SciCombinator

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Concept: Newton

27

The purpose of the study was to quantify tongue protrusion force and compare its characteristics between participants with severely weak tongues and those with normal lingual strength. The sample consisted of 11 participants with severe lingual strength deficits and 11 age- and sex-matched participants with normal lingual strength. Tongue force was evaluated quantitatively using the Forling instrument, and the average force, maximum force, average force application rate, and area under the graphic curve were analysed. These parameters were compared between the groups. In the participants with severely weak tongues, the average and the maximum forces in N (Newton) were 2.03 ± 1.17 and 3.56 ± 1.77, respectively. The average force application rate in N/s (Newton per second) was 1.25 and the area under the graphic curve in Ns (Newton times second) was 18.6. The values of the participants with normal lingual strength were, respectively, 13.27 ± 6.15 N, 18.91 ± 7.95 N, 10.46 N/s, and 108.08 Ns. All parameters analysed differed significantly between the groups. The data collected could aid speech-language pathologists in diagnosing problems related to tongue force.

Concepts: Tensile stress, Mass, Lingual nerve, Newton, Classical mechanics, Tongue, Force

10

Complex biological systems sense, process, and respond to their surroundings in real time. The ability of such systems to adapt their behavioral response to suit a range of dynamic environmental signals motivates the use of biological materials for other engineering applications. As a step toward forward engineering biological machines (bio-bots) capable of nonnatural functional behaviors, we created a modular light-controlled skeletal muscle-powered bioactuator that can generate up to 300 µN (0.56 kPa) of active tension force in response to a noninvasive optical stimulus. When coupled to a 3D printed flexible bio-bot skeleton, these actuators drive directional locomotion (310 µm/s or 1.3 body lengths/min) and 2D rotational steering (2°/s) in a precisely targeted and controllable manner. The muscle actuators dynamically adapt to their surroundings by adjusting performance in response to “exercise” training stimuli. This demonstration sets the stage for developing multicellular bio-integrated machines and systems for a range of applications.

Concepts: Mathematics, Newton, The Stage, Behavior, Skeleton, Motivation

9

Biological machines consisting of cells and biomaterials have the potential to dynamically sense, process, respond, and adapt to environmental signals in real time. As a first step toward the realization of such machines, which will require biological actuators that can generate force and perform mechanical work, we have developed a method of manufacturing modular skeletal muscle actuators that can generate up to 1.7 mN (3.2 kPa) of passive tension force and 300 μN (0.56 kPa) of active tension force in response to external stimulation. Such millimeter-scale biological actuators can be coupled to a wide variety of 3D-printed skeletons to power complex output behaviors such as controllable locomotion. This article provides a comprehensive protocol for forward engineering of biological actuators and 3D-printed skeletons for any design application. 3D printing of the injection molds and skeletons requires 3 h, seeding the muscle actuators takes 2 h, and differentiating the muscle takes 7 d.

Concepts: Skeleton, DNA, Conservative force, Newton, Work, Potential energy, Force, Energy

4

Measuring vital physiological pressures is important for monitoring health status, preventing the buildup of dangerous internal forces in impaired organs, and enabling novel approaches of using mechanical stimulation for tissue regeneration. Pressure sensors are often required to be implanted and directly integrated with native soft biological systems. Therefore, the devices should be flexible and at the same time biodegradable to avoid invasive removal surgery that can damage directly interfaced tissues. Despite recent achievements in degradable electronic devices, there is still a tremendous need to develop a force sensor which only relies on safe medical materials and requires no complex fabrication process to provide accurate information on important biophysiological forces. Here, we present a strategy for material processing, electromechanical analysis, device fabrication, and assessment of a piezoelectric Poly-l-lactide (PLLA) polymer to create a biodegradable, biocompatible piezoelectric force sensor, which only employs medical materials used commonly in Food and Drug Administration-approved implants, for the monitoring of biological forces. We show the sensor can precisely measure pressures in a wide range of 0-18 kPa and sustain a reliable performance for a period of 4 d in an aqueous environment. We also demonstrate this PLLA piezoelectric sensor can be implanted inside the abdominal cavity of a mouse to monitor the pressure of diaphragmatic contraction. This piezoelectric sensor offers an appealing alternative to present biodegradable electronic devices for the monitoring of intraorgan pressures. The sensor can be integrated with tissues and organs, forming self-sensing bionic systems to enable many exciting applications in regenerative medicine, drug delivery, and medical devices.

Concepts: Biology, Pascal, Integral, Transducer, Newton, Sensors, Liver, Pressure

4

Neural progenitor cell (NPC) culture within three-dimensional (3D) hydrogels is an attractive strategy for expanding a therapeutically relevant number of stem cells. However, relatively little is known about how 3D material properties such as stiffness and degradability affect the maintenance of NPC stemness in the absence of differentiation factors. Over a physiologically relevant range of stiffness from ∼0.5 to 50 kPa, stemness maintenance did not correlate with initial hydrogel stiffness. In contrast, hydrogel degradation was both correlated with, and necessary for, maintenance of NPC stemness. This requirement for degradation was independent of cytoskeletal tension generation and presentation of engineered adhesive ligands, instead relying on matrix remodelling to facilitate cadherin-mediated cell-cell contact and promote β-catenin signalling. In two additional hydrogel systems, permitting NPC-mediated matrix remodelling proved to be a generalizable strategy for stemness maintenance in 3D. Our findings have identified matrix remodelling, in the absence of cytoskeletal tension generation, as a previously unknown strategy to maintain stemness in 3D.

