WO2024182509A1 - Multifunctional materials strategies for enhanced safety of wireless, skin-interfaced bioelectronic devices and applications of same - Google Patents

Multifunctional materials strategies for enhanced safety of wireless, skin-interfaced bioelectronic devices and applications of same Download PDF

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Publication number
WO2024182509A1
WO2024182509A1 PCT/US2024/017663 US2024017663W WO2024182509A1 WO 2024182509 A1 WO2024182509 A1 WO 2024182509A1 US 2024017663 W US2024017663 W US 2024017663W WO 2024182509 A1 WO2024182509 A1 WO 2024182509A1
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Prior art keywords
composite
pdms
matrix
skin
capsule
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PCT/US2024/017663
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French (fr)
Inventor
John A. Rogers
Claire Liu
Da Som Yang
Donghwi CHO
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Northwestern University
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Publication of WO2024182509A1 publication Critical patent/WO2024182509A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
    • G01K11/12—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in colour, translucency or reflectance
    • G01K11/16—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in colour, translucency or reflectance of organic materials
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
    • C09B67/00—Influencing the physical, e.g. the dyeing or printing properties of dyestuffs without chemical reactions, e.g. by treating with solvents grinding or grinding assistants, coating of pigments or dyes; Process features in the making of dyestuff preparations; Dyestuff preparations of a special physical nature, e.g. tablets, films
    • C09B67/0097—Dye preparations of special physical nature; Tablets, films, extrusion, microcapsules, sheets, pads, bags with dyes
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/02—Details of sensors specially adapted for in-vivo measurements
    • A61B2562/0204—Acoustic sensors
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/02—Details of sensors specially adapted for in-vivo measurements
    • A61B2562/0219—Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/12—Manufacturing methods specially adapted for producing sensors for in-vivo measurements
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/16—Details of sensor housings or probes; Details of structural supports for sensors
    • A61B2562/164—Details of sensor housings or probes; Details of structural supports for sensors the sensor is mounted in or on a conformable substrate or carrier
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/16—Details of sensor housings or probes; Details of structural supports for sensors
    • A61B2562/166—Details of sensor housings or probes; Details of structural supports for sensors the sensor is mounted on a specially adapted printed circuit board
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/103—Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes
    • A61B5/11—Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb
    • A61B5/1102—Ballistocardiography

Definitions

  • the dye comprises a microencapsulated leuco dye, wherein the microencapsulated leuco dye comprises a tertiary component system having a color former, a developer, and a solvent.
  • the microencapsulated leuco dye has a switching temperature at which the microencapsulated leuco dye reversibly changes its color.
  • the switching temperature ranges between about 44°C to 48°C.
  • the at least one encapsulation composite comprises a hollow glass microspheres (HGMs) composite, wherein the HGMs composite comprises multiple HGMs incorporated in a second matrix.
  • the serpentine mesh structures have a serpentine angle ( ⁇ ) of about 120° and a serpentine width (w) about 100 ⁇ m.
  • the patterned nylon composite comprises a viewing window section, wherein the viewing window section comprises the third matrix free of the patterned nylon mesh.
  • the device comprises a water contact indicator disposed inside the SH capsule, and wherein the water contact indicator is configured to reversibly change its color when it contacts water.
  • the water contact indicator is disposed directly next to the viewing window section such that the water contact indicator is configured to be visible outside of the SH capsule.
  • the at least one encapsulation composite comprises a mechanochromic (MC) hydroxypropyl cellulose (HPC) composite, wherein the MC HPC composite comprises at least one MC HPC sheet integrated in a fourth matrix.
  • the MC HPC composite is configured to reversibly change its color when a strain force is applied to the MC HPC composite.
  • the electronic module comprises a flexible electronic component and a battery coupled to the flexible electronic component.
  • the at least one encapsulation composite comprises a poly(dimethylsiloxane) PDMS matrix.
  • a composite capsule for encapsulating a skin- interfaced electronic device comprising at least one encapsulation composite.
  • the at least one encapsulation composite comprises a thermochromic (TC) composite having a dye integrated in a first matrix.
  • the dye comprises a microencapsulated leuco dye, wherein the microencapsulated leuco dye comprises a tertiary component system having a color former, a developer, and a solvent.
  • the microencapsulated leuco dye has a switching temperature at which the microencapsulated leuco dye reversibly changes its color.
  • the switching temperature ranges between about 44°C to 48°C.
  • the at least one encapsulation composite further comprises a hollow glass microspheres (HGMs) composite, wherein the HGMs composite comprises multiple HGMs incorporated in a second matrix.
  • the multiple HGMs are configured to migrate in the second matrix.
  • the multiple HGMs have a mass fraction ranges between about 2.5-5.0 wt%.
  • the TC composite is disposed closer to an individual’s skin compared to the HGMs composite.
  • the patterned nylon composite further comprises a viewing window section, wherein the viewing window section comprises the third matrix free of the patterned nylon mesh.
  • the at least one encapsulation composite further comprises a mechanochromic (MC) hydroxypropyl cellulose (HPC) composite, wherein the MC HPC composite comprises at least one MC HPC sheet integrated in a fourth matrix.
  • the MC HPC composite is configured to reversibly change its color when a strain force is applied to the MC HPC composite.
  • the composite capsule comprises a self healing elastomer.
  • the SH elastomer comprises dynamic covalent elastomer.
  • a self-healing (SH) dynamic covalent elastomer capsule for encapsulating a skin-interfaced electronic device comprises a thermochromic (TC) SH poly(dimethylsiloxane) (PDMS) composite has a microencapsulated leuco dye integrated in a first PDMS matrix; a SH PDMS hollow glass microspheres (HGMs) composite has multiple HGMs incorporated in a second PDMS matrix; a SH PDMS patterned nylon composite has a patterned nylon mesh embedded in a third PDMS matrix; and a SH PDMS mechanochromic (MC) hydroxypropyl cellulose (HPC) composite has at least one MC HPC sheet integrated in a fourth PDMS matrix.
  • TC thermochromic
  • HGMs hollow glass microspheres
  • MC mechanochromic
  • HPC hydroxypropyl cellulose
  • Fig.1A illustrates potential safety hazards associated with wireless, skin-interfaced bioelectronic devices.
  • Fig.1B shows a schematic diagram of the structural configuration and the encapsulation material choices for the wireless, skin-interfaced bioelectronic device on the left; and the Schiff-base chemical reaction forms dynamic covalent imine bonds that serve as autonomic self-healing points in the SH PDMS elastomer matrix on the right.
  • Fig.2A shows photographs illustrating the synthesized dynamic covalent elastomer (SH PDMS) self-healing after a damage event.
  • Fig.2B shows a scanning electron microscopy image illustrating the self-healed region of the synthesized SH PDMS.
  • Fig.2C shows a plot of FTIR spectra of the synthesized SH PDMS, illustrating the characteristic peak for the dynamic covalent imine bond.
  • Fig.2D shows a schematic diagram of the thermochromic (TC) properties of a leuco dye (microcapsule form) with an activation temperature of 47°C.
  • Fig.2E shows a schematic diagram of color changes associated with a temperature increase from 37°C to 47°C of SH PDMS with varying mass fractions of the TC leuco dye.
  • Fig.2F shows a chart of UV spectra of the SH PDMS with varying mass fractions of the TC leuco dye.
  • Fig.2G shows photographs illustrating the synthesized TC SH PDMS, integrated with 0.5 wt% TC leuco dye, undergoing autonomic self-healing after a damage event.
  • Fig.2H shows a schematic diagram of the mechanochromic (MC) properties of the cholesteric liquid crystalline nanostructure O f aqueous hydroxypropyl cellulose (HPC).
  • Fig.2I shows a photograph illustrating the cholesteric liquid crystalline HPC encapsulated within thin, flexible layers of SH PDMS.
  • Fig.2J shows color changes associated with increasing mechanical strain of the encapsulated cholesteric liquid crystalline HPC.
  • Fig.2K shows digital image correlation experiments for simultaneous mechanical and chromic analysis of the encapsulated cholesteric liquid crystalline HPC, in a serpentine configuration, undergoing uniaxial strain.
  • Fig.3A shows photographs depicting the synthesized dynamic covalent elastomer Attorney Docket No.0116936.281WO2 (SH PDMS) integrated with a thin serpentine patterned nylon mesh for mechanical reinforcement.
  • Fig.3B shows a chart reflecting the nonlinear stress/strain profile of a thin serpentine patterned nylon mesh, along with corresponding photographs of the mesh.
  • Fig.3C shows a chart reflecting the strain limit threshold as a function of the nylon serpentine mesh angle( ⁇ ), with finite element analysis (FEA) modeling results.
  • Fig.3E shows a chart reflecting stress/strain curve of the SH PDMS + patterned nylon mesh composite material, compared to SH PDMS without the patterned nylon mesh, along with corresponding strain distribution profiles obtained via digital image correlation (DIC) experiments.
  • DIC digital image correlation
  • Fig.3F shows a chart reflecting tear force measurements of SH PDMS and SH PDMS + patterned nylon mesh composite material, as obtained from trouser tear-propagation testing.
  • Fig.3G shows a chart reflecting stepwise tearing profile (stress/strain curve) of the SH PDMS + patterned nylon mesh composite material.
  • Fig.3H shows photograph of the heterogeneous serpentine patterned nylon mesh, featuring thicker serpentine widths at the edge.
  • Fig.3I shows DIC experiments illustrating spatially varying strain distribution profiles of the SH PDMS + heterogeneous patterned nylon mesh composite material undergoing uniaxial strain.
  • Fig.4A shows photograph depicting the synthesized dynamic covalent elastomer (SH PDMS) integrated with varying mass fractions of HGMs.
  • Fig.4B shows scanning electron microscopy micrographs of the cross-sectional areas of SH PDMS + HGMs composites.
  • Fig.4C shows a chart reflecting stress/strain curves of SH PDMS (left) and SH PDMS+ HGMs composites (middle and right), after various time periods for self-healing.
  • Fig.4D shows photograph illustrating an epidermal thermal depth sensor (e-TDS) on the top surface of the SH PDMS + HGMs composite.
  • e-TDS epidermal thermal depth sensor
  • Fig.4E shows a chart reflecting density (p) and thermal conductivity (k)of the SH PDMS + HGMs composites.
  • Fig 4F shows a chart reflecting temperature profiles, including those obtained from finite element analysis (FEA), of the encapsulated battery with heater (BwH) during an overheating simulation, with an inset of photograph illustrating the simulation test setup for an overheating lithium-polymer (LiPo) battery.
  • Fig.4H shows photographs illustrating the burning-via candle flame-of the SH PDMS (top row) and the improved flame resistance of the SH PDMS + HGMs composites (middle and bottom rows).
  • Fig.4I shows a chart reflecting thermogravimetric analysis curves of SH PDMS and SH PDMS + HGM composites.
  • Fig.5A shows a photograph depicting the side-view of a wireless skin-interfaced MA device, encapsulated with self-healing PDMS (SH PDMS) and its variations.
  • Fig.5B shows photographs illustrating the color change of the TC SH PDMS outlined in white associated with heating.
  • Fig.5C shows photographs illustrating the color change of the SH PDMS + MC HPC outlined in white associated with strain from bending of the device, with a water contact indicator, outlined in red, as viewed through transparent SH PDMS.
  • Fig.5D shows a photograph illustrating the SH PDMS + patterned nylon section outlined in white of the encapsulation structure, with a water contact indicator, outlined in red as viewed through transparent SH PDMS.
  • Fig.5E shows photographs illustrating the self-healing behavior of the encapsulation structure.
  • Fig.5F shows a chart reflecting time-lapse of the color changes associated with water exposure to the water contact indicator material.
  • Fig.5G shows photographs of the water contact indicators overlaid on top of the printed circuit board changing color as water is introduced.
  • Fig.5H shows a photograph of the encapsulated MA device on the suprasternal notch of an adult female subject.
  • Fig.5I shows a chart reflecting representative triaxial accelerometry signals obtained from the encapsulated MA device worn by an adult female subject performing various physical Attorney Docket No.0116936.281WO2 activities.
  • Fig.5J shows charts of Z-axis accelerometry signals which illustrate unique signatures of different body processes including cardiac activity in the form of the seismocardiogram (SCG) waveform with distinct Si and S2 heart sounds (left), physical motions such as walking and jumping (middle), and respiration waveforms during deep breaths (right).
  • SCG seismocardiogram
  • Fig.6 shows a DIC analysis of the autonomic self-healing behavior of the dynamic covalent elastomer (SH PDMS);
  • panel (A) shows photographs (left column) and the corresponding strain distribution maps (right column) via DIC experiments of a slit film of SH PDMS undergoing uniaxial strain (top row, red), which is then allowed to self-heal for 15 mins (bottom row, blue) and undergo uniaxial strain again; while panel (B) is a plot reflecting measured strain magnitude at the slit (red) and self-healed (blue) region of the SH PDMS film.
  • Fig.7 shows a chart reflecting thermochromic properties, as illustrated by the change in RGB values between the relaxed and heated states of the dynamic covalent elastomer matrix integrated with leuco dye (TC SH PDMS), with varying mass fractions.
  • Fig.8 shows a plot reflecting stress/strain curves of the TC SH PDMS, including those after different time periods of self-healing.
  • Fig.9 shows photographs of the SH PDMS with integrated mechanochromic hydroxypropyl cellulose (MC HPC).
  • Fig.10 shows a diagram illustrating finite element analysis (FEA) of the strain distribution field of the SH PDMS + MC HPC.
