Need help with an anatomy model repair

Machine Shop Plastics & Composites
#1

Hello! I need some help fixing a model for an anatomy class. The model has a vertical piece with horizontal “filaments” sticking out:
Whole Sarcomere small

These models are old, and the red filaments have been falling off for years. Here is a pic of the end of one of these filaments. It’s got wire encased by some kind of plastic.

20240207_132236
20240207_132236952×462 139 KB

I have no idea what plastic the model is made out of. Probably ABS, but not certain.

I have attempted to repair with superglue, but that won’t hold.

My limited experience says to try e6000 next, but then I need some way to hold the filaments in place while it cures. Plus, I have no idea if there’s a better fix

The vertical portion can be removed from the model and laid flat, like so:
Flat small

Unfortunately, we will need the models for the month of March, and also the last week of April. I can happily bring a filament for you to look at at any point, but the models themselves can’t leave until there is a concrete repair plan. (Not my personal models is why)

Please let me know what suggestions or ideas you have that might be able to fix this problem!
Lyndsey

#2

It may not be possible with clearances however we have two different styles of plastic welders in the machine shop plastics area that might work. I’ve been impressed with the strength of those kind of repairs so far but it’s not always possible and may not be very pretty.

#3

I have no idea what a plastic welder even looks like… I will need help doing this repair…

#5

IDK if the plastic welder is the right answer because I don’t know anything about it … but if is isn’t, I find that 2-part epoxy holds almost everything. I use it on plastic all the time. JB Weld 2-part epoxy (clear) with about 5 minutes working time can be bought in all the big box hardware stores.

You’ll probably have to make some kind of a cardboard template to hold things in place during the 5-10 minutes it takes for it to get hard enough to “let go” of it.

#6

What is the model depicting? If repair is not an option in the timeframe, is there a potential for replacement?

#8

I agree with @John_Marlow : 2 part Epoxy (specifically a 5 minute version) would be my go-to in this situation. Strong, waterproof, immune to most cleaners, sticks to many things, and not as brittle/shock sensitive as CA “super” glue.

Thistothat.com (a great resource for glue advice) also recommends epoxy.

5 min epoxy sets up quickly enough that just holding the parts in place with your hand is an option. Another plan would be to use some strips of painters tape (aka bluetape) to hold a glued-up strand to its neighbors.

Glue up a few, tape them in place, let the glue cure. 10 mins later, repeat with a few more strands. Waiting 10 mins ensures that the glue has kicked off and hardened. Note that full strength requires a 24 hour cure.

IMG_8363

1 Like
#9

How vigorously are the models handled? I agree that 2part epoxy would be best, but you might try low melt hot glue applied carefully and sparingly. I say low melt because you do not know the melting point of the plastic parts. That is not as strong, but it may hold and it has the advantage of setting instantly. There are also quick cure uv resin glues that could work. They are applied and cured with a uv flashlight that usually comes with the kit. Something like this:

https://www.amazon.com/LETS-RESIN-Bonding-Flashlight-Adhesive/dp/B0BJ65T85R/ref=asc_df_B0BJ65T85R/?tag=hyprod-20&linkCode=df0&hvadid=652429219324&hvpos=&hvnetw=g&hvrand=12227503502427914672&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9026950&hvtargid=pla-2008211854251&psc=1&mcid=3d9bfaf9ef5e3fd2b77d1c0299567694

#10

Unfortunately replacement is not an available option. And technically the model is still useful with some of the red filaments missing. It just drives me a little batty that we have this collection of them that have fallen off over the years and it seems like it should be easy to fix. I’ve heard rumors that the class is getting a bunch of money for new things, but this isn’t the only model that is in bad shape.

#11

Generally i have found hot glue to actually be pretty flexible in holding, but variable in longevity. So that actually seems like it would be a good option. I will test a filament before going full scale.

And I’m also hearing y’all suggesting the 5- minute epoxy. I think i will try the hot glue first. That’s quick and simple enough i can do before the next round of use, in mid- late March. And that will give it a chance to see if the hot glue will hold. If not, then i can go with the 5- minute epoxy.

Thanks so much for the suggestions y’all!
Lyndsey

#12

Swimcoyote, I have a different approach. That looks like a sarcomere to me. If so, you may have another option, upgrade instead of repair. If it were me I would incorporate simulated micro-trauma using some 3-d printed collagen bonds to simulated a muscle adhesion. You could also simulate more of the myofibril and use the sarcoplasmic reticulum only on the actin side and possibly along the broken pieces with something white for a sheathe on the outside to help provide support.

I don’t know if either of these approaches are quite right for what you are teaching but perhaps a similar approach may work for you?

#13

I was going to say all of those big words, too, but I thought I would go with “use hot glue” first. Seriously, this is an amazing community.

1 Like
#14

Keoliver, you’re awesome. Have a great one

#15

The model is not just depicting a sarcomere, the important part is how the filaments slide past each other as the myosin heads pull the actin filaments to shorten the whole unit. These models predate decent animation by quite a bit, so it’s true they were more important than they are now. It still helps some students to be able to see/ touch a model in 3 dimensions to understand how a sarcomere actually works. And know what the parts are.

Lyndsey