Mechanical vibrations increase the proliferation of articular chondrocytes in high-density culture

In vitro neuronal and glial response to magnetically stimulated piezoelectric poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV)/cobalt ferrite (CFO) microspheres

Polymer biomaterials are being considered for tissue regeneration due to the possibility of resembling different extracellular matrix characteristics. However, most current scaffolds cannot respond to physical-chemical modifications of the cell microenvironment. Stimuli-responsive materials, such as electroactive smart polymers, are increasingly gaining attention once they can produce electrical potentials without external power supplies. The presence of piezoelectricity in human tissues like cartilage and bone highlights the importance of electrical stimulation in physiological conditions. Although poly(vinylidene fluoride) (PVDF) is one of the piezoelectric polymers with the highest piezoelectric response, it is not biodegradable. Poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) is a promising copolymer of poly(hydroxybutyrate) (PHB) for tissue engineering and regeneration applications. It offers biodegradability, piezoelectric properties, biocompatibility, and bioactivity, making it a superior option to PVDF for biomedical purposes requiring biodegradability. Magnetoelectric polymer composites can be made by combining magnetostrictive particles and piezoelectric polymers to further tune their properties for tissue regeneration. These composites convert magnetic stimuli into electrical stimuli, generating local electrical potentials for various applications. Cobalt ferrites (CFO) and piezoelectric polymers have been combined and processed into different morphologies, maintaining biocompatibility for tissue engineering. The present work studied how PHBV/CFO microspheres affected neural and glial response in spinal cord cultures. It is expected that the electrical signals generated by these microspheres due to their magnetoelectric nature could aid in tissue regeneration and repair. PHBV/CFO microspheres were not cytotoxic and were able to impact neurite outgrowth and promote neuronal differentiation. Furthermore, PHBV/CFO microspheres led to microglia activation and induced the release of several bioactive molecules. Importantly, magnetically stimulated microspheres ameliorated cell viability after an in vitro ROS-induced lesion of spinal cord cultures, which suggests a beneficial effect on tissue regeneration and repair.

The role of mitochondrial reactive oxygen species in chondrocyte mechanotransduction

Chondrocytes are mechanosensitive cells able to sense and respond to external mechanical stimuli through the process of mechanotransduction. Previous studies have demonstrated that mechanical stimulation causes mitochondrial deformation leading to mitochondrial reactive oxygen species (ROS) release in a dose-dependent manner. For this reason, we focused on elucidating the role of mitochondrial ROS as anabolic signaling molecules in chondrocyte mechanotransduction. Chondrocyte-seeded agarose gels were subjected to mechanical stimuli and the effect on matrix synthesis, ROS production, and mitogen-activated protein kinases (MAPK) signaling was evaluated. Through the use of ROS-specific staining, superoxide anion was the primary ROS released in response to mechanical stimuli. The anabolic effect of mechanical stimulation was abolished in the presence of electron transport chain inhibitors (complexes I, III, and V) and superoxide anion scavengers. Subsequent studies were centered on the involvement of MAPK pathways (ERK1/2, p38, and JNK) in the mechanotransduction cascade. While disruption of the ERK1/2 pathway had no apparent effect, the anabolic effect of mechanical stimulation was abolished in the presence of p38 and JNK pathway inhibitors. This suggest the involvement of apoptosis stimulating kinase 1 (ASK1), an upstream redox-sensitive MAP3K shared by both the JNK and p38 pathways. Future experiments will focus on the involvement of the thioredoxin-ASK1 complex which disassociates in the presence of oxidative stress, allowing ASK1 to phosphorylate several MAP2Ks. Overall, these findings indicate superoxide anion as the primary ROS released in response to mechanical stimuli and that the resulting anabolic effect on chondrogenic matrix biosynthesis arises from the ROS-dependent activation of the p38 and JNK MAPKs.

