Biomaterials with structural hierarchy and controlled 3D nanotopography guide endogenous bone regeneration

Sequential activation of osteogenic microenvironment via composite peptide-modified microfluidic microspheres for promoting bone regeneration

The osteogenic microenvironment (OME) significantly influences bone repair; however, reproducing its dynamic activation and repair processes remains challenging. In this study, we designed injectable porous microspheres modified with composite peptides to investigate cascade alterations in OME and their underlying mechanisms. Poly l-lactic acid microfluidic microspheres underwent surface modifications through alkaline hydrolysis treatment, involving heterogeneous grafting of bovine serum albumin nanoparticles with stem cell-homing peptides (BNP@SKP) and BMP-2 mimicking peptides (P24), respectively. These modifications well-organized the actions of initial release and subsequent in situ grafting of peptides. Cellular experiments demonstrated varied degrees of chemotactic recruitment and osteogenic differentiation in mesenchymal stem cells. Further biological analysis revealed that BNP@SKP targeted the Ras/Erk axis and upregulated matrix metalloproteinase (MMP)2 and MMP9 expression, thereby enhancing initial chemotaxis and recruitment. In vivo studies validated the establishment of a dynamically regulated OME centered on the microspheres, resulting in increased stem cell recruitment, sequential activation of the differentiation microenvironment, and facilitation of in situ osteogenesis without ectopic ossification. In conclusion, this study successfully fabricated composite peptide-modified microspheres and systematically explored the mechanisms of bone formation through sequential activation of OME via heterogeneous grafting of signaling molecules. This provides theoretical evidence for biomaterials based on microenvironment regulation.

Dual-sided centripetal microgrooved poly (D,L-lactide-co-caprolactone) disk encased in immune-regulating hydrogels for enhanced bone regeneration

Well-designed artificial scaffolds are urgently needed due to the limited self-repair capacity of bone, which hampers effective regeneration in critical defects. Optimal scaffolds must provide physical guidance to recruit cells and immune regulation to improve the regenerative microenvironment. This study presents a novel scaffold composed of dual-sided centripetal microgrooved poly(D,L-lactide-co-caprolactone) (PLCL) film combined with a dynamic hydrogel containing prednisolone (PLS)-loaded Prussian blue nanoparticles (PB@PLS). The microgrooves on the surface of the PLCL film were imprinted using a micropatterned polydimethylsiloxane (PDMS) template. Following aminolysis, the PLCL film was covalently grafted with the EM-7 peptide via glutaraldehyde. Functional group analysis, surface morphology and hydrophilicity were evaluated using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and an optical contact angle measuring instrument, respectively. Bone regeneration-related cells (e.g., bone marrow mesenchymal stem cells, macrophages, Schwann cells, and endothelial cells) cultured on PLCL films tended to align along the stripes and migrate from the periphery toward the center region in vitro. Subsequently, the PLCL film was encapsulated in an immune-regulating hydrogel synthesized from thiol-modified gelatin and Cu2+ in the presence of PB@PLS nanoparticles, which demonstrated excellent antioxidant properties. This scaffold significantly accelerated critical-sized bone regeneration, as evidenced by an increase in the volume of newly formed bone and histological images in vivo. This innovative approach holds substantial promise for clinical applications in bone regeneration and broader tissue repair.

Leveraging the nanotopography of filamentous fungal chitin-glucan nano/microfibrous spheres (FNS) coated with collagen (type I) for scaffolded fibroblast spheroids in regenerative medicine

Numerous naturally occurring biological structures have inspired the development of innovative biomaterials for a wide range of applications. Notably, the nanotopographical architectures found in natural materials have been leveraged in biomaterial design to enhance cell adhesion and proliferation and improve tissue regeneration for biomedical applications. In this study, we fabricated three-dimensional (3D) chitin-glucan micro/nanofibrous fungal-based spheres coated with collagen (type I) to mimic the native extracellular matrix (ECM) microenvironment. These collagen-coated fungal nano/microfibrous spheres (C-FNS) were utilized to construct 3D scaffolded spheroids of human fibroblasts through suspension culture for tissue engineering and regenerative medicine. The particle sizes of C-FNS ranged from 1.4 to 3.25 µm (average: 2.27 ± 0.38 µm), with a porosity of 81.17 %. Field emission-scanning electron microscopy (FE-SEM) revealed that C-FNS comprised continuous chitin-glucan fibers with an average diameter of 363 ± 61 nm (range: 203-512 nm), exhibiting a highly interconnected structure. The reduced arithmetic average roughness (Ra) and root mean square roughness (Rq) values of C-FNS compared to uncoated FNS suggested that collagen coating reduced surface roughness, resulting in a smoother surface that enhanced hydrophilicity, crucial for mammalian cell adhesion and spheroid formation. Moreover, the in vitro cytocompatibility of C-FNS with fibroblasts was evaluated using a resazurin-based PrestoBlue assay, which demonstrated a time-dependent increase in the metabolic activity of C-FNS/fibroblast spheroids during suspension culture for up to 14 days. FE-SEM images of C-FNS/fibroblast spheroids further revealed enhanced adhesion and proliferation of fibroblasts on the nano/microfibrous mycelial architecture, accompanied by the secretion of ECM components and formation of multilayered cell sheets over the 14-day culture period. Similarly, an assessment of the hemocompatibility of C-FNS with erythrocytes revealed the non-hemolytic properties of the biomaterial. Overall, the interaction between collagen-coated fungal chitin-glucan nano/microfibrous structures and mammalian cells holds significant potential for the development of novel, sustainable biomaterials with tailored properties for a myriad of biomedical applications, including tissue engineering, regenerative medicine, drug screening, and wound healing.

Functional antimicrobial peptide-loaded 3D scaffolds for infected bone defect treatment with AI and multidimensional printing

Infection is the most prevalent complication of fractures, particularly in open fractures, and often leads to severe consequences. The emergence of bacterial resistance has significantly exacerbated the burden of infection in clinical practice, making infection control a significant treatment challenge for infectious bone defects. The implantation of a structural stent is necessary to treat large bone defects despite the increased risk of infection. Therefore, there is a need for the development of novel antibacterial therapies. The advancement in antibacterial biomaterials and new antimicrobial drugs offers fresh perspectives on antibacterial treatment. Although antimicrobial 3D scaffolds are currently under intense research focus, relying solely on material properties or antibiotic action remains insufficient. Antimicrobial peptides (AMPs) are one of the most promising new antibacterial therapy approaches. This review discusses the underlying mechanisms behind infectious bone defects and presents research findings on antimicrobial peptides, specifically emphasizing their mechanisms and optimization strategies. We also explore the potential prospects of utilizing antimicrobial peptides in treating infectious bone defects. Furthermore, we propose that artificial intelligence (AI) algorithms can be utilized for predicting the pharmacokinetic properties of AMPs, including absorption, distribution, metabolism, and excretion, and by combining information from genomics, proteomics, metabolomics, and clinical studies with computational models driven by machine learning algorithms, scientists can gain a comprehensive understanding of AMPs' mechanisms of action, therapeutic potential, and optimizing treatment strategies tailored to individual patients, and through interdisciplinary collaborations between computer scientists, biologists, and clinicians, the full potential of AI in accelerating the discovery and development of novel AMPs will be realized. Besides, with the continuous advancements in 3D/4D/5D/6D technology and its integration into bone scaffold materials, we anticipate remarkable progress in the field of regenerative medicine. This review summarizes relevant research on the optimal future for the treatment of infectious bone defects, provides guidance for future novel treatment strategies combining multi-dimensional printing with new antimicrobial agents, and provides a novel and effective solution to the current challenges in the field of bone regeneration.

