Patent Application
20250107925
This invention relates to a biopolymer/plant-based substrate for flexible and stretchable electronics and a method of fabricating the same. The biopolymer/plant-based substrate may be from plant pollen.
The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.
The development of ultrathin, portable, and flexible electronic devices and components has catalyzed rapid technological advances across a wide range of domains, including medicine, telecommunication, energy, and robotics. Synthetic polymers such as polyimide (PI), polystyrene, polypropylene, and polyethylene terephthalate (PET) are widely used as substrate materials in applications that incorporate transistors, light-emitting diodes, biosensors, and organic photovoltaics. However, the use of these chemically processed synthetic polymers, which are non-reusable and non-degradable, can lead to environmental degradation on land and in oceans. Consequently, the development and deployment of materials derived from abundant natural resources that are sustainable, eco-friendly, biocompatible, and biodegradable are receiving increasing attention.
Researchers have explored materials such as chitin, nanocellulose, and silk as substrate materials to replace synthetic chemicals in electronics applications. For example, chitin, a fibrous material, has been considered a candidate substrate material for organic light-emitting diodes (OLEDs), glucose sensors, and heaters owing to its robustness, non-toxicity, and biocompatibility. In addition, nanocellulose-based substrates with a low surface roughness, high transparency, and high elastic modulus (E=6-17 GPa) have been developed for use in energy storage devices, OLEDs, and organic photovoltaics. Notably, the extraction of chitin and cellulose from diverse sources such as crabs, wood, algae, and bacteria is challenging in terms of the high extraction costs, low yield, and considerable processing time. Silk-based substrates exhibit high mechanical strength (E=5-12 GPa) and can be conveniently fabricated in large volumes. However, despite its excellent biocompatibility and biodegradability, silk is highly soluble in water, which limits its long-term reliable use in flexible and stretchable electronics.
Thus, there exists a need for alternatives to synthetic materials for electronic applications and more specifically for flexible and stretchable electronics.
It has been surprisingly found that a material that solves some or all of the problems discussed hereinbefore can be manufactured based on a pollen-based substrate material.
Aspects and embodiments of the invention will now be discussed by reference to the following non-limiting clauses.
1. A conductive composite material, comprising:
2. The conductive composite material according to Clause 1, wherein the pollen-based substrate comprises a plurality of pollen microgels.
3. The conductive composite material according to Clause 2, wherein the plurality of pollen microgels are derived from pollen grains from one or more of the group selected from sunflower (Helianthus annuus L.) pollen grains, pine (Pinus taeda) pollen grains, daisy (Baccharis halimifolia L.) pollen grains, cattail (Typhae angustfolia) pollen grains, camellia (Camellia Sinensis L.) pollen grains, bee pollen grains, and lycopodium (Lycopodium clavatum) spores (S-type).
4. The conductive composite material according to any one of the preceding clauses, wherein the elastomeric adhesive layer on top of the pollen-based substrate layer is formed from a silicone elastomer or an acrylic adhesive.
5. The conductive composite material according to Clause 4, wherein the elastomeric adhesive layer on top of the pollen-based substrate layer is a platinum-cured silicone elastomer.
6. The conductive composite material according to any one of the preceding clauses, wherein the biocompatible polymer substrate layer on top of the elastomeric adhesive layer is formed from one or more of polyimide, polyethylene terephthalate (PET), a polyurethane, and a parylene.
7. The conductive composite material according to Clause 6, wherein the biocompatible polymer substrate layer on top of the elastomeric adhesive layer is formed from polyimide.
8. The conductive composite material according to any one of the preceding clauses, wherein the metal layer on top of the biocompatible polymer substrate layer is formed from one or more of the group consisting of chromium (Cr), titanium (Ti), copper (Cu), platinum (Pt), silver (Ag), and gold (Au).
9. The conductive composite material according to Clause 8, wherein the metal layer on top of the biocompatible polymer substrate layer is presented as a first layer and a second layer, with the first layer in direct contact with the biocompatible polymer substrate layer.
