Recent advances in bone tissue engineering scaffolds

Synthesis and use of thermoplastic polymers for tissue engineering purposes

Thermoplastic polymers provide a versatile platform to mimic various aspects of physiological extracellular matrix properties such as chemical composition, stiffness, and topography for use in cell and tissue engineering applications. In this review, we provide a brief overview of the most promising thermoplastic polymers, and in particular the thermoplastic polyesters, such as poly(lactic acid), poly(glycolic acid), and polycaprolactone, and the thermoplastic elastomers, such as polyurethanes, polyhydroxyalkanoates, and poly(butyl cyanoacrylate). A particular focus has been made on the synthesis processes, the processability and the biocompatibility. We also discuss how these materials can be applied in tissue engineering, mimicking tissues' structure and function, and stimulate mesenchymal stem cells differentiation and mechanotransduction.

Hierarchically porous 3D-printed ceramic scaffolds for bone tissue engineering

Sacrificial templating offers the ability to create interconnected pores within 3D printed filaments and to control pore morphology. Beta-tricalcium phosphate (TCP) bone tissue engineering (BTE) scaffolds were fabricated with multiscale porosity: (i) macropores from direct ink writing (DIW, a material extrusion 3D printing technique), (ii) micropores from oil templating, and (iii) smaller micropores from partial sintering. The hierarchically porous scaffolds possessed a total porosity of 58-70 %, comprising 54-63 % interconnected open pores. The in vitro results demonstrated that scaffolds with macroporosity promoted human osteoblast growth more than scaffolds with only microporosity. The elongated pores from the capillary suspension filament microstructure induced greater cell spreading than the sphere-like pores from the emulsion. Overall, the hierarchically porous scaffold with capillary suspension TCP filaments provided a superior microenvironment for significantly higher cell viability and proliferation than the other scaffolds, including a poly(ε-caprolactone) (PCL) control, a material currently used clinically as porous BTE scaffolds. The cellular response was further enhanced when macropore size was in the range of 570-590 μm. Therefore, the hierarchically porous scaffolds in this study are promising as BTE scaffolds, and the reported process of DIW of oil-templated colloidal pastes is a feasible strategy with potential for further customization.

Antibacterial and osteogenic properties of chitosan-polyethylene glycol nanofibre-coated 3D printed scaffold with vancomycin and insulin-like growth factor-1 release for bone repair

3D printing, as a layer-by-layer manufacturing technique, enables the customization of tissue engineering scaffolds. Surface modification of biomaterials is a beneficial approach to enhance the interaction with living cells and tissues. In this research, a polylactic acid/polyethylene glycol scaffold containing 30 % bredigite nanoparticles (PLA/PEG/B) was fabricated utilizing fused deposition modeling (FDM) 3D printing. To modify the surface properties and facilitate the loading and release of therapeutics, the scaffold was coated with chitosan-polyethylene glycol (CS-PEG) nanofibers incorporating vancomycin (V) and insulin-like growth factor-1 (IGF1). The characterization was conducted using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results demonstrated that the release of V (93.43 %) and IGF1 (95.86 %) from the fabricated scaffolds persisted for 28 days in a phosphate-buffered saline (PBS) solution. The release of V resulted in antibacterial activity against Staphylococcus aureus (S. aureus), forming an inhibition zone of 21.16 mm. Additionally, it was demonstrated that the release of IGF1 could counteract the adverse effect of V release on cell behavior, and enhance the adhesion and proliferation of MG63 cells. Preclinical in vivo studies conducted on a rat calvarial defect model validated that the bone repair was fully completed in the group treated with the fabricated scaffold within 8 weeks. Consequently, the scaffold designed in this study can serve as a versatile scaffold for achieving perfect repair of craniofacial defects.

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.

Enhanced effects of levan hydrogels and bovine grafts on guided bone regeneration: In-vitro and in-vivo analysis

This study was performed to evaluate the regenerative capabilities of levan hydrogels when combined with conventional bone graft materials (Bio-Oss®) in guided bone regeneration (GBR). With the growing interest in the application of levan polysaccharide for regenerative purposes over the last decade, a noticeable gap in in-vivo validations remains. This research therefore fills this gap by utilizing the cytocompatibility and cell proliferation potential of levan hydrogels and marks a preliminary effort in its use in combination with Bio-Oss® for bone regeneration, which was examined both in-vitro and in-vivo for the first time. Considerable increases in cell viability (nearly 180 %) attributed to the addition of levan hydrogels alone and with Bio-Oss® (2:2) was detected. In parallel, a histological examination revealed a significant increase in new bone formation compared with the administration of Bio-Oss® alone. The results conclusively demonstrate for the first time that the combination of levan hydrogel with Bio-Oss® results in histopathologically superior new bone formation compared to Bio-Oss® used alone. Additionally, this combination promoted greater osteoblast density and neovascularization. These outcomes not only emphasize the potential of levan hydrogels in enhancing GBR but also suggest their broader applicability in bone regeneration strategies.

Critical roles of miR-21 in promotions angiogenesis: friend or foe?

MiRNAs are small RNA strands that are managed following transcription and are of substantial importance in blood vessel formation. It is essential to oversee the growth, differentiation, death, movement and construction of tubes by angiogenesis-affiliated cells. If miRNAs are not correctly regulated in regard to angiogenesis, it can deteriorate the health and lead to various illnesses, which include cancer, cardiovascular disorder, critical limb ischemia, Crohn's disease, ocular diseases, diabetic microvascular complications, and more. Consequently, it is vital to understand the crucial part that miRNAs play in the development of blood vessels, so we can develop reliable treatment plans for vascular diseases. This write-up will assess the critical role of miR-21/exosomal miR-21 in managing angiogenesis associated with bone growth, wound recovery, and other pathological conditions like tumor growth, ocular illnesses, diabetes, and other diseases connected to formation of blood vessels. Previous investigations have demonstrated that miR-21 is present at higher amounts in certain cancerous cells, and it influences a multitude of genes that moderate the increased creation of blood vessels. Furthermore, studies demonstrated that exosomal miR-21 has the capacity to interact with endothelial cells to foster tumor angiogenesis. For that reason, this review explains the critical importance of miR-21/exosomal miR-21 in managing both healthy and diseased states of angiogenesis.

Investigation to Understand the Role of Phase Variation in Red Emitting Eu3+-Doped Calcium Magnesium Silicate Phosphor for In Vitro Bioimaging

Eu3+-doped silicate phosphors are gaining significant attention for bioimaging and scaffold development due to their narrow red emission, high color purity, quantum yield (QY), and large Stokes shift. These phosphors offer several advantages over conventional imaging techniques, such as good selectivity and sensitivity, simpler operation, reduced data acquisition time, cost-effectiveness, and nondestructive imaging. The luminescence properties of these phosphors can be enhanced by modifying synthesis methods, annealing conditions, and hosts and introducing multiple dopants. This study explores a novel approach for improving luminescence by modifying the crystal structures of Eu3+ doped calcium magnesium silicate (CMS:Eu3+) phosphors for in vitro bioimaging and potential scaffold development. The synthesized diopside (CaMgSi2O6:xEu3+; x = 10, 15, and 20 mol %), merwinite (Ca3MgSi2O8:15 mol % Eu3+), and akermanite (Ca2MgSi2O7:15 mol % Eu3+) phases of CMS:Eu3+ exhibit distinct coordination environments for Eu3+, leading to unique excitation wavelength tunability from ultraviolet (UV) to the visible region, high emission intensity, decay time, QY > 40%, and color purity >83%. A comparative analysis of their structural and photoluminescence properties reveals the impact of phase modifications on luminescence for in vitro bioimaging by optimizing the dopant concentration. The results indicate that CaMgSi2O6: 15 mol % Eu3+ is the most efficient phosphor for in vitro bioimaging, with the highest relative emission intensity in the red region, decay time ∼2 ms, QY ∼ 77%, and color purity ∼86%. The unique morphology of Ca3MgSi2O8:15 mol %Eu3+ and Ca2MgSi2O7:15 mol % Eu3+ also supports cell adhesion, suggesting their potential in scaffold development. In brief, the study highlights the potential of CMS:Eu3+ phosphors for in vitro bioimaging and scaffold development by modifying phases and dopant concentrations.

