Question

how do the resorbable polymers PLGA and PCL differ in their mechanisms of resorption? how are the resorption rates affected by molecular weight, degree of crystallinity and crosslinking. in considering the biocompatibility of a resorbable polymer, how do the rates of resorption and resorption by-products affect the cellular response? describe the inflammatory response associated with resorbable polymers.

Answer 1

Answer :)

PLGA can be processed into nearly any size and shape and can encapsulate molecules of almost any size. It is soluble in a wide kind of common solvents including tetrahydrofuran, chlorinated solvents, ethyl acetate or acetone. In water, PLGA gets biodegrade by hydrolysis of its ester linkages. The existence of methyl side groups in polylactic acid (PLA) creates more hydrophobic than PGA (polyglycolic acid) and hereafter lactide rich PLGA copolymers absorb less water and consequently degrade more gradually. Because of the hydrolysis of PLGA, factors that are usually considered invariant explanations of a solid formulation can alter with time, such as the moisture content glass transition temperature, and molecular weight.

Mechanical strength, capacity to undergo hydrolysis, swelling behavior, and successively biodegradation rate of the polymer are unswervingly affected by the degree of crystallinity of the PLGA. Melting point and Degree of crystallinity of the polymers are directly connected to the molecular weight of the polymer. Crystalline PGA, when copolymerized with polylactic acid, decreases the degree of crystallinity of PLGA and consequently increases the rate of hydration and hydrolysis. The glass transition temperature (Tg) of the PLGA copolymers is described to be above the bodily temperature of 37 °C and therefore are glassy in nature, so exhibiting a properly rigid chain structure. It has been further stated that Tg of PLGAs reduces with a decrease of lactide content in the copolymer configuration and with a decrease in molecular weight.

PCL (poly-ε-caprolactone) is degraded by hydrolysis of its ester bonds in physiological conditions and has thus received large attention in order to be castoff as an implantable biomaterial. PCL may be entirely degraded and resorbed via an intracellular mechanism when the molecular weight was condensed to 3000 or less. PCL goes through a two-stage degradation process: initially, the non-enzymatic hydrolysis of ester groups. Secondly, once the polymer is highly crystalline and attains a low molecular weight (<3000), the polymer is exposed to experience intracellular degradation in which PCL fragments uptake occurs in phagosomes of giant cells and macrophages within fibroblasts. PCL is appropriate for controlled drug delivery because of high permeability to many drugs, outstanding biocompatibility and its ability to be completely excreted from the body when resorbed. The rate of hydrolysis can change by copolymerization with other glycolides/lactides or lactones. Biodegradation of PCL is gentle in assessment to other polymers, thus it is more appropriate for long-term delivery, which ranges over a period of more than one year.