Bone tissue engineering: recent advances and challenges

Electroconductive gelatin/hyaluronic acid/hydroxyapatite scaffolds for enhanced cell proliferation and osteogenic differentiation in bone tissue engineering

Addressing the challenge of bone tissue regeneration requires creating an optimal microenvironment that promotes both osteogenesis and angiogenesis. Electroconductive scaffolds have emerged as promising solutions for bone regeneration; however, existing conductive polymers often lack biofunctionality and biocompatibility. In this study, we synthesized poly(3,4-ethylenedioxythiophene) nanoparticles (PEDOT NPs) using chemical oxidation polymerization and incorporated them into gelatin/hyaluronic acid/hydroxyapatite (Gel:HA:HAp) scaffolds to develop Gel:HA:HAp:PEDOT-NP scaffolds. Morphological analysis by scanning electron microscopy (SEM) showed a honeycomb-like structure with pores of 228-250 μm in diameter. The addition of the synthesized PEDOT NPs increased the conductive capabilities of the scaffolds to 1 × 10-6 ± 1.3 × 10-7 S/cm. Biological assessment of PEDOT NP scaffolds using human foetal osteoblastic 1.19 cells (hFOB), and human bone marrow-derived mesenchymal stem cells (hBMSCs) revealed enhanced cell proliferation and viability compared to control scaffold without NPs, along with increased osteogenic differentiation, evidenced by higher levels of alkaline phosphatase activity, osteopontin (OPN), alkaline phosphatase (ALP), and osteocalcin (OCN) expression, as observed through immunofluorescence, and enhanced expression of osteogenic-related genes. The conductive scaffold shows interesting mineralization capacity, as shown by Alizarin red and Osteoimage staining. Furthermore, PEDOT-NP scaffolds promoted angiogenesis, as indicated by improved tube formation abilities of human umbilical vein endothelial cells (HUVECs), especially at the higher concentrations of NPs. Overall, our findings demonstrate that the integration of PEDOT NPs scaffold enhances their conductive properties and promotes cell proliferation, osteogenic differentiation, and angiogenesis. Gel:HA:HAp:PEDOT-NP scaffolds exhibit promising potential as efficient biomaterials for bone tissue regeneration, offering a potential engineered platform for clinical applications.

Acetylation of H3K18 activated by p300 promotes osteogenesis in human adipose-derived mesenchymal stem cells

Human adipose-derived mesenchymal stem cells (hAD-MSCs) have garnered significant interest as a viable alternative source of stem cells for applications in bone tissue engineering due to their high and ease availability. At present, the limited studies on potential epigenetic regulatory mechanism in hAD-MSCs greatly hinders its clinical application in bone repair. Histone acetylation has been identified as a critical regulator of the osteogenic differentiation of mesenchymal stem cells (MSCs), with increased levels of histone acetylation sites frequently correlating with enhanced osteogenic differentiation. However, their specific roles in MSCs osteogenesis remain unclear. In this study, we observed a significant up-regulation of H3K18 acetylation (H3K18ac) during the osteogenic induction of hAD-MSCs. This modification was notably enriched in the promoter regions of genes associated with osteogenesis, thereby facilitating osteogenic differentiation. Furthermore, the treatment of histone acetyltransferases p300 inhibitor A-485 in hAD-MSCs resulted in a reduction of H3K18 acetylation levels during the osteogenic differentiation, which corresponded with a diminished osteoblast phenotype and function. These results indicated that p300-mediated acetylation of H3K18 enhances the osteogenic differentiation of hAD-MSCs. It provides a novel insight into understanding the mechanism of osteogenic differentiation of hAD-MSCs and promoting its application in bone tissue engineering.

Development of Poly(ether sulfone)/Poly(vinyl alcohol)/Magnesium-Doped Carbon Quantum Dot Scaffolds for Bone Tissue Engineering

Bone tissue engineering plays a critical role in overcoming the limitations of traditional bone grafts and implants by enhancing bone integration and regeneration. In this study, we developed a novel membrane scaffold comprising poly(ether sulfone) (PES), poly(vinyl alcohol) (PVA), and magnesium-doped carbon quantum dots (CQDs.Mg) for potential bone tissue engineering applications. Four distinct scaffold formulations (PE-CM0, PE-CM2, PE-CM3, and PE-CM4) were developed using a film applicator machine. The morphology and porosity of the scaffolds, characterized via scanning electron microscopy (SEM), revealed increased porosity with higher CQDs.Mg content. Fourier transform infrared spectroscopy (FTIR) confirmed the successful integration of functional groups from each component. Water contact angle (WCA) measurements indicated improved hydrophilicity with the addition of CQDs.Mg, which is beneficial for cell attachment and proliferation. Mechanical testing demonstrated that the scaffolds maintained adequate tensile strength and flexibility, with PE-CM3 and PE-CM4 exhibiting superior properties. Swelling assays indicated enhanced water absorption with increased CQDs.Mg content, while 14-day degradation studies showed excellent structural stability. Biocompatibility was also assessed using L929 and NIH3T3 cell lines, with cytotoxicity assays demonstrating nearly 100% cell viability across all samples. These findings suggest that the PES/PVA/CQDs.Mg scaffolds exhibit a promising combination of mechanical robustness, hydrophilicity, and biocompatibility, making them strong candidates for bone tissue engineering applications.

Bioactive hydrogel formulations for regeneration of pathological bone defects

Bone defects caused by osteoporosis, infection, diabetes, post-tumor resection, and nonunion often cause severe pain and markedly increase morbidity and mortality, which remain a significant challenge for orthopedic surgeons. The precise local treatments for these pathological complications are essential to avoid poor or failed bone repair. Hydrogel formulations serve as injectable innovative platforms that overcome microenvironmental obstacles and as delivery systems for controlled release of various bioactive substances to bone defects in a targeted manner. Additionally, hydrogel formulations can be tailored for specific mechanical strengths and degradation profiles by adjusting their physical and chemical properties, which are crucial for prolonged drug retention and effective bone repair. This review summarizes recent advances in bioactive hydrogel formulations as three-dimensional scaffolds that support cell proliferation and differentiation. It also highlights their role as smart drug-delivery systems with capable of continuously releasing antibacterial agents, anti-inflammatory drugs, chemotherapeutic agents, and osteogenesis-related factors to enhance bone regeneration in pathological areas. Furthermore, the limitations of hydrogel formulations in pathological bone repair are discussed, and future development directions are proposed, which is expected to pave the way for the repair of pathological bone defects.

Surgical Bioengineering of the Microvasculature and Challenges in Clinical Translation

Tissue and organ dysfunction are major causes of worldwide morbidity and mortality with all medical specialties being impacted. Tissue engineering is an interdisciplinary field relying on the combination of scaffolds, cells, and biologically active molecules to restore form and function. However, clinical translation is still largely hampered by limitations in vascularization. Consequently, a thorough understanding of the microvasculature is warranted. This review provides an overview of (1) angiogenesis, including sprouting angiogenesis, intussusceptive angiogenesis, vascular remodeling, vascular co-option, and inosculation; (2) strategies for vascularized engineered tissue fabrication such as scaffold modulation, prevascularization, growth factor utilization, and cell-based approaches; (3) guided microvascular development via scaffold modulation with electromechanical cues, 3D bioprinting, and electrospinning; (4) surgical approaches to bridge the micro- and macrovasculatures in order to hasten perfusion; and (5) building specific vasculature in the context of tissue repair and organ transplantation, including skin, adipose, bone, liver, kidney, and lung. Our goal is to provide the reader with a translational overview that spans developmental biology, tissue engineering, and clinical surgery.

Visible light-induced simultaneous bioactive amorphous calcium phosphate mineralization and in situ crosslinking of coacervate-based injectable underwater adhesive hydrogels for enhanced bone regeneration

The field of bone tissue engineering is vital due to increasing bone disorders and limitations of traditional grafts. Injectable hydrogels offer minimally invasive solutions but often lack mechanical integrity and biological functionality, including osteoinductive capacity and structural stability under physiological conditions. To address these issues, we propose a coacervate-based injectable adhesive hydrogel that utilizes the dual functionality of in situ photocrosslinking and osteoinductive amorphous calcium phosphate formation, both of which are activated simultaneously by visible light irradiation. The developed hydrogel formulation integrated a photoreactive agent with calcium ions and phosphonodiol in a matrix of tyramine-conjugated alginate and RGD peptide-fused bioengineered mussel adhesive protein, promoting rapid setting, robust underwater adhesion, and bioactive mineral deposition. The hydrogel also exhibited superior mechanical properties, including enhanced underwater tissue adhesive strength and compressive resistance. In vivo evaluation using a rat femoral tunnel defect model confirmed the efficacy of the developed adhesive hydrogel in facilitating easy application to irregularly shaped defects through injection, rapid bone regeneration without the addition of bone grafts, and integration within the defect sites. This injectable adhesive hydrogel system holds significant potential for advancing bone tissue engineering, providing a versatile, efficient, and biologically favorable alternative to conventional bone repair methodologies.

