Polycaprolactone (PCL) is a synthetic, semi-crystalline, biodegradable polyester with a melting point of about 60 °C and a glass transition temperature of about −60 °C. The most common use of polycaprolactone is in the production of speciality polyurethanes. Polycaprolactones impart good resistance to water, oil, solvent and chlorine to the polyurethane produced.

This polymer is often used as an additive for resins to improve their processing characteristics and their end use properties (e.g., impact resistance). Being compatible with a range of other materials, PCL can be mixed with starch to lower its cost and increase biodegradability or it can be added as a polymeric plasticizer to polyvinyl chloride (PVC).

Polycaprolactone is also used for splinting, modeling, and as a feedstock for prototyping systems such as fused filament fabrication 3D printers.

PCL is prepared by ring opening polymerization of ε-caprolactone using a catalyst such as stannous octoate. A wide range of catalysts can be used for the ring opening polymerization of caprolactone. Low molecular weight alcohols are commonly added to regulate the molecular weight of the polymer.

PCL is degraded by hydrolysis of its ester linkages in physiological conditions (such as in the human body) and has therefore received a great deal of attention for use as an implantable biomaterial. In particular it is especially interesting for the preparation of long term implantable devices, owing to its degradation which is even slower than that of polylactide.

PCL has been widely used in long-term implants and controlled drug release applications. However, when it comes to tissue engineering, PCL suffers from some shortcomings such as slow degradation rate, poor mechanical properties, and low cell adhesion. The incorporation of calcium phosphate-based ceramics and bioactive glasses into PCL has yielded a class of hybrid biomaterials with remarkably improved mechanical properties, controllable degradation rates, and enhanced bioactivity that are suitable for bone tissue engineering. PCL–Hydroxyapatite composite scaffolds for bone tissue engineering can mimic the composition and morphology of the bone mineral phase and can be 3D printed into intricate designs.

PCL has been approved by the Food and Drug Administration (FDA) in specific applications used in the human body as (for example) a drug delivery device, suture, or adhesion barrier. PCL is used in the rapidly growing field of human esthetics following the recent introduction of a PCL-based microsphere dermal filler belonging to the collagen stimulator class (Ellansé).

Through the stimulation of collagen production, PCL-based products are able to reduce facial ageing signs such as volume loss and contour laxity, providing an immediate and long-lasting natural effect. It is being investigated as a scaffold for tissue repair by tissue engineering, GBR membrane. It has been used as the hydrophobic block of amphiphilic synthetic block copolymers used to form the vesicle membrane of polymersomes.