Page 135 - IJB-8-3

Dong, et al.
hydrogels, due to their tensile strength and stiffness [8-10] . It CNs were aligned after extrusion. Furthermore, the printed
has been reported that CNs can also increase the viscosity well-oriented hydrogels induced L929 fibroblasts to grow
of hydrogels and enhance their printability, which is in a specific direction, paving the way for potential use in
beneficial in extrusion printing . CNs are one of the ordered biological soft-tissue repair [34-36] .
[11]
most promising fiber additives with multiple functions
in 3D printing applications . The polymer networks 2. Materials and methods
[12]
of CNs hydrogels are generally uniform and isotropic. 2.1. Materials
Although traditional CNs hydrogels can achieve a high
degree of biomimetic composition, they lack the ability (HA, MW 100-200 kDa) was purchased from Lifecore
to mimic the complex structure of biological tissues, for Biomedical (Chaska, MN, USA). Methacrylic anhydride
example, well-ordered structures . Recently, several and Irgacure 2959 were purchased from Sigma-Aldrich (St.
[13]
well-ordered hydrogels have been synthesized through Louis, MO, USA). The cotton linter pulps were provided
directional freezing [14,15] , electrostatic repulsion , by Hubei Chemical Fiber Group Ltd., (Xiangfan, China).
[16]
magnetic methods , stain- or compression-induced Other analytical grade chemicals were purchased from
[17]
reorientation , and self-assembly . It has been reported Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).
[18]
[19]
in some literatures, epichlorohydrin was applied to form
the loosely cross-linked points to mediate the cellulose 2.2. Preparation of CN+HAMA hydrogel
chains’ self-assembly and external stretching was used to precursors and hydrogels
promote fiber orientation [20-22] . Compared with the above Lithium hydroxide (LiOH) (4.5 wt%) and urea (15 wt%)
cellulose hydrogels synthesis processes, epichlorohydrin were dissolved in water and stirred sufficiently to obtain
and external force stretching were removed in our a homogenous solution. The cotton linter pulps were
study. Inspired by the fact that external forces induce mechanically ground for 1 h. At freezing temperatures,
rearrangement of hydrogel structures, we used extrusion- cotton linter pulps were added to the mixed solution with
based 3D printing process to promote fiber alignment . vigorous stirring. After several freeze–thaw cycles and
[23]
Alignment of the CNs along the hydrogel flow direction full stirring, a clear and transparent viscose solution of
occurs due to the shearing and extensional forces of the cellulose with a concentration of 4.5 wt% was obtained,
print nozzle . Siqueira et al. reported a shape morphing and the concentration of CN (4.5 wt%) is kept constant
[24]
and self-actuating alignment nanocellulose hydrogels across all formulations in the paper. The cellulose
prepared by extrusion-based 3D printing process . solution was ground using a super mass grinder to obtain
[25]
On the other hand, hyaluronic acid (HA) is known to act CN suspension.
as biocompatible and effectively adhesive material for HAMA was synthesized according to a previously
various cells [26-28] . For instance, Xavier Acasigua et al. published procedure . HAMA was added to the CN
[37]
prepared natural bacterial cellulose/HA as scaffolds for solution, and then, the system was stirred for 2–3 h
culturing human dental pulp stem cells. The cells were under an ice bath to obtain different concentrations of the
adhered to the fibers and well distributed in composite CN+HAMA solution. After full dissolution, the solution
scaffolds . Fan et al. developed a mechanically reinforced temperature was increased to 30°C to obtain CN+HAMA
[29]
hydrogel for the 3D culture of chondrogenic cells. In this hydrogel precursors (Figure S1). CN+HAMA hydrogels
model, CNs and GelMA/HAMA serve as the structural were formed after irradiation with UV light (365 nm).
support while GelMA/HAMA as the cytogel containing
a mouse chondrogenic cell line . Zhao et al. developed 2.3. Characterization of hydrogels
[30]
nanocomposite hydrogels composed of methacrylate-
functionalized CNs and HA methacrylate (HAMA), which Scanning electron microscopy (SEM, Zeiss/Sigma 300,
provided a good microenvironment for bone marrow America) was used to examine the morphology of the
mesenchymal stem cell proliferation, as well as exhibited freeze-dried CNs, HAMA, and CN+HAMA hydrogels at
prominent repair effect in the cartilage defect . different concentrations. All specimens were coated with
[31]
In our study, the CNs showed a reversible state change a conductive layer of sputtered gold. An accelerating
with temperature. The reversible temperature-sensitive voltage of 5 kV and a working distance of 5 mm were
property of the CN-related hydrogel precursors enables applied.
them to gel in situ (at body temperature) and return to 2.4. Temperature and UV dual-responsiveness of
original liquid state at low temperatures. Besides, HAMA CN+HAMA hydrogels
can respond quickly to ultraviolet (UV) irradiation.
Therefore, temperature and UV dual-responsive The prepared CN+HAMA hydrogel precursors of 1 mL
CN+HAMA hydrogels are promising candidates for were added into a straightly standing vial. To verify the
biomaterial inks in biofabrication [32,33] . Importantly, the reversible temperature-responsiveness of the hydrogel

International Journal of Bioprinting (2022)–Volume 8, Issue 3 127