10. The conductive composite material according to Clause 9, wherein the first layer is formed from one or more of chromium (Cr), titanium (Ti), and copper (Cu), and the second layer is formed from one or more of platinum (Pt), silver (Ag), and gold (Au), optionally wherein the first layer is chromium (Cr) and the second layer is gold (Au).
11. The conductive composite material according to Clause 9 or Clause 10, wherein the first layer has a thickness of from 1 to 50 nm, such as from 2 to 25 nm, such as about 5 nm and the second layer has a thickness of from 100 to 250 nm, such as from 125 to 200 nm, such as about 150 nm.
12. The conductive composite material according to any one of the preceding clauses, wherein the metal layer is patterned to provide electrodes.
13. The conductive composite material according to any one of the preceding clauses, wherein the adhesive layer is an acrylic adhesive.
14. A method of forming a conductive composite material as described in any one of Clauses 1 to 13, the method comprising the steps of:
15. The method according to Clause 14, wherein the conductive intermediate is provided by the steps of:
16. The method according to Clause 15, wherein the metal layer if formed from a first metal layer and a second metal layer, where the first metal layer is formed from one or more of chromium (Cr), Titanium (Ti), and Copper (Cu), and the second metal layer is formed from one or more of Platinum (Pt), Silver (Ag), and gold (Au), optionally wherein the first layer is chromium (Cr) and the second layer is gold (Au).
17. The method according to Clause 16, wherein the first metal layer has a thickness of from 1 to 50 nm, such as from 2 to 25 nm, such as about 5 nm and the second metal layer has a thickness of from 100 to 250 nm, such as from 125 to 200 nm, such as about 150 nm.
18. A stretchable biopolymer-based heating pad, comprising:
19. The stretchable biopolymer-based heating pad according to Clause 18, wherein the encapsulation coating further encapsulates the pollen-based substrate layer.
20. The stretchable biopolymer-based heating pad according to Clause 18 or Clause 19, wherein, when present, the metal layer on top of the pollen-based substrate layer is formed from one or more of the group consisting of chromium (Cr), titanium (Ti), copper (Cu), platinum (Pt), silver (Ag), and gold (Au).
21. The stretchable biopolymer-based heating pad according to Clause 20, wherein the metal layer on top of the pollen-based substrate layer is presented as a first layer and a second layer, with the first layer in direct contact with the pollen-based substrate layer, optionally wherein:
22. The stretchable biopolymer-based heating pad according to any one of Clauses 18 to 21, wherein the pollen-based substrate comprises a plurality of pollen microgels.
23. The stretchable biopolymer-based heating pad according to Clause 22, wherein the plurality of pollen microgels are derived from pollen grains from one or more of the group selected from sunflower (Helianthus annuus L.) pollen grains, pine (Pinus taeda) pollen grains, daisy (Baccharis halimifolia L.) pollen grains, cattail (Typhae angustfolia) pollen grains, camellia (Camellia Sinensis L.) pollen grains, bee pollen grains, and lycopodium (Lycopodium clavatum) spores (S-type).
24 The stretchable biopolymer-based heating pad according to any one of Clauses 18, 19 and 22 to 23, wherein, when present, the cured polymeric material is selected from one or more of a polyurethane and a silicone elastomer, optionally wherein the cured polymeric material is a polyurethane.
25. The stretchable biopolymer-based heating pad according to any one of Clauses 18, 19 and 22 to 24, wherein, when the cured polymeric material is present, the metal in the cured polymeric material is selected from one or more of the group consisting of platinum (Pt), silver (Ag), and gold (Au), optionally wherein the metal is silver (Ag).
26. The stretchable biopolymer-based heating pad according to any one of Clauses 18 to 25, wherein the encapsulation coating is a silicone elastomer, optionally wherein the encapsulation coating is polydimethylsiloxane (PDMS).
