Rational design of viscoelastic hydrogels for periodontal ligament remodeling and repair.

The periodontal ligament (PDL) is a distinctive yet critical connective tissue vital for maintaining the integrity and functionality of tooth-supporting structures. However, PDL repair poses significant challenges due to the complexity of its mechanical microenvironment encompassing hard-soft-hard tissues, with the viscoelastic properties of the PDL being of particular interest. This review delves into the significant role of viscoelastic hydrogels in PDL regeneration, underscoring their utility in simulating biomimetic three-dimensional microenvironments. We review the intricate relationship between PDL and viscoelastic mechanical properties, emphasizing the role of tissue viscoelasticity in maintaining mechanical functionality. Moreover, we summarize the techniques for characterizing PDL's viscoelastic behavior. From a chemical bonding perspective, we explore various crosslinking methods and characteristics of viscoelastic hydrogels, along with engineering strategies to construct viscoelastic cell microenvironments. We present a detailed analysis of the influence of the viscoelastic microenvironment on cellular mechanobiological behavior and fate. Furthermore, we review the applications of diverse viscoelastic hydrogels in PDL repair and address current challenges in the field of viscoelastic tissue repair. Lastly, we propose future directions for the development of innovative hydrogels that will facilitate not only PDL but also systemic ligament tissue repair. STATEMENT OF SIGNIFICANCE.

Hydrogels with tunable mechanical plasticity regulate endothelial cell outgrowth in vasculogenesis and angiogenesis.

The endothelial cell (EC) outgrowth in both vasculogenesis and angiogenesis starts with remodeling surrounding matrix and proceeds with the crosstalk between cells for the multicellular vasculature formation. The mechanical plasticity of matrix, defined as the ability to permanently deform by external traction, is pivotal in modulating cell behaviors. Nevertheless, the implications of matrix plasticity on cell-to-cell interactions during EC outgrowth, along with the molecular pathways involved, remain elusive. Here we develop a collagen-hyaluronic acid based hydrogel platform with tunable plasticity by using compositing strategy of dynamic and covalent networks. We show that although the increasing plasticity of the hydrogel facilitates the matrix remodeling by ECs, the largest tubular lumens and the longest invading distance unexpectedly appear in hydrogels with medium plasticity instead of the highest ones. We unravel that the high plasticity of the hydrogels promotes stable integrin cluster of ECs and recruitment of focal adhesion kinase with an overenhanced contractility which downregulates the vascular endothelial cadherin expression and destabilizes the adherens junctions between individual ECs. Our results, further validated with mathematical simulations and in vivo angiogenic tests, demonstrate that a balance of matrix plasticity facilitates both cell-matrix binding and cell-to-cell adherens, for promoting vascular assembly and invasion.

[Biomechanical properties of epithelial mesenchymal transition in idiopathic pulmonary fibrosis].

Idiopathic pulmonary fibrosis (IPF) is a progressive scar-forming disease with a high mortality rate that has received widespread attention. Epithelial mesenchymal transition (EMT) is an important part of the pulmonary fibrosis process, and changes in the biomechanical properties of lung tissue have an important impact on it. In this paper, we summarize the changes in the biomechanical microenvironment of lung tissue in IPF-EMT in recent years, and provide a systematic review on the effects of alterations in the mechanical microenvironment in pulmonary fibrosis on the process of EMT, the effects of mechanical factors on the behavior of alveolar epithelial cells in EMT and the biomechanical signaling in EMT, in order to provide new references for the research on the prevention and treatment of IPF.

Fiber Microarchitecture in Interpenetrating Collagen-Alginate Hydrogel with Tunable Mechanical Plasticity Regulates Tumor Cell Migration.