Evaluation of the comparative efficacy and safety of surgical strategies for long bone defects: a network meta-analysis

BACKGROUND

To evaluate the safety and efficacy of various surgical treatments for long bone defects. Despite numerous observational studies, randomized controlled trials (RCTs), and meta-analyses, the optimal surgical treatment for long bone defects remains undetermined.

METHODS

A network meta-analysis (NMA) was conducted. PubMed, Embase, and the Cochrane Library were searched for articles published between 1 January 2000 and 12 January 2023 on surgical treatments for long bone defects. RCTs and observational studies comparing five surgical treatments were selected: the Masquelet technique (MT), bone transport (BT), vascularized bone graft (VBG), non-VBG (NVBG), and bone tissue engineering (BTE). Data were extracted by two independent reviewers. The NMA aggregated direct and indirect evidence. Treatments were ranked using the surface under the cumulative ranking curve (SUCRA) scores. Data are presented as mean differences and 95% confidence intervals. The primary outcomes were the postoperative healing rate, with subgroup analysis based on defect size (4-8 cm and >8 cm). The secondary outcomes included postoperative complications.

RESULTS

This NMA included 23 studies (three RCTs and 20 observational studies) with 930 participants (median age, 35 years). There were no significant differences in clinical outcomes among the treatments. VBG (SUCRA, 75.1%) was rated as optimal for healing, and BTE (SUCRA, 28.5%) was the least effective. BTE had the highest complication rate (SUCRA, 90.9%), whereas NVBG had the lowest complication rate (SUCRA, 27.6%). Subgroup analysis showed reduced heterogeneity: for 4-8 cm defects, VBG (SUCRA, 80.4%) was optimal, and for >8 cm defects, BT (SUCRA, 76.2%) was optimal.

CONCLUSIONS

VBG and BT may offer superior clinical outcomes for long bone defects compared to MT, NVBG, and BTE. However, BTE is associated with a high risk of complications. Further high-quality, large-sample RCTs are required to confirm these findings.

4D Biofabrication of Magnetically Augmented Callus Assembloid Implants Enables Rapid Endochondral Ossification via Activation of Mechanosensitive Pathways

The use of magnetic-driven strategies for non-contact manipulation of engineered living modules opens up new possibilities for tissue engineering. The integration of magnetic nanoparticles (MNPs) with cartilaginous microtissues enables model-driven 4D bottom-up biofabrication of remotely actuated assembloids, providing unique properties to mechanoresponsive tissues, particularly skeletal constructs. However, for clinical use, the long-term effects of magnetic stimulation on phenotype and in vivo functionality need further exploration. Magnetic-driven biofabrication includes both rapid processes, such as guided microtissue assembly, and slower biological processes, like extracellular matrix secretion. This work explores the interplay between magnetic fields and MNP-loaded cartilaginous microtissues through mathematical modeling and experimental approaches, investigating long-term stimulation effects on ECM maturation and chondrogenic hypertrophy. Transcriptomic analysis reveal that magnetic stimulation activated mechanosensitive pathways and catabolic processes, driving accelerated cartilage-to-bone transitions via endochondral ossification, outcomes not observed in non-stimulated controls. This study paves the way for pre-programmed, remotely actuated skeletal assembloids with superior bone-forming capacity for regenerating challenging bone fractures.

Leveraging the predictive power of a 3D in vitro vascularization screening assay for hydrogel-based tissue-engineered periosteum allograft healing

A common strategy for promoting bone allograft healing is the design of tissue-engineered periosteum (TEP) to orchestrate host-tissue infiltration. However, evaluating requires costly and time-consuming in vivo studies. Therefore, in vitro assays are necessary to expedite TEP designs. Since angiogenesis is a critical process orchestrated by the periosteum, this study investigates in vitro 3D cell spheroid vascularization as a predictive tool for TEP-mediated in vivo healing. Spheroids of human umbilical vein endothelial cells (HUVECs) and human mesenchymal stem cells (hMSCs) are encapsulated in enzymatically-degradable poly (ethylene glycol)-based hydrogels and sprout formation, network formation, and angiogenic growth factor secretion are quantified. Hydrogels are also evaluated as TEP-modified allografts for in vivo bone healing with graft vascularization, callus formation, and biomechanical strength quantified as healing metrics. Evaluation of hydrogels highlights the importance of degradation, with 24-fold greater day 1 sprouts observed in degradable hydrogels in vitro and 4-fold greater graft-localized vascular volume at 6-weeks in vivo compared to non-degradable hydrogels. Correlations between in vitro and in vivo studies elucidate linear relationships when comparing in vitro sprout formation and angiocrine production with 3- and 6-week in vivo graft vascularization, 3-week cartilage callus, and 6-week bone callus, with a Pearson's R2 value equal to 0.97 for the linear correlation between in vitro sprout formation and 6-week in vivo vascular volume. Non-linear relationships are found between in vitro measures and bone torque strength at week 6. These correlations suggest that the in vitro sprouting assay has predictive power for in vivo vascularization and bone allograft healing.

Enhancing Bioactivity of Titanium-Based Materials Through Chitosan Based Coating and Calcitriol Functionalization

Titanium (Ti)-based materials are favored for hard tissue applications, yet their bioinertness limits their success. This study hypothesizes that functionalizing Ti materials with chitosan nano/microspheres and calcitriol (VD) will enhance their bioactivity by improving cellular activities and mineralization. To test this, chitosan particles were applied uniformly onto Ti surfaces using electrophoretic deposition (EPD) at 20 V for 3 minutes. VD was then loaded onto the coated surfaces, and the release profile of VD was monitored. Human fetal osteoblastic cells (hFOB) were cultured on the VD-loaded Ti surfaces. Cellular activities such as proliferation, Alkaline phosphatase (ALP) activity, osteogenic gene expression (runt-related transcription factor 2 (Runx2), collagen type 1 (Col I), osteocalcin ( OCn), osteopontin (OP)), and mineralization were assessed. Von Kossa staining was performed to analyze mineralization, and the expression of cell adhesion proteins (N-cadherin (NC), integrin alpha V (IaV), integrin beta 3, (Ib3)) was measured. The results showed that approximately 50% of the VD released over 50 hours. The chitosan coating increased surface roughness three-fold, and this, combined with VD release, resulted in reduced cell proliferation but increased ALP activity, suggesting enhanced differentiation. VD-functionalized Ti surfaces showed statistically significant differences in osteogenic gene expressions, particularly on rougher surfaces. Additionally, the expression of cell adhesion proteins (NC, IaV, Ib3) was upregulated on VD-containing coated surfaces. Von Kossa analysis revealed that surface roughness significantly enhanced mineralization, particularly on VD-free surfaces by day 7, while mineralization on VD-containing bare surfaces started on day 14. These findings demonstrate that VD-loaded chitosan coatings significantly enhance the biocompatibility and bioactivity of Ti-based materials, highlighting their potential for applications in bone regeneration.

Leveraging the Shape Fidelity of 3D Printed Bone Scaffolds Through Architectural Tailoring of an Emulsion Ink: A Combined Experimental and Computational Analysis

Hierarchical porous, bioactive, and biocompatible scaffolds with customizable multi-functionality are promising alternatives for autografts and allografts in bone tissue engineering. Combining high internal phase emulsion (HIPE) templating with additive manufacturing provides possibilities to produce such multiscale porous scaffolds. 3D printing of HIPE remains a challenging task due to the intense phase separation under high shear extrusion and reported printability (Pr) of either less than or greater than 1. Tuning viscoelastic properties of emulsion is therefore required to achieve a Pr ≈1. This study addresses these issues by preparing Pickering HIPEs using dual networks with synergistic viscous and elastic properties, stabilized by Cloisite 30B interphase. This configuration enhances viscoelasticity and achieves Pr values close to 1 (0.98-1.02). The printed scaffolds exhibit trabecular bone-like, hierarchical interconnected porosity (77%-86%). Computational simulations accurately predict the mechanical, biological, and degradation behavior. Functionalization with Cissus quadrangularis bioactivates the scaffolds, demonstrates in vivo biocompatibility, promotes MC3T3-E1 adhesion, and proliferation, accelerates osteogenesis, and reduces oxidative stress compared to neat PCL scaffolds. This work introduces a facile strategy for "engineering printability" to produce regenerative materials with hierarchical design and holds the potential for developing optimized bone tissue engineering scaffolds.

