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Objective To investigate the influence of graft-host diameter ratio on the flow field of fully-occluded artery bypass grafts and provide a theoretical guidance for reducing restenosis in artery bypass graft surgery. Methods Five models were employed to numerically investigate the influence of graft-host diameter ratio on the flow field of fully-occluded artery bypass grafts. The distributions of hemodynamic parameters such as velocity, second flow, wall shear stress (WSS) and wall shear stress gradient (WSSG) and their change in line with the increase of diameter ratio were analyzed. In addition, comparison of hemodynamic differences in a fully-occluded complete model (Model A), a fully-occluded partial model (Model B) and a 75% stenosis complete model (Model C) with graft-host diameter ratio of 1.0 was conducted to validate the fully-occluded complete model established in this study. Results The hemodynamic performance of Model A was totally different from that of Model C, and the velocity distribution at the graft top had an obvious influence on the WSS distribution at host artery bed in the downstream anastomosis, with maximum WSS differences reaching 79%. A large graft-host diameter ratio resulted in a large size of low WSS region at the host artery bed, but with uniformly distributed WSS and small WSSG. A small graft-host diameter ratio resulted in a small size of low WSS region at the host artery bed, but with large WSSG. Conclusions It is necessary to adopt a complete model to study the influence of graft-host diameter ratio on the flow field of fully-occluded artery bypass grafts. The diameter ratio had a significant impact on the flow field of fully-occluded artery bypass graft, thus a large ratio could be helpful to reduce the occlusion resulted from the restenosis at the downstream anastomosis in artery bypass graft.
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Objective To investigate effects of pressure and tail suspension on the growth of rat skeletal muscles by establishing the tail-suspended rat model and pressure-induced rat model, respectively. Methods Thirty-six male Sprague-Dawley rats were randomly divided into three groups: the control-group (CON), the tail-suspended group (SUS), the pressure group (PRE), and each group was undergoing two stages (7, 14 d) for observation. At the end of the experiment, the muscle wet weight/body weight (Mww/Bw), muscle fiber cross-sectional area (MFCSA), muscle fiber diameter (MFD) of soleus and extensor digitorum longus (EDL) and the IGF-1 concentration were measured, respectively. Results For both the SUS group and PRE group with 7 d, their Mww/Bw, MFCSA and MFD of soleus were significantly reduced (P<0.05) as compared to the CON group, which were reduced by 23.52%, 14.26%, 13.47% in PRE group, respectively, while these indexes in SUS group were reduced by 23.52%, 33.07%, 25.09%, respectively. Meanwhile, the decrease of Mww/Bw, MFCSA and MFD in PRE group with 14 d was reduced by 20.51%, -10.49%, -5.73%, respectively, which was less than that in PRE group with 7 d. However, the decrease of Mww/Bw in SUS group with 14 d reached 46.15%, showing significantly higher than that of the SUS group with 7 d. For the IGF-1 concentration and EDL changes, no remarkable differences were found among the CON, PRE and SUS groups. Conclusions The impact of pressure on the process of soleus growth is different from that of the suspension (disuse). During the early stage of pressure application, the deep tissue injury mainly with inflammatory responses can be found in the muscle. When the muscle cells adapt to the pressure environment, they may produce a functional adaptation to growth. Therefore, such effect of socket pressure on skeletal muscle should be considered in clinic for prosthetic socket design or rehabilitation training, which will help protect the muscle tissues.
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Objective To investigate effects from the protrusion height of drug-eluting stent (DES) on kinetics of drug release and hemodynamics, so as to provide references for the optimization of DES design. Methods Based on computational fluid dynamics (CFD), coupling analysis on kinetics of drug release and hemodynamics was conducted by studying three stent models with different protrusion height to numerically investigate the distribution of drug concentration and wall shear stress. Results The increase in protrusion height of the stent was beneficial to the drug deposition; however, it could also increase the length in the low shear stress area. Comparatively, the increase percentage of drug concentration with the increasing protrusion height was remarkably less than that of the increasing length in low shear stress area. Conclusions By comprehensive consideration of both the drug concentration and wall shear stress, lower protrusion height is recommended for DES so as to effectively reduce the risk of restenosis.
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Objective To study the effect from drug diffusion coefficient of atherosclerotic plaque on drug diffusion within the arterial wall, so as to truly reflect the drug distributions. Methods Using computational fluid dynamics (CFD) method, five plaque models with different diffusion coefficients were employed to numerically investigate the distributions of drug concentration both within the arterial wall and the plaque. Results The drug concentration in the arterial wall was increased gradually with the diffusion coefficient of the plaque increased; however, the increment would become gentle. Conclusions When the diffusion coefficient in the plaque was smaller than the tissue, the plaque inhibited the drug diffusion within the arterial wall, or conversely, it would promote the diffusion. Especially when the diffusion coefficient in the plaque was much larger than the tissue, it no longer affected the drug diffusion within the arterial wall. It is necessary to consider the impact of plaque in further research, which is beneficial to the optimization design of drug-eluting stents.
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Objective To investigate the influence of the location of drug release and the stent spacing on drug deposition in curved artery walls. Method 2D curved artery and strut models were employed to carry out a numerical investigation on drug deposition under different drug release surfaces or stent spacing ( 1 strut length, 3 strut lengths, 7 strut lengths ). The results were compared with those in a straight artery. Results The drug depositions produced by four different surfaces of a single strut were quite different. Compared with the curved artery, the superiority of drug release from the top surface of the straight artery was reduced, while the weakness of drug release from proximal surface was substantially increased. There was no significant change for drug release from the distal surface. The average drug concentration increased with interstrut spacing increasing, but the percentage increase was less than that in the straight artery. Concentration differences were observed between the inside and outside of the curved artery, which on the outside showed much lower. Conclusions The local flow alteration, the drug release location and the stent spacing have significant effects on drug deposition in a curved artery and the result is obviously different from that in a straight artery.
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Objective To study the flow field of a new vascular bioreactor with small diameter at different operating conditions. Method To investigate the flow field of a new vascular bioreactor with small diameter under three operating conditions by numerical simulation: outer box rotating, inner box rotating and both inner box and outer box rotating. A comparison of parameters such as flow velocity and shear stress was made. Results The culture medium in the bioreactor rotated with the inner box and outer box, and the velocity was uniformly distributed; the bioreactor could therefore provide a low shear stress environment that is nondestructive for the cells in the medium; the shear stress in bioreactor had a quadratic function relation with the rotation rate. Conclusions This bioreactor could provide a good culture environment for vascular tissue regeneration, and this study provided theoretical basis for the experimental research of bioreactors.