The fiber structures of tumor microenvironment (TME) are well-known in regulating tumor cell behaviors, and the plastic remolding of TME has recently been suggested to enhance tumor metastasis as well. However, the interrelationship between the fiber microarchitecture and matrix plasticity is inextricable by existing in vitro models. The individual roles of fiber microarchitecture and matrix plasticity in tuning tumor cell behaviors remain elusive. This study develops an interpenetrating collagen-alginate hydrogel platform with independently tunable matrix plasticity and fiber microarchitecture through an interpenetrating strategy of alginate networks and collagen I networks. With this hydrogel platform, it is demonstrated that tumor cells in high plasticity hydrogels are more extensive and aggressive than in low plasticity hydrogels and fiber structures only have influence in high plasticity hydrogels. The study further elucidates the underlying mechanisms through analyzing the distribution of forces within the matrix and tracking the focal adhesions (FAs) and finds that highly plastic hydrogels can activate the FAs formation, whereas the maturation and stability of FAs are dominated by fiber dispersion. This study not only establishes new ideas on how cells interact with TME cues but also would help to further finely tailor engineered hydrogel platforms for studying tumor behaviors in vitro.

Hyaluronate- and gelatin-based hydrogels encapsulating doxycycline as a wound dressing for burn injury therapy.

Infection is a critical challenge in burn wound therapy. Wound dressings with antibacterial and multifunctional abilities associated with rapid burn wound healing are urgently needed. Here, we developed a bioadhesive and injectable ECM-mimicking hydrogel dressing with antibacterial capacity for burn injury therapy, which is crosslinked by dynamic boronate ester bonds between modified hyaluronate and gelatin (HG). The antibiotic doxycycline (Doxy) was encapsulated in HG networks for drug delivery around the wound sites. The HG/Doxy hydrogel dressing shows biocompatibility and antibacterial activity against Gram-positive and Gram-negative bacteria. Applying to a rat model of burn wound, the HG/Doxy hydrogel significantly speeds up wound closure by reducing the inflammatory reaction. Furthermore, the HG/Doxy hydrogel accelerates the regeneration of the skin structure by promoting collagen deposition, blood vessel regeneration, and hair follicle formation, eventually shortening the healing periods of burn wounds. These findings demonstrated the clinical potential of the HG/Doxy hydrogels as a promising burn wound dressing. STATEMENT OF SIGNIFICANCE: A bioadhesive and injectable hydrogel dressing has been developed for burn injury therapy. The ECM-mimicking hyaluronate-gelatin (HG) hydrogel with antibacterial ability is crosslinked by dynamic boronate ester bonds for delivering antibiotic doxycycline (Doxy). The HG/Doxy hydrogels exhibit bioadhesive, shape-adaptive, and water retention abilities in closing the irregular-shaped wound and providing a moist environment. The HG/Doxy hydrogels significantly shorten the healing periods of burn wounds in rat models within 10~14 days and promote the regeneration of skin structure, which have high potential for clinical applications.

Hydrogel dressing integrating FAK inhibition and ROS scavenging for mechano-chemical treatment of atopic dermatitis.

Atopic dermatitis (AD) is a chronic skin disease caused by skin immune dyshomeostasis and accompanied by severe pruritus. Although oxidative stress and mechanical scratching can aggravate AD inflammation, treatment targeting scratching is often overlooked, and the efficiency of mechano-chemically synergistic therapy remains unclear. Here, we find that enhanced phosphorylation of focal adhesion kinase (FAK) is associated with scratch-exacerbated AD. We then develop a multifunctional hydrogel dressing that integrates oxidative stress modulation with FAK inhibition to synergistically treat AD. We show that the adhesive, self-healing and antimicrobial hydrogel is suitable for the unique scratching and bacterial environment of AD skin. We demonstrate that it can scavenge intracellular reactive oxygen species and reduce mechanically induced intercellular junction deficiency and inflammation. Furthermore, in mouse AD models with controlled scratching, we find that the hydrogel alleviates AD symptoms, rebuilds the skin barrier, and inhibits inflammation. These results suggest that the hydrogel integrating reactive oxygen species scavenging and FAK inhibition could serve as a promising skin dressing for synergistic AD treatment.

A viscoelastic alginate-based hydrogel network coordinated with spermidine for periodontal ligament regeneration.