Fabrication of porous collagen-stem cells-dexamethasone scaffold as a novel approach for regeneration of mandibular bone defect

BACKGROUND

Bone defects, particularly in the mandible, pose significant clinical challenges due to the limited regenerative capacity. Effective bone tissue engineering requires biomaterials that promote both osteogenesis and angiogenesis. This study developed an optimized collagen-nano hydroxyapatite scaffold loaded with dexamethasone and stem cells to enhance bone regeneration.

METHODS

The scaffold was fabricated using the freeze-dryer method. Characterization was performed using Fourier Transform Infrared Spectroscopy (FTIR), energy-dispersive X-ray (EDX) analysis, and scanning electron microscopy (SEM). Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) were incorporated into the scaffold, and in vitro and in vivo assessments were conducted.

RESULTS

FTIR and EDX analyses confirmed the successful incorporation of nano-hydroxyapatite and dexamethasone. SEM revealed an interconnected porous structure with an average pore size of 28.55 µm. The scaffold loaded with WJ-MSCs significantly enhanced osteocyte and osteoblast populations, leading to improved mandibular bone formation. Histopathological evaluations demonstrated superior osteogenesis and angiogenesis.

CONCLUSION

The developed porous nanohybrid scaffold shows potential as a promising biomaterial for bone tissue engineering applications.

New Three Dimensional-Printed Polyethylene Terephthalate Glycol Liners for Hip Joint Endoprostheses: A Bioactive Platform for Bone Regeneration

Osteoporosis and bone defects are commonly observed in postmenopausal women, often linked to decreased folic acid levels, which play a crucial role in bone metabolism and regeneration. This study investigates 3D-printed polyethylene terephthalate glycol (PETG)-based porous scaffolds impregnated with chitosan (CS), hydroxyapatite (HAp), and folic acid (FA) for bone tissue engineering applications. The PETG-CS scaffold serves as the primary structural framework, with HAp incorporated to enhance bioactivity through its osteoconductive and osteoinductive properties. FA was included to address potential deficiencies in bone quality and to stimulate cellular differentiation. The scaffolds were fabricated using precise 3D printing techniques, yielding structures with controlled porosity. Physicochemical analyses confirmed the successful integration of HAp and FA into the PETG-CS matrix. Biological evaluations using preosteoblast cell lines demonstrated enhanced cell viability, proliferation, and biocompatibility of the scaffolds. These findings highlight the promising applications of PETG-CS-HAp-FA scaffolds in bone tissue engineering, providing a platform for future investigations into personalized regenerative therapies.

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.

Clinical challenges in bone tissue engineering - A narrative review

Bone tissue engineering (BTE) has emerged as a promising approach to address large bone defects caused by trauma, infections, congenital malformations, and tumors. This review focuses on scaffold design, cell sources, growth factors, and vascularization strategies, highlighting their roles in developing effective treatments. We explore the complexities of balancing mechanical properties, porosity, and biocompatibility in scaffold materials, alongside optimizing mesenchymal stem cell delivery methods. The critical role of growth factors in bone regeneration and the need for controlled release systems are discussed. Vascularization remains a significant hurdle, with strategies such as angiogenic factors, co-culture systems, and bioprinting under investigation. Mechanical challenges, tissue responses, and inflammation management are examined, alongside gene therapy's potential for enhancing osteogenesis and angiogenesis via both viral and non-viral delivery methods. The review emphasizes the impact of patient-specific factors on bone healing outcomes and the importance of personalized approaches. Future directions are described, emphasizing the necessity of interdisciplinary cooperation to advance the field of BTE and convert laboratory results into clinically feasible solutions.

Porcine Bone Extracellular Matrix Hydrogel as a Promising Graft for Bone Regeneration

Bone defects resulting from trauma, tumors, or congenital conditions pose significant challenges for natural healing and often require grafting solutions. While autografts remain the gold standard, their limitations, such as restricted availability and donor site complications, underscore the need for alternative approaches. The present research investigates the potential of porcine-derived bone extracellular matrix (pbECM) hydrogel as a highly promising bioactive scaffold for bone regeneration, comparing it to the human-derived bECM (hbECM). Porcine and human cancellous bones were decellularized and characterized in terms of their composition and structure. Further, the ECMs were processed into hydrogels, and their rheological properties and cytocompatibility were studied in vitro while their biocompatibility was studied in vivo using a mouse model. The potential of the pbECM hydrogel as a bone graft was evaluated in vivo using a rat femoral defect model. Our results demonstrated the excellent preservation of essential ECM components in both the pbECM and hbECM with more than 90% collagen out of all proteins. Rheological analyses revealed the superior mechanical properties of the pbECM hydrogel compared to the hbECM, with an approximately 10-fold higher storage modulus and a significantly later deformation point. These stronger gel properties of the pbECM were attributed to the higher content of structural proteins and residual minerals. Both the pbECM and hbECM effectively supported mesenchymal stem cell adhesion, viability, and proliferation, achieving a 20-fold increase in cell number within 10 days and highlighting their strong bioactive potential. In vivo, pbECM hydrogels elicited a minimal immunogenic response. Most importantly, when implanted in a rat femoral defect model, pbECM hydrogel had significantly enhanced bone regeneration through graft integration, stem cell recruitment, and differentiation. New bone formation was observed at an average of 50% of the defect volume, outperforming the commercial demineralized bone matrix (DBM), in which the new bone filled only 35% of the defect volume. These results position pbECM hydrogel as a highly effective and biocompatible scaffold for bone tissue engineering, offering a promising alternative to traditional grafting methods and paving the way for future clinical applications in bone repair.

Enhancement of In Vivo Bone Regeneration by the Carbohydrate Derivative DP2

Background/Objectives: Delays in bone healing and complications of remodeling constitute a major medical problem-particularly in older adults and patients with comorbidities. Current therapeutic approaches are based on strategies that promote bone regeneration. We recently identified a disaccharide compound (DP2) that enhances in vitro mineralization in human osteoblast cells via the early activation of Runx2 and the induction of osteoblast differentiation. Methods: First, a calcium quantification assay was performed to assess mineralization in MC3T3-E1 cells. Next, microcomputed tomography and histological analyses were used to examine in vivo bone repair in a rat 5 mm cranial defect model following the implantation of DP2 coupled to a micro/macroporous biphasic CaP ceramic (MBCP+) or collagen scaffold. Results: Here, we demonstrated that DP2 induced osteogenic differentiation and significantly elevated calcium matrix deposition in the murine preosteoblast cell line MC3T3-E1. We found that treatment with DP2 coupled to MBCP+ repaired the calvarial defect on post-implantation day 91. It significantly increased bone mineral density starting on day 29 post-treatment. In addition, DP2 did not induce ectopic bone formation. Conclusions: Taken as a whole, these results show that DP2 is a promising candidate treatment for delayed bone healing.

A Mechanically Stimulated Co-culture in 3-Dimensional Composite Scaffolds Promotes Osteogenic and Anti-osteoclastogenic Activity and M2 Macrophage Polarization

Bone is subjected to a plethora of mechanical stresses, which have been found to directly influence the equilibrium between bone resorption and formation. Taking this into account, we present herein a novel biomimicking 3-dimensional model that applies cyclic uniaxial compression onto cells co-cultured on 3-dimensionally printed scaffolds consisting of poly L-lactic acid/poly(ε-caprolactone)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/Sr-nanohydroxyapatite. The aim is to investigate how compression can modulate the balance between osteogenesis and osteoclastogenesis in co-culture, as well as the polarization of macrophages. One of the key aspects of the current study is the unprecedented development of a growth-factor-free co-culture, sustainable solely by the cross talk between human bone marrow mesenchymal stem cells and human peripheral blood mononuclear cells for their survival and osteogenic/osteoclastogenic differentiation capacity, respectively. Real-time polymerase chain reaction gene expression analysis of the mechanically stimulated constructs revealed up-regulation of the osteogenesis-related markers osteocalcin, osteoprotegerin, and runt-related transcription factor 2, with concurrent down-regulation of the osteoclastogenic markers dendritic-cell-specific transmembrane protein, nuclear factor of activated T cells 1, and tartrate acid phosphatase. The secretion of the receptor activator of nuclear factor kappa-Β ligand and macrophage colony-stimulating factor, as determined from enzyme-linked immunosorbent assay, was also found to depict lower levels compared to static conditions. Finally, macrophage polarization was examined via confocal imaging of tumor necrosis factor-α and interleukin-10 secretion levels, as well as through nitric oxide synthase and arginase 1 markers' gene expression, with the results indicating stronger commitment toward the M2 phenotype after mechanical stimulation.

