We report a strategy to create photodegradable poly(ethylene glycol)-based hydrogels through rapid polymerization of cytocompatible macromers for remote manipulation of gel properties in situ. ...Postgelation control of the gel properties was demonstrated to introduce temporal changes, creation of arbitrarily shaped features, and on-demand pendant functionality release. Channels photodegraded within a hydrogel containing encapsulated cells allow cell migration. Temporal variation of the biochemical gel composition was used to influence chondrogenic differentiation of encapsulated stem cells. Photodegradable gels that allow real-time manipulation of material properties or chemistry provide dynamic environments with the scope to answer fundamental questions about material regulation of live cell function and may affect an array of applications from design of drug delivery vehicles to tissue engineering systems.
We present the results from a litter translocation experiment along a 2800-m elevation gradient in Peruvian tropical forests. The understanding of the environmental factors controlling litter ...decomposition is important in the description of the carbon and nutrient cycles of tropical ecosystems, and in predicting their response to long-term increases in temperature. Samples of litter from 15 species were transplanted across all five sites in the study, and decomposition was tracked over 448 d. Species' type had a large influence on the decomposition rate (k), most probably through its influence on leaf quality and morphology. When samples were pooled across species and elevations, soil temperature explained 95% of the variation in the decomposition rate, but no direct relationship was observed with either soil moisture or rainfall. The sensitivity of the decay rate to temperature (𝒦 T ) varied seven-fold across species, between 0.024 and 0.169°C⁻¹, with a mean value of 0.118 ± 0.009°C⁻¹ (SE). This is equivalent to a temperature sensitivity parameter (Q₁₀) for litter decay of 3.06 ± 0.28, higher than that frequently assumed for heterotrophic processes. Our results suggest that the warming of approx. 0.9°C experienced in the region in recent decades may have increased decomposition and nutrient mineralization rates by c. 10%.
Context. Deuterium fractionation has been used to study the thermal history of prestellar environments. Their formation pathways trace different regions of the disk and may shed light into the ...physical structure of the disk, including locations of important features for planetary formation. Aims. We aim to constrain the radial extent of the main deuterated species; we are particularly interested in spatially characterizing the high and low temperature pathways for enhancing deuteration of these species. Methods. We observed the disk surrounding the Herbig Ae star HD 163296 using ALMA in Band 6 and obtained resolved spectral imaging data of DCO+ (J = 3 − 2), DCN (J = 3 − 2) and N2D+ (J = 3 − 2) with synthesized beam sizes of 0.̋53 × 0.̋42, 0.̋53 × 0.̋42, and 0.̋50 × 0.̋39, respectively. We adopted a physical model of the disk from the literature and use the 3D radiative transfer code LIME to estimate an excitation temperature profile for our detected lines. We modeled the radial emission profiles of DCO+, DCN, and N2D+, assuming their emission is optically thin, using a parametric model of their abundances and our excitation temperature estimates. Results. DCO+ can be described by a three-region model with constant-abundance rings centered at 70 AU, 150 AU, and 260 AU. The DCN radial profile peaks at about 60 AU and N2D+ is seen in a ring at 160 AU. Simple models of both molecules using constant abundances reproduce the data. Assuming reasonable average excitation temperatures for the whole disk, their disk-averaged column densities (and deuterium fractionation ratios) are 1.6–2.6×1012 cm-2 (0.04–0.07), 2.9–5.2×1012 cm-2 (~0.02), and 1.6–2.5×1011 cm-2 (0.34–0.45) for DCO+, DCN, and N2D+, respectively. Conclusions. Our simple best-fit models show a correlation between the radial location of the first two rings in DCO+ and the DCN and N2D+ abundance distributions that can be interpreted as the high and low temperature deuteration pathways regimes. The origin of the third DCO+ ring at 260 AU is unknown but may be due to a local decrease of ultraviolet opacity allowing the photodesorption of CO or due to thermal desorption of CO as a consequence of radial drift and settlement of dust grains. The derived Df values agree with previous estimates of 0.05 for DCO+/HCO+ and 0.02 for DCN/HCN in HD 163296, and 0.3−0.5 for N2D+/N2H+ in AS 209, a T Tauri disk. The high N2D+/N2H+ confirms N2D+ as a good candidate for tracing ionization in the cold outer disk.
