Permeable bioelectronic systems and methods of making same

Abstract

A permeable bioelectronic system includes a stretchable multilayer circuit containing a liquid metal (LM), and an LM interconnect for bonding one or more inorganic electronic circuit elements to the stretchable multilayer circuit.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to permeable bioelectronics. BACKGROUND

[0002] The reference in this specification to any prior publication or

[0003] Permeable, soft, and stretchable integrated electronic systems with continuous sensing and intervention capabilities, and wearability / implantability, are critical for a wide range of emerging applications such as intensive care, rehabilitation, closed-loop diagnosis / treatment, and virtual / augmented reality. Tremendous progress has been made in the past two decades in developing new materials and structures for stretchable electronics. In particular, structural approaches based on lateral strain-tolerant island-bridge engineering (wrinkles, serpentine structures, springs) and vertical strain-isolation engineering (thickness, stiffness, and elasticity) have provided superior tools for integrating traditional rigid integrated circuit (IC) components—transistors, capacitors, resistors, sensors, communication, and energy components, etc.—into high-stretch polymer substrates to produce stretchable hybrid electronic products that not only take advantage of the benefits of mature IC design and fabrication, but also meet the mechanical requirements of soft organs and tissues. SUMMARY

[0004] It is an object of the present disclosure to overcome or substantially ameliorate one or more of the disadvantages of the prior art, or to at least provide the public with a useful alternative.

[0005] According to one or more embodiments, there is provided a permeable bioelectronic system comprising a stretchable multilayer circuit containing liquid metal (LM), and LM interconnects for bonding one or more inorganic electronic circuit components to the stretchable multilayer circuit.

[0006] According to one or more embodiments, there is provided a method for manufacturing a permeable bioelectronic system, the method comprising: generating a microcircuit having a first side and a second side; transferring the microcircuit onto a fibrous mat such that the first side of the microcircuit contacts the fibrous mat; forming a paste mask layer on the second side of the microcircuit; forming a base circuit layer on a side of the fibrous mat distal from the first side of the microcircuit, the base circuit layer comprising liquid metal (LM); forming stretchable vertical interconnect access (VIA) for electrically connecting the microcircuit, the base circuit layer, and the paste mask layer, the VIA being filled with the LM; forming hybrid LM (hLM) solder on the paste mask layer for bonding one or more inorganic electronic circuit components; and forming an encapsulation layer for encapsulating the one or more inorganic electronic circuit components, the paste mask layer, the base circuit layer, and the microcircuit.

[0007] Other example embodiments are discussed herein. BRIEF DESCRIPTION OF DRAWINGS

[0008] The detailed description is set forth with reference to the accompanying drawings. The drawings are provided for purposes of illustration only and merely depict example embodiments of the disclosure. The drawings are not intended to limit the breadth, scope, or applicability of the disclosure. Certain parts of the drawings may be exaggerated in scale or drawn out of proportion for illustrative purposes. The drawings are not necessarily to scale, with the intent of providing a clear disclosure, as being merely exemplary. Certain aspects of the drawings may be shown exaggerated or in schematic form and the contours of the elements in the figures do not necessarily illustrate the true shape of the elements and are provided merely for clarity.

[0009] Figure 1A An exploded view of a permeable three-dimensional integrated electronic skin (P3D- electronic skin) is shown in accordance with certain embodiments of the present disclosure. Liquid metal (LM) microelectrodes are employed as a reliable interface between a soft, rough fibrous mat substrate and rigid elements. Vertical interconnect access (VIA) is used for electrical connections in intermediate layers. Electronic circuit elements in each layer can include microcontroller units (MCU), oscillators, multiplexers (MUX), current mirrors, digital-to-analog converters (DAC), operational amplifiers (OP-AMP), high voltage modules (HV, 20V), and low dropout regulators (LDO, 3.3V). Dotted lines represent the distribution and location of VIA in the system.

[0010] Figure 1B A digital image of a permeable 3D LM circuit and partially oxidized LM (oLM) mat is depicted.

[0011] Figure 1C A digital image of a soft and stretchable P3D-electronic skin with hybrid LM (hLM) solder is depicted.

[0012] Figure 1D A digital image demonstrating stable electrical performance of a bended (550% strain) P3D-electronic skin is depicted.

[0013] Figure 1E A digital image demonstrating stable electrical performance of a stretched (550% strain) P3D-electronic skin is depicted.

[0014] Figure 1F Permeability of P3D-electronic skin to air and moisture is shown.

[0015] Figure 1G Permeability and moisture vapor transmission of several wearable substrates, including P3D-electronic skin, PDMS-electronic skin, wound dressing, medical tape, and cotton fabric, are depicted in accordance with certain embodiments. Each type of substrate corresponds to a pair of columns, where the left column represents moisture vapor transmission rate and the right column represents air permeability. Error bars represent standard deviation (SD), and the height of the bars represents the mean value.

[0016] Figure 1H Digital images are depicted showing (a) skin covered with P3D-electronic skin (top) and PDMS-electronic skin (bottom), and (b) the skin condition one week after application of P3D-electronic skin (top) and PDMS-electronic skin (bottom). The skin area covered with P3D-electronic skin showed no inflammation, while the skin area covered with PDMS-electronic skin showed severe skin erythema.

[0017] Figure 1I The circuit design of the P3D electronic skin system using Bluetooth technology according to certain embodiments is depicted. The electronic circuit elements in each layer include MCU, oscillator, MUX, current mirror, DAC, OP-AMP, HV (20V) and LDO (3.3V).

[0018] Figure 2A Depicted is a process flow for layer-by-layer fabrication of P3D-electronic skin according to certain embodiments of the present disclosure.

[0019] Figure 2B Depicted are digital images showing the structure and function of each layer in the P3D-electronic skin: (a) upper layer of LM3D circuit; (b) base layer of LM 3D circuit; (c) oLM paste mask layer; (d) electronic components; (e) permeable upper layer.

[0020] Figure 3A Digital images depicting stencil printing of complex, high-density patterns in an upper circuit layer and a coil antenna, according to certain embodiments of the present disclosure: (a) laser cutting mask for the upper circuit layer; (b) laser cutting mask for the coil antenna. For complex, high-density patterns in the upper circuit layer and the antenna coil, stencil printing is not a reliable technique, as it is likely to cause the mask to peel off and, thus, damage the pattern.

[0021] Figure 3B Depicted are digital images showing stencil printing of simple patterns in the base layer and paste mask layer of an LM 3D circuit according to certain embodiments of the present disclosure. It shows that stencil printing is well suited for these simple patterns.

[0022] Figure 4A Depicted is a laser cutting machine (LPKF U4) compatible with printed circuit board (PCB) manufacturing according to certain embodiments of the present disclosure.

[0023] Figure 4B Depicted is a fixed frame with markings for stencil printing.

[0024] Figure 4CThe resolution and trace density of the modified stencil printing with patternable line widths are depicted: (a) 500 μm lines without gaps; (b) 200 μm lines without gaps; (c) 100 μm lines and gaps, with a success rate of approximately 70% (i.e., approximately 70% of the line array can be successfully patterned by the stencil printing technique); and (d) 50 μm lines with gaps.

[0025] Figure 5 Scanning electron microscope (SEM) and elemental mapping images according to certain embodiments of the present disclosure are depicted, which show (a) selective wetting of micropatterned Ag and LM and (b) formation of Ag-In alloy. The selective wetting of LM lies in the contrast between the LM lyophobic properties of the poly(styrene-block-butadiene-block-styrene) (SBS) pad and the LM lyophilic properties of Ag. Therefore, in the manufacture of LM microcircuits, EGaIn only wets the areas covered by Ag and dewets from the SBS surface. When EGaIn is applied to Ag, the reaction alloying between Ag and In forms an AgIn alloy. Additional EGaIn then wets the AgIn alloy layer and forms an EGaIn / AgIn / Ag triple layer, which shows a stronger Ga signal and a weaker Ag signal (deeper detection distance) in elemental mapping.

[0026] Figure 6 Digital images of (a) a Bluetooth-equipped battery-powered P3D-electronic skin, (b) a battery-powered P3D-electronic skin worn on a user's arm, and (c) a battery-free P3D-electronic skin on an NFC reader are depicted according to certain embodiments of the present disclosure.

[0027] Figure 7 Depicted are (a) a breathable / moisture-permeable yet waterproof P3D-electronic skin system, (b) its mechanism, and (c) the contact angle (CA) of water on a monolithic and hydrophobic P3D-electronic skin system, according to certain embodiments of the present disclosure. The microporous fiber structure of the electrospun fiber mat allows air molecules and moisture (water vapor) to pass through it. Meanwhile, the SBS fiber mat is inherently hydrophobic, exhibiting a large water contact angle, thereby preventing liquid substances from penetrating the entire electronic system.

[0028] Figure 8 Depicted are rain tests of a P3D-electronic skin system according to certain embodiments of the present disclosure, including (a) a schematic diagram of the rain test setup, (b) a digital image of the rain test setup, (c1) a digital image showing the water resistance of a P3D-electronic skin system having a hydrophobic surface, (c2) the surface of a water-resistant P3D-electronic skin system, and (d1) a digital image showing that blotting paper is not water-resistant and there is no observable water on the blotting paper, and (d2) the surface of the blotting paper.

[0029] Figure 9 Digital images depicting the electrical stability of P3D-E-skin systems (a) in water and (b) in artificial sweat (pH: 4.7 ± 0.1) and (c) in artificial sweat (pH: 4.7 ± 0.1) showing stable LED brightness.

[0030] Figure 10A Digital images depicting the overall thickness of PDMS-E-skin showing according to certain embodiments of the present disclosure.

[0031] Figure 10B Digital images depicting the overall thickness of P3D-E-skin showing according to certain embodiments of the present disclosure. In the fabrication of P3D-E-skin, all layers including the substrate, the intermediate layer, and the encapsulation layer are made of soft, porous, and super-elastic fiber mats. The electrospun encapsulation fiber mat presents conformal contact with the underlying rigid element, which is distributed along the topography of the element and largely reduces the volume of the system.

[0032] Figure 10C Stress-strain curves of PDMS-E-skin of Figure 10A and P3D-E-skin of Figure 10B .

[0033] Figure 10D Modulus values of PDMS-E-skin of Figure 10A and P3D-E-skin of Figure 10B . Due to the compact and thin-film layout following the traditional spin-coating and casting process, PDMS-E-skin has about 54% thicker thickness and about 60% greater rigidity.

[0034] Figure 11A SEM images of LM / SBS with different heating durations before and after stretching according to certain embodiments of the present disclosure. oLM was prepared by oxidizing LM in air. After heating LM with increasing heating durations ranging from 0 to 24 hours, the size of gallium oxide increased from several μm to several hundred μm. After pre-stretching for 12 cycles at 1500% strain, the continuous film (heating duration less than 16 hours) self-organizes into a transverse network and vertical wrinkle structure, where nodes are formed by strong oxidation layers.

