System and method for lignin ink composition

Abstract

This disclosure relates to compositions of lignin that are useful in the chemical arts, such as in the manufacture of products, such as inks, films, and devices. In particular, the present disclosure pertains to tribonegative compositions and films including lignin, a binder such as gelatin, and a plasticizer such as urea.

Description

[0001] Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0002] SYSTEM AND METHOD FOR LIGNIN INK COMPOSITION

[0003] RELATED APPLICATIONS

[0004] This application claims the benefit of U.S. Provisional Application No. 63 / 735,387, filed December 18, 2024, the entire disclosure of which is incorporated herein by reference.

[0005] STATEMENT OF GOVERNMENT RIGHTS

[0006] This invention was made with government support under 2019-38502-30120 awarded by the USDA. The government has certain rights in the invention.

[0007] BACKGROUND

[0008] Cardiovascular disease is the leading cause of death in the U.S., with over 1.04 million deaths annually. Longitudinal monitoring of cardiovascular abnormalities can enable timely intervention and personalized treatment to prevent progression and improving outcomes. Cardiac mortality can decrease by up to 67% if conditions such as ventricular fibrillation are treated within 60 seconds of onset. Mental workload stress increases cardiovascular disease risk by 1.2 to 2.0 times, affecting over 15% of U.S. adults. Current methods assess mental workload by deriving heart rate and variability from electrocardiogram (ECG). However, ECG requires multiple electrodes positioned specifically on the chest, making its long-term use cumbersome. Moreover, ECG cannot directly measure peripheral circulatory changes that are sensitive to stress. PPG allows monitoring of these changes but is less reliable because of factors such as skin pigmentation and low perfusion. Wearable sensors that measure skin and artery motion can address PPG limitations and offer better insights into cardiovascular dynamics, although they face challenges such as limited dynamic range, poor signal-to-noise ratios, and power consumption constraints.

[0009] Skin-integrated triboelectric sensors (SITS) have garnered significant interest for tactile perception, motion sensing, and healthcare monitoring. SITS converts subtle skin deformations into sensing signals via contact triboelectrification between the skin and sensor. The strong positive triboelectric properties of the human skin necessitate triboelectric negative materials for effective skin contact in SITS. For example, high-performance skin-integrated triboelectronics require materials with strong tribonegativity to generate robust signals against tribopositive human skin. Synthetic triboelectric negative materials, such as polytetrafluoroethylene (PTFE), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) have been explored for SITS. However, environmental sustainability and Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 biocompatibility concerns limit their practical application. Biopolymers, such as chitosan and protein, have been studied for use in triboelectric sensors, but they generally exhibit poor tribonegativity owing to limited electron-withdrawing capabilities and are typically tribopositive or weakly tribonegative. Strategies such as dielectric engineering, corona discharge, and surface functionalization have been employed to enhance the triboelectric performance of biopolymers: however, these methods offer limited durability and performance improvement.

[0010] Lignin has recently emerged as a biopolymer with characteristics appealing for SITS. Lignin accounts for about 20-30% of the solid weight of plants, and is the second most abundant biomass on earth. Lignin, despite being the second most abundant biopolymer on earth, has few practical applications and a small market value starting from around $300 per ton. Current applications of lignin are scarce, using only approximately 2%-5% of all lignin produced, and primarily utilize lignosulphonate, a chemically modified water-soluble lignin.

[0011] Valorizing lignin, the second most abundant biopolymer on earth and a vast underutilized waste stream from the paper industry, represents a cornerstone of the circular bioeconomy. Annually, over 98% of the tens of millions of tons of lignin produced is incinerated as low-grade fuel, forfeiting its immense potential as a sustainable chemical feedstock. Although the aromatic structure of lignin is an ideal platform for functional polymers, this potential has not been realized because of a processing barrier: harsh processing methods that irreversibly degrade its molecular integrity and, consequently, its electronic and mechanical properties are typically used due to the poor solubility in benign solvents. Overcoming this processing challenge may be important for resolving the fundamental tradeoff between performance and sustainability that can be an issue in current applications such as wearable electronics.

[0012] The naturally abundant lignin is a potentially sustainable alternative to plastics for SITS. Lignin has a complex structure, composed of polar (hydroxyl, carboxyl and ether) and non-polar (methoxy and aromatic groups) molecular nature. Reports have shown that aromatic groups can increase the dielectric constant and surface potential of triboelectric materials, elevating their electron-withdrawing capability and surface charge density, thus making lignin more tribonegative. Given the significant aromatic nature of lignin (e.g., pine lignin contains more than 75% guaiacyl content), it appears to be a good candidate as a biopolymer-based triboelectric sensor. Thus, the aromatic-rich structure of lignin may be suitable to enhance its tribonegativity. Yet, its potential has remained inaccessible by the same processing barrier that prevents its general valorization. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0013] The contact triboelectrification of lignin is not yet completely understood. In addition, the non-polar groups in lignin render it poorly soluble in water. Solvents such as dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, surfactant solutions, strong alkaline solutions, binary mixtures of nonpolar and polar solvents, and deep eutectic solvents are used for its solubilization. In particular, strong bases and basic solutions are often necessary for the dispersion of lignin in aqueous compositions. A lignin-based biopolymer and triboelectric nanogenerator including a reaction product of a mixture comprising a lignin and a starch has shown promise in the use of lignin in triboelectric applications. See, U.S. Patent No. 10,630,206. However, including hydrophilic compounds such as starch and glycerol in ligninbased biopolymers can cause a decrease of triboelectric properties, as an increase in hydrophilic nature can decrease the electron affinity of the triboelectric films.

[0014] Current approaches to utilize lignin in triboelectric applications face tremendous obstacles, such as high temperatures and the use of toxic chemicals. Moreover, these methods cannot preserve the structural integrity of lignin molecules, and hence their SITS-appealing properties after processing.

[0015] Accordingly, there remains a need for lignin-based biopolymer compositions and methods of preparing lignin-based biopolymer compositions without harsh processing conditions for use as skin-integrated triboelectric sensors.

[0016] SUMMARY

[0017] In one aspect, the present disclosure provides a composition comprising lignin, a plasticizer, and a binder as described herein. In some embodiments, the composition does not comprise a starch.

[0018] In another aspect, the present disclosure provides a film comprising: a layer comprising a composition comprising lignin, a plasticizer, and a binder. In some embodiments, the layer is arranged to provide an outer surface and an inner surface.

[0019] In yet another aspect, the present disclosure provides a wearable device for measuring a physiological property, the device comprising: a triboelectric sensor comprising the film as described herein. In some embodiments, the device further comprises a fixation element configured to secure the triboelectric sensor to exposed skin of a user; and a communication module configured to receive a signal from the triboelectric sensor and output data.

[0020] In yet another aspect, the present disclosure provides a method of preparing a film as described herein. In some embodiments, the method comprises the steps of: mixing lignin, a Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 plasticizer, and a binder in water, thereby forming an ink composition; and coating a substrate with the ink composition, thereby forming a film.

[0021] In one aspect, the present disclosure provides an environmentally friendly process that blends gelatin and urea with lignin to achieve an aqueous lignin dispersibility of 100 mg / mL, which is two orders of magnitude higher than previously reported. In some embodiments, the protocol as described herein may preserve the aromatic groups and enable the spontaneous formation of a nanotextured surface in printed lignin films, which may enhance triboelectrification.

[0022] In one aspect, the present disclosure provides the scalable printing of ultrathin (down to 1 pm thickness) lignin wearables with superior tribonegative performance, ten times higher than that of comparative biopolymers and comparable to that of synthetic plastics such as polyethylene, when in contact with skin. In some embodiments, the lignin wearables as described herein can monitor cardiovascular activities through contact triboelectrification with the skin and provide information for classifying non-subjective mental workload and stress conditions in various scenarios, achieving an accuracy (>95%) on par with electrocardiogram (ECG) measurement.

[0023] Additional embodiments, features, and advantages of the disclosure will be apparent from the following detailed description and through practice of the disclosure. The compounds and methods of the present disclosure can be described as embodiments in any of the following enumerated clauses. It will be understood that any of the embodiments described herein can be used in connection with any other embodiments described herein to the extent that the embodiments do not contradict one another.

[0024] BRIEF DESCRIPTION OF THE FIGURES

[0025] Fig. 1 A shows a schematic of lignin molecular structure and dispersed lignin ink.

[0026] Fig. IB shows a 2D-HSQC-NMR aromatic region of pure lignin solution.

[0027] Fig. 1C shows a 2D-HSQC-NMR aromatic region of urea-gelatin-lignin solution.

[0028] Fig. ID shows a 2D-HSQC-NMR aliphatic region of pure lignin solution.

[0029] Fig. IE shows a 2D-HSQC-NMR aliphatic region of urea-gelatin-lignin solution.

[0030] Fig. IF shows a schematic of aromatic nature of lignin sub-structures. Substructures of lignin: Molecular Structures of Lignin Monolignol Units: guaiacyl (G) and oxidized guaiacyl (G’) (1,2). Alkylic groups of lignin (specific C-H pairs of St: Stilbene (3), I: cinnamyl alcohol (4), A: P-O-4’ linkage (5), B: P-5’ linkage (6), A’: / -acylated P-O-4’ linkage (7), and C: P~P' linkage (8). Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0031] Fig. 2 shows a Teas graph of the Hansen Solubility Parameters (HSP) of lignin, urea, gelatin, water and several organic solvents. Teas graph shows the representation of the mathematical fractional contributions of ST and the HSP. The proximity of all the components of the lignin ink is shown. Lignin and urea are the closest molecules in this plot.

[0032] Fig. 3 shows a section (0.18-0.64 for all axis) of the Teas graph shown in Fig. 2. The fractional contributions of the HSP of common lignin solvents (DMSO, DMF, THF, acetone and others) are pointed by arrows. The proximity of all the common solvents of the lignin ink and urea indicates that urea is the closest molecule to lignin.

[0033] Fig. 4 shows an H-NMR verification of the presence of lignin, urea, and gelatin in the lignin ink.

[0034] Fig. 5A shows images of mixtures of various ratios of gelatin, lignin and urea. Scale: 1cm.

[0035] Fig. 5B shows a gelatin-lignin-urea ternary plot of the lignin dispersion degree.

[0036] Fig. 5C shows an image of an instrument for blade-coating manufacturing of the lignin ink on a substrate of aluminum foil. Scale: 1 cm.

[0037] Fig. 5D shows a schematic of the scalable blade-coating process to spread the lignin ink and form flexible thin films.

[0038] Fig. 5E shows optical images of the lignin ink films showing their flexibility and transparency. Scale: 1 cm.

[0039] Fig. 5F shows microscopy images of fluorescence (1,5), topography (2,6), phase retrace (3,7) and surface potential (4,8) of gelatin and lignin films. Scale: 2pm.

[0040] Fig. 5G shows a graph of measured surface potential of lignin films.

[0041] Fig. 5H shows a graph of ATR-FTIR of urea, lignin, lignin-gelatin films and gelatin.

[0042] Fig. 51 shows a schematic diagram of a mechanistic model showing the molecular organization of lignin, gelatin, and urea in the films.

[0043] Fig. 6 shows HSCQ-NMR of lignin mixture, pure lignin, and gelatin. The HSQC spectrum displays correlations between protons H) and carbons (13C) that are directly bonded to each other. In an HSQC spectrum: X-Axis (13C): Represents the chemical shifts of carbon atoms. Y-Axis CH): Represents the chemical shifts of hydrogen atoms. Cross Peaks: Each spot (cross peak) on the 2D plot indicates a correlation between a proton and its directly attached carbon atom, providing insight into the molecular structure. The provided figure is an HSQC NMR plot that compares the molecular structure of three different substances: lignin mix, lignin, and gelatin. The key features of the figure are: Aromatic Region (Bottom left): Shows correlations related to aromatic rings, which are likely present in lignin. This region has higher Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 electron density, often associated with non-polar side groups. Aliphatic Region (Center): Displays peaks corresponding to aliphatic chains (non-aromatic hydrocarbons) which are likely involved in polar side groups. Allylic Region (Top right): Contains peaks associated with allylic carbons, often found in the structure of lignin. HSQC peaks of the lignin mix indicate how its molecular structure differs or overlaps with pure lignin and gelatin. Pure lignin shows its structural characteristics, particularly in the aromatic and aliphatic regions. Gelatin, which has a different structure, shows distinct peaks in the aliphatic and allylic regions. Side Chain Abundance: The side chain abundance data compares the relative percentages of specific linkages or side chains (P-O-4, 0-0, and P-5) between lignin and the lignin mix. For instance, the P-O-4 linkage is more abundant in pure lignin (75.8%) compared to the lignin mix (74.1 %).

[0044] Fig. 7 shows images of solutions of lignin, gelatin, and urea at various mixture ratios. G: gelatin, L: Lignin, U: Urea.

[0045] Fig. 8A shows a fluorescence image of a gelatin film.

[0046] Fig. 8B shows a fluorescence image of a lignin mixture (30G:50L:20U) film.

[0047] Fig. 9 shows microscopy optical images of the laser position for fluorescence assays of various features on lignin films. G: gelatin, L: Lignin, U: Urea.

[0048] Fig. 10 shows fluorescence spectra of various features on lignin films. G: gelatin, L: Lignin, U: Urea.

[0049] Fig. 11 A shows a graph of the distribution of particle sizes of the lignin mixture sample (30G:50L:20U).

[0050] Fig. 1 IB shows a graph of the height distribution in the topographic images of the lignin mixture sample (30G:50L:20U).

[0051] Fig. 12 shows a surface potential measurement by KPFM. During the characterization, the metallic part is gold and the dielectric are the dielectric films.

[0052] Fig. 13A shows topographic images of various lignin mixtures. The surface potential is at the same scale for all the mixtures. G: gelatin, L: Lignin, U: Urea, eV: Electron-volts.

[0053] Fig. 13B shows phase images of various lignin mixtures. The surface potential is at the same scale for all the mixtures. G: gelatin, L: Lignin, U: Urea, eV: Electron-volts.

[0054] Fig. 13C shows surface potential KPFM images of various lignin mixtures. The surface potential is at the same scale for all the mixtures. G: gelatin, L: Lignin, U: Urea, eV: Electronvolts.

[0055] Fig. 14A shows a schematic diagram of contact-separation triboelectric mechanism of the lignin films.

[0056] Fig. 14B shows a graph of a polarity shift of gelatin after mixing with lignin. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0057] Fig. 14C shows an image of a triboelectric film of a lignin / gelatin mixture.

