Bone Tissue Engineering Scaffolds: Function of Multi-Material Hierarchically Structured Scaffolds

3D-printed microfibers encapsulating stem cells in scaffold with tri-culture and two-stage metformin release for bone/vasculature/nerve regeneration in rats

Introduction

Regeneration of critical-sized bone defects remains a major clinical challenge. Solely promoting osteogenesis is inadequate, because vasculature and neural innervation are critical for establishing the bone regenerative microenvironment.

Objective

For the first time, the present study developed 3D bio-printed hydrogel microfibers (aMF) encapsulating human periodontal ligament stem cells (hPDLSCs) in a tri-culture system in calcium phosphate cement (CPC) scaffold with a two-stage metformin release for regeneration of nerve, vasculature, and bone.

Materials and methods

This tri-culture system consisted of hPDLSCs, human umbilical vein endothelial cells (hUVECs), and pericytes (PCs). Moreover, we employed 3D-bioprinted aMF in CPC scaffold with a controlled two-stage release system for metformin release to promote bone, vasculature, and nerve regeneration.

Results

Our innovative construct increased the regenerated amounts of bone, vasculature and nerve significantly by 2.5-fold, 3-fold, and 3.5-fold, respectively, than control group, in cranial defects in rats.

Conclusion

This novel hPDLSCs tri-culture system in aMF-CPC scaffold with two-stage metformin release is highly promising for the regeneration of all three tissues of bone, vasculature, and nerves in a wide range of craniofacial and orthopedic applications.

Gouqi-derived Nanovesicles (GqDNVs) promoted MC3T3-E1 cells proliferation and improve fracture healing

BACKGROUND

Lycium barbarum L., also known as Gouqi, a traditional Chinese herbal medicine, is widely utilized in health care products and clinical therapies. Its muscle and bone strengthening efficacy has been recorded in medical classics for a long time. In addition, plant exosome-like nanovesicles (PELNVs) have attracted more and more attention owing to their biological traits. Therefore, we intended to explore the functions, regulatory role, and underlying mechanism of Gouqi-derived Nanovesicles (GqDNVs) on fracture healing.

METHODS

In this study, we employed the sucrose density gradient differential ultracentrifugation to isolate GqDNVs. The effects of GqDNVs on the proliferation and differentiation of MC3T3-E1 cells were evaluated using the CCK-8 assay, ALP activity measurement, and cell scratch assay. Additionally, leveraging a fracture mouse model, we utilized Micro-CT, immunological staining, and histologic analyses to comprehensively assess the impact of GqDNVs on fracture healing in mice.

RESULTS

GqDNVs stimulated cell viability, increased ALP activity, and promoted cellular osteogenic protein expression (OPN, ALP, and RUNX2). Subsequently, in the mouse fracture model, trabecular thickness, and bone marrow density were increased in the GqDNVs treatment group after 28 days of injection. Meanwhile, the expressions of OPN and BGP were significantly elevated after both 14 and 28 days. Additionally, the expressions of p-PI3K/PI3K, p-Akt/Akt, p-mTOR/mTOR, p-4EBP1/4EBP1 and p-p70S6K/ p70S6K were also increased after14 days of treatment.

CONCLUSIONS

GqDNVs effectively promoted the proliferation and differentiation of MC3T3-E1 cells. Furthermore, GqDNVs could improve fracture healing, which is associated with PI3K/Akt/mTOR/p70S6K/4EBP1 signaling pathway.

A green synthetic nanosilver photo-crosslinked injectable gelatin/hyaluronic acid hydrogel for infected cranial defect repair

Currently, gelatin hydrogels are widely used in the field of tissue engineering due to its good biocompatibility, but its weak osteoinductive activity, insufficient mechanical properties, and lack of antimicrobial activity hindered its progress. Therefore, the development of a functional gelatin hydrogels not only resist bacterial infection, but also promote the differentiation of mesenchymal stem cells (MSCs) into osteoblasts, as well as accurately match the site of bone defects, is particularly important for the treatment of patients with bone defects. In this study, an in-situ forming injectable, dual-network methacrylate gelatin/methacrylate hyaluronic acid/silver nanoparticles (GelMA/HAMA/Ag) hydrogels with antibacterial and osteoinductive activities were designed, which were constructed by using methacrylic anhydride-modified gelatin and hyaluronic acid (GelMA/HAMA) as the carrier, well-dispersed silver nanoparticles (AgNPs) were fabricated by a green synthesis method, which were then embedded within the GelMA/HAMA hydrogel. The GelMA/HAMA/Ag hydrogels boasted a dense pore structure and excellent mechanical properties. Additionally, GelMA/HAMA/Ag hydrogels effectively promoted the differentiation of Bone marrow mesenchymal stem cells (BMSCs), which promoted the expression of a variety of osteogenic genes such as ALP, OPN, COL-I and RUNX-2 in vitro, as well as demonstrating notable inhibitory effects on Staphylococcus aureus and Escherichia coli. Furthermore, the Micro-CT analysis and histological analysis have demonstrated that the GelMA/HAMA/Ag-3 hydrogel effectively enhanced cranial defect reconstruction in vivo rat cranial defect repair experiments. Overall, this novel double-network GelMA/HAMA/Ag hydrogels with multifunctional responsiveness exhibit promising application prospects in bone defects repair.

Adhesive hydrogel barriers synergistically promote bone regeneration by self-constructing microstress and mineralization microenvironment

Mechanical loading is a key factor in bone growth and regeneration. In bone defect repair, combining micro-stress stimulation with an excellent inorganic microenvironment offers a more effective strategy for promoting bone regeneration. In this study, guided by the strategy to create both micro-stress and a mineralization microenvironment in the bone defect area, a membrane-like hydrogel barrier (PN-GEL@BP-PE) was designed. The hydrogel barrier adheres tightly to the bone surface via polyethyleneimine/polyacrylic acid (PEI/PAA) and generates micro-stress through the volume deformation of poly(N-isopropylacrylamide) at body temperature. Meanwhile, the inorganic microenvironment that promotes bone mineralization is induced by the calcium recruitment properties of black phosphorus nanosheets (BPNs). This membrane activates the cellular micro-stress response in mesenchymal cells, working synergistically with the calcium recruitment effect of BPNs to enhance osteogenic mineralization. In vivo, the bone regeneration effect of the hydrogel membrane is approximately 50% higher than that of conventional treatments, indicating that PN-GEL@BP-PE exhibits strong osteogenic efficacy. This synergistic strategy, combining osteogenic physical and chemical microenvironments, represents a promising direction for future research.

Unveiling the Power of Magnetic-Driven Regenerative Medicine: Bone Regeneration and Functional Reconstruction

To improve the treatment outcomes for large bone defects and osteoporosis, researchers have been committed to reducing bone loss and accelerating bone regeneration through cell transplantation, biomaterial intervention, and biophysical stimulation over the past few decades. Magnetism, as a noninvasive biophysical stimulus, has been employed in the repair of the musculoskeletal system, achieving a series of promising results. In this review, we provide a retrospective analysis and perspective of research on magnetic-driven bone regeneration and functional reconstruction. This review aims to delineate safe and efficient magnetic application modalities and to summarize the potential mechanisms by which magnetism regulates the behavior of skeletal lineage cells, thereby providing insights for the expansion and translational application of magnetic-driven regenerative medicine.

