Development of viscoelastic tubes similar to blood pump

本研究的目的是制造粘弹性管，其解剖学上相同，功能上等同于天然主动脉。最初在新加坡国立大学开发的旋转成型工作站被用于这项研究。首先，我们尝试用传统的方法制造主动脉弓形管；硅胶液体用刷子涂在模具上后，采用单轴转动。然而，很难制造出均匀厚度的管，也很难控制质量。下一步，使用旋转成型工作站在不同的两轴转速组合、不同的喷涂量、间隔和时间下进行了多次试验和错误。最后确定了1mm厚度管的最佳显影条件为：长、小轴转速分别为0.02rpm和8rpm，硅胶重量为20g，共三次，涂刷间隔为3h。这样，厚度偏差（即标准偏差与平均厚度之比）就可以从30%降低到20%。众所周知，天然主动脉具有特定的力学性能；在增量体积较小的范围内，压力的增加较小，而在增量体积较大的范围内，压力的增加较大。我们尝试过制作多层管，但是没有得到好的结果。因此，其他的实验包含了与硅胶不同的特性。海绵层中间夹着柔软和坚硬的硅胶层。在体积增量大于40%的范围内，该三层管的顺应性值为0.41 1/mmHg，但在体积增量大于40%的范围内，顺应性值降至0.36 1/mmHg，这是由于主要的弹性效应从外部硬硅层转移到内部软硅层。以上发现对旋转成型机的进一步改进具有一定的参考价值。

The purpose of this study was to fabricate viscoelastic tubes, which was anatomically identical and functionally equivalent to the natural aorta. A rotational molding workstation which was originally developed at the National University of Singapore was used for this research. First of all, we tried to fabricate aortic arch-shaped tubes by a conventional method ; a single rotational axis was employed after silicone liquid was painted onto the mold by a brush. However, it was hard to make an even thickness tube, and it was also hard to control the quality. For the next step, several trials and errors were conducted using a rotational molding workstation under various combination of rotational speeds between two axis with different painting volume, interval and times. At last, the optimal condition to develop 1mm-thickness tube was determined as follows : rotational speeds of major and minor axis were 0.02rpm and 8rpm, respectively, a weight of silicone was 20g each for three times, and painting interval was 3hours. Then, thickness deviation which was defined as a ratio between standard deviation and average thickness culd be reduced from 30% to 20%.It was well-known that natural aorta had specific mechanical properties ; increase in pressure is small for the range of less incremental volume, whereas it becomes more for the range of higher incremental volume. We have tried to fabricated multi-layr tube, however, we haven't get a favorable result. So, other trials that contained different properties from silicone was carried out. A sponge layr was sandwiched with soft and stiff silicone layrs. The compliance values of this 3-layr tube was 0.41 1/mmHg in the range of small incremental volume up tp 40%, but it was decreased to 0.36 1/mmHg for over 40%, due to a shift of major elasctic effects from outer stiff to inner soft silicon layr.Above findings were worthwhile for the further improvements of the rotational molding machine.