Periodontitis can cause irreversible defects in the periodontal ligament (PDL), the regeneration of which is the major obstacle to the clinical treatment of periodontitis. Implanting hydrogel for releasing anti-inflammatory drugs is a promising treatment to promote PDL regeneration. However, existing hydrogel systems fail to mimic the typical viscoelastic feature of native periodontium, which may have been shown as an important role in tissue regeneration. Meanwhile, the synergistic benefits of mechanical cues and biochemical agents for PDL regeneration remain elusive. In this study, we developed a bi-crosslinking viscoelastic hydrogel (Alg-PBA/Spd) by integrating phenylboronic acid-modified alginate with anti-inflammatory agent (spermidine) through borate ester and B-N coordination bonds, where spermidine will be released with the degradation of the hydrogel. Alg-PBA/Spd hydrogel is biocompatible, injectable and can quickly adapt to complex periodontal structures due to the dynamic crosslinking. We demonstrated in rat models that the viscoelastic Alg-PBA/Spd hydrogel significantly promotes the deposition of periodontal collagen and accelerates the repair of periodontal damage. Our results suggest that the viscoelastic Alg-PBA/Spd hydrogel would be a promising mechano-biochemically synergistic treatment for periodontal regeneration.

REVIEW ARTICLE Engineering bio-inks for 3D bioprinting cell mechanical microenvironment.

144Three-dimensional (3D) bioprinting has become a promising approach to constructing functional biomimetic tissues for tissue engineering and regenerative medicine. In 3D bioprinting, bio-inks are essential for the construction of cell microenvironment, thus affecting the biomimetic design and regenerative efficiency. Mechanical properties are one of the essential aspects of microenvironment, which can be characterized by matrix stiffness, viscoelasticity, topography, and dynamic mechanical stimulation. With the recent advances in functional biomaterials, various engineered bio-inks have realized the possibility of engineering cell mechanical microenvironment in vivo. In this review, we summarize the critical mechanical cues of cell microenvironments, review the engineered bio-inks while focusing on the selection principles for constructing cell mechanical microenvironments, and discuss the challenges facing this field and the possible solutions for them.

ANTXR1 as a potential sensor of extracellular mechanical cues.

Cell adhesion molecules mediate cell-cell or cell-matrix interactions, some of which are mechanical sensors, such as integrins. Emerging evidence indicates that anthrax toxin receptor 1 (ANTXR1), a newly identified cell adhesion molecule, can also sense extracellular mechanical signals such as hydrostatic pressure and extracellular matrix (ECM) rigidity. ANTXR1 can interact with ECM through connecting intracellular cytoskeleton and ECM molecules (just like integrins) to regulate numerous biological processes, such as cell adhesion, cell migration or ECM homeostasis. Although with high structural similarity to integrins, its functions and downstream signal transduction are independent from those of integrins. In this perspective, based on existing evidence in literature, we analyzed the structural and functional evidence that ANTXR1 can act as a potential sensor for extracellular mechanical cues. To our knowledge, this is the first in-depth overview of ANTXR1 from the perspective of mechanobiology. STATEMENT OF SIGNIFICANCE: An overview of ANTXR1 from the perspective of mechanobiology; An analysis of mechanical sensitivity of ANTXR1 in structure and function; A summary of existing evidence of ANTXR1 as a potential mechanosensor.

An endoscopically compatible fast-gelation powder forms Janus-adhesive hydrogel barrier to prevent postoperative adhesions.