[0035] Figure 11B XPS results of oLM after different heating durations. Ga 2p(3 / 2) spectra show a main peak with a binding energy of 1118.8 eV from Ga2O3, where there are Ga metal (1116.5 eV) and Ga2O (1118.2 eV).

[0036] Figure 11CFormation of gallium oxide (Ga2O3 and Ga2O) during LM heating process is depicted. The signal of Ga2O3 and Ga2O becomes stronger as the heating duration increases.

[0037] Figure 11D Young's modulus of oLM / SBS after different heating durations is depicted. Error bars represent standard deviation (SD) and the scatter points represent the average. Due to the strong oxidizing effect of LM, the average modulus of oLM / SBS increases from ~0.1 MPa (9841 Pa) for heating duration of 0 h (i.e. LM / SBS) to ~0.31 MPa for heating duration of 24 h. Thus, the stiffness is also enhanced by ~2 times while the thickness remains the same.

[0038] Figure 11E Conductivity of oLM / SBS after different heating durations is depicted. oLM / SBS with heating duration of 16 hours maintains a high conductivity of over 28,300 S / cm. Error bars represent SD and the scatter points represent the average.

[0039] Figure 11F Resistance change of hybrid LM (hLM) (weight ratio of oLM and LM = 1:2, oLM with different heating durations) on SBS fiber mat as a function of tensile strain is depicted.

[0040] Figure 12 Wetting behavior of (a) pristine LM on fiber mat and (b) partially oxidized LM (oLM) on fiber mat with the same loading amount (20 mg) in air is depicted. The droplet of pristine LM exhibits metastable and non-spherical shape on the fiber mat in the oxidizing environment (in air). After the oxidation treatment, oLM has a very high wettability to the fiber mat, forming a super-lyophilic surface coating.

[0041] Figure 13A Schematic and scanning electron microscope images (scale bar = 200 pm) showing the electrical interface of rigid elements using pristine LM according to certain embodiments of the present disclosure are depicted.

[0042] Figure 13B Schematic and scanning electron microscope images (scale bar = 200 pm) showing the electrical interface of rigid elements using oLM according to certain embodiments of the present disclosure are depicted.

[0043] Figure 13C Schematic and scanning electron microscope images (scale bar = 200 pm) showing the electrical interface of rigid elements using hLM solder according to certain embodiments of the present disclosure are depicted.

[0044] Figure 13DFinite element analysis (FEA) depicting stress distribution of electrical interface using super-stretchable hLM solder.

[0045] Figure 13E Depiction of electrical resistance (0603, ~100 Ω) of micro-resistor electrical interface using pristine LM, oLM, and hLM solders, respectively, where "0603" refers to the footprint size of the electronic component.

[0046] Figure 13F 3D electrical connection and interface between rigid IC and super-stretchable hLM solder is shown. oLM acts as a contact pad, while pristine LM is used as patterned in-plane interconnects, VIA, and additional contact paste.

[0047] Figure 13G Depiction of cross-sectional SEM image showing rigid microchip integrated with 3D LM circuit at zero strain.

[0048] Figure 13H Depiction of cross-sectional SEM image showing rigid microchip integrated with 3D LM circuit at 50% strain. The interface between the rigid chip and LM circuit remains good under large tensile strain, and the LM circuit is stretched in 3D space.

[0049] Figure 13I Depiction of resistance of a series of highly stretchable micro-resistor integrated 3D LM circuits at zero strain.

[0050] Figure 13J Depiction of resistance of a series of highly stretchable micro-resistor integrated 3D LM circuits at 1500% strain for 1000 cycles. The resistance exhibits excellent stability when the circuit is stretched to 1500% and for 1000 cycles.

[0051] Figure 13K Depiction of transfer characteristics of stretchable P-type metal-oxide-semiconductor field-effect transistor (MOSFET).

[0052] Figure 13L Depiction of transfer characteristics of stretchable N-type MOSFET.

[0053] Figure 13M Digital image of stretchable logic circuit (clocked switch) fabricated with stretchable MOSFET, where the circuit is shown connected to a flexible printed circuit board (FPCB) and encapsulated with a permeable super-elastic fiber pad.

[0054] Figure 13N Depiction of logic output of stretchable logic circuit (clocked switch) fabricated with stretchable MOSFET.

[0055] Figure 14 FEA depicting stress distribution of electrical interface using single component LM solder according to certain embodiments of the present disclosure. It shows the FEA results of stress distribution at 50% tensile strain for the connection interface between a rigid microchip and single component LM solder. Maximum stress occurs at the interface between the rigid microchip and single component LM solder. The stress concentration factor (maximum stress to average stress, i.e. σ max / σ avg ) at the interface between the rigid chip and soft fiber mat is 30% greater than using hybrid LM (hLM) solder.

[0056] Figure 15 Digital images depicting the stable performance of light emitting diodes (LEDs) lit before (a) and after (b) stretching using hLM solder. Traditionally, pristine LM is difficult to apply directly on various solid surfaces due to its inherent high surface tension. Here, the multiple wettabilities of the oLM solder pads to the pins of the components, pristine fluid LM, and fiber mat ensure both in-plane and out-of-plane electrically stable connections. Furthermore, by encapsulating a thin permeable super-elastic fiber mat, electronic components can be secured onto the hLM solder, resulting in better electrical stability at large strains.

[0057] Figure 16A Output characteristics of stretchable P-channel enhancement mode MOSFET using hLM as electrical interface at 0% strain according to certain embodiments of the present disclosure.

[0058] Figure 16B Output characteristics of stretchable P-channel enhancement mode MOSFET using hLM as electrical interface at 500% strain according to certain embodiments of the present disclosure.

[0059] Figure 16C Output characteristics of stretchable N-channel enhancement mode MOSFET using hLM as electrical interface at 0% strain according to certain embodiments of the present disclosure.

[0060] Figure 16D Output characteristics of stretchable N-channel enhancement mode MOSFET using hLM as electrical interface at 500% strain according to certain embodiments of the present disclosure.

[0061] Figure 17A Design of permeable stretchable logic circuit including (a) NOT gate, (b) NOR gate, and (c) clocked switch according to certain embodiments of the present disclosure.

[0062] Figure 17BDigital images depicting the output of logic circuits verified with rigid printed circuit boards: (a) NOT gate; (b) NOR gate; (c) switch.

[0063] Figure 17C Digital images depicting Figure 17A a NOT gate.

[0064] Figure 17D Digital images depicting Figure 17A a NOR gate.

[0065] Figure 17E Digital images depicting Figure 17A the logic output of a NOT gate.

[0066] Figure 17F Digital images depicting Figure 17A the logic output of a NOR gate.

[0067] Figure 17G A permeable 3D integrated stretchable switch array is shown in accordance with certain embodiments of the present disclosure.

[0068] Figure 17H Threshold drive voltage of the switch array at 100% strain is depicted.

[0069] Figure 17I Statistical analysis of the transconductance of a 64-channel switch array is depicted. The switches are used to control a load and a complementary metal-oxide-semiconductor (CMOS) digital circuit when they are operated between their cutoff and saturation regions. The multi-channel switch array has a uniform threshold drive voltage (Vg) of ~1.75 V and an average transconductance of ~100 mS at 50% strain.

[0070] Figure 17J Digital images of a permeable 3D integrated stretchable switch array at 100% strain are depicted.

[0071] Figure 18A Resistance changes of LM circuit traces (200 pm line width, stored in air for 8 months and not stored) during stretch release cycling tests at 100% strain are depicted.

[0072] Figure 18B Resistance of a series of highly stretchable integrated 3D LM circuits with micro resistors stored in air for 8 months is depicted.

[0073] Figure 19ASEM images showing Mode 1 of mechanical failure: long-term continuous mechanical wear / tear of the way the stress concentrated rigid-soft interface depends on cycling. This happens when the solder / through-hole is subjected to a very large number of repeated loading-unloading processes at low strain (e.g., 100% strain for more than 10,000 cycles).

[0074] Figure 19B SEM images showing Mode 2 of mechanical failure: fracture of the substrate material. This happens when the solder / through-hole is subjected to repeated loading-unloading processes at high strain (e.g., 1500% strain for more than 1000 cycles), the substrate material breaks, while the solder is still well encapsulated by the upper fiber mat. However, in this case the whole system also fails.

[0075] Figure 19C FEA of stress distribution of an electrical interface with a soft and super-elastic encapsulation mat. The maximum stress occurs at the rigid-soft interface between the rigid microchip and the soft SBS fiber mat.

[0076] Figure 19D Tension of SBS fiber mat (n = 10) as a function of elongation.

[0077] Figure 20A Digital images showing no LM residue leakage to the skin under various press loads: (a) pressure: 0 kPa, (b) pressure: 12.5 kPa, (c) pressure: 25 kPa, and (d) pressure: 50 kPa.

[0078] Figure 20B Digital images showing the intact pattern of the LM 3D circuit with no LM leakage to the skin during the press test: (a) original LM 3D circuit before mounting the elements, (b) pressing the LM 3D circuit onto the skin, (c) skin indentation appearance, no LM leakage, and (d) LM 3D circuit intact after the press test.

[0079] Figure 21 Digital images of the over-stretched P3D-electronic skin system encapsulated with permeable super-elastic fiber mat without LM leakage.

[0080] Figure 22A Block diagram of the sensing system and customized mobile application according to certain embodiments of the disclosure. Electrical stimulation can be delivered to the rat's biceps femoris muscle and the corresponding electromyography (EMG) signals are recorded using LM microelectrodes.

[0081] Figure 22B Digital image showing the remote wireless communication of the sensing system at a distance of 15 m.

[0082] Figure 22C Generated stimulation pulses with controlled duty cycle ranging from 1% to 10% with fixed frequency at 100 Hz are depicted.

[0083] Figure 22D Generated stimulation pulses with controlled repetition frequency ranging from 5 Hz to 100 Hz in dry state are depicted.

[0084] Figure 22E Generated stimulation pulses with controlled repetition frequency ranging from 5 Hz to 100 Hz in steaming state are depicted.

[0085] Figure 22F Digital image showing P3D-E-skin steamed on top of boiling water is depicted.

[0086] Figure 22G Generated stimulation current pulses with controlled current intensity in dry and steaming state (fixed load: 1 kQ) under different wireless transmission commands (0x40 to 0x60) are depicted.

[0087] Figure 22H Digital image of a wireless transcutaneous electrical stimulation and electrophysiological sensing system based on P3D-E-skin platform is depicted. The system is attached on the rat's biceps femoris muscle.

[0088] Figure 22I EMG response signals evoked at (a) 1 Hz, (b) 5 Hz, and (c) 10 Hz stimulation frequency, respectively, are depicted.

[0089] Figure 22J Spectrogram of EMG signals in response to electrical stimulation input generated by P3D-E-skin at 5 Hz frequency is depicted.

