Polymer Gradient Materials: Can Nature Teach Us New Tricks?

Abstract

Nature offers interesting examples of structures with a gradually changing composition that provides unique mechanical properties. Today, the transfer of biological principles to technical applications is gaining increasing attention. One prominent example of the transfer of biomimetic principles to materials science is the mussel byssus. Byssus threads possess gradually changing mechanical properties from soft to stiff in order to efficiently attach the mussel to the rock. This design is the basis for polymer gradient materials. Herein, we give a comprehensive overview of the most recent developments in the field of PGMs. In addition to basic terminology and definitions, selected highlights of PGMs are presented, followed by experimental techniques and characterization methods.magnified image

Discovery of the surface polarity gradient on iridescent Morpho butterfly scales reveals a mechanism of their selective vapor response

“…Gradients of different origin in biological materials are known, but rarely with nanopattern features (33)(34)(35). For the observed gradient in the Morpho scales, there are several potential origins: (i) variations in spatial patterning in the scale epicuticle during scale formation; such patterning may arise from stresses from elastic buckling of the outer epicuticle to produce the ridge lamellae (36), or may arise from propagating molecular signaling to provide local orientation and polarity (37); (ii) variable subsurface contributions to van der Waals and other surface interactions of the same surface molecules (15,38); (iii) active deposition of various molecules by the epidermal cell (35); and (iv) preferential covering of the cuticle with mobile lipid layers (39) that could accumulate in the narrow spaces on the ridge.…”

Electric field‐driven preparation of elastomer/plastic nanoparticles gradient films with enhanced damping property

“…Polymer‐gradient materials (PGMs) have a continuous change of compositions/properties from one side to the other. By taking advantages of gradient change in properties such as modulus and hydrophibility of the PGMs, one of the applications of PGMs is joining two materials of different stiffness to avoid stress concentrations in the contact zone. For example, in the aerospace and electronics and electric application, the polymer material often was adhered between the substrates of a different hardness and temperature .…”

Protein Gradient Films of Fibroin and Gelatine

“…Recently, we reported on a method for the facile and highly reproducible preparation of longitudinal polymer gradient materials (PGMs) on a centimeter scale. [31,32] These PGMs are based on a commercially available poly(dimethyl siloxane) (PDMS) system, and a variety of mechanical gradients along the length of the sample (14 cm) could be established. Apart from the mechanical gradient, this system was used to prepare surfaces with continuously changing topography.…”