Carbon biological response

Only a few in vivo dermal toxicity studies have been reported so far. Huczko and Lange [50] evaluated the potential of raw CNTs to induce skin irritation by conducting two routine dermatological tests (patch test on 40 volunteers with allergy susceptibilities and Draize rabbit eye test on four albino rabbits). Koyama etal. [51] showed the biological responses to four different types of carbon nanotubes (SWNTs, two types of MWNTs with different diameters, and cup-stacked carbon nanotubes) after their subcutaneous implantation in mice. Both tests [50, 51] showed no or poor irritation effects. However, the in vitro studies in epidermal cell lines exposed to CNTs, and also a more recent report on the toxic outcomes of topical exposure of mice to SWNTs [46], have raised concerns over these assessments. Clearly, this is an area requiring further scientific evaluation. 

LEH is primarily composed of a combination of saturated high-carbon phospholipids and cholesterol. Synthetic phospholipids replaced hydrogenated soy lecithin when the latter was found to induce several untoward biological responses (40). Current choice of a saturated high-carbon phospholipid is mostly between distearoyl phosphatidylcholine (DSPC, 55°C) and... 

The fatty acid alkyl chain is susceptible to oxidation both at double bonds and adjacent allylic carbons. Eree-radical and photooxidation at aUylic carbons are responsible for deterioration of unsaturated oils and fats, resulting in rancid flavors and reduced nutritional quality, but they are also used deliberately to polymerize drying oils. Oxidation of double bonds is used in oleochemical production either to cleave the alkyl chain or to introduce additional functionality along the chain. Enzyme catalyzed oxidation is the initial step in the production of eicosanoids and jasmonates (biologically active metabolites in animals and plants respectively) but is not discussed further here. 

The biological response to metals can be improved by modifications to the surface composition of an implantable metal alloy. This follows from the work on bioactive glasses which, when implanted into the body, produce a modified surface that facilitates apatite precipitation (Hench 1998a). Various chemical enrichment treatments have been proposed to aid the precipitation of a carbonate apatite. 

Figure 21.5 Strategies for understanding nanomaterial enviromnental health and safely, toxicity and biological response include nanomaterial classihcalion, that is, compositional classification (metal, metal oxide, polymer, senticonductor, carbon-based, etc.) for a material that has one dimension between 1 and 100 mn chentical composition in terms of bulk and surface size considerations, primary and secondary (aggregate) sizes and geometric structure which includes shape and porosity.

Jockish, K.A., Brown, S.A., Bauer, T.W., and Merritt, K. 1992. Biological response to chopped carbon reinforced PEEK,/. Biomed. Mater. Res., 26,133-146. 

Ceramics are fully oxidized materials and are therefore chemically very stable. Thus ceramics are less likely to elicit an adverse biological response than metals, which only oxidize at their surface. Three types of inert ceramics are of interest in musculoskeletal applications carbon, alumina, and zirconia. 

A bioactive material is one that elicits a specific biological response at the interface of the material which results in the formation of a bond between the tissues and the material. A common characteristic of bioactive glasses, bioactive glass-ceramics, and bioactive ceramics is that their surface develops a biologically active hydroxy carbonate apatite (HCA) layer which bonds with collagen fibrils. The HCA phase that forms on bioactive implants is equivalent chemically and structurally to the mineral phase of bone. It is that equivalence which is responsible for interfacial bonding ". ... 

Muckle DS, Minns RJ, Biological response to woven carbon-fiber pads in the knee - a clinical and experimental-study. Journal of Bone and Joint Surgery-British Volume, 72(1), 60-62, 1990. 

Carbon nanotubes are the subject of many research studies from drug delivery systems to many other medical applications. Only a few references and examples have been mentioned here. This dmg delivery application by CNTs constitutes in itself the wide potential of fibrous material for smart implantable medical device designing, going beyond just the biological response impact and including physical and mechanical features. 

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