Regulation of localized corrosion of 316L stainless steel on osteogenic differentiation of bone morrow derived mesenchymal stem cells

Localized corrosion has become a concerning issue in orthopedic implants as it is associated with peri-implant adverse tissue reactions and implant failure. Here, the pitting corrosion of 316 L stainless steels (316 L SSs) was initiated by electrochemical polarization to simulate the in vivo localized corrosion of orthopedic implants. The effect of localized corrosion on osteogenic differentiation of bone marrow derived mesenchymal stem cells (BMSCs) was systematically studied. The results suggest that pitting corrosion of 316 L SS reduced the viability, adhesion, proliferation, and osteogenic differentiation abilities of BMSCs, especially for the cells around the corrosion pits. The relatively high concentrations of metallic ions such as Cr3+ and Ni2+ released by pitting corrosion could cause cytotoxicity to the BMSCs. The inhomogeneous electrochemical environment resulted from localized corrosion could promote reactive oxygen species (ROS) generation around the corrosion pits and cause oxidative stress of BMSCs. In addition, localized corrosion could also electrochemically interact with the cells and lead to cell membrane depolarization. The depolarized cell membranes and relatively high levels of ROS mediated the degradation of the osteogenic capacity of BMSCs. This work provides new insights into corrosion-mediated cell function degeneration as well as the material-cell interactions.

Numerical approach to investigate MR imaging artifacts from orthopedic implants at different field strengths according to ASTM F2119

OBJECTIVE

This study presents an extended evaluation of a numerical approach to simulate artifacts of metallic implants in an MR environment.

METHODS

The numerical approach is validated by comparing the artifact shape of the simulations and measurements of two metallic orthopedic implants at three different field strengths (1.5 T, 3 T, and 7 T). Furthermore, this study presents three additional use cases of the numerical simulation. The first one shows how numerical simulations can improve the artifact size evaluation according to ASTM F2119. The second use case quantifies the influence of different imaging parameters (TE and bandwidth) on the artifact size. Finally, the third use case shows the potential of performing human model artifact simulations.

RESULTS

The numerical simulation approach shows a dice similarity coefficient of 0.74 between simulated and measured artifact sizes of metallic implants. The alternative artifact size calculation method presented in this study shows that the artifact size of the ASTM-based method is up to 50% smaller for complex shaped implants compared to the numerical-based approach.

CONCLUSION

In conclusion, the numerical approach could be used in the future to extend MR safety testing according to a revision of the ASTM F2119 standard and for design optimization during the development process of implants.

Simplified modeling of implanted medical devices with metallic filamentary closed loops exposed to low or medium frequency magnetic fields

BACKGROUND AND OBJECTIVES

Electric currents are induced in implanted medical devices with metallic filamentary closed loops (e.g., fixation grids, stents) when exposed to time varying magnetic fields, as those generated during certain diagnostic and therapeutic biomedical treatments. A simplified methodology to efficiently compute these currents, to estimate the altered electromagnetic field distribution in the biological tissues and to assess the consequent biological effects is proposed for low or medium frequency fields.

METHODS

The proposed methodology is based on decoupling the handling of the filamentary wire and the anatomical body. To do this, a circuital solution is adopted to study the metallic filamentary implant and this solution is inserted in the electromagnetic field solution involving the biological tissues. The Joule losses computed in the implant are then used as a forcing term for the thermal problem defined by the bioheat Pennes' equation. The methodology is validated against a model problem, where a reference solution is available.

RESULTS

The proposed simplified methodology is proved to be in good agreement with solutions provided by alternative approaches. In particular, errors in the amplitude of the currents induced in the wires result to be always lower than 3%. After the validation, the methodology is applied to check the interactions between the magnetic field generated by different biomedical devices and a skull grid, which represents a complex filamentary wire implant.

CONCLUSIONS

The proposed simplified methodology, suitable to be applied to closed loop wires in the low to intermediate frequency range, is found to be sufficiently accurate and easy to apply in realistic exposure scenarios. This modeling tool allows analyzing different types of small implants, from coronary and biliary duct stents to orthopedic grids, under a variety of exposure scenarios.