[0090] Figure 23A Digital image for showing impermeability of PDMS-E-skin. When the whole PDMS-E-skin is steamed on top of boiling water, due to its poor permeability, a large amount of water droplets accumulate on the surface of the PDMS-E-skin.

[0091] Figure 23B is a close-up view of Figure 23A

[0092] Figure 24 ​A schematic of the current control module of the P3D-E-skin system for wireless transcutaneous electrical stimulation and electrophysiological sensing functionality is depicted. The current control module consists of two basic parts, including a control part and a monitoring part. In the control part, the intensity of the controlled stimulation current (ICTL) is the same as one of the reference currents due to the current mirror circuit. The reference current intensity is determined by the DAC output signal voltage amplitude, which is controlled by the MCU. In the monitoring part, the current mirror is in series with a fixed resistance (50 Ω) before grounding, where the voltage is linearly related to the actual current intensity (ICTL = V / 100). The sensed voltage is copied by a voltage follower before input to the ADC on the MCU to prevent sudden overload.

[0093] Figure 25A A current characteristic versus time relationship of wireless electrical stimulation output of the P3D-E-skin system in a 0% stretched state is depicted in accordance with certain embodiments of the present disclosure.

[0094] Figure 25B A current characteristic versus time relationship of wireless electrical stimulation output of the P3D-E-skin system in a 20% stretched state is depicted in accordance with certain embodiments of the present disclosure.

[0095] Figure 25C A current characteristic versus time relationship of wireless electrical stimulation output of the P3D-E-skin system in a 50% stretched state is depicted in accordance with certain embodiments of the present disclosure.

[0096] Figure 25D A current characteristic versus time relationship of wireless electrical stimulation output of the P3D-E-skin system in a 100% stretched state is depicted in accordance with certain embodiments of the present disclosure.

[0097] Figure 25E A voltage characteristic versus time relationship of wireless electrical stimulation output of the P3D-E-skin system in a 0% stretched state is depicted in accordance with certain embodiments of the present disclosure.

[0098] Figure 25F A voltage characteristic versus time relationship of wireless electrical stimulation output of the P3D-E-skin system in a 20% stretched state is depicted in accordance with certain embodiments of the present disclosure.

[0099] Figure 25G A voltage characteristic versus time relationship of wireless electrical stimulation output of the P3D-E-skin system in a 50% stretched state is depicted in accordance with certain embodiments of the present disclosure.

[0100] Figure 25H A voltage characteristic versus time relationship of wireless electrical stimulation output of the P3D-E-skin system in a 100% stretched state is depicted in accordance with certain embodiments of the present disclosure.

[0101] Figure 26A A battery-free P3D-electronic skin using NFC technology, according to certain embodiments of the present disclosure, is shown. The system includes a stretchable LM antenna, a stretchable printed LM microcircuit integrated with microchips (MCU, ADC, and sensors for NFC), and a permeable fiber mat as both encapsulation and substrate.

[0102] Figure 26B A digital image depicting a near-field communication (NFC) P3D-electronic skin before encapsulation with a permeable superelastic fiber mat.

[0103] Figure 26C Depicted is a digital image of the NFC P3D-electronic skin after encapsulation with a permeable superelastic fiber mat.

[0104] Figure 26D A digital image depicts a stretchable NFC antenna using a traditional serpentine copper (Cu) coil stretched at 50% strain.

[0105] Figure 26E Digital image depicting the intrinsically stretchable LM coil of a stretchable NFC antenna stretched at 50% strain.

[0106] Figure 26F Depicted is the FEA of the stress distribution of a stretchable antenna using a Cu serpentine coil and an intrinsically stretchable LM under biaxial stretching (50% strain).

[0107] Figure 26G The inductance of a serpentine Cu antenna (5 turns) and an intrinsically stretchable LM antenna (10 turns) with the same footprint are plotted as a function of frequency under various strains.

[0108] Figure 26H The Q factors of the stretchable LM antennas under various strains are described.

[0109] Figure 26I Depicted are the phases of the stretchable LM antenna under various strains.

[0110] Figure 26J The impedance of the stretchable LM antenna under various strains is plotted.

[0111] Figure 26K Digital images depicting the inflammatory state of the skin after 30 minutes of exercise after being covered with P3D-electronic skin.

[0112] Figure 26L Digital images depicting the inflammatory state of the skin after 30 minutes of exercise after being covered with PDMS-electronic skin.

[0113] Figure 26MThermal images of an adult body using forty NFC P3D-e-skin arrays to depict multi- location body temperature in a cool / dry environment.

[0114] Figure 26N Thermal images of an adult body using forty NFC P3D-e-skin arrays to depict multi- location body temperature in a warm / humid environment.

[0115] Figure 26O Continuous temperature monitoring of an adult body during sleep using P3D-e-skin, PDMS-e-skin, and the gold standard (commercial infrared thermal imager) is depicted. Error bars in the figure represent SD, while the scatter values represent the mean.

[0116] Figure 27A Digital images showing a stable electrical interface between the ultra-stretchable hLM solder and the rigid element for NFC are depicted.

[0117] Figure 27B Digital images of the stretchable P3D-e-skin system at 250% and 50% tensile strain, respectively, are depicted.

[0118] Figure 27C Digital images of the stretchable PDMS-e-skin system at 250% and 50% tensile strain, respectively, are depicted.

[0119] Figure 27D Inductance of structured Cu antenna as a function of frequency at various strains is depicted. It can be seen that at the same frequency, inductance increases with increasing strain.

[0120] Figure 27E Inductance of intrinsically stretchable LM antenna as a function of frequency at various strains is depicted. It can be seen that at the same frequency, inductance increases with increasing strain.

[0121] Figure 28 Multi-location physiological monitoring of a human body using forty near field communication (NFC) P3D-e-skin tags is depicted. Black dots in the image represent the measurement locations of body temperature. A graphical user interface (GUI) on a mobile device displays real-time and continuous monitoring using the NFC P3D-e-skin tags.

[0122] Figure 29 Stress concentration factor as a function of LM circuit modulus input from finite element analysis (FEA) is depicted.

[0123] Figure 30A Impedance of intrinsically stretchable LM antenna as a function of frequency at various working distances according to certain embodiments of the present disclosure is depicted.

[0124] Figure 30B Phase of the intrinsically stretchable LM antenna as a function of frequency at various working distances. Figure 30A Phase of the intrinsically stretchable LM antenna as a function of frequency at various working distances.

[0125] Figure 31 Continuous monitoring of body temperature during some daily activities. By using the NFC P3D-e-skin tag, the body temperature signal can be stably monitored during some daily activities including sitting, walking, and exercising using a customized mobile application.

[0126] Figure 32A Infrared images showing the cooling load and thermal effects of P3D-e-skin and PDMS-e-skin in a cool environment: (a) the beginning of thermal monitoring, (b) the epidermal attachment of e-skin, (c) the removal of e-skin, and (d) 1 min after e-skin removal.

[0127] Figure 32B Digital images showing the attachment position on the skin and their weight of P3D-e-skin and PDMS-e-skin.

[0128] Figure 33A Schematic diagram of the structure of ten-layer P3D-e-skin. The vertical dotted line indicates the position of VIA.

[0129] Figure 33B Digital images for showing the ten-layer P3D-e-skin fabricated layer by layer by repeatedly electrospinning fiber mats and micro-patterned LM circuits in situ.

[0130] Figure 33C Digital images showing the total thickness of ten-layer P3D-e-skin.

[0131] Figure 33D Digital images for showing all stretchable layers and VIA of ten-layer P3D-e-skin visualized by backlighting of the panel. The ten-layer LM trace in the "E, L, E, C, T, R, O, N, I, C" shape in each layer is connected by nine LM VIA. Six LEDs are interconnected by "E" shaped LM circuits and mounted on the first layer of P3D-e-skin using hybrid LM solder. The anode of the LED is directly connected to the positive terminal on the first layer (5.2 V, powered by an external DC power supply). The cathode is connected to the negative terminal on the 10th layer (ground) through all nine intermediate layers and VIA. The brightness of the six LEDs remains good stability when the sample is stretched to different strains (up to 100%), indicating the reliability of this ten-layer stretchable LM circuit.

[0132] Figure 34A permeable bioelectronic system according to certain embodiments of the present disclosure is shown.

[0133] Figure 35 A permeable bioelectronic system according to certain embodiments of the present disclosure is shown.

[0134] Figure 36 A method for manufacturing a permeable bioelectronic system according to certain embodiments of the present disclosure is shown. DETAILED DESCRIPTION

[0135] The present disclosure will now be described with reference to the following examples, which are to be regarded as illustrative in all respects, rather than restrictive.

[0136] Throughout the specification and claims, the word "comprise" and variations of the word, such as "comprising" and "comprises," will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers; that is, "including but not limited to."

[0137] Further, as used herein, the use of the ordinal adjectives "first," "second," "third," etc., are to be interpreted in an ordinal sense, and are used merely to indicate different instances of similar objects, rather than to imply that a given sequence or order is intended, unless otherwise indicated.

[0138] Example embodiments relate to permeable bioelectronic systems and methods of manufacturing thereof having one or more technical advantages.

[0139] To date, the development of three-dimensional (3D) stretchable electronics is still in its early stage. The present inventors have recognized several key challenges in this field. First, creating robust interfaces between rigid elements (e.g., inorganic electronic circuit elements) and stretchable circuits in 3D space or stacks is technically challenging. Second, the fabrication of 3D stretchable electronics today is mainly based on the sequential casting of multiple layers of elastomer films, such as polydimethylsiloxane (PDMS), and the bonding of rigid chips. The thickness of the entire 3D stack is typically greater than 1 millimeter (mm). Comfort and stretchability are significantly compromised compared to single-layer electronic skins. Third, the thick- and thin-film-based 3D stacks lack permeability, which is unsatisfactory in terms of wear comfort and long-term biocompatibility. The present inventors have further recognized that it is technically challenging to integrate functional electronic elements with fibrous mats to achieve highly integrated, stretchable, and permeable electronic products.

[0140] Example embodiments address one or more of these problems associated with the prior art by overcoming one or more technical obstacles, including but not limited to those described above.

[0141] One or more embodiments include a permeable bioelectronic system. The permeable bioelectronic system includes a stretchable multilayer circuit including a liquid metal (LM) and LM interconnects for coupling one or more inorganic electronic circuit elements to the stretchable multilayer circuit. In some embodiments, the LM includes gallium, a gallium alloy, or a mixture thereof. In some further embodiments, the LM includes a eutectic gallium-indium alloy (EGaIn), a gallium-indium-tin alloy (GaInSn), or a mixture thereof.

[0142] One or more embodiments provide a permeable three-dimensional integrated electronic skin (P3D-electronic skin) that mixes high-density inorganic electronic components with organic stretchable fiber substrates using 3D patterning, multilayer LM circuits, and super-stretchable hybrid LM solder. The P3D-electronic skin leverages skin-like softness and durability, fabric-like permeability and long-term biocompatibility, and complex system-level functionality, including stable sensing, signal processing and analysis, intervention, and wireless communication.

