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