Degradation properties

In all types of PHAs, P4HB is of the most interest because it was used in the degradable scaffold that resulted in the first successful demonstration of a tissue-engineered tri-leaflet heart valve in a sheep animal model. Its copolymers with PHB and polyhydroxyoctanoate (PHO) are also promising in tissue engineering because of their nontoxic degradation products, stability in tissue culmre media, and the potential to tailor the mechanical and degradation properties to match soft tissue. 

T.K.Rehfeldt, Polymeric Coatings Degradation Properties. Report Number AFWAL-TR-84-4174, Air Force Wright Aeronautical Laboratory, (1984). 

Polyalphaolefin Hydraulic Fluids. The transformation and degradation properties of the polyalphaolefin hydraulic fluids in air will be similar to the mineral oil fluids since they contain similar hydrogen isomers. 

From this fundamental level the model can be advanced to more complex levels. Inclusion of the dynamics of flow or transfer rates between compartments and degradation properties within compartments can transform the model to a nonequilibrium, steady state description of a chemical s fate. 

Mechanical and Degradation Properties. Studies characterizing the mechanical properties of these highly crosslinked materials indicate properties that are intermediate between those of cortical and trabecular bone. Table I summarizes these results along with the mechanical properties of bone. 

Utaisincharoen, P., Mackessy, S, P., Miller, R. A., and Ju, A. T. (1993). Complete primaty structure and biochemical properties of gilatoxin, a serine protease with kallikrein-like and angiotensin-degrading properties. Journa/ of Biological Chemistry 268,21975-21985. 

Incorporation Into a co- or terpolymer of a d1ol containing monomer such as solketal acrylate (SA, H, a comonomer readily hydrolyzed by aqueous add to a diol) likewise Increases crosslinking (Scheme 4). Such polymers exhibit Improved dry, wet and solvent resistance (Table V). Alternatively, half of the ABDA comonomer can be substituted with SA, without significantly degrading properties vs the Initial ABDA only sample. 

Changes in the specific properties of the polymer can also be taken as a hint of some form of degradation. Properties examined include different aspects of physical behaviour of the polymer, different microscopic images, or changes in simple parameters such as the total weight of the polymer in the test or an altered molecular mass of the polymer under evaluation. 

Initial current, voltage, luminance, color coordinate properties, and luminance degradation properties were evaluated for the step 5 product and a styryl comparative. Testing results are provided in Table 1. 

Poly(esters) (Table 11.2) are the first class of polymers discussed, as they are the most widely investigated of all of the polymer families for oral protein delivery. Poly(esters) used for oral drug delivery have primarily been biodegradable polymers (Figure 11.1). Biodegradation is the primary delivery mechanism for poly(ester) polymers used for protein and peptide delivery. The degradation properties of poly(esters) are dependent on the monomers used to produce the poly(ester). Several poly(esters) are discussed in detail in the following sections. 

Use of catalysts, reaction temperature, etc. may affect the degradation properties of the polymer... 

Nakamura, F., et al. 1992. Lysozyme-catalyzed degradation properties of the conjugates between chitosans having some deacetylation degrees and methotrexate. Yakuzaigaku 52 59. 

Extremely stable compounds high resistance to thermal and chemical degradation properties vary with mixtures.1 Mobile oil to white solid bp, 274-475X.2... 

The tacticity of PLA influences the physical properties of the polymer, including the degree of crystallinity which impacts both thermo-mechanical performance and degradation properties. Heterotactic PLA is amorphous, whereas isotactic PLA (poly(AA-lactide) or poly (55-lac tide)) is crystalline with a melting point of 170-180°C [26]. The co-crystallization of poly (RR-lactide) and poly(55-lactide) results in the formation of a stereocomplex of PLA, which actually shows an elevated, and highly desirable, melting point at 220-230°C. Another interesting possibility is the formation of stereoblock PLA, by polymerization of rac-lactide, which can show enhanced properties compared to isotactic PLA and is more easily prepared than stereocomplex PLA [21]. 

The discontinuous two phases drug release can be controlled and avoided by manipulating the degradation properties of the polymer so that it is possible for the Zoladex implant to provide continuous release over a 28-day period. 

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