A hot area in IP law is the issue of repair versus reconstruction of medical devices. Repairing a patented object is fine, but if you "reconstruct" it, you may be infringing the patent. See "Reusing Patented Medical Devices" by Don V. Kelly over at IPFrontline.com.
When you are developing a device for commercialization and preparing your patent, it may be wise to carefully consider the issue of repair vs. reconstruction, and to take pains to address business models around repair and aftermarket service. Neglect of those areas can lead to lost profits later on. The business model you pursue may include providing a license for users that stipulates conditions for repairs and replacement of parts. And the patent strategy may wish to consider patenting key parts of the device that are most likely to be replaced.