Freestanding nanowires have ultrahigh elastic strain limits (4 to 7%) and yield strengths, but exploiting their intrinsic mechanical properties in bulk composites has proven to be difficult. We exploited the intrinsic mechanical properties of nanowires in a phase-transforming matrix based on the concept of elastic and transformation strain matching. By engineering the microstructure and residual stress to couple the true elasticity of Nb nanowires with the pseudoelasticity of a NiTi shape-memory alloy, we developed an in situ composite that possesses a large quasi-linear elastic strain of over 6%, a low Young's modulus of ~28 gigapascals, and a high yield strength of ~1.65 gigapascals. Our elastic strain-matching approach allows the exceptional mechanical properties of nanowires to be exploited in bulk materials.
The development of effective antibacterial
surfaces to prevent
the attachment of pathogenic bacteria and subsequent bacterial colonization
and biofilm formation is critically important for medical devices
and public hygiene products. In the work reported herein, a smart
antibacterial hybrid film based on tannic acid/Fe3+ ion
(TA/Fe) complex and poly(N-isopropylacrylamide) (PNIPAAm)
is deposited on diverse substrates. This surface is shown to have
bacteria-killing and bacteria-releasing properties based on, respectively,
near-infrared photothermal activation and subsequent cooling. The
TA/Fe complex has three roles in this system: (i) as a universal adhesive
“anchor” for surface modification, (ii) as a high-efficiency
photothermal agent for ablation of attached bacteria (including multidrug
resistant bacteria), and (iii) as a robust linker for immobilization
of NH2-terminated PNIPAAm via either Michael addition or
Schiff base formation. Moreover, because of the thermoresponsive properties
of the immobilized PNIPAAm, almost all of the killed bacteria and
other debris can be removed from the surface simply by lowering the
temperature. It is shown that this hybrid film can maintain good antibacterial
performance after being used for multiple “kill-and-release”
cycles and can be applied to various substrates regardless of surface
chemistry or topography, thus providing a broadly applicable, simple,
and reliable solution to the problems associated with surface-attached
bacteria in various healthcare applications.
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