Research advances in bioactive bone graft materials and bone marrow enrichment techniques for bone defect treatment

Abstract

Bone defects arise from trauma, infection, tumor resection, or congenital deformities, with large defects often progressing to nonunion. Autologous bone grafting is considered the gold standard therapy due to its osteoconductive, osteoinductive, and osteogenic properties, but it is limited by insufficient graft volume and donor-site complications. Allogeneic grafts and early synthetic bone substitutes partially addressed these limitations but typically provided only osteoconductive function and performed poorly in complex microenvironments. Bone tissue engineering utilizes bioactive scaffolds, cells, and factors to promote bone repair through mechanical support, osteogenic regulation, and cellular adhesion/proliferation/differentiation mechanisms. This review synthesizes current evidence on bioactive scaffold materials and bone marrow enrichment strategies for bone defect repair within a scaffold–bone marrow coupling framework. It also highlights key roles of pore architecture, angiogenesis, osteoimmunomodulation, and defect-specific material selection, while critically discussing current limitations, evidence gaps, and future translational directions.

Keywords

bone marrow enrichment bone marrow concentration scaffold porosity vascularization bone immunology bone defect stem cells growth factors

Introduction

Bone tissue consists of cortical bone, cancellous bone, and various cell types, performing functions such as support, protection, storage, and maintenance of electrolyte balance. Its metabolic processes are influenced by multiple factors, including nutrition and hormones, maintaining a dynamic equilibrium during bone formation and repair¹. Nonunion of bone defects is a category of bone healing disorders secondary to trauma, infection, or tumor resection. The treatment of this condition has consistently been a research focus in the field of orthopedics². Within the field, autologous bone grafting is widely regarded as the gold standard for treating bone defects, as it possesses bone conduction, bone induction, and bone formation capabilities. However, this method is constrained by issues such as insufficient autologous bone supply, high technical demands on orthopedic surgeons, and complex procedures, making it difficult to implement in primary care settings³. In addition to compromising bone function and stability, bone defects may also lead to secondary complications such as infection, deformity, and osteonecrosis in some individuals⁴. The treatment of this disease poses a significant challenge in the field of orthopedics, often requiring individualized therapeutic strategies tailored to the specific circumstances of each patient.

In recent years, autologous bone marrow–based repair strategies have attracted increasing attention as promising approaches for the treatment of bone defects. Rather than simply concentrating “bioactive components,” these strategies aim to enrich regenerative cellular populations and soluble bioactive mediators derived from autologous bone marrow, thereby enhancing the local regenerative potential⁵. When combined with bioactive scaffold materials, these marrow-derived regenerative elements can be better retained within the defect site while receiving the spatial, mechanical, and biological support required for osteogenesis. In this context, successful bone defect repair should not be viewed as the result of a single material or factor, but as the outcome of coordinated interactions among scaffold composition and architecture, marrow-derived regenerative cells and soluble factors, host immune-vascular responses, and defect-specific mechanical demands. Accordingly, this review is organized around a scaffold–bone marrow coupling framework. It aims to summarize recent advances in bioactive scaffold materials and bone marrow enrichment strategies for bone defect treatment, while critically discussing their current limitations, evidence gaps, and future translational directions.

To improve transparency, this narrative review was informed by a structured literature search of PubMed, Web of Science, and Embase for studies published up to November 2025. The search covered multiple areas relevant to bone scaffolds and bone marrow enrichment technologies and used the following keywords: “bone defect,” “scaffold,” “bioactive scaffold,” “bone marrow enrichment,” “bone marrow concentrate,” “BMAC,” “MSC,” “angiogenesis,” “osteoimmunology,” “3D printing,” and “bone tissue engineering.” The literature considered included clinical studies, in vitro and in vivo experimental studies, as well as relevant review articles. Titles and abstracts were first screened for relevance, followed by full-text assessment of potentially eligible studies. Studies addressing bioactive scaffolds, bone marrow enrichment strategies, and their applications in bone defect repair or spinal fusion were included, whereas purely basic biological studies without clear relevance to bone defect repair, studies unrelated to the topic, duplicate publications, and articles without accessible full text were excluded. The following sections synthesize current evidence on scaffold material design, biological functionalization, bone marrow enrichment techniques, evidence levels, and major translational challenges.

Application of scaffold materials in bone defects

The treatment of bone defects aims to restore bone continuity and function. Primary methods include autogenous bone grafting, allogeneic bone grafting, the Ilizarov technique, and the Masquelet technique. Previous studies have extensively documented the fundamental principles, advantages, and clinical applications of these treatment strategies^6–9. To facilitate comparative analysis and synthesis, this article compiles the core information from relevant research into Table 1.

Table 1.

Overview of biological properties and clinical applications of primary treatment methods for bone defect repair.

Treatment modality	Biological mechanism	Advantages	Disadvantages	Clinical indications
Autograft	OC++ / OI++ / OG++	“Gold standard”; Rapid osseointegration	Limited volume; donor-site morbidity; increased operative time	All types of bone defects
Allograft	OC++ / OI± / OG−	Broad availability	Slow absorption; immunogenicity	Extensive defects; structural filling
Xenograft	OC+ / OI− / OG−	Readily accessible	Immunogenicity/infection concerns	Cavity/contour filling (craniofacial defects)
Artificial bone grafting	OC+–++ / OI± / OG−	Designability; serving various biological functions	Lack of living cells and intrinsic vascularity	Different material properties can meet different indications
Ilizarov technique	Distraction osteogenesis	Treat large bone defects	Prolonged treatment, external-fixator complications; high patient burden	Large-segment bone defect
Masquelet technique	Induced membrane formation	Effective for complex/infected defects	Two-stage surgery; long overall course	Large defects associated with trauma/infection/tumor resection

Semi-quantitative grading: ++ strong, + moderate, ± weak/variable, − absent. OC: osteoconductive; OI: osteoinductive; OG: osteogenic.

Although previous studies have reported numerous promising treatments for bone defects using the aforementioned methods, challenges remain—including limited material sources, high surgical burden, and insufficient controllability of outcomes for complex defects. This necessitates the development of novel strategies that integrate spatial structural support with bioactive regulation. Bone tissue engineering (BTE) offers a crucial approach to address these challenges. BTE is an interdisciplinary field integrating biology, materials science, and engineering. Its ultimate goal is to construct biologically active bone tissue in vitro or in vivo for the repair, replacement, or regeneration of bone defects caused by trauma, disease, tumor resection, or congenital deformities¹⁰. The three key elements of this discipline are seed cells, scaffold materials, and bioactive factors¹¹. The scaffold material used for bone grafting forms the foundation of BTE. It provides a three-dimensional (3D) temporary structure for cell adhesion, proliferation, and differentiation, offering both the space and mechanical support necessary for new bone growth.

Types of scaffold materials, key characteristics, and selection considerations in combined bone marrow enrichment strategies

Scaffold materials for bone defect repair should provide not only mechanical support, angiogenic and osteogenic potential, and controllable degradation, but also functional compatibility with marrow-derived regenerative cells and soluble mediators when combined with bone marrow enrichment strategies. Accordingly, scaffold selection should be tailored not only to the type, location, and size of the defect, but also to the intended mode of bone marrow delivery, local retention, and microenvironmental regulation¹². Major categories include metals, bioceramics, natural polymers, synthetic polyesters, and composite material^13–16. These materials adapt to different therapeutic needs based on their biophysical properties. They can be categorized into non-degradable and degradable materials according to their degradability. Non-degradable materials, particularly titanium alloys, are most suitable for defects requiring sustained mechanical reliability, such as load-bearing long bones and segmental mandibular reconstruction¹⁷. In the context of bone marrow enrichment, however, these materials function mainly as structural frameworks rather than intrinsically favorable cell-loading matrices. Their limited surface bioactivity means that they are generally less effective as stand-alone retention carriers for marrow-derived cells or cytokines unless additional surface roughening, topological modification, or bioactive coatings/fillers are introduced. Therefore, metal scaffolds are advantageous when mechanical stability is the dominant requirement, but they usually need secondary biofunctionalization or combination with porous/degradable bioactive phases to become optimal partners for marrow-based regenerative strategies¹⁸. By contrast, biodegradable porous scaffolds are generally more favorable for combined marrow-based therapies because they can serve simultaneously as delivery vehicles, local retention carriers, and microenvironmental regulatory platforms. Their porous architecture and surface physicochemical properties directly affect marrow-derived cell adhesion, migration, distribution, and early survival after implantation. In addition, their larger accessible surface area and interconnected pores make them more suitable for adsorbing and retaining marrow-derived regenerative cells and bioactive components within enriched marrow products¹⁹. These features make biodegradable scaffolds particularly attractive for intraoperative one-step composite preparation, selective retention approaches, and defect sites where cell retention and microenvironmental modulation are prioritized over long-term structural permanence. Nevertheless, their use requires careful control of degradation kinetics and mechanical integrity, since premature loss of support or mismatch with new bone formation may compromise bridging stability²⁰.

