Influence of Laser Power on Achieving Ultra Low Stiffness in Resistive Strain Gauges Through on Laser Bonding Transfer‐Patterning of Multiwall Carbon Nanotubes (MWCNTs) onto Polydimethylsiloxane (PDMS) Film

This study describes a novel stretchable and very sensitive strain gauge enabled by laser‐joining carbon nanotubes, resulting in unique architectures forming macroscopic web networks. The stiffness of the resistive strain sensor created by laser material patterning is reduced significantly, from 1.5824 to 0.142 kN m−1, corresponding to a change in laser power from 0 to 0.436 W. Many benefits of laser‐based bonding include precise and flexible local pattern production with minimal energy impact on the flexible substrate. Furthermore, the maximum Gauge factor of the sensor exhibits diverse trends with different strains, generating values of GF = 12.8 for strains less than 2.5% and GF = 165 for strains greater than 2.5% during extension‐retraction cycles. These disparities are the result of a dynamic fight between network degradation and regeneration.


Introduction
Soft sensors are becoming more and more popular, due to the worldwide upsurge in wearable technology breakthroughs. [1]OI: 10.1002/admi.202300842 As a result, laser processing has undergone continuous development and has found widespread application across various engineering fields, owing to its distinct advantages in enhancing device performance. [2]For instance, laser processing minimizes damage during bending or stretching of sensing of multiwall carbon nanotubes and allows fine control of heat input as a non-contact technique appropriate for easily deformable and sensitive objects. [3]One of its many useful uses is the selective heating and joining of a wide range of materials, including polymers, which are crucial components of common commercial products, using laser light. [4]For effective material processing in laser welding techniques involving polymers and carbon nanotubes, careful control of laser light absorption is essential.Furthermore, to provide accurate and regulated heat input, process parameters like scanning speed and pulse length must be optimized. [5]Crucial elements include choosing the right laser wavelength, adjusting the laser power levels, and paying close attention to material characteristics like transparency and absorption coefficients [6] Controlling beam focus and spot size, adding additives, and altering surfaces all help to improve absorption efficiency.By carefully balancing these variables, the laser welding process may be customized to the unique properties of polymers and carbon nanotubes, resulting in efficient material fusion with less heat-affected zones and possible damage. [7]The joining surfaces in this case of laser butt welding are heated by a coaxial optical lens and then fused together in a molten state, bonding the polymeric substrate with carbon nanotubes.As a result, the intermolecular force between the carbon atoms affects the surface electrical resistance, and laser-material interaction can involve thermal effects on the surface and enhance the material flexibility with low material stiffness.Consequently, heat effects on the surface increased material flexibility with reduced material stiffness can result from laser-material interaction. [8]Controlling the number of conductive layers at the nanoscale level after laser ablation, on the other hand, poses difficulties in both experimental and industrial applications for creating super flexible conductive electronic devices.
Our study looks at how laser bonding transfer-patterning, multiwall carbon nanotubes (MWCNTs), and Polydimethylsiloxane (PDMS) can be used to obtain ultra-low stiffness in resistive strain gauges.The innovative aspect the emphasizing how varying laser power levels influence cutting, joining, and engraving outcomes in this process, with the goal of optimizing the bonding and patterning of MWCNTs onto PDMS sheets.The emphasis on ultra-low stiffness is especially important for applications requiring flexibility and conformability, such as wearable devices and biological sensors.The utilization of laser power as a controllable component in this context, together with the specific transferpatterning technique, adds a level of accuracy to MWCNT deposition.The potential influence extends to stretchable sensors, flexible electronics, and new technologies that require highly adaptable sensing components.