Engineered Living Systems Based on Gelatin: Design, Manufacturing, and Applications

Engineered living systems (ELSs) represent purpose-driven assemblies of living components, encompassing cells, biomaterials, and active agents, intricately designed to fulfill diverse biomedical applications. Gelatin and its derivatives have been used extensively in ELSs owing to their mature translational pathways, favorable biological properties, and adjustable physicochemical characteristics. This review explores the intersection of gelatin and its derivatives with fabrication techniques, offering a comprehensive examination of their synergistic potential in creating ELSs for various applications in biomedicine. It offers a deep dive into gelatin, including its structures and production, sources, processing, and properties. Additionally, the review explores various fabrication techniques employing gelatin and its derivatives, including generic fabrication techniques, microfluidics, and various 3D printing methods. Furthermore, it discusses the applications of ELSs based on gelatin in regenerative engineering as well as in cell therapies, bioadhesives, biorobots, and biosensors. Future directions and challenges in gelatin fabrication are also examined, highlighting emerging trends and potential areas for improvements and innovations. In summary, this comprehensive review underscores the significance of gelatin-based ELSs in advancing biomedical engineering and lays the groundwork for guiding future research and developments within the field.

Application and progress of 3D printed biomaterials in osteoporosis

Osteoporosis results from a disruption in skeletal homeostasis caused by an imbalance between bone resorption and bone formation. Conventional treatments, such as pharmaceutical drugs and hormone replacement therapy, often yield suboptimal results and are frequently associated with side effects. Recently, biomaterial-based approaches have gained attention as promising alternatives for managing osteoporosis. This review summarizes the current advancements in 3D-printed biomaterials designed for osteoporosis treatment. The benefits of biomaterial-based approaches compared to traditional systemic drug therapies are discussed. These 3D-printed materials can be broadly categorized based on their functionalities, including promoting osteogenesis, reducing inflammation, exhibiting antioxidant properties, and inhibiting osteoclast activity. 3D printing has the advantages of speed, precision, personalization, etc. It is able to satisfy the requirements of irregular geometry, differentiated composition, and multilayered structure of articular osteochondral scaffolds with boundary layer structure. The limitations of existing biomaterials are critically analyzed and future directions for biomaterial-based therapies are considered.

A Procedural Overview of the Involvement of Small Molecules in the Nervous System in the Regulation of Bone Healing

Clinically, a multitude of factors can contribute to the development of bone defects. In the process of bone healing, the nervous system plays a vital role in bone regeneration. Small molecules from the nervous system, such as neurotrophic factors and neuropeptides, have been found to stimulate osteoblast proliferation and differentiation by activating signaling pathways associated with bone calcification and angiogenesis. These small molecules play a crucial regulatory role at various stages of bone healing. The systematic release mechanism of small molecules within the nervous system through diverse bone tissue engineering materials holds significant clinical implications for the controlled regulation of the bone healing process. This review provides an overview of the involvement of various nervous system small molecules at different stages of bone healing and discusses their regulatory mechanisms, aiming to establish a theoretical foundation for programmed regulation in bone regeneration and design of replacement materials in bone tissue engineering.

Regional Gene Therapy for Bone Tissue Engineering: A Current Concepts Review

The management of segmental bone defects presents a complex reconstruction challenge for orthopedic surgeons. Current treatment options are limited by efficacy across the spectrum of injury, morbidity, and cost. Regional gene therapy is a promising tissue engineering strategy for bone repair, as it allows for local implantation of nucleic acids or genetically modified cells to direct specific protein expression. In cell-based gene therapy approaches, a variety of different cell types have been described including mesenchymal stem cells (MSCs) derived from multiple sources-bone marrow, adipose, skeletal muscle, and umbilical cord tissue, among others. MSCs, in particular, have been well studied, as they serve as a source of osteoprogenitor cells in addition to providing a vehicle for transgene delivery. Furthermore, MSCs possess immunomodulatory properties, which may support the development of an allogeneic "off-the-shelf" gene therapy product. Identifying an optimal cell type is paramount to the successful clinical translation of cell-based gene therapy approaches. Here, we review current strategies for the management of segmental bone loss in orthopedic surgery, including bone grafting, bone graft substitutes, and operative techniques. We also highlight regional gene therapy as a tissue engineering strategy for bone repair, with a focus on cell types and cell sources suitable for this application.

Adaptability of Electrospun PVDF Nanofibers in Bone Tissue Engineering

This study focused on the development of a suitable synthetic polymer scaffold for bone tissue engineering applications within the biomedical field. The investigation centered on electrospun polyvinylidene fluoride (PVDF) nanofibers, examining their intrinsic properties and biocompatibility with the human osteosarcoma cell line Saos-2. The influence of oxygen, argon, or combined plasma treatment on the scaffold's characteristics was explored. A comprehensive design strategy is outlined for the fabrication of a suitable PVDF scaffold, encompassing the optimization of electrospinning parameters with rotating collector and plasma etching conditions to facilitate a subsequent osteoblast cell culture. The proposed methodology involves the fabrication of the PVDF tissue scaffold, followed by a rigorous series of fundamental analyses encompassing the structural integrity, chemical composition, wettability, crystalline phase content, and cell adhesion properties.

Oyster Shell Powder/PCL Composite Scaffolds Loaded with Psoralen Nanospheres Promote Large Bone Defect Repair

Research on bone substitutes for repairing bone defects has drawn increasing attention, and the efficacy of three-dimensional (3D) printed bioactive porous scaffolds for bone defect repair has been well documented. Our previous studies have shown that psoralen can promote osteogenesis by activating the Wnt/β-catenin and BMP/Smad signaling pathways and their crosstalk effects, and psoralen nanospheres have a good osteogenesis-promoting effect in vitro with low cytotoxicity. The Chinese medicine oyster shell powder, characterized by its porous structure, strong adsorption, and unique bioactivity, has potential in fracture-promoting repair materials. However, the effect of loading psoralen nanospheres onto oyster shell powder/polycaprolactone (OSP/PCL) scaffolds to repair bone defects is unclear. In this study, composite scaffolds consisting of OSP PCL were prepared by 3D printing, and psoralen nanospheres were adhered to the scaffolds. The characterization features of the composite scaffold system were investigated in vitro concerning the biocompatibility of bone mesenchymal stem cells (BMSCs). The efficacy of the composite scaffolds for repairing bone defects was explored in vivo through a rat cranial bone defect model. The results showed that the composite scaffolds were homogeneous porous structures with high mechanical strength and could be adhered well by the psoralen-loaded nanospheres. In vitro studies showed that the scaffolds had good biocompatibility with BMSCs and positively affected the expression of osteogenic differentiation-related proteins. In vivo studies showed that the composite scaffolds could more effectively promote the formation of new bone in the defect area (Φ5 mm) compared to the pure PCL scaffolds. At the same time, the composite scaffolds containing psoralen had a more significant stimulating effect on the healing of the cranial defects compared with the OSP/PCL scaffolds without psoralen.

Mimicking the Bone Extracellular Matrix through a Calcium Phosphate-Containing Thiol-Ene Cross-Linked Gelatin Composite

Hydroxyapatite (HAP) and amorphous calcium phosphate (ACP) nanoparticles were incorporated into a thiol-ene clickable gelatin network to elucidate to what extent osteogenic differentiation of human dental pulp- and adipose-derived stem cells (HDPSCs/HASCs) could be further boosted. ACP nanoparticles increased the specific surface area by 23% and reduced the density by 13% while maintaining a comparable particle size (ACP: 25 ± 3 nm; HAP: 27 ± 3 nm). Overall, the incorporation of ceramic nanoparticles did not significantly alter the mechanical properties of the ceramic-containing composites compared to the unsubstituted thiol-ene network. ACP nanoparticles at high concentrations promoted a 21-day osteogenic response in HASCs (72.09 ± 20.20 ng Ca2+/ng DNA) comparable to HDPSCs, with the latter showing high calcium production irrespective of the ceramic content (78.45 ± 10.87 ng Ca2+/ng DNA), suggesting that the provided cues must be optimized according to the investigated cell type toward a cell-interactive coating application stimulating osteogenesis.

