e‐Bandage: Exploiting Smartphone as a Therapeutic Device for Cutaneous Wound Treatment

Near‐infrared (NIR) radiation has demonstrated significant promise in skin tissue engineering and wound healing. However, the high cost and operational complexity associated with current specialized apparatuses have hindered their practical household use. In response to these issues, a flexible, battery‐free, wireless sensor–actuator NIR therapy system, offering real‐time physiological monitoring and active treatment to cutaneous wounds, is developed. The wound management system can be wirelessly powered, and transmits data to any near‐field communication‐compatible smartphone. The therapeutic prowess of our system for wound closure is computationally and experimentally demonstrated by promoting epithelial migration and modulating inflammation. Moreover, a novel feature is reported: the smartphone‐enabled system can precisely predict the wound stage via a temperature sensor pair, which can provide an effective timely intervention strategy for NIR wound therapy. Studies based on rat wound model successfully confirm the efficacy of the proposed strategy, showcasing a remarkable 30% enhancement in wound closure compared to control groups. The user‐friendly, effective wound management platform promises a revolutionary step toward accessible and efficient at‐home wound care.

Near-infrared (NIR) radiation has demonstrated significant promise in skin tissue engineering and wound healing.However, the high cost and operational complexity associated with current specialized apparatuses have hindered their practical household use.In response to these issues, a flexible, battery-free, wireless sensor-actuator NIR therapy system, offering real-time physiological monitoring and active treatment to cutaneous wounds, is developed.The wound management system can be wirelessly powered, and transmits data to any nearfield communication-compatible smartphone.The therapeutic prowess of our system for wound closure is computationally and experimentally demonstrated by promoting epithelial migration and modulating inflammation.Moreover, a novel feature is reported: the smartphone-enabled system can precisely predict the wound stage via a temperature sensor pair, which can provide an effective timely intervention strategy for NIR wound therapy.Studies based on rat wound model successfully confirm the efficacy of the proposed strategy, showcasing a remarkable 30% enhancement in wound closure compared to control groups.The user-friendly, effective wound management platform promises a revolutionary step toward accessible and efficient at-home wound care.
stimulate the production of adenosine triphosphate, [4] increase blood circulation, [5] and promote tissue repair, [6] all of which can help the wound healing process.NIR therapy also has great potential to promote more innovative or effective treatments for cancer, diabetes, and neuronal disorder and has been frequently used in the treatment and caring of chronic ulcers, postburn infection, arthritis, [7] etc.
However, current clinical NIR therapy practices use specialized apparatuses that are not readily available for general household use.Even the commercial NIR devices are bulky and heavy, which are not meant to be carried around for field applications.Additionally, for wounds protected by plaster, current clinical monitoring and treatment methods require frequent removal of the plaster, which may cause secondary damage to wound and nearby healthy tissues.
In this article, we explore the possibility to used smartphones as therapeutic devices for cutaneous wound healing.The smartphone is paired with an electronic bandage (referred as e-Bandage in this article) that can harvest electromagnetic energy from the near-field communication (NFC) function of the phone.With the harvested energy, the circuits on the e-Bandage can power up two NIR light-emitting diodes (LEDs) with the center wavelength around 940 nm that falls into the spectrum of NIR therapy. [8]lso embedded in the e-Bandage circuits is a pair of precise temperature sensors that can monitor the healing progress of the wound by comparing the temperature differences (TDs) between the centric area of the wound and the areas of healthy regions. [9]onitoring the healing process through TD is much more robust than direct and absolute temperature monitoring used in previous study. [10]The controlling functions of the NIR LEDs, together with the data processing of the temperature sensors, are implemented on a low-power microcontrol unit, which is also powered from the harvested energy and communicates with the smartphone application (APP) through NFC functions.

