Biodegradable oxygen biosensors via electrospinning

Abstract

Monitoring oxygenation in vivo is critical to ensuring human health, particularly in the context of ‘silent’ hypoxia. Utilizing blends of biodegradable polycaprolactone (PCL) and gelatine, we sought to develop an electrospun oxygen sensor that maintains the advantages of robust, phosphorescent oxygen-sensing chromophores while providing resorbable polymeric scaffolds benefiting from tailorable degradation times ranging from hours to weeks. Electrospun sensors successfully provide accurate oxygen measurements for periods >1 month. In vitro testing took place in a custom aqueous testing system over five weeks in 37°C phosphate-buffered saline (PBS); dissolved oxygen concentrations were maintained at 0–5% O₂ where physoxia characteristic of the subdermal environment is defined as 2–5% O₂. Excited state chromophore lifetime (τ) is quenched in the presence of dissolved diatomic oxygen and is influenced by characteristics of the surrounding matrix. The observed final deoxygenated τ (τ₀) values were split into 3 groups: polysulphone (PSU)-PCL (~397 µs) >75:25, 50:50 and 25:75 PCL:gelatine (~191–182 µs) > PCL, 10:90 PCL:gelatine, 1:99 crosslinked PCL:gelatine (~145–135 µs). Highly linear Stern–Volmer activity enabling accurate and precise calibration was observed even after 35 days of exposure; this proves that non-core–shell fibres consisting of blends of PCL and gelatine can yield predictable lifetime values for >30 days in vitro. Scanning electron microscopy and mass loss data revealed that sensor degradation is highly tailorable, allowing for the fabrication of sensors engineered for a specific biomedical time frame. In contrast, core–shell fibre sensors showed more variability in lifetime following internal degradation likely caused by caproic acid entrapment by the PCL ‘shell’. This work demonstrates that biodegradable and biocompatible optically monitored sensors can be fabricated to provide direct, accurate assessments of oxygenation, even as the sensor platform degrades in a controlled manner. Such technologies have the potential to substantially change respiratory disease management.