A systematic search for relevant articles was performed by the recommendation of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (Figure 1) to evaluate the impact of 3D printed scaffolds in bone tissue engineering of femoral and tibial defects of animal models. The preclinical studies were identified through a systematic search across electronic databases including PubMed, Web of Science, and Google Scholar, published from January 2013 to October 2023. The terms used for the search included “3D bioprinting, bone, animal studies,” “3D bioprinting, bone, in vivo studies,” “3D bioprinting, bioink, animal models,” “3D bioprinting, bioink, bone tissue engineering,” “3D bioprinting, bone tissue engineering, animal studies,” “3D bioprinting, biomaterials, femur defects, in vivo,” “3D bioprinting, biomaterials, tibia defects, in vivo,” and “3D bioprinting, bone, clinical studies.” The results of the literature review and study screening are displayed in the PRISMA flow diagram in Figure 1.

The inclusion criteria were as follows:

Articles published from January 2013 to October 2023, on the utilization of 3D bioprinting-based scaffolds in bone tissue engineering of femoral and tibial defects in animal models (rat, dog, rabbit, sheep, and pig) were included. The database collection strategy was kept broad to avoid the exclusion of any relevant papers. The literature search results of quantitative data are outlined in the PRISMA flow chart (Figure 1). Inclusion criteria were discussed to assess the relevance of the included in vivo studies in the meta-analysis study and to minimize data heterogenicity. Data extraction encompassed a range of information, including but not limited to descriptions of the cells utilized, and materials employed for constructing the structures. Evaluation methods for tissue characterization such as µCT scan, histological, and histomorphometric analysis were assessed for proof-of-concept. Data from animal models was also included. The material characterization for each scaffold, rheological properties (porosity %, compressive modulus, and other relevant parameters) as well as qualitative details of animal models with the femur and tibial defects were extracted from each study included in Supplementary Table S1.

The exclusion criteria were as follows:

1) Articles published before 2013, 2) review articles, 3) short communications, 4) duplication information, 4) case reports, 5) articles written in non-English languages, 6) articles that do not meet the definition of 3D bioprinting or were published in a journal with impact factor (IF, Clarivate) < 1 were excluded. In addition, all in vivo studies on 3D-printed templates for craniofacial, mandibular reconstructions, calvarial, and tumor-associated bone defects were also excluded.

In this systematic review, two authors (NS and AN) independently searched PubMed, Web of Science, and Google Scholar for all studies. The bibliographies of relevant articles were studied to identify further relevant publications. Titles were initially screened to exclude duplicates and further screened using the abstracts against inclusion and exclusion criteria. Finally, a full-text review of the remainder was performed to assess eligibility.

Two investigators (NS and AN) independently conducted literature screening and disagreements were resolved by discussion with other authors. The data were extracted in numeric form from bar plots of each article using the WebPlotDigitilizer program and from the tables according to PRISMA guidelines. The data were presented in a Microsoft Excel spreadsheet (Windows 10 edition; Microsoft Corporation, Lisbon, Portugal) to record the author name with publication year, types of scaffolds, material characterization, cell type, in vitro assay (cell viability), rheological properties, animal models for bone defects such as femur or tibia and defect size, sample size and duration of treatment. Data extracted from all articles included in the meta-analysis is shown in Table 2. The quantitative assessment of the regeneration of femur and tibial defects for each scaffold was calculated and collected for animal models including rabbits, pigs, sheep, dogs, and rats (Table 2). The primary outcome of this study includes the evaluation of immediate and long-term bone repair by analyzing bone volume to tissue volume ratio (BV/TV), bone mineral density (BMD), bone volume (BV), new bone area (NBA), trabecular thickness (Tb. Th.), trabecular number (Tb. N.), and trabecular separation (Tb. S.) using histological or radiographic methods (Table 2).

Cochran’s Q test and heterogeneity index (I²) were used for assessing heterogeneity across studies (Rajput et al., 2023). Due to the low stringency of the heterogeneity test, p values <0.10 were considered statistically significant. I² heterogeneity scale of low heterogeneity (<25%), moderate heterogeneity (50%), and high heterogeneity (>75%) was used for quantitative assessment. The pooled effect size was computed using the fixed effect and random effects models and one of the models was adopted depending upon the quantum of heterogeneity. Pooled data analysis was performed using the Comprehensive Meta-Analysis Software (CMA). A sub-group analysis was performed, stratifying the data based on the type of animals and bone defects (whether femoral or tibial defects).