e-Bandage System Configuration
An e-Bandage is a battery-less flexible sensor-actuator platform that uses NFC functions both as an energy harvesting source and as a wireless communication channel to simultaneously extract energy and exchange data with a smartphone.The structure of e-Bandage is shown in Figure 1a, where the electronic components and circuitry, such as a low-power micro control unit (MCU), an NFC transceiver chip, a pair of NIR LEDs, and a pair of temperature sensors, are mounted on a flexible PI substrate.The NIR LEDs and temperature sensors are mounted on the downside of PI that adheres to the skin through a layer of hydrogel, while other components, along with the etched NFC loop antennas, are on the opposite side, as shown in Figure 1b,c.The flexible circuit layer is sandwiched between two extremely thin and transparent hydrogel layers that provide protection and encapsulation of the circuit.In the meantime, the hydrogel can also provide conformability when e-Bandage is applied directly on the wound area (WA) (illustrated in Figure S1, Supporting Information) or wounds protected by plaster (Figure 1d).The schematic of e-Bandage embedded circuitry is illustrated in Figure 1e,f.An NFC transceiver chip provides the wireless interface as well as energy harvesting capabilities (Figure S2, Supporting Information).Within 2 cm distance from the smartphone, e-Bandage can harvest and convert electromagnetic (EM) energy into a 2.0 ≈ 3.0 volts DC supply with the power around 15 ≈ 20 mW.The NFC chip connects to the low-power MCU chip through the I 2 C interface.The MCU (Figure S3, Supporting Information) also controls the pair of temperature sensors (Figure S4, Supporting Information) and the pair of NIR LEDs through I 2 C ports.The NIR LEDs can be switched on/off by the MCU.In case the skin and WA are overheated by the NIR energy (>45 °C as measured from the temperature sensor pair), NIR LEDs can be automatically turned off for protection.
The temperature sensor pair can detect TDs within 0.1 °C.One sensor in the pair is located at the center of e-Bandage on top of the wounded area, while the other is located on the side, intended to be on top of the healthy area.The TD measured by the pair indicates the healing process of the wound (as discussed in detail in the Section 2.6).

NIR Radiation and Penetration
A pair of NIR LEDs is placed on top of the WA with a relative radiation radius of 1 mm, generating a radiation intensity of 62 mW cm À2 .In order to analyze the penetration effect of NIR, a multiplayer skin model is constructed in COMSOL (Figure 2a) that includes the epidermis, dermis, and hypodermis layers.Details of the parameters and coefficients used in the simulation can be referred in Experimental Section.The simulation results demonstrate that deep into the hypodermis layer (3.64 mm under the skin), NIR radiation energy is around 0.332 mW cm À2 , which can increase the blood flow, stimulate the collagen production to promote tissue repair, and help fibroblasts growth.These factors play a key role in the formation of new tissues.

Differential Temperature Sensing
A temperature pair is used to monitor the healing process of the wound by comparing the TD between the wounded area and the healthy area.The e-Bandage prototype (with temperature sensor pair) is first calibrated in a water-bath thermostat (CF41, JULABO).Calibration results are illustrated in Figure 2b, where errors of both sensors (against precalibrated thermometer) of each 5 min measurement are plotted.The vertical segments represent the range from the maximum to the minimum TD between the temperature pair, the green boxes represent range from the lower quartile to the upper quartile of TD measurements, and the horizontal bars within the box represent the median of the measurements.From these measurement results, we are confident that the calibrated accuracy of 0.1 °C can be achieved at different temperature readings from 20 to 45 °C (maximum temperature variation range for a human).
The equilibrium time of the temperature sensor pair is also measured.The e-Bandage prototype is first placed inside a chamber with lower ambient temperature and then suddenly (within 1 s) transferred to a chamber with higher temperature.The equilibrium times from of 2 °C ≈ 36 °C, 16 °C ≈ 36 °C, and 28 °C ≈ 36 °C are measured respectively and plotted in Figure 2c.The temperature sensor can reach the equilibrium within 10 s within these temperature transition ranges.
Wound healing process monitoring based on the TD between the WA and the healthy area is more reliable than the absolute temperature measurement used by previous reported approaches. [10]The differential temperature can effectively minimize the ambient temperature interferes as well as other variations in the healing process.

Wireless Energy Harvesting and Communication
The NFC function is used both as an energy harvesting source and as a communication channel between e-Bandage and the smart phone.The RF frontend equivalent circuit is illustrated in Figure 2d, where the smartphone is modeled as a transmitter with a source signal V s and internal impedance Z 0 .The transmission NFC coil on the smartphone and the reception coil on e-Bandage form a mutual inductance circuit that resonates at 13.56 MHz.
High-frequency structure simulator tool is used to optimize the design and the setup of e-Bandage operation (see Experimental Section for details).This double-coil mutual inductance circuit model can be regarded as a four-terminal network, as shown in Figure 2d.Simulation results demonstrate that by varying the distance between the smartphone and e-Bandage, the |S11| parameter varies.During normal operation, the smartphone is designed to operate at 20 mm on top of e-Bandage; therefore, the pair of coils is optimized to achieve the minimum |S11| value (À100 dB) at the 20 mm separation (Figure 2e).At this distance, |S12| parameter also reaches its maximum such that the best energy transfer is achieved and the measured quality factor (Q) value is stabilized at 18.The 20 mm distance is used in our subsequent animal experimental operations.Based on this equivalent circuit model, we have designed a seven-turn flexible square coil that achieves optimal RF performance with a higher-quality factor.

