Cold spray coating of submicronic ceramic particles on poly(vinyl alcohol) in dry and hydrogel states

International audienceThis study demonstrates that cold spray technology offers a route to functionalize the surface of PVA pieces with ceramic (HA) coatings. Swollen PVA hydrogels could not sustain the heat and deformation produced by the spraying process. Dry PVA substrates, however, could be efficiently coated using a technologically relevant range of spraying energy parameters. By adjusting the fragmentation of the sprayed powder, one can produce fine HA coatings of submicron fragments embedded into the PVA substrate surface. The binding of these HA particles to the PVA substrate is strong enough to withstand swelling in water, enabling formation of HA-coated hydrogels by immersion in water after spraying. A microscopic picture of the coating formation is proposed, where the PVA substrate melts superficially within a microscopic layer and sprayed aggregates fragment upon impact with the substrate, therefore inducing surface roughening and strong binding of the HA fragments to the molten PVA layer. More generally, these results using one type of aggregated powder suggest that adjusting the nature of the sprayed powder (aggregate size, cohesiveness, porosity, composition, etc.) could be a promising strategy to tailor the morphology of such coatings produced by cold spray; For instance, thick layers could be deposited by cold spray on various substrates, including PVA and Ti-6Al-V, thanks to the binding action of residual byproducts of the chemical synthesis of HA particles (Ref 39). With the recent progress in the design of bioactive ceramics (Ref 40), such a cold-spray-based approach offers an interesting possibility to functionalize the surface of polymer implants with fine control of the ceramic composition and crystallinity

Hiding in the background: community-level patterns in invertebrate herbivory across the tundra biome

© 2019, Springer-Verlag GmbH Germany, part of Springer Nature. Invertebrate herbivores depend on external temperature for growth and metabolism. Continued warming in tundra ecosystems is proposed to result in increased invertebrate herbivory. However, empirical data about how current levels of invertebrate herbivory vary across the Arctic is limited and generally restricted to a single host plant or a small group of species, so predicting future change remains challenging. We investigated large-scale patterns of invertebrate herbivory across the tundra biome at the community level and explored how these patterns are related to long-term climatic conditions and year-of-sampling weather, habitat characteristics, and aboveground biomass production. Utilizing a standardized protocol, we collected samples from 92 plots nested within 20 tundra sites during summer 2015. We estimated the community-weighted biomass lost based on the total leaf area consumed by invertebrates for the most common plant species within each plot. Overall, invertebrate herbivory was prevalent at low intensities across the tundra, with estimates averaging 0.94% and ranging between 0.02 and 5.69% of plant biomass. Our results suggest that mid-summer temperature influences the intensity of invertebrate herbivory at the community level, consistent with the hypothesis that climate warming should increase plant losses to invertebrates in the tundra. However, most of the observed variation in herbivory was associated with other site level characteristics, indicating that other local ecological factors also play an important role. More details about the local drivers of invertebrate herbivory are necessary to predict the consequences for rapidly changing tundra ecosystems