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Topical skin care products and hydrating compositions (moisturizers or injectable fillers) have been used for years to improve the appearance of, for example facial wrinkles, or to increase “plumpness”. Most of the studies have addressed these changes based on the overall mechanical changes associated with an increase in hydration state. However, little is known about the water mobility contribution to these changes as well as the consequences to the specific skin layers. This is important as the biophysical properties and the biochemical composition of normal stratum corneum, epithelium, and dermis vary tremendously from one another. Our current studies and results reported here have focused on a novel approach (dynamic atomic force microscopy-based nanoindentation) to quantify biophysical characteristics of individual layers of ex vivo human skin. We have discovered that our new methods are highly sensitive to the mechanical properties of individual skin layers, as well as their hydration properties. Furthermore, our methods can assess the ability of these individual layers to respond to both compressive and shear deformations. In addition, since human skin is mechanically loaded over a wide range of deformation rates (frequencies), we studied the biophysical properties of skin over a wide frequency range. The poroelasticity model used helps to quantify the hydraulic permeability of the skin layers, providing an innovative method to evaluate and interpret the impact of hydrating compositions on water mobility of these different skin layers.

AbstractBiological structures integrate morphometry (shape-based rules) with materials design to maximize organism survival. The exoskeleton of the armored fish,Polypterus senegalus, balances flexibility with protection from predatory and territorial threats. Material properties of the exoskeleton are known; however, the geometric design rules underlying its anisotropic flexibility are uncharacterized. Here, we show how scale shape, articulation, and composite architecture produce anisotropic mechanics using bio-inspired, multi-material 3D-printed prototypes. Passive loading (draping) shows that compliant connections between the scales contribute to mechanical anisotropy. Simulated and experimental active loading (bending) show orientation-dependent stiffness ranging over orders of magnitude, including ‘mechanical invisibility’ of the scales where they do not add stiffness to the exoskeleton. The results illustrate how morphometry provides a powerful tool to tune flexibility in composite architectures independent of varying constituent materials composition. We anticipate that introducing morphometric design strategies will enable flexible, protective systems tuned to complex shapes and functions.

AbstractBiological structures integrate morphometry (shape-based rules) with materials design to maximize organism survival. The exoskeleton of the armored fish,Polypterus senegalus, balances flexibility with protection from predatory and territorial threats. Material properties of the exoskeleton are known; however, the geometric design rules underlying its anisotropic flexibility are uncharacterized. Here, we show how scale shape, articulation, and composite architecture produce anisotropic mechanics using bio-inspired, multi-material 3D-printed prototypes. Passive loading (draping) shows that compliant connections between the scales contribute to mechanical anisotropy. Simulated and experimental active loading (bending) show orientation-dependent stiffness ranging over orders of magnitude, including ‘mechanical invisibility’ of the scales where they do not add stiffness to the exoskeleton. The results illustrate how morphometry provides a powerful tool to tune flexibility in composite architectures independent of varying constituent materials composition. We anticipate that introducing morphometric design strategies will enable flexible, protective systems tuned to complex shapes and functions.

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. In recent years, structural color has burgeoned into a vibrant and dynamic field of study. Many structurally colored organisms rely on comparatively few materials to create a large diversity of optical responses and a broad array of compelling and functional features. Scientists and engineers often explore such systems as examples of sustainable, robust solutions to complex problems. By looking to existing hierarchical material systems in biological systems, we aim to determine guidelines for fabrication of material structures with pre-determined functionality and properties. Here, we compare approaches for producing surfaces that reflect color and discuss tunable design parameters. Methods discussed include bottom up self assembly, abstracted lithographic replication of structures, and top down systematically designed surfaces. We consider existing techniques and levers available to control output, and present the components of an inverse design approach. We compare different methods on the basis of scalability, tunability, and achievable responses, and provide practical guidelines for producing bio-inspired surface structures. Our proposed designs are constrained for realizable fabrication using additive direct laser writing techniques such as two-photon polymerization that are suitable for producing arbitrary structures with sub-wavelength resolution. These evaluated and characterized structures could eventually be adapted to roll to roll or imprint based systems for scale-up and manufacturing on a commercial scale. Here we contribute to a broader vision of systematic materials design by exploring tools for generating color.

Introduction: Blacks in the United States experience greater persistent pain than non-Hispanic Whites across a range of medical conditions, but to our knowledge no longitudinal studies have examined the risk factors or incidence of persistent pain among Blacks experiencing common traumatic stress exposures such as after a motor vehicle collision (MVC). We evaluated the incidence and predictors of moderate to severe axial musculoskeletal pain (MSAP) and widespread pain six weeks after a MVC in a large cohort of Black adults presenting to the emergency department (ED) for care.Methods: This prospective, multi-center, cohort study enrolled Black adults who presented to one of 13 EDs across the US within 24 hours of a MVC and were discharged home after their evaluation. Data were collected at the ED visit via patient interview and self-report surveys at six weeks after the ED visit via internet-based, self-report survey, or telephone interview. We assessed MSAP pain at ED visit and persistence at six weeks. Multivariable models examined factors associated with MSAP persistence at six weeks post-MVC.Results: Among 787 participants, less than 1% reported no pain in the ED after their MVC, while 79.8 (95% confidence interval [CI], 77.1 – 82.2) reported MSAP and 28.3 (95% CI, 25.5 – 31.3) had widespread pain. At six weeks, 67% (95% CI, 64, 70%) had MSAP and 31% (95% CI, 28, 34%) had widespread pain. ED characteristics predicting MSAP at six weeks post-MVC (area under the curve  = 0.74; 95% CI, 0.72, 0.74) were older age, peritraumatic dissociation, moderate to severe pain in the ED, feeling uncertain about recovery, and symptoms of depression.Conclusion: These data indicate that Blacks presenting to the ED for evaluation after MVCs are at high risk for persistent and widespread musculoskeletal pain. Preventive interventions are needed to improve outcomes for this high-risk group.

