Corrosion of stainless steel sternal wire after long-term implantation

Biocompatibility of titanium from the viewpoint of its surface

Among metals, Ti and majority of its alloys exhibit excellent biocompatibility or tissue compatibility. Although their high corrosion resistance is a factor in the biocompatibility of Ti and Ti alloys, it is clear that other factors exist. In this review, the corrosion resistance and passive film of Ti are compared to those of other metallic biomaterials, and their band gap energies, E_gs, are compared to discuss the role of E_g in the reactivity with living tissues. From the perspective of the material's surface, it is possible to explain the excellent biocompatibility of Ti by considering the following factors: Ti ions are immediately stabilized not to show toxicity if it is released to body fluids; good balance of positive and negative charges by the dissociation of surface hydroxyl groups on the passive film; low electrostatic force of the passive film inducing a natural adsorption of proteins maintaining their natural conformation; strong property as n-type semiconductor; lower band gap energy of the passive film on Ti generating optimal reactivity; and calcium phosphate formation is caused by this reactivity. The results suggest that due to the passive oxide film, the optimal balance between high corrosion resistance and appropriate reactivity of Ti is the predominate solution for the excellent biocompatibility of Ti.

A prospective study on long-term trace metal accumulation in hair: Is there any difference between minimally invasive repair of pectus excavatum and carinatum?

BACKGROUND

To date, there is no study about trace metal level increases in hair after stainless steel pectus bar implantation. We aimed to determine whether there was any significant increase in the levels of trace metals in the hair of children who underwent minimally invasive repair of pectus excavatum (MIRPE) and minimally invasive repair of pectus carinatum (MIRPC).

MATERIALS AND METHODS

In this prospective study, we collected the data of 223 patients who underwent MIRPE and MIRPC between November 2013 and August 2020. The levels of main components of the stainless steel pectus bar ("PES", Medxpert GmbH, Escbach, Germany) namely Cr, Fe, Ni, and Mo in hair were analyzed. The study involved two study groups: A group of patients who underwent MIRPE with a single bar (n = 112) and a group of patients who underwent MIRPC (n = 71). Both groups were analyzed in two different timelines: A group of consecutive patients prior to bar implantation and a group of the same patients who underwent bar removal after a mean time of 34.6 ± 5.1 months.

RESULTS

Statistically significant increases in all studied trace metal levels were observed in the single-bar MIRPE group. In the MIRPC group, the accumulation of studied trace metals was no statistically significant. The double-bar MIRPE group had higher trace metal increase rates compared to single-bar MIRPE group (p>0.05).

CONCLUSION

In our study; increases in iron, chrome, nickel and molybdenum levels were observed in both MIRPE and MIRPC patients by hair trace metal analysis; but these increases were statistically significant in only MIRPE group.

Microstructure/Mechanical Characterization of Plasma Nitrided Fine-Grain Austenitic Stainless Steels in Low Temperature

Fine-grained austenitic stainless steels (FGSS) were plasma nitrided below 700 K to describe their microstructure evolution during the nitrogen supersaturation process and to investigate the post-stressing effect on the microstructure and mechanical properties of nitrided FGSS. Normal- and fine-grained AISI304 plates were nitrided at 623 K and 673 K to investigate the grain size effect on the nitrogen supersaturation process as well as the microstructure evolution during the nitriding process. Fine-grained AISI316 (FGSS316) wires were nitrided at 623 K to demonstrate that their outer surfaces were uniformly nitrided to have the same two-phase, refined microstructure with high nitrogen solute content. This nitrided FGSS316 wire had a core structure where the original FGSS316 core matrix was bound by the nitrided FGSS316 layer. The nitrided wire had higher stiffness, ultimate strength, and elongation in the uniaxial tensile testing than its un-nitrided wires. The core microstructure was refined and homogenized by this applied loading together with an increase of nitrided layer hardness.

The effects of surface processing on in-vivo corrosion of Nitinol stents in a porcine model

A major limitation with current assessments of corrosion in metallic medical devices is the lack of correlation between in-vitro and in-vivo corrosion performance. Therefore, the objective of this study was to elucidate the relationship between pitting corrosion measured by breakdown potentials (E_b) in ASTM F2129 testing and corrosion resistance in-vivo. Four groups of Nitinol stents were manufactured using different processing methods to create unique surface properties. The stents were implanted into iliac arteries of minipigs for six months and explanted for corrosion analysis. Scanning electron microscopy and energy dispersive X-ray spectrometry analyses indicated that stents with a thick complex thermal oxide (420nm) and high corrosion resistance in-vitro (E_b=975±94mV) were free from detectable corrosion in-vivo and exhibited no changes in Ni/Ti ratio when compared to non-implanted controls. This result was also found in mechanically polished stents with a thin native oxide (4nm; E_b=767±226mV). In contrast, stents with a moderately thick thermal oxide (130nm) and low corrosion resistance in-vitro (E_b=111±63mV) possessed corrosion with associated surface microcracks in-vivo. In addition, Ni/Ti ratios in corroded regions were significantly lower compared to non-corroded adjacent areas on explanted stents. When stents were minimally processed (i.e. retained native tube oxide from the drawing process), a thick thermal oxide was present (399nm) with low in-vitro corrosion resistance (E_b=68±29mV) resulting in extensive in-vivo pitting. These findings demonstrate that functional corrosion testing combined with a detailed understanding of the surface characteristics of a Nitinol medical device can provide insight into in-vivo corrosion resistance.