Effect of nutrient metabolism on cartilaginous tissue formation

A major shortcoming in cartilage tissue engineering is the low biosynthetic response of chondrocytes. While different strategies have been investigated, a novel approach may be to control nutrient metabolism. Although known for their anaerobic metabolism, chondrocytes are more synthetically active under conditions that elicit mixed aerobic-anaerobic metabolism. Here, we postulate this metabolic switch induces HIF-1α signaling resulting in improved growth. Transition to different metabolic states can result in the pooling of metabolites, several of which can stabilize HIF-1α by interfering with PHD2. Chondrocytes cultured under increased media availability accelerated tissue deposition with the greatest effect occurring at 2 ml/10⁶ cells. Under higher media availability, metabolism switched from anaerobic to mixed aerobic-anaerobic. Around this transition, maximal changes in PHD2 activity, HIF-1α expression, and HIF-1 target gene expression were observed. Loss-of-function studies using YC-1 confirmed the involvement of HIF-1. Lastly, targeted metabolomic studies revealed that intracellular lactate and succinate correlated with PHD2 activity. This study demonstrates that cartilaginous tissue formation can be regulated by nutrient metabolism and that this response is mediated through changes in HIF-1α signaling. By harnessing this newly identified metabolic switch, engineered cartilage implants may be developed without the need for sophisticated methods which could aid translation to the clinic.

Low-frequency mechanical vibration induces apoptosis of A431 epidermoid carcinoma cells

Cancer research is increasingly focused on discovering strategies to induce cancer cell apoptosis without affecting surrounding normal cells. One potential biocompatible method is mechanical vibration, which has been developed as part of the emerging field of mechanomedicine. Previous studies of mechanical vibration have employed high-frequency vibration, which damages healthy cells. In this study, we examined the effects of brief (1 h) low-frequency (20 Hz) mechanical vibration on glucose consumption and survival (apoptosis, necrosis, HMGB1 release) of the human epidermoid carcinoma cell line A431. We found that apoptosis, but not necrosis, was significantly increased at 48 h after mechanical vibration compared with cells maintained in static culture. In keeping with this, extracellular release of HMGB1, a necrosis marker, was lower in cultures of A431 cells subjected to mechanical vibration compared with control cells. Glucose consumption was increased in the first 24 h after mechanical vibration but returned to control levels before the onset of apoptosis. Although the precise intracellular mechanisms by which low-frequency mechanical vibration triggers apoptosis of A431 cells is unknown, these results suggest a possible role for metabolic pathways. Mechanical vibration may thus represent a novel application of mechanomedicine to cancer therapy.

Stochastic Resonance with Dynamic Compression Improves the Growth of Adult Chondrocytes in Agarose Gel Constructs

Dynamic mechanical stimulation has been an effective method to improve the growth of tissue engineering cartilage constructs derived from immature cells. However, when more mature cell populations are used, results are often variable due to the differing responses of these cells to external stimuli. This can be especially detrimental in the case of mechanical loading. In previous studies, multi-modal mechanical stimulation in the form of stochastic resonance was shown to be effective at improving the growth of young bovine chondrocytes. Thus, the aim of this study was to investigate the short-term and long-term effects of stochastic resonance on two groups of bovine chondrocytes, adult (> 30 month) and juvenile (~ 18 months). While the juvenile cells outperformed the adult cells in terms of their anabolic response to loading, combined mechanical loading for both age groups resulted in greater matrix synthesis compared to compressive loading alone. In the adult cells, potential pathological tissue formation was evident with the presence of cell clustering. However, the presence of broad-band mechanical vibrations (alone or with compressive loading) appeared to mitigate this response and allow these cells to attain a growth response similar to the juvenile, unstimulated cells. Therefore, the use of stochastic resonance appears to show promise as a method to improve the formation and properties of tissue engineered cartilage constructs, irrespective of cell age.

"Naturalization" of Routine Assisted Reproductive Technologies by In Vitro Culture of Embryos with Microvibration: Sex Ratio, Body Length, and Weight of 2,456 Live-Birth Deliveries after Transfer of 9,624 Embryos In Vitro Cultured in Static System and with Microvibration

Aim was to determine whether there is any difference in the sex ratio, body length, and body weight of 2,456 deliveries after transfer of 9,624 embryos derived using in vitro culture under static and mechanical microvibration conditions. Pronuclear embryos from 4435 patients were cultured in vitro under two different conditions: without (n = 4821) and with mechanical agitation (n = 4803). Sex ratio, body length, and weight of 2,456 live-birth deliveries after transfer of 9,624 embryos were noted. The proportion of males at birth was significantly associated with mode of in vitro culture of embryos only among women aged 40 years and older. The rate "body length" was significantly associated with mode of in vitro culture of embryos only among women aged 29 and younger. In the same time, among twins, this ratio positively associated with in vitro culture of embryos under microvibration only among women aged 30-34 years as well as ≥40 years and negatively among women aged 35-39 years. It was concluded that birth weight of infants was positively associated with mode of in vitro culture of embryos under microvibration among women of all age groups. This trial registration number is ISRCTN13773904, registered 6 April 2016.

