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What is the main reaction by which polylactic acid (PLA), used in absorbable sutures and bone fixation pins, degrades in the body?

  1. AUV photodegradation of the main chain
  2. BHydrolysis of the ester bonds in the main chain
  3. CThermal decomposition (depolymerization) of the main chain at body temperature
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Answer: B. Hydrolysis of the ester bonds in the main chain

In aliphatic polyesters such as PLA and polyglycolic acid (PGA), the ester bonds of the main chain are hydrolyzed by water in the body, the molecular weight falls, and they finally become lactic acid or glycolic acid. These are metabolized and ultimately leave the body as carbon dioxide and water. Hydrolysis proceeds even without enzymes, and because the acid of the carboxyl groups produced accelerates further degradation (autocatalysis), large parts can degrade from the inside. Ultraviolet light hardly reaches the inside of the body, so photodegradation is not a mechanism of degradation there. At 37℃ thermal decomposition (depolymerization) hardly occurs; it is a phenomenon to watch during molding at around 200℃.

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  1. A bone fixation pin of crystalline poly-L-lactic acid (PLLA), made only of the L-isomer, takes several years to be fully resorbed in the body. Which is a correct way to make it degrade faster?
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