Atoh8 is one such bHLH factor with unique characteristics in the ‘atonal’ family. Consistent with the other homologs of its family, Atoh8 was identified to regulate cell fate and differentiation during development. Furthermore, it was also found to regulate other mechanisms in adult and mature organisms such as cancer, iron homeostasis and stress response. This review systematically outlines the role of Atoh8 in development and pathologies. At the same time, this review also anticipates its potential involvement in basic cellular mechanisms such as proliferation, metabolism, apoptosis and autophagy.Atoh8 belongs to a large superfamily of transcriptional regulators called basic helix-loop-helix (bHLH) proteins. bHLH proteins have been identified in a wide range of organisms from yeast to humans. The members of this special group of transcription factors were found to be involved not only in embryonic development but also in disease initiation and its progression. Given their importance in several fundamental processes, the translation, subcellular location and turnover of bHLH proteins is tightly regulated. Alterations in the expression of bHLH proteins have been associated with multiple diseases also in context with Atoh8 which seems to unfold its functions as both transcriptional activator and repressor. Like many other bHLH transcription factors, so far, Atoh8 has also been observed to be involved in both embryonic development and carcinogenesis where it mainly acts as tumor suppressor. This review summarizes our current understanding of Atoh8 structure, function and regulation and its complex and partially controversial involvement in development and disease. The basic helix-loop-helix (bHLH) proteins are an evolutionarily ancient superfamily of transcription factors that control a wide range of functions from proliferation to differentiation of tissues. Members of the bHLH family possess two highly conserved and functionally distinct domains namely ‘basic’ and ‘Helix-Loop-Helix’. The ‘basic’ domain enables the binding of these transcription factors to the major groove of DNA at the consensus sequences such as E-Boxes or N-Boxes. The ‘HLH’ domain aids in the interaction with other proteins either to form homodimers or heterodimers . Based obHLH transcription factors have been identified to be integral to multiple developmental processes. However, studying them broadly shows distinct expression patterns. The proteins that are expressed tissue- and cell-specifically and the proteins that are ubiquitously expressed. Concerning tissue-specific transcription factors, to date, several bHLH transcription factors have been identified to be essential for organogenesis such as in neurogenesis , myogenesis  and cardiac development (Hand1 and Hand2) . These tAtoh8 belongs to Group A of bHLH transcription factors that bind to the core consensus DNA sequence ‘CACCTG’ or ‘CAGCTG’ called E-Box. It is a member of the ‘Net’ family within the ‘Atonal’ superfamily ,10. AtohAmong metazoans, Atoh8 has undergone high sequence diversification making it difficult to predict its likely functions. Yet, the bHLH domain was observed to have remained highly conserved . As oppoConcerning regulatory aspects of Atoh8, the comparison of sequences upstream to Atoh8 in zebrafish, chicken, mice and humans revealed that the Atoh8 promoter has evolved from a ‘TATA box’ with a single transcriptional initiation site to the much more flexible ‘CpG islands’ with multiple transcriptional start sites that assist in fine-tuning of gene expression. This evolution in the promoter sequence also implies that Atoh8 has evolved from performing a specific function in zebrafish and chicken to multiple other functions in mice and humans, which is also in line with current literature where Atoh8 was shown to be ubiquitously expressed in mice during development ,15. ConcAtoh8 can be detected very early during mouse embryonic development. Its expression was identified in the inner cell mass of the blastocyst (E3.5) where the cells are pluripotent. In addition to this, the dynamics in its localization was also reported, where the presence of Atoh8 protein was detected in the cytoplasm of the pluripotent stem cells and upon the onset of differentiation Atoh8 was found to readily translocate into the nucleus raising several questions regarding its role in the exit of pluripotent state . At the Until now, the role of Atoh8 has been studied either in the context of pluripotency or murine organogenesis during development. However, its involvement in early embryonic morphogenesis following implantation, during gastrulation remained to be examined. This is particularly interesting because of the influence that TGF-ß and BMP signaling have on the early embryonic morphogenesis and at the same time on the expression of Atoh8. Recent studies performed to understand the transcriptional network involved in gastrulation at single-cell resolution confirmed the expression of Atoh8 in all three germ layers during gastrulation. However, in light of our recent report where we have shown that the absence of Atoh8 primes murine pluripotent stem cells towards mesendodermal fate, it would be interesting to know how Atoh8 is engaged in early embryonic development particularly during gastrulation ,23,24.During development, bHLH transcription factors regulate the expression of genes that are involved in cell fate determination and differentiation by acting as either transcriptional activators or repressors ,26. AtohDuring kidney development, Atoh8 was primarily identified to be expressed in the metanephric mesenchyme and later in the tissues derived from it such as in the developing Bowman’s capsule and the tubule system with no evident expression in the uretic bud or uretic bud-derived cells. Intriguingly, the highest expression of Atoh8 was found in the least differentiated cell types of the nephrogenic zone with elevated levels of BMP4 signaling ,29.In 2008, Lynn and his colleagues identified Atoh8 expression in endocrine and exocrine precursor cells of the developing pancreas. This study emphasized Atoh8 as a direct target of Neurog3, which is essential for pancreatic development. It was further shown that Atoh8 possesses the ability to modulate the proendocrine functions of Neurog3 . SimilarFurthermore, in murine pancreatic ductal adenocarcinoma cells, it was shown that Atoh8 with the help of its proline-rich domain represses Neurog3-mediated gene function by competing with the transcriptional activity of E47 and Neurog3 . As AtohDuring skeletal myogenesis, Atoh8 (Cath6) was identified to be predominantly expressed in the myotomal compartment of chicken embryos. To understand the significance of Atoh8 in myogenesis, Atoh8 expression was inhibited in the hypaxial myotome region, which resulted in the blockage of terminal differentiation of myoblasts restricting them to a pre-determined state. Similarly, experiments performed on the C2C12 murine myoblasts revealed a dynamic expression of Atoh8. Atoh8 was observed to upregulate following induction of differentiation suggesting a regulatory role during the transition of myoblasts from proliferative state to differentiation .A study performed in order to understand the role of Atoh8 in the developing heart showed Atoh8 expression primarily in the atria. However, in mature animals, its expression was observed to be restricted to the right atrium suggesting a specific function. Apart from that, this study also identified a strong expression of Atoh8 in lung mesenchyme. Furthermore, subtle defects in the function of the lung, associated with mesenchymal-epithelial signaling, were also observed .Atoh8 expression was first identified in the chondrocytes derived from proliferative and hypertrophic zones of the epiphysial growth plate . Recentlor in utero development is being compensated by either another bHLH factor as we observe in myogenesis or by another non-bHLH factor with functional similarity [Atoh8 was recently identified to play a major role in murine placenta development. Loss of Atoh8 was shown to lead to irregular development of the placenta during late mid-gestation with abnormal decidualization and vascularization, which ultimately led to hemorrhagic crisis and miscarriage of most of the fetuses with surprising survival of few fetuses despite their genotype, suggesting that Atoh8 has no or only a limited role to play during early embryonic development . Howevermilarity ,45,46.Previously, Atoh8 was shown to be a shear stress-responsive gene in human endothelial cells . In addiGiven the ubiquitous expression and multiple regulatory roles of Atoh8 during embryonic development, it is not at all surprising to see its involvement in cancer and several other disorders. The high-grade gliomas are diagnosed on the basis of different molecular markers. The 1p19q codeletion is one characteristic marker for oligodendroglioma. In contrast, the epidermal growth factor receptor (EGFR) amplification is seen in glioblastoma. In 2008, a study performed to understand the two mutually exclusive groups of gliomas carrying ‘1p19q codeletion’ and ‘EGFR amplification’, identified Atoh8 as one of the multiple differentially regulated genes. Higher expression of Atoh8 was found to be correlated with the pro-neural group of gliomas particularly oligodendroglioma with ‘1p19q codeletion’ and lower expression of Atoh8 was found to be correlated with a proliferative and mesenchymal group of gliomas with ‘EGFR amplification’. Likewise, another study which was performed to ascertain the copy number variations in glioblastomas has also revealed aberrant expression of Atoh8 further suggesting it as a potential candidate involved in carcinogenesis ,51. FollIn nasopharyngeal carcinomas (NPC), similar to the findings in hepatic carcinomas, the inhibition of Atoh8 was shown to enhance the malignant phenotype, whereas its transgenic expression was shown to reverse the phenotype. In this study, the authors identified the silencing of Atoh8 in tumor cells as an epigenetic mechanism induced by the tumorigenic LMP1 (Latent Membrane Protein-1). In