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Qian, et al.
Mesoporous silica (MS) particles have been widely ethanol, and dried at 80°C for 12 h. Finally, the powders
used in biomedicine, diagnostics, and tissue repair fields were heated at 500°C for 2 h.
due to their good biocompatibility, adjustable morphology,
controllable particle size, and mesoporous structure [14-16] . 2.2 Physicochemical characterization of Zn-MS
Particularly, MS is also a good vehicle for loading and Zn-MS particles were observed by a transmission
sustained release of active constituents or functional drugs electron microscopy (TEM, JEOL, 2100F, Japan). The
through mesopores . Meanwhile, MS possesses stable microstructure of Zn-MS was analyzed using a scanning
[17]
Si-O-Si network structure, which gives the flexibility electron microscope (SEM, EVO18, ZEISS, Germany).
for doping metal element into MS framework by partial The phases of Zn-MS were determined using an X-ray
substituting Si sites and forming Si-O-M bond (M=Ca, diffractometry (XRD, DY2472, Malvern PANalytical,
Mg, and Zn) . The Si-O-Zn bond is more stable than the Netherlands). The nitrogen adsorption desorption
[18]
Zn-O-Zn bond of ZnO, thus guaranteeing the sustained isotherm of Zn-MS was recording using a surface area
release of Zn ion and its long-term stability. and porosity analyzer (ASAP2460, Micromeritics, USA).
Ideal artificial bones not only require excellent The chemical compositions of Zn-MS were measured
osteogenic activity but also need to possess three- using an X-ray photoelectron spectrometer (XPS,
dimensional (3D) interconnected pore structures for Thermo, USA).
ingrowth of new bone and blood vessel [19-21] . 3D printing
technology is a layer-by-layer manufacturing process 2.3 Preparation of Zn-MS/PLLA composite
based on computer model, which can prepare scaffolds scaffolds
with sophisticated shape and internal structure . More
[22]
encouragingly, bioprinting is able to print personalized As for the preparation of mixed powders, Zn-MS powders
live tissues/organs and is expected to achieve the were mixed with PLLA powders by manual grinding for
substitute of patient-specific tissues/organs. Selective 1 h, and then the mixed powders were added in anhydrous
laser sintering (SLS), as one of the 3D printing techniques, ethanol and were agitated for 4 h under ultrasound
involves powder bed laser fusion additive manufacturing condition. After vacuum filtration and dry, the mixed
processes [23,24] . SLS exhibits great advantages in the powders were collected for laser forming. Zn-MS/PLLA
preparation of artificial bones, because there is no need composite scaffolds were prepared by self-developed SLS
for support materials, binders, or organic solvents during system. Specifically, the mixed powders were uniformly
laser forming [25,26] . Meanwhile, it possesses high printing spread on the platform, and the laser beam selectively
accuracy and material utilization rate. melts powders according to the designed pattern. After
In the present study, Zn-MS particles were finishing one layer, the platform moved down based on
synthesized through one-pot hydrothermal method, and the designed layer thickness, and then the powders were
then incorporated into the PLLA scaffold fabricated by spread on the platform again before melting by laser
SLS technology to improve its osteogenic activities. beam; finally, the scaffolds were prepared after layer-by-
The morphology, size, mesoporous structure, and layer melting. During the process of laser forming, the
compositions of the synthesized Zn-MS particles were laser power, scanning speed, spot diameter, scanning
analyzed. Meanwhile, the effect of Zn-MS on the line space, powder bed temperature, and powder layer
hydrophilicity, mechanical properties, ionic release, thickness were set to 2.4 W, 200 mm/s, 580 μm, 0.8 mm,
and cellular behaviors of the PLLA scaffold was 20°C, and 0.2 mm, respectively. The composite scaffolds
systematically evaluated. prepared with 2 wt.%, 4 wt.%, and 6 wt.% Zn-MS (with
respect to total weight of Zn-MS and PLLA powders)
2 Materials and methods were abbreviated as 2Zn-MS/PLLA, 4Zn-MS/PLLA, and
6Zn-MS/PLLA.
2.1 Preparation of Zn-MS
2.4 Characterization of Zn-MS/PLLA composite
In a typical method, 0.55 g of Zn(CH COO) (Aladdin, scaffolds
3
2
China) and 10 g of N,N-dimethylethanolamine (DMEA,
Aladdin, China) were dissolved in 5 mL of ultrapure The photos of Zn-MS/PLLA composite scaffolds were
water. Then, 3.32 g of tetraethyl orthosilicate (TEOS, took by a digital camera. The tensile fracture surfaces
Aladdin, China) was added. After reacting under an of the composite scaffolds were observed by SEM
ultrasonic condition at 50°C for 10 min, the gels were then equipped with an energy dispersive spectrometer (EDS).
moved to Teflon vessels which were placed in stainless The hydrophilic property of the composite scaffolds
steel autoclaves, and then hydrothermally reacted in an was measured using a surface contact angle analyzer
oven at 160°C for 24 h. Afterward, the white precipitates (DSA100, KRUSS, Germany). The compressive
were washed 3 times with ultrapure water and twice with strengths and stress-strain curves of the composite

International Journal of Bioprinting (2021)–Volume 7, Issue 2 93