Engineered Customizable Microvessels for Progressive Vascularization in Large Regenerative Implants

Application and Mechanism of Adipose Tissue-Derived Microvascular Fragments in Tissue Repair and Regeneration

One of the long-standing challenges in the field of tissue repair and regeneration is the rapid establishment of local microvascular circulation and restoration of perfusion at the site of defects or injuries. Recently, adipose tissue-derived microvascular fragments (ad-MVFs) have attracted increasing attention from researchers. Adipose tissue is rich in blood vessels, and significant progress has been made in the extraction and preservation techniques for microvascular fragments within it. Ad-MVFs promote tissue and organ repair and regeneration through three main mechanisms. First, they accelerate rapid and efficient vascularization at the injury site, enabling early vessel perfusion. Second, the stem cell components within ad-MVFs provide a rich source of cells for tissue and organ regeneration. Third, they play a role in immune regulation, facilitating integration with host tissues after implantation. The application methods of ad-MVFs are diverse. They can be directly implanted or pre-cultivated, facilitating their combination with various scaffolds and broadening their application scope. These properties have led to the wide use of ad-MVFs in tissue engineering, with promising prospects. This review demonstrates that ad-MVFs can serve as a reliable and highly feasible unit for tissue regeneration.

Hyaluronic Acid Role in Biomaterials Prevascularization

Tissue vascularization is a major bottleneck in tissue engineering. In this review, the state of the art on the intricate role of hyaluronic acid (HA) in angiogenesis is explored. HA plays a twofold role in angiogenesis. First, when released as a free polymer in the extracellular matrix (ECM), HA acts as a signaling molecule triggering multiple cascades that foster smooth muscle cell differentiation, migration, and proliferation thereby contributing to vessel wall thickening. Simultaneously, HA bound to the plasma membrane in the pericellular space functions as a polymer block, participating in vessel formation. Starting with the HA origins in native vascular tissues, the approaches aimed at achieving vascularization in vivo are reviewed. The significance of HA molecular weight (MW) in angiogenesis and the challenges associated with utilizing HA in vascular tissue engineering (VTE) are conscientiously addressed. The review finally focuses on a thorough examination and comparison of the diverse strategies adopted to harness the benefits of HA in the vascularization of bioengineered materials. By providing a nuanced perspective on the multifaceted role of HA in angiogenesis, this review contributes to the ongoing discourse in tissue engineering and advances the collective understanding of optimizing vascularization processes assisted by functional biomaterials.

Reversible bonding in thermoplastic elastomer microfluidic platforms for harvestable 3D microvessel networks

Transplantable ready-made microvessels have therapeutic potential for tissue regeneration and cell replacement therapy. Inspired by the natural rapid angiogenic sprouting of microvessels in vivo, engineered injectable 3D microvessel networks are created using thermoplastic elastomer (TPE) microfluidic devices. The TPE material used here is flexible, optically transparent, and can be robustly yet reversibly bonded to a variety of plastic substrates, making it a versatile choice for microfluidic device fabrication because it overcomes the weak self-adhesion properties and limited manufacturing options of poly(dimethylsiloxane) (PDMS). By leveraging the reversible bonding characteristics of TPE material templates, we present their utility as an organ-on-a-chip platform for forming and handling microvessel networks, and demonstrate their potential for animal-free tissue generation and transplantation in clinical applications. We first show that TPE-based devices have nearly 6-fold higher bonding strength during the cell culture step compared to PDMS-based devices while simultaneously maintaining a full reversible bond to (PS) culture plates, which are widely used for biological cell studies. We also demonstrate the successful generation of perfusable and interconnected 3D microvessel networks using TPE-PS microfluidic devices on both single and multi-vessel loading platforms. Importantly, after removing the TPE slab, microvessel networks remain intact on the PS substrate without any structural damage and can be effectively harvested following gel digestion. The TPE-based organ-on-a-chip platform offers substantial advantages by facilitating the harvesting procedure and maintaining the integrity of microfluidic-engineered microvessels for transplant. To the best of our knowledge, our TPE-based reversible bonding approach marks the first confirmation of successful retrieval of organ-specific vessel segments from the reversibly-bonded TPE microfluidic platform. We anticipate that the method will find applications in organ-on-a-chip and microphysiological system research, particularly in tissue analysis and vessel engraftment, where flexible and reversible bonding can be utilized.

