Biofunctional additives

The next generation of implantable devices are likely to require biomaterials that are more interactive with tissues, being designed to interact with specific target biomolecules of relevance to the specific application. Although conventional PPy and PTh films have shown adequate biocompatibility for many biomedical applications, their lack of biofunctional activity results in poor cell interactions and limits their potential as an implantable material. 

Both biomolecule doping and entrapment are likely to maintain CP biofunctionality for a longer period than if the biological molecules are adsorbed to the polymer surface postprocessing. Adsorption relies on ionic interactions at a material surface which dynamically alters when placed in a biological environment. The presence of molecules with stronger affinities for either the target molecule or the CP will result in displaeement of the biomolecule from the CP surface. 

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Figure 18.4 Schematic of conventional biological modification routes of CPs, shown for po y(3,4-ethylene dioxythiophene). The green molecule represents the biofunctional additive and the negatively charged purple molecule is the dopant anion (See colour Plate 10)...

Of course, knowledge in synthetic reactions and techniques in organic experiments including purification methods are essential requirements to execute synthesis of biofunctional molecules. However, two additional things must be learned. 

Surface engineering aims for a defined physical, chemical, or biomolecular modification of material surfaces in order to create biofunctional surfaces that ensure biocompatibility (noninteractive materials) and in many cases additionally bioactivity of the material (interactive biomaterials) for a certain application. The design of appropriate biofunctional surfaces is important for the proper function of biosensors, membranes or implants, for the use as... 

The sodium phosphates are sometimes regarded as the most important salts of phosphoric acid both from an industrial and from a laboratory point of view. The calcium salts (Table 5.17), in addition to their importance in both these fields, however, serve not only as the principal mineral source of phosphorus, but have essential biofunctions as well (Figure 12.4) (Chapter 5.2). 

This information determines the stmctures and properties of the protein. Typical examples of important proteins are enzymes, receptors, and antibodies, which cany ont the desired biofunctions. When the genetic information of DNA is transferred to proteins, the necessary small part of DNA is copied to a kind of RNA (messenger RNA), which is ultimately used as template for producing the protein. In addition to messenger RNA, there are two other important RNAs named transfer RNA and ribosomal RNA. 

The cell biocompatibility problem of PLA materials can be resolved by Biofunctional modifications. However, such polymers on their own are too weak to be used in load bearing situations and not generally considered osteoinductive. PLA molecules would lower the in situ pH level, which raises difficulties in controlling its degradation rate and may induce an inflammatory reaction. In addition, PLA materials tend to be too flexible and of insufficient strength to meet the mechanical demands as hard tissue replacement. 

The 5-nitrosation of cysteine residues to produce 5-nitrosothiols is one of the most important NO-mediated modifications of proteins. In addition, it has been suggested that the interactions of NO (or NO-derived species) with selenocysteine residues are also involved in NO-mediated biofunctions. For example, GPx is inactivated by treatment with an 5-nitrosothiol as well as by endogenous NO, presumably through 5e-nitrosation of the SeH groups of selenoproteins to produce 5 -nitrososelenols (RSeNO).s4.66.67... 

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