Postoperative adhesions occur widely in various tissues, bringing the risk of secondary surgery and increased medical burden. Hydrogel barriers with Janus-adhesive ability can achieve physical isolation of adjacent tissues and are therefore considered an ideal solution. However, integrating endoscopic delivery convenience and viscoelastic Janus hydrogel formation remains a great challenge. Here, we present a report of the in situ formation of Janus-adhesive hydrogel barrier using a sprayable fast-Janus-gelation (FJG) powder. We first methacrylate the polysaccharide macromolecules to break the intermolecular hydrogen bonds and impart the ability of rapid hydration. FJG powder can rapidly absorb interfacial water and crosslink through borate ester bonds, forming a toughly adhesive viscoelastic hydrogel. The Janus barrier can be simply formed by further hydrating the upper powder with cationic solution. We construct rat models to demonstrate the antiadhesions efficiency of viscoelastic FJG hydrogels in organs with different motion modalities (e.g., intestine, heart, liver). We also developed a low-cost delivery device with a standardized surgical procedure and further validated the feasibility and effectiveness of FJG powder in minimally invasive surgery using a preclinical translational porcine model. Considering the advantages in terms of therapeutic efficacy, clinical convenience, and commercialization, our results reveal the great potential of Janus-gelation powder materials as a next-generation antiadhesions barrier.

An ECM-Mimicking, Injectable, Viscoelastic Hydrogel for Treatment of Brain Lesions.

Brain lesions can arise from traumatic brain injury, infection, and craniotomy. Although injectable hydrogels show promise for promoting healing of lesions and health of surrounding tissue, enabling cellular ingrowth and restoring neural tissue continue to be challenging. It is hypothesized that these challenges arise in part from the mismatch of composition, stiffness, and viscoelasticity between the hydrogel and the brain parenchyma, and this hypothesis is tested by developing and evaluating a self-healing hydrogel that not only mimics the composition, but also the stiffness and viscoelasticity of native brain parenchyma. The hydrogel is crosslinked by dynamic boronate ester bonds between phenylboronic acid grafted hyaluronic acid (HA-PBA) and dopamine grafted gelatin (Gel-Dopa). This HA-PBA/Gel-Dopa hydrogel could be injected into a lesion cavity in a shear-thinning manner with rapid hemostasis, high tissue adhesion, and efficient self-healing. In an in vivo mouse model of brain lesions, the multi-functional injectable hydrogel is found to support neural cell infiltration, decrease astrogliosis and glial scars, and close the lesions. The results suggest a role for extracellular matrix-mimicking viscoelasticity in brain lesion healing, and motivate additional experimentation in larger animals as the technology progresses toward potential application in humans.

CellVisioner: A Generalizable Cell Virtual Staining Toolbox based on Few-Shot Transfer Learning for Mechanobiological Analysis.

Visualizing cellular structures especially the cytoskeleton and the nucleus is crucial for understanding mechanobiology, but traditional fluorescence staining has inherent limitations such as phototoxicity and photobleaching. Virtual staining techniques provide an alternative approach to addressing these issues but often require substantial amount of user training data. In this study, we develop a generalizable cell virtual staining toolbox (termed CellVisioner) based on few-shot transfer learning that requires substantially reduced user training data. CellVisioner can virtually stain F-actin and nuclei for various types of cells and extract single-cell parameters relevant to mechanobiology research. Taking the label-free single-cell images as input, CellVisioner can predict cell mechanobiological status (e.g., Yes-associated protein nuclear/cytoplasmic ratio) and perform long-term monitoring for living cells. We envision that CellVisioner would be a powerful tool to facilitate on-site mechanobiological research.

Targeting the tumor biophysical microenvironment to reduce resistance to immunotherapy.

Immunotherapy based on immune checkpoint inhibitors has evolved into a new pillar of cancer treatment in clinics, but dealing with treatment resistance (either primary or acquired) is a major challenge. The tumor microenvironment (TME) has a substantial impact on the pathological behaviors and treatment response of many cancers. The biophysical clues in TME have recently been considered as important characteristics of cancer. Furthermore, there is mounting evidence that biophysical cues in TME play important roles in each step of the cascade of cancer immunotherapy that synergistically contribute to immunotherapy resistance. In this review, we summarize five main biophysical cues in TME that affect resistance to immunotherapy: extracellular matrix (ECM) structure, ECM stiffness, tumor interstitial fluid pressure (IFP), solid stress, and vascular shear stress. First, the biophysical factors involved in anti-tumor immunity and therapeutic antibody delivery processes are reviewed. Then, the causes of these five biophysical cues and how they contribute to immunotherapy resistance are discussed. Finally, the latest treatment strategies that aim to improve immunotherapy efficacy by targeting these biophysical cues are shared. This review highlights the biophysical cues that lead to immunotherapy resistance, also supplements their importance in related technologies for studying TME biophysical cues in vitro and therapeutic strategies targeting biophysical cues to improve the effects of immunotherapy.

