Microstructure and property evolutions of titanium/nano-hydroxyapatite composites in-situ prepared by selective laser melting

Informatics guided FE design of bioactive titanium alloy/composite multi-layered dental implants

A dental implant with three distinct layers, of titanium alloy at core, porous titanium alloy at the intermediate layer and titanium alloy hydroxyapatite composite at the outer layer, is designed to achieve low elastic modulus and adequate strength with bioactive surface. Artificial Neural Network (ANN) along with Rule of Mixture (ROM) is used to generate the objective functions for the Genetic Algorithm (GA) based multi-objective optimization for achieving the optimal designs, which are validated using Finite Element Analysis (FEA) simulations. The composition and processing parameters are correlated with the yield strength and elastic modulus of titanium alloy using ANN. The ANN models are generated to express the strength and effective modulus of the implant using ROM. To determine the optimal composition of titanium alloys, porous layers, and composite layers for a three-layer dental implant, multi-objective genetic algorithm is employed. The Pareto optimal solutions provide the guidelines for designing the implant. A few selected non-dominated solutions are used for studying the actual stress distribution at the bone-implant interface using FEA, and showed significant improvements compared to conventional implants.

Mechanical Properties of Titanium/Nano-Fluorapatite Parts Produced by Laser Powder Bed Fusion

Laser powder bed fusion (L-PBF) has attracted great interest in recent years due to its ability to produce intricate parts beyond the capabilities of traditional manufacturing processes. L-PBF processed biomedical implants are usually made of commercial pure titanium (CP-Ti) or its alloys. However, both alloys are naturally bio-inert, and thus reduce the formation of apatite as implants are put into the human body. Accordingly, in an attempt to improve the bioactivity of the materials used for making orthopedic implants, the present study decomposed fluorapatite material (FA, (Ca₁₀(PO₄)₆F₂)) into the form of nano-powder and mixed this powder with CP-Ti powder in two different ratios (99%Ti + 1%FA (Ti-1%FA) and 98%Ti + 2%FA (Ti-2%FA)) to form powder material for the L-PBF process. Experimental trials were conducted to establish the optimal processing conditions (i.e., laser power, scanning speed and hatching space) of the L-PBF process for the two powder mixtures and the original CP-Ti powder with no FA addition. The optimal parameters were then used to produce tensile test specimens in order to evaluate the mechanical properties of the different samples. The hardness of the various samples was also examined by micro-Vickers hardness tests. The tensile strength of the Ti-1%FA sample (850 MPa) was found to be far higher than that of the CP-Ti sample (513 MPa). Furthermore, the yield strength of the Ti-1%FA sample (785 MPa) was also much higher than that of the CP-Ti sample (472 MPa). However, the elongation of the Ti-1%FA sample (6.27 %) was significantly lower than that of the CP-Ti sample (16.17%). Finally, the hardness values of the Ti-1%FA and Ti-2%FA samples were around 63.8% and 109.4%, respectively, higher than that of the CP-Ti sample.

Synthesis of Ti6Al4V/SrFHA Composites by Microwave-Assisted Liquid Phase Deposition and Calcination

The feasibility of synthesis of Ti6Al4V/SrFHA (Ca9.37Sr0.63(PO4)6F2) composites via coating strontium and fluorine co-doped HA to Ti6Al4V substrate by microwave-assisted liquid phase deposition and calcination was evaluated, with a focus on the effect of the deposition temperature from 30 °C to 70 °C. The outcomes demonstrate that strontium and fluorine can be successfully doped into HA to form a SrFHA coating with modified micromorphology which is deposited on the alloy. When the deposition temperature was 50 °C, the coating with the largest uniform continuous SrFHA coverage was obtained. After calcination, the adhesion strength and Vickers microhardness of the Ti6Al4V/SrFHA composite increased from 0.68 MPa and 323 HV to 2.41 MPa and 329 HV, respectively, with a decrease in the water contact angle from 10.88° to 7.24°, exhibiting enhancement of both mechanical properties and wettability. Moreover, the composite obtained at the deposition temperature of 50 °C exhibited good bioactivity based on the simulate body fluid (SBF) test. On account of the above features primarily as a result of the combined effect of the co-doping of strontium and fluorine, high crystallinity of SrFHA, large surface roughness, and formation of the titanium oxide transition layer, the Ti6Al4V/SrFHA composite shows great potential in dental implantology.

