Degradation Characteristics

Once implanted in the body, the scaffold should undergo degradation at a rate matching that of tissue regeneration. For individual nanofibers, the degradation profile is mainly determined by the polymer itself as hydrolysis of the polymer backbone is believed to be the prevailing mechanism [45]. Most of the synthetic polymers are semi-crystalUne, implying that their chains fold into crystalline 

When assembled into a scaffold, the structure of the scaffold also plays a very important role in determining the degradation profile of nanofibers. When compared with a thin film cast from the same polymer, a scaffold made of electrospun nanofibers has a higher porosity and therefore the degradation product will be able to diffuse away more quickly. Otherwise, the accumulation of acidic degradation products will act as a catalyst to make the degradation process faster. 

As a result, a scaffold based on electrospun nanofibers would require a longer time to degrade than a bulk film of the same mass due to the difference in porosity [48]. Some researchers have also attributed the slow degradation rates of nanofiber scaffolds to the increase in chain orientation and thus higher crystallinity [49], as the strong electric field involved in an electrospiiming process tended to align the polymer chains parallel to the field [50]. 

The porosity of a nanofiber-based scaffold is a key factor in controlling the degradation profile. A number of methods have been developed for manipulating the porosity of a nanofiber scaffold, including those based on variation of the size of nano fibers, salt leaching, cryogenic electrospinning, and removal of a sacrificial component. These methods will be discussed in Section 9.2.6, as cell infiltration is also affected by the porosity. 

AHgnment of nanofibers results in significant stiffening in the direction of alignment and increased scaffold anisotropy [55]. This is an important feature to mimic when engineering anisotropic load-bearing tissues such as tendons, annulus 

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This long-term thermal performance of a material is tested alongside a second, control, material which already has an established RTI and which exhibits a good performance. Such a control is necessary because thermal degradation characteristics are sensitive to variables in the testing programme. Since the control material will also be affected by the same unique combination of these factors during the tests, there is a valid basis for comparison of test and control materials. 

Lewis et al. [52,53] have also determined labile chlorines in PVC by a crown ether catalyzed acetoxylation of PVC and the thermal degradation characteristics of the modified polymer. The values were comparable with those obtained by the phenolysis method. 

Wang Y, Kim YM, and Danger R. In vivo degradation characteristics of poly(glycerol sebacate). 

The fate of a given compound in the soil depends upon its partition between the soil particles themselves and the water, air and organisms it contains. Certain physicochemical properties of pesticides can be used to predict which are most likely to be leached. The most diagnostic properties are the sorption and degradation characteristics. 

As a result of their sorption and degradation characteristics, pesticides tend to be retained and eliminated within the soil horizon. These processes are well illustrated by some British field data [36] relating to the fate of a winter application of two pesticides of contrasting properties, the nematocide Aldoxycarb and the herbicide Fluometruron, in relation to a... 

The sorption and degradation characteristics listed for most pesticide compounds in terms of partition coefficients and half-lives relate only to a (standard) fertile, organic clayey soil and must not to be taken as representative of the permeable sandy soils widely developed on aquifer outcrops. Thus leaching of 1% of original application rates, and perhaps significantly higher, could easily occur for certain compounds on permeable soils. 

Degradation characteristics of the various solvents taken from Ref.1 23). 

Tirey, D.A., Dellinger, B., Rubey, W., and Taylor, P. Thermal degradation characteristics of environmentally sensitive pesticides products. Office of Research and Development, U.S. EPA Report-600/R-93-102, 1993, 54 p. 

Qualitatively all of the observed GPC degradation characteristics can be rationalized by the above loop model. Reasonable estimates of the onset of degradation in GPC can be made, and estimates of the percent degradation can be made cautiously. 

Crommen, J.H.L., Schacht, E.H., and Mense, E.H.G. (1992). Biodegradable Polymers. 2. Degradation Characteristics of Hydrolysis-Sensitive Poly[(Qrgano)Phosphazenes]. Biomaterials, 13, 601-611. 

According to his interpretation, both the degradation characteristics and the extent of drag reduction are determined by the relationship between compact and flexible chain segments. As a consequence of this, it is not the absolute volume of the (gel) coil which is the decisive value, but the behavior of the polymer chain. 

Microbial biosensors have been developed based on key hydrocarbon degradation pathways. These biosensors can be used as tools to examine the regulation of the degradation pathways. In addition to the use of empirically derived data from laboratory studies, a selective meta-analysis of published data from literature sources using catabolic hydrocarbon biosensors was conducted. The aim of this work was to demonstrate that biosensor specific QSARs may be developed to first assess the specificity of degradation pathways and then to assess the possibility of predicting analyte-specific degradation characteristics. 

However, the intrinsic thermal degradation characteristics of any polymer may be influenced by impurity species present, as polymers are rarely pure in the true chemical sense. Such impurities may include one or more of the following ... 

Shenglong Wan and Jianqiu Wang, Stndy on degradation characteristics of polyolefins, Petroleum Processing and Petrochemicals, 28(9), 41-45 (1997). 

Cho K. S., Hirai M., and Shoda M. (1991) Degradation characteristics of hydrogen sulfide, methanethiol, dimethyl sulfide, and dimethyl disulfide by Thiobacillus thioparus DW44 isolated from peat biofilter. J. Ferment. Bioeng. 71, 384-389. 

Acidification of the microenvironment Counteracting acidification by coencapsulating antacid excipients/" increasing permeability of the polymer matrix/ modifying degradation characteristics of the polymer. ... 

According to Jellinek three parameters may determine mainly the degradation characteristics of a polymer. These are ... 

Jiang, H.L. Zhu, K.J. Preparation, characterization and degradation characteristics of polyanhydrides containing poly(ethylene glycol). Polym. Int. 1999, 48, 47-52. 

Erdmann, L. Uhrich, K.E. Synthesis and degradation characteristics of salicylic acid-derived poly(anhydride-esters). Biomaterials 2000, 21 (19), 1941-1946. 

Thoma K, Schluetermann B. Relationships between manufacturing parameters and pharmaceutical-technological requirements for biodegradable microparticles. 5. Relationships between manufacturing parameters, surface properties and degradation characteristics. Pharmazie 1992 47 368-373. 

Federal Test Method Standard No 791C. Lubricants, Liquid Fuels, and Related Products Methods of Testing. Method 3410, High Temperature Deposit and Oil Degradation Characteristics of Aviation Turbine Oils. 

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