Bioactive polymer surfaces via supercritical fluids

Supercritical CO2 (scCO2) can reversibly swell thermoplastic polymers. We use this phenomenon to enhance the impregnation of a fluorescently-labeled protein into a polymethylmethacrylate (PMMA) matrix. Exposure to scCO2 provides simultaneous sterilization and foamed morphologies similar to those found in both hard and soft tissues in vivo. This combination of enhanced diffusion, foaming, and sterilization can conceivably be exploited to produce or modify a variety of biomedical materials. In the current study, efforts were made to control the scCO2-induced foaming in PMMA. Fundamental information regarding solid state swelling (via laser dilatometry) and foaming (via microfocus X-ray computed tomography) were used to explore the interactions between process variables. This is the first application of laser dilatometry to measure scCO2 swelling of and desorption from a polymer in situ. scCO2 at 40 °C was also used to impregnate PMMA with a fluorescently-labeled protein, a rhodamine-labeled antibody to immunoglobin. Protein impregnation was verified using confocal microscopy.