Living tissue

The ability to control and ehcit specific reactions between biomaterials and living tissues is a long pursued aim. This has led to several strategies to study, understand, and control the interactions occurring at the interface. It is known that cell processes such as adhesion, proflferation, differentiation, migration or apoptosis, depend on cell responses that are controlled by intracellular signaling pathways tri ered by the interaction between the transmembrane proteins and the substrates surface, where multiple surface properties play a role. 

The possibility of producing surfaces, where the chemistry, pattern geometry and physical properties are spatially and temporally controlled, represents a powerful tool towards the aim of understanding fundamental aspects of the biological material-surface interactions in implantable materials, which additionally has found practical applications on biosensors and drug discovery. 

Gaseous plasma treatments have also been studied on several biopolymers for blood-contacting applications, where biomaterial-related thromboembohc compfica-tions remain a significant risk.  

The study of the interaction of biomaterials with other tissues and cells, such as neuronal cells or stem cells, e.g. O plasmas on polyimide or polyurethane to attach adipose derived stem cells prior to implantation, have also profited from plasma-based treatments. 

On the other hand, sometimes the desired result is not to elicit a specific response, but avoiding eliciting a foreign body reaction and the consequent rejection. This is for example the case in Ni containing NiTi shape memory alloys used in dental devices 

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Albumins. Soluble proteins both in water and in dilute aqueous salt solutions found in all living tissue. Typical albumins are ovalbumin from eggs and lactalbumin from milk. 

Catalase living tissues of plants and animals hydrogen peroxide HjO and inactive molecular O, 70... 

The octanol—water partition coefficient, which is used as an iadicator of the tendency of an organic chemical to accumulate ia living tissue, was low. This iadicates that naphthalene is unlikely to accumulate ia the body. 

Research based on Wolff s law of bone transformation has resulted in some other important observations. Fluctuating loads, such as those that occur in walking, are better for bone than consistentiy appUed loads, such as weight gain. However, if the effective appUed load becomes extreme, pressure necrosis, ie, bone death, occurs. Pressure necrosis is a significant concern in hip arthroplasty. Necrosis means the localized death of living tissue. Undue pressure on living cells causes death. Some total hip replacement failures are the direct result of pressure necrosis. 

Two groups of substituted l,4-ben2oquiaones are associated with photosynthetic and respiratory pathways the plastoquinones, eg, plastoquinone [4299-57-4] (34), and the ubiquinones, eg, ubiquinone [1339-63-5] (35), are involved in these processes. Although they are found in all living tissue and are central to life itself, a vast amount remains to be learned about their biological roles. 

Biomedical. Heart-valve parts are fabricated from pyrolytic carbon, which is compatible with living tissue. Such parts are produced by high temperature pyrolysis of gases such as methane. Other potential biomedical apphcations are dental implants and other prostheses where a seal between the implant and the living biological surface is essential. Plasma and arc-wire sprayed coatings are used on prosthetic devices, eg, hip implants, to achieve better bone/tissue attachments (see Prosthetic and BiOLffiDiCALdevices). 

Processing in Hquid sterilants results in wet products which require highly specialized packaging. Therefore, Hquid sterilization should only be considered if the sterilized article is to be used almost immediately. Liquid sterilants or their residues can be harmful to living tissues. Therefore it is always necessary to rinse articles with sterile water or saline solution foUowing treatment. Whereas Hquid sterilization is an extremely useful method for articles that caimot withstand the conditions of steam sterilization, the problems associated with its use limit its appHcation. 

Although silk and cotton are classified as nonabsorbable sutures, these do lose strength gradually in living tissue and slowly break up after long periods of implantation (18). The USP specifications for Class I nonabsorbable sutures (silk or synthetic fibers) are shown in Table 4. 

Cysteine [52-90 ] is a thiol-bearing amino acid which is readily isolated from the hydrolysis of protein. There ate only small amounts of cysteine and its disulfide, cystine, in living tissue (7). Glutathione [70-18-8] contains a mercaptomethyl group, HSCH2, and is a commonly found tripeptide in plants and animals. Coenzyme A [85-61-0] is another naturally occurring thiol that plays a central role in the synthesis and degradation of fatty acids. 