Complex immunotoxic effects of T-2 Toxin on the murine spleen and thymus: Oxidative damage, inflammasomes, apoptosis, and immunosuppression

T-2 toxin (T-2), a highly stable and toxic mycotoxin, poses a significant public health risk as an inevitable environmental pollutant. However, the mechanisms behind its immunotoxic and immunosuppressive effects are not fully understood. For this study, sixty healthy 4-week-old male C57BL/6 N mice were divided randomly into four groups and treated for 28 days with T-2 concentrations of 0, 0.5, 1.0, and 2.0 mg/kg. Our findings revealed significant damage to the thymus and spleen that was proportional to the dose administered, as evidenced by changes in organ indices and histopathological abnormalities. We observed mitochondrial swelling, chromatin condensation, and nuclear structure disruptions in these organs. Even at low doses (0.5 mg/kg), T-2 administration resulted in significant immunosuppression, as evidenced by disturbed blood parameters and altered CD4 + /CD8 + ratios. Elevated ROS and MDA levels indicate oxidative damage, whereas SOD, T-AOC, CAT, and GSH levels are reduced in both the thymus and spleen. Furthermore, the levels of NLRP3, ASC, caspase-1, and IL-1β proteins were significantly elevated, indicating the activation of the NLRP3 inflammasome pathway. Additionally, activation of the apoptosis pathway was demonstrated by an increased Bax/Bcl-2 ratio and heightened activation of caspase-3 and -9. Transcriptomic analysis elucidated the pivotal role of mitochondrial pathways in T-2-induced immunotoxicity. This study elucidates the significant immunotoxic effects of T-2 on the murine spleen and thymus, detailing the underlying mechanisms of T-2-induced immunosuppression. The key mechanisms identified include oxidative stress, activation of the NLRP3 inflammasome, apoptosis, and mitochondrial dysfunction. These findings reveal critical pathways through which T-2 impairs immune system functionality and provide a basis for developing targeted therapeutic strategies to mitigate its immunotoxic effects.

Mineralized collagen plywood contributes to bone autograft performance

Autologous bone (AB) is the gold standard for bone-replacement surgeries1, despite its limited availability and the need for an extra surgical site. Traditionally, competitive biomaterials for bone repair have focused on mimicking the mineral aspect of bone, as evidenced by the widespread clinical use of bioactive ceramics2. However, AB also exhibits hierarchical organic structures that might substantially affect bone regeneration. Here, using a range of cell-free biomimetic-collagen-based materials in murine and ovine bone-defect models, we demonstrate that a hierarchical hybrid microstructure-specifically, the twisted plywood pattern of collagen and its association with poorly crystallized bioapatite-favourably influences bone regeneration. Our study shows that the most structurally biomimetic material has the potential to stimulate bone growth, highlighting the pivotal role of physicochemical properties in supporting bone formation and offering promising prospects as a competitive bone-graft material.

Advances in the Development of Gradient Scaffolds Made of Nano-Micromaterials for Musculoskeletal Tissue Regeneration

The intricate hierarchical structure of musculoskeletal tissues, including bone and interface tissues, necessitates the use of complex scaffold designs and material structures to serve as tissue-engineered substitutes. This has led to growing interest in the development of gradient bone scaffolds with hierarchical structures mimicking the extracellular matrix of native tissues to achieve improved therapeutic outcomes. Building on the anatomical characteristics of bone and interfacial tissues, this review provides a summary of current strategies used to design and fabricate biomimetic gradient scaffolds for repairing musculoskeletal tissues, specifically focusing on methods used to construct compositional and structural gradients within the scaffolds. The latest applications of gradient scaffolds for the regeneration of bone, osteochondral, and tendon-to-bone interfaces are presented. Furthermore, the current progress of testing gradient scaffolds in physiologically relevant animal models of skeletal repair is discussed, as well as the challenges and prospects of moving these scaffolds into clinical application for treating musculoskeletal injuries.

A 3D radially aligned nanofiber scaffold co-loaded with LL37 mimetic peptide and PDGF-BB for the management of infected chronic wounds

Diabetic foot ulcers, pressure ulcers, and bedsores can easily develop into chronic wounds with bacterial infections, complicating wound healing. This work reports a two-step strategy for treating infected chronic wounds. Firstly, LL37 mimetic peptide-W379 peptides were rapidly released to eliminate the bacterial biofilm on the wound. Then, 3D radially aligned nanofiber scaffolds loaded with W379 antimicrobial peptide and PDGF-BB were used to treat the wound to prevent bacterial infection recurrence and promote angiogenesis and granulation tissue regeneration, thereby accelerating wound healing. In the presented study, we found that the combined use of burst and controlled release of W379 antimicrobial peptide effectively clears the bacterial biofilm and prevents the recurrence of bacterial infection. Additionally, we found that the removal of the bacterial biofilm contributed to modulating the local inflammatory response from a pro-inflammatory type to a pro-regenerative type. Furthermore, the use of PDGF-BB significantly promotes neovascularization and granulation tissue regeneration in the wound bed, resulting in accelerating re-epithelialization and wound closure. Our study provides a promising treatment method for the repair of infected chronic wounds.

Barrier Membrane with Janus Function and Structure for Guided Bone Regeneration

Guided bone regeneration (GBR) technology has been demonstrated to be an effective method for reconstructing bone defects. A membrane is used to cover the bone defect to stop soft tissue from growing into it. The biosurface design of the barrier membrane is key to the technology. In this work, an asymmetric functional gradient Janus membrane was designed to address the bidirectional environment of the bone and soft tissue during bone reconstruction. The Janus membrane was simply and efficiently prepared by the multilayer self-assembly technique, and it was divided into the polycaprolactone isolation layer (PCL layer, GBR-A) and the nanohydroxyapatite/polycaprolactone/polyethylene glycol osteogenic layer (HAn/PCL/PEG layer, GBR-B). The morphology, composition, roughness, hydrophilicity, biocompatibility, cell attachment, and osteogenic mineralization ability of the double surfaces of the Janus membrane were systematically evaluated. The GBR-A layer was smooth, dense, and hydrophobic, which could inhibit cell adhesion and resist soft tissue invasion. The GBR-B layer was rough, porous, hydrophilic, and bioactive, promoting cell adhesion, proliferation, matrix mineralization, and expression of alkaline phosphatase and RUNX2. In vitro and in vivo results showed that the membrane could bind tightly to bone, maintain long-term space stability, and significantly promote new bone formation. Moreover, the membrane could fix the bone filling material in the defect for a better healing effect. This work presents a straightforward and viable methodology for the fabrication of GBR membranes with Janus-based bioactive surfaces. This work may provide insights for the design of biomaterial surfaces and treatment of bone defects.

Orthogonally woven 3D nanofiber scaffolds promote rapid soft tissue regeneration by enhancing bidirectional cell migration

Repairing large-area soft tissue defects caused by traumas is a major surgical challenge. Developing multifunctional scaffolds with suitable scalability and favorable cellular response is crucial for soft tissue regeneration. In this study, we developed an orthogonally woven three-dimensional (3D) nanofiber scaffold combining electrospinning, weaving, and modified gas-foaming technology. The developed orthogonally woven 3D nanofiber scaffold had a modular design and controlled fiber alignment. In vitro, the orthogonally woven 3D nanofiber scaffold exhibited adjustable mechanical properties, good cell compatibility, and easy drug loading. In vivo, for one thing, the implantation of an orthogonally woven 3D nanofiber scaffold in a full abdominal wall defect model demonstrated that extensive granulation tissue formation with enough mechanical strength could promote recovery of abdominal wall defects while reducing intestinal adhesion. Another result of diabetic wound repair experiments suggested that orthogonally woven 3D nanofiber scaffolds had a higher wound healing ratio, granulation tissue formation, collagen deposition, and re-epithelialization. Taken together, this novel orthogonally woven 3D nanofiber scaffold may provide a promising and effective approach for optimal soft tissue regeneration.

Personalized PLGA/BCL Scaffold with Hierarchical Porous Structure Resembling Periosteum-Bone Complex Enables Efficient Repair of Bone Defect

Using bone regeneration scaffolds to repair craniomaxillofacial bone defects is a promising strategy. However, most bone regeneration scaffolds still exist some issues such as a lack of barrier structure, inability to precisely match bone defects, and necessity to incorporate biological components to enhance efficacy. Herein, inspired by a periosteum-bone complex, a class of multifunctional hierarchical porous poly(lactic-co-glycolic acid)/baicalein scaffolds is facilely prepared by the union of personalized negative mold technique and phase separation strategy and demonstrated to precisely fit intricate bone defect cavity. The dense up-surface of the scaffold can prevent soft tissue cell penetration, while the loose bottom-surface can promote protein adsorption, cell adhesion, and cell infiltration. The interior macropores of the scaffold and the loaded baicalein can synergistically promote cell differentiation, angiogenesis, and osteogenesis. These findings can open an appealing avenue for the development of personalized multifunctional hierarchical materials for bone repair.

