The ability to measure blood pressure inside the chambers of the heart or at other specific places in the cardiovascular system is essential to the early diagnosis and treatment of heart disease. Ideally, these measurements should be non-invasive. One approach to measuring pressure involves injecting very small gas bubbles, about one micrometer in diameter, called "microbubbles" into the blood. Microbubbles work by rapidly contracting and expanding in response to an ultrasound beam. The frequency of the expansion and contraction can be used to measure the pressure near the bubble. However, it is difficult to detect the very small changes in pressure that can signal health problems using this approach. This research project involves exploring a novel scheme for coating these bubbles to make them both more stable and more sensitive to changes in the local blood pressure. The researchers are making and characterizing a library of coating materials, and then testing the idea that the coatings will create an enhanced response of the bubble to the surrounding pressure. If successful, this approach could enable the use of coated microbubbles in a range of ultrasound diagnostics. The research project also involves training of students and young researchers in experimental methods, and several outreach activities are being pursued, including research open houses and science lectures for the general public.
In this project researchers are developing approaches to combine microfluidics, rheology, polymer synthesis, and graphene chemistry to produce and characterize polyethylene glycol-graphene oxide (PEG-GO) encapsulated carbon dioxide microbubbles and to manipulate their pressure sensitivity. The research leverages recent work on the synthesis and rheology of cross-linkable PEG-GO hydrogels and on the role of the PEG-GO hydrogel coating in controlling the pressure response of the microbubbles. A library of PEG-GO materials with different properties are being synthesized by systematically varying the molecular weight of the PEG and the average number and type of reactive functional groups per GO. Samples are being characterized using nuclear magnetic resonance spectroscopy, infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, atomic force microscopy, and rheometry methods to determine structure-property relationships. Preliminary results suggest that the hydrogel will stabilize carbon dioxide microbubbles. The researchers hypothesize that the coating will produce a synergistic effect on the pressure-bubble size relationship through the variation of the coating permeability as the ambient pressure changes. This modification should produce a dramatic response of bubble size to pressure changes, which should allow detection of very small changes in pressure. The researchers are using microfluidic platforms to generate PEG-GO encapsulated carbon dioxide bubbles and then using imaging to determine their dissolution in response to pressure changes.
