Lijie Duan

Injectable polysaccharide hybrid hydrogels as scaffolds for burn wound healing

In this study, a type of injectable polysaccharide-based hydrogels were prepared via the Schiff-base crosslinking reaction between the amino groups of carboxymethyl chitosan (CMC) and the aldehyde groups of oxidized dextran (Odex). The gelation time of the CMC/Odex hybrid hydrogels was 25–50 s, depending on the CMC/Odex weight ratio. The hydrogel displayed a storage modulus of ∼1 kPa, and the freeze-dried hydrogel showed an interconnected porous structure. The in vitro degradation test of the hydrogel in PBS showed a fast mass loss in the first 2 days, and then a gradual degradation profile over 4 weeks. The in vitro cytotoxicity and the ability to support cell attachment of the hydrogels were tested by incubation with L929 cells. The results indicated that the hydrogels displayed good cytocompatibility, and the hydrogels with relatively higher CMC content supported the attachment of L929 cells. Moreover, the potential application of the hydrogels in burn wound healing was tested on SD rats with a deep second-degree burn wound. It was found that the group treated with the CMC/Odex hydrogel showed nearly complete wound closure at 21 days after the treatment compared to unsatisfactory wound healing efficiency of the untreated group. Additionally, the histological analysis by H&E and Massons trichrome staining indicated clearly the regeneration of skin appendages, including hair follicles, sebaceous glands and dermal papillary, suggesting that the treatment with the hydrogel promoted the wound healing and skin regeneration. Overall, the injectable polysaccharide hybrid hydrogels may serve as suitable scaffolds for promoting burn wound healing and skin regeneration.

Robust, tough and anti-fatigue cationic latex composite hydrogels based on dual physically cross-linked networks

Dual physically cross-linked hydrogels, which are triggered by cationic latexes as hydrophobic association and ionic crosslinking centers, were easily fabricated via a one-pot in situ polymerization method. First, the hydrophobic alkyl chains of hydrophobic monomers are adsorbed on the surface of latex microspheres and stabilized in the presence of surfactants, forming hydrophobic association centers as the first physical crosslinking points. Meanwhile, the anionic sulfate radicals dissociated by persulphate are attracted towards the cationic molecular chains of latex microspheres through ionic interactions, forming the secondary physical crosslinking centers, and initiate the copolymerization between acrylamide and hydrophobic vinyl monomers. The fabricated hydrogel exhibited high tensile strength of 1.32MPa, a remarkable toughness of 4.53MJm-3, excellent self-recovery properties and fatigue resistance. Therefore, the current work provides a promising strategy for designing novel hydrogels via multiple physical interactions and devoid of any chemical crosslinking. The novel design of hydrogels can enhance their mechanical properties and expand their biomedical applications.

Enhancing the self-recovery and mechanical property of hydrogels by macromolecular microspheres with thermal and redox initiation systems

In this investigation, a tough hydrogel was reinforced by macromolecular microspheres (MMs) as hydrophobic association centers via free radical polymerization with different initiation systems. The thermal initiator is potassium persulfate and the redox initiators include potassium persulfate and N,N,N′,N′-tetramethylethylenediamine (TMEDA). The mechanical measurements showed that the hydrogel with a redox initiation system possesses a tensile strength of 1.55 MPa, which is much higher than the hydrogel with a thermal initiator. Moreover, the hydrogel with redox initiators exhibited rapid self-recovery to its 90% original dimension in several seconds and low swelling property. The large difference in the morphology of hydrogels before and after swelling was due to the tight entanglement of molecular chains in the internal structure of hydrogels with redox initiators. As a result, the hydrophobic association hydrogels toughened by MMs with excellent mechanical properties would be useful for biomedical applications of tough tissue engineering, such as tendon, muscle, and blood vessel.