Incorporation of forsterite nanoparticles in a 3D printed polylactic acid/polyvinylpyrrolidone scaffold for bone tissue regeneration applications

Three-dimensional (3D) printing has facilitated the fabrication of customized scaffolds for the repair of complex bone defects. In this study, 3D-printed scaffolds composed of a mixture of polylactic acid-polyvinylpyrrolidone (PLA-PVP) incorporating different amounts of forsterite (F; Mg2SiO4) nanoparticles were fabricated using fused deposition modeling (FDM) technique. The incorporation of PVP and F nanoparticles into the PLA scaffold significantly decreased the water drop contact angle. The mechanical properties of the PLA-PVP scaffold were enhanced with the addition of 10 % F nanoparticles, as the compressive yield strength increased from 10.8 to 16.0 MPa and the elastic modulus from 83.52 to 108.41 MPa. However, the addition of F nanoparticles increased the degradation rate of the PLA-PVP scaffold over 8 weeks. Importantly, the addition of 10 % F nanoparticles into the PLA-PVP scaffold improved bioactivity and formation of apatite deposits on the scaffold after 4 weeks of immersion in simulated body fluid. Moreover, the PLA-PVP/10F scaffold showed strong MG63 cell adhesion and proliferation, as well as promoting osteogenic differentiation of rat bone marrow mesenchymal stem cells. At last, these findings suggest the PLA-PVP/10F scaffold is a promising candidate for application in bone defect repair.

Role of phosphate-modified cellulose into the scaffold based on poly (glycerol azelaic acid)-co-poly(ε-caprolactone) for using bone regenerative medicine

Advancements in bone tissue engineering critically depend on the development of specialized scaffolds that promote effective bone regeneration. This study introduces innovative scaffolds composed of poly (glycerol azelaic acid) (PGAz) and poly (caprolactone) (PCL), enhanced with varying concentrations of phosphate modified cellulose (PMC) nanofibers. Utilizing citric acid as a green cross-linker enhances the eco-friendliness and biocompatibility of these scaffolds. The molecular structures were verified using Hydrogen 1H NMR and Carbon 13CNMR spectroscopy. Fourier Transform Infrared (FTIR) Spectroscopy confirmed successful integration of vital phosphate groups for biological functionality. Morphological and compositional analysis through Field Emission Scanning Electron Microscopy (FESEM) and Energy-Dispersive X-ray (EDX) mapping revealed homogeneous phosphate distribution and increased porosity across the scaffolds. Thermogravimetric Analysis (TGA) demonstrated that higher PMC concentrations improve thermal stability, enhancing scaffold resilience. Mechanical testing showed that scaffolds with 5 % PMC provide an optimal balance of compressive strength, compressive modulus, and compressive strain, suitable for bone tissue engineering. Dynamic water contact angle studies highlighted significant hydrophilic enhancements, crucial for cell attachment and proliferation. Hydrolytic degradation tests indicated that increased PMC accelerates degradation rates, aligning with tissue regeneration timelines. Hematoxylin and Eosin (H&E) staining and MTT assays, along with FESEM imaging of L929 mouse fibroblast cells cultured on the scaffolds, confirmed biocompatibility and cellular proliferation, particularly with 5 % PMC. These findings underscore the potential of PGAz-co-PCL scaffolds in advancing bone tissue regeneration through superior mechanical, thermal, and biological properties.

Induced mesenchymal stem cells generated from periodontal ligament fibroblast for regenerative therapy

Bone fractures and bone loss represent significant global health challenges, with their incidence rising due to an aging population. Despite autologous bone grafts remain the gold standard for treatment, challenges such as limited bone availability, immune reactions, and the risk of infectious disease transmission have driven the search for alternative cell-based therapies for bone regeneration. Stem cells derived from oral tissues and umbilical cord mesenchymal stem cells (MSCs) have shown potential in both preclinical and clinical studies for bone tissue regeneration. However, their limited differentiation capacity and wound healing abilities necessitate the exploration of alternative cell sources. In this study, we generated induced pluripotent stem cells (iPSCs) using a safe, nonviral and mRNA-based approach from human periodontal ligament fibroblasts (PDLF), an easily accessible cell source. These iPSCs were subsequently differentiated into MSCs, referred to as induced MSCs (iMSCs). The resulting iMSCs were homogeneous, highly proliferative, and possessed anti-inflammatory properties, suggesting their potential as a superior alternative to traditional MSCs for regenerative therapy. These iMSCs demonstrated trilineage differentiation potential, giving rise to osteocytes, chondrocytes, and adipocytes. The iMSC-derived osteocytes (iOSTs) were homogeneous, patient-specific and showed excellent attachment and growth on commercial collagen-based membranes, highlighting their suitability for bone tissue regeneration applications. Given their promising characteristics compared to traditional MSCs, PDLF-derived iMSCs are strong candidates for future clinical studies in bone regeneration and other regenerative dental therapies.

Advances in three-dimensional printing of hydrogel formulations for vascularized tissue and organ regeneration

Over the last decades, three-dimensional (3D) printing has emerged as one of the most promising alternative tissue and organ regeneration technologies. Recent advances in 3D printing technology, particularly in hydrogel-derived bioink formulations, offer promising solutions for fabricating intricate, biomimetic scaffolds that promote vascularization. In this review, we presented numerous studies that have been conducted to fabricate 3D-printed hydrogel vascularized constructs with significant advancements in printing integumentary systems, cardiovascular systems, vascularized bone tissues, skeletal muscles, livers, and kidneys. Furthermore, this work also discusses the engineering considerations, current challenges, proposed solutions, and future outlooks of 3D bioprinting.

Effect of graphene oxide in an injectable hydrogel on the osteogenic differentiation of mesenchymal stem cells

Graphene oxide (GO) is widely used in bone tissue engineering due to its good biocompatibility and proliferation, and is often used in combination with other hydrogels, which not only reduces the cytotoxicity of GO but also improves the mechanical properties of the hydrogels. We developed injectable carboxymethyl chitosan (CMC)/hydroxyethyl cellulose (HEC)/β-tricalcium phosphate (β-TCP)/GO hydrogel via hydrogen bonding cross-linked between (CMC) and (HEC), also, calcium cross-linked by β-TCP was also involved to further improvement of mechanical properties of the hydrogel, and incorporate different concentration of GO in these hydrogel systems. The characterization of the novel hydrogel was tested by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The swelling ratio and mechanical properties were investigated, the results showed that the addition of GO was able to reduce the swelling rate of hydrogels and improve their mechanical properties, with the best effect in the case of 1 mg/mL content. In vivo experimental studies showed that the hydrogel significantly promoted the osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs), with the best effect at a concentration of 2 mg/mL. The results of the cellular experiments were similar. Therefore, the novel environment-friendly and non-toxic injectable CMC/HEC/β-TCP/GO hydrogel system may have potential applications in bone tissue engineering.