Abstract A thiol–acrylate photopolymerization was used to incorporate enzymatically cleavable peptide sequences into PEG hydrogels to induce chondrogenic differentiation of encapsulated human ...mesenchymal stem cells (hMSCs). An adhesive sequence, RGD, was designed with an MMP-13 specific cleavable linker. RGD promotes survival of hMSCs encapsulated in PEG gels and has shown to induce early stages of chondrogenesis, while its persistence can limit complete differentiation. Therefore, an MMP-13 cleavage site was incorporated into the peptide sequence to release RGD mimicking the native differentiation timeline. Active MMP-13 production of encapsulated hMSCs was seen to increase from day 9 to 14 and only in chondrogenic differentiating cultures. Seeded hMSCs attached to the material prior to enzymatic cleavage, but a significant population of the cells detach after cleavage and release of RGD. Finally, hMSCs encapsulated in RGD-releasing gels produce 10 times as much glycosaminoglycan as cells with uncleavable RGD functionalities, by day 21 of culture. Furthermore, 75% of the cells stain positive for collagen type II deposition where RGD is cleavable, as compared to 19% for cultures where RGD persists. Collectively, these data provide evidence that temporal regulation of integrin-binding peptides is important in the design of niches in differentiating hMSCs to chondrocytes.
Aboveground primary productivity is widely considered to be limited by phosphorus (P) availability in lowland tropical forests and by nitrogen (N) availability in montane tropical forests. However, ...the extent to which this paradigm applies to belowground processes remains unresolved. We measured indices of soil microbial nutrient status in lowland, sub-montane and montane tropical forests along a natural gradient spanning 3400 m in elevation in the Peruvian Andes. With increasing elevation there were marked increases in soil concentrations of total N, total P, and readily exchangeable P, but a decrease in N mineralization determined by in situ resin bags. Microbial carbon (C) and N increased with increasing elevation, but microbial C : N : P ratios were relatively constant, suggesting homeostasis. The activity of hydrolytic enzymes, which are rich in N, decreased with increasing elevation, while the ratio of enzymes involved in the acquisition of N and P increased with increasing elevation, further indicating an increase in the relative demand for N compared to P with increasing elevation. We conclude that soil microorganisms shift investment in nutrient acquisition from P to N between lowland and montane tropical forests, suggesting that different nutrients regulate soil microbial metabolism and the soil carbon balance in these ecosystems.
Context. The gas and dust in circumstellar disks provide the raw materials to form planets. The study of organic molecules and their building blocks in such disks offers insight into the origin of ...the prebiotic environment of terrestrial planets. Aims. We aim to determine the distribution of formaldehyde, H2CO, in the disk around HD 163296 to assess the contribution of gas- and solid-phase formation routes of this simple organic. Methods. Three formaldehyde lines were observed (H2CO 303–202, H2CO 322–221, and H2CO 321–220) in the protoplanetary disk around the Herbig Ae star HD 163296 with ALMA at ~0.5″ (60 AU) spatial resolution. Different parameterizations of the H2CO abundance were compared to the observed visibilities, using either a characteristic temperature, a characteristic radius or a radial power law index to describe the H2CO chemistry. Similar models were applied to ALMA Science Verification data of C18O. In each scenario, χ2 minimization on the visibilities was used to determine the best-fit model in each scenario. Results. H2CO 303–202 was readily detected via imaging, while the weaker H2CO 322–221 and H2CO 321–220 lines required matched filter analysis to detect. H2CO is present throughout most of the gaseous disk, extending out to ~550 AU. An apparent 50 AU inner radius of the H2CO emission is likely caused by an optically thick dust continuum. The H2CO radial intensity profile shows a peak at ~100 AU and a secondary bump at ~300 AU, suggesting increased production in the outer disk. In all modeling scenarios, fits to the H2CO data show an increased abundance in the outer disk. The overall best-fit H2CO model shows a factor of two enhancement beyond a radius of 270 ± 20 AU, with an inner abundance (relative to H2) of 2 − 5 × 10-12. The H2CO emitting region has a lower limit on the kinetic temperature of T> 20 K. The C18O modeling suggests an order of magnitude depletion of C18O in the outer disk and an abundance of 4 − 12 × 10-8 in the inner disk. Conclusions. There is a desorption front seen in the H2CO emission that roughly coincides with the outer edge of the 1.3 millimeter continuum. The increase in H2CO outer disk emission could be a result of hydrogenation of CO ices on dust grains that are then sublimated via thermal desorption or UV photodesorption. Alternatively, there could be more efficient gas-phase production of H2CO beyond ~300 AU if CO is photodisocciated in this region.
