One thing I haven't tried that's used in fluid simulations is velocity smoothing. Basically you average out the velocity of the particles around another particle, where the weight they have in the average depends on the distance.
Your example is super, i will using some ideas from the distance. But you are a bit misunderstood my message. I'm not trying to make a liquid - I create a world with lots of organisms, and apply all the forces of physics for all I have not included in the plans. Well, I'm talking about the first three examples. And I'm trying to do it all with dynamic figures, now I will explain.
That is the concept like this: there is a cell, it is divided, creating around himself another cell, and so on. These cells create a single microorganism having the force of movement ONLY FROM the original CELL.
That is the idea with joints look more than attractive. I also wanted to cover all the cells of some plastic shell, but the features of the program is not allowed. In your example, I try to think of something, but unfortunately, it is very clumsy method, because the body - it's not a bunch of rabid cells. In general, I will make its source code, look, if not more difficult.