Large
surface area-to-volume ratio with plenty of accessible electrochemically
active sites presents metal nanosheets a highly efficient catalyst
material. However, a facile and effective synthesis of metal nanosheets
with nanoscale thicknesses, macroscopic sizes, and desired crystal
facets is still a grand challenge. Here, we report the synthesis of
free-standing Pd nanosheets by ionic layer epitaxy (ILE), which employs
a cationic oleylamine monolayer at the water–air interface
as a soft template to guide the nanosheet growth. The Pd nanosheets
exhibited a quasi-square morphology with a uniform thickness of ∼2
nm and sizes ranging from 1 to 6 μm. Owing to the extremely
large surface-to-volume ratio and the exposure of mixed surface crystal
facets, the Pd nanosheets exhibited high activity in formic acid oxidation
compared to the commercial Pd black and other reported Pd nanostructures.
This work presents a simple and effective way to prepare metal nanosheets
with nanometer-scale thickness control.
Determining which time point is optimal for bone marrow-derived cell (BMC) transplantation for acute myocardial infarction (AMI) has attracted a great deal of attention. Studies have verified the interaction between cell treatment effect and transfer timing and have suggested that the optimal time frame for BMC therapy is day 4 to day 7 after AMI. However, the potential mechanism underlying the time-dependent therapeutic response remains unclear. Recently, a growing body of in vitro evidence has suggested that stem cells are able to feel and respond to the stiffness of their microenvironment to commit to a relevant lineage, indicating that soft matrices that mimic brain are neurogenic, stiffer matrices that mimic muscle are myogenic and comparatively rigid matrices that mimic collagenous bone prove osteogenic. Simultaneously, considering the fact that the myocardium post-infarction experiences a time-dependent stiffness change from flexible to rigid as a result of myocardial remodelling following tissue necrosis and massive extracellular matrix deposition, we presume that the myocardial stiffness within a certain time frame (possibly day 4–7) post-AMI might provide a more favourable physical microenvironment for the phenotypic plasticity and functional specification of engrafted BMCs committed to some cell lineages, such as endothelial cells, vascular smooth muscle cells or cardiomyocytes. The beneficial effect facilitates angiogenesis and myocardiogenesis in the infarcted heart, and subsequently leads to more amelioration of cardiac functions. If the present hypothesis were true, it would be of great help to understand the mechanism underlying the optimal timing for BMC transplantation and to establish a direction for the time selection of cell therapy.
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