Enhancing in vitro osteogenic differentiation of mesenchymal stem cells via sustained dexamethasone delivery in 3D-Printed hybrid scaffolds based on polycaprolactone-nanohydroxyapatite/alginate-gelatin for bone regeneration

Despite the natural ability of bone repair, its limitations have led to advanced organic-inorganic-based biomimetic scaffolds and sustained drug release approaches. Particularly, dexamethasone (DEX), a widely used synthetic glucocorticoid, has been shown to increase the expression of bone-related genes during the osteogenesis process. This study aims to develop a hybrid 3D-printed scaffold for controlled delivery of dexamethasone. Hence, hybrid scaffolds were fabricated using a layer-by-layer 3D-printing of combined materials comprising polycaprolactone (PCL)-nanohydroxyapatite (nHA) composite, and DEX-loaded PCL microparticles embedded in the alginate-gelatin hydrogel. Encapsulation efficiency, loading capacity, and in vitro kinetics of DEX release were evaluated. Osteogenic differentiation of human endometrial mesenchymal stem cells (hEnMSCs) on DEX-loaded hybrid scaffolds was assessed by evaluating osteogenic gene expression levels (collagen I, osteonectin, RUNX2), alkaline phosphatase (ALP) activity, and scaffold mineralization. The hybrid scaffolds exhibited favorable morphology, mechanical-properties, biocompatibility, and biodegradability, enhancing osteogenesis of hEnMSCs. DEX-loaded PCL microparticles within hybrid scaffolds exhibited a controlled release pattern and promoted osteogenic differentiation during the sustained release period through a significant increase in osteonectin and COL1A1 expression. Also, increased mineralization was demonstrated by SEM and alizarin red staining. This study proposes that drug-loaded 3D-printed hybrid organic-inorganic nanocomposite scaffolds are promising for advanced bone tissue engineering applications.

3D Bioprinting of Prevascularized Bone Organoids for Rapid In Situ Cranial Bone Reconstruction

Despite rapid advances in the field of bone tissue engineering, cranial bone defects of critical size remain difficult to repair due to the limited self-regeneration capacity of the bone. Developmental engineering with mesenchymal stem cells (MSCs) aggregates has shown promise for enhanced bone regeneration; however, these MSCs aggregates require extended in vitro osteogenic induction time and lack sufficient vascularization to enable rapid in situ osteogenesis. To address these issues, a novel strategy is introduced for the large-scale generation of prevascularized bone organoids with self-organized vascularization and enhanced osteogenic properties by combining MSCs, human umbilical vein endothelial cells, and osteogenic microparticles. The osteogenic differentiation effects across different microparticles were systematically evaluated and identified graphene oxide as the most effective, which primarily promoted osteogenesis through the focal adhesion and PI3K/Akt pathway. Further, the prevascularized bone organoid-laden hydrogels can be 3D printed into complex tissue constructs with high cell density and osteogenic capacity. In vivo experiments confirmed that this approach promoted rapid vascularized bone tissue formation, achieving effective in situ regeneration and repair of cranial bone defects. This innovative developmental engineering strategy provides a promising, scalable, and effective approach to bone regeneration, advancing developmental tissue engineering for therapeutic applications.

Osteoimmunity-Regulating biospun 3D silk scaffold for bone regeneration in critical-size defects

INTRODUCTION

Silk-based biomaterials have received a great deal of attention in tissue engineering research for bone repair. Current silk-based materials are typically derived from silk protein solutions, but the limited solubility and solution stability of silk protein solution, coupled with problems such as high preparation cost and low productivity, which severely restrict the application of silk-based materials.

OBJECTIVE

To address the challenges associated with the complex extraction process and inferior mechanical properties of silk protein or silk fiber-based materials in bone scaffold preparation, flat cocoon silk-based materials were developed to assess their potential for repairing large bone defects.

METHODS

We converted the upper cluster mesh's three-dimensional structure into a two-dimensional flattened plate and controlled the thickness and area of the flattened silkworm cocoons by adjusting the number of mature silkworms and spitting time to match the needs of different sites and bone defect areas. After being hot-pressed, the flattened silkworm cocoons were mixed with PLA to form an excellent tissue engineering scaffold material with a highly porous structure.

RESULTS

The 3D FSC/PLA scaffold demonstrated superior mineralization, mechanical resilience, and biocompatibility. Notably, it promoted anti-inflammatory gene expression, suppressed inflammatory responses through M2 macrophage polarization, and enhanced bone formation and angiogenesis by modulating key pathways, including PI3K-AKT, Wnt, MAPK, and Notch.

CONCLUSIONS

By using silkworm larvae to directly create a scaffold, a three-dimensional matrix with properties similar to extracellular matrix and a gradient structure that closely resembles cortical bone was created. This process effectively modulates the immune balance for fibroin dissolution and regeneration. The targeted infiltration of PLA within the 3D silk matrix enabled precise control over porosity and degradation, fostering optimal cellular adhesion and proliferation. As an osteoimmunity-regulating scaffold, it holds significant promise for enhancing bone regeneration and offers a robust foundation for repairing large-scale bone defects.

Bayesian neural networks for probabilistic modeling of thermal dynamics in multiscale tissue engineering scaffolds

Multiscale tissue engineering integrated with thermal dynamics exhibits a critical role as scaffolds in maintaining the structural integrity and functionality in fabrication applications. Thermal dynamics influence the properties such as thermal conductivity, the capacity of heat, and thermal expansion of materials to maintain the scaffold stability in various physiological conditions. However, the scaffold's heat distribution in a uniform manner is varied due to variations in pore size and geometrics. Additionally, variation in scales affects the thermal gradient impacts on the cell growth and integrity. This paper proposes the 3D Scaffolds Probabilistic Weighted Bayesian Neural Network (3D-SP-WBNN) for tissue engineering with a multiscale scaffold model. It uses the 3D scaffolds for the multiscale design estimation. The weighted Probabilistic Bayesian Neural Network model is employed for estimating features in tissues and evaluating the cell growth and proliferation. Thermal gradients measured were in between 1 °C and 4 °C for human bone, skin, and cartilage tissues. For low and moderate temperatures of 1 °C and 2 °C, the cell proliferation rates in cartilage tissues were 15-20 % per day. The scaffold design uses the Hybrid Hydrogel/PCL composite to achieve a higher proliferation rate of 25-35 % per day. The estimated forecasting achieves an accuracy range of 82-96 % for different cell densities and thermal conditions.

Construction of multifunctional tracheal substitute based on silk fibroin methacryloyl and hyaluronic acid methacryloyl with decellularized cartilaginous matrix for tracheal defect repair

The regeneration and functional recovery of tracheal tissue are of paramount importance in the research of tissue-engineered trachea. Current constructs still face some limitations in simulating the complex natural microenvironment and achieving better regenerative capacity and functional recovery. To address these challenges, the application of hydrogels with three-dimensional (3D) network structure and extracellular matrix derived from decellularized tissues and cells has become a more promising strategy. This study aims to introduce a novel bilayer multifunctional tissue-engineered tracheal substitute. Firstly, the mesh polycaprolactone (PCL) scaffold was printed by 3D printing technology, and the concentration of Silk Fibroin Methacryloyl (SilMA) hydrogel suitable for cell adhesion and proliferation and the concentration of Hyaluronic Acid Methacryloyl (HAMA) hydrogel suitable for 3D culture of chondrocytes were selected. Subsequently, the decellularized cartilaginous matrix (DCM) solution was obtained and the concentration that promotes chondrocyte proliferation and migration was screened. Finally, the multifunctional tracheal substitute, which features a HAMA-DCM composite hydrogel loaded with autologous chondrocytes as the basic framework to simulate the outer cartilaginous layer, and a 3D-printed PCL mesh scaffold coated with SilMA hydrogel loaded with autologous epithelial cells serves as internal support to simulate the inner airway epithelial layer, was prepared. Whether it was for repairing window-shape defect for 8 w or conducting long-segment in situ transplantation for 12 w, it achieved satisfactory surgical outcomes, including epithelial crawling, cartilage regeneration, and vascular remodeling.

ROS-Activated Nanohydrogel Scaffolds with Multi-Factors Controlled Release for Targeted Dual-Lineage Repair of Osteochondral Defects

Achieving self-healing for osteochondral defects caused by trauma, aging, or disease remains a significant challenge in clinical practice. It is an effective therapeutic strategy to construct gradient-biomimetic biomaterials that replicate the hierarchical structure and complex microenvironment of osteochondral tissues for dual-lineage regeneration of both cartilage and subchondral bone. Herein, ROS-activated nanohydrogels composite bilayer scaffolds with multi-factors controlled release are rationally designed using the combination of 3D printing and gelatin placeholder methods. The resulting nanohydrogel scaffolds exhibit micro-nano interconnected porous bilayer structure and soft-hard complex mechanical strength for facilitating 3D culture of BMSCs in vitro. More importantly, multi-stage continuous responses of anti-inflammation, chondrogenesis and osteogenesis, are effectively induced via the sequential release of multi-factors, including diclofenac sodium (DS), kartogenin (KGN) and bone morphogenetic protein 2 (BMP-2), from ROS-activated nanohydrogel scaffolds, thereby improved dual-lineage regeneration of cartilage and subchondral bone tissue in the osteochondral defect model of SD rats. These findings suggest that ROS-activated nanohydrogel scaffolds with such specific soft-hard bilayer structure and sequential delivery of functional factors, provides a promising strategy in dual-lineage regeneration of osteochondral defects.

