Single Mechanical Stimulus Research Articles

Biomechanical Effects of Mechanical Stress on Cells Involved in Fracture Healing.

Fracture healing is a complex staged repair process in which the mechanical environment plays a key role. Bone tissue is very sensitive to mechanical stress stimuli, and the literature suggests that appropriate stress can promote fracture healing by altering cellular function. However, fracture healing is a coupled process involving multiple cell types that balance and limit each other to ensure proper fracture healing. The main cells that function during different stages of fracture healing are different, and the types and molecular mechanisms of stress required are also different. Most previous studies have used a single mechanical stimulus on individual mechanosensitive cells, and there is no relatively uniform standard for the size and frequency of the mechanical stress. Analyzing the mechanisms underlying the effects of mechanical stimulation on the metabolic regulation of signaling pathways in cells such as in bone marrow mesenchymal stem cells (BMSCs), osteoblasts, chondrocytes, and osteoclasts is currently a challenging research hotspot. Grasping how stress affects the function of different cells at the molecular biology level can contribute to the refined management of fracture healing. Therefore, in this review, we summarize the relevant literature and describe the effects of mechanical stress on cells associated with fracture healing, and their possible signaling pathways, for the treatment of fractures and the further development of regenerative medicine.

Stimuli‐Responsive Liquid Metal Hybrids for Human‐Interactive Electronics

AbstractThe development of stimuli‐responsive liquid metal hybrids (SrLMHs) is of great interest, owing to their ability to induce responsivity and innovative properties to liquid metal (LM) when hybridized. Various stimuli‐responsivities yield new realms for SrLMHs in the fields of human‐interactive electronics (HIEs). This review provides an overview on the development of SrLMHs for HIEs. First, discussion is on SrLMH systems regarding their configuration, the materials utilized for the establishment of new hybrid materials, various stimuli‐responsive systems, their operation mechanisms, and applications. Followed by the characterization and summary of SrLMHs, details on how SrLMHs are incorporated for HIEs, and their progression is reviewed, from a single mechanical stimulus sensing capability to multi‐modal functionality. Finally, the review concludes on the overall progress of SrLMH‐based HIEs, their advancement direction, and the challenges that still remain.

The Individual and Combined Effects of Shear, Tension, and Flexure on Aortic Heart Valve Endothelial Cells in Culture

The necessity of living engineered heart valves to treat patients with severe heart disease poses a challenge to tissue engineers. To reach such goal it is crucial to fully understand the role and the activities of valvular endothelial cells (VECs) when they face different types of mechanical stimuli. This study focuses on decomposing the roles of different mechanical stimuli on heart valve endothelial surfaces and the response of VECs in terms of morphology and phenotype change. This study utilizes soft hydrogel-based scaffolds to use as a substrate for cell culture to mimic heart valve tissue leaflet. VECs were cultured as a monolayer on the gel surface and different types of mechanical stimuli were applied. Finally, the response of cells was investigated in terms of morphology and protein expression changes. Single stimuli introduces actin fibers reorganization in VECs, change in cell morphology, and higher mesenchymal protein expression. On the other hand, combined stimuli application has lower impact on actin fibers reorganization and cell morphology change, with lower mesenchymal protein expression. When VECs face a single mechanical stimuli, they undergo transdifferentiation and transform into mesenchymal cells. However, when these cells face a combination of mechanical stimuli, the rate of transformation decreases compared to single stimuli applications. This indicates that a single stimulus induces endothelial to mesenchymal transition in VECs while the process is slower under the combination of multiple mechanical stimuli.

Towards 4D printed scaffolds for tissue engineering: exploiting 3D shape memory polymers to deliver time-controlled stimulus on cultured cells

Tissue engineering needs innovative solutions to better fit the requirements of a minimally invasive approach, providing at the same time instructive cues to cells. The use of shape memory polyurethane has been investigated by producing 4D scaffolds via additive manufacturing technology. Scaffolds with two different pore network configurations (0/90° and 0/45°) were characterized by dynamic-mechanical analysis. The thermo-mechanical analysis showed a Tg at about 32 °C (Tg = Ttrans), indicating no influence of the fabrication process on the transition temperature. In addition, shape recovery tests showed a good recovery of the permanent shape for both scaffold configurations. When cells were seeded onto the scaffolds in the temporary shape and the permanent shape was recovered, cells were significantly more elongated after shape recovery. Thus, the mechanical stimulus imparted by shape recovery is able to influence the shape of cells and nuclei. The obtained results indicate that a single mechanical stimulus is sufficient to initiate changes in the morphology of adherent cells.