Concepts: Progenitor cell, Adult stem cell, Newton, Stem cell, Cytoplasm, Cell biology, Developmental biology, Young's modulus

3

Förster resonance energy transfer (FRET)-based tension sensor modules (TSMs) are available for investigating how distinct proteins bear mechanical forces in cells. Yet, forces in the single piconewton (pN) regime remain difficult to resolve, and tools for multiplexed tension sensing are lacking. Here, we report the generation and calibration of a genetically encoded, FRET-based biosensor called FL-TSM, which is characterized by a near-digital force response and increased sensitivity at 3-5 pN. In addition, we present a method allowing the simultaneous evaluation of coexpressed tension sensor constructs using two-color fluorescence lifetime microscopy. Finally, we introduce a procedure to calculate the fraction of mechanically engaged molecules within cells. Application of these techniques to new talin biosensors reveals an intramolecular tension gradient across talin-1 that is established upon integrin-mediated cell adhesion. The tension gradient is actomyosin- and vinculin-dependent and sensitive to the rigidity of the extracellular environment.

Concepts: Atom, Mass, Tension, DNA, Cell biology, Sensors, Newton, Force

3

Increasing preferred step rate during running is a commonly used strategy in the management of running-related injuries. This study investigated the effect of different step rates on plantar pressures during running. Thirty-two healthy runners ran at a comfortable speed on a treadmill at five step rates (preferred, ±5%, and ±10%). For each step rate, plantar pressure data were collected using the pedar-X in-shoe system. Compared to running with a preferred step rate, a 10% increase in step rate significantly reduced peak pressure (144.5 ± 46.5 vs. 129.3 ± 51 kPa; p=0.033) and maximum force (382.3 ± 157.6 vs. 334.0 ± 159.8 N; p=0.021) at the rearfoot, and reduced maximum force (426.4 ± 130.4 vs. 400.0 ± 116.6 N; p=0.001) at the midfoot. In contrast, a 10% decrease in step rate significantly increased peak pressure (144.5 ± 46.5 vs. 161.5 ± 49.3 kPa; p=0.011) and maximum force (382.3 ± 157.6 vs. 425.4 ± 155.3 N; p=0.032) at the rearfoot. Changing step rate by 5% provided no effect on plantar pressures, and no differences in plantar pressures were observed at the medial forefoot, lateral forefoot or hallux between the step rates. This study’s findings indicate that increasing preferred step rate by 10% during running will reduce plantar pressures at the rearfoot and midfoot, while decreasing step rate by 10% will increase plantar pressures at the rearfoot. However, changing preferred step rate by 5% will provide no effect on plantar pressures, and forefoot pressures are unaffected by changes in step rate. This article is protected by copyright. All rights reserved.

Concepts: Bar, All rights reserved, Torr, Atmospheric pressure, Newton, Copyright, Pascal, Pressure

3

Mechanical stimuli profoundly alter cell fate, yet the mechanisms underlying mechanotransduction remain obscure because of a lack of methods for molecular force imaging. Here to address this need, we develop a new class of molecular tension probes that function as a switch to generate a 20- to 30-fold increase in fluorescence upon experiencing a threshold piconewton force. The probes employ immobilized DNA hairpins with tunable force response thresholds, ligands and fluorescence reporters. Quantitative imaging reveals that integrin tension is highly dynamic and increases with an increasing integrin density during adhesion formation. Mixtures of fluorophore-encoded probes show integrin mechanical preference for cyclized RGD over linear RGD peptides. Multiplexed probes with variable guanine-cytosine content within their hairpins reveal integrin preference for the more stable probes at the leading tip of growing adhesions near the cell edge. DNA-based tension probes are among the most sensitive optical force reporters to date, overcoming the force and spatial resolution limitations of traction force microscopy.

Concepts: Protein, American films, Tension, Molecular biology, Newton, Optics, DNA, Force

2

Mechanical forces are integral to many biological processes; however, current techniques cannot map the magnitude and direction of piconewton molecular forces. Here, we describe molecular force microscopy, leveraging molecular tension probes and fluorescence polarization microscopy to measure the magnitude and 3D orientation of cellular forces. We mapped the orientation of integrin-based traction forces in mouse fibroblasts and human platelets, revealing alignment between the organization of force-bearing structures and their force orientations.

Concepts: Euclidean vector, Magnetic field, Map, Electric charge, Tension, Newton, Integral, Force

2

The aim of this study was to quantify the load that maximized peak and mean power, as well as impulse applied to these loads, during the push press and to compare them to equivalent jump squat data. Resistance-trained men performed two push press (n = 17; age: 25.4 ± 7.4 years; height: 183.4 ± 5 cm; body mass: 87 ± 15.6 kg) and jump squat (n = 8 of original 17; age: 28.7 ± 8.1 years; height: 184.3 ± 5.5 cm; mass: 98 ± 5.3 kg) singles with 10-90% of their push press and back squat 1 RM, respectively, in 10% 1 RM increments while standing on a force platform. Push press peak and mean power was maximized with 75.3 ± 16.4 and 64.7 ± 20% 1RM, respectively, and impulses applied to these loads were 243 ± 29 N.s and 231 ± 36 N.s. Increasing and decreasing load, from the load that maximized peak and mean power, by 10% and 20% 1RM reduced peak and mean power by 6-15% (p < 0.05). Push press and jump squat maximum peak power (7%, p = 0.08) and the impulse that was applied to the load that maximized peak (8%, p = 0.17) and mean (13%, p = 0.91) power were not significantly different, but push press maximum mean power was significantly greater than the jump squat equivalent (∼9.5%, p = 0.03). The mechanical demand of the push press is comparable to the jump squat and could provide a time-efficient combination of lower-body power and upper-body and trunk strength training.

Concepts: Exercise, Military press, Newton, Peak power, Monotonic function, Weight training, Weight training exercises, Mass