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Hydrogels are commonly used materials in tissue engineering and organ-on-chip devices. This study investigated the nanomechanical properties of monolithic and multilayered poly(ethylene glycol) diacrylate (PEGDA) hydrogels manufactured using bulk polymerization and layer-by-layer projection lithography processes, respectively. An increase in the number of layers (or reduction in layer thickness) from 1 to 8 and further to 60 results in a reduction in the elastic modulus from 5.53 to 1.69 and further to 0.67 MPa, respectively. It was found that a decrease in the number of layers induces a lower creep index (CIT) in three-dimensional (3D) printed PEGDA hydrogels. This reduction is attributed to mesoscale imperfections that appear as pockets of voids at the interfaces of the multilayered hydrogels attributed to localized regions of unreacted prepolymers, resulting in variations in defect density in the samples examined. An increase in the degree of cross-linking introduced by a higher dosage of ultraviolet (UV) exposure leads to a higher elastic modulus. This implies that the elastic modulus and creep behavior of hydrogels are governed and influenced by the degree of cross-linking and defect density of the layers and interfaces. These findings can guide an optimal manufacturing pathway to obtain the desirable nanomechanical properties in 3D printed PEGDA hydrogels, critical for the performance of living cells and tissues, which can be engineered through control of the fabrication parameters.

Single crystals of aspirin form I were cleaved and indented on their dominant face. Upon inspection, it was possible to observe strongly anisotropic shallow lateral cracks due to the extreme low surface roughness after cleavage. Atomic force microscopy (AFM) imaging showed spalling fractures nucleating from the indent corners, forming terraces with a height of one or two interplanar spacings d100. The formation of such spalling fractures in aspirin was rationalized using basic calculations of attachment energies, showing how (100) layers are poorly bonded when compared to their relatively higher intralayer bonding. An attempt at explaining the preferential propagation of these fractures along the [010] direction is discussed.

Nanoindentation measurements of the mechanical properties of the (020), (002) and (101) crystal faces in carbamazepine (CBZ) form III revealed that the (020) face had a greater elastic modulus and hardness than the (002) and (101) faces, which had similar modulus and hardness values. Atomic force microscopy (AFM) imaging of the indents showed that whilst no surface plastic displacement was observed around the residual indents on the (020) face, indents on both (002) and (101) faces nucleated cracks in multiple orientations and showed slip bands parallel to (020). The computed compliance matrix of CBZ form III was in good agreement with the experimental results and predicted anisotropic stiffness, with E(020) > E(002) > E(101). Modelling also revealed that the molecular flexibility of CBZ results in a less stiff material than that of an equivalent rigid compound. Indentation in one direction results in the opening of the CBZ-butterfly wings whilst in the other two results in their closing. Molecular dynamics simulations confirmed the primary (020) slip plane, consistent with the AFM images of the indents. It was also found that shear on the primary (020) slip plane, requires the breaking and forming of CBZ hydrogen bonded dimers. The slip plane, (020), was identified as having the lowest structural rugosity and hydrogen bonding density but not the lowest attachment energy.

We report on nanoindentation data for two pairs of polymorphic compounds of p-aminobenzoic acid (pABA) and p-nitrobenzoic acid (pNBA). Variations of 60% or higher are observed in both stiffness and hardness data between the two forms of each pair. We interpret these observations through variations of periodic bond chains (PBCs), i.e. variations in continuous intermolecular interactions strength and nature. Aided with hardness data of polymorphs from the literature, we then further assess how PBCs can be used to assess and compare mechanical properties of polymorphs. We define a new parameter, s-PBC, which quantifies the strongest PBC interaction that needs breaking so as to allow a switch of the PBC network from 3D to 2D/1D. We found that higher values of s-PBCs, normalised by the mean molecular volumes, usually led to higher values of mechanical properties. Although not infallible, this trend seemed to hold well when comparing polymorphs of a given compound, but not so much when comparing across different compounds.

