In vivo evaluation of implant-host tissue interaction using morphology-controlled hydroxyapatite-based biomaterials

In medicine, micro-electro-mechanical systems (MEMS) perform several specific functions. The design of bio-packages for MEMS to be implanted into the human body has been an increasing challenge in the last years. Mechanical, chemical and thermal resistance, as well as excellent bonding to silicon surfaces, are needed. Furthermore, ideal bio-packages should minimize post-operative complications and be well accepted by the host. To reach this goal, two different morphology-controlled hydroxyapatite-based porous biomaterials were synthesized, implanted in rats and evaluated mechanically and histologically. The novel biomaterials were prepared at room temperature using synthetic hydroxyapatite micro-particles, silica nanoparticles and water-based resin and compared with a standard hydroxyapatite biomaterial. The morphology (porosity) was controlled to obtain interconnected pores with appropriated pore size and pore volume fraction. All biomaterials were implanted in rats at the dorsal area near the third thoracic vertebra. The rats were killed 2, 7 and 21 days after surgery. Histological analysis revealed that the implants were well accepted by the host and minimal local inflammation was observed. The acute inflammatory response disappeared 21 days after surgery for both novel biomaterials. Additionally, organic matter (collagen) was produced in the interior of the porous biomaterial, indicating that an incipient vascularization process was in progress after 21 days of implantation. Both new biomaterials showed high abrasion resistance, high Young modulus, the appropriate porosity to allow possible vascularization, and good bonding to silicon surfaces.