Functional surface microstructures inspired by nature : From adhesion and wetting principles to sustainable new devices

In the course of evolution nature has arrived at startling materials solutions to ensure survival. Investigations into biological surfaces, ranging from plants, insects and geckos to aquatic animals, have inspired the design of intricate surface patterns to create useful functionalities. This paper reviews the fundamental interaction mechanisms of such micropatterns with liquids, solids, and soft matter such as skin for control of wetting, self-cleaning, anti-fouling, adhesion, skin adherence, and sensing. Compared to conventional chemical strategies, the paradigm of micropatterning enables solutions with superior resource efficiency and sustainability. Associated applications range from water management and robotics to future health monitoring devices. We finally provide an overview of the relevant patterning methods as an appendix

Functional surface microstructures inspired by nature – From adhesion and wetting principles to sustainable new devices

In the course of evolution nature has arrived at startling materials solutions to ensure survival. Investigations into biological surfaces, ranging from plants, insects and geckos to aquatic animals, have inspired the design of intricate surface patterns to create useful functionalities. This paper reviews the fundamental interaction mechanisms of such micropatterns with liquids, solids, and soft matter such as skin for control of wetting, self-cleaning, anti-fouling, adhesion, skin adherence, and sensing. Compared to conventional chemical strategies, the paradigm of micropatterning enables solutions with superior resource efficiency and sustainability. Associated applications range from water management and robotics to future health monitoring devices. We finally provide an overview of the relevant patterning methods as an appendix

Piscine defense and hydro-actuated deformation strategies: Paths to Bioinspired Design

Mother nature is an ingenious master on developing efficient structural and functional materials, which manifest various fascinating properties that are superior to synthetic materials. Here, we systematically investigate two topics: the materials design for piscine defense and hydro-actuated reversible deformation of plant organs. In each topic, we selected several types of biological materials to study and unravel the connection between their intelligent hierarchical structure and superb mechanical properties. We selected three fish and fully investigated the structure and mechanical properties of their scales. The first is the legendary lobe-finned fish coelacanth, which is extant for 400 million years. This defense is provided by primitive elasmoid scales having a double-twisted Bouligand structure of collagenous lamellae. The collagen fibrils in coelacanth scale form bundles which are embedded in a matrix composed of fibers arranged perpendicular to the layered structure, providing added rigidity and resistance to deformation. The second one we studied is a more evolved scale from common carp. Carp has typical modern elasmoid fish scales which are commonly found on most current teleosts. Like coelacanth scale, the outer surface of carp scale is composed of mineralized layers and the inner core is comprised of collagenous lamellae. The lamella orientations in carp scale follows a single twisted Bouligand pattern, with a rotation angle of 36°. Moreover, perpendicular to the lamellae, thinner collagen fibrils, which are called threading fibrils here, form a “sheet-like” structure oriented from the basal part to the external layer. Using in situ synchrotron small-angle x-ray scattering during uniaxial tensile testing, the deformation mechanisms of the collagen in these two scales are identified in terms of fibril stretching, reorientation, sliding, bending and delamination. The third scale we studied is from one of the largest freshwater fish, Arapaima, which has successfully survived in piranha-infested seasonal lakes of the Amazon. To quantitatively investigate the scale’s fracture toughness, we developed a new fixture and measured the J-integral based fracture toughness of the scale and find that the crack-growth toughness as high as ~200 kJm-2, which is one of the toughest flexible biological materials. This toughness is primarily the result of multiple mechanisms which are identified by in situ SEM observation. Our results may bring some critical thinking for developing novel armor materials. Instead of evolving body armor to protect themselves passively, some fish develop powerful weapons to defend actively. We fully investigated the thorny catfish (Doradidae; order Siluriforme), which has barbed pectoral fin spines and mid-lateral scutes that work in concert to provide an active mechanical defense capability. The structural design of these two weapons is very impressive, including a hollow structure, porous components, and gradient transitions, leading to an outstanding performance by maintaining strength, toughness and light weight synergistically. These designs can provide inspiration for developing new structural materials.The second topic we studied is the hydro-actuated reversible deformation in plant organs. Plants have developed many intelligent strategies to respond to external stimuli, significantly benefiting their survival. Here we studied a classic: pine cone, which opens to release the pods upon drying and can reclose upon rehydrating. We unraveled a novel mechanism of reversible deformation actuated by hydration. Our findings provide an interdisciplinary perspective combining materials science, structural engineering and biology, as well as offering some design models for development of novel smart responsive materials which have improved mechanical properties and biocompatibility yet simpler strategy

Piscine defense and hydro-actuated deformation strategies: Paths to Bioinspired Design