  • FEA finite element analysis
  • Fig.11 shows diagrams illustrating displacement fields of the uniaxially-strained SH PDMS + MC HPC; panel (A) shows digital image correlation (2D-DIC), and panel (B) shows FEA.
  • Fig.12 shows charts reflecting measurements from dynamic mechanical analysis of panel (A) total elongation, panel (B) ultimate tensile strength, and panel (C) toughness, of various commercially available or natural polymers.
  • Fig.13 shows photographs illustrating the tear/fracture behavior of the SH PDMS + patterned nylon mesh composite material.
  • Fig.14 shows anisotropic mechanical behavior of a patterned nylon mesh in a triangular serpentine layout in panel (A), illustrating a chart in panel (B) which shows different strain threshold limits when subject to strain along the X-Axis vs. the Y-Axis.
  • Attorney Docket No.0116936.281WO2 [00100]
  • Fig.15 shows a plot reflecting UV-Vis transmittance spectra of SH PDMS and the dynamic covalent elastomer integrated with varying mass fractions of hollow glass microspheres (HGMs) (SH PDMS + HGMs).
  • HGMs hollow glass microspheres
  • Fig.16 shows a schematic diagram illustrating the HGM migration process in SH PDMS matrix upon heating.
  • Fig.17 shows a plot reflecting differential thermogravimetric (DTG) curves of SH PDMS and SH PDMS + HGMs composite materials.
  • Fig.18 shows a plot reflecting representative triaxial accelerometry and gyroscope signals as obtained from the encapsulated mechanoacoustic device, worn by an adult female subject.
  • Fig.19 shows charts reflecting representative SCGs derived from Z-axis accelerometry signals as obtained from the mechanoacoustic (MA) device encapsulated with varying materials, including SH PDMS-based materials and a conventional medical-grade silicone in panel (A); and signal-to-noise ratio (SNR) of obtained accelerometry data from the MA device encapsulated with varying materials, including SH PDMS-based materials and a conventional medical-grade silicone in panel (B).
  • MA mechanoacoustic
  • SNR signal-to-noise ratio
  • first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the invention.
  • relative terms such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe one element’s relationship to another element as illustrated in the figures.
  • relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. For example, if the device in one of the figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The exemplary term “lower”, can therefore, encompasses both an orientation of “lower” and “upper,” depending of the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below.
  • “around”, “about”, “approximately” or “substantially” shall generally mean within 20 percent, preferably within 10 percent, and more preferably within 5 percent of a given value or range. Numerical quantities given herein are approximate, meaning that the term “around”, “about”, “approximately” or “substantially” can be inferred if not expressly stated. [00116] As used in the disclosure, the phrase “at least one of A, B, and C” should be construed to mean a logical (A or B or C), using a non-exclusive logical OR. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
  • the term “wearable” refers to articles, adornments or items designed to be worn by a user, incorporated into another item worn by a user, act as an orthosis for the user, or interfacing with the contours of a user's body.
  • “biocompatible” material is a material that is compatible with living tissue or a living system by not being toxic or injurious and not causing immunological rejection.
  • the term “therapy” refers to any protocol, method, and/or agent that can be used in the management, treatment, and/or amelioration of a given disease, or a symptom related thereto.
  • the terms “therapies” and “therapy” refer to a biological therapy, supportive therapy, and/or other therapies known to one of skill in the art, such as medical personnel, useful in the management or treatment of a given disease, or symptom related thereto.
  • “treat”, “treatment”, and “treating” refer to the reduction or Attorney Docket No.0116936.281WO2 amelioration of the progression, severity, and/or duration of a given disease resulting from the administration of one or more therapies (including, but not limited to, the administration of microspheres disclosed herein).
  • Present system described herein features a self-healing poly(dimethylsiloxane) (PDMS) dynamic covalent matrix embedded with chemistries that provide thermochromism, mechanochromism, strain-adaptive stiffening, and thermal insulation, as a collection of attributes relevant to safety.
  • PDMS poly(dimethylsiloxane)
  • demonstrations of this materials system and associated encapsulation strategy involve a wireless, skin-interfaced device that captures mechanoacoustic signatures of health status.
  • the present invention is applicable immediately to many other related bioelectronic devices.
  • the present invention discloses the development of materials with these attributes and modes for their use with wireless, skin-interfaced bioelectronic devices.
  • a self-healing PDMS (SH PDMS) material serves as a foundational matrix for chemistries that support various stimuli-responsive functionalities and safety characteristics.
  • the present invention discloses companion processing approaches which provide routes for using these materials in soft, encapsulating structures as water-proof enclosures around multifunctional electronic systems. This strategy represents a materials-based complement to traditional safety mechanisms based on circuit designs and mechanical layouts.
  • the present invention in one embodiment, illustrates the applicability of these schemes in miniaturized, wireless mechanoacoustic sensors, previously demonstrated for capturing a broad range of physiological parameters, along with bulk movements of the body.
  • Example 1 Multifunctional Materials Design Approach
  • the operation of wireless, skin-interfaced bioelectronic devices involves intrinsic safety risks, such as those that may arise from mechanical damage to the encapsulating structure or an overheating battery.
  • the multifunctional materials design approach of the present invention addresses these concerns through using of a composite structural system that can reversibly and autonomically self-heal upon mechanical damage and change color upon Attorney Docket No.0116936.281WO2 certain excitative stimuli, such as temperature and strain. Additional features provide protection against excessive mechanical or thermal loads.
  • Self-healing properties within an elastomeric material can be achieved using extrinsic or intrinsic means.
  • the former relies on capsules of healing agent distributed within an elastomer matrix. Upon a damage event, the affected capsules break open to release a healing agent that flows into open cracks or other defects where it then solidifies.
  • This method while attractive, suffers from limited self-healing efficiency (i.e., the ability for the healed material to stretch to its original maximum elongation length) and supports only a single cycle of healing.
  • the present invention discloses an intrinsic form of self-healing which relies on reversible, dynamic chemical bond formation within the material itself, thereby providing a reversible mechanism for healing. Furthermore, given sufficient time for self-healing, the efficiency can be high. [00126] As shown in Fig.1B, these latter attractive features motivate the use of intrinsic self- healing concepts in the form of a dynamic covalent SH PDMS formulation that features imine bonding as the primary mechanism for self-healing, which can be used as an advanced encapsulation material for skin-interfaced bioelectronic devices.
  • the chemistry relies on a one-pot, Schiff base condensation reaction between ⁇ , ⁇ -telechelic aminopropyl PDMS and 1,3,5-triformylbenzene.
  • the present invention discloses that with additional chemical and structural components, including thermochromic (TC) leuco dyes, mechanochromic (MC) hydroxypropyl cellulose (HPC) sheets, patterned nylon meshes, and hollow glass microspheres (HGMs), the present invention provides a range of important stimuli-responsive properties within this SH PDMS matrix.
  • TC thermochromic
  • MC mechanochromic
  • HPC hydroxypropyl cellulose
  • HGMs hollow glass microspheres
  • a skin-interfaced electronic device may include flexible/foldable electronics 113, couple to a battery, e.g. thin LiPo battery 115, a water contact indicator 111 optionally, and an capsule of SH PDMS material.
  • the capsule in one embodiment, includes a composite of SH PDMS matrix with MC HPC sheets 101, a composite of SH PDMS matrix embedded with a patterned nylon mesh 103, a composite of SH PDMS matrix with HGMs 107, and a composite of SH PDMS matrix with TC 109.
  • thermochromism in the SH PDMS matrix follows from incorporation of a microencapsulated leuco dye, tertiary component systems that consist of a dye (color former), developer, and solvent.
  • the dye forms a colored complex with the developer at temperatures below the melting point of the solvent. At temperatures above this value, the phase change of the solvent destroys the colored complex between the dye and developer, thereby inducing a reversible change in color.
  • the dye used here has a “switching temperature” of 47°C and a corresponding reversible change in color from magenta/pink to colorless, as shown in Fig.2D. This temperature represents the approximate value at which pain/discomfort is expected on human skin.
  • the switching temperature is about 47°C. In one embodiment, the switching temperature ranges between about 46-48°C. In one embodiment, the switching temperature ranges between about 45-47°C. In one embodiment, the switching temperature ranges between about 44-46°C. In one embodiment, the switching temperature ranges between about 43-45°C. In one embodiment, the switching temperature ranges between about 42-44°C. In one embodiment, the switching temperature ranges between about 42-48°C.
  • Various mass fractions of the leuco dye can be incorporated to yield desired properties, as shown in Fig.2E.
  • Increasing the mass fraction of the dye to 0.5 wt% increases the visual vibrancy of the initial magenta state, as reflected in the increased absorbance for green wavelengths observed in the UV-Vis absorption spectra of the composite material, according to Fig.2F.
  • This loading level also enables high color contrast, as shown in Fig.7. Therefore, according to one embodiment, a mass fraction of 0.5 wt% in the given film thickness ( ⁇ 300 ⁇ m) provides the most effective thermochromism, as further loading generally degrades the uniformity of the composite material due to aggregation of the dye.
  • TC SH PDMS 109 This formulation, designated as TC SH PDMS 109, serves as the basis for device encapsulation results described subsequently.
  • mechanochromism in SH PDMS is realized using an aqueous solution of HPC, which enters the cholesteric liquid crystalline phase at a polymer weight percentage of at least 60%.
  • the pitch size of the cholesteric liquid crystal helical nanostructure decreases as the material undergoes increasing strain/stress, thereby causing a blue-shift in the spectrum of the reflected light and a corresponding visible color change, as shown in Fig.2H.
  • the SH Attorney Docket No.0116936.281WO2 PDMS + MC HPC composite 101 exhibits a significant blue-shift and the initial amber-hued color of the MC HPC component disappears, revealing vibrant green/blue tones, as shown in Figs.2J.
  • Fig.9 shows photographs illustrating the integration of MC HPC within SH PDMS elastomer layers.
  • the initial state of the SH PDMS + MC HPC composite material exhibits an amber/red color (left).
  • uniaxial strain is slowly applied (middle)
  • a blue-shift occurs due to the pitch decrease of the cholesteric liquid crystalline structure of HPC and green/blue colors are observed in the material.
  • DIC experiments quantify the displacement and strain distribution fields of a uniaxially stretched structure of this composite material in a serpentine shape as shown in Fig.2K, enabling direct comparison with the mechanochromic behavior.
  • the Triangular Cosserat Point Elements (TCPE) method reveals the strain distribution field, in a manner that allows separation of rigid body motions.
  • the approach uses high-throughput laser ablation methods to pattern triangular serpentine mesh structures in films of polyamide (Nylon-6, Attorney Docket No.0116936.281WO2 E bulk ⁇ 1.97 GPa, thickness ⁇ 250 ⁇ m) that are then embedded in thin layers of SH PDMS as a composite structure, as shown in Fig.3A.
  • Fig.3B The results are nonlinear stress/strain behaviors as shown in Fig.3B.
  • Corresponding photographs illustrate the structural deformations of a representative pattern as applied strain increases—transitioning from the original “toe” state, then to the “heel” state, and finally to the “linear” state.
  • This scheme and design also apply to mesh structures of other types of polymers according to Fig.12, including poly(ethylene terephthalate) (PET), poly(methyl methacrylate) (PMMA)), or even bioresorbable materials (e.g., cellulose acetate (CA), silk, poly-L-lactic acid (PLLA)).
  • PET poly(ethylene terephthalate)
  • PMMA poly(methyl methacrylate)
  • CA cellulose acetate
  • PLLA poly-L-lactic acid
  • a strain limit threshold of ⁇ 20% corresponding to the strain at which the stiffness of the encapsulation material dramatically increases, is a reasonable design goal. This level of strain is also the point at which the SH PDMS + MC HPC composite material undergoes a strong blue-shift, as shown in Figs.2J-K.
  • the serpentine mesh pattern determines the strain limit threshold response, via the serpentine angle ( ⁇ ) according to Fig.3C and the serpentine width (w) according to Fig.3D.
  • the serpentine mesh structures can be fabricated into a non- triangular pattern.
  • Fig.3E shows the nonlinear stress/strain behavior of the SH PDMS + nylon mesh composite material, as compared to SH PDMS.
  • the composite shows the desired strain- adaptive stiffening response, as the initial modulus of the composite material (E ⁇ 0.82 MPa) increases by more than ⁇ 90% to 1.58 MPa at ⁇ 20% strain.
  • this mechanical reinforcement at ⁇ 20% strain dramatically increases the modulus of the SH PDMS by ⁇ 532%, to E ⁇ 1.58 MPa.
  • the patterned mesh also increases the tear resistance, resulting in a ⁇ 30x larger tear force as shown in Fig.3F, and a stepwise tear profile as shown in Figs.3G and 13 that ultimately delays the complete fracture of the material.
  • serpentine mesh lends itself to an inherent anisotropy that yields different strain threshold limits along different directions of strain, as shown in Fig.14. This unique property could be leveraged for applications that require differing levels of stretchability/mechanical reinforcement along the major axis vs. the minor axis of the device, such as a previously reported rectangular-shaped, wireless ECG device with electrodes that primarily stretch ( ⁇ 20%) along the major axis.
  • Another design option is to introduce spatial heterogeneity in the serpentine mesh design, such as increasing the serpentine width at the edge regions of the mesh, as shown in Fig. 3H.
  • HGMs which include a thin outer borosilicate shell, are frequently utilized as inert additives in polymer matrices to reduce the thermal conductivity (k) and density ( ⁇ ) of the composite material.
