Strength retention of 70:30 poly(L-lactide-co-D,L-lactide) following real-time aging.

This study evaluated the in vitro strength retention and polymer characteristics of plates and screws made from commercially available 70:30 poly(L-lactide-co-D,L-lactide) over a 2-year time period. Test samples included three routine manufacturing lots each of plates (1.2 mm thick, 41.70 mm long, with 2.5-mm holes), which were machined from compression-molded sheets, and screws (2.4-mm major diameter and 1.86-mm minor diameter), which were manufactured by injection molding. All samples were sterilized by e-beam irradiation prior to in vitro aging following a standard methodology. Mechanical testing and polymer analysis was performed after 0, 6, 13, 26, 39, 52, 65, 78, and 104 weeks. The initial (time zero) tensile strength of the plates averaged 33.2+/-1.9 MPa; the plates retained 100% of this strength at 6 weeks, 84% at 13 weeks, and 34% at 39 weeks. The screws had an initial (time zero) shear strength of 29.8+/-4.2 MPa, and maintained 97% of this strength at 26 weeks and 73% of this strength at 39 weeks. The inherent viscosity and molecular weight (M(w)) at time zero averaged approximately 1.4 dL/g and 165,000 g/mol, respectively, and decreased at similar rates for both the plates and screws. These results demonstrate excellent strength retention of devices fabricated from 70:30 poly(L-lactide-co-D,L-lactide) over time periods exceeding those associated with normal bone healing.

A three-dimensional osteochondral composite scaffold for articular cartilage repair.

There is a recognized and urgent need for improved treatment of articular cartilage defects. Tissue engineering of cartilage using a cell-scaffold approach has demonstrated potential to offer an alternative and effective method for treating articular defects. We have developed a unique, heterogeneous, osteochondral scaffold using the TheriForm three-dimensional printing process. The material composition, porosity, macroarchitecture, and mechanical properties varied throughout the scaffold structure. The upper, cartilage region was 90% porous and composed of D,L-PLGA/L-PLA, with macroscopic staggered channels to facilitate homogenous cell seeding. The lower, cloverleaf-shaped bone portion was 55% porous and consisted of a L-PLGA/TCP composite, designed to maximize bone ingrowth while maintaining critical mechanical properties. The transition region between these two sections contained a gradient of materials and porosity to prevent delamination. Chondrocytes preferentially attached to the cartilage portion of the device, and biochemical and histological analyses showed that cartilage formed during a 6-week in vitro culture period. The tensile strength of the bone region was similar in magnitude to fresh cancellous human bone, suggesting that these scaffolds have desirable mechanical properties for in vivo applications, including full joint replacement.