Synthesis of photocrosslinkable hydrogels for engineering three-dimensional vascular-like constructs by surface tension-driven assembly

Tendon-Inspired Anisotropic Hydrogels with Excellent Mechanical Properties for Strain Sensors

Anisotropic conductive hydrogels mimicking the natural tissues with high mechanical properties and intelligent sensing have played an important role in the field of flexible electronic devices. Herein, tensile remodeling, drying, and subsequent ion cross-linking methods were used to construct anisotropic hydrogels, which were inspired by the orientation and functionality of tendons. Due to the anisotropic arrangement of the polymer network, the mechanical performance and electrical conductivity were greatly improved in specific directions. The tensile stress and elastic modulus of the hydrogel along the network orientation were 29.82 and 28.53 MPa, which were higher than those along the vertical orientation, 9.63 and 11.7 MPa, respectively. Moreover, the hydrogels exhibited structure-dependent anisotropic sensing. The gauge factors (GFs) parallel to the prestretching direction were greater than the GF along the vertical direction. Thus, the tendon-inspired conductive hydrogels with anisotropy could be used as flexible sensors for joint motion detection and voice recognition. The anisotropic hydrogel-based sensors are highly expected to promote the great development of emerging soft electronics and medical detection.

Biomimetic Mineralized Hydroxyapatite Nanofiber-Incorporated Methacrylated Gelatin Hydrogel with Improved Mechanical and Osteoinductive Performances for Bone Regeneration

Purpose

Methacrylic anhydride-modified gelatin (GelMA) hydrogels exhibit many beneficial biological features and are widely studied for bone tissue regeneration. However, deficiencies in the mechanical strength, osteogenic factors and mineral ions limit their application in bone defect regeneration. Incorporation of inorganic fillers into GelMA to improve its mechanical properties and bone regenerative ability has been one of the research hotspots.

Methods

In this work, hydroxyapatite nanofibers (HANFs) were prepared and mineralized in a simulated body fluid to make their components and structure more similar to those of natural bone apatite, and then different amounts of mineralized HANFs (m-HANFs) were incorporated into the GelMA hydrogel to form m-HANFs/GelMA composite hydrogels. The physicochemical properties, biocompatibility and bone regenerative ability of m-HANFs/GelMA were determined in vitro and in vivo.

Results

The results indicated that m-HANFs with high aspect ratio presented rough and porous surfaces coated with bone-like apatite crystals. The incorporation of biomimetic m-HANFs improved the biocompatibility, mechanical, swelling, degradation and bone regenerative performances of GelMA. However, the improvement in the performance of the composite hydrogel did not continuously increase as the amount of added m-HANFs increased, and the 15m-HANFs/GelMA group exhibited the best swelling and degradation performances and the best bone repair effect in vivo among all the groups.

Conclusion

The biomimetic m-HANFs/GelMA composite hydrogel can provide a novel option for bone tissue engineering in the future; however, it needs further investigations to optimize the proportions of m-HANFs and GelMA for improving the bone repair effect.

Muscle-Inspired Anisotropic Hydrogel Strain Sensors

Hydrogel strain sensors have attracted tremendous attention in medical monitoring, flexible wearable devices, and human-machine interfaces. However, traditional hydrogels exhibit isotropic sensing performance based on their isotropic structure. Therefore, it is challenging to fabricate a hydrogel with an anisotropic structure similar to human tissues for achieving anisotropic sensing characteristics. Herein, we proposed a simple and effective method for preparing anisotropic poly(vinyl alcohol) (PVA) conductive hydrogels, which demonstrated anisotropic mechanical properties and anisotropic ion conductivity. The anisotropic hydrogel was successfully constructed through first thermal stretching and then directional freezing. The mechanical strength of hydrogels along the parallel stretching direction (stress of 1596 kPa and toughness of 3.69 MJ/m³) was higher than that of the hydrogels along the vertical stretching direction (stress of 883.1 kPa and toughness of 1.96 MJ/m³). Moreover, the hydrogel showed anisotropic conductivity on the advantage of the different ion channels. The prepared hydrogel sensor exhibited anisotropic sensing for multidirectional stress in the strain range from 0.5 to 100%. The gauge factors (GF) parallel to the stretching direction were greater than the GF vertical to the stretching direction. The anisotropic hydrogel sensors are expected to have broad application prospects in flexible wearable devices and medical monitoring.

Preparation and antibacterial properties of an AgBr@SiO2/GelMA composite hydrogel

Pure gelatin hydrogels lack antibacterial function and have poor mechanical properties, which restrict their application in wound dressings. In this study, nanosized silver bromide-doped mesoporous silica (AgBr@SiO2) microspheres with hollow structures were prepared by a modified Stober method. The novel microspheres can not only release silver ions to treat bacteria but also release drugs to treat skin wound. Furthermore, AgBr@SiO2 microspheres were modified with propyl methacrylate, incorporated into methacrylated gelatin (GelMA), and crosslinked by UV light to prepare AgBr@SiO2/GelMA dressings consisting of composite hydrogels. The results showed that the AgBr@SiO2 microspheres could enhance the mechanical properties of the hydrogels. With the increase in the AgBr@SiO2 concentration from 0.5 to 1 mg/mL, the dressings demonstrated effective antimicrobial activity against both Staphylococcus aureus and Escherichia coli. Furthermore, full-thickness skin wounds in vivo wound healing studies with Sprague-Dawley rats were evaluated. When treated with AgBr@SiO2/GelMA containing 1 mg/mL AgBr@SiO2, only 15% of the wound area left on day 10. Histology results also showed the epidermal and dermal layers were better organized. These results suggest that AgBr@SiO2/GelMA-based dressing materials could be promising candidates for wound dressings.

How Microgels Can Improve the Impact of Organ-on-Chip and Microfluidic Devices for 3D Culture: Compartmentalization, Single Cell Encapsulation and Control on Cell Fate

The Organ-on-chip (OOC) devices represent the new frontier in biomedical research to produce micro-organoids and tissues for drug testing and regenerative medicine. The development of such miniaturized models requires the 3D culture of multiple cell types in a highly controlled microenvironment, opening new challenges in reproducing the extracellular matrix (ECM) experienced by cells in vivo. In this regard, cell-laden microgels (CLMs) represent a promising tool for 3D cell culturing and on-chip generation of micro-organs. The engineering of hydrogel matrix with properly balanced biochemical and biophysical cues enables the formation of tunable 3D cellular microenvironments and long-term in vitro cultures. This focused review provides an overview of the most recent applications of CLMs in microfluidic devices for organoids formation, highlighting microgels' roles in OOC development as well as insights into future research.