Preparation of Strain Sensor-Based MWCNT/Epoxy
The proposed sensing structure was fabricated on the squared substrate in which MWCNT/Epoxy composite was coated on one side of PDMS film of 3cm x 3cm.First 0.5 g of MWCNTS were immersed into epoxy resin NPEL-128 based on Bisphenol A/F having the following molecular structure(C 15 H 10 F 6 O 2 ) to improve and maximize the carbon nanotubes distribution with the epoxy a mixture was sonicated using a sonicated (Bandelin GM 3200, sonication temperature: 25 • C, sonication power:15 W, duty cycle: 50%) for1800 s.The MWCNTS was used without other techniques of purification it had a degree of purity of 95% with an average diameter of 30-50 nm and length of 0.5-3 μm respectively.The mixture of carbon nanotubes with epoxy was dispersed for 6000 s with a temperature of 353K and a rotating speed 350 rpm of with a magnetic stirrer to get better homogeneity.For fast curing and for promoting impregnation and wetting of fibers.After realizing that electronics machines were used to fabricate regular structures on the flexible substrate before printing the substrate was cleaned with isopropanol and distilled (DI) water.All chemicals and reagents obtained were highly purified and were used directly without any thorough modification (the electrical resistance of the ink obtained is ≈1.1 MΩ).

Electronics Printing Spinning Coating Process
Electronic printing is a procedure of uniformly applying a suspension or a film to a polymeric substrate using a high rotating velocity and the subsequent centrifugal force.The Polyethylene Terephthalate substrates used in this experiment were first ultrasonically cleaned both in acetone and alcohol solutions for 15 min and rinsed with deionized water for 5 min, then dried by highpressure nitrogen.The substrates were fixed on the spin coater and rotated at a certain speed (500 r min −1 in 5 s, to overcome the surface tension of water molecular clusters and the effect of surface impurities and dispersants, then dried naturally.The whole process took place at room temperature.

Laser Irradiation System
During laser-assisted nano joining U-V nanosecond laser 355 nm is used to bond carbon nanotube structures on polymeric surfaces.Therefore, carbon nanotubes transformed into few-layer graphene with stiffness decreases sharply as a function of laser power during micro-bonding of carbon nanotubes to PDMS film. [9]This predominated stretchability mechanism was connected to pulsed laser nanosecond laser-based bonding, which was taken into account in three important stages: First, heat energy generated by the laser power source was absorbed by the carbon nanotubes layer through a package of electromagnetic radiation to eject electrons from the lower to high energy level to re-establish the Fermi-Dirac distribution. [10]The second stage is the energy distribution to the lattice. [11]The farther the distance between the ions in a lattice, the weaker the electrostatic forces holding them together, and the lower the lattice energy, and the last stage perpendicular energy diffused into an amount of electron-electron collision, which dominated the heat transfer process. [12]Because of the high entropy value of temperature change in which PDMS film rotated around more, the shortening of its end-to-end length had consequences. [13]As the previous research indicated that most materials when heated their physical and chemical behaviors modified thus the stiffness is temperature dependent with a negative thermal expansion coefficient given by Equation (1) [14] It shows that material linear expansion is linearly proportional to temperature.It should be noticed that tensile strain is linearly proportional to the temperature as shown in Equation (2) By introducing an equation into Hooke's law of elasticity, the influence of temperature can be analyzed at the interface on the reduction of material stiffness as shown in Equation (3) Where k is the material stiffness, Fis the force used to stretch the material, is a linear expansion, l 0 is the initial length of sensing carbon nanotube-based material, and ΔTis the change in temperature at the interface during laser-based material processing.From the Equation (3) the change in temperature depends on the laser parameters used during the laser irradiation process. [15]onsidering that the linear dependence at high temperature is probably characteristic of such a high degree of excitation of the vibrational modes, and based on the requirement of the third law of thermodynamics that the derivative of any elastic constant concerning temperature must approach zero as the temperature approaches absolute zero, and proposed an empirical formula of temperature-dependent Young's modulus. [16]where, E 0 is Young's modulus of untreated material (at absolute zero), and B is the slope of Young's modulus-temperature curve at high temperatures depending on the laser power used.T m is the melting point that depends on materials and is suggested to correlate with Debye temperature.
As the force perpendicular to the sample is activated the generation of mechanical strain is at a high level resulting in a larger electrical resistance change rate and the young's modulus of sensing material increases.The experimental design of laserassisted Micro/Nano bonding of carbon nanotubes is demonstrated in Figure 1 The variation of working parameters during experiments is illustrated in the Table 1.