Effects of Insulin-like Growth Factor 1 on the Maintenance of Cell Viability and Osteogenic Differentiation of Gingiva-Derived Mesenchymal Stem Cell Spheroids

Background and Objectives: Insulin-like growth factor-1 (IGF-1) plays a vital role in various cellular processes, including those involving stem cells. This study evaluated the effects of IGF-1 on cell survival, osteogenic differentiation, and mRNA expression in gingiva-derived mesenchymal stem cell spheroids. Materials and Methods: Using concave microwells, spheroids were generated in the presence of IGF-1 at concentrations of 0, 10, and 100 ng/mL. Cellular vitality was qualitatively assessed using microscopy, while a water-soluble tetrazolium salt-based assay kit quantified cellular viability. Osteogenic differentiation was evaluated via alkaline phosphatase activity and an anthraquinone dye test to measure calcium deposition. Additionally, quantitative polymerase chain reaction (qPCR) analysis was performed to determine the expression of RUNX2 and COL1A1. Results: By day 1, the stem cell spheroids had successfully formed, and their morphology remained stable over the following 7 days. The IGF-1 concentrations tested showed no significant differences in cell viability. Similarly, alkaline phosphatase activity on day 7 revealed no observable changes. However, on day 7, the incorporation of IGF-1 led to an increase in Alizarin Red staining, indicative of enhanced calcium deposition. Notably, an IGF-1 concentration of 100 ng/mL significantly upregulated the expression of COL1A1. Conclusions: These findings suggest that IGF-1 supports the maintenance of cell viability and promotes the expression of COL1A1 in gingiva-derived mesenchymal stem cell spheroids, highlighting its potential role in enhancing osteogenic differentiation. Future research should include long-term studies to evaluate the sustainability of IGF-1-induced effects on stem cell spheroids.

Controlled delivery of mesenchymal stem cells via biodegradable scaffolds for fracture healing

Biodegradable controlled delivery systems for mesenchymal stem cells (MSCs) have emerged as novel advancements in the field of regenerative medicine, particularly for accelerating bone fracture healing. This detailed study emphasizes the importance of quick and adequate fracture treatment and the limitations of existing methods. New approaches employing biodegradable scaffolds can be placed within a fracture to serve as a mechanical support and allow controlled release of in situ MSCs and bioactive agents. They are made up of polymers and composites which degrade over time, aiding in natural tissue regrowth. The fabrication methods, including 3D printing, electrospinning, and solvent casting, with particulate leaching that enable precise control over scaffold architecture and properties, are discussed. Progress in controlled drug delivery systems including encapsulation techniques and release kinetics is described, highlighting the potential of such strategies to maintain therapeutic benefits over a prolonged time as well as improving outcomes for fracture repair. MSCs play a role in bone regeneration through differentiation using biodegradable scaffolds, paracrine effects, and regulation of inflammation focusing on fracture healing. Current trends and future directions in scaffold technology and MSC delivery, including smart scaffolds with growth factor incorporation and innovative delivery approaches for fracture healing are also discussed.

Tissue Engineering 3D-Printed Scaffold Using Allograft/Alginate/Gelatin Hydrogels Coated With Platelet-Rich Fibrin or Adipose Stromal Vascular Fraction Induces Osteogenesis In Vitro

Incorporating autologous patient-derived products has become imperative to enhance the continually improving outcomes in bone tissue engineering. With this objective in mind, this study aimed to evaluate the osteogenic potential of 3D-printed allograft-alginate-gelatin scaffolds coated with stromal vascular fraction (SVF) and platelet-rich fibrin (PRF). The primary goal was to develop a tissue-engineered construct capable of facilitating efficient bone regeneration through the utilization of biomaterials with advantageous properties and patient-derived products. To achieve this goal, 3D-printed gelatin, allograft, and alginate scaffolds were utilized, along with stem cells derived from the buccal fat pad and human-derived components (PRF, SVF). Cells were seeded onto scaffolds, both with and without SVF/PRF, and subjected to comprehensive assessments including adhesion, proliferation, differentiation (gene expression and protein secretion levels), penetration, and gene expression analysis over 14 days. The data was reported as mean ± standard deviation (SD). Two-way or one-way analysis of variance (ANOVA) was performed, followed by a Tukey post hoc test for multiple comparisons. Statistical significance was determined as a p value below 0.05. The scaffolds demonstrated structural integrity, and the addition of PRF coatings significantly enhanced cellular adhesion, proliferation, and differentiation compared to other groups. Gene expression analysis showed increased expression of osteogenic and angiogenic markers in the PRF-coated scaffolds. These findings highlight the promising role of PRF-coated scaffolds in promoting osteogenesis and facilitating bone tissue regeneration. This study emphasizes the development of patient-specific tissue-engineered constructs as a valuable approach for effective bone regeneration.

Wharton's Jelly Mesenchymal Stem Cells: Shaping the Future of Osteoarthritis Therapy with Advancements in Chitosan-Hyaluronic Acid Scaffolds

This review explores the potential of Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) in cartilage regeneration and osteoarthritis treatment. It covers key factors influencing chondrogenesis, including growth factors, cytokines, and hypoxia, focusing on precise timing. The effectiveness of three-dimensional cultures and scaffold-based strategies in chondrogenic differentiation is discussed. Specific biomaterials such as chitosan and hyaluronic acid are highlighted for tissue engineering. The document reviews clinical applications, incorporating evidence from animal research and early trials and molecular and histological assessments of chondrogenic differentiation processes. It addresses challenges and strategies for optimizing MSC-derived chondrocyte therapy, emphasizing the immunomodulatory properties of these cells. The review concludes as a comprehensive road map for future research and clinical applications in regenerative medicine.

Standardization and consensus in the development and application of bone organoids

Organoids, self-organized structures derived from stem cells cultured in a specific three-dimensional (3D) in vitro microenvironment, have emerged as innovative platforms that closely mimic in vivo cellular behavior, tissue architecture, and organ function. Bone organoids, a frontier in organoid research, can replicate the complex structures and functional characteristics of bone tissue. Recent advancements have led to the successful development of bone organoids, including models of callus, woven bone, cartilage, trabecular bone, and bone marrow. These organoids are widely utilized in establishing bone-related disease models, bone injury repair, and drug screening. However, significant discrepancies remain between current bone organoids and human skeletal tissues in terms of morphology and functionality, limiting their ability to accurately model human bone physiology and pathology. To address these challenges and promote standardization in the construction, evaluation, and application of bone organoids, we have convened experts and research teams with substantial expertise in the field. By integrating existing research findings, this consortium aims to establish a consensus to guide future research and application of bone organoids.

Bone Tissue Engineering: From Biomaterials to Clinical Trials

Bone tissue engineering is a promising field that aims to rebuild the bone tissue using biomaterials, cells, and signaling molecules. Materials like natural and synthetic polymers, inorganic materials, and composite materials are used to create scaffolds that mimic the hierarchical microstructure of bone. Stem cells, particularly mesenchymal stem cells (MSCs), play a crucial role in bone tissue engineering by promoting tissue regeneration and modulating the immune response. Growth factors like bone morphogenetic proteins (BMPs), vascular endothelial growth factor (VEGF), and platelet-derived growth factor (PDGF) are utilized to accelerate bone regeneration. Clinical applications include treating nonunion and mal-union fractures, osteonecrosis, orthopedic surgery, dental applications, and spinal cord injuries. Recent advances in the field include nanotechnology, 3D printing, bioprinting techniques, gene editing technologies, and microfluidic devices for drug testing. However, challenges remain, such as standardization of protocols, large-scale biomaterial production, personalized medicine approaches, cost-effectiveness, and regulatory issues. Current clinical trials are investigating the safety and efficacy of various bone tissue engineering approaches, with the potential to modernize patient care by providing more adequate treatments for bone defects and injuries.

Biocompatibility and Bone Regeneration by Shape Memory Polymer Scaffolds

Biodegradable, shape memory polymer (SMP) scaffolds based on poly(ε-caprolactone) (PCL) offer unique advantages as a regenerative treatment strategy for critical-sized bone defects. In particular, a conformal fit may be achieved following exposure to warm saline, thereby improving osseointegration and regeneration. Advancing the clinical translation of these SMP scaffolds requires establishment of efficacy not only in non-loading models, but also load-bearing or load-sharing models. Thus, the present study evaluated the biocompatibility and bone regeneration potential of SMP scaffolds in a rabbit distal femoral condyle model. Two distinct SMP scaffold compositions were evaluated, a "PCL-only" scaffold formed from PCL-diacrylate (PCL-DA) and a semi-interpenetrating network (semi-IPN) formed from PCL-DA and poly(L-lactic acid) (PCL:PLLA). Semi-IPN PCL:PLLA scaffolds possess greater rigidity and faster rates of degradation versus PCL scaffolds. In vivo biocompatibility was assessed with a rat subcutaneous implantation model, whereas osseointegration was assessed with a 4 mm × 8 mm rabbit distal femoral condyle defect model. Both types of SMP scaffolds exhibited excellent biocompatibility marked by infiltration with fibrous tissue and a minimal inflammatory response. When implanted in the rabbit distal femur, both SMP scaffolds supported bone ingrowth. Collectively, these results demonstrate that the SMP scaffolds are biocompatible and integrate with adjacent host osseous tissues when implanted in vivo in a load-sharing environment. This study provides key proof-of-concept data necessary to proceed with large animal translational studies and clinical trials in human subjects.

