Bio-packaged transponder MEMS implanted in rats

A novel hydroxyapatite-based hybrid material with controlled porosity was designed as a bio-package to implant micro-electro-mechanical systems (MEMS) in living organisms. The biomaterial was prepared using synthetic stoichiometric hydroxyapatite powder reacted with a chemical-active, solvent-free, alkyd-based polyurethane. This porous material has interconnected pores with sizes between 100 and 350 μm and a pore volume fraction of 50%, fulfilling the requirements for implants. The biomaterial additionally has high wearing resistance and hydrolytic stability providing high endurance properties. The bio-package was characterized mechanically and morphologically using X-ray diffraction, scanning electron microscopy, densitometry, abrasion and mechanical tests. Twelve packaged micro-electro-mechanical systems were implanted subcutaneously into rats and tested for up to 9 months with good acceptance as revealed by the histological analysis performed on the soft tissue surrounding each implant.