Surface integrity modification of CoCrMo alloy by deep rolling in combination with sub-zero cooling as potential implant application.

Alloys made of CoCrMo are well established as implants materials since decades in orthopedic surgery. The good mechanical properties, biocompatibility and especially the corrosion resistance are important rationales for the use of these alloys. Nevertheless, retrieved implants from revision surgery showed the occurrence of abrasion and corrosion. The wear mechanisms and the occurring corrosion processes might be reduced with a functionalization of the surface. The hexagonal phase of the cobalt chromium matrix plays an important role in the surface functionalization. It can be specifically transformed and set during the manufacturing process. One possibility for the induction of the transformation is the use of a deep rolling process in combination with a novel "sub-zero" cooling strategy during machining. The influence of force and temperature during the deep rolling process on the formation of the hexagonal Co-phase is examined in this study. The results from the targeted setting of the hexagonal Co-phase in the subsurface are shown. For this purpose, EBSD studies have been carried out to detect and quantify the proportion of Co-hex phase in the subsurface of the modified alloys. To analyze the mechanical properties, we measured the residual stress and hardness in the near surface layer under conditions close to the application. Furthermore, we performed biological tests to show a potential influence of the modification on the biocompatibility when using the sub-zero cooling approach. We observed no negative effect on the osteoblastic cell line which attached similarly to all tested surfaces. The investigations provide first insights into the potential use of "sub-zero" cooling in modifying orthopedic implant materials, but also the respective limits with regard to the surface functionalization. Deep rolling in combination with an innovative cooling strategy has a great potential to improve the mechanical properties of CoCr28Mo6 wrought alloy, by subsurface hardening and phase transformation.

Microstructure-dependent crevice corrosion damage of implant materials CoCr28Mo6, TiAl6V4 and REX 734 under severe inflammatory conditions.

Fretting corrosion is associated with increased risk of premature implant failure. In this complex in vivo corrosion system, the contribution of static crevice corrosion of the joined metal alloys is still unknown. The aim of this study was to develop a methodology for testing crevice corrosion behavior that simulates the physiological conditions of modular taper junctions and to identify critical factors on corrosion susceptibility. Samples of medical grade CoCr28Mo6 cast and wrought alloy, TiAl6V4 wrought alloy and REX 734 stainless steel were prepared metallographically and the microstructure was investigated using scanning electron microscopy (SEM). Crevice formers that mimic typical geometries of taper junctions were developed. Crevice corrosion immersion tests were performed in different physiological fluids (bovine serum or phosphate buffered saline with additives of 30 mM H2 O2 at pH = 1) for 4 weeks at 37°C. SEM with energy dispersive X-ray spectroscopy as well as focused ion beam were used to characterize the surface morphology, investigate present damages and identify the chemical composition of residues. Macroscopic inspection showed increased crevice corrosion susceptibility of TiAl6V4 and REX 734 under severe simulated inflammatory conditions. CoCr28Mo6 cast alloy exhibited degraded areas next to Cr- and Mo-rich precipitations that were located within the opposed crevices. The results indicate that aggressive electrolyte composition and crevice heights of 50-500 µm are critical influencing factors on crevice corrosion of biomedical alloys. Furthermore, manufacturing-related microstructure of common implant alloys determines the deterioration of corrosion resistance. The developed method should be used to enhance the corrosion resistance of common implant biomaterials by an adapted microstructure.

Pretreatment with interferon-alpha2a modulates perioperative immunodysfunction in patients with renal cell carcinoma.

INTRODUCTION: Complex perioperative immunodysfunction occurs in patients with renal cell carcinoma undergoing surgery. Here, we report on the effect of preoperative treatment with interferon-alpha2a (IFN-alpha2a). MATERIALS AND METHODS: 30 patients with a renal tumour received preoperative IFN-alpha2a for 6 days beginning 1 week before nephrectomy, 30 did not. Parameters of cellular and humoral immunity were measured in venous blood at various intervals using flow cytometry and ELISA. Endpoints included effects on immune parameters, toxicity, and survival. RESULTS: Toxicity was grade 1 in 52%, 2 in 30%, and 3 in 4%. During IFN-alpha2a administration, leukocytes, monocytes, granulocytes, B-cell marker CD19, activation markers, CD4+CD25+ regulatory T-cells, and vascular endothelial growth factor (VEGF) dropped significantly, but no difference was observed in T-cell and natural killer (NK)-cell markers, and IL-10. Postoperatively, T-cell and activation markers decreased in both groups, but CD4, CD28, IL-6, IL-10, and HLA-DR alterations were significantly less accentuated in patients who had been treated with IFN-alpha2a. After a median follow-up of 23 months, survival did not differ between the groups (p = 0.54). CONCLUSIONS: Perioperative immunodysfunction can be modulated by preoperative administration of IFN- alpha2a. IFN-alpha2a decreased the level of VEGF and CD4+CD25+ regulatory T-cells implicating a potential combination with tyrosine kinase inhibitors and vaccines.