Experiment Setup
The energy harvested from NFC function can power up NIR LEDs that generate radiation energy around 62 mW cm À2 , which is equivalent to the NIR radiation received by the exposed skin from Red Light Therapy Device (HGPRO300, Hooga, USA) equipment positioned from a distance of 30 centimeters with an output power of 300 watts (as measured from infrared light meter (LH-131, PUYAN, China) devices.The performance comparison between the HGPRO300 and our e-bandage is shown in Table S1 (Supporting Information).The existing commercial device exhibits higher power consumption, bulkiness, and larger dimensions.In contrast, our e-bandage features wireless capability, lightweight design (only 0.23 g), high flexibility, and comparable radiation efficacy.Our NIR therapy system, including NFC coil antenna, NIR LEDs, and temperature sensors, along with NFC and MCU chips, are all embedded on flexible polyimide (PI) substrates and encapsulated into the form factor of a bandage.Because the NFC chip can serve both as an energy harvesting device and as a communication device, no batteries are needed for the e-Bandage system.The therapeutic procedure includes 60 min of NIR treatment daily for 14 days that can be controlled and administered on the smartphone APP.The pair of temperature sensors embedded on e-Bandage can monitor the temperature of the NIR radiation area to prevent it from overheating.In the meantime, the wound healing process can also be wirelessly and constantly monitored by the APP through comparing the TD of the temperature sensor pair.e-Bandage proposed in this study can be used as a platform to integrate other sensors, actuators, or remedial devices for various wearable medical applications.