Electrophoretic deposition of novel semi-permeable coatings on 3D-printed Ti-Nb alloy meshes for guided alveolar bone regeneration

OBJECTIVE

Guided bone regeneration (GBR) techniques use barrier membranes to augment the alveolar ridge for the site-specific growth of bone defects. However, current approaches using cast metal substructures exhibit poor adaptation to the surgical site and increased risk of infection. This study aimed to fabricate multi-functional coatings with 3D-printed porous titanium-niobium (Ti-Nb) alloy meshes to maintain space, prevent the ingrowth of fibroblasts and inhibit the colonization of bacteria for GBR.

METHODS

Ti-Nb alloy meshes were prepared by selective laser melting (SLM) and used as substrates for novel surface coatings. Porous chitosan (CS)/ gelatin (G)/ doxycycline (Dox) coatings were formed on the meshes using electrophoretic deposition (EPD) and freeze-drying. The process of EPD was characterized through Fourier transform infrared spectroscopy (FT-IR), zeta potential, and particle size analysis. The cytotoxicity of the coatings was evaluated through the culture of osteoblasts and immunostaining. The antibacterial activity of the coatings was tested using inhibition zone tests against Staphylococcus aureus (S. aureus) and scanning electron microscope (SEM). The inhibition of fibroblasts infiltration and nutrients transfer properties were analyzed using immunostaining and permeability tests.

RESULTS

High yield strength (567.5 ± 3.5 MPa) and low elastic modulus (65.5 ± 0.2 GPa) were achieved in Ti-Nb alloy bulk samples. The data of zeta potential, FT-IR and SEM indicated that porous spongy coatings were chemically bonded following EPD. In vitro analysis of CSGDox1 (containing Dox at 1 mg·mL^-1) coating revealed its antibacterial effect and biocompatibility. Moreover, the CSGDox1 coating was proved to be effective for preventing the ingrowth of fibroblasts, whilst allowing the infiltration of nutrients.

SIGNIFICANCE

This study verified that the EPD of CSGDox coatings on the 3D-printed Ti-Nb meshes can maintain space, provide antibiotic release whilst maintaining a barrier against soft-tissue growth, which is essential for the success of GBR treatment.

Polycrystalline diamond coating on 3D printed titanium scaffolds: Surface characterisation and foreign body response

Titanium-based implants are the leading material for orthopaedic surgery, due to their strength, versatility, fabrication via additive manufacturing and invoked biological response. However, the interface between the implant and the host tissue requires improvement to better integrate the implant material and mitigate foreign body response. The interface can be manipulated by changing the surface energy, chemistry, and topography of the Titanium-based implant. Recently, polycrystalline diamond (PCD) has emerged as an exciting coating material for 3D printed titanium scaffolds showing enhanced mammalian cell functions while inhibiting bacterial attachment in vitro. In this study, we performed in-depth characterisation of PCD coatings investigating the surface topography, thickness, surface energy, and compared its foreign body response in vivo with uncoated titanium scaffold. Coating PCD onto titanium scaffolds resulted in a similar microscale surface roughness (RMS_(PCD-coated) = 24 μm; RMS_(SLM-Ti) = 28 μm), increased nanoscale roughness (RMS_(PCD-coated) = 35 nm; RMS_(SLM-Ti) = 66 nm) and a considerable decrease in surface free energy (E_(PCD-coated) = 4 mN m^-1; E_(SLM-Ti) = 16 mN m^-1). These surface property changes were supported by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy as corresponding to observed surface chemistry changes induced by the coating. The underlying mechanism of how the diamond coatings chemical and physical properties changes the wettability of implants was examined. In vivo, the coated scaffolds induced similar level of fibrous encapsulation with uncoated scaffolds. This study thus provides further insight into the physicochemical characteristics of PCD coatings, adding evidence to the promising potential of PCD-coatings of medical implants.