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.

Revolutionizing tissue regeneration: the art of mimicking diverse collagen-based extracellular matrix hierarchies with decellularized tendon via bioskiving

Precisely simulating the collagen-based extracellular matrix (ECM) hierarchy is essential for advancing tissue regeneration. Although decellularized ECM (dECM) demonstrates considerable potential in fostering tissue regeneration by maintaining the inherent hierarchy, its application remains restricted to homologous tissues due to hierarchical variability. The current challenge involves overcoming obstacles that impede the application of dECM across diverse tissues, with particular emphasis on re-engineering one type of dECM to mimic the complex hierarchies of other tissues. The decellularized tendon, distinguished by its aligned collagen fibers, has garnered substantial interest due to its favorable structural and mechanical properties. Recently, a novel technique termed bioskiving has been developed, which uniquely disassembles macroscale decellularized tendons into microscale collagen sheets via microtome sectioning, thereby preserving micro/nano architecture of fiber alignment without chemical denaturation. These sheets can be further rotationally stacked or rolled to engineer 2D or 3D constructs replicating diverse ECM hierarchies. Bioskiving effectively dismantles the persistent hindrance that traditionally impeded the application of dECM across various tissues. This review offers an in-depth analysis of the fabrication procedure and characterization of constructs produced through bioskiving. It specifically elucidates the applications of constructs across various domains in tissue engineering, demonstrating its potential in overcoming tissue-specific constraints of dECM.

Poly(propylene fumarate) Composite Scaffolds for Bone Tissue Engineering: Innovation in Fabrication Techniques and Artificial Intelligence Integration

Over the past three decades, the biodegradable polymer known as poly(propylene fumarate) (PPF) has been the subject of numerous research due to its unique properties. Its biocompatibility and controllable mechanical properties have encouraged numerous scientists to manufacture and produce a wide range of PPF-based materials for biomedical purposes. Additionally, the ability to tailor the degradation rate of the scaffold material to match the rate of new bone tissue formation is particularly relevant in bone tissue engineering, where synchronized degradation and tissue regeneration are critical for effective healing. This review thoroughly summarizes the advancements in different approaches for PPF and PPF-based composite scaffold preparation for bone tissue engineering. Additionally, the challenges faced by each approach, such as biocompatibility, degradation, mechanical features, and crosslinking, were emphasized, and the noteworthy benefits of the most pertinent synthesis strategies were highlighted. Furthermore, the synergistic outcome between tissue engineering and artificial intelligence (AI) was addressed, along with the advantages brought by the implication of machine learning (ML) as well as the revolutionary impact on regenerative medicines. Future advances in bone tissue engineering could be facilitated by the enormous potential for individualized and successful regenerative treatments that arise from the combination of tissue engineering and artificial intelligence. By assessing a patient's reaction to a certain drug and choosing the best course of action depending on the patient's genetic and clinical characteristics, AI can also assist in the treatment of illnesses. AI is also used in drug research and discovery, target identification, clinical trial design, and predicting the safety and effectiveness of novel medications. Still, there are ethical issues including data protection and the requirement for reliable data management systems. AI adoption in the healthcare sector is expensive, involving staff and facility investments as well as training healthcare professionals on its application.

Biomaterial-based drug delivery systems in the treatment of inner ear disorders

Inner ear disorders are among the predominant etiology of hearing loss. The blood-labyrinth barrier limits the ability of drugs to attain pharmacologically effective concentrations within the inner ear; consequently, delivering drugs systemically is insufficient for effectively treating inner ear disorders. Hence, it is imperative to create efficient, minimal or non-invasive methods for administering drugs to the inner ear. However, the development of such a system is hindered by three main factors: anatomical unavailability, the lack of sustained drug delivery, and individual variability. Advances in biomaterials technology have created new opportunities for overcoming existing barriers, offering great hope for the effective treatment of inner ear disorders. Hydrogel- and nanoparticle-based drug delivery systems can carry drugs to targeted designated anatomical locations in the inner ear for long-term, sustained release. Furthermore, a range of devices, including microneedles, micropumps, and cochlear implants, when paired with biomaterials, enhance the delivery of drugs to the inner ear, making the treatment of inner ear disorders more effective. Therefore, biomaterial-based drug delivery systems offer the possibility for extensive clinical uses and promise to restore hearing to millions of patients with inner ear disorders.

Artificial Bone Materials for Infected Bone Defects: Advances in Antimicrobial Functions

Infected bone defects, caused by bacterial contamination following disease or injury, result in the partial loss or destruction of bone tissue. Traditional bone transplantation and other clinical approaches often fail to address the therapeutic complexities of these conditions effectively. In recent years, advanced biomaterials have attracted significant attention for their potential to enhance treatment outcomes. This review explores the pathogenic mechanisms underlying infected bone defects, including biofilm formation and bacterial internalization into bone cells, which allow bacteria to evade the host immune system. To control bacterial infection and facilitate bone repair, we focus on antibacterial materials for bone regeneration. A detailed introduction is given on intrinsically antibacterial materials (e.g., metal alloys, oxide materials, carbon-based materials, hydroxyapatite, chitosan, and Sericin). The antibacterial functionality of bone repair materials can be enhanced through strategies such as the incorporation of antimicrobial ions, surface modification, and the combined use of multiple materials to treat infected bone defects. Key innovations discussed include biomaterials that release therapeutic agents, functional contact biomaterials, and bioresponsive materials, which collectively enhance antibacterial efficacy. Research on the clinical translation of antimicrobial bone materials has also facilitated their practical application in infection prevention and bone healing. In conclusion, advancements in biomaterials provide promising pathways for developing more biocompatible, effective, and personalized therapies to reconstruct infected bone defects.

Engineered 3D mesenchymal stem cell aggregates with multifunctional prowess for bone regeneration: Current status and future prospects

BACKGROUND

Impaired efficacy of in vitro expanded mesenchymal stem cells (MSCs) is a universal and thorny situation, which cast a shadow on further clinical translation of exogenous MSCs. Moreover, the relatively lengthy healing process, host metabolic heterogeneity and the sophisticated cell recognition and crosstalk pose rigorous challenges towards MSC-based bone regeneration strategies. Three-dimensional (3D) cell aggregates facilitate more robust intercellular communications and cell-extracellular matrix (ECM) interactions, providing a better mimicry of microarchitectures and biochemical milieus in vivo, which is conducive for stemness maintenance and downstream bone formation.

AIM OF REVIEW

This review enunciates the phenotypic features of MSCs in aggregates, which deepens the knowledge of the MSC fate determination in 3D microenvironment. By summarizing current empowerment methods and biomaterial-combined techniques for establishing functionalized MSC aggregates, this review aims to spark innovative and promising solutions for exalting the translational value of MSCs and improve their therapeutic applications in bone tissue repair.

KEY SCIENTIFIC CONCEPTS OF REVIEW

3D aggregates optimize regenerative behaviors of in vitro cultured MSCs including cell adhesion, viability, proliferation, pluripotency and immunoregulation capacity, etc. Biomaterials hybridization endows MSC aggregates with tailored mechanical and biological properties, which offers more possibilities in adapting various clinical scenarios.