3D-printed microstructured alginate scaffolds for neural tissue engineering

Alginate (Alg) is a versatile biopolymer for scaffold engineering and a bioink component widely used for direct cell printing. However, due to a lack of intrinsic cell-binding sites, Alg must be functionalized for cellular adhesion when used as a scaffold. Moreover, direct cell-laden ink 3D printing requires tedious disinfection procedures and cell viability is compromised by shear stress. Here, we demonstrate proof-of-concept, bioactive additive-free, microstructured Alg (M-Alg) scaffolds for neuron culture. The M-Alg scaffold was formed by introducing tetrapod-shaped ZnO (t-ZnO) microparticles into the ink as structural templates for interconnected channels and textured surfaces in the 3D-printed Alg scaffold, which were subsequently removed. Neurons exhibited significantly improved adhesion and growth on these M-Alg scaffolds compared with pristine Alg (P-Alg) scaffolds, with extensive neurite outgrowth and spontaneous neural activity, indicating the maturation of neuronal networks. These transparent, porous, additive-free Alg-based scaffolds with neuron affinity are promising for neuroregenerative and organoid-related research.

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.

3D-Printed PCL-Based Scaffolds with High Nanosized Synthetic Smectic Clay Content: Fabrication, Mechanical Properties, and Biological Evaluation for Bone Tissue Engineering

Background

The 3D printing of macro- and mesoporous biomimetic grafts composed of polycaprolactone (PCL) infused with nanosized synthetic smectic clay is a promising innovation in biomaterials for bone tissue engineering (BTE). The main challenge lies in achieving a uniform distribution of nanoceramics across low to high concentrations within the polymer matrix while preserving mechanical properties and biological performance essential for successful osseointegration.

Methods

This study utilized 3D printing to fabricate PCL scaffolds enriched with nanosized synthetic smectic clay (LAP) to evaluate its effects on structural, chemical, thermal, mechanical, and degradative properties, with a focus on in vitro biological performance and non-toxicity. Scaffolds were created with varying proportions of PCL and LAP. Comprehensive characterization included scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), mechanical testing, swelling analysis, and degradation studies. Biological performance was assessed through MTT assays (cell viability), alkaline phosphatase activity, histological analysis, and Raman spectroscopy, highlighting the scaffolds' biocompatibility and potential applications in regenerative medicine.

Results

The developed inks demonstrated excellent injectability, and the 3D-printed PCL/LAP scaffolds exhibited a microporous and rough structure, good structural fidelity, low degradability, thermal stability, and sufficient mechanical strength across all formulations. Intrinsic properties of the scaffolds revealed no cytotoxicity while enhancing bioactivity and promoting in vitro mineralization when cultured with mesenchymal stem cells in all analyzed groups. Notably, the high concentration of LAP within the PCL matrices did not induce in vitro cytotoxicity but rather stimulated in vitro mineralization and differentiation.

Conclusion

This study demonstrated the feasibility of 3D printing PCL/LAP scaffolds with high concentrations of nanoceramics. Both in vitro and in vivo assays validated the regenerative potential of these scaffolds, emphasizing their efficacy as a promising approach for developing advanced biomimetic grafts.

3D-Printed Gelatin-Based Scaffold Crosslinked by Genipin: Evaluation of Mechanical Properties and Biological Effect

In this study, scaffolds based on natural polymer gelatin A, blended with polyvinylpyrrolidone were crosslinked by genipin (0.5 and 1 wt%), in order to investigate their mechanical performance and potential for biomedical application. Semi-solid extrusion (SSE) 3D printing technique was used, enabling in situ crosslinking of the blend during processing. Swelling test showed that the swelling ratio reduces with higher concentration of genipin due to an increased crosslinking. The FTIR analysis confirmed the crosslinking of scaffolds by genipin. DSC analysis and mechanical testing have shown improved thermal and mechanical properties. Morphological analysis of scaffolds by FESEM showed increased toughening of the material with the crosslinking. Tensile strength and microhardness showed a significant rise in scaffolds with the increase in genipin content, which was up to 93.8% and 125.3%, respectively. These findings were in accordance with morphological features present in samples. The biological effect of the scaffold matrix system was evaluated by qualitative and quantitative cytotoxicity assessment in vitro, demonstrating the absence of cytotoxicity in tested preparations in a direct test. The cytotoxicity index based on the metabolic activity of cells in an indirect test showed up to 20% reduction of viability compared with the control, confirming the absence of cytotoxicity, which was additionally verified by propidium iodine staining of the cells exposed to scaffolds. The presented gelatin-based crosslinked scaffolds obtained by 3D printing represent good candidates for biomedical application and future research that includes further in vitro and in vivo analysis.

Efficacy of Bone Regeneration Cell Therapy Using Mesenchymal Stem Cells Originating from Embryonic Stem Cells in Animal Models; Bone Defects and Osteomyelitis

BACKGROUND

Bone defects are commonly encountered due to accidents, diseases, or aging, and the demand for effective bone regeneration, particularly for dental implants, is increasing in our aging society. Mesenchymal stem cells (MSCs) are promising candidates for regenerative therapies; however, obtaining sufficient quantities of these cells for clinical applications remains challenging. DW-MSCs, derived from embryonic stem cells and developed by Daewoong Pharmaceutical, exhibit a robust proliferative capacity even after extensive culture.

METHODS

This study explores the therapeutic potential of DW-MSCs in various animal models of bone defects. DW-MSCs were expanded for over 13 passages for in vivo use in rat and canine models of bone defects and osteomyelitis. The research focused on the in vivo osteogenic differentiation of DW-MSCs, the establishment of a fibrin-based system for bone regeneration, the assessment of bone repair following treatment in animal models, and comparisons with commercially available bone grafts.

RESULTS

Results showed that DW-MSCs exhibited superior osteogenic differentiation compared to other materials, and the fibrinization process not only preserved but enhanced their proliferation and differentiation capabilities through a 3D culture effect. In both bone defect models, DW-MSCs facilitated significant bone regeneration, reduced inflammatory responses in osteomyelitis, and achieved effective bone healing. The therapeutic outcomes of DW-MSCs were comparable to those of commercial bone grafts but demonstrated qualitatively superior bone tissue restructuring.

CONCLUSION

Our findings suggest that DW-MSCs offer a promising approach for bone regeneration therapies due to their high efficacy and anti-inflammatory properties.

Poly(L-lactide)/nano-hydroxyapatite piezoelectric scaffolds for tissue engineering

The development of bone tissue engineering, a field with significant potential, requires a biomaterial with high bioactivity. The aim of this manuscript was to fabricate a nanofibrous poly(L-lactide) (PLLA) scaffold containing nano-hydroxyapatite (nHA) to investigate PLLA/nHA composites, particularly the effect of fiber arrangement and the addition of nHA on the piezoelectric phases and piezoelectricity of PLLA samples. In this study, we evaluated the effect of nHA particles on a PLLA-based electrospun scaffold with random and aligned fiber orientations. The addition of nHA increased the surface free energy of PLLA/nHA (42.9 mN/m) compared to PLLA (33.1 mN/m) in the case of aligned fibers. WAXS results indicated that at room temperature, all the fibers are in an amorphous state indicated by a lack of diffraction peaks and amorphous halo. DSC analysis showed that all samples located in the amorphous/disordered alpha' phase crystallize intensively at temperatures just above the Tg and recrystallize on further heating, achieving significantly higher crystallinity for pure PLLA than for doped nHA, 70 % vs 40 %, respectively. Additionally, PLLA/nHA fibers show a lower heat capacity for PLLA in the amorphous state, indicating that nHA reduces the molecular mobility of PLLA. Moreover, piezoelectric constant d33 was found to increase with the addition of nHA and for the aligned orientation of the fibers. In vitro tests confirmed that the addition of nHA and the aligned orientation of nanofibers increased osteoblast proliferation.