Bioactive Ceramic Scaffolds for Bone Tissue Engineering by Powder Bed Selective Laser Processing: A Review

The implementation of a powder bed selective laser processing (PBSLP) technique for bioactive ceramics, including selective laser sintering and melting (SLM/SLS), a laser powder bed fusion (L-PBF) approach is far more challenging when compared to its metallic and polymeric counterparts for the fabrication of biomedical materials. Direct PBSLP can offer binder-free fabrication of bioactive scaffolds without involving postprocessing techniques. This review explicitly focuses on the PBSLP technique for bioactive ceramics and encompasses a detailed overview of the PBSLP process and the general requirements and properties of the bioactive scaffolds for bone tissue growth. The bioactive ceramics enclosing calcium phosphate (CaP) and calcium silicates (CS) and their respective composite scaffolds processed through PBSLP are also extensively discussed. This review paper also categorizes the bone regeneration strategies of the bioactive scaffolds processed through PBSLP with the various modes of functionalization through the incorporation of drugs, stem cells, and growth factors to ameliorate critical-sized bone defects based on the fracture site length for personalized medicine.

Anodizing/Anaphoretic Electrodeposition of Nano-Calcium Phosphate/Chitosan Lactate Multifunctional Coatings on Titanium with Advanced Corrosion Resistance, Bioactivity, and Antibacterial Properties

The aim of this work was to investigate corrosion resistivity, bioactivity, and antibacterial activity of novel nano-amorphous calcium phosphate (ACP) potentially multifunctional composite coatings with and without chitosan oligosaccharide lactate (ChOL), ACP + ChOL/TiO₂ and ACP/TiO₂ ACP + ChOL/TiO₂, respectively, on the titanium substrate. The coatings were obtained by new single-step in situ anodization of the substrate to generate TiO₂ and the anaphoretic electrodeposition process of ACP and ChOL. The obtained coatings were around 300 ± 15 μm thick and consisted of two phases, namely, TiO₂ and hybrid composite phases. Both ACP/TiO₂ and ACP + ChOL/TiO₂ have improved corrosion stability, whereas the ACP + ChOL/TiO₂ coating showed better corrosion stability. It was shown that at the very start of the deposition process, the formation of the ChOL/TiO₂ layer takes place predominantly, which is followed by the inclusion of ChOL into ACP with simultaneous growth of TiO₂. This deposition mechanism resulted in the formation of strongly bonded uniform stable coating with high corrosion resistance. In vitro bioactivity was investigated by immersion of the samples in simulated body fluid (SBF). There is in-bone-like apatite formation on both ACP/TiO₂ and ACP + ChOL/TiO₂ surfaces upon immersion into SBF, which was proven by X-ray diffraction and Fourier transform infrared spectroscopy. While ACP/TiO₂ shows no antibacterial activity, ACP + ChOL/TiO₂ samples exhibited three- to fourfold decreases in the number of Staphylococcus aureus and Pseudomonas aeruginosa, respectively, after 420 min. The probable mechanism is binding ChOL with the bacterial cell wall, inhibiting its growth, altering the permeability of the cell membrane, and leading to bacterial death.

Recent Advances on High-Entropy Alloys for 3D Printing

Boosted by the success of high-entropy alloys (HEAs) manufactured by conventional processes in various applications, the development of HEAs for 3D printing has been advancing rapidly in recent years. 3D printing of HEAs gives rise to a great potential for manufacturing geometrically complex HEA products with desirable performances, thereby inspiring their increased appearance in industrial applications. Herein, a comprehensive review of the recent achievements of 3D printing of HEAs is provided, in the aspects of their powder development, printing processes, microstructures, properties, and potential applications. It begins with the introduction of the fundamentals of 3D printing and HEAs, as well as the unique properties of 3D-printed HEA products. The processes for the development of HEA powders, including atomization and mechanical alloying, and the powder properties, are then presented. Thereafter, typical processes for printing HEA products from powders, namely, directed energy deposition, selective laser melting, and electron beam melting, are discussed with regard to the phases, crystal features, mechanical properties, functionalities, and potential applications of these products (particularly in the aerospace, energy, molding, and tooling industries). Finally, perspectives are outlined to provide guidance for future research.