The effect of hydrophobic alkyl chain length on the mechanical properties of latex particle hydrogels

Herein, different long alkyl chains (C1, C6, C12, and C16) were introduced as hydrophobic segments to enhance the performance of hydrogels reinforced by latex particles (LP-Gel). Poly(butyl acrylate) (PBA) latex particles (LPs) were employed as hydrophobic association cross-linking centers. First, the PBA latex particles were prepared via emulsion polymerization, and then, LP-Gel with high mechanical strength was prepared via one-pot free radical polymerization using acrylamide as a monomer, LP as a cross-linking center, and methacrylate as a hydrophobic molecule. It was found that the length of the hydrophobic alkyl chains from methacrylate has a significant effect on the mechanical performance and swelling degree of the hydrogels. The short alkyl chains exhibited weak hydrophobic interactions, and the resulting LP-Gel had a low mechanical strength. However, the long alkyl chains can effectively entangle with LPs through strong hydrophobic interactions, which significantly enhance the mechanical strength of the hydrogels. As a result, the LP-Gel exhibits a maximum fracture stress of 1.2 MPa and elongation of 2336%. This study will have a profound impact on the understanding of hydrogels toughened by hydrophobic alkyl chains of different lengths.

A rapidly responsive photochromic hydrogel with high mechanical strength for ink-free printing

Ink-free printing based on photochromism has attracted great attention as a new generation of printing technology. However, the current photochromic materials are limited due to slow response and high cost. In this investigation, a rapidly responsive photochromic hydrogel with high mechanical strength was explored through the introduction of cheap ammonium molybdate into gelatin and hydrophobic associative polyacrylamide. The photochromic hydrogel exhibited excellent mechanical strength of 750 kPa and a rapidly responsive photochromic process of 5 seconds with UV light irradiation. Moreover, the hydrogel could withstand long elongation and high compressive stress with shape recovery ability. The rapid photochromic properties gave hydrogels with fast and easy “printing” performance. More importantly, the “printed” text or pattern in hydrogels could be erased at 70 °C in an oxygen environment. In addition, the hydrogel could be written on in characters by using reducing reagents. Photochromic hydrogels with ink-free printing ability would demonstrate a new design strategy for soft materials with low-cost, rapid response and high mechanical properties.

Multipurpose and Durable Adhesive Hydrogel Assisted by Adenine and Uracil from Ribonucleic Acid

Nucleobase pairs of adenine and uracil (A-U) from ribonucleic acid are of particular interest for various promising material properties. Herein, a novel polyacrylamide hydrogel with adhesive properties that are assisted by adenine and uracil has been designed and investigated. The incorporation of adenine and uracil enables the formation of a polyacrylamide hydrogel with remarkable adhesive behaviour with various materials including polytetrafluoroethylene (PTFE), plastics, rubber, glasses, metal, ceramics and wood. Moreover, the adhesive hydrogel can easily and directly adhere to humid biological tissues without any extra process, including heart, liver, spleen, lung, kidney, bone and muscle of mouse. More impressively, even after repeated peeling tests (10×), the AU-mediated polyacrylamide hydrogel still exhibits excellent durable adhesion for various materials. From mechanical contact tests, the adhesion energy of the A-U adhesive hydrogel is 47.9 J m-2 , which is nearly nine times that of polyacrylamide hydrogel (5.3 J m-2 ). The 90° peeling strength for aluminium, titanium, silica rubbers, glasses, PTFE and hogskin is 518, 645, 445, 396, 349, and 119 N m-1 , respectively. The multipurpose and durable adhesive behaviour of hydrogels assisted by adenine and uracil indicated the promise of nucleobase pairs from ribonucleic acid for the future development of adhesive materials.

Tough, sticky and remoldable hydrophobic association hydrogel regulated by polysaccharide and sodium dodecyl sulfate as emulsifiers

Hydrophobic association hydrogels have been extensively studied during the past decades. However, the fracture stress of hydrophobic association hydrogels obtained with anionic surfactants (such as sodium dodecyl sulfate) achieved hundreds of Pascal. In this investigation, combined surfactants consisting of polysaccharide (gum arabic) and sodium dodecyl sulfate were utilized to stabilize hydrogels with high fracture stress of more than 1 MPa. Moreover, the hydrogels exhibited excellent self-healing capacity and remoldable behavior without any stimulation. Simultaneously, the hydrogels demonstrated an adhesive behavior for various solid substrates including polytetrafluoroethylene, plastics, rubbers, glasses, metals and woods. The hydrogel with toughness, self-healing, stickiness and remoldable properties would be expected to be applied in the medical fields, such as wound dressing, medical electrodes, tissue adhesives and portable equipment.