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- ItemLighting the Path: Light Delivery Strategies to Activate Photoresponsive Biomaterials In Vivo(Weinheim : Wiley-VCH, 2021) Pearson, Samuel; Feng, Jun; del Campo, AránzazuPhotoresponsive biomaterials are experiencing a transition from in vitro models to in vivo demonstrations that point toward clinical translation. Dynamic hydrogels for cell encapsulation, light-responsive carriers for controlled drug delivery, and nanomaterials containing photosensitizers for photodynamic therapy are relevant examples. Nonetheless, the step to the clinic largely depends on their combination with technologies to bring light into the body. This review highlights the challenge of photoactivation in vivo, and presents strategies for light management that can be adopted for this purpose. The authors’ focus is on technologies that are materials-driven, particularly upconversion nanoparticles that assist in “direct path” light delivery through tissue, and optical waveguides that “clear the path” between external light source and in vivo target. The authors’ intention is to assist the photoresponsive biomaterials community transition toward medical technologies by presenting light delivery concepts that can be integrated with the photoresponsive targets. The authors also aim to stimulate further innovation in materials-based light delivery platforms by highlighting needs and opportunities for in vivo photoactivation of biomaterials. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH.
- ItemElectrocatalytic fuel cell desalination for continuous energy and freshwater generation(Maryland Heights, MO : Cell Press, 2021) Zhang, Yuan; Wang, Lei; Presser, VolkerAdvanced hydrogen technologies contribute essentially to the decarbonization of our industrialized world. Large-scale hydrogen production would benefit from using the abundantly available water reservoir of our planet’s oceans. Current seawater-desalination technologies suffer from high energy consumption, high cost, or low performance. Here, we report technology for water desalination at seawater molarity, based on a polymer ion-exchange membrane fuel cell. By continuously supplying hydrogen and oxygen to the cell, a 160-mM concentration decrease from an initial value of 600 mM is accomplished within 40 h for a 55-mL reservoir. This device’s desalination rate in 600 mM NaCl and substitute ocean water are 18 g/m2/h and 16 g/m2/h, respectively. In addition, by removing 1 g of NaCl, 67 mWh of electric energy is generated. This proof-of-concept work shows the high application potential for sustainable fuel-cell desalination (FCD) using hydrogen as an energy carrier.
- ItemChoosing the right carbon additive is of vital importance for high-performance Sb-based Na-ion batteries(London [u.a.] : RSC, 2020) Pfeifer, Kristina; Arnold, Stefanie; Budak, Öznil; Luo, Xianlin; Presser, Volker; Ehrenberg, Helmut; Dsoke, SoniaElectrodes based on alloying reactions for sodium-ion batteries (NIB) offer high specific capacity but require bespoken electrode material design to enable high performance stability. This work addresses that issue by systematically exploring the impact of carbon properties on antimony/carbon composite electrodes for NIBs. Since the Sb surface is covered by an insulating oxide layer, carbon additives are crucial for the percolation and electrochemical activity of Sb based anodes. Instead of using complex hybridization strategies, the ability of mechanical mixing to yield stable high-performance Sb/C sodium-ion battery (NIB) electrodes is shown. This is only possible by considering the physical, chemical, and structural features of the carbon phase. A comparison of carbon nanohorns, onion-like carbon, carbon black, and graphite as conductive additives is given in this work. The best performance is not triggered by the highest or lowest surface area, and not by highest or lowest heteroatom content, but by the best ability to homogenously distribute within the Sb matrix. The latter provides an optimum interaction between carbon and Sb and is best enabled by onion-like carbon. A remarkable rate performance is attained, electrode cracking caused by volume expansion is successfully prevented, and the homogeneity of the solid/electrolyte interphase is significantly improved as a result of it. With this composite electrode, a reversible capacity of 490 mA h g-1 at 0.1 A g-1 and even 300 mA g-1 at 8 A g-1 is obtained. Additionally, high stability with a capacity retention of 73% over 100 cycles is achieved at charge/discharge rates of 0.2 A g-1 This journal is © The Royal Society of Chemistry.
