catalyst for the oxygen reduction reaction

CoN4 complexes like Co phthalocyanines (CoPc) have been extensively studied as electrocatalysts for the oxygen reduction reaction (ORR) but they only promote the 2-electron reduction of O2 to give peroxide. In contrast, vitamin B12 a Co macrocyclic naturally occurring molecule has attracted the attention of the scientific community because instead of catalysing the 2-electron reduction of O2 to H2O2 like the other Co macrocycles it promotes the 4-electron reduction to H2O. Vitamin B12 possesses an axial back ligand and this seems to be the reason for its higher activity and selectivity for the 4-electron reduction of O2. To test this hypothesis, we synthetized a CoPc axially coordinated to pyridine anchored to carbon nano-tubes (CoPc-Py-CNT). The Co centre is therefore coordinated to 5 N as in vitamin B12. The modified CoPc containing catalytic material was characterized by EPR and XPS spectroscopy. Ab initio calculations, Koutecky– Levich extrapolation and Tafel plots well describe the similarities between the 2 complexes and reveal insights into the mechanism of action of Co penta-coordinated complexes. According to our results the pyridine back ligand increases the Co-O2 binding energy and making it more similar to that of Vitamin B12, favouring the splitting of the O-O bond. The back ligand then plays a crucial role in modifying Co-O2 binding energy which is a well know reactivity descriptor.

Improvement in Radicular Symptoms but Continued Facet Arthropathy and Axial Back Pain Following Rupture of a Facet Joint Synovial Cyst

Lumbar synovial cysts are benign fluid collections thought to form in a background of facet joint degeneration, allowing for fluid to leak from the joint capsule and form cysts in the synovium. Although often asymptomatic, patients with symptomatic synovial cysts will present with low back pain and possibly an associated radiculopathy. Clinicians can consider conservative management, epidural steroid injection, surgical intervention, or facet joint block with aspiration and rupture. This case describes a 59-year-old male facilities manager with intermittent low back pain for one year with worsening right-sided radicular symptoms secondary to a lumbar facet joint synovial cyst in the context of severe facet arthropathy and microinstability. The patient’s low back pain and radicular symptoms were refractory to conservative treatment. Imaging demonstrated a lumbar synovial cyst and subsequent management included transforaminal epidural steroid injection and facet joint block with cyst aspiration and rupture. The patient’s radicular pain resolved but axial lumbar pain returned after 3 weeks of relief. Follow-up imaging demonstrated decreased cyst size with fluid accumulation and joint space widening. Although the cyst was successfully decompressed with resolution of radicular pain, the underlying facet arthropathy remains contributing to persistent axial low back pain and potential for continued degenerative changes including cyst recurrence.