Nanostructured polymer composites for bone and tissue regeneration

Nanostructured polymer composites have gained significant attention in recent years for their remarkable potential in bone and tissue regeneration. Moreover, with the integration of 3D printing technology, these composites hold promise for use in personalized medicine, where patient-specific scaffolds can be tailored to enhance therapeutic outcomes. Therefore, this review article aims to provide a comprehensive overview of the latest advancements in the development and application of nanostructured polymeric composites within the field of tissue engineering and bone regeneration. Here, the potential of biopolymers, natural polymers, and 3D-printed polymers to craft biocompatible, non-toxic, and mechanically robust composites is discussed in brief. Further, the fabrication techniques for 3D scaffolds and various forms of nanocomposites, including nanoparticles, nanocapsules, nanofibers, nanogels, and micelles for bone and tissue regeneration, are listed. Also, particular emphasis is placed on the role of nano-scaffolds and in situ hydrogels in bone and tissue regeneration. Overall, this review provides a concise and authoritative summary of the current state-of-the-art in nanostructured polymer composites for regenerative medicine, highlighting future directions and potential clinical applications.

Microstructural Analysis of the Human Scapula: Mandibular Bone Tissue Engineering Perspectives

Mandibular bone defect reconstruction remains a significant challenge for surgeons worldwide. Among multiple biodegradable biopolymers, allogeneic bone scaffolds derived from human sources have been used as an alternative to autologous bone grafts, providing optimal conditions for cell recruitment, adhesion, and proliferation and demonstrating significant osteogenic properties. This study aims to investigate the bone microstructure of the human scapula as a source for allogeneic bone scaffold fabrication for mandibular tissue engineering purposes. We created color-coded anatomical maps of the scapula and the mandible, reflecting the best anatomical and geometrical match. In this pilot study, we hypothesized a microstructural similarity of these bone structures and evaluated the human scapula's bone tissue engineering potential for mandibular bone tissue engineering by focusing on the microstructural characteristics. Lyophilized human scapular and mandibular bioimplants were manufactured and sterilized. Experimental bone samples from the scapula's acromion, coracoid, and lateral border from the mandibular condyle, mandibular angle, and mental protuberance were harvested and analyzed using micro-CT and quantitative morphometric analysis. This pilot study demonstrates significant microstructural qualitative and quantitative intra-group differences in the scapular and mandibular experimental bone samples harvested from the various anatomical regions. The revealed microstructural similarity of the human scapular and mandibular bone samples, to a certain extent, supports the stated hypothesis and, thus, allows us to suggest the human scapula as an alternative off-the-shelf allogeneic scaffold for mandibular reconstruction and bone tissue engineering applications.

Intrafibrillar calcium carbonate mineralization of electrospinning polyvinyl alcohol/collagen films with improved mechanical and bioactive properties

Collagen films play an essential role in guided bone-regeneration (GBR) techniques, which create space, promote cell adhesion, and induce osteogenic differentiation. It is therefore crucial to design appropriate GBR films to facilitate bone regeneration. However, current electrospun collagen scaffolds used as bioactive materials have limited clinical applications due to their poor mechanical properties. In this study, polyvinyl alcohol (PVA)/collagen (Col) films were electrospun by mixing PVA and type I collagen solution. For the first time, the intrafibrillar mineralization of aragonite nanocrystals within the PVA/Col fibrils was achieved, resulting in the formation of a hierarchical, bioactive film. The PVA/Col-CaCO3 film exhibited good mechanical properties, with hardness and Young's modulus values of 211.6 ± 0.1 MPa and 5.6 ± 1.7 GPa, respectively. Furthermore, bone marrow mesenchymal stem cells (BMSCs) inoculated onto the PVA/Col-CaCO3 film demonstrated robust adhesion and proliferation. The mineralized fibrils effectively stimulated the growth of BMSCs while suppressing cell apoptosis. Besides, the PVA/Col-CaCO3 film significantly induced the osteogenic differentiation of BMSCs, revealing its potential biomedical applications in hard tissue engineering.

3D printed scaffolds with quercetin and vitamin D3 nanocarriers: In vitro cellular evaluation

Increasing bone diseases and anomalies significantly challenge bone regeneration, necessitating the development of innovative implantable devices for effective healing. This study explores the potential of 3D-printed calcium phosphate (CaP) scaffolds functionalized with natural medicine to address this issue. Specifically, quercetin and vitamin D3 (QVD) encapsulated solid lipid nanoparticles (QVD-SLNs) are incorporated into the scaffold to enhance bone regeneration. The melt emulsification method is utilized to achieve high drug encapsulation efficiency (~98%) and controlled biphasic release kinetics. The process-structure-property performance of these systems allows more controlled release while maintaining healthy cell-material interactions. The functionalized scaffolds show ~1.3- and ~-1.6-fold increase in osteoblast cell proliferation and differentiation, respectively, as compared with the control. The treated scaffold demonstrates a reduction in osteoclastic activity as compared with the control. The QVD-SLN-loaded scaffolds show ~4.2-fold in vitro chemopreventive potential against osteosarcoma cells. Bacterial assessment with both Staphylococcus aureus and Pseudomonas aeruginosa shows a significant reduction in bacterial colony growth over the treated scaffold. These findings summarize that the release of QVD-SLNs through a 3D-printed CaP scaffold can treat various bone-related disorders for low or non-load-bearing applications.

Mechanical deviation in 3D-Printed PLA bone scaffolds during biodegradation

Large or carcinogenic bone defects may require a challenging bone tissue scaffold design ensuring a proper mechanobiological setting. Porosity and biodegradation rate are the key parameters controlling the bone-remodeling process. PLA presents a great potential for geometrically flexible 3-D scaffold design. This study aims to investigate the mechanical variation throughout the biodegradation process for lattice-type PLA scaffolds using both experimental observations and simulations. Three different unit-cell geometries are used for creating the scaffolds: basic cube (BC), body-centered structure (BCS), and body-centered cube (BCC). Three different porosity ratios, 50 %, 62.5 %, and 75 %, are assigned to all three structures by altering their strut dimensions. 3-D printed scaffolds are soaked in PBS solution at 37 °C for 15, 30, 60, 90, and 120 days both unloaded and under dead load. Water absorption, weight loss, and compression stiffness are measured to characterize the first-stage degradation and investigate the possible influences of these parameters on the whole biodegradation process. The strength reduction stage of biodegradation is simulated by solving pseudo-first-order kinetics-based molecular weight change equation using FEA with equisized cubic (voxel-like) elements. For the first stage, mechanical load does not have a statistically significant effect on biodegradation. BCC with 62.5 % porosity shows a maximum water absorption rate of around 25 % by the 60th day which brings an advantage in creating an aquatic environment for cell growth. Results indicate a significant water deposition inside almost all scaffolds and water content is determined to be the main reason for the retained or increased compression stiffness. A distinguishable stiffness increase in the initial degradation process occurs for 75 % porous BC and 50 % porous BCC scaffolds. Following the quasi-stable stage of biodegradation, almost all scaffolds lost their rigidity by around 44-48 % within 120 days based on numerical results. Therefore, initial stiffness increase in the quasi-stable stage of biodegradation can be advantageous and BCC geometry with a porosity between 50% and 62 % is the optimum solution for the whole biodegradation process.

Study on porous coral scaffolds containing a hydroxyapatite layer doped with selenium and their properties

The repair of bone defects caused by osteosarcoma is still a significant clinical issue, and new scaffolds need to be developed to solve this problem. The ocean is a treasure trove for developing new biomedical materials, and coral is widely thought to be suitable as a scaffold for bone implant materials due to its porous structure and mechanical properties. Selenium is known for its antioxidant and antitumor effects, inducing tumor cell cycle arrest. In this study, we hydrothermally transformed corals to grow a hydroxyapatite layer on the scaffold surface (CHAp) and combined it with selenium to obtain selenium-doped scaffolds (Se-CHAp) without affecting the porous structure of the coral. The research successfully validates their biocompatibility and the antitumor efficacy against 143B osteosarcoma cells. The results indicate that the Se-CHAp scaffolds yielded an obvious inhibitory effect on the proliferation of osteosarcoma cells, highlighting that they have huge prospects for application in biomedical technology.