In practical applications, the most promising scaffold-bone marrow combinations are typically not based on a single material category, but rather on layered or composite designs²¹. Materials with high mechanical strength (such as metals or high-strength bioceramics) can provide core support for load-bearing regions, while degradable polymers, collagen-rich matrices, or bioactive glass materials can be incorporated into the surface or pore networks to enhance the retention of bone marrow-derived cells, factor delivery, and integration with angiogenesis. Such designs are particularly relevant to bone marrow enrichment strategies because they reconcile two seemingly conflicting requirements: immediate structural reliability and biocompatible load-bearing capacity²².

Taken together, scaffold selection in marrow-enriched bone repair should be interpreted as a problem of functional matching rather than simple material classification. Materials with superior mechanical strength are not always optimal for cell loading or cytokine retention, whereas highly cytocompatible and degradable systems may require structural reinforcement in load-bearing settings. Therefore, future scaffold design should emphasize defect-specific and marrow-specific integration, with composite and multi-scale architectures representing the most rational direction for translational application.

Translational application scenarios of different scaffold materials in bone defect repair and spinal fusion

The following section outlines the bone- and tissue-filling practices for different scaffold materials listed in this article, based on various clinical scenarios. Overall, the clinical value of different scaffold materials should be interpreted based on the specific characteristics of the defect, rather than generalized to the material itself²³. Metal scaffolds with high mechanical strength appear to be more suitable for large-scale weight-bearing defects, while bioceramic and hydrogel-based systems may offer unique advantages in craniofacial reconstruction, cavity filling, and minimally invasive repair of irregular defects. However, the current evidence base for these applications remains uneven, ranging from case reports and small case series to animal studies and early translational research, with relatively few high-quality comparative clinical trials. Therefore, although these materials show promising prospects for application, their relative advantages, long-term performance, and indications still need to be further clarified through more rigorously designed clinical and translational studies.

To facilitate comparison of scaffold selection across different defect scenarios, representative scaffold systems and their design characteristics are summarized in Table 2.

Table 2.

Representative scaffold systems for bone defect repair and their design characteristics.

Application scenario	Scaffold system	Design/key feature	Main finding	References
Segmental mandibular defect	Porous Ti-based metallic scaffold	3D-printed, patient-specific load-bearing construct	Supported osteogenesis at defect margins while maintaining mechanical integrity	Li et al.²⁴
Craniofacial defect reconstruction	Customized HA or HA/β-TCP bioceramic implant	Personalized contour-matched bioceramic reconstruction	Improved contour restoration and osteoconductive integration	Verbist et al.²⁵
Cavity-type bone defects	Porous β-TCP granules or blocks	Osteoconductive bone void filling material	Gradual replacement by new bone reported in many cases	Lu et al.²⁶
Lumbar interbody fusion	PCL/β-TCP biodegradable cage	3D-printed degradable composite cage	Showed fusion and radiographic bone bridging with gradual degradation	Liu et al.²⁷ and Laubach et al.²⁸
Irregular or minimally invasive defects	Injectable/in-situ hydrogel scaffold	ECM-mimicking hydrogel with local conformability	Enabled soft filling and localized biological regulation	Zhou et al.²⁹ and Graupe et al.³⁰

Representative systems are listed to illustrate scenario-specific scaffold selection rather than formal evidence ranking. HA: hydroxyapatite; β-TCP: beta-tricalcium phosphate; PCL: polycaprolactone.

Defect in the weight-bearing bone and a large segment of the jawbone (partial weight-bearing bone)

For large-segment bone defects in weight-bearing or partially weight-bearing bones such as the femur, tibia, and mandible, the primary clinical requirements are early stability and long-term mechanical reliability. Therefore, porous metal scaffolds, particularly 3D-printed Ti-6Al-4V constructs, have become important options for such defects because they can provide patient-specific structural support and adequate mechanical strength²⁴. However, Ti-6Al-4V is not intrinsically bioactive and mainly functions as a structural framework; its osteointegrative capacity depends largely on pore architecture and, in many cases, additional surface modification or biofunctionalization. Current studies suggest that personalized porous titanium scaffolds can support bony union at the defect margins while maintaining mechanical integrity in mandibular and other load-bearing reconstructions²⁴. Nevertheless, these data remain preliminary and are based mainly on limited pilot clinical observations together with supportive preclinical evidence rather than high-level clinical trials.

Craniofacial reconstruction and cavity-type defects with high morphological demands

For craniofacial bones, cranial lamellar defects, and focal defects following excision of benign bone tumors, mechanical loading are relatively moderate, whereas the demands for anatomical matching and aesthetic restoration are particularly high²⁵. In these settings, customized bioceramic implants based on hydroxyapatite (HA) or HA/beta-tricalcium phosphate (β-TCP) have emerged as promising translational options. However, the current evidence is still limited and consists mainly of case reports, small case series, and supportive preclinical studies rather than robust comparative clinical trials. Preliminary findings suggest that compared with titanium plates or PEEK implants, such customized bioceramic implants may provide advantages in contour restoration, osteoconductive integration, and soft-tissue compatibility¹⁴. In addition, β-TCP and related porous granules or blocks have been widely used as bone void fillers after benign tumor resection, especially in cavity-type defects of long bones and small joints²⁶. Available clinical observations indicate gradual replacement by new bone in many cases, although excessive resorption and delayed healing have also been reported²⁶. Therefore, these materials should currently be viewed as encouraging morphology-oriented reconstructive options with osteoconductive potential, while their clinical value still requires confirmation in larger and better-controlled studies.

Spinal fusion and interbody reconstruction

In degenerative spinal disorders such as lumbar spondylolisthesis and spinal stenosis, intervertebral fusion devices serve as the core implants for achieving decompression, restoring intervertebral height, and ensuring long-term stability²⁷. Traditional titanium alloy or PEEK intervertebral fusion cages have been widely adopted, but in recent years, biodegradable composite intervertebral fusion cages represented by polycaprolactone (PCL)/β-TCP and PCL/HA have emerged²⁷. Research indicates that in adult goat models and early clinical studies, 3D-printed PCL/β-TCP intervertebral fusion cages demonstrated favorable fusion rates and radiographic bone bridging formation at 12-month follow-up after posterior lumbar interbody fusion surgery. Furthermore, the cages exhibited progressive degradation and replacement by bone tissue according to their structural design²⁸. Although the above studies have yielded encouraging results, the current evidence remains limited to animal models and early clinical observations, rather than rigorous comparative clinical trials.

Minimally invasive surgery for complex geometric defects

In cases of certain cranial lamellar defects, alveolar/periodontal defects, and osteoporosis-related microfractures, injectable or in situ gel-forming hydrogel scaffolds have attracted increasing attention because of their adaptability to irregular defect geometries and their potential for minimally invasive delivery²⁹. Current studies suggest that hydrogels such as methacrylate-modified hydrogels (GelMA), collagen/chitosan, and polyethylene oxide-polypropylene oxide copolymers can serve as 3D extracellular matrix (ECM)-mimicking networks. What makes these systems attractive is not only their injectability, but also their ability to conform to irregular defects and serve as local carriers for multiple biological cues³⁰. However, the above studies are still preclinical and early-stage translational research and should be interpreted with caution.

The regulatory role of scaffold pore structure in bone regeneration

The porous structure of scaffold materials resembles that of a sponge, with a composition and function analogous to the trabeculae of bone tissue. It is not merely a geometric parameter that “provides space for cells,” but directly participates in multiple processes, including mechanical force transmission, cell–matrix interactions, angiogenesis, degradation behavior, and the delivery of bioactive molecules. It stands as one of the core structural elements determining the efficacy of bone repair³¹.