Chondrocyte dedifferentiation increases cell stiffness by strengthening membrane-actin adhesion

OBJECTIVE

Chondrocyte dedifferentiation is known to influence cell mechanics leading to alterations in cell function. This study examined the influence of chondrocyte dedifferentiation in monolayer on cell viscoelastic properties and associated changes in actin organisation, bleb formation and membrane-actin cortex interaction.

METHOD

Micropipette aspiration was used to estimate the viscoelastic properties of freshly isolated articular chondrocytes and the same cells after passage in monolayer. Studies quantified the cell membrane-actin cortex adhesion by measuring the critical pressure required for membrane detachment and bleb formation. We then examined the expression of ezrin, radixin and moesin (ERM) proteins which are involved in linking the membrane and actin cortex and combined this with theoretical modelling of bleb dynamics.

RESULTS

Dedifferentiated chondrocytes at passage 1 (P1) were found to be stiffer compared to freshly isolated chondrocytes (P0), with equilibrium modulus values of 0.40 and 0.16 kPa respectively. The critical pressure increased from 0.59 kPa at P0 to 0.74 kPa at P1. Dedifferentiated cells at P1 exhibited increased cortical F-actin organisation and increased expression of total and phosphorylated ERM proteins compared to cells at P0. Theoretical modelling confirmed the importance of membrane-actin cortex adhesion in regulating bleb formation and effective cellular elastic modulus.

CONCLUSION

This study demonstrates that chondrocyte dedifferentiation in monolayer strengthens membrane-actin cortex adhesion associated with increased F-actin organisation and up-regulation of ERM protein expression. Thus dedifferentiated cells have reduced susceptibility to bleb formation which increases cell modulus and may also regulate other fundamental aspects of cell function such as mechanotransduction and migration.

Magnetically actuated tissue engineered scaffold: insights into mechanism of physical stimulation

Providing the right stimulatory conditions resulting in efficient tissue promoting microenvironment in vitro and in vivo is one of the ultimate goals in tissue development for regenerative medicine. It has been shown that in addition to molecular signals (e.g. growth factors) physical cues are also required for generation of functional cell constructs. These cues are particularly relevant to engineering of biological tissues, within which mechanical stress activates mechano-sensitive receptors, initiating biochemical pathways which lead to the production of functionally mature tissue. Uniform magnetic fields coupled with magnetizable nanoparticles embedded within three dimensional (3D) scaffold structures remotely create transient physical forces that can be transferrable to cells present in close proximity to the nanoparticles. This study investigated the hypothesis that magnetically responsive alginate scaffold can undergo reversible shape deformation due to alignment of scaffold's walls in a uniform magnetic field. Using custom made Helmholtz coil setup adapted to an Atomic Force Microscope we monitored changes in matrix dimensions in situ as a function of applied magnetic field, concentration of magnetic particles within the scaffold wall structure and rigidity of the matrix. Our results show that magnetically responsive scaffolds exposed to an externally applied time-varying uniform magnetic field undergo a reversible shape deformation. This indicates on possibility of generating bending/stretching forces that may exert a mechanical effect on cells due to alternating pattern of scaffold wall alignment and relaxation. We suggest that the matrix structure deformation is produced by immobilized magnetic nanoparticles within the matrix walls resulting in a collective alignment of scaffold walls upon magnetization. The estimated mechanical force that can be imparted on cells grown on the scaffold wall at experimental conditions is in the order of 1 pN, which correlates well with reported threshold to induce mechanotransduction effects on cellular level. This work is our next step in understanding of how to accurately create proper stimulatory microenvironment for promotion of cellular organization to form mature tissue engineered constructs.

