Strategies for Enhancing Vascularization of Biomaterial-Based Scaffold in Bone Regeneration

Design, fabrication, and application of bioengineering vascular networks based on microfluidic strategies

Vascularization is a critical component of tissue engineering research and is essential for enhancing the success rate of tissue construction and function. Over the past decade, researchers have explored various methods to construct in vitro vascular networks, including 3D printing, cell sphere technology, and microfluidics. Microfluidic technology has garnered significant attention due to its notable advantages in precision, controllability, flexibility, and applicability. It can be primarily classified into two modes: (i) the pre-designed mode, which involves creating vascular networks by pre-designing vascular channels and seeding endothelial cells, encompassing microfluidic chips and microfluidic spinning technologies; and (ii) the self-assembly mode, where cell spheres are fabricated using microfluidic technology and subsequently self-assemble into vascular networks. In this review, we first provide a brief overview of the normal physiological and pathological characteristics of vascular networks, followed by a discussion of the factors to be considered in designing in vitro vascular networks, and conclude with an examination of the classification of technologies for the preparation of microfluidic vascular networks and recent advancements. It is anticipated that in vitro vascular network models will soon be successfully applied in regenerative medicine and drug development.

Polydopamine-functionalized calcium-deficient hydroxyapatite 3D-printed scaffold with sustained doxorubicin release for synergistic chemo-photothermal therapy of osteosarcoma and accelerated bone regeneration

Interior bone-tissue regeneration and rapid tumor recurrence post-resection are critical challenges in osteosarcoma and other bone cancers. Conventional bone tissue engineering scaffolds lack inhibitory effects on bone tumor recurrence. Herein, multifunctional scaffolds (named DOX/PDA@CDHA) were designed through the spontaneous polymerization of Dopamine (PDA) on the surface of Calcium Deficient Hydroxyapatite (CDHA) scaffolds, followed by in situ loading of the chemotherapeutic drug Doxorubicin (DOX). The PDA coating endowed the scaffolds with significant photothermal properties, while the gradual release of DOX provided an effective chemotherapeutic effect. The on-demand release of DOX at tumor sites, triggered by dual stimulation (near-infrared (NIR) light and the acidic pH typical of tumor microenvironments), specifically targets cancer cells, thereby mitigating systemic side effects. These unique characteristics facilitated effective osteosarcoma eradication both in vitro and in vivo. Moreover, the scaffold's composition, which mimics the mineral phase of natural bone and is enhanced by PDA's biocompatibility, promotes critical osteogenic and angiogenic processes. This facilitates not only tumor eradication but also the regeneration of healthy bone tissue. Collectively, this study presents a potent candidate for the regeneration of bone defects induced by osteosarcoma.

Spatiotemporal controlled released hydrogels for multi-system regulated bone regeneration

Bone defect is one of the urgent problems to be solved in clinics, and it is very important to construct efficient scaffold materials to facilitate bone tissue regeneration. Hydrogels, characterized by their unique three-dimensional network structure, serve as excellent biological scaffold materials. Their internal pores are capable of loading osteogenic drugs to expedite bone formation. The rate and quality of new bone formation are intimately linked with immune regulation and vascular remodeling. The strategic sequential release of drugs to balance inflammation and regulate vascular remodeling is crucial for initiating the osteogenic process. Through the design of hydrogel microstructures, it is possible to achieve sequential drug release and the drug action time can be prolonged, thereby catering to the multi-systemic collaborative regulation needs of osteosynthesis. The drug release rate within the hydrogel is governed by swelling control systems, physical control systems, chemical control systems, and environmental control systems. Utilizing these control systems to design hydrogel materials capable of multi-drug delivery optimizes the construction of the bone microenvironment. Consequently, this facilitates the spatiotemporal controlled released of drugs, promoting bone tissue regeneration. This paper reviews the principles of the controlled release system of various sustained-release hydrogels and the advancements in research on hydrogel multi-drug delivery systems for bone tissue regeneration.

Recent trends in bone tissue engineering: a review of materials, methods, and structures

Bone tissue engineering (BTE) provides the treatment possibility for segmental long bone defects that are currently an orthopedic dilemma. This review explains different strategies, from biological, material, and preparation points of view, such as using different stem cells, ceramics, and metals, and their corresponding properties for BTE applications. In addition, factors such as porosity, surface chemistry, hydrophilicity and degradation behavior that affect scaffold success are introduced. Besides, the most widely used production methods that result in porous materials are discussed. Gene delivery and secretome-based therapies are also introduced as a new generation of therapies. This review outlines the positive results and important limitations remaining in the clinical application of novel BTE materials and methods for segmental defects.