Sensitivity analysis was performed based on the exclusion of one study at a time. For this, the pooled effect size was computed upon the exclusion of studies one at a time to estimate the sensitive nature of a particular study.

We undertook publication bias analysis qualitatively based on asymmetry in the funnel plot and quantitatively based on Egger’s intercept test and Begg and Mazumdar rank correlation test respectively. In the presence of publication bias, the adjusted values from Duval and Tweedie’s trim and fill method were used to conclude.

A total of 1336 potential articles were identified from the literature search. As shown in Figure 1, after reviewing abstracts and titles, 350 potentially eligible studies of animal models for bone defects were assessed carefully by full-text review. 313 studies were excluded due to the unavailability of full text and useful information on 3D bioprinting in bone tissue engineering. Finally, 37 studies of 3D bio-printed scaffolds were considered to meet the inclusion criteria and included in the systematic review and meta-analysis to investigate the advantage of scaffolds in bone tissue regeneration, specifically focusing on animal models with femoral and tibial defects. Among the selected studies, 25 were evaluated for femoral bone defects, while 12 were considered for tibial bone defects in animal models. We summarized the qualitative data from selected studies, providing the details of scaffolds in Supplementary Table S1 and detailed information of animal models with bone defects in Table 1. Notably, we extracted the quantitative data encompassing BV/TV, NBA, Tb. Th., Tb. N., Tb. S. and BV from only 15 out of the 35 studies involving animal models included in the systematic review. Details for the inclusion of studies in the meta-analysis, aligning with the inclusion criteria checklist mentioned earlier, have been incorporated into Table 2. Of these selected studies, 7 studies were conducted to analyze BV/TV specifically for femoral defects (Liu et al., 2016; Lin et al., 2016; Feng et al., 2021; Fairag et al., 2021; Chai et al., 2022; Lei et al., 2023; Ho et al., 2022), and 3 studies focused on tibial defects in animal models (Zhang et al., 2017; Li et al., 2021; Teotia et al., 2020). Among these, 2 studies were excluded due to incomparable control and experimental groups (Chai et al., 2022; Li et al., 2021). Furthermore, for the analysis of NBA, 3 studies about the femur and 2 studies related to the tibia in animal models were selected (Feng et al., 2021; Lei et al., 2023; Tarafder et al., 2015). Notably, 5 studies were undertaken to analyze trabecular thickness Tb. Th., Tb. N., Tb. S. and BV (Fairag et al., 2021; Chai et al., 2022; Ho et al., 2022; Zhang et al., 2017; Li et al., 2021). Two studies were excluded from this analysis due to the incomparable groups of control vs. treatment (Chai et al., 2022; Li et al., 2021). The sample size in these studies ranged from 3 to 15 per group, and treatment duration ranged from 4 weeks to 16 weeks. Subsequently, a meta-analysis was conducted to assess the impact of composite scaffolds on bone tissue regeneration, including parameters such as BV/TV, NBA, Tb. Th. and BV. We used the random-effects model for making inferences due to significant heterogeneity across the studies unless stated otherwise. The pooled and subgroup analyses of all parameters including BV/TV, NBA, Tb. Th and BV have been summarized in Table 3. Most of the studies employed a scaffold-only approach as their control, while their treatment groups utilized 3D-printed composite scaffolds. However, it’s important to note that some studies used a sham as a control which was not included in our analysis.

The research articles included in this systematic review were published from January 2013- October 2023, focusing on the advancement of 3D-printed scaffolds for the repair of femoral and tibial defects in animal models. Indeed, 3D-printed scaffolds have emerged as a promising alternative for bone regeneration. Based on the qualitative data as shown in Supplementary Table S1, it is evident that a total of 37 articles were published over the last 10 years, a mean of 3.7 articles per year. Research groups in the USA and China predominantly initiated these studies. Within the past 5 years (2018–2023), the field was rapidly growing with 30 published articles dominated by research groups in the USA and China (Figure 2).