  • the present invention discloses small mass fractions (2.5 – 5.0 wt%) of HGMs integrated with SH PDMS yield a white appearance consistent with an expected increase in optical scattering, as shown in Figs.4A and 15. Scanning electron microscopy (SEM) of fracture surfaces of composites with 2.5 and 5.0 wt% HGMs according to Fig.4B shows well- dispersed collections of HGMs within the SH PDMS matrix, in closed-shell morphologies.
  • SEM scanning electron microscopy
  • the thermal conductivities of the 2.5 wt% and 5.0 wt% HGMs composite materials are ⁇ 8% and ⁇ 25% lower, respectively, than that of SH PDMS.
  • the densities of the 2.5 wt% and 5.0 wt% HGMs composites similarly decrease ⁇ 14% and ⁇ 27%, respectively, compared to SH PDMS, as shown in Fig.4E and Table 2. These decreases in thermal conductivity enhance the thermal insulation properties.
  • SH PDMS and SH PDMS + HGMs structures that fully encapsulate a LiPo battery housing that contains a resistive heater designed to simulate thermal runaway.
  • the temperature of the heater of the 2.5 wt% and 5.0 wt% HGMs composites are ⁇ 10.2°C and ⁇ 14.5°C higher, respectively, than that of SH PDMS, indicating that the thermally insulating nature of the HGMs helps to contain and isolate the heat to the battery structure, according to Fig.4G.
  • the thermal insulating aspects of the HGMs can be combined with other thermal protective strategies that exploit materials, layouts, and circuit designs.
  • HGMs as a low-density filler component, migrate to the top surface during extreme cases of heating that liquify the matrix material, as shown in Fig.16. This migration creates a heat-reflective barrier that influences the thermal stability of the SH PDMS + HGMs composites. For example, flame-retardant properties begin to emerge with increasing mass fractions of HGMs, specifically in delays for combustion when the SH PDMS + HGMs composites are exposed to a flame, as shown in Fig.4H. In the case of SH PDMS, the material rapidly ignites at t ⁇ 3 s.
  • the 2.5 wt% HGMs composite material begins to show signs of charring on the surface, but ignition does not occur until t ⁇ 7 s.
  • the 5.0 Attorney Docket No.0116936.281WO2 wt% HGMs composite displays even higher levels of flame-retardant properties, igniting only after 10 s of exposure to the flame and with minimal signs of charring.
  • the thermal stability of SH PDMS and SH PDMS + HGMs composite materials are further characterized by the thermogravimetric analysis (TGA) in Fig.4I and differential thermogravimetric (DTG) measurements, as shown in Fig.17.
  • TGA thermogravimetric analysis
  • TMG differential thermogravimetric
  • the peak degradation temperatures of the 2.5 wt% and 5.0 wt% HGMs composite materials are 543°C and 577°C, respectively, both significantly higher than that of SH PDMS (518°C). 5.
  • the SH PDMS material and its various composite forms can be used in encapsulating structures for a wide range of skin-interfaced bioelectronic devices.
  • the present invention discloses a wireless sensor that mounts on the suprasternal notch to capture mechanoacoustic signatures of health-related parameters and motions of the core body.
  • Fig.5A illustrates the encapsulated device in a dual-sided construct that uses SH PDMS + HGMs (2.5 wt% HGMs) and TC SH PDMS, as shown in Fig.5A inset, on the side of the device adjacent to the embedded thin LiPo battery, as shown in Fig.1B, which poses the highest thermal safety risk.
  • Fig.5B highlights the TC SH PDMS component of the encapsulation structure, as the device is heated from 38°C to 49°C, showing the characteristic color change as the device exceeds the activation/switching temperature of 47°C.
  • the other side uses SH PDMS + MC HPC, SH PDMS + patterned nylon, and SH PDMS.
  • the SH PDMS + MC HPC resides at the location of the device, according to Fig.5C, that experiences the largest mechanical deformations, typically bending associated with removal of the device from the skin.
  • the remaining area uses SH PDMS + patterned nylon, as shown I Fig.5D outlined in white to increase mechanical robustness, with small windows of transparent SH PDMS for purposes described below, as shown in Figs.5C-D outlined in red.
  • the encapsulation structure demonstrates autonomic self-healing behavior, as shown in Fig.5E, in Attorney Docket No.0116936.281WO2 response to a severe cut that exposes the internal electronic components. A significant portion of the cut self-heals after only 5 mins, with full healing after 20 h.
  • an additional safety hazard follows from electrical shock mediated by water or biofluids.
  • Thin hydrochromic paper materials inserted into the encapsulating package at locations visually observable through transparent windows can serve as useful indicators of water exposure. In the example reported here, as water reaches a commercial indicator of this type, its color changes from white to red, according to Fig.5F-G.
  • the device mounted on a volunteer subject appears in Fig.5H.
  • Triaxial accelerometry of Fig.5I and gyroscopic measurements of Fig.18 at this location allow for continuous capture of various signals including those associated with cardiac cycles (represented in the form of seismocardiograms (SCGs)), large physical motions (e.g., walking and jumping), and respiratory activity (both inhalation and exhalation) derived from the acceleration data in the direction normal to the surface of the skin, as shown in Fig.5J.
  • SCGs seismocardiograms
  • large physical motions e.g., walking and jumping
  • respiratory activity both inhalation and exhalation
  • pre-synthesized SH PDMS films were re-processed by dissolving them in chloroform (Sigma-Aldrich). After dissolution, a magenta thermochromic (TC) leuco dye powder (LCR Hallcrest), with an activation/switching temperature at 47°C, was added to the solution at Attorney Docket No.0116936.281WO2 varying mass fractions (0.1-0.5 wt%). The dye was pulverized by a mortar and pestle before use. The solution with the dye powder was then thoroughly mixed by using a vortex mixer. The mixture was poured into a target well to control the film thickness. Overnight drying at room temperature yielded a magenta TC SH PDMS elastomer.
  • TC thermochromic
  • TC SH PDMS Thin ( ⁇ 300 ⁇ m) films of TC SH PDMS, with varying mass fractions of TC leuco dye, were placed on a hot plate and heated to 55°C. Videos were captured of the samples during, and the changes in color were analyzed via ImageJ software to determine the changes in RGB values, as well as the response times.
  • MC Mechanochromic
  • HPC Liquid Crystalline Hydroxypropyl Cellulose
  • HPC hydroxypropyl cellulose
  • the DIC subset radius and spacing were set as 10 pixels and 5 pixels, respectively, resolving over 1500 displacement grids with the grid resolution of ⁇ 400 ⁇ m.
  • the strain magnitude and shear strain were computed based on the Triangular Cosserat Point Theory.
  • FEA for MC HPC Analysis The commercial FEA software ABAQUS was used to determine the mechanical performance of SH PDMS + MC HPC when subjected to uniaxial strain. A 3D rectangular model with dimensions of 70 mm x 30 mm x 6 mm was used for the fluidic channel mold, which includes the serpentine pattern of the MC HPC with a thickness of Attorney Docket No.0116936.281WO2 ⁇ 2 mm.
  • Displacement boundary conditions were imposed at the ends of the 3D rectangular elastomer encapsulation model to stretch uniaxially along the longitudinal direction by up to 30%.
  • the strain ⁇ and in-plane displacement Ux and Uy fields were computed at 30% uniaxial stretch, as shown in Figs.18-19, where the simulation closely matches the DIC field measurements.
  • the elastomer encapsulation and MC HPC were modeled by hexahedron elements (C3D8R) and the total number of elements used in the simulation is 125,000.
  • Example Summary [00182] The collective results disclosed in the present invention suggest that advanced materials strategies can be used in wireless, skin-interfaced bioelectronic devices to manage safety risks in a manner that can complement and extend capabilities based on traditional sensor and electronic circuit methods.
  • a self-healing formulation of a silicone polymer serves as a matrix material in soft encapsulating structures that offer various stimuli-responsive properties, such as reversible thermochromism/mechanochromism and strain-adaptive stiffening, in addition to other improved thermal-related characteristics.
  • This multifunctional material construct of the present invention addresses various risks in mechanical, thermal, and electrical modes of device failure.

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Abstract

A self-healing (SH) capsule for encapsulating a skin-interfaced electronic device being used on an individual. The SH capsule comprises one or more of a thermochromic SH composite; a SH hollow glass microspheres composite; a SH patterned nylon composite; and a SH mechanochromic (MC) hydroxypropyl cellulose (HPC) composite.

Description

Attorney Docket No.0116936.281WO2 MULTIFUNCTIONAL MATERIALS STRATEGIES FOR ENHANCED SAFETY OF WIRELESS, SKIN-INTERFACED BIOELECTRONIC DEVICES AND APPLICATIONS OF SAME CROSS-REFERENCE TO RELATED PATENT APPLICATIONS [0001] This application claims priority to and the benefit of U.S. Provisional Patent Application Serial No.63/448,689, filed February 28, 2023, which is incorporated herein in its entirety by reference. FIELD OF THE INVENTION [0002] The present disclosure relates generally to the field of biomedical engineering, and more particularly to a self-healing poly(dimethylsiloxane) (PDMS) dynamic covalent matrix embedded with chemistries that provide thermochromism, mechanochromism, strain-adaptive stiffening, and thermal insulation, and skin-interfaced electronic devices incorporating the same. BACKGROUND OF THE INVENTION [0003] The background description provided herein is for the purpose of generally presenting the context of the present invention. The subject matter discussed in the background of the invention section should not be assumed to be prior art merely as a result of its mention in the background of the invention section. Similarly, a problem mentioned in the background of the invention section or associated with the subject matter of the background of the invention section should not be assumed to have been previously recognized in the prior art. The subject matter in the background of the invention section merely represents different approaches, which in and of themselves may also be inventions. [0004] Wireless, skin-interfaced bioelectronic devices are increasingly popular for unobtrusive, noninvasive, and continuous monitoring of essential health parameters, ranging from traditional vital signs to various emerging metrics of patient status. The most mature of these devices consist of thin, flexible printed circuit boards (PCBs) structured into open mesh geometries with electronic components, sensing modules, and hardware for wireless communication. Power can be delivered using wireless schemes or provided by integrated batteries, which are encapsulated with the other constituent parts within a soft, flexible, and Attorney Docket No.0116936.281WO2 stretchable polymeric structure, typically of a medical-grade thermoset silicone elastomer. Ensuring that these wireless electronic device systems operate reliably and safely while adhered to the skin is a critical concern in engineering design. While many safeguards, spanning careful quality control to voltage/current protection circuits, are important, they do not address all possible safety hazards. For example, mechanical failures in the encapsulation structure that follow from prolonged cycles of use can expose the user to mechanical and electrical hazards associated with the electronic components. [0005] Materials having self-healing capabilities and strain-limiting features would have advantages over simple silicones as encapsulants and are thus highly desired. Adding into these materials species for visual, colorimetric indication of these and other forms of device failure, are also of interest. [0006] Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies. SUMMARY OF THE INVENTION [0007] In light of the foregoing, this invention discloses a skin-interfaced electronic device having a self-healing (SH) dynamic covalent elastomer capsule. The device comprises a SH dynamic covalent elastomer capsule; and an electronic module disposed inside the SH dynamic covalent elastomer capsule. The SH capsule comprises a thermochromic (TC) SH PDMS composite having a microencapsulated leuco dye integrated in a first poly(dimethylsiloxane) (PDMS) matrix; a SH PDMS hollow glass microspheres (HGMs) composite having multiple HGMs incorporated in a second PDMS matrix; a SH PDMS patterned nylon composite having a patterned nylon mesh embedded in a third PDMS matrix; and a SH PDMS mechanochromic (MC) hydroxypropyl cellulose (HPC) composite having at least one MC HPC sheet integrated in a fourth PDMS matrix. The SH dynamic covalent elastomer capsule has a self-healing reaction comprising a Schiff base condensation reaction between α, ω-telechelic aminopropyl PDMS and 1,3,5-triformylbenzene. [0008] In another aspect of the invention, a skin-interfaced electronic device having a self- healing (SH) capsule comprises a SH capsule; and an electronic module disposed inside the SH capsule; wherein the SH capsule comprises at least one encapsulation composite. [0009] In one embodiment, the at least one encapsulation composite comprises a Attorney Docket No.0116936.281WO2 thermochromic (TC) composite having a dye integrated in a first matrix. [0010] In one embodiment, the dye comprises a microencapsulated leuco dye, wherein the microencapsulated leuco dye comprises a tertiary component system having a color former, a developer, and a solvent. [0011] In one embodiment, the microencapsulated leuco dye has a switching temperature at which the microencapsulated leuco dye reversibly changes its color. [0012] In one embodiment, the switching temperature ranges between about 44°C to 48°C. [0013] In one embodiment, the at least one encapsulation composite comprises a hollow glass microspheres (HGMs) composite, wherein the HGMs composite comprises multiple HGMs incorporated in a second matrix. [0014] In one embodiment, the multiple HGMs are configured to migrate in the second matrix. [0015] In one embodiment, the multiple HGMs have a mass fraction ranges between about 2.5-5.0 wt%. [0016] In one embodiment, the at least one encapsulation composite comprises a SH patterned nylon composite, wherein the SH patterned nylon composite comprises a patterned nylon mesh embedded in a third matrix. [0017] In one embodiment, the patterned nylon mesh comprises a polyamide film. [0018] In one embodiment, the patterned nylon mesh comprises serpentine mesh structures. [0019] In one embodiment, the serpentine mesh structures have a triangular shape. [0020] In one embodiment, the serpentine mesh structures have a serpentine angle (θ) of about 120° and a serpentine width (w) about 100 μm. [0021] In one embodiment, the patterned nylon composite comprises a viewing window section, wherein the viewing window section comprises the third matrix free of the patterned nylon mesh. [0022] In one embodiment, the device comprises a water contact indicator disposed inside the SH capsule, and wherein the water contact indicator is configured to reversibly change its color when it contacts water. [0023] In one embodiment, the water contact indicator is disposed directly next to the viewing window section such that the water contact indicator