## Abstract

Medical tapes often hold critical devices to the skin so having high adhesion for the lifespan of this product is of great importance. However, the removal process is challenging for caregivers and patients alike, often a painful process that can cause medical adhesive-related skin injury (MARSI). By using an industrial thermally sensitive tape, a surrogate photosensitive tape was developed that switched from the equivalent of high-adhesion medical tape to low-adhesion medical tape. This resulted in an 86% reduction in the average peel strength when heated from 45 to 55 °C using a custom test apparatus. To photo-release the prototype tape (PT), a near-infrared (NIR) absorbing layer was painted on the visibly clear thermal-sensitive tape and an NIR optical wand using 15-LEDs (940 nm) with thermal feedback control was designed and tested. Preliminary performance of photo-to-thermal conversion was numerically modeled with transient results matching experimental measurements with 96.8% correspondence. Using the verified energy conversion model of the surrogate photosensitive tape, a new NIR optical wand was designed for rapid and noncontact release of a future medical tape at 10 deg lower than the release temperature (RTemp) of the custom adhesive, called UnTape. Numerical simulations compared to the thermal skin pain threshold of 45 °C predicts photo-release within 1.1 s of NIR exposure (85.5% absorption in PT at < 1.3 W/cm2). The unique properties of the multifunctional UnTape system (tape and portable NIR wand) may allow even stronger skin adhesion for critical medical devices while concurrently reducing the risk of MARSI upon photo release and easy removal.

## Introduction

Medical adhesive tapes are a class of ubiquitous medical devices that consist of a plastic or fabric backing, coated on one side with an adhesive layer. According to the FDA Code of Federal Regulations Title 21 Section 880.5240 [1], “the device is used to cover and protect wounds, to hold together the skin edges of a wound, to support an injured part of the body, or to secure objects to the skin.” Adhesion to the skin is the primary objective of these functions. However, a stronger and more stable adhesive bond to the skin requires a more laborious and often painful removal process, which can lead to anxiety for patient and caregiver [2] and medical adhesive-related skin injuries (MARSIs) [3].

Medical adhesive-related skin injury is defined as an occurrence of erythema or cutaneous abnormality (including blister, erosion, tear) that persists 30 min or more after adhesive removal [3]. The prevalence rates of MARSI vary significantly between studies for patient populations and the type and location of the medical adhesive. One study reported a total MARSI incidence of 29.83% at the peripherally inserted central catheter insertion sites of oncology patients [4]. Another study reported a MARSI incidence of 5.8% with 207 patient visits in an outpatient vascular clinic over 3 months [5]. MARSI is potentially underreported in many areas of care, as it is not considered an unexpected or adverse injury [6]. From one study in a pediatric intensive care unit, 76.3% of MARSI was caused by the securements of tracheal intubation, vascular access, and electrocardiogram monitor [7]. Because accidental dislocation of those critical medical devices can result in serious events, the problems resulting from limited choices in medical tape are expected to be well beyond MARSI prevalence. Although the probability of MARSI is based on the combination of various risk factors, it is highest with neonatal patients [3], as neonatal skin is nearly 50% thinner than adult skin, and with geriatric patients [5] who often have compromised skin. In a study published in 2015, the daily MARSI prevalence ranged from 3.4% to 25.0% with a mean of 13.0% and a patient median age of 58 years [8]. In a pilot study with pediatric patients who required central venous access devices secured by clear medical tape, skin injuries were a substantial issue affecting 9% of patients and causing an additional 4% to withdraw due to skin irritation [9].

We used a surrogate system to demonstrate the mechanism of rapid and gentle removal of an NIR photothermal sensitive tape (UnTape), and propose the future design of a medical tape system based on experiments and numerical analyses. The overall procedure of this study consists of following steps: (1) experimental verification that an industrial thermal-release tape can be a medical tape surrogate based on a comparative study of the peel strengths of commercially available products, (2) develop a prototype tape (PT) demonstrating the rapid and noncontact photothermal release by applying an NIR absorbing dye to the outer layer of the thermal-release tape, (3) fabricate an NIR light source device with a temperature control feature, (4) numerically model the adhesive thermal switching using a realistic skin substrate, (5) compare the experimental and modeling results and establish a relationship of energy flow from the electrical input to thermal heating of the PT, and (6) determine the design parameters for a future clinical UnTape system.

