Regeneration Kinetics Research Articles

Characterization of Macroglia Response during Tissue Repair in a Laser-Induced Model of Retinal Degeneration.

Reactive gliosis is a hallmark of chronic degenerative diseases of the retina. As gliosis involves macroglia, we investigated their gliotic response to determine the role of S100β and intermediate filaments (IFs) GFAP, vimentin, and nestin during tissue repair in a laser-induced model of retinal degeneration. We validated the results with human retinal donor samples. Experiments were performed in zebrafish and mice using an argon laser (532 nm) to induce focal lesions in the outer retina. At different time points following injury induction, the kinetics of retinal degeneration and regeneration were assessed using hematoxylin and eosin staining (H&E). Immunofluorescence was performed to evaluate Müller cell (GS) and astrocyte (GFAP) injury response and to distinguish between both cell types. Additionally, staining was performed in human retinal sections containing drusen. Focal laser treatment elevated the expression of gliotic markers in the area of the damage, which was associated with increased expression of S100β, GFAP, vimentin, and nestin in mice and humans. In zebrafish, we detected S100β at the first time point, but not GFAP or nestin. Double-positive cells with the selected glia markers were detected in all models. However, in zebrafish, no double-positive GFAP/GS cells were found on days 10 and 17, nor were S100β/GS double-positive cells found on day 12. Macroglia cells showed a different pattern in the expression of IFs in degenerative and regenerative models. In particular, S100β may prove to be a target for suppressing chronic gliosis in retinal degeneration.

Triggering sustainable regeneration of Fe2+ by S-scheme Bi2Fe4O9/BiOBr heterojunction toward highly efficient peroxymonosulfate activation for visible-light-driven removal of thiabendazole

Peroxymonosulfate (PMS)-assisted photocatalytic processes are economical and green strategies for the treatment of pesticide pollution. However, its degradation efficiency is severely hindered by the sluggish kinetics of active centers regeneration and low charge-transfer. Herein, S-scheme Bi2Fe4O9/BiOBr heterogeneous material was designed to activate PMS for thiabendazole (TBZ) degradation. Bi2Fe4O9 and BiOBr have similar structural unit of [Bi2O2]2+ to share the Bi-O bonds, which is favorable to form asymmetric interface and enhance the polarization. Based on these unique characteristics between Bi2Fe4O9 and BiOBr, a robust internal electric field in the S-scheme heterojunction is built, which could provide driving force to boost the electron-transfer process and encourage the sustainable regeneration of Fe2+. After optimizing the proportion of Bi2Fe4O9 on the composite, it was found that 50 wt% Bi2Fe4O9/BiOBr (BFB-50) exhibits the best TBZ removal efficiency after 30 min visible light irradiation, which is 2.25 and 12 folds compared to Bi2Fe4O9 and BiOBr, respectively. Furthermore, electron paramagnetic resonance (EPR) and radical trapping experiments indicate that 1O2 and SO4•- involving oxidation mechanism impart maximum contribution towards TBZ degradation. The possible pathways of TBZ degradation are reasonably proposed by the HPLC-MS and the toxicity evolution of TBZ is appraised using the ECOSAR software. This study provides an insight into the fabrication of S-scheme heterojunction for environment remediation through the photocatalysis/sulfate-mediated advanced oxidation process.

Nanoparticle-based targeting of microglia improves the neural regeneration enhancing effects of immunosuppression in the zebrafish retina

