Nanointerfacial strength between non-collagenous protein and collagen fibrils in antler bone

This research was supported by the Engineering and Physical Science Research Council, UK (grant award EP/E039928/1)

Development of sustainable biodegradable lignocellulosic hemp fiber/polycaprolactone biocomposites for light weight applications

Biocomposites with poly(ε-caprolactone) (PCL) as matrix and lignocellulosic hemp fiber with varying average aspect ratios (19, 26, 30 and 38) as reinforcement were prepared using twin extrusion process. The influence of fiber aspect ratio on the water absorption behavior and mechanical properties are investigated. The percentage of moisture uptake increased with the aspect ratio, following Fickian behavior. The hemp fiber/PCL biocomposites showed enhanced properties (tensile, flexural and low-velocity impact). The biocomposite with 26 aspect ratio showed the optimal properties, with flexural strength and modulus of 169% and 285% respectively, higher than those of neat PCL. However, a clear reduction on the mechanical properties was observed for water-immersed samples, with reduction in tensile and flexural moduli for the aspect ratio of 26 by 90% and 62%, respectively than those of dry samples. Summarily, the optimal sample provides an eco-friendly alternative to conventional, petroleum-based and non-renewable composites for various applications.Peer reviewedFinal Accepted Versio

Extreme strength observed in limpet teeth

The teeth of limpets exploit distinctive composite nanostructures consisting of high volume fractions of reinforcing goethite nanofibres within a softer protein phase to provide mechanical integrity when rasping over rock surfaces during feeding. The tensile strength of discrete volumes of limpet tooth material measured using in situ atomic force microscopy was found to range from 3.0 to 6.5 GPa and was independent of sample size. These observations highlight an absolute material tensile strength that is the highest recorded for a biological material, outperforming the high strength of spider silk currently considered to be the strongest natural material, and approaching values comparable to those of the strongest man-made fibres. This considerable tensile strength of limpet teeth is attributed to a high mineral volume fraction of reinforcing goethite nanofibres with diameters below a defect-controlled critical size, suggesting that natural design in limpet teeth is optimized towards theoretical strength limits

Extreme Toughness Exhibited in Electrospun Polystyrene Fibers

Polystyrene (PS) commonly exhibits brittle behavior and poor mechanical properties due to the presence of structural heterogeneities promoting localized failure. The removal of this localized failure is shown here by processing PS into fibers with a range of diameters using electrospinning. Mechanical properties of individual electrospun fibers were quantified with atomic force microscopy based nanomechanical tensile testing. The resultant stress–strain behavior of PS fibers highlights considerable enhancement of mechanical properties when fiber diameter decreases below 600 nm such that polystyrene toughness increases significantly by over two orders of magnitude compared to the bulk. Consideration of the network properties of polystyrene is used to demonstrate the increase of draw ratio toward a theoretical limit and is potentially applicable to a range of glassy polymeric materials

X-ray Imaging of Transplanar Liquid Transport Mechanisms in Single Layer Textiles

Understanding the penetration of liquids within textile fibers is critical for the development of next-generation smart textiles. Despite substantial research on liquid penetration in the plane of the textile, little is known about how the liquid penetrates in the thickness direction. Here we report a time-resolved high-resolution X-ray measurement of the motion of the liquid–air interface within a single layer textile, as the liquid is transported across the textile thickness following the deposition of a droplet. The measurement of the time-dependent position of the liquid meniscus is made possible by the use of ultrahigh viscosity liquids (dynamic viscosity from 10⁵ to 2.5 × 10⁶ times larger than water). This approach enables imaging due to the slow penetration kinetics. Imaging results suggest a three-stage penetration process with each stage being associated with one of the three types of capillary channels existing in the textile geometry, providing insights into the effect of the textile structure on the path of the three-dimensional liquid meniscus. One dimensional kinetics studies show that our data for the transplanar penetration depth Δ<i>x</i>_L vs time do not conform to a power law, and that the measured rate of penetration for long times is smaller than that predicted by Lucas–Washburn kinetics, challenging commonly held assumptions regarding the validity of power laws when applied to relatively thin textiles