27. A method of forming a stretchable biopolymer-based heating pad as described in any one of Clauses 18 to 26, wherein the method comprises the steps of:
28. The method according to Clause 27, wherein the encapsulating step (cii) further encapsulates the pollen-based substrate layer.
29. The method according to Clause 27 or Clause 28, wherein the heating pad intermediate is formed by the steps of:
30. The method according to Clause 29, wherein the patterned pollen-based substrate layer is formed by:
It has been surprisingly found that pollen grains can provide a substrate material that is readily available, economical, biodegradable, and biocompatible that can be used as a replacement for synthetic substrate materials in electronics. This material can be used to create a variety of flexible shapes with customized mechanical, geometrical, electronic, and functional properties and performance characteristics such as thermal, chemical, and mechanical stability and optical transparency. Thus, in a first aspect of the invention, there is provided a conductive composite material, comprising:
In embodiments herein, the word “comprising” may be interpreted as requiring the features mentioned, but not limiting the presence of other features. Alternatively, the word “comprising” may also relate to the situation where only the components/features listed are intended to be present (e.g. the word “comprising” may be replaced by the phrases “consists of” or “consists essentially of”). It is explicitly contemplated that both the broader and narrower interpretations can be applied to all aspects and embodiments of the present invention. In other words, the word “comprising” and synonyms thereof may be replaced by the phrase “consisting of” or the phrase “consists essentially of” or synonyms thereof and vice versa.
The phrase, “consists essentially of” and its pseudonyms may be interpreted herein to refer to a material where minor impurities may be present. For example, the material may be greater than or equal to 90% pure, such as greater than 95% pure, such as greater than 97% pure, such as greater than 99% pure, such as greater than 99.9% pure, such as greater than 99.99% pure, such as greater than 99.999% pure, such as 100% pure.
As used herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a composition” includes mixtures of two or more such compositions, and the like.
Pollen is primarily composed of structural proteins, lipids, and sporopollenin in the exine (outer layer), and cellulose, hemicellulose, and pectin in the intine (inner layer). Sporopollenin has high strength and can protect cellular materials from harsh environmental conditions such as high or low temperatures or exposure to acidic or alkaline solvents. Considering its practically indestructible structural characteristics, sporopollenin may be considered for several applications such as micromotors and drug delivery systems. Pollen is also less expensive than commercial polymers such as polylactic acid (PLA) and polyamide (PA).
The pollen-based substrate layer may be made from any suitable pollen-based material. For example, a suitable pollen-based substrate may be a material that comprises a plurality of pollen microgels.
The pollen microgels may be obtained from pollen grains from a suitable source (e.g. sunflower and/or commercial raw bee pollen). The process to make pollen microgels may involve defatting the pollen, which can then be mixed with a solution (e.g. 10% w/w) of KOH at an elevated temperature (e.g. about 80° C.) for a suitable period of time (e.g. about 5 hours) to produce soft pollen microgels. These soft pollen microgels can then be collected and washed, cast into a mold and then left to dry to produce a pollen-based substrate comprising the soft pollen microgels, which has a microscopically rough surface topography, owing to the intrinsic nano- and microstructures of the self-assembled pollen grains. As will be appreciated, the dimensions of the substrate are only limited by the casting mold used. It will be appreciated that any suitable pollen may be used to manufacture a pollen-based substrate (e.g. sunflower pollen).
As noted hereinbefore, the plurality of pollen grains may be derived from any suitable source. For example, the plurality of pollen microgels may be derived from pollen grains from one or more of the group including, but not limited to, sunflower (Helianthus annuus L.) pollen grains, pine (Pinus taeda) pollen grains, daisy (Baccharis halimifolia L.) pollen grains, cattail (Typhae angustfolia) pollen grains, camellia (Camellia Sinensis L.) pollen grains, bee pollen grains, and lycopodium (Lycopodium clavatum) spores (S-type).