Statistical Analysis
This was appeared from the research work that it was examining how various laser powers affect resistive strain gauges' ability to attain ultra-low stiffness.ANOVA one side-testing and F- test were performed to assess the significance of the changes that were seen.Here's one way you could go about it.The null hypothesis (H0) states that there was no substantial variation in ultra-low stiffness attained in resistive strain gauges across different laser powers.
The alternative Hypothesis (H1) was the achieved ultra-low stiffness in resistive strain gauges varies significantly across laser powers.The rejection of the null hypothesis suggested that the mean of all levels was equal.The largest significance level determined (alpha) was p ≤ 0.1 and the minimum significance level was p ≤ 0.05.The independent variable was laser power (samples into categories based on their laser power level were sorted).Ultra-low stiffness in resistive strain gauges was the dependent variable.If the p-value was smaller than the chosen chance of committing error level, the null hypothesis was rejected, indicating that there was a significant difference in ultra-low stiffness across laser powers.
If the p-value exceeded the chance of committing an error level, the null hypothesis was not rejected, indicating that there was insufficient evidence to declare a substantial difference.The Origin software was used to thoroughly analyze the reliability and validity of the conclusions produced from inquiry, this method enabled a complete investigation of the relationship between electrical resistance changes and tensile strain in MWCNT-polymer composites exposed to mechanical stress and bending after laser irradiation.

Bonding Mechanism, Morphology Analysis, and Chemical Characterization
To study the advantages of laser-based material processing for enhancement of electromechanical properties like carbon nanotubes Epoxy composite with a single side interconnected on PDMS.The fabricated MWCNTs fiber exhibits remarkable mechanical stability; for instance, the multiwall carbon nanotube fibers are not standing only but also compressible and stretchable which means that MWCNTs (multiwall carbon nanotubes) are a remarkable class of materials with distinct structural and mechanical features.Traditionally known for their upright or standing structure, recent improvements reveal an intriguing aspect MWCNT fibers not only preserve their upright orientation but also display greater flexibility and stretchability during material processing when exposed to laser irradiation.
MWCNT fibers' vertical structure is a distinguishing feature, offering inherent strength and stability.These fibers, however, undergo a metamorphosis during material processing due to precise laser irradiation.The use of laser energy adds a level of flexibility and stretchability not previously seen in MWCNT materials.
This increased flexibility and stretchability opens up new possibilities in a variety of applications.MWCNT is used in industries like as electronics, where flexibility is essential for wearable devices or flexible displays.The heat distribution in the vertical direction during laser-assisted bonding of carbon nanotubes on PDMS substrate is one of the critical points.Apart from the theoretical study, experimental results are correlated with it, therefore adhesive force between atoms of both materials at the interfacing region increases by adjusting laser power from 0.290 to 0. 436 W, above this range, all carbon nanotube layers are removed observed in Figure 2c1-c3.
The experiment results show that energy penetration size increases concerning the laser power and the mechanism of parallel microgrooves is fabricated.The influence of high laser power on the destruction of carbon nanotubes and the substrate is illustrated.According to the Raman spectrometer data interpretation, laser power plays an important role during material modification for improved mechanical stretchability of carbon nanomaterials.In this research, the attempt is based on the bending stiffness of few-layer graphene decreasing sharply as a function of laser power used during laser assistant micro-bonding of carbon nanotubes to PDMS film.The study of the Raman spectrometer and tensile test analysis shows us that when doublelayer graphene is compressed out-of-plane, some -electrons exert pressure through the graphene planes, which are impossible to enter small molecules.
The results presented in Figure 3 explain in detail the increase of the peak intensity of 2D-Band concerning the laser power, this swift analysis makes the material softer and much easier to compress.
Being almost to the temperature influence on the changes of the wavenumbers of the Raman peaks of MWCNTs, applying laser power can have particular results to either increasing intensity of the Raman peaks of Multiwall carbon nanotubes More detail is illustrated in Figure 4 Laser power influences the change of the Raman peak intensity ratio, which yields a proportional relationship between the change of the wavenumber of the Raman peak.The equations demonstrate in Figure 4b-d explain the positive exponential function equivalent to the laser power and represent the peak intensity of the D, G, and 2D bands respectively.If the ( I D ∕I G ) ratio is higher than the untreated material, it means that there are defects in the carbon material.As the ratio ( I D ∕I G ) of carbon material decreased, this means that graphitization is the domain [17] .
The information about layers transformation during laser assistant bonding of MWCNTs/Epoxy is presented in Table 2 The calculations are carried out for three different samples, an untreated sample, and two treated samples by 0.290 and 0.436 W respectively.The positions of Raman ratio Intensity (I D /I G) are different in dependence on the laser power excitation.The ratio of the intensity of D-band Raman peak and G-band Raman peak (I D /I G ) is often used for the characterization of diamond-like carbon films, for example, to estimate the number and size of the sp 2 clusters.we investigate how laser interference affects the film layers.high compactness and large sp 2 cluster sizes should be obtained simultaneously to improve their mechanical performance.