## Methods

The UnTape system consists of a photothermal sensitive tape (named UnTape) and an NIR light source (named NIR wand). For the proof-of-concept investigation of the UnTape system, we used the combination of two off-the-shelf products as a PT, (1) thermal-switchable tape with clear backing and (2) NIR-absorbing liquid coating. The commercial adhesive film, used in the electronics industry, offers decreased adhesion when heated, which is marketed as Intelimer® Tape (IT), manufactured by Nitta Corporation (Osaka, Japan) under license from the Landec Corporation (Menlo Park, CA). The adhesion strength of IT is significantly reduced near the switch temperature (STemp) of 50 °C. The maximum peel strength decreases from 90% (45 °C) to 10% (55 °C).

To increase the temperature of the IT using NIR light, we applied an NIR dye coating (LD920C, Clearweld®, Gentex Corporation, Carbondale, PA) on the top surface of the IT backing. The NIR dye coating efficiently converts the NIR (940–1100 nm) optical power into thermal energy. Our measurements showed that a thick layer of the NIR dye coating (four strokes of a dye applicator) could reduce the IT light transmission near 900 nm by more than 95%, while retaining transmission in the visible spectrum (Fig. 1), providing NIR dye coating transmittance results similar to those in related Refs. [17,18]. Light transmission in the visible region (400–700 nm) is a necessary feature of medical tape used to secure intravenous devices to allow for monitoring of proper fluid delivery. The absorption of the NIR light depends on the amount of dye material deposited on the IT backing surface. However, the low viscosity, acetone-based NIR dye coating solution uses a marker pen type dispenser, which hindered the deposition of a uniform coating with a consistent thickness. To combat this, a single batch of PT was fabricated with two strokes of the dye applicator, providing a more uniform dye layer. This was used for experimental testing, which reduced the PT transmission near 900 nm to 46%.

Fig. 1
Fig. 1
Close modal

One study reported that the temperature threshold of heat-induced pain for human skin is approximately 45 °C based on a study with 106 people who were tested on the radial side of the palm and the top of foot [19]. The skin's pain sensation and thermal damage depend on the contact temperature and the duration of exposure [20]. When the contact temperature was 45 °C, the results showed that it took more than 30 min to induce skin injury [21,22], indicating that the threshold temperature of skin pain at 45 °C for an NIR exposure time of less than 10 s is a conservative estimate for our analyses. However, due to the lack of a commercial source of a lower STemp adhesive tape, the higher STemp Nitta IT with NIR dye coating on its backing was used as the PT throughout the preliminary in vitro testing.

### Peel Strength Measurement.

To assess the peel strength of the PT in comparison to other medical pressure-adhesive tapes, we constructed a peel strength test apparatus with a temperature-controlled plate, shown in Fig. 2. The apparatus was designed based on Test Method F of ASTM D 3330/D 3330 M [23]. The peel strength test apparatus was framed with aluminum extrusion components and the main components are a linear motion system, a load cell, a heating and temperature sensing platform, and a clamp for holding the tape. The bright annealed 304 stainless steel testing plate is horizontally located under the tape holder, setting an adjustable peeling angle of 90–135 deg. The testing has a controllable heating system on the backside. A proportional–integral–derivative (PID) controller and solid-state relay were used to modulate power to the thin film heater. A thermocouple (SA1 Type T, Omega Engineering, Inc., Norwalk, CT) was affixed to the testing plate alongside the tape to monitor the temperature of the adhesion surface.

Fig. 2
Fig. 2
Close modal

To measure the peel strength, a tape sample is attached on the testing plate with one end of the tape clamped with the tape holder. The peeling speed is set to 50 mm/min for the peeling distance of 18 mm.

### Near-Infrared Light Source.

The NIR dye coating converts optical energy to heat energy leading to reduced adhesion of the PT. Thus, the adhesive heating mechanism depends on the optical power of the NIR light source, which is a function of the radiometric power, beam angle, and illumination area. To avoid overheating the substrate, the light source needs to sense and monitor the temperature of the PT in real-time. While using the NIR wand on the PT, the temperature is monitored, and when it hits the target temperature (i.e., 55 °C), the user is alerted to initiate the peeling process in order to avoid excess heat application. 15 NIR (940 nm) LEDs (L1I0-0940060000000, Lumileds, San Jose, CA) were used in the prototype NIR light source (shown in Fig. 3), and an infrared (IR) thermometer (MLX90614, Melexis, Concord, NH) was used to monitor the target surface temperature. An Arduino Nano platform was used to manage the custom-made LED driver, IR thermometer, and PID controller. The LED optical power was modulated by the PID controller to maintain the target temperature as sensed by the IR sensor with minimal latency. The prototype NIR light source was later packaged with a three-dimensional printed case.

