From microspheres, factors affecting

Yang J, Cleland J L (1997). Factors affecting the in vitro release of recombinant human interferon-y (rhlFN-y) from PLGA microspheres. J. Pharm. Sci. 86 908-914. 

Drug Release from Microspheres 45.4.3.1 Factors Affecting Drug Release... 

Many factors are known to impact the release rates and profiles of medicaments from microspheres. These parameters may include the following physicochemical properties of the drug and the matrix former, porosity of the individual microsphere, thickness of matrix former, particle size and size distribution of microspheres, core particle size, and medicament loading affects. Release rates for many microspheres (especially nonerodible ones) were found inversely proportional to the square of the particle size as a result of the increased surface area exposed to the dissolution medium. Often, a linear relationship exists between the mean microsphere size and the time for 50% of the encapsulated drug to be released. - Therefore, as microsphere size decreases, the surface area-to-volume ratio of the particle increases, thus, the rate of drug release out of the microsphere increases. 

Another major factor affecting the particle uptake is the nature of the material used to prepare the particles. Uptake of nanoparticles prepared from hydrophobic polymers seems to be higher than that from particles with more hydrophilic surfaces. Microspheres composed of polystyrene, poly(methylmethacrylate), poly(hydroxybutyrate), poly(D,L-lactide), poly(L-lactide), and poly(o,L-lactide-co-glycolide) were absorbed into the Peyer s patches of the small intestine, whereas those composed of ethyl cellulose, cellulose acetate hydrogen phthalate, and cellulose triacetate were not absorbed. Residual poly(vinyl alcohol) in the surface of PLGA nanoparticles significantly reduced the intercellular uptake, in spite of the smaller particle size." Similarly, poloxamer coating of... 

The nonlineaxity of a stress-strain trace is caused by the material properties, a transition from elastic deformation to plastic deformation, and/or a large change in the configuration of the specimen [57]. The same applies to a stress intensity/displacement (SD) trace. The stress intensity in the case of a cracked body is quantified by the stress intensity factor for Mode I (ifj). The SD trace is linear for linear, elastic solids (before gross plastic deformation occurs). When a cracked solid contains compressive stresses arormd microspheres (practically in the form of residual stresses), as illustrated in Figure 3.22, also the compressive stresses affect the SD trace and then manifest as nonlinearity. The reason is that, as the applied load increases, the compressive stresses around microspheres in the vicinity... 

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