Mechanical Performance of Multiwall Carbon Nanotube Strain Sensor Based on Laser-Assisted Bonding
The laser-based bonding and patterning of Multiwall Carbon Nanotubes (MWCNTs) onto Polydimethylsiloxane (PDMS) provide a versatile method for controlling the mechanical properties of nanocomposite materials.Laser methods' accuracy enables regulated alignment of MWCNTs within the PDMS matrix, altering the overall stiffness of the composite.Laser-induced bonding strengthens the interfacial interface between MWCNTs and PDMS, influencing load transfer mechanisms and, as a result, the stiffness of the final material.The patterning density, shape, and uniformity all play important roles in defining mechanical behavior, providing the potential to improve the MWCNT-PDMS composite's Young's modulus.Laser-induced patterns that are properly constructed contribute to a more uniform strain distribution, which influences the overall mechanical response of the nanocomposite.
The strain sensor device based on carbon nanotube arrays was tested by using the tensile machine, a sample size of the tested material was 2.5cm × 1.0 cm and the results output of material stiffness and elasticity modulus are illustrate in Figures 5 and  6 for the chosen three sample.The response of sample elongation against normal force during the tensile test predicts the laws of elasticity which demonstrate the dependence of laser power values on mechanical properties of multiwall carbon nanotubes embedded on PDMS film-like Elastomer materials. [18].
To explain the phenomena of mechanical stretchability first, the stiffness of carbon nanotubes sensing material decreases for the sample treated by a laser power of 0.436 W and generally gets more compliant when they are interconnected based on laserassisted bonding mechanism with stiffness's ratio of 0.0918 compared to untreated sample this was influenced by the higher- entropy energy state during laser material modification (corresponding to a higher temperature).The energy state level is one in which the PDMS chains move around more, which has the consequence of shortening their end-to-end length of carbon nanotubes. [19]n accordance with the guidelines of Hooke's law of elasticity, this computation uses the first derivative of the stress-strain hysteresis curve, with their corresponding Figures.The findings provide evidence that the material's elongation does not follow a linear function in response to external forces.The paper's experimental results provide a thorough description of how the laserassisted method affects chemical bond modification, leading to a softer material and a decrease in stiffness.As shown in Figure 6d, Young's modulus values were obtained for three distinct arbitrary samples that were modified using different laser powers.
Interestingly, Young's modulus showed a decline that increases with laser intensity, signifying a reduction of stiffness.The amount of softening brought about by the laser-assisted alteration is highlighted by Young's modulus ratio of 0.814.

