Recent advances on bioactive baghdadite ceramic for bone tissue engineering applications: 20 years of research and innovation (a review)

Biomimetic Scaffolds of Calcium-Based Materials for Bone Regeneration

Calcium-based materials, such as calcium carbonate, calcium phosphate, and calcium silicate, have attracted significant attention in biomedical research, owing to their unique physicochemical properties and versatile applications. The distinctive characteristics of these materials, including their inherent biocompatibility and tunable structures, hold significant promise for applications in bone regeneration and tissue engineering. This review explores the biomedical applications of calcium-containing materials, particularly for bone regeneration. Their remarkable biocompatibility, tunable nanostructures, and multifaceted functionalities make them pivotal for advancing regenerative medicine, drug delivery system, and biomimetic scaffold applications. The evolving landscape of biomedical research continues to uncover new possibilities, positioning calcium-based materials as key contributors to the next generation of innovative biomaterial scaffolds.

Engineering Wet-Resistant and Osteogenic Nanocomposite Adhesive to Control Bleeding and Infection after Median Sternotomy

Median sternotomy surgery stands as one of the prevailing strategies in cardiac surgery. In this study, the cutting-edge bone adhesive is designed, inspired by the impressive adhesive properties found in mussels and sandcastle worms. This work has created an osteogenic nanocomposite coacervate adhesive by integrating a cellulose-polyphosphodopamide interpenetrating network, quaternized chitosan, and zinc, gallium-doped hydroxyapatite nanoparticles. This adhesive is characterized by robust catechol-metal coordination which effectively adheres to both hard and soft tissues with a maximum adhesive strength of 900 ± 38 kPa on the sheep sternum bone, surpassing that of commercial bone adhesives. The release of zinc and gallium cations from nanocomposite adhesives and quaternized chitosan matrix imparts remarkable antibacterial properties and promotes rapid blood coagulation, in vitro and ex vivo. It is also proved that this nanocomposite adhesive exhibits significant in vitro bioactivity, stable degradability, biocompatibility, and osteogenic ability. Furthermore, the capacity of nanocomposite coacervate to adhere to bone tissue and support osteogenesis contributes to the successful healing of a sternum bone defect in a rabbit model in vivo. In summary, these nanocomposite coacervate adhesives with promising characteristics are expected to provide solutions to clinical issues faced during median sternotomy surgery.

3D-Printed Polycaprolactone-Based Containing Calcium Zirconium Silicate: Bioactive Scaffold for Accelerating Bone Regeneration

There is an essential clinical need to develop rapid process scaffolds to repair bone defects. The current research presented the development of calcium zirconium silicate/polycaprolactone for bone tissue engineering utilising melt extrusion-based 3D printing. Calcium zirconium silicate (CZS) nanoparticles were added to polycaprolactone (PCL) porous scaffolds to enhance their biological and mechanical properties, while the resulting properties were studied extensively. No significant difference was found in the melting point of the samples, while the crystallisation temperature points of the samples containing bioceramic increased from 36.1 to 40.2 °C. Thermal degradation commenced around 350 °C for all materials. According to our results, increasing the CZS content from 0 to 40 wt.% (PC40) in porous scaffolds (porosity about 55-62%) improved the compressive strength from 2.8 to 10.9 MPa. Furthermore, apatite formation ability in SBF solution increased significantly by enhancing the CZS percentage. According to MTT test results, the viability of MG63 cells improved remarkably (~29%) in PC40 compared to pure PCL. These findings suggest that a 3D-printed PCL/CZS composite scaffold can be fabricated successfully and shows great potential as an implantable material for bone tissue engineering applications.

Transformable Carbonate Apatite Chains as a Novel Type of Bone Graft

The aging global population is generating an ever-increasing demand for bone regeneration. Various materials, including blocks, granules, and sponges, are developed for bone regeneration. However, blocks require troublesome shaping and exhibit poor bone-defect conformities; granules migrate into the surrounding tissues during and after filling of the defect, causing handling difficulties and complications; and sponges contain polymers that are subject to religious restrictions, lack osteoconductivity, and may cause inflammation and allergies. Herein, carbonate apatite chains that overcome the limitations of conventional materials are presented. Although carbonate apatite granules migrate, causing inflammation and ectopic calcification, the chains remain in the defects without causing any complications. The chains conform to the defect shape and transform into 3D porous structures, resulting in faster bone regeneration than that observed using granules. Thus, these findings indicate that even traditional calcium phosphates materials can be converted to state-of-the-art materials via shape control.