[0058] Fig. 14D shows a graph of current density versus time for lignin films with varying lignin concentrations. Scale: 1 cm.

[0059] Fig. 14E shows a ternary phase diagram representing triboelectric performance based on lignin, gelatin, and urea compositions.

[0060] Fig. 14F shows a graph of current density versus time for lignin films processed at different temperatures and the influence of the processing temperature in lignin-TENG cunent output (triboelectric performance).

[0061] Fig. 14G shows a graph of current density versus time and the influence of the film thickness in lignin-TENG current output (triboelectric performance).

[0062] Fig. 14H shows a graph of current density versus time and the influence of the drying time in lignin-TENG current output (triboelectric performance).

[0063] Fig. 15 shows images of blade-coated lignin films on Al substrate at various mixtures ratios. G: gelatin, L: Lignin, U: Urea.

[0064] Fig. 16A shows graphs of current TENG performance of blade-coated lignin-based films using PTFE as a counterpart. G: gelatin, L: Lignin, U: Urea.

[0065] Fig. 16B shows graphs of current TENG performance of blade-coated lignin-based films using cellulose as a counterpart. G: gelatin, L: Lignin, U: Urea.

[0066] Fig. 17A shows an optical microscope image showing the segregation and dispersion of lignin in blade-coated film without urea.

[0067] Fig. 17B shows an optical microscope image showing the segregation and dispersion of lignin in blade-coated film with urea.

[0068] Fig. 18 shows AFM topographic images and roughness correlation. G: gelatin, L: Lignin, U: Urea.

[0069] Fig. 19A shows a graph of current density of lignin-films at different frequencies.

[0070] Fig. 19B shows a graph of open-circuit voltage of lignin-films at different frequencies.

[0071] Fig. 19C shows a graph of electrical output as a function of load resistance, specifically voltage (•) and current density (o) at different resistances.

[0072] Fig. 19D shows a graph of electrical output as a function of load resistance, specifically power density at different resistances.

[0073] Fig. 19E shows a graph of durability of triboelectric performance of lignin-films.

[0074] Fig. 20A shows an image of a heart rate device based on the triboelectric sensor.

[0075] Fig. 20B shows a schematic of the SITS sensor architecture when using skin as a tribocounterpart. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0076] Fig. 20C shows a graph of performance of various biopolymer-based SITS devices compared to the lignin SITS.

[0077] Fig. 20D shows a graph of heart rate over 30s measured by the triboelectric- cardiovascular sensor.

[0078] Fig. 20E shows a graph of heart pulse shape from Fig. 20D, resolving the characteristic Pi, Pj, and P peaks of the cardiac cycle.

[0079] Fig. 20F shows a graph of heart rate variability (HRV), mean peak-to-peak intervals.

[0080] Fig. 20G shows a graph of Atcvp derived from the 35 seconds pulse periods shown in Fig. 20E.

[0081] Fig. 20H shows a graph of Alr(augmentation index) derived from the 35 seconds pulse periods shown in Fig. 20E.

[0082] Fig. 201 shows a graph of DAI (augmentation index) derived from the 35 seconds pulse periods shown in Fig. 20E.

[0083] Fig. 20J shows graph showing the relationship between mental workload (MW) conditions and bpm.

[0084] Fig. 20K shows a graph of influence of mental workload conditions on HRV mean.

[0085] Fig. 20L shows a graph of influence of mental workload conditions on DVP mean.

[0086] Fig. 20M shows a graph of influence of mental workload conditions on Alr.

[0087] Fig. 20N shows images of experimental setup showing the six mental demand conditions tested: WO (Weightlifting), S (Phone call), F (Focused work), EmQ (Emotional query), InQ (Intellectual query), and MQ (Multitasking query), and R (Resting).

[0088] Fig. 200 shows a graph of the correlation between several conditions and the MW aspects. The six aspects recommended by the subjective NASA-TLX test were utilized, with each aspect ranked from 1 to 6 as recommended.

[0089] Fig. 20P shows a graph of principal component analysis (PCA)-based classification accuracy of mental workload conditions (WO, S, F, EmQ, InQ, MQ) using lignin-SITS.

[0090] Fig. 20Q shows a graph of the SITS sensor and ECG sensor comparison showing the SITS sensor, achieving over 95% accuracy, comparable to ECG measurements.

[0091] Fig. 21 shows an image of the experimental setup for the characterization of the triboelectric performance of the against dry skin. Figure 21 describes the customized setup used to characterize the triboelectric films against dry skin on the forearm (as a counter tribopositive material), where the lignin films were attached to a copper lead for current measurements. Measurements of output voltages in TENGs were conducted with a Keithley 6514 engaged with LabView software. The current outputs were measured by using a low-noise current Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 preamplifier, Stanford Research Systems SR570, following an appropriate configuration. The results of the characteristics are shown in Figure 22.

[0092] Fig. 22 shows graphs of a demonstration of the current output generated by the customized setup to characterize the triboelectric films against dry skin. The plots show a comparison of the performance of lignin and gelatin-based triboelectric films against dry skin.

[0093] Fig. 23 shows a graph of the current characteristics of the triboelectric performance of synthetic films against skin as a counter tribopositive material. Comparison of the performance against dry skin of 30G:50L:20U sample with polyethylene (PE), acrylonitrile butadiene rubber (NBR), polyimide (PI) and polypropylene (PP) is shown.

[0094] Fig. 24 shows graphs of heart rate (y-axis current, x-axis seconds), heart rate variability (y-axis seconds, x-axis seconds), differential volumetric pulse (y-axis milliseconds), and radial augmented index (y-axis AL) of R condition.

[0095] Fig. 25 shows graphs of heart rate (y-axis current, x-axis seconds), heart rate variability (y-axis seconds, x-axis seconds), differential volumetric pulse (y-axis milliseconds), and radial augmented index (y-axis AL) of WO condition.

[0096] Fig. 26 shows graphs of heart rate (y-axis current, x-axis seconds), heart rate variability (y-axis seconds, x-axis seconds), differential volumetric pulse (y-axis milliseconds), and radial augmented index (y-axis AL) of S condition.

[0097] Fig. 27 shows graphs of heart rate (y-axis current, x-axis seconds), heart rate variability (y-axis seconds, x-axis seconds), differential volumetric pulse (y-axis milliseconds), and radial augmented index (y-axis AL) of F condition.

[0098] Fig. 28 shows graphs of heart rate (y-axis current, x-axis seconds), heart rate variability (y-axis seconds, x-axis seconds), differential volumetric pulse (y-axis milliseconds), and radial augmented index (y-axis AL) of EmQ condition.

[0099] Fig. 29 shows graphs of heart rate (y-axis current, x-axis seconds), heart rate variability (y-axis seconds, x-axis seconds), differential volumetric pulse (y-axis milliseconds), and radial augmented index (y-axis AL) of InQ condition.

[0100] Fig. 30 shows graphs of heart rate (y-axis current, x-axis seconds), heart rate variability (y-axis seconds, x-axis seconds), differential volumetric pulse (y-axis milliseconds), and radial augmented index (y-axis AL) of MQ condition.

[0101] Fig. 31 A shows an electrocardiogram (ECG) of the heart rate and heart rate variability under following (F) condition. HRV: Heart rate variability, SD: standard deviation. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0102] Fig. 3 IB shows an electrocardiogram (ECG) of the heart rate and heart rate variability under mathematical questions (MatQ / MQ) condition. HRV: Heart rate variability, SD: standard deviation.

[0103] Fig. 31C shows an electrocardiogram (ECG) of the heart rate and heart rate variability under resting (R) condition. HRV: Heart rate variability, SD: standard deviation.

[0104] Fig. 3 ID shows an electrocardiogram (ECG) of the heart rate and heart rate variability under interview questions (InQ) condition. HRV : Heart rate variability, SD: standard deviation.

[0105] Fig. 31E shows an electrocardiogram (ECG) of the heart rate and heart rate variability under emotional questions (EmQ) condition. HRV: Heart rate variability, SD: standard deviation.

[0106] Fig. 3 IF shows an electrocardiogram (ECG) of the heart rate and heart rate variability under singing (S) condition. HRV: Heart rate variability, SD: standard deviation.

[0107] Fig. 31G shows an electrocardiogram (ECG) of the heart rate and heart rate variability under working out (WO) condition. HRV: Heart rate variability, SD: standard deviation.

[0108] Fig. 32 shows a graph of a NASA-TLX test measured by the gold standard electrocardiogram (ECG) of heart rate.

[0109] Fig. 33 shows a graph of a NASA-TLX test measured by the gold standard electrocardiogram (ECG) of heart rate variability.

[0110] Fig. 34 shows a graph of a principal component analysis of mental workload condition using the ECG cardiac parameters from Table 3. Resting (R), working out (WO), singing (S), following (F), emotional questions (EmQ), interview questions (InQ) and mathematical questions (MatQ / MQ).

[0111] Fig. 35 shows a graph of quantified standard clustering metrics.

[0112] DETAILED DESCRIPTION

[0113] Before the present disclosure is further described, it is to be understood that this disclosure is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present disclosure will be limited only by the appended clauses.

[0114] For the sake of brevity, the disclosures of the publications cited in this specification, including patents, are herein incorporated by reference. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this disclosure belongs. All patents, applications, published Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 applications and other publications referred to herein are incorporated by reference in their entireties. If a definition set forth in this section is contrary to or otherwise inconsistent with a definition set forth in a patent, application, or other publication that is herein incorporated by reference, the definition set forth in the present disclosure prevails over the definition incorporated herein by reference.

[0115] As used herein and in the appended clauses, the singular forms “a," “an,” and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the clauses may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of clause elements, or use of a “negative” limitation.

[0116] As used herein, the terms “including,” “containing,” and “comprising” are used in their open, non-limiting sense.

[0117] To provide a more concise description, some of the quantitative expressions given herein are not qualified with the term “about.” It is understood that, whether the term “about” is used explicitly or not, every quantity given herein is meant to refer to the actual given value, and it is also meant to refer to the approximation to such given value that would reasonably be inferred based on the ordinary skill in the art, including equivalents and approximations due to the experimental and / or measurement conditions for such given value. Whenever a yield is given as a percentage, such yield refers to a mass of the entity for which the yield is given with respect to the maximum amount of the same entity that could be obtained under the particular stoichiometric conditions. Concentrations that are given as percentages refer to mass ratios, unless indicated differently.

[0118] To the extent the present disclosure includes various terms for components and / or processes of the disclosed devices, systems, methods, and the like, one skilled in the art, in view of the claims, present disclosure, and knowledge of the skilled person, will understand such terms are merely examples of such components and / or processes, and other components, designs, processes, and / or actions are possible. To the extent terms such as front, back, top, bottom, proximal, distal, etc. are used to describe a location of various components of the various disclosures, such usage is by no means limiting, and is often used for convenience when describing various possible configurations. The foregoing notwithstanding, a person skilled in the art will recognize the common vernacular used with respect to medical devices and will give terms of those nature their commonly understood meaning.

[0119] It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 embodiment. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination. All combinations of the embodiments pertaining to the chemical groups represented by the variables are specifically embraced by the present disclosure and are disclosed herein just as if each and every combination was individually and explicitly disclosed, to the extent that such combinations embrace compounds that are stable compounds (i.e., compounds that can be isolated, characterized, and tested for biological activity). In addition, all subcombinations of the chemical groups listed in the embodiments describing such variables are also specifically embraced by the present disclosure and are disclosed herein just as if each and every such sub-combination of chemical groups was individually and explicitly disclosed herein.

[0120] DEFINITIONS

[0121] Unless otherwise defined herein, scientific and technical terms used in this application shall have the meanings that are commonly understood by those of ordinary skill in the art. Generally, nomenclature used in connection with, and techniques of, chemistry, polymers, and materials chemistry, described herein, are those well-known and commonly used in the art.

[0122] The methods and techniques of the present disclosure are generally performed, unless otherwise indicated, according to conventional methods well known in the art and as described in various general and more specific references that are cited and discussed throughout the present specification. See, e.g., Loudon, Organic Chemistry, Fourth Edition, New York: Oxford University Press, 2002, pp. 360-361, 1084-1085; Smith and March, March's Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, Fifth Edition, Wiley-Interscience, 2001.

[0123] Chemistry terms used herein, unless otherwise defined herein, are used according to conventional usage in the art, as exemplified by “The McGraw-Hill Dictionary of Chemical Terms”, Parker S., Ed., McGraw-Hill, San Francisco, Calif. (1985). Chemical nomenclature for compounds and compositions described herein has generally been derived using the commercially available ACD / Name 2014 (ACD / Labs) or ChemBioDraw Ultra 13.0 (Perkin Elmer).

[0124] All of the above, and any other publications, patents and published patent applications referred to in this application are specifically incorporated by reference herein. In case of conflict, the present specification, including its specific definitions, will control. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0125] As used herein, the terms “optional” or “optionally” mean that the subsequently described event or circumstance may occur or may not occur, and that the description includes instances where the event or circumstance occurs as well as instances in which it does not. For example, “optionally coupled to a substrate” refers to the element or component that may be coupled to a substrate as well as where the element or component is not coupled to a substrate.

[0126] A “patient,” “user,” “subject," or “individual” are used interchangeably and refer to either a human or a non-human animal. These terms include mammals, such as humans, primates, livestock animals (including bovines, porcines, etc.), companion animals (e.g., canines, felines, etc.) and rodents (e.g., mice and rats).

[0127] The tern “blend” as used herein, refers to a mixture of two or more components. Blends or mixtures can be homogeneous mixtures or heterogeneous mixtures. A homogeneous mixture refers to a composition that is uniform throughout the mixture. A heterogeneous mixture refers to a composition that includes two or more phases. A heterogeneous mixture, for example, includes regions with properties that are distinct from those of another region even if they are in the same state of matter (e.g., liquid or solid).

[0128] The term “Log of solubility”, “LogS” or “logS,” as used herein, is used in the art to quantify the aqueous solubility of a compound. The aqueous solubility of a compound significantly affects its absorption and distribution characteristics. A low solubility often goes along with a poor absorption. LogS value is a unit stripped logarithm (base 10) of the solubility measured in mol / liter.

[0129] The term “base,” as used herein, refers to a substance that can accept hydrogen ions in water and can neutralize an acid. Basicity is measured on a scale called the pH scale. On this scale, a pH value of 7 is neutral, and a pH value of more than 7 to a pH of 14 shows increasing basicity. Examples of bases are the hydroxides of the alkali and alkaline earth metals (sodium, calcium, etc.) and the water solutions of ammonia or its organic derivatives (amines). Such substances produce hydroxide ions (OH — ) in water solutions.

