In Situ Oxygen Generation Enhances the SCAP Survival in Hydrogel Constructs

Dual roles of photosynthetic hydrogel with sustained oxygen generation in promoting cell survival and eradicating anaerobic infection

Tissue engineering offers a promising alternative for oral and maxillofacial tissue defect rehabilitation; however, cells within a sizeable engineered tissue construct after transplantation inevitably face prolonged and severe hypoxic conditions, which may compromise the survivability of the transplanted cells and arouse the concern of anaerobic infection. Microalgae, which can convert carbon dioxide and water into oxygen and glucose through photosynthesis, have been studied as a source of oxygen supply for several biomedical applications, but their promise in orofacial tissue regeneration remains unexplored. Here, we demonstrated that through photosynthetic oxygenation, Chlamydomonas reinhardtii (C. reinhardtii) supported dental pulp stem cell (DPSC) energy production and survival under hypoxia. We developed a multifunctional photosynthetic hydrogel by embedding DPSCs and C. reinhardtii encapsulated alginate microspheres (CAMs) within gelatin methacryloyl hydrogel (GelMA) (CAMs@GelMA). This CAMs@GelMA hydrogel can generate a sustainable and sufficient oxygen supply, reverse intracellular hypoxic status, and enhance the metabolic activity and viability of DPSCs. Furthermore, the CAMs@GelMA hydrogel exhibited selective antibacterial activity against oral anaerobes and remarkable antibiofilm effects on multispecies biofilms by disrupting the hypoxic microenvironment and increasing reactive oxygen species generation. Our work presents an innovative photosynthetic strategy for oral tissue engineering and opens new avenues for addressing other hypoxia-related challenges.

Enhancing Vasculogenesis in Dental Pulp Development: DPSCs-ECs Communication via FN1-ITGA5 Signaling

BACKGROUND

Dental pulp regeneration therapy is a challenge to achieve early vascularization during treatment. Studying the regulatory mechanisms of vascular formation during human dental pulp development may provide insights for related therapies. In this study, we utilized single-cell sequencing analysis to compare the gene expression of dental pulp stem cells (DPSCs) and vascular endothelial cells (ECs) from developing and mature dental pulps.

METHOD

Immunohistochemistry, Western blot, and real-time polymerase chain reaction (RT-PCR) were used to detect fibronectin 1 (FN1) expression and molecules, such as PI3K/AKT. Cell proliferation assay, scratch assay, tube formation assay and were used to investigate the effects of DPSCs on the vasculogenetic capability of ECs. Additionally, animal experiments involving mice were conducted.

RESULT

The results revealed that DPSCs exist around dental pulp vasculature. FN1 expression was significantly higher in DPSCs from young permanent pulps than mature pulps, promoting HUVEC proliferation, migration, and tube formation via ITGA5 and the downstream PI3K/AKT signaling pathway.

CONCLUSION

Our data indicate that intercellular communication between DPSCs and ECs mediated by FN1-ITGA5 signaling is crucial for vascularizationduring dental pulp development, laying an experimental foundation for future clinical studies.

Oxygen enrichment mediated by calcium peroxide loaded gelatin methacrylate hydrogel eradicates periodontal biofilms

The low oxygen environment of the periodontal pocket favors pathogenic anaerobes' growth, biofilm formation, and quick recurrence after periodontal treatment. In contrast, oxygen is detrimental to anaerobes, such as Porphyromonas gingivalis (P. gingivalis), since they lack a complete anti-oxidation mechanism to detoxify the oxygen challenge. Therefore, consistently feeding pathogenic anaerobes with abundant oxygen would be an effective strategy to combat them. Here, we reported injectable oxygen-generating hydrogels as oxygen mediators to alleviate the local anaerobic environment and eliminate periodontal pathogens. Gelatin methacrylate (GelMA) hydrogels loaded with calcium peroxide (CPO) possessed excellent injectability and exhibited burst releases of oxygen within 24 h with a 40 % oxygen tension peak. CPO-GelMA hydrogels with CPO concentrations of 5, 10, and 15 % reduced 60, 99, and 89.9 % viable P. gingivalis, respectively. Five percentage CPO-GelMA hydrogel downregulated gingipain and fimA gene expression in P. gingivalis without resistance development. Moreover, the CPO-GelMA hydrogels remarkably prevented biofilm formation and eradicated both monospecies and multispecies bacterial biofilms. In conclusion, CPO-GelMA hydrogels exert remarkable antimicrobial and antibiofilm effects on subgingival biofilms, providing a promising strategy for periodontal treatment.

