102. That is, for example, hydrophobic properties and/or conductive properties of the substrate 102 can vary across the substrate 102.

It can be further noted that, being formed of starch-based materials, the substrate 102 is compostable. As such, the PCM device 100 can be described as sustainable and environmentally friendly. For example, electrical components (e.g., of one or more of the sensing system 104, the processing system 106, the communications system 108, and the energy system 110) can be detached from the substrate 102, and the substrate 102 can be composted. Some or all of the electrical components can be recycled.

It can be noted that the adhesive and/or substrate can be provided using any number of compatible sustainable materials, such as bamboo fibers, chitosan, lignin or cellulose materials. In some implementations, the adhesive and/or the substrate 102 can be provided using biodegradable gelatin methacryloyl (GelMA) aerogels. GelMA has been used widely in bioprinting, implants, tissue engineering, and slight modifications to the chemical process makes this material flexible and suitable for use in wearable devices, such as PCMs.

FIGS. 2A-2D depict respective example PCM devices in accordance with implementations of the present disclosure.

With particular reference to FIG. 2A, a PCM device 100a is depicted and includes the substrate 102, the sensing system 104, the processing system 106, a communications system 108a, and the energy system 110. In the example of FIG. 2A, the communications system 108a is provided as a near-field communication (NFC) system and includes an NFC chip 202 and an antenna 204. In some examples, the NFC chip 202 and/or the antenna 206 can be fabricated using LIG, as discussed herein. In some examples, the PCM device 100a can be prompted to broadcast physiological characteristic data to an external device (e.g., a smartphone). In this manner, the physiological characteristic data can be recorded in and displayed on the external device. Although NFC is discussed, it is contemplated that other technologies, such as passive radio frequency (RF) can be used. More generally, any appropriate communication protocol and components can be implemented.

With particular reference to FIG. 2B, a PCM device 100b is depicted and includes the substrate 102, the sensing system 104, the processing system 106, a communications system 108b, and the energy system 110. In the example of FIG. 2B, the communications system 108b is provided as a display system and includes an electrochemical display (ECD) 210. In some examples, the PCM device 100b can be prompted to generate an image on the ECD 210 that depicts physiological characteristic data. In this manner, the physiological characteristic data can be viewed by a user. In some examples, the ECD 210 can display an image of a machine-readable code that encodes physiological characteristic data. Example machine-readable codes include, without limitation, bar codes and quick response (QR) codes. In some examples, an external device (e.g., a smartphone) can scan the machine-readable code to decode the physiological characteristic data and display physiological characteristic data. In some examples, the machine-readable code is visibly displayed, such that a human is able to see the machine-readable code. In some examples, the machine-readable code is not visible to humans (e.g., is displayed as an infrared image or near infrared (NIR) image). In such examples, the machine-readable code can only be read by an external device (e.g., smartphone) having an infrared (or NIR) imager.

With regard to encoding physiological characteristic data, blood glucose levels rarely fall outside the bounds of 60-200 mg/dL. As such, each measurement of blood glucose can be stored as a byte of data (physiological characteristic data). Furthermore, commercially-available continuous glucose meters only offer integer (not floating point) precision. With regard to QR codes, in particular, a QR code can store up to 2953 bytes of data. At a glucose sampling rate of once per minute (or 1440 times per day), approximately 1440 bytes of data is generated per day. As such, a QR code can store up to two full days of glucose monitoring data.

In some examples, the machine-readable code can refresh over time to encode physiological characteristic data as it is recorded. This is represented in FIG. 2B, depicting a first QR code 220 at a first time (t₁) and a second QR code 222 at a second time (t₂), the second QR code 222 encoding more physiological characteristic data than the first QR code 220.

The ECD 210 provides the PCM device 100b with a tattoo-like appearance on the user. For example, the ECD 210 can display customizable content for multiple purposes including, but not limited to, aesthetics, user personalization, and advertising.

