Would carbon fiber be a good choice to strengthen human bones, and how would that work?

Question

Background

Hi all, I'm revisiting my musings on plausibly strengthening the human skeleton to better withstand the stresses of combat, melee in particular. If y'all don't care about background, skip to "The Question" two paragraphs below.

In my setting, space marines (in the sense of soldiers who board space-/star-ships, not the Warhammer kind) have always preferred melee combat during boarding actions. In the early days of space-flight, people were still using kinetic weapons to defend themselves, and this practice remains widespread planetside. Aboard starships, however, it was quickly discovered that the bulkheads separating the warring marines and the Void weren't quite up to the challenge of shards of metal flying at obscene speeds.

Rather than wait for starship manufacturers to catch up to this, many pirate factions switched to melee weapons such as swords, spears and shields. These shields are the key: being made of a MacGuffinite alloy (haven't gotten around to naming it yet), it is able to stop most kinetic small-arms fire with very minimal damage to the user. This lead to guard crews and eventually the Space Marine Corps to adopt similar weapons. Nowadays, an advanced and ancient race of humans from another planet has decided for various reasons to adapt the biology of their marines to this new melee combat, so as to not need the obscenely intricate and finnicky powered armor that other factions have taken to using.

The Question

Now, I'm going to address changes to the overall structure (e.g. bone shape, placement, etc.) in another question. For this one, I'm more concerned with the materials, composition, and structure of the bones and ligaments themselves. First off, I've seen somewhere that someone suggested coating the bones in a cartilage membrane. Now, what if we took that to the next level, and interwove that with carbon fiber? Also, could we actually embed a sort of carbon-fiber "rebar" within the bone itself, and potentially even include a core made of more rigid CF (sorta like that stuff new fancy bikes are made of)? This leads to another concern: is it plausible that there are certain enzymes within the cells of the skeletal system that are able to synthesize and lay down this carbon fiber matrix, a sort of carbon-fibrase? As for ligaments, would making them out of pure carbon fiber be better than a mix of carbon fiber and normal cartilage, and would either of those be better than just the cartilage as it was before messing with it?

Alternatively, might another material be preferred over carbon fiber in this context, either for mechanical or chemical reasons? I was thinking carbon fiber because, well, we're carbon based life forms after all, and I reckon that the materials to make it wouldn't exactly be hard to come across in the diet. Plus, my understanding is its strength-to-weight ratio is outstanding compared to bone. Note also, I'm wanting this metahuman to be much stronger than a normal human too, so that's another reason to strengthen his skeleton to better cope with the increased stresses exerted by his musculature.

Thanks in advance for your answers!

Answer 1

Kevlar

Kevlar would probably be a better choice of reinforcing fibre: It's almost as strong per weight, and more shock resistant. And what you want to avoid at all cost is a fracture, so shock resistance is important.

The mechanism would be mostly the same, though.

Implants

Absolutely not, unless you are switching out the entire bones and ligaments at a time. If you try putting plates or bars or anything of the sort onto the bones, then it's just the places where they are fixed which will break instead, and the artificial part is likely to make the injury worse, like a blunt knife being moved around you. The following assumes you want to make the body grow the enhancements by itself, but if you want to go with implants you can fabricate replacements bones and ligaments and muscles outside the body and implant them - but the body growing them by itself, that could have somewhat plausibly appeared during evolution. Replacing so much of a body with artificially grown stuff requires an extremely high technology level.

How to arrange the fibers

If the body could grow carbon fibre, it would use the bones as they are now (or from a slightly different material) as the matrix which surrounds individual carbon fibres and glues them together. The carbon fibres could either cross through the entire cross section or just an outer ring, and with respect to the length of the bone would need to be straight or helix-like with varying steepness depending on which bone and how it is usually stressed.

How to create the bone-fiber composite

I'm not sure how bones are usually grown, but it would be most plausible to grow carbon fibre like hairs and at the same rate grow bone matrix surrounding the fibres. The thing growing the carbon "hairs" would need to be able to rotate to produce the mentioned helixes that are optimal for some loads.

Or if you start with a thin bone, then the "hair" would need to be grown along the surface of the bone at the same time as a new outer layer of bone. This sounds more complicated, but maybe it's possible to move the follicles growing the carbon fibre.

How to repair after a fracture

Either through the very hard process of reconnecting the ends of every ripped fibre, or more realistically by adding new fibres on the outside, so the bone would become noticeably thicker than before for the same strength.