Ultrasound-responsive smart biomaterials for bone tissue engineering

Bone defects resulting from trauma, tumors, or other injuries significantly impact human health and quality of life. However, current treatments for bone defects are constrained by donor shortages and immune rejection. Bone tissue engineering has partially alleviated the limitations of traditional bone repair methods. The development of smart biomaterials that can respond to external stimuli to modulate the biofunctions has become a prominent area of research. Ultrasound technology is regarded as an optimal "remote controller" and "trigger" for bone repair biomaterials. This review reports the comprehensive and systematic overview of ultrasound-responsive bone repair smart biomaterials. It presents the fundamental theories of bone repair, the definition of ultrasound, and its applications. Furthermore, the review summarizes the ultrasound effect mechanisms of biomaterials and their roles in bone repair, including detailed studies on anti-inflammation, immunomodulation, and cell therapy. Finally, the advantages of ultrasound-responsive smart biomaterials and their future prospects in this field are discussed.

Antioxidant scaffolds for enhanced bone regeneration: recent advances and challenges

Bone regeneration is integral to maintaining bone function and integrity in the body, as well as treating bone diseases, such as osteoporosis and defects. However, oxidative stress often poses a significant obstacle during bone regeneration, leading to cell damage, inflammatory responses, and subsequent impediment of normal bone tissue formation. Therefore, to maintain bone regeneration, antioxidant therapy is essential. Bone scaffolds, serving as a temporary support for bone tissue, can provide an ideal microenvironment for cell proliferation and differentiation, effectively promoting bone tissue formation. In recent years, with in-depth research on antioxidants and their mechanisms of action, the development and application of antioxidant bone scaffolds have shown tremendous potential. These antioxidant bone scaffolds not only promote osteogenic differentiation and angiogenesis, but also effectively inhibit the inflammatory response and osteoclast formation, significantly improving the efficiency of bone regeneration. Notably, with the rapid development of nanotechnology, nanozymes with multi-enzyme-like activities have been successfully constructed and encapsulated within bone scaffolds, leading to the proposal of multifunctional antioxidant strategies. Therefore, this review summarizes recent research progress, categorically introducing types of bone scaffolds and antioxidants, elucidating therapeutic strategies of antioxidant bone scaffolds, and identifying current challenges, aiming to provide valuable guidance for subsequent research.

Impact of Cerium Doping on the Osteogenic Properties of a 3D Biomimetic Piezoelectric Scaffold with Sustained Mg2+ Release

Background

In the realm of bone tissue engineering, the role of biomimetic piezoelectric scaffolds made from whitlockite (WH) nanoparticles is increasingly recognized. WH, the second most abundant mineral in human bone, possesses piezoelectric properties and the capacity to release magnesium ions (Mg2+), both of which are vital for osteogenic differentiation. This study investigates the osteogenic effects of cerium (Ce) doping on three-dimensional biomimetic piezoelectric scaffolds composed of whitlockite (WH) nanoparticles.

Methods

WH nanoparticles with varying Ce concentrations were synthesized and scaffolds were prepared using a freeze-drying process with sodium alginate as the matrix. In vitro experiments with human bone marrow mesenchymal stem cells (hBMSCs) assessed cell proliferation and differentiation, while animal studies employed a rat calvarial defect model to evaluate new bone formation and mineralization.

Results

Our findings revealed that Ce doping modifies the crystallinity and electrical properties of WH nanoparticles, thereby affecting their osteogenic potential. In vitro studies indicated that scaffolds with a Ce/Ca ratio of 0.06 significantly boosted osteogenic marker expression. Furthermore, animal studies confirmed that Ce-doped WH scaffolds, especially those with the 0.06 ratio, markedly improved both new bone formation and mineralization.

Conclusion

The study demonstrates that Ce doping can significantly enhance the osteogenic properties of WH-based scaffolds, with the optimal Ce/Ca ratio of 0.06 being particularly effective in promoting bone formation. This research provides a promising approach for the development of advanced materials in bone tissue engineering.

CircAars-Engineered ADSCs Facilitate Maxillofacial Bone Defects Repair Via Synergistic Capability of Osteogenic Differentiation, Macrophage Polarization and Angiogenesis

Adipose-derived stem cells (ADSCs) hold significant promise in bone tissue engineering due to their self-renewal capacity and easy accessibility. However, their limited osteogenic potential remains a critical challenge for clinical application in bone repair. Emerging evidence suggests that circular RNAs (circRNAs) play a key role in regulating stem cell fate and osteogenesis. Despite this, the specific mechanisms by which circRNAs influence ADSCs in the context of bone tissue engineering are largely unexplored. This study introduces a novel strategy utilizing circAars, a specific circRNA, to modify ADSCs, which are then incorporated into gelatin methacryloyl (GelMA) hydrogels for the repair of critical-sized maxillofacial bone defects. The findings reveal that circAars predominantly localizes in the cytoplasm of ADSCs, where it acts as a competitive sponge for miR-128-3p, enhancing the osteogenic differentiation and migration capabilities of ADSCs. Furthermore, circAars-engineered ADSCs facilitate macrophage polarization from the M1 to M2 phenotype and enhance endothelial cell (EC) angiogenic potential through a paracrine mechanism. Additionally, GelMA scaffolds loaded with circAars-engineered ADSCs accelerate the repair of critical-sized maxillofacial bone defects by synergistically promoting osteogenesis, macrophage M2 polarization, and angiogenesis. This approach offers a promising therapeutic strategy for the treatment of critical-sized maxillofacial defects.

High-Strength Gelatin Hydrogel Scaffold with Drug Loading Remodels the Inflammatory Microenvironment to Enhance Osteoporotic Bone Repair

Osteoporosis is a widespread condition that induces an inflammatory microenvironment, limiting the effectiveness of conventional therapies and presenting significant challenges for bone defect repair. To address these issues, a high-strength gelatin hydrogel scaffold loaded with roxadustat is developed, specifically designed to remodel the inflammatory microenvironment and enhance osteoporotic bone regeneration. By incorporating minimal methacrylated hyaluronic acid (HAMA) into an o-nitrobenzyl functionalized gelatin (GelNB) matrix, a gelatin hydrogel with a fracture strength of 10 MPa is achieved, providing exceptional structural stability and enabling precise scaffold fabrication through digital light processing (DLP) 3D printing. Validated through cell experiments and animal studies, the hydrogel scaffold supports cell adhesion and migration, offers excellent tissue compatibility, and is fully degradable, meeting the requirements of a therapeutic scaffold. Including roxadustat further enhances the scaffold's functionality by regulating the inflammatory microenvironment via hypoxia-inducible factor-1α (HIF-1α) signaling, significantly improving bone defect repair in osteoporotic models. This drug-loaded scaffold effectively addresses inflammation-induced limitations and enhances the regenerative capacity of the affected area, paving the way for improved therapeutic outcomes in osteoporotic bone repair.

3D-Printed Polycaprolactone/Hydroxyapatite Bionic Scaffold for Bone Regeneration

The limitations of traditional, autologous bone grafts, such as the scarcity of donor material and the risks of secondary surgical trauma, have spurred the development of alternatives for the repair of large bone defects. Bionic bone scaffolds fabricated via fused deposition modeling (FDM)-a three-dimensional (3D) printing technique-are considered promising. While gyroid-structured scaffolds mimic the complex micro-architecture of cancellous bone, their application in FDM 3D printing remains understudied. Furthermore, no consensus has been reached on the ideal pore size for gyroid scaffolds, which is influenced by the infill density. In this study, we fabricated five groups of polycaprolactone/hydroxyapatite (PCL/HA) scaffolds with different infill densities (40%, 45%, 50%, 55%, and 60%) using a solvent-free filament preparation method. Scanning electron microscopy (SEM) observation showed that all scaffolds exhibit an interconnected porous structure. The scaffold with the 55% infill density, featuring a pore size of 465 ± 63 μm, demonstrated optimal hydrophilicity and mechanical properties comparable to natural cancellous bone. In addition, this scaffold supported cellular bridging within its pores and showed the highest alkaline phosphatase (ALP) activity and calcium salt deposition. Our findings offer novel insights into the design of gyroid-like scaffolds and their fabrication via FDM, paving the way for potential clinical applications.