Multi-material additive manufacturing technologies for Ti-, Mg-, and Fe-based biomaterials for bone substitution

The growing interest in multi-functional metallic biomaterials for bone substitutes challenges the current additive manufacturing (AM, =3D printing) technologies. It is foreseeable that advances in multi-material AM for metallic biomaterials will not only allow for complex geometrical designs, but also improve their multi-functionalities by tuning the types or compositions of the underlying base materials, thereby presenting unprecedented opportunities for advanced orthopedic treatments. AM technologies are yet to be extensively explored for the fabrication of multi-functional metallic biomaterials, especially for bone substitutes. The aim of this review is to present the viable options of the state-of-the-art multi-material AM for Ti-, Mg-, and Fe-based biomaterials to be used as bone substitutes. The review starts with a brief review of bone tissue engineering, the design requirements, and fabrication technologies for metallic biomaterials to highlight the advantages of using AM over conventional fabrication methods. Five AM technologies suitable for metal 3D printing are compared against the requirements for multi-material AM. Of these AM technologies, extrusion-based multi-material AM is shown to have the greatest potential to meet the requirements for the fabrication of multi-functional metallic biomaterials. Finally, recent progress in the fabrication of Ti-, Mg-, and Fe-based biomaterials including the utilization of multi-material AM technologies is reviewed so as to identify the knowledge gaps and propose the directions of further research for the development of multi-material AM technologies that are applicable for the fabrication of multi-functional metallic biomaterials. STATEMENT OF SIGNIFICANCE: Addressing a critical bone defect requires the assistance of multi-functional porous metallic bone substitutes. As one of the most advanced fabrication technology in bone tissue engineering, additive manufacturing is challenged for its viability in multi-material fabrication of metallic biomaterials. This article reviews how the current metal additive manufacturing technologies have been and can be used for multi-material fabrication of Ti-, Mg-, and Fe-based bone substitutes. Progress on the Ti-, Mg-, and Fe-based biomaterials, including the utilization of multi-material additive manufacturing, are discussed to direct future research for advancing the multi-functional additively manufactured metallic bone biomaterials.

Laser-Based Ablation of Titanium-Graphite Composite for Dental Application

Biocompatible materials with excellent mechanical properties as well as sophisticated surface morphology and chemistry are required to satisfy the requirements of modern dental implantology. In the study described in this article, an industrial-grade fibre nanosecond laser working at 1064 nm wavelength was used to micromachine a new type of a biocompatible material, Ti-graphite composite prepared by vacuum low-temperature extrusion of hydrogenated-dehydrogenated (HDH) titanium powder mixed with graphite flakes. The effect of the total laser energy delivered to the material per area on the machined surface morphology, roughness, surface element composition and phases transformations was investigated and evaluated by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), confocal laser-scanning microscopy (CLSM) and X-ray diffraction analysis (XRD). The findings illustrate that the amount of thermal energy put to the working material has a remarkable effect on the machined surface properties, which is discussed from the aspect of the contact properties of dental implants.

Insights into unit cell size effect on mechanical responses and energy absorption capability of titanium graded porous structures manufactured by laser powder bed fusion

Schwartz diamond graded porous structures (SDGPSs), constructed by a triply-periodic-minimal-surface diamond unit cell topology, were developed with various unit cell sizes and printed by laser powder bed fusion (LPBF) from a commercially pure titanium powder for bone implant applications. The effect of unit cell size on the printability, strut dimensions, stress and strain distributions, mechanical properties and energy absorption capability of SDGPSs was investigated. The results indicate the good printability of SDGPSs via LPBF with multiple unit cell sizes from 3.5 mm to 5.5 mm through the three-dimensional reconstruction from micro-computed tomography. The unit cell size plays a critical role in both strut diameters and specific surface areas of SDGPSs. An increase in the unit cell size leads to a reduction in the experimental Young's modulus from 673.08 MPa to 518.71 MPa and compressive yield strength from 11.43 MPa to 7.73 MPa. The mechanical properties of LPBF-printed SDGPSs are higher than those predicted by the finite element method, which is attributed to the higher volume fractions of the printed SDGPSs than the designed values. Furthermore, a rise in unit cell size leads to the decrease of energy absorption capability from 6.06 MJ/mm³ to 4.32 MJ/mm³ and exhibits little influence on the absorption efficiency. These findings provide a good understanding and guidance to the optimization on the unit cell size of functionally graded porous structures for desirable properties.

