Controlled release of vanadium from titanium oxide coatings for improved integration of soft tissue implants

Silver carboxylate-doped titanium dioxide-polydimethylsiloxane coating decreases Cutibacterium acnes adherence and biofilm formation on polyether ether ketone

BACKGROUND CONTEXT

Cutibacterium acnes (C. acnes) is a gram-positive facultative anaerobe found in the deep sebaceous follicles of the skin on the shoulder and back. C. acnes has been increasingly recognized as a pathogen in spinal surgical site infection (SSI) especially in the presence of instrumentation.

PURPOSE

This study assesses whether a silver carboxylate-doped titanium dioxide-polydimethylsiloxane (TiO₂-PDMS) coating can decrease C. acnes adherence and biofilm formation on PEEK and four other commonly used spinal implant materials, stainless steel, cobalt chromium, titanium, and titanium alloy.

STUDY DESIGN

We compared the adherence of C. acnes over 24 hours between uncoated, 95:5 TiO₂ to PDMS ratio with 10× silver carboxylate coating and a 100% silver carboxylate coating on each implant material, which were uniformly saw cut and sterilized. Implants were then subjected to scanning electron microscopy (SEM) and confocal scanning laser microscopy (CSLM).

METHODS

Samples were coated using 95:5 TiO₂-PDMS 10× silver carboxylate, 100% silver carboxylate, or left uncoated. C. acnes was applied onto the samples and allowed to adhere for periods of 4, 8, 12, 16, or 20 hours. Nonadherent bacteria were then washed from the samples. These samples were then allowed to continue incubating for a total of 24 hours. SEM and confocal laser scanning microscope were used to visualize all samples for the presence of biofilm and quantification of C. acnes adherence at each time point.

RESULTS

The 95:5 TiO₂-PDMS 10× silver carboxylate coating was able to significantly decrease C. acnes adherence on PEEK after 8, 12, 16, and 20 hours of adherence. No statistical difference was found between the 95:5 TiO₂-PDMS 10× silver carboxylate coating and the 100% silver carboxylate positive control. We previously observed extensive C. acnes biofilm formation on uncoated PEEK, but none on PEEK coated with either the 95:5 TiO₂-PDMS 10× silver carboxylate or 100% Ag coating . Furthermore, no biofilm formation was observed on stainless steel, cobalt chromium, titanium, and titanium alloy coated with 95:5 TiO₂-PDMS 10× silver carboxylate or 100% Ag coating.

CONCLUSION

A 95:5 TiO₂-PDMS 10× silver carboxylate coating decreases C. acnes adhesion and prevents biofilm formation on PEEK and other common orthopedic implant materials.

CLINICAL SIGNIFICANCE

A 95:5 TiO₂-PDMS 10× silver carboxylate coating may help decrease spinal SSI due to C. acnes, especially in procedures with instrumentation.

Vanadium Dioxide Nanocoating Induces Tumor Cell Death through Mitochondrial Electron Transport Chain Interruption

A biomaterials surface enabling the induction of tumor cell death is particularly desirable for implantable biomedical devices that directly contact tumor tissues. However, this specific antitumor feature is rarely found. Consequently, an antitumor-cell nanocoating comprised of vanadium dioxide (VO2) prepared by customized reactive magnetron sputtering has been proposed, and its antitumor-growth capability has been demonstrated using human cholangiocarcinoma cells. The results reveal that the VO2 nanocoating is able to interrupt the mitochondrial electron transport chain and then elevate the intracellular reactive oxygen species levels, leading to the collapse of the mitochondrial membrane potential and the destruction of cell redox homeostasis. Indeed, this chain reaction can effectively trigger oxidative damage in the cholangiocarcinoma cells. Additionally, this study has provided new insights into designing a tumor-cell-inhibited biomaterial surface, which is modulated by the mechanism of mitochondria-targeting tumor cell death.

