One of my coworkers asked me if I could build a model of human heart for an elementary school anatomy unit. I took the challenge to heart. After looking at what the internet had to offer (ie: here and here) I decided that I could do better.
I wanted to use one-way valves (found at the entrance and exit of the ventricles) so that a fluid could be pumped realistically through the model. I was able to find some one-way valves at a local hardware store: the rest of the design followed from the valves.
The model has (of course) four chambers. Each chamber is a sealed Ziploc bag — more about these later. The chambers sit in plastic tubs, which hold the valves in place in addition to catching any leakage.
The circulatory system is simplified greatly: I have about 1 metre of plastic tubing to represent the arteries/veins to and from the lungs and the body. The emphasis here was to construct a 4-cycle pump, but adding some T-joints to create a more realistic aorta wouldn’t be too difficult. In the following picture, you can see that the tubing fits snugly onto the adaptor, which is screwed onto the one-way valve using plumber’s tape to get a good seal. I used some hot glue to hold the whole mess in place.
The most difficult part of this project was the Ziploc bags. I tried using balloons and a variety of plastic bags and sealing techniques before settling on the following approach. I cut small holes in the bottom corners of the Ziploc bag, then passed an inch-long piece of tubing through the bag from the inside. This gave a pretty good seal, which I held in place with electrical tape. Heat-shrinking the plastic didn’t work for me.
When squeezing the chambers, the Ziploc bags have a tendency to leak. Most of this comes from the zip seal popping open, but the bottom corners (as in the above photo) leak as well. The difficulty is getting a good, steady pressure on the Ziploc bag. Now it’s up to the fourth grade students to show me whether this model is feasible for use in the classroom!