Introduction: Blacks in the United States experience greater persistent pain than non-Hispanic Whites across a range of medical conditions, but to our knowledge no longitudinal studies have examined the risk factors or incidence of persistent pain among Blacks experiencing common traumatic stress exposures such as after a motor vehicle collision (MVC). We evaluated the incidence and predictors of moderate to severe axial musculoskeletal pain (MSAP) and widespread pain six weeks after a MVC in a large cohort of Black adults presenting to the emergency department (ED) for care.Methods: This prospective, multi-center, cohort study enrolled Black adults who presented to one of 13 EDs across the US within 24 hours of a MVC and were discharged home after their evaluation. Data were collected at the ED visit via patient interview and self-report surveys at six weeks after the ED visit via internet-based, self-report survey, or telephone interview. We assessed MSAP pain at ED visit and persistence at six weeks. Multivariable models examined factors associated with MSAP persistence at six weeks post-MVC.Results: Among 787 participants, less than 1% reported no pain in the ED after their MVC, while 79.8 (95% confidence interval [CI], 77.1 – 82.2) reported MSAP and 28.3 (95% CI, 25.5 – 31.3) had widespread pain. At six weeks, 67% (95% CI, 64, 70%) had MSAP and 31% (95% CI, 28, 34%) had widespread pain. ED characteristics predicting MSAP at six weeks post-MVC (area under the curve  = 0.74; 95% CI, 0.72, 0.74) were older age, peritraumatic dissociation, moderate to severe pain in the ED, feeling uncertain about recovery, and symptoms of depression.Conclusion: These data indicate that Blacks presenting to the ED for evaluation after MVCs are at high risk for persistent and widespread musculoskeletal pain. Preventive interventions are needed to improve outcomes for this high-risk group.

Man-made armors often rely on rigid structures for mechanical protection, which typically results in a trade-off with flexibility and maneuverability. Chitons, a group of marine mollusks, evolved scaled armors that address similar challenges. Many chiton species possess hundreds of small, mineralized scales arrayed on the soft girdle that surrounds their overlapping shell plates. Ensuring both flexibility for locomotion and protection of the underlying soft body, the scaled girdle is an excellent model for multifunctional armor design. Here we conduct a systematic study of the material composition, nanomechanical properties, three-dimensional geometry, and interspecific structural diversity of chiton girdle scales. Moreover, inspired by the tessellated organization of chiton scales, we fabricate a synthetic flexible scaled armor analogue using parametric computational modeling and multi-material 3D printing. This approach allows us to conduct a quantitative evaluation of our chiton-inspired armor to assess its orientation-dependent flexibility and protection capabilities., National Science Foundation (U.S.) (Grant DMR-0819762), United States. Army Research Office (Contract W911NF-07-D-0004), United States. Department of Defense. National Defense Science and Engineering Graduate (NDSEG) Fellowship (N00244-09-1-0064), United States. Department of Energy. Office of Science (Contract DE-AC02-06CH11357)

Man-made armors often rely on rigid structures for mechanical protection, which typically results in a trade-off with flexibility and maneuverability. Chitons, a group of marine mollusks, evolved scaled armors that address similar challenges. Many chiton species possess hundreds of small, mineralized scales arrayed on the soft girdle that surrounds their overlapping shell plates. Ensuring both flexibility for locomotion and protection of the underlying soft body, the scaled girdle is an excellent model for multifunctional armor design. Here we conduct a systematic study of the material composition, nanomechanical properties, three-dimensional geometry, and interspecific structural diversity of chiton girdle scales. Moreover, inspired by the tessellated organization of chiton scales, we fabricate a synthetic flexible scaled armor analogue using parametric computational modeling and multi-material 3D printing. This approach allows us to conduct a quantitative evaluation of our chiton-inspired armor to assess its orientation-dependent flexibility and protection capabilities.

Man-made armors often rely on rigid structures for mechanical protection, which typically results in a trade-off with flexibility and maneuverability. Chitons, a group of marine mollusks, evolved scaled armors that address similar challenges. Many chiton species possess hundreds of small, mineralized scales arrayed on the soft girdle that surrounds their overlapping shell plates. Ensuring both flexibility for locomotion and protection of the underlying soft body, the scaled girdle is an excellent model for multifunctional armor design. Here we conduct a systematic study of the material composition, nanomechanical properties, three-dimensional geometry, and interspecific structural diversity of chiton girdle scales. Moreover, inspired by the tessellated organization of chiton scales, we fabricate a synthetic flexible scaled armor analogue using parametric computational modeling and multi-material 3D printing. This approach allows us to conduct a quantitative evaluation of our chiton-inspired armor to assess its orientation-dependent flexibility and protection capabilities.

Man-made armors often rely on rigid structures for mechanical protection, which typically results in a trade-off with flexibility and maneuverability. Chitons, a group of marine mollusks, evolved scaled armors that address similar challenges. Many chiton species possess hundreds of small, mineralized scales arrayed on the soft girdle that surrounds their overlapping shell plates. Ensuring both flexibility for locomotion and protection of the underlying soft body, the scaled girdle is an excellent model for multifunctional armor design. Here we conduct a systematic study of the material composition, nanomechanical properties, three-dimensional geometry, and interspecific structural diversity of chiton girdle scales. Moreover, inspired by the tessellated organization of chiton scales, we fabricate a synthetic flexible scaled armor analogue using parametric computational modeling and multi-material 3D printing. This approach allows us to conduct a quantitative evaluation of our chiton-inspired armor to assess its orientation-dependent flexibility and protection capabilities.

Man-made armors often rely on rigid structures for mechanical protection, which typically results in a trade-off with flexibility and maneuverability. Chitons, a group of marine mollusks, evolved scaled armors that address similar challenges. Many chiton species possess hundreds of small, mineralized scales arrayed on the soft girdle that surrounds their overlapping shell plates. Ensuring both flexibility for locomotion and protection of the underlying soft body, the scaled girdle is an excellent model for multifunctional armor design. Here we conduct a systematic study of the material composition, nanomechanical properties, three-dimensional geometry, and interspecific structural diversity of chiton girdle scales. Moreover, inspired by the tessellated organization of chiton scales, we fabricate a synthetic flexible scaled armor analogue using parametric computational modeling and multi-material 3D printing. This approach allows us to conduct a quantitative evaluation of our chiton-inspired armor to assess its orientation-dependent flexibility and protection capabilities.

