Effect of solvent-matrix interactions on structures and mechanical properties of micelle-crosslinked gels

Mechano-Responsive, Tough, and Antibacterial Zwitterionic Hydrogels with Controllable Drug Release for Wound Healing Applications

Acute wounds subject to frequent deformations are difficult to be treated because the healing process was easily interfered by external mechanical forces. Traditional wound dressings have limited efficacy because of their poor mechanical properties and skin adhesiveness and difficulty in the delivery of therapeutic drugs effectively. As such, tough and skin-adhesive wound dressings with sustainable and stimuli-responsive drug release properties for treatment of those wounds are highly desirable. For this purpose, we have developed a mechano-responsive poly(sulfobetaine methacrylate) hydrogel which aims to control the delivery of antibiotic drug upon application of mechanical forces. Diacrylated Pluronic F127 micelles were used as a macro-cross-linker of the hydrogel and loaded with hydrophobic antimicrobial drugs. The micelle-cross-linked hydrogel has excellent mechanical properties, with the ultimate tensile strength and tensile strain of up to 112 kPa and 1420%, respectively, and compressive stress of up to 1.41 MPa. Adhesiveness of the hydrogel to the skin tissue was ∼6 kPa, and it did not decrease significantly after repetitive adhesion cycles. Protein adsorption on the hydrogel was significantly inhibited compared to that on commercial wound dressings. Because of the mechano-responsive deformation of micelles, the release of drug from the hydrogel could be precisely controlled by the extent and cycles of mechanical loading and unloading, endowing the hydrogel with superior antibacterial property against both Gram-positive and Gram-negative bacteria. In addition, drug penetration into the skin tissue was enhanced by mechanical stress applied to the hydrogel. The micelle-cross-linked zwitterionic hydrogel also showed good cell biocompatibility, negligible skin irritation, and healing capacity to acute skin wounds in mice. Such a tough mechano-responsive hydrogel holds great promise as wound dressings for acute wounds subjected to frequent movements.

Reinforced macromolecular micelle-crosslinked hyaluronate gels induced by water/DMSO binary solvent

Introducing macromolecular micelles into a biocompatible hyaluronic acid (HA) hydrogel is a promising strategy to improve its mechanical properties for biomedical applications. However, it is still unclear whether the solvent nature has an influence on the structure and property of HA gels especially when they are used for those cases containing binary solvents because reversible hydrophobic association within micelles could be weakened or even dissociated by organic solvents. In this work, we demonstrated that a binary solvent consisting of water and low-toxic dimethyl sulfoxide (DMSO), a commonly used cryoprotectant agent in biomedicine, can enhance the mechanical properties of hydrophobic-associated methacrylated hyaluronate (MeHA) gels crosslinked by diacrylated PEO99-PPO65-PEO99 (F127DA) macromolecular micelles, namely FH gels. The resulting FH hydro/organo-gels showed a crystalline structure due to polymer/solvent interactions. The FH gels showed a low swelling degree and the maximum strength (10.12 MPa), modulus (106.8 kPa) and toughness (1540 J m-2) in DMSO with a volume fraction of around 0.6. Moreover, the FH gels displayed a rapid recoverability under cyclic loading-unloading stress particularly in the presence of DMSO within the network due to their dual-dynamic dissipation networks. Such novel hydrophobic associated polysaccharide gels with tunable mechanical properties in binary solvents would be attractive in a cryopreservation system for cell-based applications.

Structural evolution of dispersed hydrophobic association in a hydrogel analyzed by the tensile behavior

The use of dispersed cross-links with different levels of strength is one of the most successful strategies for toughening a hydrogel. By using a model hydrogel having dispersed association of single-component short alkyl chains, this work demonstrates that the differential modulus-elongation relation derived from tensile curves can reflect the structural evolution of dispersed cross-links at a molecular level. This analysis method allows for decoupling the mechanical contribution of strong and weak hydrophobic clusters, which serve as the minor and major cross-links in our system, respectively. At small deformation, the weak hydrophobic associations majorly determine the stiffness, and their rupture releases folded partial chains to endow deformation capacity. At large deformation, the strength ratio of strong and weak hydrophobic association should be balanced to achieve the optimal strength. Furthermore, the structural parameters of these partial chains, including the Kuhn number, the Kuhn length and the chain conformation, are determined based on scaling theory of extensibility. These results allow for correlating the apparent mechanics to the structural parameters of the dispersed hydrophobic association, paving the way for customized mechanics for specific applications.

Stiff micelle-crosslinked hyaluronate hydrogels with low swelling for potential cartilage repair

Pluronic F127 diacrylate (F127DA) nano-micelle crosslinked methacrylated hyaluronic acid (MeHA) hydrogels (NMgels) with strong compressive properties have been demonstrated in our previous study. The current study further focuses on how the F127DA micelles and long-term swelling affect the mechanical performance of hydrogels from the view of in vitro/in vivo applications. Co-contributions of the F127DA micelles and MeHA to the compression performance are first investigated through mechanical analysis and cyclic loading/unloading tests before and after swelling. The optimized NMgel with F127DA micelles of 15 wt% and MeHA of 1.5 wt% (F15H1.5) exhibits a low swelling ratio and a well-maintained network in pH = 7.4 phosphate buffered saline. The abundant hydration significantly affects the initial mechanical properties of the hydrogels. After swelling, the compressive strength, modulus and fracture energy of F15H1.5 NMgel decrease from ∼3.44 MPa, ∼312 kPa and ∼407.5 kJ m-3 to 0.59 MPa, ∼55 kPa, and ∼81.8 kJ m-3, respectively. The energy dissipation of the first loading-unloading cycle dramatically decreases from ∼21.5 kJ m-3 to ∼6.0 kJ m-3 as well. Nevertheless, the gel still retains excellent stiffness, toughness and self-recovery due to the dense and strong micelle linkages. In vivo studies show that the implantation of F15H1.5 hydrogel in thyroid cartilage defects of rabbit larynx effectively promotes the regeneration of cartilage after 8 weeks. These results indicate that the stiff NMgel is a promising cartilage tissue engineering scaffold for the regeneration of cartilage in vivo.