The analysis was conducted on 96L/4D PLA and 80L/20D,L PLA polymers. When analyzing the shear strength as a function of degradation time it was found that the ? 1.2 mm samples showed more rapid strength loss than the ? 4.0 mm samples (Fig. 3A). It was also observed selleck kinase inhibitor that the ? 1.2 mm samples with a draw ratio of 3.8 had a noticeably higher initial shear strength than the ? 4.0 mm samples with a slightly higher draw ratio of 4. This difference most probably stems from the fact that there is a more profound molecular orientation in the smaller diameter samples, which results in a more homogeneous molecular orientation in the direction of the draw. There was no obvious difference between the small and large samples when plotting the shear strength values (% of initial) as a function of the corresponding inherent viscosities (Fig.

3B). As our previous study has proven that these ? 1.2 mm samples had a faster iv loss than the ? 4.0 mm samples,18 the more profound strength loss shown in Figure 3A can be assumed to be a consequence of the faster degradation. The sample diameter did not, however, seem have any effect on the threshold iv at which the rapid strength loss begins (Fig. 3B). Table 1. The sample codes and the initial measured values for oriented and sterilized rods Figure 3. Effect of the sample diameter on shear strength retention of oriented 96L/4D PLA and 80L/20D,L PLA samples. Shear strength as a function of degradation time (A) and inherent viscosity (B). Values are averages of the mentioned parallel …

Residual monomer content The effect of the residual monomer content on shear strength retention was analyzed by using oriented ? 1.5?3.1 mm 96L/4D PLA samples with different residual monomer contents. Due to the limited quantity of raw materials available, different sample diameters were used. Even the relatively low increase in monomer content which was studied (from 0.09% to 0.33%) shortened the time at which the strength remained at the initial level from 30 to 12 weeks (Fig. 4A). However, the profile of the plotted curve of the shear strength loss against hydrolysis time was similar. Figure 4. Effect of the residual monomer content on shear strength retention of ? 1.5?3.1 mm 96L/4D PLA samples. Shear strength as a function of degradation time (A) and inherent viscosity (B). Values are averages of the mentioned …

When the remaining shear strength values (% of initial) were plotted as a function of inherent viscosity (Fig. 4B) it was seen that the strength retention Cilengitide was practically identical for all the analyzed samples. Regardless of the residual monomer content, the samples were able to retain at least 50% of their initial shear strength until the inherent viscosity had degraded to a value of ca. 0.5 dl/g. Materials and Methods The samples were manufactured in the same manner as earlier by means of single-screw melt extrusion followed by die drawing (orientation process).