Osmotic cavitation of elastomeric intraocular lenses.

In recent years, traditional rigid materials have been replaced with softer elastomers in intraocular lenses to minimize the size of the required surgical incision, thereby reducing patient recuperation time. However, water-filled cavities that may impact visual acuity are found in many of these new implants. We demonstrate that the cavitation observed in vivo can occur due to an osmotic pressure difference between the aqueous solution within the cavity and the external media in which the lens is immersed. By reducing the osmolarity of the external solution from 300 to 0mM, we observe an increase in cavity volume of almost a factor of 30. Further, we have developed a model for cavity growth assuming the controlling factor is diffusion of hydrophilic molecules from the polymer matrix into the cavity. We find that the experimental observations are consistent with the model and suggest that oligomeric species generated during polymerization are responsible for the observed cavitation.

Biaxial flex-fatigue and viral penetration of natural rubber latex gloves before and after artificial aging.

Barrier integrity of unaged and oven-aged (at 70 degrees C) natural rubber latex examination gloves was assessed with a biaxial flex-fatigue method where failure was detected electronically, and by live viral penetration testing performed according to a modified version of ASTM F1671-97a. When no change in barrier properties was detected during flex testing, no virus passage was found after viral challenge. Conversely, when a change in the barrier properties was indicated by the electrical signal, virus passage was found in 74% of the specimens. Flex-fatigue results indicated that unaged test specimens from powdered (PD) and powder-free (PF) nonchlorinated gloves had significantly longer fatigue lives than powder-free chlorinated (CL) gloves from the same manufacturer. Biaxial flexing of oven-aged glove specimens showed a marginal increase in fatigue life for the PF gloves, but no increase for the PD gloves. The fatigue life of the CL gloves was observed to increase significantly after oven aging. However, this appears to be due to a design feature of the test apparatus, wherein peak volume displacement of the worked specimen is held constant. An aging-induced change in the viscoelastic properties of the CL gloves-permanent deformation of the specimens early in the fatigue test-relieves the stress magnitude applied as the test progresses. Thus, permanent deformation acts as a confounding factor in measuring durability of latex gloves by fixed displacement flex-fatigue.