Dose‐dependent effects of developmental mercury exposure on C‐start escape responses of larval zebrafishDanio rerio

ZebrafishDanio rerioembryos were exposed to 0, 25, 50 or 75 ppb Hg2+from 0 to 24 h post‐fertilization (hpf) then placed into Hg2+‐free water. Inductively coupled plasma‐mass spectrophotometer analysis of whole embryo Hg2+content at 24 hpf showed a positive correlation with exposure regime (Pearson's one‐tailed,r2= 0·698,P< 0·01); at 5 days post‐hatch (dph), whole larval Hg2+content was not detectable. Hg2+‐induced behavioural deficits in larvae were, therefore, due to changes during embryogenesis and not to residual Hg2+in the larvae. At 5 dph, larvae were tested for responses to different frequencies but equal intensities of vibrational stimuli generated by a remotely controlled plastic hammer. Data were recorded by high‐speed videography and computer‐analysed for latency of response (ms), amplitude of the response as measured by maximum initial velocity [normalized as body (standard) lengths s−1;Vmax] and duration of behaviour from initial head movement to cessation of caudal tail movement (ms). A single mechanical stimulus resulted in behavioural outcomes that were related to embryonic Hg2+uptake. Response latency increased with exposure level and displayed an increase of ×1·5–2·5 over control values (ANOVA,P< 0·01). TheVmaxdecreased with exposure level to a low of 71% of control at the highest Hg2+concentration (ANOVA,P< 0·01). Duration of behaviour displayed a biphasic response pattern in which exposure to 0, 50 or 75 ppb Hg2+did not result in a significantly different response yet exposure to 25 ppb Hg2+caused a significantly longer time of active response (ANOVA,P< 0·01). Repeated stimulation (1, 2 or 4 hits s−1) resulted in a concentration‐dependent increase in response failures. Regardless of stimulation frequency, larvae exposed to 0 or 25 ppb Hg2+as embryos maintained higherVmaxlevels for longer intervals during the testing period than those exposed as embryos to either 50 or 75 ppb Hg2+.

A New Experimental System for the Extended Application of Cyclic Hydrostatic Pressure to Cell Culture

Mechanical forces have been shown to be important stimuli for the determination and maintenance of cellular phenotype and function. Many cells are constantly exposed in vivo to cyclic pressure, shear stress, and/or strain. Therefore, the ability to study the effects of these stimuli in vitro is important for understanding how they contribute to both normal and pathologic states. While there exist commercial as well as custom-built devices for the extended application of cyclic strain and shear stress, very few cyclic pressure systems have been reported to apply stimulation longer than 48 h. However, pertinent responses of cells to mechanical stimulation may occur later than this. To address this limitation, we have designed a new cyclic hydrostatic pressure system based upon the following design variables: minimal size, stability of pressure and humidity, maximal accessibility, and versatility. Computational fluid dynamics (CFD) was utilized to predict the pressure and potential shear stress within the chamber during the first half of a 1.0 Hz duty cycle. To biologically validate our system, we tested the response of bone marrow progenitor cells (BMPCs) from Sprague Dawley rats to a cyclic pressure stimulation of 120/80 mm Hg, 1.0 Hz for 7 days. Cellular morphology was measured using Scion Image, and cellular proliferation was measured by counting nuclei in ten fields of view. CFD results showed a constant pressure across the length of the chamber and no shear stress developed at the base of the chamber where the cells are cultured. BMPCs from Sprague Dawley rats demonstrated a significant change in morphology versus controls by reducing their size and adopting a more rounded morphology. Furthermore, these cells increased their proliferation under cyclic hydrostatic pressure. We have demonstrated that our system imparts a single mechanical stimulus of cyclic hydrostatic pressure and is capable of at least 7 days of continuous operation without affecting cellular viability. Furthermore, we have shown for the first time that BMPCs respond to cyclic hydrostatic pressure by alterations in morphology and increased proliferation.

