The Glomerulus > Bowman’s Capsule > Nephron > Kidney.

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A recent animation project has provided me the opportunity to build one of the most interesting looking structures within the human body as far as I’m concerned, the glomerulus: a jumble of capillaries within the nephrons of the kidneys responsible for filtering urine from the blood. I have actually gotten the chance to build this intricate and beautiful micro organ two times before: once about 8 years ago and then one more time maybe 5 years ago. In both situations I needed to resort to kind of “shorthand” representation of the structure, partly due to time constraints (always a challenging factor in medical animation) but to be totally honest, mostly due to lack of know how as to how best to model it at the time of the projects.

This time, I really wanted to take a step back before diving in and figure out the most efficient and most accurate way to approach the modeling process. After studying several scanning electron microscopy images online, as well as looking at how other medical illustrators have approached it, I decided to begin by building the intricate multi-tentacled octopus-like cells called podocytes separately from the capillaries that they wrap around.

I began in Cinema 4D using the old metaballs object. I drew dozens of spheres from the top view to block out the interlocking “pseudopods”, the feature which gives the podocytes their distinctive look. I then played with the metaball settings until I got the tightest skin around the spheres, while keeping the resolution light enough to be able to almost paint the meatball shape in realtime.

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I built about 4 or 5 variations of the podocytes at different sizes, some large and complex and some simple and small, so I could pick and choose the perfect fit for each section of blood vessel I would be wrapping them onto. In order to begin the wrapping process, I first needed to break up my tubules into small sections. Each cylindrical piece of the tube would need to be individually UV mapped, which I accomplished using the built in bodypaint UV tools. The reason I needed to UV map the glomerulus tubules was that I would be using C4D’s Surface Deformer to wrap the podocytes around the tubes.

This process, although tedious (lots of time spent UV’ing about 20 parts of the tubes) worked pretty well, but I still found that there were still lots of areas beween the separarately wrapped podocytes where there were noticeable gaps. I wasnt getting the feeling that the podocytes were continuous throughout the surfaces of the tubules. I then turned to the plugin Paint On Surface to draw the spheres DIRECTLY onto the surface of the tubules. This proved to be a MUCH MORE efficient way to create the podocytes, and soon realized that I should have done it this way from the start! Here is a VIDEO from the DNS plugin site showing how this workflow works.

If I would do this again, I’d probably take a stab at this via ZBrush which is probably the ultimate way to go for most complex organic shapes like this one. I actually just bought a license of Zbrush recently from a friend who no longer had much use for it, so I do plan on getting up to speed with it soon.

Sometimes you just have to accept that there just isn’t enough time or budget in a project to do things exactly the way you want to, but the results are still good and more importantly, your clients are still over the moon with the end product despite your feelings of not hitting the mark. In time however, and especially with medical animation, where the subjects tend to run in cycles, you will eventually have the chance to do things right.

12 thoughts on “The Glomerulus > Bowman’s Capsule > Nephron > Kidney.

  • Fab work as usual! So funny, as I was reading your description, I started thinking, “Hmm, maybe you could use PaintonSurface, I don’t wanna mess with UVs!” Cheers, thanks for posting. Seems like every medical job I do, I learn 5 new things that make the next one better and faster.

    • Thanks Jeremy. And yes, the process almost always seems to go this way–ie: learning new techniques. I actually learned a lot about the UV tools for this job as well as the surface deformer. The worst is when you finish a long challenging project, and only then realize you could have done it in a fraction of the time using a different workflow. I actually wanted to use the new SKINNER object which is part of the fantastic X-Particles 2 plugin tool set, as it gives the user much more control and is also much faster than the clunky metaball object. I used metaballs as there wasnt a way to get the Skinner to work with the Paint On Surface approach. Thanks for looking!

  • Hi Joel,

    Welcome back to your blog! I’m a big fan of your work and check for new postings every week. Thanks for the great info you share here. Your work is always top-notch and inspirational.

    • Hi Dave–thanks! I’ve been terrible about keeping up with the blog. Too much else going on lately. Thanks for checking it out–I’ll try keep the postings little more regular.

  • Great job, Joel– looks great! It’s been fun watching you work through the process first-hand. Keep pushing yourself and others to do the best work possible🙂

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