Synthesis of multifunctional high strength, highly swellable, stretchable and self-healable pH-responsive ionic double network hydrogels

Constructing a self-healing injectable SABA/Borax/PDA@AgNPs hydrogel for synergistic low-temperature photothermal antibacterial therapy

Infections caused by bacteria are one of the biggest challenges humans face around the world. Photothermal therapy (PTT) has been regarded as a promising strategy in combating pathogenic infection, however the high temperatures (55-65 °C) required during a single PTT process can induce injury to healthy tissues nearby. Combination therapy could overcome this problem by reducing the photothermal temperature. Here, we developed a self-healing and injectable hydrogel to realize low-temperature PTT (LT-PTT, ≤45 °C) for antisepsis with high-efficiency. The hybrid hydrogel is prepared by incorporating borax into a mixture of 3-aminophenylboronic acid grafted sodium alginate and nano-silver decorated polydopamine nanoparticles. Our results showed that the SABA/Borax/PDA@AgNPs hydrogel possesses satisfactory mechanical properties and self-healing capacity, and as a result, it can repair itself after being damaged mechanically, retaining its integrality and recovering its initial functionalities. Furthermore, through utilizing the photothermal property of polydopamine nanoparticles and broad-spectrum antibacterial activity of nano-silver, the hybrid hydrogel achieves excellent LT-PTT for sterilization both in vitro as well as in an in vivo mice skin wound model with no distinct injury to normal tissues. Overall, our prepared hydrogel is expected to be an excellent candidate for treating bacterial infections.

Modulation of hydrogel networks by metal ions

Self-assembling hydrogels are receiving great attention for both biomedical and technological applications. Self-assembly of protein/peptides as well as organic molecules is commonly induced in response to external triggers such as changes of temperature, concentration, or pH. An interesting strategy to modulate the morphology and mechanical properties of the gels implies the use of metal ions, where coordination bonds regulate the dynamic cross-linking in the construction of hydrogels, and coordination geometries, catalytic, and redox properties of metal ions play crucial roles. This review aims to discuss recent insights into the supramolecular assembly of hydrogels involving metal ions, with a focus on self-assembling peptides, as well as applications of metallogels in biomedical fields including tissue engineering, sensing, wound healing, and drug delivery.

Recent Advances in Smart Hydrogels Prepared by Ionizing Radiation Technology for Biomedical Applications

Materials with excellent biocompatibility and targeting can be widely used in the biomedical field. Hydrogels are an excellent biomedical material, which are similar to living tissue and cannot affect the metabolic process of living organisms. Moreover, the three-dimensional network structure of hydrogel is conducive to the storage and slow release of drugs. Compared to the traditional hydrogel preparation technologies, ionizing radiation technology has high efficiency, is green, and has environmental protection. This technology can easily adjust mechanical properties, swelling, and so on. This review provides a classification of hydrogels and different preparation methods and highlights the advantages of ionizing radiation technology in smart hydrogels used for biomedical applications.

Microgel-integrated, high-strength in-situ formed hydrogel enables timely emergency trauma treatment

High-strength hydrogels formed in situ through a convenient gel transition process are highly desirable for emergency treatment due to their ability to quickly respond to accidents. However, current in-situ formed hydrogels require a laborious precursor preparation process or lack sufficient mechanical strength. Herein, we reported a series of microgels that were capable of convenient in-situ transition to high-strength hydrogels from their easily portable form, thereby facilitating emergency treatment. Three kinds of microgels were derived from two types of hydrogen bonds (H-bonds; OH⋯OC, NH⋯OC) crosslinked preformed hydrogels, and all exhibited excellent stability when stored at room temperature. After mixing with water, all these microgels could undergo a quick hydration process and then transform into high-strength hydrogels in situ through H-bonds. Specifically, stronger H-bond crosslinked microgels could build hydrogels with higher mechanical strength, albeit at the cost of longer hydration and operation time. Nevertheless, the whole operation process could be finished within several minutes, and the resultant hydrogels could exhibit maximally megapascal-level compressive strength and tens of kilopascal storage modulus. In the comparison of emergency application performance with commercial chitosan hemostatic powder (CHP), we found that the microgels could stop accidental bleeding almost immediately, and the whole process from taking out the stored microgels to hemostasis could be completed within 15 s, which was superior to CHP. Overall, the results indicated that the in-situ formed microgel-based hydrogels with convenient gel-transition ability and high strength showed great potential in emergency treatments.

An UV-photo and ionic dual responsive interpenetrating network hydrogel with shape memory and self-healing properties

Shape memory hydrogels have attracted extensive attention in fields such as artificial tissues, biomimetic devices and diagnostics, and intelligent biosensors. However, the practical applications were hindered by the absence of self-healing capability and multi-stimuli-responsiveness. To address these issues, we developed a shape memory hydrogel with self-healing and dual stimuli-response performance. The hydrogel system was constructed via an interpenetrating network consisting of in situ radical polymerization and host-guest interaction. The hydrogel exhibited rapid self-healing property, which can be stretched after self-healing for 1 min at 25 °C. Besides, the hydrogel displayed varied swelling performance in different light or solvent conditions. Moreover, the hydrogel showed a dual stimuli-responsive shape memory effect to ultraviolet (UV) light and ionic strength in 1 min. Such a shape memory hydrogel with self-healing ability and multi-stimuli-responsive properties will offer an option toward intelligent soft materials for biomedical and bionic research.