The world of design has been dominated since the Industrial Revolution by the rigors of manufacturing and mass production. Assembly lines have dictated a world made of standard parts framing the imagination of designers and builders who have been taught to think about their design objects and systems in terms of assemblies of parts with distinct functions. The assumption that parts are made of single material and fulfill predetermined specific functions is deeply rooted in design and usually goes unquestioned; it is also enforced by the way that industrial supply chains work. These age-old design paradigms have been reincarnated in Computer-aided Design (CAD) tools as well as Computer-aided Manufacturing (CAM) technologies where homogeneous materials are formed into pre-defined shapes at the service of pre-determined functions.

This study aimed to quantify the biomechanical properties of murine meniscus surface. Atomic force microscopy (AFM)-based nanoindentation was performed on the central region, proximal side of menisci from 6- to 24-week old male C57BL/6 mice using microspherical tips (R[subscript tip]≈5 µm) in PBS. A unique, linear correlation between indentation depth, D, and response force, F, was found on menisci from all age groups. This non-Hertzian behavior is likely due to the dominance of tensile resistance by the collagen fibril bundles on meniscus surface that are mostly aligned along the circumferential direction. The indentation resistance was calculated as both the effective modulus, E[subscript ind], via the isotropic Hertz model, and the effective stiffness, S[subscript ind] = dF/dD. Values of S[subscript ind] and E[subscript ind] were found to depend on indentation rate, suggesting the existence of poro-viscoelasticity. These values do not significantly vary with anatomical sites, lateral versus medial compartments, or mouse age. In addition, E[subscript ind] of meniscus surface (e.g., 6.1±0.8 MPa for 12 weeks of age, mean±SEM, n=13) was found to be significantly higher than those of meniscus surfaces in other species, and of murine articular cartilage surface (1.4±0.1 MPa, n=6). In summary, these results provided the first direct mechanical knowledge of murine knee meniscus tissues. We expect this understanding to serve as a mechanics-based benchmark for further probing the developmental biology and osteoarthritis symptoms of meniscus in various murine models., National Institutes of Health (U.S.) (Grants AR033236)

Many exoskeletons exhibit multifunctional performance by combining protection from rigid ceramic components with flexibility through articulated interfaces. Structure-to-function relationships of these natural bioarmors have been studied extensively, and initial development of structural (load-bearing) bioinspired armor materials, most often nacre-mimetic laminated composites, has been conducted. However, the translation of segmented and articulated armor to bioinspired surfaces and applications requires new computational constructs. We propose a novel hierarchical computational model, MetaMesh, that adapts a segmented fish scale armor system to fit complex “host surfaces”. We define a “host” surface as the overall geometrical form on top of which the scale units are computed. MetaMesh operates in three levels of resolution: (i) locally—to construct unit geometries based on shape parameters of scales as identified and characterized in the Polypterus senegalus exoskeleton, (ii) regionally—to encode articulated connection guides that adapt units with their neighbors according to directional schema in the mesh, and (iii) globally—to generatively extend the unit assembly over arbitrarily curved surfaces through global mesh optimization using a functional coefficient gradient. Simulation results provide the basis for further physiological and kinetic development. This study provides a methodology for the generation of biomimetic protective surfaces using segmented, articulated components that maintain mobility alongside full body coverage., Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract No. W911NF-13-D-0001), United States. Army Research Office (Institute for Collaborative Biotechnologies (ICB), contract no. W911NF-09-D-0001), United States. Department of Defense (National Security Science and Engineering Faculty Fellowship Program (Grant No. N00244-09-1-0064))

Murine models of osteoarthritis (OA) and post-traumatic OA have been widely used to study the development and progression of these diseases using genetically engineered mouse strains along with surgical or biochemical interventions. However, due to the small size and thickness of murine cartilage, the relationship between mechanical properties, molecular structure and cartilage composition has not been well studied. We adapted a recently developed AFM-based nano-rheology system to probe the dynamic nanomechanical properties of murine cartilage over a wide frequency range of 1 Hz to 10 kHz, and studied the role of glycosaminoglycan (GAG) on the dynamic modulus and poroelastic properties of murine femoral cartilage. We showed that poroelastic properties, highlighting fluid–solid interactions, are more sensitive indicators of loss of mechanical function compared to equilibrium properties in which fluid flow is negligible. These fluid-flow-dependent properties include the hydraulic permeability (an indicator of the resistance of matrix to fluid flow) and the high frequency modulus, obtained at high rates of loading relevant to jumping and impact injury in vivo. Utilizing a fibril-reinforced finite element model, we estimated the poroelastic properties of mouse cartilage over a wide range of loading rates for the first time, and show that the hydraulic permeability increased by a factor ~16 from k[subscript normal] = 7.80 × 10[superscript −16] ± 1.3 × 10[superscript −16] m[superscript 4]/N s to k[subscript GAG-depleted] = 1.26 × 10[superscript −14] ± 6.73 × 10[superscript −15] m[superscript 4]/N s after GAG depletion. The high-frequency modulus, which is related to fluid pressurization and the fibrillar network, decreased significantly after GAG depletion. In contrast, the equilibrium modulus, which is fluid-flow independent, did not show a statistically significant alteration following GAG depletion., National Institutes of Health (U.S.) (Grant 060331), Whitaker Foundation (Health Sciences Fund Fellowship), Arthritis Australia