[0143] One or more embodiments provide a P3D-electronic skin system that mixes inorganic electronic components with organic stretchable fiber substrates in a 3D architecture similar to high-density 3D integrated circuit boards. The P3D-electronic skin system has stable and complex electronic functionality (sensing, signal processing and analysis, intervention, or wireless communication), skin-like softness and stretchability, and excellent permeability to enable continuous and comfortable physiological monitoring and intervention.

[0144] One or more embodiments provide one or more stretchable integrated electronic systems that enable high density and multifunctionality of stretchable electronics and outperform prior art systems, as shown in Table 1 below. As can be seen from the table, the permeable bioelectronic system according to certain embodiments has significantly improved stretchability and permeability.

[0145] Table 1. Comparison of system performance between prior art integrated flexible stretchable electronic systems and the permeable bioelectronic system according to certain embodiments of the present disclosure.

[0146]

[0147]

[0148] The last column of Table 1 refers to prior art references, except for the last row, as described below:

[0149] 1. Jun, J. J. et al. Fully integrated silicon probes for high-density recording of neural activity. Nature 551, 232-236 (2017).

[0150] 2. Gao, W. et al. Fully integrated wearable sensor arrays for multiplexed in situ perspiration analysis. Nature 529, 509-514 (2016).

[0151] 3. Niu, S. et al. A wireless body area sensor network based on stretchable passive tags. Nat. Electron. 2, 361-368 (2019).

[0152] 4. Jiang, Y. et al. A universal interface for plug-and-play assembly of stretchable devices. Nature 614, 456-462 (2023).

[0153] 5. Xu, S. et al. Soft microfluidic assemblies of sensors, circuits, and radios for the skin. Science 344, 70-74 (2014).

[0154] 6. Chung, H. U. et al. Binodal, wireless epidermal electronic systems within-sensor analytics for neonatal intensive care. Science 363, 947 (2019).

[0155] 7. Kim, J. et al. Battery-free, stretchable optoelectronic systems for wireless optical characterization of the skin. Sci. Adv. 2, e1600418 (2016).

[0156] 8. Jang, K.I. et al. Self-assembled three dimensional network designs for soft electronics. Nat. Commun. 8, 15894 (2017).

[0157] 9. Huang, Z. et al. Three-dimensional integrated stretchable electronics. Nat. Electron. 1, 473-480 (2018).

[0158] 10. Song, H. et al. Systems Based on Stacked Multilayer Network Materials. Sci. Adv. 3785, eabm3785 (2022).

[0159] 11. Lu, T., Markvicka, E.J., Jin, Y. & Majidi, C. Soft-Matter Printed Circuit Board with UV Laser Micropatterning. ACS Appl. Mater. Interfaces 9, 22055-22062 (2017).

[0160] 12. Jeong, YR et al. “A skin-attachable, stretchable integrated system based on liquid GaInSn for wireless human motion monitoring with multi-site sensing capabilities.” NPG Asia Mater. 9, e443 (2017).

[0161] 13. Lopes, PA, Santos, BC, de Almeida, AT, and Tavakoli, M. “Reversible polymer-gel transition for ultra-stretchable chip-integrated circuits through self-soldering and self-coating and self-healing.” Nat. Commun. 12, 4666 (2021).

[0162] 14. Votzke, C., Daalkhaijav, U., Menguc, Y., and Johnston, M. L. “3D-Printed Liquid Metal Interconnects for Stretchable Electronics.” IEEE Sens. J. 19, 3832-3840 (2019).

[0163] 15. Varnava, C. “Liquid metals take stretchable circuits to new heights.” Nat. Electron. 2, 52 (2019).

[0164] 16. Tang, L. et al. Metal-hygroscopic polymer conductors that can secrete solders for connections in stretchable devices. Mater. Horizons 7, 1186-1194 (2020).

[0165] 17. Liu, S., Shah, D. S. and Kramer-Bottiglio, R. Highly stretchable multilayer electronic circuits using biphasic gallium-indium. Nat. Mater. 20, 851-858 (2021).

[0166] 18. Li, G. et al. Three-dimensional flexible electronics using solidified liquid metal with regulated plasticity. Nat. Electron. 6, 154-163 (2023).

[0167] 19. Lee, W. et al. Universal assembly of liquid metal particles in polymers enables elastic printed circuit board. Science 378, 637-641 (2022).

[0168] Inventive work: Permeable bioelectronic systems according to certain embodiments of the present disclosure.

[0169] One or more embodiments provide a permeable 3D integrated electronic skin (P3D- electronic skin). The P3D-electronic skin molds non-permeable rigid printed circuit boards (PCBs) into a skin-like stretchable, soft, and breathable form factor size while maintaining complex system-level functionality, including multi-location physiological data acquisition, signal processing and analysis, intervention, and continuous and comfortable wireless communication with mobile devices.

[0170] According to one or more embodiments, the P3D-E-skin includes a micro-patterned permeable and stretchable multi-layered circuit board that includes liquid metal (LM) and a fibrous mat, 3D integration between different layers by using super-stretchable hybrid LM (hLM) solder to firmly bond between functional rigid IC components and soft LM interconnects to ensure stable stretchability without electrical failure, and by designing vertical permeation of LM to form stretchable vertical interconnect access (VIA).

[0171] According to one or more embodiments, the P3D-E-skin based system or P3D-E-skin platform presented herein enables unprecedented air and moisture permeability, reduces system-level thickness by ~54%, increases softness by ~60%, and prevents skin inflammation caused by long-term skin attachment, compared to prior art thin film based stretchable 3D electronics. These systems or platforms are also superior to those prior art permeable electronics in terms of advanced, complex, and monolithic system-level integration without the use of external PCBs (Table 2).

[0172] Table 2. Comparison of system performance between prior art permeable integrated electronics and permeable bio-electronic systems according to certain embodiments of the present disclosure.

[0173]

[0174]

[0175] The last column of Table 2, except for the last row, is a prior art reference, described as follows:

[0176] 20. Wicaksono, I. et al. “A tailored, electronic textile conformable suit for large-scale spatiotemporal physiological sensing in vivo.” npj Flex. Electron. 4, 5 (2020).

[0177] 21. Choi, HW et al. “Smart textile lighting / display system with multifunctional fibre devices for large scale smart home and IoT applications.” Nat. Commun. 13, 814 (2022).

[0178] 22. Lin, R. et al. “Digitally-embroidered liquid metal electronic textiles for wearable wireless systems.” Nat. Commun. 13, 2190 (2022).

[0179] 23. Yang, Y. et al. “A non-printed integrated-circuit textile for wireless theranostics.” Nat. Commun. 12, 4876 (2021).

[0180] 24. Jeong, GS et al. “Solderable and electroplatable flexible electronic circuit on a porous stretchable elastomer.” Nat. Commun. 3, 977 (2012).

[0181] 25. Kim, Y. et al. “Chip-less wireless electronic skins by remote epitaxial freestanding compound semiconductors.” Science 377, 859-864 (2022).

[0182] Inventors’ work: Permeable bioelectronic systems according to certain embodiments of the present disclosure.

[0183] According to one or more embodiments, it has been demonstrated that using the P3D- eSkin platform to fabricate a range of functional permeable bioelectronics to continuously record and wirelessly transmit multi-site physiological signals of the human body.

[0184] One or more embodiments achieve one or more technical advantages over prior art systems. These technical advantages can be one or more of, including but not limited to: more comfortable and biocompatible long-term wearable / implantable bioelectronics, more complex system-level functionality, more accurate and reliable chirp signal acquisition, more durable under various wearable / implanted deformations, etc.

[0185] Reference Figure 1A and Figure 1I By way of example only and for illustrative purposes, the P3D-eSkin includes four stretchable and permeable layers. As shown, the multi-layer P3D-eSkin includes a base circuit layer in the form of a base LM circuit layer (which can also be referred to as a base layer in some embodiments), an upper circuit layer in the form of an upper LM circuit layer (which can also be referred to as an upper layer in some embodiments), a paste mask layer, and an encapsulation layer. In the current embodiment, the paste mask layer is bonded with rigid electronic components using stretchable hLM solder. The LM can contain one or more eutectic gallium-based alloys because they have infinite stretchability and low modulus, high conductivity as a liquid, excellent biocompatibility, and patternability.

[0186] The P3D-eSkin can be fabricated through appropriate processes. Figure 2A and Figure 2B An example fabrication process is shown in FIGS. 1A-1C. According to one or more embodiments, a combination of photolithography, pattern transfer, and stencil printing processes are used to form the base circuit layer (~100 pm) and the upper circuit layer (~100 pm) on a stretchable fiber mat (FIGS. 1A-1C). Figure 3A 、 3B , 4A, and 4B). The thickness of the base circuit layer or the upper circuit layer can be different from 100 pm. In some embodiments, the thickness of the base circuit layer or the upper circuit layer can be in a range from about 25 pm to about 500 pm, such as in a range from 25 pm to 100 pm, or from 50 pm to 200 pm, or from 100 pm to 400 pm, or from 300 pm to 500 pm, or from 25 pm to 500 pm, any other subset of ranges.

[0187] The base layer and the upper circuit layer comprise LM micro-patterns or micro-patterned LMs. The micro-patterned LMs are used as electrical devices, such as stretchable antennas, interconnects, pads, and / or contacts. Vertical electrical connections between the base layer and the upper circuit layer are achieved using LM VIA. Subsequently, rigid electronic components (e.g., inorganic electronic circuit components, such as inorganic semiconductor components or elements) are integrated onto the LM circuit using hLM. The hLM comprises a partially oxidized LM (oLM) and a combination of LMs. The oLM is formed (e.g., printed) on a paste mask layer (~30 pm) made of thin fiber styrene-butadiene-styrene SBS, where the thin SBS has been pre-formed (e.g., deposited) on the upper circuit layer Figure 1B ) layer. The thickness of the paste mask layer can be different from 30 pm. In some embodiments, the thickness of the paste mask layer can be in the range of 10 pm to 50 pm, such as in the range of 10 pm to 30 pm, or 20 pm to 40 pm, or 30 pm to 50 pm, or any other subset of the range of 10 pm to 50 pm. In certain embodiments, the paste mask layer can comprise one or more biocompatible elastomeric fibers other than fiber SBS. The one or more biocompatible elastomeric fibers can comprise styrene-isoprene-styrene block copolymer, styrene-polybutadiene-styrene block copolymer, styrene-butadiene block copolymer, poly(styrene-block-butadiene-block-styrene) copolymer, polyisoprene rubber, butadiene rubber, polyurethane, thermoplastic polyurethane, polyvinyl alcohol, polycaprolactone, polycaprolactone, or mixtures thereof.

