Polyether-ether-ketone (PEEK) is one of the most common materials used for load-bearing orthopaedic devices due to its radiolucency and favorable mechanical properties. However, current ...smooth-surfaced PEEK implants can lead to fibrous encapsulation and poor osseointegration. This study compared the in vitro and in vivo bone response to two smooth PEEK alternatives: porous PEEK and plasma-sprayed titanium coatings on PEEK. MC3T3 cells were grown on smooth PEEK, porous PEEK, and Ti-coated PEEK for 14 days and assayed for calcium content, osteocalcin, VEGF and ALP activity. Osseointegration was investigated by implanting cylindrical implants into the proximal tibiae of male Sprague Dawley rats for 8 weeks. Bone-implant interfaces were evaluated using μCT, histology and pullout testing. Cells on porous PEEK surfaces produced more calcium, osteocalcin, and VEGF than smooth PEEK and Ti-coated PEEK groups. Bone ingrowth into porous PEEK surfaces was comparable to previously reported porous materials and correlated well between μCT and histology analysis. Porous PEEK implants exhibited greater pullout force, stiffness and energy-to-failure compared to smooth PEEK and Ti-coated PEEK, despite Ti-coated PEEK exhibiting a high degree of bone-implant contact. These results are attributed to increased mechanical interlocking of bone with the porous PEEK implant surface. Overall, porous PEEK was associated with improved osteogenic differentiation in vitro and greater implant fixation in vivo compared to smooth PEEK and Ti-coated PEEK. These results suggest that not all PEEK implants inherently generate a fibrous response and that topography has a central role in determining implant osseointegration.
Most cancer patients die from metastasis. Recent studies have shown that gold nanoparticles (AuNPs) can slow down the migration/invasion speed of cancer cells and suppress metastasis. Since nuclear ...stiffness of the cell largely decreases cell migration, our hypothesis is that targeting AuNPs to the cell nucleus region could enhance nuclear stiffness, and therefore inhibit cell migration and invasion. Our results showed that upon nuclear targeting of AuNPs, the ovarian cancer cell motilities decrease significantly, compared with nontargeted AuNPs. Furthermore, using atomic force microscopy, we observed an enhanced cell nuclear stiffness. In order to understand the mechanism of cancer cell migration/invasion inhibition, the exact locations of the targeted AuNPs were clearly imaged using a high-resolution three-dimensional imaging microscope, which showed that the AuNPs were trapped at the nuclear membrane. In addition, we observed a greatly increased expression level of lamin A/C protein, which is located in the inner nuclear membrane and functions as a structural component of the nuclear lamina to enhance nuclear stiffness. We propose that the AuNPs that are trapped at the nuclear membrane both (1) add to the mechanical stiffness of the nucleus and (2) stimulate the overexpression of lamin A/C located around the nuclear membrane, thus increasing nuclear stiffness and slowing cancer cell migration and invasion.
Increased tissue stiffness and epithelial‐to‐mesenchymal transitions (EMTs) are two seemingly discrete hallmarks of fibrotic diseases. Despite recent findings highlighting the influence of tissue ...mechanical properties on cell phenotype, it remains unclear what role increased tissue stiffness has in the regulation of previously reported fibronectin‐mediated EMTs associated with pulmonary fibrosis. Nano‐indentation testing of lung interstitial spaces showed that in vivo cell‐level Young's moduli increase with the onset of fibrosis from ∼2 to ∼17 kPa. In vitro, we found that stiff, but not soft, fibronectin substrates induce EMT, a response dependent on cell contraction‐mediated integrin activation of TGFβ. Activation or suppression of cell contractility with exogenous factors was sufficient to overcome the effect of substrate stiffness. Pulse‐chase experiments indicate that the effect of cell contractility is dose‐ and time‐dependent. In response to low levels of TGFβ on soft surfaces, either added exogenously or produced through thrombin‐induced contraction, cells will initiate the EMT programme, but upon removal revert to an epithelial phenotype. These results identify matrix stiffness and/or cell contractility as critical targets for novel therapeutics for fibrotic diseases.
Leukocytes normally marginate toward the vascular wall in large vessels and within the microvasculature. Reversal of this process, leukocyte demargination, leads to substantial increases in the ...clinical white blood cell and granulocyte count and is a well-documented effect of glucocorticoid and catecholamine hormones, although the underlying mechanisms remain unclear. Here we show that alterations in granulocyte mechanical properties are the driving force behind glucocorticoid- and catecholamine-induced demargination. First, we found that the proportions of granulocytes from healthy human subjects that traversed and demarginated from microfluidic models of capillary beds and veins, respectively, increased after the subjects ingested glucocorticoids. Also, we show that glucocorticoid and catecholamine exposure reorganizes cellular cortical actin, significantly reducing granulocyte stiffness, as measured with atomic force microscopy. Furthermore, using simple kinetic theory computational modeling, we found that this reduction in stiffness alone is sufficient to cause granulocyte demargination. Taken together, our findings reveal a biomechanical answer to an old hematologic question regarding how glucocorticoids and catecholamines cause leukocyte demargination. In addition, in a broader sense, we have discovered a temporally and energetically efficient mechanism in which the innate immune system can simply alter leukocyte stiffness to fine tune margination/demargination and therefore leukocyte trafficking in general. These observations have broad clinically relevant implications for the inflammatory process overall as well as hematopoietic stem cell mobilization and homing.