Fabrication of a Whitlockite/PLGA Scaffold with Hierarchical Porosity for Bone Repair

Regenerating functional bone tissue in critical-sized defects remains a formidable issue. Bone-tissue engineering (BTE) scaffolds are emerging as potential alternatives to bone transplantation for the repair of bone defects. However, developing BTE scaffolds with unique bone-healing properties and natural bone porous structure is challenging. Herein, we presented a biomimetic scaffold with hierarchical porosity via a solvent casting/particulate leaching method. The scaffold comprises osteoinductive whitlockite (WH) nanoparticles evenly dispersed in a poly(lactic-co-glycolic acid) (PLGA) matrix. Highly interconnected pores with hierarchical variations are present in the scaffold, enabling superior solution diffusion and compressive strength. Notably, the WH/PLGA scaffold effectively promoted osteoblast differentiation in vitro and induced bone formation in rat tibia defects, surpassing the performance of both the hydroxyapatite (HAP)/PLGA scaffold and the PLGA scaffold. This study provides a low-cost, facile, and scalable strategy for fabricating BTE scaffolds with favorable mechanical properties, biocompatibility, and bone repair capability.

Piezoelectricity Promotes 3D-Printed BTO/β-TCP Composite Scaffolds with Excellent Osteogenic Performance

Piezoelectricity is reported to be able to promote bone scaffolds with excellent osteogenic performance. Herein, barium titanate/β-tricalcium phosphate (BTO/β-TCP) piezoelectric composite scaffolds were 3D printed, and their osteogenic performances were investigated in detail. The fabrication of BTO/β-TCP piezoelectric composite scaffolds employed cutting-edge DLP 3D printing technology. The scaffolds, featuring a triply periodic minimal surface (TPMS) design with a porosity of 60%, offered a unique structural framework. A comprehensive assessment of the composition, piezoelectric properties, and mechanical characteristics of the BTO/β-TCP scaffolds was conducted. Notably, an increase in the BTO volume fraction from 50 to 80 vol % within the scaffolds led to a reduction in compressive strength, decreasing from 2.47 to 1.74 MPa. However, this variation was accompanied by a substantial enhancement in the piezoelectric constant d33, soaring from 1.4 pC/N to 21.6 pC/N. Utilizing mouse osteoblasts (MC3T3-E1) in a live/dead cell staining assay, under the influence of external ultrasound, demonstrated the commendable biocompatibility of these piezoelectric composite ceramic bone scaffolds. Furthermore, thorough analyses of alkaline phosphatase (ALP) activity and polymerase chain reaction (PCR) findings provided compelling evidence of the scaffolds' superior osteogenic properties, underpinning their effectiveness at the cellular protein and gene levels. In conclusion, this study offers a groundbreaking strategy for the employment of BTO/β-TCP piezoelectric composite scaffolds in bone implant applications, harnessing their unique blend of biocompatibility, piezoelectricity, and osteogenic potential.

Mimicking bone remodeling scaffolds of polyvinylalcohol/silk fibroin with phytoactive compound of soy protein isolate as surgical supporting biomaterials for tissue formation at defect area in osteoporosis; characterization, morphology, andin-vitrotesting

Mimicking bone remodeling scaffolds were developed as supportive biomaterials to promote tissue formation at defect sites in osteoporosis. Scaffolds made of polyvinyl alcohol (PVA) were mixed with varying weight ratios of silk fibroin (SF) and a phytoactive compound-based soy protein isolate (SPI); PVA30SF, PVA20SF10SPI, PVA15SF15SPI, PVA10SF20SPI, PVA30SPI. PVA was used as control. These components were mixed into aqueous solution and crosslinking with EDC before freeze thawing and freeze drying, respectively. Then, the scaffolds were characterized at the molecular level using Fourier transform infrared spectroscopy and their morphology was observed using scanning electron microscopy. Physical properties including swelling and degradation were tested, as well as mechanical properties like stress-strain behavior and modulus. The biological performance of the scaffolds was evaluated through osteoblast cell culturing, assessing cell viability, proliferation, alkaline phosphatase (ALP) activity, calcium content, and calcium deposition. The results demonstrate that the scaffolds with both SF and SPI had greater molecular mobility of -OH, amide I, II, and III groups, compared to the scaffold with only SF or SPI. These scaffolds also displayed larger pore sizes. Scaffolds with both SF and SPI showed higher swelling and degradation rates than those with only SF or SPI. Additionally, they exhibited better cell viability and calcium deposition, along with increased cell proliferation, ALP activity, and calcium content. Notably, the scaffold with a higher amount of SPI, PVA10SF20SPI, exhibited the most suitable performance for enhancing cell response, thereby promoting bone formation. This scaffold is proposed as a supportive biomaterial to be incorporated with plates and screws for bone fixation at defect sites in osteoporosis.

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.

In Situ Preparation of Composite Scaffolds Based on Polyurethane and Hydroxyapatite Particles for Bone Tissue Engineering

This article details the in situ preparation of composite scaffolds using polyurethane (PU) and HAp (hydroxyapatite), focusing on the unique properties of buriti oil (Mauritia flexuosa L.) applicable to tissue engineering. PU derived from vegetable oils, particularly buriti oil, has shown promise in bone tissue repair due to its rich bioactive compounds. Buriti oil is an excellent candidate for manufacturing these materials as it is an oil rich in bioactive compounds such as carotenoids, tocopherols, and fatty acids, which have antioxidant and anti-inflammatory properties. Furthermore, buriti oil has oleic acid as its principal fatty acid, which has been investigated as an excellent HAp dispersant. This research aimed to synthesize PU scaffolds from a polyol derived from buriti oil and incorporate HAp in different concentrations into the polymeric matrix through in situ polymerization. The chemical composition of the materials obtained, the distribution of hydroxyapatite particles in the polyurethane matrix, and the thermal stability were evaluated using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), and thermogravimetry (TGA). In addition, to investigate biocompatibility, MTT tests (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium) were conducted using rat bone-marrow-derived mesenchymal stem cells (BMMSC). Characterizations confirm the formation of PU and the presence of HAp in the polymeric matrix, and the materials did not show cytotoxicity.

Bone regeneration: The influence of composite HA/TCP scaffolds and electrical stimulation on TGF/BMP and RANK/RANKL/OPG pathways

The repair of critical-sized bone defects represents significant clinical challenge. An alternative approach is the use of 3D composite scaffolds to support bone regeneration. Hydroxyapatite (HA) and tri-calcium phosphate (β-TCP), combined with polycaprolactone (PCL), offer promising mechanical resistance and biocompatibility. Bioelectrical stimulation (ES) at physiological levels is proposed to reestablishes tissue bioeletrocity and modulates cell signaling communication, such as the BMP/TGF-β and the RANK/RANK-L/OPG pathways. This study aimed to evaluate the use HA/TCP scaffolds and ES therapy for bone regeneration and their impact on the TGF-β/BMP pathway, alongside their relationship with the RANK/RANKL/OPG pathway in critical bone defects. The scaffolds were implanted at the bone defect in animal model (calvarial bone) and the area was subjected to ES application twice a week at 10 µA intensity of current for 5 min each session. Samples were collected for histomorphometry, immunohistochemistry, and molecular analysis. The TGF-β/BMP pathway study showed the HA/TCP+ES group increased BMP-7 gene expression at 30 and 60 days, and also greater endothelial vascular formation. Moreover, the HA/TCP and HA/TCP+ES groups exhibited a bone remodeling profile, indicated by RANKL/OPG ratio. HA/TCP scaffolds with ES enhanced vascular formation and mineralization initially, while modulation of the BMP/TGF pathway maintained bone homeostasis, controlling resorption via ES with HA/TCP.