Within the included studies, 3D-printed composite scaffolds were employed in addressing femoral and tibial defects across five distinct animal models. Specifically, 20 studies were conducted in New Zealand White (NZW) rabbits, 11 studies involved rats (comprising 5 studies with the Wistar strain and 6 studies with Sprague-Dawley rats), 3 studies utilized dogs (2 studies involving beagle dogs and 1 study with canines), 1 study involved sheep, and 2 studies employed pigs. The predominant focus of the studies centered on rabbits, examining the impact of a variety of printed biomaterials, scaffolds, and templates with different combinations and ratios (Supplementary Table S1). More than half of the included studies were found to combine printed templates with cells, growth factors, or both. Histology or micro-computed tomography (µCT) or both emerged as the most common methods to assess the repair of femoral and tibial bone defects. Importantly, critical-sized bone defects (CSD) are not expected to heal spontaneously within the lifetime of the animal. In this systematic study, all the defects made in animals were performed in the femur or tibia. Still, only 9 could be considered as CSD, performed in the femur of rabbit (N = 4) and rat (N = 3) and tibia of rabbit (N = 2) respectively.

In our current study, we conducted a meta-analysis that was stratified based on two key factors: bone defects (specifically femoral or tibial) and animal models. This approach was taken to prevent any potential bias in the results stemming from differences in methodology and species used across various studies included in our analysis.

We pooled data from the studies that used 3D bioprinted composite scaffolds to determine the overall effect of fabrication in bone tissue engineering on a BV/TV of the femur and tibia of animal models. Six studies were included in the meta-analysis for femoral defects of BV/TV (Liu et al., 2016; Lin et al., 2016; Feng et al., 2021; Fairag et al., 2021; Chai et al., 2022; Lei et al., 2023; Ho et al., 2022). The pooled analysis was performed using a random-effect model which showed a significant increase in BV/TV of the femur after implantation of fabricated 3D printed composite scaffolds in animal models (rabbits, rats, beagle dogs) compared with control groups (SDM = 4.545, 95% CI = 3.383 to 5.707, p = 0.000) (Figure 3A). The funnel plots did not demonstrate apparent asymmetry for BV/TV (Supplementary Figure S1A) and the heterogeneity among studies was significant (p = 0.000, I² = 89.990%, Q = 181.661).

A subgroup analysis was performed to analyze the effect of implantation of 3D printed scaffolds in rabbit femur. This analysis showed that 3D printed composite scaffolds significantly increased BV/TV of rabbit femur (SDM = 4.736, 95% CI = 3.443 to 6.029, p = 0.000) (Figure 3B). The heterogeneity among studies was relatively high (I² = 90.090, Q = 181.642, p = 0.000) and funnel plots did not demonstrate apparent asymmetry for BV/TV of rabbit femur (Supplementary Figure S1B). In addition to that, another subgroup of rabbit tibial defect showed that implantation of 3D printed composite scaffolds significantly increased BV/TV of rabbit tibia in comparisons to control with significant heterogeneity among studies (SDM = 20.024, 95% CI = 0.738 to 39.309, p = 0.042 and I² = 95.233, Q = 41.953, p = 0.000) (Figure 3C). The funnel plots also did not demonstrate apparent asymmetry for BV/TV of rabbit tibia (Supplementary Figure S1C).

Three studies were included in the meta-analysis for NBA regeneration in animal models of femoral defects. The pooled analysis was performed using a random-effect model which showed a significant increase in the regeneration of NBA of the femur after implantation of fabricated 3D printed composite scaffolds in animal models (rabbits, and beagle dogs) compared with control groups (SDM = 2.252, 95% CI = 1.138 to 3.365, p = 0.000) (Figure 4A) and significant heterogeneity was observed among studies (I² = 67.987, Q = 15.619, p = 0.008). A subgroup analysis was performed to analyze the effect of implantation of 3D printed scaffolds in rabbit femur. This analysis showed that 3D printed composite scaffolds significantly increased NBA of rabbit femur (SDM = 2.282, 95% CI = 0.958 to 3.606, p = 0.001) (Figure 4B). The heterogeneity among studies was relatively high (I² = 74.152, Q = 15.475, p = 0.004). Another subgroup of rabbit tibia showed that 3D printed composite scaffolds increased NBA (SDM = 9.219, 95% CI = 7.475 to 10.964, p = 0.000) (Figure 4C). The heterogeneity among studies was relatively high (I² = 52.408, Q = 10.506, p = 0.062).

Three studies were included for the analysis of trabecular thickness. A pooled analysis of femoral defects of animal models (rabbit and rat) showed that 3D-printed composite scaffolds significantly increased Tb. Th. of the femur (SDM = 2.401, 95% CI = 1.594 to 3.208, p = 0.000) (Figure 5A). The heterogeneity among studies was relatively low (I² = 7.872, Q = 5.427, p = 0.366). A subgroup analysis of rabbit femoral models also showed a significant increase in Tb. Th. after the implantation of 3D printed scaffolds (SDM = 2.514, 95% CI = 1.376 to 3.653, p = 0.000 and I² = 26.292, Q = 5.427, p = 0.246) (Figure 5B).