[0188] The rigid electronic components can include, but are not limited to, one or more of the following: light emitting diodes (LEDs), microcontroller units (MCUs), oscillators, multiplexers (MUXs), current mirrors, digital-to-analog converters (DACs), operational amplifiers (OP-AMPS), high voltage modules (HV, 20V), and low dropout regulators (LDO, 3.3V). The rigid electronic components can be adhered to the printed oLM pads. Additional LM paste can be applied on the pin / oLM interface Figure 1C ) layer can be directly electrospun to conformally cover the entire 3D hybrid electronic circuit. The thickness of the encapsulation layer is not equal to 50 pm. In some embodiments, the thickness of the encapsulation layer can be in the range of 50 pm to 500 pm, such as in the following ranges: 50 pm to 100 pm, or 100 pm to 300 pm, or 200 pm to 400 pm, or 300 pm to 500 pm, or any other subset of the range of 50 pm to 500 pm. The encapsulation layer can include a permeable but water-resistant SBS pad.

[0189] According to one or more embodiments, for the purpose of fabricating P3D- electronic skin, processing solvents are used as received. Dextran (Sigma-Aldrich), LM - implemented as eutectic GaIn (LM, melting point 15.7 °C, Sigma-Aldrich), negative photoresist (NR9-1500P, Futurrex, USA), developer for NR9-1500P (DR6, Futurrex, USA), poly(styrene-b-butadiene-b-styrene) (SBS, Kraton) are used as received.

[0190] For example, the fabrication process of multilayer LM circuits combines photopatterning - pattern transfer - selective wetting approach and template printing of LM. Thus, the fabrication utilizes both photopatterning and template printing techniques. Figure 3A 、 3B , 4A, 4B and 4C). Permeable and stretchable LM microelectrodes are patterned and can be used as stretchable antennas, traces, connections and / or contacts of microcircuits. Reference is made to Figure 2AFor example, a sacrificial layer is prepared on a wafer by spin-coating a dextran solution (10% by weight in water) at 4000 rpm for 40 seconds. After a bake treatment at 80°C for 1 minute and then at 180°C for 30 minutes, a negative photoresist (NR9-1500P) is spin-coated on the dextran-coated wafer, followed by photolithography and development. Silver (Ag) microcircuits 20 (serving as the upper layer of the 3D circuit) are produced by thermally evaporating a deposited Ag film (300 nm thick) and performing a lift-off process. In step 202, a fibrous SBS mat (100 μm thick insulating layer) is electrospun directly onto the Ag microcircuits 20. The polymer solution is prepared by dissolving a 13% by weight SBS polymer in a mixed solvent (tetrahydrofuran / dimethylformamide = 3:1). The voltage is set to 18 kV, and the collection distance is 15 cm. After dissolving the dextran layer with deionized water, the Ag microcircuit 20 is then transferred to the SBS pad in step 204. In step 206, the Ag microcircuit layer is selectively wetted with LM in a glove box, cut into square pieces, and covered with a thin electrospun SBS pad (~30μm thick paste mask layer) in step 208. The selective wetting by LM creates a sharp contrast between the LM lyophobic properties of the SBS pad and the LM lyophilic properties of Ag. In the fabrication of LM microcircuits, EGaIn (eutectic GaIn) wets only the Ag covered areas due to reactive alloying and dewets from the SBS surface due to the high intrinsic surface tension of LM. When EGaIn is applied on Ag, reactive alloying occurs between Ag and indium (In) to form an AgIn alloy. The additional EGaIn will then wet the AgIn alloy layer and form an EGaIn / AgIn / Ag trilayer ( Figure 5 ).

[0191] At step 210, the upper circuit layer is then flipped and the LM traces of the base circuit layer are stencil printed. After electrospinning another SBS mat (100 pm thick) as a substrate, at step 212, the vertical interconnection channels between the two layers of 3D LM circuits are machined by employing a laser cutting method (LPKF ProtoLaser U4), and these VIA are filled with LM. At step 214, the circuit board is flipped again and a partially oxidized LM (oLM) ink is stencil printed. The oLM ink is prepared by heating the original LM at a set temperature of 80 °C in air for 16 hours. The oLM is printed through a custom mask onto the paste mask layer as a contact pad for the electronic component. After placing the component on the paste mask layer at step 216, an additional original LM paste is applied at the pin / oLM interface to form a hyper-stretchable hybrid LM (hLM) solder. In this embodiment, the weight ratio between the oLM pad and the LM paste is 1 :2. In some other embodiments, the weight ratio can be in the range of 1 :0.5 to 1 :8, such as in the range of 1 :0.5 to 1 :3, or in the range of 1 :2 to 1 :6, or in the range of 1 :3 to 1 :7, or in any subset of the range of 1 :0.5 to 1 :8.

[0192] Detailed circuit diagram design and printed circuit board (PCB) design are shown in FIGS. 3A-3B. Figure 1I The circuit elements in each layer can include one or more of the following: a microcontroller unit (MCU), an oscillator, a multiplexer (MUX), a current mirror, a digital-to-analog converter (DAC), an operational amplifier (OP-AMP), a high voltage module (HV, 20 V), and a low dropout regulator (LDO, 3.3 V). For wireless communication, the P3D-e-skin system can be equipped with a built-in Bluetooth (BLE) 5.1 MCU (CC2640, Texas Instruments) and a matching 2.4 GHz LM BLE antenna (planar inverted-F antenna) to enable data acquisition, transmission, and function control by simply using a smartphone with a mobile application. Code Composer Studio (CCS) is used for MCU programming. The Android application for mobile device communication is developed by Android Studio. The power supply of the P3D-e-skin is powered by a lithium-ion battery, and the voltage is regulated by an LDO ( Figure 6 ). Finally, in step 218, the entire permeable stretchable circuit board is conformally encapsulated with a permeable and waterproof SBS mat to ensure stable operation, thus completing the P3D-e-skin 22.

[0193] According to one or more embodiments, for P3D-electronic skin equipped with Bluetooth functionality, the upper layer of the LM 3D circuit contains a high-density complex LM micropattern, such as trace tracks, pins forming island-shaped or peninsula-shaped paths (e.g., circles), and many densely packed long tracks. For battery-free P3D-electronic skin, the stretchable antenna coil is compactly designed with a large number of turns. Due to the large surface roughness and porosity, it is extremely challenging to pattern such complex and high-density micropatterns on a permeable, ultra-soft and stretchable substrate while maintaining excellent mechanical, electrical and electromagnetic properties. Therefore, a combination of methods including photolithography, pattern transfer and selective wetting methods is used to manufacture the complex and high-density upper circuit layer.

[0194] Simple stencil printing techniques are used to create complex patterns such as those described in this paper ( Figure 3A ) is challenging, and the template printing process is likely to separate the mask, thereby destroying the pattern. However, circuit traces and contacts in the base circuit layer and pads in the paste mask layer ( Figure 3B ) can be obtained by template printing technology, which is more cost-effective and time-saving.

[0195] According to one or more embodiments, the inventors have addressed several technical challenges to achieve relatively high resolution micro LM circuits without agglomeration by stencil printing. First, a high-precision PCB manufacturing compatible laser cutting machine (LPKF U4, Figure 4A ) to make the template. In principle, the laser beam focus can reach about 15μm, and thus provides a powerful tool for making high-resolution templates. Secondly, a polyimide (PI) film (12.5-25μm thickness) is used as a template, so that the template is conformally laminated to a substrate with a fixed frame and markings ( Figure 4B Densely packed line arrays indicate a minimum trace size of ∼100 μm (50 μm lines show substantial disconnection) and ∼70 lines / cm from stencil printing techniques. 2 The highest trace density ( Figure 4C This resolution is comparable to the patternability of conventional PCB manufacturing, where typical line widths are around 10 mils (254 μm). Therefore, the proposed manufacturing process is an optimal solution for this complex 3D integrated circuit board with stretchability, flexibility, moisture permeability, and waterproofing.

[0196] Fabrication of polydimethylsiloxane electronic skin (PDMS-electronic skin). For reference and comparison to demonstrate the improved performance of the P3D-electronic skin or multiple P3D-electronic skins described herein, 3D electronic skins were fabricated with the same device design and configuration using thin PDMS as the substrate, intermediate layer, and encapsulation material. First, a layer of PDMS ( 184, 10:1) was spin-coated (500 rpm, 30 seconds) onto a clean and dry glass plate and cured in an oven (80°C, 30 minutes). At the same time, two copper / polyimide (Cu / PI) films (18 / 12.5 μm) were laser cut (LPKF ProtoLaser U4) to form the patterns of the top and bottom layers of the circuit respectively. Picked up by water-soluble tape, its PI side was deposited with a Ti / SiO2 layer (5 / 100 nm) by electron beam evaporation as an adhesive interface between the circuit and the PDMS substrate. After treating both surfaces with ultraviolet ozone (UVO) for 5 minutes, the base layer of the circuit pattern was transferred to the PDMS substrate with strong bonding, and then rinsed with water to remove the water-soluble tape. Another layer of PDMS was spin-coated on top of the bottom layer circuit in the same way and cured, which served as an intermediate insulating layer. VIA was made on the PDMS layer using a laser cutting method. After UV-ozone (UVO) treatment and alignment with the base layer, the top copper circuit is transferred and printed onto the insulating layer in the same manner. The vias are then filled with commercial solder paste, and the electronic components are placed on the paste-coated pads. A hot air blower is used to solder the components to the multilayer circuit. Finally, the circuit board is fully encapsulated by pouring a PDMS solution and curing it in an oven (80°C for 15 minutes).

[0197] Characterization. The morphology of the LM 3D circuit and the surface oxidation state of the oLM were explored using scanning electron microscopy (SEM, TESCAN VEGA3) and X-ray photoelectron spectroscopy (XPS, Thermo Fisher Scientific Xesa), respectively. Both air permeability and moisture permeability tests were performed at constant temperature (22°C) and humidity (63%). The air permeability test was performed using a MO21S air permeability tester (SDL Americus) according to ASTM D737-08 standard with an air flow pressure of 100 kPa. The moisture permeability test was performed by the cup method according to standard E96 / E96M-13. The test duration was 72 hours. The waterproofness of the P3D-electronic skin system was characterized by a standard rain test according to AATCC test method 35-2006. The sample size was set to 20 cm × 20 cm, and the water spray duration was 2 minutes. The sweat resistance test of the P3D-electronic skin system was carried out by immersing the P3D-electronic skin system in water and artificial sweat (ZW-HY-1000, pH: 4.7±0.1, Zhongwei Equipment Co., Ltd.) and stirring at a speed of 300 rpm. The brightness stability of the embedded LED in the P3D-electronic skin system indicates the sweat resistance of the system. Statistical values ​​(mean, standard deviation (SD)) were obtained from at least three parallel samples. Each sample was tested at least three times. The mechanical properties of the material were characterized using a universal testing machine (Instron 5566). Using a source meter (Keithley 2400) coupled to a customized tensile machine (Zolix), the resistance of the resistors connected to LM, oLM and hLM under different strains was measured by the four-terminal method. The output and transmission characteristics of the stretchable metal oxide semiconductor field effect transistor (MOSFET) and the multilayer stretchable switch array were characterized using a semiconductor analyzer (Keithley4200A-SCS parameter analyzer) connected to a probe station (Micromanipulator) and a customized stretching setup. The stretchable logic circuit was characterized using a digital oscilloscope (Rigol).

