Surface Roughness of CoCr and ZrO2 Femoral Heads with Metal Transfer: A Retrieval and Wear Simulator Study

Metal transfer to femoral heads may result from impingement against the metallic acetabular shell following subluxation/dislocation, or when metallic debris enters the articulation zone. Such transfers roughen the head surface, increasing polyethylene wear in total hip replacements. Presently, we examined the surface roughness of retrieved femoral heads with metallic transfer. Profilometry revealed roughness averages in regions of metal transfer averaging 0.380 μm for CoCr and 0.294 μm for ZrO2 which were one order of magnitude higher than those from non-implanted controls. Scanning electron microscopy (SEM) revealed adherent transfers on these retrievals, with titanium presence confirmed by electron dispersive spectroscopy. Due to the concern for increased wear, metal transfer was induced on non-implanted heads, which were then articulated against flat polyethylene discs in multidirectional sliding wear tests. Increased polyethylene wear was associated with these specimens as compared to unaltered controls. SEM imaging provided visual evidence that the transfers remained adherent following the wear tests. Pre- and post-test roughness averages exceeded 1 μm for both the CoCr and ZrO2 heads. Overall, these results suggest that metal transfer increases the surface roughness of CoCr and ZrO2 femoral heads and that the transfers may remain adherent following articulation against polyethylene, leading to increased polyethylene wear

Impact of Optimized Breastfeeding on the Costs of Necrotizing Enterocolitis in Extremely Low Birthweight Infants

To estimate risk of NEC for ELBW infants as a function of preterm formula and maternal milk (MM) intake and calculate the impact of suboptimal feeding on NEC incidence and costs

In-vitro biomechanical studies of endovascular devices

Preliminary studies have revealed that stainless steel (SS) and nickel titanium (NiTi) stents undergo corrosion in vivo, with significant release of metallic ions into surrounding tissues. It is believed that high concentrations of metal ions from both SS and NiTi stents are toxic to vascular smooth muscle cells and stimulate both inflammatory and fibrotic reactions leading to neointimal formation and a predisposition to device failure. To separate the mechanical effects from the local environmental effects on the stent surface, invitro mechanical studies were performed on various combinations of stents under low and high curvature and in overlapping positions to compare the results of fretting, pitting and gouging with the explanted stents

Biocorrosion and biomechanical analysis of explant devices

Introduction: Preliminary studies have revealed that stainless steel (SS) and nickel titanium (NiTi) stents undergo corrosion in vivo, with significant release of metallic ions into surrounding tissues. It is believed that high concentrations of metal ions from both SS and NiTi stents are toxic to vascular smooth muscle cells and stimulate both inflammatory and fibrotic reactions leading to neointimal formation and a predisposition to device failure. To separate the mechanical effects from the local environmental effects on the stent surface, in-vitro mechanical studies were performed on various combinations of stents under low and high curvature and in overlapping positions to compare the results of fretting, pitting and gouging with the explanted stents. Methods: Accelerated biomechanical studies were performed on SS, NiTi and Cobalt-Chromium (CoCr) stents using Bose®ElectroForce®9110 Stent/Graft Test (Bose Corporation, Bethel, WA) mechanical testing instrument. The stents were deployed in latex tubing mock arteries and the system was exposed to flow of saline representative of coronary flow under physiologic wall motion 5-10% and was programmed to perform several million of cycles to simulate several years of operation. The tested stents underwent surface evaluation by Scanning Electron Microscope (SEM) and optical microscope Keyence to identify locations of pitting, fretting and cracking phenomena due to interfacial conditions. Results: Wear features were observed on the stents surface in both straight and low curvature modes especially in the overlapping cases where we observed localized fret features in the areas where there is significant crossing of the wire from both stents. Fracture was also observed in addition to fretting features on both the NiTi and CoCr stents placed in a curved latex tube at 40% overlap under 104 million cycles. Fracture surfaces show a fatigue mechanism. Discussion and conclusion: In some occasions the fretting features from cadaver specimens were similar to the fretting features from the mechanical studies. High curvature and the factor of stent overlap increased the corroded regions and the degree of corrosion. This will provide insights into the mechanisms of stent corrosion and vascular responses and indicate possible cause-effect relationships for biological reactions leading to restenosis