System Validation in Animal Wound Models
We have tested the therapeutic effects of e-Bandage on rats.Four rats were used in a 14-day trial to verify the cutaneous wound healing processes, as well as the monitoring capabilities of e-Bandage.Among these four rats, two rats were randomly subjected to NIR treatment, while the other two were served as controls.A full-thickness cutaneous incision, measured 10 mm by 10 mm in opening, reaching the hypodermic layer of the skin, was inflicted on all rats (Figure 3a).The setup of the therapy experiment is depicted in Figure 3b, which illustrates the use of an NFC-enabled smartphone for healing and real-time monitoring.The TD of each rat was continuously calculated in real time and saved onto the smartphone during the daily experiment.The smartphone used in the treatment were positioned ≈20 mm on top of the wounded area.The treatment process lasted 60 min daily for 14 consecutive days on the NIR treatment group administered with an anesthetic dose of 2%.The control group was treated with a normal bandage at the same time under the same dose of anesthesia.
The healing process of both groups (model and control) is illustrated in Figure 3c, where images of the wounds on Day 1, 3, 5, 7, 9, and 11 are shown.In order to compare the changes of the WA, the wound trance is also processed to exhibit only the contour of the WA and the contour images are shown in Figure 3f.These images demonstrate that the wounds treated with NIR radiation heal much faster than that of the control group.
Wound healing process normally goes through three stages, that is, the inflammation stage, the tissue formation stage, and the remodeling stage.The healing processes of both groups also demonstrated these three stages.At Day 0, both groups started with the same square-shaped wound cut, because skin around the wound retracted after the original cut, the WA could not maintain a square shape.The wounds on the rats in the NIR treatment group stayed in inflammation stage from Day 0 to Day 4, scabs were formed on Day 5, starting the tissue formation stage.The scabs fell off the skin on Day 11 and the wounds went into the remodeling stage.In comparison, in the control group, the healing processes progressed much slower.Scabs began to form on Day 6 (2 days later than the NIR treatment group) and did not fall off the skin on Day 11.From these pictures, we can see that the WAs of the control group are all larger than that of the NIR treatment group at each particular time stamp of the healing process.
Figure 3g plots the relative WA over the 14-day period recorded from the NIR treatment group and the control group.The relative sizes were quantified using ImageJ software, and calculation formula is introduced in Equation (3).Obviously, NIR treatment significantly accelerated the wound healing process and stimulated the healing metabolism as compared to the control group.
To address the convincingness of our experimental data, we performed t-tests on the relative wound size data for each day (from day 0 to day 13) to assess the statistical power of our results.Notably, the results for Day 3 to Day 5 and Day 9 demonstrate significant statistical power (p-value <0.05, denoted by '*').Additionally, the results for Day 1, from Day 6 to Day 8, and Day10 show marginal significance (p-value <0.1, denoted by '.').Therefore, the observed intergroup differences and statistical power support the credibility of our results.
The incisional tissue samples from wound center were collected on Day 13 from both groups for postintervention histological examination using hematoxylin and eosin (H&E) staining.The results of representation are shown in Figure 3d and Figure S5 (Supporting Information), where levels of epithelialization, granulation tissue, and cellular content in each wound were shown.The H&E stains of skin at the wound site revealed that both treatment group and control group have achieved complete healing at the end of the experiment since they both developed continuous epidermis and dermis layers in the WA (Figure 3d).Further, the tissues of the NIR treatment groups achieved better epithelialization in the center of the wounds, exhibiting more new epidermis that was tightly connected to the granulation tissue underneath.Figure 3e represents the average width of scar area of two groups.The connection between the new epidermis and granulation tissue was loose and its healing tissue area is wider than that of the NIR treatment group (scar areas of control group are wider than that of NIR treatment group), indicating a weaker healing process.
Daily temperature changes of the WA measured from the temperature sensor pair are also recorded in the smartphone APP and shown in Figure 4, where Figure 4a and Figure S6 (top) (Supporting Information) illustrate the temperature changes of the NIR treatment group and Figure 4b and Figure S6 (bottom) (Supporting Information) illustrate the temperature changes of the control group.The temperature variations also demonstrate the three stages of the wound healing process.Taking Figure 4a acquired from the NIR treatment group as an example, the wound inflammation stage (left part of Figure 4c) occurred from Day 0 to Day 4 (the WA had higher temperature as compared to the healthy area, where Day 2 exhibited the most severe inflammation).Tissue formation stage (right part of Figure 4c) occurred from Day 5 to Day 10 (the WA had lower temperature as compared to the healthy area because scab layer was formed and shielded the WA).The wounds were almost recovered from Day 11 and stayed in the remodeling stage (the TD was  minimized to almost 0).In comparison, the healing process, as indicated from the temperature variations acquired from the control group, is much slower.Tissue formation stage started on Day 6, and remodeling stage started around Day 12, which was almost consistent with the WA changes described earlier.
Based on the presented findings, our NIR therapy system exhibits exceptional flexibility, therapeutic effectiveness, and the capability for integrated sensing and actuation.Rigorous simulations and calculations affirm the system's remarkable attributes, including a high-quality factor, stable wireless energy transfer, and deep subcutaneous NIR penetration.The results of animal experiments and pathological analyses provide compelling evidence of our system's prowess in expediting wound healing by modulating inflammation, facilitating epithelial migration, and minimizing scar tissue formation.
Notably, our innovative approach uses temperature sensor pairs to accurately predict wound stages, enabling timely interventions, particularly for nonvisible wounds concealed beneath bandages.
To further elucidate our system's strengths, we conducted a comparative analysis with recently reported intelligent wound dressing technologies concerning their capacity to sense physiological conditions and facilitate incisional wound treatment.As depicted in Table 1, while recent advancements encompass smart dressings using bioelectric hydrogels, electrical stimulation, mechanical regulation, and drug delivery to enhance wound healing, [11] they lack real-time physiological monitoring during the healing process.In contrast, our integrated sensing and actuation NIR therapy system not only expedites wound healing but also offers continuous monitoring for prompt intervention.Systems dependent on wired connections or batteries [10c,11a,11d,11f,12] could result in patient discomfort and compliance issues.Conversely, our wireless, batteryfree wound management platform offers substantial advantages, particularly for in-home intelligent wound care and wounds concealed beneath bandages.Furthermore, devices necessitating prolonged wear and frequent wound treatment operations [11aÀc] cannot guarantee reliable functionality in complex wound environments, patient mobility.Consequently, our developed, flexible, wireless, smartphone-based, integrated sensing, and actuation device hold significant potential for advancing wound care and disease management.