Compositionally graded doped hydroxyapatite coating on titanium using laser and plasma spray deposition for bone implants

Plasma sprayed hydroxyapatite (HA) coating is known to improve the osteoconductivity of metallic implants. However, the adhesive bond strength of the coating is affected due to a mismatch in coefficients of thermal expansion (CTE) between the metal and HA ceramic. In this study, a gradient HA coating was prepared on Ti6Al4V by laser engineered net shaping (LENS™) followed by plasma spray deposition. In addition, 1 wt% MgO and 2 wt% Ag2O were mixed with HA to improve the biological and antibacterial properties of the coated implant. Results showed that the presence of an interfacial layer by LENS™ enhanced adhesive bond strength from 26 ± 2 MPa for just plasma spray coating to 39 ± 4 MPa for LENS™ and plasma spray coatings. Presence of MgO and Ag2O did not influence the adhesive bond strength. Also, Ag+ ions release dropped by 70% less with a gradient HA LENS™ layer due to enhanced crystallization of the HA layer. In vitro human osteoblast cell culture revealed presence of Ag2O had no deleterious effect on proliferation and differentiation when compared to pure HA as control and provided antibacterial properties against E. coli and S. aureus bacterial strands. This study presents an innovative way to improve interfacial mechanical and antibacterial properties of plasma sprayed HA coating for load-bearing orthopedic as well as dental implants. STATEMENT OF SIGNIFICANCE: Implants are commonly composed of metals that lack osteoconductivity. Osteoconductivity is a property where bone grows on the surface meaning the material is compatible with the surrounding bone tissue. Plasma sprayed hydroxyapatite (HA) coating improves the osteoconductivity of metallic implants, however, the adhesive bond strength can be weak. This study incorporates a gradient HA coating by using an additive manufacturing technique, laser engineered net shaping (LENS™), followed by plasma spray deposition to enhance the adhesive bond strength by incorporating a thermal barrier. The proposed system has not been well studied in the current literature and the results presented bring forth an innovative way to improve the interfacial mechanical and antibacterial properties of plasma sprayed HA coating for load-bearing orthopedic implants.

Microstructure and Mechanical Properties of Nano-Carbon Reinforced Titanium Matrix/Hydroxyapatite Biocomposites Prepared by Spark Plasma Sintering

Nano-carbon reinforced titanium matrix/hydroxyapatite (HA) biocomposites were successfully prepared by spark plasma sintering (SPS). The microstructure, mechanical properties, biocompatibility, and the relationship between microstructure and properties of biocomposites were systematically investigated. Results showed there are some new phases in sintered composites, such as β-Ti, TiO₃, ZrO₂, etc. Moreover, a small amount of Ti₁₇P₁₀, CaTiO₃, Ca₃(PO₄)₂ were also detected. The reaction that may occur during the preparation process is suppressed to some extent, which is because that the addition of second phases can prevent the direct contact of titanium with HA and reduce the contact areas. Transmission electron microscope (TEM) analysis proved the existence of elemental diffusion and chemical reactions in sintered composites. Compared with results of composites prepared by hot-pressed sintering before, mechanical properties (microhardness, compressive strength, and shear strength) of 0.5-GNFs composites prepared by SPS were increased by about 2.8, 4.8, and 4.1 times, respectively. The better mechanical properties of 0.5-GNFs composite in nano-carbon reinforced composites are mainly due to the lower degree of agglomeration of tubular carbon nanotubes (CNTs) compared to lamellar graphene nanoflakes (GNFs). Moreover, the strengthening and toughening mechanisms of nano-carbon reinforced titanium alloy/HA biocomposite prepared by spark plasma sintering (SPS) mainly included second phase strengthening, grain refinement strengthening, solution strengthening, graphene extraction, carbon nanotubes bridging, crack tail stripping, etc. In addition, in vitro bioactivity test revealed that the addition of nano-carbon was beneficial to promote the adhesion and proliferation of cells on the surface of titanium alloy/HA composite, because nano-carbon can enhance the formation of mineralized necks in the composites after transplantation, stimulate biomineralization and promote bone regeneration.