Platelets: A Potential Factor that Offers Strategies for Promoting Bone Regeneration

Bone defects represent a prevalent category of clinical injuries, causing significant pain and escalating health care burdens. Effectively addressing bone defects is thus of paramount importance. Platelets, formed from megakaryocyte lysis, have emerged as pivotal players in bone tissue repair, inflammatory responses, and angiogenesis. Their intracellular storage of various growth factors, cytokines, and membrane protein receptors contributes to these crucial functions. This article provides a comprehensive overview of platelets' roles in hematoma structure, inflammatory responses, and angiogenesis throughout the process of fracture healing. Beyond their application in conjunction with artificial bone substitute materials for treating bone defects, we propose the potential future use of anticoagulants such as heparin in combination with these materials to regulate platelet number and function, thereby promoting bone healing. Ultimately, we contemplate whether manipulating platelet function to modulate bone healing could offer innovative ideas and directions for the clinical treatment of bone defects.

Effects of Space Dimensionality within Scaffold for Bone Regeneration with Large and Oriented Blood Vessels

The internal structure of the scaffolds is a key factor for bone regeneration. In this study, we focused on the space dimensionality within the scaffold that may control cell migration and evaluated the effects on the size and orientation of blood vessels and the amount of bone formation in the scaffold. The carbonate apatite scaffolds with intrascaffold space allowing one-dimensional (1D), two-dimensional (2D), or three-dimensional (3D) cell migration were fabricated by 3D printing. These scaffolds had the same space size, i.e., distances between the struts (~300 µm). The scaffolds were implanted into the medial condyle of rabbit femurs for four weeks. Both the size and orientation degree of the blood vessels formed in the scaffolds allowing 1D cell migration were 2.5- to 4.0-fold greater than those of the blood vessels formed in the scaffolds allowing 2D and 3D cell migration. Furthermore, the amount of bone formed in the scaffolds allowing 1D cell migration was 1.4-fold larger than that formed in the scaffolds allowing 2D and 3D cell migration. These are probably because the 1D space limited the direction of cell migration and prevented the branching of blood vessels, whereas 2D and 3D spaces provided the opportunity for random cell migration and blood vessel branching. Thus, scaffolds with 1D space are advantageous for inducing large and oriented blood vessels, resulting in a larger amount of bone formation.

Novel barium-doped-baghdadite incorporated PHBV-PCL composite fibrous scaffolds for bone tissue engineering

Bioceramic/polymer composites have dragged a lot of attention for treating hard tissue damage in recent years. In this study, we synthesized barium-doped baghdadite (Ba-BAG), as a novel bioceramic, and later developed fibrous composite poly (hydroxybutyrate) co (hydroxyvalerate)- polycaprolactone (PHBV-PCL) scaffolds containing different amounts of baghdadite (BAG) and Ba-BAG, intended to be used in bone regeneration. Our results demonstrated that BAG and Ba-doped BAG powders were synthesized successfully using the sol-gel method and their microstructural, physicochemical, and cytotoxical properties results were evaluated. In the following, PHBV/PCL composite scaffolds containing different amounts of BAG and Ba-BAG (1, 3, and 5 wt%) were produced by the wet electrospinning method. The porosity of scaffolds decreased from 78% to 72% in Ba-BAG-incorporated PHBV/PCL scaffolds. The compressive strength of the scaffolds was between 4.69 and 9.28 kPa, which was increased to their maximum values in the scaffolds with Ba-BAG. The presence of BAG and Ba-BAG in the polymer scaffolds resulted in increasing bioactivity, and it was introduced as a suitable way to control the degradation rate of scaffolds. The presence of the BAG component was a major reason for higher cell proliferation in reinforced PHBV/PCL polymeric scaffolds, while Ba existence played its influential role in the higher osteogenic activity of cells on Ba-BAG incorporated PHBV/PCL scaffolds. Thus, the incorporation of Ba-BAG bioceramic materials into the structure of polymeric PHBV/PCL scaffolds promoted their various properties, and allow these scaffolds to be used as promising candidates in bone tissue engineering applications.

