Effect of construction of TiO2 nanotubes on platelet behaviors: Structure-property relationships

Platelet interaction and performance of antibacterial bioinspired nanostructures passivated with human plasma

The ever-increasing ageing of the world population is demanding superior orthopedic devices. Issues such as implant infection, poor osseointegration, or chronic inflammation remain problematic to the lifespan and long-term efficacy of implants. Fabrication of materials with bioinspired nanostructures is one emerging antibacterial strategy to prevent implant infection, however their interactions with blood components, and whether they retain their bactericidal properties in an environment displaying a complex protein corona, remains largely unexplored. In the present study, titanium alloy, commercially pure and plasma-sprayed titania were hydrothermally etched, passivated with human native plasma to develop a protein corona, and then incubated with either Staphylococcus aureus, Pseudomonas aeruginosa or human platelets. Surface analysis was first used to characterize the topography, chemical composition or crystallinity of each material. Fluorescence staining and SEM were performed to evaluate the nanostructure bactericidal properties, as well as to study platelet attachment and morphology. Composition of platelet supernatant was studied using ELISA and flow cytometry. Overall, our study showed that the bioinspired nanostructured surfaces displayed both impressive antibacterial properties in a complex environment, and a superior blood biocompatibility profile in terms of platelet activation (particularly for titanium alloy). Additionally, the amount of pro-inflammatory cytokines released by platelets was found to be no different to that found in native plasma (background levels) and, in some cases, presented a more pro-healing profile with an increased secretion of factors such as TGF-β, PDGF-BB or BMP-2. The nanostructured surfaces performed equally, or better, than hydroxyapatite-coated titanium which is one of the current gold standards in orthopedics. Although further in vivo studies are required to validate these results, such bioinspired nanostructured surfaces certainly show promise to be safely applied to medical device surfaces used in orthopedics and other areas.

Nanotexture and crystal phase regulation for synergistic enhancement in re-endothelialization on medical pure titanium surface

Re-endothelialization has been recognized as a promising strategy to address the tissue hyperplasia and subsequent restenosis which are major complications associated with vascular implant/interventional titanium devices. However, the uncontrollable over-proliferation of smooth muscle cells (SMCs) limits the clinical application of numerous modified strategies. Herein, a novel modified strategy involving with a two-step anodic oxidation and annealing treatment was proposed to achieve rapid re-endothelialization function regulated by regular honeycomb nanotexture and specific anatase phase on the titanium surface. Theoretical calculation revealed that the presence of nanotexture reduced the polar component of surface energy, while the generation of anatase significantly enhanced the polar component and total surface energy. Meanwhile, the modified surface with regular nanotexture and anatase phase produced positive effect on the expression of CD31, VE-Cadherin and down-regulated α-SMA proteins expression, indicating excellent capacity of pro-endothelial regeneration and inhibition of SMCs proliferation and migration. One-month in vivo implantation in rabbit carotid arteries further confirmed that modified tube implant surface effectively accelerated confluent endothelial monolayer formation and promoted native-like endothelium tissue regeneration. By contrast, original titanium tube implant induced a disorganized tissue proliferation in the lumen with a high risk of restenosis. Collectively, this study opens us an alternative route to achieve the function that selectively promotes endothelial cells (ECs) growth and suppresses SMCs on the medical titanium surface, which has a great potential in facilitating re-endothelialization on the surface of blood-contacting titanium implant.

Overview of strategies to improve the antibacterial property of dental implants

The increasing number of peri-implant diseases and the unsatisfactory results of conventional treatment are causing great concern to patients and medical staff. The effective removal of plaque which is one of the key causes of peri-implant disease from the surface of implants has become one of the main problems to be solved urgently in the field of peri-implant disease prevention and treatment. In recent years, with the advancement of materials science and pharmacology, a lot of research has been conducted to enhance the implant antimicrobial properties, including the addition of antimicrobial coatings on the implant surface, the adjustment of implant surface topography, and the development of new implant materials, and significant progress has been made in various aspects. Antimicrobial materials have shown promising applications in the prevention of peri-implant diseases, but meanwhile, there are some shortcomings, which leads to the lack of clinical widespread use of antimicrobial materials. This paper summarizes the research on antimicrobial materials applied to implants in recent years and presents an outlook on the future development.

Controlled drug delivery from chitosan-coated heparin-loaded nanopores anodically grown on nitinol shape-memory alloy

Nitinol (NiTi shape-memory alloy) is an interesting candidate in various medical applications like dental, orthopedic, and cardiovascular devices, owing to its unique mechanical behaviors and proper biocompatibility. The aim of this work is the local controlled delivery of a cardiovascular drug, heparin, loaded onto nitinol treated by electrochemical anodizing and chitosan coating. In this regard, the structure, wettability, drug release kinetics, and cell cytocompatibility of the specimens were analyzed in vitro. The two-stage anodizing process successfully developed a regular nanoporous layer of Ni-Ti-O on nitinol, which considerably decreased the sessile water contact angle and induced hydrophilicity. The application of the chitosan coatings controlled the release of heparin mainly by a diffusional mechanism, where the drug release mechanisms were evaluated by the Higuchi, first-order, zero-order, and Korsmeyer-Pepass models. Human umbilical cord endothelial cells (HUVECs) viability assay also showed the non-cytotoxicity of the samples, so that the best performance was found for the chitosan-coated samples. It is concluded that the designed drug delivery systems are promising for cardiovascular, particularly stent applications.