Fig. 3
Fig. 3
Close modal

### Heat Transfer Experiments and Finite Element Simulation

#### Acrylic Substrate as a Test Model.

The UnTape photothermal heating mechanism by NIR light exposure was evaluated using an acrylic substrate as a test model for heat transfer analysis. The averaged thermal properties of skin [24], acrylic (polymethylmethacrylate), and 304 stainless steel are listed in Table 1. Because of the lower conductivity and specific heat of acrylic, the thermal inertia (I = $kρcp$) of acrylic is approximately one half of the averaged skin thermal inertia. The standard for testing adhesive tapes uses 304 stainless steel as the substrate, which has a thermal inertia 3× higher than skin. This significantly higher thermal inertia of stainless steel prevents temperature increases on the illumination surface. Thus, the 6 mm thick acrylic substrate was used for NIR heating experiments since it has comparable thermal conductivity to skin and also has well-characterized thermal properties that work well with finite element analysis. In addition, the low thermal inertia of acrylic adds additional safety factors in future human skin experiments, because the sensible temperature at the skin surface is expected to be lower than at the acrylic surface.

Table 1

Thermal properties of skin [24], acrylic, and 304 stainless steel

Skin (epidermis + dermis)Acrylic304 stainless steel
Thermal conductivity, k (W/(m K))0.3430.190160
Density, ρ (kg/m3)120012007800
Specific heat, Cp (kJ/(kg K))3.441.470.480
Thermal inertia, I (kJ/(m2 K s1/2))37.618.1244.8
Skin (epidermis + dermis)Acrylic304 stainless steel
Thermal conductivity, k (W/(m K))0.3430.190160
Density, ρ (kg/m3)120012007800
Specific heat, Cp (kJ/(kg K))3.441.470.480
Thermal inertia, I (kJ/(m2 K s1/2))37.618.1244.8

#### Near-Infrared Heating Experiments.

To examine the performance of the NIR LED arrays and proposed operating specifications, experimental temperature measurements were conducted with the acrylic substrate and PT. For each LED, a constant-current driver supplied three different input currents of 500.0, 666.7, and 833.3 mA, and the corresponding forward voltages of 2.67, 2.78, and 2.83 V, respectively. The threshold temperature in the PID controller was set to 55 °C, which is the release temperature (RTemp) of the PT. When the temperature reading reached the threshold, the pulse width modulation output from the microcontroller modulated the light intensity to maintain a constant temperature at this threshold value.

#### comsol Simulations.

The numerical modeling was performed to establish the correlation of energy conversion between the experimental measurements and the simulation. After the correlation is established, the future photothermal sensitive tape with a lower adhesion STemp of 40 °C and a higher NIR absorption can be designed based on the numerical model.

The finite element method simulations using comsolmultiphysics Version 5.4 platform were conducted to analyze the NIR heating experimental results and to adjust the performance of the NIR LED board and control system for human skin. Figure 4(a) shows the geometry and mesh of the PT and acrylic substrate model. The thermophysical properties of the materials are included in Table 2. A two-dimensional time-dependent study for was performed for 5 s for the parameter sweep of qrad, the radiative heat flux on the surface of the PT, between 0.3 and 1.0 W/cm2. This heat flux was equivalent to the net NIR exposure converted to heat energy after subtracting the reflection and transmittance of NIR from the PT. Meshing consists of a linearly mapped mesh for the PT domain and a triangular mesh for the acrylic domain. All surfaces were set to a diffusive surface to adjust to the room temperature, 22 °C.

Fig. 4
Fig. 4
Close modal
Table 2

Thermophysical properties of the components in the comsol models: PET, acrylic, epidermis, dermis, fat, and muscle (human skin properties are from Okabe et al. [24])

PETAcrylicEpidermisDermisFatMuscle
Thicknessdmm0.1360.11.126.8
Thermal conductivitykW/(m K)0.1550.190.2350.4450.1850.51
Densityρkg/m3139012001200120010851030
Heat capacityCpkJ/(kg K)1.171.473.593.302.673.80
PETAcrylicEpidermisDermisFatMuscle
Thicknessdmm0.1360.11.126.8
Thermal conductivitykW/(m K)0.1550.190.2350.4450.1850.51
Densityρkg/m3139012001200120010851030
Heat capacityCpkJ/(kg K)1.171.473.593.302.673.80