Retinal Müller glia function as injury-induced stem-like cells in zebrafish but not mammals. However, insights gleaned from zebrafish have been applied to stimulate nascent regenerative responses in the mammalian retina. For instance, microglia/macrophages regulate Müller glia stem cell activity in the chick, zebrafish, and mouse. We previously showed that post-injury immunosuppression by the glucocorticoid dexamethasone accelerated retinal regeneration kinetics in zebrafish. Similarly, microglia ablation enhances regenerative outcomes in the mouse retina. Targeted immunomodulation of microglia reactivity may therefore enhance the regenerative potential of Müller glia for therapeutic purposes. Here, we investigated potential mechanisms by which post-injury dexamethasone accelerates retinal regeneration kinetics, and the effects of dendrimer-based targeting of dexamethasone to reactive microglia. Intravital time-lapse imaging revealed that post-injury dexamethasone inhibited microglia reactivity. The dendrimer-conjugated formulation: (1) decreased dexamethasone-associated systemic toxicity, (2) targeted dexamethasone to reactive microglia, and (3) improved the regeneration enhancing effects of immunosuppression by increasing stem/progenitor proliferation rates. Lastly, we show that the gene rnf2 is required for the enhanced regeneration effect of D-Dex. These data support the use of dendrimer-based targeting of reactive immune cells to reduce toxicity and enhance the regeneration promoting effects of immunosuppressants in the retina.

Kinetics of endogenous thymic regeneration following chemotherapy-induced involution

Abstract The thymus is a primary lymphoid organ where T cell development occurs. Besides the naturally transpiring age-dependent involution, the thymus also undergoes acute involution from cytotoxic stimuli. Establishing thymic regeneration strategies would, thus, be immensely critical for pediatric cancer and transplantation patients receiving cytoablative chemotherapies. Several signaling pathways (e.g., KGF, BMP4) promote thymic regeneration, albeit with suboptimal therapeutic potential, mainly due to poor insight of the detailed mechanisms of endogenous thymic repair. To address this issue, we developed a mouse model of cyclophosphamide-induced thymic involution and monitored thymic reconstitution for up to 5 weeks post-treatment. Macroscopic assessment via thymic weight index and MRI-based volumetric analysis, along with histopathology, revealed that endogenous thymic regeneration is a non-linear, multistep process, consisting of a: (a) Reconstitution phase, during which recuperation occurs at an exponential rate, (b) Rebound phase, in which abnormal thymic hyperplasia is observed, and (c) Recoil phase, where thymic homeostasis ensues. Quantification of peripheral blood lymphocytes, however, revealed that thymic hyperplasia at Rebound does not correlate with restored thymic functions and output. Detailed investigation via flow cytometry revealed the stalling of T cell development at the Double Positive (CD4 +CD8 +) stage, implying cortical defects during thymic repair. Currently, we employ single-cell RNA sequencing with single cell resolution imaging, to define the molecular pathways disrupting cortical Thymic Epithelial Cell (cTEC) renewal post-chemotherapy, leading to impaired thymopoiesis. Supported by AAI's Career in Immunology Fellowship PI's funding supported by Albert Einstein College of Medicine: New Investigator Start-up funds

Insights into boron accelerated Fenton-like chemistry: Sustainable and fast FeIII/FeII circulation

In this work, amorphous boron (A-Boron) as a metal-free co-catalyst was applied to address the slow kinetics of FeII regeneration and inactive FeIII accumulation in Fenton-like peroxydisulfate (PDS) activation. The A-Boron/FeIII/PDS system can rapidly degrade bisphenol A (BPA) for ten cyclic runs without performance decline. Based on chemical probing, radical quenching and in situ capturing tests, Fe(IV) and radicals (OH and SO4−) are identified as the primary reactive species, and the combined ROS can achieve universal pollutants oxidation with high PDS utilization efficiency. QSAR study unveils that the kobs values of pollutants linearly depend on their EHOMO. A-Boron can bind with FeIII species for catalytic reduction, and meanwhile, the semi-metallic surface experiences stepwise transformation. The fast dissolution of inactive surface boron oxide enabled a self-cleaned and reactive boron surface for long-lasting iron circulation. Also, BPA degradation pathways were proposed based on UHPLC-QTOF-MS tests and Fukui index calculation.