Role of nanostructured materials in hard tissue engineering

The rise in the use of biomaterials in bone regeneration in the last decade has exponentially multiplied the number of publications, methods, and approaches to improve and optimize their functionalities and applications. In particular, biomimetic strategies based on the self-assembly of molecules to design, create and characterize nanostructured materials have played a very relevant role. We address this idea on four different but related points: self-setting bone cements based on calcium phosphate, as stable tissue support and regeneration induction; metallic prosthesis coatings for cell adhesion optimization and prevention of inflammatory response exacerbation; bio-adhesive hybrid materials as multiple drug delivery localized platforms and finally bio-inks. The effect of the physical, chemical, and biological properties of the newest biomedical devices on their bone tissue regenerative capacity are summarized, described, and analyzed in detail. The roles of experimental conditions, characterization methods and synthesis routes are emphasized. Finally, the future opportunities and challenges of nanostructured biomaterials with their advantages and shortcomings are proposed in order to forecast the future directions of this field of research.

Management of metallic implants in radiotherapy

The number of patients with metallic implant and treated with radiotherapy is constantly increasing. These hardware are responsible for the deterioration in the quality of the CT images used at each stage of the radiation therapy, during delineation, dosimetry and dose delivery. We present the update of the recommendations of the French society of oncological radiotherapy on the pros and cons of the different methods, existing and under evaluation, which limit the impact of metallic implants on the quality and safety of radiation treatments.

Development and evaluation of a numerical simulation approach to predict metal artifacts from passive implants in MRI

Objective

This study presents the development and evaluation of a numerical approach to simulate artifacts of metallic implants in an MR environment that can be applied to improve the testing procedure for MR image artifacts in medical implants according to ASTM F2119.

Methods

The numerical approach is validated by comparing simulations and measurements of two metallic test objects made of titanium and stainless steel at three different field strengths (1.5T, 3T and 7T). The difference in artifact size and shape between the simulated and measured artifacts were evaluated. A trend analysis of the artifact sizes in relation to the field strength was performed.

Results

The numerical simulation approach shows high similarity (between 75% and 84%) of simulated and measured artifact sizes of metallic implants. Simulated and measured artifact sizes in relation to the field strength resulted in a calculation guideline to determine and predict the artifact size at one field strength (e.g., 3T or 7T) based on a measurement that was obtained at another field strength only (e.g. 1.5T).

Conclusion

This work presents a novel tool to improve the MR image artifact testing procedure of passive medical implants. With the help of this tool detailed artifact investigations can be performed, which would otherwise only be possible with substantial measurement effort on different MRI systems and field strengths.

Multimodal imaging of composite carbon fiber-based implants for orthopedic spinal fixation

OBJECTIVE

As cancer treatments continue to improve, the incidence of spinal metastases and the need for surgical management of these with fixation procedures are growing rapidly. Traditionally metallic implants, composed of titanium alloy, have been used in surgical fixation of unstable or symptomatic vertebral metastases or traumatic injuries. Metallic implants, however, cause significant artifact on post-operative imaging, degrading image quality and limiting interpretation, and can also impair the planning and delivery of radiotherapy. Composite carbon fiber-based materials, such as carbon fiber-reinforced polyetheretherketone (PEEK), have been developed to overcome these issues and are now available for spinal fixation procedures. We aimed to review the multimodal imaging features of these new implants.

MATERIALS AND METHODS

Current literature and a case example from our institution were used to describe the multimodal imaging characteristics and considerations of new carbon fiber-based spinal fixation implants.

RESULTS

New carbon fiber-based spinal implants allow far greater visualization of surrounding structures on post-operative cross-sectional imaging, significantly improving diagnostic accuracy and precision of radiotherapy planning, and do not significantly absorb or scatter X-ray photons during radiotherapy delivery. There are, however, important surgical and radiologic considerations associated with the use of carbon fiber-based implants which radiologists must be aware of, such as implications for surgical planning and intra-operative fluoroscopic and post-operative plain radiographic imaging.

CONCLUSION

The use of carbon fiber-based implants, rather than traditional metallic implants, for spinal fixation offers significant advantages for post-operative diagnostic imaging and radiotherapy planning and delivery.

Metallic implants and CT artefacts in the CTV area: Where are we in 2020?

