For treating bone defects in periarticular fractures, there is a lack of biomaterial with injectable characteristics, tough structure, and osteogenic capacity for providing a whole‐structure support and osteogenesis in the defect area. An injectable hydrogel is an ideal implant, however is weak as load‐bearing scaffolds. Herein, a new strategy, i.e., an in situ formation of “active” composite double network (DN), is raised for the preparation of an injectable strong hydrogel particularly against compression. As a demonstration, 4‐carboxyphenylboronic acid grafted poly(vinyl alcohol) (PVA) is crosslinked using calcium ions to provide a tough frame while bioactive glass (BG) microspheres are associated by poly(ethylene glycol) to obtain an interpenetrated inorganic network for reinforcement. The injected PVA/BG DN hydrogel gains compressive strength, modulus, and fracture energy of 34 MPa, 0.8 MPa, and 40 kJ m−2, respectively. Then, the properties can be “autostrengthened” to 57 MPa, 2 MPa, and 65 kJ m−2 by mineralization in 14 days. In vivo experiments prove that the injected DN hydrogel is more efficient to treat femoral supracondylar bone defects than the implanted bulk DN gel. The work suggests a facile way to obtain a strong hydrogel with injectability, cytocompatibility, and tailorable functionality.
A high-performance hydrogel was synthesized by a facile dual dynamic crosslinking strategy that showed injectability, cytocompatibility, broadly tunable mechanical properties and the potential for repair of load-bearing tissues.
The regeneration of dental pulp tissue is very important, but difficult, in dentistry. The biocompatibility, water content, and viscoelastic properties of pulp-like tissue must be optimized to achieve the efficient transfer of metabolites and nutrients, a suitable degradation rate, distribution of encapsulated cells, injectability, and gelation in situ under physiological conditions. As promising materials for pulp regeneration, hydrogel scaffolds have been produced to simulate the extracellular matrix and transmit signaling molecules. It is imperative to develop hydrogels to effectively regenerate pulp tissue for clinical application. Here, two injectable double-network (DN) hydrogelbased three-dimensional (3D) cell culture systems were developed for regenerating dental pulp. The microstructure, mechanical property, rheology property, and degradation behavior of the injectable DN glycol chitosan-based hydrogels in a simulated root canal model were characterized and compared to a single-network (SN) glycol chitosan-based hydrogel. Human dental pulp stem cells (hDPSCs) were then encapsulated into the GC-based hydrogels for the regeneration of pulp tissue, and the biological performance was investigated both in vitro and in vivo. The results showed that the DN hydrogels had ideal injectability under physiological conditions due to the dynamic nature of the crosslinks. Besides, the DN hydrogels exhibited better mechanical properties and longer degradation duration than the corresponding SN hydrogel. As a 3D cell culture system, the characteristics of the DN hydrogel facilitated odontogenic differentiation and mineralization of hDPSCs in vitro. Further in vivo analysis confirmed that the chemical composition, matrix stiffness, and degradation rate of the DN hydrogel matched those of pulp-like fibrous connective tissue, which might be related to Smad3 activation. These findings demonstrate that DN glycol chitosan-based hydrogels are suitable for the regeneration of pulp tissue.
Periarticular injury usually causes the defects of superficial cartilage and the underlying subchondral bone. Although some efficacious outcomes have been achieved by the existing therapeutic methods both in clinics and research, like symptomatic treatment, microfracture surgery, and tissue engineering technology, they still present specific disadvantages and complications. To improve this situation, we designed a biphasic (bi-) scaffold aiming to repair the structure of cartilage and subchondral bone synchronously. The scaffold consisted of a superior double-network (DN) hydrogel layer and a lower bioactive glass (BG) reinforced hydrogel layer, and the DN hydrogel included glycol chitosan (GC) and dibenzaldhyde functionalized poly(ethylene oxide) network, and sodium alginate (Alg) and calcium chloride (CaCl 2 ) network. To investigate its effectiveness, we applied this biphasic scaffold to repair osteochondral full-thickness defects in rabbit models. We set up six observation groups in total, including Untreated group, Microfracture group, BG only group, DN gel group, bi-DN gel group, and bi-DN/TGF-β gel group. With a follow-up period of 24 weeks, we evaluated the treatment effects by gross observation, micro-CT scan and histological staining. Besides, we further fulfilled the quantitative analysis of the data from ICRS score, O’Driscoll score and micro-CT parameters. The results revealed that neat GC/Alg DN hydrogel scaffold was only conductive to promoting cartilage regeneration and neat BG scaffold merely showed the excellent ability to reconstruct subchondral bone. While the biphasic scaffold performed better in repairing osteochondral defect synchronously, exhibiting more well-integrated cartilage-like tissue with positive staining of toluidine blue and col II immunohistochemistry, and more dense trabecular bone connecting closely with the surrounding host bone. Therefore, this method possessed the clinical application potential in treating articular injury, osteochondral degeneration, osteochondral necrosis, and sclerosis.
To overcome the issue of the compromise between processability and mechanical property of hydrogels, a percolation-driven programmable processing method is proposed toward the preparation of plastic composite hydrogels with a high compressive modulus in a megapascal scale. The hydrogel was constructed by the incorporation of a thixotropic fluid, for example, a silica microsphere (SiMP)/sodium alginate composite, into an elastic polymer network, such as dynamically cross-linked poly(vinyl alcohol)/4-carboxyphenyl boronic acid, followed by the adjustment of interpolymer interactions. Above a threshold of SiMP content, the isolated particle lattice in the gel was interconnected by the highly entangled alginate as well as PVA chains to form a percolation double network (p-DN), leading to enhanced thixotropy to allow the processing of the hydrogel into desired shapes. Subsequently, the plasticity of the p-DN hydrogel was converted to stiffness by confining the movement of polymer chains through additional cross-linking using multivalent cationic ions. The rigidity of calcium alginate resists the dislocation of the particles in the percolation network while the elasticity of PVA holds the integrity of the hydrogel to obtain the high compressive modulus against force loading. This strategy is general to achieve processable high-performance p-DN hydrogels with varied compositions.
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