Nano vanadium dioxide films deposited on biomedical titanium: a novel approach for simultaneously enhanced osteogenic and antibacterial effects

Vanadium is a trace element in the human body, and vanadium compounds have a promising future in biological and medical applications due to their various biological activities and low toxicity. Herein, a novel pure vanadium dioxide (VO₂) nanofilm was deposited on a substrate of biomedical titanium by magnetron sputtering. The antibacterial effect of VO₂ against the methicillin-resistant Staphylococcus aureus (MRSA) was validated in vitro and in vivo. Moreover, the biocompatibility of VO₂ and its osteogenic effects were systematically illustrated. A possible osteogenic mechanism involving the amelioration of highly reactive oxygen species (ROS) levels were investigated. According to the results of our present and previous studies, the simultaneous antibacterial and osteogenic effects of VO₂ are attributed to its differential regulation of ROS levels in rat bone marrow mesenchymal stem cells (rBMSCs) and bacteria. This study is the first to report the simultaneous effects of VO₂ on bactericidal and osteogenic activities through its differential modification of ROS activity in eukaryotic (rBMSCs) and prokaryotic (MRSA) cells. The findings in this work may yield a deeper understanding of the biological activities of vanadium compounds while also paving the way for the further investigation and application of VO₂ in biological and medical materials.

Applications of Metals for Bone Regeneration

The regeneration of bone tissue is the main purpose of most therapies in dental medicine. For bone regeneration, calcium phosphate (CaP)-based substitute materials based on natural (allo- and xenografts) and synthetic origins (alloplastic materials) are applied for guiding the regeneration processes. The optimal bone substitute has to act as a substrate for bone ingrowth into a defect, as well as resorb in the time frame needed for complete regeneration up to the condition of restitution ad integrum. In this context, the modes of action of CaP-based substitute materials have been frequently investigated, where it has been shown that such materials strongly influence regenerative processes such as osteoblast growth or differentiation and also osteoclastic resorption due to different physicochemical properties of the materials. However, the material characteristics needed for the required ratio between new bone tissue formation and material degradation has not been found, until now. The addition of different substances such as collagen or growth factors and also of different cell types has already been tested but did not allow for sufficient or prompt application. Moreover, metals or metal ions are used differently as a basis or as supplement for different materials in the field of bone regeneration. Moreover, it has already been shown that different metal ions are integral components of bone tissue, playing functional roles in the physiological cellular environment as well as in the course of bone healing. The present review focuses on frequently used metals as integral parts of materials designed for bone regeneration, with the aim to provide an overview of currently existing knowledge about the effects of metals in the field of bone regeneration.

A functionalized surface modification with vanadium nanoparticles of various valences against implant-associated bloodstream infection

Bloodstream infection, especially with implants involved, is an often life-threatening condition with high mortality rates, imposing a heavy burden on patients and medical systems. Herein, we firstly deposited homogeneous vanadium metal, V₂O₃, VO₂, and V₂O₅ nanofilms on quartz glass by magnetron sputtering. Using these platforms, we further investigated the potential antimicrobial efficiency of these nano-VO_x films and the interactions of human erythrocytes and bacteria (methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa) with our samples in a novel cell–bacteria coculture model. It was demonstrated that these nano-VO_x precipitated favorable antibacterial activity on both bacteria, especially on S. aureus, and this effect increased with higher vanadium valence. A possible mechanism accountable for these results might be elevated levels of vanadium-induced intracellular reactive oxygen species. More importantly, based on hemolysis assays, our nano-VO_x films were found to be able to kill prokaryotic cells but were not toxic to mammalian cells, holding the potential for the prevention of implant-related hematogenous infections. As far as we know, this is the first report wherein such nano-VO_x films have assisted human erythrocytes to combat bacteria in a valence-dependent manner. Additionally, vanadium ions were released from these nano-VO_x films in a sustained manner, and low-valence films possessed better biocompatibility with human fibroblasts. This work may provide new insights for biomedical applications of inorganic vanadium compounds and attract growing attention in this field. From the perspective of surface modification and functionalization, this study holds promise to avail the prophylaxis of bloodstream infections involving implantable biomedical devices.

Design of a multifunctional vanadium pentoxide/polymer biocomposite for implant-coating applications

In this study we designed a multifunctional implant coating by exploiting the properties of V₂O₅, i.e. the antibacterial activity via myeloperoxidase-like catalytic activity and the bioactivity of low concentrations of vanadate ions.