Stochastic resonance is a method to improve the biosynthetic response of chondrocytes to mechanical stimulation

Cellular mechanosensitivity is an important factor during the mechanical stimulation of tissue engineered cartilage. While the application of mechanical stimuli improves tissue growth and properties, chondrocytes also rapidly desensitize under prolonged loading thereby limiting its effectiveness. One potential method to mitigate load-induced desensitization is by superimposing noise on the loading waveforms ("stochastic resonance"). Thus, the purpose of this study was to investigate the effects of stochastic resonance on chondrocyte matrix metabolism. Chondrocyte-seeded agarose gels were subjected to dynamic compressive loading, with or without, superimposed vibrations of different amplitudes and frequency bandwidths. Changes in matrix biosynthesis were determined by radioisotope incorporation and subsequent effects on intracellular calcium signaling were evaluated by confocal microscopy. Although dependent on the duration of loading, superimposed vibrations improved cellular sensitivity to mechanical loading by further increasing matrix synthesis between 20-60%. Stochastic resonance also appeared to limit load-induced desensitization by maintaining sensitivity under desensitized loading conditions. While superimposed vibrations had little effect on the magnitude of intracellular calcium signaling, recovery of mechanosensitivity after stimulation was achieved at a faster rate suggesting that less time may be required between successive loading applications. Thus, stochastic resonance appears to be a valuable tool during the mechanical stimulation of cartilage constructs, even when suboptimal stimulation conditions are used.

Effect of whole body vibration training on quadriceps muscle strength in individuals with knee osteoarthritis: a systematic review and meta-analysis

BACKGROUND

Several studies have reported the effects of whole body vibration (WBV) training on muscle strength. This systematic review investigates the current evidence regarding the effects of WBV training on quadriceps muscle strength in individuals with knee osteoarthritis (OA).

DATA SOURCES

We searched PubMed, CINAHL, Embase, Scopus, PEDro, and Science citation index for research articles published prior to March 2015 using the keywords whole body vibration, vibration training, strength and vibratory exercise in combination with the Medical Subject Heading 'Osteoarthritis knee'.

STUDY SELECTION

This meta-analysis was limited to randomized controlled trials published in the English language.

DATA EXTRACTION

The quality of the selected studies was assessed by two independent evaluators using the PEDro scale and criteria given by the International Society of Musculoskeletal and Neuronal Interactions (ISMNI) for reporting WBV intervention studies. The risk of bias was assessed using the Cochrane collaboration's tool for domain-based evaluation. Isokinetic quadriceps muscle strength was calculated for each intervention.

RESULTS

Eighteen studies were identified in the search. Of these, four studies met the inclusion criteria. Three of these four studies reached high methodological quality on the PEDro scale. Out of the four studies, only one study found significantly greater quadriceps muscle strength gains following WBV compared to the control group.

CONCLUSIONS

In three of the four studies that compared a control group performing the same exercise as the WBV groups, no additional effect of WBV on quadriceps muscle strength in individuals with knee OA was indicated.

Effective cell collection method using collagenase and ultrasonic vibration

This study proposes a novel cell collection method based on collagenase treatment and ultrasonic vibration. The method collects calf chondrocytes from a reusable metal cell culture substrate. To develop our concept, we calculated the natural vibration modes of the cell culture substrate by a finite element method, and conducted eigenvalue and piezoelectric-structural analyses. Selecting the first out-of-plane vibration mode of the substrate, which has a single nodal circle, we designed and fabricated the cell collection device. The excited vibration mode properly realized our intentions. We then evaluated the cell collection ratio and the growth response, and observed the morphology of the collected cells. The collagenase and ultrasonic vibration treatment collected comparable numbers of cells to conventional trypsin and pipetting treatment, but improved the proliferating cell statistics. Morphological observations revealed that the membranes of cells collected by the proposed method remain intact; consequently, the cells are larger and rougher than cells collected by the conventional method. Therefore, we present a promising cell collection method for adhesive cell culturing process.

Potential regenerative rehabilitation technology: implications of mechanical stimuli to tissue health

BACKGROUND

Mechanical loads induced through muscle contraction, vibration, or compressive forces are thought to modulate tissue plasticity. With the emergence of regenerative medicine, there is a need to understand the optimal mechanical environment (vibration, load, or muscle force) that promotes cellular health. To our knowledge no mechanical system has been proposed to deliver these isolated mechanical stimuli in human tissue. We present the design, performance, and utilization of a new technology that may be used to study localized mechanical stimuli on human tissues. A servo-controlled vibration and limb loading system were developed and integrated into a single instrument to deliver vibration, compression, or muscle contractile loads to a single limb (tibia) in humans. The accuracy, repeatability, transmissibility, and safety of the mechanical delivery system were evaluated on eight individuals with spinal cord injury (SCI).

