Degradable hydrogels are designed to undergo hydrolytic degradation and are used

Question

Degradable hydrogels are designed to undergo hydrolytic degradation and are used to deliver cells and therapeutic molecules. Swelling of the material (water entering the pores of the material to cause increased volume) happens simultaneously during hydrolysis and is controlled by the density of the linkages in the polymer. Low density of the linkages allows more expansion in the polymer volume. A poly(lactic acid)-poly(ethylene glycol)-poly(lactic acid) (PLA-b-PEG-b-PLA) copolymer hydrogel experiences both degradation and swelling when comes in contact with water. The polymer chains of this copolymer are currently connected by esters bonds (highly hydrolytic) to form a network.

Relation between the swelling characteristics and degradation of this degradable hydrogel can be estimated by the equation: Q~ E^ 6/5 JKT where, Q = volumetric swelling ratio, j = number of degradable linkages present, k = reaction rate constant for the hydrolysis, t = time. Based on this equation, to discuss how the design parameters (i.e. design of the hydrogel structure) can be varied to achieve high degradation with low swelling or vice versa. Please note the reaction rate constant can be varied by the type of chemical bonds presented in the polymer. Please focus your discussion on parameters j and k.

Explanation / Answer

Reaction rate constant is inversely proportional to J (number of degradable linkages present). If we increase the reaction rate constant, the number of degradable linkages will be reduced with time, so the polymer will degrade less. Such a polymer will have low degradation.

Obtaining polymers with high degradation can be done by decreasing the reaction rate constant. Changes in reaction rate constant can be achieved by changing the concentration of the reactanting substrates.

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