With particular reference to FIG. 2C, a PCM device 100c is depicted and includes the substrate 102, a sensing system 104c, the processing system 106, the communications system 108, and the energy system 110. In the example of FIG. 2C, the sensing system 104c includes a blood glucose sensor 230.

In some examples, the blood glucose sensor 230 includes a probe that is inserted beneath the surface of the skin (sub-cutaneous), where glucose sampled in the interstitial fluid can be measured. In some examples, the blood glucose sensor 230 can be biodegradable or bioabsorbable. In some examples, the probe leverages a glucose-enzyme reaction that is detected by an amperometric sensor. The sensor electrode can be decorated with a glucose oxidase (GOx) enzyme, whose oxidation-reduction (redox) reaction with glucose generates a current (I_glu) in the electrode. More particularly, the (GOx) enzyme is used to convert glucose into gluconic acid and hydrogen peroxide. The hydrogen peroxide can be oxidized, which produces electrons that are proportional to the glucose concentration. The flow of the electrons produces the current (I_glu) that can be measured (i.e., amperometric sensing). However, the current (I_glu) can be a relatively small, weak signal. In view of this, current signals are processed in the AFE 130, which can include amplifiers, filters, and the like to produce an accurate and precise digital signal.

In some examples, the blood glucose sensor 230 is a sweat-based glucose sensor that generates a current (I_glu) responsive to glucose levels in sweat of a patient. Sweat contains a number of analytes (e.g., ammonia, ethanol, lactate, urea) that provide indications of the physiological state of a patient. Sweat also contains glucose, which can be sensed using non-invasive sensors, which interact with the surface of the skin instead of puncturing the skin or drawing blood. In some examples, the sweat-based glucose sensor can be created using LIG. For example, graphene foams can be soaked in a solution of enzyme and phosphate-buffered saline (PBS) to produce robust electrode and cathodes for a biofuel cell. Glucose oxidase plays an important role in the body converting glucose into a form that cells can use, such as adenosine triphosphate (ATP) molecules. During this process (known as glycolysis), electrons are freed in the oxidation of glucose. These electrons eventually pass to oxygen available in the blood where it is reduced to H₂O.

In sweat-based glucose sensing, the electron pathway can be simplified after the oxidation of glucose at the anode. The current generated by the oxidation of glucose can be correlated to the concentration of glucose in the media (e.g., sweat) that the sensor is touching. Sustainable materials can be used in the fabrication of the anode and cathode. In this manner, at least portions of the PCM device 100 can safely biodegrade in a landfill or compost. For example, and without limitation, cotton can be used for a biofuel cell, the cotton being modified with gold nanoparticles (Au NPs), poly(ethylenimine) (PEI), GOx, and tris-(2-aminoethyl)amine, a small molecule that can covalently bond with Au NPs and link to the GOx and efficiently shuttle electrons. Further, devices for glucose sensing and biofuel cells can be provided using chitosan and graphene with glucose oxidase immobilized on the surface. A sensitivity down to a 0.02 mM detection limit has been shown.

In some examples, the blood glucose sensor 230 is an odor-based glucose sensor that generates a current (I_glu) responsive to glucose levels correlated with volatiles emitted by the body, such as isoprene, a byproduct produced when glucose levels are very low. In some examples, sensing can include using neurons to detect volatiles. For example, synthetic biotechnology can be incorporated to sense and detect volatile compounds using neurons and proteins to signal when a small molecule interacts with the sensing capability of the neuron.

With particular reference to FIG. 2D, a PCM device 100d is depicted and includes the substrate 102, a sensing system 104d, a processing system 106d, the communications system 108, and the energy system 110. In the example of FIG. 2D, the sensing system 104d includes the blood glucose sensor 230 and a temperature sensor 240 that generates a current (I_temp) responsive to a temperature of the patient. The processing system 106d includes a data acquisition unit 122d that includes a temperature module 242 to provide temperature data based on a signal from the temperature sensor 240. The temperature data can be stored in the memory and can be communicated through the one or more devices 124 of the communications system 108, as described herein. In some examples, the temperature data can be used to correct measurements and/or ensure accurate data by accounting for temperature affecting analog signals read by other peripheral components.