An injectable carboxymethyl chitosan-based hydrogel with controlled release of BMP-2 for efficient treatment of bone defects

Although biological scaffolds containing bone morphogenetic protein-2 (BMP-2) have been widely used for osteogenic therapy, achieving stable and controlled release of BMP-2 remains a challenge. Herein, a novel BMP-2 sustained-release system composed of carboxymethyl chitosan (CMCS)/polyethylene glycol (PEG)/heparin sulfate (HS) (CMCS/PEG/HS) was constructed with a Schiff base reaction, yielding an injectable hydrogel for the release of BMP-2 in a controlled manner. For the CMCS/PEG/HS/BMP-2 hydrogel, the HS component had a negatively charged structure, which can bind to positively charged growth factors and prevent early hydrolytic metabolism of growth factors, thus achieving sustainable release of BMP-2. Notably, the release of BMP-2 in hydrogels was dependent mainly on degradation of the hydrogel matrix rather than simple diffusion. Generally, the CMCS/PEG/HS/BMP-2 hydrogel scaffold demonstrated excellent recoverability, good injectability, excellent biocompatibility and high adaptability, as well as efficient self-healing features to occupy irregularly shaped bone marrow cavities. The in vitro results revealed that the CMCS/PEG/HS/BMP-2 hydrogel promoted the osteogenic differentiation of MC3T3-E1 cells. Furthermore, the in vivo results suggest that the hydrogel has promising osteogenic effects that promote bone regeneration in a skull bone defect model. The injectable hydrogel scaffold shows great promise for bone treatment in the future.

3D printed polylactic acid/polyethylene glycol/bredigite nanocomposite scaffold enhances bone tissue regeneration via promoting osteogenesis and angiogenesis

Recently, the fabrication of personalized scaffolds with high accuracy has been developed through 3D printing technology. In the current study, polylactic acid/polyethylene glycol (PLA/PEG) composite scaffolds with varied weight percentages (0, 5, 10, 20 and 30 %) of bredigite nanoparticles (B) were fabricated using the 3D printing and then characterized through scanning electron microscopy and Fourier transform infra-red spectroscopy. The addition of B nanoparticles up to 20 wt% to PLA/PEG scaffold increased the compressive strength (from 7.59 to 13.84 MPa) and elastic modulus (from 142.42 to 268.33 MPa). The apatite formation ability as well as inorganic ion release in simulated body fluid were investigated for 28 days. The MG-63 cells viability and adhesion were enhanced by increasing the amount of B in the PLA/PEG scaffold and the osteogenic differentiation of the rat bone marrow mesenchymal stem cells was confirmed by alkaline phosphatase activity test and alizarin red staining. According to chorioallantoic membrane assay, the highest angiogenesis occurred around the PLA/PEG/B30 scaffold. In vivo experiments on a rat calvarial defect model demonstrated an almost complete recovery in the PLA/PEG/B30 group within 8 weeks. Based on the results, the PLA/PEG/B30 composite scaffold is proposed as an optimal scaffold to repair bone defects.

Sustained BMP-2 delivery via alginate microbeads and polydopamine-coated 3D-Printed PCL/β-TCP scaffold enhances bone regeneration in long bone segmental defects

Background/Objective

Repair of long bone defects remains a major challenge in clinical practice, necessitating the use of bone grafts, growth factors, and mechanical stability. Hence, a combination therapy involving a 3D-printed polycaprolactone (PCL)/β-tricalcium phosphate (β-TCP) scaffold coated with polydopamine (PDA) and alginate microbeads (AM) for sustained delivery of bone morphogenetic protein-2 (BMP-2) was investigated to treat long bone segmental defects.

Methods

Several in vitro analyses were performed to evaluate the scaffold osteogenic effects in vitro such as PDA surface modification, namely, hydrophilicity and cell adhesion; cytotoxicity and BMP-2 release kinetics using CCK-8 assay and ELISA, respectively; osteogenic differentiation in canine adipose-derived mesenchymal stem cells (Ad-MSCs); formation of mineralized nodules using ALP staining and ARS staining; and mRNA expression of osteogenic differentiation markers using RT-qPCR. Bone regeneration in femoral bone defects was evaluated in vivo using a rabbit femoral segmental bone defect model by performing radiography, micro-computed tomography, and histological observation (hematoxylin and eosin and Masson's trichrome staining).

Results

The PDA-coated 3D-printed scaffold demonstrated increased hydrophilicity, cell adhesion, and cell proliferation compared with that of the control. BMP-2 release kinetics assessment showed that BMP-2 AM showed a reduced initial burst and continuous release for 28 days. In vitro co-culture with canine Ad-MSCs showed an increase in mineralization and mRNA expression of osteogenic markers in the BMP-2 AM group compared with that of the BMP-2-adsorbed scaffold group. In vivo bone regeneration evaluation 12 weeks after surgery showed that the BMP-2 AM/PDA group exhibited the highest bone volume in the scaffold, followed by the BMP-2/PDA group. High cortical bone connectivity was observed in the PDA-coated scaffold groups.

Conclusion

These findings suggest that the combined use of PDA-coated 3D-printed bone scaffolds and BMP-2 AM can successfully induce bone regeneration even in load-bearing bone segmental defects.

The translational potential of this article

A 3D-printed PCL/β-TCP scaffold was fabricated to mimic the cortical bone of the femur. Along with the application of PDA surface modification and sustained BMP-2 release via AM, the developed scaffold could provide suitable osteoconduction, osteoinduction, and osteogenesis in both in vitro settings and in vivo rabbit femoral segmental bone defect models. Therefore, our findings suggest a promising therapeutic option for treating challenging long bone segmental defects, with potential for future clinical application.

In vivo endocultivation of CAD/CAM hybrid scaffolds in the omentum majus in miniature pigs

PURPOSE

Correction of bony mandibular defects is a challenge in oral and maxillofacial surgery due to aesthetic and functional requirements. This study investigated the potential of a novel hybrid scaffold for bone regeneration and degradation assessment of the ceramic within the omentum majus over 6 months and the extent to which rhBMP-2 as a growth factor, alone or combined with a hydrogel, affects regeneration.

MATERIALS AND METHODS

In this animal study, 10 Göttingen minipigs each had one scaffold implanted in the greater omentum. Five animals had scaffolds loaded with a collagen hydrogel and rhBMP-2, and the other five animals (control group) had scaffolds loaded with rhBMP-2 only. Fluorochrome injections and computed tomography (CT) were performed regularly. After 6 months, the animals were euthanized, and samples were collected for microCT and histological evaluations.

RESULTS

Fluorescent and light microscopic and a CT morphological density evaluation showed continuous bone growth until week 16 in both groups. Regarding the ratio of bone attachment to the Zr02 support struts, the rhBMP-2 loaded collagen hydrogel group showed with 63% a significantly higher attachment (p > 0.001) than the rhBMP-2 control group (49%).

CONCLUSION

In this study, bone growth was induced in all omentum majus specimens until post-operative week 16. Furthermore, hydrogel and rhBMP-2 together resulted in better bone-scaffold integration than rhBMP-2 alone. Further studies should investigate whether implantation of the scaffolds in the jaw after an appropriate period of bone regeneration leads to a stable situation and the desired results.

Drug delivery strategies through 3D-printed calcium phosphate

3D printing has revolutionized bone tissue engineering (BTE) by enabling the fabrication of patient- or defect-specific scaffolds to enhance bone regeneration. The superior biocompatibility, customizable bioactivity, and biodegradability have enabled calcium phosphate (CaP) to gain significance as a bone graft material. 3D-printed (3DP) CaP scaffolds allow precise drug delivery due to their porous structure, adaptable structure-property relationship, dynamic chemistry, and controlled dissolution. The effectiveness of conventional scaffold-based drug delivery is hampered by initial burst release and drug loss. This review summarizes different multifunctional drug delivery approaches explored in controlling drug release, including polymer coatings, formulation integration, microporous scaffold design, chemical crosslinking, and direct extrusion printing for BTE applications. The review also outlines perspectives and future challenges in drug delivery research, paving the way for next-generation bone repair methodologies.

