Hey folks,
I've been considering a bit of a project idea for a while and since I have no idea if it's really feasible I thought I'd pop over here and see if anyone might be able to offer a bit of advice or guidance.

To give a bit of background, I work as a technician in a university anatomy department, assisting with teaching of medical, dental, nursing and science students. A while ago I thought it might be quite fun to see if it's possible to make a replica of a bone out of carbon fibre. My thinking is that it's a nice merger of human anatomy and modern engineering techniques, and that drawing interest to the design will help with engagement. The end product would more be about the aesthetics while replicating accurate anatomy, rather than functionality or anything like that. I'm thinking of something fairly small at the moment, like a collar bone - enough details to be recognisable, but not huge!

I've never worked with composites or moulds before, so wouldn't really know where to begin. I thought that the easiest way might be to make a two part silicone mould, use the mould to do a wet lay up before performing some sort of miracle by trimming down the excess and hoping that the two halves will join up as they should. After gluing them together and an extensive polish it should make quite a replica.

Of course, bones have lots of compound curves and bumps, so getting sheets of CF to conform nicely to the mould without distorting the weave significantly, or even convincing it to fit the mould nicely to get the detail could be tricky. I considered filling the moulds with chopped carbon fibre and resin, which gives a really unique finish but not quite what I'm after.

If anyone has any thoughts, suggestions or guidance I would be more than happy to hear it!

A clavicle shouldn't be TOO difficult, depending on scale. But moulding carbon fiber in a silicone mould is a really tricky thing - you basically cant do it unless you are doing a matched compression moulding technique, and even then it is very difficult to get the carbon to conform to the surface nicely without distorting the silicone.

That said, I cant see this being an easy thing to do with a fibreglass mould, and so I think silicone may still be your best bet. The main part of the bone is dead easy, but the projections will present a challenge. They will cause a lock in a rigid mould, and I daresay they will cause you problems with trapping air. 

It's definitely a tricky little project, and I hope you aren't easily discouraged by a few bad results!

Bad results?! You mean it won't come out perfectly first time?! I think the overall size will be small enough that it won't be too disheartening to have a few that don't work. 

I'm hoping to have it as a 'life size' model - we have a stock of plastic replica teaching bones (so a bit of damage during moulding isn't the end of the world) that are still detailed and accurate. I think in terms of shape a femur would probably be easier to do but the size would make it much more challenging to get right. 

One of my colleagues has done work in making anatomical models and moulds before I shall pick their brain and see what tricks they have up their sleeve. I had considered fibreglass with some sort of release agent but having the piece get stuck in the mould would be a pain. I presume that if you have an excess of resin it will help fill the more detailed projections and bumps but you would still get the weave showing through for the most part. I had considered compression moulding but due to the nature of the original model it would be incredibly difficult to somehow get it evenly smaller. 

I do have access to a vacuum oven so degassing silicone and resin is an option, which may prove useful once i can start trying things. It's quite small, and I think out of autoclave prepreg is going to be prohibitively expensive. At a push, for something I knew would definitely work, it might be doable depending on curing times. I've never really looked into it because I thought it wouldn't be doable - I think vacuum bagging it before going in our tiny oven may be a big enough problem to make it a non starter anyway