The elastomeric adhesive layer may be any suitable adhesive material that can be used in a flexible and stretchable electronic applications. For example, the elastomeric adhesive layer on top of the pollen-based substrate layer is formed from a silicone elastomer and/or an acrylic adhesive. The silicone elastomer may be any suitable silicone elastomer. In more particular embodiments of the invention that may be mentioned herein, the elastomeric adhesive layer on top of the pollen-based substrate layer may be a platinum-cured silicone elastomer. Examples of suitable silicone elastomers include polydimethylsiloxane (PDMS), and platinum-cure silicones, such as those sold under the tradenames Silbione™, EcoFlex™ silicones, and Solaris™ silicones. Any suitable acrylic adhesive may be used herein and in certain embodiments the adhesive layer may be an acrylic adhesive.
The biocompatible polymer substrate layer on top of the elastomeric adhesive layer may be any suitable polymeric material. More particularly, it may be any suitable polymeric material that will not dissolve in any processing conditions applied during the manufacture of the conductive composite material discussed herein. In particular embodiments of the invention that may be mentioned herein, the biocompatible polymer substrate layer on top of the elastomeric adhesive layer may be formed from one or more of polyimide, polyethylene terephthalate (PET), a polyurethane, and a parylene. In more particular embodiments of the invention that may be discussed herein, the biocompatible polymer substrate layer on top of the elastomeric adhesive layer may be formed from polyimide
The metal layer on top of the biocompatible polymer substrate layer may be formed from any suitable metal or alloy. In particular embodiments of the invention that may be mentioned herein, the metal layer on top of the biocompatible polymer substrate layer may be formed from chromium (Cr), titanium (Ti), copper (Cu), platinum (Pt), silver (Ag), gold (Au), and alloys thereof.
In certain embodiments the metal layer may actually be in the form of two layers. That is, the metal layer on top of the biocompatible polymer substrate layer may be presented as a first layer and a second layer, with the first layer in direct contact with the biocompatible polymer substrate layer. The first layer may be formed from any suitable metal. For example, the metal in the first layer may be formed from one or more of chromium (Cr), titanium (Ti), and copper (Cu), and the second layer may be formed from one or more of platinum (Pt), silver (Ag), and gold (Au). In particular embodiments of the invention that may be mentioned herein, the first layer may be chromium (Cr) and the second layer may be gold (Au).
The metal layer (as a whole) may have any suitable thickness, provided that it is useful in flexible electronics. In embodiments where the metal layer is provided as a first and second layer, then the first layer may have a thickness of from 1 to 50 nm, such as from 2 to 25 nm, such as about 5 nm and the second layer may have a thickness of from 100 to 250 nm, such as from 125 to 200 nm, such as about 150 nm. As will be appreciated, the sum totals of these values may also provide a suitable thickness for the metal layer if it is formed from a single layer.
As noted herein, the conductive composite material may be useful for using in flexible electronics. With that in mind, it will be appreciated that the metal layers may be patterned to provide suitable circuitry and/or electrodes. For example, in certain embodiments of the invention that may be mentioned herein, the metal layer may be patterned to provide electrodes.
As discussed herein, the patterning process will generally take place after the after the deposition of the metal layer on the biocompatible polymer substrate layer. Given this, the biocompatible polymer substrate layer may also be patterned at the same time as the metal layer. Additionally or alternatively, the patterning may take place after assembly of the conductive composite material, so that all layers are patterned.
The conductive composite material disclosed herein may be used in electronic devices for health monitoring and wearable wireless heating, amongst other uses. Further applications include, but are not limited to wearable sensors, implantable devices, and soft robotics.
The pollen-based substrate layer disclosed herein can function as an ideal platform for a broad range of applications such as wearable biomedical devices, flexible/stretchable electronics, and soft robotics, and represents a low-cost and scalable solution to replace plastic substrates across electronic sensor applications.
The conductive composite material as disclosed herein may be formed by any suitable method. In a second aspect of the invention, there is provided a method of forming a conductive composite material as described herein, the method comprising the steps of:
The conductive intermediate in the method above may be provided by the steps of:
As these methods provide the conductive composite material disclosed hereinbefore, a discussion of the same materials mentioned hereinbefore will be omitted for the purposes of brevity.