Cost-effective production of ammonia via electrochemical nitrogen reduction reaction (NRR) hinges on N2 electrolysis at high current densities with suitable selectivity and activity. Here, we report ...our findings in electrochemical NRR for ammonia synthesis using porous bimetallic Pd–Ag nanocatalysts in both gas-phase and liquid-phase electrochemical cells at current densities above 1 mA cm–2 under ambient conditions. While the gas-phase cell has lower Ohmic losses and higher energy efficiency, the liquid-phase cell achieved higher selectivity and Faradaic efficiency, attributed to the presence of concentrated N2 molecules dissolved in an aqueous electrolyte and the hydration effects. The liquid cell demonstrated notable performance for electrocatalytic NRR, achieving an NH3 production rate of 45.6 ± 3.7 μg cm–2 h–1 at a cell voltage of −0.6 V (vs RHE) and current density of 1.1 mA cm–2, corresponding to a Faradaic efficiency of ∼19.6% and an energy efficiency of ∼9.9%. Similarly, the gas-phase cell achieved a NH3 yield rate of 19.4 ± 2.1 μg cm–2 h–1 at −0.07 V (vs RHE) and 1.15 mA cm–2 with a Faradaic efficiency of 7.9% and an energy efficiency of 27.1%. Further, operando surface-enhanced Raman spectroscopy and density functional theory (DFT) are used to identify intermediate species relevant to the NRR at the electrode–electrolyte interfaces to provide insights into the NRR mechanism on Pd–Ag nanoparticles. This work highlights the importance of design and optimization of cell configuration in addition to the modification of the catalyst to achieve high-performance N2 electrolysis for ammonia synthesis.
Cytotoxic effector cells are an integral component of the immune response against pathogens and diseases such as cancer and thus of great interest to researchers who wish to enhance the native immune ...response. Although researchers routinely use particles to stimulate cytotoxic T cells, few studies have comprehensively investigated: (1) beyond initial activation responses (i.e., proliferation and CD25/CD69 expression) to downstream cancer-killing effects and (2) how to drive cytotoxic T-cell responses by adjusting biomolecular and physical properties of particles. In this study, we designed particles displaying an anti-CD3 antibody to activate cytotoxic T cells and study their downstream cytotoxic effects. We evaluated the effect of antibody immobilization, particle size, molecular surface density of an anti-CD3 antibody, and the inclusion of an anti-CD28 antibody on cytolytic granule release by T cells. We found that immobilizing the anti-CD3 antibody onto smaller nanoparticles elicited increased T-cell activation products for an equivalent delivery of the anti-CD3 antibody. We further established that the mechanism behind increased cancer cell death was associated with the proximity of T cells to cancer cells. Functionalizing particles additionally with the anti-CD28 antibody at an optimized antibody density caused increased T-cell proliferation and T-cell binding but we observed no effective increase in cytotoxicity. Meaningfully, our results are discussed within the context of commercially available and widely used anti-CD3/28 Dynabeads. These results showed that T-cell activation and cytotoxicity can be optimized with a molecular presentation on smaller particles and thus, offer exciting new possibilities to engineer T-cell activation responses for effective outcomes.
Free-energy landscapes govern the behavior of all interactions in the presence of thermal fluctuations in the fields of physical chemistry, materials sciences, and the biological sciences. From the ...energy landscape, critical information about an interaction, such as the reaction kinetic rates, bond lifetimes, and the presence of intermediate states, can be determined. Despite the importance of energy landscapes to understanding reaction mechanisms, most experiments do not directly measure energy landscapes, particularly for interactions with steep force gradients that lead to premature jump to contact of the probe and insufficient sampling of transition regions. Here we present an atomic force microscopy (AFM) approach for measuring energy landscapes that increases sampling of strongly adhesive interactions by using white-noise excitation to enhance the cantilever’s thermal fluctuations. The enhanced fluctuations enable the recording of subtle deviations from a harmonic potential to accurately reconstruct interfacial energy landscapes with steep gradients. Comparing the measured energy landscape with adhesive force measurements reveals the existence of an optimal excitation voltage that enables the cantilever fluctuations to fully sample the shape and depth of the energy surface.
Measurements of free energy landscapes are critical for understanding the basis of many physical, chemical, and biological interactions. Statistical mechanics provide exact equations to calculate ...free energies, but are built on the assumption that all possible configurations of the system are sampled. The most pronounced limit to accurate free energy computations is therefore the imperfect sampling of a potential field, particularly in the case of interactions with steep gradients and short reaction coordinates. We show through simulations that increasing the stochastic fluctuations of a harmonic probe by active excitation results in increased sampling times of high gradient adhesive interactions and leads to the reconstruction of a more accurate energy landscape. We use Brownian dynamics simulations to test the impact of probe approach velocity, stiffness, and thermal energy to sample complex energy landscapes with multiple wells of various depths and slopes to understand the accuracy of energy surface reconstruction. We then show experimentally that through the application of optimal stochastic excitations, we are able to obtain accurate energy landscape reconstructions for different probe and landscape parameters due to improved sampling of previously poorly probed interactions.
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