Enhancing soundproofing performance of polypropylene nanocomposites for implantable electrodes inside the body through graphene and nanoclay; thermomechanical analysis

The brain, being the most intricate organ in the human body, is made up of numerous neurons and glial cells.¹ These neurons and cells enable information transmission through electrical signals, known as action potentials, as well as chemical signals via neurotransmitters.^2,3 Signals from pacemaker devices can be affected by external noise, which can hinder their performance, making the outlet gate of the pacemaker particularly important in this process.⁴ While various materials used in pacemakers include polymer-based nanocomposites, not all are effective in minimizing sound and noise.⁴ At present, research on pacemaker electrodes for use in the brain, heart, and muscles is still in its early stages, revealing many unknown factors. There has been limited investigation into the selection of materials for the outlet gates of pacemakers. Therefore, studying the properties of electrodes and their materials, alongside noise reduction within the dense network of neurons in brain tissue, is crucial for advancing our understanding of pacemakers.

Recent advancements in polymer nanocomposites have led to improvements in their physical and mechanical properties, as well as enhanced thermal stability, increased electrical and thermal conductivity, better dielectric performance, and superior gas barrier properties. By incorporating small amounts of nanofillers into a polymer matrix, it becomes possible to create lightweight, flexible, and transparent materials with properties similar to those of nanomaterials. The distinctive characteristics of the nanofillers, including their size, shape, and compatibility with the polymer matrices, are critical in influencing the attributes of the resulting polymer nanocomposites.⁴ Studies have shown that nanocomposites strengthened with layered materials like clay montmorillonite (MMT) and graphene exhibit improved fracture toughness due to effective dispersion and a high surface area. However, research on the soundproofing capabilities of these nanocomposites is still limited. We applied this principle to improve the soundproofing performance of polypropylene nanocomposites for implantable electrodes within the body, utilizing graphene and nanoclay, particularly sensitive to low frequencies. The proposed biomaterials show promising performance in the output gate of pacemakers and have the potential to revolutionize the field of biomaterials.

Nanocomposites, especially in porous forms, have significant potential as sound-absorbing materials due to their effective sound absorption influenced by environmental factors like humidity and temperature.⁴ Clay and graphene nanocomposites are highlighted for their mechanical properties and functionalities, with clay nanoparticles (e.g., MMT) having diverse applications, while graphene is prized for its remarkable characteristics. These nanomaterials are also considered for biomedical uses, such as in pacemakers, due to their biocompatibility. Recent advancements in the medical field aim to improve pacemaker performance through polymer nanocomposites, emphasizing biocompatibility, mechanical strength, electrical conductivity, thermal stability, and longevity.

Noise reduction and vibration damping methods are divided into passive and active categories. Active media use external energy via sensors and actuators to mitigate noise, whereas passive media dampen the sound by converting energy into heat through their internal structure. The effectiveness of passive absorption varies with frequency, and mechanisms like internal friction contribute to heat loss. Passive methods can include resonators that convert noise into vibration. New active resonators can also change shape in response to vibrations. Active noise control employs sensors to detect and cancel noise. In materials science, enhancing sound absorption with nanofillers is common, and metal matrix composites using cobalt and chromium can optimize signal-to-noise ratios for specific applications.⁵ Multi-layered composite structures are effective in detecting acoustic waves, and research is ongoing into using transient reflectivity changes from pulse absorption to enhance signal clarity for industrial uses.⁶ 

Furthermore, efforts to enhance pacemaker effectiveness, reliability, and lifespan involve the integration of nanocomposites. Studies by Mohammed et al.⁷ focus on the buckling behavior of microcomposite shells in pacemakers, aiming to identify durable materials that withstand strong electromagnetic forces. Their findings address the relationship between thickness, material properties, and critical buckling loads, contributing to the development of robust micro-electromechanical systems and efficient pacemaker nanocomposite shells.

Graphene, a single-layer material, is renowned for its extraordinary strength, boasting a Young’s modulus of ∼1 TPa and a tensile strength of 130 GPa, making it the strongest known material.⁸ Its extraordinary characteristics have sparked considerable fascination across various technological domains, particularly in the realm of polymer nanocomposites, which facilitate the creation of adaptable materials exhibiting superior mechanical, thermal, electrical, optical, and chemical attributes.^9,10 The efficacy of graphene-infused composites is critically influenced by the techniques employed during fabrication and the consistent distribution of graphene throughout the polymer matrix.¹¹ Nevertheless, attaining this uniformity presents difficulties due to the intrinsic nature of graphene, frequently requiring chemical surface modifications to improve compatibility and adhesion.⁸ Various fabrication techniques for these composites include solution-based and melt-based methods.¹² Although there has been research on clay and graphene nanocomposites, the precise role of the interface in these layered materials remains incompletely understood. Future sections of this article will delve into the preparation and synthesis processes of graphene to achieve powdered reduced graphene oxide (RGO).

An implantable pacemaker is a device that sends signals to an internal electrode in the body. This article discusses the materials used in these devices. The significant impact of implantable technology on modern medicine is highlighted by various statistics.¹³ Although extensive research has been dedicated to finding appropriate materials for electrodes, there is a lack of studies on the outlet gate materials in pacemakers, which this work seeks to investigate. Figure 1 displays different applications of implantable electrodes in the body, including those for brain and heart pacemakers. Another key application involves implantable electrodes placed within muscles, surgically secured to the epimysium of specific muscle groups.^14,15 The effectiveness of pacemakers in transmitting signals is crucial for optimal functionality, especially in electrically noisy environments. Furthermore, bioelectrodes are devices that create or measure the body’s electrical activity, used for electrophysiological stimulation or monitoring. Electrical muscle stimulation involves sending electrical impulses to muscles, which can enhance blood flow and strengthen the muscles. It may also influence pain signals, alleviating discomfort. This form of electrical muscle stimulation is available to address various muscle problems and pain.