In a further aspect of the invention, there is provided a stretchable biopolymer-based heating pad, comprising:
While this aspect of the invention is discussed herein in relation to a heating pad, it will be appreciated that this aspect may relate to any device or apparatus having the components mentioned above, which may have other alternative applications.
The encapsulation coating may in certain embodiments only encapsulate the cured polymeric layer or the metal layer. However, in other embodiments that may be mentioned herein the encapsulation coating may further encapsulate the pollen-based substrate layer.
When the cured polymeric layer or the metal layer on top of the pollen-based substrate layer is a metal layer it may be formed from any suitable metal. For example, the metal layer on top of the pollen-based substrate layer may be formed from one or more of the group consisting of chromium (Cr), titanium (Ti), copper (Cu), platinum (Pt), silver (Ag), and gold (Au). This material may be provided
As mentioned previously, the metal layer on top of the pollen-based substrate layer may be presented as a first layer and a second layer, with the first layer in direct contact with the pollen-based substrate layer. Given this, the first layer may be formed from one or more of chromium (Cr), titanium (Ti), and copper (Cu), and the second layer may be formed from one or more of platinum (Pt), silver (Ag), and gold (Au), optionally wherein the first layer is chromium (Cr) and the second layer is gold (Au). Additionally or alternatively, the first layer may have a thickness of from 1 to 50 nm, such as from 2 to 25 nm, such as about 5 nm and the second layer may have a thickness of from 100 to 250 nm, such as from 125 to 200 nm, such as about 150 nm.
The pollen-based substrate layer is identical to the pollen-based substrate layer described in relation to the conductive composite material in the first aspect of invention hereinbefore. As such, discussion of the pollen-based substrate layer to this aspect of invention is omitted for the sake of brevity.
When the cured polymeric layer or the metal layer on top of the pollen-based substrate layer is a cured polymeric layer, then it may be provided in the form of a cured polymeric material and a metal. For example, the metal may be distributed within the cured polymer in the form of metal flakes.
The cured polymeric material may be any suitable cured polymeric material for use in flexible electronics. For example, the cured polymeric material may be selected from one or more of a polyurethane and a silicone elastomer. In particular embodiments of the invention that may be discussed herein, the cured polymeric material may be a polyurethane.
The metal used in the metal in the cured polymeric material may be any suitable metal. For example, the metal in the cured polymeric material may be selected from one or more of the group consisting of platinum (Pt), silver (Ag), and gold (Au), optionally wherein the metal is silver (Ag). This metal may be in any suitable form that enables it to be distributed within the cured polymeric material. For example, the metal may be provided in the form of metal flakes.
As discussed below, the cured polymeric material and the metal may be printed onto the pollen-based substrate layer. As such, a formulation comprising an uncured polymeric material suitable for curing and a metal (e.g. metal flakes) may be used for the printing step.
As will be appreciated, the encapsulation coating may be any suitable material that can be used in a flexible and wearable electronic device. For example, the encapsulation coating may be a silicone elastomer. Examples of suitable silicone elastomers include polydimethylsiloxane (PDMS), and platinum-cure silicones, such as those sold under the tradenames Silbione™, EcoFlex™ silicones, and Solaris™ silicones. In particular embodiments of the invention, the encapsulation coating may be polydimethylsiloxane (PDMS).
In a further aspect of the invention, there is provided a method of forming a stretchable biopolymer-based heating pad as described herein, wherein the method comprises the steps of:
The encapsulation coating is the same as described hereinbefore. Therefore, the encapsulation coating may be a silicone. More particularly, the encapsulation coating may be polydimethylsiloxane (PDMS).
In the method above, the encapsulating step (cii) further encapsulate the pollen-based substrate layer. That is, the encapsulating step may not only encapsulate the cured polymeric layer or a metal layer on top of the pollen-based substrate, but also the pollen-based substrate too.