tumor cells, the occupancy of active H3K4me3 of the Atoh8 promoter sequence was found to be replaced by a repressive H3K27me3 mark. Lastly, this study further described Atoh8 as a regulator of epithelial-mesenchymal transition (EMT) because of its correlation with EMT markers .In colorectal cancer (CRC), higher expression of Atoh8 was found to correlate with the poor prognosis of CRC patients. The knockdown of Atoh8 in CRC cells was shown to reduce proliferation with an accumulation of cells in the S phase of the cell cycle. Additionally, the depletion of Atoh8 in CRC cells was observed to increase apoptosis with no apparent changes to the migratory ability of the cells which is in clear contrast to the findings observed in HCC and NPC . AnotherIn breast cancer, a study was performed to identify the enriched tissue-specific transcription factors which connected Atoh8 to the dysregulated transcriptional regulatory network which affected the proliferation, differentiation, cell adhesion and metastasis . InteresIn prostate cancer, Atoh8 was reported to be epigenetically active with high expression . SimilarSo far, Atoh8 has been implicated to be involved in cellular stress response, hypoxia response, and iron metabolism. Atoh8 was identified to be activated by shear stress during endothelial cell differentiation. It was further reported that overexpression of Atoh8 mimicked shear-stress treatment attributing a major role to Atoh8 in stress management. In addition to shear stress, IFN-γ, TNF-α and oxidative stress were shown to act upstream and activate Atoh8 expression in endothelial cells. Furthermore, eNOS which plays a major role in endothelial cell protection, nitric oxide production was shown to be positively regulated, at the same time as a direct target of Atoh8 ,47. The Atoh8 was identified as a downstream factor for activating transcription factor 4 (ATF4) in pancreatic ß-cells. ATF4 is a transcriptional regulator for integrated stress response (ISR) and unfolded proteins. Severe diabetes is led by dysregulation of ISR. Thereby ATF4 senses endoplasmic reticulum stress in cellular pathologies and is responsible for the maintenance of homeostasis in the endoplasmic reticulum. The ISR enhancer Sephin1 increased the ATF4 expression in the pancreatic islets and increased the insulin secretion .Lately, Atoh8 was also shown to regulate hypoxic response. A study by Morikawa’s group showed that Atoh8 binds hypoxia-inducible factor 2α (HIF-2α) and decreases its abundance leading to the attenuation of the hypoxic response. It was further shown that the Alk1/Smad/Atoh8 axis acts as a regulator of the hypoxic response. Interestingly, analysis performed on HPAECs showed the HLH domain of Atoh8 to be crucial for hypoxic response with no functional role of the basic domain . RecentlIn addition to stress and hypoxia regulation, Atoh8 was also shown to regulate metabolism, especially iron metabolism. Atoh8 was observed to regulate hepcidin which prevents the overloading of iron in the body. In hepatocytes, BMP6 was shown to activate Atoh8 , which fIntriguingly, a recent study showed an increase in the number of M-Cells in the intestine of Atoh8 knockout mice whose main function is to uptake and transfer the bacterial antigens to dendritic cells as part of immunosurveillance. Iron plays a crucial role in bacterial growth, overloading of iron leads to a significant increase in gut microbiota resulting in inflammation. It is logical to think that the increase in the number of M-Cells in the case of Atoh8 knockout mice could be a compensatory mechanism adapted by these animals to counter prolonged bacterial infections ,66.Atoh8 is a transcription factor that belongs to a large superfamily of transcriptional regulators called bHLH proteins. In spite of two decades of research, multiple questions regarding its molecular function and involved mechanisms remain elusive. The current literature shows that Atoh8 is involved in the regulation of pluripotency and organogenesis during embryonic development. Additionally, Atoh8 was also shown to regulate several physiological processes such as stress response, hypoxic response and iron homeostasis in adult and mature animals. It has further been attributed to influence cellular mechanisms such as proliferation, cellular survival, EMT in cancers and MET in reprogramming.So far, multiple studies performed in different contexts confirmed that Atoh8 is a direct target of the Smad-dependent TGF-ß/BMP signaling pathway. Although Atoh8 seems to be a tissue-restricted factor during organogenesis controlling cellular fate and differentiation, its ubiquitous expression in adult animals suggests a much larger role. Based on contemporary studies, Atoh8 can be considered as a negative regulator of multiple basic cellular mechanisms starting from proliferation to metabolism. Since these mechanisms are inextricably connected to proper cellular function, Atoh8 must be thoroughly studied in the regulation of basic cellular mechanisms such as cell metabolism, cell cycle, apoptosis and autophagy.


This cohort study assesses whether removal of a warning against use of cephalosporins in the electronic health record (EHR) of patients with penicillin allergy was associated with changes in the dispensing or administration of cephalosporins. Is removal of a warning to avoid cephalosporin use in patients with penicillin allergies associated with an increase in cephalosporin dispensing or administration?In this cohort study of 4 398 792 patients who had received antibiotic treatment, after an alert in the electronic health record system to avoid prescribing of cephalosporins to patients with a penicillin allergy was removed at 1 of 2 health system sites, cephalosporin dispensing or administration increased significantly among patients with a penicillin allergy at that site compared with patients without a penicillin allergy at the same site and patients at the comparison site that retained the warning.In this study, removal of a warning in the electronic health record to avoid cephalosporin use in patients with penicillin allergies was associated with increased dispensing and administration of cephalosporin. Electronic health records (EHRs) often include default alerts that can influence physician selection of antibiotics, which in turn may be associated with a suboptimal choice of agents and increased antibiotic resistance.To examine whether removal of a default alert in the EHR to avoid cephalosporin use in patients with penicillin allergies is associated with changes in cephalosporin dispensing or administration in these patients.This retrospective cohort study of a natural experiment included data on patients who had received antibiotic treatment in the hospital or outpatient setting in 2 regions of a large, integrated health system in California from January 1, 2017, to December 31, 2018. Of 4 398 792 patients, 4 206 480 met the eligibility criteria: enrollment in the health system during antibiotic use, availability of complete demographic data, and use of antibiotics outside of the washout period.Oral or parenteral antibiotics dispensed or administered after removal of an EHR alert to avoid cephalosporin use in patients with a recorded penicillin allergy.Probability that an antibiotic course was a cephalosporin. A multinomial logistic regression model was used to examine the change in rates of cephalosporin use before and after an EHR penicillin allergy alert was removed in 1 of the study regions. Temporal changes in use rates were controlled for by comparing changes in cephalosporin use among patients with or without a penicillin allergy at the site that removed the warning and among patients at a comparison site that retained the warning. Regression models were used to examine adverse events.Clostridioides difficile: RRRR, 1.02; 95% CI, 0.84-1.22; methicillin-resistant Staphylococcus aureus: RRRR, 0.87; 95% CI, 0.75-1.00; and vancomycin-resistant Enterococcus: RRRR, 0.82; 95% CI, 0.55-1.22) at the patient level.Of the 4 206 480 patients who met all inclusion criteria, 2 465 849 (58.6%) were women; the mean (SD) age was 40.5 (23.2) years. A total of 10 652 014 antibiotic courses were administered or dispensed, divided approximately evenly between the period before and after removal of the warning. Before removal of an alert in the electronic health record system to avoid prescribing of cephalosporins to patients with a penicillin allergy at 1 of the 2 sites, 58 228 courses of cephalosporins  were used among patients with a penicillin allergy; after removal of the alert, administration or dispensing of cephalosporins increased by 47% compared with cephalosporin administration or dispensing among patients without a penicillin allergy at the same site and patients at the comparison site that retained the warning  . No significant differences in anaphylaxis , new allergies , or treatment failures  were found at the course level. No significant differences were found in all-cause mortality , hospital days , and new infections (In this cohort study, removal of a warning in the electronic health record to avoid cephalosporin use in patients with penicillin allergies was associated with increased administration and dispensing of cephalosporin. This simple and rapidly implementable system-level intervention may be useful for improvement in antibiotic stewardship. In response to Meaningful Use requirements issued by the Office of the National Coordinator for Health Information Technology, many EHRs include an imbedded function to warn against prescribing cephalosporins to patients with a penicillin allergy.In December 2017, after a review of the literature and clinical deliberations among leaders in infectious diseases in the Southern California Permanente Medical Group, Kaiser Permanente Southern California removed a warning in its EHR to avoid prescribing cephalosporins to patients with a penicillin allergy. In the current study, we examined the association of this change with choice of antibiotic, incidence of antibiotic allergy, incidence of cephalosporin-associated anaphylaxis, and rate