Mechanical vibratory stimulation of feline forepaw skin induces long‐lasting potentiation in the secondary somatosensory cortex

We investigated the long-lasting effects of mechanical vibratory stimulation of the skin on the excitability of feline cortical neurons in the forelimb areas of the primary (SI) and secondary (SII) somatosensory cortices. Conditioning mechanical stimuli were 300 bursts of 10 pulses at 200 Hz delivered with a 10-s interburst interval from a mechanical stimulator. Test field potentials and unit discharges were evoked by electrical stimulation to the ventral posterolateral thalamic nucleus (VPL) or by single mechanical stimuli applied to the skin. In SII, the mechanical burst stimulation to the skin increased the amplitudes of field potentials and the frequency of unit discharges elicited by single mechanical stimuli applied to the skin. The vibratory conditioning stimulus also produced a similar potentiation of the VPL-evoked field potentials (126-139% increase in amplitude, P < 0.05) with an associated increase in firing rates of extracellularly recorded neuronal activity (117%, P < 0.001). These potentiations persisted through the entire experimental period of 120 min. The translaminar current source density analysis calculated from the VPL-evoked field potentials increased to 127% of the control value (P < 0.01). In contrast, in SI we observed no significant changes in the field potential amplitudes or in the currents generated in superficial layers (91-117%). Taken together with the previous finding that tetanic electrical stimulation of VPL induces long-lasting potentiation of the VPL-evoked cortical responses in SII but not of those in SI, the present results suggest that SII has a large capacity for the rapid functional plasticity involved in the learning that occurs during repeated tactile experiences.

An electrophysiological study of the mechanoreceptory function of abdominal sense organ of the scallop Patinopecten yessoensis (JAY)

1. 1. Functional properties of mechanoreceptor cells of the scallop abdominal sense organ were investigated by recording impulse activity from thin bundles of nerve fibres. 2. 2. A nerve innervating the organ contains three groups of fibres differing in the nature of the impulse activity. Fibres of groups I and II innervate mechanoreceptor cells of the organ and fibres of group III mechanoreceptors located at its base. 3. 3. Fibres of group I showed a response to vibrostimulation of the abdominal sense organ at a frequency 20–1000 Hz. The maximal sensitivity of mechanoreceptors innervated by these fibres was detected at a frequency of 250–300 Hz. In some cases the threshold of response was attained at a vibrostimulus amplitude of 0.006 μm. 4. 4. In fibres of group II impulse reaction to vibration of the abdominal sense organ was registered at 20–340 Hz. The minimal threshold values for mechanoreceptors innervated by this group of fibres was 0.008 μm. 5. 5. Mechanoreceptors innervated by fibres of group III showed a fast adaptation to low frequency vibration. The threshold of response of these mechanoreceptors to single mechanical stimuli was 0.8 μm. 6. 6. The measurements showed that the conductance rates of fibre groups innervating the abdominal sense organ were respectively, 0.32 and 0.42 m/sec and that of fibres innervating mechanoreceptors at the base of the organ was 0.91 m/sec.

Sensory functions in chronic neuralgia.

Eleven patients with sustained neuralgia, in most cases after traumatic nerve lesion, were subjected to quantitative sensory testing with thermal and non-noxious mechanical stimuli. Measurements were made in the pain area and at a homologous site on the contralateral normal side. All patients were hypoaesthetic with raised thresholds for warm and cold or touch, or both. Thermal pain thresholds were also raised in some patients but lowered in others indicating hypersensitivity of the nociceptor system or dysaesthesia for thermal input. In six patients single mechanical stimuli produced a painful response above the touch detection threshold. Reaction time measurements indicated that this painful response to suprathreshold mechanical pulses was measured by magnitude estimation as a function of stimulus amplitude. The results were fitted by power functions, as in normal skin, but with steeper slopes on the abnormal side. Suprathreshold hyperaesthesia (recruitment) may exist in the presence of normal threshold functioning.

THE RELATIONS OF THE INDIVIDUAL AMPULLÆ OF THE SEMICIRCULAR CANALS TO THE INDIVIDUAL EYE MUSCLES

1. The reflex effect of direct mechanical stimulation of the exposed ampulla of the horizontal canal has been graphically recorded for each of the six extrinsic muscles of the eyeball. 2. Stimulation of a horizontal ampulla evokes a strong contraction of the homolateral rectus internus and of the contralateral rectus externus; at the same time the homolateral rectus externus and the contralateral rectus internus relax. 3. A single mechanical stimulus applied to the horizontal ampulla is sometimes followed by a nystagmus resulting from a series of rhythmic contractions of the externus and internus muscles. 4. Excitation of a horizontal ampulla gives rise to weak contractions of the superior and inferior recti and of the two oblique muscles of both eyes, simultaneously with the stronger contractions of the externus and internus respectively. 5. It is pointed out that the small simultaneous contractions of the four muscles just mentioned provide a virtual axis upon which the eyeball rotates. In other words these four act as fixation muscles. 6. It is suggested that some of the abnormal responses to horizontal rotation, seen in clinical cases, are due to the inaction of one or more of the fixation muscles.