Polysaccharide-Based Double-Network Hydrogels: Polysaccharide Effect, Strengthening Mechanisms, and Applications

Konjac glucomannan-based hydrogels with tunable mechanical strength and frictional resistance for biomedical applications

Hydrogels with favorable biocompatibility are regarded as ideal biomedical materials. However, their poor mechanical and tribological properties limit their further clinical applications. Konjac glucomannan (KGM), a safe natural polysaccharide, has the potential to bridge this gap by regulating the mechanical and tribological properties of hydrogels. This work prepares physical-physical and physical-chemical composite hydrogels to validate the enhancement effect of KGM. Within both types of hydrogels, KGM macromolecules aggregate and regulate their compression properties. As an additive, KGM enhances the compressive strength of polyacrylamide (PAM) hydrogel from 140.78 KPa to 638.79 KPa and reduces the coefficient of friction (CoF) of polyvinyl alcohol (PVA) and PAM substrates by 52.57 % and 60.60 %, respectively. Moreover, KGM exhibits excellent biocompatibility. In summary, KGM emerges as a safe and effective candidate for regulating the mechanical and tribological properties of hydrogels, thereby demonstrating great potential for further biomedical applications.

Polysaccharide-Based Hydrogels for Advanced Biomedical Engineering Applications

In recent years, numerous applications of hydrogels using polysaccharides have evolved, benefiting from their widespread availability, excellent biodegradability, biocompatibility, and nonpoisonous nature. These natural polymers are typically sourced from renewable materials or from manufacturing processes, contributing collaboratively to waste management and demonstrating the potential for enhanced and enduring sustainability. In the field of novel bioactive molecule carriers for biotherapeutics, natural polymers are attracting attention due to their inherent properties and adaptable chemical structures. These polymers offer versatile matrices with a range of architectures and mechanical properties, while retaining the bioactivity of incorporated biomolecules. However, conventional polysaccharide-based hydrogels suffer from inadequate mechanical toughness with large swelling properties, which prohibit their efficacy in real-world applications. This review offers insights into the latest advancements in the development of diverse polysaccharide-based hydrogels for biotherapeutic administrations, either standalone or in conjunction with other polymers or drug delivery systems, in the pharmaceutical and biomedical fields.

Polyvinyl alcohol/sodium alginate hydrogels with tunable mechanical and conductive properties for flexible sensing applications

Despite the significant advantages of conductive hydrogels in flexible sensing, their further development is often hindered by limitations in strength and conductivity. In this work, the ionic conductive hydrogels with tunable mechanical and conductive properties were designed by utilizing sodium alginate (SA) to reinforce the polyvinyl alcohol (PVA) networks, followed by the respective introduction of Li2SO4, ZnSO4, and Fe2(SO4)3, leveraging the Hofmeister effect and metal coordination. Consequently, the mechanical properties (σ = 0.40-2.70 MPa) and conductivity (IC = 0.18-1.02 S/m) can be extensively tuned by adjusting the metal salts with varying oxidation states. Notably, Fe3+ ions can significantly enhance the mechanical properties, while Li+ ions more effectively improve conductivity. Interestingly, the PVA/SA/Zn2+ hydrogel achieves a balance between mechanical properties (σ = 1.86 MPa, ε = 1110 %) and conductivity (0.92 S/m), ascribing it to the multiple interactions including densification of polymer networks, formation of nanocrystalline domains, and ionic coordination effects. Furthermore, the conductive hydrogel also exhibits low strain detection limit (2.0 %), and demonstrated enormous potential in personal health monitoring and information transmission applications. This work presents a highly efficient and eco-friendly strategy for constructing hydrogels with tunable properties, while elucidating the mechanisms behind the enhanced mechanical and conductive performance.

