The degradation mechanism of PLA

Polylactic acid (PLA) has a molecular structure in which the ester bond is easily hydrolyzed and can be degraded by microorganisms in the body or in the soil to produce lactic acid. The final products of metabolism are water and carbon dioxide, so it will not cause toxic and side effects to the human body and is very safe to use. Therefore, polylactic acid has been used in many aspects such as medicine and pharmacy, such as surgical sutures, drug controlled release systems and so on.

Due to the optical activity of lactic acid, there are three corresponding polylactic acids: PDLA, PLLA, and PDLLA (racemization).

PLLA and PDLA are partially crystalline polymers with good mechanical strength, and are often used as medical sutures and surgical orthopedic materials. Drug controlled release preparations often use PLLA and PDLLA, but more often use PDLLA. The degradation product of PLLA, L-lactic acid, can be completely metabolized by the human body, so it is more competitive than D-PLA.

In vivo degradation

The hydrolysis of PLA is a complex process, mainly including four phenomena: water absorption, breaking of ester bonds, diffusion of soluble oligomers and decomposition of fragments.

The main way of degradation: body erosion.

After the PLA material is immersed in an aqueous medium or implanted in the human body, the material absorbs water first. The aqueous medium penetrates into the polymer matrix, resulting in the relaxation of the polymer molecular chain, the initial hydrolysis of the ester bond, the decrease of the molecular weight, and the gradual degradation into oligomers.

The terminal carboxyl group of polylactic acid (produced by polymerization introduction and degradation) catalyzes its hydrolysis. As the degradation progresses, the amount of terminal carboxyl group increases and the degradation rate accelerates, resulting in an autocatalytic phenomenon

Internal degradation was faster than surface degradation, which was attributed to the self-accelerating effect of degradation products with carboxyl-terminated degradation products retained in the sample.

As the degradation progresses, there will be more and more carboxyl groups inside the material to accelerate the degradation of the internal material, further increasing the difference between the inside and outside. When the inner material is completely transformed into a soluble oligomer and dissolved in an aqueous medium, a hollow structure with a surface composed of a polymer that is not fully degraded is formed. Further degradation causes oligomers to be hydrolyzed into small molecules, which are finally dissolved in aqueous media.

The entire dissolution process is from a water-insoluble solid to a water-soluble substance.

Macroscopically, the overall structure of the material is destroyed, the volume becomes smaller, gradually becomes fragments, and finally dissolves completely and is absorbed or excreted by the human body;

The hydrolysis of PLA is a complex process, mainly including four phenomena: water absorption, breaking of ester bonds, diffusion of soluble oligomers and decomposition of fragments.

The main way of degradation: body erosion.

After the PLA material is immersed in an aqueous medium or implanted in the human body, the material absorbs water first. The aqueous medium penetrates into the polymer matrix, resulting in the relaxation of the polymer molecular chain, the initial hydrolysis of the ester bond, the decrease of the molecular weight, and the gradual degradation into oligomers.

The terminal carboxyl group of polylactic acid (produced by polymerization introduction and degradation) catalyzes its hydrolysis. As the degradation progresses, the amount of terminal carboxyl group increases and the degradation rate accelerates, resulting in an autocatalytic phenomenon

Internal degradation was faster than surface degradation, which was attributed to the self-accelerating effect of degradation products with carboxyl-terminated degradation products retained in the sample.

As the degradation progresses, there will be more and more carboxyl groups inside the material to accelerate the degradation of the internal material, further increasing the difference between the inside and outside. When the inner material is completely transformed into a soluble oligomer and dissolved in an aqueous medium, a hollow structure with a surface composed of a polymer that is not fully degraded is formed. Further degradation causes oligomers to be hydrolyzed into small molecules, which are finally dissolved in aqueous media.

The entire dissolution process is from a water-insoluble solid to a water-soluble substance.

Macroscopically, the overall structure of the material is destroyed, the volume becomes smaller, gradually becomes fragments, and finally dissolves completely and is absorbed or excreted by the human body

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