Multi‐Functional Actuators Made with Biomass‐Based Graphene‐Polymer Films for Intelligent Gesture Recognition and Multi‐Mode Self‐Powered Sensing

Abstract Multi‐functional actuation systems involve the mechanical integration of multiple actuation and sensor devices with external energy sources. The intricate combination makes it difficult to meet the requirements of lightweight. Hence, polypyrrole@graphene‐bacterial cellulose (PPy@G‐BC) films are proposed to construct multi‐responsive and bilayer actuators integrated with multi‐mode self‐powered sensing function. The PPy@G‐BC film not only exhibits good photo‐thermoelectric (PTE) properties but also possesses good hydrophilicity and high Young's modulus. Thus, the PPy@G‐BC films are used as active layers in multi‐responsive bilayer actuators integrated with self‐powered sensing functions. Here, two types of multi‐functional actuators integrated with self‐powered sensing functions is designed. One is a light‐driven actuator that realizes the self‐powered temperature sensing function through the PTE effect. Assisted by a machine learning algorithm, the self‐powered bionic hand can realize intelligent gesture recognition with an accuracy rate of 96.8%. The other is humidity‐driven actuators integrated a zinc‐air battery, which can realize self‐powered humidity sensing. Based on the above advantages, these two multi‐functional actuators are ingeniously integrated into a single device, which can simultaneously perform self‐powered temperature/humidity sensing while grasping objects. The highly integrated design enables the efficient utilization of environmental energy sources and complementary synergistic monitoring of multiple physical properties without increasing system complexity.

added to ethanol solution to configure 0.2 mol/L pyrrole solution, and iron chloride hexahydrate was added to ethanol solution to configure 0.2 mol/L FeCl3 solution.Then, the above pyrrole solution and iron chloride hexahydrate solution were added successively to the petri dish in which the G-BC composite was placed.Then, the petri dish was placed in a refrigerator at 5 ℃ for 12 h to obtain the PPy@G-BC film with in-situ polymerized polypyrrole nanoparticles.
Then, after careful rinsing with alcohol and deionized water in turn, the polymerized PPy@G-BC film was dried at 40 °C for 2 h.The thickness of the PPy@G-BC film was 26 μm.Finally, the BOPP film was tightly adhered to the PPy@G-BC film through acrylic ester to obtain a PPy@G-BC/BOPP actuator with a bilayer structure.The thickness of the PPy@G-BC/BOPP actuator was about 64 μm.

TE property test
First, a PPy@G-BC film with dimensions of 3 cm × 1 cm (length × width) was prepared.Then, two copper foils were embedded into the ends of the PPy@G-BC film through silver glue as electrodes (the position of the copper foils is shown in Figure 2a and Figure S10).Finally, the PPy@G-BC film was placed between the two platforms, with a length of 1 cm in the middle overhang.In the TE test, the cold platform was used as the cold end, and the hot platform was used as the hot end.The left and right ends of the PPy@G-BC film (both 1 cm in length) were fixed to the hot platform and the cold platform with polyimide tape.During the heating process of the hot platform, the temperature difference and the open circuit voltage (Voc) between the two electrodes of the PPy@G-BC film were measured simultaneously.Isc was measured during the same heating process.ΔT is defined as the temperature difference between the two electrodes of the PPy@G-BC film.

PTE property test
First, a U-shaped glass frame was prepared, and a BOPP film was attached to the PPy@G-BC film with dimensions of 3.5 cm × 1 cm (length × width).Then, two copper foils were embedded into the ends of the PPy@G-BC/BOPP actuator as electrodes, and the position of the copper foils is shown in Figure S16.Finally, a copper tape with a length of 2.5 cm was pasted on the PPy@G-BC/BOPP actuator, leaving an irradiated portion with a length of 1 cm.During the irradiation of NIR light with different power densities (50,100,150,200,250, and 300 mW cm -2 ), the temperature difference and Voc between the two electrodes of the PPy@G-BC/BOPP actuator were measured simultaneously.

Light-driven actuation and self-powered sensing test
First, a U-shaped glass frame was prepared.Then, a BOPP film was attached to a PPy@G-BC film with dimensions of 4.5 cm × 1 cm (length × width).The lengths of the non-deformable part and the free bending part of the PPy@G-BC/BOPP actuator were 3 cm and 1.5 cm, respectively.Then, a copper tape with a length of 2.5 cm was pasted on the PPy@G-BC/BOPP actuator as a photomask, leaving an irradiated portion with a length of 2 cm.Finally, two copper foils were embedded into the ends of the PPy@G-BC/BOPP actuator as electrodes, and the position of the copper foils is shown in Figure 3a and Figure S19.During the irradiation of NIR light with different power densities (50,100,150,200,250, 300 mW cm -2 ), the temperature difference and Voc between the two electrodes of the PPy@G-BC/BOPP actuator were measured simultaneously.At the same time, the bending deformation of the PPy@G-BC/BOPP actuator was recorded in real time by a smartphone.

