The XLE liners are manufactured using Ultra High Molecular Weight Polyethylene (UHMWPE) blended with vitamin E prior to consolidation and crosslinking. This provides a uniform distribution of the vitamin E and minimizes the elution effect found in diffused vitamin E liners.1 The gamma crosslinking and annealing process, developed in conjunction with Massachusetts General Hospital, grafts the vitamin E to the polyethylene molecule, resulting in a highly crosslinked material with excellent oxidative stability.3
Novation Crown Cup XLE Liner
Novation Crown Cup XLE Liner
Novation® Crown Cup® XLE Liner
Crown Cup XLE highly crosslinked vitamin E enhanced acetabular liners provide low wear while maintaining mechanical strength, reducing free radicals and oxidative degradation.3
Hip Simulator Wear Rate*
y-axis: Mg per Million Cycles
Low Wear
A patented gamma irradiation and mechanical annealing process, tailored to the vitamin E content, is used to achieve the desired crosslink density. An irradiation dose of 10 Megarad (Mrad) or 100 KiloGray (kGy) is imparted to the material prior to final gamma sterilization. This highly crosslinked polyethylene yields a reduced wear rate compared to conventional polyethylene.3
Mechanical Strength
The mechanical annealing process quenches free radicals below the melt temperature, which maintains the crosslink density and provides improved mechanical strength over conventional polyethylene.1,3
Ultimate Tensile Strength
y-axis: MPa
*TEST PARAMETERS:
Novation Crown Cup XLE [3]: Test parameters: 40mm diameter CoCr head; 4.4mm thick liner; 5 million cycles; 90% bovine serum; 1.1Hz; 2kN peak load; Wear rate: Slope of the linear regression for corrected mass change in the steady-state cycles
Conventional UHMWPE [2]: Test parameters: Not specified
10Mrd irradiated and melted UHMWPE [2,4]: Test parameters: 46mm head; 3mm thick liner; 11 million cycles; 100% bovine serum; 3.3kN peak load; Wear rate: Slope of the linear regression for corrected mass change over the full number of cycles
10Mrd irradiated, vitamin E diffused UHMWPE [5]: Test parameters: 36mm CoCr head; 4.9mm thick liner; 5 million cycles; 100% bovine serum; 2Hz, 3kN peak load; Wear rate: Slope of the linear regression for corrected mass change over the full number of cycles
Oxidative Stability
Blending the vitamin E prior to consolidation allows the antioxidant to distribute uniformly throughout the material. Gamma crosslinking grafts the vitamin E molecules onto the polyethylene chains. This minimizes the elution effect found in diffused or doped vitamin E liners.1 The mechanical annealing process further quenches free radicals.3,9,10 The cumulative result is a material with oxidative stability that reduces oxidative degradation.3
Manufacturing Process
Developed by Massachusetts General in conjunction with Cambridge Polymer.3 1
- Compression molded, vitamin E blended polyethylene sheet is turned into bar stock
- Bar stock is gamma irradiated at 10Mrd
- Preheat bar and platen
- Compress 2:1 under heat and cool
- Recover at sub-melt temperature
- Turn to final diameter
- Oral, E, Muratoglu, O, “The effects of high dose irradiation on the cross-linking of vitamin E-blended ultrahigh molecular weight polyethylene,” Biomaterials 29 (2008) 3557-3560
- Oral, E, Muratoglu, O, “Vitamin E diffused, highly crosslinked UHMWPE: a review,” Int Orthop. 2011 Feb; 35(2): 215-223
- Data on file at Exactech.
- Muratoglu OK, Bragdon CR, O’Connor DO, Perinchief RS, Estok DM, Jasty M, Harris WH (2001) Larger diameter femoral heads used in conjunction with a highly cross-linked ultra-high molecular weight polyethylene: A new concept. J Arthroplasty 16(8 Suppl):24 -30
- Oral E, Christensen S, Malhi A, Wannomae K, Muratoglu O (2006) Wear resistance and mechanical properties of highly crosslinked UHMWPE doped with vitamin E. J Arthroplasty 21 (4):580 -591
- Muratoglu OK, Bragdon CR, O’Connor DO, Jasty M, Harris WH,Gul R, McGarry F (1999) Unified wear model for highly crosslinked ultra-high molecular weight polyethylenes (UHMWPE). Biomaterials 20(16):1463 -1470
- Ries M, Pruitt L (2005) Effect of crosslinking on the microstructure and mechanical properties of ultra-high molecular weight polyethylene. Clin Orthop Relat Res 440:149 -156
- Oral E, Wannomae KK, Hawkins NE, Harris WH, Muratoglu OK (2004) a-Tocopherol doped irradiated UHMWPE for high fatigue resistance and low wear. Biomaterials 25(24):5515 -5522
- Bhattacharyya, S, Spiegelberg, S.H, Harris, W.H, Muratoglu, O.K. “Mechanical Elimination of Free Radicals in UHMWPE After Radiation.” 50th Annual Meeting of the Orthopaedic Research Society. Paper No: 0184
- Ebru Oral, Bassem W. Ghali, Orhun K. Muratoglu. “The elimination of free radicals in irradiated UHMWPEs with and without vitamin E stabilization by annealing under pressure.” J Biomed Mater Res B Appl Biomater. 2011 Apr;97(1):167-74. doi: 10.1002/jbm.b.31799. Epub 2011 Feb 24