How Crystallographic Orientation-Induced Fibrinogen Conformation Affects Platelet Adhesion and Activation on TiO2

Control of protein adsorption is essential for successful integration of healthcare materials into the body. Human plasma fibrinogen (HPF), especially its conformation is a key upstream regulator for platelet behavior and thus pathological clot formation at the blood-biomaterial interface. A previous study by the authors revealed that the conformation of adsorbed HPF can be controlled by rutile surface crystallographic orientation. Therefore, it is hypothesized that pre-adsorbed HPF on specific rutile orientation can regulate platelets adhesion and activation. Here, it is shown that platelets exposed to the four low index (110), (100), (101), (001) facets of TiO2 (rutile) exhibit surface-specific behavior. Scanning electron microscopy (SEM) observations of platelets morphology and P-selectin expression measurement revealed that on (110) facets, platelets adhesion and activation are suppressed. In contrast, extensive surface coverage by fully activated platelets is observed on (001) facets. Platelets' behavior has been linked to the HPF conformation and thereby availability of platelet-binding sequences. Atomic force microscopy (AFM) imaging supported by immunochemical analysis shows that on (110) facets, HPF is adsorbed in trinodular conformation rendering the γ400-411 platelet-binding sequence inaccessible. This research has potential implications on the bioactivity of different materials crystal facets, reducing the risk of pathological clot formation and thromboembolic complications.

Blood Coagulation on Titanium Dioxide Films with Various Crystal Structures on Titanium Implant Surfaces

Background: Titanium (Ti) is one of the most popular implant materials, and its surface titanium dioxide (TiO₂) provides good biocompatibility. The coagulation of blood on Ti implants plays a key role in wound healing and cell growth at the implant site; however, researchers have yet to fully elucidate the mechanism underlying this process on TiO₂. Methods: This study examined the means by which blood coagulation was affected by the crystal structure of TiO₂ thin films (thickness < 50 nm), including anatase, rutile, and mixed anatase/rutile. The films were characterized in terms of roughness using an atomic force microscope, thickness using an X-ray photoelectron spectrometer, and crystal structure using transmission electron microscopy. The surface energy and dielectric constant of the surface films were measured using a contact angle goniometer and the parallel plate method, respectively. Blood coagulation properties (including clotting time, factor XII contact activation, fibrinogen adsorption, fibrin attachment, and platelet adhesion) were then assessed on the various test specimens. Results: All of the TiO₂ films were similar in terms of surface roughness, thickness, and surface energy (hydrophilicity); however, the presence of rutile structures was associated with a higher dielectric constant, which induced the activation of factor XII, the formation of fibrin network, and platelet adhesion. Conclusions: This study provides detailed information related to the effects of TiO₂ crystal structures on blood coagulation properties on Ti implant surfaces.

Rutile facet-dependent fibrinogen conformation: Why crystallographic orientation matters

Previous studies implied that single crystalline rutile surfaces have the ability to guide the functionality of adsorbed blood plasma proteins. However, a clear relation between the rutile crystallographic orientation and conformation of adsorbed proteins is still missing. Here, we examine the adsorption characteristics of human plasma fibrinogen (HPF) on atomically flat single rutile crystals with (110), (100), (101) and (001) facets. By direct visualization of individual protein molecules through atomic force microscopy (AFM) imaging, the distinct conformations of HPF were determined depending on rutile surface crystallographic orientation. In particular, dominant trinodular and globular conformation was found on (110) and (001) facets, respectively. The observed variations of HPF conformation were reasoned from the surface water contact angle and surface energy point of view. By analyzing AFM-based force measurements, statistically significant changes in surface energies of rutile surfaces covered with HPF were determined and linked to HPF conformation. Furthermore, the facet-dependent structural rearrangement of HPF was indirectly confirmed through deconvolution of high-resolution X-ray photoelectron spectroscopy (XPS) carbon and nitrogen spectra. The globular, and thus native-like HPF conformation observed on (001) facet, was reflected in the lowest level of amino group formation. We propose that the mechanism behind the crystallographic orientation-induced HPF conformation is driven by the facet-specific surface hydrophilicity and energy. From the biomedical material perspective, our results demonstrate that the conformation of HPF can be guided by controlling the crystallographic orientation of the underlying material surface. This might be beneficial to the field of titanium-based biomaterials design and development.