Application of collagen in bone regeneration

At present, there is a significant population of individuals experiencing bone deficiencies caused by injuries, ailments affecting the bones, congenital abnormalities, and cancer. The management of substantial bone defects a significant global orthopedic challenge due to the intricacies involved in promoting and restoring the growth of fresh osseous tissue. Autografts are widely regarded as the "gold standard" for repairing bone defects because of their superior tissue acceptance and ability to control osteogenesis. However, patients undergoing autografts may encounter various challenges, including but not limited to hernia, bleeding, nerve impairment, tissue death. Therefore, researchers in regenerative medicine are striving to find alternatives. Collagen is the most abundant protein in the human body, and its triple helix structure gives it unique characteristics that contribute to its strength and functionality in various tissues. Collagen is commonly processed into various forms such as scaffolds, sponges, membranes, hydrogels, and composite materials, due to its unique compatibility with the human body, affinity for water, minimal potential for immune reactions, adaptability, and ability to transport nutrients or drugs. As an alternative material in the field of bone regeneration, collagen is becoming increasingly important. The objective of this review is to provide a comprehensive analysis of the primary types and sources of collagen, their processes of synthesis and degradation, as well as the advancements made in bone regeneration research and its potential applications. A comprehensive investigation into the role of collagen in bone regeneration is undertaken, providing valuable points of reference for a more profound comprehension of collagen applications in this field. The concluding section provides a comprehensive overview of the prospective avenues for collagen research, underscoring their promising future and highlighting their significant potential in the field of bone regeneration. The Translational Potential of this Article. The comprehensive exploration into the diverse functions and translational potential of collagen in bone regeneration, as demonstrated in this review, these findings underscore their promising potential as a treatment option with significant clinical implications, thus paving the way for innovative and efficacious therapeutic strategies in this domain.

Impact of Vascular Endothelial Growth Factor on the Shape, Survival, and Osteogenic Transformation of Gingiva-Derived Stem Cell Spheroids

Background and Objectives: Vascular endothelial growth factor (VEGF) is a protein which stimulates the formation of new blood vessels, playing a crucial role in processes such as wound healing and tumor growth. Methods: This study investigated the effects of VEGF on cell viability and osteogenic differentiation in mesenchymal stem cell (MSC) spheroids. Stem cell spheroids were fabricated using concave microwells and cultured with VEGF at concentrations of 0, 0.01, 0.1, 1, and 10 ng/mL. Morphological assessments were conducted on days 1, 3, 5, and 7, while cell viability was evaluated using the LIVE/DEAD assay and Cell Counting Kit-8. Alkaline phosphatase activity (ALP) and calcium deposition were measured to assess osteogenic differentiation, and qPCR was used to analyze osteogenic marker expression. Results: The spheroids maintained their shape across all VEGF concentrations, with the largest diameter being at 0.01 ng/mL on day 1, which decreased over time. Cell viability was highest at 0.01 ng/mL VEGF, while calcium deposition peaked at 0.1 ng/mL. Osteogenic markers, including RUNX2, osteocalcin, and COL1A1, showed significant upregulation at 1 ng/mL VEGF. Conclusions: These results suggest that VEGF enhances early osteogenic differentiation in MSC spheroids, indicating its potential for bone repair and tissue regeneration. VEGF could be applied in clinical settings for bone healing, fracture repair, and regenerative dentistry treatments.

Medical applications and prospects of polylactic acid materials

Polylactic acid (PLA) is a biodegradable and bio-based polymer that has gained significant attention as an environmentally friendly alternative to traditional petroleum-based plastics. In clinical treatment, biocompatible and non-toxic PLA materials enhance safety and reduce tissue reactions, while the biodegradability allows it to breakdown over time naturally, avoiding a second surgery. With the emergence of nanotechnology and three-dimensional (3D) printing, medical utilized-PLA has been produced with more structural and biological properties at both micro and macro scales for clinical therapy. This review summarizes current applications of the PLA-based biomaterials in drug delivery systems, orthopedic treatment, tissue regenerative engineering, and surgery and medical devices, providing viewpoints regarding the prospective medical utilization.

Nanoarchitectonics for Advancing Bone Graft Technology: Integration of Silver Nanoparticles Against Bacteria and Fungi

Silver nanoparticles have garnered significant attention for their antimicrobial applications. The aim of this study was to develop and characterize a silver nanoparticle-enhanced bone graft and assess its antimicrobial and antibiofilm activities. Bone granules from bovine cancellous femur were impregnated with silver nanoparticles (50 nm). The antimicrobial and antibiofilm activity was tested against various pathogens, including Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans, Enterococcus faecalis, Acinetobacter baumannii, and Escherichia coli. Biocompatibility and resorption were evaluated in a mouse calvaria model. All the tested pathogens showed susceptibility to silver nanoparticles, with minimal inhibitory concentrations ranging from 0.25 to 4 mg/L. The silver nanoparticle scaffolds demonstrated a significant reduction in biofilm formation across all microorganisms. The graft exhibited a biocompatibility comparable to that of autologous bone, with reduced resorption rates. Additionally, the presence of nanoparticles did not impact radiolucency, and cytotoxicity remained minimal. Bone grafts impregnated with silver nanoparticles effectively reduce biofilm formation, suggesting their potential as a strategic material for various implant applications.

Hijacking plant skeletons for biomedical applications: from regenerative medicine and drug delivery to biosensing

The field of biomedical engineering continually seeks innovative technologies to address complex healthcare challenges, ranging from tissue regeneration to drug delivery and biosensing. Plant skeletons offer promising opportunities for these applications due to their unique hierarchical structures, desirable porosity, inherent biocompatibility, and adjustable mechanical properties. This review comprehensively discusses chemical principles underlying the utilization of plant-based scaffolds in biomedical engineering. Highlighting their structural integrity, tunable properties, and possibility of chemical modification, the review explores diverse preparation strategies to tailor plant skeleton properties for bone, neural, cardiovascular, skeletal muscle, and tendon tissue engineering. Such applications stem from the cellulosic three-dimensional structure of different parts of plants, which can mimic the complexity of native tissues and extracellular matrices, providing an ideal environment for cell adhesion, proliferation, and differentiation. We also discuss the application of plant skeletons as carriers for drug delivery due to their structural diversity and versatility in encapsulating and releasing therapeutic agents with controlled kinetics. Furthermore, we present the emerging role played by plant-derived materials in biosensor development for diagnostic and monitoring purposes. Challenges and future directions in the field are also discussed, offering insights into the opportunities for future translation of sustainable plant-based technologies to address critical healthcare needs.

Shape Memory Polymer Scaffolds-Utility for In Vitro Osteogenesis of Canine Multipotent Stromal Cells

A biodegradable, shape memory polymer (SMP) scaffold based on poly(ε-caprolactone) (PCL) represents an attractive alternative therapy for the repair of critically sized bone defects given its ability to press-fit within irregular defects. Clinical translation of SMP scaffolds requires successful movement beyond proof-of-concept rodent studies through a relevant large-animal model and into the clinical setting. In addition to representing a clinical veterinary population, the canine species is a strong translational model for humans due to similarities in orthopedic disorders, biomechanics, and bone healing. The present study was performed to assess in vitro cytocompatibility and osteogenic differentiation of canine multipotent stromal cells (cMSCs) cultured on SMP scaffolds in preparation for future canine in vivo studies. Two different SMP scaffold compositions were utilized: a "PCL-only" scaffold prepared from PCL-diacrylate (PCL-DA) and a semi-interpenetrating network (semi-IPN) formed from PCL-DA and poly(L-lactic acid) (PCL:PLLA). The PCL:PLLA scaffolds degrade faster and are more mechanically rigid versus the PCL scaffolds. Canine bone marrow-derived MSCs (cMSCs) were evaluated in terms of attachment, proliferation, and osteogenic differentiation. cMSCs exhibited excellent cytocompatibility, attachment, and proliferation on both SMP scaffold compositions. PCL scaffolds were more conducive to both early- and late-stage in vitro osteogenesis of cMSCs versus PCL:PLLA scaffolds. However, cMSCs deposited mineralized extracellular matrix over 21 days when cultured on both SMP scaffold compositions. These results demonstrate that the SMP scaffolds are suitable for in vitro cMSC attachment, proliferation, and osteogenic differentiation, representing a significant step toward canine in vivo studies and potential translation to human patients.