Comparative evaluation of melt- vs. solution-printed poly(ε-caprolactone)/hydroxyapatite scaffolds for bone tissue engineering applications

Material extrusion-based three-dimensional (3D) printing is a widely used manufacturing technology for fabricating scaffolds and devices in bone tissue engineering (BTE). This technique involves two fundamentally different extrusion approaches: solution-based and melt-based printing. In solution-based printing, a polymer solution is extruded and solidifies via solvent evaporation, whereas in melt-based printing, the polymer is melted at elevated temperatures and solidifies as it cools post-extrusion. Solution-based printing can also be enhanced to generate micro/nano-scale porosity through phase separation by printing the solution into a nonsolvent bath. The choice of the printing method directly affects scaffold properties and the biological response of stem cells. In this study, we selected polycaprolactone (PCL), a biodegradable polymer frequently used in BTE, blended with hydroxyapatite (HA) nanoparticles, a bioceramic known for promoting bone formation, to investigate the effects of the printing approach on scaffold properties and performance in vitro using human mesenchymal stem cells (hMSCs). Our results showed that while both printing methods produced scaffolds with similar strut and overall scaffold dimensions, solvent-based printing resulted in porous struts, higher surface roughness, lower stiffness, and increased crystallinity compared to melt-based printing. Although stem cell viability and proliferation were not significantly influenced by the printing approach, melt-printed scaffolds promoted a more spread morphology and exhibited pronounced vinculin staining. Furthermore, composite scaffolds outperformed their neat counterparts, with melt-printed composite scaffolds significantly enhancing bone formation. This study highlights the critical role of the printing process in determining scaffold properties and performance, providing valuable insights for optimizing scaffold design in BTE.

Hydroxyapatite Chitosan Gradient Pore Scaffold Activates Oxidative Phosphorylation Pathway to Induce Bone Formation

BACKGROUND

In this study, we prepared a porous gradient scaffold with hydroxyapatite microtubules (HAMT) and chitosan (CHS) and investigated osteogenesis induced by these scaffolds.

METHODS

The arrangement of wax balls in the mold can control the size and distribution of the pores of the scaffold, and form an interconnected gradient pore structure. The scaffolds were systematically evaluated in vitro and in vivo for biocompatibility, biological activity, and regulatory mechanisms.

RESULTS

The porosity of the four scaffolds was more than 80%. The 50% and 70% HAMT-CHS scaffolds formed an excellent gradient pore structure, with interconnected pores. Furthermore, the 70% HAMT-CHS scaffold showed better anti-compressive deformation ability. In vitro experiments indicated that the scaffolds had good biocompatibility, promoted the expression of osteogenesis-related genes and proteins, and activated the oxidative phosphorylation pathway to promote bone regeneration. Eight weeks after implanting the HAMT-CHS scaffold in rat skull defects, new bone formation was observed in vivo by micro-computed tomographic (CT) staining. The obtained data were statistically analyzed, and the p-value < 0.05 was statistically significant.

CONCLUSION

HAMT-CHS scaffolds can accelerate osteogenesis in bone defects, potentially through the activation of the oxidative phosphorylation pathway. These results highlight the potential therapeutic application of HAMT-CHS scaffolds.

3D scaffold of hydroxyapatite/β tricalcium phosphate from mussel shells: Synthesis, characterization and cytotoxicity

Bone tissue substitutes are increasing in importance. Hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) act as a cell matrix and improve its mechanical properties. One of their raw materials is marine-origin by-products.

OBJECTIVES

To synthesize, characterize, and evaluate the cellular cytotoxicity of a 3D biomaterial based on HA and β-TCP from mussel shells.

METHODS

We prepared pellets with 150, 200, and 250 mg and evaluated them through sintering, XRD, FTIR, ICP-OES, Scanning Electron Microscopic (SEM), and immunocytochemical tests. The Alamar Blue method was applied to the Balb-T3T cell line within 72 h to evaluate cytotoxicity.

RESULTS

Our biomaterials presented a smooth surface with slight irregularity and porosities presenting different diameters and morphologies and showed chemical, morphological, and ultrastructural similarity to bone hydroxyapatite, mainly the 150 and 200 mg pellets.

SIGNIFICANCE

We produced promising HA/β-TCP bioceramics with characteristics that allowed cell culture, promoting adhesion, spreading, and proliferation.

Novel Decellularization Scheme for Preparing Acellular Fish Scale Scaffolds for Bone Tissue Engineering

In bone tissue engineering, a suitable scaffold is the key. Due to their similar composition to bone tissue, special structure, good mechanical properties, and osteogenic properties, acellular fish scale scaffolds are potential scaffolds for bone tissue engineering. At present, the fish scale decellularization scheme mostly uses a combination of sodium dodecyl sulfate and ethylenediamine tetraacetic acid (EDTA), but this method has problems. We optimized this method using a combined method of Triton X-100, EDTA, and nuclease. In this study, the optimal scheme was screened with respect to the decellularization effect, extracellular matrix composition and structure retention, mechanical properties, cell biocompatibility, and osteogenic differentiation ability. The results showed that the optimal scheme was as follows: the native fish scales were incubated in 0.1% EDTA for 24 h, and then the cellular components were removed with 1% Triton X-100 for 4 days, followed by nuclease digestion for 24 h. On that basis, we proposed a novel and more suitable fish scale decellularization scheme, and the acellular fish scale scaffold prepared by this decellularization scheme may have great potential in bone tissue engineering.

Unlocking Osseointegration: Surface Engineering Strategies for Enhanced Dental Implant Integration

Tooth loss is a prevalent problem faced by individuals of all ages across the globe. Various biomaterials, such as metals, bioceramics, polymers, composites of ceramics and polymers, etc., have been used for the manufacturing of dental implants. The success of a dental implant primarily depends on its osseointegration rate. The current surface modification techniques fail to imbibe the basics of tooth development, which can impart better mineralization and osseointegration. This can be improved by developing an understanding of the developmental pathways of dental tissue. Stimulating the correct signaling pathways through inductive material systems can bring about a paradigm shift in dental implant materials. The current review focuses on the developmental pathway and mineralization process that happen during tooth formation and how surface modifications can help in biomimetic mineralization, thereby enhancing osseointegration. We further describe the effect of dental implant surface modifications on mineralization, osteoinduction, and osseointegration; both in vitro and in vivo. The review will help us to understand the natural process of teeth development and mineralization and how the surface properties of dental implants can be further improved to mimic teeth development, in turn increasing osseointegration.

Bacterial Cellulose/Graphene Oxide/Hydroxyapatite Biocomposite: A Scaffold from Sustainable Sources for Bone Tissue Engineering

Bone tissue engineering demands advanced biomaterials with tailored properties. In this regard, composite scaffolds offer a strategy to integrate the desired functionalities. These scaffolds are expected to provide sufficient cellular activities while maintaining the required strength necessary for the bone repair for which they are intended. Hence, attempts to obtain efficient composites are growing. However, in most cases, the conventional production methods of scaffolds are energy-intensive and leave an impact on the environment. This work aims to develop a biocomposite scaffold integrating bacterial cellulose (BC), hydroxyapatite (HAp), and graphene oxide (GO), designated as "BC/HAp/GO". All components are sourced primarily from agricultural and food waste as alternative means. BC, known for its biocompatibility, fine fiber network, and high porosity, serves as an ideal scaffold material. HAp, a naturally occurring bone component, contributes osteoconductive properties, while GO provides mechanical strength and biofunctionalization capabilities. The biomaterials were analyzed and characterized using a scanning electron microscope, a X-ray diffractometer, and a Fourier transform infrared spectrometer. The produced biocomposite scaffolds were tested for thermal stability, mechanical strength, and biocompatibility. The results showed a nanofibrous, porous network of BC, highly crystalline HAp particles, and well-oxygenated GO flakes with slight structural deformities. The synthesized biocomposite demonstrated promising characteristics, such as increased tensile strength due to added GO particles and higher bioactivity through the introduction of HAp. These inexpensively synthesized materials, marked by suitable surface morphology and cell adhesion properties, open potential applications in bone repair and regeneration.

Osteochondral Tissue Engineering: Scaffold Materials, Fabrication Techniques and Applications

Osteochondral damage, caused by trauma, tumors, or degenerative diseases, presents a major challenge due to the limited self-repair capacity of the tissue. Traditional treatments often result in significant trauma and unpredictable outcomes. Recent advances in bone/cartilage tissue engineering, particularly in scaffold materials and fabrication technologies, offer promising solutions for osteochondral regeneration. This review highlights the selection and design of scaffolds using natural and synthetic materials such as collagen, chitosan (Cs), and polylactic acid (PLA), alongside inorganic components like bioactive glass and nano-hydroxyapatite (nHAp). Key fabrication techniques-freeze-drying, electrospinning, and 3D printing-have improved scaffold porosity and mechanical properties. Special focus is placed on the design of multiphasic scaffolds that mimic natural tissue structures, promoting cell adhesion and differentiation and supporting the regeneration of cartilage and subchondral bone. In addition, the current obstacles and future directions for regenerating damaged osteochondral tissues will be discussed.