Nanostructured Titanium Implant Surface Facilitating Osseointegration from Protein Adsorption to Osteogenesis: The Example of TiO2 NTAs

Titanium implants have been widely applied in dentistry and orthopedics due to their biocompatibility and resistance to mechanical fatigue. TiO₂ nanotube arrays (TiO₂ NTAs) on titanium implant surfaces have exhibited excellent biocompatibility, bioactivity, and adjustability, which can significantly promote osseointegration and participate in its entire path. In this review, to give a comprehensive understanding of the osseointegration process, four stages have been divided according to pivotal biological processes, including protein adsorption, inflammatory cell adhesion/inflammatory response, additional relevant cell adhesion and angiogenesis/osteogenesis. The impact of TiO₂ NTAs on osseointegration is clarified in detail from the four stages. The nanotubular layer can manipulate the quantity, the species and the conformation of adsorbed protein. For inflammatory cells adhesion and inflammatory response, TiO₂ NTAs improve macrophage adhesion on the surface and induce M2-polarization. TiO₂ NTAs also facilitate the repairment-related cells adhesion and filopodia formation for additional relevant cells adhesion. In the angiogenesis and osteogenesis stage, TiO₂ NTAs show the ability to induce osteogenic differentiation and the potential for blood vessel formation. In the end, we propose the multi-dimensional regulation of TiO₂ NTAs on titanium implants to achieve highly efficient manipulation of osseointegration, which may provide views on the rational design and development of titanium implants.

Surface functionalized bioceramics coated on metallic implants for biomedical and anticorrosion performance - a review

In modern days, the usage of trauma fixation devices has significantly increased due to sports injury, age-related issues, accidents, and revision surgery purposes. Numerous materials such as stainless steel, titanium, Co-Cr alloy, polymers, and ceramics have been used to replace the missing or defective parts of the human body. After implantation, body fluids (Na⁺, K⁺, and Cl^-), protein, and blood cells interact with the surface of metallic implants, which favours the release of ions from the metallic surface to surrounding body tissues, leading to a hypersensitive reaction. Body pH, temperature, and interaction of immune cells also cause metal ion leaching and lose host cell interaction and effective mineralization for better durability. Moreover, microbial invasion is another important crisis, which produces extracellular compounds onto the biomaterial surface through which it escapes from the antimicrobial agents. To enhance the performance of materials by improving mechanical, corrosion resistance, antimicrobial, and biocompatibility properties, surface modification is a prerequisite method in which chemical vapour deposition (CVD), physical vapour deposition (PVD), sol-gel method, and electrochemical deposition are generally involved. The properties of bioceramics such as chemical inertness, bioactivity, biocompatibility, and corrosion protection make them most suitable for the surface functionalization of metallic implants. To the best of our knowledge, very limited literature is available to discuss the interaction of body proteins, pH, and temperature onto bioceramic coatings. Hence, the present review focuses on the corrosion behaviour of different ceramic composite coating materials with different conditions. This review initially briefs the properties and surface chemistry of metal implants and the need for surface modifications by different deposition techniques. Further, mechanical, cytotoxicity, antimicrobial property, and electrochemical behaviour of ceramics and metal nitride coatings are discussed. Finally, future perspectives of coatings are outlined for biomedical applications.

Anodic TiO2 Nanotubes: Tailoring Osteoinduction via Drug Delivery

TiO₂ nanostructures and more specifically nanotubes have gained significant attention in biomedical applications, due to their controlled nanoscale topography in the sub-100 nm range, high surface area, chemical resistance, and biocompatibility. Here we review the crucial aspects related to morphology and properties of TiO₂ nanotubes obtained by electrochemical anodization of titanium for the biomedical field. Following the discussion of TiO₂ nanotopographical characterization, the advantages of anodic TiO₂ nanotubes will be introduced, such as their high surface area controlled by the morphological parameters (diameter and length), which provides better adsorption/linkage of bioactive molecules. We further discuss the key interactions with bone-related cells including osteoblast and stem cells in in vitro cell culture conditions, thus evaluating the cell response on various nanotubular structures. In addition, the synergistic effects of electrical stimulation on cells for enhancing bone formation combining with the nanoscale environmental cues from nanotopography will be further discussed. The present review also overviews the current state of drug delivery applications using TiO₂ nanotubes for increased osseointegration and discusses the advantages, drawbacks, and prospects of drug delivery applications via these anodic TiO₂ nanotubes.

Deciphering controversial results of cell proliferation on TiO2 nanotubes using machine learning

With the rapid development of biomedical sciences, contradictory results on the relationships between biological responses and material properties emerge continuously, adding to the challenge of interpreting the incomprehensible interfacial process. In the present paper, we use cell proliferation on titanium dioxide nanotubes (TNTs) as a case study and apply machine learning methodologies to decipher contradictory results in the literature. The gradient boosting decision tree model demonstrates that cell density has a higher impact on cell proliferation than other obtainable experimental features in most publications. Together with the variation of other essential features, the controversy of cell proliferation trends on various TNTs is understandable. By traversing all combinational experimental features and the corresponding forecast using an exhausted grid search strategy, we find that adjusting cell density and sterilization methods can simultaneously induce opposite cell proliferation trends on various TNTs diameter, which is further validated by experiments. This case study reveals that machine learning is a burgeoning tool in deciphering controversial results in biomedical researches, opening up an avenue to explore the structure-property relationships of biomaterials.