[0130] The terms “alkaline solvent” or “basic solvent,” as used herein, refer to a solvent (e.g., an aqueous solution) with a pH of greater than 7. Examples of alkaline solvents include aqueous solutions of bases including, but not limited to, sodium hydroxide (lye, caustic soda), potassium hydroxide, calcium hydroxide (slaked lime), magnesium hydroxide, and aqueous ammonia (ammonium hydroxide).

[0131] The term “lignin,” as used herein, refers to a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignin can be categorized based on both biomass source and its extraction process. Biomass sources can be hardwood Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0132] (e.g., beech, birch, oak, ash, etc.), softwood (pine, spruce, fir, larch, cedar, etc.) and / or herbaceous plants (mainly poaceae such as cereals, bamboo, rice, reeds, maize or sugarcane). The relative amounts of the precursor “monomers” (lignols or monolignols) vary according to the plant source. Lignins are typically classified according to their syringyl / guaiacyl (S / G) ratio.

[0133] The term “modified-lignin,” refers to by-products derived from pulp and paper processing. Examples of modified-lignin include lignosulfonate or sulfonated lignin.

[0134] The term “covalent side chain bond,” when used with respect to lignin, refers to the covalent linkages between lignin backbone moieties, such as aromatic (e.g., guaiacyl) groups and aliphatic (e.g., alkyl) groups. Examples of covalent side chain bonds in lignin include, but are not limited to, aryl-aryl bonds (e.g., 5-5’), alkyl-alkyl bonds (e.g., B-B’, such as resinol), alkyl-aryl bonds (e.g., B-5’, such as phenylcoumarin), alkyl-aryl ether bonds (e.g., B-O-4’), aryl-aryl ether bonds (e.g., 4-0-5’, such as biphenyl ether), and the like.

[0135] The term “pure,” refers to a composition consisting essentially of a single component, such as a composition having a single component in a concentration of greater than about 99.5 wt%. For example, the term “pure lignin” can refer to a composition consisting of lignin, and “pure gelatin” can refer to a composition consisting of gelatin.

[0136] The term “guaiacyl,” refers to a functional group derived from guaiacol (e.g., 2- methoxy phenol). For example, a guaiacyl group present in lignin may be represented by the following structure , w ere n represents a point of covalent attachment to the remainder of the lignin polymer. The point of covalent attachment may include a covalent bond between the guaiacyl group and one or more carbon atoms of the remainder of the lignin polymer.

[0137] The term “triboelectric,” as used herein, refers to a charge of electricity generated by friction. For example, triboelectricity can include the electric charge transfer between two objects when they contact or slide against each other. It can occur with different materials, such as the sole of a shoe on a carpet, or between two pieces of the same material. The triboelectric effect is the process by which two objects become charged when they are brought together and then separated. When a tribonegative material comes into contact with a tribopositive material, the tribopositive material donates electrons to the tribonegative material. The separation of the Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 two materials can create an electrical current. Triboelectric nanogenerators (TENGs) are devices that use the triboelectric effect to convert mechanical energy into electricity. TENGs can be used to harvest energy from the environment, such as kinetic energy from wind or vibrational energy from sound.

[0138] The term “skin-integrated triboelectric sensors (SITS),” as used herein, can refer to sensors based on TENGs that convert measured information into electrical signals through the relative motion of contact or non-contact between two electrode pairs with different electronegative properties can be. SITS can find use in tactile perception, motion sensing, and healthcare monitoring. SITS converts subtle skin deformations into sensing signals via contact triboelectrification between the skin and sensor. The strong positive triboelectric properties of the human skin necessitate triboelectric negative materials for effective skin contact in SITS.

[0139] The term “plasticizer,” as used herein, refers to an additive incorporated into polymers to increase their flexibility, workability, and softness by reducing intermolecular forces within the polymer matrix. For example, urea can be used to plasticize the solid polymeric phases of lignin and gelatin. Examples of plasticizers include, but are not limited to, urea, glycerol, polyethylene glycol, a citric acid ester, and sorbitol.

[0140] The term “binder,” as used herein, refers to a material or substance that holds or draws other materials together to form a cohesive whole mechanically, chemically, by adhesion or cohesion. For example, gelatin can be used as a binder because of its partial compatibility with lignin through intermolecular hydrogen-bond and aromatic non-polar interactions. Examples of binders include, but are not limited to, gelatin, starch, polyethylene glycol, and polyvinyl alcohol.

[0141] The term “dispersibility,” as used herein, refers to the ability of a substance to distribute evenly throughout water without necessarily fully dissolving. For example, dispersibility may indicate how well a substance can be spread out in water, even if it does not dissolve completely.

[0142] The term “water-miscible solvent,” as used herein, refers to a liquid that can mix completely with water in any proportion, meaning they dissolve fully when combined. Examples of water-miscible solvents include ethanol, acetone, methanol, isopropanol, acetonitrile, THF, dioxane, DMSO, and the like.

[0143] The term “solubility,” as used herein, refers to the maximum amount of a substance that can completely dissolve in water to form a homogeneous solution. The term “water-soluble,” as used herein, refers to a substance or compound that can be dissolved in water. The term “water-insoluble,” as used herein, refers to a substance or compound that cannot be dissolved Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 in water or dissolved to a slight degree. For example, a water-insoluble substance or compound may have a solubility in water of less than about 0.01 M.

[0144] REPRESENTATIVE EMBODIMENTS

[0145] In some embodiments, the present disclosure relates to a composition comprising lignin, a plasticizer, and a binder. In some embodiments, the present disclosure relates to a composition comprising lignin; a plasticizer (e.g., urea, glycerol, polyethylene glycol, a citric acid ester, and sorbitol); and a binder (e.g., gelatin, polyethylene glycol, and polyvinyl alcohol). In some embodiments, the present disclosure relates to a composition comprising lignin; urea; and gelatin.

[0146] In some embodiments, the composition does not include a polysaccharide (e.g., a starch, a cellulose, or a chitin). In some embodiments, the composition does not include a starch. In some embodiments, the composition does not include a glycol, glycerol, a glycol derivative, a glycerol derivative, or any combination thereof. In some embodiments, the composition does not include glycerol. In some embodiments, the composition does not include a synthetic polymer, such as polyethylene (PE), acrylonitrile butadiene rubber (NBR), polyimide (PI), or polypropylene (PP).

[0147] In some embodiments, the plasticizer is selected from the group consisting of urea, glycerol, polyethylene glycol, a citric acid ester, and sorbitol, preferably wherein the plasticizer is urea. In some embodiments, the plasticizer does not include a glycol, glycerol, a glycol derivative, a glycerol derivative, or any combination thereof. In some embodiments, the plasticizer does not include glycerol.

[0148] In some embodiments, the binder is selected from the group consisting of gelatin, polyethylene glycol, and polyvinyl alcohol, preferably wherein the binder is gelatin. In some embodiments, the binder does not include a polysaccharide (e.g., a starch, a cellulose, or a chitin). In some embodiments, the binder does not include a starch.

[0149] In some embodiments, the composition comprises about 10 wt% to about 70 wt% of lignin, such as about 20 wt% to about 70 wt% of lignin, about 30 wt% to about 70 wt% of lignin, about 40 wt% to about 70 wt% of lignin, about 20 wt% to about 60 wt% of lignin, about 30 wt% to about 60 wt% of lignin, or about 40 wt% to about 60 wt% of lignin. The composition may comprise, for example, about 20 wt% lignin, about 30 wt% lignin, about 40 wt% lignin, about 45 wt% lignin, about 50 wt% lignin, about 55 wt% lignin, about 60 wt% lignin, or about 70 wt% lignin. In certain preferred embodiments, the composition comprises about 40 wt% to about 60 wt% of lignin (e.g., about 50 wt% lignin). Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0150] In some embodiments, the composition comprises about 10 wt% to about 70 wt% of plasticizer (e.g., urea), such as about 10 wt% to about 60 wt% of plasticizer, about 10 wt% to about 50 wt% of plasticizer, about 10 wt% to about 40 wt% of plasticizer, or about 10 wt% to about 30 wt% of plasticizer. The composition may comprise, for example, about 10 wt% plasticizer, about 15 wt% plasticizer, about 20 wt% plasticizer, about 25 wt% plasticizer, about 30 wt% plasticizer, about 35 wt% plasticizer, about 40 wt% plasticizer, about 50 wt% plasticizer, about 60 wt% plasticizer, or about 70 wt% plasticizer. In certain preferred embodiments, the composition comprises about 10 wt% to about 30 wt% of plasticizer (e.g., about 20 wt% plasticizer).

[0151] In some embodiments, the composition comprises about 10 wt% to about 70 wt% of binder (e.g., gelatin), such as about 10 wt% to about 60 wt% of binder, about 10 wt% to about 50 wt% of binder, about 10 wt% to about 40 wt% of binder, about 20 wt% to about 70 wt%, about 20 wt% to about 60 wt%, about 20 wt% to about 50 wt%, or about 20 wt% to about 40 wt% of binder. The composition may comprise, for example, about 10 wt% binder, about 20 wt% binder, about 25 wt% binder, about 30 wt% binder, about 35 wt% binder, about 40 wt% binder, about 50 wt% binder, about 60 wt% binder, or about 70 wt% binder. In certain preferred embodiments, the composition comprises about 20 wt% to about 40 wt% of binder (e.g., about 30 wt% binder).

[0152] In some embodiments, the composition comprises a weight ratio of lignin to the plasticizer (e.g., urea) of about 1 : 10 to about 10: 1, such as about 1 : 5 to about 5: 1, about 1: 2 to about 3: 1, or about 1: 1 to about 3: 1. The composition may comprise, for example, a weight ratio of lignin to the plasticizer of about 1 : 1, about 1.5: 1 (i.e., about 3:2), about 2: 1, about 2.5: 1 (i.e., about 5:2), about 3: 1, about 3.5: 1 (i.e., about 7:2), or about 4: 1. In some embodiments, the composition comprises a weight ratio of lignin to the plasticizer of about 1 :2 to about 3: 1. In certain preferred embodiments, the composition comprises a weight ratio of lignin to the plasticizer of about 5: 2.

[0153] In some embodiments, the composition comprises a weight ratio of lignin to the binder (e.g., gelatin) of about 1: 10 to about 10:1, such as about 1:5 to about 5: 1, about 1:1 to about 2: 1. The composition may comprise, for example, a weight ratio of lignin to the binder of about 1: 1, about 5: 4, about 1.5: 1 (i.e., about 3:2), about 5: 3, about 2: 1, about 2.5: 1 (i.e., about 5:2), about 3: 1, about 3.5: 1 (i.e., about 7:2), about 4: 1, or about 5: 1. In some embodiments, the composition comprises a weight ratio of lignin to the binder of about 1 : 1 to about 2: 1. In certain preferred embodiments, the composition comprises a weight ratio of lignin to the binder of about 5: 3. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0154] In some embodiments, the lignin has a molecular weight (weight average molecular weight) of greater than about 500 Da, such as greater than about 600 Da, greater than about 800 Da, or greater than about 1 kDa. The lignin, for example, may have a molecular weight of about 800 Da, about 900 Da, about 1.0 kDa, about 1.1 kDa, about 1.2 kDa, about 1.3 kDa, about 1.4 kDa, or about 1.5 kDa.

[0155] In some embodiments, the composition comprises a solvent. The composition comprising a solvent may be referred to as an ink composition.

[0156] In some embodiments, the composition (or ink composition) comprises about 5 wt.% to about 99 wt.% solvent (e.g., water). For example, the composition (or ink composition) may comprise about 25 wt.% to about 95 wt.%, about 50 wt.% to about 95 wt.%, about 60 wt.% to about 95 wt.%, about 70 wt.% to about 95 wt.%, about 75 wt.% to about 95 wt.%, about 25 wt.% to about 90 wt.%, about 50 wt.% to about 90 wt.%, about 60 wt.% to about 90 wt.%, about 70 wt.% to about 90 wt.%, or about 75 wt.% to about 90 wt.% solvent.

[0157] The solvent may have a neutral or acidic pH. In some embodiments, the solvent has a pH of about 6 to about 8, such as about 7. The composition (or ink composition) may have a neutral or acidic pH. In some embodiments, the composition (or ink composition) has a pH of about 6 to about 8, such as about 7.

[0158] In some embodiments, the composition does not comprise an organic solvent, a surfactant solvent, a basic solvent (e.g., an alkaline solvent), a binary mixture of a nonpolar and a polar solvent, or a deep eutectic solvent. In some embodiments, the composition does not comprise a base (e.g., an alkali or alkaline earth metal hydroxide).

[0159] In some embodiments, the composition comprises water. In some embodiments, the composition is in an aqueous solution. In some embodiments, the composition comprises water and a water-miscible solvent, such as an alcohol (e.g., methanol, ethanol, and isopropanol).

[0160] In some embodiments, the composition has an aqueous lignin dispersibility of greater than about 10 mg / mL (e.g., greater than about 25 mg / mL greater than about 50 mg / mL, or greater than about 75 mg / mL), preferably wherein the composition has an aqueous lignin dispersibility of about 100 mg / mL.

[0161] In some embodiments, the composition has a surface potential of greater than about 3 eV, such as greater than about 4 eV or greater than about 5 eV. The composition, for example, may have a surface potential of about 3 eV to about 10 eV, about 3 eV to about 8 eV, about 3 eV to about 6 eV, about 4 eV to about 10 eV, about 4 eV to about 8 eV, or about 4 eV to about 6 eV. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0162] In some embodiments, the composition is tribonegative. In some embodiments, tribonegative behavior that can be attributed to high aromatic content of lignin. In contrast, compositions with other biopolymers, such as starch, cellulose, chitosan, gelatin, alginate polyvinyl alcohol, and polyacrylate acid, do not contain aromatic side groups in their backbone.

[0163] In some embodiments, lignin is derived from softwoods, hardwoods, grasses, or a combination thereof. For example, lignin may be derived from a softwood, such as pine. In some embodiments, the lignin is a Kraft lignin. Kraft lignin, for example, can comprise less than about 5%, preferably less than about 3% sulfur. In some embodiments, the lignin does not comprise a modified-lignin (e.g., a lignosulfonate or a sulfonated lignin).

[0164] In some embodiments, lignin (e.g., pine lignin) comprises greater than about 75% guaiacyl content. The lignin, for example, may comprise a guaiacyl content of greater than about 70%, greater than about 75%, or greater than about 80%.

[0165] In some embodiments, lignin comprises a syringyl / guaiacyl (S / G) ratio of less than about 0.1.