is configured to be visible outside of the SH capsule. Attorney Docket No.0116936.281WO2 [0024] In one embodiment, the at least one encapsulation composite comprises a mechanochromic (MC) hydroxypropyl cellulose (HPC) composite, wherein the MC HPC composite comprises at least one MC HPC sheet integrated in a fourth matrix. [0025] In one embodiment, the MC HPC composite is configured to reversibly change its color when a strain force is applied to the MC HPC composite. [0026] In one embodiment, the electronic module comprises a flexible electronic component and a battery coupled to the flexible electronic component. [0027] In one embodiment, the at least one encapsulation composite comprises a poly(dimethylsiloxane) PDMS matrix. [0028] In another aspect of the invention, a composite capsule for encapsulating a skin- interfaced electronic device, the composite capsule comprising at least one encapsulation composite. [0029] In one embodiment, the at least one encapsulation composite comprises a thermochromic (TC) composite having a dye integrated in a first matrix. [0030] In one embodiment, the dye comprises a microencapsulated leuco dye, wherein the microencapsulated leuco dye comprises a tertiary component system having a color former, a developer, and a solvent. [0031] In one embodiment, the microencapsulated leuco dye has a switching temperature at which the microencapsulated leuco dye reversibly changes its color. [0032] In one embodiment, the switching temperature ranges between about 44°C to 48°C. [0033] In one embodiment, the at least one encapsulation composite further comprises a hollow glass microspheres (HGMs) composite, wherein the HGMs composite comprises multiple HGMs incorporated in a second matrix. [0034] In one embodiment, the multiple HGMs are configured to migrate in the second matrix. [0035] In one embodiment, the multiple HGMs have a mass fraction ranges between about 2.5-5.0 wt%. [0036] In one embodiment, the TC composite is disposed closer to an individual’s skin compared to the HGMs composite. [0037] In one embodiment, the at least one encapsulation composite further comprises a patterned nylon composite, wherein the patterned nylon composite comprises a patterned nylon Attorney Docket No.0116936.281WO2 mesh embedded in a third matrix. [0038] In one embodiment, the patterned nylon mesh comprises a polyamide film. [0039] In one embodiment, the patterned nylon mesh comprises serpentine mesh structures. [0040] In one embodiment, the serpentine mesh structures have a triangular shape. [0041] In one embodiment, the serpentine mesh structures have a serpentine angle (θ) of about 120° and a serpentine width (w) about 100 μm. [0042] In one embodiment, the patterned nylon composite further comprises a viewing window section, wherein the viewing window section comprises the third matrix free of the patterned nylon mesh. [0043] In one embodiment, the at least one encapsulation composite further comprises a mechanochromic (MC) hydroxypropyl cellulose (HPC) composite, wherein the MC HPC composite comprises at least one MC HPC sheet integrated in a fourth matrix. [0044] In one embodiment, the MC HPC composite is configured to reversibly change its color when a strain force is applied to the MC HPC composite. [0045] In one embodiment, the composite capsule comprises a self healing elastomer. [0046] In one embodiment, the SH elastomer comprises dynamic covalent elastomer. [0047] In one embodiment, at least one of the first matrix, the second matrix, the third matrix, and the fourth matrix comprises a poly(dimethylsiloxane) (PDMS) matrix. [0048] In yet another embodiment of the invention, a self-healing (SH) dynamic covalent elastomer capsule for encapsulating a skin-interfaced electronic device comprises a thermochromic (TC) SH poly(dimethylsiloxane) (PDMS) composite has a microencapsulated leuco dye integrated in a first PDMS matrix; a SH PDMS hollow glass microspheres (HGMs) composite has multiple HGMs incorporated in a second PDMS matrix; a SH PDMS patterned nylon composite has a patterned nylon mesh embedded in a third PDMS matrix; and a SH PDMS mechanochromic (MC) hydroxypropyl cellulose (HPC) composite has at least one MC HPC sheet integrated in a fourth PDMS matrix. BRIEF DESCRIPTION OF THE DRAWINGS [0049] The accompanying drawings illustrate one or more embodiments of the invention and together with the written description, serve to explain the principles of the invention. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or Attorney Docket No.0116936.281WO2 like elements of an embodiment. [0050] Fig.1A illustrates potential safety hazards associated with wireless, skin-interfaced bioelectronic devices. [0051] Fig.1B shows a schematic diagram of the structural configuration and the encapsulation material choices for the wireless, skin-interfaced bioelectronic device on the left; and the Schiff-base chemical reaction forms dynamic covalent imine bonds that serve as autonomic self-healing points in the SH PDMS elastomer matrix on the right. [0052] Fig.2A shows photographs illustrating the synthesized dynamic covalent elastomer (SH PDMS) self-healing after a damage event. [0053] Fig.2B shows a scanning electron microscopy image illustrating the self-healed region of the synthesized SH PDMS. [0054] Fig.2C shows a plot of FTIR spectra of the synthesized SH PDMS, illustrating the characteristic peak for the dynamic covalent imine bond. [0055] Fig.2D shows a schematic diagram of the thermochromic (TC) properties of a leuco dye (microcapsule form) with an activation temperature of 47°C. [0056] Fig.2E shows a schematic diagram of color changes associated with a temperature increase from 37°C to 47°C of SH PDMS with varying mass fractions of the TC leuco dye. [0057] Fig.2F shows a chart of UV spectra of the SH PDMS with varying mass fractions of the TC leuco dye. [0058] Fig.2G shows photographs illustrating the synthesized TC SH PDMS, integrated with 0.5 wt% TC leuco dye, undergoing autonomic self-healing after a damage event. [0059] Fig.2H shows a schematic diagram of the mechanochromic (MC) properties of the cholesteric liquid crystalline nanostructure Of aqueous hydroxypropyl cellulose (HPC). [0060] Fig.2I shows a photograph illustrating the cholesteric liquid crystalline HPC encapsulated within thin, flexible layers of SH PDMS. [0061] Fig.2J shows color changes associated with increasing mechanical strain of the encapsulated cholesteric liquid crystalline HPC. [0062] Fig.2K shows digital image correlation experiments for simultaneous mechanical and chromic analysis of the encapsulated cholesteric liquid crystalline HPC, in a serpentine configuration, undergoing uniaxial strain. [0063] Fig.3A shows photographs depicting the synthesized dynamic covalent elastomer Attorney Docket No.0116936.281WO2 (SH PDMS) integrated with a thin serpentine patterned nylon mesh for mechanical reinforcement. [0064] Fig.3B shows a chart reflecting the nonlinear stress/strain profile of a thin serpentine patterned nylon mesh, along with corresponding photographs of the mesh. [0065] Fig.3C shows a chart reflecting the strain limit threshold as a function of the nylon serpentine mesh angle(θ), with finite element analysis (FEA) modeling results. [0066] Fig.3D shows a chart reflecting stress/strain curves of the patterned nylon mesh (θ = 120°) with varying serpentine widths (w). [0067] Fig.3E shows a chart reflecting stress/strain curve of the SH PDMS + patterned nylon mesh composite material, compared to SH PDMS without the patterned nylon mesh, along with corresponding strain distribution profiles obtained via digital image correlation (DIC) experiments. [0068] Fig.3F shows a chart reflecting tear force measurements of SH PDMS and SH PDMS + patterned nylon mesh composite material, as obtained from trouser tear-propagation testing. [0069] Fig.3G shows a chart reflecting stepwise tearing profile (stress/strain curve) of the SH PDMS + patterned nylon mesh composite material. [0070] Fig.3H shows photograph of the heterogeneous serpentine patterned nylon mesh, featuring thicker serpentine widths at the edge. [0071] Fig.3I shows DIC experiments illustrating spatially varying strain distribution profiles of the SH PDMS + heterogeneous patterned nylon mesh composite material undergoing uniaxial strain. [0072] Fig.4A shows photograph depicting the synthesized dynamic covalent elastomer (SH PDMS) integrated with varying mass fractions of HGMs. [0073] Fig.4B shows scanning electron microscopy micrographs of the cross-sectional areas of SH PDMS + HGMs composites. [0074] Fig.4C shows a chart reflecting stress/strain curves of SH PDMS (left) and SH PDMS+ HGMs composites (middle and right), after various time periods for self-healing. [0075] Fig.4D shows photograph illustrating an epidermal thermal depth sensor (e-TDS) on the top surface of the SH PDMS + HGMs composite. [0076] Fig.4E shows a chart reflecting density (p) and thermal conductivity (k)of the SH PDMS + HGMs composites. Attorney Docket No.0116936.281WO2 [0077] Fig 4F shows a chart reflecting temperature profiles, including those obtained from finite element analysis (FEA), of the encapsulated battery with heater (BwH) during an overheating simulation, with an inset of photograph illustrating the simulation test setup for an overheating lithium-polymer (LiPo) battery. [0078] Fig.4G shows results of temperature distributions, obtained from FEA, of the encapsulated BwH during an overheating simulation, at t = 180s. [0079] Fig.4H shows photographs illustrating the burning-via candle flame-of the SH PDMS (top row) and the improved flame resistance of the SH PDMS + HGMs composites (middle and bottom rows). [0080] Fig.4I shows a chart reflecting thermogravimetric analysis curves of SH PDMS and SH PDMS + HGM composites. [0081] Fig.5A shows a photograph depicting the side-view of a wireless skin-interfaced MA device, encapsulated with self-healing PDMS (SH PDMS) and its variations. [0082] Fig.5B shows photographs illustrating the color change of the TC SH PDMS outlined in white associated with heating. [0083] Fig.5C shows photographs illustrating the color change of the SH PDMS + MC HPC outlined in white associated with strain from bending of the device, with a water contact indicator, outlined in red, as viewed through transparent SH PDMS. [0084] Fig.5D shows a photograph illustrating the SH PDMS + patterned nylon section outlined in white of the encapsulation structure, with a water contact indicator, outlined in red as viewed through transparent SH PDMS. [0085] Fig.5E shows photographs illustrating the self-healing behavior of the encapsulation structure. [0086] Fig.5F shows a chart reflecting time-lapse of the color changes associated with water exposure to the water contact indicator material. [0087] Fig.5G shows photographs of the water contact indicators overlaid on top of the printed circuit board changing color as water is introduced. [0088] Fig.5H shows a photograph of the encapsulated MA device on the suprasternal notch of an adult female subject. [0089] Fig.5I shows a chart reflecting representative triaxial accelerometry signals obtained from the encapsulated MA device worn by an adult female subject performing various physical Attorney Docket No.0116936.281WO2 activities. [0090] Fig.5J shows charts of Z-axis accelerometry signals which illustrate unique signatures of different body processes including cardiac activity in the form of the seismocardiogram (SCG) waveform with distinct Si and S2 heart sounds (left), physical motions such as walking and jumping (middle), and respiration waveforms during deep breaths (right). [0091] Fig.6 shows a DIC analysis of the autonomic self-healing behavior of the dynamic covalent elastomer (SH PDMS); panel (A) shows photographs (left column) and the corresponding strain distribution maps (right column) via DIC experiments of a slit film of SH PDMS undergoing uniaxial strain (top row, red), which is then allowed to self-heal for 15 mins (bottom row, blue) and undergo uniaxial strain again; while panel (B) is a plot reflecting measured strain magnitude at the slit (red) and self-healed (blue) region of the SH PDMS film. [0092] Fig.7 shows a chart reflecting thermochromic properties, as illustrated by the change in RGB values between the relaxed and heated states of the dynamic covalent elastomer matrix integrated with leuco dye (TC SH PDMS), with varying mass fractions. [0093] Fig.8 shows a plot reflecting stress/strain curves of the TC SH PDMS, including those after different time periods of self-healing. [0094] Fig.9 shows photographs of the SH PDMS with integrated mechanochromic hydroxypropyl cellulose (MC HPC). [0095] Fig.10 shows a diagram illustrating finite element analysis (FEA) of the strain distribution field of the SH PDMS + MC HPC. [0096] Fig.11 shows diagrams illustrating displacement fields of the uniaxially-strained SH PDMS + MC HPC; panel (A) shows digital image correlation (2D-DIC), and panel (B) shows FEA. [0097] Fig.12 shows charts reflecting measurements from dynamic mechanical analysis of panel (A) total elongation, panel (B) ultimate tensile strength, and panel (C) toughness, of various commercially available or natural polymers. [0098] Fig.13 shows photographs illustrating the tear/fracture behavior of the SH PDMS + patterned nylon mesh composite material. [0099] Fig.14 shows anisotropic mechanical behavior of a patterned nylon mesh in a triangular serpentine layout in panel (A), illustrating a chart in panel (B) which shows different strain threshold limits when subject to strain along the X-Axis vs. the Y-Axis. Attorney Docket No.0116936.281WO2 [00100] Fig.15 shows a plot reflecting UV-Vis transmittance spectra of SH PDMS and the dynamic covalent elastomer integrated with varying mass fractions of hollow glass microspheres (HGMs) (SH PDMS + HGMs). [00101] Fig.16 shows a schematic diagram illustrating the HGM migration process in SH PDMS matrix upon heating. [00102] Fig.17 shows a plot reflecting differential thermogravimetric (DTG) curves of SH PDMS and SH PDMS + HGMs composite materials. [00103] Fig.18 shows a plot reflecting representative triaxial accelerometry and gyroscope signals as obtained from the encapsulated mechanoacoustic device, worn by an adult female subject. [00104] Fig.19 shows charts reflecting representative SCGs derived from Z-axis accelerometry signals as obtained from the mechanoacoustic (MA) device encapsulated with varying materials, including SH PDMS-based materials and a conventional medical-grade silicone in panel (A); and signal-to-noise ratio (SNR) of obtained accelerometry data from the MA device encapsulated with varying materials, including SH PDMS-based materials and a conventional medical-grade silicone in panel (B). DETAILED DESCRIPTION OF THE INVENTION [00105] The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout. [00106] The terms used in this specification generally have their ordinary meanings in the art, within the context of the invention, and in the specific context where each term is used. Certain terms that are used to describe the invention are discussed below, or elsewhere in the specification, to provide additional guidance to the practitioner regarding the description of the invention. For convenience, certain terms may be highlighted, for example using italics and/or quotation marks. The use of highlighting has no influence on the scope and meaning of a term; Attorney Docket No.0116936.281WO2 the scope and meaning of a term is the same, in the same context, whether or not it is highlighted. It will be appreciated that same thing can be said in more than one way. Consequently, alternative language and synonyms may be used for any one or more of the terms discussed herein, nor is any special significance to be placed upon whether or not a term is elaborated or discussed herein. Synonyms for certain terms are provided. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification including examples of any terms discussed herein is illustrative only, and in no way limits the scope and meaning of the invention or of any exemplified term. Likewise, the invention is not limited to various embodiments given in this specification. [00107] One of ordinary skill in the art will appreciate that starting materials, biological materials, reagents, synthetic methods, purification methods, analytical methods, assay methods, and biological methods other than those specifically exemplified can be employed in the practice of the invention without resort to undue experimentation. All art-known functional equivalents, of any such materials and methods are intended to be included in this invention. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims. [00108] Whenever a range is given in the specification, for example, a temperature range, a time range, or a composition or concentration range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the invention. It will be understood that any subranges or individual values in a range or subrange that are included in the description herein can be excluded from the claims herein. [00109] It will be understood that, as used in the description herein and throughout the claims that follow, the meaning of “a”, “an”, and “the” includes plural reference unless the context clearly dictates otherwise. Thus, for example, reference to “a cell” includes a plurality of such cells and equivalents thereof known to those skilled in the art. As well, the terms “a” (or “an”), Attorney Docket No.0116936.281WO2 “one or more” and “at least one” can be used interchangeably herein. It is also to be noted that the terms “comprising”, “including”, and “having” can be used interchangeably. [00110] It will be understood that when an element is referred to as being “on”, “attached” to, “connected” to, “coupled” with, “contacting”, etc., another element, it can be directly on, attached to, connected to, coupled with or contacting the other element or intervening elements may also be present. In contrast, when an element is referred to as being, for example, “directly on”, “directly attached” to, “directly connected” to, “directly coupled” with or “directly contacting” another element, there are no intervening elements present. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed “adjacent” another feature may have portions that overlap or underlie the adjacent feature. [00111] It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the invention. [00112] Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe one element’s relationship to another element as illustrated in the figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. For example, if the device in one of the figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The exemplary term “lower”, can therefore, encompasses both an orientation of “lower” and “upper,” depending of the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below. [00113] It will be further understood that the terms “comprises” and/or “comprising”, or “includes” and/or “including”, or “has” and/or “having”, or “carry” and/or “carrying”, or “contain” and/or “containing”, or “involve” and/or “involving”, “characterized by”, and the like Attorney Docket No.0116936.281WO2 are to be open-ended, i.e., to mean including but not limited to. When used in this disclosure, they specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. [00114] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the invention, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. [00115] As used in the disclosure, “around”, “about”, “approximately” or “substantially” shall generally mean within 20 percent, preferably within 10 percent, and more preferably within 5 percent of a given value or range. Numerical quantities given herein are approximate, meaning that the term “around”, “about”, “approximately” or “substantially” can be inferred if not expressly stated. [00116] As used in the disclosure, the phrase “at least one of A, B, and C” should be construed to mean a logical (A or B or C), using a non-exclusive logical OR. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. [00117] As used in the disclosure, the term “wearable” refers to articles, adornments or items designed to be worn by a user, incorporated into another item worn by a user, act as an orthosis for the user, or interfacing with the contours of a user's body. [00118] As used in the disclosure, “biocompatible” material is a material that is compatible with living tissue or a living system by not being toxic or injurious and not causing immunological rejection. [00119] As used in the disclosure, the term “therapy” refers to any protocol, method, and/or agent that can be used in the management, treatment, and/or amelioration of a given disease, or a symptom related thereto. In certain embodiments, the terms “therapies” and “therapy” refer to a biological therapy, supportive therapy, and/or other therapies known to one of skill in the art, such as medical personnel, useful in the management or treatment of a given disease, or symptom related thereto. [00120] As used in the disclosure, “treat”, “treatment”, and “treating” refer to the reduction or Attorney Docket No.0116936.281WO2 amelioration of the progression, severity, and/or duration of a given disease resulting from the administration of one or more therapies (including, but not limited to, the administration of microspheres disclosed herein). [00121] Present system described herein features a self-healing poly(dimethylsiloxane) (PDMS) dynamic covalent matrix embedded with chemistries that provide thermochromism, mechanochromism, strain-adaptive stiffening, and thermal insulation, as a collection of attributes relevant to safety. In one embodiment, demonstrations of this materials system and associated encapsulation strategy involve a wireless, skin-interfaced device that captures mechanoacoustic signatures of health status. In another embodiment, the present invention is applicable immediately to many other related bioelectronic devices. [00122] In one embodiment, the present invention discloses the development of materials with these attributes and modes for their use with wireless, skin-interfaced bioelectronic devices. Specifically, in one embodiment, a self-healing PDMS (SH PDMS) material serves as a foundational matrix for chemistries that support various stimuli-responsive functionalities and safety characteristics. In one embodiment, the present invention discloses companion processing approaches which provide routes for using these materials in soft, encapsulating structures as water-proof enclosures around multifunctional electronic systems. This strategy represents a materials-based complement to traditional safety mechanisms based on circuit designs and mechanical layouts. The present invention, in one embodiment, illustrates the applicability of these schemes in miniaturized, wireless mechanoacoustic sensors, previously demonstrated for capturing a broad range of physiological parameters, along with bulk movements of the body. These results not only offer immediate, broad potential across wide ranging classes of devices, but also motivate the development of additional, complementary materials strategies for safe operation of bioelectronic systems. Example 1. Multifunctional Materials Design Approach [00123] As shown in Fig.1A, the operation of wireless, skin-interfaced bioelectronic devices involves intrinsic safety risks, such as those that may arise from mechanical damage to the encapsulating structure or an overheating battery. The multifunctional materials design approach of the present invention addresses these concerns through using of a composite structural system that can reversibly and autonomically self-heal upon mechanical damage and change color upon Attorney Docket No.0116936.281WO2 certain excitative stimuli, such as temperature and strain. Additional features provide protection against excessive mechanical or thermal loads. [00124] Self-healing properties within an elastomeric material, including commonly used silicones such as PDMS, can be achieved using extrinsic or intrinsic means. The former relies on capsules of healing agent distributed within an elastomer matrix. Upon a damage event, the affected capsules break open to release a healing agent that flows into open cracks or other defects where it then solidifies. This method, while attractive, suffers from limited self-healing efficiency (i.e., the ability for the healed material to stretch to its original maximum elongation length) and supports only a single cycle of healing. [00125] The present invention discloses an intrinsic form of self-healing which relies on reversible, dynamic chemical bond formation within the material itself, thereby providing a reversible mechanism for healing. Furthermore, given sufficient time for self-healing, the efficiency can be high. [00126] As shown in Fig.1B, these latter attractive features motivate the use of intrinsic self- healing concepts in the form of a dynamic covalent SH PDMS formulation that features imine bonding as the primary mechanism for self-healing, which can be used as an advanced encapsulation material for skin-interfaced bioelectronic devices. [00127] Specifically, the chemistry relies on a one-pot, Schiff base condensation reaction between ^, ^-telechelic aminopropyl PDMS and 1,3,5-triformylbenzene. [00128] In one embodiment, the present invention discloses that with additional chemical and structural components, including thermochromic (TC) leuco dyes, mechanochromic (MC) hydroxypropyl cellulose (HPC) sheets, patterned nylon meshes, and hollow glass microspheres (HGMs), the present invention provides a range of important stimuli-responsive properties within this SH PDMS matrix. [00129] As shown in Fig.2B, in one embodiment, a skin-interfaced electronic device may include flexible/foldable electronics 113, couple to a battery, e.g. thin LiPo battery 115, a water contact indicator 111 optionally, and an capsule of SH PDMS material. The capsule, in one embodiment, includes a composite of SH PDMS matrix with MC HPC sheets 101, a composite of SH PDMS matrix embedded with a patterned nylon mesh 103, a composite of SH PDMS matrix with HGMs 107, and a composite of SH PDMS matrix with TC 109. Attorney Docket No.0116936.281WO2 [00130] In one embodiment, the composite of SH PDMS matrix embedded with the patterned nylon mesh 103 may include a SH PDMS matrix section free of the patterned nylon layer 105. In one embodiment, this patterned nylon layer free section 105 is transparent or semi-transparent such that any elements disposed under this section, e.g. water contact indicator 111, is visible from the outside of the skin-interfaced electronic device. In one embodiment, one or more these elements may be removed so as to providing customized capsules for the skin-interfaced bioelectronics with special needs. 2. An Autonomic Self-Healing Dynamic Covalent Elastomer with Thermochromic (TC) and Mechanochromic (MC) Properties [00131] As shown in Figs.2A-2B, the SH PDMS matrix described above includes a light- yellow, transparent elastomer with dynamic covalent imine bonds for self-healing, as shown in characteristic peaks in the FTIR spectra, according to Fig.2C. Digital image correlation (DIC) experiments reveal that self-healing of SH PDMS occurs as soon as 15 minutes after a damage event, as shown in Fig.6. [00132] In the present invention, self-healing can be quantified by the self-healing efficiency ( ^), defined as the ratio of the maximum strain of the self-healed sample to the maximum strain of the pristine sample (Table 1). After 15 minutes of self-healing from initial damage, while ^SH PDMS = 32.2%, the material still can sustain strain levels above 100%. Moreover, after 24 hours of self-healing, ^SH PDMS = 99.9% and the material is essentially restored to its pristine mechanical state. [00133] Thermochromism represents an important safety feature in the context of device encapsulation, as a visual warning of overheating that can enable early removal of a device to minimize or eliminate collateral damage to the skin. As disclosed in the present invention, thermochromism in the SH PDMS matrix follows from incorporation of a microencapsulated leuco dye, tertiary component systems that consist of a dye (color former), developer, and solvent. The dye forms a colored complex with the developer at temperatures below the melting point of the solvent. At temperatures above this value, the phase change of the solvent destroys the colored complex between the dye and developer, thereby inducing a reversible change in color. The dye used here has a “switching temperature” of 47°C and a corresponding reversible change in color from magenta/pink to colorless, as shown in Fig.2D. This temperature represents the approximate value at which pain/discomfort is expected on human skin. The Attorney Docket No.0116936.281WO2 International Electrotechnical Commission (IEC) defines 48°C as the maximum temperature that healthy adult human skin can be in contact with a medical device part, for contact times between 1-10 min. [00134] In one embodiment, the switching temperature is about 47°C. In one embodiment, the switching temperature ranges between about 46-48°C. In one embodiment, the switching temperature ranges between about 45-47°C. In one embodiment, the switching temperature ranges between about 44-46°C. In one embodiment, the switching temperature ranges between about 43-45°C. In one embodiment, the switching temperature ranges between about 42-44°C. In one embodiment, the switching temperature ranges between about 42-48°C. [00135] Various mass fractions of the leuco dye can be incorporated to yield desired properties, as shown in Fig.2E. Increasing the mass fraction of the dye to 0.5 wt% increases the visual vibrancy of the initial magenta state, as reflected in the increased absorbance for green wavelengths observed in the UV-Vis absorption spectra of the composite material, according to Fig.2F. This loading level also enables high color contrast, as shown in Fig.7. Therefore, according to one embodiment, a mass fraction of 0.5 wt% in the given film thickness (~300 ^m) provides the most effective thermochromism, as further loading generally degrades the uniformity of the composite material due to aggregation of the dye. This formulation, designated as TC SH PDMS 109, serves as the basis for device encapsulation results described subsequently. [00136] As shown in Fig.2G, the TC SH PDMS composite 109 retains self-healing capabilities that are comparable to those of SH PDMS. After 24 hrs of self-healing, the TC SH PDMS composite achieves a healing efficiency of ^TC SH PDMS = 92.2%, as shown in Fig.8 and Table 1. [00137] In one embodiment, mechanochromism in SH PDMS is realized using an aqueous solution of HPC, which enters the cholesteric liquid crystalline phase at a polymer weight percentage of at least 60%. The pitch size of the cholesteric liquid crystal helical nanostructure decreases as the material undergoes increasing strain/stress, thereby causing a blue-shift in the spectrum of the reflected light and a corresponding visible color change, as shown in Fig.2H. By integrating the MC HPC within thin layers of transparent SH PDMS (SH PDMS + MC HPC composite 101) according to Fig.2I, the iridescent color changes as the material undergoes increasing levels of strain, as shown in Fig.2J. At strains of approximately ~20-30%, the SH Attorney Docket No.0116936.281WO2 PDMS + MC HPC composite 101 exhibits a significant blue-shift and the initial amber-hued color of the MC HPC component disappears, revealing vibrant green/blue tones, as shown in Figs.2J. In addition, Fig.9 shows photographs illustrating the integration of MC HPC within SH PDMS elastomer layers. The initial state of the SH PDMS + MC HPC composite material exhibits an amber/red color (left). As uniaxial strain is slowly applied (middle), a blue-shift occurs due to the pitch decrease of the cholesteric liquid crystalline structure of HPC and green/blue colors are observed in the material. Applied pressure/stress from bending/folding of the material (right) also induces a blue-shift, as green/blue colors are observed along the folded/bent regions of the material. DIC experiments quantify the displacement and strain distribution fields of a uniaxially stretched structure of this composite material in a serpentine shape as shown in Fig.2K, enabling direct comparison with the mechanochromic behavior. The Triangular Cosserat Point Elements (TCPE) method reveals the strain distribution field, in a manner that allows separation of rigid body motions. These results reflected in Fig.2K are consistent with the color changes observed in the composite material as shown in Fig.2K inset, as further validated by finite element analysis (FEA), according to Figs.10-11. 