- ItemBreakdown of continuum models for spherical probe adhesion tests on micropatterned surfaces(Amsterdam [u.a.] : Elsevier Science, 2021) Bettscheider, Simon; Yu, Dan; Foster, Kimberly; McMeeking, Robert; Arzt, Eduard; Hensel, René; Booth, Jamie A.The adhesion of fibrillar dry adhesives, mimicking nature's principles of contact splitting, is commonly characterized by using axisymmetric probes having either a flat punch or spherical geometry. When using spherical probes, the adhesive pull-off force measured depends strongly on the compressive preload applied when making contact and on the geometry of the probe. Together, these effects complicate comparisons of the adhesive performance of micropatterned surfaces measured in different experiments. In this work we explore these issues, extending previous theoretical treatments of this problem by considering a fully compliant backing layer with an array of discrete elastic fibrils on its surface. We compare the results of the semi-analytical model presented to existing continuum theories, particularly with respect to determining a measurement system- and procedure-independent metric for the local adhesive strength of the fibrils from the global pull-off force. It is found that the discrete nature of the interface plays a dominant role across a broad range of relevant system parameters. Accordingly, a convenient tool for simulation of a discrete array is provided. An experimental procedure is recommended for use in conjunction with this tool in order to extract a value for the local adhesive strength of the fibrils, which is independent of the other system properties (probe radius, backing layer thickness, and preload) and thus is suitable for comparison across experimental studies.
- ItemOptoacoustically induced auditory brainstem responses in the mouse model enhanced through an absorbing film(Bellingham, Wash. : SPIE, 2021) Sorg, Katharina; Heimann, Larissa; Lana, Gabriela Moreira; Langenbucher, Achim; Schick, Bernhard; Arzt, Eduard; Wenzel, Gentiana IoanaSignificance: Optoacoustic stimulation offers an alternative stimulation strategy for the hearing organ. To serve as the base for a novel auditory prosthesis, the optoacoustic stimulation must be biocompatible and energy-saving. Aim: Enhancing the efficiency of optoacoustic stimulation while reducing the energy input in a suited animal model. Approach: Optoacoustically induced auditory brainstem responses (oABRs) were recorded after the pulsed laser irradiation of the tympanic membrane (TM) in mice. The results were compared with the ABRs induced through acoustic click stimulation. In addition, self-adhesive absorbing films were applied on the TM before the optoacoustic stimulation to investigate their effect on the resulting ABRs.Results: Using an absorbing film on the TM during optical stimulation led to considerably enhanced oABR wave I amplitude values compared with the stimulation of the bare TM. When using our stimulation strategy, we induced oABR waves in the 50% to 60% range of the acoustical stimulation reached with 80-dB SPL click stimuli. Conclusions: The mouse model can be used for certain developmental work for an optoacoustic auditory prosthesis. Using absorbing films on the TM during optical stimulation considerably enhances oABR wave I amplitude. Optimization of the stimulation strategy could further enhance the efficiency within biocompatibility margins.
- ItemPerspective on statistical effects in the adhesion of micropatterned surfaces(Melville, NY : American Inst. of Physics, 2021) Booth, Jamie A.; Hensel, RenéBioinspired micropatterned adhesives have attracted extensive research interest in the past two decades. In modeling the performance of these adhesives, the common assumption has been that the adhesive strength of each sub-contact is identical. Recent experiments, however, have shown that interfacial defects of different characters lead to a distribution of the adhesive strength within a fibrillar array. Based on experimental observations of detachment events, a statistical model for the distribution of the local adhesive strength and the resulting performance of a micropatterned adhesive are presented. This approach constitutes a paradigm shift, providing better understanding of micropatterned adhesives under real conditions. Examples presented include the prediction of unstable detachments in compliant systems. Future directions are discussed, including the extension of the statistical approach to non-uniform loading and rate-dependent effects, the contribution of suction to adhesion and aging of contacts over specific time periods, as well as the necessity for a more in-depth understanding of defect formation considering surface roughness and other imperfections in the system.
- ItemOn the viscous dissipation caused by randomly rough indenters in smooth sliding motion(Amsterdam : Elsevier, 2021) Sukhomlinov, Sergey; Müser, Martin H.The viscous dissipation between rigid, randomly rough indenters and linearly elastic counter bodies sliding past them is investigated using Green’s function molecular dynamics. The study encompasses a variety of models differing in the height spectra properties of the rigid indenter, in the viscoelasticity of the elastomer, and in their interaction. All systems reveal the expected damping linear in sliding velocity at small and a pronounced maximum at intermediate . Persson’s theory of rubber friction, which is adopted to the studied model systems, reflects all observed trends. However, close quantitative agreement is only found up to intermediate sliding velocities. Relative errors in the friction force become significant once the contact area is substantially reduced by sliding.