FINDINGS

The limb loading system was linear, repeatable, and accurate to less than 5, 1, and 1 percent of full scale, respectively, and transmissibility was excellent. The between session tests on individuals with spinal cord injury (SCI) showed high intra-class correlations (>0.9).

CONCLUSIONS

All tests supported that therapeutic loads can be delivered to a lower limb (tibia) in a safe, accurate, and measureable manner. Future collaborations between engineers and cellular physiologists will be important as research programs strive to determine the optimal mechanical environment for developing cells and tissues in humans.

Calcium signaling as a novel method to optimize the biosynthetic response of chondrocytes to dynamic mechanical loading

Chondrocyte sensitization and desensitization to mechanical stimuli are complex phenomena that have not been fully described. In this study, we investigated the temporal response of chondrocytes to dynamic mechanical loading and whether changes in calcium signaling could be used a predictor of the biosynthetic response. Cell-seeded agarose gels pre-incubated with an intracellular [Formula: see text] dye (Fluo-4) were subjected to dynamic compressive loading under varying conditions (amplitude and duration). Induced changes in Ca(2+) signaling were determined by confocal imaging and matrix biosynthesis by radioisotope incorporation. It was observed that chondrocytes required a minimum amount of stimulation in order to elicit an anabolic response and they quickly became insensitive to the imposed stimulus. The response appeared to be amplitude dependent and could be predicted by measuring resultant changes in Ca(2+) signaling. A positive correlation between Ca(2+) signaling and matrix synthesis was achieved when changes in Ca(2+) signaling was expressed as a relative number of cells experiencing multiple transients. In addition, these changes in Ca(2+) signaling were effective at determining optimal recovery period between successive applications of intermittent mechanical loading, in which full mechanosensitivity was achieved when [Formula: see text] signaling was allowed to return to baseline (control) levels. The use of Ca(2+) signaling to predict the effectiveness of a particular mechanical stimulus as well as to determine optimal refractory periods appears to be advantageous over empirical-based approaches. Future work will investigate the process of Ca(2+) ion sequestration into intracellular stores to elucidate potential desensitization mechanisms to dynamic mechanical loading.

The effect of moving point of contact stimulation on chondrocyte gene expression and localization in tissue engineered constructs

Tissue engineering is a promising approach for articular cartilage repair. However, using current technologies, the developed engineered constructs generally do not possess an organized superficial layer, which contributes to the tissue's durability and unique mechanical properties. In this study, we investigated the efficacy of applying a moving point of contract-type stimulation (MPS) to stimulate the production of a superficial-like layer in the engineered constructs. MPS was applied to chondrocyte-agarose hydrogels at a frequency of 0.5, 1 or 2 Hz, under a constant compressive load of 10 mN for durations between 5 and 60 min over 3 consecutive days. Expression and localization of superficial zone constituents was conducted by qRT-PCR and in situ hybridization. Finite element modeling was also constructed to gain insight into the relationship between the applied stimulus and superficial zone constituent expression. Gene expression of superficial zone markers were affected in a frequency dependent manner with a physiologic frequency of 1 Hz producing maximal expression of PRG4, biglycan, decorin and collagen II. In situ hybridization revealed that localization of these markers predominantly occurred at 500-1000 μm below the construct surface which correlated to sub-surface strains between 10 and 25% as determined by finite element modeling. These results indicate that while mechanical stimuli can be used to enhance the expression of superficial zone constituents in engineered cartilage constructs, the resultant subsurface loading is a critical factor for localizing expression. Future studies will investigate altering the applied stimulus to further localize superficial zone constituent expression at the construct surface.