Pore size and porosity

Extensive in vitro and in vivo experiments demonstrate that, given a specific material type, pore size and total porosity are the key geometric parameters determining bone tissue ingrowth and vascularization³². It is generally believed that pore sizes greater than approximately 100–200 μm are more conducive to reducing fibrous tissue occupation and promoting bone/vascular ingrowth, while the 300–600 μm range demonstrates superior osteogenic and osseointegration effects across various material systems³³. Macro-pores provide pathways for cell migration and angiogenesis, while micro-pores of approximately 1–10 μm primarily enhance cell spreading and osteogenic gene expression by significantly increasing specific surface area, boosting protein adsorption, and facilitating ion exchange. Microporous HA can upregulate osteogenesis-related genes (e.g. ALP, COL1, OCN) and increase mineralized nodules, suggesting that the microporous structure itself possesses certain osteogenic induction potential³⁴. At the smaller nanoscale, surfaces exhibiting mildly disordered nanoscale topography can induce bone-like mineralization deposits in bone marrow–derived mesenchymal stem cells without exogenous inducers. This mechanism is closely associated with integrin-mediated adhesion, cytoskeletal tension, and the activation of mechanosensory pathways such as YAP/TAZ³⁵.

In terms of overall porosity, scaffold design must strike a balance between pore connectivity and mechanical stability³². Research on porous tantalum and 3D-printed porous titanium alloys simulating cancellous bone structure indicates that controlling the overall porosity within approximately 50%–80% (with 60%–70% being a more balanced compromise in some studies) can maintain suitable elastic modulus and fatigue properties while ensuring sufficient cellular/vascular infiltration³⁶. Excessively high porosity, while beneficial for mass transport and degradation, significantly reduces scaffold strength and fatigue resistance; conversely, excessively low porosity tends to result in inadequate tissue ingrowth into the central defect area³⁷. Therefore, how to introduce an appropriate amount of micro-/nanoscale topologies within a suitable macropore size range and synergistically optimize them with an overall porosity of 50%–80% remains one of the core challenges in the geometric parameter design of porous scaffolds (see Figure 1).

Hierarchical pore architecture

Natural bone serves as an excellent template for porous structure design, featuring a hierarchical pore network that integrates macro-scale beam-column structures, micro- and nanoscale pore networks, and collagen fiber-scale roughness. It is widely utilized in scaffold structural design. Feng et al.³⁸ constructed hierarchical scaffolds based on β-TCP featuring 400-μm interconnected pores and microporous structures with distinct morphologies (spherical/fibrous). Results revealed that samples with an optimized microporous network significantly outperformed the control group—which possessed only a pure macroporous design—in terms of new bone volume fraction, mineralization degree, and vascular density. This demonstrates the critical importance of the “amplification effect” exerted by microporous structures on macroporous architecture.

The effect of coupled pore structure-mechanics-degradation-mass transport on osteogenic outcomes

At the mechanical level, porosity and topological shape directly determine the scaffold’s elastic modulus, yield strength, and fatigue behavior. As porosity increases, the material not only exhibits stronger “spongy bone-like” characteristics but also becomes more susceptible to local buckling and fatigue cracking. By optimizing pore shapes (e.g. circular, elliptical, curved) and constructing gradient porosity, a more uniform stress distribution can be achieved while maintaining high porosity^31,39,40. Meanwhile, pore structure influences material degradation performance. Larger pore sizes and more open channels facilitate fluid infiltration and diffusion of degradation products, accelerating the degradation rate of biodegradable polymers or ceramics. Conversely, higher specific surface area (micro/nanopores) provides more reaction interfaces. Thus, degradation rates depend not only on material chemical composition but are also highly correlated with pore structure^31,41,42. The interconnectedness and permeability of the channels also determine the flow and diffusion behavior of oxygen, nutrients, drugs, and growth factors within the scaffold, which is particularly crucial for cell survival in the central defect area. Highly interconnected channels can shorten diffusion distances, reduce hypoxia risks, and simultaneously facilitate waste removal and pH buffering^39,42.

Therefore, structural parameters such as porosity, pore size, and topological morphology not only determine the scaffold’s mechanical stability and material transport efficiency but also jointly influence bone regeneration outcomes by regulating cell adhesion/migration, vascular ingrowth, and tissue replacement processes. More importantly, these pore characteristics directly influence the loading capacity and local retention efficiency of bone marrow–enriched products within the scaffold, thereby establishing a structural basis for elucidating the mechanisms and optimizing strategies of the “combined system of bone marrow enrichment technology and bioactive scaffolds.”

Vascularization of scaffold materials

The formation of bone tissue involves osteogenesis and angiogenesis⁴³. Bone formation relies not only on the osteogenic activity of stem cells and osteoblasts but also on the synergistic action of growth factors such as bone morphogenetic proteins (BMPs), transforming growth factor-β (TGF-β), and platelet-derived growth factor (PDGF)⁴⁴. Angiogenesis refers to the process during defect repair where existing blood vessels sprout and form new capillary networks locally. This process begins with the activation of endothelial cells (ECs) and under the coordinated action of diverse angiogenic factors such as insulin-like growth factor (IGF), fibroblast growth factor (FGF), vascular endothelial growth factor (VEGF), among others. This coordinated action facilitates EC migration and proliferation to form blood vessels, providing essential nutritional support for stem cell differentiation, osteoblast mineralization, and the formation of new bone cells. The synergistic growth of bone and blood vessels, driven by the collaborative action of their respective progenitor cells and corresponding growth factors, is termed “angiogenesis–osteogenesis coupling” (see Figure 2). Among these, the migration and proliferation of ECs, along with the regulatory role of VEGF, play a crucial role in the process of bone vascularization⁴⁵.

The field of orthopedic scaffolds is now also focusing on inducing vascularization. Beyond ensuring essential biocompatibility, mechanical support, and porous structure, grafts now incorporate materials or drugs that promote angiogenesis to accelerate the formation of new bone. Zhou et al.⁴⁶ incorporated strontium into HA/poly(lactide-co-glycolide) scaffolds loaded with mesoporous silica-supported dimethyloxallyl glycine (DMOG), where strontium exerts effects in promoting angiogenesis and modulating macrophage phenotypes. DMOG, a prolyl hydroxylase inhibitor, induces angiogenesis by stabilizing hypoxia-inducible factor-1α (HIF-1α). Together within the porous scaffold, they jointly induce scaffold vascularization. Results indicate this scaffold promotes osteogenesis and angiogenesis, activating the HIF-1α pathway and immunomodulatory effects to stabilize vascularized regeneration. Building upon this, bone marrow enrichment/concentration techniques show potential to accelerate scaffold vascularization. Beyond preserving mesenchymal stem cells and osteogenic-related cells, bone marrow enrichment can also concentrate endothelial progenitor cells along with multiple angiogenic factors such as VEGF and PDGF. Loading these onto porous scaffolds via selective retention creates a high-density angiogenic microenvironment early on. This shortens the post-implantation “avascular window period,” promotes rapid capillary invasion toward the defect center, and strengthens “angiogenesis-osteogenesis coupling” across a larger area. Consequently, it enhances the efficiency and quality of scaffold-based reconstruction for large bone defects⁴⁷. Taken together, these findings suggest that vascularization should not be treated as a secondary event in scaffold-assisted bone repair, but as a central requirement for sustaining osteogenesis in large or biologically challenging defects. On this basis, future scaffold design should move beyond structural–mechanical optimization alone and toward integrated strategies that combine pro-angiogenic factor delivery, bone marrow enrichment, and immunomodulatory regulation. Such an approach may provide a more effective means of coordinating angiogenesis with osteogenesis throughout the repair process.

The role of scaffold materials in immunomodulatory strategies within the body

Biologically active materials for transplantation serve functions such as restoring surgical site function and providing mechanical support to surrounding tissues. Researchers have developed specific biomimetic structures based on natural principles to maximize functional recovery in transplanted areas, exemplified by applications like heart valves and vascular scaffolds. Scaffold materials for bone repair must possess the aforementioned characteristics while additionally meeting requirements for osteoinductivity, osteogenesis, angiogenesis induction, biocompatibility, and controlled degradability⁴⁸. Immune rejection of transplanted materials plays a critical role in patients’ long-term quality of life. Transplant materials prone to immune rejection can cause severe adverse reactions in patients, including intense pain, inflammatory responses, tissue destruction, and even life-threatening complications⁴⁹. Thus, how to avoid strong immune rejection reactions to scaffold materials is also one of the pressing issues in this field.