Relationship Between the Change in Electrical Resistance and the Mechanical Strain Based on Laser Power Used to Bond Multiwall Carbon Nanotube Structures onto Pdms Substrate
The link between electrical resistance and mechanical strain in multiwall carbon nanotube structures connected to a Polydimethylsiloxane (PDMS) substrate by laser power modulation is critical for constructing strain sensors.The laser power utilized during bonding has a substantial impact on the CNT-PDMS interface, altering the structural integrity and piezoresistive characteristics of the CNT network.The laser power must be carefully adjusted to optimize the sensitivity of the CNT network to mechanical strain, ensuring a balance between strong bonding and the maintenance of electrical properties. [20]It is critical to establish a quantitative relationship through accurate characterization and calibration experiments, allowing for the reliable correlation of electrical resistance changes with applied mechanical strain, allowing for the effective use of CNT-based strain sensors in various applications such as structural health.The electrical resistance seems upon removal of the applied strain and increases with increasing elongation, regardless of the static and dynamic activating force on the sensing material.In Figure 7b the presented results highlight a noteworthy observation regarding the electrical resistance of multiwall carbon nanotubes subjected to laser-based bonding.The data indicate that even after to 9000 cyles of continuous bending those joined and patterned MWCNTs maintain a low level of electrical resistance such resilence in electrical properties is a crucial for applications where flexibility and durability are paramount.
The difference in vibration frequencies seen during resistive strain sensing techniques between treated and untreated multiwalled carbon nanotubes (MWCNTs) can be related to structural changes caused by the treatment procedure.The treatment, whether by laser modification or chemical functionalization, changes the length, diameter, and inter-tube interactions of the nanotube, changing its inherent vibrational frequencies.Furthermore, variations in stiffness, mass loading owing to additional functional groups or coatings, damping effects, surface energy changes, and changes in the electrical structure all contribute to the observed discrepancies.These subtle structural and mechanical differences explain why treated and untreated MWC-NTs respond differently to applied strains, resulting in different vibration frequencies in the context of resistive strain sensing as depicted in Figure 7c-e.
According to the micro/nano-mechanism, the correlation between interlayer debonding and change in electrical resistance was examined, electrical resistance was measured under simple tension and repeated loading-unloading after ten cycles and observed to remain after removing Normal force. [21]The failure processes of two types (pristine and treated by laser irradiation) of carbon nanotubes/PDMS samples were characterized.Consequently, it was revealed that the behaviors of electrical resistance change of two specimens had a close relationship with their elasticity failure mechanisms. [22]Moreover, the relationship between the applied strain corresponding to the damage, and the electrical resistance changed rapidly until the ultimate values.In Figure 7d-f, first cycle illustrated shows that PDMS/MWCNTs treated material by 0.436 under stretching and relaxing exhibits 40% larger elongation than untreated sensing material.Contrast with MWCNTs that haven't undergone treated, the treated sensor may have improved sensitivity and altered mechanical and electrical properties, resulting in a different signal response over time.This signifies the effectiveness of the bonding process in significantly improving the material's ability to withstand and sustain mechanical deformation. [23]

