Figure 3. Characterization of CMC-DA hydrogel. (A) SEM
morphology of the 4% hydrogels (Scale bar: 20 μm) and (B) statistical
results of hydrogel pore size. (C) Swelling property of hydrogels in
different buffer with pH of 7, 6 and 5 respectively. (D) Hydrogels in
different buffer with pH of 8, 7 and 6 in 3 days, and the (E)
representative images, the pH is 8, 7 and 6 from left to right,
rhodamine B staining was applied to the hydrogel to enhance contrast.
Stress–strain curves of 5% (F) and 4% (G) hydrogels in pH of 8, 7 and
6. (H) The Young’s modulus of 5%
and 4% hydrogels in pH of 8, 7 and 6. Strain sweep of (I) 5% and (J)
4% hydrogels under an angular frequency of 1 Hz, the crossover of
storage modulus (G’) and loss modulus (G”) indicates the breakage
strain. Frequency-sweep curves of the (K) 5% and (L) 4% hydrogels at a
fixing strain of 3%. (M) Evolution of 4% hydrogel viscosity with shear
rate. (N) The injectability and the appearance of the 4% hydrogel.
Through early research of click chemistry based on activated alkynes and
amines, it was found that an amino groups containing long-chain polymer
can spontaneously react with ester-actived alkyne-modified linkers to
form a cross-linked network structure. [40.41]When water molecules are tightly interlocked within the cross-linked
network structure, the hydrogel can be formed. Commercially accessible
and water-soluble CMC contains abundant amino groups, as well as good
bacteriostatic, coagulative, biocompatible and biodegradable
characteristics.[42] In this work, we prepared and
characterized a di-actived alkyne modified PEG-4000 cross-linking agent
(PEG-DA) (Figure S11), which was utilized for a catalytic free hydrogel
(CMC-DA) preparation with CMC at room temperature.
The micromorphology of the CMC-DA hydrogel was observed by scanning
electron microscope (SEM) (Figure 3A). The hydrogel exhibits a uniform
pore size distribution, as shown in Figure 3B, with an average diameter
of approximately 4.0 μm. The high porosity percentage and interconnected
pores of hydrogel provide sufficient space for loading nanovesicles and
facilitate nutrient transport. The successful preparation of the
hydrogel can also be confirmed by the Fourier transform infrared (FT-IR)
spectrum (Figure S12). According
to the test with a concentration of 1.5%~5% and a
ratio of activated alkyne and
amine groups at 1:1 (Table S1), gelation can proceed smoothly when the
concentration exceeds 3%. The increase in concentration promoted the
speed of gelation and mechanical strength.