Phosphorescent Microneedle Array for the Measurement of Oxygen Partial Pressure in Tissue

Abstract

The knowledge of the exact oxygen partial pressure in tissue is crucial for patient care and in the treatment of ischemic medical conditions. However, current methods to assess oxygen partial pressure in tissue suffer from a variety of disadvantages, including complex equipment and procedures that necessitate trained personnel. Additionally, the barrier function of the stratum corneum reduces oxygen exchange and can consequently hamper surface measurements of rapidly changing oxygen partial pressure in tissue. To overcome these challenges, a novel, easy-to-use technique to monitor the oxygen partial pressure in tissue using microneedle arrays (MNAs) has been developed. The MNAs can be made from poly(ethyl methacrylate) and poly(propyl methacrylate) and overcome the skin's barrier function to measure oxygen in the capillary bed and interstitial fluid of the skin. The MNAs' tips are embedded with an oxygen-sensitive phosphorescent metalloporphyrin, where the oxygen partial pressure inversely correlates to changes in both emission intensity and phosphorescence lifetime of the in-house developed red emitting Ptcore porphyrin. It was demonstrated that the oxygen-sensing MNAs are sufficiently robust to puncture human skin via rupture of the stratum corneum, and that the MNAs can detect changes in oxygen partial pressure in skin within the physiologically relevant range (0−160 mmHg). Additionally, the MNAs can be combined with a wearable wireless optical readout system, making these oxygensensing MNAs a novel wearable and portable method for user-friendly monitoring of oxygen partial pressure in skin.

Calculation of Tissue Oxygenation via an Inverse Boundary Problem for Transcutaneous Oxygenation Wearable Applications

“…This phosphor can be readily embedded within polymer-based films, resulting in ultrathin, breathable films that exhibit bright emission throughout the physiological pO 2 range and are impervious to changes in relative humidity. , The device improves on existing technology, as it is a true wearable (does not require external readout electronics or cabled leads), it is light and entirely self-contained, and it measures tissue oxygenation without the use of heating elements. The porphyrin has been successfully implemented in different applications with multiple form factors, such as a paintable bandage that has been tested clinically, wound-care hydrogel dressings, devices that can be worn on the skin, , intramuscular needles, and subdermal microneedles …”

“…The porphyrin has been successfully implemented in different applications with multiple form factors, such as a paintable bandage that has been tested clinically, 10 wound-care hydrogel dressings, 17 devices that can be worn on the skin, 12,18 intramuscular needles, 19 and subdermal microneedles. 20 In the TCOM wearable, the oxygen sensing film is composed of: a medical grade semipermeable transparent membrane partially occluding the skin from atmospheric oxygen (Bioclusive, McKesson), a thin poly(propyl methacrylate) (PPMA) layer with the embedded metalloporphyrins, and a highly breathable white scattering layer which increases the collected phosphorescence signal reaching the photodetector and serves as optical insulation (Figure 1a). The design of the O 2 -sensing film allows for short settling or equilibration times due to a conformal, airtight seal over the skin, which minimizes headspace, or the volume of trapped air between device and skin.…”

Gold Nanocluster-Based Fluorescent Microneedle Platform toward Visual Detection of ATP

“…Microneedles (MNs), an array of miniaturized needles at micrometer scales, are small and minimally invasive and can be combined with other detection technologies, which have unique advantages for in situ detection. − Compared with conventional sampling methods that usually need multiple steps or extra devices, MNs can extract analytes more easily and efficiently through capillary force or negative pressure. − Particularly, hydrogel MNs have shown great potential in developing point-of-care sensing devices because of their excellent swelling ability, good biodegradability, and biocompatibility. − For example, Al Sulaiman et al . developed MNs that are coated with an alginate-peptide nucleic acid (PNA) hybrid material for sequence-specific detection of nucleic acid from the skin interstitial fluid.…”

Wearable Sensors

“…In this regard, Luo and co-workers have described a flexible patch for continuous blood glucose level monitoring that integrates biodegradable microneedles . In a similar vein, Müller et al fabricated acrylate-based microneedle arrays to measure oxygen within the interstitial fluid of the skin . In both studies, the biocompatibility of the sensor is a critical issue in engendering long-term in vivo use.…”

“…17 In a similar vein, Muller et al fabricated acrylate-based microneedle arrays to measure oxygen within the interstitial fluid of the skin. 18 In both studies, the biocompatibility of the sensor is a critical issue in engendering long-term in vivo use. Conversely, Zhu and colleagues have used commercial contact lens materials to fabricate smart contact lenses able to perform wireless intraocular pressure measurements, using a spectacle-integrated impedance-based reader.…”