The heating pad intermediate may be formed by the steps of:
In such embodiments, the patterned pollen-based substrate layer may be formed by:
Further aspects and embodiments of the invention are described below.
The invention relates to a biopolymer/plant-based substrate for flexible and stretchable electronics and a method of fabricating the same. The biopolymer/plant-based substrate may be from plant pollen.
In a further aspect of the invention, there is provided a biopolymer substrate, comprising:
In a further aspect of the invention, there is provided a stretchable biopolymer-based heating pad, comprising:
In a further aspect of the invention, there is provided a method to fabricate a biopolymer substrate, comprising the steps of:
In a further aspect of the invention, there is provided a method to fabricate a stretchable biopolymer-based heating pad, comprising the steps of:
In a further aspect of the invention, there is provided a biopolymer substrate, comprising:
In a further aspect of the invention, there is provided a stretchable biopolymer-based heating pad, comprising:
In a further aspect of the invention, there is provided a method to fabricate a biopolymer substrate, comprising the steps of:
In a further aspect of the invention, there is provided a method to fabricate a stretchable biopolymer-based heating pad, comprising the steps of:
The present disclosure provides a pollen-based substrate and its use in flexible and stretchable electronics. The pollen-based substrate enabled compelling advantages over conventional synthetic plastics in terms of natural sourcing, environmental degradation, and sustainable processing. Various analyses were performed to characterize the pollen-based substrate in terms of its physical, chemical, and thermal stability under appropriate practical conditions of intended applications. As proofs of concept, the present disclosure provides a skin-mountable stretchable EP sensor and heating patch based on the pollen-based substrate by using indirect and direct fabrication approaches. These embodiments are only examples, and are not intended to limit the scope, applicability of the present disclosure. The pollen-based substrate can function as an ideal platform for a broad range of applications such as wearable biomedical devices, flexible/stretchable electronics, and soft robotics, and represents a low-cost and scalable solution to replace plastic substrates across electronic sensor applications.
Further aspects and embodiments of the invention will now be discussed by reference to the following non-limiting examples.
Further aspects and embodiments of the invention will be discussed by reference to the following non-limiting examples.
Chemical analysis was conducted via Fourier-transform infrared (FT-IR) spectroscopy (Frontier, PerkinElmer) with a diamond cell attenuated total reflection accessory module. Transmittance was obtained using an ultraviolet-visible (UV-Vis) spectrometer (UV-2700, SHIMADZU) and thermal analysis was conducted using a Q500 instrument (TA Instruments).
Optical micrograph and SEM images were obtained using a Nikon TS100 and a JSM-7600F Schottky field-emission scanning electron microscope (JEOL), respectively. A Park XE-100 device was used to obtain atomic force microscopy (AFM) images (non-contact mode, scan area=20 μm×20 μm, scan rate=0.2-0.5 Hz, NX-10, Park Systems) at RT by using an aluminum reflex-coated silicon cantilever, PPP-NCHR (spring constant≈42 N/m, Nanosensors).
Young's modulus measurement by AFM
To measure the Young's modulus through the AFM technique, a gold reflex-coated silicon cantilever, biosphere B2000-NCH (diameter=4 μm, spring constant≈40 N/m, Nanotools, Germany), was used to obtain the force-displacement (FD) curve from 16 points of the selected area in the pollen-based substrate (lateral dimension=10 μm×10 μm, approach speed=0.8 μm/s, and maximum loading force=6.0 uN). To remove the contaminants, the AFM cantilever was rinsed with water and ethanol, followed by UV cleaning for 30 min. To calculate Young's modulus, the Hertzian model was used for curve fitting in XEI (Park Systems) and Python. We determined Young's modulus from the FD curve according to the equation
where E is Young's modulus, v is Poisson's ratio, a is the contact radius, R is the radius of the sphere, and δ is the indentation depth. v was set as 0.5, which is a typical value for biological materials.
