Adipose Derived Stromal/Stem Cells (ASCs) have been gaining recognition as extremely versatile cell source in tissue engineering. The usefulness of ASCs in biofabrication is further enhanced by our demonstration of unique properties of these cells when they are cultured as three dimensional cellular aggregates or spheroids. As described herein, three-dimensional formulations or self-assembling ASC spheroids develop their own extracellular matrix that serves to increase the robustness of the cells to mechanical stresses. The composition of the extracellular matrix can be altered based on the external environment of the spheroids and these constructs can be grown in a reproducible manner and to a consistent size. The spheroid formulation helps preserve the viability and developmental plasticity of ASCs even in defined, serum-free media conditions. For the first time, we show that multiple generations of adherent ASCs produced from these spheroids retain their developmental plasticity and their ability to differentiate into multiple cell/tissue types. These demonstrated properties support the fact that culture expanded ASCs are an excellent candidate cellular material for “organ printing” – the approach of developing complex tissue structures from a standardized cell “ink” or cell formulation.
Summary
This paper proposes a general methodology for the design of vibration control of human‐induced vibrations. This uses a feedback loop for the design of control parameters and accounts for the nature of human excitation and how humans feel the vibration. The methodology developed considers not only single‐input single‐output control systems but also multi‐input multi‐output control systems, especially useful to cancel vibrations coming from modes with closely spaced natural frequencies. The strategy finds simultaneously the optimal placements of a set of inertial mass dampers and the design parameters (control gain matrix for active vibration control, damping ratios and tuning frequencies of tuned mass dampers for passive vibration control). To make this strategy implementable and suitable to human‐induced vibrations, elements such as input‐output frequency weighting, output time weighting, band‐pass filters, actuator dynamics, and nonlinearities are considered within the design. The proposed methodology is illustrated in an application example on a realistic open‐layout floor by designing single‐input single‐output and multi‐input multi‐output active and passive strategies with one and two dampers. Simulation tests are carried out to evaluate the performance of the controllers in terms of their vibration reduction capacity using a performance index indicator.
Active vibration control (AVC) via inertial-mass actuators is a viable technique to mitigate human-induced vibrations in civil structures. A multi-input multi-output (MIMO) AVC has been previously proposed in the literature to simultaneously find the sensor/actuator pairs' optimal placements and tune the control gains. However, the method involved local gradient-based methods, which is not affordable when the number of possible locations of actuators is large. In this case, the computation time to obtain a local solution may be huge and unaffordable, which limits the number of test points and/or actuators/sensors considered. This paper proposes an alternative approach based on a recently proposed meta-heuristic, the Coral Reefs Optimization (CRO) algorithm. More concretely, an enhanced version of the CRO is considered, the Coral Reefs Optimization with Substrate Layer (CRO-SL). The CRO-SL is a competitive co-evolution algorithm in which different exploration procedures are jointly evolved within a single population of potential solutions to the problem. The proposed algorithm is thus able to promote competition among different search methods to solve hard optimization problems. In terms of structural design, this work provides an important step to improve the applicability of AVC systems to real complex structures (with a large number of vibration modes and/or with a large number of test points) by achieving global optimum designs with affordable computation time. A finite element model of a real complex floor structure is used to illustrate the contributions of this paper.
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