Insight into the Enhanced Photo-Fenton Degradation Performance of Fe3O4@β-Ketoenamine-Linked Covalent Organic Framework

The sluggish charge-transfer kinetics of Fe(II) regeneration, unsatisfactory utilization of H2O2, and low reaction efficiency remain largely unresolved in Fe3O4-based heterogeneous photo-Fenton systems. Herein, an in situ covalent attaching strategy was employed to fabricate Fe3O4@covalent organic framework (COF) core–shell heterostructures. By virtue of this, enhanced photoresponsive behavior was obtained to tailor the regeneration kinetics for Fe(II) and ideal catalytic sites for H2O2 were provided. Molecular engineering was further employed to manipulate the linkages (β-ketoenamine or imine) of the COFs. Bearing a β-ketoenamine linkage, the Fe3O4@TpTta COF exhibited remarkably fast kinetics (0.111 min–1) as well as exceptional pH tolerance in photo-Fenton degradation of methylene blue, which stands out among the state-of-the-art photocatalysts. Combined with theoretical calculations, the electron-transfer route and interfacial interactions between the oxidant and catalysts with different linkages were fully revealed, giving insight into the synergistic relationship between photocatalysis and Fenton reactions.

Restored Thymic Output after Androgen Blockade Participates in Antitumor Immunity.

The thymus is a hormone-sensitive organ, which involutes with age in response to production of sex steroids. Thymic involution leads to a decrease in the generation of recent thymic emigrants (RTEs), resulting in a reduced response to immune challenges such as cancer. Interestingly, the standard of care for prostate cancer patients is androgen deprivation therapy (ADT), which leads to thymic regeneration and an increase in thymic output. It remains unknown whether these newly produced T cells can contribute to the antitumor immune response. This study defines the kinetics of thymic regeneration in response to ADT in mice, determining that thymic epithelial cell proliferation is critical for the increase in RTE output. Using a mouse model to track RTE in vivo, we demonstrate that these newly generated RTEs can traffic to tumors, where they become activated and produce effector cytokines at levels similar to more mature T cells. Collectively, these data suggest that RTEs produced from ADT-induced thymic regeneration could be harnessed for the antitumor immune response.

Influence of Redox Couple on the Performance of ZnO Dye Solar Cells and Minimodules with Benzothiadiazole-Based Photosensitizers.

ZnO-based dye-sensitized solar cells exhibit lower efficiencies than TiO2-based systems despite advantageous charge transport dynamics and versatility in terms of synthesis methods, which can be primarily ascribed to compatibility issues of ZnO with the dyes and the redox couples originally optimized for TiO2. We evaluate the performance of solar cells based on ZnO nanomaterial prepared by microwave-assisted solvothermal synthesis, using three fully organic benzothiadiazole-based dyes YKP-88, YKP-137, and MG-207, and alternative electrolyte solutions with the I-/I3 -, Co(bpy)3 2+/3+, and Cu(dmp)2 1+/2+ redox couples. The best cell performance is achieved for the dye-redox couple combination YKP-88 and Co(bpy)3 2+/3+, reaching an average efficiency of 4.7% and 5.0% for the best cell, compared to 3.7% and 3.9% for the I-/I3 - couple with the same dye. Electrical impedance spectroscopy highlights the influence of dye and redox couple chemistry on the balance of recombination and regeneration kinetics. Combined with the effects of the interaction of the redox couple with the ZnO surface, these aspects are shown to determine the solar cell performance. Minimodules based on the best systems in both parallel and series configurations reach 1.5% efficiency for an area of 23.8 cm2.

Regenerating MXene by a Facile Chemical Treatment Method.

A popular substance in the MXene family, titanium carbide (Ti3C2Tx), has received substantial attention mainly due to its high metallic conductivity, easy solution processability, and environment friendliness. However, the poor oxygen resistance nature of MXene has prevented its practical applications from being realized. Despite significant attempts to improve the oxidative stability of MXenes, a comprehensive understanding of the oxidation mechanism is still elusive, thus leaving an optimal strategy for recycling oxidized MXene in question. Here, by developing a facile hydrofluoric acid (HF) post-treatment, we have unraveled the regeneration kinetics of the oxidized Ti3C2Tx. A systematic and extensive investigation using a combination of Raman spectroscopy, scanning electron microscopy, X-ray diffractometer, and X-ray photoelectron spectroscopy revealed that HF post-treatment is critical for restoring the structure/morphology and surface composition of MXene nanosheets. These are ascribed to the oxidizing agent removal kinetics, while the generation of amorphous carbon and Ti(III) in fluorinated derivatives provides efficient electrical conductivity. Our findings suggested that HF post-treatment is sufficient to evade and reduce the degradation process while maintaining the conductivity for a longer time, which will not only be economically advantageous but also a step forward for the rational design of Ti3C2Tx-based devices and functional coatings.

