Measuring the maximum power of an ex vivo engineered muscle tissue with isovelocity shortening technique

The final aim of muscle tissue engineering (TE) is to create a new tissue able to restore the functionality of impaired muscles once transplanted in the site of injury. Therefore, functional contractile properties close to that of healthy muscles are desirable to allow for a good compatibility and a proper functional contribution. Since skeletal muscles deal with locomotion during their normal activity, an accurate measurement of ex vivo muscle engineered tissues' isotonic properties is crucial. In this paper, we devised an experimental system to measure the mechanical power generated by an ex vivo muscle engineered tissue, the X-MET, based on the isovelocity contraction technique. The X-MET is developed without the use of any scaffolds, so that its mechanical properties are not affected by endogenous components. Our experiments allowed for delimiting the ranges of shortening and shortening velocity for which the tissue is able to generate and maintain power for the entire stimulation, which is the condition that better reproduces muscle physiological activity. Then, we measured the power generated by the X-MET and fit the experimental results to the Hill's equation usually employed for modeling the force-velocity relationship of skeletal muscles. The use of this model yielded to the measurement of maximum power and maximum shortening velocity. Results revealed that most of the isotonic properties were consistent with that proposed in the literature for slow-twitch muscles; in particular, the X-METs were able to generate a maximum power of 2.08± 0.78 W/kg and had a maximum shortening velocity of 1.84 ± 0.57 L₀/s, on average

Remodeled eX vivo muscle engineered tissue improves heart function after chronic myocardial ischemia

: The adult heart displays poor reparative capacities after injury. Cell transplantation and tissue engineering approaches have emerged as possible therapeutic options. Several stem cell populations have been largely used to treat the infarcted myocardium. Nevertheless, transplanted cells displayed limited ability to establish functional connections with the host cardiomyocytes. In this study, we provide a new experimental tool, named 3D eX vivo muscle engineered tissue (X-MET), to define the contribution of mechanical stimuli in triggering functional remodeling and to rescue cardiac ischemia. We revealed that mechanical stimuli trigger a functional remodeling of the 3D skeletal muscle system toward a cardiac muscle-like structure. This was supported by molecular and functional analyses, demonstrating that remodeled X-MET expresses relevant markers of functional cardiomyocytes, compared to unstimulated and to 2D- skeletal muscle culture system. Interestingly, transplanted remodeled X-MET preserved heart function in a murine model of chronic myocardial ischemia and increased survival of transplanted injured mice. X-MET implantation resulted in repression of pro-inflammatory cytokines, induction of anti-inflammatory cytokines, and reduction in collagen deposition. Altogether, our findings indicate that biomechanical stimulation induced a cardiac functional remodeling of X-MET, which showed promising seminal results as a therapeutic product for the development of novel strategies for regenerative medicine

Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe

Measuring the X-MET’s maximum power: a preliminary study

The measurement of the mechanical properties is a crucial point for new engineered muscle tissues. The final aim is to implant these tissues to substitute or restore the functionality of impaired muscles, so that functional properties as close as possible to the healthy native muscles are required. We developed an engineered skeletal muscle tissue, X-MET, whose strong point is to be created without any endogenous component. This construct is able to contract spontaneously as well as to respond to electrical stimulation. In this work, we developed an experimental system to measure for the first time, the power developed by the X-MET. The power was measured by applying the isovelocity contraction technique. This technique has never been applied on muscle engineered tissues so far, so the aim of this work was to find out the optimal stimulation parameters. Once determined the range of displacement and velocity of shortening for which the X-MET was able to develop power, we proceeded looking at the optimal parameters allowing the production of its maximum power. Preliminary tests showed that the X-MET generates the optimal power when stimulated to shorten 3% of its ideal length at a speed of 0.2 L0/s

The development of an innovative embedded sensor for the optical measurement of ex-vivo engineered muscle tissue contractility

Tissue engineering is a multidisciplinary approach focused on the development of innovative bioartificial substitutes for damaged organs and tissues. For skeletal muscle, the measurement of contractile capability represents a crucial aspect for tissue replacement, drug screening and personalized medicine. To date, the measurement of engineered muscle tissues is rather invasive and not continuous. In this context, we proposed an innovative sensor for the continuous monitoring of engineered-muscle-tissue contractility through an embedded technique. The sensor is based on the calibrated deflection of one of the engineered tissue's supporting pins, whose movements are measured using a noninvasive optical method. The sensor was calibrated to return force values through the use of a step linear motor and a micro-force transducer. Experimental results showed that the embedded sensor did not alter the correct maturation of the engineered muscle tissue. Finally, as proof of concept, we demonstrated the ability of the sensor to capture alterations in the force contractility of the engineered muscle tissues subjected to serum deprivation

Electric field distribution analysis for the design of an electrode system in a 3D neuromuscular junction microfluidic device

Electrical stimulation (ES) highly influences the cellular microenvironment, affecting cell migration, proliferation and differentiation. It also plays a crucial role in tissue engineering to improve the biomechanical properties of the constructs and regenerate the damaged tissues. However, the effects of the ES on the neuromuscular junction (NMJ) are still not fully analyzed. In this context, the development of a specialized microfluidic device combined with an ad-hoc electrical stimulation can allow a better investigation of the NMJ functionality. To this aim, we performed an analysis of the electric field distribution in a 3D neuromuscular junction microfluidic device for the design of several electrode systems. At first, we designed and modeled the 3D microfluidic device in order to promote the formation of the NMJ between neuronal cells and the muscle engineered tissue. Subsequently, with the aim of identifying the optimal electrode configuration able to properly stimulate the neurites, thus enhancing the formation of the NMJ, we performed different simulation tests of the electric field distribution, by varying the electrode type, size, position and applied voltage. Our results revealed that all the tested configurations did not induce an electric field dangerous for the cell vitality. Among these configurations, the one with cylindrical pin of 0.3 mm of radius, placed in the internal position of the neuronal chambers, allowed to obtain the highest electrical field in the zone comprising the neurites