3D Printing of a Porous Zn-1Mg-0.1Sr Alloy Scaffold: A Study on Mechanical Properties, Degradability, and Biosafety

In recent years, the use of zinc (Zn) alloys as degradable metal materials has attracted considerable attention in the field of biomedical bone implant materials. This study investigates the fabrication of porous scaffolds using a Zn-1Mg-0.1Sr alloy through a three-dimensional (3D) printing technique, selective laser melting (SLM). The results showed that the porous Zn-1Mg-0.1Sr alloy scaffold featured a microporous structure and exhibited a compressive strength (CS) of 33.71 ± 2.51 MPa, a yield strength (YS) of 27.88 ± 1.58 MPa, and an elastic modulus (E) of 2.3 ± 0.8 GPa. During the immersion experiments, the immersion solution showed a concentration of 2.14 ± 0.82 mg/L for Zn2+ and 0.34 ± 0.14 mg/L for Sr2+, with an average pH of 7.61 ± 0.09. The porous Zn-1Mg-0.1Sr alloy demonstrated a weight loss of 12.82 ± 0.55% and a corrosion degradation rate of 0.36 ± 0.01 mm/year in 14 days. The Cell Counting Kit-8 (CCK-8) assay was used to check the viability of the cells. The results showed that the 10% and 20% extracts significantly increased the activity of osteoblast precursor cells (MC3T3-E1), with a cytotoxicity grade of 0, which indicates safety and non-toxicity. In summary, the porous Zn-1Mg-0.1Sr alloy scaffold exhibits outstanding mechanical properties, an appropriate degradation rate, and favorable biosafety, making it an ideal candidate for degradable metal bone implants.

Functionalized Magnesium Phosphate Cement Induces In Situ Vascularized Bone Regeneration via Surface Lyophilization of Chondroitin Sulfate

Bone defect repair poses significant challenges in orthopedics, thereby increasing the demand for bone substitutes. Magnesium phosphate cements (MPCs) are widely used for bone defect repair because of their excellent mechanical properties and biodegradability. However, high crystallinity and uncontrolled magnesium ion (Mg2+) release limit the surface bioactivity of MPCs in bone regeneration. Here, we fabricate chondroitin sulfate (CS) as a surface coating via the lyophilization method, namely CMPC. We find that the CS coating is uniformly distributed and improves the mechanical properties of MPC through anionic electrostatic adsorption, while mediating degradation-related controlled ion release of Mg2+. Using a combination of in vitro and in vivo analyses, we show that the CS coating maintained cytocompatibility while increasing the cell adhesion area of MC3T3-E1s. Furthermore, we display accelerated osteogenesis and angiogenesis of CMPC, which are related to appropriate ion concentration of Mg2+. Our findings reveal that the preparation of a lyophilized CS coating is an effective method to promote surface bioactivity and mediate Mg2+ concentration dependent osteogenesis and angiogenesis, which have great potential in bone regeneration.

Exogeneous metal ions as therapeutic agents in cardiovascular disease and their delivery strategies

Metal ions participate in many metabolic processes in the human body, and their homeostasis is crucial for life. In cardiovascular diseases (CVDs), the equilibriums of metal ions are frequently interrupted, which are related to a variety of disturbances of physiological processes leading to abnormal cardiac functions. Exogenous supplement of metal ions has the potential to work as therapeutic strategies for the treatment of CVDs. Compared with other therapeutic drugs, metal ions possess broad availability, good stability and safety and diverse drug delivery strategies. The delivery strategies of metal ions are important to exert their therapeutic effects and reduce the potential toxic side effects for cardiovascular applications, which are also receiving increasing attention. Controllable local delivery strategies for metal ions based on various biomaterials are constantly being designed. In this review, we comprehensively summarized the positive roles of metal ions in the treatment of CVDs from three aspects: protecting cells from oxidative stress, inducing angiogenesis, and adjusting the functions of ion channels. In addition, we introduced the transferability of metal ions in vascular reconstruction and cardiac tissue repair, as well as the currently available engineered strategies for the precise delivery of metal ions, such as integrated with nanoparticles, hydrogels and scaffolds.

Pro-angiogenic photo-crosslinked silk fibroin hydrogel: a potential candidate for repairing alveolar bone defects

OBJECTIVE

This study aimed to develop a pro-angiogenic hydrogel with in situ gelation ability for alveolar bone defects repair.