Electromechanical Characteristics of PDMS/MWCNTs Sensing Materials Fabricated by Laser-Assisted Micro/Nanobonding
The laser-based attachment of Multiwall Carbon Nanotubes (MWCNTs) onto Polydimethylsiloxane (PDMS) for resistive strain sensing applications has a considerable impact on sensor performance.Laser processing improves the structural integrity of the PDMS/MWCNT composite by improving the alignment and patterning of MWCNTs for improved sensitivity. [24]Furthermore, The laser-assisted bonding of PDMS/MWCNTs shows excellent change in the material properties under tensile test, the mechanism of laser treatment of is one option to enhance their behaviors for adhesive bonding. [25]The experiments revealed that the bonding quality can be enhanced with a controllable laser power, which revealed that the behavior of electrical resistance change had a close relation with failure mechanisms of composites, The relationship between the applied strain (i.e., damage of carbon nanotubes) and the electrical resistance change until ultimate failure of the composite.The tests provided critical insights, revealing that using adjustable laser power can increase the quality of bonding in composites.This advancement was notable because of the close relationship observed between the behavior of electrical resistance change and the failure mechanisms inherent in composites The study delves deeper into the intricate dynamics by investigating the relationship between applied strain, specifically the damage experienced by carbon nanotubes, and the accompanying electrical resistance changes leading up to the composite material's eventual breakdown.Figure 8 depicts and describes these occurrences in great detail, providing a realistic portrayal of the interplay between applied strain.
Electrical resistance changes with time, and overall failure mechanisms in the composite material. [26]In this context often refers to mathematical relationships, presumably linear equations, that characterize the relationship between tensile strain and some measured performance metric, such as electrical resistance.The 2.5% of strain shows that the material behaves linearly within this strain range.The term "unbonded sensing material" implies that the response of the material is being characterized without the influence of external bonding, and the emphasis on linearity may be indicative of the material's predictable and proportional response to increasing tensile strain within the specified range.When a laser power increases from 0.29 to0.436W at 2.5% strain level, the sensitivity of sensing material increases from 35.9 to 165 respectively    As shown in Figure 9a-c, a resistive-type strain sensor constructed utilizing a carbon nanotube (CNT)-PDMS composite via laser material processing has higher sensitivity than unbonded multi-walled carbon nanotubes (MWCNTs) with PDMS. Figure 9d displays mean values and standard deviations for two variables: laser power (mean SD = 0.145 0.20506) and tensile strain (mean SD = 33.25 3.74767).The statistical study, most likely performed using ANOVA, provides a substantial F-value of 155.59553 with a low probability (Prob > F) of 0.00637.This implies statistical significance at the standard significance level of 0.05.The results highlight the improved performance of the laser-processed CNT-PDMS strain sensor, showing its potential for increased sensitivity over its unbonded predecessor.
One probable explanation is that at lower laser power levels, specialized mechanisms such as local heating and intermolecular interactions dominate the nanojoining process.The effect of this dominance is a very linear increase in strain.However, as laser power increases, other elements such as heat impacts, defect formation, and structural changes in multi-walled carbon nanotubes (MWCNTs) become significant contributors.
These elements lead to a non-linear response in strain, meaning that the system enters a region where the material's behavior becomes more complex and unpredictable.The observed behavioral change highlights the complexity injected into the nanojoining process, needing a detailed understanding of the interaction between laser settings and the resulting structural alterations in MWCNTs.As seen in Figure 9, the change in electrical resistance is not a linear function of strain.
The sensitivity of multiwall carbon nanotubes for resistive strain sensors one key issue is the achieving uniform agglomeration which can affect response to strain.Additionally maintaining consistent alignment of MWCNTs is crucial for optimal sensitivity.
Furthermore, CNT mechanical characteristics might vary, resulting in non-uniform strain distribution inside the material (Table 3).
Figure 10a-d represents the effect of laser power on heat energy penetration during the nanojoining process of multiwalled carbon nanotubes (MWCNTs) onto polydimethylsiloxane  (PDMS) has a wide range of effects on a number of crucial parameters.To begin, the extent of heat energy penetration into the MWCNTs and PDMS is affected by shifting laser power levels, influencing the efficiency and effectiveness of the nanojoining process.Furthermore, the MWCNTs' tensile strain is impacted, with higher laser power potentially leading to increased strain due to stronger bonding effects as shown in Tables S7 and S9 (Supporting Information).Simultaneously, the surface roughness of the MWCNTs changes due to laser-induced modifications, influencing the overall topography of the material.Furthermore, the laser power influences the strength of the MWCNTs, with higher levels potentially leading to enhanced bonding strength between the nanotubes and the substrate.