Robust versatile nanocellulose/polyvinyl alcohol/carbon dot hydrogels for biomechanical sensing

A new type of nanocellulose/poly(vinyl alcohol)/carbon dot (NPC) multifunctional hydrogel was successfully fabricated by an one-step in-situ hydrothermal method. The one-pot strategy led to the formation of a complex hydrogen bonding/dynamic boric acid ester/nitrogen-doped carbon dots network, and endowed the hydrogel with multifunctionality. The hydrogel underwent self-healing at room temperature (25 °C) and exhibited double-emission fluorescence and high mechanical strength (tensile strength of up to 2.98 MPa). An NPC hydrogel-based capacitive sensor exhibited remarkable linear capacitance responsiveness toward pressure, strain, and glucose concentration, and enabled real-time synchronous quantitative pressure/glucose sensing with multiple linear correlations, which was a key performance criteria for biomechanical sensors. The versatility and multiple advantages of the as-prepared hydrogel demonstrate the potential of biological-mechanical sensing materials using natural cellulosic biomass.

Crucial roles of graphene oxide in preparing alginate/nanofibrillated cellulose double network composites hydrogels

In this study, a novel strategy to prepare sodium alginate (SA)/nano fibrillated cellulose (NFC) double network (DN) hydrogel beads with the aid of graphene oxide (GO) was developed. In comparison with the multi-step freezing-thawing method, this study employs a facile one-step freeze drying method with the presence of GO sheets. The crucial roles of GO were highlighted as an efficient nucleating agent of NFC and a reinforcer for the hydrogel. The adsorption property of the DN hydrogel towards crystal violet (CV) was also studied. Results indicated that the introduction of GO could greatly facilitate the formation of double networks. Furthermore, the as-prepared DN hydrogel beads exhibited an efficacious adsorption property towards CV. The maximum adsorption capacity of the hydrogels for CV was observed as 665 mg g^-1. Therefore, our approach here represents a facile method for the preparation of crystalline polymer based DN hydrogels to replace the awkward freezing-thawing process, giving inspiration for DN hydrogels design and preparation. Moreover, due to its efficient adsorption capacity, the hydrogels hold great promise for the water pollution control materials.

Facile synthesis of self-healing and layered sodium alginate/polyacrylamide hydrogel promoted by dynamic hydrogen bond

Hydrogels are widely used in many fields but generally suffer from low mechanical strength and poor self-healing performance. Here, a novel and facile method was developed to prepare a semi-interpenetrating polymer network (semi-IPN) hydrogel with layered structure and improved properties based on sodium alginate (SA) and polyacrylamide (PAM). Systematic characterizations revealed a formation mechanism of layered structure via hydrogen bonds (HBs) promoted self-assembly of SA in the porous PAM matrix. Also, HBs can also display a key role in enhancing self-healing of the hydrogel, by which the hydrogel possesses a self-healing capacity of 99 % with sprayed by a few of water. Moreover, the layered semi-IPN structure makes the tensile strength of PAMSA hydrogel reach 266 kPa. The fabricated PAMSA hydrogel with layered microstructure containing SA provides a protocol to broaden the functionality and variety of the hydrogels.

Self-healable poly(acrylic acid-co-maleic acid)/glycerol/boron nitride nanosheet composite hydrogels at low temperature with enhanced mechanical properties and water retention

Many living tissues possess excellent mechanical properties and water retention which enable them to self-heal at room temperature even below the freezing temperature of water. To mimic the unique features of living tissue, a poly(acrylic acid-co-maleic acid) composite hydrogel with enhanced mechanical properties and remarkable water retention was fabricated under accessible conditions. The hydrogel is functionalized by amino group modified boron nitride nanosheets (BNNS-NH2)/glycerol and exhibits self-healing abilities at low temperature. The self-healing process occurs through the re-establishing of hydrogen bonds and metal coordination interactions at the damaged surfaces. Its anti-freezing abilities enable the hydrogel to self-heal at -15 °C, and the self-healing efficiency based on tensile strength reaches up to ∼70%. Moreover, glycerol also endows the hydrogel with long-lasting water retention, which remains a water content of ∼99 wt% for more than 30 days. Meanwhile, the simultaneous introduction of BNNS-NH2 and glycerol significantly improved the mechanical properties of the hydrogel, which displays great stretchability (∼474%), tensile strength (∼151.3 kPa), stiffness (Young's modulus of ∼62.75 kPa) and toughness (∼355.13 kJ m-3). It is anticipated that these novel hydrogels will develop many fields and be exploited for new applications in extensive external environments.