Bio-Photonic Patch IoT Wearable for Post-Operative Skin Recovery

The engineering team was approached by a leading company in regenerative medicine focused on developing an innovative IoT connected wearable to monitor patients after they have had surgery, to reduce the likelihood of patients readmitted to the hospital due to surgical site infections (SSI) undetected and to provide continuous monitoring during the critical 14 days following surgery so that medical providers can address tissue hypoxia.

SSIs experienced by up to 5% of surgical patients contribute to longer hospital stays, increased costs, and an overall higher rate of morbidity among surgical patients.

Historically, hospitals have relied on visual inspection of wounds and intermittent checks to monitor for SSI as such, there have been many occasions when medical staff has failed to identify the first signs of biochemical changes in the wound bed.

The Bio-Photonic Patch was designed to provide proactive, continuous insight into the wound environment by providing StO₂ and pH measurements directly from the wound site and it was designed to be thin, biocompatible, and able to function properly in the moist, exudative wound environment.

This development of an IoT connected Bio-Photonic Patch fits within the context of emerging technologies around “Smart Wound Products”, and how flexible sensors can be leveraged to collect biomarker data in real-time, and enable physicians and other health care providers to provide more predictive wound care versus reactive wound care.

Three primary difficulties determined the "extreme" challenges encountered:

• The need for an ultra-thin form factor whereby the patches would accurately integrate under standard surgical dressing, without producing areas of pressure necrosis or discomfort would be ≤1mm
• The need for accurate biochemical sensing in hostile conditions. With traditional pulse oximetry not able to perform as accurately when using non-pulsatile (inflamed) tissue, we required the ability to achieve precise StO2 and pH measurements in exudate, moving, and differing skin tones
• The need for water resistant equipment as the wound fluid (which has a high ionic content) can cause short circuiting of the electronic components or delamination of adhesives over an extended period of time.

To address the challenges associated with Rigid Devices, we are using flexible hybrid electronics inspired by new developments in Stretchable Bioelectronics and Multimodal Patches.

Multi-Spectral Bio-Photonics for StO₂ Monitoring

For StO₂ Monitoring, we are using micro-LEDs, which emit light at 660 nm (red) and 940 nm (NIR), along with organic photodiodes (OPDs) mounted on a polyimide substrate to perform spectroscopic measurements using reflectance-based techniques.

The light emitted by the LED penetrates the dermis of the skin and then is backscattered back to the OPD, where it is detected and processed via a modified Beer-Lambert law algorithm.

The algorithm allows for calculating regional oxygen extraction as well as regional StO₂ values while rejecting motion artifacts. The calculated StO₂ outputs are validated against clinical near-infrared spectroscopy (NIRS) devices, and the results demonstrate that the mean absolute difference between the two methodologies (≤3%) remains consistent across both static and dynamic subject conditions.

These results suggest that our reflectance-based StO₂ system superiorly performs compared to most currently available commercial reflectance systems, as they are hindered by variability in wound characteristics.

Microfluidic-Enabled pH Sensing

A passive micro-capillary network in the medical-grade adhesive wicked microliter volumes of exudate to a chamber with a pH-sensitive chemical transducer (ion-selective membrane). Changes in hydrogen ion concentration produced a measurable potentiometric shift. This provided early detection of acidification (pH drop below 7.0 often signals bacterial overgrowth). The design minimized fluid accumulation and avoided sensor fouling.

Ultra-Low-Power Edge Processing

A passive micro-capillary network using a construction adhesive was used to collect exudate in microliter volumes and to direct them into a chamber containing a pH-sensitive chemical transducer (ion-selective membrane).

Changes in hydrogen ion concentration caused a detectable potentiometric signal shift, providing early indication of acidifying (pH <7.0) conditions often indicating an overgrowth of bacteria. Fluid build up was minimized during monitoring and there was minimal biolayer (fouling) formation on the sensors.

The development of medical devices followed the FDA V Model lifecycle to reach Class II market clearance (i.e., 510(K)), similar to the class II device clearance status of wound monitoring wearables.

Biocompatibility:

All materials (e.g., acrylic adhesive, silicone encapsulating) underwent full ISO 10993 testing (cytotoxicity, sensitization, irritation).

Performance Testing:

Bench top and ex vivo models, plus early pilot data from humans, confirmed the accuracy of the device relative to our gold standard devices (i.e., transcutaneous oxygen systems). Additionally, clinical correlation studies provided us with reliable trends in how patients are healing.

Interoperability & Integration:

The backend connected to the HL7 FHIR standards for seamless integration with Epic and Cerner electronic health record systems (displays a composite “Wound Health Score” for the clinician).

Security:

The HW root of trust (i.e., unique device key), AES-256-GCM encryption at the edge, and fail-safe modes (e.g., “integrity error” alerts in case of occlusion or contamination) all supported the device’s security. Usability per IEC 62366 ensured that anyone, including elderly patients, could easily use the device—allowing for NFC pairing with their smartphones.

The impact of the patch was based on a 6-month study with post-surgical patients who had either abdominal or orthopedic procedures. The study provided the following information:

• Infections and complications associated with surgical procedures were reduced by 35% through earlier notification of a possible infection.
• Patients could be detected with hypoxia (lack of oxygen) 22% faster than a nurse check.
• 94% of patients reported wearing the patch all day with minimal interference.

In addition, these results are in line with other smart bandage research showing that using pH, oxygen, and temperature to sense wound healing allows for early intervention, resulting in decreased readmission rates and improved healing.

This project demonstrated the use and expertise in photonics, microfluidics, and low-power Internet of Things (IoT) technologies and established the company as a leader in using regenerative monitoring.

Future projects incorporate artificial intelligence (AI) to predict outcomes associated with wound healing, as well as to provide therapeutic feedback on the use of light, while capitalizing on the rapid advancements in flexible biosensor technologies for personalized wound care.