Based on the experimental temperature data and corresponding numerical analysis from the acrylic substrate testing, an additional simulation with a human skin model was studied where the RTemp of the PT was set to 45 °C, our conservative threshold temperature of human skin pain. The geometry, mesh, and thermal properties of human skin [24] are shown in Fig. 4(b) and Table 2, and the initial temperatures of the epidermis, dermis, and fat were set to 34 °C and 35 °C for the muscle layer. In the skin model simulation, we considered a future photothermal sensitive tape (UnTape) of which the RTemp is 45 °C and the NIR absorption is 0.855. The NIR absorption of UnTape was estimated from the reflectance of 0.1 and the multilayer NIR dye coating absorption of 0.95 (shown in Fig. 1 from the multilayer NIR dye coated PT). The effective heat flux calculated from the incident NIR optical intensity and the NIR absorption of the UnTape was directly applied to the simulation.

## Results

### Peel Strength Measurement Using Acrylic Substrate.

Figure 5 shows the peel strength force comparison between the IT and other medical tapes on the market. 3M Durapore™ surgical tape and 3M Kind removal silicon tape were chosen to represent the highest and lowest adhesive forces among common medical pressure-adhesive tapes. Using the peel strength test apparatus, five measurements at the 90 deg peeling angle were collected for each tape sample attached on the acrylic substrate and were averaged to evaluate the required peel forces per unit width. The comparison clearly shows that the selected commercial surrogate thermal-sensitive IT has an adhesion strength equivalent to the 3M Durapore high-tack tape at 45 °C. After the temperature increases to 55 °C, the adhesion force drops by 86% ($percentage of drop= (0.1429−0.0198)0.1429×100=86.14%)$, which is comparable to the low adhesive strength of the 3M Kind tape.

Fig. 5
Fig. 5
Close modal

### Near-Infrared Heating Experiments With an Acrylic Substrate.

Figure 6 shows the temperature profiles of the PT during the NIR light irradiation. The elapsed times for the threshold temperature, 55 °C, at each forward current are shown. The input currents at 1500, 2000, 2500 mA were applied to three 5-LED rows so that each LED was operated at 500, 666.7, and 833.3 mA, respectively. The heating profile and operating conditions at 2000 mA were exploited to estimate the effective optical power of the NIR light source in conjunction with matlab and comsol simulations.

Fig. 6
Fig. 6
Close modal
The emissivity compensation for the IR temperature measurement was not predetermined because of the design flexibility for various surface measurement. Therefore, the emissivity compensation based on the reference emissivity ($ε$ = 0.94) of polyethylene terephthalate (PET) and the room temperature ($Tambient$= 22 °C) was followed. The corrected temperature of 56.79 °C was obtained by the following equation:
$Ttarget=Tsensor4−(1−ε)·Tambient4ε4$
(1)

### Comparison of Near-Infrared Optical Power Intensities.

From the comsol simulation model, the temperature profiles of the PT with various heat fluxes are plotted in Fig. 7. As we have the experimental results of the threshold temperature of the PT surface and the time to reach the threshold temperature, those values are overlaid in the figure: the horizontal dotted line represents the threshold temperature measured from the experiments and the vertical dotted line represents the elapsed time to reach the threshold temperature. The data point of 0.6442 W/cm2 in the simulation was interpolated as the best-fit heat flux based on the experimental results. The heat flux applied to the comsol model did not include optical power conversion parameters, such as the reflectance and transmittance of the PT. Therefore, the estimated heat flux is the net light energy absorbed by the PT backing.

Fig. 7
Fig. 7
Close modal
From the LED specification data [25], the optical intensity of the LED arrays, $I$, can be estimated as follows:
$Iest=n·ΦLED,1A·ηF.A.·ηarea·ηtemp·(1−γ−τ)Aillumination$
(2)