Antibacterial microneedle patch releases oxygen to enhance diabetic wound healing

Cell growth and metabolism require an adequate supply of oxygen. However, obtaining sufficient oxygen from the blood circulating around diabetic wounds is challenging. Nevertheless, achieving a continuous and stable oxygen supply is required for these wounds to heal. Hence, in this study, we report a novel antibacterial oxygen-producing silk fibroin methacryloyl hydrogel microneedle (MN) patch comprising tips encapsulated with calcium peroxide and catalase and a base coated with antibacterial Ag nanoparticles (AgNPs). The tip of the MN patch continuously releases oxygen and inhibits the production of reactive oxygen species. This accelerates diabetic wound healing by promoting cellular accretion and migration, macrophage M2 polarization, and angiogenesis. The AgNPs at the base of the MN patch effectively combat microbial infection, further facilitating wound repair. These findings suggest that using this multifunctional oxygen-producing MN patch may be a promising strategy for diabetic wound healing in clinical settings.

Oxygen-Generating Biomaterials for Translational Bone Regenerative Engineering

Successful regeneration of critical-size defects remains one of the significant challenges in regenerative engineering. These large-scale bone defects are difficult to regenerate and are often reconstructed with matrices that do not provide adequate oxygen levels to stem cells involved in the regeneration process. Hypoxia-induced necrosis predominantly occurs in the center of large matrices since the host tissue's local vasculature fails to provide sufficient nutrients and oxygen. Indeed, utilizing oxygen-generating materials can overcome the central hypoxic region, induce tissue in-growth, and increase the quality of life for patients with extensive tissue damage. This article reviews recent advances in oxygen-generating biomaterials for translational bone regenerative engineering. We discussed different oxygen-releasing and delivery methods, fabrication methods for oxygen-releasing matrices, biology, oxygen's role in bone regeneration, and emerging new oxygen delivery methods that could potentially be used for bone regenerative engineering.

Harnessing the potential of oxygen-generating materials and their utilization in organ-specific delivery of oxygen

The limited availability of transplantable organs hinders the success of patient treatment through organ transplantation. In addition, there are challenges with immune rejection and the risk of disease transmission when receiving organs from other individuals. Tissue engineering aims to overcome these challenges by generating functional three-dimensional (3D) tissue constructs. When developing tissues or organs of a particular shape, structure, and size as determined by the specific needs of the therapeutic intervention, a tissue specific oxygen supply to all parts of the tissue construct is an utmost requirement. Moreover, the lack of a functional vasculature in engineered tissues decreases cell survival upon implantation in the body. Oxygen-generating materials can alleviate this challenge in engineered tissue constructs by providing oxygen in a sustained and controlled manner. Oxygen-generating materials can be incorporated into 3D scaffolds allowing the cells to receive and utilize oxygen efficiently. In this review, we present an overview of the use of oxygen-generating materials in various tissue engineering applications in an organ specific manner as well as their potential use in the clinic.

Creating a Microenvironment to Give Wings to Dental Pulp Regeneration-Bioactive Scaffolds

Dental pulp and periapical diseases make patients suffer from acute pain and economic loss. Although root canal therapies, as demonstrated through evidence-based medicine, can relieve symptoms and are commonly employed by dentists, it is still difficult to fully restore a dental pulp's nutrition, sensory, and immune-regulation functions. In recent years, researchers have made significant progress in tissue engineering to regenerate dental pulp in a desired microenvironment. With breakthroughs in regenerative medicine and material science, bioactive scaffolds play a pivotal role in creating a suitable microenvironment for cell survival, proliferation, and differentiation, following dental restoration and regeneration. This article focuses on current challenges and novel perspectives about bioactive scaffolds in creating a microenvironment to promote dental pulp regeneration. We hope our readers will gain a deeper understanding and new inspiration of dental pulp regeneration through our summary.

Oxygen-Generating Scaffolds: One Step Closer to the Clinical Translation of Tissue Engineered Products

The lack of oxygen supply in engineered constructs has been an ongoing challenge for tissue engineering and regenerative medicine. Upon implantation of an engineered tissue, spontaneous blood vessel formation does not happen rapidly, therefore, there is typically a limited availability of oxygen in engineered biomaterials. Providing oxygen in large tissue-engineered constructs is a major challenge that hinders the development of clinically relevant engineered tissues. Similarly, maintaining adequate oxygen levels in cell-laden tissue engineered products during transportation and storage is another hurdle. There is an unmet demand for functional scaffolds that could actively produce and deliver oxygen, attainable by incorporating oxygen-generating materials. Recent approaches include encapsulation of oxygen-generating agents such as solid peroxides, liquid peroxides, and fluorinated substances in the scaffolds. Recent approaches to mitigate the adverse effects, as well as achieving a sustained and controlled release of oxygen, are discussed. Importance of oxygen-generating materials in various tissue engineering approaches such as ex vivo tissue engineering, in situ tissue engineering, and bioprinting are highlighted in detail. In addition, the existing challenges, possible solutions, and future strategies that aim to design clinically relevant multifunctional oxygen-generating biomaterials are provided in this review paper.

