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Purpose Despite widespread use of 3-dimensional (3D) micro-porous scaffolds to promote their potential application in cartilage tissue engineering, only a few studies have examined the response to hydrostatic pressure of engineered constructs. A high cyclic pressurization, currently believed to be the predominant mechanical signal perceived by cells in articular cartilage, was used here to stimulate bovine articular chondrocytes cultured in a synthetic 3D porous scaffold (DegraPol). Methods Construct cultivation lasted 3 days with applied pressurization cycles of amplitude 10 MPa, frequency 0.33 Hz, and stimulation sessions of 4 hours/day. Results At 3 days of culture, with respect to pre-culture conditions, the viability of the pressurized constructs did not vary, whereas it underwent a 16% drop in the unpressurized controls. Synthesis of α-actin was 34% lower in all cultured constructs. Synthesis of collagen II/collagen I did not vary in pressurized constructs, was 76% lower in unpressurized controls, and was around 230% higher in pressurized constructs with respect to unpressurized controls. Chondrocytes showed a phenotypic spherical morphology at time zero and at 3 days of pressurized culture. Conclusions Although the passage from 2D expansion to 3D geometry was effective to guide cell differentiation, only mechanical conditioning enabled the maintenance and further cell differentiation toward a mature chondrocytic phenotype.

Percutaneous pulmonary valve implantation is a potential treatment for right ventricular outflow tract (RVOT) dysfunction. However, RVOT implantation site varies among subjects and the success of the procedure depends on RVOT morphology selection. The aim of this study was to use in vitro testing to establish percutaneous valve competency in different previously defined RVOT morphologies. Five simplified RVOT geometries (stenotic, enlarged, straight, convergent, and divergent) were manufactured by silicone dipping. A mock bench was developed to test the percutaneous valve in the five different RVOTs. The bench consists of a volumetric pulsatile pump and of a hydraulic afterload. The pump is made of a piston driven by a low inertia programmable motor. The hydraulic afterload mimics the pulmonary input impedance and its design is based on a three element model of the pulmonary circulation. The mock bench can replicate different physiological and pathological hemodynamic conditions of the pulmonary circulation. The mock bench is here used to test the five RVOTs under physiological-like conditions: stroke volume range 40-70 mL, frequency range 60-80 bpm. The valved stent was implanted into the five different RVOT geometries. Pressures upstream and downstream of the valved stent were monitored. Flow rates were measured with and without the valved stent in the five mock RVOTs, and regurgitant fraction compared between the different valved stent RVOTs. The percutaneous valved stent drastically reduced regurgitant flow if compared with the RVOT without the valve. RVOT geometry did not significantly influence the flow rate curves. Mean regurgitant fractions varied from 5% in the stenotic RVOT to 7.3% in the straight RVOT, highlighting the influence of the RVOT geometry on valve competency. The mock bench presented in this study showed the ability to investigate the influence of RVOT geometry on the competence of valved stent used for percutaneous pulmonary valve treatment.

Mechanical stimuli have been shown to enhance chondrogenesis on both animal and human chondrocytes cultured in vitro. Different mechanical stimuli act simultaneously in vivo in cartilage tissue and their effects have been extensively studied in vitro, although often in a separated manner. A new bioreactor is described where different mechanical stimuli, i.e. shear stress and hydrostatic pressure, can be combined in different ways to study the mechanobiology of tissue engineered cartilage. Shear stress is imposed on cells by forcing the culture medium through the scaffolds, whereas a high hydrostatic pressure up to 15 MPa is generated by pressurizing the culture medium. Fluid-dynamic experimental tests have been performed and successful validation of the bioreactor has been carried out by dynamic culture of tissue-engineered cartilage constructs. The bioreactor system allows the investigation of the combined effects of different mechanical stimuli on the development of engineered cartilage, as well as other possible three-dimensional tissue-engineered constructs.

The design criteria of an extracorporeal circuit suitable for pulsatile flow are quite different and more entangled than for steady flow. The time and costs of the design process could be reduced if mutual influences between the pulsatile pump and other extracorporeal devices were considered without experimental trial-and-error activities. With this in mind, we have developed a new lumped-parameter mathematical model of the hydraulic behavior of the arterial side of an extracorporeal circuit under pulsatile flow conditions. Generally, components feature a resistant-inertant-compliant behavior and the most relevant nonlinearities are accounted for. Parameter values were derived either by experimental tests or by analytical analysis. The pulsatile pump is modeled as a pure pulsatile flow generator. Model predictions were compared with flow rate and pressure tracings measured during hydraulic tests on two different circuits at various flow rates and pulse frequencies. The normalized root mean square error did not exceed 24% and the model accurately describes the changes that occur in the basic features of the pressure and flow wave propagating from the pulsatile pump to the arterial cannula.

separate stages of operative corrections. 1,2 The first stage involves re-fashioning the pulmonary trunk into a neo-aorta so that it is possible to establish an unrestricted systemic circulation. An interpositional, or systemic-to-pulmonary arterial, shunt is then created between the neo-aorta and the pulmonary arteries to allow pulmonary perfusion and gas exchange. Two of the available options for the systemic-to-pulmonary shunt are the central shunt and the right modified Blalock-Taussig shunt. In the setting of a central shunt, pulmonary perfusion is derived from a conduit placed between the pulmonary arterial bed and the neo-aorta whereas, in the modified Blalock-Taussig shunt, the conduit is interposed between one of the pulmonary arteries and the brachiocephalic artery. In subsequent stages, pulmonary perfusion is provided directly by deoxygenated blood. This is achieved by connecting, first, the superior caval vein, and then the inferior caval vein, to the pulmonary arteries. It is usually during the second stage that the systemic-to-pulmonary shunt is removed.Satisfactory recovery and progression from the first stage has been the major prognostic determinant for these patients. Coronary arterial insufficiency, as a result of the diastolic run-off inherent with an interpositional shunt, in addition to having the systemic and pulmonary circulations in parallel, has long been thought to be an important limiting factor for survival. The precise mechanism for this so-called "coronary steal phenomenon", however, has been poorly understood.From the stance of modelling, the study of fluid dynamics in the first stage of the Norwood sequence is a very critical and challenging issue. Previous studies have been limited to either three-dimensional computational models, or in vitro models of the local fluid dynamics exclusively in the systemic-to-pulmonary arterial shunt. [3][4][5][6] In such studies, boundary conditions were enforced for the model, without any feedback from or to the remainder of the circulatory network. Others have used lumped-parameter models of the Norwood circulation. 7,8 Numerical simulations in one such study 7 showed that: larger shunts diverted an increased proportion of cardiac output to the lungs, away from the systemic perfusion, resulting in decreased delivery of oxygen; the systemic vascular resistance exerted a greater effect on the haemodynamics than did the pulmonary vascular resistance; saturations of oxygen in the veins correlated better with delivery of oxygen than arterial saturation; an equal ratio of pulmonary-to-systemic flows resulted in optimal delivery of oxygen in all physiological states and for all sizes of shunt.