[0166] In some embodiments, lignin comprises covalent side chain bonds, such as aryl-aryl bonds (e.g., 5-5’), alkyl-alkyl bonds (e.g., B-B’, such as resinol), alkyl-aryl bonds (e.g., B-5’, such as phenylcoumarin), alkyl-aryl ether bonds (e.g., B-O-4’), aryl-aryl ether bonds (e.g., 4- O-5’, such as biphenyl ether), or any combination thereof.

[0167] It may be advantageous for a particular amount of covalent side chain bonds in lignin to remain intact (i.e., uncleaved), for example, after mixing pure lignin with a binder, a plasticizer, and / or a solvent to provide the composition (ink composition) or film as described herein. The lignin present in the composition (ink composition) or film of the present disclosure may comprise a particular amount of intact covalent side chain bonds with respect to pure lignin.

[0168] In some embodiments, the lignin comprises at least about 80% intact covalent side chain bonds. For example, the lignin may comprise at least about 85%, at least about 90%, or at least about 95% intact covalent side chain bonds.

[0169] In some embodiments, the lignin comprises at least about 80% intact alkyl-aryl ether bonds (e.g., B-O-4’). For example, the lignin may comprise at least about 85%, at least about 90%, or at least about 95% intact alkyl-aryl ether bonds.

[0170] In some embodiments, the composition has a current density of greater than about 1 nA / cm2, such as greater than about 2 nA / cm2, greater than about 5 nA / cm2, or greater than about 10 nA / cm2. The composition, for example, may have a current density of about 1 nA / cm2to about 50 nA / cm2, about 1 nA / cm2to about 25 nA / cm2, about 1 nA / cm2to about 20 nA / cm2, Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 about 2 nA / cm2to about 50 nA / cm2, about 2 nA / cm2to about 25 nA / cm2, about 2 nA / cm2to about 20 nA / cm2, about 5 nA / cm2to about 50 nA / cm2, about 5 nA / cm2to about 25 nA / cm2, or about 5 nA / cm2to about 20 nA / cm2.

[0171] In some embodiments, the composition is used to form a film. For example, the film may be formed by the methods as described herein. The film may be used to provide a wearable device, as described herein. In some embodiments, the composition is used to form fibers. For example, the fibers may be formed by electrospinning the composition as described herein. The fibers may be used to provide fabrics, core-shell fibers, 3D porous structures, composite structures, yarns, hydrogels, aerogels, nonwoven mats, and the like.

[0172] In some embodiments, the present disclosure relates to a film including a layer comprising a composition, the composition comprising lignin, a plasticizer, and a binder, wherein the composition does not comprise a starch. In some embodiments, the film or layer comprises the composition as described herein. In some embodiments, the layer is arranged to provide an outer surface and an inner surface. In some embodiments, the film comprises an outer surface and an inner surface.

[0173] In some embodiments, the film is tribonegative. In some embodiments, the film (e.g., the outer surface, inner surface, or both of the outer surface and the inner surface) has a negative surface potential. In some embodiments, the film has a surface potential of greater than about 3 eV, such as greater than about 4 eV or greater than about 5 eV. The film, for example, may have a surface potential of about 3 eV to about 10 eV, about 3 eV to about 8 eV, about 3 eV to about 6 eV, about 4 eV to about 10 eV, about 4 eV to about 8 eV, or about 4 eV to about 6 eV.

[0174] In some embodiments, the film has a current density of greater than about 1 nA / cm2, such as greater than about 2 nA / cm2, greater than about 5 nA / cm2, or greater than about 10 nA / cm2. The composition, for example, may have a current density of about 1 nA / cm2to about 50 nA / cm2, about 1 nA / cm2to about 25 nA / cm2, about 1 nA / cm2to about 20 nA / cm2, about 2 nA / cm2to about 50 nA / cm2, about 2 nA / cm2to about 25 nA / cm2, about 2 nA / cm2to about 20 nA / cm2, about 5 nA / cm2to about 50 nA / cm2, about 5 nA / cm2to about 25 nA / cm2, or about 5 nA / cm2to about 20 nA / cm2.

[0175] In some embodiments, the outer surface comprises nanodomains. In some embodiments, the nanodomains have a lateral size of about 100 nm to about 2 pm, and the nanodomains protrude about 20 nm to about 150 nm from the outer surface.

[0176] In some embodiments, the nanostructures are formed as a result of phase separation. In some embodiments, the nanostructures are spontaneously formed.

[0177] In some embodiments, the film comprises a substrate coupled to the inner surface. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0178] In some embodiments, the present disclosure relates to a laminate including a layer comprising the composition as described herein, and a substrate. In some embodiments, the layer is arranged to provide an outer surface and an inner surface, and the substrate is coupled to the inner surface of the layer. In some embodiments, the substrate is a conductive substrate (e.g., a metal or a carbon-based material). For example, the substrate may be selected from the group consisting of aluminum, fluorine tin oxide, polyethylene terephthalate, copper foil, silver nanowires-coated foil, carbon nanotube, graphene, and any combination thereof.

[0179] In some embodiments, the film has a thickness of less than about 20 m, such as less than about 10 pm, less than about 5 pm, or less than about 2 pm. The film, for example, may have a thickness of about 0.1 pm to about 20 pm, about 0.1 pm to about 10 pm, about 0.1 pm to about 5 pm, about 0.1 pm to about 2 pm, about 1 pm to about 20 pm, about 1 pm to about 10 pm, about 1 pm to about 5 pm, or about 1 pm to about 2 pm.

[0180] In some embodiments, the film does not include a synthetic polymer, such as polyethylene (PE), acrylonitrile butadiene rubber (NBR), polyimide (PI), or polypropylene (PP).

[0181] In some embodiments, the film comprises less than about 5 wt.% solvent (e.g., water). For example, the film may comprise about 0 wt.% to about 5 wt.%, about 0 wt.% to about 4 wt.%, about 0 wt.% to about 3 wt.%, about 0 wt.% to about 2 wt.%, or about 0 wt.% to about 1 wt.% solvent.

[0182] In some embodiments, the present disclosure relates to a wearable device for measuring a physiological property comprising: a triboelectric sensor comprising the film as described herein; a fixation element configured to secure the triboelectric sensor to exposed skin of a user; and a communication module configured to receive a signal from the triboelectric sensor and output data.

[0183] In some embodiments, the fixation element (e.g., an adhesive) is configured to secure the outer surface of the film to exposed skin of a user. In some embodiments, the fixation element (e.g., an adhesive) includes medical dressings such as PVA paper, Band-aid tape, wound medical tape, adhesive patches, surgical tape, silicone tape, scar tape, transfer tape, or stretchable tape.

[0184] In some embodiments, the fixation element is configured to locate the triboelectric sensor proximal to a radial artery location (e.g., exposed skin) of the user. In some embodiments, the triboelectric sensor and the skin of the user are in direct contact. In some Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 embodiments, the fixation element is configured to locate the triboelectric sensor on the forearm, wrist, or hand of the user. In some embodiments, the user is a human.

[0185] In some embodiments, the triboelectric sensor is configured to sense skin deformation of the user wearing the device. In some embodiments, the triboelectric sensor is configured to sense skin and / or artery motion of the user wearing the device.

[0186] In some embodiments, the signal is a current output. For example, the difference from triboelectric polarities between the triboelectric sensor and skin of the user leads to electrons flowing between the two (i.e., current).

[0187] In some embodiments, the triboelectric sensor is tribonegative. A potential feature of the triboelectric sensors of the present disclosure is a greater difference in triboelectric charge density between the triboelectric sensor (e.g., tribonegative sensor) and the tribopositive skin of the user. For example, a greater difference in triboelectric charge density may improve charge transfer, thereby increasing a signal-to-noise ratio.

[0188] In some embodiments, the data is suitable for use in quantifying a cardiovascular parameter. In some embodiments, the cardiovascular parameter is selected from the group consisting of heart rate, digital volume pulse (DVP), heart rate variability (HRV), radial diastolic augmentation index (DAI), radial augmentation index (AIr), and any combination thereof.

[0189] In some embodiments, the cardiovascular parameter is suitable for use in predicting a cardiovascular condition, mental workload, or a combination thereof in the user.

[0190] In some embodiments, the device includes a lead (e.g., a copper electrode) configured to transmit the signal from the triboelectric sensor to the communication module. In some embodiments, the lead is in contact with the triboelectric sensor.

[0191] In some embodiments, the device includes a means for transmitting the data from the device to a second electronic device, the second electronic device conducting the processing of the data.

[0192] In some embodiments, the device further includes, before the processing of the data, a means for conditioning the data and extracting a plurality of features from the data, the prediction model using the extracted features as an input to determine the indication. In some examples, the method further includes, before the processing of the data, identifying one or more salient features from the plurality of features and identifying correlations between the one or more salient features, the prediction model using the identified one or more salient features and the identified correlations as an input to determine the indication. In some examples, the method further includes, before the processing of the data, determining a suitable prediction Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 model based on the one or more salient features. In some examples, extracting a plurality of features from the data includes extracting at least one of: heart rate, digital volume pulse (DVP), heart rate variability (HRV), radial diastolic augmentation index (DAI), and radial augmentation index (AIr). In some examples, the plurality of features extracted is selected based on their potential salience in predicting a future cardiovascular event based on a score that ranks their importance and potential. In some examples, the indication is based on a predicted probability of a cardiovascular event calculated by the prediction model.

[0193] In some embodiments, the device further includes a means for extracting beat morphology features from the physiological signals, and where the prediction model is configured to determine the indication as a function of the extracted morphology features.

[0194] Certain examples of the present disclosure provide for a device that can provide a noninvasive system for monitoring one or more cardiovascular parameters of the user. Furthermore, examples of the device can be utilized to alert patients, caregivers, and healthcare providers with cardiovascular events and abnormalities. In some embodiments, the device provides a noninvasive means for heart rate monitoring and mental workload assessment.

[0195] In some embodiments, the device provides a high signal-to-noise ratio (SNR) of a triboelectric signal sufficient to interface with low-power wireless telemetry systems. For example, an SNR that is 100 times greater in power corresponds to 20 dB. In some embodiments, the device provides an SNR of greater than about 20 dB, greater than about 25 dB, greater than about 30 dB, greater than about 35 dB, or greater than about 40 dB. In some embodiments, the device provides an SNR of about 20 dB to about 60 dB, such as about 25 dB to about 60 dB, about 30 dB to about 60 dB, about 35 dB to about 60 dB, or about 40 dB to about 60 dB.

[0196] In some embodiments, the present disclosure relates to a method of preparing a film comprising mixing lignin, a plasticizer, and a binder in water, thereby forming a film.

[0197] In some embodiments, the present disclosure relates to a method of preparing a film comprising: mixing lignin, a plasticizer, and a binder in water, thereby forming an ink composition; and setting the ink composition, thereby forming a film.

[0198] In some embodiments, the present disclosure relates to a method of preparing a film comprising: mixing lignin, a plasticizer, and a binder in water, thereby forming an ink composition; and coating a substrate with the ink composition, thereby forming a film.

[0199] In some embodiments, the step of setting includes drying the ink composition, thereby forming a film. In some embodiments, the step of setting includes drying the ink composition, thereby forming a film, and thereby forming nanodomains on an outer surface of the film. In Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 some embodiments, the drying is performed for a time of about 1 minute to about 360 minutes (e.g., about 120 minutes).

[0200] In some embodiments, the step of setting includes coating a substrate with the ink composition, thereby forming a film. In some embodiments, the step of setting includes coating a substrate with the ink composition and drying the ink composition, thereby forming a film.

[0201] In some embodiments, the step of mixing further comprises heating the ink composition to a temperature of about 50 °C to about 200 °C, such as about 100 °C to about 200 °C, about 100 °C to about 180 °C, about 100 °C to about 160 °C, about 100 °C to about 150 °C, about 80 °C to about 200 °C, about 80 °C to about 180 °C, or about 80 °C to about 160 °C. The ink composition, for example, may be heated to a temperature of about 80 °C, about 90 °C, about 100 °C, about 110 °C, about 120 °C, about 130 °C, about 140 °C, about 150 °C, or about 160 °C. In certain preferred embodiments, the ink composition is heated to a temperature of about 100 °C to about 150 °C (e.g., about 130 °C).

[0202] The step of coating may include any suitable coating technique, such as a suitable industrial roll-to-roll coating technique (e.g., gravure coating and slot-die coating). In some embodiments, the step of coating comprises blade coating, gravure coating, slot-die coating, printing, spray coating, or dip coating. In some embodiments, the step of coating comprises blade coating, printing, spray coating, or dip coating. In some embodiments, the step of coating comprises blade coating.

[0203] In some embodiments, the step of coating (e.g., blade coating) comprises heating a blade to a temperature of about 50 °C to about 200 °C, such as about 80 °C to about 200 °C, about 80 °C to about 160 °C, about 100 °C to about 150 °C, about 100 °C to about 140 °C, or about 100 °C to about 120 °C. The blade, for example, may be heated to about 80 °C, about 90 °C, about 100 °C, about 110 °C, or about 120 °C. In some embodiments, the step of coating comprises heating the blade and pressing the ink composition under the blade.

[0204] In some embodiments, the step of coating (e.g., blade coating) comprises heating the ink composition to a temperature of about 50 °C to about 200 °C, such as about 80 °C to about 200 °C, about 80 °C to about 160 °C, about 100 °C to about 150 °C, about 100 °C to about 140 °C, or about 100 °C to about 120 °C prior to or during the step of pressing the ink composition under the blade. The ink composition, for example, may be heated to about 80 °C, about 90 °C, about 100 °C, about 110 °C, about 120 °C, about 130 °C, about 140 °C, about 150 °C, or about 160 °C. In some embodiments, the step of coating comprises heating the ink composition and pressing the ink composition under the blade. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0205] In some embodiments, the step of coating includes a step of drying the film, thereby forming nanodomains on an outer surface of the film. In some embodiments, the drying is performed for a time of about 1 minute to about 360 minutes (e.g., about 120 minutes). In certain preferred embodiments, the drying is performed for a time of about 60 minutes to about 150 minutes.

[0206] In some embodiments, the method comprises a step of detaching the substrate from the film. For example, the substrate may be used to prepare (e.g., form or mold) the film, but not used in the end-use application of the film.

[0207] In some embodiments, the ink composition does not comprise an organic solvent, a surfactant solvent, an alkaline solvent, a binary mixture of a nonpolar and a polar solvent, or a deep eutectic solvent. In some embodiments, the ink composition does not include a base.

