Artificial lung (AL) membranes are used for blood oxygenation for patients undergoing open-heart surgery or acute lung failures. Current AL technology employs polypropylene and polymethylpentene membranes. Although effective, these membranes suffer from low biocompatibility, leading to undesired blood coagulation and hemolysis over a long term. In this work, we propose a new generation of AL membranes based on amphiphobic fluoropolymers. We employed poly­(vinylidene-co-hexafluoropropylene), or PVDF-co-HFP, to fabricate macrovoid-free membranes with an optimal pore size range of 30–50 nm. The phase inversion behavior of PVDF-co-HFP was investigated in detail for structural optimization. To improve the wetting stability of the membranes, the fabricated membranes were coated using Hyflon AD60X, a type of fluoropolymer with an extremely low surface energy. Hyflon-coated materials displayed very low protein adsorption and a high contact angle for both water and blood. In the hydrophobic spectrum, the data showed an inverse relationship between the surface free energy and protein adsorption, suggesting an appropriate direction with respect to biocompatibility for AL research. The blood oxygenation performance was assessed using animal sheep blood, and the fabricated fluoropolymer membranes showed competitive performance to that of commercial polyolefin membranes without any detectable hemolysis. The data also confirmed that the bottleneck in the blood oxygenation performance was not the membrane permeance but rather the rate of mass transfer in the blood phase, highlighting the importance of efficient module design.

Fluoropolymers exhibit very high hydrophobicity because of the presence of fluorine groups. However, they sometimes exhibit peculiar polarityreferred to as "polar hydrophobicity"depending on their crystal polymorphs. This intriguing phenomenon is not yet clearly understood, and it remains a challenge to tailor this rare property for desired applications. Particularly, water desalination via membrane distillation (MD) is an emerging process, which requires hydrophobic membranes with extremely low affinity toward water molecules. In this study, we investigated the water affinity of fluoropolymers, namely, vinylidene fluoride (VDF) and hexafluoropropylene (HFP) groups, and their correlation with membrane performance. The molecular origin of fluoropolymer polarity was examined via density functional theory analysis, which unveiled that β-phase VDF crystals have twice as many water-favorable sites as the α-phase, whereas HFP groups exhibit lowest interaction energy with water. To maximize membrane hydrophobicity, we synthesized P(VDFco-HFP) polymers with varying VDF-to-HFP ratios and fabricated porous membranes with similar pore sizes using the electrospinning technique. Upon thorough characterization, a clear inverse correlation was observed between the β-phase VDF crystals and the observed hydrophobicity and performance, confirming the source of fluoropolymer polarity. The polymorphcontrolled membranes exhibited a unique optimum at 8% HFP content with 35-fold enhancement in MD long-term stability compared to that of pristine polyvinylidene fluoride membranes. It is highlighted in this work that the polymer mechanical properties cannot be compromised over the desired hydrophobic properties in membrane contactor processes.

Hollow-fiber membranes are widely used in various fields of membrane processes because of their numerous properties, e.g., large surface area, high packing density, mass production with uniform quality, obvious end-of-life indicators, and so on. However, it is difficult to control the pores and internal properties of hollow-fiber membranes due to their inherent structure: a hollow inside surrounded by a wall membrane. Herein, we aimed to control pores and the internal structure of hollow-fiber membranes by fabricating a dual layer using a dual nozzle. Two different pore formers, polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP), were separately prepared in the dope solutions and used for spinning the dual layer. Our results show that nanoscale pores could be formed on the lumen side (26.8–33.2 nm), and the open pores continuously increased in size toward the shell side. Due to robust pore structure, our fabricated membrane exhibited a remarkable water permeability of 296.2 ± 5.7 L/m2·h·bar and an extremely low BSA loss rate of 0.06 ± 0.02%, i.e., a high BSA retention of 99.94%. In consideration of these properties, the studied membranes are well-suited for use in either water treatment or hemodialysis. Overall, our membranes could be considered for the latter application with a high urea clearance of 257.6 mL/min, which is comparable with commercial membranes.