Archaeological findings prove the appearance and use of birch bark tar since the Middle Palaeolithic. The production and use of birch bark tar and pine wood tar has overlapped since at least the late Neolithic, but probably for much longer. The reliable chemical identification of such archaeological tar residues can offer valuable insights into, for example, ancient technical complexity, trade and culture. In this context, the scarcity of these mainly organic residue findings in the archaeological record bears the need for non-destructive analytical tools. However, there is currently no systematic proposed way for this purpose. We aim here to verify the organic nature and test the reliability of the identification of archaeological pine wood tar and birch bark tar with a combination of SEM-EDS, FTIR microspectroscopy in reflectance mode and XRD. We examined a set of experimental adhesive replicas of pine tar and birch tar in pristine form, but also after a three-year-long weathering experiment. Additionally, we studied a set of archaeological samples, consisting of Mesolithic bone/antler points with adhering hafting residues, form the Dutch North Sea. This research shows that degradation negatively influences the reliable verification and identification of the organic residue constituents significantly. SEM-EDS as a starting point of analysis verifies the residue's organic nature, but it cannot be used to identify birch or pine tar. XRD can identify crystalline additives in the adhesive mixture, like ochre and wax, as well as phases related to the artefact's environment of burial and provenance. Micro-FTIR is also capable of verifying the organic matter of the residue constituents. The differentiation of birch and pine tars is hindered by vibrational modes occurring in neighbouring wavenumbers for both tars, and by the limited research on degradation markers indicative of thermal treatment to prove tar production. Until reference collections also account for degradation and include a wide variety of adhesives, results of FTIR collected in reflectance mode are best treated with some caution.

@en

The most widely accepted test for bond durability analysis in aerospace metal-bonded structures is the bondline corrosion test introduced in the late 90s. Little progress has been made however on non-destructive testing methods that allow determining the bond quality after years of use. Here, a non-destructive method based on dielectric spectroscopy is introduced to evaluate the state of a metal-adhesive-metal bond exposed to salt fog spray up to 180 days. Several samples were evaluated with broadband dielectric spectroscopy (BDS), floating roller peel (FRP) tests and bondline corrosion (BLC) after exposure to salt fog spray test for different times. Relaxation processes and conductivity phenomena extracted from the BDS data (e.g. apparent conductivity relaxation time (τ_max) using electric modulus) are found to correlate well with the bond strength measured in peel test and BLC progression. The BDS-based protocol was able to identify the local interfacial degradation stages in a non-destructive mode and with high resolution. The protocol has the potential to be further developed into a test method for durability on coupon level.

@en

Gelatins are proteinaceous natural materials that are widely used in areas such as conservation and restoration of artifacts as adhesives and consolidants, in pharmaceutics as drug delivery carriers, and in the food industry as structurants. Herein, type A porcine gelatin adhesive films are prepared via solution casting method and their physical and mechanical properties are investigated using X-ray diffraction (XRD), differential scanning calorimetry, contact angle measurement, dynamic mechanical analysis, and uniaxial tensile tests. The results demonstrate a linear correlation between microstructure of gelatin films in terms of their triple-helix content and their macroscopic mechanical properties such as tensile strength and gel (Bloom) strength. Moreover, the findings of this study can help the scientists, in, e.g., art conservation and restoration, to predict the mechanical performance of these adhesives by performing a less material demanding and nondestructive physical measurement such as XRD.

@en

Shape memory polymers (SMPs) are dynamic materials able to recover previously defined shapes when activated by external stimuli. The most common stimulus is thermal energy applied near thermal transitions in polymers, such as glass transition (T_g) and melting (T_m) temperatures. The magnitude of the geometrical changes as well as the amount of force and energy that a SMP can output are critical properties for many applications. While typically deformation steps in the shape memory cycles (SMC) are performed at temperatures well above thermal transitions used to activate shape changes, significantly greater amounts of strain, stress, and mechanical energy can be stored in T_g-based SMPs when deformed near their T_g. Since maximum shape memory storage capacity can be appraised by evaluating the viscoelastic length transitions (VLTs) in a single dynamic mechanical analysis (DMA) experiment, this study correlates VLTs with the measured storage capacities obtained from stress-strain experiments for a broad range of well-defined crosslinked acrylates, epoxies, and polyurethanes. This systematic approach allows for assessment of crosslink/junction density (ν_j), viscoelasticity, and chemical composition effects on maximum deformability, and enables predictions of the magnitude of shape memory properties across a wide variety of polymers. These studies demonstrate that the maximum storable strain (ε-store_max) can be accurately predicted using junction density (ν_j) and shape memory factor (SMF), the latter accounting for the contribution of chemical makeup.

