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In vivo evaluation of a high-strength, high-ductility stainless steel for use in surgical implants.

A high-strength, high-ductility, austenitic stainless steel has been evaluated for use in surgical implants by performing in vivo tests in rats, rabbits, dogs, and rhesus monkeys. This stainless steel, a TRIP (Transformation Induced Plasticity) steel containing about 4% Mo, was compared with two alloys in current clinical use: Type 316L stainless steel and cast Vitallium. Compared with the other two alloys, cast Vitallium generally had higher resistance to corrosion and superior biocompatibility in all animals. The tests in rats and dogs indicated that the corrosion resistances of the TRIP steel and the Type 316L stainless steel were similar and that the tissue reactions caused by these alloys were also similar. However, in rhesus monkeys, the TRIP steel was shown to be susceptible to stress-corrosion cracking and much more susceptible to crevice corrosion than Type 316L stainless steel. Limited tests in rabbits supported the observation that the TRIP steel is susceptible to stress-corrosion cracking. These inconsistencies in the in vivo tests underline the need for a reevaluation of the popular test techniques and of the animals commonly chosen for assessing the suitability of candidate implant materials. The "worst case" results from the rhesus monkey tests were entirely consistent with previous results obtained from in vitro studies. However, further work must be performed before the behavior of metals in humans, rhesus monkeys, or any other animal, can be predicted with confidence from an in vitro test program.

Animals

Tissue reaction to middle ear prostheses: in vivo observation (rabbit ear lobe) of polyethylene tube, stainless steel wire and absorbable gelatin sponge used in middle ear surgery.

Over the past ten years, polyethylene tube, stainless steel wire and absorbable gelatin sponge have come to be used in middle ear surgery. A modified Williams' steel chamber with a transparent central area was embedded in a rabbit ear lobe surgically, and cross-sectioned polyethylene tube, stainless steel wire or absorbable gelatin sponge were inserted respectively. The in vivo tissue reaction to each of these installed materials was observed daily microscopically. Finally, in the case of both the cross-sectioned polyethylene tube and the stainless steel wire, the chambers were fixed with 10% formalin solution and the contents stained for histological study. The results were as follows: Absorbable gelatin sponge was absorbed completely by phagocytosis in 62 days. Polyethylene tube was encapsulated by a layer of fibroblasts by day 110 in one case and by day 140 in another case; these findings were confirmed histologically on day 110 and 281. Almost all the surface of the stainless steel wire was encapsulated by a layer consisting of giant cells, on which a dense fibrous layer was superimposed by day 82. It is concluded that polyethylene tube, stainless steel wire, and absorbable gelatin sponge should be well tolerated in middle ear surgery.

Absorption

Leaching of nickel from stainless steel consumer commodities.

Sweat and household detergents were shown to have the capacity to release nickel from stainless steel. This finding substantiates the thesis that the American-style stainless steel kitchen and other stainless steel commodities can be sources of skin contact allergy with nickel. Furthermore, a negative spot test (DMG) does not reflect the "safety" of a nickel alloy.

Cooking and Eating Utensils

A specimen carrier, storage disc system for scanning electron microscopy (SEM): evaluation of stainless steel as a substratum for cell culture in vitro.

A method of sample preparation for scanning electron microscopy (SEM) studies based on the use of stainless steel discs as a cell culture substratum is described in detail. A number of different cell lines were grown on stainless steel, and the growth patterns and biocompatibility of cells cultured on stainless steel were compared to identical cells cultured on aluminium, glass and plastic substrata. Stainless steel provides cells with an excellent growth surface which allows these cells to retain their normal growth characteristics and appearance. The non-toxic stainless steel discs can be manipulated through any combination of fixatives and organic solvents. The discs have been incorporated into a versatile system of sample preparation for SEM.

Alloys

Mutagenicity of fume particles from metal arc welding on stainless steel in the Salmonella/microsome test.

Mutagenic activity of fume particles produced by metal arc welding on stainless steel (ss) is demonstrated by using the Salmonella/microsome mutagenicity test described by Ames et al., with strain TA100 (base-pair substitution) and TA98 (frame-shift reversion). Results of a representative but limited selection of processes and materials show that mutagenic activity is a function of process and process parameters. Welding on stainless steel produces particles that are mutagenic, whereas welding on mild steel (ms) produces particles that are not. Manual metal arc (MMA) welding on stainless steel produces particles of higher mutagenic activity than does metal inert gas (MIG) welding, and fume particles produced by MIG welding under short-arc transfer. Further studies of welding fumes (both particles and gases) must be performed to determine process parameters of significance for the mutagenic activity.