The tensile mechanical properties of silver nanowires produced by the polyol process and containing the characteristic pentatwinned microstructure are compared with single crystal nanowires prepared by template electrodeposition over a range of diameters, d, from 80 to 300 nm. The plastic flow strengths of both sets of nanowires show a significant size effect, ranging from about 400 MPa at d ? 300 nm to in excess of 1 GPa with d < 100 nm. The size effect is shown to follow the same empirical scaling law seen with other fcc structured metals. Transmission electron microscopy investigation of the deformed specimens found similar deformation structures in both classes of nanowire studied with relatively low dislocation densities found even after significant plastic strain. The deformed pentatwinned nanowires showed no evidence for any characteristic deformation structures associated with the twin boundaries running parallel to the nanowire axis. © 2021 Elsevier B.V. Henry Royce Institute: EP/P025021/1, EP/P025498/1, EP/R00661X/1, EP/S019367/1; Engineering and Physical Sciences Research Council, EPSRC: EP/J021229/1, EP/S009493/1; Royal Society; University of Manchester; China Scholarship Council, CSC The authors would like to acknowledge the support of the Engineering and Physical Sciences Research Council (EPSRC) through grants EP/J021229/1 and EP/S009493/1 . This work was also supported by the Henry Royce Institute for Advanced Materials , funded through EPSRC grants EP/R00661X/1 , EP/S019367/1 , EP/P025021/1 and EP/P025498/1 . HZ would like to thank the China Scholarship Council and the University of Manchester for financial support through a scholarship. ASE acknowledges financial support from the Royal Society.

Single crystals of aspirin form I were cleaved and indented on their dominant face. Upon inspection, it was possible to observe strongly anisotropic shallow lateral cracks due to the extreme low surface roughness after cleavage. Atomic Force Microscopy (AFM) imaging showed spalling fractures nucleating from the indent corners, forming terraces with a height of one or two interplanar spacings d100. The formation of such spalling fractures in aspirin was rationalised using basic calculations of attachment energies, showing how (100) layers are poorly bonded when compared to their relatively higher intralayer bonding. An attempt at explaining the preferential propagation of these fractures along the [010] direction is discussed.

We have measured mechanical properties in molecular crystals of a series of para-substituted benzoic acids using nanoindentation. Two linear correlations were found for these materials: first between the Young’s modulus and the melting point per unit of volume, and second between the hardness and the crystal cohesive energy density. These correlations, however, were found to only hold within isomechanical groups. These are groups of materials with similar interaction strengths and dimensionalities. A close analysis of the intermolecular interactions present in these crystals revealed that structures with aromatic rings interacting through t-type interactions may achieve higher interaction dimensionalities and thus result in harder crystals than those with rings interacting through aromatic stacking. In these systems, thus, the dimensionality of the aromatic interactions in the crystals appears to play the major role in their mechanical behavior.

Diabetes mellitus (DM) is the leading cause of chronic kidney disease and diabetic nephropathy is widely studied. In contrast, the pathobiology of diabetic urinary bladder disease is less understood despite dysfunctional voiding being common in DM. We hypothesised that diabetic cystopathy has a characteristic molecular signature. We therefore studied bladders of hyperglycaemic and polyuric rats with streptozotocin (STZ)-induced DM. Sixteen weeks after induction of DM, as assessed by RNA arrays, wide-ranging changes of gene expression occurred in DM bladders over and above those induced in bladders of non-hyperglycaemic rats with sucrose-induced polyuria. The altered transcripts included those coding for extracellular matrix regulators and neural molecules. Changes in key genes deregulated in DM rat bladders were also detected in db/db mouse bladders. In DM rat bladders there was reduced birefringent collagen between detrusor muscle bundles, and atomic force microscopy showed a significant reduction in tissue stiffness; neither change was found in bladders of sucrose-treated rats. Thus, altered extracellular matrix with reduced tissue rigidity may contribute to voiding dysfunction in people with long-term DM. These results serve as an informative stepping stone towards understanding the complex pathobiology of diabetic cystopathy.

Yilmaz, Halil/0000-0003-3585-0665 The mechanical properties of the austenite and ferrite phases in a high Cr content 2205 duplex stainless steel (DSS) have been investigated using single crystal micropillars of size 200-2000 nm. Austenite pillars with axial orientation [123] show a strong size effect with strength increasing as pillar size decreases, following a powerlaw relation, with exponent -0.62. Pillars of diameter d = 300 nm show a strength >2.4 GPa. The strength of ferrite pillars with axial orientation [001] also shows a power-law with exponent -0.56 and strength > 1.5 GPa at d = 260 nm. However, [123]-orientated ferrite showed no size effect and a mean strength of 760 MPa. Both phases show localised multiple slip on non-parallel slip planes with high Schmid factors, with the ferrite showing a wider spacing of the slipped regions. On comparison with previous work, the strength of both phases in this alloy are shown to have greater strength than lower Cr content steels. Combining our data with results in the literature for larger diameter micropillar specimens supports the hypothesis that the high Cr content of the DSS leads to a larger bulk stress and a reduction in the magnitude of the apparent size effect exponent with larger pillar diameters. Engineering and Physical Sciences Research Council (EPSRC)UK Research & Innovation (UKRI)Engineering & Physical Sciences Research Council (EPSRC) [EP/S009493/1, EP/P025021/1]; Turkish Ministry of National EducationMinistry of National Education - Turkey This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) through the grants EP/S009493/1 and EP/P025021/1. HY would like to thank the Turkish Ministry of National Education for provision of a scholarship. The authors are grateful for the kind provision of Grade 2205 Duplex Stainless Steel plate by Rolled Alloys, UK. The authors also appreciate the valuable comments and discussions provided by Dr. Cem Ornek, Istanbul Technical University, Turkey.