A preliminary study of cell-based bone tissue engineering into 3D-printed β-tricalcium phosphate scaffolds and polydioxanone membranes

Treatment of complex craniofacial deformities is still a challenge for medicine and dentistry because few approach therapies are available on the market that allow rehabilitation using 3D-printed medical devices. Thus, this study aims to create a scaffold with a morphology that simulates bone tissue, able to create a favorable environment for the development and differentiation of osteogenic cells. Moreover, its association with Plenum Guide, through cell-based tissue engineering (ASCs) for guided bone regeneration in critical rat calvarial defects. The manufacturing and characterization of 3D-printed β-TCP scaffolds for experimental surgery was performed. Nine male rats were divided into three groups: β-TCP + PDO membrane (TCP/PG), β-TCP/ASCs + PDO membrane (TCPasc/PG), and β-TCP/ASCs + PDO membrane/ASCs (TCPasc/PGasc). A surgical defect with a 5-mm diameter was performed in the right parietal bone, and the defect was filled with the 3D-printed β-TCP scaffold and PDO membrane with or without ASCs. The animals were euthanized 7, 14, and 30 days after the surgical procedure for histomorphometric and immunolabeling analyses. 3D-printed β-TCP scaffolds were created with a 404 ± 0.0238 μm gyroid macro-pore and, the association to cell-based therapy promotes, especially in the TCPasc/PGasc group, a bone area formation at the defect border region and the center of the defect. The use of 3D-printed β-TCP scaffolds and PDO membranes associated with cell-based therapy could improve and accelerate guided bone regeneration, promoting an increase in osteogenic capacity and reducing the time involved in the bone formation process. Moreover, using ASCs optimized the bioceramics by increasing its osteoinductive and osteoprogenitor capacity and, even with the resorption of the printed scaffold, aided as a scaffold for mesenchymal cell differentiation, as well as in bone tissue formation.

Raman spectroscopic investigation of polymer based magnetic multicomponent scaffolds

Scaffolds acting as an artificial matrix for cell proliferation are one of the bone tissue engineering approaches to the treatment of bone tissue defects. In the presented study, novel multicomponent scaffolds composed of a poly(ε-caprolactone) (PCL), phenolic compounds such as tannic (TA) and gallic acids (GA), and nanocomponents such as silica-coated magnetic iron oxide nanoparticles (MNPs-c) and functionalized multi-walled carbon nanotubes (CNTs) have been produced as candidates for such artificial substitutes. Well-developed interconnected porous structures were observed using scanning electron microscopy (SEM). Raman spectra showed that the highly crystalline nature of PCL was reduced by the addition of nanoadditives. In the case of scaffolds containing MNPs-c and TA, the formation of a Fe-TA complex was concluded because characteristic bands of chelation of the Fe3+ ion by phenolic catechol oxygen appeared. It was found that the necessary conditions for the crystallization of the PCL/MNPs-c/TA are for the catechol groups to be able to penetrate the porous silica shell of MNPs-c, as during experiment with MNPs-c and TA without polymer, no such complexation was observed. Moreover, the number of catechol groups, the spatial structure and molecular size of this phenolic compound are also crucial for complexation process because GA does not form complexes. Therefore, the PCL/CNTs/MNPs-c/TA scaffolds are interesting candidates to consider for their possible medical applications.

A three-phase strategy of bionic drug reservoir scaffold by 3D printing and layer-by-layer modification for chronic relapse management in traumatic osteomyelitis

We have developed a novel three-phase strategy for osteomyelitis treatment, structured into three distinct phases: the "strong antimicrobial" phase, the "monitoring and osteogenesis" phase and the "bone repair" phase. To implement this staged therapeutic strategy, we engineered a bionic drug reservoir scaffold carrying a dual-drug combination of antimicrobial peptides (AMPs) and simvastatin (SV). The scaffold integrated a bilayer gel drug-carrying structure, based on an induced membrane and combined with a 3D-printed rigid bone graft using a layer-by-layer modification strategy. The mechanical strength of the composite scaffold (73.40 ± 22.44 MPa) is comparable to that of cancellous bone. This scaffold enables controlled, sequential drug release through a spatial structure design and nanoparticle drug-carrying strategy. AMPs are released rapidly, with the release efficiency of 74.90 ± 8.19 % at 14 days (pH = 7.2), thus enabling rapid antimicrobial therapy. Meanwhile, SV is released over a prolonged period, with a release efficiency of 98.98 ± 0.05 % over 40 days in vitro simulations, promoting sustained osteogenesis and facilitating the treatment of intracellular infections by activating macrophage extracellular traps (METs). The antimicrobial, osteogenic and immunomodulatory effects of the scaffolds were verified through in vitro and in vivo experiments. It was demonstrated that composite scaffolds were able to combat the chronic recurrence of osteomyelitis after debridement, by providing rapid sterilization, stimulating METs formation, and supporting osteogenic repair.

Smart Implantable Hydrogel for Large Segmental Bone Regeneration

Large segmental bone defects often lead to nonunion and dysfunction, posing a significant challenge for clinicians. Inspired by the intrinsic bone defect repair logic of "vascularization and then osteogenesis", this study originally reports a smart implantable hydrogel (PDS-DC) with high mechanical properties, controllable scaffold degradation, and timing drug release that can proactively match different bone healing cycles to efficiently promote bone regeneration. The main scaffold of PDS-DC consists of polyacrylamide, polydopamine, and silk fibroin, which endows it with superior interfacial adhesion, structural toughness, and mechanical stiffness. In particular, the adjustment of scaffold cross-linking agent mixing ratio can effectively regulate the in vivo degradation rate of PDS-DC and intelligently satisfy the requirements of different bone defect healing cycles. Ultimately, PDS hydrogel loaded with free desferrioxamine (DFO) and CaCO3 mineralized ZIF-90 loaded bone morphogenetic protein-2 (BMP-2) to stimulate efficient angiogenesis and osteogenesis. Notably, DFO is released rapidly by free diffusion, whereas BMP-2 is released slowly by pH-dependent layer-by-layer disintegration, resulting in a significant difference in release time, thus matching the intrinsic logic of bone defect repair. In vivo and in vitro results confirm that PDS-DC can effectively realize high-quality bone generation and intelligently regulate to adapt to different demands of bone defects.

Exploring the frontiers: The potential and challenges of bioactive scaffolds in osteosarcoma treatment and bone regeneration

The standard treatment for osteosarcoma combines surgery with chemotherapy, yet it is fraught with challenges such as postoperative tumor recurrence and chemotherapy-induced side effects. Additionally, bone defects after surgery often surpass the body's regenerative ability, affecting patient recovery. Bioengineering offers a novel approach through the use of bioactive scaffolds crafted from metals, ceramics, and hydrogels for bone defect repair. However, these scaffolds are typically devoid of antitumor properties, necessitating the integration of therapeutic agents. The development of a multifunctional therapeutic platform incorporating chemotherapeutic drugs, photothermal agents (PTAs), photosensitizers (PIs), sound sensitizers (SSs), magnetic thermotherapeutic agents (MTAs), and naturally occurring antitumor compounds addresses this limitation. This platform is engineered to target osteosarcoma cells while also facilitating bone tissue repair and regeneration. This review synthesizes recent advancements in integrated bioactive scaffolds (IBSs), underscoring their dual role in combating osteosarcoma and enhancing bone regeneration. We also examine the current limitations of IBSs and propose future research trajectories to overcome these hurdles.