In Vitro Biocompatibility of the Novel Ceramic Composite Baghdadite for Defect Augmentation in Revision Total Hip Arthroplasty

Biological augmentation of bony defects in weight-bearing areas of both the acetabulum and the femur remains challenging. The calcium-silicate-based ceramic Baghdadite is a very interesting material to be used in the field of revision total hip arthroplasty for the treatment of bony defects in weight-bearing and non-weight-bearing areas alike. The aim of this study was to investigate the biocompatibility of Baghdadite utilizing an osteoblast-like, human osteosarcoma cell line (MG-63) and the human monocytic leukemia-derived cell line (THP-1). THP-1-derived macrophages and MG-63 were indirectly exposed to Baghdadite for 7 days using a transwell system. Viability was assessed with MTT assay and pH analysis. To investigate proliferation rate, both cell lines were labelled using CFSE and flow cytometrically analyzed. ELISA was used to measure the secretion of IL-1ß, IL-6 and TNFα. The investigation of viability, while showing a slight difference in optical density for the MTT assays in MG-63 cells, did not present a meaningful difference between groups for both cell lines. The comparison of pH and the proportion of living cells between groups did not present with a significant difference for both THP-1 and MG-63. Baghdadite did not have a relevant impact on the proliferation rate of the investigated cell lines. Mean fluorescence intensity was calculated between groups with no significant difference. Baghdadite exerted a proinflammatory effect, which could be seen in an upregulated production of TNFα in macrophages. Production of IL-1ß and IL-6 was not statistically significant, but the IL-6 ELISA showed a trend to an upregulated production as well. A similar effect on MG-63 was not observed. No relevant cytotoxicity of Baghdadite ceramics was encountered. Baghdadite ceramics exhibit a proinflammatory potential by significantly increasing the secretion of TNFα in THP-1-derived macrophages. Whether this proinflammatory potential results in a clinically relevant effect on osteointegration is unclear and requires further investigation. Baghdadite ceramics provide an interesting alternative to conventional bone substitutes and should be further investigated in a biomechanical and in vivo setting.

Numerical and experimental investigation on creep response of 3D printed Polylactic acid (PLA) samples. Part I: The effect of building direction and unidirectional raster orientation

The main aim of this research work is to investigate the effects of building directions and raster orientations on the creep behavior of 3D-printed plastic material and to develop rheological constitutive models to estimate the creep behavior of components. These components have been manufactured through the Fused Deposition Modeling (FDM) technique in which materials are heated and extruded through a nozzle to create 3D Polylactic acid (PLA) specimens. Since 3D-printed specimens exhibit anisotropic behavior, studying their building condition is necessary. Both building direction and raster orientation are among the fabrication conditions that play a major role in the mechanical behavior of the specimens. The tensile behavior of 3D-produced PLA specimens and their creep behavior were evaluated. To model the creep behavior of 3D printed PLA, three different types of rheological constitutive models, Zener, Burgers, and modified Burgers were used analytically and numerically. The finite element (FE) model of the 3D printed unnotched samples was developed to predict the creep behavior of notched samples. The results show that 3D FE models can predict the creep behavior of AM-notched specimens with high accuracy.

Bioactive and Biodegradable Polycaprolactone-Based Nanocomposite for Bone Repair Applications