Gases

In vitro corrosion of Ti-6Al-4V and type 316L stainless steel when galvanically coupled with carbon.

In vitro corrosion experiments were conducted employing potentiostatic polarization techniques, a saline environment and candidate biomaterial alloy/carbon combinations. Corrosion currents and potentials of carbon/metal couples were predicted by mixed-potential theory utilizing the polarization curves generated. The alloys examined were annealed ELI grade Ti-6A1-4V and cold-worked 316L stainless steel while the types of carbon examined were LTI pyrolytic carbon and vapor-deposited carbon. It was determined that galvanic couples of carbon to cold-worked 316L stainless steel with carbon/metal area ratios of 10:1 to 100:1 produced coupled corrosion potentials in the range of the observed breakdown potential of the stainless steel. It was therefore predicted that localized corrosion in the form of pitting could occur on the cold-worked stainless steel when coupled to carbon with area ratios of 10:1 or greater. The titanium alloy did not exhibit a breakdown potential up to a potential of 1.2 V. Therefore, accelerated corrosion was not predicted for the titanium alloy to carbon galvanic couples under these experimental conditions. Direct carbon/alloy coupling experiments were conducted to verify the corrosion currents and potentials predicted from mixed-potential theory and polarization curve analysis. The experimental and theoretical values showed good agreement.

Alloys

[An autoclavable stainless steel isolator for small scale gnotobiotic experiments (author's transl)].

A lightweight stainless steel autoclavable pentagon isolator was designed for experiments using gnotobiotic mice. The chamber, 400 x 450 x 350 mm, has an entry port 200 mm in diameter at the back and a window at the ceiling. The globes and two filters were equipped at the front and each side, respectively. An inner stainless steel cap of the entry lock was sealed by a seamless silicone band. It was possible to ventilate this isolator by either free-flow or blower operation. After autoclaving the isolators 10 to 16 times for a year, none of them was repaired. Five mice can be kept in this isolator for about 1 month without supply of diet, water and wood shaving after the first setting.

Animals

"Mini" Gianturco stainless steel coils for transcatheter vascular occlusion.

Small stainless steel coils have been developed for transcatheter vascular occlusion procedures. The coils can be passed through a 5-French polyethylene catheter, extending the clinical applications of coil occlusion procedures for small and/or tortuous vessels. Two cases describing the use of these coils are reported.

Adult

Stainless steel markers for aorta--saphenous vein anastomosis.

A stainless steel marker for tagging the proximal aorta--saphenous vein anastomosis in a bypass operation has been devised and utilized in more than 600 patients over the past 3 years. This marker has been found superior to other methods used for marking vein grafts in that it encircles the anastomosis, providing accurate marking, and can be attached after both anastomoses are complete.

Angiography

Evaluation of a 5-mum stainless steel filter as an intravenous inline filter or prefilter.

The suitability of a 5-mum stainless steel filter as an inline filter or a protective prefilter during simulated i.v. therapy was evaluated using flow rate measurements of two routinely used i.v. fluids and parenteral nutrition fluid. As an inline i.v. filter, the 5-mum stainless steel filter was capable of maintaining suitable flow rates. The addition of antibiotic additives decreased the flow rates slightly but not below the range required for i.v. therapy. Flow rate profiles, however, when compared to a 0.45-mum membrane filter suggest that antibiotic additives contain high numbers of particles in the less than 5-mum range. Consequently many of the particles, especially those in the less than 3-mum range will pass the 5-mum filter. As a protective prefilter, the 5-mum filter device in combination with a 0.45-mum membrane filter provided more uniform flow rates over longer periods of time when additives were employed. Using the aspiration device as a prefilter for adding antibiotics to the infusion fluid resulted in improved flow rates through a 0.45-mum membrane filter for lactated Ringer's containing cephalothin sodium, while for solutions containing ampicillin or oxytetracycline, prefilteration did not change the flow rate profiles.

Ampicillin

Nickel in food: the role of stainless-steel utensils.

Nickel may be found in prepared foods (tinned foods) at markedly higher concentrations than the safe threshold laid down for hypersensitive patients. Some foodstuffs cooked in stainless-steel utensils attack the metal and thus contain much more nickel than when enamel or aluminum saucepans are used. Among the natural organic acids which may be responsible for dissolving stainless-steel, oxalic acid is the most active at equivalent concentrations.

Cooking

The effect of tooth preparation on the retention of stainless steel crowns.

Preparations maintaining the greatest amount of buccal and lingual tooth structure were the most retentive. Cement significantly increased the retention capacity of all preparations. Mechanical retention did not contribute significantly to the separation-resistance of the stainless steel crown. Factors other than retention may be of greater importance to the clinical success of stainless steel crowns.