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.

Highly Porous 3D Nanofibrous Scaffold of Polylactic Acid/Polyethylene Glycol/Calcium Phosphate for Bone Regeneration by a Two-Step Solution Blow Spinning (SBS) Facile Route

This work presents the successful production of highly porous 3D nanofibrous hybrid scaffolds of polylactic acid (PLA)/polyethylene glycol (PEG) blends with the incorporation of calcium phosphate (CaP) bioceramics by a facile two-step process using the solution blow spinning (SBS) technique. CaP nanofibers were obtained at two calcium/phosphorus (Ca/P) ratios, 1.67 and 1.1, by SBS and calcination at 1000 °C. They were incorporated in PLA/PEG blends by SBS at 10 and 20 wt% to form 3D hybrid cotton-wool-like scaffolds. Morphological analysis showed that the fibrous scaffolds obtained had a randomly interconnected and highly porous structure. Also, the mean fiber diameter ranged from 408 ± 141 nm to 893 ± 496 nm. Apatite deposited considerably within 14 days in a simulated body fluid (SBF) test for hybrid scaffolds containing a mix of hydroxyapatite (HAp) and tri-calcium phosphate-β (β-TCP) phases. The scaffolds with 20 wt% CaP and a Ca/P ration of 1.1 showed better in vitro bioactivity to induce calcium mineralization for bone regeneration. Cellular tests evidenced that the developed scaffolds can support the osteogenic differentiation and proliferation of pre-osteoblastic MC3T3-E1 cells into mature osteoblasts. The results showed that the developed 3D scaffolds have potential applications for bone tissue engineering.

Enhancing craniofacial bone tissue engineering strategy: integrating rapid wet chemically synthesised bioactive glass with photopolymerized resins

BACKGROUND

Craniofacial bone regeneration represents a dynamic area within tissue engineering and regenerative medicine. Central to this field, is the continual exploration of new methodologies for template fabrication, leveraging established bio ceramic materials, with the objective of restoring bone integrity and facilitating successful implant placements.

METHODS

Photopolymerized templates were prepared using three distinct bio ceramic materials, specifically a wet chemically synthesized bioactive glass and two commercially sourced hydroxyapatite variants. These templates underwent comprehensive characterization to assess their physicochemical and mechanical attributes, employing techniques including Fourier transform infrared spectroscopy, scanning electron microscopy, and nano-computed tomography. Evaluation of their biocompatibility was conducted through interaction with primary human osteoblasts (hOB) and subsequent examination using scanning electron microscopy.

RESULTS

The results demonstrated that composite showed intramolecular hydrogen bonding interactions with the photopolymer, while computerized tomography unveiled the porous morphology and distribution within the templates. A relatively higher porosity percentage (31.55 ± 8.70%) and compressive strength (1.53 ± 0.11 MPa) was noted for bioactive glass templates. Human osteoblast cultured on bioactive glass showed higher viability compared to other specimens. Scanning micrographs of human osteoblast on templated showed cellular adhesion and the presence of filopodia and lamellipodia.

CONCLUSION

In summary these templates have the potential to be used for alveolar bone regeneration in critical size defect. Photopolymerization of bioceramics may be an interesting technique for scaffolds fabrication for bone tissue engineering application but needs more optimization to overcome existing issues like the ideal ratio of the photopolymer to bioceramics.

3D printing of Pickering emulsions, Pickering foams and capillary suspensions - A review of stabilization, rheology and applications

Pickering emulsions and foams as well as capillary suspensions are becoming increasingly more popular as inks for 3D printing. However, a lack of understanding of the bulk rheological properties needed for their application in 3D printing is potentially stifling growth in the area, hence the timeliness of this review. Herein, we review the stability and bulk rheology of these materials as well as the applications of their 3D-printed products. By highlighting how the bulk rheology is tuned, and specifically the inks storage modulus, yield stress and critical balance between the two, we present a rheological performance map showing regions where good prints and slumps are observed thus providing clear guidance for future ink formulations. To further advance this field, we also suggest standard experimental protocols for characterizing the bulk rheology of the three types of ink: capillary suspension, Pickering emulsion and Pickering foam for 3D printing by direct ink writing.

Advancements in Tissue Engineering: A Review of Bioprinting Techniques, Scaffolds, and Bioinks

Tissue engineering is a multidisciplinary field that uses biomaterials to restore tissue function and assist with drug development. Over the last decade, the fabrication of three-dimensional (3D) multifunctional scaffolds has become commonplace in tissue engineering and regenerative medicine. Thanks to the development of 3D bioprinting technologies, these scaffolds more accurately recapitulate in vivo conditions and provide the support structure necessary for microenvironments conducive to cell growth and function. The purpose of this review is to provide a background on the leading 3D bioprinting methods and bioink selections for tissue engineering applications, with a specific focus on the growing field of developing multifunctional bioinks and possible future applications.

Bioactive polymers: A comprehensive review on bone grafting biomaterials

The application of bone grafting materials in bone tissue engineering is paramount for treating severe bone defects. In this comprehensive review, we explore the significance and novelty of utilizing bioactive polymers as grafts for successful bone repair. Unlike metals and ceramics, polymers offer inherent biodegradability and biocompatibility, mimicking the native extracellular matrix of bone. While these polymeric micro-nano materials may face challenges such as mechanical strength, various fabrication techniques are available to overcome these shortcomings. Our study not only investigates diverse biopolymeric materials but also illuminates innovative fabrication methods, highlighting their importance in advancing bone tissue engineering.

Application of decalcified bone matrix in Salmon bone for tibial defect repair in rat model

AIM

The optimal preparation conditions of Salmon decalcified bone matrix (S-DBM) were explored, and the properties of S-DBM bone particles and bone powder were studied respectively. The therapeutic effect of S-DBM on tibial defect in female Sprague Dawley (SD) rats was preliminarily verified.

METHODS

This study assessed the structural and functional similarities of Salmon bone DBM (S-DBM). The biocompatibility assessment was conducted using both in vivo and in vitro experiments, establishing an animal model featuring tibial defects in rats and on the L929 cell line, respectively. The control group, bovine DBM (bDBM), was compared to the S-DBM-treated tibial defect rats. Imaging and histology were used to study implant material changes, defect healing, osteoinductive repair, and degradation.

RESULTS

The findings of our study indicate that S-DBM exhibits favorable repairing effects on bone defects, along with desirable physicochemical characteristics, safety, and osteogenic activity.

CONCLUSIONS

The S-DBM holds significant potential as a medical biomaterial for treating bone defects, effectively fulfilling the clinical demands for materials used in bone tissue repair engineering.

BioMOF@cellulose Glycerogel Scaffold with Multifold Bioactivity: Perspective in Bone Tissue Repair

The development of new biomaterials for musculoskeletal tissue repair is currently an important branch in biomedicine research. The approach presented here is centered around the development of a prototypic synthetic glycerogel scaffold for bone regeneration, which simultaneously features therapeutic activity. The main novelty of this work lies in the combination of an open meso and macroporous nanocrystalline cellulose (NCC)-based glycerogel with a fully biocompatible microporous bioMOF system (CaSyr-1) composed of calcium ions and syringic acid. The bioMOF framework is further impregnated with a third bioactive component, i.e., ibuprofen (ibu), to generate a multifold bioactive system. The integrated CaSyr-1(ibu) serves as a reservoir for bioactive compounds delivery, while the NCC scaffold is the proposed matrix for cell ingrowth, proliferation and differentiation. The measured drug delivery profiles, studied in a phosphate-buffered saline solution at 310 K, indicate that the bioactive components are released concurrently with bioMOF dissolution after ca. 30 min following a pseudo-first-order kinetic model. Furthermore, according to the semi-empirical Korsmeyer-Peppas kinetic model, this release is governed by a case-II mechanism, suggesting that the molecular transport is influenced by the relaxation of the NCC matrix. Preliminary in vitro results denote that the initial high concentration of glycerol in the NCC scaffold can be toxic in direct contact with human osteoblasts (HObs). However, when the excess of glycerol is diluted in the system (after the second day of the experiment), the direct and indirect assays confirm full biocompatibility and suitability for HOb proliferation.