This study investigated the relationship between the structure and mechanical properties of polycaprolactone (PCL) nanocomposites reinforced with baghdadite, a newly introduced bioactive agent. The baghdadite nanoparticles were synthesised using the sol-gel method and incorporated into PCL films using the solvent casting technique. The results showed that adding baghdadite to PCL improved the nanocomposites' tensile strength and elastic modulus, consistent with the results obtained from the prediction models of mechanical properties. The tensile strength increased from 16 to 21 MPa, and the elastic modulus enhanced from 149 to 194 MPa with fillers compared to test specimens without fillers. The thermal properties of the nanocomposites were also improved, with the degradation temperature increasing from 388 °C to 402 °C when 10% baghdadite was added to PCL. Furthermore, it was found that the nanocomposites containing baghdadite showed an apatite-like layer on their surfaces when exposed to simulated body solution (SBF) for 28 days, especially in the film containing 20% nanoparticles (PB20), which exhibited higher apatite density. The addition of baghdadite nanoparticles into pure PCL also improved the viability of MG63 cells, increasing the viability percentage on day five from 103 in PCL to 136 in PB20. Additionally, PB20 showed a favourable degradation rate in PBS solution, increasing mass loss from 2.63 to 4.08 per cent over four weeks. Overall, this study provides valuable insights into the structure-property relationships of biodegradable-bioactive nanocomposites, particularly those reinforced with new bioactive agents.

Superiority of Triply Periodic Minimal Surface Gyroid Structure to Strut-Based Grid Structure in Both Strength and Bone Regeneration

The aging population has rapidly driven the demand for bone regeneration. The pore structure of a scaffold is a critical factor that affects its mechanical strength and bone regeneration. Triply periodic minimal surface gyroid structures similar to the trabecular bone structure are considered superior to strut-based lattice structures (e.g., grids) in terms of bone regeneration. However, at this stage, this is only a hypothesis and is not supported by evidence. In this study, we experimentally validated this hypothesis by comparing gyroid and grid scaffolds composed of carbonate apatite. The gyroid scaffolds possessed compressive strength approximately 1.6-fold higher than that of the grid scaffolds because the gyroid structure prevented stress concentration, whereas the grid structure could not. The porosity of gyroid scaffolds was higher than that of the grid scaffolds; however, porosity and compressive strength generally have a trade-off relationship. Moreover, the gyroid scaffolds formed more than twice the amount of bone as grid scaffolds in a critical-sized bone defect in rabbit femur condyles. This favorable bone regeneration using gyroid scaffolds was attributed to the high permeability (i.e., larger volume of macropores or porosity) and curvature profile of the gyroid structure. Thus, this study validated the conventional hypothesis using in vivo experiments and revealed factors that led to this hypothetical outcome. The findings of this study are expected to contribute to the development of scaffolds that can achieve early bone regeneration without sacrificing the mechanical strength.

Customized bioceramic scaffolds and metal meshes for challenging large-size mandibular bone defect regeneration and repair

Large-size mandible graft has huge needs in clinic caused by infection, tumor, congenital deformity, bone trauma and so on. However, the reconstruction of large-size mandible defect is challenged due to its complex anatomical structure and large-range bone injury. The design and fabrication of porous implants with large segments and specific shapes matching the native mandible remain a considerable challenge. Herein, the 6% Mg-doped calcium silicate (CSi-Mg6) and β- and α-tricalcium phosphate (β-TCP, α-TCP) bioceramics were fabricated by digital light processing as the porous scaffolds of over 50% in porosity, while the titanium mesh was fabricated by selective laser melting. The mechanical tests showed that the initial flexible/compressive resistance of CSi-Mg6 scaffolds was markedly higher than that of β-TCP and α-TCP scaffolds. Cell experiments showed that these materials all had good biocompatibility, while CSi-Mg6 significantly promoted cell proliferation. In the rabbit critically sized mandible bone defects (∼13 mm in length) filled with porous bioceramic scaffolds, the titanium meshes and titanium nails were acted as fixation and load bearing. The results showed that the defects were kept during the observation period in the blank (control) group; in contrast, the osteogenic capability was significantly enhanced in the CSi-Mg6 and α-TCP groups in comparison with the β-TCP group, and these two groups not only had significantly increased new bone formation but also had thicker trabecular and smaller trabecular spacing. Besides, the CSi-Mg6 and α-TCP groups showed appreciable material biodegradation in the later stage (from 8 to 12 weeks) in comparison with the β-TCP scaffolds while the CSi-Mg6 group showed much outstanding mechanical capacity in vivo in the early stage compared to the β-TCP and α-TCP groups. Totally, these findings suggest that the combination of customized strength-strong bioactive CSi-Mg6 scaffolds together with titanium meshes is a promising way for repairing the large-size load-bearing mandible defects.

