Ageing performance of biodegradable PLA for durable applications

The durability of 2 commercially available injection mold grades and one extrusion grade of polylactic acid (PLA) was assessed. Here, the materials were exposed to elevated temperatures/humidity for a period of several weeks. Moisture absorption, molecular weight change, mechanical properties, crystallinity changes, and microscopic imaging were all monitored at regular intervals throughout the course of the combined heat and humidity ageing study. The conditions for the ageing study were set at 60°C and 45% relative humidity and all three PLA grades showed a significant increase in crystallinity and conversely reduced mechanical performance over the 68-day ageing period. Microscopic images of the materials suggested that surface degradation was not dominant. It is known that the moisture absorption of PLA which is revealed by weight gain is usually low for PLA, but the amount absorbed is sufficient to induce bulk degradation, and the mechanical performance was reduced over the ageing period. All materials exhibited a loss in molecular weight over time. The molecular weight at any given time was reflective of the starting molecular weight and thus the extrusion grade PLA showed better mechanical performance than the injection mold grades at any given time. This behavior was satisfactorily modeled using an acid-catalyzed hydrolysis model. Interestingly the higher molecular weight PLA exhibited slower degradation kinetics as compared to the lower molecular weight injection molding grades. This study showed that commercially available PLA resins are not suitable for use in applications that require long sustained durability in environmental conditions such as these where high temperature and humidity are encountered for any appreciable amount of time

Torpedo maculopathy: A primary choroidal capillary abnormality?

A 26-year-old healthy male patient's fundus revealed findings consistent with torpedo maculopathy. Swept-source optical coherence tomography (OCT) showed a dome-shaped elevation of the retina at the level of ellipsoid zone. On OCT angiography segmented at the level of the choriocapillaris, a cluster of convoluted fine vessels was seen, and further, deeper scans of the larger choroidal vessels showed a slower flow. From these observations along with the embryological correlation of choriocapillaris development, a possibility of an abnormality preventing proper fenestration of the choriocapillaris along the horizontal raphe being responsible for this anomaly is suggested

Assessment of macular vascular plexus density using optical coherence tomography angiography in cases of strabismic amblyopia

Purpose: To evaluate the superficial retinal vascular plexus density using optical coherence tomography angiography (OCTA) in cases of strabismic amblyopia. Methods: Ten eyes of 10 patients with purely strabismic amblyopia underwent detailed ocular evaluation followed by the assessment of the superficial retinal plexus vascular density using OCTA (Topcon DRI OCT Triton, Swept Source OCT, Topcon, Japan). Ten contralateral normal eyes of the same patients were considered as control. All these 20 eyes underwent a 4.5 × 4.5 mm cube scan OCTA centered at the fovea. Using the Topcon propriety software all 20 eyes were assessed for the capillary plexus density of the superficial retinal vascular plexus along the superior, inferior, nasal, and temporal quadrants centered at the fovea. The numerical values were statistically assessed using a paired t-test with respect to each quadrant between the normal and the pathological eyes. Results: The average age of patients was 16 years and eight patients were males. The mean superficial retinal vascular plexus density along the superior, inferior, nasal, and temporal quadrants in normal and pathological eyes were 49.25 ± 30.34 and 48.93 ± 2.85, 47.22 ± 4.11 and 47.37 ± 4.8, 45.54 ± 1.55 and 43.81 ± 4.21, and 46.26 ± 4.63 and 46.38 ± 5.40, respectively. Similarly, the capillary densities along the central were 17.84 ± 3.49 and 17.24 ± 2.44 in normal and pathological eyes. The differences among all these four quadrants and central area were not statistically significant (P-values > 0.05 for all four quadrants and central area) as compared with the normal eyes. Conclusion: The superficial retinal vascular plexus density of a 4.5 × 4.5 mm cube centered at the fovea of eyes of cases of strabismic amblyopia is similar to that of normal eyes