Recent studies of micro- and nano-scale mechanics of cartilage and chondrocyte pericellular matrix have begun to relate matrix molecular structure to its mechanical response. AFM-based indentation has revealed rate-dependent stiffness at the micro-scale. While multi-scale elastic behavior has been studied, and poro-viscoelastic properties have been extensively documented at the tissue-level, time-dependent behavior and energy dissipation mechanisms of cartilage matrix at the nano-scale are not well understood. Here, we used AFM-based dynamic compression in conjunction with poroelastic finite element modeling to study the frequency-dependent behavior of cartilage using nano-scale oscillatory displacement amplitudes. We introduce the characteristic frequency f[subscript peak] at which the maximum energy dissipation occurs as an important parameter to characterize matrix time-dependent behavior. Use of micron-sized AFM probe tips with nano-scale oscillatory displacements over a 3-decade frequency range enabled clear identification of this characteristic frequency f[subscript peak]. The length-scale dependence of poroelastic behavior combined with judicious choice of probe tip geometry revealed flow-dependent and flow-independent behavior during matrix displacement amplitudes on the order of macromolecular dimensions and intermolecular pore-sizes., National Science Foundation (U.S.) (Grant CMMI-0758651), National Institutes of Health (U.S.) (National Institute of Arthritis and Musculoskeletal and Skin Diseases (U.S.) Grant AR33236)

Contains experimental data for the paper "Mechanistic Origins of Bombardier Beetle (Brachinini) Explosion-Induced Defensive Spray Pulsation," by Eric M. Arndt, Wendy Moore, Wah-Keat Lee, and Christine Ortiz, which was accepted by Science on March 16, 2015, and which is in press. Data sets are organized by beetle, with beetle numbers corresponding to those listed in Tables S1 and S2 of the paper supplement. Images stacks are ZIP-compressed. The total size of all files (compressed) is 62.9 GB. For Beetles 6-14, the raw and processed 2000-fps x-ray videos are provided as TIFF image stacks. AVI videos (25-fps playback) of all recorded sprays as well as the Matlab processing scripts for each data set (file paths redacted) are also provided. CCTV video was not recorded. The Excel spreadsheet Data_summary.xlsx is a catalog of the data and provides x-ray and (where available) CCTV frame numbers for all sprays. The citable handle for this collection is hdl.handle.net/1721.1/96123., Use of the Advanced Photon Source was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. This work was supported in part by the U. S. Army Research Laboratory and the U. S. Army Research Office through the MIT Institute of Soldier Nanotechnologies under Contract No. W911NF-13-D-0001 and in part by the National Science Foundation through the MIT Center for Materials Science and Engineering under Contract No. DMR-08-19762. This research was funded in part by the U. S. Department of Defense, Office of the Director, Defense Research and Engineering, through the National Security Science and Engineering Faculty Fellowship awarded to C.O. under Contract No. N00244-09-1-0064; in part by the National Science Foundation through funding awarded to W.M. under Contract No. DEB-0908187; and in part by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-SC0012704. Experiment data are available for download from DSpace@MIT at: http://hdl.handle.net/1721.1/96123.

Contains experimental data for the paper "Mechanistic Origins of Bombardier Beetle (Brachinini) Explosion-Induced Defensive Spray Pulsation," by Eric M. Arndt, Wendy Moore, Wah-Keat Lee, and Christine Ortiz, which was accepted by Science on March 16, 2015, and which is in press. Data sets are organized by beetle, with beetle numbers corresponding to those listed in Tables S1 and S2 of the paper supplement. Images stacks are ZIP-compressed. The total size of all files (compressed) is 62.9 GB. For Beetles 2-4, the raw 250-fps x-ray and 30-fps CCTV videos are provided as TIFF image stacks. The Excel spreadsheet Data_summary.xlsx is a catalog of the data and provides x-ray and (where available) CCTV frame numbers for all sprays. The citable handle for this collection is hdl.handle.net/1721.1/96123., Use of the Advanced Photon Source was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. This work was supported in part by the U. S. Army Research Laboratory and the U. S. Army Research Office through the MIT Institute of Soldier Nanotechnologies under Contract No. W911NF-13-D-0001 and in part by the National Science Foundation through the MIT Center for Materials Science and Engineering under Contract No. DMR-08-19762. This research was funded in part by the U. S. Department of Defense, Office of the Director, Defense Research and Engineering, through the National Security Science and Engineering Faculty Fellowship awarded to C.O. under Contract No. N00244-09-1-0064; in part by the National Science Foundation through funding awarded to W.M. under Contract No. DEB-0908187; and in part by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-SC0012704. Experiment data are available for download from DSpace@MIT at: http://hdl.handle.net/1721.1/96123.

Contains experimental data for the paper "Mechanistic Origins of Bombardier Beetle (Brachinini) Explosion-Induced Defensive Spray Pulsation," by Eric M. Arndt, Wendy Moore, Wah-Keat Lee, and Christine Ortiz, which was accepted by Science on March 16, 2015, and which is in press. Data sets are organized by beetle, with beetle numbers corresponding to those listed in Tables S1 and S2 of the paper supplement. Images stacks are ZIP-compressed. The total size of all files (compressed) is 62.9 GB. For Beetle 5, the raw and processed 1000-fps x-ray videos are provided as TIFF image stacks. An AVI video (25-fps playback) of the recorded spray as well as the Matlab processing script (file path redacted) are also provided. CCTV video was not recorded. The Excel spreadsheet Data_summary.xlsx is a catalog of the data and provides x-ray and (where available) CCTV frame numbers for all sprays. The citable handle for this collection is hdl.handle.net/1721.1/96123., Use of the Advanced Photon Source was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. This work was supported in part by the U. S. Army Research Laboratory and the U. S. Army Research Office through the MIT Institute of Soldier Nanotechnologies under Contract No. W911NF-13-D-0001 and in part by the National Science Foundation through the MIT Center for Materials Science and Engineering under Contract No. DMR-08-19762. This research was funded in part by the U. S. Department of Defense, Office of the Director, Defense Research and Engineering, through the National Security Science and Engineering Faculty Fellowship awarded to C.O. under Contract No. N00244-09-1-0064; in part by the National Science Foundation through funding awarded to W.M. under Contract No. DEB-0908187; and in part by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-SC0012704. Experiment data are available for download from DSpace@MIT at: http://hdl.handle.net/1721.1/96123.

