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Nanoparticle Skin Patch Monitors Tumor Size During Cancer Care

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Medical researchers and chemical engineers at Taiwan’s National Tsing Hua University have developed a new wearable patch that can provide continuous monitoring of tumors under the skin.

The patch, which consists of a thermoplastic polyurethane (TPU) film embedded with hafnium oxide (HfO2) nanoparticles, can also transmit real-time data to a smartphone to support the tracking of tumor growth and regression.

The use of the patch to monitor tumor size in mouse models of cancer is reported in ACS Nano.

Better tumor tracking

In clinical practice, tumors are normally measured and monitored using computed tomography (CT) scans or using mechanical instruments such as calipers. This kind of tumor size assessment is very helpful for doctors in determining treatment initiation, dosing optimization and the general effectiveness of a specific treatment.

However, neither CT scans nor the caliper method are particularly ideal for making these measurements. In vivo CT scans are expensive and typically only provide a two-dimensional image of the tumor. The use of calipers allows for three-dimensional measurement, but they also introduce a significant amount of measurement error that could interfere with continuous assessment.

To simplify tumor monitoring, researchers developed a new wearable skin patch that can accurately detect variations in tumor shape and wirelessly send data and alerts to a smartphone app.

The skin patch acts as a dielectric strain sensor – a type of mechanical sensor that measures the deformation or pressures acting on a material. As the TPU-HfO2 nanoparticle film is stretched, this deformation increases the distance between the embedded nanoparticles, causing a proportional change in the material’s capacitance. This generates fluctuations in the patch’s electrical impedance, which can be measured and used to observe how the film has been stretched.

Electronic properties of materials

A material’s capacitance is its ability to store electric charge. Electrical impedance is a measure of how well electricity travels through a given material, with a high impedance meaning a high resistance to electrical current.

By applying the patch over the top of the skin, directly over the site of a tumor, any fluctuations in the tumor size will change the amount of strain on the patch and be reflected in the impedance measurements. In this way, the patch can accurately monitor changes the size of a tumor before or after treatment.

To further ease the practice of monitoring tumor growth and regression, the researchers have built the sensor so that it wirelessly transmits its impedance data to a smartphone. This data is processed using a companion smartphone app, which also emits alerts if any critical changes in tumor volume are detected.

Skin patch monitors tumor growth in mouse model

After successfully demonstrating the use of the TPU-HfO2 nanoparticle film on 3D-printed models of tumor shapes, the researchers went on to use the skin patch to monitor tumor progression in mice.

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A skin patch, along with two carbon-tape electrodes, was placed onto the skin of the mice above the site of a small subcutaneous tumor. Relative impedance as recorded by the skin patch was recorded over seven days, with caliper measurements of the tumor also being taken at regular intervals.

The skin patch was able to effectively track the growth of the subcutaneous tumor before treatment, with its impedance measurements increasing consistently with the growth of the tumor. Once the tumor volume hit a predefined critical limit, it sent an alert to the researcher’s smartphone to signal that treatment needed to begin. The patch was also able to detect impediment in the tumor growth once anti-tumor treatments had begun. 

“The wearable TPU-HfO2 DE [dielectric elastomer] strain sensor developed demonstrates exceptional precision in measurements, maintaining accuracy even when dealing with minute tumor volumes, as evidenced by a significantly lower error percentage (averaging around 5 to 10%) compared to those obtained by the caliper (ranging from approximately 10 to 20%) in in vivo experiments,” the researchers wrote.

The team noted that the use of such a skin sensor would be useful in meeting the demands of personalized medicine and in providing continuous data and support to telehealth professionals as they monitor a patient’s care.

Reference: Siboro PY, Sharma AK, Lai PJ, et al. Harnessing HfO2 nanoparticles for wearable tumor monitoring and sonodynamic therapy in advancing cancer care. ACS Nano. 2024;18(3):2485-2499. doi: 10.1021/acsnano.3c11346