Dual-Cross-linked Liquid Crystal Hydrogels with Controllable Viscoelasticity for Regulating Cell Behaviors

Creating a bionic scaffold via light-curing liquid crystal ink to reveal the role of osteoid-like microenvironment in osteogenesis

Osteoid plays a crucial role in directing cell behavior and osteogenesis through its unique characteristics, including viscoelasticity and liquid crystal (LC) state. Thus, integrating osteoid-like features into 3D printing scaffolds proves to be a promising approach for personalized bone repair. Despite extensive research on viscoelasticity, the role of LC state in bone repair has been largely overlooked due to the scarcity of suitable LC materials. Moreover, the intricate interplay between LC state and viscoelasticity in osteogenesis remains poorly understood. Here, we developed innovative hydrogel scaffolds with osteoid-like LC state and viscoelasticity using digital light processing with a custom LC ink. By utilizing these LC scaffolds as 3D research models, we discovered that LC state mediates high protein clustering to expose accessible RGD motifs to trigger cell-protein interactions and osteogenic differentiation, while viscoelasticity operates via mechanotransduction pathways. Additionally, our investigation revealed a synergistic effect between LC state and viscoelasticity, amplifying cell-protein interactions and osteogenic mechanotransduction processes. Furthermore, the interesting mechanochromic response observed in the LC hydrogel scaffolds suggests their potential application in mechanosensing. Our findings shed light on the mechanisms and synergistic effects of LC state and viscoelasticity in osteoid on osteogenesis, offering valuable insights for the biomimetic design of bone repair scaffolds.

Chitin whisker/chitosan liquid crystal hydrogel assisted scaffolds with bone-like ECM microenvironment for bone regeneration

Natural bone exhibits a complex anisotropic and micro-nano hierarchical structure, more importantly, bone extracellular matrix (ECM) presents liquid crystal (LC) phase and viscoelastic characteristics, providing a unique microenvironment for guiding cell behavior and regulating osteogenesis. However, in bone tissue engineering scaffolds, the construction of bone-like ECM microenvironment with exquisite microstructure is still a great challenge. Here, we developed a novel polysaccharide LC hydrogel supported 3D printed poly(l-lactide) (PLLA) scaffold with bone-like ECM microenvironment and micro-nano aligned structure. First, we prepared a chitin whisker/chitosan polysaccharide LC precursor, and then infuse it into the pores of 3D printed PLLA scaffold, which was previously surface modified with a polydopamine layer. Next, the LC precursor was chemical cross-linked by genipin to form a hydrogel network with bone-like ECM viscoelasticity and LC phase in the scaffold. Subsequently, we performed directional freeze-casting on the composite scaffold to create oriented channels in the LC hydrogel. Finally, we soaked the composite scaffold in phytic acid to further physical cross-link the LC hydrogel through electrostatic interactions and impart antibacterial effects to the scaffold. The resultant biomimetic scaffold displays osteogenic activity, vascularization ability and antibacterial effect, and is expected to be a promising candidate for bone repair.

Tunable Stress Relaxing Biomimetic Matrices: Hyaluronan/Hydroxyapatite Hybridization Mediates Assembly of Collagen Fibrils