FIGS. 3A and 3B depict an example PCM device 300 in accordance with implementations of the present disclosure. Although each is not explicitly and entirely depicted in FIGS. 3A and 3B, the PCM device 300 includes a sensing system, a processing system, a communications system, and an energy system, such as described herein with reference to FIGS. 1-2D. In the example of FIGS. 3A and 3B, the PCM device 300 includes a substrate 302 (starch-based and/or other appropriate materials), a sensor 320, a data acquisition module 322, devices 324a, 324b, EHUs 326, and ESDs 328. The device 324a includes an ECD (e.g., that includes a biodegradable substrate) that can display images, such as a machine-readable code, to communicate physiological data and/or aesthetic images. The device 324b includes an NFC device that can be used to communicate physiological data. While the example of FIGS. 3A and 3B depict both devices 324a, 324b, the PCM 300 can include only one of the devices 324a, 324b and/or can include another device for communicating physiological data. In some examples, the EHUs 326 include thermoelectric EHUs.

As depicted in FIG. 3B, electrical traces (e.g., laser-induced graphene-rich traces) can be formed as serpentine interconnects. For example, human skin can strain up to ~20%. To account for this stretchability, serpentine interconnects enable the electrical traces to stretch/deform without damage or adverse effect to electrical conductance. The winding of the electrical traces enables stretchability of up to, for example, 300%.

FIGS. 4A-4F depicts an example process for creating a PCM device in accordance with implementations of the present disclosure. With reference to FIG. 4A, a starch-based substrate 402 is provided and a laser 410 is used to form graphene-rich traces 404 (LIG) in the substrate 402. In some examples, the laser 410 is set to a relatively low fluence (e.g., 3-60 J cm⁻², correlating roughly to powers of 2-18 W and speeds of 10-72 cm s⁻¹used in combination) to form the graphene. In some examples, the fluence of the laser 410 can be increased (e.g., >70 J cm−2, correlating for example to a power of 55 W and speeds of 10 cm s⁻¹used in combination) to cut the substrate 402 to a desired shape. In accordance with implementations of the present disclosure, the graphene 404 can be formed in the substrate (or other coatings) to define conductive electrical traces. With reference to FIG. 4B, electrical components 420 can be mounted to the substrate using an electrically conductive adhesive 422. For example, the electrically conductive adhesive 422 can be used to adhere an electrical component to the graphene 404 and/or the substrate 402.

With reference to FIGS. 4C and 4D, a spin-coated layer 430 is applied to encapsulate the graphene 404 and the electrical components 422. Curing (e.g., by baking) can be used to solidify the layer 430 and to integrate the layer 430 with the substrate 402 as a single, continuous substrate 402′. With reference to FIG. 4E, the laser 410 can be used to form a graphene-rich layer 440 on the substrate 402′. In some examples, the graphene-rich layer 440 can be made hydrophobic to provide a liquid (e.g., water, sweat) repellent surface. In some examples, this is achieved by lasing under a nitrogen (N₂) atmosphere. In some examples, the graphene-rich layer 440 can be made omniphobic to provide a surface with more broadly repellant characteristics. With reference to FIG. 4F, an adhesive layer 450 is applied to a skin-facing surface of the substrate 402′. In some examples, the adhesive is starch-based and its adhesive properties are enhanced by sweat. As discussed herein, the adhesive layer 450 is free of allergens including, but not limited to, colophony (rosin), balsam of Peru (3.9%), 2-hydroxyethyl methacrylate, and carba mix (which includes, for example, diphenylguanidine, zincdibutyldithiocarbamate, and zincdiethyldithiocarbamate). In the example of FIG. 4F, the PCM device has a thickness (t) of less than or equal to 1 mm. In some examples, a thickness of the PCM device can vary between a minimum thickness and a maximum thickness. In some examples, the maximum thickness is 1 mm.