Micro-Arc Oxidation Enhances the Blood Compatibility of Ultrafine-Grained Pure Titanium

Lin Xu, Kun Zhang, Cong Wu, Xiaochun Lei, Jianning Ding, Xingling Shi, Chuncheng Liu.

Full text link: https://pubmed.ncbi.nlm.nih.gov/29257104/

Micro-Arc Oxidation Enhances the Blood Compatibility of Ultrafine-Grained Pure Titanium

1. Scientific Reference

• Study Title: Micro-Arc Oxidation Enhances the Blood Compatibility of Ultrafine-Grained Pure Titanium
• Authors: Lin Xu, Kun Zhang, Cong Wu, Xiaochun Lei, Jianning Ding, Xingling Shi, Chuncheng Liu
• Journal: Materials
• Year of Publication: 2017
• DOI: 10.3390/ma10121446

2. Scientific Background

The long-term success of blood-contacting biomaterials depends not only on their mechanical performance but also on their ability to interact safely with circulating blood components. Titanium has been widely adopted in biomedical applications because of its favorable biocompatibility and corrosion resistance. However, when implanted in direct contact with blood, titanium surfaces may still contribute to thrombus formation and platelet activation.

Ultrafine-grained pure titanium produced through equal-channel angular pressing (ECAP) has attracted increasing interest because it combines improved mechanical properties with the absence of potentially harmful alloying elements. This makes it a promising candidate for cardiovascular and orthopedic applications. Nevertheless, further improvements in blood compatibility remain necessary before broader clinical implementation.

Surface engineering strategies have therefore become a major area of research. Among them, micro-arc oxidation (MAO) offers the possibility of generating porous titanium dioxide-based coatings enriched with bioactive elements, potentially influencing coagulation behavior and cellular interactions at the blood-material interface.

3. Study Objective

The purpose of this investigation was to evaluate whether micro-arc oxidation could improve the blood compatibility of ultrafine-grained pure titanium.

The researchers specifically examined how different oxidation times influenced coating morphology, surface roughness, wettability, surface energy, hemolytic behavior, coagulation parameters, and platelet adhesion in order to identify conditions associated with the most favorable biological response.

4. Methodology

This work was designed as a preclinical in vitro experimental study. Ultrafine-grained commercially pure titanium specimens produced through ECAP processing were subjected to micro-arc oxidation using an electrolyte containing sodium silicate, sodium polyphosphate, and calcium acetate.

Five oxidation durations were investigated: 3, 6, 9, 12, and 15 minutes.

Surface characterization included scanning electron microscopy, elemental analysis, X-ray diffraction, coating thickness measurements, roughness evaluation, contact angle assessment, and surface energy calculations.

Blood compatibility was assessed through hemolysis testing, dynamic coagulation assays, prothrombin time (PT), activated partial thromboplastin time (APTT), and platelet adhesion analysis.

The number of biological samples used was not specified in the information provided.

5. Main Findings

Micro-arc oxidation generated porous ceramic coatings composed primarily of titanium dioxide with both anatase and rutile crystalline phases. Increasing oxidation time resulted in thicker coatings, larger pore structures, and higher surface roughness.

The treated surfaces exhibited substantially improved wettability compared with untreated ultrafine-grained titanium. Contact angles decreased markedly after oxidation, while surface energy increased. The specimen oxidized for 9 minutes demonstrated the highest surface energy, reaching 92.65 mJ/m².

Blood compatibility measurements consistently favored the MAO-treated groups. Compared with the untreated substrate, oxidized specimens showed lower hemolysis rates, prolonged coagulation times, increased PT and APTT values, reduced platelet adhesion, and less platelet deformation.

Among all experimental conditions, the 9-minute oxidation treatment produced the most favorable overall biological profile, including the lowest reported hemolysis rate (1.93%), the highest PT and APTT values, and minimal platelet activation.

6. Clinical Analysis

This study highlights the importance of surface characteristics in determining how metallic biomaterials interact with blood. The findings suggest that blood compatibility is influenced by a combination of physicochemical parameters rather than by surface chemistry alone.

The MAO process altered multiple surface features simultaneously, including topography, porosity, roughness, wettability, and energy profile. According to the authors, these modifications may affect protein adsorption mechanisms and reduce platelet activation, thereby contributing to a more favorable hemocompatible environment.

From a clinical perspective, these observations are relevant for the development of blood-contacting devices such as vascular stents and cardiovascular implants. Improved resistance to thrombogenic reactions could theoretically contribute to safer long-term implant performance.

However, the findings should be interpreted cautiously. The study was conducted under laboratory conditions and does not provide direct evidence of clinical effectiveness in humans. Additional animal studies and clinical investigations would be required before translating these results into therapeutic recommendations.

For clinicians involved in implantology, biomaterials research, and medical device development, the study reinforces the growing role of surface modification technologies in optimizing biological responses to implantable materials.

7. Clinical Applications

The potential applications discussed by the authors include medical devices that require direct and prolonged contact with blood. Examples mentioned in the article include:

• Vascular stents;
• Cardiac valve prostheses;
• Hip prostheses;
• Other titanium-based implantable biomaterials.

Although the study is not directly related to dental implantology, it contributes to the broader understanding of how titanium surface engineering can influence biological interactions. Such knowledge may also be relevant to future developments in implant surface optimization across multiple medical disciplines.

8. Level of Evidence, Limitations, and Transparency

This investigation should be classified as a preclinical in vitro experimental study.

As such, the level of evidence remains limited when compared with clinical trials or prospective human studies. The reported findings provide mechanistic and biological insights but do not establish clinical efficacy.

One important limitation is the absence of in vivo validation within the study. The authors explicitly acknowledge that additional research is needed to evaluate both short-term and long-term biological responses following implantation.

No conflicts of interest were declared by the authors.

The available information does not indicate other major methodological limitations beyond those inherent to laboratory-based investigations.

9. Key Study Points

• Study Type: Preclinical in vitro experimental study
• Level of Evidence: Preclinical laboratory evidence
• Population or Studies Included: Not applicable
• Number of Patients or Implants: Not specified in the provided information
• Follow-up Duration: Not applicable
• Primary Outcome: Blood compatibility of ultrafine-grained pure titanium after MAO treatment
• Main Result: MAO significantly improved multiple hemocompatibility parameters
• Scientific Conclusion: Porous TiO₂ coatings generated by micro-arc oxidation enhanced the blood compatibility of ultrafine-grained pure titanium
• Potential Limitations: In vitro design and lack of clinical validation

10. Scientific Impact

This study contributes to the growing body of literature exploring how surface engineering can improve the biological performance of titanium-based biomaterials.

Rather than focusing exclusively on mechanical properties, the authors investigated the relationship between coating architecture and blood-material interactions. Their findings support the concept that carefully controlled surface modifications can influence coagulation behavior, platelet activity, and hemocompatibility.

The work also provides useful insight into the role of surface energy and wettability in regulating biological responses. The identification of a specific oxidation duration associated with optimal performance offers a foundation for future investigations aimed at refining MAO treatment protocols.

Although additional validation is necessary, the study strengthens the rationale for incorporating advanced surface modification technologies into the design of next-generation implantable devices.

11. Editorial Conclusion

This research demonstrates that micro-arc oxidation can substantially improve the blood compatibility of ultrafine-grained pure titanium through the creation of a porous TiO₂-based surface. The observed reductions in hemolysis, platelet activation, and coagulation tendency suggest that surface engineering may play a significant role in enhancing the biological performance of blood-contacting implants. While the findings remain preclinical, they provide a valuable scientific basis for further translational and clinical research in biomaterials development.