Conclusion
In summary, we have developed an NIR therapy system with flexibility, biocompatibility, wireless energy supply, and integrated sensing and actuation capabilities for wound monitoring and promotion of healing.The system exhibits a high-quality factor, stable wireless energy transfer, and deep subcutaneous NIR penetration, validated through extensive animal experiments.It effectively accelerates wound healing by modulating inflammation, enhancing epithelial migration, and reducing scar tissue formation.Notably, the unique temperature sensor pair enables precise wound stage prediction, facilitating timely interventions.
Our user-friendly, efficient wound management platform holds broad potential in disease management, leading the way in closed-loop bioelectronic medicine and home-based intelligent wound care.However, while we have validated the potential of this device for more effective wound care, it does face certain challenges.First, we envision the expansion of its functionality, such as programmable drug delivery and integration with multimodal sensors (e.g., pH, humidity, and uric acid monitoring).Second, the animal study in a bigger sample size needs to be conducted further to reach stronger statistical power.Additionally, considerations for low-cost production scalability, prolonged lifespan, and reduced electronic hardware overhead are paramount.Our forthcoming endeavors involve enhancing our e-bandage into a multimodal sensor-actuator, ultraflexible system capable of accommodating various wound shapes and diseases, in largesize animal models before human trials.

Experimental Section
Circuit Design and e-Bandage Construction: An e-Bandage circuit consists of an NFC chip (NXP NT3H2111), MCU chip (Texas Instruments MSP430F2132), a pair of temperature sensor chips (Texas Instruments TMP117), a pair of NIR LEDs (GaAlAs, EVERLIGHT IR19-21C/TR8, EVERLIGHT), and a p-channel metal oxide semiconductor (PMOS) switching transistor.
Energy harvesting, as well as data communication between e-Bandage and the smartphone, was performed by the NFC chip NT3H2111, connected with an NFC antenna tuned at 13.56 MHz located within a range of 20 mm from the smartphone (Redmi K30, Android, Xiaomi).NT3H2111 can output a DC voltage of around 2.0-3.0V (Figure S7, Supporting Information) with a driving power around from 15 to 20 mW.The temperature sensor pair and the NIR LED pair were controlled by the MCU chip through the interintegrated Circuit (I 2 C) bus.An NIR LED had a center wavelength of 940 nm and can be turned on by a bias voltage from 1.1 to 3 V, which was provided from the DC output of the NFC chip.The NIR LED pair was separated by a distance of 2.6 mm on the flexible substrate.
The e-Bandage circuit was built on a double-layered flexible copper-clad laminated PI substrate with all components surface mounted on both sides of the board.In particular, the NFC antenna, the NFC chip, and MCU chip were mounted on the top side while the temperature sensor pair and NIR LED pair were mounted on the bottom side that contacted directly the skin.The circuit was encapsulated inside a commercial medical hydrogel (Cofoe, G1308) with a thickness of 1 mm.The prototype of e-Bandage was 20 mm by 30 mm in dimension.
NIR Skin-Penetration Simulation: In order to quantitatively analyze the therapeutic effectiveness of e-Bandage, the NIR LED's radiation model, along with the cutaneous penetration model under NIR band, was constructed and simulated in COMSOL Multiphysics software (COMSOL Inc.) (Figure S8 and S9, Supporting Information).The cutaneous structure consisted of several parallel layers, where the epidermis layer had a Remark: "NA" signifies that the content is not addressed in the cited references.
thickness of 0.8 mm, the dermis layer had a thickness of 2.84 mm, and the subcutaneous tissue layer had a thickness of 5 mm. [13]In the NIR band, the light absorption of epidermis and dermis was determined by the water content, [14] the absorption coefficient μ a is defined as where λ is the wavelength of the incident light, k is scattering coefficient, and φ w is the water content (in percentage) in the skin tissue. [15]ypically, the water content of epidermis was about 20%, and that of dermis was about 70%. [16]Using these parameters, the absorption coefficients of epidermis and dermis were 145.85 and 41.67 m À1 , respectively.The skin can be conceptualized as a complex material comprised of both hydrated and dehydrated components.The hydration level of the skin is defined as the volume fraction of water within the skin tissue.The refractive index of skin can be estimated by the formula proposed by Ray, [17] where a set of parameters, referred to as A-F, were calculated by fitting the refractive index values of water (Equation ( 2)).The refractive index of the skin tissue at different wavelengths determines the traveling speed of light in skin tissues.Assuming that the refractive index =1.5 of protein is constant, the refractive index n of skin tissue can be empirically formulated as where the wavelength λ is 940 nm, A = 1.58,B = 8.4 Â 10 À4 nm À1 , C = 1.10 Â 10 À6 nm À2 , D = 7.19 Â 10 À10 nm À3 , E = 2.32 Â 10 À13 nm À4 , and F = 2.98 Â 10 À17 nm À5 .Based on these parameters, the scattering coefficient n of skin tissue was estimated to be 1.37.
Wound Model on Rats: Animal experiments were conducted in the Animal Center Laboratory with the approval of the Animal Subjects Ethics Committee, Southern University of Science and Technology (SUSTech).The assigned approval/accreditation number was SUSTech-SL202201002.The study protocol used in this experiment complied with the guideline of SUSTech and all animals received humane care in the whole procedure.Four female Sprague-Dawley rats (12 weeks, 280-320 g)  were supplied by Beijing Vital River Laboratory Animal Technology Co., Ltd., and housed separately in the Animal Center Laboratory at SUSTech.The wound models on four rats were set up for evaluating therapeutic performance of e-Bandage.A 10 Â 10 mm full-thickness square-shaped skin wound was established as the wound model on the nape of each rat after isoflurane inhalation anesthesia (3%-4%) and analgesic carprofen injection (4 mg kg À1 ) subcutaneously.The wound model created on the nape could effectively prevent scratching and biting by itself and avoid secondary injury to the wound.The wound was covered with a sterile gauze to avoid exposure and to prevent infection during the separate housing period.
Wireless Monitoring and NIR Treatment: Four rats were randomly allocated into either the NIR treatment group (n = 2) or the control group (n = 2).The rats in the NIR treatment group received daily 1 h NIR treatment while being maintained under isoflurane inhalation anesthesia (2%) (shown in Figure S10 and S11, Supporting Information) during the observation period.The rats in the control group only received inhaled maintenance anesthesia using 2% isoflurane without any other treatment.
The wound status was monitored continuously for 14 days with an android phone (Redmi K30, Android, Xiaomi) connected through the NFC function to e-Bandage attached on the rats.The readings of the temperature sensor pair were collected and recorded through the APPs installed on the smartphone every day.The WA was recorded and assessed immediately after the establishment of the wound model (Day 0) and continued to be recorded on consequent 13 days (Day 1 to Day 13).Photographs of the wounds were taken using a digital camera on the smartphone (Redmi K30, Android, Xiaomi).The WA on each day of assessment (WA x ) was calculated using Image J software (National Institutes of Health, USA).The percentage of relative WA (RW%) was calculated using the following formula.
Histological Staining: On Day 14, all four rats used in this study were euthanized by being overdosed of ketamine and xylazine.For histological assessment, the wound tissue and normal skin tissue was excised in full thickness with subcutaneous fat including a margin of at least 5 mm of healed skin.The specimens were fixed in 4% paraformaldehyde in phosphate-buffered saline and were processed for embedding in paraffin.Sections with a thickness of 5 μm were cut for routine H & E staining to observe the levels of epithelialization, cellular content, and granulation tissue in each wound.