Nicotinamide adenine dinucleotide hydrogen regeneration in a microbial electrosynthesis system by Enterobacter aerogenes

Costly cofactors such as nicotinamide adenine dinucleotide hydrogen (NADH) are essential to have high activity in many redox enzymatic processes. Cofactor regeneration methods have been suggested to improve the economic aspects of the system. Here, we introduce a microbial electrosynthesis process to regenerate NADH in a two-chamber set-up with Enterobacter aerogenes biofilm as the bio-cathode. The effects of several important factors on the regeneration efficiency were studied and the highest NADH regeneration yield was achieved equal to 65 % at the potential of −1.5 V and the initial NAD+ concentration of 1 mM after 8 h of operation. The regenerated cofactor was highly enzymatically active (93 ± 4 %) which was a great merit of the process. Studying the kinetics of regeneration revealed that the electron transfer rate to the biofilm was the limiting factor. We tried to remove the limitation through co-culturing Pseudomonas aeruginosa and producing more electrochemical active compounds in the biofilm. Although, this modification was not effective for the regeneration yield, it showed that the external potential implicitly influenced the regeneration process by changing the internal microbial cell metabolic fluxes. Finally, it can be concluded that the microbial electrosynthesis is a promising green process for NADH regeneration.

Solid-state decomposition of Ca2CuO3 enhances its CO2 reactivity and cycle stability

We evaluated the carbonation/decarbonation performance of Ca2CuO3 sorbents with different degrees of reductive decomposition for post-combustion CO2 capture. Three sorbents, non-decomposed (N-CCO), partially decomposed (P-CCO), and fully decomposed (F-CCO) Ca2CuO3 were tested. We found a higher CO2 capacity with a high content of in situ generated copper. Through temperature-resolved in situ X-ray diffraction, we confirmed that F-CCO started to form calcium carbonate at lower temperatures (∼400 °C) than N-CCO, which does not react with CO2 until 600 °C. F-CCO demonstrated faster regeneration kinetics as well. At 600 °C, a significant recovery of 85 % was achieved for F-CCO compared to 16 % for N-CCO. F-CCO also showed a higher degree of carbonation than P-CCO and N-CCO under isothermal carbonation/decarbonation at 800 °C. The conversion of F-CCO reached 52 % after just 26 min, while the conversion was only 46 % for P-CCO and 48 % for N-CCO even after the longer reaction time of 39 min. The F-CCO sorbent showed an extremely high regeneration rate at 800 °C compared to the other sorbents. The regeneration of F-CCO was completed in less than 3.5 min. By contrast, the full regeneration of other sorbents did not take place even after 26 min (95 % recovery for P-CCO and 78 % recovery for N-CCO). Finally, when regenerated under 4 % H2 in N2, the sorbents' average conversion over ten cycles was estimated at 79.2 %, 44.7 %, and 45.5 % for F-CCO, P-CCO, and CaO. The high thermal conductivity of copper particles is attributed to the efficient performance of F-CCO.

Optical Control of Tissue Regeneration through Photostimulation of Organic Semiconducting Nanoparticles.