Application of Carbon Nanotubes Resistive Strain Sensor for Detecting Health Conditions and the Joint Motion of the Human Body
An appropriate test was designed for the estimation of movement and angle measurement of the elbow, and wrist joint testing, the strain sensor was capable of distinguishing wrist, and elbow joint angles following the variation of electrical resistance greatly with respect to time.The results reveal that the PDMS/MWCNTs strain sensor displays corresponding piezoresistive responses to different bending angles, namely the larger the bending, the larger the ΔR/R 0 signals.Moreover, it can also be in the way of examining elbow and wrist bending proposing possible use for body motion detection in health care testing to make decisions with respect to the variation of bending angle as illustrated in Figure 11a,b.
As the heart beats, the strain on the PDMS substrate hosting MWCNTs fluctuates causing the change in electrical resistance of the nanotubes the resistance can be detected and correlated with the pulsatile nature of the heart, providing a real-time of heat beat phenomenon as illustrated on Figure 11d.The stability of change in electrical resistance during heat beat detection is related to the carbon nanotube adhesive behaviors as stated. [35]ecause of changes in strain distribution and contact resistance, the open and closed configurations of Multi-Walled Carbon Nanotube (MWCNT) strain sensors can provide distinct electrical resistance signals.The nanotubes may be less constrained in the open arrangement, allowing for more freedom of movement and possibly greater sensitivity to strain changes.In the closed arrangement, however, the nanotubes may be more constrained, affecting their response to strain.Furthermore, Figure 12a indicates that untreated MWCNTs may have structural imperfections that cause variances in conductivity.MWCNTs' surface and structure can be altered by laser treatment, altering their electrical characteristics.When MWCNTs are connected or patterned, the overall conductivity and strain distribution within the sensor are affected, resulting in changes in electrical resistance signals.Herein, a carbon nanotube strain sensor fabricated by laserassisted bonding can examine several types of human body movements important for making decisions in biomedical engineering applications reported by previous researchers. [36]The experimental results are represented for evaluation of PDMS/MWCNTs sensor used for sensing human body movement and the electrical resistance varies for different levels of human body stretching phenomena our strain sensor fabricated by laser has high sensitivity compared to the sensor fabricated by CNT/PDMs mixed with citric acid monohydrate particles. [37]Through more, the results described in Figure 11b indicate the ability of the MWCNT/PDMS sensor to detect the wresting angle (by using statistical analysis our results are valid and reliable based on the hypothesis), Figure 11c indicates that the integration of multiwall carbon nanotube resistive strain sensors with a zero-order hold in breathing detection system addresses the need stability efficient data processing and improved interpretability of breathing patterns this approach contributes to the reliability and accuracy multiwall carbon nanotubes of resistive strain sensor designed monitoring human respiratory behaviors.In addition, the inclusion of Figure 11d allows for a visual representation of how MWCNTs-based resistive strain sensor fabricated by laser joining and patterning respond to heartbeats.Herein, the peak of heartbeat signal represents the highest point after 42 s during a single cardiac cycle.Our sensor provides valuable information about heart contraction, contributes to determine the heart rate, and is essential for assessing the rhythm of the cardiac cycle.
These dynamic changes cause strain distribution differences, which affect the response of the MWCNTs strain sensor.The sensor's sensitivity to dynamic loading, combined with its precise positioning on or near the knee joint, adds to its enhanced responsiveness during sitting-to-standing transitions, revealing fine details. [38]

Conclusion
In summary, a highly stretchable conductive and sensitive carbon nanotubes/PDMS resistive strain sensor based on laser-assisted bonding was successfully fabricated by combining an electronics printing machine with laser-assisted bonding.Comparing the experimental results of unbonded sensing material to the material modified by laser-based bonding the applied laser power had a great effect on the resistive property of the sensing material.It is indicated that an appropriate laser power could contribute to a high gauge factor of the composite strain sensor even with a low external force applied to the material addition(lower mechanical strain).The highest gauge factor of the resistive strain sensor was found at the material bonded by a laser power of 0.436 W which is 165 at a strain >2.5%.The reliability and lifetime of carbon nanotube sensing material suffers from large and repeated strain during human motion detection.In the future, high-repetitionrate laser nanojoining and patterning techniques are expected to be useful in fabricating MWCNTs/silver nanowires composite materials for ultra-stretchable electronics, providing a path to improve conductivity, flexibility, and mechanical resilience, thereby expanding the possibilities for advanced wearable technologies and flexible electronic devices.

Figure 1 .
Figure 1.Dismantling design of experiment for laser-based micro nano bonding of multi-walled carbon nanotubes (MWCNTs) film on polydimethylsiloxane (PDMS)

Figure 2 .
Figure 2. a1-c1) Comparative of surface morphology of multiwall carbon nanotubes interconnected on PDMS Film by laser-based bonding for different laser power of (0.29-0.50 W) respectively.a2-c2) Laser energy density distribution along two dimensions a3-c3) Finite element analysis of temperature distribution on the interface.