In-vitro biomechanical studies of endovascular devices

Preliminary studies have revealed that stainless steel (SS) and nickel titanium (NiTi) stents undergo corrosion in vivo, with significant release of metallic ions into surrounding tissues. It is believed that high concentrations of metal ions from both SS and NiTi stents are toxic to vascular smooth muscle cells and stimulate both inflammatory and fibrotic reactions leading to neointimal formation and a predisposition to device failure. To separate the mechanical effects from the local environmental effects on the stent surface, invitro mechanical studies were performed on various combinations of stents under low and high curvature and in overlapping positions to compare the results of fretting, pitting and gouging with the explanted stents

Biocorrosion and biomechanical analysis of explant devices

Introduction: Preliminary studies have revealed that stainless steel (SS) and nickel titanium (NiTi) stents undergo corrosion in vivo, with significant release of metallic ions into surrounding tissues. It is believed that high concentrations of metal ions from both SS and NiTi stents are toxic to vascular smooth muscle cells and stimulate both inflammatory and fibrotic reactions leading to neointimal formation and a predisposition to device failure. To separate the mechanical effects from the local environmental effects on the stent surface, in-vitro mechanical studies were performed on various combinations of stents under low and high curvature and in overlapping positions to compare the results of fretting, pitting and gouging with the explanted stents. Methods: Accelerated biomechanical studies were performed on SS, NiTi and Cobalt-Chromium (CoCr) stents using Bose®ElectroForce®9110 Stent/Graft Test (Bose Corporation, Bethel, WA) mechanical testing instrument. The stents were deployed in latex tubing mock arteries and the system was exposed to flow of saline representative of coronary flow under physiologic wall motion 5-10% and was programmed to perform several million of cycles to simulate several years of operation. The tested stents underwent surface evaluation by Scanning Electron Microscope (SEM) and optical microscope Keyence to identify locations of pitting, fretting and cracking phenomena due to interfacial conditions. Results: Wear features were observed on the stents surface in both straight and low curvature modes especially in the overlapping cases where we observed localized fret features in the areas where there is significant crossing of the wire from both stents. Fracture was also observed in addition to fretting features on both the NiTi and CoCr stents placed in a curved latex tube at 40% overlap under 104 million cycles. Fracture surfaces show a fatigue mechanism. Discussion and conclusion: In some occasions the fretting features from cadaver specimens were similar to the fretting features from the mechanical studies. High curvature and the factor of stent overlap increased the corroded regions and the degree of corrosion. This will provide insights into the mechanisms of stent corrosion and vascular responses and indicate possible cause-effect relationships for biological reactions leading to restenosis

Biocorrosion and biomechanical analysis of vascular stents

Despite advances in endovascular stent design, stent structural integrity and in-stent restenosis remains a significant clinical problem worldwide. The role of stent corrosion and metallic ion release has not been thoroughly studied and little attention has been given to the interaction of stent materials with the surrounding vessel wall and the mechanical forces involved after implantation. Our recent studies on Stainless Steel (SS), Cobalt-Chromium (CoCr) and Nickel-Titanium (NiTi) stents obtained from a tissue retrieval resource from cadavers with accompanying clinical histories, have revealed that these stents undergo corrosion in vivo, with significant release of metallic ions into surrounding tissues [1]. It is believed that high concentrations of metal ions from stents are toxic to vascular smooth muscle cells [2] and stimulate both inflammatory and fibrotic reactions leading to neointimal formation and a predisposition to device failure [3]. When this is combined with altered biomechanics of flow and motion, it creates a favourable environment for the development of restenosis. To separate the mechanical effects from the local environmental effects on the stent surface, we performed in-vitro mechanical studies on various combinations of stents under low and high curvature and in overlapping positions to compare the results of fretting, pitting and gouging with the explanted stents