Two studies at different time points were included in this study to analyze the BV of rabbit femur after implantation of fabricated 3D printed composite scaffolds in comparison with control groups. This analysis showed that 3D-printed composite scaffolds significantly increased the BV of rabbit tibia (SDM = 1.314, 95% CI = 0.352 to 2.276, p = 0.007) (Figure 6). The heterogeneity among studies was relatively high (I² = 58.229, Q = 9.576, p = 0.048).

We undertook publication bias analysis qualitatively based on asymmetry in the funnel plot and quantitatively based on Egger’s intercept test. We conclude that the estimated effects are free of bias for most parameters; however, for the remainder, we have provided unbiased estimates using the trim and fill method.

The sensitivity analysis was performed with the exclusion of one study at a time. No study was found to be sensitive enough to change the conclusion.

Tissue engineering presents a diverse range of innovative approaches to regenerate bone tissue, with the fabrication of 3D porous scaffolds using biodegradable materials emerging as a prominent method. This strategy effectively mimics key characteristics of natural bone tissue, contributing to innovative solutions for bone regeneration (Shin et al., 2003). The major forms of 3D printing used for bone-tissue engineering materials include extrusion, stereolithography, selective laser sintering, and inkjet printing. This systematic review and meta-analysis aimed to evaluate the possible use of 3D-printed composite scaffolds in bone tissue engineering, especially in the femur and tibial defects of animal models. Femur and tibia of animals are of significant interest due to their load-bearing roles, anatomical similarities to human bones, high incidence of clinically relevant fractures, and utility as robust models for testing and validation. These bones often present critical-sized defects that cannot heal on their own, making them ideal candidates for tissue-engineered solutions that can fill and repair large gaps. The composite scaffolds provide a 3D environment for cell seeding and proliferation as well as repair of bone defects in animals while ensuring mechanical strength during the process of bone regeneration.

The internal architecture of scaffolds is recognized as a pivotal factor in tissue engineering, influencing both mechanical and biological properties. Scaffolds featuring highly interconnected 3D pores offer advantages by promoting cell adhesion, facilitating mechanical interlocking between the host tissue and scaffold through bone ingrowth, and supporting the transport of nutrients and metabolic waste. However, scaffolds need to possess adequate strength to withstand in vivo stresses at the application site until the biodegradable scaffold matrix is replaced by newly formed bone through the process of bone regeneration. The critical parameters investigated in this study include pore interconnection, microporosity, macroporosity, overall porosity, pore size, and pore shape within the 3D bio-printed composite scaffold which play a critical role in the joining of bone-implant boundary (Otsuki et al., 2006; Van Bael et al., 2012). A diverse range of pore sizes is applicable for bone regeneration, where macroporosity generally supports osteogenesis, and microporosity enhances surface area for protein adsorption, providing attachment points for bone-forming cells. Studies suggest an optimal pore size ranging from 200 to 500 µM, with a minimum size of 100 μm to avoid non-mineralized osteoid or fibrous tissue formation, which could limit oxygen and nutrient diffusion throughout the scaffolds (Bohner et al., 2005). Maintaining pores above 300 μm is recommended to facilitate cell proliferation and enhance neovascularization. Pore interconnectivity positively influences the rate and depth of bone deposition, improving nutrient and oxygen supply to the scaffold’s inner part and facilitating cell infiltration. AKT-H-N scaffolds featuring hollow channels and a micro-nano surface were successfully created by 3D printing approach coupled with hydrothermal treatment, leading to a slight improvement in mechanical strength (Feng et al., 2021). The AKT-H-N scaffolds demonstrated enhanced attachment and proliferation of BMSCs in vitro, with the hollow channels proving capable of accommodating more cells than solid scaffolds. The scaffold, characterized by its micro-nano surface and hollow channels, overcomes limitations associated with traditional scaffolds and exhibits synergistic effects in promoting bone regeneration.