@en

Natural materials provide an increasingly important role model for the development and processing of next-generation polymers. The velvet worm Euperipatoides rowelli hunts using a projectile, mechanoresponsive adhesive slime that rapidly and reversibly transitions into stiff glassy polymer fibers following shearing and drying. However, the molecular mechanism underlying this mechanoresponsive behavior is still unclear. Previous work showed the slime to be an emulsion of nanoscale charge-stabilized condensed droplets comprised primarily of large phosphorylated proteins, which under mechanical shear coalesce and self-organize into nano- and microfibrils that can be drawn into macroscopic fibers. Here, we utilize wide-angle X-ray diffraction and vibrational spectroscopy coupled with in situ shear deformation to explore the contribution of protein conformation and mechanical forces to the fiber formation process. Although previously believed to be unstructured, our findings indicate that the main phosphorylated protein component possesses a significant β-crystalline structure in the storage phase and that shear-induced partial unfolding of the protein is a key first step in the rapid self-organization of nanodroplets into fibers. The insights gained here have relevance for sustainable production of advanced polymeric materials.

@en

The room temperature abrasive wear behavior of three selected MAX phases, Ti₃SiC₂, solution strengthened Ti_2.7Zr_0.3SiC₂ and Cr₂AlC, is investigated by low velocity scratch testing using a diamond conical indentor with a final radius of 100 μm and a cone angle of 120° and applied loads of up to 20 N. All three materials showed a relatively low wear resistance in comparison to most engineering ceramics such as Al₂O_3, Si₃N₄ and SiC. For all three materials, the wear rate scaled more or less linearly with the applied load. The softer Ti₃SiC₂ with a hardness of 2.8 GPa showed the lowest wear resistance with extensive ploughing and grain breakout damage, both within and outside the direct wear track, in particular at the highest load. The hardest material, Ti_2.7Zr_0.3SiC₂, with a hardness of 7.3 GPa, showed a 5 times better wear resistance. The Cr₂AlC with a hardness of 4.8 GPa showed a wear resistance equal to or even better than that of the Ti_2.7Zr_0.3SiC₂. The wear mechanism depends on the applied load and the microstructure of the MAX phase materials tested. For the Ti₃SiC₂ sample, a quasi-plastic deformation behavior occurs below a point load of 10 N, resulting in grain bending, kink band formation and delamination, grain de-cohesion, as well as trans-and intra-granular fracture near the scratch groove. At this load, the Ti_2.7Zr_0.3SiC₂ and Cr₂AlC MAX samples display plastic ploughing, grain boundary cracks and material dislodgments.

@en

Micro- and nanomotors and their use for biomedical applications have recently received increased attention. However, most designs use top-down methods to construct inorganic motors, which are labour-intensive and not suitable for biomedical use. Herein, we report a high-throughput design of an asymmetric hydrogel microparticle with autonomous movement by using a microfluidic chip to generate asymmetric, aqueous, two-phase-separating droplets consisting of poly(ethylene glycol) diacrylate (PEGDA) and dextran, with the biocatalyst placed in the PEGDA phase. The motor is propelled by enzyme-mediated decomposition of fuel. The speed of the motors is influenced by the roughness of the PEGDA surface after diffusion of dextran and was tuned by using higher molecular weight dextran. This roughness allows for easier pinning of oxygen bubbles and thus higher speeds of the motors. Pinning of bubbles occurs repeatedly at the same location, thereby resulting in constant circular or linear motion.

@en

Micro- and nanomotors and their use for biomedical applications have recently received increased attention. However, most designs use top-down methods to construct inorganic motors, which are labour-intensive and not suitable for biomedical use. Herein, we report a high-throughput design of an asymmetric hydrogel microparticle with autonomous movement by using a microfluidic chip to generate asymmetric, aqueous, two-phase-separating droplets consisting of poly(ethylene glycol) diacrylate (PEGDA) and dextran, with the biocatalyst placed in the PEGDA phase. The motor is propelled by enzyme-mediated decomposition of fuel. The speed of the motors is influenced by the roughness of the PEGDA surface after diffusion of dextran and was tuned by using higher molecular weight dextran. This roughness allows for easier pinning of oxygen bubbles and thus higher speeds of the motors. Pinning of bubbles occurs repeatedly at the same location, thereby resulting in constant circular or linear motion.@en