Antiseptic. An antiseptic is a chemical substance that prevents or inhibits the action or growth of microorganisms but may not necessarily kill them, and is used topically on living tissue. The distinction between a disinfectant and an antiseptic is that the former is expected to kill all vegetative cells and is used only on inanimate objects, whereas the latter may not kill all cells and is used on the body. 

In extreme eases irritant ehemieals ean have a eoiTosive aetion. Corrosive substanees ean also attaek living tissue (e.g. to eause skin uleeration and, in severe eases, ehemieal burns with degradation of bioehemieals and ehan ing), kill eells and possibly predispose to seeondary baeterial invasion. Thus whilst aeute irritation is a loeal and reversible response, eorrosion is iiTeversible eell destruetion at the site of the eontaet. The outeome is influeneedby the nature of the eompound, the eoneentration, duration of exposure, the pH (see Figure 5.1) and also, to some extent, by individual suseeptibility ete. Tims dilute mineral aeids may be irritant whereas at higher eoneentrations they may eause eoirosion. 

A substance which may on contact with living tissues destroy them. 

H8 Corrosive substances and preparations which may destroy living tissue on contact... 

Despite the universal use of sutures for wound closure, there is a need to utilize adhesives instead, because of their ease of use and the reduced risk of infection. Alkyl cyanoacrylate adhesives have been studied extensively for this use, and a significant amount of research has been performed to evaluate their interaction with living tissue [40,41 J. They have been approved for external use only, because of concerns with the fact that the polymers do not readily biodegrade and can cause inflammation around the area to which it was applied. However, these concerns are reduced for -butyl cyanoacrylate, as compared to the ethyl cyanoacrylate. There is even some evidence that their use as liquid sutures actually reduces the rate of infection around the healing wound or surgical incision [42J. 

Bioaccumulation-Accumulation of a chemical substance in living tissue. 

Plastics continue to make inroads regarding medical applications. Certain plastics have been found to exist in the environment of living tissues. In addition to being of direct aid in medicine, they are also important in medical devices and packaging medical items. 

Fig. 11-4. Schematic diagram of apparatus for determining dry weight of living tissues. (Courtesy of Lindstrom, Ada Radiol. SuppL, 125, 1955, page G5.)...

Owing to the complexity of living tissue, the x-ray techniques described above will often need to be supplemented with others. Recent work shows the progress that can be expected to follow from such a concerted analytical approach.16"21... 

Dry weight of living tissues, determined by long-wavelength x-ray absorptiometry, 297-300 Duane and Hunt, law of, 7 Dynodes, 56... 

Inflammation occurs when a living tissue is injured or infected by microorganisms. It is a beneficial, self-limited response that requires phagocytic cells and elements of circulating plasma to enter the affected area. In principle it may achieve resolution and repair as the ideal outcome of inflammation. The persistent accumulation and activation of leukocytes is a hallmark of chronic inflammation. 

The strength of an acid depends on the solvent and an acid that is strong in water may be weak in another solvent or vice versa (see Section 10.8). However, because almost all reactions in living tissues and most reactions in laboratories take place in water, in almost every case the only solvent we consider in this chapter will be water. 

Carbohydrates of Living Tissues, M. Stacey and S. A. Barker, Van Nostrand Co. Ltd., London,... 

A number of articles considered the association of chitosan with polylactic acid or similar compounds [47-49] another group of articles presented new data on highly cationic chitosans [ 50 - 55]. More data have also been made available on the delivery of growth factors [56] and ophthalmic drugs [57,58], on the activation of the complement, macrophages [59-61] and fibroblasts [62], on mucoadhesion [63] and functionalization of chitin [64]. The development of new carriers for the delivery of drugs, and the interactions of chitosans with living tissues seem therefore to be major topics in the current research on chitosan. Therefore, this chapter will place emphasis on these aspects. 

Chance, B., Leigh, J.S., Kent, J., McCully, K., Nioka, S., Clark, B.J., Marris, J.M., Graham, T. (1986). Multiple controls of oxidative metabolism in living tissues as studied by phosphorous magnetic resonance. Proc. Natl. Acad. Sci. USA 83,9458-9462. 

Medicine has made major advances in the past 50 or so years partly by the use of devices to improve patient health. These devices include artificial hearts and pacemakers, machines for artificial kidney dialysis, replacement joints for hips, knees, and fingers, and intraocular lenses. These devices need to survive in sustained contact with blood or living tissue. 

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