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.