The effect of supercritical carbon dioxide sterilization on the anisotropy of bovine cortical bone.

Bone allografts are used to replace bone that has been removed or to augment bone tissue in a number of clinical scenarios. In order to minimize the risk of infection and immune response, the bone is delipidated and terminally sterilized prior to implantation. The optimal method for bone graft sterilization has been the topic of considerable research and debate. Recently, supercritical carbon dioxide (SCCO(2)) treatments have been shown to terminally sterilize bone against a range of bacteria and viruses. This study aimed to evaluate the effect of these SCCO(2) treatments on the anisotropic mechanical properties of cortical bone. Adult bovine cortical cubes were prepared and treated using SCCO(2) and a range of common processing additives (ethanol, peracetic acid and hydrogen peroxide). The bone was mechanically tested in uniaxial compression in the axial, radial and tangential orientations. Ultimate stress, strain, elastic modulus, energy and stiffness were evaluated. This study found that SCCO(2) treatment without additive did not alter the ultimate stress, stiffness or energy to failure depreciably in any orientation. The addition of sterilants peracetic acid and hydrogen peroxide also preserved mechanical function, with no deleterious effect on stress or stiffness. This study highlights the expediency of SCCO(2) treatment for bone allograft processing as terminal sterilization can be achieved while maintaining the intrinsic mechanical properties of the graft.

Corrosion resistance, surface evaluation, and geometric design comparison of five self-expanding nitinol stents used in clinical practice.

PURPOSE: To investigate the corrosion resistance properties of 5 commercially available nitinol stents used to treat peripheral artery disease and compare their surface quality, elemental composition, and geometrical design. METHODS: Samples of 5 different designs of nitinol peripheral stents [LifeStent (n=4), Philon (n=6), Epic (n=6), S.M.A.R.T. Control (n=7), and Complete SE (n=7)] were examined using stereomicroscopy, environmental scanning electron microscopy, and x-ray photoelectron spectroscopy. Corrosion resistance testing was performed in accordance with ASTM International Standard F2129-08. RESULTS: Thirteen (43%) of 30 stents corroded during this experiment. Stent fracture was observed in 12 (92%) of these corroded stents. Mean breakdown potentials ranged from 517 to 835 mV (vs. Ag/AgCl) for the Philon, Complete SE, S.M.A.R.T. Control, Epic, and LifeStent models from lowest to highest. A statistically significant difference in breakdown potential was observed between the LifeStent vs. Philon stents (835 vs. 517 mV, p=0.01) and Epic vs. Philon stents (833 vs. 517 mV, p=0.03). Stents with lower breakdown potential and relative breakdown potentials were associated with a higher fracture frequency (Spearman correlation coefficient -0.44, p=0.015 and -0.869, p<0.01, respectively). CONCLUSION: In this in vitro study, corrosion led independently to stent fracture. There is a significant association between lower mean breakdown/relative breakdown potentials and stent fracture.

The effect of sterilization on the mechanical properties of intact rabbit humeri in three-point bending, four-point bending and torsion.

Load bearing bone allografts are used to replace the mechanical function of bone that has been removed or to augment bone that has been damaged in trauma. In order to minimize the risk of infection and immune response, the bone is delipidated and terminally sterilized prior to implantation. The optimal method for bone graft sterilization has been the topic of considerable research. Recently, supercritical carbon dioxide (SCCO(2)) treatments have been shown to terminally sterilize bone against a range of bacteria and viruses. This study aimed to evaluate the effect of SCCO(2) treatment compared with two doses of gamma irradiation, on the mechanical properties of whole bone. Paired rabbit humeri were dissected and randomly assigned into either SCCO(2) control, SCCO(2) additive or gamma irradiation at 10 or 25 kGy treatment groups. The bones were mechanically tested in three-point and four-point bending and torsion, with the lefts acting as controls for the treated rights. Maximum load, energy to failure and stiffness were evaluated. This study found that SCCO(2) treatment with or without additive did not alter maximum load, energy to failure or stiffness significantly under any loading modality. Gamma irradiation had a deleterious dose dependant effect, with statistically significant decreases in all mechanical tests at 25 kGy; while at 10 kGy there were reductions in all loading profiles, though only reaching statistical significance in torsion. This study highlights the expediency of SCCO(2) treatment for bone allograft processing as terminal sterilization can be achieved while maintaining the intrinsic mechanical properties of the graft.