Decellularized extracellular matrix-decorated 3D nanofiber scaffolds enhance cellular responses and tissue regeneration

The use of decellularized extracellular matrix products in tissue regeneration is quite alluring yet practically challenging due to the limitations of its availability, harsh processing techniques, and host rejection. Scaffolds obtained by either incorporating extracellular matrix (ECM) material or coating the surface can resolve these challenges to some extent. However, these scaffolds lack the complex 3D network formed by proteins and growth factors observed in natural ECM. This study introduces an approach utilizing 3D nanofiber scaffolds decorated with dECM to enhance cellular responses and promote tissue regeneration. Notably, the dECM can be customized according to specific cellular requirements, offering a tailored environment for enhanced therapeutic outcomes. Two types of 3D expanded scaffolds, namely radially aligned scaffolds (RAS) and laterally expanded scaffolds (LES) fabricated by the gas-foaming expansion were utilized. To demonstrate the proof-of-concept, human dermal fibroblasts (HDFs) seeded on these scaffolds for up to 8 weeks, resulted in uniform and highly aligned cells which deposited ECM on the scaffolds. These cellular components were then removed from the scaffolds through decellularization (e.g., SDS treatment and freeze-thaw cycles). The dECM-decorated 3D expanded nanofiber scaffolds can direct and support cell alignment and proliferation along the underlying fibers upon recellularization. An in vitro inflammation assay indicates that dECM-decorated LES induces a lower immune response than dECM-decorated RAS. Further, subcutaneous implantation of dECM-decorated RAS and LES shows higher cell infiltration and angiogenesis within 7 and 14 days than RAS and LES without dECM decoration. Taken together, dECM-decorated 3D expanded nanofiber scaffolds hold great potential in tissue regeneration and tissue modeling. STATEMENT OF SIGNIFICANCE: Decellularized ECM scaffolds have attained widespread attention in biomedical applications due to their intricate 3D framework of proteins and growth factors. Mimicking such a complicated architecture is a clinical challenge. In this study, we developed natural ECM-decorated 3D electrospun nanofiber scaffolds with controlled alignments to mimic human tissue. Fibroblasts were cultured on these scaffolds for 8 weeks to deposit natural ECM and decellularized by either freeze-thawing or detergent to obtain decellularized ECM scaffolds. These scaffolds were tested in both in-vitro and in-vivo conditions. They displayed higher cellular attributes with lower immune response making them a good grafting tool in tissue regeneration.

Nanofibrous Microspheres: A Biomimetic Platform for Bone Tissue Regeneration

Bone, a fundamental constituent of the human body, is a vital scaffold for support, protection, and locomotion, underscoring its pivotal role in maintaining skeletal integrity and overall functionality. However, factors such as trauma, disease, or aging can compromise bone structure, necessitating effective strategies for regeneration. Traditional approaches often lack biomimetic environments conducive to efficient tissue repair. Nanofibrous microspheres (NFMS) present a promising biomimetic platform for bone regeneration by mimicking the native extracellular matrix architecture. Through optimized fabrication techniques and the incorporation of active biomolecular components, NFMS can precisely replicate the nanostructure and biochemical cues essential for osteogenesis promotion. Furthermore, NFMS exhibit versatile properties, including tunable morphology, mechanical strength, and controlled release kinetics, augmenting their suitability for tailored bone tissue engineering applications. NFMS enhance cell recruitment, attachment, and proliferation, while promoting osteogenic differentiation and mineralization, thereby accelerating bone healing. This review highlights the pivotal role of NFMS in bone tissue engineering, elucidating their design principles and key attributes. By examining recent preclinical applications, we assess their current clinical status and discuss critical considerations for potential clinical translation. This review offers crucial insights for researchers at the intersection of biomaterials and tissue engineering, highlighting developments in this expanding field.

Piezocatalytically-induced controllable mineralization scaffold with bone-like microenvironment to achieve endogenous bone regeneration

Orderly hierarchical structure with balanced mechanical, chemical, and electrical properties is the basis of the natural bone microenvironment. Inspired by nature, we developed a piezocatalytically-induced controlled mineralization strategy using piezoelectric polymer poly-L-lactic acid (PLLA) fibers with ordered micro-nano structures to prepare biomimetic tissue engineering scaffolds with a bone-like microenvironment (pcm-PLLA), in which PLLA-mediated piezoelectric catalysis promoted the in-situ polymerization of dopamine and subsequently regulated the controllable growth of hydroxyapatite crystals on the fiber surface. PLLA fibers, as analogs of mineralized collagen fibers, were arranged in an oriented manner, and ultimately formed a bone-like interconnected pore structure; in addition, they also provided bone-like piezoelectric properties. The uniformly sized HA nanocrystals formed by controlled mineralization provided a bone-like mechanical strength and chemical environment. The pcm-PLLA scaffold could rapidly recruit endogenous stem cells, and promote their osteogenic differentiation by activating cell membrane calcium channels and PI3K signaling pathways through ultrasound-responsive piezoelectric signals. In addition, the scaffold also provided a suitable microenvironment to promote macrophage M2 polarization and angiogenesis, thereby enhancing bone regeneration in skull defects of rats. The proposed piezocatalytically-induced controllable mineralization strategy provides a new idea for the development of tissue engineering scaffolds that can be implemented for multimodal physical stimulation therapy.

3D nanofiber scaffolds from 2D electrospun membranes boost cell penetration and positive host response for regenerative medicine

The ideal tissue engineering scaffold should facilitate rapid cell infiltration and provide an optimal immune microenvironment during interactions with the host. Electrospinning can produce two-dimensional (2D) membranes mimicking the extracellular matrix. However, their dense structure hinders cell penetration, and their thin form restricts scaffold utility. In this study, latticed hydrogels were three-dimensional (3D) printed onto electrospun membranes. This technique allowed for layer-by-layer assembly of the membranes into 3D scaffolds, which maintained their resilience impressively under both dry and wet conditions. We assessed the cellular and host responses of these 3D nanofiber scaffolds by comparing random membranes and mesh-like membranes with three different mesh sizes (250, 500, and 750 μm). It was found that scaffolds with a mesh size of 500 μm were superior for M2 macrophage phenotype polarization, vascularization, and matrix deposition. Furthermore, it was confirmed by subsequent experiments such as RNA sequencing that the mesh-like topology may promote polarization to the M2 phenotype by affecting the PI3K/AKT pathway. In conclusion, our work offers a novel method for transforming 2D nanofiber membranes into 3D scaffolds. This method boasts flexibility, allowing for the use of varied electrospun membranes and hydrogels in terms of structure and composition. It has vast potential in tissue repair and regeneration.

Correlation between Ca Release and Osteoconduction by 3D-Printed Hydroxyapatite-Based Templates

The application of hydroxyapatite (HA)-based templates is quite often seen in bone tissue engineering since that HA is an osteoconductive bioceramic material, which mimics the inorganic component of mineralized tissues. However, the reported osteoconductivity varies in vitro and in vivo, and the levels of calcium (Ca) release most favorable to osteoconduction have yet to be determined. In this study, HA-based templates were fabricated by melt-extrusion 3D-printing and characterized in order to determine a possible correlation between Ca release and osteoconduction. The HA-based templates were blended with poly(lactide-co-trimethylene carbonate) (PLATMC) at three different HA ratios: 10, 30, and 50%. The printability and physical properties of the HA templates were compared with those of pristine PLATMC. In vitro, osteoconductivity was assessed using seeded human bone marrow-derived mesenchymal stem cells. A mild rate of Ca release was observed for HA10 templates, which exhibited higher mineralized extracellular matrix (ECM) secretion than PLATMC at 14 and 21 days. In contrast, the high rate of Ca release exhibited by HA30 and HA50 templates was associated with reduced osteoconduction and impeded mineralized ECM secretion in vitro. Similar results were observed in vivo. In the calvarial defect model in rabbit, PLATMC and HA10 templates exhibited the highest amount of new bone formation, with obvious contact osteogenesis on their surfaces. In contrast, HA30 and HA50 exhibited distant osteogenesis and reduced amounts of new bone ingrowth. It is concluded that HA-based templates are osteoconductive only at low rates of Ca release.