Fabrication of Electrochemical Biosensor Based on Titanium Dioxide Nanotubes and Silver Nanoparticles for Heat Shock Protein 70 Detection

This paper presents the fabrication methodology of an electrochemical biosensor for the detection of heat shock protein 70 (HSP70) as a potential tumor marker with high diagnostic sensitivity. The sensor substrate was a composite based on titanium dioxide nanotubes (TNTs) and silver nanoparticles (AgNPs) produced directly on TNTs by electrodeposition, to which anti-HSP70 antibodies were attached by covalent functionalization. This manuscript contains a detailed description of the production, modification, and the complete characteristics of the material used as a biosensor platform. As-formed TNTs, annealed TNTs, and the final sensor platform—AgNPs/TNTs, were tested using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction analysis (XRD). In addition, open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) of these substrates were used to assess the influence of TNTs modification on their electrochemical characteristics. The EIS technique was used to monitor the functionalization steps of the AgNPs/TNTs electrode and the interaction between anti-HSP70 and HSP70. The produced composite was characterized by high purity, and electrical conductivity improved more than twice compared to unmodified TNTs. The linear detection range of HSP70 of the developed biosensor was in the concentration range from 0.1 to 100 ng/mL.

In Vivo Blood-Repellent Performance of a Controllable Facile-Generated Superhydrophobic Surface

Fabrication of a blood-repellent surface is essential for implantable or interventional medical devices to avoid thrombosis which can induce several serious complications. In this research, a novel micropatterned surface was fabricated via a facile and cost-effective method, and then, the in vitro and in vivo blood-repellent performances of the controllable superhydrophobic surface were systematically evaluated. First, a facile and cost-effective strategy was proposed to fabricate a controllable superhydrophobic surface on a medically pure titanium substrate using an ultraviolet laser process, ultrasonic acid treatment, and chemical modification. Second, the superhydrophobicity, durability, stability, and corrosion resistance of the superhydrophobic surface were confirmed with advanced testing techniques, which display a high contact angle, low adhesion to water and blood, and excellent resistant element precipitation. Third, the platelet-rich plasma and whole blood were applied to evaluate the hemocompatibility of the superhydrophobic surface by means of an in vitro experiment, and no blood cell activation or aggregation was observed on the superhydrophobic surface. Finally, hollow tubes with an inner superhydrophobic surface were implanted into the left carotid artery of rabbits for 2 weeks to verify the biocompatibility in vivo. The superhydrophobic surface could effectively eliminate blood cell adhesion and thrombosis. No obvious inflammation or inordinate proliferation was found by histological analysis. This research provides a facile and cost-effective strategy to prepare a blood-repellent surface, which may have promising applications in implanted biomedical devices.

Hemocompatibility of polyzwitterion-modified titanium dioxide nanotubes

Titanium dioxide nanotubes (TNTs) have attracted increasing interest as implantable materials due to their many desirable properties. However, their blood compatibility remains an issue. In this paper, TNTs of different diameters were modified with two types of zwitterionic polymers, poly(sulfobetaine methacrylate) (pSBMA) and poly(carboxybetaine methacrylate) (pCBMA), which were grafted onto the TNTs using ARGET-ATRP (activators regenerated by electron transfer atom transfer radical polymerization) method. Both pSBMA and pCBMA brushes coatings were found to greatly reduce adsorption of bovine serum albumin (BSA) and fibrinogen (Fib) onto the TNTs, showing excellent protein resistance. Moreover, the effects of the surface topography on the amount of protein adsorption were largely suppressed by the polyzwitterion coatings. The conformation of the protein adsorbed to the substrates was analyzed at the molecular level by Fourier-transform infrared reflection spectroscopy (FT-IR), which revealed that the BSA adsorbed on the polyzwitterion-modified TNTs adopted significantly different secondary structures from that on the virgin TNTs, whereas the conformation of the adsorbed Fib remained basically the same. The polyzwitterion-modified TNTs were found to be non-hemolytic, and platelet adhesion and activation was significantly reduced, showing excellent blood compatibility.

Overview of Antibacterial Strategies of Dental Implant Materials for the Prevention of Peri-Implantitis

As dental implants have become one of the main treatment options for patients with tooth loss, the number of patients with peri-implant diseases has increased. Similar to periodontal diseases, peri-implant diseases have been associated with dental plaque formation on implants. Unconventional approaches have been reported to remove plaque from infected implants, but none of these methods can completely and permanently solve the problem of bacterial invasion. Fortunately, the constant development of antibacterial implant materials is a promising solution to this situation. In this review, the development and study of different antibacterial strategies for dental implant materials for the prevention of peri-implantitis are summarized. We hope that by highlighting the advantages and limitations of these antimicrobial strategies, we can assist in the continued development of oral implant materials.

