RESUMO
The conformal nanoporous inorganic coatings with accessible pores that are stable under applied thermal and mechanical stresses represent an important class of materials used in the design of sensors, optical coatings, and biomedical systems. Here, we synthesize porous AlOx and ZnO coatings by the sequential infiltration synthesis (SIS) of two types of polymers that enable the design of porous conformal coatings-polymers of intrinsic microporosity (PIM) and block co-polymer (BCP) templates. Using quartz crystal microbalance (QCM), we show that alumina precursors infiltrate both polymer templates four times more efficiently than zinc oxide precursors. Using the quartz crystal microbalance (QCM) technique, we provide a comprehensive study on the room temperature accessibility to water and ethanol of pores in block copolymers (BCPs) and porous polymer templates using polystyrene-block-poly-4-vinyl pyridine (PS75-b-P4VP25) and polymers of intrinsic microporosity (PIM-1), polymer templates modified by swelling, and porous inorganic coatings such as AlOx and ZnO synthesized by SIS using such templates. Importantly, we demonstrate that no structural damage occurs in inorganic nanoporous AlOx and ZnO coatings synthesized via infiltration of the polymer templates during the water freezing/melting cycling tests, suggesting excellent mechanical stability of the coatings, even though the hardness of the inorganic nanoporous coating is affected by the polymer and precursor selections. We show that the hardness of the coatings is further improved by their annealing at 900 °C for 1 h, though for all the cases except ZnO obtained using the BCP template, this annealing has a negligible effect on the porosity of the material, as is confirmed by the consistency in the optical characteristics. These findings unravel new potential for the materials being used across various environment and temperature conditions.
RESUMO
Avascular necrosis (AVN) is a degenerative bone condition characterized by cellular death and bone collapse from compromised subchondral blood circulation. AVN begins with vascular interruption, hypertension, intravascular occlusion, or extravascular compression which reduces bone circulation. Although corticosteroids are frequently used to treat acute COVID-19 infections, patients are prone to its side effects, particularly AVN. Furthermore, COVID-19 produces coagulopathies, specifically hypercoagulability, that may contribute to venous thrombosis, which may serve as the impetus of AVN. While the literature discussing COVID-19, AVN, and corticosteroid use is not conclusive, patients being treated with corticosteroids for COVID-19 are at an increased risk for AVN possibly due to the combination of COVID-19 infection and corticosteroid use, or the use of high-dose steroids alone. The purpose of this case series is to elucidate AVN as a long-term sequalae of COVID-19, describe our management of COVID-19 and steroid-induced AVN, and discuss the current literature regarding AVN and COVID-19. Three patients hospitalized for COVID-19 infections were treated with corticosteroids and subsequently developed AVN. All patients, but one, had multiple sites of infarction and were treated with core decompression in the hip where there was no collapse of the subchondral bone. One of these patients had multiple infarcts in bilateral femoral heads, femoral shafts, and knees. This patient had a history of end-stage renal disease, and, therefore, total knee replacement was postponed until medical clearance. Core decompression was performed on the femoral head that showed no collapse to delay osteoarthritis of the hip. Multiple articles in the current literature support the idea that the combination of COVID-19 and corticosteroid use increases the risk of AVN and reduces the onset of COVID-19-related respiratory symptoms. The patient cases discussed in this case series suggest a possible association between COVID-19, corticosteroid use, and AVN.