Iodine-Loaded Calcium Titanate for Bone Repair with Sustainable Antibacterial Activity Prepared by Solution and Heat Treatment

Enhancement of in vitro antibacterial activity and bioactivity of iodine-loaded titanium by micro-scale regulation using mixed-acid treatment

Postoperative infection and subsequent device loss are serious complications in the use of titanium dental implants and plates for jawbone reconstruction. We have previously reported that NaOH-CaCl2 -thermal-ICl3 -treated titanium (NaCaThIo) has a nano-scale surface and exhibits antibacterial activity against Staphylococcus aureus. The present study examined the surface properties of mixed-acid treated and then iodine-treated titanium (MA-NaCaThIo), and evaluated oral antibacterial activity and cytotoxicity compared with the results obtained with NaCaThIo. MA-NaCaThIo formed a surface layer with a nano-scale network structure having microscale irregularities, and both the thickness of the surface layer (1.49 ± 0.16 μm) and the average surface roughness (0.35 ± 0.03 μm) were significantly higher than those of NaCaThIo. Furthermore, MA-NaCaThIo maintained high hydrophilicity with a contact angle of 7.5 ± 1.7° even after 4 weeks, as well as improved apatite formation, iodine ion release, and antibacterial activity against Prevotella intermedia compared to NaCaThIo. Cell culture test revealed that MA-NaCaThIo exhibited no cytotoxicity against MG-63 and Vero cells, while increased cell proliferation, ALP activity and mineralization of MG-63 compared to NaCaThIo. This treated titanium is expected to be useful for the development of next-generation titanium devices having both bone-bonding and antibacterial properties.

Mechanical, bioactive, and long-lasting antibacterial properties of a Ti scaffold with gradient pores releasing iodine ions

The ideal bone implant would effectively prevent aseptic as well as septic loosening by minimizing stress shielding, maximizing bone ingrowth, and preventing implant-associated infections. Here, a novel gradient-pore-size titanium scaffold was designed and manufactured to address these requirements. The scaffold features a larger pore size (900 μm) on the top surface, gradually decreasing to small sizes (600 μm to 300 μm) towards the center, creating a gradient structure. To enhance its functionality, the additively manufactured scaffolds were biofunctionalized using simple chemical and heat treatments so as to incorporate calcium and iodine ions throughout the surface. This unique combination of varying pore sizes with a biofunctional surface provides highly desirable mechanical properties, bioactivity, and notably, long-lasting antibacterial activity. The target mechanical aspects, including low elastic modulus, high compression, compression-shear, and fatigue strength, were effectively achieved. Furthermore, the biofunctional surface exhibits remarkable in vitro bioactivity and potent antibacterial activity, even under conditions specifically altered to be favorable for bacterial growth. More importantly, the integration of small pores alongside larger ones ensures a sustained high release of iodine, resulting in antimicrobial activity that persisted for over three months, with full eradication of the bacteria. Taken together, this gradient structure exhibits obvious superiority in combining most of the desired properties, making it an ideal candidate for orthopedic and dental implant applications.

Preparation and characterizations of antibacterial iodine-containing coatings on pure Ti

Iodine-containing coatings were prepared on pure Ti surfaces via electrochemical deposition to enhance their antibacterial properties. The factors influencing iodine content were analyzed using an orthogonal experiment. The electrochemically deposited samples were characterized using scanning electron microscopy with energy dispersive spectroscopy and X-ray photoelectron spectroscopy, and their antibacterial properties and cytotoxicity were evaluated. The results showed that changing the deposition time is an effective way to control the iodine content. The iodine content, coating thickness, and adhesion of the samples increased with deposition time. Iodine in the coatings mainly exists in three forms, which are I2, I3-, and pentavalent iodine. For samples with iodine-containing coatings, the antibacterial ratios against E. coli and S. aureus were greater than 90% and increased with increasing iodine content. Although the samples with iodine-containing coatings showed some inhibition of the proliferation of MC3T3-E1 cells, the cell viabilities were all higher than 80%, suggesting that iodine-containing coatings are biosafe.

Research progress on antibacterial activity of medical titanium alloy implant materials

Titanium and its alloys are the preferred materials for medical implants. However, easy infection is a fatal shortcoming of Ti implants. Fortunately, the ongoing development of antibacterial implant materials is a promising solution, and Ti alloys with antibacterial properties hold immense potential for medical applications. In this review, we briefly outline the mechanisms of bacterial colonization and biofilm formation on implants; discuss and classify the major antimicrobials currently in use and development, including inorganic and organic antimicrobials; and describe the important role of antimicrobials in the development of implant materials for clinical applications. Strategies and challenges related to improving the antimicrobial properties of implant materials as well as the prospects of antibacterial Ti alloys in the medical field are also discussed.