Recently reported piezoresponse force microscopy (PFM) measurements have proposed that porcine aortic walls are ferroelectric. This finding may have great implications for understanding biophysical properties of cardiovascular diseases such as arteriosclerosis. However, the complex anatomical structure of the aortic wall with different extracellular matrices appears unlikely to be ferroelectric. The reason is that a prerequisite for ferroelectricity, which is the spontaneous switching of the polarization, is a polar crystal structure of the material. Although the PFM measurements were performed locally, the phase-voltage hysteresis loops could be reproduced at different positions on the tissue, suggesting that the whole aorta is ferroelectric. To corroborate this hypothesis, we analyzed entire pieces of porcine aorta globally, both with electrical and electromechanical measurements. We show that there is no hysteresis in the electric displacement as well as in the longitudinal strain as a function of applied electric field and that the strain depends on the electric field squared. By using the experimentally determined quasi-static permittivity and Young's modulus of the fixated aorta, we show that the strain can quantitatively be explained by Maxwell stress and electrostriction, meaning that the aortic wall is neither piezoelectric nor ferroelectric, but behaves as a regular dielectric material.

@en

Self-powered artificial nanomotors are currently attracting increased interest as mimics of biological motors but also as potential components of nanomachinery, robotics, and sensing devices. We have recently described the controlled shape transformation of polymersomes into bowl-shaped stomatocytes and the assembly of platinum-driven nanomotors. However, the platinum encapsulation inside the structures was low; only 50% of the structures contained the catalyst and required both high fuel concentrations for the propelling of the nanomotors and harsh conditions for the shape transformation. Application of the nanomotors in a biological setting requires the nanomotors to be efficiently propelled by a naturally available energy source and at biological relevant concentrations. Here we report a strategy for enzyme entrapment and nanomotor assembly via controlled and reversible folding of polymersomes into stomatocytes under mild conditions, allowing the encapsulation of the proteins inside the stomach with almost 100% efficiency and retention of activity. The resulting enzyme-driven nanomotors are capable of propelling these structures at low fuel concentrations (hydrogen peroxide or glucose) via a one-enzyme or two-enzyme system. The confinement of the enzymes inside the stomach does not hinder their activity and in fact facilitates the transfer of the substrates, while protecting them from the deactivating influences of the media. This is particularly important for future applications of nanomotors in biological settings especially for systems where fast autonomous movement occurs at physiological concentrations of fuel.

@en

Every living cell is a compartmentalized out-ofequilibrium system exquisitely able to convert chemical energy into function. In order to maintain homeostasis, the flux of metabolites is tightly controlled by regulatory enzymatic networks. A crucial prerequisite for the development of lifelike materials is the construction of synthetic systems with compartmentalized reaction networks that maintain out-of-equilibrium function. Here, we aim for autonomous movement as an example of the conversion of feedstock molecules into function. The flux of the conversion is regulated by a rationally designed enzymatic reaction network with multiple feedforward loops. By compartmentalizing the network into bowl-shaped nanocapsules the output of the network is harvested as kinetic energy. The entire system shows sustained and tunable microscopic motion resulting from the conversion of multiple external substrates. The successful compartmentalization of an out-of-equilibrium reaction network is a major first step in harnessing the design principles of life for construction of adaptive and internally regulated lifelike systems.

@en

External small-molecule triggers were used to reversibly control dynamic protein-ligand interactions in giant vesicles. An alcohol dehydrogenase was employed to increase or decrease the interior pH upon conversion of two different small-molecule substrates, thereby modulating the pH-sensitive interaction between a Ni-NTA ligand on the vesicle membrane and an oligohistidine-tagged protein in the lumen. By alternating the small-molecule substrates the interaction could be reversed.@en

Polyisocyanopeptides have been synthesised containing acetylene groups on the side arms as scaffolds for multifunctional derivatisation by the copper-catalysed click reaction with a variety of azides. By using ethylene glycol azide and perylene azide chromophoric water-soluble polymeric nanowires (Mw 1-2 million Daltons) were formed. The potential to incorporate multiple chromophores was also demonstrated by the reaction of the acetylene-containing polymers with perylene azide and azidocoumarin dyes. In the latter case a blue-shifted emission of the coumarin was observed due to the interaction with the coupled perylene molecules. In particular the ability to form water-soluble dye-containing polymers, which can be modified by the addition of biomolecules, such as antibodies, proteins and peptides, give materials that are very promising as novel biomarker materials.@en