A tensile test was performed using electromechanical universal test systems (MTS 42, MTS Systems Corporation), and the tensile speed was 1 cm/min at RT. The sample was prepared using a dumbbell-shaped cutter (dimension of the center=7.6 mm×3.2 mm, SDL-100, DUMBBELL CO., LTD.). The thickness and weight were measured using a micrometer (MDC-25PX, Mitutoyo Asia Pacific Pte Ltd.) and analytical weighing balance (BBX 22, BOECO, Germany), respectively. Moreover, a resistance-strain test was conducted using a dynamic mechanical analyzer (ESM303, Mark-10 Corp.) and source measure unit (Keithley 2400, Tektronix, Inc.). The temperature was measured using an IR camera (SC645, FLIR Systems, Inc.).
Recording of EP Signals from the Skin
The EP sensor was attached to the forearm skin and chest of a volunteer (age: 30 y) to capture the EMG and ECG signals, respectively. The generated EP signals were recorded using a preamplifier and data acquisition unit (Octal Bio Amp and Power Lab, ADInstruments) and transmitted to an external computing system. A commercial software (LabChart, ADInstruments) was used to process the collected data with a 60 Hz notch filter with a bandpass filter admitting frequencies of 10-500 Hz and 0.5-100 Hz for the EMG and ECG signals, respectively. The conventional EP recording electrodes were RedDot™ (3M).
The deformations of the pollen-based substrate, Ag flake/PU, and PDMS were modeled by linear elastic behavior with the effective mechanical modulus (E) being 410 MPa, 60.8 GPa, and 1.84 MPa, respectively. The rule of mixtures was used to calculate the elastic modulus of Ag flake/PU ink (80% Ag and 20% PU). The entities were modeled using eight-node brick element with reduced integration (C3D8R) solid elements. Displacement boundary conditions were applied to both edges of the structure to produce uniaxial tension for strains of 10%, 20%, 30%, and 40%.
To produce the defatted Camellia pollen particles, 250 g of natural bee pollen granules (Xi'an Yuenum Biological Technology Company Ltd., Shannxi Xian, China) were refluxed with 500 mL of acetone (Sigma-Aldrich) in a round-bottom flask (1 L) under stirring (200 rpm, IKA® RCT) at 50° C. for 3 h. After stirring the pollen granules at 50° C. for 1 h with 1 L of deionized (DI) water (Direct-Q® Water Purification System, Merck), the pollen solution was sequentially filtered using a nylon mesh (ELKO Filtering Co., diameter=6 μm) and filter paper (diameter=6 μm, Whatman) to remove the contaminant. The pollen particles were refluxed in 500 ml of acetone while stirring at 50° C. for 3 h. Subsequently, the particles were subjected to vacuum filtration and dried for 12 h in a fume hood to remove acetone residues. Next, 20 g of dried pollen powder was refluxed with 250 mL of diethyl ether (Sigma-Aldrich) while stirring at 25° C. for 2 h, followed by two cycles of vacuum filtration to remove the low-polarity fat compound. Finally, the pollen solution, after stirring with diethyl ether at 25° C. for 12 h, was filtrated and dried for 12 h in a fume hood.
To remove the cytoplasm, the defatted pollen particles were suspended in 200 ml of potassium hydroxide (KOH) solution (Sigma-Aldrich, 10 wt % in DI water) to form a suspension 102. The suspension 102 was refluxed while stirring at 80° C. for 2 h in a round-bottom flask in a step 104. The suspension was then transferred to a conical tube 106 and centrifuged at 4500 rpm for 5 min (Allegra X-15R, Beckman Coulter, Inc.) to remove the KOH solution. The pollen particles were resuspended in 40 mL of fresh KOH and the suspension was centrifuged again in a washing step 108. The KOH washing step 108 was repeated for five times. After the fifth KOH washing step 108, the supernatant was discarded from the suspension 110 and the pollen particles were collected in a beaker (1 L) with 300 mL of DI water. The suspension was incubated while stirring at 50° C. for 5 min. The suspension was then filtered using a nylon mesh (pore size=10 μm) in a step 112. The filtration step 112 was repeated five times to neutralize the pollen solution 114 to a pH level of 7-7.5. After the fifth filtration step 112, the pollen solution 114 was cast into a mold 118 in a step 116 and then left to dry to produce a pollen-based substrate 122 comprising the soft pollen microgel.