Masquelet Technique in the Management of Segmental Bone Defect of the Ulna: A Case Report

Surgeons periodically encounter challenging clinical scenarios that require them to develop nuanced management strategies to achieve the best outcome for the patient. This is especially true in medically underserved patient populations, where follow-up and proper recovery protocols are often not accomplished. In this report, we discuss the case of a 26-year-old female with a history of medical non-compliance who presented to the emergency department with signs and symptoms of surgical site infection two months following the repair of her comminuted ulna fracture caused by a gunshot wound. The decision was made to perform the Masquelet-induced membrane technique, as it is an option when confronted with segmental bone defects in patients in whom there is suspicion of noncompliance with recovery recommendations.

An In Vivo Assessment of Different Mesenchymal Stromal Cell Tissue Types and Their Differentiation State on a Shape Memory Polymer Scaffold for Bone Regeneration

A combined biomaterial and cell-based solution to heal critical size bone defects in the craniomaxillofacial area is a promising alternative therapeutic option to improve upon autografting, the current gold standard. A shape memory polymer (SMP) scaffold, composed of biodegradable poly(ε-caprolactone) and coated with bioactive polydopamine, was evaluated with mesenchymal stromal cells (MSCs) derived from adipose (ADSC), bone marrow (BMSC), or umbilical cord (UCSC) tissue in their undifferentiated state or pre-differentiated toward osteoblasts for bone healing in a rat calvarial defect model. Pre-differentiating ADSCs and UCSCs resulted in higher new bone volume fraction (15.69% ± 1.64%) compared to empty (i.e., untreated) defects and scaffold-only (i.e., unseeded) groups (4.41% ± 1.11%). Notably, only differentiated UCSCs exhibited a significant increase in new bone volume, surpassing both undifferentiated UCSCs and unseeded scaffolds. Further, differentiated ADSCs and UCSCs had significantly higher trabecular numbers than their undifferentiated counterparts, unseeded scaffolds, and untreated defects. Although the mineral density regenerated within the unseeded scaffold surpassed that achieved with cell seeding, the connectivity of this bone was diminished, as the regenerated tissue confined itself to the spherical morphology of the scaffold pores. The SMP scaffold alone, with undifferentiated BMSCs, with undifferentiated and differentiated ADSCs, and differentiated UCSCs (29.72 ± 1.49 N) demonstrated significant osseointegration compared to empty defects (14.34 ± 2.21 N) after 12 weeks of healing when assessed by mechanical push-out testing. Based on these results and tissue availability to obtain the cells, pre-differentiated ADSCs and UCSCs emerge as particularly promising candidates when paired with the SMP scaffold for repairing critical size bone defects in the craniofacial skeleton.

Quercetin-based biomaterials for enhanced bone regeneration and tissue engineering

Quercetin, a natural flavonoid, has been extensively researched for its potential in promoting bone regeneration and tissue engineering. This review aimed to provide a comprehensive overview of the applications of quercetin-based biomaterials in bone regeneration and tissue engineering. The review discusses several studies that have integrated quercetin into biomaterials such as electrospun fibers, hydrogels, microspheres, and nanoparticles. These biomaterials are engineered to imitate the natural extracellular matrix of bone, creating an environment conducive to cell attachment, growth, and differentiation. The investigations presented emphasize the potential of quercetin-derived biomaterials in improving bone regeneration, decreasing oxidative stress and inflammation, and facilitating bone tissue restoration. These biomaterials have demonstrated the ability to facilitate cell encapsulation, maintain consistent quercetin release patterns, and have been applied in a range of uses such as bone grafts, implants, and tissue engineering scaffolds. Biomaterials derived from quercetin are utilized in the treatment of bone-related disorders, including osteoporosis and bone defects. These materials enhance bone regeneration by providing a scaffold for new bone growth, promoting the development of new bone tissue, and improving the mechanical properties of bone tissue.

Chitosan microcarriers loaded with functional drug for stimulating osteogenesis and angiogenesis in vitro

Angiogenesis-osteogenesis coupling plays important roles in bone regeneration; therefore, biomaterials capable of stimulating both osteogenesis and angiogenesis show significant influence in bone repair. Herein, chitosan (CS) microcarriers loaded with functional drug dimethyloxalylglycine (DMOG) were prepared using the emulsion phase separation and impregnation method for stimulating osteogenesis and angiogenesis. FTIR and zeta potential analyses confirmed successful DMOG loading into CS microcarriers, primarily through physical adsorption, particularly hydrogen-bond interaction. As the impregnation concentration of DMOG increased, the amounts of DMOG loaded into the microcarriers increased, while the drug encapsulation efficiency decreased. All microcarriers, ranging in size from 200 to 400 μm, revealed quasi-spherical shapes and an interconnected porous structure with pore sizes mainly between 15 and 30 μm, suitable for cell attachment and proliferation. The introduction of DMOG increased the residues of the microcarriers during thermogravimetric analysis. CS/DMOG microcarriers exhibited sustained drug release (for >19 days) and good degradation ability. Furthermore, CS/DMOG microcarriers supported stem cell adhesion and proliferation. They also enhanced stem cell osteogenesis verified by strengthening alkaline phosphatase expression and mineralization. Moreover, they promoted angiogenesis, as evidenced by stimulating endothelial cell migration and tube formation. These results suggest that CS/DMOG microcarriers have the potential to be used for bone tissue regeneration.

Borosilicate bioactive glasses with added Mg/Sr enhances human adipose-derived stem cells osteogenic commitment and angiogenic properties

Bioactive glasses are one of the most promising materials for applications in bone tissue engineering. In this study, the focus was on borosilicate bioactive glasses with composition 47.12 SiO2 - 6.73 B2O3 - 21.77-x-y CaO - 22.65 Na2O - 1.72 P2O5 - x MgO - y SrO (mol%). These compositions are based on silicate S53P4 bioactive glass, from where 12.5% of SiO2 is replaced with B2O3, and additionally, part of CaO is substituted for MgO and/or SrO. The impact of ion release, both as extract and in direct contact, on human adipose-derived stem cells' (hADSCs) viability, proliferation, ECM maturation, osteogenic commitment and endothelial marker expression was assessed. Osteogenic media supplements were utilized with the extracts, and in part of the direct cell/material culturing conditions. While it has been reported in other studies that boron release can induce cytotoxicity, the glasses in this study supported cells viability and proliferation. Moreover, borosilicate's, especially with further Mg/Sr substitutions, upregulated several osteogenic markers (such as RUNX2a, OSTERIX, DLX5, OSTEOPONTIN), as well as angiogenic factors (e.g., vWF and PECAM-1). Furthermore, the studied glasses supported collagen-I production even in the absence of osteogenic supplements, when hADSCs were cultured in contact with the glasses, suggesting that while the bioactive glass degradation products are beneficial for osteogenesis, the glasses surface physico-chemical properties play a significant role on hADSCs differentiation. This study brings critical information on the impact of bioactive glass compositional modification to control glass dissolution and the subsequent influence on stem cells proliferation and differentiation. Furthermore, the role of the material surface chemistry on promoting cell differentiation is reported.

The Future of Bone Repair: Emerging Technologies and Biomaterials in Bone Regeneration

Bone defects and fractures present significant clinical challenges, particularly in orthopedic and maxillofacial applications. While minor bone defects may be capable of healing naturally, those of a critical size necessitate intervention through the use of implants or grafts. The utilization of traditional methodologies, encompassing autografts and allografts, is constrained by several factors. These include the potential for donor site morbidity, the restricted availability of suitable donors, and the possibility of immune rejection. This has prompted extensive research in the field of bone tissue engineering to develop advanced synthetic and bio-derived materials that can support bone regeneration. The optimal bone substitute must achieve a balance between biocompatibility, bioresorbability, osteoconductivity, and osteoinductivity while simultaneously providing mechanical support during the healing process. Recent innovations include the utilization of three-dimensional printing, nanotechnology, and bioactive coatings to create scaffolds that mimic the structure of natural bone and enhance cell proliferation and differentiation. Notwithstanding the advancements above, challenges remain in optimizing the controlled release of growth factors and adapting materials to various clinical contexts. This review provides a comprehensive overview of the current advancements in bone substitute materials, focusing on their biological mechanisms, design considerations, and clinical applications. It explores the role of emerging technologies, such as additive manufacturing and stem cell-based therapies, in advancing the field. Future research highlights the need for multidisciplinary collaboration and rigorous testing to develop advanced bone graft substitutes, improving outcomes and quality of life for patients with complex defects.