Silver doped titanium oxide-PDMS hybrid coating inhibits Staphylococcus aureus and Staphylococcus epidermidis growth on PEEK

Bacterial infection remains one of the most serious issues affecting the successful installation and retention of orthopedic implants. Many bacteria develop resistance to current antibiotics, which complicates or prevents traditional antibiotic-dependent eradication therapy. In this study, a hybrid coating of titanium dioxide and polydimethylsiloxane (PDMS) was synthesized to regulate the release of silver. The coatings were benefited from the antimicrobial activity of silver ion, the biocompatibility of titanium dioxide, and the flexibility of the polymer. Three studied silver doped coatings with different titanium dioxide-PDMS ratios effectively inhibited the attachment and growth of Staphylococcus aureus and Staphylococcus epidermidis in a dose-dependent manner. The coatings were successfully applied on the discs of polyether ether ketone (PEEK), a common spinal implant material and antibacterial property of these coatings was assessed via Kirby Bauer assay. More importantly, these selected coatings completely inhibited biofilm formation. The release study demonstrated that the release rate of silver from the coating depended on doping levels and also the ratios of titanium dioxide and PDMS. This result is crucial for designing coatings with desired silver release rate on PEEK materials for antimicrobial applications.

Characterization and bioactive properties of zirconia based polymeric hybrid for orthopedic applications

Zirconia is a transition metal oxide with current applications to orthopedic implants. It has been shown to up-regulate specific genes involved in bio-integration and injury repair. This study examines the effects of zirconia and polydimethylsiloxane (PDMS) hybrids on the proliferation and viability of human primary osteoblast and fibroblast cells. In this study, zirconia-PDMS hybrid coatings were synthesized using a modified sol gel process. The hybrid material was characterized using optical microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and contact angle analysis. This study demonstrates that Zr-PMDS surface materials display hydrophobic surface properties coupled with a preferential deposition of polymer near the surface. Primary osteoblast and fibroblast proliferation and viability on hybrid coated surfaces were evaluated via a rapid screening methodology using WST-1 and calcein AM assays. The cells were seed at 5,000 cells per well in 96-well plates coated with various composition of Zr-PDMS hybrids. The results showed increasing cell proliferation with increasing zirconia concentration, which peaked at 90 % v/v zirconia. Proliferation of osteoblasts and fibroblasts displayed similar trends on the hybrid material, although osteoblasts displayed a bi-phasic dose response by the calcein AM assay. The results of this current study show that Zr-PDMS may be used to influence tissue-implant integration, supporting the use of the hybrid as a promising coating for orthopedic trauma implants.

In vivo caprine model for osteomyelitis and evaluation of biofilm-resistant intramedullary nails

Bone infection remains a formidable challenge to the medical field. The goal of the current study is to evaluate antibacterial coatings in vitro and to develop a large animal model to assess coated bone implants. A novel coating consisting of titanium oxide and siloxane polymer doped with silver was created by metal-organic methods. The coating was tested in vitro using rapid screening techniques to determine compositions which inhibited Staphylococcus aureus growth, while not affecting osteoblast viability. The coating was then applied to intramedullary nails and evaluated in vivo in a caprine model. In this pilot study, a fracture was created in the tibia of the goat, and Staphylococcus aureus was inoculated directly into the bone canal. The fractures were fixed by either coated (treated) or non-coated intramedullary nails (control) for 5 weeks. Clinical observations as well as microbiology, mechanical, radiology, and histology testing were used to compare the animals. The treated goat was able to walk using all four limbs after 5 weeks, while the control was unwilling to bear weight on the fixed leg. These results suggest the antimicrobial potential of the hybrid coating and the feasibility of the goat model for antimicrobial coated intramedullary implant evaluation.

Investigation of nickel suppression and cytocompatibility of surface-treated nickel-titanium shape memory alloys by using plasma immersion ion implantation

Nickel-titanium (NiTi) shape memory alloys are increasingly being used in orthopedic applications. However, there is a concern that Ni is harmful to the human body. We have recently investigated the use of nitrogen, or oxygen plasma immersion ion implantation to mitigate this deleterious effect. Our results reveal that the near-surface Ni concentration in all the treated samples is significantly suppressed. In addition, our in vitro tests show that the plasma-treated surfaces are cytologically compatible allowing the attachment and proliferation of osteoblasts. Among the two types of samples, the best biological effects are found on the samples with nitrogen implantation.