Various scaffolds have been developed and tested in animal models to facilitate bone tissue regeneration (Giron et al., 2021). CaP bioceramics have been widely used in bone tissue engineering due to their outstanding bioactivity, osteoconductivity, and similarity in composition to natural bone. Notably, CaPs, such as β-TCP stand out due to their bioresorbable nature, allowing for gradual degradation over time with concurrent host tissue ingrowth, making it suitable for diverse applications. Besides biocompatibility, three crucial factors contribute to the success of scaffold material for bone implants: osteoinduction, osseointegration, and osteoconduction (Habibovic et al., 2005). β-TCP is recognized for its osteoconductive properties; however, it inherently lacks osteoinductive capabilities. Substantial efforts have been directed toward enhancing this quality through the incorporation of pharmaceuticals and biologics (Matsumoto et al., 2007; Yoshinari et al., 2002; Lan Levengood et al., 2010). Among 37 studies, only nine studies specify employing a 3D-printed β-TCP template. These templates involve different combinations of biomaterials and are applied in addressing femoral and tibial bone defects within animal models.

3D printed akermanite scaffolds were introduced by a research group from China at Zhejiang University, Hangzhou, China in 2016 with desirable interconnected pores and appreciable compressive strength (>70 MPa). The akermanite scaffolds were fabricated and applied in critical size defects (6 × 6 mm Ø) in male NZW rabbits for its osteogenesis effect and mechanical evolution at 6 and 12 weeks, in comparison with the clinically available β-TCP material which is fabricated by the same 3D printing technique (Liu et al., 2016). The akermanite scaffolds enhance tissue regeneration and repair of load-bearing bone defects. 3D-printed akermanite scaffolds (Ca2MgSi2O7), utilizing the well-established osteoinductive properties and predictable degradation rate of akermanite, represent a significant advancement in bone graft technology, manufactured by the widely-adopted ceramic ink writing technique. Notably, their degradation rate surpasses that of β-TCP counterparts. An intriguing aspect of the akermanite scaffolds is the unique release of Si and Mg. Furthermore, the concentration of calcium (Ca) release from akermanite scaffolds is more than three times higher than that from β-TCP scaffolds (Wu and Chang, 2007). This distinctive feature contributes to the overall efficacy of the akermanite scaffolds in promoting bone regeneration for load bearing bone defects (Liu et al., 2016).

PLA is a biocompatible and degradable polymer derived from lactic acid which can be easily fabricated into porous scaffolds and used for synthesizing composite scaffolds. In recent years, PLA-HA scaffolds have proven effective in the regeneration of new bone (Zhang et al., 2017). Notably, large segmental defects typically manifest as critical bone damage, often characterized by a circumferential loss surpassing 50% or a length above 2 cm in adult patients (Nauth et al., 2011). Lauer et al. addressed CSD (6 mm) by 3D printing a PLA cylinder matching the dimensions of a rat femur defect. This PLA cylinder, incorporating type I collagen and immobilized SDF-1 or BMP-7 within the collagen matrix, was implanted into the rat femur defect (Lauer et al., 2020). After 8 weeks, bone regeneration analysis was confirmed by µCT and histological staining methods which showed the osteoinductive properties of this composite scaffold (Lauer et al., 2020; Bierbaum et al., 2012; Sarker et al., 2015). This study validates the osteoinductive nature of a novel, cell-free biomaterial fabricated through 3D bioprinting, opening up new possibilities for its utilization in the realm of bone tissue regeneration (Lauer et al., 2020).

Furthermore, 3D printed PLA combined with recombinant human bone morphogenetic protein-2 (rhBMP-2) and/or mesenchymal stem cells (MSCs) with Biogel composed of gelatin and alginate were investigated for bone regeneration both in vitro and in vivo studies (Han et al., 2020). In vitro studies revealed that PLA scaffold filled with both BMP-2 and MSCs loaded on Biogel (P-BG-B2-M) increased osteogenesis. After 4 weeks post-operation of NZW rabbits, µCT analysis revealed that within the tibial defect site, the P-BG-B2 group had significantly higher percent bone volume (BV/TV) than the PLA and P-BG-M groups. Outside the defect site, the P-BG-B2-M group showed significantly higher BV/TV than the PLA group (p < 0.05) (Han et al., 2020). A scaffold P-BG-B2-M displayed excellent biocompatibility and enhanced bone regeneration in critical-size bone defect in rabbit tibia. It holds promise as a highly effective bone graft material.