Tendons and muscles

After you have reinforced the bones, the tendons and muscles need to be reinforced too or they will be the weak point. In principle that can work the same, only that for a flexible material where only tensile strength matters the fibers aren't interlinked by the matrix and thus fixed rigidly but are embedded in a flexible material (for example the same material as in real tendons and muscles).

Why I think you can just assume the existence of fiber producing follicles

Now, at the beginning I made the assumption that the body can grow carbon fibre (if it can do that, then like a hair, everything else is comparably very difficult). In industry, this is extremely energy intensive and uses extremely high temperatures. There is obviously no known organism which can do that with a sensible amount of energy at low temperature (otherwise carbon fibre would be harvested from it), but there is no physical or chemical reason such an organism couldn't exist. So you can just assume that if you want, and the explanations I gave above should be plenty to explain some of the mechanism to the reader without giving them a lecture on chemistry and biology.

Answer 2

Reality Check

(WARNING! Do not look at the third image if you are squeamish.)

Probably not. Implants are, obviously, a thing, but the realities of putting them inside the body at the very least will preclude their use. Bones are covered by a layer of tissue called periosteum. A main function is the residence of osteoblasts, which form new bone. It's not a very tough layer of tissue, so interweaving it with carbon fibre won't do much good.

You'd want to actually strengthen the bone itself. Carbon fibre is a reasonable choice, and is already in surgical use, so the technology is sound. So that part passes the reality check test. Other materials that have been used are titanium and stainless steel. Two ways present themselves, but neither are pretty.

Plates

One is to stiffen pre-selected bones with plates. We already stabilise fractures with plates. What you're looking to do is stiffen bones to prevent fractures.

Rods

Alternatively, you can ream out the medullary canal and shove a metal rod down the inside of the bone.

Similar plates & rods exist for the wrist, thighs & calves, too. Basically, anywhere on the body you want to put a plate, you can.

Pros and Cons

On the positive side, carbon fibre is already used as a surgical implant material. The first picture above appears to be a carbon fibre composite plate.

On the negative side, anyone who undergoes this treatment is looking at multiple initial surgeries (at least eight to ten procedures to plate the major bones alone) plus regimens of physical therapy to follow each procedure.

If you wish to also plate the cranium, mandible, sternum & ribs, that can be done, but, again, at a very slow rate and with long recovery times. You could be looking at two to three years worth of procedures, recovery times & therapy. Add in the cost per procedure plus inadvertent incidents (infection being the most likely; rejection; hardware issues (screws do come loose); death and I just don't think you can justify the cost with the minimal protection this kind of process can afford. A strong hit from a melee weapon can still break or fracture bone, even when strengthened. The plate itself can be damages. The hardware --- screws --- can be knocked loose, causing further injury.

Admittedly, you might have some built in stabilisation with such implants, but your soldier will have still have to undergo corrective procedures all the same, even after a relatively easy battle.

Rationale

Basically, you want to do this on multiple parts of your soldiers' bodies. DO NOT LOOK IF YOU ARE SQUEAMISH!!

I personally would not be on board with this. This part does not pass the reality check test.

Another Option

You probably won't like this one, but since you're looking to increase the strength of your soldiers, just give them armour! Lightweight carbon fibre / composite plates (for melee weapons) in conjunction with kevlar type armour might prove a better option than messing around with surgery.

Answer 3

If you're dealing with space boarding actions in the far future, you're already talking science so advanced that the standard version of science-fiction magic, aka "nanotech", would work. Especially if you made it quasi-realistic; nanotech enhancement of bone by building up supporting carbon-fibre gradually, but taking time to do it in controlled conditions where the nanotech could be controlled remotely and issues such as waste heat (which tends to be forgotten when nanotech is involved) can be controlled.

Answer 4

I'll give you an option that I'm currently working on my story.

There's this disease called Hemochromatosis, which leads to a higher content of iron on the human body. It's not beneficial though, you got severe damage to you body because of that, but with some creativity we can create a scenario where it's an enhancement.

I, for instance, made my society go through a lot of generations, each one mutating a little bit and through natural selection the best fit for that environment survived. He survived because his body had enzymes that linked Iron to carbon(readily available for us) forming Steel alloy in different parts of the body. You wouldn't suffer the side effects of the disease because all the iron is trapped and now you have a super body.

You could do that using genetic modifications, as I see it's a high tech environment, or anything you prefer. Harder and yet flexible alloy for the bones, ligaments of steel wire and even some steel skin that could withstand weak impacts.