STATEMENT OF SIGNIFICANCE

Nitinol is a commonly used material in the medical device industry. However, correlations between surface processing of nitinol and in-vivo corrosion has yet to be established. Elucidating the link between in-vivo corrosion and pre-clinical characterization can aid in improved prediction of clinical safety and performance of nitinol devices. We addressed this knowledge gap by fabricating nitinol stents to possess distinct surface properties and evaluating their corrosion susceptibility both in-vitro and after six months of in-vivo exposure. Relationships between stent processing, surface characterization, corrosion bench testing, and outcomes from explanted devices are discussed. These findings highlight the importance of surface characterization in nitinol devices and provide in-vitro pitting corrosion levels that can induce in-vivo corrosion in nitinol stents.

Intravascular foreign bodies: what the radiologist needs to know

The intravascular foreign bodies (IFBs) can originate from many sources both iatrogenic and noniatrogenic; as the frequency of endovascular therapies increases, the incidence of lost or embolized iatrogenic foreign bodies is also increasing. As IFB can cause significant complications such as thrombosis, pulmonary and peripheral embolism, etc. It is therefore necessary to remove them, and this may be accomplished through surgery or by means of percutaneous radiologic techniques. Percutaneous approach is widely perceived as the best way to retrieve IFB. We provide an overview of recent literature, clarifying what devices are being lost, what symptoms occur as a result, and how retrieval is being performed.

In vivo evaluation of Zr-based bulk metallic glass alloy intramedullary nails in rat femora

Zr-based bulk metallic glasses (BMG) show high corrosion resistance in vitro and higher strength and lower Young's modulus than crystalline alloys with the similar composition. This study aimed to perform an in vivo evaluation of Zr65Al7.5Ni10Cu17.5 BMG. Osteotomy of the femur was done in rats and stabilized with intramedullary nails made of Zr65Al7.5Ni10Cu17.5 BMG, Ti-6Al-4V alloy, or 316L stainless steel. Systemic and local effects of each type of nail were evaluated by measuring the levels of Cu and Ni in the blood and the surrounding soft tissue. Changes of the surface of each nail were examined by scanning electron microscopy (SEM). Healing of the osteotomy was evaluated by peripheral quantitative computed tomography and mechanical testing. No increase of Cu and Ni levels was recognized. Surface of the BMG showed no noticeable change, while Ti-6Al-4V alloy showed Ca and P deposition and 316L stainless steel showed surface irregularities and pitting by SEM observation. The stress strain index, maximum torque, torsional stiffness, and energy absorption values were larger for the BMG than those for Ti-6Al-4V alloy, although there was no significant difference. The Zr-based BMG can promote osteotomy healing as fast as Ti-6Al-4V alloy, with the possible advantage of the Zr-based BMG that bone bonding is less likely, allowing easier nail removal compared with Ti-6Al-4V alloy. The Zr-based BMG is promising for the use in osteosynthetic devices that are eventually removed.

Serum metal levels after minimally invasive repair of pectus excavatum

BACKGROUND

Metal implants may wear and corrode, resulting in systemic dissemination of metallic debris that is measurable in serum. Concern exists regarding adverse health effects related to implant-derived debris. Minimally invasive repair of pectus excavatum (MIRPE) is a popular technique in which a stainless steel substernal bar is implanted to achieve deformity correction. Serum metal levels have not previously been investigated after MIRPE.

METHODS

Serum chromium, molybdenum, and nickel levels were measured in this cross-sectional study of 11 children implanted with pectus bars after MIRPE. Samples were analyzed using high-resolution inductively coupled plasma mass spectrometry.

RESULTS

Median serum chromium and nickel values were elevated 3.3-fold (P = .0003) and 2.3-fold (P = .25), respectively, compared with age-matched controls. Serum chromium and nickel levels were abnormally elevated in 6 (55%) of 11 and 5 (45%) of 11, respectively. In patients whom postexplantation metal levels were measured, previously elevated levels were lowered. Serum chromium levels in children after MIRPE are comparable with adult cohorts with hip arthroplasty implants measured 1-year postoperatively. No acute metal toxicity was observed.

CONCLUSIONS

Abnormally elevated levels of serum metal levels are measurable in children implanted with pectus bars. These findings warrant further investigation to assess the biocompatibility of this surgical implant in children.

