MATERIALS FOR ORTHOPEDIC APPLICATIONS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 68

3.4.4.2 Other Bioglass-Ceramics. Besides Macor - based glass ceram-
ics, several other glass ceramics were developed in the last few decades. Among
various glass ceramic materials, 45S5 glass, originally invented by Hench &
co-workers, is known to be the best bioactive glass material 42 . Its typical composi-
tion 43 is SiO 2 : 46.1, P 2 O 5 : 2.6, CaO: 26.9, Na 2 O: 24.4. A recent study by Chevalier
& co - workers 44 report crystallization kinetics of 45S5 glass. It is known that 45S5
glass undergoes a series of structural transformations, leading to the formation of
Na 2 CaSi 2 O 6 crystals at 610 °C. However, poor mechanical properties and lack of
machinability has been a major concern for 45S5 glass. Therefore, these materials
cannot be used for dental applications or any biomedical applications requiring
the complex shape.
Besides 45S5 glass, Bioverit ® I base glass has wider clinical applications in-
cluding the possibility of using Bioverit II base glass as a matrix for Ti particle
reinforced composite coatings 45 . The coatings were prepared by a single step vac-
uum plasma spray method on Ti - 6Al - 4V substrates. The mechanical characteriza-
tion showed a good adherence of the coatings to the substrate and the toughening
effect of the dispersed Ti particles.
In another study, Bioverit ® III base glass- and glass-ceramic matrix/Ti parti-
cles composites were prepared by means of a simple pressureless sintering
method 46 . The sintering process was carefully optimized by means of differential
scanning calorimetry (DSC) and hot stage microscopy. The optimized sintering
conditions were accomplished by a viscous fl ow process, obtaining nearly full den-
sity amorphous matrix composites that were subsequently ceramised to obtain
glass-ceramic matrix composites. Better mechanical properties were exhibited by
both the glass- and glass-ceramic matrix composites when compared with the cor-
responding pure matrices. Such a comparison was also found true for the glass-
ceramic matrix composite, when compared with the glass-matrix. The cell growth
of fi broblasts on the surface of the glass-ceramic matrix composites confi rms their
biocompatibility.
In a different system, complex reactions between Ti and hydroxyapatite
occurred during the sintering of Ti/HAp/BG composites 47 . Moreover, the addi-
tion of bioactive glass to Ti/HAp showed little effect on the phase components of
the composites. Bioverit ® III glass - ceramic matrix/Y - PSZ particulate composites,
successfully prepared by means of pressureless sintering, also confi rmed the
toughening effect of the Y-PSZ particles 48 .
A different study reported that highly dense ( 98% of relative density)

Si 3 N 4 - bioglass composite 49 has potential advantage of each constituent, that is,
the high fracture toughness of Si 3 N 4 with the bioactivity of a bioglass. The most
signifi cant feature concerning the mechanical properties of this new biomaterial
composite is the improvement in fracture toughness (4.4 MPam 1/2 ) and bending
strength (383

>

47 MPa) with respect to currently used mechanical bioceramics,
glasses and glass ceramics for load bearing applications. However, a detailed bio-
compatibility study on Si 3 N 4 /bioglass composite is yet to be carried out. Barrors
et al. 50 investigated the in vivo bone tissue response of another fl uoride contain-
ing

±

canasite glass - ceramic (0.47K 2 O 0.94Na 2 O 1.42CaO 5.67SiO 2 1.5CaF 2 ).