The alluring correlations of cellular behaviors with viscoelastic extracellular matrices have driven increasing endeavors directed toward the understanding of mechanical cues on cell growth and differentiation via preparing biomimetic scaffolds/gels with viscoelastic controllability. Indeed, systematic investigations, especially into calcium phosphate-containing biomimetics, are relatively rare. Here, oxidized hyaluronic acid/hydroxyapatite hybrids (OHAHs) were synthesized by hyaluronan-mediated biomimetic mineralization with confined ion diffusion and subsequent oxidization treatment. The collagen self-assembly was applied to fabricate tunable stress relaxing fibrillar matrices in the presence of OHAHs in which the incorporated hyaluronic acid with aldehyde groups acted to improve the component compatibility as well as to supplement the molecular interactions with the occurrence of a Schiff-base reaction. With the addition of varying OHAH contents, the self-assembly behavior of collagen was altered, and the obtained collagen-hybrid (CH) matrices presented a heterogeneous fibrillar structure interspersed with OHAHs, characterized by large fibrillar bundles coexisting with small fibrils. The OHAHs improved the hydrogel stability of pure collagen, and according to rheological and nanoindentation measurements, CH matrices also exhibited tunable stress relaxation rates, following an OHAH concentration-dependent fashion. The proliferation and spreading of MC3T3-E1 cells cultured onto such CH matrices were further found to increase with the stress relaxing rate of the matrices. The present study showed that the introduction of hydroxyapatite incorporated with active hyaluronic acid during collagen reconstitution was a simple and effective strategy to realize the preparation of tunable stress relaxing biomimetic matrices potentially used for further appraising the regulation of mechanical cues on cell behaviors.

Diffusion-Limited Processes in Hydrogels with Chosen Applications from Drug Delivery to Electronic Components

Diffusion is one of the key nature processes which plays an important role in respiration, digestion, and nutrient transport in cells. In this regard, the present article aims to review various diffusion approaches used to fabricate different functional materials based on hydrogels, unique examples of materials that control diffusion. They have found applications in fields such as drug encapsulation and delivery, nutrient delivery in agriculture, developing materials for regenerative medicine, and creating stimuli-responsive materials in soft robotics and microrobotics. In addition, mechanisms of release and drug diffusion kinetics as key tools for material design are discussed.

The Diamond Concept Enigma: Recent Trends of Its Implementation in Cross-linked Chitosan-Based Scaffolds for Bone Tissue Engineering

An increasing number of publications over the past ten years have focused on the development of chitosan-based cross-linked scaffolds to regenerate bone tissue. The design of biomaterials for bone tissue engineering applications relies heavily on the ideals set forth by a polytherapy approach called the "Diamond Concept". This methodology takes into consideration the mechanical environment, scaffold properties, osteogenic and angiogenic potential of cells, and benefits of osteoinductive mediator encapsulation. The following review presents a comprehensive summarization of recent trends in chitosan-based cross-linked scaffold development within the scope of the Diamond Concept, particularly for nonload-bearing bone repair. A standardized methodology for material characterization, along with assessment of in vitro and in vivo potential for bone regeneration, is presented based on approaches in the literature, and future directions of the field are discussed.

Bone ECM-inspired biomineralization chitin whisker liquid crystal hydrogels for bone regeneration

As a particular cell niche, natural bone extracellular matrix (ECM) is an organic-inorganic composite material formed by mineralization of liquid crystal (LC) collagen fiber network. However, designing bone repair materials that highly imitate the LC characteristic and composite components of natural bone ECM is a great challenge. Here, we report a novel kind of bone ECM-inspired biomineralization chitin whisker LC hydrogels. First, photocurable chitin whisker LC hydrogels with bone ECM-like chiral nematic LC state and viscoelasticity are created. Next, biomineralization, guided by LC hydrogels, is carried out to truly mimic the mineralization process of natural bone, so as to obtain the organic-inorganic composite materials with bone ECM-like microenvironment. The chitin whisker LC hydrogels exhibit superior biomineralization, protein adsorption and osteogenesis ability, more importantly, LC hydrogel with negatively charged -COOH groups is more conducive to biomineralization and shows more desirable osteogenic activity than that with positively charged -NH₂ groups. Notably, compared with the pristine LC hydrogels, the biomineralization LC hydrogels display more favorable osteogenesis ability due to their bone ECM-like LC texture and bone-like hydroxyapatite. This study opens an avenue toward the design of bone ECM-inspired biomineralization chitin whisker LC hydrogels for bone regeneration.