Next generation bioengineering strives to identify crucial cues that trigger regeneration of damaged tissues, and to control the cells that execute these programs with biomaterials and devices. Molecular and biophysical mechanisms driving embryogenesis may inspire novel tools to reactivate developmental programs in situ. Here nanoparticles based on conjugated polymers are employed for optical control of regenerating tissues by using an animal with unlimited regenerative potential, the polyp Hydra, as in vivo model, and human keratinocytes as an in vitro model to investigate skin repair. By integrating animal, cellular, molecular, and biochemical approaches, nanoparticles based on poly-3-hexylthiophene (P3HT) are shown able to enhance regeneration kinetics, stem cell proliferation, and biomolecule oxidation levels. Opposite outputs are obtained with PCPDTBT-NPs (Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b'] dithiophene)-alt-4,7(2,1,3-benzothiadiazole)], causing a beneficial effect on Hydra regeneration but not on the migratory capability of keratinocytes. These results suggest that the artificial modulation of the redox potential in injured tissues may represent a powerful modality to control their regenerative potential. Importantly, the possibility to fine-tuning materials' photocatalytic efficiency may enable a biphasic modulation over a wide dynamic range, which can be exploited to augment the tissue regenerative capacity or inhibit the unlimited potential of cancerous cells in pathological contexts.

Insights into the interaction between typical amines and alkaline minerals for improved CO2 absorption and mineralization

AbstractAmine scrubbing is a mature technology to cut down CO2 emissions from human activities but suffers from a high energy consumption of solvent regeneration. The integrated CO2 absorption and mineralization (IAM) process can effectively reduce the energy consumption of amine regeneration by replacing traditional thermal regeneration with chemical regeneration via CO2 mineralization. However, a fundamental understanding of the interaction between typical amines and alkaline minerals was still lacking. In this paper, the effects of amine types on amine regeneration, alkaline metal leaching, and CaCO3 precipitation during the IAM process were explored by using five typical amines and Ca(OH)2/Mg(OH)2. Results showed very different regeneration kinetics and efficiencies were observed in five selected amine solutions, which displayed a decreased performance in the order TEA > MDEA > DEA > AMP > MEA. The regeneration performance was significantly affected by the dissolution of Ca(OH)2/Mg(OH)2 which was inversely proportional to the trend of their pKa values. TEA displayed the largest regeneration efficiency of about 95% by Ca(OH)2 and 83% by Mg(OH)2, which was much larger than other amines reported in the open literature, due to its lower pKa value than other selected amines. More interestingly, the particle size of CaCO3 produced from amine solutions was smaller than that from CaCl2 solution reported in the literature. There was a rough linear relationship between CaCO3 particle size and amine pKa values. TEA induced the formation of nano scaled CaCO3, which might be attributed to the adsorbing of TEA on the CaCO3 crystal and inhibiting the crystal growth. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

The role of dark adaptation in understanding early AMD.

The main aim of the paper is to discuss current knowledge on how Age Related Macular Degeneration (AMD) affects Dark Adaptation (DA). The paper is divided into three parts. Firstly, we outline some of the molecular mechanisms that control DA. Secondly, we review the psychophysical issues and the corresponding analytical techniques. Finally, we characterise the link between slowed DA and the morphological abnormalities in early AMD. Historically, DA has been regarded as too cumbersome for widespread clinical application. Yet the technique is extremely useful; it is widely accepted that the psychophysically obtained slope of the second rod-mediated phase of the dark adaptation function is an accurate assay of photoreceptor pigment regeneration kinetics. Technological developments have prompted new ways of generating the DA curve, but analytical problems remain. A simple potential solution to these, based on the application of a novel fast mathematical algorithm, is presented. This allows the calculation of the parameters of the DA curve in real time. Improving current management of AMD will depend on identifying a satisfactory endpoint for evaluating future therapeutic strategies. This must be implemented before the onset of severe disease. Morphological changes progress too slowly to act as a satisfactory endpoint for new therapies whereas functional changes, such as those seen in DA, may have more potential in this regard. It is important to recognise, however, that the functional changes are not confined to rods and that building a mathematical model of the DA curve enables the separation of rod and cone dysfunction and allows more versatility in terms of the range of disease severity that can be monitored. Examples are presented that show how analysing the DA curve into its constituent components can improve our understanding of the morphological changes in early AMD.