of penicillin allergy–associated morbidities in patients with a penicillin allergy.STROBE) reporting guideline.17 Additional details are provided in the eMethods in the This retrospective cohort study of a natural experiment included members enrolled in either Kaiser Permanente Southern California or Kaiser Permanente Northern California health plans who received antibiotic treatment between January 1, 2017, and December 31, 2018. Kaiser Permanente Southern California, which removed the alert, was the intervention site, and Kaiser Permanente Northern California, which did not remove the EHR alert, was the comparison site for the natural experiment. The institutional review boards of both sites approved this study and waived the requirement for informed consent because the research involved no more than minimal risk to participants, the waiver would not adversely affect participants’ rights and welfare, the research could not practically be carried out without the waiver, and participants were provided with additional pertinent information after participation. The study followed the Strengthening the Reporting of Observational Studies in Epidemiology  codes T78.2 or T88.6 recorded on the same day that a course of parenteral cephalosporins was started or within 1 day of starting a course of oral cephalosporins. Each potential case was manually audited by chart review (E.M. and W.W.C. for the intervention site and M.T.N. for the comparison site) to determine whether it met the current diagnostic criteria for antibiotic-associated anaphylaxis.22 As a proxy for antibiotic treatment failure, we used the start of a new course of antibiotics in a different category within 30 days of the start of a course of monotherapy.16Potential cases of cephalosporin-associated anaphylaxis in patients with a penicillin allergy were identified with hospital days) per person-year was defined as the number of days in the period that the patient spent in the hospital (including time contributed by the emergency department and observation days that were linked to an inpatient admission) divided by the total member-days in the period. The rate of new infections per person-year was defined as patients having 1 or more new C difficile, methicillin-resistant S aureus (MRSA), or vancomycin-resistant Enterococcus (VRE) infections during the period. We selected these infections a priori based on prior studies24 and clinical input. Infections were identified based on positive laboratory results or diagnoses from encounters in the hospital or outpatient setting. ICD-10 diagnosis codes starting with A04.7 were used to identify C difficile infection; A41.02, A49.02, B95.62, or J15.212 were used to identify MRSA infection; and Z16.21 and Z16.22 were used to identify VRE infection. Infections were considered new if there were no indications of VRE or MRSA infection in the prior 30 days or C difficile infection in the prior 90 days.The rate of days spent in the hospital  calculation. Second, we examined the equivalent RORs for the comparison site to further control for temporal changes in antibiotic use. The outcome was formulated as a ratio of these 2 RORs (RROR) and was modeled with multinomial logistic regression. The regression coefficient for the 3-way interaction represents the change in antibiotic prescribing as the natural log of the RROR. We fit models for all courses and fit separate models for oral and parenteral courses.We calculated several secondary outcomes to explore whether removal of the warning was associated with patient outcomes. At the treatment-course level, we examined anaphylaxis, new antibiotic allergies, and antibiotic treatment failure. At the patient level, we assessed all-cause mortality, hospital days, and new infections per person-year. Regression models for the secondary outcomes used the same independent variables and interactions as in the model for the primary outcome. The details of the models for secondary outcomes varied, but all were formulated using the ROR approach described for the primary outcome. Course-level outcomes were RRORs, and patient-level outcomes were ratios of ratios of rate ratios (RRRRs). Dimensions of the differences included the model distributions and link functions, criteria for including courses and person-time, consideration of different cephalosporin generations, and membership criteria. More details are given in the eMethods and eTable 3 in the In addition, we fit separate models for the secondary outcomes that included the penicillin allergy indicator only as a main effect but not in interactions with other independent variables. These models estimated the extent to which patients with a penicillin allergy had a higher rate of the adverse outcome than patients without a penicillin allergy.We tested the sensitivity of the results for the primary outcome after adding covariates to the models, including indicators for allergies to other antibiotic categories, the diagnosis group associated with the course, and the presence of individual comorbidities at the start of the course and indicators that the course occurred during a hospitalization for surgery or labor and delivery. We tested how the results changed when the main variables interacted with the other covariates as well as after adding effect modification of the 3-way interaction by adding the 4-way interactions with age, sex, and race/ethnicity. In addition, we tested whether the results were sensitive to different variable definitions by assigning the penicillin allergy on the date when the treatment was first dispensed or administered (rather than the day before) and including only each patient’s first or last course in the model. Analyses were conducted using SAS, version 7.1 (SAS Institute).27 Patients contributed a mean (SD) of 2.5 (2.7) treatment courses to the study, and 9.4% of patients had a penicillin allergy at the start of the study period.We identified 4 398 792 unique patients with antibiotic use during the study period. Of these, 143 606 (3.3%) were excluded because they were not enrolled at the time of their antibiotic use; 281 (0.01%) were excluded owing to missing or inconsistent birth date, sex, or death date; and 48 425 (1.1%) were excluded because their antibiotic use occurred during the washout period. Thus, 4 206 480 patients (2 252 525 at the intervention site and 1 953 955 at the comparison site) were included in the analysis: 2 465 849 (58.6%) were women, 1 827 714 (43.4%) were non-Hispanic White, and the mean (SD) age was 40.5 (23.2) years at the start of the study period. Patient demographics differed between the 2 sites; members at the intervention site were younger, more likely to be Black or Hispanic, and less likely to be Asian or White . The cruWe included 10 652 014 antibiotic courses in the analysis ; 51.8% wWe found a significant increase of 47% in cephalosporin use among patients with penicillin allergy at the intervention site compared with patients in the other groups . The RRORs for the 12 antibiotic categories are shown in the The difference in the rates of anaphylaxis among individuals with penicillin allergies who used cephalosporin between the sites was not significant. The results for the other course-level outcome calculations are summarized in C difficile , MRSA , or VRE  infection among all patients , hospital days , or new patients . The RRRpatients .The results were robust to several sensitivity analyses  during the period after removal of the penicillin allergy warning. We found no significant differences in the rates of anaphylaxis, allergies to new antibiotic classes, antibiotic treatment failure, all-cause mortality, hospital days, and new infections after the change.28 suggesting higher rates of new antibiotic allergies among patients with a penicillin allergy who receive any antibiotic compared with patients without a penicillin allergy. The results are also consistent with prior studies showing higher rates of infection28 and mortality29 among patients with a penicillin allergy.Although the rate of adverse outcomes did not increase after removal of the warning, patients with penicillin allergy experienced worse outcomes in general than did those with no penicillin allergy. These results are consistent with prior studies7 This study’s findings may encourage other health care systems to remove the warning, which may improve antibiotic stewardship.Removal of the penicillin allergy warning in the EHR represents a simple and rapidly implementable system-level intervention to potentially improve antibiotic stewardship. In addition, removal of an unsupported warning in the EHR may be associated with reduced alert fatigue among clinicians.This study has limitations. Because it was a retrospective study, we cannot rule out that unmeasured confounders may explain some of the associations. We attempted to control for this by using a before-and-after design and making comparisons with changes in the 2 patient groups that were unaffected by the removal of the warning . Although we adjusted the results for basic confounders, it is possible that unmeasured patient characteristics were contributing biases. In addition, although none of the changes in the secondary outcomes were statistically significant, the 95% CIs were generally large enough to include at least a 10% increase or decrease in each outcome. Thus, we cannot rule out the possibility that removing the warning was associated with changes in patient outcomes.30In this cohort study, removal of a warning in the EHR to avoid cephalosporin use in patients with penicillin allergies was associated with increased prescribing of cephalosporins and decreased prescribing of some second-line antibiotics. Overall rates of adverse antibiotic-associated reactions or specific serious cephalosporin-associated morbidities were similar before and after removal of the warning. Removing the warning was not associated with a reduction in the known morbidities associated with an unconfirmed penicillin allergy. Greater attention should be given to the accuracy with which patients are labeled as having a penicillin allergy.


