Immunomodulatory Blood-Derived Hybrid Hydrogels as Multichannel Microenvironment Modulators for Augmented Bone Regeneration

3D-bioprinted functional scaffold based on synergistic induction of i-PRF and laponite exerts efficient and personalized bone regeneration via miRNA-mediated TGF-β/Smads signaling

BACKGROUND

Limited stem cells, low vascularization efficiency, and weak osteoinductive activity plague the repair and reconstruction of bone defects with cell-free scaffolds.

METHODS

Herein, injectable platelet-rich fibrin (i-PRF) was loaded into a alginate methacryloyl (AlgMA)/gelatin methacryloyl (GelMA)-methylcellulose (AGM) bioink system and constructed a porous hydrogel scaffold by 3D bioprinting. The addition of nanosilicate-laponite (Lap) further enhanced this scaffold and synergized with i-PRF to promote efficient and personalized cranial regeneration.

RESULTS

At the biochemical level, Lap significantly enhanced the ability of the scaffold to retard growth factor release, and multiple physiologically proportional growth factors in the scaffold synergistically promoted rapid neoangiogenesis and concomitantly recruited endogenous bone marrow mesenchymal stem cells (BMSCs). More importantly, the bioactive ions released by Lap markedly promoted the proliferation of BMSCs and consistently induced the osteogenic differentiation of BMSCs. At the immunological level, i-PRF-AGM@Lap significantly attenuates the inflammatory response by promoting macrophage M2 polarization. Mechanistically, miRNA sequencing and functional validation experiments demonstrated that bioactive ions released by Lap could synergize with growth factors in i-PRF to promote osteogenic differentiation of BMSCs through the miR-21 and miR-125a-mediated transforming growth factor-β/Smads signaling pathway.

CONCLUSION

The results of this study provide a new idea for the personalized treatment of bone defects.

Hydrogel promotes bone regeneration through various mechanisms: a review

Large defects in bone tissue due to trauma, tumors, or developmental abnormalities usually require surgical treatment for repair. Numerous studies have shown that current bone repair and regeneration treatments have certain complications and limitations. With the in-depth understanding of bone regeneration mechanisms and biological tissue materials, a variety of materials with desirable physicochemical properties and biological functions have emerged in the field of bone regeneration in recent years. Among them, hydrogels have been widely used in bone regeneration research due to their biocompatibility, unique swelling properties, and ease of fabrication. In this paper, the development and classification of hydrogels were introduced, and the mechanism of hydrogels in promoting bone regeneration was described in detail, including the promotion of bone marrow mesenchymal stem cell differentiation, the promotion of angiogenesis, the enhancement of the activity of bone morphogenetic proteins, and the regulation of the microenvironment of bone regeneration tissues. In addition, the future research direction of hydrogel in bone tissue engineering was discussed.

Inflammatory Microenvironment-Modulated Conductive Hydrogel Promotes Vascularized Bone Regeneration in Infected Bone Defects

Infected bone defects show a significant reduction in neovascularization during the healing process, primarily due to persistent bacterial infection and immune microenvironmental disorders. Existing treatments are difficult to simultaneously meet the requirements of antibacterial and anti-inflammatory treatments for infected bone defects, which is a key clinical therapeutic challenge that needs to be addressed. In this study, a conductive hydrogel based on copper nanoparticles was developed for controlling bacterial infection and remodeling the immune microenvironment. The hydrogel not only effectively eliminates bacteria that exist in the infected bone defect region but also transmits electrical signals to restore the disordered immune microenvironment. In vitro studies have shown that the hydrogel has excellent biocompatibility and can modulate macrophage polarization by transmitting electrical signals to reduce inflammation and promote neovascularization. In vivo studies further confirmed that the hydrogel scaffold not only rapidly cleared clinical bacterial infections but also significantly induced the formation of vascularized new bone tissue within 4 weeks. This work provides a simple and innovative strategy to fabricate copper-containing conductive hydrogels that show great potential for application in the field of therapeutics for infected bone regeneration.

Polydopamine Nanocomposite Hydrogel for Drug Slow-Release in Bone Defect Repair: A Review of Research Advances

In recent years, hydrogels have emerged as promising candidates for bone defect repair due to their excellent biocompatibility, high porosity, and water-retentive properties. However, conventional hydrogels face significant challenges in clinical translation, including brittleness, low mechanical strength, and poorly controlled drug degradation rates. To address these limitations, as a multifunctional polymer, polydopamine (PDA) has shown great potential in both bone regeneration and drug delivery systems. Its robust adhesive properties, biocompatibility, and responsiveness to photothermal stimulation make it an ideal candidate for enhancing hydrogel performance. Integrating PDA into conventional hydrogels not only improves their mechanical properties but also creates an environment conducive to cell adhesion, proliferation, and differentiation, thereby promoting bone defect repair. Moreover, PDA facilitates controlled drug release, offering a promising approach to optimizing treatment outcomes. This paper first explores the mechanisms through which PDA promotes bone regeneration, laying the foundation for its clinical translation. Additionally, it discusses the application of PDA-based nanocomposite hydrogels as advanced drug delivery systems for bone defect repair, providing valuable insights for both research and clinical translation.

