Breaking optical barriers: Transparent polymeric hollow fibers for biomedical applications

Abstract This study presents first polymeric hollow fibers (HFs) with sufficient optical transparency for real‐time and non‐invasive monitoring of biological systems, one of the most important hurdles accounted in HF bioreactor technology. Biocompatible polymers, including polyvinylidene fluoride (PVDF), polycaprolactone, and polyacrylonitrile, were processed via dry‐jet wet spinning. A comprehensive analysis of the morphological, structural, and transport properties of the HFs provided valuable insights into their optical performance. Our findings revealed the critical interplay of HF wall thickness, porosity, polymer crystal size, and intrinsic refractive index in achieving transparency. These findings may serve as a useful guidance to produce transparent polymeric HFs with similar or different polymeric systems. Remarkably, PVDF HFs achieved over 83% transmittance, exceeding standards for in vitro cell observation, and was achieved without the presence of modifiers. As a proof of concept, labeled human cerebral microvascular endothelial cells (hCMEC/D3) were cultured within the HFs and successfully monitored in real time under both static and dynamic conditions. These transparent HFs demonstrate transformative potential, enabling real‐time decision making while significantly reducing cost and time. This cutting‐edge membrane material paves the way for advanced applications in microfluidics, mass transport studies, and biomedical research, establishing these transparent HFs as key enabling materials for strategic biomedical technologies.