Hierarchically Assembled Nanofiber Scaffold Guides Long Bone Regeneration by Promoting Osteogenic/Chondrogenic Differentiation of Endogenous Mesenchymal Stem Cells

Critical-sized segmental long bone defects represent a challenging clinical dilemma in the management of battlefield and trauma-related injuries. The residual bone marrow cavity of damaged long bones contains many bone marrow mesenchymal stem cells (BMSCs), which provide a substantial source of cells for bone repair. Thus, a three-dimensional (3D) vertically aligned nanofiber scaffold (VAS) is developed with long channels and large pore size. The pore of VAS toward the bone marrow cavity after transplantation, enables the scaffolds to recruit BMSCs from the bone marrow cavity to the defect area. In vivo, it is found that VAS can significantly shorten gap distance and promote new bone formation compared to the control and collagen groups after 4 and 8 weeks of implantation. The single-cell sequencing results discovered that the 3D nanotopography of VAS can promote BMSCs differentiation to chondrocytes and osteoblasts, and up-regulate related gene expression, resulting in enhancing the activities of bone regeneration, endochondral ossification, bone trabecula formation, bone mineralization, maturation, and remodeling. The Alcian blue and bone morphogenetic protein 2 (BMP-2) immunohistochemical staining verified significant cartilage formation and bone formation in the VAS group, corresponding to the single-cell sequencing results. The study can inspire the design of next-generation scaffolds for effective long-bone regeneration is expected by the authors.

Cell-free chitosan/silk fibroin/bioactive glass scaffolds with radial pore for in situ inductive regeneration of critical-size bone defects

Tissue-engineered is an effective method for repairing critical-size bone defects. The application of bioactive scaffold provides artificial matrix and suitable microenvironment for cell recruitment and extracellular matrix deposition, which can effectively accelerate the process of tissue regeneration. Among various scaffold properties, appropriate pore structure and distribution have been proven to play a crucial role in inducing cell infiltration differentiation and in-situ tissue regeneration. In this study, a chitosan (CS) /silk fibroin (SF) /bioactive glass (BG) composite scaffold with distinctive radially oriented pore structure was constructed. The composite scaffolds had stable physical and chemical properties, a unique pore structure of radial arrangement from the center to the periphery and excellent mechanical properties. In vitro biological studies indicated that the CS/SF/BG scaffold could promote osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and the expression of related genes due to the wide range of connected pore structures and released active elements. Furthermore, in vivo study showed CS/SF/BG scaffold with radial pores was more conducive to the repair of skull defects in rats with accelerated healing speed during the bone tissue remodeling process. These results demonstrated the developed CS/SF/BG scaffold would be a promising therapeutic strategy for the repair of bone defects regeneration.

Engineered Microchannel Scaffolds with Instructive Niches Reinforce Endogenous Bone Regeneration by Regulating CSF-1/CSF-1R Pathway

Structural and physiological cues provide guidance for the directional migration and spatial organization of endogenous cells. Here, a microchannel scaffold with instructive niches is developed using a circumferential freeze-casting technique with an alkaline salting-out strategy. Thereinto, polydopamine-coated nano-hydroxyapatite is employed as a functional inorganic linker to participate in the entanglement and crystallization of chitosan molecules. This scaffold orchestrates the advantage of an oriented porous structure for rapid cell infiltration and satisfactory immunomodulatory capacity to promote stem cell recruitment, retention, and subsequent osteogenic differentiation. Transcriptomic analysis as well as its in vitro and in vivo verification demonstrates that essential colony-stimulating factor-1 (CSF-1) factor is induced by this scaffold, and effectively bound to the target colony-stimulating factor-1 receptor (CSF-1R) on the macrophage surface to activate the M2 phenotype, achieving substantial endogenous bone regeneration. This strategy provides a simple and efficient approach for engineering inducible bone regenerative biomaterials.

New dimensions of electrospun nanofiber material designs for biotechnological uses

Electrospinning technology has garnered wide attention over the past few decades in various biomedical applications including drug delivery, cell therapy, and tissue engineering. This technology can create nanofibers with tunable fiber diameters and functionalities. However, the 2D membrane nature of the nanofibers, as well as the rigidity and low porosity of electrospun fibers, lower their efficacy in tissue repair and regeneration. Recently, new avenues have been explored to resolve the challenges associated with 2D electrospun nanofiber membranes. This review discusses recent trends in creating different electrospun nanofiber microstructures from 2D nanofiber membranes by using various post-processing methods, as well as their biotechnological applications.

Biomimetic Bone-Like Composite Hydrogel Scaffolds Composed of Collagen Fibrils and Natural Hydroxyapatite for Promoting Bone Repair

Bone is a complex organic-inorganic composite tissue composed of ∼30% organics and ∼70% hydroxyapatite (HAp). Inspired by this, we used 30% collagen and 70% HAp extracted from natural bone using the calcination method to generate a biomimetic bone composite hydrogel scaffold (BBCHS). In one respect, BBCHS, with a fixed proportion of inorganic and organic components similar to natural bone, exhibits good physical properties. In another respect, the highly biologically active and biocompatible HAp from natural bone effectively promotes osteogenic differentiation, and type I collagen facilitates cell adhesion and spreading. Additionally, the well-structured porosity of the BBCHS provides sufficient growth space for bone marrow mesenchymal stem cells (BMSCs) while promoting substance exchange. Compared to the control group, the new bone surface of the defective location in the B-HA70+Col group is increased by 3.4-fold after 8 weeks of in vivo experiments. This strategy enables the BBCHS to closely imitate the chemical makeup and physical structure of natural bone. With its robust biocompatibility and osteogenic activity, the BBCHS can be easily adapted for a wide range of bone repair applications and offers promising potential for future research and development.

Anti-Inflammatory Peptide-Conjugated Silk Fibroin/Cryogel Hybrid Dual Fiber Scaffold with Hierarchical Structure Promotes Healing of Chronic Wounds

Chronic wounds resulting from diabetes, pressure, radiation therapy, and other factors continue to pose significant challenges in wound healing. To address this, this study introduces a novel hybrid fibroin fibrous scaffold (FFS) comprising randomly arranged fibroin fibers and vertically aligned cryogel fibers (CFs). The fibroin scaffold is efficiently degummed at room temperature and simultaneously formed a porous structure. The aligned CFs are produced via directional freeze-drying, achieved by controlling solution concentration and freezing polymerization temperature. The incorporation of aligned CFs into the expanded fibroin fiber scaffold leads to enhanced cell infiltration both in vitro and in vivo, further elevating the hybrid scaffold's tissue compatibility. The anti-inflammatory peptide 1 (AP-1) is also conjugated to the hybrid fibrous scaffold, effectively transforming the inflammatory status of chronic wounds from pro-inflammatory to pro-reparative. Consequently, the FFS-AP1+CF group demonstrates superior granulation tissue formation, angiogenesis, collagen deposition, and re-epithelialization during the proliferative phase compared to the commercial product PELNAC. Moreover, the FFS-AP1+CF group displays epidermis thickness, number of regenerated hair follicles, and collagen density closer to normal skin tissue. These findings highlight the potential of random fibroin fibers/aligned CFs hybrid fibrous scaffold as a promising approach for skin tissue filling and tissue regeneration.

Aligned cryogel fibers incorporated 3D printed scaffold effectively facilitates bone regeneration by enhancing cell recruitment and function

Reconstructing extensive cranial defects represents a persistent clinical challenge. Here, we reported a hybrid three-dimensional (3D) printed scaffold with modification of QK peptide and KP peptide for effectively promoting endogenous cranial bone regeneration. The hybrid 3D printed scaffold consists of vertically aligned cryogel fibers that guide and promote cell penetration into the defect area in the early stages of bone repair. Then, the conjugated QK peptide and KP peptide further regulate the function of the recruited cells to promote vascularization and osteogenic differentiation in the defect area. The regenerated bone volume and surface coverage of the dual peptide-modified hybrid scaffold were significantly higher than the positive control group. In addition, the dual peptide-modified hybrid scaffold demonstrated sustained enhancement of bone regeneration and avoidance of bone resorption compared to the collagen sponge group. We expect that the design of dual peptide-modified hybrid scaffold will provide a promising strategy for bone regeneration.