Experimental and kinetics investigations of low-concentration CO2 adsorption on several amine-functionalized adsorbents

The rapid cleanup of endogenous CO2 has become a necessity in environmental control and life support systems (ECLSSs), to ensure crew safety and long-term task execution. The extensively used non-regenerable LiOH and soda lime adsorbents, although exhibit high CO2 storage capacities and fast kinetics, can hardly fulfill the demands of reduced launch weight and storage volume in the space- and load-limited ECLSSs. New CO2 adsorbents with desirable attributes including high CO2 uptakes, good selectivity, facile regeneration, fast adsorption and desorption kinetics, and good multicycle stability are urgently needed. We developed amine-functionalized adsorbents by loading tetraethylenepentamine (TEPA) on mesoporous supports of activated carbon (AC), aluminum oxide (AO) and silica gel (SG). The adsorbents were characterized by N2 adsorption-desorption, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM) to study their microstructural properties. CO2 adsorption capacities and kinetic performance of the adsorbents with different supports and various amine loadings (10–50 wt%) were evaluated in 2%CO2 at 20 °C. The effects of support and amine loading on the structure-performance relationships of the adsorbents were demonstrated. The TEPA-SG-20 adsorbent (20 wt% TEPA loaded on silica gel support) exhibits the highest CO2 adsorption capacity of 1.90 mmol CO2/g and the maximum amine efficiency of 0.48 mmol CO2/mmol N. TEPA-SG-20 also exhibits fast CO2 adsorption kinetics, and the Avrami fractional order kinetic model provides a satisfactory correlation of the experimental CO2 uptakes. Furthermore, the TEPA-SG-20 adsorbent can be efficiently regenerated at 110 °C with a great regeneration efficacy of 97%. The desired adsorbent also exhibits good working stability with a low loss-in-capacity of 4.32% in 10 consecutive cycles. The good CO2 adsorption performance of TEPA-SG-20 is associated with the excellent microstructural properties such as high surface area, great pore volume and uniform dispersion of amine species. Overall, the desired TEPA-SG-20 adsorbent shows promise for low-concentration CO2 removal in ECLSSs.

Greywater characteristics, impacts, treatment, and reclamation using adsorption processes towards the circular economy.

The gap between water demand and available water supply led to wastewater treatment, particularly greywater.Due to specific characteristics of grey wastewater, treatmentand recycling of this type of wastewater capture global attention. This paper presents a literature review of the remediation of greywater by adsorption processes. Besides, the reclamation of the grey wastewater in the context of the circular economy is highlighted. In this regard, the characterization of various types of grey wastewater, the potential risks associated with greywater, and the properties of reclaimed water as per the regulation or guideline are summarized. These standards vary based on the application of reused water and from a country to another country. Furthermore, this review elucidates the adsorption process in terms of the type of adsorbents, modification of adsorbents and their regeneration process, adsorption isotherm, kinetics and thermodynamic of adsorption, and optimization of adsorption system. Finally, the removal of different pollutants from greywater by various adsorbents and techno-economic aspects are illustrated.

Investigation on Dye Regeneration Kinetics at P‐Type Sensitized Nanoparticle Nickel Oxide Film by Scanning Electrochemical Microscopy

The efficiency of a NiO‐sensitized solar cell is determined by the kinetics of hole injection and dye regeneration reactions at the NiO/dye/electrolyte interface. In this research, the photochemical regeneration kinetics of dye adsorbed on the NiO film was investigated by scanning electrochemical microscopy (SECM). Besides, organic C343 and P1 sensitizers in combination with iodide‐based, cobalt‐based, and thiolate‐based electrolytes were selected to understand the effect of sensitizers and redox shuttles on the dye regeneration process. As a result, a fast regeneration kinetic rate constant was conformed in the thiolate‐based sample compared with cobalt‐based and iodide‐based, demonstrating that the organic redox shuttle was an efficient mediator to optimize the performance of p‐type DSSC. Furthermore, the regeneration rate constants (keff), reduction rate constants (kred), and absorption cross section (Фhv) were investigated for organic dyes and electrolytes. That is, an effective dye regeneration rate constant kred of 6.95 × 105 mol-1cm3s-1 for NiO/P1 and kred of 3.75 × 105 mol-1cm3s-1 for NiO/C343 was found at various wavelengths. Therefore, the experimental results demonstrate that regeneration kinetics are dependent on the type of electrolyte and dye used. Moreover, the results suggest that scanning electrochemical microscopy is a powerful method for screening efficient dyes and electrolytes for charge transfer reactions in P‐type dye‐sensitized solar cells.

