Computational Hemodynamic Investigation of Bileaflet and Trileaflet Mechanical Heart Valves.

BACKGROUND AND AIM OF THE STUDY: The trileaflet heart valve is a more desirable mechanical heart valve due to its similarity to native heart valves, which produce a central blood flow with decreased blood flow disturbance. There are, however, many challenges and difficulties in designing a trileaflet valve, mainly due to a greater number of moving mechanical parts. METHODS: The flow profiles through a bileaflet mechanical heart valve (BMHV) and a trileaflet mechanical heart valve (TMHV) were compared at downstream regions. Geometric models of a 29 mm St. Jude Medical BMHV and a TMHV were used and positioned at the anatomic position in a curved aortic downstream geometry. Three-dimensional numerical simulations for both types of mechanical heart valve were performed under normal physiological pulsatile flow conditions. Flow profiles were studied under three different implantation locations at Z = 1D (D = 29 mm inlet diameter), 2D and 4D along the aorta centerline during peak systole. RESULTS: The simulation results showed different flow fields at the downstream positions at Z = 1D and 2D. The leaflets of the BMHV obstructed the flow, while the TMHV allowed a central orifice flow which resulted in a more physiological flow profile. Further downstream, at Z = 4D, the flow fields shared similarities in terms of the flow profile and velocity magnitude. CONCLUSION: The findings of this study may help to further improve the development of the TMHV.

Comparison of hinge microflow fields of bileaflet mechanical heart valves implanted in different sinus shape and downstream geometry.

The characterization of the bileaflet mechanical heart valves (BMHVs) hinge microflow fields is a crucial step in heart valve engineering. Earlier in vitro studies of BMHV hinge flow at the aorta position in idealized straight pipes have shown that the aortic sinus shapes and sizes may have a direct impact on hinge microflow fields. In this paper, we used a numerical study to look at how different aortic sinus shapes, the downstream aortic arch geometry, and the location of the hinge recess can influence the flow fields in the hinge regions. Two geometric models for sinus were investigated: a simplified axisymmetric sinus and an idealized three-sinus aortic root model, with two different downstream geometries: a straight pipe and a simplified curved aortic arch. The flow fields of a 29-mm St Jude Medical BMHV with its four hinges were investigated. The simulations were performed throughout the entire cardiac cycle. At peak systole, recirculating flows were observed in curved downsteam aortic arch unlike in straight downstream pipe. Highly complex three-dimensional leakage flow through the hinge gap was observed in the simulation results during early diastole with the highest velocity at 4.7 m/s, whose intensity decreased toward late diastole. Also, elevated wall shear stresses were observed in the ventricular regions of the hinge recess with the highest recorded at 1.65 kPa. Different flow patterns were observed between the hinge regions in straight pipe and curved aortic arch models. We compared the four hinge regions at peak systole in an aortic arch downstream model and found that each individual hinge did not vary much in terms of the leakage flow rate through the valves.

Numerical analysis of the hemodynamic performance of bileaflet mechanical heart valves at different implantation angles.

BACKGROUND AND AIM OF THE STUDY: The effects of the implantation angle of bileaflet mechanical heart valves (BMHVs) on the sinus region and downstream flow profiles were investigated. Three-dimensional numerical simulations of BMHVs were performed under physiologic pulsatile flow conditions. The study aim was to examine how the flow fields of different aortic sinus shapes and the downstream aortic arch geometry would be affected by implantation angle. METHODS: Two geometric models of sinus were investigated: a simplified axisymmetric sinus; and a three-sinus aortic root model, with two different downstream geometries, namely a straight pipe and a simplified curved aortic arch. A 29 mm St. Jude Medical BMHV geometric model was used and positioned at four different angles (0 degrees, 30 degrees, 60 degrees and 90 degrees). RESULTS: The simulation results showed variation in downstream flow profiles at different implantation angles. Generally, at position Z = 1D along the centerline (where Z refers to the axis normal to the x-y plane and D is the inlet diameter), the triple-jet structures were observed with a slight shift of the center jet for three-sinus aortic cases. Apparent differences were observed at position Z = 2D and 4D, such as higher velocity profiles at the inner arch wall. The flow field downstream of the valve implanted at 0 degrees (anatomic position) showed the smallest overall asymmetry at peak systole, while the flow field downstream of the valve implanted at 90 degrees (anti-anatomic position) exhibited high regions of recirculation. CONCLUSION: Valve orientation was found not to affect the shear stress distribution significantly in the downstream aorta, and this was in agreement with the findings of earlier studies.

Scalable alignment of three-dimensional cellular constructs in a microfluidic chip.

There have been considerable efforts to engineer three-dimensional (3D) microfluidic environments to enhance cellular function over conventional two-dimensional (2D) cultures in microfluidic chips, but few involve topographical features, such as micro/nano-grooves, which are beneficial for cell types of cardiac, skeletal and neuronal lineages. Here we have developed a cost-effective and scalable method to incorporate micro-topographical cues into microfluidic chips to induce cell alignment. Using commercially available optical media as molds for replica molding, we produced large surface areas of polydimethylsiloxane (PDMS) micro-grooved substrates and plasma-bonded them to multiple microfluidic chips. Besides aligning a 2D monolayer of cells, the micro-grooved substrate can align 3D cellular constructs on chip. C2C12 mouse myoblasts were cultured three-dimensionally in a microfluidic chip with incorporated PDMS micro-grooved substrate remodeled into an aligned 3D cellular construct, where the actin cytoskeleton and nuclei were preferentially oriented along the micro-grooves. Cells within the 3D cellular constructs can align without being in direct contact with the micro-grooves due to synergism between topography and fluid shear stress. Aligned C2C12 3D cellular constructs showed enhanced differentiation into skeletal muscles as compared to randomly aligned ones. This novel method enables the routine inclusion of micro-topographical cues into 2D or 3D microfluidic cultures to generate relevant physiological models for studying tissue morphogenesis and drug screening applications.