(80d) Supercritical Fluid Enhanced Swelling and Drug Impregnation of Biomedical Polymers

The world of biomedical implants is growing faster than ever due to technological advancement driven by societal need. The baby boomer generation is proceeding into their post retirement years when health and wellness begin to decline. The American Heart Association states that 70% of men and women in the 60-79 year-old age group have cardiovascular disease. While diet and exercise may aid in the improvement of health, medicines and biomedical devices are often required to ensure health. Often, medicines are not adequate for treatment and more invasive devices must be utilized. As an example, cardiac catheters and stents are common devices used in cardiovascular procedures to diagnose and treat cardiovascular issues respectively; and like all devices put into the body they are foreign objects which result in an immune response often resulting in inflammation and scar tissue formation. The ultimate goal should be to produce an implant which minimizes the likelihood of immune response to the device while minimizing the need for supplemental medications used to prevent irritation, scarring, rejection, or clotting about the device.

What if devices could be prepared with polymeric coatings embedded with localized immunosuppressing technology? The polymer may be impregnated with a corticosteroid such as dexamethasone in order to reduce the inflammatory response around the device. This stands to minimize inflammation during routine procedures and also may function to extend the longevity of an implanted device before it begins to induce scarring. This idea exists firmly in academia but faces particular hurdles in making it to the consumer. Impregnation of a polymer in a medically safe way is the largest concern. Swelling the polymer and impregnating it with the drug is an advantageous method. However, temperature and solvent choices are limited due to the limitations of the drug to be impregnated and solvent interactions with the body.

Supercritical fluids, namely supercritical carbon dioxide (SC-CO₂), are applied to drug impregnation of polymers. SC-CO₂ has a low critical temperature and reasonable pressure, it is nonflammable, and it readily leaves the system when pressure is relieved. Polymer solubility in SC-CO₂ is highly dependent on the type of polymer and chain length. Polymers that are hard enough to be used for biomedical purposes are not solubilized in SC-CO_2, but do swell to some extent in its presence. Corticosteroids and other inflammatory response drugs are relatively small molecules when compared to polymers and have the ability to be soluble in SC-CO₂ as a function of temperature, pressure, and presence of a co-solvent.

A Thar SC-CO₂ phase analyzer is used to swell batches of polymer rings like those used in various biomedical applications. It features video capture technologies, variable speed motorized stirring, and a varying volume cell. Various inserts have been fashioned to further modify the functionality of the cell. The polymeric rings are inspected via SEM before and after swelling to make note of structural changes. Adequate swelling must be observed such that the drug can be properly impregnated. This allows for the drug to have much better functionality due to not only having drug coated on the outer surface but also contained within polymeric pores allowing for diffusion from within.