where $n$ is the number of LEDs, $ΦLED,1A$ is the nominal radiometric power at the input current of 1.0 A, $ηF.A.$ is the proportionality of radiant power at a different input current, $ηarea$ is the radiant power ratio for the effective illumination area, $ηtemp$ is the output variation by the LED case temperature, $γ$ is the surface reflectance, $τ$ is the object transmittance, and $Aillumination$ is the area of illumination. From the specification data, the $ΦLED,1A$ is 1450 mW, and $ηF.A.$ is linearly proportional to input current (e.g., $ηF.A.$ = 0.8 if the input current is 0.8 A). At the illumination distance of 20 mm between the LED board and the PT, $ηarea$ was approximately 0.536 for the window size is 31 mm × 16 mm. The reflectance, $γ$, and transmittance, $τ$, at 940 nm were directly measured from the IT and PT, respectively, using the optical power meter (1830-C and 818-IR, Newport, Irvine, CA): $γ$ = 10.5% and $τ$ = 46.0% based on the PT that was coated twice with the Clearweld NIR dye. We assume that the reflectance of the PT and the IT are the same, so the net absorption of the PT coating layer, $α$, can be estimated as follows: $α=1−γ−τ=0.435$. As predefined in the prototype NIR wand design, $Aillumination$ and the window are considered the same size.

The net NIR optical intensity delivered by the NIR LED array was measured by the optical power meter independently from the numerical simulation and the specification calculation.

The comsol results were based on the heat energy released on the surface of the PT backing, which assumes that the net NIR optical power was absorbed only by the NIR dye coating. On the other hand, the NIR LED optical power measurement (using the optical power meter) corresponds to the raw radiant flux before hitting the PT. Therefore, in order to juxtapose the optical power measurement (using the optical power meter) with the values from NIR LED optical power calculation (using the LED specification data) and comsol results, the measurement from the optical power meter was further corrected by the absorption of the PT
$Iexp=Imeasured·α=Imeasured·1−γ−τ$
(3)

Thus, the $Icomsol$, from the numerical simulations, can be compared with the $Iest$, the estimated optical power based on the LED specification sheet, and $Iexp$, from the optical meter experiments. Table 3 shows the comparison of the results from three independent calculations and measurements, which were all based on the experimental conditions of a 2 A input current, 4.72 s illumination time, and the 20 mm distance between the LED board and the PT. The radiant flux from the optical power meter measurement can be considered as the actual NIR optical power from the LEDs. All three optical power intensities are within the error range of less than 5%.

Table 3

Comparison of the heat or NIR radiant fluxes required to increase the temperature of the PT up to 55 °C

Estimation from LED specificationNIR testing with comsol simulationOptical power measurement
MethodIestIcomsolIexp
q"net (W/cm2)0.68210.64420.6651
Error (%)+2.5−3.2N/A
Estimation from LED specificationNIR testing with comsol simulationOptical power measurement
MethodIestIcomsolIexp
q"net (W/cm2)0.68210.64420.6651
Error (%)+2.5−3.2N/A

Note: Iest was estimated from the LED specification data, Icomsol was evaluated from the comsol of a PT-acrylic model fitting the NIR heating experiment, Iexp was measured using the optical power meter and converted to the optical intensity. Iest and Iexp were calibrated by the NIR dye absorption of the PT in order to compare NIR intensity and heat flux absorbed at the NIR dye layer. The error is calculated based on the optical power measurement.

### Skin Model Simulation.

At this stage of development, the PT and NIR lighting source are not ready for human testing. However, we estimated the required thermal heat flux to reach the RTemp at 55 °C from the NIR light source device based on the simulation and NIR PT in vitro measurements. Thus, the estimated heat flux can be used as an NIR heating simulation for human skin based on the current NIR light source design. The transient heating effect on the skin model to RTemp at 45 °C was considered and the effective heat flux by NIR absorption was set to 1.2659 W/cm2. Figure 8 and Table 4 summarize the setting parameters and results of the human skin model simulation. As the UnTape has a higher NIR absorption than that of the PT, the elapsed time to reach 45 °C at the outer surface was an estimated 0.165 s and 1.12 s for the UnTape tape and skin, respectively. If heating continues to the human skin pain threshold (45 °C), the UnTape surface temperature reaches 55 °C, and cooling occurs relatively quickly (<0.2 s). This significant temperature difference (10 °C) across the small thickness of the tape (130 μm) will be reduced in future UnTape designs, in which the NIR absorbing dye is embedded in the backing, an intermediate layer, or the adhesive layer.