Anisotropy is one of the most peculiar aspects of cortical bone mechanics; however, its anisotropic mechanical behaviour should be treated only with strict relationship to the length scale of investigation. In this study, we focus on quantifying the orientation and size dependence of the spatial mechanical modulation in individual secondary osteons of bovine cortical bone using nanoindentation. Tests were performed on the same osteonal structure in the axial (along the long bone axis) and transverse (normal to the long bone axis) directions along arrays going radially out from the Haversian canal at four different maximum depths on three secondary osteons. Results clearly show a periodic pattern of stiffness with spatial distance across the osteon. The effect of length scale on lamellar bone anisotropy and the critical length at which homogenization of the mechanical properties occurs were determined. Further, a laminate-composite-based analytical model was applied to the stiffness trends obtained at the highest spatial resolution to evaluate the elastic constants for a sub-layer of mineralized collagen fibrils within an osteonal lamella on the basis of the spatial arrangement of the fibrils. The hierarchical arrangement of lamellar bone is found to be a major determinant for modulation of mechanical properties and anisotropic mechanical behaviour of the tissue., MIT-Italy Program, MIT-Italy Program. Progetto Rocca Fellowship, United States. Office of Naval Research (Grant N00014-08-1-0510), Singapore-MIT Alliance Advanced Materials for Micro and Nano Systems Programme

Current carbon nanotube (CNT) synthesis methods include the production of ordered, free-standing vertically aligned arrays, the properties of which are partially governed by interactions between adjacent tubes. Using material parameters determined by atomistic methods, here we represent individual CNTs by a simple single degree of freedom ‘lollipop’ model to investigate the formation, mechanics, and self-organization of CNT bundles driven by weak van der Waals interactions. The computationally efficient simple single degree of freedom model enables us to study arrays consisting of hundreds of thousands of nanotubes. The effects of nanotube parameters such as aspect ratio, bending stiffness, and surface energy, on formation and bundle size, as well as the intentional manipulation of bundle pattern formation, are investigated. We report studies with both single wall carbon nanotubes (SWCNTs) and double wall carbon nanotubes (DWCNTs) with varying aspect ratios (that is, varying height). We calculate the local density distributions of the nanotube bundles and show that there exists a maximum attainable bundle density regardless of an increase in surface energy for nanotubes with given spacing and stiffness. In addition to applications to CNTs, our model can also be applied to other types of nanotube arrays (e.g. protein nanotubes, polymer nanofilaments)., National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (Award DMR-0819762)

Many species rely on diverse selections of entirely organic photonic structures for the manipulation of light and the display of striking colours. Here we report the discovery of a mineralized hierarchical photonic architecture embedded within the translucent shell of the blue-rayed limpet Patella pellucida. The bright colour of the limpet’s stripes originates from light interference in a periodically layered zig-zag architecture of crystallographically co-oriented calcite lamellae. Beneath the photonic multilayer, a disordered array of light-absorbing particles provides contrast for the blue colour. This unique mineralized manifestation of a synergy of two distinct optical elements at specific locations within the continuum of the limpet’s translucent protective shell ensures the vivid shine of the blue stripes, which can be perceived under water from a wide range of viewing angles. The stripes’ reflection band coincides with the spectral range of minimal light absorption in sea water, raising intriguing questions regarding their functional significance., United States. Air Force Office of Scientific Research. Multidisciplinary University Research Initiative (FA9550-09-1-0669-DOD35-CAP), National Science Foundation (U.S.) (DMR-0819762)

The nanostructure and nanomechanical properties of aggrecan monomers extracted and purified from human articular cartilage from donors of different ages (newborn, 29 and 38 year old) were directly visualized and quantified via atomic force microscopy (AFM)-based imaging and force spectroscopy. AFM imaging enabled direct comparison of full length monomers at different ages. The higher proportion of aggrecan fragments observed in adult versus newborn populations is consistent with the cumulative proteolysis of aggrecan known to occur in vivo. The decreased dimensions of adult full length aggrecan (including core protein and glycosaminoglycan (GAG) chain trace length, end-to-end distance and extension ratio) reflect altered aggrecan biosynthesis. The demonstrably shorter GAG chains observed in adult full length aggrecan monomers, compared to newborn monomers, also reflects markedly altered biosynthesis with age. Direct visualization of aggrecan subjected to chondroitinase and/or keratanase treatment revealed conformational properties of aggrecan monomers associated with chondroitin sulfate (CS) and keratan sulfate (KS) GAG chains. Furthermore, compressive stiffness of chemically end-attached layers of adult and newborn aggrecan was measured in various ionic strength aqueous solutions. Adult aggrecan was significantly weaker in compression than newborn aggrecan even at the same total GAG density and bath ionic strength, suggesting the importance of both electrostatic and non-electrostatic interactions in nanomechanical stiffness. These results provide molecular-level evidence of the effects of age on the conformational and nanomechanical properties of aggrecan, with direct implications for the effects of aggrecan nanostructure on the age-dependence of cartilage tissue biomechanical and osmotic properties., National Science Foundation (U.S.) (Grant CMMI-0758651), National Institutes of Health (U.S.) (Grant AR33236), National Institutes of Health (U.S.) (Grant AR60331), United States. Dept. of Energy (National Security Science and Engineering Faculty Fellowship Grant N00244-09-1-0064), Shriners North America