3. An Autonomic, Self-Healing Dynamic Covalent Elastomer with Patterned Nylon Meshes for Strain-Adaptive Stiffening Properties [00138] Skin, like many other biological tissues, exhibits an increase in stiffness with increasing strain, thereby reducing the potential for damage/injury under extreme applied forces. This unique mechanical property, characterized by the so-called “J-shaped” stress/strain response, follows from its collagen/elastin composite structure and is not found in conventional silicone elastomers. The embedded elastin imparts elasticity, resulting in the initial linear stress/strain response and low modulus at low strain. At high strains, the collagen microfibers, which provide structural integrity and stiffness, begin to uncoil, straighten, and stretch. The result is a transition to a high-modulus regime and a corresponding increase in stiffness. Previous work reports the use of filamentary microstructures of polyimide embedded in low-modulus silicone elastomer gel to replicate the nonlinear mechanical stress/strain responses of biological tissues. The advances presented here extend this bioinspired materials design concept to materials for encapsulation. [00139] In one embodiment of the present invention, the approach uses high-throughput laser ablation methods to pattern triangular serpentine mesh structures in films of polyamide (Nylon-6, Attorney Docket No.0116936.281WO2 Ebulk ~1.97 GPa, thickness ~ 250 ^m) that are then embedded in thin layers of SH PDMS as a composite structure, as shown in Fig.3A. The results are nonlinear stress/strain behaviors as shown in Fig.3B. Corresponding photographs illustrate the structural deformations of a representative pattern as applied strain increases—transitioning from the original “toe” state, then to the “heel” state, and finally to the “linear” state. This scheme and design also apply to mesh structures of other types of polymers according to Fig.12, including poly(ethylene terephthalate) (PET), poly(methyl methacrylate) (PMMA)), or even bioresorbable materials (e.g., cellulose acetate (CA), silk, poly-L-lactic acid (PLLA)). [00140] For use on the skin, a strain limit threshold of ~20%, corresponding to the strain at which the stiffness of the encapsulation material dramatically increases, is a reasonable design goal. This level of strain is also the point at which the SH PDMS + MC HPC composite material undergoes a strong blue-shift, as shown in Figs.2J-K. The serpentine mesh pattern determines the strain limit threshold response, via the serpentine angle ( ^) according to Fig.3C and the serpentine width (w) according to Fig.3D. For a given serpentine width (e.g., w = 100 ^m), as ^ increases from 90° to 180°, the strain limit threshold demonstrates an increasing trend, with ^ = 120° yielding an average strain limit threshold of ~20.5%, as shown in Fig.3C, a result further confirmed by FEA simulations. For a given serpentine angle ( ^ = 120°), as w increases from 100 to 400 ^m according to Fig.3D, the initial modulus at low levels of strain demonstrates an increasing trend, with the lowest modulus of E ~ 1.08 MPa for w = 100 ^m. This change represents a ~96.7% and ~99.9% reduction from that of w = 400 ^m (E ~ 33.02 MPa) and of bulk Nylon-6 (E ~ 1.97 GPa), respectively. For a strain limit threshold of ~20% and a low modulus response at strains below this threshold, therefore, the optimized parameters of the ~250 ^m-thick films are ^ = 120° and w = 100 ^m. [00141] In another embodiment, the serpentine mesh structures can be fabricated into a non- triangular pattern. [00142] Fig.3E shows the nonlinear stress/strain behavior of the SH PDMS + nylon mesh composite material, as compared to SH PDMS. Indeed, the composite shows the desired strain- adaptive stiffening response, as the initial modulus of the composite material (E ~ 0.82 MPa) increases by more than ~90% to 1.58 MPa at ~20% strain. Compared to SH PDMS (E ~ 0.25 MPa), this mechanical reinforcement at ~20% strain dramatically increases the modulus of the SH PDMS by ~532%, to E ~ 1.58 MPa. Attorney Docket No.0116936.281WO2 [00143] The patterned mesh also increases the tear resistance, resulting in a ~30x larger tear force as shown in Fig.3F, and a stepwise tear profile as shown in Figs.3G and 13 that ultimately delays the complete fracture of the material. This behavior is consistent with conventional strategies that use randomly oriented fiber reinforcement networks. Moreover, the triangular geometry of the serpentine mesh lends itself to an inherent anisotropy that yields different strain threshold limits along different directions of strain, as shown in Fig.14. This unique property could be leveraged for applications that require differing levels of stretchability/mechanical reinforcement along the major axis vs. the minor axis of the device, such as a previously reported rectangular-shaped, wireless ECG device with electrodes that primarily stretch (~20%) along the major axis. [00144] Another design option is to introduce spatial heterogeneity in the serpentine mesh design, such as increasing the serpentine width at the edge regions of the mesh, as shown in Fig. 3H. Uniaxial stretching of such a mesh design encapsulated in SH PDMS yields a spatially varying strain distribution that illustrates lower strain at the edge regions—thereby endowing higher resistance to deformation at these regions, as shown in Fig.3I. Such design features may be relevant in the context of peeling/removal of the device from the skin, as there are typically greater stresses in these areas produced from handling of the device edges. 4. An Autonomic, Self-Healing Dynamic Covalent Elastomer with Hollow Glass Microspheres (HGMs) for Improved Thermophysical Properties [00145] Thermally insulating properties are additional important aspects in safe encapsulating structures, to minimize heat transfer from overheating electronic components or batteries. HGMs, which include a thin outer borosilicate shell, are frequently utilized as inert additives in polymer matrices to reduce the thermal conductivity (k) and density ( ^) of the composite material. [00146] In one embodiment, the present invention discloses small mass fractions (2.5 – 5.0 wt%) of HGMs integrated with SH PDMS yield a white appearance consistent with an expected increase in optical scattering, as shown in Figs.4A and 15. Scanning electron microscopy (SEM) of fracture surfaces of composites with 2.5 and 5.0 wt% HGMs according to Fig.4B shows well- dispersed collections of HGMs within the SH PDMS matrix, in closed-shell morphologies. Uniaxial tensile testing of Fig.4C, via dynamic mechanical analysis (DMA), of SH PDMS + HGM composites reveals that SH PDMS and SH PDMS + HGM (2.5 wt%) have comparable Attorney Docket No.0116936.281WO2 levels of stretchability (>450% strain) and softness (ESH PDMS ~ 0.25 MPa; E2.5wt% HGMs ~ 0.32 MPa). For an HGM mass fraction of 5.0 wt%, the stretchability decreases significantly (<40% strain) and the stiffness of the composite material increases by ~250% (E5.0wt% HGMs ~ 0.87 MPa) compared to SH PDMS. In both cases, these composites retain an ability to autonomically self- heal, comparable to SH PDMS. After a 24-hr period of autonomic self-healing, ^SH PDMS is 99.9%, ^2.5 wt% HGMs is 98.9%, and ^5.0 wt% HGMs is 82.0% (Table 1). [00147] Transient plane source (TPS) measurements performed using an epidermal thermal depth sensor (e-TDS), as shown in Fig.4D, indicate the thermal conductivity of SH PDMS and SH PDMS + HGMs composites according to Fig.4E. The thermal conductivities of the 2.5 wt% and 5.0 wt% HGMs composite materials are ~8% and ~25% lower, respectively, than that of SH PDMS. The densities of the 2.5 wt% and 5.0 wt% HGMs composites similarly decrease ~14% and ~27%, respectively, compared to SH PDMS, as shown in Fig.4E and Table 2. These decreases in thermal conductivity enhance the thermal insulation properties. Experiments to examine the relevance in the context of safety hazards associated with an overheating battery involve SH PDMS and SH PDMS + HGMs structures that fully encapsulate a LiPo battery housing that contains a resistive heater designed to simulate thermal runaway. Passing 250 mA through the heater causes a significant temperature increase, as shown in Fig.4F, in the battery structure. At 180 s after supply of current, the temperature of the heater of the 2.5 wt% and 5.0 wt% HGMs composites are ~10.2°C and ~14.5°C higher, respectively, than that of SH PDMS, indicating that the thermally insulating nature of the HGMs helps to contain and isolate the heat to the battery structure, according to Fig.4G. In practical applications, the thermal insulating aspects of the HGMs can be combined with other thermal protective strategies that exploit materials, layouts, and circuit designs. [00148] HGMs, as a low-density filler component, migrate to the top surface during extreme cases of heating that liquify the matrix material, as shown in Fig.16. This migration creates a heat-reflective barrier that influences the thermal stability of the SH PDMS + HGMs composites. For example, flame-retardant properties begin to emerge with increasing mass fractions of HGMs, specifically in delays for combustion when the SH PDMS + HGMs composites are exposed to a flame, as shown in Fig.4H. In the case of SH PDMS, the material rapidly ignites at t ~ 3 s. At approximately the same time point (t ~ 3-4 s), the 2.5 wt% HGMs composite material begins to show signs of charring on the surface, but ignition does not occur until t ~ 7 s. The 5.0 Attorney Docket No.0116936.281WO2 wt% HGMs composite displays even higher levels of flame-retardant properties, igniting only after 10 s of exposure to the flame and with minimal signs of charring. These results are consistent with previous studies of HGMs as fillers in other matrix materials (e.g., polyurethane, polypropylene, ethylene-vinyl-acetate, and poly(lactic acid)). The thermal stability of SH PDMS and SH PDMS + HGMs composite materials are further characterized by the thermogravimetric analysis (TGA) in Fig.4I and differential thermogravimetric (DTG) measurements, as shown in Fig.17. The peak degradation temperatures of the 2.5 wt% and 5.0 wt% HGMs composite materials are 543°C and 577°C, respectively, both significantly higher than that of SH PDMS (518°C). 5. An Autonomic, Self-Healing Dynamic Covalent Elastomer with Varying Functionalities for Encapsulation of a Wireless, Skin-Interfaced Mechanoacoustic Device [00149] The SH PDMS material and its various composite forms (e.g., TC SH PDMS, SH PDMS + MC HPC, SH PDMS + HGMs, and SH PDMS + patterned nylon mesh) can be used in encapsulating structures for a wide range of skin-interfaced bioelectronic devices. [00150] In one embodiment, as a representative example, the present invention discloses a wireless sensor that mounts on the suprasternal notch to capture mechanoacoustic signatures of health-related parameters and motions of the core body. Fig.5A illustrates the encapsulated device in a dual-sided construct that uses SH PDMS + HGMs (2.5 wt% HGMs) and TC SH PDMS, as shown in Fig.5A inset, on the side of the device adjacent to the embedded thin LiPo battery, as shown in Fig.1B, which poses the highest thermal safety risk. Fig.5B highlights the TC SH PDMS component of the encapsulation structure, as the device is heated from 38°C to 49°C, showing the characteristic color change as the device exceeds the activation/switching temperature of 47°C. [00151] The other side uses SH PDMS + MC HPC, SH PDMS + patterned nylon, and SH PDMS. The SH PDMS + MC HPC resides at the location of the device, according to Fig.5C, that experiences the largest mechanical deformations, typically bending associated with removal of the device from the skin. The remaining area uses SH PDMS + patterned nylon, as shown I Fig.5D outlined in white to increase mechanical robustness, with small windows of transparent SH PDMS for purposes described below, as shown in Figs.5C-D outlined in red. The encapsulation structure demonstrates autonomic self-healing behavior, as shown in Fig.5E, in Attorney Docket No.0116936.281WO2 response to a severe cut that exposes the internal electronic components. A significant portion of the cut self-heals after only 5 mins, with full healing after 20 h. [00152] In one embodiment, in addition to direct exposure of these components to the skin, an additional safety hazard follows from electrical shock mediated by water or biofluids. Thin hydrochromic paper materials inserted into the encapsulating package at locations visually observable through transparent windows can serve as useful indicators of water exposure. In the example reported here, as water reaches a commercial indicator of this type, its color changes from white to red, according to Fig.5F-G. [00153] The device mounted on a volunteer subject appears in Fig.5H. Triaxial accelerometry of Fig.5I and gyroscopic measurements of Fig.18 at this location allow for continuous capture of various signals including those associated with cardiac cycles (represented in the form of seismocardiograms (SCGs)), large physical motions (e.g., walking and jumping), and respiratory activity (both inhalation and exhalation) derived from the acceleration data in the direction normal to the surface of the skin, as shown in Fig.5J. The SCG waveforms clearly exhibit the characteristic S1 and S2 heart sounds, indicating that the encapsulating structure of the device does not interfere with or dampen such sensitive physiological data collection, as shown in Fig. 19. Experimental Section/Methods [00154] Synthesis of Self-Healing Poly(dimethylsiloxane) (SH PDMS): Starting materials and all commercially available solvents and reagents were used as received, without further purification. First, 1,3,5-triformylbenzene (TFB) (Thermo Scientific) was dissolved in N-N- dimethylformamide (DMF) (Sigma-Aldrich) to form a 0.33 M solution. This solution was then vortex mixed with ^, ^-telechelic aminopropyl PDMS (Mw ~ 5000 g mol-1, DMS-A21, Gelest) at a 1:1 molar ratio in a 20 mL glass scintillation vial for 3 min. The resulting mixture was poured into a Teflon dish