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Liang, et al.
support for cell activities. Besides, the scaffolds should structures, such as cubic pore-shaped (CPS) scaffolds, in
also have porous structures with adequate interconnected both mechanical properties and in vitro cell evaluations,
pores to facilitate the diffusion of nutrients and oxygen are scarce, and thus, deeper investigations are needed.
as well as cell ingrowth [10,12] . Notably, the characteristics To identify the difference and properties of various
of scaffold structures (pore shape, pore size, porosity, scaffolds, the fabrication approaches should be carefully
etc.) not only affect the stress distribution but also have a considered. Traditional approaches, such as salt leaching,
close relation with cell behaviors. Therefore, improving freeze drying, and gas foaming, are commonly applied in
the properties of tissue engineered scaffolds by designing HA scaffold fabrication, whereas these techniques have
different structures has been an attractive research hotspot. inevitable limitations, such as uncontrolled pore size
Especially, with the advancement of computational design and poor pore interconnectivity [18] . Recently, additive
and advanced manufacturing, the design and fabrication manufacturing, such as binder jetting (3DP), selective
of scaffolds with complex structures have gained many laser sintering (SLS), and direct ink writing (DIW), has
attentions in BTE field. emerged as an efficient way to fabricate HA scaffolds
Triply periodic minimal surface (TPMS) is nowadays with complex structures. As for 3DP and SLS, the
a popular structure that has been widely investigated general challenges include the relatively low resolution
for BTE scaffold due to the advantages of zero mean and powder entrapment in small pore of printed
curvature and large surface area. Blanquer et al. fabricated scaffolds. Sag and collapse in the DIW process are still
eight TPMS scaffolds using the biocompatible material, a big obstacle for scaffold fabrication . Digital light
[3]
poly(trimethylene carbonate), by service-level agreement processing (DLP), possessing the advantages of high
to investigate the biofunctional role of surface curvature accuracy and resolution, is a powerful way to fabricate
of scaffolds . Their results showed that different TPMS scaffolds with specific pore shape and interconnected
[13]
structures exhibited distinct permeabilities and thus pores. Before printing bioceramic 3D objects through
influenced the tissue formation. However, there were no DLP, the photosensitive slurry, containing ceramic
further illustrations about the in vitro evaluations caused powders, resin matrix, etc., should be prepared in
by the difference of the permeabilities of the scaffolds. advance. The successful printing by DLP largely
Besides, the structure stability of TPMS scaffolds was depends on the good performance of the bioceramic
investigated by Lu et al. . They manufactured the slurry. As for slurry preparation, ceramic dispersion
[14]
TPMS-based scaffolds with Ca-silicate bioceramics is a big challenge, particularly for nano-sized ceramic
and compared the structural and mechanical stability which can facilitate the mechanical properties of the
between TPMS-based and structure-based scaffolds. ceramic parts. The nano-sized particles are difficult to
It revealed that TPMS-based (skeletal- I-graph and be homogeneously dispersed in the slurry because they
wrapped package-graph, sheet gyroid) scaffolds had are prone to agglomeration due to the higher surface
higher appreciable specific flexural strength than energy. The dispersity of nano-sized ceramic slurry is
structure-based scaffolds but lack of further discussions influenced by the dispersant and concentration, which
on in vitro evaluations. The similar conclusion that the was investigated by Sun et al. [19] His work revealed that
TPMS-P HA scaffolds performed high flexural strength the nano-sized zirconia slurry was well dispersed by
up to 92.4 MPa was also reported in Yao et al.’s work . adding 3 wt. % Disperbyk (BYK). A proper dispersant
[15]
Furthermore, they also pointed out the TPMS-P had and corresponding concentration are significant to stable
good cell proliferation through the in vitro evolution . dispersity of slurry, which was also evidenced by Ding
[15]
Body-centered cubic (BCC) structure, discovered in et al.’s work [20] . Besides, the slurry containing nano-
crystals structures, was also used for tissue engineering sized ceramic particles exhibits difficulties in printing
applications. Huo et al. fabricated BCC Ti-6Al-4V (TC4) accuracy since there are more scattering centers that
scaffolds by selective laser melting and investigated the enhance the overcure in an unexpected area [21] . Ju et al.’s
compression deformation behavior of BCC structure . study showed that the printability of nano-sized zirconia
[16]
The result showed that the BCC structure could benefit slurry could be optimized by mixing in the specific
the formation of the smaller and regular α’ martensite, ratio of micron-sized powders due to the decrease of
which could improve the compressive strength of TC4 scattering center’s number and sustained solid-like
scaffolds. Meanwhile, Caravaggi et al. revealed that the behaviors [22] .
BBC structure had higher ultimate tensile strength than In this work, nano-sized HA ceramic slurry was
that of the circular pore-shaped scaffolds, and good cell prepared and processed using DLP 3D printing. The
viability and proliferation rate . Obviously, different rheological properties, curing abilities, debinding, and
[17]
advanced scaffold designs, such as TPMS and BCC, have sintering strategy were systematically investigated.
emerged in BTE in recent years. However, systematic Afterward, the TPMS-P, BCC, and CPS scaffolds with
comparisons among new structures and traditional a same porosity were designed and fabricated under

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