Conferring Antioxidant Activity to an Antibacterial and Bioactive Titanium Surface through the Grafting of a Natural Extract

The main unmet medical need of bone implants is multifunctional activity, including their ability to induce rapid and physiological osseointegration, counteract bacterial biofilm formation, and prevent in situ chronic inflammation at the same time. This research starts from an already developed c.p. titanium surface with proven bioactive (in vitro hydroxyl apatite precipitation) and antibacterial activities, due to a calcium titanate layer with nano- and micro-scale roughness and loaded with iodine ions. Here, antioxidant ability was added to prevent chronic inflammation by grafting polyphenols of a green tea extract onto the surface, without compromising the other functionalities of the surface. The surface was characterized before and after functionalization through XPS analysis, zeta potential titrations, ion release measurements, in vitro bioactivity tests, SEM and fluorescence microscopy, and Folin-Ciocalteu and biological tests. The presence of grafted polyphenols as a homogeneous layer was proven. The grafted polyphenols maintained their antioxidant ability and were anchored to the surface through the linking action of Ca²⁺ ions added to the functionalizing solution. Iodine ion release, cytocompatibility towards human mesenchymal stem cells (hMSC), and antibacterial activity were maintained even after functionalization. The antioxidant ability of the functionalized surface was effective in preserving hMSC viability in a chemically induced pro-inflammatory environment, thus showing a scavenger activity towards toxic active species responsible for inflammation.

Antibacterial Coatings for Titanium Implants: Recent Trends and Future Perspectives

Titanium and its alloys are widely used as implant materials for biomedical devices owing to their high mechanical strength, biocompatibility, and corrosion resistance. However, there is a significant rise in implant-associated infections (IAIs) leading to revision surgeries, which are more complicated than the original replacement surgery. To reduce the risk of infections, numerous antibacterial agents, e.g., bioactive compounds, metal ions, nanoparticles, antimicrobial peptides, polymers, etc., have been incorporated on the surface of the titanium implant. Various coating methods and surface modification techniques, e.g., micro-arc oxidation (MAO), layer-by-layer (LbL) assembly, plasma electrolytic oxidation (PEO), anodization, magnetron sputtering, and spin coating, are exploited in the race to create a biocompatible, antibacterial titanium implant surface that can simultaneously promote tissue integration around the implant. The nature and surface morphology of implant coatings play an important role in bacterial inhibition and drug delivery. Surface modification of titanium implants with nanostructured materials, such as titanium nanotubes, enhances bone regeneration. Antimicrobial peptides loaded with antibiotics help to achieve sustained drug release and reduce the risk of antibiotic resistance. Additive manufacturing of patient-specific porous titanium implants will have a clear future direction in the development of antimicrobial titanium implants. In this review, a brief overview of the different types of coatings that are used to prevent implant-associated infections and the applications of 3D printing in the development of antibacterial titanium implants is presented.

Bioactivity and antibacterial activity of iodine-containing calcium titanate against implant-associated infection

Developing antimicrobial biomaterials is a major challenge in the fields of orthopaedic and dental implants. In this study, we evaluated the bone-bonding ability and antibacterial activity of a novel biomaterial for preventing implant-associated infections. We have previously reported that NaOH heat treatment improved the bone-bonding ability of titanium, which was later modified to release target ions from the calcium titanate surface. Iodine, an essential nutrient, exhibits broad-spectrum antimicrobial activity; hence, we designed a calcium titanate that releases iodine ions (Ca-I-Ti). The material was prepared from a simple solution using heat treatments as well as inexpensive devices and chemical agents. MC3T3-E1 cells seeded on Ca-I-Ti displayed high degrees of bioactivity and viability, and Ca-I-Ti exhibited antibacterial activity against methicillin-susceptible Staphylococcus aureus. In vivo biomechanical and histological experiments showed that Ca-I-Ti had excellent bone-bonding ability at 8 weeks after implantation. In a subcutaneous infection model in rats, methicillin-susceptible Staphylococcus aureus on the implant was reduced by approximately 95% compared to that on commercially pure titanium, indicating that Ca-I-Ti has antibacterial effects in vivo. In addition, no local or systemic complications were observed, and active infection in the surrounding tissues was histologically inhibited. Thus, iodine-containing calcium titanate is a safe biomaterial with excellent bioactivity and antibacterial properties, indicating its potential in preventing implant-associated infections.

Drug-Releasing Gelatin Coating Reinforced with Calcium Titanate Formed on Ti–6Al–4V Alloy Designed for Osteoporosis Bone Repair

Ti–6Al–4V alloy has been widely used in the orthopedic and dental fields owing to its high mechanical strength and biocompatibility. However, this alloy has a poor bone-bonding capacity, and its implantation often causes loosening. Osteoporosis increases with the aging of the population, and bisphosphonate drugs such as alendronate and minodronate (MA) are used for the medical treatment. Reliable and multifunctional implants showing both bone bonding and drug releasing functions are desired. In this study, we developed a novel organic-inorganic composite layer consisting of MA-containing gelatin and calcium-deficient calcium titanate (cd–CT) with high bone-bonding and scratch resistance on Ti–6Al–4V alloy. The alloy with the composite layer formed apatite within 7 days in a simulated body fluid and exhibited high scratch resistance of an approximately 50 mN, attributable to interlocking with cd ± CT. Although the gelatin layer almost completely dissolved in phosphate-buffered saline within 6 h, its dissolution rate was significantly suppressed by a subsequent thermal crosslinking treatment. The released MA was estimated at more than 0.10 μmol/L after 7 days. It is expected that the Ti alloy with the MA-containing gelatin and cd–CT composite layer will be useful for the treatment of osteoporosis bone.