[0198] The microporous fiber structure of the electrospun fiber mat allows air and moisture (such as water vapor) to pass through it ( Figure 7 A), while the inherent hydrophobicity of SBS fiber mat ( Figure 7 B)—it shows a large water contact angle (CA) of 127° ( Figure 7 C) - Can repel water droplets. That is, it achieves both permeability and waterproofness at the same time.

[0199] P3D-Electronic Skin is extremely soft ( Figure 1D ) and is highly stretchable and exhibits stable electrical functionality under a large tensile strain of 550% ( Figure 1EIt provides wireless, continuous, and comfortable physiological monitoring and intervention of the human body through a mobile device interface. Importantly, because P3D-electronic skin is made based on a porous fiber substrate, an intermediate layer, and an encapsulation, it also offers unprecedented permeability compared to those impermeable 3D stretchable electronic devices made of elastic films and blocks ( Figure 1F The air permeability and moisture permeability of P3D-electronic skin reached 177 mm / s and 676 g / m respectively. 2 / day (g / m2 / day), which are 15 times and 44 times higher than medical tape, and 3 times and 22 times higher than commonly used wound dressings ( Figure 1G ). According to the standard rain test, the water resistance of the P3D-electronic skin system reached an "excellent" level. After spraying water on the front of the P3D-electronic skin system for 2 minutes, no observable water was found on the blotting paper ( Figure 8 ). In addition, the stability of the P3D-electronic skin system was also tested in water and artificial sweat (pH: 4.7±0.1). A P3D-electronic skin system embedded with LEDs was fabricated and immersed in both liquids. The stable brightness of the LEDs in both water and artificial sweat indicated excellent electrical stability ( Figure 9 ).

[0200] According to one or more embodiments, the P3D-electronic skin exhibits excellent long-term biocompatibility, and the skin area covered by the P3D-electronic skin remains inflammation-free during the one-week attachment period. For reference, a similar 3D electronic skin was fabricated using thin PDMS as a substrate, an intermediate layer, and an encapsulation material. Figure 10A 、 10B , 10C, and 10D) with a compact and thin-film type layout, the thickness of the PDMS-electronic skin increased by ∼54%, the rigidity increased by ∼60%, and it showed almost no air permeability and poor moisture permeability of less than 50 g / m2 / day. Although PDMS is known as a biocompatible material, the impermeability of the multilayer PDMS-electronic skin resulted in severe skin erythema under skin attachment test ( Figure 1H ).

[0201] Ultra-stretchable hLM solder is used for reliable 3D interfaces between rigid components and LM circuits. To achieve high stretchability and stability of P3D-electronic skin, the inventors have recognized that ensuring seamless interfaces between different vertical layers to provide the necessary electrical insulation and connections, as well as a stable interface that can withstand large deformations between the soft LM and the rigid electronic chip are crucial challenges. To address this challenge, two different types of LM inks were formulated, namely original LM and oLM ( Figures 11A to 11F), used as a super-stretchable hLM solder for 3D circuits.

[0202] The pristine LM exhibits high flowability, but low wettability to the fibrous SBS substrate Figure 12 ), and it is used to fabricate stretchable circuit antennas, interconnects, and VIA on the base and upper circuit layers. Thus, the base and upper circuits maintain excellent in-plane stretchability and out-of-plane insulation, unless they are connected through a VIA. However, connecting a rigid pin to the pristine LM results in poor stretchability, and the pin / LM interface breaks during stretching due to dewetting of the LM Figure 13A ). In contrast, the wettability of oLM is much higher because oxidation lowers the surface tension of the LM. Therefore, oLM is chosen to be printed as a contact pad on the paste mask layer, providing good adhesion between the underlying soft LM circuit and the rigid pin of an electronic component. However, due to the low stretchability of oLM, the pin / oLM interface also breaks when the 3D circuit is stretched Figure 13B ).

[0203] According to one or more embodiments, a super-stretchable hLM solder is developed that takes advantage of both the wettability benefits of oLM and the stretchability properties of LM. As shown in Figure 13C , an additional pristine LM paste is applied at the pin / oLM interface to form a hLM solder Figure 13C ). Compared to those using either pristine LM or oLM as the connecting material (see Table 3 below), the hybrid connecting method reduces the stress concentration factor (ratio of maximum stress to average stress, i.e., σ max / σ avg ) at the interface between the rigid chip and soft SBS by 30% Figure 13D and Figure 14 ). Thus, the hybrid connection provides excellent interface stability even under large stretching strains. When the circuit is stretched to 1500% strain, the resistance of a 100Ω rigid micro-resistor combined with the hLM solder shows negligible change Figure 13E . In contrast, the same circuit using LM or oLM as the solder fails when stretched to less than 50% strain.

[0204] Table 3. Summary of input parameters and stress distribution output results in finite element analysis (FEA) of chip interface, LM antenna, and Cu antenna.

[0205]

[0206] Figure 13FA schematic structure of a 3D circuit using hLM solder is shown. Notably, with good wettability, oLM spontaneously penetrates through the thin paste mask SBS layer and connects with the underlying LM circuit trace (in this case, the upper LM circuit layer). As a result, a vertical electrical connection is formed between the pin / oLM and the underlying LM 3D circuit. Meanwhile, the upper LM circuit layer is connected with the underlying LM circuit layer using stretchable LM VIA. As shown in FIG. 1, the 3D LM circuit is fabricated on a flexible substrate (e.g., Kapton®) and is connected with the pin using a stretchable LM VIA. The LM circuit is connected with the micro-resistor using a stretchable LM VIA. The LM circuit is connected with the LED using a stretchable LM VIA. Figure 13G and 13H As shown in FIG. 2, there is no apparent interface gap between different layers of the P3D-electronic skin, as all the fiber SBS pads are deposited using the electrospinning method. The interface remains seamless during tensile or bending deformation.

[0207] As a proof of the stable 3D interface concept, different types of rigid electronic elements in the stretchable 3D LM circuit, including micro-resistors, metal oxide semiconductor field effect transistors (MOSFETs), and LEDs, were tested for their performance under large strain. When connected to different micro-resistors ranging from 100 Ω to 1 MΩ, the resistance of the circuit shows negligible change Figure 13I ) when stretched to 1500% strain, and remains stable Figure 13J ) during 1000 cycles of stretch-release tests. The stable brightness of LEDs during the stretching process also indicates the resistance constancy of the stretchable circuit Figure 15 ). Stretchable P-type Figure 13K and Figure 16A ) and N-type Figure 13L and Figure 16B ) MOSFET circuits also exhibit stable transfer and output characteristics under large strain up to 500%. Further, stretchable logic circuits were fabricated, including clock-controlled switches Figure 13J and Figure 13N ), NOR gates, and 3D switch arrays with MOSFETs Figures 17A to 17J . These logic circuits function properly in logic output states under various strains.

[0208] After storage for 8 months, the initial resistance of the LM circuit before cycling increased slightly from 0.33 Ω to 0.42 Ω. During the stretch tests, the samples previously stored in air showed similar excellent electrical stability and robustness. After the cycling tests, the resistance only increased by 0.119 Ω and 0.083 Ω, respectively, for the freshly prepared sample and the stored sample Figure 18A . Moreover, the electrical interface between the LM circuit and the micro-resistor also has excellent stretchability and electrical stability Figure 18B after storage for eight months.

[0209] Referring to 19A to 19Dfailure modes of the solder joints after long-term repeated cycling tests. The inventors have discovered two typical failure modes of the electrical interface, which behave differently under low strain (e.g., 100%, Figure 19A ) and high strain (e.g., 1500%, Figure 19B ). At low strain (e.g., 100%), the interface between the rigid electronic component and the soft encapsulation pad (rigid-soft interface) fails after long cycles (e.g., over 10,000 cycles) of the sample undergoing repeated tensile release processes. This is due to the long-term continuous mechanical wear and tear of the rigid-soft interface with stress concentration Figure 19C ). Finite element analysis (FEA) shows that the maximum stress occurs at the rigid-soft interface between the rigid microchip and the soft SBS fiber pad. At very high strain (e.g., 1500%) close to the substrate material fracture strain, the substrate breaks after 1,000 cycles of tensile release testing, while the interface at the solder joint remains well encapsulated. According to the force-elongation curve of the SBS pad (n = 10), the average breaking force is ~2.013 N Figure 19D ) at which time the solder joint is still not broken.

[0210] For the leakage issue, the LM 3D circuit does not leak onto the skin even under high pressure up to 50 kPa when pressed on the arm before mounting the components Figure 20A ). After the press test on the skin, the LM 3D circuit remains intact without any circuit merging Figure 20B ). In addition, the P3D-E-skin system with an upper layer of coverage is still well encapsulated under a very large strain of 850% Figure 21 ).

[0211] Remote wireless transcutaneous electrical stimulation and electrophysiological sensing system. Wireless transcutaneous electrical stimulation and recording of corresponding electromyography (EMG) signals. All procedures involving attachment of P3D-E-skin and PDMS-E-skin on human body followed the ethical guidelines, which were approved by the Hong Kong Polytechnic University (HSEARS20230101001).

[0212] The animal experiments described herein followed the Research Ethics Review of Studies Involving Animal Subjects approved by the Research Committee of City University of Hong Kong (Animal Subjects Ethics Review Committee) (A-0664). Prior to transcutaneous electrical stimulation and electrophysiological signal recording, healthy male Sprague Dawley (SD) rats (4-5 weeks old, ~200 g) were used for quadriceps stimulation. The SD rats were first treated with gaseous light anesthesia (isoflurane, 3%) and then deep anesthesia with a mixed solution of ketamine (100 mg / kg) and xylazine (10 mg / kg) intraperitoneally injected. To attach the P3D-E-skin patch, the hair on the skin of both legs was shaved off.

[0213] The edges of the e-skin (PDMS-e-skin and P3D-e-skin) were adhered to the skin using a biocompatible, soft, wet adhesive before attachment to the skin. The electrical stimulation process was wirelessly controlled through a mobile phone based on a mobile Android system. An anode and a common cathode were applied to the animal's skin to form a closed circuit. A current control module was connected between the ground (GND) of the circuit and the common cathode to provide a virtual ground (VGND) potential that varied according to the allowed current. The allowed current intensity was controlled by a simple current mirror circuit. By sharing the same gate (G) and source (S), the current intensity in the second transistor was the same as the reference current through the first transistor. By sending a predefined serial command to the DAC, the voltage was precisely controlled in the range of 0-3.3 V. This voltage was then applied to the drain (D) and G of the transistor to define the reference current intensity. A fixed resistance (50 Ω) was connected in series to the common D and GND, where the voltage on D reflected the total current. This voltage could be read by a 14-bit analog-to-digital converter (ADC) on the MCU. To prevent damage to the MCU from an overload voltage, an operational amplifier was added between D and the MCU, which acted as a voltage follower (provided the same voltage). Next, the output voltage and current data were measured by a DAQ (data acquisition) multimeter system (Keithley DAQ6510) at a sampling frequency of 10 kHz. The EMG signal was measured using a high-precision data acquisition system (PowerLab 16 / 35 by AD Instruments) and a bio-signal amplifier (BioAmp FE132 by AD Instruments) with a sampling rate of 10 kHz. The raw signal data was digitally filtered by two notch filters at 50 Hz and 100 Hz to obtain representative EMG waveforms, thus avoiding baseline noise.