Fig. 8
Fig. 8
Close modal
Table 4

Simulation settings and the results of the human skin—UnTape model

 RTemp (° C) 45 °C NIR absorption of a tape 0.855 Incident NIR optical intensity (W/cm2) 1.4806 Effective heat flux input (W/cm2) (absorbed by the tape) 1.2659 Elapsed time for RTemp at tape surface (s) 0.165 Elapsed time for RTemp at skin surface (s) 1.12
 RTemp (° C) 45 °C NIR absorption of a tape 0.855 Incident NIR optical intensity (W/cm2) 1.4806 Effective heat flux input (W/cm2) (absorbed by the tape) 1.2659 Elapsed time for RTemp at tape surface (s) 0.165 Elapsed time for RTemp at skin surface (s) 1.12

## Discussion

This study investigated the feasibility of a photothermal mechanism for rapid and gentle removal of high-tack adhesive tape, and yielded thermal properties for future UnTape development. Commercially available NIR absorbing dye was coated on the outer surface of a commercially available thermal-sensitive tape. Our tests demonstrated that using the absorbed optical energy supplied by the NIR LEDs (Fig. 5), the tape adhesion force dropped an average of 86% at the RTemp (55 °C). This has demonstrated that the NIR light source can efficiently increase the tape's bulk and surface temperature to ease removal. Additionally, the industrial thermal-release film tape (IT) successfully acted as a surrogate for comparing medical tape adhesion levels. The peel strength test showed that the PT can have stronger adhesion than high-tack surgical tape (3M Durapore) while exhibiting release properties at the RTemp equivalent to extra gentle silicone-base medical tape (3M Kind). Retaining the PT visible light transparency ensures that the medical staff can view the skin beneath the dressing, allowing the applicator to accurately attach the taped device to the skin and to observe any skin damage or irritation.

In this study, an adhesion RTemp of 55 °C is considered higher than the 45 °C [19] threshold of human skin pain level. The application of the NIR absorbing dye solution on the backing of the IT was done without professional coating techniques, which produced a nonuniform coating layer, possibly leading to irregular NIR absorbing on the PT surface area. Despite this variation, the preliminary measurements with the engineered prototype tape and light source device provided valuable insight for the design of a future UnTape system. This system will consist of a flashlight-like NIR light source and NIR-sensitized medical tape that efficiently switches adhesion at 40 °C, allowing for the future UnTape to achieve full release at 45 °C.

### Experimental–Theoretical Correlation.

We investigated the prototype NIR light source optical power intensity and heat flux required to heat the PT to RTemp (55 °C), as shown in Table 3. Based on the optical power measurement, the estimated NIR optical power intensities from the LED specification data and the numerical simulation were in agreement to within 5%. The NIR energy conversion can be attributed to multiple factors including NIR reflection, transmission, and NIR dye coating absorption. Additionally, other operating conditions in NIR LEDs, such as case temperature and power stability, may cause the variations in calculations. Furthermore, every experimental factor cannot be precisely controlled, estimated, or measured due to the nature of our prototype fabrication and the dependence of these parameters upon the NIR dye absorption.

Detailed information of the model (tape backing and adhesive layer) may improve the comsol models. These simulations were based on reference material properties and simple modeling assumptions. For example, the adhesive layer was defined as part of the tape backing, eliminating the thermal resistance within the adhesive interface among skin, adhesive, trapped air, and tape backing. The IR temperature meter measured the temperature of the surface of the tape and the emissivity compensation for the temperature calibration was based on the bulk emissivity of PET, which is 0.94. However, a recent study showed the emissivity of a PET film is as low as 0.8 [26]. Therefore, proper IR wavelength of a thermometer sensor and the thickness and surface condition of the tape backing will be important design factors for future UnTape designs to avoid temperature measurement errors.

The NIR dye absorption depended significantly on the amount of dye coating. The twice coated PT was used to provide consistent NIR dye coating, but the high NIR transmittance of the PT, 46%, was not desirable. Adding more layers of the NIR dye coating only slightly increases absorbance above 95%, with diminishing returns due to surface reflection, as shown in Fig. 1. Although we need more information about the photo-thermal transduction mechanism, including multiple reflections in a multilayer NIR dye coating structure with various illumination angles on different skin conditions and pigmentation, for this analysis we will assume that the dye layer absorbs 95% of the NIR incident illumination around 940 nm without significant reduction of visible light transparency.

### Skin Model Discussion.

We investigated the temperature change on a human skin model based on the heat flux value and fitting data from the experiments and simulations using the acrylic substrate. Using the NIR light source, it took only 1.12 s to heat UnTape to the human skin pain threshold. The one second NIR exposure for medical tape removal is a promising result for the future UnTape system, which will have an optimized tape design and NIR illumination approach. However, the rapid heating near the skin will require strict temperature control that may extend the heating time to reduce the risk of overheating.