Vat-Based 3D-Bioprinted Scaffolds from Photocurable Bacterial Levan for Osteogenesis and Immunomodulation

Emerging techniques of additive manufacturing, such as vat-based three-dimensional (3D) bioprinting, offer novel routes to prepare personalized scaffolds of complex geometries. However, there is a need to develop bioinks suitable for clinical translation. This study explored the potential of bacterial-sourced methacrylate levan (LeMA) as a bioink for the digital light processing (DLP) 3D bioprinting of bone tissue scaffolds. LeMA was successfully synthesized, characterized, and used to fabricate 3D-bioprinted scaffolds with excellent printability and physicochemical properties. In vitro studies demonstrated superior cytocompatibility of 15% w/v LeMA gels compared to 20% gels. 15% LeMA gels supported osteogenic differentiation , as evidenced by alkaline phosphatase activity and mineral deposition by MC3T3 pre-osteoblasts. Importantly, the LeMA hydrogels positively modulated the macrophage phenotype, promoting the expression of the anti-inflammatory marker CD206. These findings suggest that 3D-printed LeMA scaffolds can create a favorable microenvironment for bone regeneration, highlighting their potential for tissue repair and regeneration applications.

Dual scalable osteogenic microtissue engineering via GelMA microsphere-inspired mechanical training and autonomous assembling of dental pulp stem cell

Large bone tissue defects present a significant clinical challenge due to the lack of stem cells and an osteogenic microenvironment, leading to fibrotic healing and impaired bone regeneration. Microsphere-based cell-on three-dimensional (3D) culture systems show great promise for constructing osteogenic microtissues. However, the underlying mechanisms require further investigation. In this study, we propose a simple, scalable framework for highly efficient osteogenic microtissue construction, utilizing gelatin methacryloyl (GelMA) microspheres and dental pulp stem cells (DPSCs). The GelMA microspheres provide an extensive, scalable 3D framework for the autonomous adhesion, migration, and proliferation of DPSCs. Within the enormous 3D space created by the microspheres, DPSCs anchor to the microspheres and neighboring cells, inducing intrinsic tensile stress and simulating a mechanical force akin to "rock climbing training". Transcriptomic sequencing results reveal that the 3D spatial and mechanical microenvironment modulates biological processes involved in cell adhesion, extracellular matrix organization, and the positive regulation of cell migration. Further investigations demonstrate that triggering the FAK/YAP pathway mediate mechanical driven differentiation of DPSCs into the osteoblastic lineage in the excellent osteogenic microtissues. Moreover, this simple scalable 3D framework strategy is expected to enable the efficient and large-scale preparation of stem cell-based microtissues.

Polydopamine-Based Biomaterials in Orthopedic Therapeutics: Properties, Applications, and Future Perspectives

Polydopamine is a versatile and modifiable polymer, known for its excellent biocompatibility and adhesiveness. It can also be engineered into a variety of nanoparticles and biomaterials for drug delivery, functional modification, making it an excellent choice to enhance the prevention and treatment of orthopedic diseases. Currently, the application of polydopamine biomaterials in orthopedic disease prevention and treatment is in its early stages, despite some initial achievements. This article aims to review these applications to encourage further development of polydopamine for orthopedic therapeutic needs. We detail the properties of polydopamine and its biomaterial types, highlighting its superior performance in functional modification on nanoparticles and materials. Additionally, we also explore the challenges and future prospects in developing optimal polydopamine biomaterials for clinical use in orthopedic disease prevention and treatment.

Immunoregulatory role of platelet derivatives in the macrophage-mediated immune response

Background

Macrophages are innate immune cells that display remarkable phenotypic heterogeneity and functional plasticity. Due to their involvement in the pathogenesis of several human conditions, macrophages are considered to be an attractive therapeutic target. In line with this, platelet derivatives have been successfully applied in many medical fields and as active participants in innate immunity, cooperation between platelets and macrophages is essential. In this context, the aim of this review is to compile the current evidence regarding the effects of platelet derivatives on the phenotype and functions of macrophages to identify the advantages and shortcomings for feasible future clinical applications.

Methods

A total of 669 articles were identified during the systematic literature search performed in PubMed and Web of Science databases.