Electrodes Based on a Titanium Dioxide Nanotube-Spherical Silver Nanoparticle Composite for Sensing of Proteins

The aim of the research was to provide electrochemical, chemical, phase, and microscopic characteristics of electrodes based on titanium dioxide nanotubes (TNTs) containing uniformly deposited, nonagglomerated spherical silver nanoparticles (AgNPs). The nanoparticles were produced with the use of electrodeposition and sputter deposition methods. This paper presents the results of research of these platforms with the use of the following techniques: electrochemical impedance spectroscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, and scanning electron microscopy. Evaluation of the adsorption of proteins-bovine serum albumin (BSA)-was carried out to establish the possibility of the use of the electrodes in a low-cost, simple detection system without surface functionalization. The research proved that the AgNP deposition facilitated the electron transfer increasing their conductivity properties as well as promoting the protein adsorption. The AgNPs/TNT electrodes showed a high selectivity to the BSA-anti-BSA complex. Half an hour of immobilization was enough to completely saturate the TNT electrodes, whereas for AgNPs/TNTs, 1 h of immobilization seemed to be not enough. The impedance parameter changes for electrodes with the AgNPs reached even about 300%. The biggest changes were noted for the platform obtained using cyclic voltammetry, so it is the best detection platform for biosensing.

Bioinspired surfaces with wettability: biomolecule adhesion behaviors

Surface wettability plays an important role in regulating biomolecule adhesion behaviors. The biomolecule adhesion behaviors of superwettable surfaces have become an important topic as an important part of the interactions between materials and organisms. In addition to general research on the moderate wettability of surfaces, the studies of biomolecule adhesion behaviors extend to extreme wettability ranges such as superhydrophobic, superhydrophilic and slippery surfaces and attract both fundamental and practical interest. In this review, we summarize the recent studies on biomolecule adhesion behaviors on superwettable surfaces, especially superhydrophobic, superhydrophilic and slippery surfaces. The first part will focus on the influence of extreme wettability on cell adhesion behaviors. The second part will concentrate on the adhesion behaviors of biomacromolecules on superwettable surfaces including proteins and nucleic acids. Finally, the influences of wettability on small molecule adhesion behaviors on material surfaces have also been investigated. The mechanism of superwettable surfaces and their influences on biomolecule adhesion behaviors have been studied and highlighted.

How Nanotopography-Induced Conformational Changes of Fibrinogen Affect Platelet Adhesion and Activation

The conformational state of adsorbed human plasma fibrinogen (HPF) has been recognized as the determinant factor in platelet adhesion and thrombus formation on blood-contacting biomaterials. Studies have highlighted the ability to control the HPF conformation merely by tailoring surface nanotopographical features. However, a clear relationship between the conformational changes of adsorbed HPF and the degree of platelet adhesion and activation achieved with different surface nanotopographies is still unclear. Here, we examined HPF assembly characteristics on nanostructured polybutene-1 (PB-1) surfaces with nanosized lamellar crystals (LCs), needle-like crystals (NLCs), and a nanostructured high-density polyethylene (HDPE) surface with shish-kebab crystals (SKCs), at a biologically relevant HPF concentration. By exposing the nanostructured surfaces with preadsorbed HPF to human platelets, significant differences in platelet response on LCs/SKCs and NLCs were identified. The former presented a uniform monolayer in the advanced stage of activation, whereas the latter exhibited minimal adhesion and the early stage of activation. Distinct platelet response was related to the postadsorption conformational changes in HPF, which were confirmed by topography-dependent shifts of the amide I band in attenuated total reflection-Fourier transform infrared (ATR-FTIR) analysis. Supported by atomic force microscopy (AFM) characterization, we propose that the mechanism behind the nanotopography-induced HPF conformation is driven by the interplay between the aspect ratios of polymeric crystals and HPF. From the biomedical perspective, our work reveals that surface structuring in a nanoscale size regime can provide a fine-tuning mechanism to manipulate HPF conformation, which can be exploited for the design of thromboresistant biomaterials surfaces.

Nanointeraction: The profound influence of nanostructured and nano-drug delivery biomedical implant surfaces on cell behavior

Nanostructured surfaces feature promising biological properties on biomaterials attracting large interest at basic research, implant industry development, and bioengineering applications. Thou, nanoscale interactions at a molecular and cellular level are not yet completely understood and its biological and clinical implications need to be further elucidated. As follows, the aim of this comprehensive review was to evaluate nanostructured surfaces at biomedical implants focusing on surface development, nanostructuration, and nanoengineered drug delivery systems that can induce specific cell interactions in all relevant aspects of biological, reparative, anti-bacterial, anti-inflammatory and clinical processes. The methods and the physio-chemical properties involved in nanotopography performance, the main cellular characteristics involved at surface/cell interaction, and a summary of results and outlooks reported in studies applying nanostructured surfaces and nano-drug delivery systems is presented. The future prospects and commercial translation of this developing field, particularly concerning multifunctional nanostructured surfaces and its clinical implications are further discussed. At a cellular level, nanostructured biomedical implant surfaces can enhance osteogenesis by targeting osteoblasts, osteocytes, and mesenchymal cells, stimulate fibroblast/epithelial cells proliferation and adherence, inhibit bacterial cell proliferation and biofilm accumulation, and act as immune-modulating surfaces targeting macrophages and reducing pro-inflammatory cytokine expression. Moreover, several methodological options to create drug-delivery systems on metallic implant surfaces are available, however, the clinical translation is yet incomplete. The efficiency of which nanostructured/nano-delivery surfaces may target specific cell interactions and favor clinical outcomes needs to be further elucidated in pre-clinical and clinical studies, along with engineering solutions for commercial translation and approval of controlling agencies.