Recent advances of bone tissue engineering: carbohydrate and ceramic materials, fundamental properties and advanced biofabrication strategies ‒ a comprehensive review

Bone is a dynamic tissue that can always regenerate itself through remodeling to maintain biofunctionality. This tissue performs several vital physiological functions. However, bone scaffolds are required for critical-size damages and fractures, and these can be addressed by bone tissue engineering. Bone tissue engineering (BTE) has the potential to develop scaffolds for repairing critical-size damaged bone. BTE is a multidisciplinary engineered scaffold with the desired properties for repairing damaged bone tissue. Herein, we have provided an overview of the common carbohydrate polymers, fundamental structural, physicochemical, and biological properties, and fabrication techniques for bone tissue engineering. We also discussed advanced biofabrication strategies and provided the limitations and prospects by highlighting significant issues in bone tissue engineering. There are several review articles available on bone tissue engineering. However, we have provided a state-of-the-art review article that discussed recent progress and trends within the last 3-5 years by emphasizing challenges and future perspectives.

A novel semi-flexible coaxial nozzle based on fluid dynamics effects and its self-centering performance study

Coaxial nozzles are widely used to produce fibers with core-shell structures. However, conventional coaxial nozzles cannot adjust the coaxiality of the inner and outer needles in real-time during the fiber production process, resulting in uneven fiber wall thickness and poor quality. Therefore, we proposed an innovative semi-flexible coaxial nozzle with a dynamic self-centering function. This new design addresses the challenge of ensuring the coaxiality of the inner and outer needles of the coaxial nozzle. First, based on the principles of fluid dynamics and fluid-structure interaction, a self-centering model for a coaxial nozzle is established. Second, the influence of external fluid velocity and inner needle elastic modulus on the centering time and coaxiality error is analyzed by finite element simulation. Finally, the self-centering performance of the coaxial nozzle is verified by observing the coaxial extrusion process online and measuring the wall thickness of the formed hollow fiber. The results showed that the coaxiality error increased with the increase of Young's modulus E and decreased with the increase of flow velocity. The centering time required for the inner needle to achieve force balance decreases with the increase of Young's modulus ( E ) and fluid velocity ( v f ). The nozzle exhibits significant self-centering performance, dynamically reducing the initial coaxiality error from 380 to 60 μm within 26 s. Additionally, it can mitigate the coaxiality error caused by manufacturing and assembly precision, effectively controlling them within 8 μm. Our research provides valuable references and solutions for addressing issues such as uneven fiber wall thickness caused by coaxiality errors.

Engineering pre-vascularized 3D tissue and rapid vascular integration with host blood vessels via co-cultured spheroids-laden hydrogel

Recent advances in regenerative medicine and tissue engineering have enabled the biofabrication of three-dimensional (3D) tissue analogues with the potential for use in transplants and disease modeling. However, the practical use of these biomimetic tissues has been hindered by the challenge posed by reconstructing anatomical-scale micro-vasculature tissues. In this study, we suggest that co-cultured spheroids within hydrogels hold promise for regenerating highly vascularized and innervated tissues, bothin vitroandin vivo. Human adipose-derived stem cells (hADSCs) and human umbilical vein cells (HUVECs) were prepared as spheroids, which were encapsulated in gelatin methacryloyl hydrogels to fabricate a 3D pre-vascularized tissue. The vasculogenic responses, extracellular matrix production, and remodeling depending on parameters like co-culture ratio, hydrogel strength, and pre-vascularization time forin vivointegration with native vessels were then delicately characterized. The co-cultured spheroids with 3:1 ratio (hADSCs/HUVECs) within the hydrogel and with a pliable storage modulus showed the greatest vasculogenic potential, and ultimately formedin vitroarteriole-scale vasculature with a longitudinal lumen structure and a complex vascular network after long-term culturing. Importantly, the pre-vascularized tissue also showed anastomotic vascular integration with host blood vessels after transplantation, and successful vascularization that was positive for both CD31 and alpha-smooth muscle actin covering 18.6 ± 3.6μm2of the luminal area. The described co-cultured spheroids-laden hydrogel can therefore serve as effective platform for engineering 3D vascularized complex tissues.

Intelligent Vascularized 3D/4D/5D/6D-Printed Tissue Scaffolds

Blood vessels are essential for nutrient and oxygen delivery and waste removal. Scaffold-repairing materials with functional vascular networks are widely used in bone tissue engineering. Additive manufacturing is a manufacturing technology that creates three-dimensional solids by stacking substances layer by layer, mainly including but not limited to 3D printing, but also 4D printing, 5D printing and 6D printing. It can be effectively combined with vascularization to meet the needs of vascularized tissue scaffolds by precisely tuning the mechanical structure and biological properties of smart vascular scaffolds. Herein, the development of neovascularization to vascularization to bone tissue engineering is systematically discussed in terms of the importance of vascularization to the tissue. Additionally, the research progress and future prospects of vascularized 3D printed scaffold materials are highlighted and presented in four categories: functional vascularized 3D printed scaffolds, cell-based vascularized 3D printed scaffolds, vascularized 3D printed scaffolds loaded with specific carriers and bionic vascularized 3D printed scaffolds. Finally, a brief review of vascularized additive manufacturing-tissue scaffolds in related tissues such as the vascular tissue engineering, cardiovascular system, skeletal muscle, soft tissue and a discussion of the challenges and development efforts leading to significant advances in intelligent vascularized tissue regeneration is presented.