[0208] In some embodiments, the present disclosure relates to a composition comprising lignin, preferably wherein the lignin is dispersed therein (for example preferably wherein the composition has an aqueous lignin dispersibility of about 100 mg / mL); a plasticizer (e.g., urea, glycerol, polyethylene glycol, a citric acid ester, and sorbitol, and preferably urea); and a binder (e.g., gelatin, polyethylene glycol, and polyvinyl alcohol, and preferably gelatin). The composition may have a neutral or acidic pH. The weight ratio of lignin to the plasticizer may be about 1 :2 to about 2: 1. The weight ratio of lignin to the plasticizer may be about 1:3 to about 3:1. In some embodiments, the weight ratio of lignin to the plasticizer is about 1:1 to about 3: l, such as about 5: 2. The weight ratio of lignin to the binder may be about 1:2 to about 2:1. In some embodiments, the weight ratio of lignin to the binder may be about 1 :2 to about 2: 1 , such as about 5: 3.

[0209] In some embodiments, the disclosure relates to an eco-friendly composition (or ink composition) and method of preparing a composition (or ink composition) to significantly improve the aqueous dispersibility of lignin. In some embodiments, the disclosure relates to a lignin-based wearable film (or wearable device) as a sustainable alternative to plastic-based skin-integrated triboelectric sensors (SITS) for cardiovascular monitoring.

[0210] Additional embodiments, features, and advantages of the disclosure will be apparent from the following detailed description and through practice of the disclosure. The compositions of the present disclosure can be described as embodiments in any of the following enumerated clauses. It will be understood that any of the embodiments or clauses described herein can be used in connection with any other embodiments or clauses described herein to the extent that the embodiments do not contradict one another.

[0211] 1. A composition comprising: Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 lignin; a plasticizer; and a binder; wherein the composition does not comprise a starch.

[0212] 2. The composition of clause 1 , wherein the plasticizer is selected from the group consisting of urea, polyethylene glycol, a citric acid ester, and sorbitol, preferably wherein the plasticizer is urea.

[0213] 3. The composition of clause 1 or 2, wherein the binder is selected from the group consisting of gelatin, polyvinyl alcohol, and polyethylene glycol, preferably wherein the binder is gelatin.

[0214] 4. The composition of any one of the preceding clauses, wherein the composition comprises about 10 wt% to about 70 wt% of lignin, preferably wherein the composition comprises about 50 wt% lignin.

[0215] 5. The composition of any one of the preceding clauses, wherein the composition comprises about 10 wt% to about 70 wt% of plasticizer, preferably wherein the composition comprises about 20 wt% of the plasticizer.

[0216] 6. The composition of any one of the preceding clauses, wherein the composition comprises about 10 wt% to about 70 wt% of binder, preferably wherein the composition comprises about 30 wt% of the binder.

[0217] 7. The composition of any one of the preceding clauses, wherein the composition comprises a weight ratio of lignin to the plasticizer of about 1: 10 to about 10: 1, preferably wherein the composition comprises a weight ratio of lignin to the plasticizer of about 1 :5 to about 5:1, more preferably wherein the composition comprises a weight ratio of lignin to the plasticizer of about 1:2 to about 3: 1.

[0218] 8. The composition of any one of the preceding clauses, wherein the composition comprises a weight ratio of lignin to the binder of about 1:10 to about 10:1, preferably wherein the composition comprises a weight ratio of lignin to the binder of about 1 :5 to about 5: 1, more preferably wherein the composition comprises a weight ratio of lignin to the binder of about 1: 1 to about 2: 1.

[0219] 9. The composition of any one of the preceding clauses, wherein the lignin has a molecular weight of greater than about 1 kDa (e.g., about 1.1 kDa).

[0220] 10. The composition of any one of the preceding clauses, wherein the composition does not comprise an organic solvent, a surfactant solvent, an alkaline solvent, a binary mixture of a nonpolar and a polar solvent, or a deep eutectic solvent. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0221] 11. The composition of any one of the preceding clauses, further comprising water.

[0222] 12. The composition of clause 11, wherein the composition has an aqueous lignin dispersibility of greater than about 10 mg / mL (e.g., greater than about 25 mg / mL greater than about 50 mg / mL, or greater than about 75 mg / mL), preferably wherein the composition has an aqueous lignin dispersibility of about 100 mg / mL.

[0223] 13. The composition of any one of the preceding clauses, wherein the composition has a surface potential of greater than about 3 eV (e.g., greater than about 4 eV or greater than about 5 eV).

[0224] 14. The composition of any one of the preceding clauses, wherein the composition is tribonegative.

[0225] 15. The composition of clause 14, wherein the composition has a current density of greater than about 1 nA / cm2(e.g., greater than about 2 nA / cm2, greater than about 5 nA / cm2, or greater than about 10 nA / cm2).

[0226] 16. A film comprising: a layer comprising a composition, the composition comprising lignin, a plasticizer, and a binder, wherein the composition does not comprise a starch, wherein the layer is arranged to provide an outer surface and an inner surface spaced apart from the outer surface.

[0227] 17. The film of clause 16, wherein the outer surface comprises nanodomains.

[0228] 18. The film of clause 17, wherein the nanodomains have a lateral size of about 100 nm to about 2 pm, and the nanodomains protrude about 20 nm to about 150 nm from the outer surface.

[0229] 19. The film of any one of clauses 16-18, further comprising a substrate coupled to the inner surface.

[0230] 20. The film of clause 19, wherein the substrate is a conductive substrate (e.g., aluminum, fluorine tin oxide, polyethylene terephthalate, copper foil, silver nanowires-coated foil, carbon nanotubes, or graphene).

[0231] 21. The film of any one of clauses 16-20, wherein the film has a thickness of less than about 20 pm (e.g., less than about 10 pm, less than about 5 pm, or less than about 2 pm).

[0232] 22. A wearable device for measuring a physiological property when worn by a user, the device comprising: a triboelectric sensor comprising the film of any one of clauses 16-21; Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 a fixation element configured to secure the triboelectric sensor to exposed skin of the user; and a communication module configured to receive a signal from the triboelectric sensor and output data.

[0233] 23. The device of clause 22, wherein the fixation element (e.g., an adhesive, such as PVA paper) is configured to secure the outer surface of the film to exposed skin of a user.

[0234] 24. The device of clause 22 or 23, wherein the fixation element is configured to locate the triboelectric sensor proximal to a radial artery location of the user.

[0235] 25. The device of any one of clauses 22-24, wherein the triboelectric sensor is configured to sense skin deformation of the user wearing the device.

[0236] 26. The device of any one of clauses 22-25, wherein the signal is a current output.

[0237] 27. The device of any one of clauses 22-26, wherein the data is suitable for use in quantifying a cardiovascular parameter.

[0238] 28. The device of clause 27, wherein the cardiovascular parameter is selected from the group consisting of heart rate, digital volume pulse (DVP), heart rate variability (HRV), radial diastolic augmentation index (DAI), radial augmentation index (AIr), and any combination thereof.

[0239] 29. The device of clause 27 or 28, wherein the cardiovascular parameter is suitable for use in predicting a cardiovascular condition, mental workload, or a combination thereof in the user.

[0240] 30. A method of preparing a film, the method comprising the steps of: mixing lignin, a plasticizer, and a binder in water, thereby forming an ink composition; and coating a substrate with the ink composition, thereby forming a film.

[0241] 31. The method of clause 30, wherein the step of mixing further comprises heating the ink composition at a temperature between about 50 °C and about 200 °C (e.g., about 130 °C).

[0242] 32. The method of clause 30 or 31, wherein the step of coating comprises blade coating, gravure coating, slot-die coating, printing, spray coating, or dip coating.

[0243] 33. The method of clause 30 or 31, wherein the step of coating comprises blade coating.

[0244] 34. The method of clause 33, wherein the blade coating comprises heating the ink composition to a temperature of about 80 °C to about 160 °C (e.g., about 110 °C) and pressing the ink composition under a blade. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0245] 35. The method of any one of clauses 30-34, wherein the step of coating further comprises drying the film, thereby forming nanodomains on an outer surface of the film.

[0246] 36. The method of clause 35, wherein the drying is performed for a time of about 1 minute to about 360 minutes (e.g., about 120 minutes).

[0247] 37. The method of clause 35, wherein the nanodomains have a lateral size of about 100 nm to about 2 pm, and the nanodomains protrude about 20 nm to about 150 nm from the outer surface.

[0248] 38. The method of any one of clauses 30-37, wherein the substrate is a conductive substrate (e.g., aluminum, fluorine tin oxide, polyethylene terephthalate, copper foil, silver nanowires-coated foil, carbon nanotubes, or graphene).

[0249] 39. The method of any one of clauses 30-38, wherein the film has a thickness of less than about 20 pm (e.g., less than about 10 pm, less than about 5 pm, or less than about 2 pm).

[0250] 40. The method of any one of clauses 30-39, wherein the method further comprises detaching the substrate from the film.

[0251] 41. The method of any one of clauses 30-40, wherein the plasticizer is selected from the group consisting of urea, polyethylene glycol, a citric acid ester, and sorbitol, preferably wherein the plasticizer is urea.

[0252] 42. The method of any one of clauses 30-41, wherein the binder is selected from the group consisting of gelatin, polyethylene glycol, and polyvinyl alcohol, preferably wherein the binder is gelatin.

[0253] 43. The method of any one of clauses 30-42, wherein the composition comprises about 10 wt% to about 70 wt% of lignin, preferably wherein the composition comprises about 50 wt% lignin.

[0254] 44. The method of any one of clauses 30-43, wherein the composition comprises about 10 wt% to about 70 wt% of plasticizer, preferably wherein the composition comprises about 20 wt% of the plasticizer.

[0255] 45. The method of any one of clauses 30-44, wherein the composition comprises about 10 wt% to about 70 wt% of binder, preferably wherein the composition comprises about 30 wt% of the binder.

[0256] 46. The method of any one of clauses 30-45, wherein the composition comprises a weight ratio of lignin to the plasticizer of about 1: 10 to about 10: 1, preferably wherein the composition comprises a weight ratio of lignin to the plasticizer of about 1 : 5 to about 5: 1, more Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 preferably wherein the composition comprises a weight ratio of lignin to the plasticizer of about 1:2 to about 3: 1.

[0257] 47. The method of any one of clauses 30-46, wherein the composition comprises a weight ratio of lignin to the binder of about 1 :10 to about 10: 1, preferably wherein the composition comprises a weight ratio of lignin to the binder of about 1 :5 to about 5:1, more preferably wherein the composition comprises a weight ratio of lignin to the binder of about 1: 1 to about 2:1.

[0258] 48. The method of any one of clauses 30-47, wherein the lignin has a molecular weight of greater than about 1 kDa (e.g., about 1.1 kDa).

[0259] 49. The method of any one of clauses 30-48, wherein the ink composition does not comprise an organic solvent, a surfactant solvent, an alkaline solvent, a binary mixture of a nonpolar and a polar solvent, or a deep eutectic solvent.

[0260] EXAMPLES

[0261] The examples and preparations provided below further illustrate and exemplify particular aspects of embodiments of the disclosure. It is to be understood that the scope of the present disclosure is not limited in any way by the scope of the following examples.

[0262] EXAMPLE 1

[0263] Materials and Methods

[0264] Lignin extraction

[0265] Lignin was extracted from a pine source (softwood kraft lignin). The lignin was pulped in a PaiT 4520 reactor with a 10% NaOH solution. The cooking temperature was maintained at 180 °C for 30 min. The black liquor was acquired by subsequently filtrating and centrifuging the pulp. The lignin pulp was obtained via acidification and precipitation of the black liquor, which was acidified to a pH of 2.0 by dropwise addition of hydrochloric acid. Then the sluiTy / precipitate was washed twice with purified water. The dry lignin powders have been collected after air drying overnight.

[0266] Lignin-gelatin-urea ink preparation

[0267] Lignin was mixed with gelatin and urea in a 25 mL flask at various ratios of concentrations for a total weight of 800 mg. Distilled water (4 mL) was added to mix the components. Then the flask with the dispersed components was placed on the hot plate at 130 °C and stirred at 300 rpm for 1 h. Afterwards, a viscous ink / slurry was obtained, and this ink was cooled down to room temperature prior to use. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0268] Structural and Chemical Characterization

[0269] Evaluation of dispersibility of Lignin

[0270] The dispersibility of lignin was evaluated by measuring the gravimetric dispersibility. The lignin solutions were magnetically stirred for 1 h at 130 °C. Any insoluble residues were separated by centrifugation at room temperature (5000 rpm, 10 min), and the supernatant was decanted. After being filtered (Whatman paper), any insoluble residues / renmants on the paper were dried at 100 °C for 1 h, and weighed to determine the percentage of non-dispersed lignin. The mixtures ratios of G:L:U that displayed residues on the paper were considered as nondispersed lignin (wt.%).

[0271] Hansen Solubility Parameters (HSP) description.

[0272] The Hansen solubility parameters allow fomiulators to predict which solvents best dissolve certain polymers or which polymers will be compatible with each other, facilitating the design of materials with specific solubility characteristics.

[0273] The following equation states that the total solubility parameter squared is the sum of the contributions from dispersive forces, polar forces, and hydrogen bonding. The total solubility parameter is a measure of a substance's ability to dissolve in or mix with another substance, and it comprises these three components. al = al + s$ + a

[0274] Teas graph description.

[0275] The molecular compatibility between the ink components was analyzed using the HSP framework, which partitions the total cohesive energy density (ST) into contributions from dispersion (3D), polar (8p), and hydrogen bonding (3H) forces. The fractional contributions of these parameters were visualized using a Teas graph to predict the miscibility.

[0276] On a TEAS graph, the position of a point relative to the axes reflects the balance of the three types of interactions (dispersive, polar, and hydrogen bonding) that a molecule can possess. The following three equations define the fractional contributions of each component (dispersive, polar, and hydrogen bonding) to the total solubility parameter. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0277] Each fraction is the respective component's solubility parameter divided by the sum of all three components. These fractions can be useful for understanding the relative importance of each type of intermolecular force in the solubility of a substance.

[0278] The fractions of all three components can be checked regarding whether they add up to 1 (or 100%) by the following equation: fo + fp + fn = 1

[0279] Equations that represent the open-circuit voltage and short-circuit transferred charge of triboelectric sensors.