The Plasticity of Nanofibrous Matrix Regulates Fibroblast Activation in Fibrosis.

Natural extracellular matrix (ECM) mostly has a fibrous structure that supports and mechanically interacts with local residing cells to guide their behaviors. The effect of ECM elasticity on cell behaviors has been extensively investigated, while less attention has been paid to the effect of matrix fiber-network plasticity at microscale, although plastic remodeling of fibrous matrix is a common phenomenon in fibrosis. Here, a significant decrease is found in plasticity of native fibrotic tissues, which is associated with an increase in matrix crosslinking. To explore the role of plasticity in fibrosis development, a set of 3D collagen nanofibrous matrix with constant modulus but tunable plasticity is constructed by adjusting the crosslinking degree. Using plasticity-controlled 3D culture models, it is demonstrated that the decrease of matrix plasticity promotes fibroblast activation and spreading. Further, a coarse-grained molecular dynamic model is developed to simulate the cell-matrix interaction at microscale. Combining with molecular experiments, it is revealed that the enhanced fibroblast activation is mediated through cytoskeletal tension and nuclear translocation of Yes-associated protein. Taken together, the results clarify the effects of crosslinking-induced plasticity changes of nanofibrous matrix on the development of fibrotic diseases and highlight plasticity as an important mechanical cue in understanding cell-matrix interactions.

Matrix stiffness controls cardiac fibroblast activation through regulating YAP via AT1 R.

Cardiac fibrosis is a common pathway leading to heart failure and involves continued activation of cardiac fibroblasts (CFs) into myofibroblasts during myocardium damage, causing excessive deposition of the extracellular matrix (ECM) and thus increases matrix stiffness. Increasing evidence has shown that stiffened matrix plays an important role in promoting CF activation and cardiac fibrosis, and several signaling factors mediating CF mechanotransduction have been identified. However, the key molecules that perceive matrix stiffness to regulate CF activation remain to be further explored. Here, we detected significantly increased expression and nuclear localization of Yes-associated protein (YAP) in native fibrotic cardiac tissues. By using mechanically regulated in vitro cell culture models, we found that a stiff matrix-induced high expression and nuclear localization of YAP in CFs, accompanied by enhanced cell activation. We also demonstrated that YAP knockdown decreased fibrogenic response of CFs and that YAP overexpression promoted CF activation, indicating that YAP plays an important role in mediating matrix stiffness-induced CF activation. Further mechanistic studies revealed that the YAP pathway is an important signaling branch downstream of angiotensin II type 1 receptor in CF mechanotransduction. The findings help elucidate the mechanism of fibrotic mechanotransduction and may contribute to the development of new approaches for treating fibrotic diseases.

Synthesis of Chromium Carbide Nanopowders by Microwave Heating and Their Composition and Microstructure Change under Gamma Ray Irradiation.

Chromium carbide nanopowders were synthesized by mechanical alloying-assisted microwave heating. The effect of gamma irradiation on phase composition and microstructure of chromium carbide nanopowders synthesized by the microwave heating method was analyzed. The samples were characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) techniques. The results showed that well-dispersed chromium carbide nanopowders can be synthesized by maintaining the temperature at 1000 °C for 1 h. Gamma ray irradiation had an important effect on the microstructure of chromium carbide nanopowders. The interplanar spacings of chromium carbide (110) crystal faces before and after gamma ray irradiation were 0.3725 nm and 0.3824 nm, respectively. The crystal structure of chromium carbide was changed by gamma ray irradiation. Gamma ray irradiation can also increase the binding energy of chromium carbide, which is beneficial to improve the thermal stability and mechanical properties of chromium carbide at high temperature.