Reinforcement of Dextran Methacrylate-Based Hydrogel, Semi-IPN, and IPN with Multivalent Crosslinkers

The need for new biomaterials to meet the needs of advanced healthcare therapies is constantly increasing. Polysaccharide-based matrices are considered extremely promising because of their biocompatibility and soft structure; however, their use is limited by their poor mechanical properties. In this light, a strategy for the reinforcement of dextran-based hydrogels and interpenetrated polymer networks (semi-IPNs and IPNs) is proposed, which will introduce multifunctional crosslinkers that can modify the network crosslinking density. Hydrogels were prepared via dextran methacrylation (DexMa), followed by UV photocrosslinking in the presence of diacrylate (NPGDA), triacrylate (TMPTA), and tetraacrylate (PETA) crosslinkers at different concentrations. The effect of these molecules was also tested on DexMa-gellan semi-IPN (DexMa/Ge) and, later, on IPN (DexMa/CaGe), obtained after solvent exchange with CaCl2 in HEPES and the resulting Ge gelation. Mechanical properties were investigated via rheological and dynamic mechanical analyses to assess the rigidity, resistance, and strength of the systems. Our findings support the use of crosslinkers with different functionality to modulate the properties of polysaccharide-based scaffolds, making them suitable for various biomedical applications. While no significative difference is observed on enriched semi-IPN, a clear improvement is visible on DexMa and DexMa/CaGe systems when TMPTA and NPGDA crosslinker are introduced at higher concentrations, respectively.

In the process of polysaccharide gel formation: A review of the role of competitive relationship between water and alcohol molecules

Polysaccharides have emerged as versatile materials capable of forming gels through diverse induction methods, with alcohol-induced polysaccharide gels demonstrating significant potential across food, medicinal, and other domains. The existing research mainly focused on the phenomena and mechanisms of alcohol-induced gel formation in specific polysaccharides. Therefore, this review provides a comprehensive overview of the intricate mechanisms underpinning alcohol-triggered gelation of different polysaccharides and surveys their prominent application potentials through rheological, mechanical, and other characterizations. The mechanism underlying the enhancement of polysaccharide network structures by alcohol is elucidated, where alcohol displaces water to establish hydrogen bonding and hydrophobic interactions with polysaccharide chains. Specifically, alcohols change the arrangement of water molecules, and the partial hydration shell surrounding polysaccharide molecules is disrupted, exposing polysaccharides' hydrophobic groups and enhancing hydrophobic interactions. Moreover, the pivotal influences of alcohol concentration and addition method on polysaccharide gelation kinetics are scrutinized, revealing nuanced dependencies such as the different gel-promoting capabilities of polyols versus monohydric alcohols and the critical threshold concentrations dictating gel formation. Notably, immersion of polysaccharide gels in alcohol augments gel strength, while direct alcohol addition to polysaccharide solutions precipitates gel formation. Future investigations are urged to unravel the intricate nexus between the mechanisms underpinning alcohol-induced polysaccharide gelation and their practical utility, thereby paving the path for tailored manipulation of environmental conditions to engineer bespoke alcohol-induced polysaccharide gels.

Building covalent crosslinks of carboxymethyl konjac glucomannan with boronic ester bonds for fabricating multimodal hydrogel sensor

As the derivative of konjac glucomannan (KGM), carboxymethyl konjac glucomannan (CMK) has attracted increasing attention in the polysaccharide hydrogel fields with the aim of improving the performance related to drug delivery and release. In this study, we prepared a CMK-based hydrogel with dual characteristic crosslinks, and unlocked new applications of this type of hydrogel in soft sensor fields. CMK and poly (vinyl alcohol) were used as substrates, and physical crosslinks were constructed via the freeze-thawing treatments and covalent crosslinks were built via the boronic ester bonding. As-prepared hydrogel possessed significantly improved mechanical performance because the boronic ester bonding, on the one hand, well associated the two kinds of polymer chains, and on the other hand, played the role of 'sacrificial crosslinks'. Furthermore, the occurrence of dynamic boronic ester bonding gave the hydrogel strain- and temperature-sensitive ionic conductivity, and therefore, the hydrogels could be used to identify human motions and as-resulted environmental temperature alterations, and worked well in various scenarios. This work activates new application of CMK in the multimodal sensing field, and also proposes an intriguing way of building multiple crosslinks in the KGM derivative-based hydrogels.