Plasma-immersion ion implantation surface oxidation on a cobalt-chromium alloy for biomedical applications

Co-Cr alloys such as L605 are widely applied for the manufacture of medical devices, including tiny cardiovascular stents. The presence of potentially toxic and allergenic release of Ni, Co, and Cr ions from these devices remains an unsolved concern. Surface modification by oxygen plasma immersion implantation (PIII) could be an excellent technique to create a dense and thin passive oxide layer on a relatively complex shape of a tiny device, such as a stent, thus reducing the potential release of metallic ions. The effect of oxygen PIII was investigated on L605 alloy specimens, from 5 to 50 mTorr gas pressures, and under pulsed bias voltages from -0.1 to -10 kV. The surface chemistry was investigated by x-ray photoelectron spectroscopy, while its morphology and surface energy were evaluated, respectively, by atomic force microscopy and scanning electron microscopy and by a sessile drop static contact angle. Electrochemical characterization was performed by potentiodynamic tests in the saline solution. Mechanical properties of the modified surface layer, specifically film adhesion and hardness (H), were assessed by scratch and nanoindentation tests. Results shown that the oxidized layers were composed of a mixture of Co and Cr oxides and hydroxides and were rich in Co. The corrosion rate was considerably reduced after O PIII, even for treatments using low bias voltage (-0.1 kV) and with consequent low oxygen implantation depth. Moreover, O PIII also improved surface hardness. The oxidized layers were found to have good adhesion and to be scratch resistant.

Crystallized TiO2 Nanosurfaces in Biomedical Applications

Crystallization alters the characteristics of TiO2 nanosurfaces, which consequently influences their bio-performance. In various biomedical applications, the anatase or rutile crystal phase is preferred over amorphous TiO2. The most common crystallization technique is annealing in a conventional furnace. Methods such as hydrothermal or room temperature crystallization, as well as plasma electrolytic oxidation (PEO) and other plasma-induced crystallization techniques, present more feasible and rapid alternatives for crystal phase initiation or transition between anatase and rutile phases. With oxygen plasma treatment, it is possible to achieve an anatase or rutile crystal phase in a few seconds, depending on the plasma conditions. This review article aims to address different crystallization techniques on nanostructured TiO2 surfaces and the influence of crystal phase on biological response. The emphasis is given to electrochemically anodized nanotube arrays and their interaction with the biological environment. A short overview of the most commonly employed medical devices made of titanium and its alloys is presented and discussed.

Biomedical Applications of TiO2 Nanostructures: Recent Advances

Titanium dioxide (TiO2) nanostructures are one of the most plentiful compounds that have emerged in various fields of technology such as medicine, energy and biosensing. Various TiO2 nanostructures (nanotubes [NTs] and nanowires) have been employed in photoelectrochemical (PEC) biosensing applications, greatly enhancing the detection of targets. TiO2 nanostructures, used as reinforced material or coatings for the bare surface of titanium implants, are excellent additive materials to compensate titanium implants deficiencies-like poor surface interaction with surrounding tissues-by providing nanoporous surfaces and hierarchical structures. These nanostructures can also be loaded by diversified drugs-like osteoporosis drugs, anticancer and antibiotics-and used as local drug delivery systems. Furthermore, TiO2 nanostructures and their derivatives are new emerging antimicrobial agents to overcome human pathogenic microorganisms. However, like all other nanomaterials, toxicity and biocompatibility of TiO2 nanostructures must be considered. This review highlights recent advances, along with the properties and numerous applications of TiO2-based nanostructure compounds in nano biosensing, medical implants, drug delivery and antibacterial fields. Moreover, in the present study, some recent advances accomplished on the pharmaceutical applications of TiO2 nanostructures, as well as its toxicity and biocompatibility, are presented.

Effects of diameters and crystals of titanium dioxide nanotube arrays on blood compatibility and endothelial cell behaviors

Titanium dioxide nanotube arrays (TNTAs) have attracted extensive attention in the fields of biomaterials and biomedicine due to their unique tubular structure and good biocompatibility. In this paper, TNTAs with different nanotube diameters and lengths were in situ prepared on the titanium surface by the anodic oxidation, and their crystal structures were further changed by annealing treatment. The effects of TNTAs with different diameters and crystals on the blood compatibility and endothelial cell behaviors were investigated. The results showed that TNTAs with the diameter of 30∼90 nm can be obtained by controlling the anodization voltage, and annealing treatment did not obviously change the diameters and lengths of the nanotube arrays. However, annealing treatment can transform the amorphous TNTAs into the anatase structure. The diameter and crystal structure of the nanotube arrays played a key role in the surface wettability and protein adsorption. The nanotube array with larger diameter displayed better surface hydrophilicity as compared to the pristine titanium, and annealing treatment further enhanced the hydrophilicity. As compared to the pristine titanium, the nanotube array structure had the characteristic of selective protein adsorption, and the nanotube array can promote the bovine serum albumin (BSA) adsorption and prevent the fibrinogen (FIB) adsorption, however, the increase of nanotube diameter could reduce BSA adsorption and increase FIB adsorption. Besides, the nanotube array with anatase structure can promote BSA adsorption while reduce FIB adsorption. Therefore, the TNTAs with smaller diameter and anatase crystal had good blood compatibility and cell compatibility, they can not only reduce platelet adhesion and hemolysis rate but also increase endothelial cell adhesion and proliferation. In conclusion, the nanotube arrays of the present study can be used to improve the cell compatibility and blood compatibility of the titanium implants.

