Stability of Polyethylene Glycol and Zwitterionic Surface Modifications in PDMS Microfluidic Flow Chambers.

Blood-material interactions are crucial to the lifetime, safety, and overall success of blood contacting devices. Hydrophilic polymer coatings have been employed to improve device lifetime by shielding blood contacting materials from the natural foreign body response, primarily the intrinsic pathway of the coagulation cascade. These coatings have the ability to repel proteins, cells, bacteria, and other micro-organisms. Coatings are desired to have long-term stability, so that the nonthrombogenic and nonfouling effects gained are long lasting. Unfortunately, there exist limited studies which investigate their stability under dynamic flow conditions as encountered in a physiological setting. In addition, direct comparisons between multiple coatings are lacking in the literature. In this study, we investigate the stability of polyethylene glycol (PEG), zwitterionic sulfobetaine silane (SBSi), and zwitterionic polyethylene glycol sulfobetaine silane (PEG-SBSi) grafted by a room temperature, sequential flow chemistry process on polydimethylsiloxane (PDMS) over time under ambient, static fluid (no flow), and physiologically relevant flow conditions and compare the results to uncoated PDMS controls. PEG, SBSi, and PEG-SBSi coatings maintained contact angles below 20° for up to 35 days under ambient conditions. SBSi and PEG-SBSi showed increased stability and hydrophilicity after 7 days under static conditions. They also retained contact angles ≤40° for all shear rates after 7 days under flow, demonstrating their potential for long-term stability. The effectiveness of the coatings to resist platelet adhesion was also studied under physiological flow conditions. PEG showed a 69% reduction in adhered platelets, PEG-SBSi a significant 80% reduction, and SBSi a significant 96% reduction compared to uncoated control samples, demonstrating their potential applicability for blood contacting applications. In addition, the presented coatings and their stability under shear may be of interest in other applications including marine coatings, lab on a chip devices, and contact lenses, where it is desirable to reduce surface fouling due to proteins, cells, and other organisms.

Design Analysis and Optimization of a Single-Layer PDMS Microfluidic Artificial Lung.

OBJECTIVE: Microfluidic artificial lungs (µALs) are being researched for future clinical use due to the potential for increased gas exchange efficiency, small blood contacting surface area, small priming volume, and biomimetic blood flow paths. However, a current roadblock to clinical use is the need to stack hundreds to thousands of these small-scale µALs in parallel to reach clinically relevant blood flows. The need for so many layers not only increases the complexity and projected cost to manufacture a µAL, but also could result in devices which are cumbersome, and, therefore, not suitable for portable artificial lung systems. METHODS: Here, we describe the design analysis and optimization of a single-layer µAL that simultaneously calculates rated blood flow, blood contacting surface area, blood volume, pressure drop, and shear stress as a function of blood channel height using previously developed closed-form mathematical equations. A µAL designed using this procedure is then implemented and tested. RESULTS: The resulting device exhibits a rated flow of 17 mL/min and reduces the number of layers required for clinically relevant µAL devices by a factor of up to 32X compared to previous work. CONCLUSION: This procedure could significantly reduce manufacturing complexity as well as eliminate a barrier to the clinical application of these promising devices. SIGNIFICANCE: The described method results in the highest rated flow for any single-layer µAL to date.