- ItemOscillatory Microrheology, Creep Compliance and Stress Relaxation of Biological Cells Reveal Strong Correlations as Probed by Atomic Force Microscopy(Lausanne : Frontiers Media, 2021) Flormann, D.A.D.; Anton, C.; Pohland, M.O.; Bautz, Y.; Kaub, K.; Terriac, E.; Schäffer, T.E.; Rheinlaender, J.; Janshoff, A.; Ott, A.; Lautenschläger, F.The mechanical properties of cells are important for many biological processes, including wound healing, cancers, and embryogenesis. Currently, our understanding of cell mechanical properties remains incomplete. Different techniques have been used to probe different aspects of the mechanical properties of cells, among them microplate rheology, optical tweezers, micropipette aspiration, and magnetic twisting cytometry. These techniques have given rise to different theoretical descriptions, reaching from simple Kelvin-Voigt or Maxwell models to fractional such as power law models, and their combinations. Atomic force microscopy (AFM) is a flexible technique that enables global and local probing of adherent cells. Here, using an AFM, we indented single retinal pigmented epithelium cells adhering to the bottom of a culture dish. The indentation was performed at two locations: above the nucleus, and towards the periphery of the cell. We applied creep compliance, stress relaxation, and oscillatory rheological tests to wild type and drug modified cells. Considering known fractional and semi-fractional descriptions, we found the extracted parameters to correlate. Moreover, the Young’s modulus as obtained from the initial indentation strongly correlated with all of the parameters from the applied power-law descriptions. Our study shows that the results from different rheological tests are directly comparable. This can be used in the future, for example, to reduce the number of measurements in planned experiments. Apparently, under these experimental conditions, the cells possess a limited number of degrees of freedom as their rheological properties change.
- ItemHighly Tunable Nanostructures in a Doubly pH-Responsive Pentablock Terpolymer in Solution and in Thin Films(Weinheim : Wiley-VCH, 2021) Jung, Florian A.; Schart, Maximilian; Bührend, Lukas; Meidinger, Elisabeth; Kan, Jia-Jhen; Niebuur, Bart-Jan; Ariaee, Sina; Molodenskiy, Dmitry S.; Posselt, Dorthe; Amenitsch, Heinz; Tsitsilianis, Constantinos; Papadakis, Christine M.Multiblock copolymers with charged blocks are complex systems that show great potential for enhancing the structural control of block copolymers. A pentablock terpolymer PMMA-b-PDMAEMA-b-P2VP-b-PDMAEMA-b-PMMA is investigated. It contains two types of midblocks, which are weak cationic polyelectrolytes, namely poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(2-vinylpyridine) (P2VP). Furthermore, these are end-capped with short hydrophobic poly(methyl methacrylate) (PMMA) blocks in dilute aqueous solution and thin films. The self-assembly behavior depends on the degrees of ionization α of the P2VP and PDMAEMA blocks, which are altered in a wide range by varying the pH value. High degrees of ionization of both blocks prevent structure formation, whereas microphase-separated nanostructures form for a partially charged and uncharged state. While in solutions, the nanostructure formation is governed by the dependence of the P2VP block solubility of the and the flexibility of the PDMAEMA blocks on α, in thin films, the dependence of the segregation strength on α is key. Furthermore, the solution state plays a crucial role in the film formation during spin-coating. Overall, both the mixing behavior of the 3 types of blocks and the block sequence, governing the bridging behavior, result in strong variations of the nanostructures and their repeat distances.
- ItemBioinspired Underwater Adhesion to Rough Substrates by Cavity Collapse of Cupped Microstructures(Weinheim : Wiley-VCH, 2021) Wang, Yue; Hensel, RenéUnderwater or wet adhesion is highly desirable for numerous applications but is counteracted by the liquids in the contact which weaken intermolecular attraction. The problem is exacerbated in conjunction with surface roughness when liquids partially remain in grooves or dimples of the substrate. In the present study, a cupped microstructure with a cavity inspired by suction organs of aquatic animals is proposed. The microstructures (cup radius of 100 µm) are made from polyurethane using two-photon lithography followed by replica molding. Adhesion to rough substrates is emulated experimentally by a micropatterned model substrate with varying channel widths. Pull-off stresses are found to be about 200 kPa, i.e., twice atmospheric pressure. Evaluation of force–displacement curves together with in situ observations reveal the adhesion mechanism, which involves adaptation to surface roughness and an elastic force induced by the collapse of the cavity that holds sealed contact with the substrate during retraction. This new microarchitecture may pave the way for next generation microstructures applicable to real, rough surfaces under wet conditions.