Surgical implant

Several groups have been studying both [Ca(P03)2]n and [NaCa(P03)3]/i fibers for potential use as reinforcing fibers for bone implants and dental materials. Some of the results were encouraging, but naturally, much of the work was terminated when it was discovered that the product would not be available at any price. 

On March 29, 1994, Paul Harvey, a well-known news reporter in the United States, reported that a child, a young girl, had been to the dentist. The dentist pulled one of her teeth. She requested that she be given the tooth to place under her pillow for the Tooth Fairy. The dentist informed her that he could not give her back her tooth because it was against OSHA regulations. I do not know whether the tooth was considered a toxic substance or a biohazard. 

All phosphates are being considered as toxic substances. That includes your teeth and your bones. Maybe it is I who should be locked up to protect you from me. If it makes sense to class phosphates as toxic substances, there is surely something dangerously wrong with my thinking  

Phosphate fibers should have been excellent materials for the insulation of pipes in submarines and similar naval uses. Its insulating properties are similar to chrysotile without the concerns that have been developed around that substance. 

The fibers should have been an excellent additive for toothpaste to supplement the normal abrasives. They were soft and may well have behaved as a brush within the tube to assist both the toothbrush and paste without causing additional abrasiveness to a tooth. 

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Phospha.tes. Many phosphates cl aim unique material advantages over siUcates that make them worth the higher material costs for certain apphcations. Glass-ceramics containing the calcium orthophosphate apatite, for example, have demonstrated good biocompatibiUty and, in some cases even bioactivity (the abiUty to bond with bone) (25). Recent combinations of fluorapatite with phlogopite mica provide bioactivity as well as machinability and show promise as surgical implants (26). 

A prolonged action/controlled release system developed to deUver levonorgestrel for contraceptive therapy involves implantation of a set of flexible closed capsules made of demethylsiloxane—methylvinyl—sdoxane copolymer (see Contraceptives). Each capsule measures 2.4 mm in diameter and 34 mm in length. A set of six such capsules is surgically implanted beneath the skin of the upper arm. These capsules are intended to be removed by the end of the fifth year after implantation. 

Polylactic Acid. Polylactic acid (PLA) was introduced in 1966 for degradable surgical implants. Hydrolysis yields lactic acid, a normal intermediate of carbohydrate metaboHsm (23). PolyglycoHc acid sutures have a predictable degradation rate which coincides with the healing sequence of natural tissues. 

Nonferrous Metals-, Electrodeposition Coatings-, Metal Powders-, Surgical Implants, Part 7, 1972 Annual Book ofASTM Standards, American Society for Testing Materials, Philadelphia, Pa., 1972. 

P Injection, blow, extrusion and rotational Pipe, pipe fittings, surgical implants, coatings, wire and cable insulation... 

A surgical implant is constantly bathed in extracellular tissue fluid. Basically water, this fluid contains electrolytes, complex compounds, oxygen and carbon dioxide. Electrolytes present in the largest amounts are sodium (Na ) and chloride (Cl ) ions. Most of the fluids existing in the body (such as blood, plasma and lymph) have a chloride content (and pH) somewhat similar to that of sea water (about 5 to 20g/l and pH about 8) . 

Pitting and stress corrosion cracking, although usually associated with stainless steels in chloride media, have not been observed on recovered surgical implants. Implants often exhibit cracks and surface pitting, but these are most likely the result of improper manufacture rather than corrosion . 

One of the most serious corrosion problems associated with type 316 stainless steel is its susceptibility to crevice corrosion. The incidence and extent of this type of corrosion in surgical implants was stressed by Scales eta/. who reported the presence of crevice corrosion in 24% of type 316L bone plates and screws examined after removal from patients. This record however compared favourably with the presence of crevice corrosion in 51 % of 18-8 stainless plates, demonstrating the superiority of the molybdenum-containing grade. 

Intercrystalline corrosion was a serious problem with the austenitic stainless steels early in their development since carbon contents then were relatively high, e.g. En58J contained up to 0.12type stainless steel contained up to 0.08 Vo C. The problem in relation to surgical implants has been reported by Scales eta/. and as a result of this and several other reports the British, American and International Standards specified the use of a 316S12 type austenitic stainless steel which contains 0.03 Vo C max. The use of the lower carbon content stainless steels as specified in the various standards has now eliminated the problem of sensitisation of implants. If manufacturers do use the 0.08% C versions they have to be very careful with the forging temperatures or anneal the prostheses afterwards. 

Wickstrom, J. K., Surgical Implants —The Mechanical and Environmental Problems, Journal of Materials, 1, 366-312 (1966)... 

Luckey, H. A., Kubli, Jr. F., Editors Introduction , in Titanium Alloys in Surgical Implants, ASTM Publication STP 796, 1-3, Philadelphia (1983)... 

Greene, N. D., Corrosion of Surgical Implant Alloys A Few Basic Ideas , in Corrosion and Degradation of Implant Materials, Second Symposium, (Eds) A. C. Fraker and C. D. Griflin, 5-10 ASTM Publication STP 859, Philadelphia (1985)... 

British Standards Institution Surgical Implants, Specification Numbers BS7251 to BS 7254, London (1990-93)... 

Hughes, A. N., Jordan, B. A. and Orman, S., The Corrosion Fatigue Properties of Surgical Implant Materials. Third Progress Report — May 1973 , Engineering in Medicine, 7, 135-141 (1978)... 

Revie, R. W. and Greene, N. D., Corrosion Behaviour of Surgical Implant Materials 1 Effects of Sterilisation , Corrosion Science, 9, 755-761 (1969)... 

Syrett, B. C. and Wing, S S., An Electrochemical Investigation of Fretting Corrosion of Surgical Implant Materials , Corrosion, 34, 379-386 (1978)... 

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