Preparation of light-driven bionic hand
First, a bilayer copper foil paper was sandwiched between two palm-shaped black cardboard to form a photomask.Then, copper foils were embedded in five PPy@G-BC/BOPP actuators through silver glue.Finally, five PPy@G-BC/BOPP actuators were attached in position to the palm-shaped photomask to form the bionic five-fingered palm.The exact position and dimensions of the films and the copper foils embedded in them are shown in Figure S23.The Voc of the PPy@G-BC/BOPP actuator was recorded in real time during the light-driven process.

Preparation of KOH/PVA gel electrolyte
First, 30 mL deionized water was preheated to 90 °C.Then, 3 g polyvinyl alcohol (PVA) powder was added to the preheated deionized water in three portions and mixed under strong magnetic stirring until transparent.Next, the ground KOH powder was added to the PVA gel solution in three portions and mixed under strong magnetic stirring until the mixed gel solution was transparent and pale yellow in color.Then, the mixed gel solution was poured into a petri dish and frozen at -40 °C for 12 h followed by thawing at 25 °C for 2 h for three cycles.Finally, the prepared KOH/PVA gel sheet was peeled off the petri dishes to obtain a flexible gel electrolyte.

Humidity-driven actuation and humidity-sensitive properties test
First, a PPy@G-BC/BOPP actuator with dimensions of 5 cm × 1 cm (length × width) was prepared under 25% RH.Then, the middle part of the PPy@G-BC/BOPP actuator with a size of 4.5 cm × 0.2 cm (length × width) was cut off, and the resulting U-shaped actuator was shown in Figure 5a and Figure S24.Finally, two copper foils were attached to the two ends of the arms of the U-shaped PPy@G-BC/BOPP actuator as electrodes through silver glue.In a self-made humidity-controlled chamber, the change of the room RH from 25% to 90% was controlled by a dehumidifier and humidifier in cooperation.During the RH change, the room RH and the resistance of the PPy@G-BC/BOPP actuator were recorded simultaneously.At the same time, the bending deformation of the PPy@G-BC/BOPP actuator was recorded in real time by a smartphone.

Humidity-driven actuation and self-powered humidity sensing test
First, a PPy@G-BC/BOPP actuator with dimensions of 5 cm × 1 cm (length × width) was cut into a U-shape.Then, a KOH/PVA gel electrolyte and flexible zinc foil with the same dimensions of 0.5 cm × 0.5 cm were integrated in-situ into the end of a single arm of the Ushaped PPy@G-BC/BOPP actuator as a power supply unit.Then, two copper foils were attached to the zinc foil and the end of the other arm of the actuator through silver glue as electrodes, respectively.Finally, the zinc-air battery was encapsulated through BOPP films to obtain a humidity-driven actuator with self-powered sensing function.The detailed shape and dimensions of this actuator are shown in Figure 6a and Figure S26.During humidity changes, the RH of the room and the output current signal of the PPy@G-BC/BOPP actuator were recorded simultaneously.At the same time, the bending deformation of the PPy@G-BC/BOPP actuator was recorded in real time through a smartphone.

Preparation of the intelligent gripper integrated with self-powered sensing function
As shown in Figure 7a and Figure S29, the rectangular PPy@G-BC/BOPP actuator and the Ushaped PPy@G-BC/BOPP actuator were fixed to two U-shaped frames, respectively.The rectangular PPy@G-BC/BOPP actuator was used as a light-driven actuator for self-powered temperature monitoring, and the U-shaped PPy@G-BC/BOPP actuator was used as a humiditydriven actuator for self-powered humidity monitoring.And the copper tape as a photomask was placed 2.5 cm away from the tail of the PPy@G-BC/BOPP actuator.These two PPy@G-BC/BOPP actuators were placed face-to-face in a symmetrical configuration to form an intelligent gripper integrated with self-powered sensing functions.When the NIR light was switched on, only the tail (2 cm) of the PPy@G-BC/BOPP actuators would bend from irradiation.The weight of the object grasped by the intelligent gripper was 35 mg.While, the weights of the actuation parts of the PPy@G-BC/BOPP light-driven actuator and the PPy@G-BC/BOPP humidity-driven actuator were approximately 18 mg and 15 mg, respectively.

Characterization and measurements
The morphologies and microstructures of the materials were characterized with a transmission electron microscope (TEM) (JEM-2100) and a scanning electron microscope (SEM) (SU8000, JPN).Their molecular compositions and phase structures were identified with a Fourier transform infrared spectrometer (FTIR) (Thermo Fisher, Nicolet 6700, USA) and an X-ray diffractometer (XRD) (Bruker Corporation, D8 advance, GER).The tensile properties of the samples were obtained using a universal testing machine (Instron,3343).The temperature of the hot and cold ends of the materials in the TE test was recorded by a digital thermometer (UNI-T, UT325).Thermal conductivity was measured by Hot Disk thermal constant analyzer (TPS2500S).Light power density was measured by an infrared power meter (Linshang, LS122).
The surface temperature and heat distribution of the materials were recorded by using an infrared thermometer (Optris, MS Pro) with a temperature resolution of 0.1 °C and an infrared thermal camera (Hikvision, H16), respectively.A benchtop digital multimeter (UNI-T, UT805A+) was used to record electrical signals.The RH was recorded by a digital hygrometer (UNI-T, UT332+).Optical photos and videos were recorded by a smartphone (iPhone 12).