The treatment of wastewater from the oil and gas industry presents a very specific problem because the wastewater produced is comprised of a complex mixture of oil and water that can be difficult to treat. In this work, polybenzimidazole (PBI), graphene oxide (GO) and reduced GO (rGO) nanocomposite membranes were developed via the common blade coating and phase inversion technique for the treatment of produced water from the oil and gas industry. The nanocomposite membranes were dip-coated by polydopamine (PDA), which is known for its antifouling properties. For the industrially relevant produced water, stable emulsions with high salinity, sharp unimodal size distribution and average oil droplet size of less than 500 nm were prepared. The incorporation of just a few weight percent GO into the PBI matrix resulted in superior oil-removal efficiency up to 99.9%, while maintaining permeance as high as 91.3 ± 3.4 L m−2 h−1 bar−1. The presence of GO also increased the mechanical stability of the membrane. The biofouling test of the nanocomposite membrane over 180 days showed remarkable improvement compared to the pristine PBI membrane. The nanocomposite membranes described in this work demonstrated promising long-term performance for oil-in-water emulsion separation as well as antifouling and antimicrobial properties without any alkaline or acidic cleaning. The membranes were capable of de-oiling high salinity emulsions with excellent reusability, highlighting that these membranes are promising for produced water treatment under harsh industrial conditions.

Cell migration through extracellular matrices requires nuclear deformation, which depends on nuclear stiffness. In turn, chromatin structure contributes to nuclear stiffness, but the mechanosensing pathways regulating chromatin during cell migration remain unclear. Here, we demonstrate that WD repeat domain 5 (WDR5), an essential component of H3K4 methyltransferase complexes, regulates cell polarity, nuclear deformability, and migration of lymphocytes in vitro and in vivo, independent of transcriptional activity, suggesting nongenomic functions for WDR5. Similarly, depletion of RbBP5 (another H3K4 methyltransferase subunit) promotes similar defects. We reveal that a 3D environment increases the H3K4 methylation dependent on WDR5 and results in a globally less compacted chromatin conformation. Further, using atomic force microscopy, nuclear particle tracking, and nuclear swelling experiments, we detect changes in nuclear mechanics that accompany the epigenetic changes induced in 3D conditions. Indeed, nuclei from cells in 3D environments were softer, and thereby more deformable, compared with cells in suspension or cultured in 2D conditions, again dependent on WDR5. Dissecting the underlying mechanism, we determined that actomyosin contractility, through the phosphorylation of myosin by MLCK (myosin light chain kinase), controls the interaction of WDR5 with other components of the methyltransferase complex, which in turn up-regulates H3K4 methylation activation in 3D conditions. Taken together, our findings reveal a nongenomic function for WDR5 in regulating H3K4 methylation induced by 3D environments, physical properties of the nucleus, cell polarity, and cell migratory capacity.

Scanning acoustic microscopy (SAM), when applied to biological samples has the potential to resolve the longitudinal acoustic wave speed and hence stiffness of discrete tissue components. The heterogeneity of biological materials combined with the action of cryosectioning and rehydrating can, however, create variations in section topography. Here, we set out to determine how variations in specimen thickness influence apparent acoustic wave speed measurementsCryosections (5μm nominal thickness) of human skin biopsies were adhered to glass slides before washing and rehydrating in water. Multiple regions (200x200 μm; n = 3) were imaged by SAM to generate acoustic wave speed maps. Subsequently co-localised 30x30 μm sub-regions were imaged by atomic force microscopy (AFM) in fluid. The images were then registered using Image J. Each pixel was allocated both a height and wave speed value before their relationship was then plotted on a scattergram. The mean section thickness measured by AFM was 3.48 ± 1.12 (SD) μm. Regional height variations influenced apparent wave speed measurements. A 3.5 μm height difference was associated with a 400 ms-1 increase in wave speed. In the present study we show that local variations in specimen thickness influence apparent wave speed. We also show that a true measure of wave speed can be calculated if the thickness of the specimen is known at each sampling point.