Mechanically resilient hybrid aerogels containing fibers of dual-scale sizes and knotty networks for tissue regeneration

The structure and design flexibility of aerogels make them promising for soft tissue engineering, though they tend to come with brittleness and low elasticity. While increasing crosslinking density may improve mechanics, it also imparts brittleness. In soft tissue engineering, resilience against mechanical loads from mobile tissues is paramount. We report a hybrid aerogel that consists of self-reinforcing networks of micro- and nanofibers. Nanofiber segments physically entangle microfiber pillars, allowing efficient stress distribution through the intertwined fiber networks. We show that optimized hybrid aerogels have high specific tensile moduli (~1961.3 MPa cm3 g-1) and fracture energies (~7448.8 J m-2), while exhibiting super-elastic properties with rapid shape recovery (~1.8 s). We demonstrate that these aerogels induce rapid tissue ingrowth, extracellular matrix deposition, and neovascularization after subcutaneous implants in rats. Furthermore, we can apply them for engineering soft tissues via minimally invasive procedures, and hybrid aerogels can extend their versatility to become magnetically responsive or electrically conductive, enabling pressure sensing and actuation.

Transforming layered 2D mats into multiphasic 3D nanofiber scaffolds with tailored gradient features for tissue regeneration

Multiphasic scaffolds with tailored gradient features hold significant promise for tissue regeneration applications. Herein, this work reports the transformation of two-dimensional (2D) layered fiber mats into three dimensional (3D) multiphasic scaffolds using a 'solids-of-revolution' inspired gas-foaming expansion technology. These scaffolds feature precise control over fiber alignment, pore size, and regional structure. Manipulating nanofiber mat layers and Pluronic F127 concentrations allows further customization of pore size and fiber alignment within different scaffold regions. The cellular response to multiphasic scaffolds demonstrates the number of cells migrated and proliferated onto the scaffolds are mainly dependent on the pore size rather than fiber alignment. In vivo subcutaneous implantation of multiphasic scaffolds to rats reveals substantial cell infiltration, neo tissue formation, collagen deposition, and new vessel formation within scaffolds, greatly surpassing the capabilities of traditional nanofiber mats. Histological examination indicates the importance of optimizing pore size and fiber alignment for promotion of cell infiltration and tissue regeneration. Overall, these scaffolds have potential applications in tissue modeling, studying tissue-tissue interactions, interface tissue engineering, and high-throughput screening for optimized tissue regeneration.

Small Joint Organoids 3D Bioprinting: Construction Strategy and Application

Osteoarthritis (OA) is a chronic disease that causes pain and disability in adults, affecting ≈300 million people worldwide. It is caused by damage to cartilage, including cellular inflammation and destruction of the extracellular matrix (ECM), leading to limited self-repairing ability due to the lack of blood vessels and nerves in the cartilage tissue. Organoid technology has emerged as a promising approach for cartilage repair, but constructing joint organoids with their complex structures and special mechanisms is still challenging. To overcome these boundaries, 3D bioprinting technology allows for the precise design of physiologically relevant joint organoids, including shape, structure, mechanical properties, cellular arrangement, and biological cues to mimic natural joint tissue. In this review, the authors will introduce the biological structure of joint tissues, summarize key procedures in 3D bioprinting for cartilage repair, and propose strategies for constructing joint organoids using 3D bioprinting. The authors also discuss the challenges of using joint organoids' approaches and perspectives on their future applications, opening opportunities to model joint tissues and response to joint disease treatment.

Bioactive Scaffolds as a Promising Alternative for Enhancing Critical-Size Bone Defect Regeneration in the Craniomaxillofacial Region

Reconstruction of critical-size bone defects (CSDs) in the craniomaxillofacial (CMF) region remains challenging. Scaffold-based bone-engineered constructs have been proposed as an alternative to the classical treatments made with autografts and allografts. Scaffolds, a key component of engineered constructs, have been traditionally viewed as biologically passive temporary replacements of deficient bone lacking intrinsic cues to promote osteogenesis. Nowadays, scaffolds are functionalized, giving rise to bioactive scaffolds promoting bone regeneration more effectively than conventional counterparts. This review focuses on the three approaches most used to bioactivate scaffolds: (1) conferring microarchitectural designs or surface nanotopography; (2) loading bioactive molecules; and (3) seeding stem cells on scaffolds, providing relevant examples of in vivo (preclinical and clinical) studies where these methods are employed to enhance CSDs healing in the CMF region. From these, adding bioactive molecules (specifically bone morphogenetic proteins or BMPs) to scaffolds has been the most explored to bioactivate scaffolds. Nevertheless, the downsides of grafting BMP-loaded scaffolds in patients have limited its successful translation into clinics. Despite these drawbacks, scaffolds containing safer, cheaper, and more effective bioactive molecules, combined with stem cells and topographical cues, remain a promising alternative for clinical use to treat CSDs in the CMF complex replacing autografts and allografts.

Liver-Inspired Polyetherketoneketone Scaffolds Simulate Regenerative Signals and Mobilize Anti-Inflammatory Reserves to Reprogram Macrophage Metabolism for Boosted Osteoporotic Osseointegration

Tissue regeneration is regulated by morphological clues of implants in bone defect repair. Engineered morphology can boost regenerative biocascades that conquer challenges such as material bioinertness and pathological microenvironments. Herein, a correlation between the liver extracellular skeleton morphology and the regenerative signaling, namely hepatocyte growth factor receptor (MET), is found to explain the mystery of rapid liver regeneration. Inspired by this unique structure, a biomimetic morphology is prepared on polyetherketoneketone (PEKK) via femtosecond laser etching and sulfonation. The morphology reproduces MET signaling in macrophages, causing positive immunoregulation and optimized osteogenesis. Moreover, the morphological clue activates an anti-inflammatory reserve (arginase-2) to translocate retrogradely from mitochondria to the cytoplasm due to the difference in spatial binding of heat shock protein 70. This translocation enhances oxidative respiration and complex II activity, reprogramming the metabolism of energy and arginine. The importance of MET signaling and arginase-2 in the anti-inflammatory repair of biomimetic scaffolds is also verified via chemical inhibition and gene knockout. Altogether, this study not only provides a novel biomimetic scaffold for osteoporotic bone defect repair that can simulate regenerative signals, but also reveals the significance and feasibility of strategies to mobilize anti-inflammatory reserves in bone regeneration.

Overview of Electrospinning for Tissue Engineering Applications

Tissue engineering (TE) is an emerging field of study that incorporates the principles of biology, medicine, and engineering for designing biological substitutes to maintain, restore, or improve tissue functions with the goal of avoiding organ transplantation. Amongst the various scaffolding techniques, electrospinning is one of the most widely used techniques to synthesise a nanofibrous scaffold. Electrospinning as a potential tissue engineering scaffolding technique has attracted a great deal of interest and has been widely discussed in many studies. The high surface-to-volume ratio of nanofibres, coupled with their ability to fabricate scaffolds that may mimic extracellular matrices, facilitates cell migration, proliferation, adhesion, and differentiation. These are all very desirable properties for TE applications. However, despite its widespread use and distinct advantages, electrospun scaffolds suffer from two major practical limitations: poor cell penetration and poor load-bearing applications. Furthermore, electrospun scaffolds have low mechanical strength. Several solutions have been offered by various research groups to overcome these limitations. This review provides an overview of the electrospinning techniques used to synthesise nanofibres for TE applications. In addition, we describe current research on nanofibre fabrication and characterisation, including the main limitations of electrospinning and some possible solutions to overcome these limitations.