Ceramic Materials for Biomedical Applications: An Overview on Properties and Fabrication Processes

A growing interest in creating advanced biomaterials with specific physical and chemical properties is currently being observed. These high-standard materials must be capable to integrate into biological environments such as the oral cavity or other anatomical regions in the human body. Given these requirements, ceramic biomaterials offer a feasible solution in terms of mechanical strength, biological functionality, and biocompatibility. In this review, the fundamental physical, chemical, and mechanical properties of the main ceramic biomaterials and ceramic nanocomposites are drawn, along with some primary related applications in biomedical fields, such as orthopedics, dentistry, and regenerative medicine. Furthermore, an in-depth focus on bone-tissue engineering and biomimetic ceramic scaffold design and fabrication is presented.

Protocol for Cell Colonization and Comprehensive Monitoring of Osteogenic Differentiation in 3D Scaffolds Using Biochemical Assays and Multiphoton Imaging

The goal of bone tissue engineering is to build artificial bone tissue with properties that closely resemble human bone and thereby support the optimal integration of the constructs (biografts) into the body. The development of tissues in 3D scaffolds includes several complex steps that need to be optimized and monitored. In particular, cell-material interaction during seeding, cell proliferation and cell differentiation within the scaffold pores play a key role. In this work, we seeded two types of 3D-printed scaffolds with pre-osteoblastic MC3T3-E1 cells, proliferated and differentiated the cells, before testing and adapting different assays and imaging methods to monitor these processes. Alpha-TCP/HA (α-TCP with low calcium hydroxyapatite) and baghdadite (Ca₃ZrSi₂O₉) scaffolds were used, which had comparable porosity (~50%) and pore sizes (~300-400 µm). Cell adhesion to both scaffolds showed ~95% seeding efficiency. Cell proliferation tests provided characteristic progression curves over time and increased values for α-TCP/HA. Transmitted light imaging displayed a homogeneous population of scaffold pores and allowed us to track their opening state for the supply of the inner scaffold regions by diffusion. Fluorescence labeling enabled us to image the arrangement and morphology of the cells within the pores. During three weeks of osteogenesis, ALP activity increased sharply in both scaffolds, but was again markedly increased in α-TCP/HA scaffolds. Multiphoton SHG and autofluorescence imaging were used to investigate the distribution, morphology, and arrangement of cells; collagen-I fiber networks; and hydroxyapatite crystals. The collagen-I networks became denser and more structured during osteogenic differentiation and appeared comparable in both scaffolds. However, imaging of the HA crystals showed a different morphology between the two scaffolds and appeared to arrange in the α-TCP/HA scaffolds along collagen-I fibers. ALP activity and SHG imaging indicated a pronounced osteo-inductive effect of baghdadite. This study describes a series of methods, in particular multiphoton imaging and complementary biochemical assays, to validly measure and track the development of bone tissue in 3D scaffolds. The results contribute to the understanding of cell colonization, growth, and differentiation, emphasizing the importance of optimal media supply of the inner scaffold regions.

Development of Strong and Tough β-TCP/PCL Composite Scaffolds with Interconnected Porosity by Digital Light Processing and Partial Infiltration

Strong and tough β-TCP/PCL composite scaffolds with interconnected porosity were developed by combining digital light processing and vacuum infiltration. The composite scaffolds were comprised of pure β-TCP, β-TCP matrix composite and PCL matrix composite. The porous β-TCP/PCL composite scaffolds showed remarkable mechanical advantages compared with ceramic scaffolds with the same macroscopic pore structure (dense scaffolds). The composite scaffolds exhibited a significant increase in strain energy density and fracture energy density, though with similar compressive and flexural strengths. Moreover, the composite scaffolds had a much higher Weibull modulus and longer fatigue life than the dense scaffolds. It was revealed that the composite scaffolds with interconnected porosity possess comprehensive mechanical properties (high strength, excellent toughness, significant reliability and fatigue resistance), which suggests that they could replace the pure ceramic scaffolds for degradable bone substitutes, especially in complex stress environments.