When pursuing future product design, we will investigate how and where the target temperature of the tape will be measured and how deep the NIR absorbing layer will be embedded in the tape. Additionally, this skin model may need adjustments, such as the thickness of epidermis/dermis for neonate or geriatric patients.

The environmental temperature is also an important variable as it affects tape adhesion. At this stage, we are assuming a controlled environment in hospitals or caregiving facilities. Additional experiments and simulations are needed to understand the stability of the product during transportation and storage at extreme temperatures. Regardless, once applied, the tape temperature is regulated by body temperatures, as the heat conduction rate is significantly higher than the convection rate.

### Future UnTape System Product Design.

UnTape aims to create a new medical tape that provides strong adhesion and rapid and gentle removal upon application of NIR by a portable NIR light device in order to avoid MARSI. We believe that the UnTape project will not only limit MARSI, pain, lifelong scars, and potential emotional stress [7], but also improve the quality of care when adhering critical devices to the skin. Although our system adds cost with the addition of NIR light absorbing dye and the LED NIR wand, limiting MARSI cases and reducing clinical workloads will save the healthcare system significant capital [6].

Based on the PT experiments and numerical analyses for NIR heating, we propose the future UnTape product design, described below.

#### Photothermal Sensitive Tape, UnTape.

The new photothermal sensitive tape, named UnTape, will have a lower adhesive STemp and RTemp, and a higher NIR light absorption, leading to improved heat conversion. The NIR absorbing dye will be uniformly distributed in the UnTape adhesion layer. The tape will not exceed the human skin pain threshold. The temperature dependence of the adhesive will allow for higher adhesion forces without the difficult removal process. The adhesive layer can be designed in different ways based on the target patients. For example, retention of a peripheral intravenous catheter on the skin provides stabilization and avoids risk of infection [27]. As UnTape can have high adhesion, it can be highly perforated for other medical functions. A highly perforated tape with a hydrophobic backing layer may allow for breathability, elasticity, and water resistance. Perforated UnTape will disperse the heat over the skin surface, minimizing the risk of skin pain.

#### Near-Infrared Wand.

Power consumption is an important consideration for the NIR light source design. Due to the inefficient conversion process from electrical energy to heat energy, the input power for the wand was often as high as 30 W. In addition, energy was lost due to unfocused NIR illumination and the limited window size of the wand. An improved NIR wand design is based on the optical intensity value estimated from the NIR LED specification data, which is a conservative approach because of the highest power requirement (see Table 3).

The same NIR LED specification was considered and all other calculations were also adapted with these potential improvements. The new illumination approach is “hand scanning.” A user holds the NIR wand by hand and manually sweeps over UnTape. A 18 mm × 65 mm rechargeable lithium-ion battery was considered as a power source. This 3000 mAh battery has a nominal voltage of 3.6 V and an end-of-discharge voltage of 2.8 V. This design suffices to show the proper intensity of NIR illumination in a battery powered system without any further improvements on the NIR absorbing dye coating or the industrial tape backing.

Table 5 presents the power consumption based on the experimental results and numerical simulations. One or two 18650 batteries were considered, and continuous running times of >30 min and >60 are expected, respectively. The battery capacity was conservatively applied at the end-of-discharge voltage. Therefore, incorporating a voltage regulator will operate the LEDs more efficiently. In addition to the current IR thermometer sensor, the improved NIR wand will have a red guiding light located between the two NIR LEDs so that the lens-focused NIR illumination beams can be visualized. The power consumption of the IR thermometer and guiding LED are less than 30 mA, and the sizes are small enough to be embedded in the LED board. The feedback signal for the temperature alert can be included. Color change on a LED indicator, an alarm, or a tactile signal can tell the user when the temperature has been reached.

Table 5

Power consumption calculation. General operating parameters, LED driving conditions, NIR optical power, and possible battery-powered plan are presented

