The interactions between solid surfaces and cells are crucial to many biological phenomena for all biomaterials. This chapter provides an overview of metallic and ceramic biomaterials, along with a discussion of microstructure and surface changes that promote biocompatibility. For a material to be deemed biocompatible, any adverse reactions which may ensue at the blood/material or tissue/material interface must be minimal, while resistance to biodegeneration must be high. Implantable materials should not [27]: cause thrombus-formations, destroy, or sensitize the cellular elements of blood, alter plasma proteins (including enzymes) so as to trigger undesirable reactions, cause adverse immune responses, cause cancer and eratological effects, produce toxic and allergic responses, deplete electrolytes,

and ϐinally be affected by sterilization. Till now, there are no known materials which totally satisfy these criteria so when a foreign material is placed into a biological environment, inevitable reactions occurs which are detrimental to both the host and the material. The surface properties of biomaterials are associated with cell adhesion and subsequent various cell behaviors, such as proliferation, migration, cytoskeletal arrangement, differentiation, and apoptosis [12, 99]. In particular, a large number of studies on cell adhesion to various substrate surfaces have been conducted. Cell adhesion and its performance have been reported to depend on the characteristics of substrates, including the chemical composition, surface charge, water wettability, roughness, and size of the cytophilic area [5, 23, 44, 62, 63, 67, 68, 90, 104, 106, 107, 133, 135, 138, 141−143]. Understanding the mechanisms whereby cells sense and respond to chemical, physical and biological signals from material surfaces will facilitate the development of novel biomaterials for the control of cell behavior. All implantable materials possess inherent morphological, chemical, and electrical surface qualities which elicit reactionary responses from the surrounding biological environment. In fact, biocompatibility can be described as multifactorial in that simultaneous stimuli from any of these material properties can affect the host response. Using nanotechnology for regenerative medicine becomes obvious when examining nature [153]. Bone is a nanocomposite that consists of a protein based soft hydrogel template (i.e., collagen, non-collagenous proteins (laminin, ϐibronectin, vitronectin), and water) and hard inorganic components (hydroxyapatite, HA, Ca10(PO4)6(OH)2) [139, 154]. Speciϐically, 70% of the bone matrix is composed of nanocrystalline HA [57]. In addition to the dimensional similarity to bone/cartilage tissue, nanomaterials also exhibit unique surface properties (such as surface topography, surface chemistry, surface wettability, and surface energy) due to their signiϐicantly increased surface area and roughness compared to conventional or micron structured materials. As known, material surface properties mediate speciϐic protein (such as ϐibronectin, vitronectin, and laminin) adsorption and bioactivity before cells adhere on implants, further regulating cell behavior and dictating tissue regeneration [139]. Furthermore, an important criterion for designing medical implant materials is the formation

of sufϐicient osseointegration between synthetic materials and bone tissue.