Atrial septum defect closure device in a beating heart, from the perspective of a researcher in artificial organs

Transcatheter closure of atrial septum defect (ASD) with a closure device is increasing, but the history of clinical use of this procedure is still short, and the efficacy and long-term safety remain unproved. The total number of closure devices implanted throughout the world has not been counted accurately. Therefore, the probability of complications occurring after implantation is uncertain. Device-related complications that occur suddenly late after implantation are life-threatening, and quite often necessitate emergency surgical intervention. In Japanese medical journals, authors reporting closure devices have mentioned no complications and problems in their facilities. Detailed studies of device-related complications and device removal have not been reported in Japan. In fact, this literature search found an unexpectedly large number of reports of various adverse events from many overseas countries. When follow-up duration is short and the number of patients is small, the incidence of complications cannot be determined. Rare complications may emerge in a large series with a long observation period. Consequently, the actual number of incidents related to ASD closure devices is possibly several times higher than the number reported. Guidelines for long-term patient management for patients with an implanted closure device are necessary and post-marketing surveillance is appropriate. Development of a national database, a worldwide registration system, and continuous information disclosure will improve the quality of treatment. The devices currently available are not ideal in view of reports of late complications requiring urgent surgery and the need for life-long follow-up. An ideal device should be free from complications during life, and reliability is indispensable.

Failure analysis of the fractured wires in sternal perichronal loops

We report failure analysis of sternal wires in two cases in which a perichronal fixation technique was used to close the sternotomy. Various characteristics of the retrieved wires were compared to those of unused wires of the same grade and same manufacturer and with surgical wire specifications. In both cases, wire fracture was un-branched and transgranular and proceeded by a high cycle fatigue process, apparently in the absence of corrosion. However, stress anlysis indicates that the effective stress produced during strong coughing is lower than the yield strength. Our findings suggest that in order to reduce the risk for sternal dehiscence, the diameter of the wire used should be increased.

Recovery of motor deficit, cerebellar serotonin and lipid peroxidation levels in the cortex of injured rats

The sensorimotor cortex and the cerebellum are interconnected by the corticopontocerebellar (CPC) pathway and by neuronal groups such as the serotonergic system. Our aims were to determine the levels of cerebellar serotonin (5-HT) and lipid peroxidation (LP) after cortical iron injection and to analyze the motor function produced by the injury. Rats were divided into the following three groups: control, injured and recovering. Motor function was evaluated using the beam-walking test as an assessment of overall locomotor function and the footprint test as an assessment of gait. We also determined the levels of 5-HT and LP two and twenty days post-lesion. We found an increase in cerebellar 5-HT and a concomitant increase in LP in the pons and cerebellum of injured rats, which correlated with their motor deficits. Recovering rats showed normal 5-HT and LP levels. The increase of 5-HT in injured rats could be a result of serotonergic axonal injury after cortical iron injection. The LP and motor deficits could be due to impairments in neuronal connectivity affecting the corticospinal and CPC tracts and dysmetric stride could be indicative of an ataxic gait that involves the cerebellum.

Intravascular foreign bodies: danger of unretrieved fragmented medical devices

A warning on the danger of unretrieved device fragments and recommendations to mitigate the danger were issued by the Food and Drug Administration in January 2008. The causes of intravascular foreign bodies are classified into three main categories: improper manipulation and usage, device defects, and others, such as patient and anatomical factors. Device failure after long-term use is rarely predicted at the time of approval, since device abnormality is rarely experienced in animal studies and clinical trials conducted during development of the device. Stent fracture due to metal fatigue is one example. Complex complications could occur from simultaneous use of two or more devices with diverse characteristics. The success rate of percutaneous retrieval of intravascular foreign bodies has improved with the advances in commercially available devices. However, the procedure is not always successful and sometimes surgical removal becomes necessary. Appropriate device selection and acquisition of experience in using the device are important. When an intravascular foreign body cannot be retrieved, the risk of complication could be high. Magnetic resonance imaging examination sometimes causes adverse events, including burns due to the heat generated by metal movement. Such information should be correctly recorded. Furthermore, it is necessary to provide patients with adequate information about the characteristics of implanted devices and unretrieved fragments. We reviewed the literature on unretrieved medical device fragments and include articles that describe the Japanese experience.

Materials for metallic stents

Stents are expandable tubes of metallic mesh that were developed to address the negative sequelae of balloon angioplasty and are currently used in cardiovascular medicine. In this review, the use of particular metals to make stents is discussed from the viewpoint of materials engineering. The properties and characteristics of metals used for stents, such as stainless steels, nickel-titanium alloys, tantalum, cobalt-chromium alloys, and magnesium alloys, are explained. In addition, problems and disadvantages related to metallic stents and their possible solutions are given.

Corrosion of pure titanium sternal wire

Titanium and its alloys are considered reliable materials commonly used in heart surgeries. A patient had severe inflammation at the median sternotomy wound develop after open heart surgery. Sternal wires were removed and were found to be seriously corroded on most of the surface. Energy dispersive spectroscopy identified titanium as the only elemental component of the explanted wire with grade 2 purity, and the polarization curve showed satisfactory corrosion resistance similar to commercial pure titanium. Prolonged inflammation might have caused extensive corrosion of titanium in the present case.