Polyhydroxyalkanoates: Medical Applications and Potential for Use in Dentistry

Polyhydroxyalkanoates (PHAs) are promising biopolymers as an alternative to traditional synthetic polymers due to their biodegradability and biocompatibility. The PHA market is blooming in response to the growing demand for biodegradable and environmentally friendly plastics. These biopolyesters are produced and degraded by a variety of microorganisms, making them environmentally friendly, while offering benefits such as biocompatibility (when adequately processed) and biodegradability. Their versatility extends to various areas, from biomedicine to agriculture and composite materials, where they pave the way for significative innovations. In the field of regenerative medicine, some PHAs have key applications, namely in vascular grafts, oral tissue regeneration, and development of self-healing polymers. In addition, PHAs have the potential to be used in the creation of dental implant materials and dental medical devices. PHAs can also be used to encapsulate hydrophobic drugs, providing an approach for more targeted and effective treatments. To summarize, PHAs open new perspectives in the field of medicine by improving drug delivery and offering ecologically biocompatible solutions for medical devices. The aim of this review is to present the medical and dental applications of PHA, their advantages, disadvantages, and indications.

Cellulose nano-dispersions enhanced by ultrasound assisted chemical modification drive osteoblast proliferation and differentiation in PVA/HA bone tissue engineering scaffolds

To develop a biological bone tissue scaffold with uniform pore size and good cell adhesion was both challenging and imperative. We prepared modified cellulose nanocrystals (CNCs) dispersants (K-PCNCs) by ultrasound-assisted alkylation modification. Subsequently, nano-hydroxyapatite (HC-K) was synthesized using K-PCNCs as a dispersant and composited with polyvinyl alcohol (PVA) to prepare the scaffold using the ice template method. The results showed that the water contact angle and degree of substitution (135°, 1.53) of the K-PCNCs were highest when the ultrasound power was 450 W and the time was 2 h. The dispersion of K-PCNCs prepared under this condition was optimal. SEM showed that the pore distribution of the composite scaffolds was more homogeneous than the PVA scaffold. The porosity, equilibrium swelling rate, and mechanical properties of the composite scaffolds increased and then decreased with the increase of HC-K content, and reached the maximum values (56.1 %, 807.7 %, and 0.085 ± 0.004 MPa) at 9 % (w/w) of HC-K content. Cell experiments confirmed scaffold has good cytocompatibility and mineralization capacity. The ALP activity reached 1.71 ± 0.25 (ALP activity/mg protein). In conclusion, the scaffolds we developed have good biocompatibility and mechanical properties and have great potential in promoting bone defect repair.

Combining three-dimensionality and CaP glass-PLA composites: Towards an efficient vascularization in bone tissue healing

Bone regeneration often fails due to implants/grafts lacking vascular supply, causing necrotic tissue and poor integration. Microsurgical techniques are used to overcome this issue, allowing the graft to anastomose. These techniques have limitations, including severe patient morbidity and current research focuses on stimulating angiogenesis in situ using growth factors, presenting limitations, such as a lack of control and increased costs. Non-biological stimuli are necessary to promote angiogenesis for successful bone constructs. Recent studies have reported that bioactive glass dissolution products, such as calcium-releasing nanoparticles, stimulate hMSCs to promote angiogenesis and new vasculature. Moreover, the effect of 3D microporosity has also been reported to be important for vascularisation in vivo. Therefore, we used room-temperature extrusion 3D printing with polylactic acid (PLA) and calcium phosphate (CaP) based glass scaffolds, focusing on geometry and solvent displacement for scaffold recovery. Combining both methods enabled reproducible control of 3D structure, porosity, and surface topography. Scaffolds maintained calcium ion release at physiological levels and supported human mesenchymal stem cell proliferation. Scaffolds stimulated the secretion of vascular endothelial growth factor (VEGF) after 3 days of culture. Subcutaneous implantation in vivo indicated good scaffold integration and blood vessel infiltration as early as one week after. PLA-CaP scaffolds showed increased vessel maturation 4 weeks after implantation without vascular regression. Results show PLA/CaP-based glass scaffolds, made via controlled 3D printing, support angiogenesis and vessel maturation, promising improved vascularization for bone regeneration.

Enhancing bone repair through improved angiogenesis and osteogenesis using mesoporous silica nanoparticle-loaded Konjac glucomannan-based interpenetrating network scaffolds

We have fabricated and characterized novel bioactive nanocomposite interpenetrating polymer network (IPN) scaffolds to treat bone defects by loading mesoporous silica nanoparticles (MSNs) into blends of Konjac glucomannan, polyvinyl alcohol, and polycaprolactone. By loading MSNs, we developed a porous nanocomposite scaffold with mechanical strengths comparable to cancellous bone. In vitro cell culture studies proved the cytocompatibility of the nanocomposite scaffolds. RT-PCR studies confirmed that these scaffolds significantly upregulated major osteogenic markers. The in vivo chick chorioallantoic membrane (CAM) assay confirmed the proangiogenic activity of the nanocomposite IPN scaffolds. In vivo studies were performed using Wistar rats to evaluate the scaffolds' compatibility, osteogenic activity, and proangiogenic properties. Liver and renal function tests confirmed that these scaffolds were nontoxic. X-ray and μ-CT results show that the bone defects treated with the nanocomposite scaffolds healed at a much faster rate compared to the untreated control and those treated with IPN scaffolds. H&E and Masson's trichrome staining showed angiogenesis near the newly formed bone and the presence of early-stage connective tissues, fibroblasts, and osteoblasts in the defect region at 8 weeks after surgery. Hence, these advantageous physicochemical and biological properties confirm that the nanocomposite IPN scaffolds are ideal for treating bone defects.

Considerations of growth factor and material use in bone tissue engineering using biodegradable scaffolds in vitro and in vivo

Bone tissue engineering aims to harness materials to develop functional bone tissue to heal 'critical-sized' bone defects. This study examined a robust, coated poly(caprolactone) trimethacrylate (PCL-TMA) 3D-printable scaffold designed to augment bone formation. Following optimisation of the coatings, three bioactive coatings were examined, i) elastin-like polypeptide (ELP), ii) poly(ethyl acrylate) (PEA), fibronectin (FN) and bone morphogenetic protein-2 (BMP-2) applied sequentially (PEA/FN/BMP-2) and iii) both ELP and PEA/FN/BMP-2 coatings applied concurrently. The scaffold material was robust and showed biodegradability. The coatings demonstrated a significant (p < 0.05) osteogenic response in vitro in alkaline phosphatase gene upregulation and alkaline phosphatase production. The PCL-TMA scaffold and coatings supported angiogenesis and displayed excellent biocompatibility following evaluation on the chorioallantoic membrane assay. No significant (p < 0.05) heterotopic bone formed on the scaffolds within a murine subcutaneous implantation model, compared to the positive control of BMP-2 loaded collagen sponge following examination by micro-computed tomography or histology. The current studies demonstrate a range of innovative coated scaffold constructs with in vitro efficacy and clearly illustrate the importance of an appropriate in vivo environment to validate in vitro functionality prior to scale up and preclinical application.

Sclerostin Antibody-Loaded Dense Collagen Hydrogels Promote Critical-Size Bone Defect Repair

The management of extensive bone loss remains a clinical challenge. Numerous studies are underway to develop a combination of biomaterials, biomolecules, and stem cells to address this challenge. In particular, the systemic administration of antibodies against sclerostin, a regulator of bone formation, was recently shown to enhance the bone repair efficiency of dense collagen hydrogels (DCHs) hosting murine dental pulp stem cells (mDPSCs). The aim of the present study was to assess whether these antibodies, encapsulated and released from DCHs, could promote craniofacial bone repair by the local inhibition of sclerostin. In vitro studies showed that antibody loading modified neither the hydrogel structure nor the viability of seeded mDPSCs. When implanted in a mouse calvaria critical-size bone defect, antibody-loaded DCHs showed repair capabilities similar to those of acellular unloaded DCHs combined with antibody injections. Importantly, the addition of mDPSCs provided no further benefit. Altogether, the local delivery of antisclerostin antibodies from acellular dense collagen scaffolds is highly effective for bone repair. The drastic reduction in the required amount of antibody compared to systemic injection should reduce the cost of the procedure, making the strategy proposed here a promising therapeutic approach for large bone defect repair.