[0280] The open-circuit voltage of a triboelectric sensor can be given as:

[0281] The short-circuit transferred charge can be written as:

[0282] S x(t) Qoc =d0+ x(t)1

[0283] 2D-Heteronuclear single quantum coherence spectroscopy (HSQC)-NMR characterization of lignin-gelatin-urea ink

[0284] Nuclear magnetic resonance (NMR) spectra of the raw lignin and lignin-urea-gelatin mixture were acquired in a Bruker Avance III 500-MHz spectrometer with a N2 cryo-platform prodigy probe. About 50 mg of lignin or the freeze-dried mixture was suspended in 0.5 mL DMSO-de in NMR tube. The 2D13C-’H heteronuclear single quantum coherence (HSQC) experiments were carried out with a Bruker pulse sequence (hsqcetgpspsi2.2) on a N2 cry oprobe (BBO lH&19F-5mm) with the following acquisition parameters: spectra width 12 ppm in F2 (XH) dimension with 1024 data points (acquisition time 85.2 ms), 200 ppm in Fl (13C) dimension with 256 increments (acquisition time 5.1 ms), a 1.0-s delay, a ^C-H of 145 Hz, and 256 scans. The acquired spectra were processed using a Bruker Topspin 4.0 (Mac) software. The central DMSO solvent peak (8C / 8H at 39.5 / 2.49) was used for chemical shifts calibration. Assignments of lignin compositional subunits and interunit linkage were based on Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 the reported contours in HSQC spectra. A semi-quantitative analysis of the HSQC cross-signal intensities was performed for the measurement of S, G, and side chain linkages. The Casignals were used for contour integration for inter-unit linkage estimation.

[0285] In NMR spectroscopy, the chemical shift (ppm) quantitatively indicates how shielded or deshielded a nucleus is: High ppm (downfield): Values above -6 ppm for 'H or above -100 ppm for13C suggest a deshielded environment. This often occurs near electronegative atoms or aromatic rings, where electron density is pulled away from the nucleus. Low ppm (upfield): Values below -3 ppm for ‘H or below -50 ppm for13C indicate a shielded environment. This is typical in simple aliphatic chains, where electron density is higher around the nucleus, reducing its exposure to the magnetic field.

[0286] Atomic force microscopy (AFM).

[0287] The film morphology was characterized using atomic force microscope (AFM) (Keysight 5500) in the tapping mode in air to characterize the morphology of peptide selfassembled structures. It was equipped with a silicon cantilever (ACTA, AppNano, USA) with a typical spring constant of 37 N / m, resonance frequency of 300 kHz, and a tip radius lower than 10 nm.

[0288] Kelvin probe force microscopy (KPFM).

[0289] The AFM Keysight 5500 was used to simultaneously measure the surface potential using KPFM of the samples. It was equipped with a gold-coated silicon cantilever (ACTGG, AppNano, USA) with a typical spring constant of 37 N / m, resonance frequency of 300 kHz, and a tip radius lower than 10 nm.

[0290] Fluorescence microscopy .

[0291] The excitation wavelength was 632.8 nm, and the spectra were recorded between 650 and 800 nm, detecting an emission wavelength peak between 650 and 750 nm. The spectra were recorded by a SpectraPro 300i Spectrograph with a grating of 1800 Grooves / mm. The image was taken at 100 points per line with a scan width and height of 10 pm. The sampling pitch was 1 nm. A speed of sampling of 50 lines / min was employed to guarantee the sensitivity. All the measurements were performed with a WITec AFM / Raman device.

[0292] Fourier transformed infrared spectroscope.

[0293] Attenuated total reflection Fourier transformed infrared spectroscopy (ATR-FTIR) tests were performed with an Thermo Nicolet Nexus FTIR spectrometer equipped with a universal ATR sampling accessory and with a MCT detector using a liquid cell (Fixed Cell, suitable for volatile solvents), averaging 8 scans at a resolution of 4 cm-1in the range of 4000 to 800 cm-1. Scanning electron microscopy (SEM). Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0294] Ultra-high-Resolution Field Emission Scanning Electron Microscope (FE-SEM) was used to assess the morphology of samples, such as for verification of nanostructure and surface. SEM tests were carried out using a Hitachi SU8230 at 0.8, 3 and 6 kV, depending on magnification. Specimens were attached to a copper tape and analyzed without using sputtering.

[0295] Device Fabrication and Performance Characterization

[0296] Triboelectric sensor fabrication.

[0297] The triboelectric nanogenerators were fabricated by cutting the lignin / Al films into size of 1 cm2. They were attached to a glass substrate for mechanical support. Then, a copper lead was attached to the Al film for electrical characterization.

[0298] Triboelectric characterization.

[0299] For the measurement of the electric outputs of the triboelectric devices, an external force was applied by using a linear motor (LinMot PS01-23 x 80) and applying a programmed strain (operating distance, 20 mm; maximum speed, 1 m s-1; acceleration, 1 m s-2; deceleration, 1 m s-2). The thickness of the films was measured by a mechanical micrometer and a coating thickness gauge (CM-205FN). Measurements of output voltages in the triboelectric devices were carried out with a Keithley 6514 engaged with LabView software. The current outputs were measured by a low-noise current preamplifier (Stanford Research Systems SR570) following an appropriate configuration.

[0300] Proof-of-Concept Physiological Monitoring Study

[0301] Cardiovascular monitoring: Heart rate device.

[0302] The heart rate device was fabricated by using the lignin / Al films as a tribo-negative material and the skin was used as a counter tribo-positive material. The lignin / Al films were coated onto PVA paper and attached to the skin (e.g., wrist) for heart rate measurement.

[0303] Subject recruitment.

[0304] The validation and evaluation of the wearable device were performed on healthy human subjects in compliance with the protocols (IRB-2019-156) approved by the Institutional Review Board at Purdue University. Participating subjects were recruited from the Purdue campus through advertisement by posted notices, word of mouth and email distribution. One healthy subject (male, age 33) was included in this study. All subjects gave written informed consent before participation in the study. The study was fully voluntary, and no compensation was given. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0305] EXAMPLE 2

[0306] Complex structure of lignin and engineered dispersion in Urea

[0307] Rational design unlocks high-concentration aqueous lignin processing

[0308] The present disclosure provides an environmentally friendly process for obtaining well- dispersed lignin ink and printing ultrathin (down to 1 pm) soft robust lignin films with designer- engineered triboelectric properties. Fig. 1A shows the complex nature of the unfragmented softwood pine kraft lignin used in this study, which is mainly composed of polar groups such as hydroxyl, carboxyl, and ether, and non-polar groups such as aromatic guaiacyl units (G) linked via guaiacyl-type P-O-4’. Pine is easily accessible in the U.S. and is one of the main sources of pulp. Owing to its aromatic polymeric structure, unfragmented lignin is extremely difficult to disperse in water (only up to 1 mg / niL). The isolated Kraft lignin powder was mixed with gelatin and urea to increase its aqueous dispersibility to 100 mg / mL (100 times higher than that in distilled water and 10 times higher than that in alkaline solutions), enabling the processing of lignin-based aqueous ink.

[0309] The rational selection of urea and gelatin as key components was guided by Hansen Solubility Parameter (HSP) analysis (Figs. 2 and 3), a predictive framework that assesses molecular compatibility based on dispersion (3D), polar (8p), and hydrogen bonding (8H) forces. Urea plasticizes the solid polymeric phases of lignin and gelatin, preventing large-scale phase segregation between lignin and gelatin binder. In the aqueous phase, urea acts as a hydrotrope, disrupting the intermolecular self-association of lignin and mediating its interaction with water. Urea is also a good keratolytic agent typically used in skincare products. Gelatin was utilized as a binder because of its partial compatibility with lignin through intermolecular hydrogenbond and aromatic non-polar interactions.

[0310] The dispersibility of lignin was studied for several concentrations of the gelatin-lignin- urea mixture. The Hansen solubility parameter (HSP) 8t2= 5D2+ 8p2+ 5H2was used, which indicates the molecular compatibility between solvents and molecules, to evaluate the ability of urea to disperse lignin. St denotes the total HSP. 8D is the energy of the dispersion forces between molecules. 8p is the energy of the dipolar intermolecular forces between molecules. 6H is the energy of the hydrogen bonds between molecules. Figures 2 and 3 show the representation of the HSP in a Teas graph (the representation of the mathematical fractional contributions of St and HSP), where the HSP of urea (3D 22.9, 8p 14.9, Sir 21.3), lignin (3D 21.9, 8p 14.1, 8H 16.9), and other reported solvents of lignin are located. The locations of the urea and lignin molecules are close, indicating that urea is highly compatible with lignin at the molecular level. Lignin has a similar ability to form intermolecular bonds between its hydroxyl, Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 carboxyl, ether, and aromatic groups as urea does with its carbonyl and amine groups. In both lignin and urea, these bonds are formed through hydrogen bonding, dipole-dipole interactions, or dispersion forces, which makes lignin miscible in a urea solution.

[0311] EXAMPLE 3

[0312] Demonstration of lignin structure preservation after dispersion

[0313] Benign aqueous processing preserves lignin’s molecular integrity

[0314] An advantage of the benign aqueous process used to form the lignin films of the present disclosure is the preservation of the native molecular structure of lignin, which can be a critical prerequisite for achieving both a high triboelectric performance and biocompatibility. To gain insight into the structural preservation of lignin molecules after mixing with gelatin and urea, the 2D-heteronuclear single quantum coherence spectroscopy nuclear magnetic resonance (2D-HSQC-NMR) spectra was collected, which characterized the structural information of complex molecules, such as pure lignin and lignin in the mixture, and identified different structural units and linkages within the lignin polymer (Figs. 1B-1E, 4, and 6).

[0315] Figs. IB to IE show the 2D-HSQC-NMR spectra of lignin and the lignin mixture in the aliphatic (5C / 5H 50-90 / 2.5-6.0) and aromatic (5C / 5H 95-135 / 6.0-8.0) regions, respectively, providing information on the subunits and linkages of the lignin molecule. 5C / 5H refers to the chemical shift of two different types of nuclei, commonly protons <1H ) and carbons (13C), and provides information about the connectivity of the two types of nuclei in the lignin molecule (Fig. 4). The presence of lignin, urea, and gelatin was verified using full 'H-NMR and 2D HSQC-NMR spectroscopy, as shown in Fig. 4 and Fig. 6. Fig. 4 shows the characteristic spectral patterns of the three components, and Fig. 6 shows the full 2D-HSQC-NMR spectra for pure lignin and the mixture, with detailed descriptions of the aliphatic and aromatic regions below. The spectra of the lignin mixture and pure lignin showed that the side aromatic groups were preserved (specific carbon-hydrogen (C-H) pairs of guaiacyl and oxidized guaiacyl are labeled as G2, G’2, Gs, and Ge) (Figs. 1B-1C), which are essential for tribonegativity. Furthermore, the spectra show that the alky lie / ally lie (aliphatic) groups of lignin (specific C-H pairs of I: cinnamyl alcohol, A: P-O-4’ linkage, A’: y-acylated -O-4’ linkage, B: P-5’ linkage, and C: P-P’ linkage) are present in both pure lignin and lignin in the mixture (Fig. 1D-1E). The spectra provided definitive evidence of structural preservation, confirming the retention of both the key aromatic guaiacyl (G, G’) units and, critically, 97.6% of the fragile P-O-4’ ether linkages. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0316] Overall, the aromatic and alkylic / allylic (aliphatic) contents of lignin were retained after mixing and processing with gelatin and urea. The surface potential increases with increasing aromatic content, which influences the triboelectric properties of the lignin films. Regarding the alkylic / allylic (aliphatic) bonds, the P-O-4’, (3-(3 ' and the P-5’ bond were studied as they are the covalent bonds of the backbone of lignin and prone to break during lignin processing. Typical methods of lignin dispersion unintentionally fractionate molecules, reducing their molecular weight to 490 Da. Without being bound by any theory, molecules with molecular weights lower than 500 Da can penetrate the skin; hence, verifying the integrity of the molecular structure is important. The P-O-4’ ether bond is present in an abundance of 75.8% in pure lignin and 74.0% in the lignin mixture. P~P’ bond is present in an abundance of 14.0% in pure lignin and 14.1% in lignin mixture. P-5’ bond presents an abundance of 10.1% in pure lignin and 11.9% in lignin mixture. Fig. IF shows a schematic of the most abundant lignin substructures found by 2D-HSQC NMR, including the monomeric aromatic guaiacyl units (Fig. 1F-1,2), conserved ether bonds P-O-4’ (Fig. lF-5,7), and carbon-carbon bonds p~P' and P-5’ (Fig. lF-6,8). The C-C signals of the mixed lignin are prevalent (Fig. 1F-1,2), which may imply that the C-C bonds of the non-polar guaiacyl units in the lignin remain stable after mixing with gelatin and urea. Previous methods to disperse lignin in deep eutectic solvents triggered the breakage of lignin molecules, thus losing most of the structural properties that are desired in SITS applications. The lignin used in the instant examples has a molecular weight of over 1.1 kDa, hence the lignin mixtures are safe for contact with the skin by demonstrating the preservation of the molecular structure even after mixing. In addition, the stability of triboelectric properties of polymers is related to their structural stability. High molecular weights ensure mechanical durability against long-term continuous friction. Because the triboelectric properties of a triboelectric sensor are related to the aromatic structure of polymers, it was encouraging that the disclosed method of sustainably processing lignin in an aqueous solution preserved the aromatic content.

[0317] Process-driven self-assembly creates a functional triboelectric surface

[0318] Regarding the preparation of lignin ink, the highest dispersibility of lignin was identified by mixing it with gelatin and urea (from 0% to 70% wt / wt %, the limit where lignin precipitation was observed). Fig. 5A shows aqueous lignin dispersions with different ratios (wt / ' / wt / wt %) of lignin (L), gelatin (G), and urea (U). Precipitation was observed at the bottom of the flasks for the 10G:50L:40U and 10G:70L:20U flasks. The measured gravitational dispersibility is also shown in the ternary phase diagram in Fig. 5B (a complete set of images of the mixtures used in the ternary plot is shown in Fig. 7). This ternary phase diagram shows Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 the degree of dispersion at several proportions of lignin, gelatin, and urea (the corners of the ternary plot represent the pure component). The dispersibility of the lignin increases when gelatin and urea are introduced. The highest lignin degree of dispersion (0.8) was obtained for the mixture of ratio around 30G:50L:20U, shown in the central region of the ternary phase diagram plot. Thus, the composition of 30G:50L:20U was identified as the optimal lignin ink composition for high dispersibility. At concentrations lower than 50%, the lignin exhibited high dispersibility in the mixture.

