Currently, biodegradable
hydrogels are one of the most promising
materials in tissue engineering. From the perspective of clinical
needs, hydrogels with high strength and minimally invasive implantation
are preferred for the reconstruction of load-bearing tissues. In this
work, a biodegradable, high-strength, and injectable hydrogel was
developed by one-step photo-cross-linking of two biomacromolecules,
polyethylene glycol acrylated poly(l-glutamic acid) (PLGA-APEG)
and methacrylated gellan gum (GG-MA). The hydrogels, named as PLGA/GG
hydrogels, exhibited high mechanical properties. The compression stress
of the hydrogels was 0.53 MPa, and the fracture energy was 7.7 ±
0.2 kJ m–2. Meanwhile, the storage modulus could
reach 44.0 ± 0.6 kPa. The hydrogel precursor solution loaded
with adipose-derived stem cells (ASCs) was subcutaneously injected
into C57BL/6 mice and then cross-linked via in situ transdermal irradiation,
which demonstrated the excellent injectability and subcutaneous gelatinization
of PLGA/GG hydrogels as cell carriers. Furthermore, three-dimensional
encapsulation of ASCs in hydrogels after 7, 14, and 21 days showed
outstanding cytocompatibility, and the viability of ASCs was up to
84.0 ± 1.7%. The PLGA/GG hydrogels exhibited ideal behaviors
of degradation, with 60 ± 5% of hydrogels degraded in phosphate
buffered solution (PBS) after 11 weeks. H&E staining demonstrated
that the hydrogels degraded gradually after 6 weeks and supported
tissue invasion without inflammatory reactions, which indicated the
laudable biodegradability of hydrogels. Hence, the biodegradable and
high-strength hydrogels with well-performed injectability and biocompatibility
possessed high potential applications in tissue engineering, especially
in load-bearing tissue regeneration.
A new generation of osteochondral integrated scaffolds is needed for articular osteochondral regeneration, which can not only facilitate the accurate construction of osteochondral scaffolds in a minimally invasive manner but also firmly combine the subchondral bone layer and cartilage layer. Herein, an osteochondral integrated hydrogel scaffold was constructed by the poly(L-glutamic acid) (PLGA) based self-healing hydrogels with phenylboronate ester (PBE) as the dynamic cross-linking. The bone layer self-healing hydrogel (hydrogel O-S) was prepared by physically blending nanohydroxyapatite (nHA) into the self-healing hydrogel PLGA-PBE-S, which was fabricated by 3-aminophenylboronic acid/glycidyl methacrylate-modified PLGA (PLGA-GMA-PBA) and 3-amino-1,2-propanediol/N-(2-aminoethyl) acrylamide-modified PLGA (PLGA-ADE-AP). The cartilage layer self-healing hydrogel (hydrogel C-S) was prepared by PLGA-GMA-APBA and glucosamine- modified PLGA-ADE-AP (PLGA-ADE-AP-G). Excellent injectability and self-healing profiles of hydrogel O-S and C-S were observed, the self-healing efficiencies were 97.02 ± 1.06% and 99.06 ± 0.57%, respectively. Based on the injectability and spontaneous healing on the interfaces of hydrogel O-S and C-S, the osteochondral hydrogel (hydrogel OC) was conveniently constructed in a minimally invasive manner. In addition, in situ photocrosslinking was used to enhance the mechanical strength and stability of the osteochondral hydrogel. The osteochondral hydrogels exhibited good biodegradability and biocompatibility. The osteogenic differentiation genes BMP-2, ALPL, BGLAP and COL I of ASCs in the bone layer of the osteochondral hydrogel were significantly expressed, and the chondrogenic differentiation genes SOX9, aggrecan and COL II of ASCs in the cartilage layer of the osteochondral hydrogel were obviously upregulated after 14 days of induction. The osteochondral hydrogels could effectively promote repair of osteochondral defects after 3 months post-surgery.
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