Injectable Biomimetic Hydrogel Guided Functional Bone Regeneration by Adapting Material Degradation to Tissue Healing

The treatment of irregular bone defects remains a clinical challenge since the current biomaterials (e.g., calcium phosphate bone cement (CPC)) mainly act as inert substitutes, which are incapable of transforming into a regenerated host bone (termed functional bone regeneration). Ideally, the implant degradation rate should adapt to that of bone regeneration, therefore providing sufficient physicochemical support and giving space for bone growth. This study aims to develop an injectable biomaterial with bone regeneration‐adapted degradability, to reconstruct a biomimetic bone‐like structure that can timely transform into new bone, facilitating functional bone regeneration. To achieve this goal, a hybrid (LP‐CPC@gelatin, LC) hydrogel is synthesized via one‐step incorporation of laponite (LP) and CPC into gelatin hydrogel, and the LC gel degradation rate is controlled by adjusting the LP/CPC ratio to match the bone regeneration rate. Such an LC hydrogel shows good osteoinduction, osteoconduction, and angiogenesis effects, with complete implant‐to‐new bone transformation capacity. This 2D nanoclay‐based bionic hydrogel can induce ectopic bone regeneration and promote ligament graft osseointegration in vivo by inducing functional bone regeneration. Therefore, this study provides an advanced strategy for functional bone regeneration and an injectable biomimetic biomaterial for functional skeletal muscle repair in a minimally invasive therapy.

Bioinspired Mild Photothermal Effect-Reinforced Multifunctional Fiber Scaffolds Promote Bone Regeneration

Bone fractures are often companied with poor bone healing and high rates of infection. Early recruitment of mesenchymal stem cells (MSCs) is critical for initiating efficient bone repair, and mild thermal stimulation can accelerate the recovery of chronic diseases. Here, a bioinspired, staged photothermal effect-reinforced multifunctional scaffold was fabricated for bone repair. Uniaxially aligned electrospun polycaprolactone nanofibers were doped with black phosphorus nanosheets (BP NSs) to endow the scaffold with excellent near-infrared (NIR) responsive capability. Apt19S was then decorated on the surface of the scaffold to selectively recruit MSCs toward the injured site. Afterward, microparticles of phase change materials loaded with antibacterial drugs were also deposited on the surface of the scaffold, which could undergo a solid-to-liquid phase transition above 39 °C, triggering the release of payload to eliminate bacteria and prevent infection. Under NIR irradiation, photothermal-mediated up-regulation of heat shock proteins and accelerated biodegradation of BP NSs could promote the osteogenic differentiation of MSCs and biomineralization. Overall, this strategy shows the ability of bacteria elimination, MSCs recruitment, and bone regeneration promotion with the assistance of photothermal effect in vitro and in vivo, which emphasizes the design of a bioinspired scaffold and its potential for a mild photothermal effect in bone tissue engineering.

Transcriptomic Changes toward Osteogenic Differentiation of Mesenchymal Stem Cells on 3D-Printed GelMA/CNC Hydrogel under Pulsatile Pressure Environment

Biomimetic soft hydrogels used in bone tissue engineering frequently produce unsatisfactory outcomes. Here, it is investigated how human bone-marrow-derived mesenchymal stem cells (hBMSCs) differentiated into early osteoblasts on remarkably soft 3D hydrogel (70 ± 0.00049 Pa). Specifically, hBMSCs seeded onto cellulose nanocrystals incorporated methacrylate gelatin hydrogels are subjected to pulsatile pressure stimulation (PPS) of 5-20 kPa for 7 days. The PPS stimulates cellular processes such as mechanotransduction, cytoskeletal distribution, prohibition of oxidative stress, calcium homeostasis, osteogenic marker gene expression, and osteo-specific cytokine secretions in hBMSCs on soft substrates. The involvement of Piezo 1 is the main ion channel involved in mechanotransduction. Additionally, RNA-sequencing results reveal differential gene expression concerning osteogenic differentiation, bone mineralization, ion channel activity, and focal adhesion. These findings suggest a practical and highly scalable method for promoting stem cell commitment to osteogenesis on soft matrices for clinical reconstruction.

Biomimetic natural biomaterials for tissue engineering and regenerative medicine: new biosynthesis methods, recent advances, and emerging applications

Biomimetic materials have emerged as attractive and competitive alternatives for tissue engineering (TE) and regenerative medicine. In contrast to conventional biomaterials or synthetic materials, biomimetic scaffolds based on natural biomaterial can offer cells a broad spectrum of biochemical and biophysical cues that mimic the in vivo extracellular matrix (ECM). Additionally, such materials have mechanical adaptability, microstructure interconnectivity, and inherent bioactivity, making them ideal for the design of living implants for specific applications in TE and regenerative medicine. This paper provides an overview for recent progress of biomimetic natural biomaterials (BNBMs), including advances in their preparation, functionality, potential applications and future challenges. We highlight recent advances in the fabrication of BNBMs and outline general strategies for functionalizing and tailoring the BNBMs with various biological and physicochemical characteristics of native ECM. Moreover, we offer an overview of recent key advances in the functionalization and applications of versatile BNBMs for TE applications. Finally, we conclude by offering our perspective on open challenges and future developments in this rapidly-evolving field.

Bioinspired Piezoelectric Periosteum to Augment Bone Regeneration via Synergistic Immunomodulation and Osteogenesis

Ideal periosteum materials are required to participate in a sequence of bone repair-related physiological events, including the initial immune response, endogenous stem cell recruitment, angiogenesis, and osteogenesis. However, conventional tissue-engineered periosteal materials have difficulty achieving these functions by simply mimicking the periosteum via structural design or by loading exogenous stem cells, cytokines, or growth factors. Herein, we present a novel biomimetic periosteum preparation strategy to comprehensively enhance the bone regeneration effect using functionalized piezoelectric materials. The resulting biomimetic periosteum possessing an excellent piezoelectric effect and improved physicochemical properties was prepared using a biocompatible and biodegradable poly(3-hydroxybutyric acid-co-3-hydrovaleric acid) (PHBV) polymer matrix, antioxidized polydopamine-modified hydroxyapatite (PHA), and barium titanate (PBT), which were further incorporated into the polymer matrix to fabricate a multifunctional piezoelectric periosteum by a simple one-step spin-coating method. The addition of PHA and PBT dramatically enhanced the physicochemical properties and biological functions of the piezoelectric periosteum, resulting in improved surface hydrophilicity and roughness, enhanced mechanical performance, tunable degradation behavior, and stable and desired endogenous electrical stimulations, which is conducive to accelerating bone regeneration. Benefiting from endogenous piezoelectric stimulation and bioactive components, the as-fabricated biomimetic periosteum demonstrated favorable biocompatibility, osteogenic activity, and immunomodulatory functions in vitro, which not only promoted adhesion, proliferation, and spreading as well as osteogenesis of mesenchymal stem cells (MSCs) but also effectively induced M2 macrophage polarization, thereby suppressing reactive oxygen species (ROS)-induced inflammatory reactions. Through in vivo experiments, the biomimetic periosteum with endogenous piezoelectric stimulation synergistically accelerated the formation of new bone in a rat critical-sized cranial defect model. The whole defect was almost completely covered by new bone at 8 weeks post treatment, with a thickness close to that of the host bone. Collectively, with its favorable immunomodulatory and osteogenic properties, the biomimetic periosteum developed here represents a novel method to rapidly regenerate bone tissue using piezoelectric stimulation.

Nanotopographic micro-nano forces finely tune the conformation of macrophage mechanosensitive membrane protein integrin β2 to manipulate inflammatory responses

Finely tuning mechanosensitive membrane proteins holds great potential in precisely controlling inflammatory responses. In addition to macroscopic force, mechanosensitive membrane proteins are reported to be sensitive to micro-nano forces. Integrin β2, for example, might undergo a piconewton scale stretching force in the activation state. High-aspect-ratio nanotopographic structures were found to generate nN-scale biomechanical force. Together with the advantages of uniform and precisely tunable structural parameters, it is fascinating to develop low-aspect-ratio nanotopographic structures to generate micro-nano forces for finely modulating their conformations and the subsequent mechanoimmiune responses. In this study, low-aspect-ratio nanotopographic structures were developed to finely manipulate the conformation of integrin β2. The direct interaction of forces and the model molecule integrin αXβ2 was first performed. It was demonstrated that pressing force could successfully induce conformational compression and deactivation of integrin αXβ2, and approximately 270 to 720 pN may be required to inhibit its conformational extension and activation. Three low-aspect-ratio nanotopographic surfaces (nanohemispheres, nanorods, and nanoholes) with various structural parameters were specially designed to generate the micro-nano forces. It was found that the nanorods and nanohemispheres surfaces induce greater contact pressure at the contact interface between macrophages and nanotopographic structures, particularly after cell adhesion. These higher contact pressures successfully inhibited the conformational extension and activation of integrin β2, suppressing focal adhesion activity and the downstream PI3K-Akt signaling pathway, reducing NF-κB signaling and macrophage inflammatory responses. Our findings suggest that nanotopographic structures can be used to finely tune mechanosensitive membrane protein conformation changes, providing an effective strategy for precisely modulating inflammatory responses.