The strength of focussed ion beam (FIB) machined [001] orientation single crystal micropillars of body centred cubic structured (bcc) metals Fe, Nb and V, with diameters 200–5000 nm, have been measured at 296 K and 193 K using nanoindentation equipment. The metals have similar critical temperatures for screw dislocation mobility, Tc, close to 350 K. All three metals deform on the (110) plane at both test temperatures and show very similar behaviour of the plastic flow stress, ?p, normalised by the shear modulus resolved on the slip plane, ?, as a function of pillar diameter, d, normalised by the Burgers vector, b. At room temperature all metals show a size effect on strength described by power law relation ?p/?=A(d/b)n with n ? ?0.6 and this is shown to mirror the behaviour of face centred cubic metals. At 193 K the three metals show a higher strength and larger size exponent n ? ?0.3 and again their normalised flow data is very similar. The behaviour is consistent with the observation that the deformation size effect in bcc materials converges to that seen with face centred cubic (fcc) structure metals as testing temperature approaches Tc. The temperature and size dependence of the experimental data shows similarity with the prediction of strength models based on the geometric confinement of dislocation sources (the single dislocation arm model) and a temperature dependent friction stress. However the model cannot consistently capture the behaviour for the three metals studied. © 2019 Acta Materialia Inc. Engineering and Physical Sciences Research Council: EP/S009493/1, EP/J021229/1 We would like to thank Doug Stauffer of Bruker Hysitron for helpful comments on the manuscript. HY would like to thank the Turkish government for provision of a graduate scholarship. We would also like to thank the Worshipful Company of Ironmongers (London, UK) for travel support for HY to visit Bruker Hysitron to carry out the low temperature nanoindentation work. This work was also supported through by the EPSRC through grants EP/J021229/1 and EP/S009493/1 .

Patterned structures were created by exposing SiO2 sol-gel films containing nano-silicon particles to a Clark MXR CPA-2010 fs laser (387 nm). A refractive index variation of 0.2 was obtained, similar to that of polymer films, however in an entirely superior stability class (structural, chemical, thermal, radiation, etc). The useful optical range of refractive index modulation is beyond 800 nm, respectively near-IR. Material characteristics were investigated with atomic force microscopy (AFM), Raman spectroscopy and spectro-ellipsometry measurements. Material properties were also investigated on different substrates in order to determine the influence of substrate type in laser processing.

The mechanical properties of the cell nucleus change to allow cells to migrate, but how chromatin modifications contribute to nuclear deformability has not been defined. Here, we demonstrate that a major factor in this process involves epigenetic changes that underpin nuclear structure. We investigated the link between cell adhesion and epigenetic changes in T-cells, and demonstrate that T-cell adhesion to VCAM1 via α4β1 integrin drives histone H3 methylation (H3K9me2/3) through the methyltransferase G9a. In this process, active G9a is recruited to the nuclear envelope and interacts with lamin B1 during T-cell adhesion through α4β1 integrin. G9a activity not only reorganises the chromatin structure in T-cells, but also affects the stiffness and viscoelastic properties of the nucleus. Moreover, we further demonstrated that these epigenetic changes were linked to lymphocyte movement, as depletion or inhibition of G9a blocks T-cell migration in both 2D and 3D environments. Thus, our results identify a novel mechanism in T-cells by which α4β1 integrin signaling drives specific chromatin modifications, which alter the physical properties of the nucleus and thereby enable T-cell migration.

In the twenty years since Ashkin’s influential paper, optical trapping has become a widely used technique in a wide range of research areas. The work in this paper uses the technique of optical trapping as an approach to the production of novel surfaces. The optical trapping capability alongside laser micromachining allows for the production of functional surface material combinations in specific and accurate arrays. This is achieved by using a laser to trap and ‘pull’ a microsphere down to a microscope slide surface which has a thin resin coating and then using either the trapping laser or a secondary laser source to selectively cure the resin with the spheres embedded on the resin surface. This capability could lead to applications in a variety of fields, including micro assembly, for example the ability to create a reusable mask with defined geometry for use in near field processing.In the twenty years since Ashkin’s influential paper, optical trapping has become a widely used technique in a wide range of research areas. The work in this paper uses the technique of optical trapping as an approach to the production of novel surfaces. The optical trapping capability alongside laser micromachining allows for the production of functional surface material combinations in specific and accurate arrays. This is achieved by using a laser to trap and ‘pull’ a microsphere down to a microscope slide surface which has a thin resin coating and then using either the trapping laser or a secondary laser source to selectively cure the resin with the spheres embedded on the resin surface. This capability could lead to applications in a variety of fields, including micro assembly, for example the ability to create a reusable mask with defined geometry for use in near field processing.