Results

A total of 27 articles met the inclusion criteria. Based on published findings, platelet derivatives may play an important role in inducing a dynamic M1/M2 balance and promoting a timely M1-M2 shift. However, the differences in procedures regarding platelet derivatives and macrophages polarization and the occasional lack of information, makes reproducibility and comparison of results extremely challenging. Furthermore, understanding the differences between human macrophages and those derived from animal models, and taking into account the peculiarities of tissue resident macrophages and their ontogeny seem essential for the design of new therapeutic strategies.

Conclusion

Research on the combination of macrophages and platelet derivatives provides relevant information on the function and mechanisms of the immune response.

Macrophage-mediated fracture healing: Unraveling molecular mechanisms and therapeutic implications using hydrogel-based interventions

Fracture healing is a complex biological process that involves the orchestrated interplay of various cells and molecular signaling pathways. Among the key players, macrophages have emerged as critical regulators of fracture repair, influencing inflammation, tissue remodeling, and angiogenesis. Recent advances in hydrogel-based therapeutics have provided exciting opportunities to leverage the modulatory effects of macrophages for improving fracture healing outcomes. In the present study, we review the importance of macrophages in fracture repair and their potential therapeutic role in hydrogel-based interventions. We discuss the molecular mechanisms underlying macrophage-mediated effects on fracture healing, and how hydrogels can be utilized as a platform for macrophage modulation. Furthermore, we highlight the translation of hydrogel-based therapies from bench to bedside, including preclinical and clinical studies, and the challenges and opportunities in harnessing the therapeutic potential of macrophages in fracture repair. Overall, understanding the importance of macrophages in fracture healing and the potential of hydrogel-based therapeutics to modulate macrophage responses can pave the way for developing innovative approaches to improve fracture healing outcomes.

Balance between the CMC/ACP Nanocomplex and Blood Assimilation Orchestrates Immunomodulation of the Biomineralized Collagen Matrix

Calcium phosphate-based biomineralized biomaterials have broad application prospects. However, the immune response and foreign body reactions elicited by biomineralized materials have drawn substantial attention recently, contrary to the immune microenvironment optimization concept. Therefore, it is important to clarify the immunomodulation properties of biomineralized materials. Herein, we prepared the biomineralized collagen matrix (BCM) and screened the key immunomodulation factor carboxymethyl chitosan/amorphous calcium phosphate (CMC/ACP) nanocomplex. The immunomodulation effect of the BCM was investigated in vitro and in vivo. The BCM triggered evident inflammatory responses and cascade foreign body reactions by releasing the CMC/ACP nanocomplex, which activated the potential TLR4-MAPK/NF-κB pathway, compromising the collagen matrix biocompatibility. By contrast, blocking the CMC/ACP nanocomplex release via the blood assimilation process of the BCM mitigated the inflammation and foreign body reactions, enhancing biocompatibility. Hence, the immunomodulation of the BCM was orchestrated by the balance between the CMC/ACP nanocomplex and the blood assimilation process. Controlling the release of the CMC/ACP nanocomplex to accord the biological effects of ACP with the temporal regenerative demands is key to developing advanced biomineralized materials.

New strategy of personalized tissue regeneration: when autologous platelet concentrates encounter biomaterials

Components in blood play an important role in wound healing and subsequent tissue regeneration processes. The fibrin matrix and various bioactive molecules work together to participate in this complex yet vital biological process. As a means of personalized medicine, autologous platelet concentrates have become an integral part of various tissue regeneration strategies. Here, we focus on how autologous platelet concentrates play a role in each stage of tissue healing, as well as how they work in conjunction with different types of biomaterials to participate in this process. In particular, we highlight the use of various biomaterials to protect, deliver and enhance these libraries of biomolecules, thereby overcoming the inherent disadvantages of autologous platelet concentrates and enabling them to function better in tissue regeneration.

Recent advances in immunomodulatory hydrogels biomaterials for bone tissue regeneration

There is a high incidence of fractures in clinical practice and therapy. The repairment of critical size defects in the skeletal system remains a huge challenge for surgeons and researchers, which can be overcame by the application of bone tissue-engineered biomaterials. An increasing number of investigations have revealed that the immune system plays a vital role in the repair of bone defects, especially macrophages, which can modulate the integration of biomaterials and bone regeneration in multiple ways. Therefore, it has become increasingly important in regenerative medicine to regulate macrophage polarization to prevent inflammation caused by biomaterial implantation. Recent studies have stressed the importance of hydrogel-based modifications and the incorporation of various cellular and molecular signals for regulating immune responses to promote bone tissue regeneration and integrate biomaterials. In this review, we first elaborate briefly on the described the general physiological mechanism and process of bone tissue regeneration. Then, we summarized the immunomodulatory role macrophages play in bone repair. In addition, the role of hydrogel-based immune modification targeting macrophage modulation in accelerating and enhancing bone tissue regeneration was also discussed. Finally, we highlighted future directions and research strategies related to hydrogel optimization for the regulation of the immune response during bone regeneration and healing.