Influence of the Silver Nanoparticles (AgNPs) Formation Conditions onto Titanium Dioxide (TiO2) Nanotubes Based Electrodes on Their Impedimetric Response

This paper presents the comparison of the effects of three methods of production of silver spherical and near-spherical nanoparticles (AgNPs) on the titanium dioxide nanotubes (TNT) base: cyclic voltammetry, chronoamperometry, and sputter deposition. It also evaluates the influence of silver nanoparticles on the electrochemical properties of the developed electrodes. The novelty of this research was to fabricate regular AgNPs free of agglomerates uniformly distributed onto the TNT layer, which has not been accomplished with previous attempts. The applied methods do not require stabilizing and reducing reagents. The extensive electrochemical characteristic of AgNP/TNT was performed by open circuit potential and electrochemical impedance spectroscopy methods. For AgNPs/TNT obtained by each method, the impedance module of these electrodes was up to 50% lower when compared to TNT, which means that AgNPs enabled more efficient electron transfer due to the effective area increase. In addition, the presence of nanoparticles increases the corrosion resistance of the prepared electrodes. These substrates can be used as electrochemical sensors due to their high electrical conductivity, and also as implants due to the antibacterial properties of both the TNT and AgNPs.

Antibacterial potential associated with drug-delivery built TiO2 nanotubes in biomedical implants

The fast evolution of surface treatments for biomedical implants and the concern with their contact with cells and microorganisms at early phases of bone healing has boosted the development of surface topographies presenting drug delivery potential for, among other features, bacterial growth inhibition without impairing cell adhesion. A diverse set of metal ions and nanoparticles (NPs) present antibacterial properties of their own, which can be applied to improve the implant local response to contamination. Considering the promising combination of nanostructured surfaces with antibacterial materials, this critical review describes a variety of antibacterial effects attributed to specific metals, ions and their combinations. Also, it explains the TiO2 nanotubes (TNTs) surface creation, in which the possibility of aggregation of an active drug delivery system is applicable. Also, we discuss the pertinent literature related to the state of the art of drug incorporation of NPs with antibacterial properties inside TNTs, along with the promising future perspectives of in situ drug delivery systems aggregated to biomedical implants.

Plasma-Induced Crystallization of TiO₂ Nanotubes

Facile crystallization of titanium oxide (TiO₂) nanotubes (NTs), synthesized by electrochemical anodization, with low pressure non-thermal oxygen plasma is reported. The influence of plasma processing conditions on TiO₂ NTs crystal structure and morphology was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). For the first time we report the transition of amorphous TiO₂ NTs to anatase and rutile crystal structures upon treatment with highly reactive oxygen plasma. This crystallization process has a strong advantage over the conventional heat treatments as it enables rapid crystallization of the surface. Thus the crystalline structure of NTs is obtained in a few seconds of treatment and it does not disrupt the NTs’ morphology. Such a crystallization approach is especially suitable for medical applications in which stable crystallized nanotubular morphology is desired. The last part of the study thus deals with in vitro biological response of whole blood to the TiO₂ NTs. The results indicate that application of such surfaces for blood connecting devices is prospective, as practically no platelet adhesion or activation on crystallized TiO₂ NTs surfaces was observed.

TiO2 ALD Coating of Amorphous TiO2 Nanotube Layers: Inhibition of the Structural and Morphological Changes Due to Water Annealing

The present work presents a strategy to stabilize amorphous anodic self-organized TiO₂ nanotube layers against morphological changes and crystallization upon extensive water soaking. The growth of needle-like nanoparticles was observed on the outer and inner walls of amorphous nanotube layers after extensive water soakings, in line with the literature on water annealing. In contrary, when TiO₂ nanotube layers uniformly coated by thin TiO₂ using atomic layer deposition (ALD) were soaked in water, the growth rates of needle-like nanoparticles were substantially reduced. We investigated the soaking effects of ALD TiO₂ coatings with different thicknesses and deposition temperatures. Sufficiently thick TiO₂ coatings (≈8.4 nm) deposited at different ALD process temperatures efficiently hamper the reactions between water and F⁻ ions, maintain the amorphous state, and preserve the original tubular morphology. This work demonstrates the possibility of having robust amorphous 1D TiO₂ nanotube layers that are very stable in water. This is very practical for diverse biomedical applications that are accompanied by extensive contact with an aqueous environment.