Electronic Supplementary Material

Supplementary material (primer sequences of target genes in RT-qPCR assay; the results of solvent accessible surface area during equilibrium simulation, the ligplut results of hydrogen bonds, and hydrophobic interactions; the density of different nanotopographic structures; interaction analysis of the downregulated leading genes of "focal adhesion" signaling pathway in nanohemispheres and nanorods groups; and the GSEA results of "Rap 1 signaling pathway" and "regulation of actin cytoskeleton" in different groups) is available in the online version of this article at 10.1007/s12274-023-5550-0.

Early osteoimmunomodulation by mucin hydrogels augments the healing and revascularization of rat critical-size calvarial bone defects

The design principle of osteogenic bone grafts has shifted from immunological inertness to limiting foreign body response to combined osteoimmunomodulatory activity to promote high-quality endogenous bone regeneration. Recently developed immunomodulatory mucin hydrogels have been shown to elicit very low complement activation and suppress macrophage release and activation after implantation in vivo. However, their immunoregulatory activity has not yet been studied in the context of tissue repair. Herein, we synthesized mucin-monetite composite materials and investigated their early osteoimmunomodulation using a critical-size rat bone defect model. We demonstrated that the composites can polarize macrophages towards the M2 phenotype at weeks 1 and 2. The early osteoimmunomodulation enhanced early osteogenesis and angiogenesis and ultimately promoted fracture healing and engraftment (revascularization of the host vasculature) at weeks 6 and 12. Overall, we demonstrated the applicability of mucin-based immunomodulatory biomaterials to enhance tissue repair in tissue engineering and regenerative medicine.

Tissue Bioengineering with Fibrin Scaffolds and Deproteinized Bone Matrix Associated or Not with the Transoperative Laser Photobiomodulation Protocol

Extending the range of use of the heterologous fibrin biopolymer, this pre-clinical study showed a new proportionality of its components directed to the formation of scaffold with a lower density of the resulting mesh to facilitate the infiltration of bone cells, and combined with therapy by laser photobiomodulation, in order to accelerate the repair process and decrease the morphofunctional recovery time. Thus, a transoperative protocol of laser photobiomodulation (L) was evaluated in critical bone defects filled with deproteinized bovine bone particles (P) associated with heterologous fibrin biopolymer (HF). The groups were: BC_L (blood clot + laser); HF; HF_L; PHF (P+HF); PHF_L (P+HF+L). Microtomographically, bone volume (BV) at 14 days, was higher in the PHF and PHF_L groups (10.45 ± 3.31 mm³ and 9.94 ± 1.51 mm³), significantly increasing in the BC_L, HF_L and PHF_L groups. Histologically, in all experimental groups, the defects were not reestablished either in the external cortical bone or in the epidural, occurring only in partial bone repair. At 42 days, the bone area (BA) increased in all groups, being significantly higher in the laser-treated groups. The quantification of bone collagen fibers showed that the percentage of collagen fibers in the bone tissue was similar between the groups for each experimental period, but significantly higher at 42 days (35.71 ± 6.89%) compared to 14 days (18.94 ± 6.86%). It can be concluded that the results of the present study denote potential effects of laser radiation capable of inducing functional bone regeneration, through the synergistic combination of biomaterials and the new ratio of heterologous fibrin biopolymer components (1:1:1) was able to make the resulting fibrin mesh less dense and susceptible to cellular permeability. Thus, the best fibrinogen concentration should be evaluated to find the ideal heterologous fibrin scaffold.

Immune evaluation of granulocyte-macrophage colony stimulating factor loaded hierarchically 3D nanofiber scaffolds in a humanized mice model

Background: Immune evaluation of biomaterials for tissue regeneration is a critical preclinical evaluation. The current evaluation criterion (ISO 10993-1 or GB/T 16886) uses rodents to perform the immune evaluation. However, the immune system of rodents is different from humans, the obtained results may not be reliable, which could lead directly to the failure of clinical trials. Granulocyte-macrophage colony-stimulating factor (GM-CSF) shows a great potential application in tissue regeneration by regulating local immune responses. The presented work combines the advantages of GM-CSF (immunoregulation) and hierarchically 3D nanofiber scaffolds (tissue regeneration). Methods: Firstly, we fabricated GM-CSF loaded 3D radially aligned nanofiber scaffolds, and then subcutaneous implantation was performed in humanized mice. The whole scaffold and surrounding tissue were harvested at each indicated time point. Finally, the cell infiltration and local immune responses were detected by histological observations, including H&E and Masson staining and immunochemistry. Results: We found significant cell migration and extracellular matrix deposition within the 3D radially aligned nanofiber scaffold after subcutaneous implantation. The locally released GM-CSF could accelerate the expression of human dendritic cells (CD11c) only 3 days after subcutaneous implantation. Moreover, higher expression of human cytotoxic T cells (CD3⁺/CD8⁺), M1 macrophages (CD68/CCR7) was detected within GM-CSF loaded radially aligned nanofiber scaffolds and their surrounding tissues. Conclusions: The 3D radially aligned scaffold can accelerate cell migration from surrounding tissues to regenerate the wound area. And the locally released GM-CSF enhances dendritic cell recruitment and activation of cytotoxic T cells and M1 macrophages. Taken together, the GM-CSF loaded 3D radially aligned nanofiber scaffolds have a promising potential for achieving tissue regeneration.

Breaking the resolution limits of 3D bioprinting: future opportunities and present challenges

Bioprinting aims to produce 3D structures from which embedded cells can receive mechanical and chemical stimuli that influence their behavior, direct their organization and migration, and promote differentiation, in a similar way to what happens within the native extracellular matrix. However, limited spatial resolution has been a bottleneck for conventional 3D bioprinting approaches. Reproducing fine features at the cellular scale, while maintaining a reasonable printing volume, is necessary to enable the biofabrication of more complex and functional tissue and organ models. In this opinion article we recount the emergence of, and discuss the most promising, high-definition (HD) bioprinting techniques to achieve this goal, discussing which obstacles remain to be overcome, and which applications are envisioned in the tissue engineering field.

Small extracellular vesicles with nanomorphology memory promote osteogenesis

Nanotopographical cues endow biomaterials the ability to guide cell adhesion, proliferation, and differentiation. Cellular mechanical memory can maintain the cell status by retaining cellular information obtained from past mechanical microenvironments. Here, we propose a new concept “morphology memory of small extracellular vesicles (sEV)” for bone regeneration. We performed nanotopography on titanium plates through alkali and heat (Ti8) treatment to promote human mesenchymal stem cell (hMSC) differentiation. Next, we extracted the sEVs from the hMSC, which were cultured on the nanotopographical Ti plates for 21 days (Ti8-21-sEV). We demonstrated that Ti8-21-sEV had superior pro-osteogenesis ability in vitro and in vivo. RNA sequencing further confirmed that Ti8-21-sEV promote bone regeneration through osteogenic-related pathways, including the PI3K-AKT signaling pathway, MAPK signaling pathway, focal adhesion, and extracellular matrix-receptor interaction. Finally, we decorated the Ti8-21-sEV on a 3D printed porous polyetheretherketone scaffold. The femoral condyle defect model of rabbits was used to demonstrate that Ti8-21-sEV had the best bone ingrowth. In summary, our study demonstrated that the Ti8-21-sEV have memory function by copying the pro-osteogenesis information from the nanotopography. We expect that our study will encourage the discovery of other sEV with morphology memory for tissue regeneration.

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Nanotopography fabricated on titanium plates has superior promoted hMSCs differentiation ability.

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sEV extracted from hMSCs which were cultured on Ti8 plates for 21 days had the superior pro-osteogenesis ability.

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Ti8-21-sEV have memory function through copy the pro-osteogenesis information from nanotopography.

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RNA sequencing confirmed that Ti8-21-sEV promote bone regeneration through osteogenic-related pathways.