Nature provides a multitude of examples of multifunctional structural materials in which trade-offs are imposed by conflicting functional requirements. One such example is the biomineralized armor of the chiton Acanthopleura granulata, which incorporates an integrated sensory system that includes hundreds of eyes with aragonite-based lenses. We use optical experiments to demonstrate that these microscopic lenses are able to form images. Light scattering by the polycrystalline lenses is minimized by the use of relatively large, crystallographically aligned grains. Multiscale mechanical testing reveals that as the size, complexity, and functionality of the integrated sensory elements increase, the local mechanical performance of the armor decreases. However, A. granulata has evolved several strategies to compensate for its mechanical vulnerabilities to form a multipurpose system with co-optimized optical and structural functions., Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract W911NF-07-D-0004), United States. Dept. of Defense. Assistant Secretary of Defense for Research & Engineering (National Security Science and Engineering Faculty Fellowship Program N00244-09-1-0064), National Science Foundation (U.S.) (Designing Materials to Revolutionize and Engineer our Future Program DMR 1533985), Alexander von Humboldt-Stiftung (Feodor Lynen Research Fellowship), Massachusetts Institute of Technology. Department of Mechanical Engineering

Bombardier beetles (Brachinini) use a rapid series of discrete explosions inside their pygidial gland reaction chambers to produce a hot, pulsed, quinone-based defensive spray. The mechanism of brachinines’ spray pulsation was explored using anatomical studies and direct observation of explosions inside living beetles using synchrotron x-ray imaging. Quantification of the dynamics of vapor inside the reaction chamber indicates that spray pulsation is controlled by specialized, contiguous cuticular structures located at the junction between the reservoir (reactant) and reaction chambers. Kinematics models suggest passive mediation of spray pulsation by mechanical feedback from the explosion, causing displacement of these structures., Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract W911NF-13-D-0001), National Science Foundation (U.S.) (Contract DMR-08-19762), United States. Dept. of Defense (National Security Science and Engineering Faculty Fellowship Contract N00244-09-1-0064), United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-SC0012704))

Utilizing a newly developed atomic-force-microscopy-based wide-frequency rheology system, we measured the dynamic nanomechanical behavior of normal and glycosaminoglycan (GAG)-depleted cartilage, the latter representing matrix degradation that occurs at the earliest stages of osteoarthritis. We observed unique variations in the frequency-dependent stiffness and hydraulic permeability of cartilage in the 1 Hz-to-10 kHz range, a frequency range that is relevant to joint motions from normal ambulation to high-frequency impact loading. Measurement in this frequency range is well beyond the capabilities of typical commercial atomic force microscopes. We showed that the dynamic modulus of cartilage undergoes a dramatic alteration after GAG loss, even with the collagen network still intact: whereas the magnitude of the dynamic modulus decreased two- to threefold at higher frequencies, the peak frequency of the phase angle of the modulus (representing fluid-solid frictional dissipation) increased 15-fold from 55 Hz in normal cartilage to 800 Hz after GAG depletion. These results, based on a fibril-reinforced poroelastic finite-element model, demonstrated that GAG loss caused a dramatic increase in cartilage hydraulic permeability (up to 25-fold), suggesting that early osteoarthritic cartilage is more vulnerable to higher loading rates than to the conventionally studied “loading magnitude”. Thus, over the wide frequency range of joint motion during daily activities, hydraulic permeability appears the most sensitive marker of early tissue degradation., Whitaker Foundation (Fellowship), National Science Foundation (U.S.) (grant CMMI- 0758651), National Institutes of Health (U.S.) (grant AR060331)

Chondroadherin (CHAD), a class IV small leucine rich proteoglycan/protein (SLRP), was hypothesized to play important roles in regulating chondrocyte signaling and cartilage homeostasis. However, its roles in cartilage development and function are not well understood, and no major osteoarthritis-like phenotype was found in the murine model with CHAD genetically deleted (CHAD(-/-)). In this study, we used atomic force microscopy (AFM)-based nanoindentation to quantify the effects of CHAD deletion on changes in the biomechanical function of murine cartilage. In comparison to wild-type (WT) mice, CHAD-deletion resulted in a significant ≈70-80% reduction in the indentation modulus, Eind, of the superficial zone knee cartilage of 11weeks, 4months and 1year old animals. This mechanical phenotype correlates well with observed increases in the heterogeneity collagen fibril diameters in the surface zone. The results suggest that CHAD mainly plays a major role in regulating the formation of the collagen fibrillar network during the early skeletal development. In contrast, CHAD-deletion had no appreciable effects on the indentation mechanics of middle/deep zone cartilage, likely due to the dominating role of aggrecan in the middle/deep zone. The presence of significant rate dependence of the indentation stiffness in both WT and CHAD(-/-) knee cartilage suggested the importance of both fluid flow induced poroelasticity and intrinsic viscoelasticity in murine cartilage biomechanical properties. Furthermore, the marked differences in the nanomechanical behavior of WT versus CHAD(-/-) cartilage contrasted sharply with the relative absence of overt differences in histological appearance. These observations highlight the sensitivity of nanomechanical tools in evaluating structural and mechanical phenotypes in transgenic mice.

Chondroadherin (CHAD), a class IV small leucine rich proteoglycan/protein (SLRP), was hypothesized to play important roles in regulating chondrocyte signaling and cartilage homeostasis. However, its roles in cartilage development and function are not well understood, and no major osteoarthritis-like phenotype was found in the murine model with CHAD genetically deleted (CHAD[superscript −/−]). In this study, we used atomic force microscopy (AFM)-based nanoindentation to quantify the effects of CHAD deletion on changes in the biomechanical function of murine cartilage. In comparison to wild-type (WT) mice, CHAD-deletion resulted in a significant ≈ 70–80% reduction in the indentation modulus, E[subscript ind], of the superficial zone knee cartilage of 11 weeks, 4 months and 1 year old animals. This mechanical phenotype correlates well with observed increases in the heterogeneity collagen fibril diameters in the surface zone. The results suggest that CHAD mainly plays a major role in regulating the formation of the collagen fibrillar network during the early skeletal development. In contrast, CHAD-deletion had no appreciable effects on the indentation mechanics of middle/deep zone cartilage, likely due to the dominating role of aggrecan in the middle/deep zone. The presence of significant rate dependence of the indentation stiffness in both WT and CHAD[superscript −/−] knee cartilage suggested the importance of both fluid flow induced poroelasticity and intrinsic viscoelasticity in murine cartilage biomechanical properties. Furthermore, the marked differences in the nanomechanical behavior of WT versus CHAD[superscript −/−] cartilage contrasted sharply with the relative absence of overt differences in histological appearance. These observations highlight the sensitivity of nanomechanical tools in evaluating structural and mechanical phenotypes in transgenic mice., National Science Foundation (U.S.) (Grant CMMI-0758651), National Institutes of Health (U.S.) (Grant AR60331), United States. Dept. of Defense. Assistant Secretary of Defense for Research & Engineering (National Security Science and Engineering Faculty Fellowship Grant N00244-09-1-0064), Shriners Hospital for Children

