REVIEW Bioactive metals: preparation and properties

Abstract

Some ceramics, such as Bioglass, sintered hydroxyapatite, and glass-ceramic A-W, spontaneously form a bone-like apatite layer on their surface in the living body, and bond to bone through the apatite layer. These materials are called bioactive ceramics, and are clinically important for use as bone-repairing materials. However, they cannot be used at high-load sites, such as is found in femoral and tibial bones, because their fracture toughness values are not as high as that of human cortical bone. Titanium metal and its alloys have high fracture toughness, and form a sodium titanate layer on its surface when soaked in a 5 M-NaOH solution at 60 degrees C for 24 h, followed by a heat treatment at 600 degrees C for 1 h. On moving toward the metal interior, the sodium titanate layer gradually changes into the pure metal within a distance of 1 microm from the surface. The mechanical strength of the titanium metal or a titanium alloy is not adversely affected by these chemical and thermal treatments. The titanium metal and its alloys resulting from the above treatment can release Na+ ions from its surface into a surrounding body fluid via an ion exchange reaction with H3O+ ions, resulting in many Ti-OH groups forming on its surface. These Ti-OH groups initially combine with Ca2+ ions to form amorphous calcium titanate in the body environment, and later the calcium titanate combines with phosphate ions to form amorphous calcium phosphate. The amorphous calcium phosphate eventually transforms into bone-like apatite, and by this process the titanium metals are soon tightly bonded to the surrounding living bone through the bone-like apatite layer. The treated metals have already been subjected to clinical trials for applications in artificial total hip joints. Metallic tantalum has also been found to bond to living bone after it has been subjected to the NaOH and heat treatment to form a sodium tantalate layer on its surface.

Silk based biomaterials to heal critical sized femur defects

“…However, harvesting autologous bone is associated with second site morbidity and hampered by insufficient amounts of collected bone substance to fill the entire defect [57]. Apart from other options such as the use of allograft bone, which is associated with the risk of disease transmission or immune rejection, metals and ceramics are used to treat larger defects [58]. Metals provide instant mechanical stability but are associated with poor overall integration and can fail because of infection or due to fatigue loading [7].…”

Bioactive Glass 13-93 as a Subchondral Substrate for Tissue-engineered Osteochondral Constructs: A Pilot Study

“…The limitations of 45S5 glass and related glass ceramics include unfavorable flow characteristics secondary to their low SiO 2 content and low fracture toughness when compared to human cortical bone [23]. Our work with an alternative silicate-based glass composition, Bioactive Glass 13-93 (BG 13-93), shows this composition can be readily shaped into porous constructs of complex shapes, while retaining the desirable in vitro bioactive characteristics of 45S5 glass and higher mechanical strength [16,32].…”

Porous Apatite Coating on Various Titanium Metallic Materials via Low Temperature Processing

“…The rods were cleaned in deionized water and acetone by using an ultrasonic cleaner. Recently, it has been reported that surface modifications for forming bonelike apatite can induce the high bioactivity of bioinert materials in simulated body fluid (SBF) [Kokubo et al, 2004]. In our previous research [Onoki et al, 2003], bonding HA ceramics and Ti alloys (Ti-15Mo-5Zr-3Al and Ti-6Al-2Nb-1Ta) was achieved by the HHP method through the surface modification of Ti alloys with alkali solution (5M NaOH).…”