PEXEL® Crosslinked Polyethylene

Conventional UHMWPE (Ultra High Molecular Weight Polyethylene) is a very tough material, with the highest impact strength of any thermoplastic presently available. It is highly resistant to corrosive chemicals with exception of oxidizing acids; has extremely low moisture absorption and a very low coefficient of friction; is self-lubricating; and is highly resistant to abrasion.

Since the early 2000s, crosslinked variants of the conventionall UHMWPE have been used and validated both in vitro and in vivo. The crosslinking process is generally made by irradiating the material (or by exposing it to electrons) at a level in-between 25 and 100 kGy. The crosslinking modifies deeply the mechanical characteristics of the material and provides an increase in hardness and wear resistance. But this improvement is counterbalanced by a reduction of the tensile strength compared with the natural state of the material and a reduction of the elongation percentage under load.

PEXEL: THE SAFETY AND LONGEVITY OF A PROVEN TECHNOLOGY

L’élaboration d’un polyéthylène articulaire reste un compromis entre le contrôle de l’usure et ses propriétés mécaniques, auquel s’ajoutent

The development of an othopaedic joint polyethylene is a compromise between the wear resistance and the mechanical characteristics. Also, other manufacturing steps will come over the crosslinking process to maintain the characteristics of the material over time and to limit the oxidation of the material.

Evolutis has developed a proprietary technology of crosslinked polyethylene: the polyethylene PEXEL.

The PEXEL technology includes:

• A systematic control of the raw material and of the implants at different steps of the process in order to detect any defect of consolidation or homogeneity in the material
• a method of high precision and low-temperature machining
• a crosslinking of the molecular chains by moderate gamma irradiation
• a resistant and opaque air-vacuum packaging</li

The shelf-aged polyethylene PEXEL demonstrated a wear reduction of more than 50% in comparison wit a conventional polyethylene (CERAH test according to ISO standards 14242-1 and 14242-2 on shelf aged implants at 5 millions cycles).

CHARACTERISTICS

• Initial molecular weight of more than 7 millions gr/mol (2 to 4 millions for a conventional UHMWPE)
• 40 kGy gamma irrdiation minimum
• VacUpac air-vacuum packaging

Reduction in wear compared to conventional polyethylene sterelized by gamma radiation at 25 kgy.