The force-depth behavior of indentation into fibrillar-structured surfaces such as those consisting of forests of micro- or nanoscale tubes or rods is a depth-dependent behavior governed by compression, bending, and buckling of the nanotubes. Using a micromechanical model of the indentation process, the effective elastic properties of the constituent tubes or rods as well as the effective properties of the forest can be deduced from load-depth curves of indentation into forests. These studies provide fundamental understanding of the mechanics of indentation of nanotube forests, showing the potential to use indentation to deduce individual nanotube or nanorod properties as well as the effective indentation properties of such nanostructured surface coatings. In particular, the indentation behavior can be engineered by tailoring various forest features, where the force-depth behavior scales linearly with tube areal density (m, number per unit area), tube moment of inertia (I), tube modulus (E), and indenter radius (R) and scales inversely with the square of tube length (L[superscript 2]), which provides guidelines for designing forests whether to meet indentation stiffness or for energy storage applications in microdevice designs., National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (Award DMR-0819762), Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies Contract (W911NF-07-D- 0004)

Many biological systems possess hierarchical and fractal-like interfaces and joint structures that bear and transmit loads, absorb energy, and accommodate growth, respiration, and/or locomotion. In this paper, an elastic deterministic fractal composite mechanical model was formulated to quantitatively investigate the role of structural hierarchy on the stiffness, strength, and failure of suture joints. From this model, it was revealed that the number of hierarchies (N) can be used to tailor and to amplify mechanical properties nonlinearly and with high sensitivity over a wide range of values (orders of magnitude) for a given volume and weight. Additionally, increasing hierarchy was found to result in mechanical interlocking of higher-order teeth, which creates additional load resistance capability, thereby preventing catastrophic failure in major teeth and providing flaw tolerance. Hence, this paper shows that the diversity of hierarchical and fractal-like interfaces and joints found in nature have definitive functional consequences and is an effective geometric-structural strategy to achieve different properties with limited material options in nature when other structural geometries and parameters are biologically challenging or inaccessible. This paper also indicates the use of hierarchy as a design strategy to increase design space and provides predictive capabilities to guide the mechanical design of synthetic flaw-tolerant bioinspired interfaces and joints., Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract No. DAAD-19-02-D0002), National Security Science and Engineering Faculty Fellowship Program (Grant No. N00244-09-1-0064), United States. Army Research Office. Institute for Collaborative Biotechnologies (Grant No. W911NF-09-0001)

Biological materials have developed hierarchical and heterogeneous material microstructures and nanostructures to provide protection against environmental threats that, in turn, provide bioinspired clues to improve human body armor. In this study, we present a multiscale experimental and computational approach to investigate the anisotropic design principles of a ganoid scale of an ancient fish, Polypterus senegalus, which possesses a unique quad-layered structure at the micrometer scale with nanostructured material constituting each layer. The anisotropy of the outermost prismatic ganoine layer was investigated using instrumented nanoindentations and finite element analysis (FEA) simulations. Nanomechanical modeling was carried out to reveal the elastic-plastic mechanical anisotropy of the ganoine composite due to its unique nanostructure. Simulation results for nanoindentation representing ganoine alternatively with isotropic, anisotropic, and discrete material properties are compared to understand the apparent direction-independence of the anisotropic ganoine during indentation. By incorporating the estimated anisotropic mechanical properties of ganoine, microindentation on a quad-layered FEA model that is analogous to penetration biting events (potential threat) was performed and compared with the quad-layered FEA model with isotropic ganoine. The elastic-plastic anisotropy of the outmost ganoine layer enhances the load-dependent penetration resistance of the multilayered armor compared with the isotropic ganoine layer by (i) retaining the effective indentation modulus and hardness properties, (ii) enhancing the transmission of stress and dissipation to the underlying dentin layer, (iii) lowering the ganoine/dentin interfacial stresses and hence reducing any propensity toward delamination, (iv) retaining the suppression of catastrophic radial surface cracking, and favoring localized circumferential cracking, and (v) providing discrete structural pathways (interp, National Science Foundation (U.S.) (MIT Center for Materials Science and Engineering (DMR-0819762)), Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (DAAD-19-02-D-0002), United States. Dept. of Defense (National Security Science and Engineering Faculty Fellowship)

Biological materials have developed hierarchical and heterogeneous material microstructures and nanostructures to provide protection against environmental threats that, in turn, provide bioinspired clues to improve human body armor. In this study, we present a multiscale experimental and computational approach to investigate the anisotropic design principles of a ganoid scale of an ancient fish, Polypterus senegalus, which possesses a unique quad-layered structure at the micrometer scale with nanostructured material constituting each layer. The anisotropy of the outermost prismatic ganoine layer was investigated using instrumented nanoindentations and finite element analysis (FEA) simulations. Nanomechanical modeling was carried out to reveal the elastic-plastic mechanical anisotropy of the ganoine composite due to its unique nanostructure. Simulation results for nanoindentation representing ganoine alternatively with isotropic, anisotropic, and discrete material properties are compared to understand the apparent direction-independence of the anisotropic ganoine during indentation. By incorporating the estimated anisotropic mechanical properties of ganoine, microindentation on a quad-layered FEA model that is analogous to penetration biting events (potential threat) was performed and compared with the quad-layered FEA model with isotropic ganoine. The elastic-plastic anisotropy of the outmost ganoine layer enhances the load-dependent penetration resistance of the multilayered armor compared with the isotropic ganoine layer by (i) retaining the effective indentation modulus and hardness properties, (ii) enhancing the transmission of stress and dissipation to the underlying dentin layer, (iii) lowering the ganoine/dentin interfacial stresses and hence reducing any propensity toward delamination, (iv) retaining the suppression of catastrophic radial surface cracking, and favoring localized circumferential cracking, and (v) providing discrete structural pathways (interp, National Science Foundation (U.S.) (MIT Center for Materials Science and Engineering (DMR-0819762)), Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (DAAD-19-02-D-0002), United States. Dept. of Defense (National Security Science and Engineering Faculty Fellowship)

