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Composite Scaffolds for Skin Repair
can promote cell migration, oxygen permeability, and purchased from Sigma-Aldrich Co., Ltd. (USA),
ingrowth of surrounding tissue [8-10] . Thus, 3D-printed methacrylic anhydride (MA) was purchased from
scaffolds have great potential to satisfy the requirements Shanghai Titan Scientific Co., Ltd. (China).
of ideal wound dressings .
[7]
With the aim to endow wound dressings with multiple 2.2. Synthesis of GelMA hydrogel
biofunctions, the novel approach of incorporating various A 20 g of gelatin was weighed and dissolved in 200 mL
inorganic biomaterials into soft polymers has been of deionized water at 50°C, and then, 12 mL of MA was
explored. In the past few years, silica has aroused great added to react for 3 h. After the reaction completed,
attention in the field of tissue engineering [11-13] , due to the centrifugation was performed at 3500 rpm/min for 3 min.
enhanced collagen deposition and blood vessel formation Then, the supernatant was collected and diluted for 3 –
induced by silicon (Si) element during the wound healing 5 times. Next, the product was put into a dialysis bag and
process [14,15] . However, traditional methods for preparing dialyzed at 40°C for 7 days. Finally, GelMA was obtained
silica with nanostructure are cumbersome procedures by freeze-drying the product.
and may introduce organic impurities , which limit its
[16]
application to a certain extent . 2.3. Synthesis of DE-GelMA composite inks
[17]
Encouragingly, diatomite (DE, SiO ·nH O) is
2
2
siliceous skeleton deposited by natural diatom. With DE microparticles were sieved using a 500 mesh screen
and sterilized under ultraviolet light for 1 h. Next, sterile
uniform porous architecture, DE possesses several phosphate-buffered saline (PBS) was added and followed
superior properties, including good mechanical strength, by sonication for at least 1 h to form DE dispersion.
excellent absorption performance, high specific surface Besides, the same volume of PBS was added to dissolve
area, and hydrophilicity [18-20] . As a natural occurring the weighed GelMA and LAP powders at 65°C to obtain a
mineral compound, the applications of DE in biomedical 12% (v/v) GelMA solution. After that, the DE dispersion
engineering such as reinforcement, sensing, drug and GelMA solution were thoroughly mixed to obtain a
delivery, and hemostasis have been investigated [21-25] . DE-containing ink with a GelMA concentration of 6% for
More importantly, DE exhibits great potential to serve the following 3D printing.
as a stable Si source to release bioactive Si ion which
can improve tissue regeneration . On this ground, it is 2.4. 3D printing of DE-Gel scaffolds
[26]
reasonable to speculate that this natural cost-effective
filler can be used to construct a composite wound dressing The fabrication of 3D-printed scaffolds in the study
with desirable bioactive properties. relied on a bioprinting platform with a cooling channel
Herein, we successfully prepared a bioactive DE (BioScaffolder 3.2, GeSiM, Germany). The composite
incorporated composite scaffold through 3D printing inks with gradient DE content (Gel, 5DE-Gel, 10DE-Gel,
technology for the treatment of burn damaged skin. 20DE-Gel, and 30DE-Gel) were stored in 4°C refrigerator
The biocompatible DE microparticles were sieved and to form pre-gel and then used for extrusion 3D printing,
embedded in gelatin methacryloyl (GelMA) hydrogel respectively. During the printing process, the pre-gelled
to form inorganic/organic composite ink for the ink was extruded out through a 27 G needle (250 μm)
development of 3D-printed scaffold. Taking advantage under proper air pressure (40 – 60 kPa) at 10°C. After
of DE, the 3D-printed composite scaffolds exhibited that, the printed scaffold was exposed to blue light about
prominent abilities to support cell spreading, promote 45 s for cross-linking.
cell proliferation, and enhance vascularization in vitro. 2.5. Characterization of DE microparticles, DE-
In addition, the effective influences of 3D-printed GelMA inks, and the 3D- printed scaffolds
DE incorporated scaffolds on blood vessel formation,
collagen deposition, and tissue regeneration of skin The morphologies, structure, and elemental distribution
wounds were confirmed in the deep second-degree burn of the freeze-dried DE-containing 3D-printed scaffolds
wound model. Therefore, the DE incorporated scaffolds were detected by applying a scanning electron
can be considered as promising candidates to facilitate microscopy (SEM, SU8220, Hitachi, Japan) with an
the regeneration of vascularized tissue in a convenient equipment of energy-dispersive spectroscopy (EDS). The
and efficient manner. SEM (SU9000, Hitachi, Japan) was used to determine
the morphology of DE microparticles. The phase
2. Materials and methods identification of DE microparticles was conducted rely on
2.1. Materials X-ray diffraction (Rigaku D/Max-2550 V, Geiger-Flex,
Japan). Besides, a MCR301 rotational rheometer (Anton
Diatomaceous silica (DE), gelatin, and lithium phenyl- Paar GmbH, Austria) was used to test the viscosity of
2,4,6-trimethyl-benzoylphosphinate (LAP) were DE-GelMA composite inks at changing shear rate (0.1

164 International Journal of Bioprinting (2022)–Volume 8, Issue 3