Note S1. Bending curvature calculation principle for PPy@G-BC/BOPP actuator
The parameters are defined as follows (shown in Figure S18): L: The length of the PPy@G-BC/BOPP actuator.
ρ: The radius of the arc of the curved PPy@G-BC/BOPP actuator.
x: The horizontal free-end displacement of the PPy@G-BC/BOPP actuator.
y: The vertical free-end displacement of the PPy@G-BC/BOPP actuator.
θ: The bending angle of the arc of the PPy@G-BC/BOPP actuator.
The curvature is defined as the reciprocal radius (1/ρ).
The chord tangent angle is given by As the bending angle is given by  =   the curvature 1/ρ is deduced as Hence, the curvature of the actuator can be calculated by achieving the bending angle and length of the actuator.

Note S2. Overall discharge reactions of flexible zinc-air battery
At the air cathode, oxygen (O2) absorbs electrons from the air and combines with protons (H + ) in water (H2O) to form hydroxide ions (OH -).The reaction of the air cathode is: At the metal anode, zinc metal loses two electrons and gets oxidized to Zn 2+ , which accumulates at the anode.The reaction of the zinc anode is: The electrons generated by this reaction flow through the external circuit to the cathode, thus completing the closed circuit of the zinc-air battery.At the same time, zinc ions (Zn 2+ ) and hydroxide ions (OH -) move through the electrolyte to maintain the charge balance in the battery.
The overall reaction is:

Figure S1 .
Figure S1.TEM images of the graphene nanosheets at different magnifications.

Figure S2 .
Figure S2.TEM images of the BC nanofibers at different magnifications.

Figure S3 .
Figure S3.(a) Optical photo of the G-BC film.(b) Optical photo of the PPy@G-BC film.Scale

Figure S4 .
Figure S4.TEM images of the G-BC composite at different magnifications.

Figure S5 .
Figure S5.(a)-(b) SEM images of the surface of the G-BC film at different magnifications.(c)-

Figure S6 .
Figure S6.(a) Optical photo of the G-BC film in the bending state.(b) Optical photo of the

Figure S8 .
Figure S8.Tensile stress-strain curves of the BC film, the G-BC film, and the PPy@G-BC film.

Figure S9 .
Figure S9.Mechanical stability of PPy@G-BC film.(a) Optical photos of the PPy@G-BC

Figure S10 .
Figure S10.Dimensions of the PPy@G-BC film when heated by a hot platform.

Figure S11 .
Figure S11.Isc of the PPy@G-BC film when heated by a hot platform.

Figure S12 .
Figure S12.TE property of G-BC film.(a) ΔT and Voc of the G-BC film heated by a hot plate.

Figure S13 .
Figure S13.Electrical and thermoelectric properties of the G-BC film under different

Figure S14 .
Figure S14.(a) Comparison of thermal conductivity of the PPy@G-BC film and the G-BC film.

Figure S16 .
Figure S16.Dimensions of the PPy@G-BC/BOPP actuator when irradiated by NIR light.

Figure S17 .
Figure S17.PTE property of PPy@G-BC/BOPP actuator.(a) Infrared thermal images of the

Figure S18 .
Figure S18.Actuation part of actuator with correlative parameters for calculating the bending

Figure S19 .
Figure S19.Dimensions of the PPy@G-BC/BOPP actuator when irradiated by NIR light.

Figure S21 .
Figure S21.Output voltage as a function of bending curvature of the PPy@G-BC/BOPP lihgt-

Figure S22 .
Figure S22.Repeatability test of the bending curvature of PPy@G-BC/BOPP lihgt-driven actuator with NIR light irradiation for 300 cycles (light power density of 200 mW cm -2 ).C1

Figure S23 .
Figure S23.Dimensions of the light-driven bionic hand.

Figure S25 .
Figure S25.Hydrophilicity test.(a) Water contact angle of the G-BC film.(b) Water contact

Figure S26 .
Figure S26.Dimensions of the PPy@G-BC/BOPP actuator integrated with zinc-air battery

Figure S28 .
Figure S28.(a) Optical photos of the deformation of the PPy@G-BC/BOPP actuator under

Figure S29 .
Figure S29.Dimensions of the intelligent gripper with multi-responsive actuation and self-

Table S1 .
Comparison of mechanical properties of PPy@G-BC film with similar flexible materials in the field of multifunctional actuator.

PPy@G-BC film 93.53 MPa 3.08% 5.55 GPa Our workTable S2 .
Comparison of thermoelectric properties of PPy@G-BC film with PPy or graphene based thermoelectric materials.