The net primary productivity, carbon (C) stocks and turnover rates (i.e. C dynamics) of tropical forests are an important aspect of the global C cycle. These variables have been investigated in ...lowland tropical forests, but they have rarely been studied in tropical montane forests (TMFs). This study examines spatial patterns of above‐ and belowground C dynamics along a transect ranging from lowland Amazonia to the high Andes in SE Peru. Fine root biomass values increased from 1.50 Mg C ha⁻¹ at 194 m to 4.95 ± 0.62 Mg C ha⁻¹ at 3020 m, reaching a maximum of 6.83 ± 1.13 Mg C ha⁻¹ at the 2020 m elevation site. Aboveground biomass values decreased from 123.50 Mg C ha⁻¹ at 194 m to 47.03 Mg C ha⁻¹ at 3020 m. Mean annual belowground productivity was highest in the most fertile lowland plots (7.40 ± 1.00 Mg C ha⁻¹ yr⁻¹) and ranged between 3.43 ± 0.73 and 1.48 ± 0.40 Mg C ha⁻¹ yr⁻¹ in the premontane and montane plots. Mean annual aboveground productivity was estimated to vary between 9.50 ± 1.08 Mg C ha⁻¹ yr⁻¹ (210 m) and 2.59 ± 0.40 Mg C ha⁻¹ yr⁻¹ (2020 m), with consistently lower values observed in the cloud immersion zone of the montane forest. Fine root C residence time increased from 0.31 years in lowland Amazonia to 3.78 ± 0.81 years at 3020 m and stem C residence time remained constant along the elevational transect, with a mean of 54 ± 4 years. The ratio of fine root biomass to stem biomass increased significantly with increasing elevation, whereas the allocation of net primary productivity above‐ and belowground remained approximately constant at all elevations. Although net primary productivity declined in the TMF, the partitioning of productivity between the ecosystem subcomponents remained the same in lowland, premontane and montane forests.
Arrayed complexes of a water‐soluble deep cavitand and two fluorescent indicators show selective sensing of anabolic‐androgenic steroids in aqueous environments. By combining the host–guest complexes ...with small amounts of heavy metal ions, discrimination between steroids that vary in structure by only a single π bond is possible. The sensing occurs through a triggered aggregation mechanism, which can be mediated by both the presence of metal ions and the steroids. The use of both “turn‐on” and “turn‐off” fluorophores is essential for good discrimination. As low as 10 μm steroid can be detected, and the discrimination is selective in steroid samples spiked into human urine.
Arrayed complexes of a water‐soluble deep cavitand and two fluorescent indicators show selective sensing of anabolic‐androgenic steroids in aqueous environments.
To assess our determination to continue transplant activity in Colombia during the coronavirus disease 2019 (COVID-19) pandemic, this study seeks to describe the risk of infection and mortality of ...transplanted patients vs those on the waiting list. Therefore, a descriptive study of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2)/COVID-19 infection in transplant recipients and patients on the waiting list was conducted. The data sources were the information systems of the Instituto Nacional de Salud of Colombia: National Donation and Transplant Information System, the National Public Health Surveillance System, and the National COVID-19 Data Repository. Characteristics of the patients who tested positive were analyzed, and the mortality rate was determined. An Real Time-PCR test for SARS-CoV-2/COVID-19 was performed in 7% of the transplant recipients included in this study, and 14.8% of those recipients tested positive. Among patients on the waiting list, 15.2% were tested, and 16.7% showed positive results. Overall, 1% (84/8108) of the transplant recipients and 2.5% (74/2926) of patients on the waiting list were infected with SARS-CoV-2/COVID-19. There were no differences in mortality between these groups (P = .8748). In conclusion, with the data obtained so far, the hospital availability, and the adoption of safety protocols in the institutions, our findings can support the continuity of the transplant activities in this country.
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