and placed into a vacuum oven at 50°C for 24 h for crosslinking and drying, which eventually yielded a yellow, transparent, and self-healing elastomer (SH PDMS). [00155] Synthesis of Thermochromic SH PDMS (TC SH PDMS): Starting materials and all commercially available solvents and reagents were used as received, without further purification. First, pre-synthesized SH PDMS films were re-processed by dissolving them in chloroform (Sigma-Aldrich). After dissolution, a magenta thermochromic (TC) leuco dye powder (LCR Hallcrest), with an activation/switching temperature at 47°C, was added to the solution at Attorney Docket No.0116936.281WO2 varying mass fractions (0.1-0.5 wt%). The dye was pulverized by a mortar and pestle before use. The solution with the dye powder was then thoroughly mixed by using a vortex mixer. The mixture was poured into a target well to control the film thickness. Overnight drying at room temperature yielded a magenta TC SH PDMS elastomer. [00156] Characterization of TC SH PDMS: Thin (~300 ^m) films of TC SH PDMS, with varying mass fractions of TC leuco dye, were placed on a hot plate and heated to 55°C. Videos were captured of the samples during, and the changes in color were analyzed via ImageJ software to determine the changes in RGB values, as well as the response times. [00157] Synthesis of Mechanochromic (MC) Liquid Crystalline Hydroxypropyl Cellulose (HPC): Starting materials and all commercially available solvents and reagents were used as received, without further purification. A 60 wt% aqueous solution of hydroxypropyl cellulose (HPC) (Mw ~ 100,000 g mol-1, Sigma-Aldrich), with 0.5 wt% of black silicone dye (Silc Pig, Smooth-On), was formed by mixing in a planetary centrifugal mixer (Thinky ARE-310) for 30 min at 2000 RPM. The resulting mixture was allowed to rest in a closed container placed inside a humid environment to prevent drying. This process yielded an iridescent, amber-hued and mechanochromic (MC) HPC gel. [00158] Integration of MC HPC with SH PDMS: The synthesized MC HPC gel was cast onto the middle region of a thin (~50 ^m) SH PDMS layer via a piping bag with a 1-mm diameter opening. Another thin (~50 ^m) SH PDMS layer was carefully placed on top of the deposited MC HPC gel and the bare edges of the top and bottom SH PDMS films were pressed against each other and permanently bonded via autonomic self-healing and self-adhesion. This process produced a fully sealed and encapsulated MC HPC gel within the SH PDMS layers. [00159] Synthesis of SH PDMS + Hollow Glass Microsphere (HGM) Composites: Starting materials and all commercially available solvents and reagents were used as received, without further purification. First, 1,3,5-triformylbenzene (TFB) (Thermo Scientific) was dissolved in N,N-dimethylformamide (DMF) (Sigma-Aldrich) to form a 0.33 M solution. This solution was then vortex mixed with ^, ^-telechelic aminopropyl PDMS (Mw ~ 5000 g mol-1, DMS-A21, Gelest) at a 1:1 molar ratio, with varying mass fractions (0.25-0.50 wt%) of hollow glass microspheres (HGMs) (Q-Cel 300, Potters Industries), in a 20 mL glass scintillation vial for 3 min. The resulting mixture was poured into a Teflon dish and placed into a vacuum oven at 50°C Attorney Docket No.0116936.281WO2 for 24 h for crosslinking and drying. The result was a whitish, self-healing elastomer composite (SH PDMS + HGMs). [00160] Fourier Transform Infrared (FTIR) Spectroscopy: Solid state FTIR transmission spectra were measured with the use of a Thermo Scientific Nicolet iS50, over a range of 4000 to 400 cm-1. FTIR of SH PDMS (cm-1): ^^ = 2962 (w; ^^(C–H)), 1650 (w; ^^(C=N)), 1257 (m; ^^(C– H)), 1009 (s; (Si–O–Si)), 786 (s; ^^(Si–C)). [00161] Scanning Electron Microscopy (SEM): Samples were first coated with 18 nm of osmium using a Filgen Osmium Plasma Coater. Surface morphologies of coated samples were then characterized with a Hitachi SU-8030 SEM, with an acceleration voltage of 5.0 kV and a working distance of 12.5 mm. [00162] UV-Vis Spectroscopy: Solid state UV-Vis absorption and transmission spectra were measured with a Perkin Elmer LAMBDA 1050 spectrophotometer, over a range from 200 to 800 nm. [00163] Design and Characterization of Mechanically-Reinforcing and Strain-Adaptive Stiffening Meshes: Poly-L-lactic acid (PLLA, #233-146-54), poly(methyl methacrylate) (PMMA, #676-315-97), cellulose acetate (CA, #502-330-14), and nylon-6 (#142-214-93) films were purchased from Goodfellow Corporation. Poly(ethylene terephthalate) (PET, #P04DW0912) was purchased from Grafix Plastics. Details for the basic design principles of the patterned mesh networks for mechanical reinforcement and strain-adaptive stiffening of SH PDMS can be found elsewhere. Desired reinforcing patterns were defined by a laser cutter system (ProtoLaser R, LPKF). Stress/strain profiles were determined from uniaxial tensile tests (strain rate = 0.5 mm s- 1) with a dynamic mechanical analyzer (RSA-G2 Solids Analyzer, TA Instruments). [00164] Preparation of Silk/Glycerol Blend Films: An aqueous silk solution was formed using Bombyx mori silkworm cocoon following the previous study. After the degumming and dissolution in 9.3 M of LiBr solution, the solution was dialyzed in deionized (DI) water with a dialysis flask (Thermo Scientific) for 7 days. The final concentration was 6.5% (w/v). The solution was mixed with glycerol (Sigma-Aldrich) for plasticization. Glycerol was added to the solution at weight ratios of 0%, 10%, 20%, 30%, 40%, and 50% and mixed. The mixed solution was poured into a petri dish and dried overnight at room temperature to obtain the glycerol- plasticized silk (Silk/Gly) films. Attorney Docket No.0116936.281WO2 [00165] Integration of Patterned Serpentine Nylon Mesh with SH PDMS: The patterned serpentine nylon mesh was placed on top of a layer of SH PDMS (thickness ~500 ^m). Another SH PDMS layer (thickness ~500 ^m) was carefully placed on top of the nylon mesh/SH PDMS and the exposed surfaces of the top and bottom SH PDMS films were pressed together and permanently bonded via autonomic self-healing and self-adhesion. The result was a patterned nylon mesh fully integrated within the SH PDMS layers. [00166] Mechanical Characterization of SH PDMS, SH PDMS + HGM Composites, and SH PDMS + Patterned Nylon: Stress/strain profiles were determined from uniaxial tensile tests (strain rate = 0.1 mm s-1) with a dynamic mechanical analyzer (RSA-G2 Solids Analyzer, TA Instruments). [00167] Digital Image Correlation (DIC) for Self-Healing Analysis: The experiments involved recording a set of uniaxially-stretched SH PDMS films using a high-speed camera (2048 x 1088 resolution, HT-2000M, Emergent) with 35 mm imaging lenses (F1.4 manual focus, Kowa) at the frame rate of 100 fps. A slit film of SH PDMS was investigated at two different healing times: 1) immediately after attaching the slit portions together, and 2) after 15 mins of self-healing. The film was uniformly coated with black speckles, as shown in Fig.6, by the spray-painting method. The opensource 2D-DIC software, Ncorr, was used to measure material deformation of the self-healed film. To achieve high-resolution and accurate deformation characteristics, the DIC subset radius and spacing were set as 10 pixels and 5 pixels, respectively, resolving over 1500 displacement grids with the grid resolution of ~400 ^m. The strain magnitude and shear strain were computed based on the Triangular Cosserat Point Theory. [00168] Digital Image Correlation (DIC) for MC HPC Analysis: Fluidic channel molds with a serpentine pattern (inner radius = 3.5 mm, cross-sectional width = 3.0 mm, height = 2.0 mm, length = 65.0 mm) were prepared by 3D-printing (printer: Form 3, Formlabs, material: Clear V4). These molds were used for full encapsulation of MC HPC gel within the elastomer channels. Resulting color changes of the MC HPC system, induced by uniaxial stretching, were compared with strain values as measured by DIC. [00169] FEA for MC HPC Analysis: The commercial FEA software ABAQUS was used to determine the mechanical performance of SH PDMS + MC HPC when subjected to uniaxial strain. A 3D rectangular model with dimensions of 70 mm x 30 mm x 6 mm was used for the fluidic channel mold, which includes the serpentine pattern of the MC HPC with a thickness of Attorney Docket No.0116936.281WO2 ~2 mm. Displacement boundary conditions were imposed at the ends of the 3D rectangular elastomer encapsulation model to stretch uniaxially along the longitudinal direction by up to 30%. The strain ε and in-plane displacement Ux and Uy fields were computed at 30% uniaxial stretch, as shown in Figs.18-19, where the simulation closely matches the DIC field measurements. The elastomer encapsulation and MC HPC were modeled by hexahedron elements (C3D8R) and the total number of elements used in the simulation is 125,000. [00170] Thermal Conductivity Measurements of SH PDMS and SH PDMS + HGM Composites: A thin epidermal thermal depth sensor (e-TDS) (R = 1.5 mm, q = 2 mW mm-2) placed onto the surface of the test sample enabled measurements of the thermal conductivity (k), via the transient plane source (TPS) technique (heating time (t) = 30 s). Presented results are the average and standard deviation of 3 consecutive measurements per sample. [00171] Density Measurements of SH PDMS and SH PDMS + HGM Composites: The density of the material of interest was determined by dividing the mass by the cubic volume of rectangular film samples. The density of the filler HGMs was provided by the manufacturer (Potters Industries). To determine the theoretical densities of the SH PDMS/HGM composite materials, the volume fraction of the filler was first calculated using the known mass fractions and densities of the filler and matrix: ^^ ( ^^ ^ ^ ) ^ ^ ^^ (1)
Figure imgf000029_0001
filler density matrix mass fraction, and matrix density, respectively. [00173] Then, the rule of mixtures was used to determine the theoretical density of the composite material: ^^ ^^ = ^^ ^^ ^^ ^^ + ^^ ^^ ^^ ^^ (2) [00174] where ^^ ^^ , ^^ ^^ , ^^ ^^, ^^ ^^, ^^ ^^ represent the composite material density, filler density, filler volume fraction, matrix density, and matrix volume fraction. Presented results are the average and standard deviation of 3 measurements taken per sample. [00175] Overheating Battery Simulation: The process for simulating an overheating battery (thermal runaway) appears elsewhere. Briefly, 250 mA of current was applied to a SH PDMS or SH PDMS + HGM composite-encapsulated battery enclosure with heater (BwH) device, Attorney Docket No.0116936.281WO2 consisting of a lithium polymer (LiPo) battery enclosure (DNK201515, DNK Power) with a copper resistive heating element. The resulting temperature increase inside the BwH was monitored via measurement of the voltage drop across the BwH. [00176] FEA of overheating battery: The commercial software COMSOL Multiphysics revealed aspects of heat conduction and convection from the BwH and the encapsulation material. The heat generated by Joule heating conducted through the battery and the encapsulation material. The BwH and encapsulation material experienced natural convection of air at room temperature (Tair = 22°C), which were introduced as thermal-fluid boundary conditions in the FEA model. To compare thermal insulation functions of different encapsulation materials, the heat generation from the heater was kept constant by setting the current as 250 mA. Higher heater temperature indicates that more heat is trapped in the battery by the encapsulation material with a higher thermal impedance (Rencapsulation material = (Theater – Tair)/Q – Rnc). FEA results of heater temperatures are summarized in Figs.4F-G. [00177] Thermophysical properties of the BwH were analyzed from the heater and surface temperatures as a function of the heater power without the encapsulation material. The effective heat capacity and the density are average properties weighted by the mass of electrodes and electrolytes. Effective thermophysical properties of the SH PDMS + HGM composite materials were obtained from experiments using the TPS method, as previously described. [00178] To verify the mesh independence and time step independence, different models with mesh densities ranging from 12 elements per cubic millimeter to 20 elements per cubic millimeter and time steps ranging from 0.05 s to 0.1 s were analyzed. A temperature difference of < 0.1°C between these models confirmed that the mesh density of 12.3 elements per cubic millimeter and time step of 0.1 s were selected for the FEA analysis. Additionally, effective heat capacities of the SH PDMS + HGM composite materials were estimated by comparing FEA results with experimental results. [00179] Thermogravimetric Analysis: Thermal stability of SH PDMS and SH PDMS + HGM composite materials was determined with a thermogravimetric analyzer (STA 449, Netzsch) over a temperature range from 30°C to 700°C, at a heating rate of 20°C min-1 under nitrogen atmosphere. [00180] Device Encapsulation: A wireless, skin-interfaced mechanoacoustic sensor, as previously reported, was encapsulated with the SH PDMS elastomer and various composites Attorney Docket No.0116936.281WO2 (e.g., TC SH PDMS, SH PDMS + HGMs, SH PDMS + MC HPC, SH PDMS + patterned nylon), with the use of concave and convex aluminum molds. Layers of SH PDMS and associated composites were permanently bonded to each other via autonomic self-healing and self-adhesion, which eventually yielded a fully encapsulated device within the SH PDMS-based materials. [00181] Device Application, Data Collection, and Data Processing: The encapsulated mechanoacoustic device was applied onto the suprasternal notch of a 27-year-old female subject and secured with a medical-grade, double-sided silicone/acrylate adhesive (2477P, 3M). The device was wirelessly connected to an iPhone with a customized application for data transmission, collection, and storage. Triaxial accelerometry and gyroscopic measurements were downloaded from the iPhone’s internal memory. Z-axis accelerometry data were bandpass filtered (15-30 Hz) to extract seismocardiogram (SCG) waveforms. Example Summary [00182] The collective results disclosed in the present invention suggest that advanced materials strategies can be used in wireless, skin-interfaced bioelectronic devices to manage safety risks in a manner that can complement and extend capabilities based on traditional sensor and electronic circuit methods. Specifically, a self-healing formulation of a silicone polymer serves as a matrix material in soft encapsulating structures that offer various stimuli-responsive properties, such as reversible thermochromism/mechanochromism and strain-adaptive stiffening, in addition to other improved thermal-related characteristics. This multifunctional material construct of the present invention addresses various risks in mechanical, thermal, and electrical modes of device failure. Demonstrations of use with a mechanoacoustic sensor platform suggest wide-ranging applicability across other types of body-integrated bioelectronic systems. Extending these ideas to other levels of materials function in safety and optimizing these strategies for cost-effective manufacturing represent promising directions for future research. [00183] The foregoing description of illustrative embodiments of the invention has been presented for purposes of illustration and of description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and as practical applications of the invention to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as suited to the particular use Attorney Docket No.0116936.281WO2 contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.