Early artificial bone scaffolds were largely designed using relatively inert biomaterials with acceptable biocompatibility, aiming to minimize excessive host immune reactions and thereby reduce the risk of implant failure⁵⁰. With advances in osteoimmunology and biomaterials science, it has become evident that the immune response is not merely an unavoidable side effect but can be actively tuned by rational material design. Specifically, immune modulation can be achieved by engineering surface physicochemical cues (e.g. chemistry, wettability, charge, and topography), optimizing pore architecture and interconnectivity, and integrating bioactive cues. For example, anti-inflammatory cytokines (e.g. IL-10) can attenuate pro-inflammatory signaling and promote a pro-resolving immune milieu, which may help mitigate adverse immune reactions and support subsequent tissue regeneration⁵¹.

In recent years, macrophage regulation from the perspective of osteoimmunology has increasingly become a focal point. Macrophages serve as crucial effector cells of the innate immune system, capable of transforming into distinct phenotypes based on different microenvironments. They are primarily categorized into M0 (unactivated state), M1 (pro-inflammatory), and M2 (anti-inflammatory) types. Some researchers also propose the existence of a transitional phenotype representing a shift from pro-inflammatory to reparative functions⁵². Upon entering the body, implants first induce acute inflammation and a foreign body reaction. Neutrophils are rapidly recruited to the implantation site, where they phagocytose necrotic tissue debris and wear particles (and eliminate microorganisms if contamination is present) and release multiple chemokines. Subsequently, monocytes/macrophages migrate to the implant interface under chemotactic signals, undergoing classical activation to polarize into M1 type. These M1 macrophages secrete abundant pro-inflammatory cytokines and chemokines, aiding in pathogen clearance, necrotic tissue removal, and recruitment of additional immune cells and bone marrow mesenchymal stem cells (BMSCs). As bone repair progresses, cytokines secreted by helper T cells, BMSCs, and other cells promote the transition of macrophages from M1 to M2 type. The latter releases multiple factors with anti-inflammatory and pro-regenerative effects, promoting angiogenesis and processes related to osteogenesis/bone remodeling, while synergistically regulating ECM remodeling. Overall, macrophages gradually shift from a predominantly M1-like (pro-inflammatory) response to a predominantly M2-like (repair/anti-inflammatory) response. If an artificial bone scaffold exhibits excessive immunogenicity, leading to persistent stimulation or inflammatory imbalance (often accompanied by sustained pro-inflammatory signaling activation), it can induce a foreign body reaction (foreign body giant cells, fibroblast activation) and form a dense fibrous capsule. This prevents the adhesion of osteogenic progenitor cells and the ingrowth of new bone into the scaffold material, ultimately resulting in transplant failure^53,54. Hence, rationally guiding macrophages to transition to a predominantly M2-type reparative phenotype after completing essential clearance and defense tasks in the early stages of injury is considered a crucial immunomodulatory strategy for enhancing bone repair quality. Researchers can further reshape the immune microenvironment through material composition and surface/structural design. For instance, by employing ion doping, regulating surface wettability and roughness, implementing topological structure design, or loading immunomodulatory factors such as IL-4, IL-10, and dexamethasone, they can induce macrophage polarization toward the M2 phenotype. This approach facilitates the establishment of an “immunologically favorable” microenvironment for bone repair^54,55 (see Figure 3).

Notably, the products of bone marrow enrichment/concentration technology possess inherent immunomodulatory potential. Enriched BMSCs and other bone marrow–derived cells can suppress excessive inflammation and promote an increase in the proportion of M2 macrophages by secreting anti-inflammatory factors such as IL-10 and TGF-β^55–57. The combined application of bone marrow–enriched products with immunomodulatory scaffolds holds promise for simultaneously providing osteogenic seed cells and reshaping an immune microenvironment conducive to bone repair, thereby reducing fibrous capsule formation and enhancing integration at the bone–scaffold interface. These findings indicate that immunomodulation in bone repair should not be regarded as an isolated auxiliary strategy, but as an integral component of scaffold-assisted regeneration. Accordingly, integrating bone marrow enrichment with immunoregulatory scaffold design may provide a more rational route for improving repair quality in large-segment bone defects by coordinating inflammatory resolution, vascular ingrowth, and osteogenesis within the same regenerative framework^55–58.

Novel concepts in scaffold material design

Recently, with advances in understanding the pathogenesis of bone defects, increased patient-specific medical care, and progress in BTE technologies, ongoing developments continue across various subfields. These include cytokine loading, osteogenic induction, scaffold fabrication techniques, and scaffold component doping. For instance, injectable scaffolds—primarily composed of polymers like hydrogels—deliver stem cells and growth factors to defect sites. These scaffolds offer high plasticity, compatibility with diverse materials, and adaptability to small, complexly shaped defects, thereby minimizing surgical trauma and aligning with minimally invasive principles. When biodegradable materials are selected, they also mitigate associated surgical risks. However, the safety of this technology requires further validation through clinical trials⁵⁹.

In addition, smart/stimulus-responsive scaffolds are increasingly becoming a key focus in next-generation designs. Relevant reviews indicate that external stimuli such as pH, temperature, enzymes, reactive oxygen species (ROS), stress fields, as well as light, magnetic fields, and electricity can serve as triggering signals. These signals drive the scaffolds to undergo swelling/shrinking, deformation, or pulsatile release of drugs/growth factors, thereby enabling precise spatiotemporal intervention in the microenvironment of bone defect areas^60–62. Building upon this foundation, a “programmable scaffold” based on four-dimensional (4D) printing and shape memory materials has been proposed. This scaffold undergoes predetermined deformation over time or in response to stimuli within the body, enabling in situ expansion after minimally invasive implantation, active conforming to bone surfaces, and even dynamic adjustment of its pore structure. This facilitates better alignment with the dynamic requirements of the bone repair process⁶³.

Meanwhile, the integration of medical imaging, computational mechanics, and additive manufacturing has propelled digitally and computationally driven scaffold design as another core trend. Researchers reconstruct the true geometry of patients’ defect regions using computed tomography/magnetic resonance imaging (CT/MRI) data, then combine finite element analysis (FEA), computational fluid dynamics (CFD), and topology optimization to construct personalized scaffolds featuring gradient porosity and functionalized pore structures^64–66. Complex topologies, exemplified by triply periodic minimal surfaces (TPMS), not only enable synergistic optimization of elastic modulus, stress distribution, and permeability at high porosities but also facilitate integrated design for mechanical support, mass transport, and biofactor delivery by incorporating multifunctional pores (e.g. fluid channels, drug reservoirs) within the units. This approach provides a structural foundation for subsequent multi-material, hybrid-topology scaffolds (e.g. metal/ceramic/hydrogel synergistic structures)⁶⁷.

Furthermore, scaffolds are evolving from inanimate “three-dimensional templates” into “systematic tissue engineering constructs.” By employing bioprinting and biofabrication technologies, pre-vascularized structures, bone-like organoids, or multicellular co-culture systems can be pre-assembled within the scaffold. This enables the partial reconstruction of the cell–matrix–vascular network within the bone before implantation, potentially shortening the in vivo remodeling time and enhancing the repair quality of large-volume defects⁶⁸. Subsequently, “smart monitoring scaffolds” incorporating conductive or piezoelectric components and sensing units have emerged. These structures can simultaneously promote bone formation while enabling real-time monitoring and feedback of local mechanical conditions, pH levels, or ion concentrations. This development offers new insights for future “diagnostic and intervention-capable” bone repair systems⁶⁹.

The current trend in scaffold design is shifting from single-parameter optimization toward comprehensive microenvironment engineering. This implies that future scaffold systems will be evaluated not only based on their structural and material properties, but also on their ability to coordinate immune responses, angiogenesis, nutrient exchange, and biofeedback during the repair process. Within this framework, bone marrow enrichment may become a programmable element in more adaptive and personalized regenerative strategies, rather than a secondary component added only after the scaffold has been fabricated (see Figure 4).

Application of autologous bone marrow–enriched bone repair technology in the treatment of bone defects

The development of autologous bone marrow–based repair strategies for bone defects can be broadly understood as a translational progression from direct marrow use to scaffold-assisted enrichment and, ultimately, to more integrated regenerative systems. In this context, the following sections discuss three interconnected stages: early exploration of direct bone marrow injection and simple marrow–scaffold mixing, the subsequent development of marrow enrichment/concentration strategies and their experimental and translational evaluation, and the current status and major barriers that continue to limit broader clinical adoption.

