ABSTRACT
Among all metallic biomaterials, Ti and its alloys are most widely used because of their great strength, low density, high corrosion resistance, and good biocompatibility [45, 69, 78]. However, the problem for dental as well as orthopedic implant applications is the mismatch of Young’s modulus between the bone (10-30 GPa) and metallic part (110 GPa for Ti) [24, 65]. This mismatch may result in the formation of stress and retard the bone healing, which results in increased bone porosity and failure of the implants. One way to reduce Young’s modulus of the metallic materials is to introduce the pores [64, 101], minimizing tissue damage, and extended implant life time. Pores introduced into the implant improve its
ϐixation with tissue, reducing time between surgical operations, extends implant life time, and improve quality of life of the patients. Rough surface of the implants, with pits and pores, results in tissue growth into these features, which acts as the anchors for the tissue. The strong bonding of the tissue with implant then results in the implant’s higher loading-bearing capacity. There are many possible ways to produce porous implants, for example, powder metallurgical process, metal foaming, and electrochemical etching [24, 28, 93, 101]. Micro-and nanometer diameter pores are useful. As mentioned by Webster and Ejiofor [99], the nanometer structures and molecules in the bone tissue indicate that bone-forming cells are accustomed to interacting with surfaces of nanometer roughness. Conventionally prepared and applied implant surfaces have microrough surfaces and are smooth at the nanoscale [39, 40]. For instance, woven bone has an average inorganic mineral grain size of about 10-50 nm [39]. Lamellar bone, has an average inorganic mineral grain size of about 20-50 nm long and is 2-5 nm in diameter [39]. It is commonly accepted that up to this time only rough implants at microscale are utilized and are useful in osseointegration. Now the roughness in nanoscale states a new aspect for implant producers and taking the above assumptions is necessary to ϐind the role of the nanostructures, nanoporosity, and nanoroughness played in the implant materials. For example, nanostructured substrates enhance adhesion of the osteoblasts, decrease adhesion of the ϐibroblasts, and decrease adhesion of the endothelial cells [95, 99]. Calcium deposition by osteoblasts was four, three, and two times greater on nanophase, compared to conventional microscale alumina, titania, and hydroxyapatite after 28 days of culture, respectively [96, 99]. The latest studies show increased calcium deposition by osteoblasts cultured on alumina nanoϐibers, carbon nanoϐibers, poly-lactic-glycolic acid, polyurethane, and composites [15, 42, 73, 82]. Webster [99] found increased osteoblast adhesion on nanophase compared to conventional metals, and osteoblast adhesion occurred preferentially at surface particle boundaries for both nanophase and conventional metals. Since more grain boundaries are present on the surface of nanophase compared to microcrystalline conventional metals, this may be an explanation for the measured increased of osteoblast adhesion [99]. Additional grain boundaries can be prepared in porous materials.