[0319] Furthermore, to evaluate the capability of the mixtures to form thin films used as triboelectric sensors, the ink dispersion was blade-coated on an aluminum foil. Figs. 5C-5D show the blade-coating process of the lignin ink 30G:50L:20U utilized to form a thin film of 100 pm of thickness (Fig. 5E). The printed lignin film showed transparency and good homogeneity on the PET substrate, indicating no macroscale segregation during blade coating (Fig. 5E). This homogeneous distribution was also verified by the intrinsic fluorescence of lignin in the films (Fig. 8A-8B, 9, and 10). The optimized lignin ink (30G:50L:20U) was further blade-coated (Figs. 5C-5D) to form target homogeneous ultrathin (-1 pm) films.

[0320] Moreover, the surface structure of the films was analyzed to study the lignin distribution on the film using atomic force microscopy and fluorescence, an accepted method for correlating the structure of polymeric phases in polymer blends. Fig. 5F shows the fluorescence and atomic force microscopy (AFM) of 100G (film with 100% gelatin) and lignin film 30G:50L:20U. These images show the correlation between the intrinsic fluorescence of lignin and the nanodomain distribution on the surface of the films (Figs. 5F-1 and 5F-5). These nanodomains are suggested to be caused by the formation of separated-phase polymeric blend structures due to the incompatibility of non-polar groups of lignin with the polar groups of gelatin in the mixture. This incompatibility triggers the segregation of lignin molecules from gelatin according to molecular polarity preference. The phase separation of lignin and gelatin due to the incompatibility of nonpolar and polar groups modifies the structure spontaneously during the drying of the films, forming nanodomains. The lateral size of the domains varied from 100 nm to ~1.8 pm and protruded from the surface by -30-140 nm with a mean of -53 nm (Figs. HA and 1 IB). In contrast, the pure gelatin films showed a flat surface without protrusions and aggregations (Fig. 5F-2). In addition, nanodomains appeared only at high concentrations of lignin in the mixture (Fig. 5F-6).

[0321] As described herein, as the nanodomains and fluorescence correlate in the films, it is suggested that lignin is mainly present on the nanodomain rather than in the interstitial space between the nanodomains. Without being bound by any theory, the nanodomain structure is Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 suggested to be caused by a structure-induced enthalpically driven dewetting process during film drying, which is more energetically favorable for lignin to segregate from gelatin because of the preference for intermolecular bonding explained earlier. It is important to mention that lignin should be present on the surface rather than in the bulk to leverage their triboelectric properties, for which this unexpected result benefits the sensor.

[0322] To determine the electron affinity of lignin, the contact electrification of lignin films was studied using KPFM, which demonstrated that self-assembled lignin-rich nanodomains are regions with high negative surface potentials. Contact electrification was measured in terms of surface potential (SP). The SP images of the 50% and lignin 0% films are compared in Fig. 5F- 4,8. The images of lignin 50% showed a higher SP than those of 0% lignin. Interestingly, the SP in the lignin 50% film was also correlated with the nanodomains in the topographic AFM images (Fig. 5F-3, 4, 7, and 8). Furthermore, the SP of lignin films becomes more tribonegative with the concentration of lignin, from 2.32 eV (for pure gelatin) until 5.5 eV at 50% of lignin content (Fig. 11A-1 IB, 12, 13A-13C, and Fig. 5G). This provides a clear physical mechanism that increasing the lignin concentration creates a strongly negative surface, which is the physical origin of the emergent tribonegativity. To explain the triboelectrification phenomena in lignin by KPFM analysis, the metal-dielectric contact model was used (Fig. 5G inset). When gold from the cantilever tip in KPFM and lignin come into contact with each other, surface charge transfer takes place at the contact area owing to contact electrification, resulting in lignin gaining electrons on its surface and gold losing electrons from its surface. The profile of the scanned region, as provided by KPFM, shows the surface potential distribution across the area, indicating that the lignin surface has acquired negative electrostatic charges, and hence, has a high electron affinity (Fig. 12). The aromatic groups in lignin molecules have a high electron affinity, in contrast to polar side groups (such as hydroxyl, carboxyl, and ether), which have lower electron affinities. This high electron affinity has been observed for other polymers with high aromatic content, such as polyimide and polystyrene. The self-assembly process concentrates the high-electron-affinity aromatic groups of lignin onto protruding surface domains. These domains function as charge-accumulating "hotspots" that are the origin of the enhanced contact electrification against the tribopositive human skin (Fig. 12).

[0323] To understand how the chemical structure of lignin films influences their triboelectric properties, attenuated total reflectance Fourier transform infrared (ATR-FTIR) analysis was performed to study the chemical structures of pure lignin and lignin in the mixture (Fig. 5H). The absorption bands of lignin (indicated by certain shadowed regions) appearing in the pure sample (“lignin” curve) and in the 30G:50L:20U mixture corresponded to aromatic groups. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0324] Other functional polar groups, such as -OH and -COO, were overshadowed by signals from water molecules and aromatic groups. Aromatic groups in polymers are known to affect electron-withdrawing capability. Therefore, the presence of molecular vibrations were mainly described as belonging to the aromatic groups. The bands at 1591 and 1508 cm'1belong to aromatic skeletal vibration. The band at 1450 cm'1corresponds to C-H in-plane deformation with aromatic ring stretching. The bands at 1263 and 1209 cm'1belong to the C-0 and C-C stretching of the guaiacyl ring, respectively. The bands at 1120 and 1027 cm'1belong to the aromatic C-H in-plane deformation (guaiacyl ring). Moreover, the vibration bands for pure gelatin (“gelatin” curve) and gelatin in the 30G:50L:20U mixture were identified. The vibration bands at 1626 and 1525 cm1correspond to amide I (C=O stretching vibration) and amide II (N-H bending), respectively. The intensity of the amide bands of gelatin was reduced, possibly due to hydrogen bond interactions between lignin and gelatin, as described below. Interestingly, the band at 1716 cm'1, which corresponds to the C=O stretching of a carbonyl group, appears only in the lignin mixture 30G:50L:20U, possibly because of the interaction of the carbonyl (C=O) groups in the gelatin with the hydroxyl groups of lignin through hydrogen bond, given that C=O is the most energetically favorable hydrogen bond acceptor. As the band at 1716 cm'1only appeared in the 30G:50L:20U mixture, but not in the gelatin or pure lignin spectra, it is suggested that this band is due to an intenuolecular hydrogen bond between lignin and gelatin rather than an intramolecular hydrogen bond. Thus, ATR-FTIR spectra served as spectroscopic evidence of a stabilization mechanism based on the formation of new intenuolecular hydrogen bonds (1716 cm'1) that kinetically stabilized the functional nanostructure. In addition, unlike the tendency of lignin molecules to aggregate in pure water, the presence of the 1716 cm'1band and strong aromatic bands between 1450 and 1600 cm'1suggests that lignin can be dispersed with gelatin and urea in a solid lignin film. The presence of lignin on the surface, as proved by AFM FTIR-ATR and fluorescence (Fig. 5F), is beneficial for the triboelectric properties of the SITS device.

[0325] From the observation of the structure of the lignin films by fluorescence, AFM, and KPFM, a schematic of the molecular organization model of the lignin film (Fig. 51) was drawn, where the lignin and gelatin molecules formed a hierarchical micro-nano phase-separated polymeric structure. The model summarizes the pathway from a rationally designed aqueous ink to a functional, stabilized surface via thermodynamically driven self-assembly. The process begins with a rationally designed aqueous ink, where urea acts as a hydrotrope to create a stable, high-concentration lignin dispersion. During coating and drying, thermodynamically driven phase separation induces self-assembly of protruding aromatic-rich nanodomains. These Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 domains create surface potential hotspots that are the origin of the material's strong tribonegativity. While urea serves as a molecular lubricant in the lignin ink, in the solid state, it acts as a plasticizer, maintaining the interaction between lignin and gelatin through interdiffusion, avoiding segregation of lignin in larger domains, and ensuring its homogeneous distribution in the film. Lignin has been reported to favor segregation in polymer composites and blends due to its high non-polar group content. Therefore, urea plays a major role in keeping lignin miscible with gelatin, even after removing water. The hydrophilic groups of lignin and gelatin molecules interact intermolecularly via hydrogen bonds and dipole-dipole interactions. The urea molecules are also associated with the phases separated by H-bonds and dipole-dipole interactions. Thus, this dual mechanism of urea prevents the large-scale segregation common in lignin polymer blends and ensures the uniform distribution and stability of charge-enhancing nanodomains across the film.

[0326] EXAMPLE 4

[0327] Triboelectric properties of lignin films

[0328] Systematic engineering of triboelectric performance

[0329] The influence of the lignin content in the lignin-gelatin films as a triboelectric material was evaluated in the instant example (Figs. 14A-14H). A triboelectric device (e.g., a contactseparation mode device with engineered triboelectric properties) was fabricated using the configuration shown in Fig. 14A. The triboelectric polarity of lignin films was verified using cellulose (Kimtech™), a well-known tribopositive material that is similar to the triboelectric properties of human skin. The characterization showed that the gelatin film (100G) behaves as a tribo-positive material when it comes in contact with cellulose (Fig. 14B). The left inset in Fig. 14B shows tribopositive gelatin (G) and paper, and the right inset shows tribonegative gelatimlignin (G:L). When lignin was introduced into the film, it exhibited a tribo-negative behavior upon contact with cellulose. This demonstrates that lignin shifted the triboelectric polarity of the films. These results demonstrate that the incorporation of lignin successfully inverted the polarity of the material from tribopositive (pure gelatin) to strongly tribonegative. Such tribo-negative behavior is a prerequisite for robust triboelectrification against human skin.

[0330] The relative positions of the 30G:50L:20U lignin films on the triboelectric series, are based on the results shown in Fig. 14B and Figs. 15, 16A-16B. Fig. 14D shows that 1% wt / wt of lignin diminished the triboelectric output from the gelatin film after contact with cellulose. At a lignin content of 50% wt / wt, the triboelectric current output increases to 6 nA cm'2. Thus, the current density was highly dependent on the lignin content, peaking at 50% (w / w). A Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 ternary plot of the cun-ent output of the fabricated lignin-based films shows that 30G:50L:20U composition resulted in the highest current output (Fig. 14E). Thus, the ternary plot of the current output revealed a peak performance at the 30G:50L:20U ratio. In addition, the ternary plot indicates that lignin is responsible for the increase in the current output, while gelatin and urea decrease the output performance of the films. However, at lignin concentrations greater than 50% wt / wt, the triboelectric performance decreased. This is due to the decreased dispersibility of lignin and its consequent segregation in the precursor solutions and films (Figs. 17A and 17B). Such segregation of the lignin polymer onto the film decreases the contact area of lignin-cellulose and increases the contact area of gelatin-cellulose, directly affecting the output performance. Furthermore, the ternary plot of the normalized cun-ent output correlates with the ternary phase diagram of dispersibility, as shown in Fig. 5B.

[0331] Additionally, the triboelectric performance was evaluated using various processing (blade-coating) parameters to obtain lignin thin films (Figs. 14F-14H). The performance was higher for films processed at 110 °C, with an output of 1.5 nA cm’2(Fig. 14F). The processing temperature changes the blade coating processability owing to improved fluidity at higher temperatures. Regarding the thickness, the triboelectric performance is higher for thinner films, reaching a current output of 9 nA cm’2for films of 1 pm thickness (processing temperature of 110°C) (Fig. 14G). A thickness lower than 1 pm did not improve the performance owing to air breakdown. Regarding the drying time, after 120 min, the films reach an output of 15 nA cm'2. This is attributed to the water content in the biopolymer film, which decreases the tribonegativity. The longer the drying time, the lower the water content.

[0332] By using urea as a dispersing agent for lignin, the manufacturability of the lignin ink by blade coating was increased (the complete set of all the blade-coated mixtures and their performance are shown in Figs. 15, 16A and 16B). Moreover, another particularity of the lignin ink is the capacity to create nano-micro-structure without additional steps of manufacturing, such as additional lithography steps (topography on Fig. 5F and Fig. 18).

[0333] The fabrication of microstructures on a surface has been widely investigated as a means to increase the contact area between tribo-positive and tribo-negative materials. Various methods have been reported for fabricating microstructures, including force-assembled colloidal arrays, soft lithography, electrospinning manufacturing, anodic aluminum oxide, and surface micropatterning. In the present disclosure, lignin ink that can spontaneously create films with a nanostructured surface after blade coating and drying was studied. As explained earlier, this pattern on the surface might be caused by the effect of the phase separation of lignin and gelatin polymers in the film triggered by the self-chain organization of both polymers Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 during drying. This type of segregation has also been observed in other blends of gelatin and incompatible polymers. The surface of the film changes depending on lignin concentration. The higher the concentration, the higher the roughness (Fig. 18). As the amount of lignin increases, phase separation occurs, and the polar groups within the lignin chains encapsulate polar molecules, such as water, whereas the non-polar groups encapsulate non-polar groups, such as aromatic groups. Without being bound by any theory, this roughness that was observed might also contribute to the triboelectric output by increasing the surface area and thus the contact area between the lignin films and the tribo-counter material.

[0334] Optimized device performance and scalability for manufacturing

[0335] The performance of the fully optimized film fabricated using the 30G:50L:20U ink and the optimal processing parameters was further explored in the instant example. The triboelectric performance of lignin-based films is shown in Figs. 19A-19E. The short-circuit current and open-circuit voltage of the triboelectric device showed good stability at distinct frequencies of operation, with a corresponding current density output (at 5 Hz) of 22 nA cm’2and a voltage output of more than 30V (obtained with a 30G:50L:20U film of 1 pm and processed at 110 °C with a drying time of 120 min) (Figs. 19A-19B). The current density and voltage at various resistances are shown in Fig. 19C. The highest power density of 20nW cm’2is found at a resistance of 100 M (Fig. 19D). The durability of the triboelectric device shows that the lignin films were stable after 10,000 contact-separation cycles (with a frequency of 5 Hz) (Fig. 19E). To substantiate the suitability of the ink for industrial-scale manufacturing, its rheological properties were characterized. The optimized ink exhibited a viscosity of -200 mPa- s, which is well within the operational window for scalable roll-to-roll coating techniques.