Isobutane dehydrogenation over high-performanced sulfide V-K/γ-Al2O3 catalyst: Modulation of vanadium species and intrinsic effect of potassium.

Compared with industrial used Pt- and Cr-based catalyst in dehydrogenation (DH) of light alkanes, the sulfide V-K/γ-Al2O3 catalyst reported in this study shows lower cost and toxicity, and significant DH performance. The yield to isobutene reached as high as 52.9%, which is among the highest reported to date. We attribute such high isobutene yield to the precise modulation of polymerization degree for vanadium species via doping of potassium and indicating that the synergy between vanadium species and acid sites is critical to enhance the DH performance. Our previous work showed sulfidation promoted the increase of DH performance for vanadium-based catalyst, and we go further in this study to explore the correlation between increased range of DH performance and the added potassium. The different loaded potassium leads to variation in sulfidation degree, affecting the properties of vanadium species and acid properties consequently. The potassium was distributed uniformly on surface of the sulfide vanadium-based catalyst and was predominantly bonded with the vanadium species rather than with the γ-Al2O3 support. With increasing the potassium amount from 0 to 3 wt%, the acid amount kept decreasing, and some specific strong acid sites appeared once adequate sulfur was introduced in the V-K/γ-Al2O3 catalyst. The characterization and DFT results both revealed that the doped potassium contributes to regulating the vanadium species in the oligomeric state. The synergy between vanadium species and acid properties was regulated by the added potassium simultaneously, and thus the DH performance was enhanced. This study provides promising strategy for preparation of environment-friendly model industrial DH catalyst.

Isomerization of n-hexane over silica-supported heteropoly acids promoted by the reduced Ce-Ni oxides.

The structure and catalytic properties of silica-supported heteropoly acids promoted by the reduced Ce-Ni oxides are first studied by using chemical analysis XRD, FT-Raman, XPS, EPR, TG, surface area measurements, and microreactor test. It is found that silica-supported heteropoly acids have isomerization activity, but are very easy to deactivate by coke deposition. With the promotion of the reduced Ce-Ni oxides, however, the better activity and the higher selectivity to isomers could be obtained, suggesting that the reduced Ce-Ni oxides really have hydrogenating/dehydrogenating functions. Moreover, it is found that the presence of the reduced Ce-Ni oxides is not only beneficial for eliminating the coke deposition, but also effective for maintaining the structure of silica-supported heteropoly acids during reaction. The effect of the composition of the mechanical mixtures of silica-supported heteropoly acids and the Ce-Ni oxides on the catalytic properties has been explored.

The effect of sterilization on the dynamic mechanical properties of paired rabbit cortical bone.

The optimal sterilization method for load bearing allografts remains a clinical concern. Recently, supercritical carbon dioxide (SCCO2) treatments have been shown to be capable of terminally sterilizing a range of bacteria and viruses, while preserving the static mechanical properties of cortical bone. This study evaluated the effect of SCCO2 treatment compared with two doses of gamma irradiation, on clinically relevant dynamic mechanical properties of cortical bone. Quasi-static testing was also performed to compare the impairment of treatment. Whole paired adult rabbit humeri were dissected and randomly assigned into either SCCO2 Control, SCCO2 Additive or gamma irradiation at 10 or 25kGy treatment groups. The bones were treated and mechanically tested in three-point bending, with the lefts acting as controls for the treated rights. Maximum load, energy to failure and stiffness were evaluated from static tests. The number of cycles to failure was determined for fatigue at 6-60% of the ultimate load. This study found that SCCO2 treatment with or without additive did not alter static or dynamic mechanical properties. Gamma irradiation had a deleterious dose dependent effect, with statistically significant (p<0.05) reductions in all static mechanical parameters at 25kGy. This effect was increased in fatigue with statistically significant decreases in both the 10 and 25kGy dose groups. This study highlights the expediency of SCCO2 treatment for load bearing bone allograft processing as terminal sterilization can be achieved while maintaining both the quasi-static and dynamic mechanical properties of the graft.