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Deng Y, et al.

2θ (°)

Figure 4. XRD patterns of the ZK60/xβ-TCP composites

reactions occurred between β-TCP and Mg alloys during compared with SBF for ZK60 (10.25 ± 0.12), ZK60/4β-
the laser melting. TCP (9.73 ± 0.13) and ZK60/12β-TCP (10.69 ± 0.10).
The increase of pH value was due to the generation
3.2 Mechanical Properties of OH resulting from the degradation of Mg. Thus, it
−
The obtained compressive strength of laser-melted was indicated that ZK60/8β-TCP showed the highest
ZK60/xβ-TCP composites was shown in Figure 5A. corrosion resistance. The corrosion rates of the ZK60/xβ-
ZK60 exhibited a relatively low compressive strength of TCP composites were calculated based on weight loss
111.8 ± 6.8 Mpa. After composited with 8 wt. % β-TCP, (Figure 6B). Clearly, ZK60/8β-TCP showed a decreased
the compressive strength was gradually improved corrosion rate of 0.58 ± 0.11 mm/year, as compared with
to 207.4 ± 7.7 Mpa. However, a further increase of ZK60 (1.83 ± 0.25 mm/year), ZK60/4β-TCP (1.63 ± 0.18
β-TCP to 12 wt. % resulted in a dramatically decrease mm/year) and ZK60/12β-TCP (2.14 ± 0.34 mm/year).
of compressive strength to 167.4 ± 12.2 Mpa. Besides, In order to further study the effect of β-TCP on the
the hardness of the laser rapidly solidified ZK60/β-TCP degradation behavior, the corrosion surface of the
composites was also obtained, with results shown in soaked samples were studied by SEM (Figure 7). After
Figure 5B. It could be observed that the hardness of immersed for 7 days, a compact film formed on the
ZK60/xβ-TCP composites significantly increased with surface of the ZK60/8β-TCP composite, while loose
β-TCP increasing. ZK60 exhibited a low hardness of corrosion product film with obvious cracks formed on
82.4 ± 3.8 HV, while ZK60/4β-TCP, ZK60/8β-TCP and the surface of the ZK60. As for the ZK60/12β-TCP,
ZK60/12β-TCP had an enhanced hardness of 97.6 ± 4.5 some huge gaps appeared in local areas on the surface.
Hv, 127.2 ± 5.7 Hv and 153.4 ± 12.2 Hv, respectively. The EDS analysis indicated that the degradation products
(Figure
on ZK60 were mainly composed of Mg and O
3.3 Degradation Behavior 7E), indicating a large amount of Mg(OH) coated on the
2
The degradation behavior of the ZK60/xβ-TCP com- surface of ZK60. Significantly, large amounts of calcium
pos ites was evaluated by immersion tests in SBF. and phosphorus were detected on the surface of the
Moreover, the pH variation of the SBF for ZK60/xβ-TCP composite (Figure 7F). EDS revealed that the calcium/
composites as a function of soaking time was presented phosphate atom ratio of the product on the ZK60/8β-
in Figure 6A. It could be seen that the pH values of SBF TCP composite was 1.617, which was close to that of
[20]
for different composites had similar change tendency apatite (1.67) . Thus, it was reasonable to conclude that
during the immersion period, increasing quickly at the more apatite deposited on the surface of ZK60/xβ-TCP
first 48 h and stabilizing during further immersion. After composites. In addition, the deposition of apatite resulted
immersed for 240 h, the obtained pH value of SBF for in a more compact corrosion surface film on Mg matrix
ZK60/8β-TCP exhibited a lowest value of 9.42 ± 0.09, as (Figure 7B and Figure 7C).

International Journal of Bioprinting (2018)–Volume 4, Issue 1 5