Research Progress Regarding Interfacial Characteristics and the Strengthening Mechanisms of Titanium Alloy/Hydroxyapatite Composites

Titanium alloy/Hydroxyapatite (HA) composites have become a hot research topic in biomedical materials, while there are some challenges concerning bioactivity and mechanical properties such as low interface adhesion at the interface between metal and ceramic, complex interfacial reactions, and so on. Nevertheless, composites with reinforced phases can reach special properties that meet the requirements of biomedical materials due to the strong interfacial interactions between reinforcing phases (nano-carbon, partial oxides, and so on) and Titanium alloys or HA. This review summarizes the interface properties and mechanisms of Titanium alloy/HA composites, including interfacial bonding methods, strengthening and toughening mechanisms, and performance evaluation. On this basis, the interface characteristics and mechanisms of the Titaniumalloy/HA composites with enhanced phase are prospected. The results show that the interfacial bonding methods in the Titanium alloy/HA composites include chemical reactions and mechanical effects. The strengthening and toughening mechanisms contain grain refinement strengthening, second phase strengthening, solution strengthening, cracks and pulling out mechanisms, etc. This review provides a guidline for the fabrication of biocomposites with both mechanical properties and bioactivity.

Effect of Cu on microstructure, mechanical properties, corrosion resistance and cytotoxicity of CoCrW alloy fabricated by selective laser melting

In the study, CoCrWCu alloys with differing Cu content (2, 3, 4 wt%) were prepared by selective laser melting using mixture powders consisting of CoCrW and Cu, aiming at investigating the effect of Cu on the microstructures, mechanical properties, corrosion behavior and cytotoxicity. The SEM observations indicated that the Cu content up to 3 wt% caused the Si-rich precipitates to segregate along grain boundaries and in the grains, and EBSD analysis suggested that the Cu addition decreased the recrystallization degree and increased the grain diameter and fraction of big grains. The tensile tests found that the increasing Cu content led to a decrease of mechanical properties compared with Cu-free CoCrW alloy. The electrochemical tests revealed that the addition of Cu shifted the corrosion potential toward nobler positive, but increased the corrosion current density. Also, a more protective passive film was formed when 2 wt% Cu content was added, but the higher Cu content up to 3 wt% was detrimental to the corrosion resistance. It was noted that there was no cytotoxicity for Cu-bearing CoCrW alloys to MG-63 cell and the cells could spread well on the surfaces of studied alloys. Meanwhile, the Cu-bearing CoCrW alloy exhibited an excellent antibacterial performance against E.coli when Cu content was up to 3 wt%. It is suggested that the feasible fabrication of Cu-bearing CoCrW alloy by SLM using mixed CoCrW and Cu powders is a promising candidate for use in antibacterial oral repair products. This current study also can aid in the further design of antibacterial Cu-containing CoCrW alloying powders.

Assessment of titanium metallization thin film deposited on alumina substrate: Microstructure and nano-indentation

Surface titanium (Ti) metallization was conducted on alumina (Al₂O₃) through chemical vapor deposition (CVD) method derived from non-contact pack cementation. The effects of different deposition temperature (1000 °C, 1050 °C, and 1100 °C) were examined in this scenario. The morphology, phase composition, and interfacial defects of the resulting films were systematically investigated through scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction. The nanomechanical characterization of the proposed thin films was evaluated by conducting nano-indentation tests at different depths. The results revealed that uniform Ti films were coated on the Al₂O₃ substrate. During coating, the atoms on the matrix surface were driven to form different structure due to different deposition temperature, leading to disparate morphologies of the surface and the interface, which consequently influenced the binding force between the film and the substrate. Moreover, the nanomechanical properties were found to be related to the internal and interface structure. Decreased modulus and hardness were obtained for metallization films treated at 1050 °C, and plastic deformation was the main deformation pattern.

Creating hierarchical porosity hydroxyapatite scaffolds with osteoinduction by three-dimensional printing and microwave sintering

Hierarchical porosity, which includes micropores and macropores in scaffolds, contributes to important multiple biological functions for tissue regeneration. This paper introduces a two-step method of combining three-dimensional printing (3DP) and microwave sintering to fabricate two-level hierarchical porous scaffolds. The results showed that 3D printing made the macroporous structure well-controlled and microwave sintering generated micropores on the macropore surface. The resulting hierarchical macro/microporous hydroxyapatite scaffold induced bone formation following intramuscular implantation. Moreover, when comparing the hierarchical macro/microporous hydroxyapatite scaffold to the non-osteoinductive hydroxyapatite scaffolds (either 3D printed or H₂O₂ foamed) subjected to muffle sintering which do not have micropores, the critical role of micropores in material-driven bone formation was shown. The findings presented herein could be useful for the further optimization of bone grafting materials for bone regeneration.