I'm not entirely sure about the context and whether you are proposing 'extended human body' and testing the cogency of the definition/description or if you are trying to make sense of something you found somewhere in the light of BFO. But you are asking how to model, in BFO, certain aggregates that involve an organism (human or other) and something that is not biological and, in the general case, that is located somehow in or near the organism, is that right?
First, I am not aware that 'extended organism' is something BFO has any ability to discern, this is because it sounds at first sight like you would need a definition of 'organism' in the first place and that is a biological matter and not a formal one. BFO consistently uses 'organism' as an example of object is all one can say, as far as I am aware --- when doing so there seems to be an underlying assumption that organisms of the relevant complexity are made of parts that are or are originating in living tissues, I'm not sure that's a claim that's made though.
Yet, strictly speaking in BFO, all the stuff you put together in your examples come across as aggregates, perhaps all as aggregates of objects. Objects have some causal unity. My interpretation of this is that, on a purely structural view, a body with a foreign body of any sort within it creates an aggregate and by some criterion of causal unity that aggregate may be maximal in the language of BFO 2. In principle, that does not mean that the resulting aggregate is an organism (although this is pending the definitional issue for organism) and it does not mean either that the added material, encompassed somehow by the organism, is part of the organism. On the other end of the problem, there is no way of imposing strict limits on what can be added (pretty much any aggregate somehow connected in a relevant sense, whatever it is, can be an 'extended organism'). This last claim may be perfectly fine and correct but then there is a risk of trivialising the tentative 'extended organism' --- is a naked person an organism and a person with clothes an extended organism, for example? What about a person with clothes in a car?
Alan mentions, with caution, one criterion for the integrity of organisms (species) that ties to the developmental process. Another, perhaps more important criterion is the physiologicial unity of organisms and the existence of physiological processes therein. It seems credible to me that no artifact is involved in a purely physiological process (but again, that may be only a domain specific definitional issue). The closest cases of examples in which you have aggregates of organisms and artefacts that come close to a functioning biological system would be when the artefact sustains, facilitates or triggers physiological mechanisms -- the pacemaker seems a good example of that, a mechanical aortic valve is another. But I think the story is here of relations between processes of different sorts (because their participants are of different sorts) at the level of domain analysis (these distinctions are not perceptible at the formal level).
Because of this and because there is virtually no purely structural (as in physical structure) way of distinguishing between cases of an organism having foreign parts within/around it to account for more than mereotopological differences, you will not be able to do justice to medical devices and implants without either referring to certain types of processes or certain types of SDCs.
One way of addressing purposeful placement is to use the processes that led to the implantation. It becomes a matter that is definitional of the process that some outcome was or was not intended following a procedure of sort. In practice, when modelling this, you ideally want to reuse something that allows you to offload as much as possible as you can (if you already have access to a well defined 'surgical procedure' with an account of intended outcome, this may be enough). In doing so you may be able to distinguish cases in which a mechanical aortic valve has been put in place from cases in which a sponge has been left behind.
Another (complementary) way may be to use the SDCs for the implant --- the aortic valve has a role (broader approach) or maybe a function (more detailed approach) that fits the context you are trying to capture. The same offloading principle applies, not least because SDCs are involved and exhibited in other processes. Note that there will be bodily processes, even just mechanical ones like mastication to account for the role of dental implants or walk for lower limb prosthesis, and other processes that may have no interesting narrow biological properties such as elaborate communication through bodily modifications or concealment for smuggling, say.
While it can be made definitional, I see no forthcoming account of parthood between non-living objects and organisms that does not challenge the physiological integrity of organisms and it seems that differences between deliberate and accidental augmentation do not coincide with (physiologically and broadly biologically) beneficial or hurtful. There is a clear ethical and psychological dimension to the problem that I have entirely ignored as I only mean to highlight ways in which, according to my understanding, the distinctions you seem to be trying to draw are more or less well supported by the formal aspects in BFO.
Finally, some people recently mentioned on this list desires to be dealing more explicitly with systems --- since afterall organisms are living systems and your interest is in preserving the system part for aggregates involving these and non-organismal parts, it may be an interesting route.
I'd suggest for the short term to attend to the relevant processes and SDCs that could allow you to capture the distinctions you are trying to make. This may be tackled by answering questions such as:
- What are the procedures leading to an implant?
- What are the prerequisites and success and failure criteria for these procedures?
- What are the participants? Who carries them? On who? What artefacts are involved?
- What are the processes in which the role or the function of the implant exhibit themselves?
Once you've addressed these, I'm not sure what benefit there is to use an 'extended human body' or 'extended organism' universal. What does it bring you in your context?
With many thanks and best regards,