Early translational exploration of direct autologous bone marrow injection and simple marrow–scaffold mixing

BTE offers an important conceptual framework for the treatment of bone defects by integrating biomaterials, cells, and growth factors to construct biologically functional grafts⁷⁰. Within this framework, scaffold materials may be regarded as the “soil” that provides spatial support, nutrient exchange, and mechanical stability, whereas autologous bone marrow supplies osteogenic cells and soluble bioactive factors as the “seeds” that participate in bone formation and remodeling⁷¹ (see Figure 5). As an early exploratory strategy, direct autologous bone marrow injection is technically simple and easy to implement, but the injected marrow is prone to leakage from the defect site, thereby limiting local retention and reducing the stability of therapeutic outcomes⁷². A related approach involves simply mixing autologous bone marrow with scaffold materials before implantation. Although this strategy can improve local delivery and partially enhance osteogenic efficiency, the bone marrow component may still be lost during implantation or in the early postoperative period, resulting in unstable graft composition and suboptimal repair efficacy¹⁹. Overall, these early-stage approaches take advantage of the endogenous osteogenic potential of autologous bone marrow and may show certain benefits in the treatment of small bone defects and delayed fracture healing. However, their therapeutic performance often becomes inconsistent when applied to critical-sized defects, where stable retention, structural support, and precise microenvironmental regulation are more difficult to achieve⁷³. Therefore, this stage should be regarded as an important early translational exploration rather than a definitively validated clinical solution, and further optimization of bone marrow processing, retention efficiency, and scaffold design is still required to improve consistency, safety, and clinical applicability⁷³.

Bone marrow enrichment/concentration strategies: preclinical progress and technical evaluation

Stem cells are undifferentiated or partially differentiated cells capable of self-renewal and multilineage differentiation, and they play essential roles in tissue development, homeostasis, and repair⁷⁴. However, stem cells are present in very low concentrations within human tissues; in bone marrow, mesenchymal stem cells constitute only approximately 0.001% to 0.01% of the nucleated cell population⁷⁵. This low natural abundance is one of the main reasons why direct bone marrow injection or simple marrow–scaffold mixing often shows unstable outcomes in large or critical-sized defects⁷⁶. Bone marrow enrichment/concentration technology has therefore emerged as an important strategy in regenerative medicine and tissue engineering. It generally relies on in vitro processing methods such as density-gradient centrifugation or selective retention to enrich nucleated cells, progenitor/stromal cells, growth factors, and other regenerative components from bone marrow⁷⁷. Because different enrichment/concentration approaches vary in target products, operational complexity, purity, speed, intraoperative feasibility, and cost, the key characteristics of representative methods are summarized in Table 3. Although the specific procedures and clinical pathways may differ according to indications, defect types, and material strategies, the core purpose remains the same: to enhance the regenerative potential of the local repair microenvironment by enriching marrow-derived regenerative cells and bioactive components before implantation.

Table 3.

Comparative analysis of key performance characteristics for bone marrow cell concentration/enrichment methods.

Method	Target product	Purity	Speed	Intraoperative feasibility	Cost	References
Density-gradient centrifugation	BMNC fraction	±	++	√	+	Mattei et al.⁷⁸
Immunoselection (FACS/MACS)	Phenotype-selected cells (e.g. CD271+ or CD45−/CD73+)	++	+	×	+++	Rady et al.⁷⁹
Adherence-based selection	Predominantly MSCs	+/±	±	×	+	Baghaei et al.⁸⁰
Selective retention	Scaffold-retained CTPs/MSCs/bioactive factors	+	++	√	++	Piuzzi et al.⁸¹

Purity/Speed/Cost are semi-quantitative: ++ high/fast/high cost; + moderate; ± low/variable. BMNC = bone marrow nucleated cells; MSCs: mesenchymal stromal/stem cells; CTPs: connective tissue progenitors; FACS: fluorescence-activated cell sorting; MACS: magnetic-activated cell sorting.

In bone defect repair, marrow enrichment strategies are frequently combined with graft materials or scaffold carriers to improve local retention of cells and cytokines while simultaneously providing the spatial and mechanical support required for tissue regeneration. Therefore, the distinction between bone marrow enrichment/concentration techniques and methods such as direct bone marrow injection or simple mixing of bone marrow with a scaffold lies not only in the increased cell count, but also in the attempt to regulate the composition of the implanted regenerative carrier and improve its interaction with the scaffold microenvironment⁷³. To illustrate the typical process of “harvesting–enrichment–composite preparation–implantation–regeneration,” the workflow of marrow enrichment technology in bone defect repair is shown in Figure 6.

In recent years, increasing attention has been paid to the translational value of marrow enrichment-based strategies in defects of different anatomical locations and severities. Wang et al.⁸² developed an intraoperative Screen-Enrich-Combine Circulating System (SECCS) capable of rapidly enriching mesenchymal stem cells from autologous bone marrow and combining them with porous β-tricalcium phosphate (β-TCP) without the need for ex vivo expansion. The SECCS group achieved a 90% clinical healing rate at 9 months, comparable to that of the autologous bone graft group, with no implant-related infection reported. In craniofacial bone regeneration, Kaigler et al.⁸³ reported that stem cell–based therapy significantly enhanced bone repair compared with the control group in a randomized controlled feasibility trial, suggesting that marrow-derived cellular strategies may have translational relevance beyond long-bone defects. Veronesi et al.⁸⁴ further summarized the role of bone marrow concentrates and expanded bone marrow–derived mesenchymal stem cells in cartilage disease and regeneration, highlighting their biocompatibility, regenerative potential, and anti-inflammatory effects, while also underscoring the heterogeneity of currently available products and indications. In addition, Lin et al.⁸⁵ compared bone marrow aspirate concentrate combined with cancellous allograft versus iliac crest bone graft in long-bone nonunions, indicating that marrow-based composites may provide an alternative pathway for selected clinical situations. Taken together, these studies suggest that marrow enrichment/concentration strategies have moved beyond theoretical feasibility and entered an early translational stage, although the available clinical evidence remains limited and heterogeneous. To provide a clearer overview of where bone marrow–based strategies have entered clinical, translational, or translationally relevant preclinical evaluation, representative studies are summarized in Table 4.

Table 4.

Representative translational studies of bone marrow–based repair strategies for bone defects.

Indication	Methods for utilizing bone marrow	Construct/carrier	Key outcome	Study type	References
Postoperative nonunion with focal bone defect	Direct autologous bone marrow injection	None	Simple and clinically applicable, but prone to leakage and limited retention	Clinical report/case series	Tang et al.⁷²
Spinal fusion	Selective retention of marrow-derived cells	Porous scaffold carrier	Improved local retention of marrow-derived cells within the scaffold	Preclinical animal study	Muschler et al.¹⁹
Diaphyseal bone nonunion	SECCS-processed marrow mesenchymal stem cell enrichment	Porous β-TCP scaffold	Achieved 90% healing at 9 months, comparable to autograft, without implant-related infection	Comparative clinical study	Wang et al.⁸²
Craniofacial bone regeneration	Stem cell–based marrow-derived regenerative therapy	Regenerative construct	Improved bone repair compared with controls	Randomized controlled feasibility trial	Kaigler et al.⁸³
Long-bone nonunion	Bone marrow aspirate concentrate (BMAC)-based composite grafting	Cancellous allograft	Suggested a potential alternative to iliac crest bone graft in selected cases	Retrospective cohort study	Lin et al.⁸⁵

BMAC: bone marrow aspirate concentrate; BMSCs: bone marrow mesenchymal stem cells; β-TCP: beta-tricalcium phosphate; SECCS: Screen-Enrich-Combine Circulating System.

During the preclinical phase, researchers have already tested various bone marrow enrichment methods. Electrospun polymer/HA composite scaffolds, for example, have shown excellent biocompatibility and osteogenic activity in long-bone defect models⁷⁶. Liu et al.⁸⁶ combined bone marrow–derived mesenchymal stem cells with nano-HA/chitosan materials for bone defect repair and demonstrated, through cell adhesion, differentiation, and cell-cycle assays, good cytocompatibility of the composite system. In a rat calvarial defect model, the same composite with adhered mesenchymal stem cells significantly promoted defect repair compared with the material alone and the control group. Wei et al.⁸⁷ further combined a gelatin methacrylate hydrogel scaffold with bone marrow–derived mesenchymal stem cells in a rat cranial defect model and found that this strategy promoted new bone formation and maturation, enhanced angiogenesis, and supported the osteogenic differentiation of BMSCs. Mao et al.⁸⁸ fabricated multilayer nanofiber membranes using PLLA and related materials and showed that these membranes could promote BMSC migration and stimulate osteogenic differentiation through activation of the MAPK pathway.