Figure 3 .
Figure 3. a) Raman spectra of the carbon nanotube structures patterned by laser a) original MWCNTs b) carbon nanotubes structured by 0.29W c) multiwall carbon nanotubes structured by 0.436W d-f) are the SEM image of the sample before laser and after laser structuring respectively.

Figure 4 .
Figure 4. a) Raman peak intensity ratio versus laser power, b) Peak intensity of D-band versus laser power c) Peak intensity of G-band versus laser power d) Peak intensity of 2D-band versus laser power.

Figure 5 .
Figure 5. a) Mechanical properties of MWCNT/PDMS strain sensing based on laser-assisted Micro/Nano-bonding a) Force versus elongation for untreated sample b) Force versus elongation for treated sample by 0.290W c) Force versus elongation for treated sample by0.436W d) Stiffness versus laser power.The error bars reflect the standard deviation SD of each group, with n = 3, analyzed by ANOVA one-way F-test(ns: no statistical difference, * p ≥ 0.1 and ** p ≥ 0.05).

Figure 6 .
Figure 6.Mechanical properties of MWCNT/PDMS strain sensing based on laser-assisted Micro/Nano-bonding a)stress versus strain for untreated sample b)stress versus strain for treated sample by 0.290W c) stress versus strain for treated sample by0.436W d) Young's modulus versus laser power.The error bars reflect the standard deviation SD of each group, with n = 3, analyzed by ANOVA one-way F-test (ns: no statistical difference, * p ≤ 0.1 and ** p ≤ 0.05) .63 − 71.59 with the linear fitting of R 2 = 0. 981.Bonded sensing material with Laser power of 0.29W: ( ΔR∕R 0 ) = 35.93− 65.76with a linear fitting R 2 = 0. 986.Bonded sensing material with a laser power of 0.436W: ( ΔR∕R 0 ) = 165 − 374.17 with a linear fitting R 2 = 0.987.

Figure 7 .
Figure 7. a) Electrical resistance response versus laser power before the tensile test b) electrical resistance response versus laser power after the tensile test c,d) Change in electrical resistance and material strain concerning the time of the sample treated by laser power of 0.436W e,f) Change in electrical resistance and material strain concerning the time of untreated sensing materials.Error bar represent the standard deviation SD of each group, n = 3, analyzed by ANOVA one-way F-tests: (ns: no statistical difference, * p ≤ 0.10 and ** p ≤ 0.05).

Figure 8 .
Figure 8. a)Influence of laser-based bonding on resistive strain sensing performance of the PDMS/MWCNTs output signals b) Response of PDMS/MWCNTs sensor fabricated with laser-assisted bonding respectively with a repeatedly normal loading at a small elongation of carbon nanotubes/PDMS(1-3 mm).

Figure 9 .
Figure 9. a-c) Represents a Photograph illustrating electrical signals versus strain for samples fabricated by 0,0.290 and,0.436W respectively (d) illustrates the influence of laser power on stiffness compared to the sensing material sensitivity.Error bar represent the standard deviation SD of each group, n = 3, analyzed by ANOVA one way F-test, ns: no statistical difference, * p ≤ 0.10 and ** p ≤ 0.05.

Figure 10 .
Figure 10.Colleration between physical parameters a) relationship between bonded width and material stiffness b) surface roughness versus laser power c) influence of laser power on Gauge factor d) influence of laser power on tensile strength.Error bar represent the standard deviation SD of each group, n = 3, analyzed by ANOVA one way F-test, ns: no statistical difference, * p ≤ 0.10 and ** P ≤ 0.05).

Figure 11 .
Figure 11.Application PDMS/MWCNTs resistive strain sensor: a) Recognition of elbow bending signal, b) Recognition of wrist bending signal, c) Recognition of human breathing signal, d) Recognition of heartbeat signal detected by MWCNTs resistive strain sensor

Table 1 .
Laser laboratory process parameters.

Table 2 .
Calculated Raman intensity ratio and number of layers caused by laser interference.

Table 3 .
Compared to other sensing elements reported in the literature, the relationship between the Gauge factor(GF) and tensile strain of PDMS/MWCNTs sensing material is based on the laser bonding process.