Radiation therapy (RT) is one of the main modalities of cancer treatment worldwide with computed tomography (CT), as the most commonly used imaging method for treatment planning system (TPS). Image reconstruction errors may greatly affect all the radiation therapy planning process, such as target delineation, dose calculation and delivery, particularly with particle therapy. Metallic implants, such as hip and spinal implants, and dental filling significantly deteriorate image quality. These hardware structures are often very complex in geometry leading to geometric complex artefacts in the clinical target volume (CTV) area, rendering the delineation of CTV challenging. In our review, we focus on the methods to overcome artefact consequences on CTV delineation: 1- medical approaches anticipating issues associated with imaging artefacts during preoperative multidisciplinary discussions while following standard recommendations; 2- common metal artefact reduction (MAR) methods such as manually override artefact regions, ballistics avoiding beam paths through implanted materials, megavoltage-CT (MVCT); 3- prospects with radiolucent implants, MAR algorithms and various methods of dual energy computed tomography (DECT). Despite substantial and broad evidence for their benefits, there is still no universal solution for cases involving implanted metallic devices. There is still a high need for research efforts to adapt technologies to our issue: "how do I accurately delineate the ideal CTV in a metal artefact area?"

Nickel allergy to orthopaedic implants: A review and case series

Many of the metals used in orthopaedic surgical implants are immunologically active and can cause hypersensitivity reactions. Most of these metal hypersensitivity (MHS) reactions are type IV/delayed-type hypersensitivity reactions. The most common form of all metal hypersensitivity reactions is allergic contact dermatitis (ACD) caused by nickel. The purpose of this review is to examine the evidence regarding hypersensitivity to orthopaedic implants and provide current recommendations for evaluating these patients. We report on four case examples of patients where it was determined that metal allergy led to complications related to surgery. The most common symptoms for patients with MHS-associated failures are localized soft tissue reaction including delayed wound healing and/or recurrent wound issues. The best way to avoid postoperative issues is to routinely ask patients prior to surgery if they have any known MHS including problems with cosmetic jewelry. If this is known before surgery, titanium or carbon fiber implants should be used for fracture fixation and arthroplasty implantation choice should be modified based on the specific arthroplasty performed. MHS-associated failures are a diagnosis of exclusion and must be contemplated after judicious workup of localized soft tissue reaction including delayed wound healing and/or recurrent wound issues.

Antibacterial composite hybrid coatings of veterinary medical implants

The aim of the work was to develop innovative antibacterial hybrid coatings applied on implants that are used for anastomoses of animals' long bones and to assess their physicochemical and biological properties. Plates made of the titanium alloy were covered with composite hybrid layers so as to protect the implant surface against corrosion and to enhance it with antibacterial properties.The hybrid coatings were obtained electrochemical oxidation and sol-gel. First, a layer of titanium nanotubes was applied to the implants surface through anodization. Next, the sol-gel method was used to create the second layer with silver nanoparticles. The microstructure examination of the materials was performed with the SEM. The phase composition analysis was carried out via the X-ray diffraction. The surface parameters (roughness, contact angle and free surface energy) were assessed. Biological studies of implants were conducted, including the analysis of degradation processes, cell response and bactericidal activity. The results confirmed that the hybrid antibacterial layers effectively protected the implant surface against scratches and corrosion and eliminated bacteria, which in turn would promote bone healing. The advantageous physicochemical and biological properties of metallic implants with hybrid composite layers raise hopes for their applicability in the veterinary treatment of bone fractures.

Implantable Materials Update

There are a variety of materials available for surgical reconstruction of the foot and ankle. The material that provides the best physical properties to match the mechanical stress should be chosen. Ideal implant material should be biocompatible, nontoxic, noncarcinogenic, nonpyrogenic, and nonallergenic. Key properties include strength, durability, and resistance to fatigue. The material should have ductility to provide continued strength once it has been adapted to the bone surface. The material should be readily available, affordable, and reproducible. Materials that are available for use are stainless steel, cobalt chrome alloys, titanium and titanium alloys, pyrolytic carbon, thermoplastics, and bioceramics.