Ultrashort pulse laser ablation leads to the generation of plasma plumes (consisting of highly energetic species) which expand from the substrate surface and eventually deposit back onto the substrate as debris. This debris is accumulated around the ablated area or directly ejected into a liquid in the case where ablation is done while the target is immersed in a liquid environment. Debris consists of nanoparticles and we demonstrate their formation in the case of femtosecond laser ablation (180 fs, 775 nm, 1kHz) of silicon, a neodymium magnet and nickel in ambient air, helium gas or liquids.Ultrashort pulse laser ablation leads to the generation of plasma plumes (consisting of highly energetic species) which expand from the substrate surface and eventually deposit back onto the substrate as debris. This debris is accumulated around the ablated area or directly ejected into a liquid in the case where ablation is done while the target is immersed in a liquid environment. Debris consists of nanoparticles and we demonstrate their formation in the case of femtosecond laser ablation (180 fs, 775 nm, 1kHz) of silicon, a neodymium magnet and nickel in ambient air, helium gas or liquids.

Laser peen forming has been carried out on 0.075mm thick steel samples, using relatively low power Nd:YAG lasers at 1064nm, 532nm and 355nm wavelengths. The process was found to produce a bend angle up to approximately 20 degrees, depending upon the amount of passes and laser parameters used. The results from these experiments have been compared to samples formed using continuous wave thermal forming. The results showed that laser peen forming could take place with a pulsed Nd:YAG laser, which uses less energy than a laser used for thermal forming, and that the laser peen formed samples do not have evidence of heat affected zones or changes to the bulk material, both seen with laser thermal forming. This indicates that the laser peen forming process is largely athermal or non-thermal, as there is very little heat input into the samples except for decolorisation of the surface due to the plasma generated in the process. A parameter window has been established for laser peen forming on 0.075mm thick steel using a 1064nm wavelength. The effect that the process has on the surface of the material is also being analysed using optical interferomety and scanning probe microscopy.Laser peen forming has been carried out on 0.075mm thick steel samples, using relatively low power Nd:YAG lasers at 1064nm, 532nm and 355nm wavelengths. The process was found to produce a bend angle up to approximately 20 degrees, depending upon the amount of passes and laser parameters used. The results from these experiments have been compared to samples formed using continuous wave thermal forming. The results showed that laser peen forming could take place with a pulsed Nd:YAG laser, which uses less energy than a laser used for thermal forming, and that the laser peen formed samples do not have evidence of heat affected zones or changes to the bulk material, both seen with laser thermal forming. This indicates that the laser peen forming process is largely athermal or non-thermal, as there is very little heat input into the samples except for decolorisation of the surface due to the plasma generated in the process. A parameter window has been established for laser peen forming on 0.075mm thick steel u...

Scanning Probe Microscopes (SPM) have been primarily used to date for imaging and microscopy. SPMs also offer the powerful capability of nanolithography, nano-machining or scratching and nano-robotics. These techniques combined with ultra-short pulsed laser ablation offer a unique capability for the production of micro and nano scale surface features for applications in tribology and biosciences. The work presented in this paper is concerned with the surface modification of various polymers. The nano-scratching process is capable of producing a variety of arbitrary shapes such as lines and curves as well as more complex grids and spirals. The aim of the research is to determine the maximum and minimum feature sizes possible on these materials by both SPM and laser methods and the effect this has on surface properties such as hydrophobicity. Using a SPM, features in the order of 5 to 50 nanometers in height, have been achieved over an area of 10 to 85 microns on several different polymer samples.Scanning Probe Microscopes (SPM) have been primarily used to date for imaging and microscopy. SPMs also offer the powerful capability of nanolithography, nano-machining or scratching and nano-robotics. These techniques combined with ultra-short pulsed laser ablation offer a unique capability for the production of micro and nano scale surface features for applications in tribology and biosciences. The work presented in this paper is concerned with the surface modification of various polymers. The nano-scratching process is capable of producing a variety of arbitrary shapes such as lines and curves as well as more complex grids and spirals. The aim of the research is to determine the maximum and minimum feature sizes possible on these materials by both SPM and laser methods and the effect this has on surface properties such as hydrophobicity. Using a SPM, features in the order of 5 to 50 nanometers in height, have been achieved over an area of 10 to 85 microns on several different polymer samples.