From the microspheres to scaffolds: advances in polymer microsphere scaffolds for bone regeneration applications

The treatment and repair of bone tissue damage and loss due to infection, tumours, and trauma are major challenges in clinical practice. Artificial bone scaffolds offer a safer, simpler, and more feasible alternative to bone transplantation, serving to fill bone defects and promote bone tissue regeneration. Ideally, these scaffolds should possess osteoconductive, osteoinductive, and osseointegrative properties. However, the current first-generation implants, represented by titanium alloys, have shown poor bone-implant integration performance and cannot meet the requirements for bone tissue repair. This has led to increased research on second and third generation artificial bone scaffolds, which focus on loading bioactive molecules and cells. Polymer microspheres, known for their high specific surface areas at the micro- and nanoscale, exhibit excellent cell and drug delivery behaviours. Additionally, with their unique rigid structure, microsphere scaffolds can be constructed using methods such as thermal sintering, injection, and microsphere encapsulation. These scaffolds not only ensure the excellent cell drug loading performance of microspheres but also exhibit spatial modulation behaviour, aiding in bone repair within a three-dimensional network structure. This article provides a summary and discussion of the use of polymer microsphere scaffolds for bone repair, focusing on the mechanisms of bone tissue repair and the current status of clinical bone grafts, aimed at advancing research in bone repair.

Extrusion 3D-printed tricalcium phosphate-polycaprolactone biocomposites for quercetin-KCl delivery in bone tissue engineering

Critical-sized bone defects pose a significant challenge in advanced healthcare due to limited bone tissue regenerative capacity. The complex interplay of numerous overlapping variables hinders the development of multifunctional biocomposites. Phytochemicals show promise in promoting bone growth, but their dose-dependent nature and physicochemical properties halt clinical use. To develop a comprehensive solution, a 3D-printed (3DP) extrusion-based tricalcium phosphate-polycaprolactone (TCP-PCL) scaffold is augmented with quercetin and potassium chloride (KCl). This composite material demonstrates a compressive strength of 30 MPa showing promising stability for low load-bearing applications. Quercetin release from the scaffold follows a biphasic pattern that persists for up to 28 days, driven via diffusion-mediated kinetics. The incorporation of KCl allows for tunable degradation rates of scaffolds and prevents the initial rapid release. Functionalization of scaffolds facilitates the attachment and proliferation of human fetal osteoblasts (hfOB), resulting in a 2.1-fold increase in cell viability. Treated scaffolds exhibit a 3-fold reduction in osteosarcoma (MG-63) cell viability as compared to untreated substrates. Ruptured cell morphology and decreased mitochondrial membrane potential indicate the antitumorigenic potential. Scaffolds loaded with quercetin and quercetin-KCl (Q-KCl) demonstrate 76% and 89% reduction in bacterial colonies of Staphylococcus aureus, respectively. This study provides valuable insights as a promising strategy for bone tissue engineering (BTE) in orthopedic repair.

Effect of Scaffold Geometrical Structure on Macrophage Polarization during Bone Regeneration Using Honeycomb Tricalcium Phosphate

The polarization balance of M1/M2 macrophages with different functions is important in osteogenesis and bone repair processes. In a previous study, we succeeded in developing honeycomb tricalcium phosphate (TCP), which is a cylindrical scaffold with a honeycomb arrangement of straight pores, and we demonstrated that TCP with 300 and 500 μm pore diameters (300TCP and 500TCP) induced bone formation within the pores. However, the details of the influence of macrophage polarization on bone formation using engineered biomaterials, especially with respect to the geometric structure of the artificial biomaterials, are unknown. In this study, we examined whether differences in bone tissue formation due to differences in TCP geometry were due to the polarity of the assembling macrophages. Immunohistochemistry for IBA-1, iNOS, and CD163 single staining was performed. The 300TCP showed a marked infiltration of iNOS-positive cells, which are thought to be M1 macrophages, during the osteogenesis process, while no involvement of CD163-positive cells, which are thought to be M2 macrophages, was observed in the TCP pores. In addition, 500TCP showed a clustering of iNOS-positive cells and CD163-positive cells at 2 weeks, suggesting the involvement of M2 macrophages in the formation of bone tissue in the TCP pores. In conclusion, we demonstrated for the first time that the geometrical structure of the artificial biomaterial, i.e., the pore size of honeycomb TCP, affects the polarization of M1/2 macrophages and bone tissue formation in TCP pores.

3D Melt-Extrusion Printing of Medium Chain Length Polyhydroxyalkanoates and Their Application as Antibiotic-Free Antibacterial Scaffolds for Bone Regeneration

In this work, we investigated, for the first time, the possibility of developing scaffolds for bone tissue engineering through three-dimensional (3D) melt-extrusion printing of medium chain length polyhydroxyalkanoate (mcl-PHA) (i.e., poly(3-hydroxyoctanoate-co-hydroxydecanoate-co-hydroxydodecanoate), P(3HO-co-3HD-co-3HDD)). The process parameters were successfully optimized to produce well-defined and reproducible 3D P(3HO-co-3HD-co-3HDD) scaffolds, showing high cell viability (100%) toward both undifferentiated and differentiated MC3T3-E1 cells. To introduce antibacterial features in the developed scaffolds, two strategies were investigated. For the first strategy, P(3HO-co-3HD-co-3HDD) was combined with PHAs containing thioester groups in their side chains (i.e., PHACOS), inherently antibacterial PHAs. The 3D blend scaffolds were able to induce a 70% reduction of Staphylococcus aureus 6538P cells by direct contact testing, confirming their antibacterial properties. Additionally, the scaffolds were able to support the growth of MC3T3-E1 cells, showing the potential for bone regeneration. For the second strategy, composite materials were produced by the combination of P(3HO-co-3HD-co-HDD) with a novel antibacterial hydroxyapatite doped with selenium and strontium ions (Se-Sr-HA). The composite material with 10 wt % Se-Sr-HA as a filler showed high antibacterial activity against both Gram-positive (S. aureus 6538P) and Gram-negative bacteria (Escherichia coli 8739), through a dual mechanism: by direct contact (inducing 80% reduction of both bacterial strains) and through the release of active ions (leading to a 54% bacterial cell count reduction for S. aureus 6538P and 30% for E. coli 8739 after 24 h). Moreover, the composite scaffolds showed high viability of MC3T3-E1 cells through both indirect and direct testing, showing promising results for their application in bone tissue engineering.