The Journey of SCAPs (Stem Cells from Apical Papilla), from Their Native Tissue to Grafting: Impact of Oxygen Concentration

Tissue engineering strategies aim at characterizing and at optimizing the cellular component that is combined with biomaterials, for improved tissue regeneration. Here, we present the immunoMap of apical papilla, the native tissue from which SCAPs are derived. We characterized stem cell niches that correspond to a minority population of cells expressing Mesenchymal stromal/Stem Cell (CD90, CD105, CD146) and stemness (SSEA4 and CD49f) markers as well as endothelial cell markers (VWF, CD31). Based on the colocalization of TKS5 and cortactin markers, we detected migration-associated organelles, podosomes-like structures, in specific regions and, for the first time, in association with stem cell niches in normal tissue. From six healthy teenager volunteers, each with two teeth, we derived twelve cell banks, isolated and amplified under 21 or 3% O₂. We confirmed a proliferative advantage of all banks when cultured under 3% versus 21% O₂. Interestingly, telomerase activity was similar to that of the highly proliferative hiPSC cell line, but unrelated to O₂ concentration. Finally, SCAPs embedded in a thixotropic hydrogel and implanted subcutaneously in immunodeficient mice were protected from cell death with a slightly greater advantage for cells preconditioned at 3% O₂.

Three-dimensional electroconductive carbon nanotube-based hydrogel scaffolds enhance neural differentiation of stem cells from apical papilla

The radical treatment of neurological impairments remains a major clinical challenge. Stem cells with high neural differentiation ability delivered by electroconductive hydrogel scaffolds have demonstrated promising applications in neural tissue regeneration. However, there are still challenges in designing bioactive scaffolds with good biocompatibility, appropriate electrical conductivity, and neurogenic niche. Herein, a three-dimensional (3D) electroconductive gelatin methacryloyl-multi-walled carbon nanotube/cobalt (GelMA-MWCNTs/Co) hydrogel scaffold was fabricated by incorporating MWCNTs/Co composites into a GelMA hydrogel matrix. The surface morphology, pore size, elastic modulus, swelling ratio, and conductivity of the hydrogels were measured. GelMA-MWCNTs/Co exhibited higher electrical conductivity than GelMA-MWCNTs. Live/dead and CCK8 assays demonstrated the good biocompatibility of the hydrogel for stem cells from apical papilla (SCAP) growth and differentiation. The cells encapsulated in the GelMA-MWCNTs and GelMA-MWCNTs/Co hydrogel scaffolds exhibited significant neuronal cell-like changes and a notable level of neuronal-specific marker expression after the electrical stimulation (ES) for 7 days, compared to that in the hydrogels without ES. Notably, the neurite spreading and Tuj1 fluorescent intensity of the SCAP in the electrically conductive GelMA-MWCNTs/Co hydrogel were more prominent compared to those of the other two groups. In addition, the 3D conductive hydrogel scaffolds advanced the neural differentiation of SCAP to an earlier time point. Considering these aspects, the novel electroconductive GelMA-MWCNTs/Co hydrogel synergized with ES greatly promotes SCAP neuronal differentiation.

Gelatin methacryloyl-alginate core-shell microcapsules as efficient delivery platforms for prevascularized microtissues in endodontic regeneration

Combined injectable cell-laden microspheres and angiogenesis approaches are promising for functional vascularized endodontic regeneration. However, advanced microsphere designs and production techniques that benefit practical applications are rarely developed. Herein, gelatin methacryloyl (GelMA)-alginate core-shell microcapsules were fabricated to co-encapsulate human dental pulp stem cells (hDPSCs) and human umbilical vein endothelial cells (HUVECs) based on a coaxial electrostatic microdroplet technique. This technique enables high-throughput production, convenient collection, and minimal material waste. The average diameter of core-shell microcapsules was ∼359 µm, and that of GelMA cores was ∼278 µm. There were higher proliferation rates for hDPSCs and HUVECs co-encapsulated in the GelMA cores than for hDPSCs or HUVECs monoculture group. HUVECs assembled to form 3D capillary-like networks in co-culture microcapsules. Moreover, HUVECs promoted the osteo/odontogenic differentiation of hDPSCs in microcapsules. After 14 days of cultivation, prevascularized microtissues formed in microcapsules that contained abundant deposited extracellular matrix (ECM); no microcapsule aggregation occurred. In vivo studies confirmed that better microvessel formation and pulp-like tissue regeneration occurred in the co-culture group than in hDPSCs group. Thus, an effective platform for prevascularization microtissue preparation was proposed and showed great promise in endodontic regeneration and tissue engineering applications. STATEMENT OF SIGNIFICANCE: Cell-laden microspheres combined with the proangiogenesis approach are promising in endodontic regeneration. We proposed GelMA-alginate core-shell microcapsules generated via the coaxial electrostatic microdroplet (CEM) method, which utilizes a double-lumen needle to allow for core-shell structures to form. The microcapsules were used for co-culturing hDPSCs and HUVECs to harvest large amounts of prevascularized microtissues, which further showed improved vascularization and pulp-like tissue regeneration in vivo. This CEM method and the microcapsule system have advantages of high-throughput generation, convenient collection, and avoid aggregation during long-term culturing. We proposed a high-effective platform for mass production of prevascularized microtissues, which exhibit great promise in the clinical transformation of endodontic regeneration and other applications in regenerative medicine.