[0214] Figure 22AA block diagram of a wireless transdermal electrical stimulation and electrophysiological sensing system fabricated based on the P3D-electronic skin platform is shown. The diagram shows a smartphone 2202 with a mobile application or APP installed on it, a stimulus generator 2210, a current controller 2220, a power manager 2230, a Bluetooth Low Energy (BLE) MCU 2240, and an animal 2250 in the form of a rat. The stimulus generator 2210 includes a 20V booster 2212 and a high voltage (HV) MUX 2214. The current controller 2220 includes a DAC 2222, an OP-AMP 2224, and a current mirror 2226. The power manager 2230 includes a 3.3V voltage regulator 2232 and a battery 2234. The MCU 3340 is a 5.1 built-in MCU, which is equipped with a 2.4GHz BLE LM antenna (planar inverted-F antenna), which can provide stable wireless control and data transmission functions with a mobile device at a distance of up to 15m Figure 22B ). The embedded electrical stimulation electrode can generate high-voltage electrical pulses with precisely controlled current intensity, frequency, and duty cycle for delivering electrical stimulation to the user / animal's body. By controlling the ON / OFF cycle of the MUX, the generated DC high voltage is converted into a periodic pulse with precisely controlled frequency (1-100Hz) and duty cycle (1-10%) Figure 22C ). Due to the high permeability of the P3D-electronic skin, even when the entire P3D-electronic skin is steamed on top of boiling water Figure 22F ), the generation of electrical pulses does not exhibit any signal drift or electrical failure Figure 22D and Figure 22E ). In contrast, water droplets accumulate on the surface of the impermeable PDMS-electronic skin Figure 23A and 23B ).

[0215] The output voltage of the DAC of the P3D-electronic skin is controlled by sending a setting command on the mobile device Figure 24 ). Through the skin interface LM stimulation electrode, the generated current pulse passes through the body and flows into the current mirror of the current control module, where the current intensity is precisely set in the range of 0 to 2mA Figure 22G ). The actual current intensity is converted to a safe sensitive voltage for the MCU by the OP-AMP. The electrical stimulation output waveform and the control current intensity remain very consistent and stable in the stretched state, demonstrating excellent system-level stability in the stretched state Figures 25A to 25H ). The P3D-electronic skin is used to deliver electrical stimulation to the bicep femoris muscle of an experimental animal Figure 22H ). Real-time electromyography (EMG) signals from the adjacent area of the rat bicep femoris muscle are recorded. During the stimulation period, the corresponding EMG responds to various frequencies (1, 5, and 10Hz) Figure 22I) and is well matched to the stimulus input ( Figure 22J ), which demonstrated that electrical stimulation was successfully transmitted using the wireless P3D-electronic skin system.

[0216] A battery-free P3D-electronic skin system using near field communication (NFC). A battery-free P3D-electronic skin ( Figure 26A ). The NFC P3D-electronic skin before and after final packaging is shown in Figure 26B and Figure 26C It is also highly flexible and stretchable ( Figure 27A ).

[0217] Characteristics of the Near Field Communication (NFC) P3D-electronic skin system. To develop a battery-free P3D-electronic skin, an MCU with embedded NFC (RF430FRL152H, Texas Instruments) was used, and the temperature sensing circuit from the reference design (TIDM-RF430-TEMPSENSE) was modified. The temperature data was acquired by a mobile Android application GUI for temperature sensing (RF430FRL152HDemo, Texas Instruments, Figure 28 ) or NFC reader (MSP-EXP430G2ET with TRF7970A NFC / RFID enhancement package, Figure 6 An impedance analyzer (E4991B, Keysight Technologies) was used to characterize the characteristics of the LM sensing antenna, including inductance, Q factor, impedance, and phase.

[0218] NFC's LM antenna coil outperforms the snake-shaped copper coil in terms of design compactness, stretchability, and electromagnetic stability. To achieve good stretchability, conventional stretchable Cu antenna coils are fabricated into a snake-shaped shape, which significantly reduces the coil density ( Figure 26D ). In contrast, due to the inherent stretchability of LM, the LM coil is more compact in the same footprint. The number of turns of the LM coil is twice that of the Cu antenna ( Figure 26E and Figure 27B Furthermore, the Cu antenna is only stretchable up to 50% strain, at which point the jumper wires and interconnects to the components break ( Figure 27C ), while the LM antenna can be well connected even under 300% strain.

[0219] FEA was used to analyze the static structural mechanics of the system. The material mechanical parameters are summarized in Table 3. The modulus of LM and oLM were measured from the stress-strain curve. Since LM or oLM is neither a self-supporting material nor a pure liquid (an oxide layer inevitably exists), the Young’s modulus of LM or oLM supported by the substrate (SBS fiber mat) was tested. Accordingly, the Young’s modulus value of LM trace (LM on SBS fiber mat) was adopted to perform FEA on the stress distribution of the electrical interface. Sensitivity test was performed by varying the LM modulus in the range from 0.1 Pa (fluid-like substance) to 1011Pa (close to the modulus of Cu), and the change of stress concentration factor (ratio of maximum stress to average stress) was observed. The LM modulus has little effect on the stress concentration factor in the range of 0.1 Pa to 1 MPa modulus, all of which are much smaller than the stress concentration factor in the simulated controlled groups (e.g., Al2O3 and Cu antenna for chip), as shown in Figure 29 Four systems were investigated, namely, the snake-shaped Cu antenna, the intrinsically stretchable LM antenna, the chip with LM or oLM solder, and the chip with hLM solder. These systems were subjected to mechanical tension with 50% strain. The stress response was collected. The ratio of maximum stress to average stress was used as the stress concentration factor, i.e., σ max / σ avg . The input parameters and output results of FEA are summarized in Table 3 above.

[0220] The FEA results show that this is because the stress distribution of the LM antenna is much more uniform than that of the Cu antenna. The stress concentration factor of the LM coil is only 1 / 586( Figure 26F , Table 3) of that of the Cu coil. In addition, the LM coil exhibits higher inductance( Figure 26G , Figure 27D and Figure 27E ) than the Cu coil. The Q factor (Fig. 27H), phase (Fig. 271), and impedance (Fig. 27J) of the LM coil are related to high stability under various tensile strains and working distances( Figure 30A and Figure 30B ) within the readable frequency of ~13.56 MHz.

[0221] A temperature-sensing NFC P3D-e-skin was developed to continuously record the temperature distribution of different locations of the human body( Figure 28 ). The body temperature continuous monitoring during other daily activities (e.g., sitting, walking, and exercising) can be stably monitored using a customized mobile application( Figure 31 ). The P3D-e-skin provides high wearing comfort and biocompatibility to skin health. Wearing the P3D-e-skin during intense exercise does not cause sweat accumulation, thereby avoiding skin wetness, allergy, and inflammation( Figure 26K), while PDMS-electronic skin covered skin showed clear skin erythema Figure 26L

[0222] Thermal images of adult male body in cool / dry Figure 26M ) and hot / humid Figure 26N ) environments can be mapped by using multi-location physiological temperature mapping with forty NFC P3D-electronic skin arrays. Body temperature Figure 26O ) was recorded during 8 hours of continuous sleep monitoring. Importantly, P3D-electronic skin not only showed more stable signal recording and lower signal variation than PDMS-electronic skin, but also the recorded temperature values from P3D-electronic skin were very consistent with standard temperature recorded by commercial infrared thermal camera. P3D-electronic skin has smaller initial cooling load under test conditions, making thermal impact on skin smaller than PDMS-electronic skin Figure 32A and Figure 32B ). In addition, the permeable nature of P3D-electronic skin allows better convective heat transfer between air and skin, which is closer to the real situation where bare skin can regulate body temperature, compared to impermeable dressing that only conducts heat. Furthermore, P3D-electronic skin is softer and more stretchable, allowing more conformal contact with skin, and thus can reduce thermal artifacts by smaller signal fluctuation.

[0223] According to one or more embodiments, permeable bioelectronics incorporating commercially available electronic components (e.g. high performance and inexpensive chips with stretchable printed circuits) can potentially provide clinical quality and continuous health monitoring and regulation beyond the scope of traditional hospitals or laboratories. For long-term wearability, 3D integrated electronic devices of permeable and stretchable type can impart long-term wear comfort and healthiness compared to traditional impermeable thin film counterparts.

[0224] The P3D-electronic skin platform described herein according to one or more embodiments provides the first demonstration of how to implement a 3D integrated circuit board with unique advantages of high-density functionality, skin-like softness and stretchability, and high permeability to air and moisture. Super-stretchable hLM solder provides a reliable and scalable solution to integrate developed mature rigid electronic components with stretchable fiber substrates into 3D configuration. This P3D-electronic skin integration strategy provides the possibility to fabricate thin, soft and stretchable multilayer circuits by repeatedly electrospinning fiber mats and micro patterning LM circuits in situ Figures 33A to 33C ​Compared to similar electronic skins made with stretchable film substrates, the P3D-electronic skin described herein according to one or more embodiments is significantly lighter, thinner, softer, more stretchable, and, most importantly, provides long-term biocompatibility in on-skin testing. The P3D-electronic skin also outperforms prior art permeable electronics in terms of superior system-level high-density integration and the elimination of the need for an external PCB.

[0225] Figure 34 A permeable bioelectronic system 3400 according to certain embodiments of the present disclosure is shown. The permeable bioelectronic system 3400 may be one or more systems as described above with reference to one or more embodiments and / or as shown in one or more of the accompanying figures.

[0226] As shown in the figure, the permeable bioelectronic system 3400 includes: a stretchable multilayer circuit 3410 including liquid metal (LM); and a LM interconnect 3420 for bonding one or more inorganic electronic circuit elements to the stretchable multilayer circuit. The stretchable multilayer circuit 3410 or the LM interconnect 3420 can be as described above with reference to one or more embodiments and / or as shown in one or more of the accompanying drawings (e.g. Figure 1A ) as shown in one or more circuits or LM interconnects.

[0227] Figure 35 A permeable bioelectronic system 3500 according to certain embodiments of the present disclosure is shown. The permeable bioelectronic system 3500 may be one or more systems as described above with reference to one or more embodiments and / or as shown in one or more of the accompanying figures.