Dye Regeneration Kinetics of C343-Sensitized Nickel Oxide Investigated by Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) feedback mode has been used to investigate kinetics of dye regeneration in DSSC. Organic dye C343 and CW1 are used as sensitizers for nickel oxide (NiO) photoelectrochemical cells. The influence of film thickness on dye regeneration kinetics in the films for NiO/C343 for six different films was investigated. SECM was used to analyze effective rate constant, keff and reduction rate kred, absorption cross section, Φhv for the dye regeneration process. The data reveal a significant variation of keff and kred with a variation of light intensity, sample thickness and dye difference. This research found remarkable dependence of the dye regeneration kinetic parameters on illumination flux, dye types and film thickness of electrode.

Impact of hydrogen on the boron-oxygen-related lifetime degradation and regeneration kinetics in crystalline silicon

We examine the impact of hydrogen on the boron-oxygen-related lifetime degradation and regeneration kinetics in boron-doped p-type Czochralski-grown silicon wafers. We introduce the hydrogen into the silicon bulk by rapid thermal annealing. The hydrogen source are hydrogen-rich silicon nitride (SiNx:H) layers. Aluminum oxide (Al2O3) layers of varying thickness are placed in-between the silicon wafer surfaces and the SiNx:H layers. By varying the Al2O3 thickness, which acts as an effective hydrogen diffusion barrier, the hydrogen bulk content is varied over more than one order of magnitude. The hydrogen content is determined from measured wafer resistivity changes. In order to examine the impact of hydrogen on the degradation kinetics, all samples are illuminated at a light intensity of 0.1 suns near room temperature. We observe no impact of the in-diffused hydrogen content on the degradation rate constant, confirming that hydrogen is not involved in the boron-oxygen degradation mechanism. The regeneration experiments at 160°C and 1 sun, however, show a clear dependence on the hydrogen content with a linear increase of the regeneration rate constant with increasing bulk hydrogen concentration. However, extrapolation of our measurements toward a zero in-diffused hydrogen content shows that the regeneration is still working even without any in-diffused hydrogen. Hence, our measurements demonstrate that there are two distinct regeneration processes taking place. This is in good agreement with a recently proposed defect reaction model and is also in agreement with the finding that the permanent boron-oxygen deactivation also works on non-fired solar cells, though at a lower rate.

Light adaptation characteristics of melanopsin

Following photopigment bleaching, the rhodopsin and cone-opsins show a characteristic exponential regeneration in the dark with a photocycle dependent on the retinal pigment epithelium. Melanopsin pigment regeneration in animal models requires different pathways to rods and cones. To quantify melanopsin-mediated light adaptation in humans, we first estimated its photopigment regeneration kinetics through the photo-bleach recovery of the intrinsic melanopsin pupil light response (PLR). An intense broadband light (~120,000 Td) bleached 43% of melanopsin compared to 86% of the cone-opsins. Recovery from a 43% bleach was 3.4X slower for the melanopsin than cone-opsin. Post-bleach melanopsin regeneration followed an exponential growth with a 2.5 min time-constant (τ) that required 11.2 min for complete recovery; the half-bleaching level (Ip) was ~ 4.47 log melanopic Td (16.10 log melanopsin effective photons.cm−2.s−1; 8.25 log photoisomerisations.photoreceptor−1.s−1). The effect on the cone-directed PLR of the level of the melanopsin excitation during continuous light adaptation was then determined. We observed that cone-directed pupil constriction amplitudes increased by ~ 10% when adapting lights had a higher melanopic excitation but the same mean photometric luminance. Our findings suggest that melanopsin light adaptation enhances cone signalling along the non-visual retina-brain axis. Parameters τ and Ip will allow estimation of the level of melanopsin bleaching in any light units; the data have implications for quantifying the relative contributions of putative melanopsin pathways to regulate the post-bleach photopigment regeneration and adaptation.