 Operating parameters Illumination area 25.4 × 5 w × h (mm×mm) # of LED in wand 4 (each) Release temperature 45 (°C) Example tape size 25.4 × 50 w × h (mm × mm) Time for single tape removal 5 (s) LED driving parameters Rated current 1.3 (A) Rated voltage 2.8 (V) Required electrical power 3.640 (W) Estimated optical power 1.885 (W) NIR illumination Required optical power 1.880 (W) Required optical intensity 1.481 (W/cm2) Single 18650 battery Rated capacity 2500 (mAh) Continuous running time 115.4 (min) Tape removal cycle 1384 (cycle) Double 18650 batteries Rated capacity 5000 (mAh) Continuous running time 230.8 (min) Tape removal cycle 2769 (cycle)
 Operating parameters Illumination area 25.4 × 5 w × h (mm×mm) # of LED in wand 4 (each) Release temperature 45 (°C) Example tape size 25.4 × 50 w × h (mm × mm) Time for single tape removal 5 (s) LED driving parameters Rated current 1.3 (A) Rated voltage 2.8 (V) Required electrical power 3.640 (W) Estimated optical power 1.885 (W) NIR illumination Required optical power 1.880 (W) Required optical intensity 1.481 (W/cm2) Single 18650 battery Rated capacity 2500 (mAh) Continuous running time 115.4 (min) Tape removal cycle 1384 (cycle) Double 18650 batteries Rated capacity 5000 (mAh) Continuous running time 230.8 (min) Tape removal cycle 2769 (cycle)

Figure 9 shows the three-dimensional rendering of the double-battery powered model of the future NIR wand using a single row of 4 NIR LEDs with a central red LED. The visible red LED will illuminate the target so the operator can easily see the NIR exposure area. A diffuser and reflector will uniformly focus the illumination from the 4 NIR LEDs.

Fig. 9
Fig. 9
Close modal

### Skin Safety.

Based on the previous in vitro and in vivo studies, the perception of skin pain in adult occurs at skin temperatures above 43 °C, and thermal damage occurs when the temperature of the basal layer (the innermost layer of epidermis) reaches 44 °C [20]. The dependence of skin pain and injury on the temperature and duration of exposure is commonly accepted. Durations of exposure to induce reversible thermal skin damage have been reported as 45 min at 46.5 °C, 60 min at 44 °C [21], and 50 min at 46 °C [28].

According to the ASTM guide C1055-99 [29], epidermis damage (first-degree burns, reversible with no permanent damage) occurs approximately 44 °C after 6 h of thermal contact, and the exposure time to skin damage is reduced by 50% for each 1 °C increase, up to around 51 °C. The guideline also included the recommendation of a 1 min exposure limit for infants, elderly, or infirmed, who have slow reaction times. An independent study by Diller [22] presents a specific suggestion for the maximum delivery temperature of domestic tap water, of which a safety standard was based on adult skin thickness. Diller found that the skin thickness ratio between a child and adult is 0.72, and showed the skin injury induced by 10 s of exposure to hot water at 48.9 °C corresponds to the same exposure at 46.7 °C with a child. Exposure to hot water may result in a worse burn injury than the NIR exposure, in which a relatively small area is covered. Thus, safety guidelines and in vitro/vivo studies imply that the UnTape removal process, which increases the temperature of the adhesive to 45 °C for 1–5 s in the local skin area, would not result in any skin burn. Human testing could not be done with the prototype system which has a higher adhesion STemp at 55 °C. We expect human subject testing can occur once the lower STemp tape is developed and experimentally measured in vitro.

## Conclusion

A prototype photothermal tape release system was demonstrated using NIR LEDs and temperature switching high-tack adhesive tape coated with an NIR absorbing dye. This combination of an optical energy source coupled to a matched light absorption coating provided a test bed for forecasting the feasibility of developing a clinically useful system that will lower the incidence of medical adhesive-related skin injuries. Reasonable agreement between the experimentally measured results and a numerical model provides a sound foundation for the design of a next generation UnTape system.

## Acknowledgment

We thank Asher Seibel for providing the motivation for the UnTape project. After falling from a tree and spending another day in the hospital with a ruptured spleen and cracked ribs, he recounted to the authors that the most painful and traumatic experience was getting the medical tape removed. We appreciate the final editing from Shawn Swanson.

## Funding Data

• University of Washington CoMotion Innovation Fund (F2016_7666_Seibel, PI: Seibel; Funder ID: 10.13039/100011248).

• Engineering Innovations in Health class, University of Washington (Funder ID: 10.13039/100007812).

• The Department of Mechanical Engineering, University of Washington (Funder ID: 10.13039/100007812).

## Nomenclature

• IR =

infrared

•
• IT =

Intelimer Tape

•
• LED =

light emitting diode

•
• MARSI =

•
• NIR =

near-infrared

•
• PET =

polyethylene terephthalate

•
• PID =

proportional–integral–derivative

•
• PT =

prototype tape; an Intelimer tape with NIR dye coating on the top

•
• RTemp =

release temperature

•
• STemp =

switch temperature

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