Mother nature is an ingenious master on developing efficient structural and functional materials, which manifest various fascinating properties that are superior to synthetic materials. Here, we systematically investigate two topics: the materials design for piscine defense and hydro-actuated reversible deformation of plant organs. In each topic, we selected several types of biological materials to study and unravel the connection between their intelligent hierarchical structure and superb mechanical properties. We selected three fish and fully investigated the structure and mechanical properties of their scales. The first is the legendary lobe-finned fish coelacanth, which is extant for 400 million years. This defense is provided by primitive elasmoid scales having a double-twisted Bouligand structure of collagenous lamellae. The collagen fibrils in coelacanth scale form bundles which are embedded in a matrix composed of fibers arranged perpendicular to the layered structure, providing added rigidity and resistance to deformation. The second one we studied is a more evolved scale from common carp. Carp has typical modern elasmoid fish scales which are commonly found on most current teleosts. Like coelacanth scale, the outer surface of carp scale is composed of mineralized layers and the inner core is comprised of collagenous lamellae. The lamella orientations in carp scale follows a single twisted Bouligand pattern, with a rotation angle of 36°. Moreover, perpendicular to the lamellae, thinner collagen fibrils, which are called threading fibrils here, form a “sheet-like” structure oriented from the basal part to the external layer. Using in situ synchrotron small-angle x-ray scattering during uniaxial tensile testing, the deformation mechanisms of the collagen in these two scales are identified in terms of fibril stretching, reorientation, sliding, bending and delamination. The third scale we studied is from one of the largest freshwater fish, Arapaima, which has successfully survived in piranha-infested seasonal lakes of the Amazon. To quantitatively investigate the scale’s fracture toughness, we developed a new fixture and measured the J-integral based fracture toughness of the scale and find that the crack-growth toughness as high as ~200 kJm-2, which is one of the toughest flexible biological materials. This toughness is primarily the result of multiple mechanisms which are identified by in situ SEM observation. Our results may bring some critical thinking for developing novel armor materials. Instead of evolving body armor to protect themselves passively, some fish develop powerful weapons to defend actively. We fully investigated the thorny catfish (Doradidae; order Siluriforme), which has barbed pectoral fin spines and mid-lateral scutes that work in concert to provide an active mechanical defense capability. The structural design of these two weapons is very impressive, including a hollow structure, porous components, and gradient transitions, leading to an outstanding performance by maintaining strength, toughness and light weight synergistically. These designs can provide inspiration for developing new structural materials.The second topic we studied is the hydro-actuated reversible deformation in plant organs. Plants have developed many intelligent strategies to respond to external stimuli, significantly benefiting their survival. Here we studied a classic: pine cone, which opens to release the pods upon drying and can reclose upon rehydrating. We unraveled a novel mechanism of reversible deformation actuated by hydration. Our findings provide an interdisciplinary perspective combining materials science, structural engineering and biology, as well as offering some design models for development of novel smart responsive materials which have improved mechanical properties and biocompatibility yet simpler strategy

The use of the h-index to evaluate and rank academic departments

A method is proposed by which the h-index of individual researchers is extended to evaluate the performance of engineering departments. For a specific department, the h-index of each faculty is plotted against the number of years since the first publication. The plot is linearized and the slope is determined, which we term Departmental Productivity Index. This index represents the collective productivity of the department members. The statistical analysis is applied to two years: 2008 and 2017. This slope is correlated with the ranking of the department from USN&WR. Mechanical Engineering and Materials Science and Engineering Departments ranked over a broad range (top, second, and third tier) and in three regions within the US (East, Central, West) are used. The dp-index is not as representative an indicator as more in-depth analyses involving many other aspects, such as teaching, resources, and size, but it can serve as a robust guideline for departmental evaluation. For 2008, the dp-indices of the ME departments varied from 0.70 for the highest ranked to 0.23 for the lowest one. For 2017, the dp-indices show a systematic increase; the highest being 0.99 and lowest increasing to 0.5. For MSE departments, the same trend is observed: in 2008, they vary from 1.36 to 0.51, while in 2017 they range from 1.89 to 0.61. There is a systematic difference between Materials Science and Engineering and Mechanical Engineering Departments, the latter having dp-indices that are in average 30% lower than the former ones. This might be a reflection of the greater resources available nationally for materials research and of the service role that many ME departments have in Engineering Schools. The increase in dp-indices in the nine-year span (2008â2017) results from the rise in individual h-index for researchers, which reflects greater emphasis on research, increased collaborations, and an evolving research landscape. An additional observation that is revealed by this statistical analysis is that the difference between first and third tier departments decreased from 2008 to 2017, a reflection of the âdemocratizationâ of research through a more equitable distribution of resources and talent. This method is also suggested to be an effective quantitative measure of departmental and faculty member performance. Keywords: h Index, Departmental productivit