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

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

Development of Soft Wrinkled Micropatterns on the Surface of 3D-Printed Hydrogel-Based Scaffolds via High-Resolution Digital Light Processing

The preparation of sophisticated hierarchically structured and cytocompatible hydrogel scaffolds is presented. For this purpose, a photosensitive resin was developed, printability was evaluated, and the optimal conditions for 3D printing were investigated. The design and fabrication by additive manufacturing of tailor-made porous scaffolds were combined with the formation of surface wrinkled micropatterns. This enabled the combination of micrometer-sized channels (100-200 microns) with microstructured wrinkled surfaces (1-3 μm wavelength). The internal pore structure was found to play a critical role in the mechanical properties. More precisely, the TPMS structure with a zero local curvature appears to be an excellent candidate for maintaining its mechanical resistance to compression stress, thus retaining its structural integrity upon large uniaxial deformations up to 70%. Finally, the washing conditions selected enabled us to produce noncytotoxic materials, as evidenced by experiments using AlamarBlue to follow the metabolic activity of the cells.

A review of computational optimization of bone scaffold architecture: methods, challenges, and perspectives

The design and optimization of bone scaffolds are critical for the success of bone tissue engineering (BTE) applications. This review paper provides a comprehensive analysis of computational optimization methods for bone scaffold architecture, focusing on the balance between mechanical stability, biological compatibility, and manufacturability. Finite element method (FEM), computational fluid dynamics (CFD), and various optimization algorithms are discussed for their roles in simulating and refining scaffold designs. The integration of multiobjective optimization and topology optimization has been highlighted for developing scaffolds that meet the multifaceted requirements of BTE. Challenges such as the need for consideration of manufacturing constraints and the incorporation of degradation and bone regeneration models into the optimization process have been identified. The review underscores the potential of advanced computational tools and additive manufacturing techniques in evolving the field of BTE, aiming to improve patient outcomes in bone tissue regeneration. The reliability of current optimization methods is examined, with suggestions for incorporating non-deterministic approaches andin vivovalidations to enhance the practical application of optimized scaffolds. The review concludes with a call for further research into artificial intelligence-based methods to advance scaffold design and optimization.

One-Step Gas Foaming Strategy for Constructing Strontium Nanoparticle Decorated 3D Scaffolds: a New Platform for Repairing Critical Bone Defects

The management of critical-sized bone defects poses significant clinical challenges, particularly in the battlefield and trauma-related injuries. However, bone tissue engineering scaffolds that satisfy high porosity and good angiogenic and osteogenic functions are scarce. In this study, 3D nanofiber scaffolds decorated with strontium nanoparticles (3DS-Sr) were fabricated by combining electrospinning and gas foaming. Sodium borohydride (NaBH4) served a dual role as both a reducing and gas-foaming agent, enabling a one-step process for expansion and modification. In vitro experimental results demonstrated that 3DS-Sr possessed an integrated multilayered porous structure. It promoted angiogenesis by upregulating the expression of hypoxia-inducible factor-1α (HIF-1α) protein and phosphorylation of ERK through the sustained release of Sr2+ and created a favorable microenvironment for osteogenesis by activating the Wnt/β-catenin pathway. In vivo experiments indicated that 3DS-Sr promoted cranial bone regeneration by synergistically promoting the effects of vascularization and osteogenesis. In summary, this study proposed a bioactive bone scaffold in a "one stone, two birds" manner, providing a promising strategy for bone defect repair.

Recent advances in layer-by-layer assembly scaffolds for co-delivery of bioactive molecules for bone regeneration: an updated review

Orthopedic implants have faced challenges in treating bone defects due to various factors, including inadequate osseointegration, oxidative stress, bacterial infection, immunological rejection, and poor individualized treatment. These challenges profoundly affect both the results of treatment and patients' daily lives. There is great promise for the layer-by-layer (LbL) assembly method in tissue engineering. The method primarily relies on electrostatic attraction and entails the consecutive deposition of electrolyte complexes with opposite charges onto a substrate, leading to the formation of homogeneous single layers that can be quickly deposited to produce nanolayer films. LbL has attracted considerable interest as a coating technology because of its ease of production, cost-effectiveness, and capability to apply diverse biomaterial coatings without compromising the primary bio-functional properties of the substrate materials. This review will look into the fundamentals and evolution of LbL in orthopedics, provide an analysis of the chemical strategy used to prepare bone implants with LbL and introduce the application of LbL bone implants in orthopedics over recent years. Among the many potential uses of LbL, such as the implementation of sustained-release and programmed drug delivery, which in turn promotes the osseointegration and the development of new blood vessels, as well as antibacterial, antioxidant, and other similar applications. In addition, we offer a thorough examination of cell behavior and biomaterial interaction to facilitate the advancement of next-generation LbL films for tissue engineering.

Bone Tissue Engineering with Adipose-Derived Stem Cells in Polycaprolactone/Graphene Oxide/Dexamethasone 3D-Printed Scaffolds

We fabricated three-dimensional (3D)-printed polycaprolactone (PCL) and PCL/graphene oxide (GO) (PGO) scaffolds for bone tissue engineering. An anti-inflammatory and pro-osteogenesis drug dexamethasone (DEX) was adsorbed onto GO and a 3D-printed PGO/DEX (PGOD) scaffold successfully improved drug delivery with a sustained release of DEX from the scaffold up to 1 month. The physicochemical properties of the PCL, PGO, and PGOD scaffolds were characterized by various analytical techniques. The biological response of these scaffolds was studied for adherence, proliferation, and osteogenic differentiation of seeded rabbit adipose-derived stem cells (ASCs) from DNA assays, alkaline phosphatase (ALP) production, calcium quantification, osteogenic gene expression, and immunofluorescence staining of osteogenic marker proteins. The PGOD scaffold was demonstrated to be the best scaffold for maintaining cell viability, cell proliferation, and osteogenic differentiation of ASCs in vitro. In vivo biocompatibility of PGOD was confirmed from subcutaneous implantation in nude mice where ASC-seeded PGOD can form ectopic bones, demonstrated by microcomputed tomography (micro-CT) analysis and immunofluorescence staining. Furthermore, implantation of PGOD/ASCs constructs into critical-sized cranial bone defects in rabbits form tissue-engineered bones at the defect site, observed using micro-CT and histological analysis.

A functional mineralized collagen hydrogel to promote angiogenic and osteogenic for osseointegration of 3D-printed titanium alloy microporous scaffolds

Bone defects, resulting from trauma, inflammation, tumors, and various other factors, affect both health and quality of life. Although autologous bone transplantation is the gold-standard treatment for bone defects, it has disadvantages such as donor site limitations, prolonged surgical durations, and potential complications, necessitating the development of alternative bone tissue engineering materials. In this study, we used 3D printing technology to fabricate porous titanium implants characterized by superior biocompatibility and mechanical properties. Sodium alginate (SA) and strontium ions (Sr2+) were integrated into mineralized collagen matrices (MCs) to develop strontium-functionalized alginate-mineralized collagen hydrogels (SAMs) with high mechanical strength and sustained metal ion release ability. SAMs were seamlessly incorporated into the porous structures of 3D-printed titanium scaffolds, establishing a novel organic-inorganic bioactive interface. This composite system exhibited high biocompatibility in vitro and increased the expression of genes important for osteogenic differentiation and angiogenesis. In a rabbit model of femoral defect, the titanium implants effectively promoted bone and vascular regeneration on their surface, highlighting their potential in facilitating bone-implant integration.

Developing fibrin-based biomaterials/scaffolds in tissue engineering

Tissue engineering technology has advanced rapidly in recent years, offering opportunities to construct biologically active tissues or organ substitutes to repair or even enhance the functions of diseased tissues and organs. Tissue-engineered scaffolds rebuild the extracellular microenvironment by mimicking the extracellular matrix. Fibrin-based scaffolds possess numerous advantages, including hemostasis, high biocompatibility, and good degradability. Fibrin scaffolds provide an initial matrix that facilitates cell migration, differentiation, proliferation, and adhesion, and also play a critical role in cell-matrix interactions. Fibrin scaffolds are now widely recognized as a key component in tissue engineering, where they can facilitate tissue and organ defect repair. This review introduces the properties of fibrin, including its composition, structure, and biology. In addition, the modification and cross-linking modes of fibrin are discussed, along with various forms commonly used in tissue engineering. We also describe the biofunctionalization of fibrin. This review provides a detailed overview of the use and applications of fibrin in skin, bone, and nervous tissues, and provides novel insights into future research directions for clinical treatment.