Camellia pollen was selected to decrease the surface roughness of the substrate, as this pollen's surface was found to be smoother than that of other plants such as sunflower (Helianthus annuus L.) and lycopodium (Lycopodium clavatum) as observed in the SEM images in
The lipids and proteins that cause allergic reactions to pollen were removed during defatting and subsequent treatment with KOH, as indicated by the Fourier-transform infrared (FT-IR) spectroscopic analysis result in
To illustrate the deformability of the pollen-based substrate and its amenability to being folded into complex shapes without cracking, an origami arrangement in the shape of a crane was made as shown in
To confirm the potential for electronic applications using the pollen-based substrate material, an electrode was formed on each of the pollen-based substrate and comparison substrates i.e., polycarbonate (PC), polyimide (PI) and polyethylene terephthalate (PET) via 3D printing. As shown in
To evaluate the thermal stability of the pollen-based substrate, the dimensions were measured after heating at different temperatures: room temperature (RT), 100° C., 200° C., and 250° C. for 30 minutes. As shown in
To demonstrate the suitability of the pollen-based substrate for flexible electronics, a pollen-based electrophysiological (EP) sensor and a stretchable pollen-based heating pad are provided by adopting two widely used fabrication methods: indirect (transfer printing) and direct (patterning) methods.
First, an electrophysiological (EP) sensor, consisting of reference, ground, and recording electrodes, was fabricated on the pollen-based substrate through transfer printing.
For reference,
High-fidelity recordings of electromyogram (EMG) and electrocardiogram (ECG) signals were obtained by attaching the fabricated pollen substrate-based EP sensor on the right forearm and chest of a healthy adult as shown in
Next, a stretchable pollen substrate-based heating patch was fabricated through direct (patterning) printing.
The Ag flake/PU ink was prepared by first dissolving 1.48 g of PU (Elastollan Soft 35A, BASF) in a solution of 1.56 mL of N,N-dimethylformamide (DMF) (Sigma-Aldrich) and 4.27 ml of tetrahydrofuran (THF) (Sigma-Aldrich). Next, 5.92 g of Ag flakes (99.95%, average particle size (APS) 2-5 μm; 47MR-10F, Inframat Advanced Materials) was mixed in a planetary mixer (ARE-310, Thinky U.S.A., Inc.) for 10 min at 2000 rpm. The resulting mixture was loaded into a 3 cc syringe (Nordson EFD) and centrifuged at 2500 rpm for 2 min to remove the air bubbles trapped in the mixture.
The printed Ag flake/PU layer was cured in a vacuum oven at 50° C. for 4 h, followed by automated dispensing of PDMS to form an encapsulation layer in a step 1318 to form the pollen-substrate based heating patch 1320. The external power source was a DP832 device (Rigol).
For reference, the pollen-based substrate was successfully patterned into a stretchable Joule heating configuration using a laser cutter that induce no thermal damage or distortion, as indicated in the optical images in
To characterize the resulting pollen substrate-based heating patch, the relative change in the resistance which is the ratio of the instantaneous resistance to the resistance at zero strain, R/R0, of the heating patch was measured at uniaxial stretching of up to 65%. The result is shown in
Articular thermotherapy is often practiced to alleviate joint pain and stiffness by inducing vasodilation to promote blood flow to the target area. To achieve therapeutic results, conformal contact with the skin must be ensured to realize efficient heat transfer and precise temperature control (˜ 40° C.). To demonstrate this, the above pollen substrate-based heating patch was applied on the wrist of a human subject and the results discussed hereon.
For reference,
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SG2023/050008 | 1/5/2023 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63297386 | Jan 2022 | US |