The commercial availability of integrated circuits with bioimpedance sensing functionality is advancing the opportunity for practical wearable systems that monitor the electrical impedance properties of tissues to identify physiological features in support of health-focused applications. This technical note characterizes the performance of the MAX3000x  and is available for on-board processing (electrode detection) for localized bioimpedance measurements. Measurements of discrete impedances that are representative of localized tissue bioimpedance support that this IC has a relative error of <10% for the resistance component of complex impedance measurements, but can also measure relative alterations in the 250 m The passive electrical impedance of biological tissues, often referred to as tissue bioimpedance, is being widely investigated as a technique for identifying physiological features in support of health-focused applications . A non-eRegardless of the application, measurement of tissue bioimpedance requires an interface with the targeted tissue, circuitry to excite the tissue and measure the response, and processing of measurements to identify relevant features for the specific application. Each of these high-level aspects of bioimpedance measurements is an area of active research and development. At the interface between circuitry and tissue, groups are exploring dry electrodes ,13 and tMany research efforts are motivated by a drive to advance bioimpedance instrumentation from portable to wearable devices. This transition is expected to increase opportunities for continuous monitoring and health-focused applications. Commercially available integrated circuits (ICs) with dedicated bioimpedance functionality provide the opportunity for development of bioimpedance wearables without expertise in designing application-specific analog circuitry. This reduces the barrier for researchers and designers interested in implementing bioimpedance sensing for their studies or products. Available ICs with bioimpedance measurement functionality include the Analog Devices AD5933, Texas Instruments AFE4300, Analog Devices ADuCM350, and Maxim Integrated MAX30001/30002. Each of these ICs have different features and functionalities. to <10 Ω . To furtto <10 Ω ,24,25,26to <10 Ω ,23 and tto <10 Ω .As additional ICs with bioimpedance functionality become available (such as the MAX30001/30002 in 2019), researchers and designers benefit from the performance and operation characterization of these devices. These details support researchers’ evaluations of these devices and their appropriateness for their specific needs. While the MAX30001/30002 has been available since 2019 and has been utilized for preliminary studies on respiratory  and ECG In this technical note, the high-level operational theory of the MAX30001/30002 and its on-board processing will be detailed. Beyond the operational theory, the accuracy of the MAX30001’s impedance measurements was experimentally evaluated. Experimental results were collected from discrete circuits  from a range of the MAX30001’s operating conditions . These experimental measurements were compared with reference values collected using a Keysight E4990A precision impedance analyzer. This technical note expands on preliminary reports by Critcher and Freeborn on the resistance and reactance accuracy of this IC  in orderThe MAX30001/30002 (collectively referred to as the MAX3000x for the remainder of this work) are single-chip integrated circuits with analog-front-end circuitry designed for bioimpedance measurements. The MAX30002 is exclusively a bioimpedance IC, while the MAX30001 also has analog-front-end circuitry for additional biopotential measurements. These ICs are capable of two-electrode (bipolar) and four-electrode (tetrapolar) measurements with a wide range of configurable features to customize the performance. The bioimpedance channel of this device is given in The voltage that is monitored by the MAX3000x  amplifies this signal. The specific gain configurations and their effects on localized bioimpedance measurements are explored in Next, the signal is demodulated to shift the signal of interest to DC  was utilized to collect measurements of discrete circuits and localized tissues. A sample development kit, shown in All bioimpedance measurements require direct interfacing of the measurement device with the tissue under study. This is most often achieved using “wet” silver/silver-chloride (Ag/AgCl) gel electrodes ,43, dry Because the presence of this impedance has been shown to degrade the performance of instruments, such as the Keysight E4990A, in previous research efforts [To characterize the MAX3000x’s performance, impedance data were collected from two resistors and three given by . While bThe specific component values in this technical note were selected to represent localized tissues based on the reported ranges of localized bicep tissues ,5 and elThe two resistors utilized for the initial characterizations were v/v instrumentation amplifier gain, While the MAX3000x has a user-configurable excitation frequency , it is limited to measuring only a single frequency. There is no internal sweep function, but the device can be reconfigured during operation to collect different measurements. This was the approach utilized in this work to collect multi-frequency measurements. Each single-frequency impedance was measured for approximately 5 s after configuration of the development kit using Maxim’s provided tools. A more detailed analysis of the timing requirements for this configuration is outlined in The reference measurements of each test circuit were collected with a Keysight E4990A precision impedance analyzer. These reference measurements were collected without the presence of the emulated electrode/tissue impedance. The Keysight E4990A has a reported accuracy of As noted previously, it is hypothesized the MAX3000x utilizes quadrature demodulation with a single multiplication for the measurement of attached materials/devices. With a single multiplication, this IC should be capable of measuring both the resistance and reactance (though not simultaneously). To confirm this hypothesis and to assess the accuracy, resistance and reactance measurements from two resistor models and three The measured resistance and reactance are shown in Both the 51 The MAX3000x measurements collected using phase offset adjustments of Analyses of localized bioimpedance have explored the relative alterations of the impedance with respect to determining an absolute value as an indicator of tissue health. As an example, Mabrouk  and HersFrom the details in Following the high-pass filtering in v/v, 20 v/v, 40 v/v, and 80 v/v. The specific gain should be selected to take advantage of the complete ADC input range’s maximum resolution. To observe the effect of the gain on measurements that are representative of localized tissues, resistance and reactance measurements were collected from the v/v. Observing the 128 kHz resistances, the error decreased from v/v to 80 v/v. This is attributed to the higher gain supporting amplified voltages that take advantage of the ADC resolution. Notice from v/v gain yielded the smallest error in these measurements for frequencies ≤40 kHz, while 80 v/v had the smallest percent error for high frequency values. These results continue to support that the MAX3000x may not be optimized for accurate reactance measurements.Following the instrumentation amplifier in the MAX3000x’s signal conditioning chain, there is a PGA prior to the digital conversion and filtering stages. This PGA has user-selectable gains of 10 After the final amplification by the PGA in the MAX3000x bioimpedance channel, the signal is converted by a R is an external resistor connected across the One source of error from the impedance calculations using  in the pgiven in Gain=1+9.Additionally, the MAX30001 has four different current modes, with a datasheet recommendation of using the “chopped w/o LPF”, where LPF refers to a low-pass filter, which is a mode for impedance applications. To assess if the current excitation mode impacts the excitation current, measurements were collected in each. The MAX3000x excitation currents  calculated from measurements of a el using  are giveactance)  may alsoThe previous sections detailed how the configuration settings of the MAX3000x impact the accuracy of the resistance and reactance measurements collected by this IC. Beyond the accuracy, factors such as measurement range and available signal conditioning are important when evaluating this device for a specific application. In support of understanding additional features of this IC, limits on the range of resistances that can be measured and internal electrode detection functionality are explored.v/v PGA gain yielded the resistance measurements with the highest accuracy (in the subset of conditions investigated) and was recommended for taking advantage of the ADC resolution. This recommendation assumes the MAX3000x’s sensed voltage does not cause saturation of the signal conditioning channel. The differential input of the sensing pins is not recommended to exceed 90 mVG is the PGA gain . The saturation condition given by  yield a maximum impedance of As an example, the configuration settings utilized throughout this work , real-time system optimization (maintaining low-power operation without data collection until electrodes are connected), or in data post-processing . To visualize the impact that electrode disconnects have on the resistance data reported by the MAX3000x, 128 kHz data were collected from two test cases (PCB test board and bicep tissue) for 60 s. For each case, a tetrapolar configuration was utilized, with the cable connected to an electrode disconnected at the 10 and 30 second timepoints and re-attached at the 20 and 40 second timepoints, respectively. urements . This hiOne on-chip electrode disconnect approach of the MAX3000x implements analog current monitoring, which detects when the voltages on the driving pins are outside of a programmed operating range. Another on-chip method uses a digital lead-off detection to monitor the output of the ADC and compares the value to a threshold defined by the user. To determine the threshold needed for a specific application, the following equation can be used:One recent application of localized bioimpedance measurements explored the monitoring of tissues during activity to identify indicators of fatigue and, potentially, injury ,5. To dev/v gain, 64 sps.For this data collection, a tetrapolar configuration of Ag/AgCl electrodes was placed on the bicep of a single participant after cleaning the site with alcohol wipes. The electrode placement on the biceps is given in the subset of (1)Multi-frequency (1 to 128 kHz) resistance and then reactance were collected prior to activity while the participant was standing with arms relaxed, resting naturally at the sides of the body.(2)The 128 kHz resistance was collected continuously during five repetitions of 10 lbs over approximately 25 s;(3)The 128 kHz reactance was collected continuously during five repetitions of 10 lbs over approximately 25 s;(4)The 128 kHz resistance was collected continuously during five repetitions of 15 lbs over approximately 25 s;(5)The 128 kHz reactance was collected continuously during five repetitions of 15 lbs over approximately 25 s;(6)Multi-frequency (1 to 128 kHz) measurements of resistance and then reactance were collected post-activity while the participant was standing with arms relaxed, resting naturally at the sides of body.The summarized activity protocol steps and measurements are detailed below:The pre- and post-exercise multi-frequency measurements are given in Freeborn ,50, whicThe 128 kHz resistance and reactance collected throughout the protocol are combined in ep curls , with a While the MAX3000x is able to measure the resistance and reactance of localized tissues, the time needed to reconfigure the type of measurement and frequency impacts multi-frequency measurements and their interpretation. That is, they cannot be interpreted as being collected simultaneously and being an instantaneous representation of the tissue. To highlight this, It is important to clarify that while the multi-frequency measurements of R < 120 The MAX3000x integrated circuit provides a small-form-factor, single-chip solution for the measurement of single- and multi-frequency bioimpedance (resistance and reactance) with significant on-chip signal conditioning options. Measurements of discrete impedances that are representative of localized tissue bioimpedance (20