Collectively, these findings indicate that combining marrow-derived regenerative cells or enriched marrow components with bioactive scaffolds can improve cell retention, enhance osteogenesis and angiogenesis, and provide a more favorable microenvironment for bone repair^86–88.

Current status, limitations, and translational barriers of marrow enrichment–based bone repair

Autologous bone marrow enrichment–based bone repair has attracted increasing attention because of its favorable bone healing potential and relatively low rate of severe complications, with encouraging results reported in terms of bone union, bone density improvement, and functional recovery⁸⁹. Nevertheless, the current status of this field should be interpreted with caution. First, bone marrow enrichment does not eliminate the invasiveness of the procedure itself, and its clinical performance still depends on multiple interrelated factors, including harvesting technique, enrichment protocol, scaffold compatibility, defect size, and anatomical location^89,90. Second, there are still no universally accepted quantitative standards to define how different processing parameters affect the yield and functional quality of autologous bone marrow–derived mesenchymal stem cells, nor how different scaffold materials and pore architectures influence cell retention efficiency and subsequent repair outcomes⁹¹. Third, although enrichment and concentration procedures are intended to improve the regenerative potency of bone marrow products, centrifugation, ex vivo manipulation, or cell culture steps may impair cell viability and reduce stem cell function⁹². These issues contribute to substantial heterogeneity across studies and make direct comparison between different techniques difficult.

In addition, broader clinical translation remains constrained by regulatory requirements, cost, quality control demands, and the lack of multicenter, large-sample randomized controlled trials^90–92. Therefore, future progress in this field should focus not only on improving enrichment efficiency, but also on establishing standardized characterization systems for marrow-derived cellular and cytokine profiles, clarifying scaffold–marrow compatibility under different defect scenarios, and developing more reproducible and clinically accessible composite repair strategies^91,92. In this context, bone marrow enrichment should no longer be viewed as a simple adjunct added to scaffold materials, but rather as one component of an integrated regenerative system that requires precise coupling with scaffold structure, the local immune-vascular microenvironment, and defect-specific mechanical demands⁹³.

Conclusion and outlook

Bone defect repair should be viewed as a comprehensive regenerative process rather than the result of a single material or cellular intervention. Successful reconstruction depends on the coordinated interaction between scaffold composition and structure, regenerative cells and soluble mediators derived from bone marrow, angiogenic support, immune regulation, and defect-specific mechanical requirements. Therefore, scaffold selection should be guided by functional matching with the clinical setting, while pore structure, vascularization, and bone immune regulation should be considered core determinants of repair quality. Bone marrow enrichment techniques demonstrate translational potential by improving the local delivery and retention of regenerative components; however, their widespread application remains limited by variations in enrichment protocols, scaffold compatibility, and the quality of evidence. Future developments require standardized characterization of bone marrow–derived products, the development of optimized scaffold–bone marrow coupling strategies, and the conduct of more rigorous translational and clinical validation studies.

Footnotes

Acknowledgements

We thank our colleagues for their valuable discussions and constructive suggestions during the preparation of this manuscript. The authors also used ChatGPT (OpenAI) for language polishing and improvement of readability. No scientific data, results, analyses, figures, or references were generated or modified by artificial intelligence. The authors take full responsibility for the accuracy and integrity of the manuscript.

ORCID iDs

Zhezheng Shen

Wei Qian

Ethical considerations

Not applicable.

Consent to participate

There are no human subjects in this article and informed consent is not applicable.

Author contributions

Z.S. and X.L.: drafted and revised the manuscript; Z.Y. and Y.Z.: contributed to literature retrieval and provided guidance for the study; D.T. and Z.T.: prepared the figures and tables; W.Q.: conceived and designed the study, critically reviewed the manuscript, and acquired funding.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was supported by the Scientific Research Project of Shaanxi Provincial Administration of Traditional Chinese Medicine (grant no. 2021-GJ-JC013).

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data availability statement

Not applicable.

Statement of human and animal rights

This article does not contain any studies with human or animal subjects.

References

Goldhaber

Some current concepts of bone physiology. N Engl J Med. 1962;266:924–31 concl.

Migliorini

La Padula

Torsiello

Spiezia

Oliva

Maffulli

Strategies for large bone defect reconstruction after trauma, infections or tumour excision: a comprehensive review of the literature. Eur J Med Res. 2021;26(1):118.

Cho

Song

HK.

Current concepts and applications of bone graft substitutes in orthopedic surgery. J Musculoskelet Trauma. 2025;38(4):169–77.

Bezstarosti

Metsemakers

van Lieshout

EMM

Voskamp

Kortram

McNally

Marais

Verhofstad

MHJ

. Management of critical-sized bone defects in the treatment of fracture-related infection: a systematic review and pooled analysis. Arch Orthop Trauma Surg. 2021;141(7):1215–30.

Goodman

Zwingenberger

Concentrated autologous bone marrow aspirate is not “stem cell” therapy in the repair of nonunions and bone defects. Biomater Biosyst. 2021;2:100017.

Ciszyński

Dominiak

Gedrange

Hadzik

Allogenic bone graft in dentistry: a review of current trends and developments. Int J Mol Sci. 2023;24(23):16598.

Aktuglu

Erol

Vahabi

Ilizarov bone transport and treatment of critical-sized tibial bone defects: a narrative review. J Orthop Traumatol. 2019;20(1):22.

Karger

Kishi

Schneider

Fitoussi

Masquelet

AC.

Treatment of posttraumatic bone defects by the induced membrane technique. Orthop Traumatol Surg Res. 2012;98(1):97–102.

Schmidt

AH.

Autologous bone graft: is it still the gold standard?

Injury. 2021;52(Suppl 2):S18–22.

10.

Percival

Paul

Husseini

GA.

Recent advancements in bone tissue engineering: integrating smart scaffold technologies and bio-responsive systems for enhanced regeneration. Int J Mol Sci. 2024;25(11):6012.

11.

Song

Wang

Shi

Zhang

Wang

Guo

Yang

Biomaterials combined with ADSCs for bone tissue engineering: current advances and applications. Regen Biomater. 2023;10:rbad083.

12.

Laubach

Hildebrand

Suresh

Wagels

Kobbe

Gilbert

Kneser

Holzapfel

Hutmacher

DW.

The concept of scaffold-guided bone regeneration for the treatment of long bone defects: current clinical application and future perspective. J Funct Biomater. 2023;14(7):341.

13.

Zhou

See

Sreenivasamurthy

Zhu

Customized additive manufacturing in bone scaffolds-the gateway to precise bone defect treatment. Research. 2023;6:0239.

14.

de Carvalho

ABG

Rahimnejad

Oliveira

Sikder

Saavedra

Bhaduri

Gawlitta

Malda

Kaigler

Trichês

Bottino

MC.

Personalized bioceramic grafts for craniomaxillofacial bone regeneration. Int J Oral Sci. 2024;16(1):62.

15.

Bharadwaz

Jayasuriya

AC.

Recent trends in the application of widely used natural and synthetic polymer nanocomposites in bone tissue regeneration. Mater Sci Eng C Mater Biol Appl. 2020;110:110698.

16.

Ashok

Ganesh

Maiti

Nallaswamy

Heboyan

Evaluation of 3D-printed polylactic acid as a bone substitute: an animal study in a rat model. Clin Exp Dent Res. 2025;11(4):e70201.

17.

Wang

Han

Zhou

Cai

Sun

Wang

The combination of a 3D-Printed porous Ti-6Al-4V alloy scaffold and stem cell sheet technology for the construction of biomimetic engineered bone at an ectopic site. Mater Today Bio. 2022;16:100433.

18.

Alonso-Fernández

Haugen

López-Peña

González-Cantalapiedra

Muñoz

Use of 3D-printed polylactic acid/bioceramic composite scaffolds for bone tissue engineering in preclinical in vivo studies: a systematic review. Acta Biomater. 2023;168:1–21.

19.

Muschler

Matsukura

Nitto

Boehm

Valdevit

Kambic

Davros

Easley

Powell

. Selective retention of bone marrow-derived cells to enhance spinal fusion. Clin Orthop Relat Res. 2005(432):242–51.

20.

Hui

Pasquier

Solberg

Agrenius

Håkansson

Chinga-Carrasco

Biocomposites containing poly(lactic acid) and chitosan for 3D printing–assessment of mechanical, antibacterial and in vitro biodegradability properties. J Mech Behav Biomed Mater. 2023;147:106136.