Impact of Composition and Autoclave Sterilization on the Mechanical and Biological Properties of ECM-Mimicking Cryogels

Cryogels represent a valid strategy as scaffolds for tissue engineering. In order to adequately support adhesion and proliferation of anchorage-dependent cells, different polymers need to be combined within the same scaffold trying to mimic the complex features of a natural extracellular matrix (ECM). For this reason, in this work, gelatin (Gel) and chondroitin sulfate (CS), both functionalized with methacrylic groups to produce CSMA and GelMA derivatives, were selected to prepare cryogel networks. Both homopolymer and heteropolymer cryogels were produced, via radical crosslinking reactions carried out at -12 °C for 2 h. All the scaffolds were characterized for their mechanical, swelling and morphological properties, before and after autoclave sterilization. Moreover, they were evaluated for their biocompatibility and ability to support the adhesion of human gingival fibroblasts and tenocytes. GelMA-based homopolymer networks better withstood the autoclave sterilization process, compared to CSMA cryogels. Indeed, GelMA cryogels showed a decrease in stiffness of approximately 30%, whereas CSMA cryogels of approximately 80%. When GelMA and CSMA were blended in the same network, an intermediate outcome was observed. However, the hybrid scaffolds showed a general worsening of the biological performance. Indeed, despite their ability to withstand autoclave sterilization with limited modification of the mechanical and morphological properties, the hybrid cryogels exhibited poor cell adhesion and high LDH leakage. Therefore, not only do network components need to be properly selected, but also their combination and ability to withstand effective sterilization process should be carefully evaluated for the development of efficient scaffolds designed for tissue engineering purposes.

Layered complexity, reorganisational ability and self-healing mechanisms of heteropolysaccharide solutions

Heteropolysaccharides are among the most widely distributed compounds in nature, acting as both tissue building blocks and as a source of nutrients. Their physicochemical and biological properties have been studied thoroughly; however, the microstructural properties of heteropolysaccharides are still poorly understood. This study aims to investigate the micro-structural peculiarities of agarose, gum arabic, hyaluronic and alginic acids by means of confocal laser scanning microscopy (CLSM) and cryogenic scanning electron microscopy (cryo-SEM). Herein, attention is paid to layered complexity of the microstructure differentiating surface, under surface, inner, and substrate interface layers. The scale and pattern of the polysaccharide's microstructure depend on the concentration, changing from lamellae to cell-like porous structures. This work provides the insight into micro- and nanoscale mechanisms of self-healing and substrate-induced reorganisation. Thus, investigation of the self-healing mechanism revealed that this diffusion-based process starts from the fibres, turning into lamellae, following by cell-like structures with smaller dimensions. Investigation of the substrate-induced reorganisation ability showed that nano-to-micro (scale) porous substrate causes reorganisation in the interface layer of the studied heteropolysaccharides. This work contributes to understanding the structural peculiarities of heteropolysaccharides by looking at them through a supramolecular, micro-level prism.

Fabrication of Tough Double-Network Hydrogels from Highly Cross-Linked Brittle Neutral Networks Using Alkaline Hydrolysis

This paper describes a simple method to synthesize tough hydrogels from a highly cross-linked neutral network. It was found that applying alkaline hydrolysis to a highly cross-linked hydrogel synthesized from acrylamide (AAm) can increase its swelling ratio dramatically. Double-network (DN) hydrogels synthesized from polymerization of loosely cross-linked AAm networks inside a highly cross-linked AAm gel were not tough. However, repeating the same recipes with a second polymerization step to synthesize a DN hydrogel from a hydrolyzed highly cross-linked AAm gel resulted in tough hydrogels. Those gels exhibited finite tensile behavior similar to that of conventional DN hydrogels. Moreover, craze-like patterns were observed during tensile loading of a DN hydrogel synthesized from a hydrolyzed highly cross-linked first network and a loosely cross-linked second network. The patterns remained in the gel even after strain hardening at high stretch ratios. The craze-like pattern formation was suppressed by increasing the concentration of cross-linking monomer in the second polymerization step. Crack propagation in DN hydrogels synthesized using hydrolysis was also studied by applying a tensile load on notched specimens.