Photochromic dye-sensitized solarcells (DSSCs) are novel semi-transparentphotovoltaic devices that self-adjust their optical properties tothe irradiation conditions, a feature that makes them especially suitablefor building integrated photovoltaics. These novel solar cells havealready achieved efficiencies above 4%, and there are multiple pathwaysto improve the performance. In this work, we conduct a full characterizationof DSSCs with the photochromic dye NPI, combining electrical impedancespectroscopy (EIS) and intensity-modulated photocurrent spectroscopy(IMPS). We argue that the inherent properties of the photochromicdye, which result in a modification of the functioning of the solarcell by the optical excitation that also acts as a probe, pose uniquechallenges to the interpretation of the results using conventionalmodels. Absorption of light in the visible range significantly increaseswhen the NPI dye is in the activated state; however, the recombinationrate also increases, thus limiting the efficiency. We identify andquantify the mechanism of enhanced recombination when the photochromicdye is activated using a combination of EIS and IMPS. From the comparisonto a state-of-the-art reference dye (RK1), we were able to detecta new feature in the IMPS spectrum that is associated with the opticalactivation of the photochromic dye, providing a useful tool for assessingthe electronic behavior of the device under different conditions oflight excitation. This study provides guidelines to adequate characterizationprotocols of photochromic solar cells and essential insights on theinterfacial electronic processes. All these features, together with the possibility to fabricatesemitransparent and colorful6 solar cells,make them appealing for mass market applications such as in building-integratedphotovoltaics (BIPV).12 Recently, we reporteda breakthrough concept on photochromic DSSCs13 that simultaneously self-adapt their level of transparency and photovoltaicperformance with sunlight intensity; an efficiency of more than 4%was achieved with the activated photochromic solar cells.Dye-sensitized solarcells (DSSCs) are an emerging photovoltaictechnology that has initiated its industrial development.13 as shown in 13 To tackle the challenge of developingnew photochromic materials with higher efficiencies and faster self-adjustableoptical properties, a better understanding of the interfacial processes,as well as the recombination and transport properties of the devicesis needed. In this regard, a thorough fundamental study and the developmentof a reliable measurement procedure that takes into account the changingbehavior of the dye under illumination are required.Ourbest photochromic dye, NPI, switches from light yellow to adark green hue under irradiation, related to a change from the closedto an open configuration, respectively,21 where a small voltage modulation is superimposed on the steady-stateopen-circuit voltage, and the modulated current is measured. On theother hand, combined with EIS, intensity-modulated photocurrent spectroscopy(IMPS),33 where a small light intensity modulation is superimposed on a constantillumination intensity, is a powerful tool to study and separate transportand recombination processes. Therefore, complementary to this EISstudy, the IMPS34 technique has been applied tothese devices.Small-signal perturbation optoelectronic techniques have been widelyused to separate the processes occurring at different time scalesin the device. The main technique to obtain information on transportand recombination processes is electrochemical impedance spectroscopy(EIS),35 as shown in Figure S2. EIS has provento be a remarkably powerful tool to understand and quantify transportand recombination processes. However, depending on the system understudy, complications may arise, for example, the time constants ofdifferent processes may be too close to separate and, for some cases,the system may not be stable under a voltage modulation. On the otherhand, IMPS is generally performed under short-circuit conditions;the results can be interpreted as a frequency-dependent external quantumefficiency (EQE), where the zero frequency limit of the transfer functiongenerally reproduces the steady-state EQE.37 Therefore, where EIS gives information on voltage-dependent processes,IMPS provides separate information on charge transport.In order to interpret EIS measurements, spectraare generally fitto an equivalent circuit, and information is extracted from the circuitelements. Generally, the equivalent circuit used to analyze DSSCswas proposed and developed by Bisquert and co-authors,2 film or even the modulated light intensity used in IMPS could alsoactivate the dye molecules. This in turn, may change the charge storedand the kinetics of the transport and recombination processes as afunction of voltage and light intensity. Therefore, a clear and simpleprocedure to measure and analyze the response of this novel type ofphotochromic devices is needed. In this work, we focus on the peculiaritiesof the small-signal perturbation analysis of a photochromic dye-sensitizedsolar cell in comparison with a conventional DSSC, and we show thatthe activation of the photochromic dye accelerates recombination withoutshifting the band edges of the oxide. With the goal to unravel howthe photochromic properties of the dye influence the photovoltaicprocesses of DSSCs, to our knowledge, this work provides the firstthorough study combining EIS and IMPS to assess the effect of voltageand light intensity modulations on the determination of the transportand recombination characteristics in photochromic devices. Furthermore,we intend to cast light on the origin of the decrease of the photovoltageobserved in DSSCs prepared with the NPI photochromic dye when thecell is optically activated.Theparticularities of photochromic dyes may result in a changeof the system during the measurement itself, because the illuminationused to define a specific quasi-Fermi level in the TiO13 we reported a new photochromicnaphtpyran-based dye that switches color upon irradiation from paleyellow to dark green. In order to enhance the transparency of thedevice, a 13 μm mesoporous TiO2 layer was used asthe working electrode, while a platinum-coated FTO served as the counterelectrode. To avoid any regeneration limitation of the device, a non-viscous,iodine-based electrolyte, optimized specifically for the NPI dye wasused. In our previous work, we also reported that when photochromicdyes are activated upon illumination, a stunning rise of the photocurrentoccurs until a photostationary state is reached. However, the activatedstate also induces a decrease of the open-circuit voltage, as canbe observed in 8 whosecurrent–voltage curve is given in Figure S1.In 2020,20 These three signals appearat 10–50 kHz and 5–500 and 0.1–1 Hz, respectively.The first, high-frequency semicircle can be related to the platinumcounter electrode,38 as shown in Figure S3. The high-frequency feature disappearsby changing the counter electrode material from platinum to PEDOT.The feature at low frequencies, on the other hand, is associated withelectrolyte diffusion.40 These two signals are of littleinterest for the focus of this study; therefore, we limit ourselvesto the discussion of the main arc of the spectra in the 5–500Hz range, linked to the recombination processes in the DSSC.20 As a simplification, the size of the real partof this arc is approximately equal to the recombination resistance.In well-performing dye solar cells, the recombination process correspondsto electron transfer from TiO2 to tri-iodide in the electrolytesolution. Hence, the recombination resistance is a charge transferresistance that can also be measured in the dark, upon applying avoltage similar to the open-circuit voltage under illumination, followingthe superposition principle approximation. We observe a decrease inthe recombination resistance for the cell under illumination as comparedto the charge transfer resistance in the dark at the same voltage,which is typical for DSSCs and is related to the local increase ofthe tri-iodide concentration due to the dye regeneration process,thus accelerating recombination.41 In accordanceto the RK1 absorbance spectrum in Figure S5, the absorption coefficient for the red light is almost zero, whichtranslates to a significantly lower recombination current at Voc and, thus, a lower triiodide generation rate; hence, therecombination behavior is very similar to the cell under dark conditions.In the Bode plot in As can be observed in panels a and b in Figure S6). Thismakes it difficult to compare the activated and non-activated statesof the cells for light excitation where the dye absorbs. This is clearlyseen in The same experiments were carried out with NPIsolar cells andthe results are presented in panels (c–f) in Toconfirm this interpretation, we have run a very quick  impedance experiment under blue light illumination restrictedto the 1–100 Hz frequency range (where the recombination arcappears). The results are shown in Figure S7, where we observethat most of the deactivation of NPI in a full cell takes place withinthe first 4 h. This result also indicates that the discoloration processin a photochromic dye based cell slows down the recombination process,or in other words, the activation of the dye accelerates recombination.The impact on the charge transfer resistance of the deactivationprocess can be observed in From the Bode plots in 35 the main arc in the 5–500 Hz range related to the chargetransfer/recombination process was fitted to a parallel -RC- element,where the resistance is considered to be the charge transfer (dark)or recombination resistance of the device (RCT), while the capacitance