21.

Turnbull

Clarke

Picard

Riches

Jia

Han

Shu

3D bioactive composite scaffolds for bone tissue engineering. Bioact Mater. 2018;3(3):278–314.

22.

Zhao

Zhang

Cai

Wang

Fan

Zhang

Preparation of porous PLGA/Ti biphasic scaffold and osteochondral defect repair. Biomater Sci. 2013;1(7):703–10.

23.

O’Brien

FJ.

Biomaterials & scaffolds for tissue engineering. Materials Today. 2011;14(3):88–95.

24.

Liu

Wang

Yan

Xiang

Zheng

Liu

3D printing titanium grid scaffold facilitates osteogenesis in mandibular segmental defects. NPJ Regen Med. 2023;8(1):38.

25.

Verbist

Vandevelde

Geusens

Sun

Shaheen

Willaert

Reconstruction of craniomaxillofacial bone defects with 3D-printed bioceramic implants: scoping review and clinical case series. J Clin Med. 2024;13(10):2805.

26.

Zhou

Xiao

Zhang

Wang

Current application of beta-tricalcium phosphate in bone repair and its mechanism to regulate osteogenesis. Front Mater. 2021;8:698915.

27.

Liu

Bao

Huang

Tang

Dong

Liu

Chen

Wang

Zhang

, et al. Clinical application of 3D-printed biodegradable lumbar interbody cage (polycaprolactone/β-tricalcium phosphate) for posterior lumbar interbody fusion. J Biomed Mater Res B Appl Biomater. 2023;111(7):1398–1406.

28.

Laubach

Kobbe

Hutmacher

DW.

Biodegradable interbody cages for lumbar spine fusion: current concepts and future directions. Biomaterials. 2022;288:121699.

29.

Zhou

Jiang

Zhou

Tan

Luo

Lei

Yang

GelMA-based bioactive hydrogel scaffolds with multiple bone defect repair functions: therapeutic strategies and recent advances. Biomater Res. 2023;27(1):86.

30.

Graupe

Ahmad

Zia

Hadjiargyrou

Ilyas

Hydrogels for bone regeneration: properties, additives, preclinical and clinical applications. Gels. 2025;11(11):914.

31.

Abbasi

Hamlet

Love

Nguyen

N-T.

Porous scaffolds for bone regeneration. J Sci Adv Mater Dev. 2020;5(1):1–9.

32.

Karageorgiou

Kaplan

Porosity of 3D biomaterial scaffolds and osteogenesis. Biomaterials. 2005;26(27):5474–91.

33.

Taniguchi

Fujibayashi

Takemoto

Sasaki

Otsuki

Nakamura

Matsushita

Kokubo

Matsuda

Effect of pore size on bone ingrowth into porous titanium implants fabricated by additive manufacturing: an in vivo experiment. Mater Sci Eng C Mater Biol Appl. 2016;59:690–701.

34.

Zhang

Fan

Dunne

Effect of microporosity on scaffolds for bone tissue engineering. Regen Biomater. 2018;5(2):115–24.

35.

Dalby

Gadegaard

Tare

Andar

Riehle

Herzyk

Wilkinson

Oreffo

RO.

The control of human mesenchymal cell differentiation using nanoscale symmetry and disorder. Nat Mater. 2007;6(12):997–1003.

36.

Jiao

Hong

Zhang

Wang

Tang

Yang

Yue

Influence of porosity on osteogenesis, bone growth and osteointegration in trabecular tantalum scaffolds fabricated by additive manufacturing. Front Bioeng Biotechnol. 2023;11:1117954.

37.

Sun

Shujaat

Braem

Politis

Jacobs

3D-printed porous Ti6Al4V scaffolds for long bone repair in animal models: a systematic review. J Orthop Surg Res. 2022;17(1):68.

38.

Feng

Liu

Wang

Diao

Kuang

Zhao

Beta-TCP scaffolds with rationally designed macro-micro hierarchical structure improved angio/osteo-genesis capability for bone regeneration. J Mater Sci Mater Med. 2023;34(7):36.

39.

Mahanani

Puspita

Dewi

AH.

The proper design of scaffold porosity for bone regeneration (literature review). AIP Conf Proc. 2024;3127(1):020018.

40.

Sebastiani

Buccino

Qin

Vergani

LM.

Structural influences on bone tissue engineering: a review and perspective. Matter. 2025;8(9):102252.

41.

yadav

Beniwal

Saxena

KK.

A review on pore and porosity in tissue engineering. Mater Today Proc. 2021;44:2623–28.

42.

Xia

Luo

Vascularization in tissue engineering: the architecture cues of pores in scaffolds. J Biomed Mater Res B Appl Biomater. 2022;110(5):1206–14.

43.

Mohammadi

Mousavi Shaegh

Alibolandi

Ebrahimzadeh

Tamayol

Jaafari

Ramezani

Micro and nanotechnologies for bone regeneration: recent advances and emerging designs. J Control Release. 2018;274:35–55.

44.

Jimi

Hirata

Shin

Yamazaki

Fukushima

Molecular mechanisms of BMP-induced bone formation: cross-talk between BMP and NF-κB signaling pathways in osteoblastogenesis. Jpn Dent Sci Rev. 2010;46(1):33–42.

45.

Saberi

Kouhjani

Mohammadi

Hosta-Rigau

Novel scaffold platforms for simultaneous induction osteogenesis and angiogenesis in bone tissue engineering: a cutting-edge approach. J Nanobiotechnology. 2023;21(1):351.

46.

Zhou

Qian

Chen

Sun

Wang

Flowerbed-Inspired Biomimetic Scaffold with Rapid Internal Tissue Infiltration and Vascularization Capacity for Bone Repair. ACS Nano. 2023;17(5):5140–56.

47.

Lana

da Fonseca

Azzini

Santos

Braga

Cardoso Junior

Murrell

Gobbi

Purita

Percope de Andrade

MA.

Bone marrow aspirate matrix: a convenient ally in regenerative medicine. Int J Mol Sci. 2021;22(5):2762.

48.

Bai

Liu

Jiao

Liu

Recent progress of 3D printed responsive scaffolds for bone repair: a review. Mater Today Bio. 2025;35:102351.

49.

Zhou

Cao

Zhu

Chen

Liu

Jia

Han

Yao

, et al. Immunocompatible elastomer with increased resistance to the foreign body response. Nat Commun. 2024;15(1):7526.

50.

Negrescu

Cimpean

The state of the art and prospects for osteoimmunomodulatory biomaterials. Materials. 2021;14(6):1357.

51.

Sanati

Pieterman

Levy

Akbari

Tavakoli

Hassani Najafabadi

Amin Yavari

Osteoimmunomodulation by bone implant materials: harnessing physicochemical properties and chemical composition. Biomater Sci. 2025;13(11):2836–70.

52.

Lavin

Winter

Blecher-Gonen

David

Keren-Shaul

Merad

Jung

Amit

Tissue-resident macrophage enhancer landscapes are shaped by the local microenvironment. Cell. 2014;159(6):1312–26.

53.

Zhao

Chu

Ouyang

Immunomodulation effect of biomaterials on bone formation. J Funct Biomater. 2022;13(3):103.

54.

Xiong

Xie

Lin

Liu

Functionalized multidimensional biomaterials for bone microenvironment engineering applications: focus on osteoimmunomodulation. Front Bioeng Biotechnol. 2022;10:1023231.

55.

Liu

Zhang

Ding

Osteoimmunity-regulating biomaterials promote bone regeneration. Asian J Pharm Sci. 2023;18(1):100774.

56.

Medhat

Rodríguez

Infante

Immunomodulatory effects of MSCs in bone healing. Int J Mol Sci. 2019;20(21):5467.

57.

Fan

Sun

Xue

Song

Deng

Macrophages-bone marrow mesenchymal stem cells crosstalk in bone healing. Front Cell Dev Biol. 2023;11:1193765.

58.

Xie

Feng

Huang

Chen

Huang

Tan

Osteoimmunomodulatory effects of biomaterial modification strategies on macrophage polarization and bone regeneration. Regen Biomater. 2020;7(3):233–45.

59.

Wang

Min

Tian

Injectable and cell-laden hydrogel in the contained bone defect animal model: a systematic review. Tissue Eng Regen Med. 2023;20(6):829–37.

60.