PLGA and PCL are the two most common resorbable polymers. PLGA, known for its non-toxicity to tissues and efficacy as a drug release carrier, exhibits minimal inflammatory response during degradation, yielding biocompatible end products. Numerous studies indicate that PLGA serves as an effective carrier for bone morphogenetic protein (BMP), thereby promoting enhanced bone healing. Calcium-deficient hydroxyapatite (CDHA)/PLGA bilayer scaffold demonstrated successful fabrication using 3D printing, achieving a favorable combination of both components. The study encompassed in vitro assessment of degradation, cytotoxicity, and cell proliferation along with in vivo evaluation of surgical safety, biodegradation, and osteogenic capacity using a rabbit femur cortical bone defect model (Wu et al., 2021). In conclusion, the CDHA/PLGA bilayer scaffold exhibited excellent biocompatibility without cytotoxic effects and holds potential for diverse clinical applications in bone repair through 3D-printing fabrication (Wu et al., 2021).

PCL shares similar advantages with PLGA but distinguishes itself by exhibiting a prolonged degradation time. This feature positions PCL as an excellent reservoir for preserving bone grafts until the completion of the bone healing process. Yu et al. (2020) innovatively devised a modified Masquelet procedure to address segmental bone defects. Their approach involved the utilization of a 3D-printed PCL scaffold combined with co-axially electrospun nanofibers containing PLGA, vancomycin, ceftazidime, and BMP-2 in a critical rabbit femoral bone defect model (Sabzevari et al., 2023). This method demonstrated the ability to maintain elevated and sustained concentrations of antibiotics and BMP-2, ultimately promoting effective bone healing (Yu et al., 2020). Moreover, PCL scaffolds containing different weights of graphene enhance bone regeneration in a large osteochondral defect in a rabbit model (Basal et al., 2022). Likewise, graphene oxide (GO) improved the physical and biological properties of PCL scaffolds and significantly enhanced new bone regeneration (Alazab et al., 2023). Finally, Newby et al. (2023). Implanted a novel 3D-printed composite scaffold with hMSCs, made of PLGA and graphene, resulting in a notable enhancement in bone mineralization within a rat segmental femoral bone defect.

An essential factor in bone scaffold manufacturing is the biodegradability of the material. Addressing the challenges posed by non-biodegradable implants, a study detailed the application of a custom bioceramic cage in treating a large domestic dog with a CrCL-deficient stifle using a modified TTA surgical technique. The cage exhibited an overall porosity of 59.2% with pore sizes measuring 845 μm. The outcome was a complete restoration of the dog’s limb function, free from lameness or adverse complications. Additionally, there was an enhancement in local biocompatibility and osteoconductivity (Castilho et al., 2014). Moreover, Li et al. investigated the feasibility of repairing sizable segmental bone defects in large living animal models, specifically swine, using in situ 3D bio-printing technology. This method, employing a robotic manipulator to control the extrusion-based layer-by-layer construction of a photopolymerization bio-ink, utilized a combination of alginate, PEGDA, and GelMA. This synergistic blend achieved an optimal degradation rate along with enhanced mechanical properties. The distinctive double network structure of this combination ensures the bio-inks stretchability while providing ample strength and stiffness throughout the bone remodeling process.

Bioactive glass is a crucial biomaterial known for its strong biocompatibility, histocompatibility, cell compatibility, and osteoinductivity (Martelli et al., 2023). Utilizing the 3-D printing technique, bioactive glass porous scaffolds (BGS)-were fabricated, demonstrating the excellent capability of apatite formation. In vitro experiments revealed that the BGS has a good ability for the adhesion and proliferation of mouse bone marrow stromal cells (BMSCs) (Martelli et al., 2023). In a rabbit model with large bone defects, 3D-printed BGS significantly enhanced bone defect reconstruction, as evidenced by X-ray imaging at 2, 4, 8, 12, and 18 weeks post-surgery (Zhao et al., 2021). Mesoporous bioactive glasses (MBGs) with highly ordered nanoporous channels, large surface area, and high pore volume exhibited improved degradability and bioactivity compared with conventional bioglasses. Ternary composite scaffolds MGPC, including microfibrous mesoporous calcium silicate (mMCS), graphene oxide (GA), and PCL were 3D-printed and evaluated for compressive strength, in vitro degradability, and cell responses. Additionally, the in vivo osteogenesis and degradability of MGPC scaffolds were investigated through implantation in rabbit femur defects. The results showed that MGPC enhanced osteogenesis and had great potential for bone tissue engineering (Zhang et al., 2018).

Overall, this systematic review and meta-analysis revealed that 3D-printed composite scaffolds hold a promising and effective option in addressing bone defects of femur and tibia in animal models.