is the chemical capacitance (Cμ). As a specific characteristic of DSSCs,both parameters generally show an exponential voltage dependence42C00 is aconstant, α is the trap distribution parameter, q is the elemental charge, V is the voltage appliedto obtain each impedance, kB is the Boltzmannconstant, and T is the temperature.R00 is aconstant and β is the transfer parameter or recombination parameter.The EIS results, as shown in 43 as was previously indicated by DFT calculations.13 Thus, we can conclude that the shift toward higher frequenciesof the main signal in Voc associated with the activation of the dye is due to kinetic reasonsonly.44 However, as shown in Figure S4, there is a band shift between the NPI and RK1 dyesof around 0.15 V. Looking at the values obtained for the recombinationresistance, as the light intensity increases and the open-circuitvoltage approaches the values obtained at 1 sun under the solar simulatorand, hence, under practical operating conditions, differences betweenthe open and closed forms of the dye become more apparent. This wasalready observed in our previous study13 and in 46 In this respect,the results of the chemical capacitance and the recombination resistancein At this point, it is important to remember that,by comparing atthe same applied/generated potential, we ensure that the electronquasi-Fermi level and the electron density in the photoanode for theexperiments carried out with different illumination sources is thesame.Tables S1 and S2 are within the range normallyreported forDSSCs (0.15–0.35 for α and 0.5–0.8 for β).49 Although there is an increase in the β valuesupon activation of the photochromic dye, this change is not sufficientto imply a change in the dominant recombination pathway correspondingto triiodide reduction. In addition to the α and β valuesobtained from fitting of the EIS to the parallel -RC- element, thetime constants associated to this recombination feature, as shownin S8, are also an important source of information.The α and β parameters included in 50 which decreasesin a dramatic way as both theillumination intensity and the open-circuit voltage increase. If wecompare this behavior to the trend shown by the recombination resistancein Figure S8. This is consistentwith the similar α and β values observed in Tables S1 and S2 and suggests that the same recombinationprocess takes place in both devices. The only difference between thetime constants obtained for the NPI and RK1 dyes is the band shiftof 0.15 V observed in Figure S4.The time constants observed in 20 with the following equationLn is thesmall-signal perturbation charge carrier diffusion length, d is thethickness of the semiconductor layer, which is known to be 13 μm, Rrec is the recombination resistance, and Rt is the transport resistance.The diffusion length, which can be described as the average distancethat an electronic carrier can travel across the active layer beforerecombining, is a very useful parameter of the cell, because it canbe directly related to the amount of charge that can be collectedby the cell. However, due to the complex kinetics of the processestaking place inside the cell, it is very hard to obtain an accuratevalue for this parameter without using complicated random walk models.Since the small-signal perturbation techniques allow us to simplifythe behavior of the cell, assuming first-order kinetics for recombination,we can obtain to a good approximation the small-signal perturbationcharge carrier diffusion length. This value can be obtained from theEIS35 because no clear transport line was present in the spectra, However, since it was notpossible to fit the EIS to the classicalBisquert and co-workers equivalent circuit24 where Dn is the electron diffusion coefficient, whichcan be obtained from IMPS, and τn is the electroneffective lifetime, as shown in 54For these cells, EIS alonefailed to provide information aboutthe small-signal perturbation electron diffusion length. Thus, thisparameter can alternatively be calculated by S9, it can be seenthat there are two distinguishable signals with the conventional non-photochromicdye RK1 as previously reported for various DSSCs and other thin-layerphotovoltaic devices.57 For a film thickness as large as the TiO2 layer of these devices (13 μm), the signal observed in the10–100 Hz range can be related to the electron transport inthis nanostructured mesoporous layer. Some differences between thespectra obtained with the two excitation wavelengths are observed,such as the size of the feature that appears at high frequencies anda shift of 1 order of magnitude of the frequency where the signalassociated to electron transport in the TiO2 layer is observed.However, the general shape and behavior of two identifiable signalsis consistent.From panels a and b in When the same IMPS experiment is carried out on deactivated andactivated NPI solar cells . However, electrontransport when the dye is not activated (red illumination before lightsoaking) appears to be somehow faster. The reason is that since thenon-activated dye absorbs much less in the red , the light illumination intensity required to obtainthe same value of the equivalent open-circuit voltage is larger. Consequently,the quasi-Fermi level in the TiO2 photoanode is higherup in energies and transport becomes faster, in accordance to themultiple trapping model. Knowing this, the small-perturbation electrondiffusion coefficient can be obtained by19tr is the time constantfor the transport process observed in IMPS, d isthe thickness of the semiconductor layer, which is known to be 13μm, and γ is a dimensionless factor that depends on thedirection of illumination and the ratio between the absorption lengthand the thickness of the film, whose value can be approximated to2.5. Since these values are being used together with the data obtainedfrom EIS at open-circuit voltage, we need to ensure that both parametersare obtained at the same trap occupancy (i.e. at the same positionof the Fermi level relative to the conduction band). To do that, acorrection, which for DSSCs is known58 tobe about 0.3 V, is applied . However, this correction is likely overestimated for the caseof the deactivated NPI dye, especially for the red LED IMPS measurementsbefore light soaking due to the low absorbance of the closed dye;at this wavelength, the Fermi level is very close to its positionunder dark conditions. Since no drift-diffusion models that includephotochromic behaviors are currently available, and for the sake ofsimplicity given that no significant differences in the qualitativebehavior under small perturbation techniques have been identifiedin this study, the same voltage correction has been applied to theNPI dye, with the precaution of only interpreting the higher lightintensity values.The behavior of the time constants represented in Figure S11) and doing the same with the diffusion coefficients calculated byapplying Figure S12),we obtain a diffusion coefficient of 3 × 10–11 m2/s for the RK1 and 4 × 10–12 – 8 × 10–11 m2/s for theNPI solar cell. These values are combined using Figure S13) which are found to be 200–500μm for RK1 and 50–110 μm for NPI. These large values(in comparison with the film thickness) suggest that charge collectionin the TiO2 approaches 100% in both cases.By extending the time constant trend line fromthe EIS measurementsto short-circuit conditions  and annealed underair at 500 °C for 20 min. The photoanode sensitization mixture(0.5 mM[dye]/5 mM [CDCA]) coadsorbant dissolved in a 1:1 mixture ofCHCl3/tBuOH for NPI-based cells and 1:1mixture of CHCl3/EtOH for RK1-based cells. Both electrodeswere sealed together using 60 μm Surlyn and then filled withthe appropriate electrolyte solution, Solaronix HI-30 for RK1 andour optimized homemade one for NPI.13 Thepre-drilled holes were sealed with a thin glass cover with Surlynunderneath.Transparent photoanodes, commerciallyavailable from Solaronix, Switzerland (Ti-Nanoxide HT/SP) with a 13μm mesoporous TiO2. The EIS studies were conductedusing an Autolab/PGSTAT12/30/302N FRA2 potentiostat. IMPS measurementswere carried out by coupling an LED to the PGSTAT302N/FRA32 moduleby means of an LED communication driver (Autolab). A 0.25 cm2 plastic mask was used to limit the area of the cell receiving illuminationduring the IMPS measurements. EIS measurements under illuminationwere performed by applying a potential equal to the observed open-circuitvoltage under constant illumination by white, blue (480 nm), and red(650 nm) Thorlabs LEDs over a wide range of DC light intensities.A 10 mV perturbation in the 10–1 to 105 Hz range was applied. The NOVA 2.1. software was used to generatethe data. Z-view equivalent circuit modeling software (Scribner) wasused to fit the spectra. A flow chart of the EIS measurements of theNPI cells to ensure that all the different experiments were performedon both the activated and deactivated forms of the dye can be observedin The solar cells werecharacterized under 1 sun, using an AM1.5G simulator previously calibratedwith a reference photodiode . The current–voltageresponse in the dark and under illumination of the devices were registeredby applying an external voltage bias to the devices, and the resultingphotocurrent was recorded with a Keithley model 2400 digital sourcemeter . A mask was used prior to delimit an illuminatedactive area of 0.25 cmThe EIS measurements under dark conditions were conductedensuringthat no external source of light interfered with the experiment andby applying an external voltage from 0.1 V to the open-circuit voltageobtained under 1 sun illumination.–1 to 104 Hz due to limitations of the setup(LED and LED driver). The perturbation amplitude was set to 10% ofthe DC background illumination intensity.37 The intensity of the monochromatic light was calibrated using aThorlabs FDS100 silicon photodiode. IMPS measurements were performedunder short-circuit conditions under blue and red illumination usingILH-GD01-SC201 ILS LEDs. The order in which the IMPS measurementswere done can be observed in The frequency range of theIMPS measurement was restricted to 102 illumination with an AM 1.5Gfilter, ensuring that the illuminated area of the solar cell had turnedto a dark green color. The light intensity was recorded using a referencemonocrystalline silicon solar cell with temperature output .In this work, we distinguishbetween the behavior of the solarcells for the deactivated and activated photochromic NPI dye. Thechange was induced by exposing the cell to the solar simulator (ABET-Sun2000)for 15 min under 100 mW/cmAn additional experiment was conducted to study theevolution ofthe recombination kinetics upon deactivation of the NPI dye to betterunderstand the relation between the activated and deactivated statesof the dye and the recombination process. For that purpose, after15 min of 1 sun illumination, EIS under dark conditions at a fixed0.35 V external voltage was conducted after different time intervalsto study the discoloration process. For more clarity, a flow chartof how this measurements were done can be observed in In order to includestatistical values, two cells of each typeof dye were completely characterized by EIS and IMPS.