Cementation

Stainless steel fiber reinforcement of polymethylmethacrylate.

The reinforcement of polymethylmethacrylate with small caliber stainless steel fibers can significantly improve its mechanical properties. While maintaining all the advantages of unreinforced polymethylmethacrylate, it can be demonstrated that compression, flexural tension, tension and impact parameters of cement reinforced with one quarter inch long steel fibers are dramatically enhanced. Careful cement preparation further improves these properties. The polymerizing composite is easily prepared within the operating room and the exothermic reaction is not as severe as the unreinforced material. Furthermore, the metal fiber reinforcement provides the potential for core heating, the capability of depolymerization to facilitate cement removal, and invites research on new prosthetic stem designs.

Acrylic Resins

Corrosion of stainless steel surgical implants.

In the light of examination of a series of failed stainless steel implants, the paper suggests that much material currently used for orthopaedic prostheses is not of a sufficiently high metallurgical quality for its purpose.

Corrosion

Mutagenicity of fume particles from stainless steel welding.

Welding fume particles collected from different welding procedures were tested for mutagenicity in Escherichia coli, with the inhibition zone in pol A- as compared to pol A+, and in Salmonella typhimurium, TA 100 strain. While no mutagenicity was found with mild steel welding, a mutagenic effect was established with samples from stainless steel welding. This mutagenicity was particularly associated with manual metal arc (MMA) welding, and less so with metal inert-gas welding. A decrease in or an elimination of the effect occurred with a liver microsomal metabolizing system (S-9 mix). The MMA samples produced the strongest mutagenic effect. More-detailed investigations on these samples showed that the mutagenic agent(s) is water soluble. An increased mutagenicity, which also revealed the induction of frame shift mutations, was found with TA 98. The same welding fume sample was used for a mutagenicity test (resistance to 6-thioguanine) with V 79 hamster cells. Because of the high toxicity of these welding fume particles on the cells, only very low concentrations could be tested, but the increase of mutations, when compared to the negative control, was significant. It is suggested that hexavalent chromium may be involved in the mutagenic effect of the welding fumes.

Air Pollutants

Measurement of chromium VI and chromium III in stainless steel welding fumes with electrom spectroscopy for chemical analysis and neutron activation analysis.

Electron Spectroscopy for Chemical Analysis (ESCA) was explored as a means of studying the oxidation state of chromium in SMAC (coated electrode) stainless steel welding fume collected on Nucleopore filters in the laboratory. Chromuim VI and III (as a percent of the total chromium) obtained from ESCA analysis was applied to results from Neutron Activation Analysis (NAA) to yield an average of 69 microgram chromium VI per sample. Diphenylcarbazide/atomic absorption (DPC/AA) results are reported for samples submitted to an industrial laboratory. Possible chemical species and solubility of chromium VI in stainless steel fumes is discussed in light of analogy between the SMAC process and the manufacturing process for chromates.

Air Pollutants

Distribution of corrosion products in teeth restored with metal crowns retained by stainless steel posts.

The nature and distribution of corrosion products in teeth restored with metal crowns retained by stainless steel posts were examined by means of energy-dispersive X-ray microanalysis, microradiography, and electron microscopy. The corrosion products consisted of calcium, phosphorous, iron, chromium, nickel, zinc, stannum and other elements. A possible root fracturing mechanism is discussed.

Corrosion

An in vitro investigation of the anodic polarization and capacitance behavior of 316-L stainless steel.

Determinations were made of how the corrosion-resistant properties of the passive film on 316-L stainless steel are influenced by the material's mechanical and surface states, and the variable pH and PO2 conditions of the interstitial fluid. Cold-rolled and annealed specimens were surface-prepared, commercially and in the laboratory, respectively, as if for orthopedic implantation. Passive film behavior was studied by the anodic polarization and pulse-potentiostatic capacitance methods. The pH and PO2 of the Ringer's test solution were varied to include interstitial fluid values occurring postoperatively and onto recovery. The anodic polarization behavior of all specimens was found to be pH- and PO2-independent. Breakdown potentials of annealed specimens were 800-950 mV (SCE), in contrast to previously reported values of approximately 350 mV. This substantial increase is related to the influence of surface preparation and, in particular, to the optimization of electropolishing time which acts to produce a microscopically smooth surface, free of debris and disarrayed material. Capacitance behavior of annealed material for potentials greater than 400 mV was consistent with a model involving the entry of chloride and metal ions (mostly Fe) into the passive film. This entry is related to the onset of pitting.

Corrosion