ABSTRACT
There is a high demand for biomaterials to assist the replacement of organs and their functions. For this reason, researchers search for new biomaterials with advanced mechanical and biological properties and develop new technologies for the enhancement of those properties. Over the past, nanoscale materials become very popular in medical application [38, 78-80]. These nanostructured materials can exhibit enhanced mechanical, biological, chemical properties compared with their conventional counterparts [50].Titanium and titanium alloys are preferred materials in the production of implants [14, 53]. These materials possess favorable
Karolina Jurczyk, DDS, PhD,a and Mieczyslaw Jurczyk, PhD, DScbaUniversity of Medical Sciences, Conservative Dentistry and Periodontology Department, Poznan, PolandbPoznan University of Technology, Institute of Materials Science and Engineering, Poznan, Poland Keywords: nanoimplant, nanosurface, scaffold, dental, dentistry, corrosion, roughness, cell viability, cell proliferation, MTT test, titanium, magnesium, hydroxyapatite, 45S5 Bioglass, silica, nanocomposite, mechanical properties, in vitro biocompatibility, osteoblast cells, fibroblast cells
properties, such as relatively low modulus, low density, and high strength. Titanium materials are resistant to corrosion because of the stable passivity of the surface oxide film [43]. Apart from that, titanium and titanium alloys are generally regarded to have good biocompatibility, although there are reports that show the accumulation of titanium in tissues adjacent to the implant, signifying metal release and corrosion in vivo [11, 12]. In addition, these metal implants may lose and even separate from the surrounding tissues during implantation [13-15]. Titanium and titanium-based alloys have relatively poor tribological properties because of their low hardness [16].Current research focuses on improving the mechanical performance and biocompatibility of Ti-based systems through variations in alloy composition, microstructure and surface treatment [22, 23, 28, 33, 49, 60, 73, 82]. In the case of titanium, significant efforts go into enhancing the strength characteristics of commercial purity grades in order to avoid potential biotoxicity of alloying elements, especially in dental implants [2, 4, 6, 20, 55, 60].To enhance the physicochemical and mechanical performance of implant materials through microstructure control, the top-down approaches known as severe plastic deformation (SPD) and mechanical alloying (MA) techniques were applied [38,68,74]. Recent studies clearly proved that nanostructuring of titanium can considerably improve not only the mechanical properties but also the biocompatibility [20, 32, 33, 60, 64, 74, 76−80, 84]. On the other hand, this approach also has the benefit of enhancing the biological response of the cp titanium surface [32, 33, 64, 79]. 37.1 Bulk Nanostructured Titanium
Until now, a number of SPD methods for producing bulk ultra fine grain metals/alloys have been developed [74−80]. Valiev and coworkers apply a process known as equal channel angular pressing (ECAP), which is a viable processing route to grain refinement and property improvement [79]. Their study reports nanostructured titanium (n-Ti)—produced as long-sized rods with superior mechanical and biomedical properties-and demonstrates its applicability for dental implants. It turns out that the extreme grain
refinement of the bulk of the metal down to nanoscale transpires to surface morphology that turns out to be conducive for enhanced adhesion and growth of living cells.Commercially pure titanium (Grade 4) of the following composition was used: 0.052% C, 0.34% O2, 0.3% Fe, 0.015% N, base material Ti (wt.%). In the as-received condition, billets produced by hot rolling had a diameter of 40 mm with an average grain size of 25 μm. Nanostructuring was performed using SPD by equal-channel angular pressing with subsequent thermomechanical processing (TMP), which made it possible to manufacture rod semiproducts with a length of 3 m and a diameter of 7 mm [74−80].This processing resulted in a large reduction in grain size, from the 25 µm equiaxed grain structure of the initial titanium rods to 150 nm after combined SPD and TMT processing, as shown in Fig. 37.1. The selected-area electron diffraction pattern (Fig. 37.1c) further suggests that the ultra fine grains contained predominantly high-angle non-equilibrium grain boundaries with increased grain-to-grain internal stresses. It is important to note, that a similar structure for cp Ti can be produced in small discs using other SPD methods, such as high-pressure torsion (HPT) [75].