During the SARS-CoV2 pandemic, protection measures, as well as visiting restrictions, had a severe impact on seriously ill and dying patients and their relatives. The study aims to describe the experiences of bereaved relatives of patients who died during the SARS-CoV2 pandemic, regardless of whether patients were infected with SARS-CoV2 or not. As part of this, experiences related to patients’ end-of-life care, saying goodbye, visiting restrictions and communication with the healthcare team were assessed.An open observational post-bereavement online survey with free text options was conducted with 81 bereaved relatives from people who died during the pandemic in Germany, with and without SARS-CoV2 diagnosis. 67/81 of the bereaved relatives were female, with a mean age of 57.2 years. 50/81 decedents were women, with a mean age of 82.4 years. The main underlying diseases causing death were cardiovascular diseases or cancer. Only 7/81 of the patients were infected with SARS-CoV2. 58/81 of the relatives felt burdened by the visiting restrictions and 60/81 suffered from pandemic-related stress. 10 of the patients died alone due to visiting restrictions. The burden for relatives in the hospital setting was higher compared to relatives of patients who died at home. 45/81 and 44/81 relatives respectively reported that physicians and nurses had time to discuss the patient’s condition. Nevertheless, relatives reported a lack of proactive communication from the healthcare professionals.Visits of relatives play a major role in the care of the dying and have an impact on the bereavement of relatives. Visits must be facilitated, allowing physical contact. Additionally, virtual contact with the patients and open, empathetic communication on the part of healthcare professionals is needed.German Clinical Trials Register (DRKS00023552). The SARS-CoV2 (severe acute respiratory syndrome coronavirus type 2) pandemic disrupted usual experiences of dying and bereavement for patients and their relatives. To mitigate the devastating impact of SARS-CoV2, patients were isolated in care facilities and died alone as visit restrictions were placed regardless of a SARS-CoV2 infection. Although there were exceptions to restrictions, e.g. allowing limited visits in the dying phase, they still had effects on the dying patient and their relatives .Funerals and burials were postponed or held remotely, often without the presence of relatives or friends. Wallace et al.  found thSelman et al.  recommenThis will likely have affected the experience of the dying and their relatives. Up to date, it is unknown what the intermediate and longer effects of these experiences will be. Recently published findings from the UK –11 descrGiven the limited data so far, understanding the impact of the current SARS-CoV2 pandemic is pertinent to provide better support for dying patients and their relatives. Our study aimed to describe the experiences of bereaved relatives of patients who died during the SARS-CoV2 pandemic in Germany related to patients’ end-of-life care, saying goodbye, visiting restrictions, and communication with the healthcare team. Results will also be used to support the development of a national strategy for the care of severely ill and dying patients and their relatives for better pandemic preparedness and response. The study is part of a German collaborative project entitled “National Strategy for Palliative Care of Severely Ill and Dying People and their Relatives in Pandemics  in Germany,“ led by the National Research Network of University Medicine (NUM) on COVID-19. PallPan aims to develop and consent a national strategy for the care of seriously ill and dying patients to ensure future pandemic preparedness. Additionally, this study was conducted jointly with the CO-LIVE-study  on end-oWe conducted an open observational post-bereavement survey to assess relatives´ experiences with end-of-life care during the SARS-CoV2 pandemic. An online survey using LimeSurvey was developed that enabled responses via computer or mobile devices. The study was conducted following the Checklist for Reporting Results of Internet E-Surveys (CHERRIES) guidelines  and apprThe questionnaire included an abbreviated version of the international Care Of the Dying Evaluation (iCODE) questionnaire that focuses on the last two days of life and the bereavement period, and asks about the characteristics of patient care and family support. It inclThere were no incentives for participation, and respondents could discontinue the survey at any time. The survey was piloted with 20 adults from July 15th to July 21st 2020 and modified accordingly.The online survey was open from July 21st to November 15th 2020.The questionnaire could be completed by all bereaved people in Germany whose relative had died between March 1st and November 15th 2020 at home, in a hospital, a nursing home, hospice or elsewhere, with or without infection with SARS-CoV2. Visiting restrictions in care facilities, 18 haveDescriptive data analysis was performed by a group of researchers and clinicians. IBM SPSS 27 was used and results are presented as mean ± SD and count (percentage), respectively. The data is presented under the topics that also guided the different questions within the survey. Subgroup analyses based on SARS-CoV2 infection, place of death and visiting ban were conducted. Free text comments were analysed using a content analysis approach.pandemic-related limitations in end-of-life care (n = 67), greatest challenges in end-of-life care due to the pandemic (n = 74), pandemic-related stress (n = 54), wishes for end-of-life care in pandemic times (n = 63), ideas and suggestions on how to better care for patients in the last phase of life during a pandemic (n = 68) and other comments (n = 56). Since relatives repeated the same themes consistently regardless of the question, the free text fields would be evaluated across questions and considered based on the predominant themes (e.g. visiting restrictions).118 bereaved relatives visited the survey site. 12 were identified as unique site visitors and further 25 did not complete the survey (participation rate: 89 %). The analysis is based on the 81 completers  of the bereaved relatives felt burdened by the visit restrictions of the dying patient and 60/81 (74 %) relatives experienced pandemic-related stress. Patients died between March and October and a third died in general hospitals  or nursing homes . Almost every tenth patient died at home  or in a hospice . 72/81 (89 %) died in care facilities, 6 relatives provided contradictory answers regarding visiting restrictions (no visits and no visit restrictions ticked) and were excluded. There were 23/66 (35 %) unrestricted visiting opportunities, compared to 17/66 (26 %) cases where no visits were allowed. In 58/66 (88 %) cases visits were possible but restricted. If there were visiting restrictions, most of these relatives were allowed to stay for one hour or/and to visit alone. 34/81 (42 %) patients died alone, 10/34 (29 %) died alone due to visiting restrictions. 53/81 (65 %) of the bereaved relatives judged that the decedent died in the right place.In the free-text comments, the relatives reported: visiting restrictions led to a lack of physical closeness, having to visit alone , the missing possibility of end-of-life care provided by relatives, no possibility of saying goodbye, and more organizational effort concerning visits. The visiting restrictions were often only reduced in the dying phase, which was felt to be too late since many patients were no longer responsive at that time to say goodbye.It was of course difficult, due to the pandemic, not to be allowed to visit my father in the hospital at first and then only to go to him alone. Saying goodbye to him all alone, without close support was difficult.That practically no end-of-life care was possible. Except for the last hours, in which he was only asleep, we were denied access to the nursing facility, which in my opinion was an unbearable situation for both sides.That I was not allowed to accompany my mother [at the end of her life], to know that she must die alone and lonely.Of the 72 patients who died in care facilities, 30 patients died during the official visiting ban and 37 patients died when it was ended. 