Construction of Tough Hydrogel Cross-Linked via Ionic Interaction by Protection Effect of Hydrophobic Domains

Most hydrogels have poor mechanical properties, severely limiting their potential applications, and numerous approaches have been introduced to fabricate more robust and durable examples. However, these systems consist of nonbiodegradable polymers which limit their application in tissue engineering. Herein, we focus on the fabrication and investigate the influence of hydrophobic segments on ionic cross-linking properties for the construction of a tough, biodegradable hydrogel. A biodegradable, poly(γ-glutamic acid) polymer conjugated with a hydrophobic amino acid, l-phenylalanine ethyl ester (Phe), together with an ionic cross-linking group, alendronic acid (Aln) resulting in γ-PGA-Aln-Phe, was initially synthesized. Rheological assessments through time sweep oscillation testing revealed that the presence of hydrophobic domains accelerated gelation. Comparing gels with and without hydrophobic domains, the compressive strength of γ-PGA-Aln-Phe was found to be six times higher and exhibited longer stability properties in ethylenediaminetetraacetic acid solution, lasting for up to a month. Significantly, the contribution of the hydrophobic domains to the mechanical strength and stability of ionic cross-linking properties of the gel was found to be the dominant factor for the fabrication of a tough hydrogel. As a result, this study provides a new strategy for mechanical enhancement and preserves ionic cross-linked sites by the addition of hydrophobic domains. The development of tough, biodegradable hydrogels reported herein will open up new possibilities for applications in the field of biomaterials.

Arrested Phase Separation Enables High-Performance Keratoprostheses

Corneal transplantation is impeded by donor shortages, immune rejection, and ethical reservations. Pre-made cornea prostheses (keratoprostheses) offer a proven option to alleviate these issues. Ideal keratoprostheses must possess optical clarity and mechanical robustness, but also high permeability, processability, and recyclability. Here, it is shown that rationally controlling the extent of arrested phase separation can lead to optimized multiscale structure that reconciles permeability and transparency, a previously conflicting goal by common pore-forming strategies. The process is simply accomplished by hydrothermally treating a dense and transparent hydrophobic association hydrogel. The examination of multiscale structure evolution during hydrothermal treatment reveals that the phase separation with upper miscibility gap evolves to confer time-dependent pore growth due to slow dynamics of polymer-rich phase which is close to vitrification. Such a process can render a combination of multiple desired properties that equal or surpass those of the state-of-the-art keratoprostheses. In vivo tests confirm that the keratoprosthesis can effectively repair corneal perforation and restore a transparent cornea with treatment outcomes akin to that of allo-keratoplasty. The keratoprosthesis is easy to access and convenient to carry, and thus would be an effective temporary substitute for a corneal allograft in emergency conditions.

Characterization and Potential of a Bilayered Hydrogel of Gellan Gum and Demineralized Bone Particles for Osteochondral Tissue Engineering

Osteochondral (OC) tissue engineering (TE) is a promising strategy to regenerate acute or degenerative chondral and OC lesions. However, advancing a proper model for OC TE is still under way. Herein, a bilayer hydrogel (BH) based on gellan gum (GG) hydrogel and demineralized bone particles (DBPs) is suggested as a new model. The BH composite can be fabricated easily with a cell-friendly biomaterial and cross-linker. The BH composite was characterized by a morphological method and physicochemical aspect. The mechanical and rheological characters were further confirmed to verify its applicability in OC TE. The thermodynamic property of the composite was determined to analyze thermal stability and interaction among matrices. The bioactivity of the material was studied by treating simulated body fluid (SBF) solution for 28 days to examine the formation of crystalline structure in the BH construct. In vitro studies were carried out to study the viability and biochemical characters of the developed biomaterial. An in vivo study was performed to analyze the biocompatibility of the material and regeneration of the injured OC region implanted with BH composites. The data displayed stable physicochemical properties and mechanical characters when the DBPs were incorporated with a proper amount. The bioactivity of the DBP-loaded hydrogels displayed a high amount of apatite formation. The cytotoxicity of the fabricated material was low, which allows application in vitro and in vivo. The biochemical studies displayed a high level of alkaline phosphatase (ALP) activity and gene expression, which shows promising application of DBP-loaded GG in the bone layer of the BH model. The long-term in vivo study displayed excellent biocompatibility and great potential in the OC defected region. Overall, these results suggest the significance of combined and innovative approaches to improve the therapeutic strategies for OC regeneration, and the BH model suggested in this study can be a promising biomaterial model for OC TE.

Tissue engineering with gellan gum

Engineering complex tissues for research and clinical applications relies on high-performance biomaterials that are amenable to biofabrication, maintain mechanical integrity, support specific cell behaviours, and, ultimately, biodegrade. In most cases, complex tissues will need to be fabricated from not one, but many biomaterials, which collectively fulfill these demanding requirements. Gellan gum is an anionic polysaccharide with potential to fill several key roles in engineered tissues, particularly after modification and blending. This review focuses on the present state of research into gellan gum, from its origins, purification and modification, through processing and biofabrication options, to its performance as a cell scaffold for both soft tissue and load bearing applications. Overall, we find gellan gum to be a highly versatile backbone material for tissue engineering research, upon which a broad array of form and functionality can be built.

Tough and durable hydrogels with robust skin layers formed via soaking treatment

Simple soaking treatment generates layered hydrogels with a combination of superior mechanics and chemical robustness.

Electrochemical determination of trace pesticide residues based on multiwalled carbon nanotube grafted acryloyloxy ferrocene carboxylates with different spacers

We report the preparation of nanohybrid composites with good electrochemical response for the detection of pesticide residues by combining esterification with ATRP.

Stiff, strong, and tough hydrogels with good chemical stability

A hybrid hydrogel, consisting of hydrophilic and crystalline polymer networks, achieves high stiffness, high strength, and high toughness, while maintaining physical integrity in concentrated electrolyte solutions.