Effect of chitosan/inorganic nanomaterial scaffolds on bone regeneration and related influencing factors in animal models: A systematic review

Bone tissue engineering (BTE) provides a promising alternative for transplanting. Due to biocompatibility and biodegradability, chitosan-based scaffolds have been extensively studied. In recent years, many inorganic nanomaterials have been utilized to modify the performance of chitosan-based materials. In order to ascertain the impact of chitosan/inorganic nanomaterial scaffolds on bone regeneration and related key factors, this study presents a systematic comparison of various scaffolds in the calvarial critical-sized defect (CSD) model. A total of four electronic databases were searched without publication date or language restrictions up to April 2022. The Animal Research Reporting of In Vivo Experiments 2.0 guidelines (ARRIVE 2.0) were used to assess the quality of the included studies. Moreover, the risk of bias (RoB) was evaluated via the Systematic Review Center for Laboratory Animal Experimentation (SYRCLE) tool. After the screening, 22 studies were selected. None of these studies achieved high quality or had a low RoB. In the available studies, scaffolds reconstructed bone defects in radically different extensions. Several significant factors were identified, including baseline characteristics, physicochemical properties of scaffolds, surgery details, and scanning or reconstruction parameters of micro-computed tomography (micro-CT). Further studies should focus on not only improving the osteogenic performance of the scaffolds but also increasing the credibility of studies through rigorous experimental design and normative reports.

A unique biomimetic modification endows polyetherketoneketone scaffold with osteoinductivity by activating cAMP/PKA signaling pathway

Osteoinductivity of a biomaterial scaffold can notably enhance the bone healing performance. In this study, we developed a biomimetic and hierarchically porous polyetherketoneketone (PEKK) scaffold with unique osteoinductivity using a combined surface treatment strategy of a sulfonated process and a nano bone-like apatite deposition. In a beagle intramuscular model, the scaffold induced bone formation ectopically after 12-week implantation. The better bone healing ability of the scaffold than the original PEKK was also confirmed in orthotopic sites. After culturing with bone marrow-derived mesenchymal stem cells (BMSCs), the scaffold induced osteogenic differentiation of BMSCs, and the new bone formation could be mainly depending on cell signaling through adenylate cyclase 9, which activates the cyclic adenosine monophosphate/protein kinase A signaling cascade pathways. The current work reports a new osteoinductive synthetic polymeric scaffold with its detailed molecular mechanism of action for bone repair and regeneration.

Recent Advances in Macroporous Hydrogels for Cell Behavior and Tissue Engineering

Hydrogels have been extensively used as scaffolds in tissue engineering for cell adhesion, proliferation, migration, and differentiation because of their high-water content and biocompatibility similarity to the extracellular matrix. However, submicron or nanosized pore networks within hydrogels severely limit cell survival and tissue regeneration. In recent years, the application of macroporous hydrogels in tissue engineering has received considerable attention. The macroporous structure not only facilitates nutrient transportation and metabolite discharge but also provides more space for cell behavior and tissue formation. Several strategies for creating and functionalizing macroporous hydrogels have been reported. This review began with an overview of the advantages and challenges of macroporous hydrogels in the regulation of cellular behavior. In addition, advanced methods for the preparation of macroporous hydrogels to modulate cellular behavior were discussed. Finally, future research in related fields was discussed.

Pearl-inspired graphene oxide-collagen microgel with multi-layer mineralization through microarray chips for bone defect repair

Biomineralization of natural polymers in simulated body fluid (SBF) can significantly improve its biocompatibility, osteoconductivity, and osteoinductivity because of the hydroxyapatite (HAp) deposition. Nevertheless, the superficial HAp crystal deposition hamper the deep inorganic ions exchange in porous microgels, thus gradually leading to a nonuniform regeneration effect. Inspired by the pearl forming process, this article uses the microarray chips to fabricate the multi-layer mineralized graphene oxide (GO)-collagen (Col)-hydroxyapatite (HAp) microgel, denoted as MMGCH. These fabricated MMGCH microgels exhibit porous structure and uniform HAp distribution. Furthermore, the suitable microenvironment offered by microgel promotes the time-dependent proliferation and osteogenic differentiation of stem cells, which resulted in upregulated osteogenesis-related genes and proteins, such as alkaline phosphatase, osteocalcin, and collagen-1. Finally, the MMGCH microgels possess favorable bone regeneration capacities both in cranial bone defects and mandibular bone defects via providing a suitable microenvironment for host-derived cells to form new bone tissues. This work presents a biomimetic means aiming to achieve full-thickness and uniform HAp deposition in hydrogel for bone defect repair.

The Bumpy Road to Stem Cell Therapies: Rational Design of Surface Topographies to Dictate Stem Cell Mechanotransduction and Fate

Cells sense and respond to a variety of physical cues from their surrounding microenvironment, and these are interpreted through mechanotransductive processes to inform their behavior. These mechanisms have particular relevance to stem cells, where control of stem cell proliferation, potency, and differentiation is key to their successful application in regenerative medicine. It is increasingly recognized that surface micro- and nanotopographies influence stem cell behavior and may represent a powerful tool with which to direct the morphology and fate of stem cells. Current progress toward this goal has been driven by combined advances in fabrication technologies and cell biology. Here, the capacity to generate precisely defined micro- and nanoscale topographies has facilitated the studies that provide knowledge of the mechanotransducive processes that govern the cellular response as well as knowledge of the specific features that can drive cells toward a defined differentiation outcome. However, the path forward is not fully defined, and the "bumpy road" that lays ahead must be crossed before the full potential of these approaches can be fully exploited. This review focuses on the challenges and opportunities in applying micro- and nanotopographies to dictate stem cell fate for regenerative medicine. Here, key techniques used to produce topographic features are reviewed, such as photolithography, block copolymer lithography, electron beam lithography, nanoimprint lithography, soft lithography, scanning probe lithography, colloidal lithography, electrospinning, and surface roughening, alongside their advantages and disadvantages. The biological impacts of surface topographies are then discussed, including the current understanding of the mechanotransductive mechanisms by which these cues are interpreted by the cells, as well as the specific effects of surface topographies on cell differentiation and fate. Finally, considerations in translating these technologies and their future prospects are evaluated.

Novel 3D Bioglass Scaffolds for Bone Tissue Regeneration

The design of scaffolds with optimal biomechanical properties for load-bearing applications is an important topic of research. Most studies have addressed this problem by focusing on the material composition and not on the coupled effect between the material composition and the scaffold architecture. Polymer-bioglass scaffolds have been investigated due to the excellent bioactivity properties of bioglass, which release ions that activate osteogenesis. However, material preparation methods usually require the use of organic solvents that induce surface modifications on the bioglass particles, compromising the adhesion with the polymeric material thus compromising mechanical properties. In this paper, we used a simple melt blending approach to produce polycaprolactone/bioglass pellets to construct scaffolds with pore size gradient. The results show that the addition of bioglass particles improved the mechanical properties of the scaffolds and, due to the selected architecture, all scaffolds presented mechanical properties in the cortical bone region. Moreover, the addition of bioglass indicated a positive long-term effect on the biological performance of the scaffolds. The pore size gradient also induced a cell spreading gradient.

Electrospun Nanofibers for Bone Regeneration: From Biomimetic Composition, Structure to Function

In recent years, a variety of novel materials and processing technologies have been developed to prepare tissue engineering scaffolds for bone defect repair. Among them, nanofibers fabricated via electrospinning technology...

Emerging concepts in bone repair and the premise of soft materials

Human bone has a strong regenerative capacity that allows for restoration of its function and structure after damage. For degenerative bone diseases or large defects, bone regeneration requirements exceed the natural potential for self-healing, so bone grafts or bone substitute materials are required to support the regeneration of bone tissue. Compared to the plethora of endogenous bioactive molecules and cells in native bone grafts, the regenerative capacity of tissue-engineered materials is limited. The modest clinical impact of tissue-engineered strategies in this domain can be attributed to a failure to fully recognize key physical and biological events during bone healing, and to recapitulate the structure and composition of the target tissue to generate truly biomimetic grafts. This limitation has motivated the emergence of new strategies such as immunomodulation, endochondral ossification routes, engineered microtissues and hematoma regulation, and the development of advanced biomaterials including gene-activated matrices, soft microgels and hierarchically designed materials.