[0336] To evaluate the performance of the lignin-SITS holistically, it was benchmarked against representative biopolymers and synthetic polymer devices across five key axes that are critical for wearable bioelectronics: sustainability, process scalability, biocompatibility, applicationspecific efficacy, and electrical output (Table A). This comparison reveals that the lignin sensor described herein resolves a long-standing trade-off in the field. While synthetic fluoropolymers, such as PTFE, offer a higher absolute power density, they do so at a significant cost to sustainability and biocompatibility. Conversely, conventional biopolymers have historically struggled to deliver the electrical output required for high-fidelity sensing, often requiring energy-intensive processing or the use of complex composites to improve performance. In the examples described herein, the lignin sensor overcomes this critical barrier, achieving an electrical output sufficient for a validated, clinical-grade sensing application Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0337] (Figs. 20A-20R), while establishing a new benchmark for the green, scalable processing of abundant waste biomass.

[0338] Table A. Performance benchmarking of wearable triboelectric sensors using biopolymers and synthetic polymers 1 Total current reported, not normalized by area. Direct comparison of current density is not possible.

[0339] 2Polytetrafluoroethylene (PTFE) is a fluoropolymer with concerns regarding environmental persistence and potential biocompatibility issues related to per- and polyfluoroalkyl substances (PFAS).

[0340] EXAMPLE 5

[0341] Cardiovascular SITS for monitoring mental workload

[0342] Validation of the sustainably engineered material for skin-integrated electronics

[0343] To validate the functional performance of the sustainably engineered lignin film, a skin- integrated triboelectric sensor (SITS) was fabricated, where the lignin film was in direct contact with the skin (Figs. 20A-20R). The lignin film was used as a cardiovascular SITS device in the instant example, as shown in Fig. 20A. The architecture of this design is shown in Fig. 20B, where lignin is used as the tribo-negative material in direct contact with bare skin (tribopositive material). Given that the lignin film was used as a tribonegative material against skin, the current output of this material was first compared with that of other biomaterials. A Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 customized setup was employed to characterize several representative biopolymers against the skin (Figs. 20C, and 21-22). The current outputs of the biopolymers and lignin films when skin was used as a tribo-counterpart are compared in Fig. 20C. The lignin film exhibits up to 4-to 6-fold higher performance than alginate, PAA, gelatin, and CMC, and up to 10-fold higher performance than starch and chitosan, which have been explored for wearable triboelectric sensing. Interestingly, the triboelectric performance of the lignin-based films was opposite to that of PVA, which showed a tribo-positive behavior against the skin. These results suggest that lignin is an ideal biomaterial for SITS that uses skin as a tribo-counterpart, achieving a current output of up to 30 nA cm'2(Fig. 20C). This current output is comparable to that of polyethylene (PE), which is a well-known highly tribo-negative synthetic material.

[0344] High-fidelity cardiovascular monitoring

[0345] Regarding cardiovascular SITS, the heart rate and each pulse period with their 3 characteristic peaks (Pi, P2, and P3) (Fig. 20D) was measured. The high signal-to-noise ratio generated by the lignin SITS enabled continuous, high-fidelity monitoring of arterial pulse waves from the wrist (Fig. 20D). The three characteristic peaks represent blood ejection (Pi), blood reflection from the lower body (P2), and blood reflection from the closed aortic valve (P3), respectively. In addition, other characteristics of the heart rate were measured, such as the time delay between the first two peaks (AtDVP=tp2-tpi), the radial diastolic augmentation index (DAI) = P3 / P1, and the radial augmentation index Air = P2 / P1, which are two critical parameters for the diagnosis of arterial stiffness. The heart rate was 70 beats / min (BPM). The mean values of Atovp and AL were calculated as 298 ms and 0.244, respectively, which are typical for a healthy person. Studies have shown that Atovp of approximately 300 ms is associated with good arterial compliance in healthy individuals. AIrtypically increases with age and arterial stiffness. Values below 0.5 are generally considered normal for young to middle-aged adults. The mean peak-to-peak interval is 836 ms, and the scatter plot is shown in Fig. 20F. Scatter plots of the parameters DAI, AtDVP, and AL are shown in Fig. 20G-20I. Heart rate variability (HRV) is the fluctuation in the time interval between adjacent heartbeats. HRV is an important indicator of cardiovascular conditions. HRV was 24.7 ms (standard deviation of the peak-to-peak interval) (Fig. 20F). Because in this case the HRV was measured in a short-term variability (1 min), values between 10-50 ms were normal, which is typical of a healthy autonomic response. These results demonstrate that the triboelectric signal from the sustainably processed material is sufficiently robust for advanced monitoring of physiological states. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0346] Objective classification of mental workload

[0347] As a rigorous test of the sensor's signal quality, a proof-of-concept study was conducted to objectively classify the user’s mental workload (MW). Moreover, the capability of the sensor was measured to determine the metal workload (MW) of a person and the correlation between several conditions and the MW aspects. The six aspects recommended by the subjective NASA-TLX test were utilized, with each aspect ranked from 1 to 6 as recommended. The six aspects considered were mental demand (MD), physical demand (PD), temporal demand (TD), performance (P), effort (E) and frustration (F). The cardiovascular data (Figs. 24-30) were recorded during seven distinct tasks designed to elicit different cognitive and physical loads: resting (R), working out (WO), singing (S), following (F), and answering emotional (EmQ), interview (InQ), and mathematical (MQ) questions (Table 1). While the extracted cardiovascular features (BPM, HRV, and AL) correlated with subjective NASA-TEX survey scores (Figs. 20J-200), the goal was to create a fully objective classification model that overcomes the limitations of subjective interpretation. Figures 20J-20M show the average BPM, DVP, HRV, and AIr, where a correlation of the BPM, HRV, and AIrwas observed for all conditions (Fig. 20N), except for the WO, with the metal demand aspect score determined by the standard NASA-TEX survey (Fig. 200). The BPM is increased for F, EmQ, InQ, and MQ, whereas the HRV and AIrdecrease for all of these conditions (Table 2). Although MW can be measured by cardiovascular measurements, the perception of mental workload can change from person to person, and the NASA-TEX survey has a subjective interpretation. To visualize the inherent separability of the data, principal component analysis (PCA) was performed on the feature space. Fig. 20P shows the principal component analysis (PCA) of four cardiovascular parameters (BPM, DVP (Digital Volume Pulse), HRV, and AL), where an evident classification of the four groups based on PCA1 and PCA2 was observed. These groups were categorized as low-MW (resting, singing), low-MW with physical demand (PD) (working out), medium-MW (following, emotional questions), and high-MW (interview, math questions) (Fig. 20P). The categorization was based on previous research on cardiovascular sensors for a non-subjective measurement of metal workload, where PD can influence the MW drastically and separate from the rest of the NASA-TLX aspects, as seen in the PCA analysis. In addition, resting and singing do not require a high mental workload, which is observed in the PCA analysis. On the other hand, questioning, such as in interviews and mathematical and psychological tests, is associated with a medium or high mental workload; hence, it enhances cardiovascular activity. These results demonstrate that the triboelectric cardiovascular sensor can provide a nonsubjective association between tasks and mental workload. Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02

[0348] Table 1. Detailed NASA-TLX survey per condition: Resting (R), working out (WO), singing (S), following (F), emotional questions (EmQ), interview questions (InQ) and mathematical questions (MQ). In addition, the capability of the SITS sensor to detect and categorize MW conditions was benchmarked with the PCA results of HR, HRV, and the standard deviation of HRV using the gold standard ECG sensor (Figs. 31 A-31G, 32, 33, 34, and 35). The sensor shows the same categorized MW groups as in the case of the ECG (low MW, low MW with PD, medium MW, and high MW), shown in Fig. 34, demonstrating that it is an alternative tool for measuring MW. Fig. 20Q shows that the lignin-SITS sensor is as good as ECG to correlate with MW conditions, as high as more than 95% of the correlation (PCA variance ratio of PC1+PC2). To quantify the quality of this class separation, standard clustering metrics were calculated. The Silhouette and Davies-Bouldin index scores for the SITS-derived data were comparable to Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02 those from the ECG data (Fig. 35), indicating that the lignin sensor produces feature clusters that are as distinct and well defined as the clinical benchmark. Unlike the traditional subjective NASA-TLX questionnaire (Fig. 200), the triboelectric cardiovascular sensor offers an objective, physiological measure of mental workload, which can complement subjective assessments.

[0349] Table 2. Statistics of the heart rate measured under each condition: Resting (R), working out (WO), singing (S), following (F), emotional questions (EmQ), interview questions (InQ) and mathematical questions (MQ). HRV: Heart rate variability. DVP: differential volumetric pulse. rAI: Radial augmented index. SD: standard deviation.

[0350] Table 3. Statistics of the ECG heart rate and heart rate variability measured under each condition: Resting (R), working out (WO), singing (S), following (F), emotional questions (EmQ), interview questions (InQ) and mathematical questions (MQ). HRV: Heart rate variability, SD: standard deviation.

Claims

Attorney Docket No.: 3220-431804 PRF Ref.: 70906-02WHAT IS CLAIMED IS:1 . A composition comprising: lignin; a plasticizer; and a binder; wherein the composition does not comprise a starch.

2. The composition of claim 1 , wherein the plasticizer is selected from the group consisting of urea, polyethylene glycol, a citric acid ester, and sorbitol.

3. The composition of claim 2, wherein the binder is selected from the group consisting of gelatin, polyvinyl alcohol, and polyethylene glycol.

4. The composition of claim 1, wherein the composition comprises about 10 wt% to about 70 wt% of lignin.

5. The composition of claim 4, wherein the composition comprises about 10 wt% to about 70 wt% of plasticizer.

6. The composition of claim 5, wherein the composition comprises about 10 wt% to about 70 wt% of binder.

7. The composition of claim 1, wherein the composition comprises a weight ratio of lignin to the plasticizer of about 1:10 to about 10:1.

8. The composition of claim 7, wherein the composition comprises a weight ratio of lignin to the binder of about 1 : 10 to about 10: 1.

9. The composition of claim 1, wherein the lignin has a molecular weight of greater than about 1 kDa.

10. The composition of claim 1, wherein the composition does not comprise an organic solvent, a surfactant solvent, an alkaline solvent, a binary mixture of a nonpolar and a polar solvent, or a deep eutectic solvent.

11. The composition of claim 1, further comprising water.

12. The composition of claim 11, wherein the composition has an aqueous lignin dispersibility of greater than about 10 mg / mL.

13. The composition of claim 1, wherein the composition has a surface potential of greater than about 3 eV.

14. The composition of claim 1, wherein the composition is tribonegative.

15. The composition of claim 1, wherein the composition has a current density of greater than about 1 nA / cm2.Attorney Docket No.: 3220-431804 PRF Ref.: 70906-0216. A film comprising: a layer comprising the composition according to claim 1, wherein the layer is arranged to provide an outer surface and an inner surface spaced apart from the outer surface.

17. The film of claim 16, wherein the outer surface comprises nanodomains.

18. The film of claim 17, wherein the nanodomains have a lateral size of about 100 nm to about 2 pm, and the nanodomains protrude about 20 nm to about 150 nm from the outer surface.

19. The film of claim 16, further comprising a substrate coupled to the inner surface.

20. The film of claim 19, wherein the substrate is a conductive substrate.

21. The film of claim 16, wherein the film has a thickness of less than about 20 pm.

22. A wearable device for measuring a physiological property when worn by a user, the device comprising: a triboelectric sensor comprising the film of claim 16: a fixation element configured to secure the triboelectric sensor to exposed skin of the user; and a communication module configured to receive a signal from the triboelectric sensor and output data.

23. The device of claim 22, wherein the fixation element is configured to secure the outer surface of the film to exposed skin of a user.

24. The device of claim 23, wherein the fixation element is configured to locate the triboelectric sensor proximal to a radial artery location of the user.

25. The device of claim 22, wherein the triboelectric sensor is configured to sense skin deformation of the user wearing the device.

26. The device of claim 22, wherein the signal is a current output.

27. The device of claim 22, wherein the data is suitable for use in quantifying a cardiovascular parameter.

28. The device of claim 22, wherein the cardiovascular parameter is selected from the group consisting of heart rate, digital volume pulse (DVP), heart rate variability (HRV), radial diastolic augmentation index (DAI), radial augmentation index (AIr), and any combination thereof.Attorney Docket No.: 3220-431804 PRF Ref.: 70906-0229. The device of claim 28, wherein the cardiovascular parameter is suitable for use in predicting a cardiovascular condition, mental workload, or a combination thereof in the user.

30. A method of preparing a film, the method comprising the steps of: mixing lignin, a plasticizer, and a binder in water, thereby forming an ink composition; and coating a substrate with the ink composition, thereby forming a film.

31. The method of claim 30, wherein the step of mixing further comprises heating the ink composition at a temperature between about 50 °C and about 200 °C.

32. The method of claim 30, wherein the step of coating comprises blade coating, gravure coating, slot-die coating, printing, spray coating, or dip coating.

33. The method of claim 31, wherein the step of coating comprises blade coating.

34. The method of claim 33, wherein the blade coating comprises heating the ink composition to a temperature of about 80 °C to about 160 °C and pressing the ink composition under a blade.

35. The method of claim 30, wherein the step of coating further comprises drying the film, thereby forming nanodomains on an outer surface of the film.

36. The method of claim 35, wherein the drying is performed for a time of about 1 minute to about 360 minutes.

37. The method of claim 35, wherein the nanodomains have a lateral size of about 100 nm to about 2 pm, and the nanodomains protrude about 20 nm to about 150 nm from the outer surface.

38. The method of claim 30, wherein the substrate is a conductive substrate.

39. The method of claim 30, wherein the film has a thickness of less than about 20 pm.

40. The method of claim 30, wherein the method further comprises detaching the substrate from the film.

41. The method of claim 30, wherein the plasticizer is selected from the group consisting of urea, polyethylene glycol, a citric acid ester, and sorbitol.

42. The method of claim 41, wherein the binder is selected from the group consisting of gelatin, polyethylene glycol, and polyvinyl alcohol.

43. The method of claim 30, wherein the composition comprises about 10 wt% to about 70 wt% of lignin.

44. The method of claim 43, wherein the composition comprises about 10 wt% to about 70 wt% of plasticizer.Attorney Docket No.: 3220-431804 PRF Ref.: 70906-0245. The method of claim 44, wherein the composition comprises about 10 wt% to about 70 wt% of binder.

46. The method of claim 30, wherein the composition comprises a weight ratio of lignin to the plasticizer of about 1:10 to about 10: 1.

47. The method of claim 46, wherein the composition comprises a weight ratio of lignin to the binder of about 1 : 10 to about 10: 1.

48. The method of claim 30, wherein the lignin has a molecular weight of greater than about 1 kDa.

49. The method of claim 30, wherein the ink composition does not comprise an organic solvent, a surfactant solvent, an alkaline solvent, a binary mixture of a nonpolar and a polar solvent, or a deep eutectic solvent.

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