5 relatives did not know the date of death and 6 relatives provided contradictory answers (no visits and no visit restrictions ticked). Answers from 61 relatives were included in the analysis: 26 relatives who lost the patient during and 35 relatives who lost the patient after the official visiting ban provided information. After ending the official visiting ban in care facilities, two facilities still did not allow visitors  patients died in a hospital, 27/81 (33 %) died in a care facility, 9/81 (11 %) died at home, 8/81 (10 %) died in a hospice and 7/81 (9 %) patients died elsewhere. All bereaved relatives of persons who died at home indicated that the decedent passed away at the right place . Relatives of patients cared for at home reported feeling less burdened by the pandemic situation To compare visiting restrictions among patients with/without SARS-CoV2 infection only answers concerning patients who died in care facilities  were included and 6 answers with contradictory information (no visits and no visit restrictions ticked) were excluded. From the resulting 66 cases were 59/66 (89 %) SARS-CoV2 negative and 6/66 (9 %) SARS-CoV2 positive . Comparing the visit restrictions among those patients with and without SARS-CoV2 infection, it became apparent, that visit restrictions for SARS-CoV2 positive patients were slightly stricter than for SARS-CoV2 negative patients: in 2/6 (33 %) of the cases were no visits allowed for SARS-CoV2 positive patients and in 12/59 (20 %) of the cases were no visits allowed for SARS-CoV2 negative patients.Relatives of patients with SARS-CoV2 infection felt more burdened by the pandemic situation compared to those from SARS-CoV2 negative patients: 7/7 (100 %) of the relatives of SARS-CoV2 positive patients answered “yes” to the question about the experience of a pandemic-related burden compared to 52/73 (71 %)of the relatives of SARS-CoV2 negative patients.In case of visiting restrictions, opportunities for digital communication (e.g. via Skype) with the patient were limited, irrespectively of the place of death: in 56/81 (69 %) cases no online communication opportunities were given, in 18/81 (22 %) cases the online communication opportunity was given but not provided by the care facility and in 7/81 (9 %) of the cases the online communication was provided by the care facility Fig. .Fig. 4ODuring the last phase of life of the patients, 45/81 (56 %) respectively 44/81 (54 %) relatives reported that physicians resp. nurses had time to listen and discuss the patient’s condition, provided enough information about the patient’s condition  and explanations were easy to understand . 60/81 (74 %) relatives were told that the patient was likely to die soon, but 45/81 (56 %) were not told about what to expect in the dying phase (e.g. symptoms). 56/81 (69 %) relatives assessed the emotional support from the healthcare team as good/excellent, and 61/81 (75 %) felt treated empathically after the death, but 11/81 (14 %) did not have any contact with the healthcare team after the death of the patient.In the free-text comments concerning the communication with the healthcare team, relatives reported a lack of open, proactive communication  and a deficit of empathy of carers towards the relatives.The nursing home had stopped all communication. No consideration was given to contact needs. The nursing staff was completely overworked. The home’s management was disastrous. We were not informed in time about the current situation, we were not involved and we were not consulted about the treatment.Our study described bereaved relatives’ experiences with end-of-life support of patients who died with or without SARS-CoV2 infection in Germany. Findings revealed that relatives not only had to cope with the stress caused by losing a relative but that they additionally experienced stress directly related to the pandemic, mainly due to the burden caused by visiting restrictions.at all, more than 88 % of the relatives were allowed to visit, but restrictions concerning duration or number of visitors were imposed on them. Common to both studies is the great distress that bereaved relatives experienced due to the visiting restrictions [Compared to UK data, which report that half of the bereaved relatives 56 %; 10) were not allowed to visit during the last days of the patient’s life, the situation in Germany was more diverse: while one-quarter of the relatives were not allowed to visit  were notVisiting restrictions are at odds with the need of being present when a relative is dying, 21, 9 aEven after the official visiting ban has been lifted, some facilities still did not allow any visitors, causing an additional burden for relatives. To our knowledge, there are no analyses of what organizational consequences care facilities drew from lifting the visiting ban. In addition, there should be uniform regulations on how visits, apart from a general ban on visits, should be handled.Relatives of patients who died at home felt less burdened by the pandemic situation than relatives of patients who died in care facilities. They mentioned that the pandemic situation (e.g. flexibility due to home office) was rather beneficial, allowing to spend more time with the patient. Vice versa, Mayland et al.  describeOf the bereaved relatives in our study, those of SARS-CoV2 positive patients felt more burdened and visiting arrangements were stricter. Often, relatives of SARS-CoV2 positive patients are also tested positive, so that quarantine regulations make visits even more difficult. As this project set the focus on palliative care patients irrespectively of a SARS-CoV2 infection, the majority of the decedents and their relatives were SARS-CoV2 negative. Still, they suffered from hygiene and safety measures, and there are signals that visiting arrangements for SARS-CoV2 positive patients were even stricter. Data concerning divergent experiences between SARS-CoV2 negative/positive patients need to be interpreted with great caution due to the descriptive data reported and group sizes differences.Given the importance of visits at the end of life, visiting regulations and infection control measures should be reconciled to avoid SARS-CoV2 infections and enable contacts. Therefore evidence-based interventions as tracing and isolating SARS-CoV2-positive cases or rapid SARS-CoV2 testing are useful , 35. Facdoing okay and creates a connection between the patient and the usual family life [When relatives were not allowed to spend face-to-face time with the patient due to the pandemic situation, video or telephone calls could be a way to achieve connectedness. Hanna et al. describeily life . The preily life . A similily life  reports ily life . Even wiThis corresponds to a recent study’s findings that virtual interactions were rare , 11 and Our survey revealed mixed experiences of bereaved relatives regarding communication with the healthcare teams. About half of the relatives indicated that the team had enough time to listen and discuss the patient’s condition and had been provided with enough information. Bereaved relatives’ judgment in the present study did differ between doctors and nurses, but data from the UK shows that relatives had a greater level of confidence in the nursing staff and that they provided care with more respect and dignity than doctors . This miAs the survey relates to the beginning pandemic situation in Germany, healthcare professionals were overwhelmed by the numerous new challenges and work overload due to the COVID-19 crisis and consequently reduced staffing levels leading to the prioritization of physical elements of care . FurtherThe strengths of this study are the collection of data on end-of-life care of patients, with and without SARS-CoV2 infection, during the first wave of the pandemic in all care settings where people die, the use of validated questionnaires, the adaptation to the pandemic situation, and the assessment of subjective experiences via free-text comments.A limitation of the study is the focus on the last two days of the patient’s life in many questions. As we adapted the survey from another planned study which used a validated questionnaire we decided to keep the time frame. However, we allowed respondents to provide free-text comments which indicated that bereaved relatives suggest, that a longer period before passing away is relevant.One limitation might be the relatively small sample size restricting the generalisability of the study. Although we used several recruiting methods, the most successful recruitment way was an interview printed in a regional newspaper that published the survey link. The newspaper has a wide catchment area which includes urban and rural areas and helps to get a wide spectrum of different experiences. Due to the survey’s online format, there was a selection bias resulting in the participation of relatives who felt able to complete an online survey.For future pandemics and waves of this pandemic, it is pertinent to reconcile the accompaniment and support of end-of-life patients and their relatives with public health measures. Staying connected with seriously ill and dying patients must be facilitated, allowing face-to-face, (shared) contact whenever possible, and allowing decisions to be made on an individual basis. It should always be possible to visit dying persons. Additionally, video and audio calls between patients and relatives should be offered more widely to support communication and closeness. Furthermore, healthcare professionals play an important role in providing health and psycho-social care in pandemic times, and relatives wish for open, empathetic, and transparent communication to feel included in care decisions – even though having to be physically distant.