Bioerosion

The triphasic pattern was more pronounced with copolymers of higher lactide content (longer bioerosion time). The 45 50 copolymer afforded efficacy in the rat over 5 weeks. The studies confirmed the homogeneous (bulk) rather than heterogeneous (surface) eroskn of the polymer. Subsequent studies (121) with 3-mm implants... 

The biomedical uses of polyphosphazenes mentioned earlier involve chemistry that could in principle be carried out on a classical petrochemical-based polymer. However, in their bioerosion reactions, polyphosphazenes display a uniqueness that sets them apart. This uniqueness stems from the presence of the inorganic backbone, which in the presence of appropriate side groups is capable of undergoing facile hydrolysis to phosphate and ammonia. Phosphate can be metabolized, and ammonia is excreted. If the side groups released in this process are also metabolizable or excretable, the polymer can be eroded under hydrolytic conditions without the danger of a toxic response. Thus, poljnners of this tjT are candidates for use as erodible biostructural materials or sutures, or as matrices for the controlled delivery of drugs. Four examples will be given to illustrate the opportunities that exist. 

Single-substituent polymers, such as the procaine derivative shown as compound 24, are insoluble in water. In principle, the bioerosion characteristics can be modified by the presence of amino acid ester, glyceryl, or glucosyl (see later) cosubstituents, and this offers the possibility of a long-term release of a local anesthetic at a targeted site in the body. 

Laurencin and coworkers213 have used a different approach to control the rate of bioerosion of polymers with amino acid ester side groups. They used hydrophobic 4-methylphenoxy cosubstituents ( 50%) to slow the rate of hydrolysis, and these polymers were employed to study the rate of release of inulin. Similar polymers are also being developed by the same investigators as tissue engineering substrates for bone regeneration.214"218... 

Table 3.2 Amino Acid Ester Side Groups That Have Been Linked to Polyphosphazenes to Generate Hydrolytic Instability and Bioerosion...

Polymer-based [ethylidene-2,4,8,10-tetraoxaspirol(5,5)undecane Bioerosion of drug polymer complex Insulin pH change ... 

C.N. Trueman, D.M. Martill, The long-term survival of bone the role of bioerosion, Archaeometry 44 (2002) 371-382. 

The feedback-regulated drug delivery concept has been applied to the development of a bioerosion-regulated CrDDS by Heller and Trescony. " This CrDDS consists of a drug-dispersed bioerodible matrix fabricated from poly(vinyl methyl ether) half-ester, which was coated with a layer of immobilized urease (Fig. 26). In a solution with near neutral pH, the polymer only erodes very slowly. In the presence of urea, urease at... 

Fig. 26 Cross-sectional view of a bioerosion-regulated hydrocortisone delivery system, a feedback-regulated drug delivery system, showing the drug-dispersed monolithic bioerodible polymer matrix with surface-immobilized ureases. The mechanism of release and time course for the urea-activated release of hydrocortisone are also shown. (From Ref > 1)...

Riitzler, K., 1975. The role of burrowing sponges in bioerosion. Oecologia, 19 203—216. 

We shall discuss the importance and occurrence of the main representatives of the carbonate-removing organisms, their boring patterns, and means of carbonate removal. The contribution of various groups of organisms to carbonate bioerosion, with respect to destruction mechanisms, trace morphology, and habitat is summarized by Neumann (1968), Milliman (1974), Warme (1975), and Schneider (1976). 

Warme, J.E., 1975. Borings as trace fossils and the processes of marine bioerosion. In R.W. Frey (Editor), The Study of Trace Fossils. Springer, Berlin, pp. 181—227. 

Polymer bioerosion can be defined as the conversion of an initially water-insoluble material to a water-soluble material and does not necessarily signify a major chemical degradation. 

In this review we do not consider a simple dissolution process, and we classify the various bioerosion mechanisms into the the three distinct types shown in Figure 1 (J[). 

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