High-Throughput Screening of Rat Mesenchymal Stem Cell Behavior on Gradient TiO2 Nanotubes

The dimension of TiO₂ nanotubes (TNTs) ranges from several nanometers to hundreds of nanometers. This variety raises the difficulty of screening suitable nanotube dimension for biomedical applications. Herein, we report the use of a simple one-step bipolar anodization method for fabrication of TNT gradients with diameter range from 30 to 100 nm. The gradient TNTs were successfully applied for high-throughput screening of TNT size effect on cell responses, including cell adhesion, proliferation, and differentiation. Results reveal that no significant difference in adherent cell number could be found within the range of 30-87 nm in both the presence and absence of serum proteins. On the contrary, large nanotubes (with outer diameter >87 nm) profoundly reduce cell adhesion in both the presence and absence of serum proteins, indicating TNT size could affect cell adhesion directly without the adsorbed proteins. The size effect on cell behavior becomes prominent with time that cell proliferation and differentiation decrease with increasing nanotube size. This size effect can be comprehended by protein adsorption and the formation of focal adhesion. Another two sample applications of gradient TNTs demonstrate gradient TNTs are promising for high-throughput screening.

Effects of Surface Nanotopography and Calcium Chemistry of Titanium Bone Implants on Early Blood Platelet and Macrophage Cell Function

Early responses of blood platelets and immunoinflammatory cells (macrophages) to titanium (Ti) bone implants affect the subsequent biological healing of implants by modulating early tissue healing-microenvironments via the formation of temporary fibrin matrix scaffolds for stem cell migration and production of growth factors and cytokines. This study investigated the effects of nanoscale surface topography and calcium ion (Ca²⁺) modification of Ti surfaces on biocompatibility regulated by blood platelets and macrophages, for the future surface design of Ti bone implants with enhanced early osteogenic capacity. A nanostructured Ti surface with or without Ca²⁺ enrichment was prepared using the hydrothermal treatment. Immediate and early functions of platelets and macrophages modulated by modified Ti surfaces were investigated by morphological observation of platelet spreading and fibrin matrix formation, platelet growth factor release, immunostaining of macrophage phenotypes, and macrophage inflammatory cytokine production. The results showed that surface nanoscale topographical modification of Ti promotes blood platelet activation and suppresses the inflammatory response of macrophages. In addition, surface chemistry modifications with Ca²⁺ enhanced the platelet response-modulating function of the nanostructured Ti surface, which accelerated immediate fibrin matrix formation and platelet-derived growth factor-AB release. Thus, nanotopographical and Ca²⁺ modifications of implant surfaces are expected to be effective approaches that favor the initial phase of wound healing around the Ti bone implants through positive modulation of immediate blood platelet function and early macrophage immunoinflammatory response.

Effects of hydrogenated TiO2 nanotube arrays on protein adsorption and compatibility with osteoblast-like cells

Background

Modified titanium (Ti) substrates with titanium dioxide (TiO₂) nanotubes have broad usage as implant surface treatments and as drug delivery systems.

Methods

To improve drug-loading capacity and accelerate bone integration with titanium, in this study, we hydrogenated anodized titanium dioxide nanotubes (TNTs) by a thermal treatment. Three groups were examined, namely: hydrogenated TNTs (H₂-TNTs, test), unmodified TNTs (air-TNTs, control), and Ti substrates (Ti, control).

Results

Our results showed that oxygen vacancies were present in all the nanotubes. The quantity of -OH groups greatly increased after hydrogenation. Furthermore, the protein adsorption and loading capacity of the H₂-TNTs were considerably enhanced as compared with the properties of the air-TNTs (P<0.05). Additionally, time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to investigate the interactions of TNTs with proteins. During the protein-loading process, the H₂-TNTs not only enabled rapid protein adsorption, but also decreased the rate of protein elution compared with that of the air-TNTs. We found that the H₂-TNTs exhibited better biocompatibility than the air-TNT and Ti groups. Both cell adhesion activity and alkaline phosphatase activity were significantly improved toward MG-63 human osteoblast-like cells as compared with the control groups (P<0.05).

Conclusion

We conclude that hydrogenated TNTs could greatly improve the loading capacity of bioactive molecules and MG-63 cell proliferation.

Progress in TiO2 nanotube coatings for biomedical applications: a review

Titanium dioxide nanotubes (TNTs) have drawn wide attention and been extensively applied in the field of biomedicine, due to their large specific surface area, good corrosion resistance, excellent biocompatibility, and enhanced bioactivity. This review describes the preparation of TNTs and the surface modification that entrust the nanotubes with better antibacterial property and enhanced osteoblast adhesion, proliferation, and differentiation. Considering the contact between TNTs' surface and surrounding tissues after implantation, the interactions between TNTs (with properties including their diameter, length, wettability, and crystalline phase) and proteins, platelets, bacteria, and cells are illustrated. The state of the art in the applications of TNTs in dentistry, orthopedic implants, and cardiovascular stents are introduced. In particular, the application of TNTs in biosensing has attracted much attention due to its ability for the rapid diagnosis of diseases. Finally, the difficulties and challenges in the practical application of TNTs are also discussed.