Zhu

Zhou

Chen

Zhu

Recent advances of responsive scaffolds in bone tissue engineering. Front Bioeng Biotechnol. 2023;11:1296881.

61.

El-Husseiny

Mady

El-Dakroury

Zewail

Noshy

Abdelfatah

Doghish

AS.

Smart/stimuli-responsive hydrogels: state-of-the-art platforms for bone tissue engineering. Appl Mater Today. 2022;29:101560.

62.

Gai

Chen

Smart responsive in situ hydrogel systems applied in bone tissue engineering. Front Bioeng Biotechnol. 2024;12:1389733.

63.

Zhang

Yang

Aimaijiang

Zhang

Zhou

Four-dimensional printing and shape memory materials in bone tissue engineering. Int J Mol Sci. 2023;24(1):814.

64.

Jiang

Huo

Peng

Zhu

Lyu

Design of novel triply periodic minimal surface (TPMS) bone scaffold with multi-functional pores: lower stress shielding and higher mass transport capacity. Front Bioeng Biotechnol. 2024;12:1401899.

65.

Sun

Wang

Dong

Yang

Understanding the relationship between pore structure and properties of triply periodic minimal surface bone scaffolds. J Mater Sci Mater Med. 2025;36(1):6.

66.

Ntousi

Roumpi

Siogkas

Polyzos

Kakkos

Matsopoulos

Fotiadis

DI.

Advances in computational modeling of scaffolds for bone tissue engineering: a narrative review of the current approaches and challenges. Biomechanics. 2025;5(4):76.

67.

Pugliese

Graziosi

Biomimetic scaffolds using triply periodic minimal surface-based porous structures for biomedical applications. SLAS Technol. 2023;28(3):165–82.

68.

Rifai

Weerasinghe

Tilaye

Nisbet

Hodge

Pasco

Williams

Samarasinghe

Williams

RJ.

Biofabrication of functional bone tissue: defining tissue-engineered scaffolds from nature. Front Bioeng Biotechnol. 2023;11:1185841.

69.

Huang

Zhang

Deng

Long

Chan

Loh

Zhuang

Ruan

A non-invasive smart scaffold for bone repair and monitoring. Bioact Mater. 2023;19:499–510.

70.

Collins

Ren

Young

Pina

Reis

Oliveira

JM.

Scaffold fabrication technologies and structure/function properties in bone tissue engineering. Adv Funct Mater. 2021;31(21):2010609.

71.

Ouyang

Current biomaterial-based bone tissue engineering and translational medicine. Int J Mol Sci. 2021;22(19):10233.

72.

Tang

Zhu

Wang

Zhou

[Treatment of focal bone defect in postoperative nonunion with autologous red bone marrow injection]. Zhongguo Gu Shang. 2009;22(7):549–50.

73.

Moyal

Adelstein

Moon

Napora

JK.

Bone marrow aspirate and bone marrow aspirate concentrate: does the literature support use in long-bone nonunion and provide new insights into mechanism of action. Eur J Orthop Surg Traumatol. 2024;34(6):2871–80.

74.

Tao

Wang

Zhang

Chen

Gao

, et al. Recent advances in tissue stem cells. Sci China Life Sci. 2021;64(12):1998–2029.

75.

Jeyaraman

Bingi

Muthu

Jeyaraman

Packkyarathinam

Ranjan

Sharma

Jha

Khanna

Rajendran

SNS

Rajendran

, et al. Impact of the process variables on the yield of mesenchymal stromal cells from bone marrow aspirate concentrate. Bioengineering (Basel). 2022;9(2):57.

76.

Kutikov

Skelly

Ayers

Song

Templated repair of long bone defects in rats with bioactive spiral-wrapped electrospun amphiphilic polymer/hydroxyapatite scaffolds. ACS Appl Mater Interfaces. 2015;7(8):4890–4901.

77.

Margiana

Markov

Zekiy

Hamza

Al-Dabbagh

Al-Zubaidi

Hameed

Ahmad

Sivaraman

Kzar

Al-Gazally

, et al. Clinical application of mesenchymal stem cell in regenerative medicine: a narrative review. Stem Cell Res Ther. 2022;13(1):366.

78.

Mattei

Santilli

Pulcini

Fabrizi

Lancia

Santacroce

Megiorni

Ceccarelli

Paldino

Gramignoli

Roubelakis

, et al. Validated methods for isolation and qualification of mesenchymal stromal/stem cells from different sources. J Transl Med. 2025;23(1):975.

79.

Rady

Abbass

MMS

El-Rashidy

El Moshy

Radwan

Dörfer

Fawzy El-Sayed

KM.

Mesenchymal stem/progenitor cells: the prospect of human clinical translation. Stem Cells Int. 2020;2020:8837654.

80.

Baghaei

Hashemi

Tokhanbigli

Asadi Rad

Assadzadeh-Aghdaei

Sharifian

Zali

MR.

Isolation, differentiation, and characterization of mesenchymal stem cells from human bone marrow. Gastroenterol Hepatol Bed Bench. 2017;10(3):208–13.

81.

Piuzzi

Khlopas

Newman

Roche

Husni

Spindler

Mont

Muschler

Bone marrow cellular therapies: novel therapy for knee osteoarthritis. J Knee Surg. 2018;31(1):22–26.

82.

Wang

Chu

Zhuang

Shi

Tao

Jin

Dai

Zhao

Gan

Bone mesenchymal stem cell-enriched β-tricalcium phosphate scaffold processed by the screen-enrich-combine circulating system promotes regeneration of diaphyseal bone non-union. Cell Transplant. 2019;28(2):212–23.

83.

Kaigler

Pagni

Park

Braun

Holman

Tarle

Bartel

Giannobile

WV.

Stem cell therapy for craniofacial bone regeneration: a randomized, controlled feasibility trial. Cell Transplant. 2013;22(5):767–77.

84.

Veronesi

Giavaresi

Tschon

Borsari

Nicoli Aldini

Fini

Clinical use of bone marrow, bone marrow concentrate, and expanded bone marrow mesenchymal stem cells in cartilage disease. Stem Cells Dev. 2013;22(2):181–92.

85.

Lin

VandenBerg

Putnam

Parks

Spraggs-Hughes

McAndrew

Ricci

Gardner

MJ.

Bone marrow aspirate concentrate with cancellous allograft versus iliac crest bone graft in the treatment of long bone nonunions. OTA Int. 2019;2(1):e012.

86.

Liu

Peng

Zhang

Cai

Chen

Zhang

OuYang

HW.

The promotion of bone regeneration by nanofibrous hydroxyapatite/chitosan scaffolds by effects on integrin-BMP/Smad signaling pathway in BMSCs. Biomaterials. 2013;34(18):4404–17.

87.

Wei

Wang

Liu

Wang

Guan

Zhou

Mao

Gelatin methacrylate hydrogel scaffold carrying resveratrol-loaded solid lipid nanoparticles for enhancement of osteogenic differentiation of BMSCs and effective bone regeneration. Regen Biomater. 2021;8(5):rbab044.

88.

Mao

Chen

Wang

Qiu

Guan

Zhou

Physiology-inspired multilayer nanofibrous membranes modulating endogenous stem cell recruitment and osteo-differentiation for staged bone regeneration. Adv Healthc Mater. 2022;11(21):e2201457.

89.

Imam

Holton

Ernstbrunner

Pepke

Grubhofer

Narvani

Snow

A systematic review of the clinical applications and complications of bone marrow aspirate concentrate in management of bone defects and nonunions. Int Orthop. 2017;41(11):2213–20.

90.

Liu

Nie

Wang

Zheng

Zhang

Peng

3D printed PCL/SrHA scaffold for enhanced bone regeneration. Chem Eng J. 2019;362:269–79.

91.

Melville

Mañón

Blackburn

Young

Current methods of maxillofacial tissue engineering. Oral Maxillofac Surg Clin North Am. 2019;31(4):579–91.

92.

Haeusner

Jauković

Kupczyk

Herrmann

Review: cellularity in bone marrow autografts for bone and fracture healing. Am J Physiol Cell Physiol. 2023;324(2):C517–C531.

93.

Lana

de Brito

Kruel

Brito

Santos

Caliari

Salamanna

Sartori

Barbanti Brodano

Costa

Jeyaraman

, et al. Evolution and innovations in bone marrow cellular therapy for musculoskeletal disorders: tracing the historical trajectory and contemporary advances. Bioengineering (Basel). 2024;11(10):979.