Biological heart valve

Calcification is also an undesirable response of the host to an implanted material, because the biomaterial becomes hard and brittle as exemplified in biological heart valves and artificial hearts. The mechanism of such calcification is not clear, thus no effective method to avoid calcification has been proposed. However, if a hydrophobic biomaterial is free of adherent cells, calcification will be greatly reduced, as calcification is thought to be due, in part, to these dead cells. On the other hand, it seems also probable that calcium and phosphate ions sorbed within the material may provide the nucleus for calcification. If this is the case, care should be taken when hydrogel-type polymers are implanted in the body. 

Guidewires, mechanical heart-valve housings and struts, biologic heart-valve stents, vascular stents, vena cava umbrellas, artificial heart housings, pacemaker leads, leads for implantable electrical stimulators, surgical staples, supereleastic properties of some nickel-titanium formulations, shape memory properties of some Ni titanium formulation, radiopaque markers... 

Lehner, G., Fischlein, T., Baretton, G., Murphy, J. G., and Reichart, B., Endothelialized biological heart valve prostheses in the non-human primate model, Eur. J. Cardiothorac. Surg., 1997 ll(3) 498-504. 

Biological fixation method, 45-11 5-12 Biological heart valves,... 

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). 

The major biological application of isotropic carbon is in heart valves. The material is performing well and several hundred thousand units have been produced so far. Other applications include dental implants, ear prostheses, and as a coating for in-dwelling catheters. 

There is a great need for strong materials such as alloys that can snap back into shape. Medical applications include prostheses— artificial limbs—and implanted devices such as heart valves. Most biological substances are smart, and the ability to replace lost or injured tissues and organs with smart materials would be a tremendous medical advance. 

An area of chemical modification that is very important to the medical support industry is concerned with the modifications for altering biological properties. An application of glutaraldehyde s cross-linking effect on proteins is in the preparation of prostheses for internal organs, e.g. heart valves (125). 

Schmidt D. et al. Engineering of biologically active living heart valve leaflets using human umbilical cord-derived progenitor cells. Tissue Eng 2006 12 3209-21. 

Substantial research has also been performed on organo compounds of the metalloids. Silicon compounds particularly have played a major role, as witness the monograph by Voronkov 270) and the articles by Fessenden and Fessenden 86) and Garson and Kirchner 107). Silicones, because of their inertness to biological processes, have been used as heart valves, blood vessels, implants, ointments, etc. 192). Other organosilicon compounds are extremely active biologically 270a). 

Calcineurin (protein phosphatase 2B) is a Ser/Thr phosphatase that is controlled by cellular calcium and regulates a large number of biological responses including lymphocyte activation, neuronal and muscle development, and the development of vertebrate heart valves. 

Hyaluronan is continuously synthesized and secreted by fibroblasts, keratino-cytes, chondrocytes and other specialized cells in the extracellular matrix (ECMs) throughout the body. It is synthesized by HA synthase (see also Chapter 9) at the inner face of the plasma membrane [98]. The level of HA synthesis is very high in skin and cartilage [99]. Hyaluronic acid is not one of the major components of the ECMs of the connective tissues, but it is found in various locations such as synovial fluid, vitreous humor, and umbilical cords [100]. Its biological functions include the maintenance of mechanical properties such as swelling in connective tissues and control of tissue hydration, providing lubricating properties in synovial fluid and heart valves. 

Many interesting correlations have been established between the critical surface tension of materials (or other approximations of surface free energy) and protein adsorption, cell adhesion, and thrombus formation (41-48). Unfortunately, very few studies in which a biological response has been related to a specific surface chemistry exist. One study in which such a relationship was established, demonstrated the power of the contact angle method in analyzing surface structure related to blood compatibility (40). The blood compatibility of Stellite alloy heart valves was not due to the alloy itself, but to the closely packed methyl group structure associated with a tallow polishing compound used to finish the valve. Very recently, the power... 

This basic structure provides for considerable flexibility in the design of biomaterials, as described in a recent review [27]. By selection of the side groups on the polymer chain, both hydrophobic and hydrophilic polymers can be produced. Hydrophobic polyphosphazenes may be useful as the basis of implantable biomaterials, such as heart valves. The hydrophilic polymers can be used to produce materials with a hydrophilic surface or, when the polymer is so hydrophilic that it dissolves in water, cross-linked to produce hydrogels or solid implants. In addition, a variety of bioactive compounds can be linked to polyphosphazene molecules allowing the creation of bioactive water-soluble macromolecules or polymer surfaces with biological activity. 

Bioprostheses Prosthetic heart valves made of biological tissue. 

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