3D nanomechanical evaluations of dermal structures in skin

Skin is a multilayered multiscale composite material with a range of mechanical and biochemical functions. The mechanical properties of dermis are important to understand in order to improve and compare on-going in vitro experiments to physiological conditions, especially as the mechanical properties of the dermis can play a crucial role in determining cell behaviour. Spatial and isotropy variations in dermal mechanics are thus critical in such understanding of complex skin structures. Atomic force microscopy (AFM) based indentation was used in this study to quantify the three dimensional mechanical properties of skin at nanoscale resolution over micrometre length scales. A range of preparation methods was examined and a mechanically non-evasive freeze sectioning followed by thawing method was found to be suitable for the AFM studies. Subsequent mechanical evaluations established macroscale isotropy of the dermis with the ground substance of the dermis dominating the mechanical response. Mechanical analysis was extended to show significant variation in the elastic modulus of the dermis between anatomical locations that suggest changes in the physiological environment influence local mechanical properties. Our results highlight dependence between an isotropic mechanical response of the dermal microenvironment at the nanoscale and anatomical location that define the variable mechanical behaviour of the dermis

Adhesion Anisotropy between Contacting Electrospun Fibers

The mechanical properties of electrospun fiber networks are critical in a range of applications from filtration to tissue engineering and are dependent on the adhesion between contacting fibers within the network. This adhesion is complex as electrospun networks exhibit a variety of contacts, including both cross-cylinder and parallel fiber configurations. In situ atomic force microscopy (AFM) was used to quantify the work of adhesion between a pair of individual electrospun polyamide fibers using controlled orientations and measurable contact areas. The work of adhesion was found to depend strongly on the fiber–fiber contact, with the separation of fibers in a parallel fiber configuration exhibiting considerably higher work of adhesion across a range of contact lengths than a cross-cylinder configuration. Our work therefore highlights direction-dependent adhesion behavior between electrospun fibers due to a suggested polymer chain orientation mechanism which increases net van der Waals interactions and indicates the variability of adhesion within a random electrospun fiber network

Extreme strength observed in limpet teeth

The teeth of limpets exploit distinctive composite nanostructures consisting of high volume fractions of reinforcing goethite nanofibres within a softer protein phase to provide mechanical integrity when rasping over rock surfaces during feeding. The tensile strength of discrete volumes of limpet tooth material measured using in situ atomic force microscopy was found to range from 3.0 to 6.5 GPa and was independent of sample size. These observations highlight an absolute material tensile strength that is the highest recorded for a biological material, outperforming the high strength of spider silk currently considered to be the strongest natural material, and approaching values comparable to those of the strongest man-made fibres. This considerable tensile strength of limpet teeth is attributed to a high mineral volume fraction of reinforcing goethite nanofibres with diameters below a defect-controlled critical size, suggesting that natural design in limpet teeth is optimized towards theoretical strength limits

Stress concentrations in nanoscale defective graphene

Defect-free graphene nanosheets are the strongest material known but manufactured graphene tends to contain flaws of different forms and dimensions, leading to the degradation of mechanical performance. Here we report a quantitative mechanical approach to quantitatively evaluate the influence of defects within exfoliated pristine graphene sheets. Results indicate stress concentrations around defects within graphene sheets that lower strength

Surface free energy analysis of electrospun fibers based on Rayleigh-Plateau/Weber instabilities

Electrospinning is an increasingly common technique used to produce fibers with a range of diameters. These electrospun fibers are used extensively in applications that exploit the material’s high surface area to volume ratio, thus requiring detailed knowledge of the surface properties of the fibers. The surface free energy of individual free standing electrospun styrene-butadiene rubber (SBR) fibers was determined here from the time-dependent break-up of long fibers driven initially by Rayleigh-Plateau/Weber instabilities. Individual free standing electrospun rubber fibers were observed to change from a cylindrical fibrous geometry to semi-spherical droplets during a time period of several days when above the glass transition temperature of the polymer. A wave-like transition from fiber to droplet was attributed to a surface tension driven break-up process occurring over a time strongly influenced by the rubber's viscosity. The surface free energy for an electrospun rubber fiber was found using a Weber approach for the free standing fibers and Diez et al theory for dynamic fluid instability of fluid ridges. Both methods lead to similar values of fiber surface free energy and were confirmed from bulk measurements exploiting Owens-Wend theory. The approach presented here is powerful as the surface free energy, indicative of the physical and chemical behavior of the fiber surface, can be determined for any fiber diameter provided the geometric break-up of the fiber is observed