Culture systems: fluid dynamic embryo culture systems (microfluidics)

The tubal/uterine lumen is a dynamic environment in which oocytes, eggs, and early embryos are submitted to different forces generated by cilia and peristaltic flow of tubal fluid. The movement of the tubal/uterine fluid, the chemical diversity, and their interaction produce a unique environment able to support embryo development and modulate gene expression. Although culture of embryos is supported in static and low complexity chemical conditions, application of fluidic dynamics in assisted reproduction technology to improve outcomes has been in development for almost a decade. Several attempts to build devices able to facilitate fertilization and embryo culture have been made, but dynamic fluidic devices are not yet available for mass scale use in clinical embryology laboratories. Indeed, such devices for embryo culture have been constructed and they are under evaluation in IRB approved studies. Fluid dynamic devices appear to enhance embryo development and they may be innovative resources for clinical and experimental embryology laboratories. This chapter reviews the principles and results of dynamic fluid systems, and the materials and methods required to produce microfunnel dynamic culture systems for use with embryos.

Mechanical stimulation of chondrocyte-agarose hydrogels

Articular cartilage suffers from a limited repair capacity when damaged by mechanical insult or degraded by disease, such as osteoarthritis. To remedy this deficiency, several medical interventions have been developed. One such method is to resurface the damaged area with tissue-engineered cartilage; however, the engineered tissue typically lacks the biochemical properties and durability of native cartilage, questioning its long-term survivability. This limits the application of cartilage tissue engineering to the repair of small focal defects, relying on the surrounding tissue to protect the implanted material. To improve the properties of the developed tissue, mechanical stimulation is a popular method utilized to enhance the synthesis of cartilaginous extracellular matrix as well as the resultant mechanical properties of the engineered tissue. Mechanical stimulation applies forces to the tissue constructs analogous to those experienced in vivo. This is based on the premise that the mechanical environment, in part, regulates the development and maintenance of native tissue(1,2). The most commonly applied form of mechanical stimulation in cartilage tissue engineering is dynamic compression at physiologic strains of approximately 5-20% at a frequency of 1 Hz(1,3). Several studies have investigated the effects of dynamic compression and have shown it to have a positive effect on chondrocyte metabolism and biosynthesis, ultimately affecting the functional properties of the developed tissue(4-8). In this paper, we illustrate the method to mechanically stimulate chondrocyte-agarose hydrogel constructs under dynamic compression and analyze changes in biosynthesis through biochemical and radioisotope assays. This method can also be readily modified to assess any potentially induced changes in cellular response as a result of mechanical stimuli.

Brief daily exposure to low-intensity vibration mitigates the degradation of the intervertebral disc in a frequency-specific manner

Hindlimb unloading of the rat causes rapid hypotrophy of the intervertebral disc (IVD) as well as reduced IVD height and glycosaminoglycan content. Here we tested the hypothesis that low-intensity mechanical vibrations (0.2 g), as a surrogate for exercise, will mitigate this degradation. Four groups of Sprague-Dawley rats (4.5 mo, n = 11/group) were hindlimb unloaded (HU) for 4 wk. In two of the HU groups, unloading was interrupted for 15 min/day by placing rats in an upright posture on a platform that was vertically oscillating at 45 or 90 Hz (HU+45, HU+90). Sham control rats stood upright on an inactive plate for 15 min/day (HU+SC). These three experimental groups were compared with HU uninterrupted by weightbearing (HU) and to normally ambulating age-matched controls. In the HU and HU+SC rats, 4 wk of unloading resulted in a 10% smaller IVD height, as well as less glycosaminoglycan in the whole IVD (7%) and nucleus pulposus (17%) and a greater collagen-to-glycosaminoglycan ratio in the whole IVD (17%). Brief daily exposure to 90 Hz mechanical oscillations mitigated this degradation; compared with HU ± SC, the IVD of HU+90 had an 8% larger height and greater glycosaminoglycan content in the whole IVD (12%) and nucleus pulposus (24%). In contrast, the 45 Hz signal failed to mitigate changes in height or glycosaminoglycan content brought with altered spinal loading, but normalized the collagen-to-glycosaminoglycan ratio to levels observed in age-matched controls. In summary, unloading caused marked phenotypic and biochemical changes in the IVD, a deterioration that was not slowed by brief weightbearing. However, low-intensity 90 Hz vibrations superimposed on weightbearing largely preserved the morphology and biochemistry of the IVD and suggest that these biomechanically based signals may help protect the IVD during long bouts of nonambulation.