[0228] The permeable bioelectronic system 3500 includes a first LM circuit layer 3510 comprising a micropatterned LM. The first LM circuit layer 3510 can be one or more layers as described above with reference to one or more embodiments. For example, the first LM circuit layer 3510 can be a base circuit layer as described above. The first LM circuit layer 3510 can include a fiber SBS mat 3512 and LM traces 3514 formed on the fiber SBS mat 3512.

[0229] The permeable bioelectronic system 3500 also includes a second LM circuit layer 3520. The second LM circuit layer 3520 includes a micropatterned LM and is formed on the first LM circuit layer 3510. The second LM circuit layer 3520 can be one or more layers as described above with reference to one or more embodiments. For example, the second LM circuit layer 3520 can be an upper circuit layer as described above. The second LM circuit layer 3520 can include a microcircuit in the form of a fiber SBS mat 3522 formed on the first LM circuit layer 3510 and an Ag microcircuit 3524 formed on the fiber SBS mat 3522.

[0230] The permeable bioelectronic system 3500 also includes a paste mask layer 3530 formed on the second LM circuit layer 3520. The paste mask layer 3530 is configured to incorporate the one or more inorganic electronic circuit elements.

[0231] The permeable bioelectronic system 3500 also includes an encapsulation layer 3540 formed on the paste mask layer 3530 for encapsulating the first LM circuit layer 3510, the second LM circuit layer 3520, and the paste mask layer 3530. The encapsulation layer 3540 can include a fibrous SBS pad.

[0232] For example, the paste mask layer 3530 can include or be made of a fibrous SBS pad (referred to as a second fibrous SBS pad) such that the Ag microcircuit 3524 is sandwiched between the second fibrous SBS pad and the fibrous SBS pad 3522 (referred to as a first fibrous SBS pad). The first fibrous SBS pad is thicker than the second fibrous SBS pad. For example, the first fibrous SBS pad can have a thickness of 100 pm. The first fibrous SBS pad can have a thickness of 30 pm.

[0233] Figure 36 A method for manufacturing a permeable bioelectronic system according to certain embodiments of the present disclosure is shown. The method can be performed by one or more systems as described above with reference to one or more embodiments and / or as shown in one or more of the figures.

[0234] Block 3602 illustrates generating a microcircuit having a first side and a second side. The microcircuit can be an Ag microcircuit. The first side and the second side can be sides of the Ag microcircuit, as shown in Figure 2A The first side can be an underside of the Ag microcircuit 3524, as shown in Figure 35 The second side can be an upside of the Ag microcircuit 3524, as shown in Figure 35 The second side can be an upside of the Ag microcircuit 3524, as shown in

[0235] Block 3604 illustrates transferring the microcircuit to a fibrous pad such that the first side of the microcircuit contacts the fibrous pad. This step can include preparing a polymer solution by dissolving a styrene-butadiene-styrene (SBS) polymer in a mixed solvent of tetrahydrofuran and dimethylformamide, and electrospinning the polymer solution onto the microcircuit.

[0236] Block 3606 illustrates forming a paste mask layer on the second side of the microcircuit. This can include selectively wetting the microcircuit by using an LM and electrospinning an SBS pad onto the microcircuit.

[0237] Block 3608 illustrates forming a base circuit layer on a side of the fiber mat that is distal to the first side of the microcircuit, the base circuit layer comprising liquid metal (LM). This may include stencil printing LM traces onto one side of the fiber mat and electrospinning an SBS mat onto the side of the fiber mat where the LM traces were printed.

[0238] Block 3610 illustrates forming a stretchable vertical interconnect via (VIA) for electrically connecting the microcircuit, base circuit layer, and paste mask layer, the VIA being filled with LM. This may include creating a via by laser cutting the microcircuit, base circuit layer, and paste mask layer and filling the via with LM.

[0239] Block 3612 illustrates forming a hybrid LM (hLM) solder on the paste mask layer for bonding one or more inorganic electronic circuit elements. Block 3614 illustrates forming an encapsulation layer for encapsulating the one or more inorganic electronic circuit elements, the paste mask layer, the base circuit layer, and the microcircuit.

[0240] In one or more embodiments described above, an SBS fiber mat is used. Those skilled in the art will appreciate that this is for illustrative purposes only. In one or more embodiments, the fiber mat may comprise styrene-isoprene-styrene block copolymer, styrene-polybutadiene-styrene block copolymer, styrene-butadiene block copolymer, poly(styrene-block-butadiene-block-styrene) copolymer, polyisoprene rubber, butadiene rubber, polyurethane, thermoplastic polyurethane, polyvinyl alcohol, polycaprolactone, polycaprolactone, or mixtures thereof. In certain embodiments, the biocompatible elastomeric fiber comprises poly(styrene-block-butadiene-block-styrene).

[0241] As used herein, the term "electronic skin" or "eskin" refers to soft and stretchable electronic devices that mimic the functions of human or animal skin.

[0242] As used herein, the terms "fibrous mat" and "fiber mat" are used interchangeably to refer to a fiber-based, layered, porous woven or textile fabric. The fiber mat can be used as various layers in a bioelectronic system or device or electronic device, such as a substrate, an intermediate layer, an encapsulation layer, or any other suitable layer.

[0243] As used herein, the term "fiber" refers to an elongated, slender, thread-like and / or filamentous structure.

[0244] As used herein, the terms "flexible," "bendable," or "stretchable" refer to the ability of a material, structure, device, or device element to be deformed into a curved or bent shape or stretched without undergoing deformation that introduces significant strain, such as strain that characterizes the failure point of the material, structure, device, or device element, such that it remains intact during bending, folding, or stretching.

[0245] As used herein, the term "rigid" refers to the non-flexible, inflexible, or inextensible capability of a material, structure, device, or device element.

[0246] It should also be understood that any features in the embodiments of the present disclosure can be combined together and are not necessarily applied in isolation from each other. Those skilled in the art can easily make similar combinations of two or more features from the above-mentioned embodiments or preferred forms of the present disclosure.

[0247] Unless otherwise defined, the technical and scientific terms used herein have the simple meanings commonly understood by those skilled in the art in the relevant art of the exemplary embodiments. The embodiments are shown in non-limiting examples. Based on the embodiments disclosed above, various modifications that can be conceived by those skilled in the art fall within the spirit of the exemplary embodiments.

Claims

1. A permeable bioelectronic system comprising: Stretchable multilayer circuits, including liquid metal LM; and LM interconnects for bonding one or more inorganic electronic circuit elements to the stretchable multilayer circuit. 2 . The permeable bioelectronic system of claim 1 , wherein the LM comprises gallium, a gallium alloy, or a mixture thereof. 3 . The permeable bioelectronic system of claim 1 , wherein the LM comprises a eutectic gallium-indium alloy EGaIn, a gallium-indium-tin alloy GaInSn, or a mixture thereof.

4. The permeable bioelectronic system of claim 1, wherein the LM interconnect comprises a hybrid liquid metal (hLM) solder.

5. The permeable bioelectronic system of claim 4, wherein the hLM solder comprises a combination of partially oxidized liquid metal oLM and LM. The permeable bioelectronic system of claim 4 , wherein the hLM solder comprises a eutectic gallium-indium alloy (EGaIn).

7. The permeable bioelectronic system of claim 1, wherein the stretchable multilayer circuit comprises a plurality of layers, and one or more of the plurality of layers comprises a fiber mat.

8. The permeable bioelectronic system of claim 7, wherein the fiber mat comprises styrene-isoprene-styrene block copolymer, styrene-polybutadiene-styrene block copolymer, styrene-butadiene block copolymer, poly(styrene-block-butadiene-block)-styrene) copolymer, polyisoprene rubber, butadiene rubber, polyurethane, thermoplastic polyurethane, polyvinyl alcohol, polycaprolactone, polycaprolactone, or mixtures thereof.

9. The permeable bioelectronic system according to claim 1, wherein the stretchable multilayer circuit comprises a plurality of layers electrically connected through stretchable vertical interconnection channels (VIA) filled with LM.

10. The permeable bioelectronic system of claim 1 , wherein the stretchable multilayer circuit comprises: a first LM circuit layer comprising a micro-patterned LM; a second LM circuit layer including a micro-patterned LM and formed on the first LM circuit layer; and A paste mask layer is formed on the second LM circuit layer and configured to bond the one or more inorganic electronic circuit elements. 11 . The permeable bioelectronic system of claim 10 , wherein each of the first LM circuit layer and the paste mask layer comprises a fibrous styrene-butadiene-styrene (SBS) mat.

12. The permeable bioelectronic system according to claim 10, wherein the stretchable multilayer circuit further comprises an encapsulation layer formed on the paste mask layer, for encapsulating the first LM circuit layer, the second LM circuit layer and the paste mask layer.

13. The permeable bioelectronic system of claim 12, wherein the encapsulation layer comprises a fibrous styrene-butadiene-styrene (SBS) mat.

14. The permeable bioelectronic system of claim 10, wherein the stretchable multilayer circuit comprises a silver (Ag) circuit sandwiched between a first fibrous styrene-butadiene-styrene (SBS) mat and a second fibrous SBS mat, in, The first fibrous SBS mat is located between the first LM circuit layer and the second fibrous SBS mat, and the first SBS fiber mat is thicker than the second fibrous SBS mat.

15. The permeable bioelectronic system according to claim 1, wherein the stretchable multilayer circuit comprises a microcontroller unit embedded with near field communication (NFC).

16. A method for fabricating a permeable bioelectronic system, the method comprising: creating a microcircuit having a first side and a second side; transferring the microcircuit to a fiber mat such that a first side of the microcircuit contacts the fiber mat; forming a paste mask layer on a second side of the microcircuit; forming a base circuit layer on a side of the fiber mat, the side being remote from the first side of the microcircuit, the base circuit layer comprising liquid metal LM; forming a stretchable vertical interconnection channel VIA for electrically connecting the microcircuit, the base circuit layer and the paste mask layer, wherein the VIA is filled with LM; forming a hybrid liquid metal hLM solder on the paste mask layer for bonding one or more inorganic electronic circuit elements; and An encapsulation layer is formed for encapsulating the one or more inorganic electronic circuit elements, the paste mask layer, the base circuit layer and the microcircuit.

17. The method of claim 16, wherein the step of transferring the microcircuit to the fiber mat comprises: A polymer solution was prepared by dissolving styrene-butadiene-styrene (SBS) polymer in a mixed solvent of tetrahydrofuran and dimethylformamide; and The polymer solution is electrospun onto the microcircuit.

18. The method according to claim 16, wherein the step of forming the paste mask layer comprises: selectively wetting the microcircuit by using a LM; and An SBS mat was electrospun onto the microcircuit.

19. The method according to claim 16, wherein the step of forming the base circuit layer comprises: stenciling LM traces onto the side of the fiber mat; and An SBS mat was electrospun onto the side of the fiber mat where the LM traces were printed.

20. The method according to claim 16, wherein the step of forming the VIA comprises: forming through-holes by laser cutting the microcircuit, the base circuit layer, and the paste mask layer; and The through-holes are filled with LM.

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