Fabrication of Bioactive Porous Ti Metal with Structure Similar to Human Cancellous Bone by Selective Laser Melting

1. Scientific Reference

• Study Title: Fabrication of Bioactive Porous Ti Metal with Structure Similar to Human Cancellous Bone by Selective Laser Melting
• Authors: D. K. Pattanayak, T. Matsushita, H. Takadama, A. Fukuda, M. Takemoto, S. Fujibayashi, K. Sasaki, N. Nishida, T. Nakamura, and T. Kokubo
• Journal: Bioceramics Development and Applications
• Year of Publication: 2011
• DOI: 10.4303/bda/D101206

2. Scientific Background

The development of porous metallic biomaterials has become an important area of research in orthopedic and dental implantology, particularly for applications requiring long-term interaction between implant surfaces and host bone. Titanium remains one of the most widely investigated biomaterials because of its favorable mechanical performance and biocompatibility. However, beyond material composition, implant architecture and surface characteristics are increasingly recognized as key factors influencing biological integration.

Advances in additive manufacturing have enabled the production of highly controlled porous structures that closely resemble the trabecular organization of cancellous bone. Such designs may improve mechanical compatibility while providing an interconnected network that supports tissue ingrowth. At the same time, surface modification strategies seek to enhance the biological activity of titanium by promoting the formation of calcium phosphate layers that are associated with bone bonding under experimental conditions.

Within this context, the present study investigates the combination of selective laser melting (SLM), thermal processing, and chemical surface treatment as an integrated approach for producing a bioactive porous titanium structure intended for future bone substitution applications.

3. Study Objective

The primary objective of this investigation was to manufacture a porous titanium structure with an internal architecture resembling human cancellous bone using selective laser melting technology. The authors also aimed to evaluate how different heat-treatment temperatures influenced the material’s microstructure and mechanical behavior. In addition, they assessed whether sequential sodium hydroxide, hydrochloric acid, and heat treatments could modify the titanium surface sufficiently to induce apatite formation after immersion in simulated body fluid (SBF), thereby demonstrating bioactivity under laboratory conditions.

4. Methodology

This work represents a preclinical materials science study focused on the fabrication and characterization of porous titanium.

Commercially pure Grade 2 titanium powder with particle sizes below 45 μm was processed by selective laser melting to produce porous specimens designed to mimic cancellous bone architecture. Following fabrication, samples underwent heat treatment in an argon atmosphere at temperatures ranging from 700°C to 1300°C.

Surface morphology was examined using field-emission scanning electron microscopy (FE-SEM). Mechanical performance was evaluated on solid titanium rods manufactured by the same SLM process to determine the influence of thermal treatment on tensile properties. Surface chemistry was subsequently modified through sequential immersion in sodium hydroxide and dilute hydrochloric acid, followed by an additional heat treatment. Raman spectroscopy was used to identify the crystalline phases generated by these surface modifications.

Finally, the treated specimens were immersed in simulated body fluid for three days to investigate their capacity for apatite formation. No animal experiments or clinical investigations were included in this study.

5. Main Findings

Microscopic examination demonstrated that selective laser melting successfully produced a porous titanium structure characterized by a fully melted core surrounded by numerous partially fused titanium particles. Heat treatment at temperatures above 1200°C promoted bonding between these particles while preserving small surface cavities within the porous framework.

Mechanical testing revealed a progressive reduction in tensile strength as heat-treatment temperature increased. Tensile strength decreased from 530 MPa in the as-fabricated condition to approximately 400 MPa following treatment at 1300°C. Conversely, ductility improved during thermal processing, with elongation increasing from 15% to 30%. According to the authors, these mechanical changes were associated with grain growth observed after heat treatment.

Surface modification produced substantial chemical changes on the titanium substrate. Sodium hydrogen titanate formed after alkaline treatment, subsequently transforming into hydrogen titanate following hydrochloric acid exposure and finally into anatase and rutile after heat treatment.

Following immersion in simulated body fluid, the chemically treated porous titanium developed a continuous apatite layer within three days. Under the experimental conditions employed, this finding indicates that the surface treatment protocol successfully imparted bioactive characteristics to the porous titanium structure.

6. Clinical Interpretation

Although this investigation is not a clinical study, it provides valuable insight into how manufacturing technology and surface engineering may jointly influence the biological performance of porous titanium biomaterials. The authors demonstrate that selective laser melting can produce a three-dimensional porous architecture that resembles human cancellous bone while maintaining mechanical properties that remain compatible with structural applications.

