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Shuai C, et al.

The XRD patterns of the PHBV/nMgO scaffolds trabecular bone (4 to12 MPa and 50 to 500 MPa,
[36]
were plotted in Figure 2. The PHBV scaffold showed respectively ).
strong diffraction peaks at 2θ = 13.4 and 16.8°, As the dispersion of fillers in polymer matrix was a
which were corresponding to (020) and (110) planes, significant factor influencing the mechanical properties
respectively; additional diffraction peaks at 2θ = 20.1, of polymer composites [37–40] , the dispersion of nMgO
21.4, 22.6, 25.5, and 27.1° were also detected, which in PHBV matrix with different nMgO content were
were assigned to (021), (101), (111), (121), and (040) characterized using SEM (Figure 4). After incorporation
planes, respectively [33,34] . After incorporating nMgO, the of nMgO, some bright spots appeared in the PHBV
scaffolds showed two new diffraction peaks at 2θ = 42.9 matrix; their amounts gradually increased with the
and 62.3°, which were just corresponding to the two nMgO content increasing. The EDS spectrums indicated
main diffraction peaks of MgO assigning to (200) and that the bright spots were just the nMgO incorporated.
(220) planes (JCPDS 87-0653), respectively. Moreover, They kept dispersing uniformly in the PHBV matrix
the intensities of the main diffraction peaks of nMgO until 5 wt%. However, severe aggregations happened
gradually increased with increasing nMgO content. This when further increasing the nMgO content. It was well
indicated nMgO kept thermal stability during the SLS known that excessive nanoparticles would easily result
process as it had a very high melting point more than in the occurrence of agglomeration due to the large
[35]
2800 °C . specific surface area and surface energy [41,42] .
The compressive strength and compressive modulus The compressive properties of the PHBV/nMgO
of the PHBV/nMgO scaffolds as a function of nMgO scaffolds increased with the nMgO content increasing as
content were depicted in Figure 3. In general, they both the total interfacial areas between the fillers and matrix
increased at first but decreased then with the nMgO keep increasing. The significant improvements in the
content increasing from 0 to 7 wt%. The compressive mechanical properties of the PHBV/nMgO scaffolds
strength and compressive modulus of the PHBV were resulted from strong reinforcing effects of MgO
scaffolds were 2.62 and 29.33 MPa, respectively. nanoparticles. There were several factors accounting for
After incorporating nMgO from 1 to 5 wt%, they keep it: (a) the elastic modulus of MgO was as high as 310
[43]
increasing from 3.37 to 5.14 MPa, and 34.36 to 44.68 GPa , ensuring the applied stress could be transferred
MPa, respectively. However, they began to decrease to the fillers from the matrix; (b) the nano-sized MgO
when the nMgO content exceeded 5 wt%. Therefore, have extremely high specific surface area, which greatly
the optimal nMgO content was considered to be 5 increased their interfacial areas with the matrix and
wt% to obtain the optimal compressive strength and thus enhanced effectiveness of the stress transfer; (c)
modulus, which were improved by 96.18% and 52.34% the uniform dispersion of MgO nanoparticles in the
compared with the PHBV scaffolds, respectively. It was PHBV matrix maximized its potential in improving the
worth noting that the optimal compressive strength and mechanical properties. However, excessive nanoparticles
modulus of the scaffolds was close to that of human would form severe agglomerations (>5 wt%), which

(A) (B)

Figure 2. (A) The XRD patterns of the PHBV/nMgO scaffolds; (B) the enlarged version from 40° to 45° and 60° to

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