Suture joints are remarkable mechanical structures found throughout nature composed of compliant interlocking seams connecting stiffer components. This study investigates the underlying mechanisms and the role of geometry governing the unique mechanical behavior of suture joints. Analytical and numerical composite models are formulated for two suture geometries characterized by a single repeating wavelength (e.g., triangular and rectangular). Stiffness, strength, and local stress distributions are predicted to assess variations in deformation and failure mechanisms. A unique homogeneous stress field is observed throughout both the skeletal and interfacial components of the triangular geometry, thus providing advantages in load transmission, weight, stiffness, strength, energy absorption, and fatigue over the rectangular geometry. The results obtained have relevance to biomimetic design and optimization, suture growth and fusion, and evolutionary phenotype diversity., Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract No. DAAD-19-02-D0002), United States. Air Force Office of Scientific Research (National Security Science and Engineering Faculty Fellowship Program (N00244-09-1-0064))

Many biological systems possess hierarchical and fractal-like interfaces and joint structures that bear and transmit loads, absorb energy, and accommodate growth, respiration, and/or locomotion. In this paper, an elastic deterministic fractal composite mechanical model was formulated to quantitatively investigate the role of structural hierarchy on the stiffness, strength, and failure of suture joints. From this model, it was revealed that the number of hierarchies (N) can be used to tailor and to amplify mechanical properties nonlinearly and with high sensitivity over a wide range of values (orders of magnitude) for a given volume and weight. Additionally, increasing hierarchy was found to result in mechanical interlocking of higher-order teeth, which creates additional load resistance capability, thereby preventing catastrophic failure in major teeth and providing flaw tolerance. Hence, this paper shows that the diversity of hierarchical and fractal-like interfaces and joints found in nature have definitive functional consequences and is an effective geometric-structural strategy to achieve different properties with limited material options in nature when other structural geometries and parameters are biologically challenging or inaccessible. This paper also indicates the use of hierarchy as a design strategy to increase design space and provides predictive capabilities to guide the mechanical design of synthetic flaw-tolerant bioinspired interfaces and joints., Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract No. DAAD-19-02-D0002), National Security Science and Engineering Faculty Fellowship Program (Grant No. N00244-09-1-0064), United States. Army Research Office. Institute for Collaborative Biotechnologies (Grant No. W911NF-09-0001)

The success of cell-based tissue engineering approaches in restoring biological function will be facilitated by a comprehensive fundamental knowledge of the temporal evolution of the structure and properties of the newly synthesized matrix. Here, we quantify the dynamic oscillatory mechanical behavior of the engineered matrix associated with individual chondrocytes cultured in vitro for up to 28 days in alginate scaffolds. The magnitude of the complex modulus (|E*|) and phase shift (δ) were measured in culture medium using Atomic Force Microscopy (AFM)-based nanoindentation in response to an imposed oscillatory deformation (amplitude ∼5 nm) as a function of frequency (f=1–316 Hz), probe tip geometry (2.5 μm radius sphere and 50 nm radius square pyramid), and in the absence and presence of growth factors (GF, insulin growth factor-1, IGF-1, and osteogenic protein-1, OP-1). |E*| for all conditions increased nonlinearly with frequency dependence approximately f[superscript 1/2] and ranged between ∼1 and 25 kPa. This result, along with theoretical calculations of the characteristic poroelastic relaxation frequency, f[subscript p], (∼50–90 Hz) suggested that this time-dependent behavior was governed primarily by fluid flow-dependent poroelasticity, rather than flow-independent viscoelastic processes associated with the solid matrix. |E*(f)| increased, (f) decreased, and the hydraulic permeability, k, decreased with time in culture and with growth factor treatment. This trend of a more elastic-like response was thought to be associated with increased macromolecular biosynthesis, density, and a more mature matrix structure/organization., National Institutes of Health (U.S.). Nanoscale Interdisciplinary Research Teams (0403903), National Institutes of Health (U.S.). Civil, Mechanical and Manufacturing Innovation (0758651), National Institute of Mental Health (U.S.) (grant AR33236), Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (contract number DAAD-19-02-D0002)

Biological exoskeletons, in particular those with unusually robust and multifunctional properties, hold enormous potential for the development of improved load-bearing and protective engineering materials. Here, we report new materials and mechanical design principles of the iron-plated multilayered structure of the natural armor of Crysomallon squamiferum, a recently discovered gastropod mollusc from the Kairei Indian hydrothermal vent field, which is unlike any other known natural or synthetic engineered armor. We have determined through nanoscale experiments and computational simulations of a predatory attack that the specific combination of different materials, microstructures, interfacial geometries, gradation, and layering are advantageous for penetration resistance, energy dissipation, mitigation of fracture and crack arrest, reduction of back deflections, and resistance to bending and tensile loads. The structure-property-performance relationships described are expected to be of technological interest for a variety of civilian and defense applications., National Science Foundation (U.S.), Massachusetts Institute of Technology. Center for Materials Science and Engineering (DMR-0819762), Singapore-MIT Alliance (Advanced Materials for Micro and Nano Systems Programme), Singapore-MIT Alliance (Computational Systems Biology Programme), Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract DAAD-19-02-D0002), Raytheon Company, United States. Dept. of Defense ((National Defense Science and Engineering Fellowship (N00244–09–1–0064)), Singapore-MIT Alliance for Research and Technology (Interdisciplinary Research Group on Infectious Diseases)