An important finding is the balance between mechanical strength and ductility observed after heat treatment. Increasing the treatment temperature reduced tensile strength but improved elongation, reflecting microstructural changes associated with grain growth. Such observations highlight the need to optimize thermal processing according to the intended clinical application rather than focusing solely on maximum mechanical resistance.

Equally significant is the effect of chemical surface modification. The sequential NaOH-HCl-heat treatment altered the surface chemistry, leading to the formation of crystalline phases that supported rapid apatite deposition in simulated body fluid. Within this experimental model, apatite formation is commonly regarded as an indicator of surface bioactivity.

From a clinical perspective, these findings emphasize that implant performance depends not only on bulk material properties but also on surface characteristics capable of influencing biological interactions. Nevertheless, the results should be interpreted with caution. Apatite formation in simulated body fluid is an in vitro observation and cannot be considered direct evidence of clinical osseointegration, implant survival, or long-term functional success in patients.

7. Clinical Applications

The findings presented in this study are primarily relevant to the development of advanced biomaterials for bone regeneration and implantable devices rather than to established clinical protocols.

The combination of additive manufacturing and surface bioactivation may contribute to the future design of porous titanium implants, customized bone substitutes, and patient-specific reconstructive devices with architectures that more closely resemble trabecular bone.

For dental implantology and oral surgery, the study supports ongoing research into porous implant designs and bioactive surface treatments intended to improve interactions at the bone–implant interface. However, no clinical outcomes, patient data, implant survival rates, or biological or prosthetic complication rates are reported. Consequently, these results should be viewed as preclinical evidence supporting further investigation rather than as validation of a therapeutic approach.

8. Level of Evidence, Limitations, and Transparency

This publication represents a preclinical experimental materials science study and therefore provides an early level of scientific evidence compared with clinical investigations.

The work is based on laboratory characterization, including microscopic analysis, mechanical testing, Raman spectroscopy, and bioactivity assessment using simulated body fluid. No animal models, human participants, or clinical follow-up are included in the reported methodology.

The article does not provide a detailed discussion of methodological limitations beyond the scope of the experimental design. Likewise, no explicit conflicts of interest or financial relationships with implant manufacturers are identified within the information available.

Accordingly, the conclusions should be interpreted within the framework of biomaterials research and should not be extrapolated directly to clinical practice without further in vivo and clinical validation.

9. Key Study Highlights

• Study design: Experimental preclinical biomaterials investigation.
• Level of evidence: Preclinical laboratory study.
• Study population: Not applicable.
• Number of patients or implants: Not reported.
• Follow-up period: Three-day immersion in simulated body fluid for bioactivity evaluation.
• Primary outcome: Influence of selective laser melting, heat treatment, and chemical surface modification on porous titanium structure, mechanical properties, and bioactivity.
• Principal finding: Sequential NaOH-HCl-heat treatment enabled apatite formation on porous titanium after immersion in simulated body fluid.
• Scientific conclusion: Selective laser melting combined with appropriate surface treatment produced a bioactive porous titanium material with an architecture resembling human cancellous bone.
• Main limitations: Laboratory-based investigation without animal or clinical validation.

10. Scientific Impact

This study represents an important contribution to the evolution of additive manufacturing for biomedical applications by combining structural design with surface biofunctionalization. Rather than focusing exclusively on manufacturing technology, the authors demonstrate that biological performance may also depend on subsequent physicochemical surface modifications.

The work contributes to the growing body of research investigating porous titanium as a potential alternative for bone substitution and implantable devices requiring enhanced biological interaction. Its significance lies in demonstrating that additive manufacturing can reproduce complex porous architectures while maintaining the possibility of further tailoring surface chemistry to improve experimental bioactivity.

Although the investigation does not establish clinical effectiveness, it provides a technological foundation for future research exploring patient-specific implants, porous metallic scaffolds, and advanced biomaterials designed to support bone regeneration. The study therefore serves as an important step in the progression from materials engineering toward clinically applicable implant technologies.

11. Editorial Conclusion

This experimental investigation demonstrates that selective laser melting can be used to fabricate porous titanium structures that closely resemble the architecture of human cancellous bone. Combined with sequential chemical and thermal surface treatments, the resulting material exhibited bioactive behavior through apatite formation under simulated physiological conditions. While these findings remain limited to laboratory evaluation, they offer meaningful insight into the development of next-generation porous titanium biomaterials and establish a solid scientific basis for future in vivo and clinical research in regenerative medicine, orthopedic reconstruction, and dental implantology.