Microenvironment-targeted strategy steers advanced bone regeneration

Treatment of large bone defects represents a great challenge in orthopedic and craniomaxillofacial surgery. Traditional strategies in bone tissue engineering have focused primarily on mimicking the extracellular matrix (ECM) of bone in terms of structure and composition. However, the synergistic effects of other cues from the microenvironment during bone regeneration are often neglected. The bone microenvironment is a sophisticated system that includes physiological (e.g., neighboring cells such as macrophages), chemical (e.g., oxygen, pH), and physical factors (e.g., mechanics, acoustics) that dynamically interact with each other. Microenvironment-targeted strategies are increasingly recognized as crucial for successful bone regeneration and offer promising solutions for advancing bone tissue engineering. This review provides a comprehensive overview of current microenvironment-targeted strategies and challenges for bone regeneration and further outlines prospective directions of the approaches in construction of bone organoids.

Novel PVAMA/GelMA aerogels prepared by liquid-phase collection of photoinitiated polymerisation: injectable and flowable low-density 3D scaffolds for bone regeneration

Nanofibrous scaffolds, which are morphologically/structurally similar to native extracellular matrix, are ideal biomaterials for tissue engineering and regenerative medicine. However, the use of traditional electrospinning techniques to produce three-dimensional (3D) nanofibrous scaffolds with desired structural properties presents difficulty. To address this challenge, we prepared a novel liquid-phase-collected photoinitiated polymerised aerogel 3D scaffold (LPPI-AG) using the thermally induced (nanofiber) self-aggregation method after liquid-phase electrospinning of the hydroxyapatite-doped methacrylated polyvinyl alcohol/methacrylated gelatine solution obtained by photoinitiated polymerisation. The fabricated aerogel scaffolds had a high porosity of approximately 99.01% ± 0.40% and an interconnected network structure with pore sizes ranging from submicron to ∼300 μm. The new aerogel rapidly became flowable when exposed to a solution, and it can fill gaps and repair gap edges effectively and be loaded with nutrients and growth factors that promote bone growth for bone tissue engineering. LPPI-AG scaffolds can considerably promote osteogenic differentiation of bone marrow mesenchymal stem cells in vitro. Furthermore, in vivo studies showed that the LPPI-AG scaffold significantly promoted bone formation in a mouse model of critical-size calvarial defects.

Lyophilized Platelet-Rich Fibrin Exudate-Loaded Carboxymethyl Chitosan/GelMA Hydrogel for Efficient Bone Defect Repair

Platelet-rich fibrin (PRF) is an autologous growth factor carrier that promotes bone tissue regeneration, but its effectiveness is restrained by poor storage capabilities, uncontrollable concentration of growth factors, unstable shape, etc. Herein, we developed a photocrosslinkable composite hydrogel by incorporating lyophilized PRF exudate (LPRFe) into the carboxymethyl chitosan methacryloyl (CMCSMA)/gelatin methacryloyl (GelMA) hydrogel to effectively solve the dilemma of PRF. The hydrogel possessed suitable physical properties and sustainable release ability of growth factors in LPRFe. The LPRFe-loaded hydrogel could improve the adhesion, proliferation, migration, and osteogenic differentiation of rat bone mesenchymal stem cells (BMSCs). Furthermore, the animal experiments demonstrated that the hydrogel possessed excellent biocompatibility and biodegradability, and the introduction of LPRFe in the hydrogel can effectively accelerate the bone healing process. Conclusively, the combination of LPRFe with CMCSMA/GelMA hydrogel may be a promising therapeutic approach for bone defects.

Smart Hydrogels for Bone Reconstruction via Modulating the Microenvironment

Rapid and effective repair of injured or diseased bone defects remains a major challenge due to shortages of implants. Smart hydrogels that respond to internal and external stimuli to achieve therapeutic actions in a spatially and temporally controlled manner have recently attracted much attention for bone therapy and regeneration. These hydrogels can be modified by introducing responsive moieties or embedding nanoparticles to increase their capacity for bone repair. Under specific stimuli, smart hydrogels can achieve variable, programmable, and controllable changes on demand to modulate the microenvironment for promoting bone healing. In this review, we highlight the advantages of smart hydrogels and summarize their materials, gelation methods, and properties. Then, we overview the recent advances in developing hydrogels that respond to biochemical signals, electromagnetic energy, and physical stimuli, including single, dual, and multiple types of stimuli, to enable physiological and pathological bone repair by modulating the microenvironment. Then, we discuss the current challenges and future perspectives regarding the clinical translation of smart hydrogels.