While gravity has its advantages in keeping us balanced and grounded here on Earth, scientists often find that they are at a disadvantage when trying to conduct research under its powerful, pulling influence. In these instances, the scientists prefer performing their studies in the weightless atmosphere of microgravity, where gravity is greatly reduced and solids, liquids, and gases behave differently.
In 1993, Paragon Vision Sciences, Inc., of Mesa, Arizona, participated in a research project with NASA’s Langley Research Center to perfect a process for developing contact lenses. The project called for three experiments that would fly onboard the Space Shuttle over the course of three separate missions, from 1993 to 1996. By unleashing contact lens materials to the microgravity settings of space, scientists from NASA and Paragon hoped to better understand how polymers — large molecules that make up plastics — are formed.
How it Works
At Paragon, a manufacturer of premium performance plastics used in gas permeable contact lenses, scientists must perform a complicated process called polymerization to ensure that the materials they are using to make contact lenses are nontoxic, highly biocompatible, extremely permeable to oxygen, durable under abrasive cleaning conditions, wettable, transparent, and machineable. Given all of these divergent properties, it is necessary for the Paragon scientists to synthesize polymer chains wherein the various links in the chains are of substantially different chemical character.
During polymerization, some of the links are preferably incorporated into the growing chains simply due to their compatibility to the environment of the chains. The result, however, is an uneven distribution of these “precursor” links in the final polymer, leading to an uneven distribution of properties throughout the final product. This can be detrimental in developing materials for contact lenses.
To avoid this consequence, it is essential to minimize the redistribution of the precursor links during polymerization. While many of the driving forces for redistribution can be restrained in laboratories on Earth, one cannot: convection, the response to density differences arising from uneven heating in the reaction mixture. Since convection is driven by gravity, it was apparent to Paragon scientists that the microgravitational atmosphere of space was the only environment where they could correctly study the properties of new polymer formulations plagued by this problem.
Paragon and Langley designed three experiments to go into space on Shuttle Missions STS-57 (Endeavor), STS-63 (Discovery), and STS-77 (Endeavor) and explore such formulations. The “Gas Permeable Polymer Materials” experiments were performed in SPACEHAB, a pressurized research laboratory within the Space Shuttle’s cargo bay that was created for scientific and commercial experimentation.
The Space Shuttle research showed which plastic formulation components made the strongest contributions to the nonuniformity and lesser permeability characteristics seen in similar formulations made on Earth (permeable plastics are ideal for extended-wear contact lenses because they allow more oxygen to reach the cornea, which is vital to preventing swelling of the eye). For Paragon, the findings led to an improved ground-based synthesis process and yielded new and better polymers for advanced uses in treating vision problems.
Paragon’s HDS® (hyperpurified delivery system) contact lenses are based on the unique technological advancements derived from the company’s experiments with NASA. HDS lenses are considered gas permeable, and therefore do not contain water, are resistant from deposits, and are less likely than soft contact lenses to harbor bacteria.
Where it Stands
The HDS line effectively eliminated “bad” silicones, making the lenses extremely oxygen efficient. HDS has been approved by the U.S. Food and Drug Administration (FDA) for up to 7 days of continuous wear. Along with this approval, HDS was the subject of the most complete and comprehensive study on gas permeable extended-wear lenses ever conducted, according to Paragon. The National Institutes of Health sponsored a study confirming the safety and efficacy of the lenses over a 5-year period, published in the August 2001 edition of the peer-reviewed journal, Ophthalmology.