PLA Degradation in the Body: How Long Do Implants Last?

2 août 2026

A surgeon planning a bioabsorbable screw fixation asks a practical question: how long will this implant last inside the patient? An R&D lead reviewing a new resorbable scaffold asks the same thing in different words: when does strength disappear, when does mass disappear, and what will regulators expect us to document? The answer hinges on how polylactic acid (PLA) degrades in vivo — a process well characterized but frequently oversimplified. This guide covers the mechanism, the timelines, and the design implications.

How PLA Degrades In Vivo: Hydrolysis, Not Enzymes

PLA does not dissolve or corrode. It degrades primarily by hydrolysis: water molecules attack the ester bonds along the polymer backbone, cleaving long chains into shorter oligomers and, eventually, into lactic acid monomers. Absorbed water penetrates the implant, so molecular weight drops throughout its volume at a similar rate — a pattern known as bulk erosion. The lactic acid released is not a waste product; it enters normal metabolism, converts to pyruvate, and is processed through the Krebs (citric acid) cycle, excreted as carbon dioxide and water.

What Controls the Degradation Rate

Several design and patient variables shift the timeline:

Molecular weight: higher-molecular-weight chains take longer to fragment into monomers.
Crystallinity: crystalline regions resist water penetration, so more crystalline PLA erodes more slowly than amorphous material.
Copolymer ratio: poly(lactic-co-glycolic acid) (PLGA) degrades faster than PLA homopolymer, and glycolide-rich formulations erode more quickly than lactide-rich ones.
Geometry: larger, thicker implants have longer diffusion distances for water and a slower overall resorption profile.
Site and patient factors: local vascularity, inflammation, pH, and patient age and metabolic status all influence the rate.

Typical In Vivo Timelines

Only general ranges are useful here; exact numbers depend on the variables above. The table reflects widely reported clinical and preclinical experience — consult a device's validated data before relying on any figure.

Material	Typical in vivo timeline	Common clinical use
High-MW PLA (PLLA)	Roughly 1–2+ years to full resorption	Bioabsorbable screws, pins, plates
PLGA 50:50	Weeks to a few months	Drug delivery microparticles, sutures
PLGA 85:15	Several months	Sutures, scaffolds

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Strength Loss Precedes Mass Loss

This is the most important concept for clinicians and engineers. Mechanical strength falls long before the implant visibly disappears. As water penetrates and chains cleave, molecular weight drops and the material becomes brittle; for many PLA fixation devices, significant strength reduction occurs within months, while bulk mass loss and full resorption stretch to years. In practice, a screw can hold a fracture through the critical healing window and be nearly gone two years later — exactly the behavior bioabsorbable fixation is designed to exploit. Imaging follow-up looking for "the implant" may find nothing long before the chemistry has fully cleared.

Clinical Examples: Fixation Devices and Sutures

PLA and PLGA are established in orthopedics as bioabsorbable fixation — interference screws for ligament reconstruction, pins, and tacks that eliminate the need for a second removal surgery. Sutures made from lactide/glycolide copolymers retain tensile strength for weeks and resorb over months, matching wound healing. In drug delivery, PLGA microparticles release their payload as the matrix hydrolyzes, with kinetics tuned by copolymer ratio and particle size. See our guide to PLA bone screws and biodegradable orthopedic implants for more on resorbable fixation in bone.

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What This Means for Device Design

For load-bearing implants, the design question is not "when does it disappear" but "how long does it hold strength" — degradation kinetics must match the tissue healing timeline. For drug delivery, erosion rate controls the release profile, so molecular weight and copolymer ratio become formulation levers. In both cases, the device must remain biocompatible as it degrades, since byproducts and particulates are released locally. Middleton and Tipton's review of biodegradable polymers in orthopedic devices remains a solid reference for these principles.

Regulatory Expectations

Regulators evaluate degradation as a safety characteristic. ISO 10993 standards govern biocompatibility testing, and degradation products must be assessed for local and systemic effects. In the U.S., FDA clearance — typically via the 510(k) pathway for resorbable fixation devices — requires demonstration of degradation behavior; Health Canada follows a comparable framework, and in vitro–in vivo correlation of degradation is routinely expected. Our overview of PLA biocompatibility and ISO 10993 testing walks through the safety evidence base in more detail.

Sources: Middleton JC, Tipton AJ, Biomaterials, 2000 (ScienceDirect); da Silva D, et al., Chemical Engineering Journal, 2018 (ScienceDirect); Makadia HK, Siegel SJ, Polymers, 2011 (MDPI/PMC).

PLA implants are not permanent — they are engineered to surrender. Understanding hydrolysis, the gap between strength loss and mass loss, and the variables that shift the timeline lets surgeons choose the right fixation and lets device teams design, test, and document degradation that regulators will accept. For questions on bioabsorbable and general surgical supplies, the CliniEco team is a practical resource.

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