METHODOLOGY

Silk fibroin was chemically modified by Glycidyl Methacrylate (GMA), which was evaluated by proton nuclear magnetic resonance (1H-NMR). Then, the photo-crosslinking ability of the modified silk fibroin was assessed. Scratch and transwell-based migration assays were conducted to investigate the effect of the photo-crosslinked silk fibroin hydrogel on the migration of human umbilical vein endothelial cells (HUVECs). In vitro angiogenesis was conducted to examine whether the photo-crosslinked silk fibroin hydrogel would affect the tube formation ability of HUVECs. Finally, subcutaneous implantation experiments were conducted to further examine the pro-angiogenic ability of the photo-crosslinked silk fibroin hydrogel, in which the CD31 and α-smooth muscle actin (α-SMA) were stained to assess neovascularization. The tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were also stained to evaluate inflammatory responses after implantation.

RESULTS

GMA successfully modified the silk fibroin, which we verified by our 1H-NMR and in vitro photo-crosslinking experiment. Scratch and transwell-based migration assays proved that the photo-crosslinked silk fibroin hydrogel promoted HUVEC migration. The hydrogel also enhanced the tube formation of HUVECs in similar rates to Matrigel®. After subcutaneous implantation in rats for one week, the hydrogel enhanced neovascularization without triggering inflammatory responses.

CONCLUSION

This study found that photo-crosslinked silk fibroin hydrogel showed pro-angiogenic and inflammation inhibitory abilities. Its photo-crosslinking ability makes it suitable for matching irregular alveolar bone defects. Thus, the photo-crosslinkable silk fibroin-derived hydrogel is a potential candidate for constructing scaffolds for alveolar bone regeneration.

Application of Nano-Inspired Scaffolds-Based Biopolymer Hydrogel for Bone and Periodontal Tissue Regeneration

This review's objectives are to provide an overview of the various kinds of biopolymer hydrogels that are currently used for bone tissue and periodontal tissue regeneration, to list the advantages and disadvantages of using them, to assess how well they might be used for nanoscale fabrication and biofunctionalization, and to describe their production processes and processes for functionalization with active biomolecules. They are applied in conjunction with other materials (such as microparticles (MPs) and nanoparticles (NPs)) and other novel techniques to replicate physiological bone generation more faithfully. Enhancing the biocompatibility of hydrogels created from blends of natural and synthetic biopolymers can result in the creation of the best scaffold match to the extracellular matrix (ECM) for bone and periodontal tissue regeneration. Additionally, adding various nanoparticles can increase the scaffold hydrogel stability and provide a number of biological effects. In this review, the research study of polysaccharide hydrogel as a scaffold will be critical in creating valuable materials for effective bone tissue regeneration, with a future impact predicted in repairing bone defects.

Functionalized 3D-Printed ST2/Gelatin Methacryloyl/Polcaprolactone Scaffolds for Enhancing Bone Regeneration with Vascularization

Growth factors were often used to improve the bioactivity of biomaterials in order to fabricate biofunctionalized bone grafts for bone defect repair. However, supraphysiological concentrations of growth factors for improving bioactivity could lead to serious side effects, such as ectopic bone formation, radiculitis, swelling of soft tissue in the neck, etc. Therefore, safely and effectively applying growth factors in bone repair biomaterials comes to be an urgent problem that needs to be addressed. In this study, an appropriate concentration (50 ng/mL) of Wnt3a was used to pretreat the 3D-bioprinting gelatin methacryloyl(GelMA)/polycaprolactone(PCL) scaffold loaded with bone marrow stromal cell line ST2 for 24 h. This pretreatment promoted the cell proliferation, osteogenic differentiation, and mineralization of ST2 in the scaffold in vitro, and enhanced angiogenesis and osteogenesis after being implanted in critical-sized mouse calvarial defects. On the contrary, the inhibition of Wnt/β-catenin signaling in ST2 cells reduced the bone repair effect of this scaffold. These results suggested that ST2/GelMA/PCL scaffolds pretreated with an appropriate concentration of Wnt3a in culture medium could effectively enhance the osteogenic and angiogenic activity of bone repair biomaterials both in vitro and in vivo. Moreover, it would avoid the side effects caused by the supraphysiological concentrations of growth factors. This functionalized scaffold with osteogenic and angiogenic activity might be used as an outstanding bone substitute for bone regeneration and repair.