Figure 1
Figure 1.e-Bandage structure, composition, and circuit diagrams.a) e-Bandage structure: hydrogel encapsulation layers, NIR LED pair, sensors pair, coil antenna, and circuit on the flexible PI substrate.b) Surface-mount components, that is, control/communication module (on the top) and monitoring and treatment modules (on the bottom).c) Flexible e-Bandage circuit before encapsulation.d) Stable wireless monitoring for wounds protected by plaster.e) Circuit diagram.f ) Block diagram illustration of the entire e-bandage system.

Figure 2 .
Figure 2. System performance of NIR penetration and temperature monitoring.a), Radiation on energy penetration and distribution beneath the skin during NIR treatment (simulated with COMSOL skin model).b) Temperature sensor pair reading errors under different temperatures.c) Equilibrium time.d) Equivalent four-port network model of NFC coils.e) |S11| parameters under different operation distances from 5 to 30 mm.

Figure 3 .
Figure 3. Therapeutic effect of NIR treatment on full-thickness skin wound in animal model.a) Illustration for development of a 10 Â 10 mm full-thickness square-shaped skin wound.b) A rat under NIR treatment powered by a smartphone.c) Wound healing process of NIR treatment group (top) and the control group (bottom).d) Histological (H&E) assessment of wound tissues of NIR treatment group (top) and the control group (bottom).e) Width of scar area of NIR treatment group (blue) and the control group (green).f ), WA contour comparison of NIR treatment group and the control group.g) Relative wound size for each group and group means (All data presented with two-tailed t-test.The p-value <0.05, denoted by '*', and p-value <0.1, denoted by '.').

Figure 4 .
Figure 4. Temperature monitoring during the healing process.a) TDs between the WA the healthy skin of NIR treatment group and b) the control group.c) Diagram illustrating the inflammatory response (left) and tissue formation (right) during the wound healing process.

Table 1 .
Comparison of current studies of wound management system.