Attorney Docket No.0116936.281WO2 Table 1. Self-Healing Efficiencies η of SH PDMS and SH PDMS composite materials at different time points. Materials Efficiency after 15 min(%) Efficiency after 24 h(%) SH PDMS 32.2 99.9 TC SH PDMS 49.7 92.2 2.5 wt% HGMs composite 6.3 98.9 5.0 wt% HGMs composite 26.0 82.0
Attorney Docket No.0116936.281WO2 Table 2. Comparison of measured and theoretical densities of the dynamic covalent elastomer (SH PDMS) and hollow glass microsphere (HGM) composite materials Materials Measured Density (g cm-3) Theoretical Density (g cm-3) SH PDMS (0 wt% HGMs) 0.947 N/A HGMs 0.120 N/A 2.5 wt% HGMs composite 0.819 0.808 5.0 wt% HGMs composite 0.689 0.704

Claims

Attorney Docket No.0116936.281WO2 CLAIMS What is claimed is: 1. A skin-interfaced electronic device having a self-healing (SH) elastomer capsule, the device comprising: a SH elastomer capsule; and an electronic module disposed inside the SH elastomer capsule; wherein the SH capsule comprises: a thermochromic (TC) SH PDMS composite having a microencapsulated leuco dye integrated in a first poly(dimethylsiloxane) (PDMS) matrix; a SH PDMS hollow glass microspheres (HGMs) composite having multiple HGMs incorporated in a second PDMS matrix; a SH PDMS patterned nylon composite having a patterned nylon mesh embedded in a third PDMS matrix; and a SH PDMS mechanochromic (MC) hydroxypropyl cellulose (HPC) composite having at least one MC HPC sheet integrated in a fourth PDMS matrix; wherein the SH elastomer capsule has a self-healing reaction comprising a Schiff base condensation reaction between α, ω-telechelic aminopropyl PDMS and 1,3,5-triformylbenzene. 2. A skin-interfaced electronic device having a self-healing (SH) capsule, the device comprising: a SH capsule; and an electronic module disposed inside the SH capsule; wherein the SH capsule comprises at least one encapsulation composite. 3. The skin-interfaced electronic device according to claim 2, wherein the at least one encapsulation composite comprises a thermochromic (TC) composite having a dye integrated in a first matrix. 4. The skin-interfaced electronic device according to claim 3, wherein the dye comprises a microencapsulated leuco dye, wherein the microencapsulated leuco dye comprises a tertiary component system having a color former, a developer, and a solvent. Attorney Docket No.0116936.281WO2 5. The skin-interfaced electronic device according to claim 4, wherein the microencapsulated leuco dye has a switching temperature at which the microencapsulated leuco dye reversibly changes its color. 6. The skin-interfaced electronic device according to claim 5, wherein the switching temperature ranges between about 44°C to 48°C. 7. The skin-interfaced electronic device according to claim 2, wherein the at least one encapsulation composite comprises a hollow glass microspheres (HGMs) composite, wherein the HGMs composite comprises multiple HGMs incorporated in a second matrix. 8. The skin-interfaced electronic device according to claim 7, wherein the multiple HGMs are configured to migrate in the second matrix. 9. The skin-interfaced electronic device according to claim 8, wherein the multiple HGMs have a mass fraction ranges between about 2.5-5.0 wt%. 10. The skin-interfaced electronic device according to claim 2, wherein the at least one encapsulation composite comprises a SH patterned nylon composite, wherein the SH patterned nylon composite comprises a patterned nylon mesh embedded in a third matrix. 11. The skin-interfaced electronic device according to claim 10, wherein the patterned nylon mesh comprises a polyamide film. 12. The skin-interfaced electronic device according to claim 11, wherein the patterned nylon mesh comprises serpentine mesh structures. 13. The skin-interfaced electronic device according to claim 12, wherein the serpentine mesh structures have a triangular shape. Attorney Docket No.0116936.281WO2 14. The skin-interfaced electronic device according to claim 13, wherein the serpentine mesh structures have a serpentine angle (θ) of about 120° and a serpentine width (w) about 100 μm. 15. The skin-interfaced electronic device according to claim 10, wherein the patterned nylon composite comprises a viewing window section, wherein the viewing window section comprises the third matrix free of the patterned nylon mesh. 16. The skin-interfaced electronic device according to claim 15, wherein the device comprises a water contact indicator disposed inside the SH capsule, and wherein the water contact indicator is configured to reversibly change its color when it contacts water. 17. The skin-interfaced electronic device according to claim 16, wherein the water contact indicator is disposed directly next to the viewing window section such that the water contact indicator is configured to be visible outside of the SH capsule. 18. The skin-interfaced electronic device according to claim 2, wherein the at least one encapsulation composite comprises a mechanochromic (MC) hydroxypropyl cellulose (HPC) composite, wherein the MC HPC composite comprises at least one MC HPC sheet integrated in a fourth matrix. 19. The skin-interfaced electronic device according to claim 19, wherein the MC HPC composite is configured to reversibly change its color when a strain force is applied to the MC HPC composite. 20. The skin-interfaced electronic device according to claim 2, wherein the electronic module comprises a flexible electronic component and a battery coupled to the flexible electronic component. 21. The skin-interfaced electronic device according to claim 2, wherein the at least one encapsulation composite comprises a poly(dimethylsiloxane) PDMS matrix. 22. A composite capsule for encapsulating a skin-interfaced electronic device, the composite Attorney Docket No.0116936.281WO2 capsule comprising at least one encapsulation composite. 23. The composite capsule according to claim 22, wherein the at least one encapsulation composite comprises a thermochromic (TC) composite having a dye integrated in a first matrix. 24. The composite capsule according to claim 23, wherein the dye comprises a microencapsulated leuco dye, wherein the microencapsulated leuco dye comprises a tertiary component system having a color former, a developer, and a solvent. 25. The composite capsule according to claim 24, wherein the microencapsulated leuco dye has a switching temperature at which the microencapsulated leuco dye reversibly changes its color. 26. The composite capsule according to claim 25, wherein the switching temperature ranges between about 44°C to 48°C. 27. The composite capsule according to claim 23, wherein the at least one encapsulation composite further comprises a hollow glass microspheres (HGMs) composite, wherein the HGMs composite comprises multiple HGMs incorporated in a second matrix. 28. The composite capsule according to claim 27, wherein the multiple HGMs are configured to migrate in the second matrix. 29. The composite capsule according to claim 28, wherein the multiple HGMs have a mass fraction ranges between about 2.5-5.0 wt%. 30. The composite capsule according to claim 28, wherein the TC composite is disposed closer to an individual’s skin compared to the HGMs composite. 31. The composite capsule according to claim 27, wherein the at least one encapsulation composite further comprises a patterned nylon composite, wherein the patterned nylon composite comprises a patterned nylon mesh embedded in a third matrix. Attorney Docket No.0116936.281WO2 32. The composite capsule according to claim 31, wherein the patterned nylon mesh comprises a polyamide film. 33. The composite capsule according to claim 32, wherein the patterned nylon mesh comprises serpentine mesh structures. 34. The composite capsule according to claim 33, wherein the serpentine mesh structures have a triangular shape. 35. The composite capsule according to claim 34, wherein the serpentine mesh structures have a serpentine angle (θ) of about 120° and a serpentine width (w) about 100 μm. 36. The composite capsule according to claim 31, wherein the patterned nylon composite further comprises a viewing window section, wherein the viewing window section comprises the third matrix free of the patterned nylon mesh. 37. The composite capsule according to claim 31, wherein the at least one encapsulation composite further comprises a mechanochromic (MC) hydroxypropyl cellulose (HPC) composite, wherein the MC HPC composite comprises at least one MC HPC sheet integrated in a fourth matrix. 38. The composite capsule according to claim 37, wherein the MC HPC composite is configured to reversibly change its color when a strain force is applied to the MC HPC composite. 39. The composite capsule according to claim 22, wherein the composite capsule comprises a self healing elastomer. 40 The composite capsule according to claim 39, wherein the SH elastomer comprises dynamic covalent elastomer. 41. The composite capsule according to claim 37, wherein at least one of the first matrix, the Attorney Docket No.0116936.281WO2 second matrix, the third matrix, and the fourth matrix comprises a poly(dimethylsiloxane) (PDMS) matrix. 42. A self-healing (SH) elastomer capsule for encapsulating a skin-interfaced electronic device, the SH capsule comprising one or more of: a thermochromic (TC) SH poly(dimethylsiloxane) (PDMS) composite has a microencapsulated leuco dye integrated in a first PDMS matrix; a SH PDMS hollow glass microspheres (HGMs) composite has multiple HGMs incorporated in a second PDMS matrix; a SH PDMS patterned nylon composite has a patterned nylon mesh embedded in a third PDMS matrix; and a SH PDMS mechanochromic (MC) hydroxypropyl cellulose (HPC) composite has at least one MC HPC sheet integrated in a fourth PDMS matrix.
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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20190110363A1 (en) * 2017-10-06 2019-04-11 The Board Of Trustees Of The Leland Stanford Junior University Flexible and self-healing elastomer-based modular electronics and applications thereof
US20190144705A1 (en) * 2015-12-04 2019-05-16 The Board Of Trustees Of The University Of Illinois Autonomic damage indication in coatings

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20190144705A1 (en) * 2015-12-04 2019-05-16 The Board Of Trustees Of The University Of Illinois Autonomic damage indication in coatings
US20190110363A1 (en) * 2017-10-06 2019-04-11 The Board Of Trustees Of The Leland Stanford Junior University Flexible and self-healing elastomer-based modular electronics and applications thereof

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
ANTONOV E V, SOSNIN I M, VLASSOV S, DOROGIN L M: "Polydimethylsiloxane/Glass-Based Composite Elastomer for Thermophysical Applications", REVIEWS ON ADVANCED MATERIALS AND TECHNOLOGIES, ITMO UNIVERSITY, vol. 4, no. 1, 31 March 2022 (2022-03-31), RU, pages 28 - 32, XP093205853, ISSN: 2687-0568, DOI: 10.17586/2687-0568-2022-4-1-28-32 *
CHEN GUOJIAN, HONG WEI: "Mechanochromism of Structural-Colored Materials", ADVANCED OPTICAL MATERIALS, vol. 8, no. 19, 5 October 2020 (2020-10-05), DE , pages 2000984-1 - 2000984-28, XP093205868, ISSN: 2195-1071, DOI: 10.1002/adom.202000984 *
LI JIE, LUO KAI-CHENG, ZHANG JIA-LE, LEI JUN, LIN HAO, TANG JIAN-HUA, ZHONG GAN-JI, YAN DING-XIANG, LI ZHONG-MING: "Flexible andWater-proof nylon mesh with ultralow silver content for effective electromagnetic interference shielding effectiveness", CHEMICAL ENGINEERING JOURNAL, vol. 439, 1 July 2022 (2022-07-01), pages 135662-1 - 135662-9, XP093205858, DOI: 10.1016/j.cej.2022.135662 *

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