Design and development of 3D printed shape memory triphasic polymer-ceramic bioactive scaffolds for bone tissue engineering

Scaffolds for bone tissue engineering require considerable mechanical strength to repair damaged bone defects. In this study, we designed and developed mechanically competent composite shape memory triphasic bone scaffolds using fused filament fabrication (FFF) three dimensional (3D) printing. Wollastonite particles (WP) were incorporated into the poly lactic acid (PLA)/polycaprolactone (PCL) matrix as a reinforcing agent (up to 40 wt%) to harness osteoconductive and load-bearing properties from the 3D printed scaffolds. PCL as a minor phase (20 wt%) was added to enhance the toughening effect and induce the shape memory effect in the triphasic composite scaffolds. The 3D-printed composite scaffolds were studied for morphological, thermal, and mechanical properties, in vitro degradation, biocompatibility, and shape memory behaviour. The composite scaffold had interconnected pores of 550 μm, porosity of more than 50%, and appreciable compressive strength (∼50 MPa), which was over 90% greater than that of the pristine PLA scaffolds. The flexural strength was improved by 140% for 40 wt% of WP loading. The inclusion of WP did not affect the thermal property of the scaffolds; however, the inclusion of PCL reduced the thermal stability. An accelerated in vitro degradation was observed for WP incorporated composite scaffolds compared to pristine PLA scaffolds. The inclusion of WP improved the hydrophilic property of the scaffolds, and the result was significant for 40 wt% WP incorporated composite scaffolds having a water contact angle of 49.61°. The triphasic scaffold exhibited excellent shape recovery properties with a shape recovery ratio of ∼84%. These scaffolds were studied for their protein adsorption, cell proliferation, and bone mineralization potential. The incorporation of WP reduced the protein adsorption capacity of the composite scaffolds. The scaffold did not leach any toxic substance and demonstrated good cell viability, indicating its biocompatibility and growth-promoting behavior. The osteogenic potential of the WP incorporated scaffolds was observed in MC3T3-E1 cells, revealing early mineralization in pre-osteoblast cells cultured in different WP incorporated composite scaffolds. These results suggest that 3D-printed WP reinforced PLA/PCL composite bioactive scaffolds are promising for load bearing bone defect repair.

3D Printing and Surface Engineering of Ti6Al4V Scaffolds for Enhanced Osseointegration in an In Vitro Study

Ti6Al4V superalloy is recognized as a good candidate for bone implants owing to its biocompatibility, corrosion resistance, and high strength-to-weight ratio. While dense metal implants are associated with stress shielding issues due to the difference in densities, stiffness, and modulus of elasticity compared to bone tissues, the surface of the implant/scaffold should mimic the properties of the bone of interest to assure a good integration with a strong interface. In this study, we investigated the additive manufacturing of porous Ti6Al4V scaffolds and coating modification for enhanced osteoconduction using osteoblast cells. The results showed the successful fabrication of porous Ti6Al4V scaffolds with adequate strength. Additionally, the surface treatment with NaOH and Dopamine Hydrochloride (DOPA) promoted the formation of Dopamine Hydrochloride (DOPA) coating with an optimized coating process, providing an environment that supports higher cell viability and growth compared to the uncoated Ti6Al4V scaffolds, as demonstrated by the higher proliferation ratios observed from day 1 to day 29. These findings bring valuable insights into the surface modification of 3D-printed scaffolds for improved osteoconduction through the coating process in solutions.

Harnessing extracellular vesicles-mediated signaling for enhanced bone regeneration: novel insights into scaffold design

The increasing prevalence of bone replacements and complications associated with bone replacement procedures underscores the need for innovative tissue restoration approaches. Existing synthetic grafts cannot fully replicate bone vascularization and mechanical characteristics. This study introduces a novel strategy utilizing pectin, chitosan, and polyvinyl alcohol to create interpenetrating polymeric network (IPN) scaffolds incorporated with extracellular vesicles (EVs) isolated from human mesenchymal stem cells (hMSCs). We assess the osteointegration and osteoconduction abilities of these modelsin vitrousing hMSCs and MG-63 osteosarcoma cells. Additionally, we confirm exosome properties through Transmission Electron Microscopy (TEM), immunoblotting, and Dynamic Light Scattering (DLS).In vivo, chick allantoic membrane assay investigates vascularization characteristics. The study did not includein vivoanimal experiments. Our results demonstrate that the IPN scaffold is highly porous and interconnected, potentially suitable for bone implants. EVs, approximately 100 nm in size, enhance cell survival, proliferation, alkaline phosphatase activity, and the expression of osteogenic genes. EVs-mediated IPN scaffolds demonstrate promise as precise drug carriers, enabling customized treatments for bone-related conditions and regeneration efforts. Therefore, the EVs-mediated IPN scaffolds demonstrate promise as precise carriers for the transport of drugs, allowing for customized treatments for conditions connected to bone and efforts in regeneration.

Acceleration of bone repairation by BMSCs overexpressing NGF combined with NSA and allograft bone scaffolds

BACKGROUND

Repairation of bone defects remains a major clinical problem. Constructing bone tissue engineering containing growth factors, stem cells, and material scaffolds to repair bone defects has recently become a hot research topic. Nerve growth factor (NGF) can promote osteogenesis of bone marrow mesenchymal stem cells (BMSCs), but the low survival rate of the BMSCs during transplantation remains an unresolved issue. In this study, we investigated the therapeutic effect of BMSCs overexpression of NGF on bone defect by inhibiting pyroptosis.

METHODS

The relationship between the low survival rate and pyroptosis of BMSCs overexpressing NGF in localized inflammation of fractures was explored by detecting pyroptosis protein levels. Then, the NGF+/BMSCs-NSA-Sca bone tissue engineering was constructed by seeding BMSCs overexpressing NGF on the allograft bone scaffold and adding the pyroptosis inhibitor necrosulfonamide(NSA). The femoral condylar defect model in the Sprague-Dawley (SD) rat was studied by micro-CT, histological, WB and PCR analyses in vitro and in vivo to evaluate the regenerative effect of bone repair.

RESULTS

The pyroptosis that occurs in BMSCs overexpressing NGF is associated with the nerve growth factor receptor (P75NTR) during osteogenic differentiation. Furthermore, NSA can block pyroptosis in BMSCs overexpression NGF. Notably, the analyses using the critical-size femoral condylar defect model indicated that the NGF+/BMSCs-NSA-Sca group inhibited pyroptosis significantly and had higher osteogenesis in defects.

CONCLUSION

NGF+/BMSCs-NSA had strong osteogenic properties in repairing bone defects. Moreover, NGF+/BMSCs-NSA-Sca mixture developed in this study opens new horizons for developing novel tissue engineering constructs.

Bone Morphogenetic Protein 7-Loaded Gelatin Methacrylate/Oxidized Sodium Alginate/Nano-Hydroxyapatite Composite Hydrogel for Bone Tissue Engineering

Background

Bone tissue engineering (BTE) is a promising alternative to autologous bone grafting for the clinical treatment of bone defects, and inorganic/organic composite hydrogels as BTE scaffolds are a hot spot in current research. The construction of nano-hydroxyapatite/gelatin methacrylate/oxidized sodium alginate (nHAP/GelMA/OSA), abbreviated as HGO, composite hydrogels loaded with bone morphogenetic protein 7 (BMP7) will provide a suitable 3D microenvironment to promote cell aggregation, proliferation, and differentiation, thus facilitating bone repair and regeneration.

Methods

Dually-crosslinked hydrogels were fabricated by combining GelMA and OSA, while HGO hydrogels were formulated by incorporating varying amounts of nHAP. The hydrogels were physically and chemically characterized followed by the assessment of their biocompatibility. BMP7-HGO (BHGO) hydrogels were fabricated by incorporating suitable concentrations of BMP7 into HGO hydrogels. The osteogenic potential of BHGO hydrogels was then validated through in vitro experiments and using rat femoral defect models.

Results

The addition of nHAP significantly improved the physical properties of the hydrogel, and the composite hydrogel with 10% nHAP demonstrated the best overall performance among all groups. The selected concentration of HGO hydrogel served as a carrier for BMP7 loading and was evaluated for its osteogenic potential both in vivo and in vitro. The BHGO hydrogel demonstrated superior in vitro osteogenic induction and in vivo potential for repairing bone tissue compared to the outcomes observed in the blank control, BMP7, and HGO groups.

Conclusion

Using hydrogel containing 10% HGO appears promising for bone tissue engineering scaffolds, especially when loaded with BMP7 to boost its osteogenic potential. However, further investigation is needed to optimize the GelMA, OSA, and nHAP ratios, along with the BMP7 concentration, to maximize the osteogenic potential.