Shock-induced Amorphization in Covalently Bonded Solids

Deposition of powerful pulsed laser energy onto a material, ablates its surface and drives a compressive shock wave propagating through it. Using this technique, unprecedented states of matter with extremely high pressures, temperatures, and strain rates can be experimentally studied. Here we report on laser-shock induced amorphization in four covalently bonded solids, namely silicon (Si), germanium (Ge), boron carbide (B4C) and silicon carbide (SiC). Post shock transmission electron microscopy reveals that the newly formed amorphous materials exhibit a shear band alike morphology, suggesting that shear stress play a dominant role in this process. The density of these amorphous band decreases as a function of the distance to the surface and eventually disappeared at certain depth, which is coincident with the decay of the shock wave and indicates that there might be a critical stress for the onset of amorphization. Synchrotron XRay tomography of a recovered silicon target shows that large amounts of cracks are formed within the materials and the density also decrease with depth. Unlike amorphous bands, these cracks can propagate through the target, albeit without shattering the entire material. It is proposed that shock-induced amorphization is a new deformation mechanism of matter under extremely high rate deformation

Shock-induced Amorphization in Covalently Bonded Solids

Deposition of powerful pulsed laser energy onto a material, ablates its surface and drives a compressive shock wave propagating through it. Using this technique, unprecedented states of matter with extremely high pressures, temperatures, and strain rates can be experimentally studied. Here we report on laser-shock induced amorphization in four covalently bonded solids, namely silicon (Si), germanium (Ge), boron carbide (B4C) and silicon carbide (SiC). Post shock transmission electron microscopy reveals that the newly formed amorphous materials exhibit a shear band alike morphology, suggesting that shear stress play a dominant role in this process. The density of these amorphous band decreases as a function of the distance to the surface and eventually disappeared at certain depth, which is coincident with the decay of the shock wave and indicates that there might be a critical stress for the onset of amorphization. Synchrotron XRay tomography of a recovered silicon target shows that large amounts of cracks are formed within the materials and the density also decrease with depth. Unlike amorphous bands, these cracks can propagate through the target, albeit without shattering the entire material. It is proposed that shock-induced amorphization is a new deformation mechanism of matter under extremely high rate deformation

Shock-induced Amorphization in Covalently Bonded Solids

Deposition of powerful pulsed laser energy onto a material, ablates its surface and drives a compressive shock wave propagating through it. Using this technique, unprecedented states of matter with extremely high pressures, temperatures, and strain rates can be experimentally studied. Here we report on laser-shock induced amorphization in four covalently bonded solids, namely silicon (Si), germanium (Ge), boron carbide (B4C) and silicon carbide (SiC). Post shock transmission electron microscopy reveals that the newly formed amorphous materials exhibit a shear band alike morphology, suggesting that shear stress play a dominant role in this process. The density of these amorphous band decreases as a function of the distance to the surface and eventually disappeared at certain depth, which is coincident with the decay of the shock wave and indicates that there might be a critical stress for the onset of amorphization. Synchrotron XRay tomography of a recovered silicon target shows that large amounts of cracks are formed within the materials and the density also decrease with depth. Unlike amorphous bands, these cracks can propagate through the target, albeit without shattering the entire material. It is proposed that shock-induced amorphization is a new deformation mechanism of matter under extremely high rate deformation

Shock-induced Amorphization in Covalently Bonded Solids

Deposition of powerful pulsed laser energy onto a material, ablates its surface and drives a compressive shock wave propagating through it. Using this technique, unprecedented states of matter with extremely high pressures, temperatures, and strain rates can be experimentally studied. Here we report on laser-shock induced amorphization in four covalently bonded solids, namely silicon (Si), germanium (Ge), boron carbide (B4C) and silicon carbide (SiC). Post shock transmission electron microscopy reveals that the newly formed amorphous materials exhibit a shear band alike morphology, suggesting that shear stress play a dominant role in this process. The density of these amorphous band decreases as a function of the distance to the surface and eventually disappeared at certain depth, which is coincident with the decay of the shock wave and indicates that there might be a critical stress for the onset of amorphization. Synchrotron XRay tomography of a recovered silicon target shows that large amounts of cracks are formed within the materials and the density also decrease with depth. Unlike amorphous bands, these cracks can propagate through the target, albeit without shattering the entire material. It is proposed that shock-induced amorphization is a new deformation mechanism of matter under extremely high rate deformation