Role of protein adsorption in the bio corrosion of metallic implants - A review

Implants are exposed to a complex physiological environment that contains various organic compounds, especially proteins. The adsorption of proteins has an immense influence on the corrosion, biocompatibility and wear properties of implantable metals. Proteins engage in multiple processes that could potentially inhibit or promote metal degradation, depending on the type of proteins, their concentration and the properties of the implant material. In the bio corrosion process, proteins are denatured and transform into a film on the metal surface, inhibiting corrosion. This film is found on many retrieved artificial joints, especially on worn areas, and can protect the passive film from scrapping due to its lubricating effect, thus decreasing tribocorroion. On the other hand, the interactions of metal ions with proteins (and amino acids) create colloidal organometallic complexes. Transport of the complex compounds away from the interface increases dissolution rates; thus, it accelerates the corrosion of metallic implants. The influence of protein adsorption on the corrosion behaviour of metallic biomaterials is presented in this review. Biocompatible metals that are favourably used as implants such as stainless steel, Co-Cr alloys, Ti alloys and biodegradable Mg and Fe alloys are specifically addressed. We have highlighted the adsorption phenomenon of protein on metallic implants, the interaction of proteins with metallic implants and the role of protein adsorption on implant biocorrosion behaviour as well as their wear resistance.

Biologically anchored chitosan/gelatin-SrHAP scaffold fabricated on Titanium against chronic osteomyelitis infection

The obstacles faced to treat chronic osteomyelitis infection clinically led to the search for an ideal biomaterial, resulted in combining two major aspects of bone tissue engineering namely surface modified metallic implant and polymer nanocomposite scaffold. In the present study Gelatin - Strontium incorporated Hydroxyapatite (SrHAP) forming HG scaffold, vancomycin loaded chitosan -gelatin polyelectrolyte complex incorporated gelatin-SrHAP, forming HV scaffolds (HV1-0.5wt% and HV2-1wt% vancomycin) were investigated. The HG, HV1 and HV2 scaffolds were successfully fabricated on Cp-Ti through anchoring by treatment with dopamine, which forms a bidentate co-ordination through NH bonding. Interconnected porous morphology of the scaffolds was confirmed, besides the globular Sr-HAP found in HV2 scaffold. The total amount of vancomycin encapsulation for HV1 and HV2 scaffolds were determined to be 47.55±1.6μg and 82.45±3.5μg respectively. Among the scaffolds studied HV2 scaffold were found to have a significant antibacterial activity for both MRSA and MSSA strains compared to Cp-Ti, HG and HV1 scaffolds. The HV2 scaffold also had significantly higher% of cell viability compared to Cp-Ti, HG and HV1 scaffolds. Furthermore, the presence of the drug vancomycin had no toxic effect on the cells, rather it aided in enhanced cell proliferation and spreading.

Approach to MR Imaging of the Elbow and Wrist: Technical Aspects and Innovation

Wrist and elbow MR imaging technology is advancing at a dramatic rate. Wrist and elbow MR imaging is performed at medium and higher field strengths with more specialized surface coils and more variable pulse sequences and postprocessing techniques. High field imaging and improved coils lead to an increased signal-to-noise ratio and increased variety of soft tissue contrast options. Three-dimensional imaging is improving in terms of usability and artifacts. Some of these advances have challenges in wrist and elbow imaging, such as postoperative patient imaging, cartilage mapping, and molecular imaging. This review considers technical advances in hardware and software and their clinical applications.

Controlled surface modification of Ti-40Nb implant alloy by electrochemically assisted inductively coupled RF plasma oxidation

Low temperature metal oxidation induced by plasma in the absence of liquid electrolytes can be useful for the surface preparation of orthopedic devices since residues from these may be harmful and need to be removed before implantation. In this study the oxidation of Ti-40Nb for biomedical application was achieved by employing an inductively coupled radio frequency oxygen plasma. The correlation between the growth mode of the surface oxide and the electric conductivity ratio of the plasma and the oxide phase were studied by varying the sample temperature, oxygen gas pressure and additional bias potential. The plasma treated samples were characterised by confocal laser microscopy, SEM, EBSD, XPS, TEM and ToF-SIMS. The surface energy was determined by contact angle measurements using the Owens-Wendt-Rabel-Kaelble method. Well adhering oxide layers consisting of TiO2 and Nb2O5 with thicknesses between 50 and 150 nm were obtained. Surface roughness values and microstructure indicate that the growth mode of the oxide can be well controlled by the sample temperature and oxygen gas pressure. At temperatures above 450°C a migration of Ti ions towards the surface controls the growth process. A bias potential higher than +50 V causes rough and defective surfaces with high surface energies.