Bone ECM-like 3D Printing Scaffold with Liquid Crystalline and Viscoelastic Microenvironment for Bone Regeneration

Implanting a 3D printing scaffold is an effective therapeutic strategy for personalized bone repair. As the key factor for the success of bone tissue engineering, the scaffold should provide an appropriate bone regeneration microenvironment and excellent mechanical properties. In fact, the most ideal osteogenic microenvironment is undoubtedly provided by natural bone extracellular matrix (ECM), which exhibits liquid crystalline and viscoelastic characteristics. However, mimicking a bone ECM-like microenvironment in a 3D structure with outstanding mechanical properties is a huge challenge. Herein, we develop a facile approach to fabricate a bionic scaffold perfectly combining bone ECM-like microenvironment and robust mechanical properties. Creatively, 3D printing a poly(l-lactide) (PLLA) scaffold was effectively strengthened via layer-by-layer electrostatic self-assembly of chitin whiskers. More importantly, a kind of chitin whisker/chitosan composite hydrogel with bone ECM-like liquid crystalline state and viscoelasticity was infused into the robust PLLA scaffold to build the bone ECM-like microenvironment in 3D structure, thus highly promoting bone regeneration. Moreover, deferoxamine, an angiogenic factor, was encapsulated in the composite hydrogel and sustainably released, playing a long-term role in angiogenesis and thereby further promoting osteogenesis. This scaffold with bone ECM-like microenvironment and excellent mechanical properties can be considered as an effective implantation for bone repair.

Hofmeister effect-enhanced gelatin/oxidized dextran hydrogels with improved mechanical properties and biocompatibility for wound healing

Compared with other types of hydrogels, natural derived hydrogels possess intrinsic advantages of degradability and biocompatibility. However, due to the low mechanical strength, their potential applications in biomedical areas are limited. In this study, Hofmeister effect-enhanced gelatin/oxidized dextran (Gel/O-Dex) hydrogels were designed with improved mechanical properties and biocompatibility to accelerate wound healing. Gel and O-Dex were chemically crosslinked through Schiff base reaction of aldehyde and amino groups. After soaking in kosmotrope solutions physical crosslinking domains were induced by Hofmeister effect including α-helix structures, hydrophobic interaction regions and helical junction zones among Gel molecular chains. The type of anions played different influence on the properties of hydrogels, which was consistent with the order of Hofmeister series. Particularly, H₂PO₄^- treated hydrogels showed enhanced mechanical strength and fatigue resistance superior to that of Gel/O-Dex hydrogels. The underlying mechanism was that the physical crosslinking domains sustained additional mechanical stress and dissipated energy through cyclic association and dissociation process. Furthermore, Hofmeister effect only induced polymer chain entanglements without triggering any chemical reaction. Due to Hofmeister effect of H₂PO₄^- ions, aldehyde groups were embedded in the center of entangled polymer chains that resulted in better biocompatibility. In the full-thickness skin defects of SD rats, Hofmeister effect-enhanced Gel/O-Dex hydrogels by H₂PO₄^- ions accelerated wound healing and exhibited better histological morphology than ordinary hydrogels. Therefore, Hofmeister effect by essential inorganic anions is a promising method of improving mechanical properties and biocompatibility of natural hydrogels to promote medical translation in the field of wound healing from bench to clinic. STATEMENT OF SIGNIFICANCE: Hofmeister effect enhanced hydrogel mechanical properties in accordance with the order of Hofmeister series through physical crosslinking that induced α-helix structures, hydrophobic interaction regions and helical junction zones among Gel molecular chains. Due to the Hofmeister effect of H₂PO₄^- ions, aldehyde groups were embedded in the center of entangled polymer chains that resulted in better biocompatibility. Hofmeister effect-enhanced Gel/O-Dex hydrogels through H₂PO₄^- ions accelerated wound healing and exhibited better histological morphology than ordinary hydrogels. Therefore, Hofmeister effect by essential inorganic anions is a promising method to improve mechanical properties and biocompatibility of natural hydrogels for their medical applications..