Tailoring biomaterials for biomimetic organs-on-chips

Organs-on-chips are microengineered microfluidic living cell culture devices with continuously perfused chambers penetrating to cells. By mimicking the biological features of the multicellular constructions, interactions among organs, vascular perfusion, physicochemical microenvironments, and so on, these devices are imparted with some key pathophysiological function levels of living organs that are difficult to be achieved in conventional 2D or 3D culture systems. In this technology, biomaterials are extremely important because they affect the microstructures and functionalities of the organ cells and the development of the organs-on-chip functions. Thus, herein, we provide an overview on the advances of biomaterials for the construction of organs-on-chips. After introducing the general components, structures, and fabrication techniques of the biomaterials, we focus on the studies of the functions and applications of these biomaterials in the organs-on-chips systems. Applications of the biomaterial-based organs-on-chips as alternative animal models for pharmaceutical, chemical, and environmental tests are described and highlighted. The prospects for exciting future directions and the challenges of biomaterials for realizing the further functionalization of organs-on-chips are also presented.

All-Aqueous Freeform Fabrication of Perfusable Self-Standing Soft Compartments

Compartmentalized structures obtained in all-aqueous settings have shown promising properties as cell encapsulation devices, as well as reactors for trans-membrane chemical reactions. While most approaches focus on the preparation of spherical devices, advances on the production of complex architectures have been enabled by the interfacial stability conferred by emulsion systems, namely mild aqueous two-phase systems (ATPS), or non-equilibrated analogues. However, the application of non-spherical structures has mostly been reported while keeping the fabricated materials at a stable interface, limiting the free-standing character, mobility and transposition of the obtained structures to different setups. Here, the fabrication of self-standing, malleable and perfusable tubular systems through all-aqueous interfacial assembly is shown, culminating in the preparation of independent objects with stability and homogeneity after disruption of the polymer-based aqueous separating system. Those hollow structures can be fabricated with a variety of widths, and rapidly printed as long structures at flow rates of 15 mm s^-1 . The materials are used as compartments for cell culture, showcasing high cytocompatibility, and can be tailored to promote cell adhesion. Such structures may find application in fields that benefit from freeform tubular structures, including the biomedical field with, for example, cell encapsulation, and benchtop preparation of microfluidic devices.

Coaxially Fabricated Dual-Drug Loading Electrospinning Fibrous Mat with Programmed Releasing Behavior to Boost Vascularized Bone Regeneration

In clinical treatment, the bone regeneration of critical-size defects is desiderated to be solved, and the regeneration of large bone segment defects depends on early vascularization. Therefore, overcoming insufficient vascularization in artificial bone grafts may be a promising strategy for critical-size bone regeneration. Herein, a novel dual-drug programmed releasing electrospinning fibrous mat (EFM) with a deferoxamine (DFO)-loaded shell layer and a dexamethasone (DEX)-loaded core layer is fabricated using coaxial electrospinning technology, considering the temporal sequence of vascularization and bone repair. DFO acts as an angiogenesis promoter and DEX is used as an osteogenesis inducer. The results demonstrate that the early and rapid release of DFO promotes angiogenesis in human umbilical vascular endothelial cells and the sustained release of DEX enhances the osteogenic differentiation of rat bone mesenchymal stem cells. DFO and DEX exert synergetic effects on osteogenic differentiation via the Wnt/β-catenin signaling pathway, and the dual-drug programmed releasing EFM acquired perfect vascularized bone regeneration ability in a rat calvarial defect model. Overall, the study suggests a low-cost strategy to enhance vascularized bone regeneration by adjusting the behavior of angiogenesis and osteogenesis in time dimension.

An Overview of Extracellular Matrix-Based Bioinks for 3D Bioprinting

As a microenvironment where cells reside, the extracellular matrix (ECM) has a complex network structure and appropriate mechanical properties to provide structural and biochemical support for the surrounding cells. In tissue engineering, the ECM and its derivatives can mitigate foreign body responses by presenting ECM molecules at the interface between materials and tissues. With the widespread application of three-dimensional (3D) bioprinting, the use of the ECM and its derivative bioinks for 3D bioprinting to replicate biomimetic and complex tissue structures has become an innovative and successful strategy in medical fields. In this review, we summarize the significance and recent progress of ECM-based biomaterials in 3D bioprinting. Then, we discuss the most relevant applications of ECM-based biomaterials in 3D bioprinting, such as tissue regeneration and cancer research. Furthermore, we present the status of ECM-based biomaterials in current research and discuss future development prospects.