Heart pacemakers are essential devices that regulate the heart’s rhythm by delivering electrical impulses, particularly for conditions like bradycardia.¹⁶ On the other hand, brain pacemakers are implanted to provide stimulation to specific brain regions, offering treatment for movement disorders and neuropsychiatric conditions.¹⁷ While heart pacemakers are typically positioned near the heart, brain pacemakers are surgically placed in targeted areas of the brain. In our research, we focus on the significance of noise reduction in brain pacemakers. It is crucial to consider the impact of noise on individuals with brain pacemakers, as higher levels of noise can lead to disruptions in the signal-to-noise ratio, directly affecting the behavior of patients with such devices. Our current study introduces a novel biomaterial in the form of a nanocomposite that exhibits enhanced strength, durability, and performance characteristics. These advanced nanocomposites are designed to minimize noise dispersion, enabling individuals to receive clearer signals without interference from surrounding noise sources. By reducing noise levels, these innovative nanocomposites aim to improve the overall effectiveness and functionality of brain pacemakers in managing various health conditions.

One significant gap identified in the existing literature review pertains to the lack of exploration into the soundproofing properties of nanocomposites comprised of a polypropylene matrix and nanofillers such as graphene nanoplatelets and montmorillonite nanoclay. Previous studies have predominantly focused on investigating the mechanical and thermal properties of these types of nanocomposites. Given the biocompatible nature of these composites and their potential application within the outlet gate of brain pacemakers, our research aims to enhance these specific nanocomposites by incorporating graphene nanoplatelets and montmorillonite nanoclay. We propose that these modifications will result in the development of nanocomposites with superior signal-to-noise ratio (SNR) characteristics, making them highly suitable for integration into the microshells of brain simulator pacemakers.

In this investigation, the polymer matrix utilized was polypropylene PP5032, procured from ExxonMobil Chemicals, recognized for its qualities suitable for extrusion and co-extrusion applications. This specific polypropylene possesses a melt flow index of 3.0 g/10 min, a density of 0.95 g/cm³, and a Vicat softening temperature of 156 °C. The MMT clay featured in the study was sourced from Dasht-Arjan in southern Iran (near Shiraz) and underwent an in-house purification process for the creation of nanocomposites. In addition, natural flake graphite, along with sulfuric and formic acids from Asbury Carbons, were integral components of the experimental methodology. The application of polypropylene as a biomaterial has been corroborated in various scholarly articles.^18,19 Mirzaali and Zadpoor¹⁹ have introduced a new concept of “metallic clay” meta-implants, enabling molding into intricate shapes and shape-fixing akin to clay. The application of both clay and polypropylene within the human body supports the present study’s assumption regarding the use of nanocomposites in pacemakers. Material selection, surface bio-functionalization, and signal delivery mechanisms are crucial areas for further advancement and refinement in the design of pacemaker microshells. This study aims to address the existing gap in material selection for microshells and the high potential for signal-to-noise ratio improvement.

Montmorillonite, commonly known as bentonite, is an aluminum silicate mineral esteemed for its remarkable characteristics, including an extensive surface area, substantial swelling potential, adsorption proficiency, and considerable mechanical strength. These traits render it an indispensable material in numerous sectors, including pharmaceuticals, cosmetics, and construction. While unrefined montmorillonite is utilized in applications such as drilling mud and ceramics, its purified form is favored in medicinal and cosmetic products due to its detoxifying and cleansing properties. The extraction of montmorillonite from contaminants is essential for preserving its efficacy, prompting ongoing research into various purification methodologies.²⁰ 

Leaching, a technique that entails extracting components from a solid into a liquid medium, plays a pivotal role in the chemical refinement of clays. This approach encompasses the decomposition of carbonates, the dissolution of hydroxides, the oxidation of organic substances, and the solubilization of silica. Carbonate minerals like calcite can be eliminated from clay through treatment with dilute hydrochloric or acetic acid. This acid treatment facilitates the exposure of crystal surfaces, rendering cations soluble and augmenting the clay’s adsorption potential. Iron, aluminum, and manganese (hydr)oxides can be exorcised by forming complexes with citrate. A variety of chemical combinations are assessed to dissolve iron hydroxides, followed by a wash with sodium chloride solution. Organic materials can be obliterated using hydrogen peroxide, sodium hypochlorite, or alternative oxidizing agents. Finally, amorphous silica can be dissolved by immersing it in a heated sodium carbonate solution.²¹ For treating montmorillonite clay, a suspension was created by combining 10 g of clay with 500 ml of deionized water in a 1-l beaker and allowed to sit for 24 h. The resultant solids were washed and centrifuged to isolate particles smaller than 15 mm.

The production of graphene oxide nanosheets from multilayer flakes involved an intricate process adhering to the modified Hummer’s technique. At the outset, a meticulously controlled procedure was undertaken, involving the addition of H₂SO₄ and KMnO₄ to graphite powder under precise conditions to generate graphite oxide. This synthesis phase required careful temperature regulation and a gradual introduction of reagents to ascertain the formation of high-quality graphite oxide.²² The resultant solution was then subjected to filtration, washing, and drying procedures to acquire the sought-after graphite oxide product. Once graphite oxide was successfully synthesized, it underwent further processing: it was mixed with deionized water and subjected to sonication, centrifugation, and drying to yield graphene oxide nanosheets. The sonication step was vital for uniformly dispersing the graphene oxide nanosheets within the solution, achieving a consistent concentration of 2 g/ml. Following this, reduction processes were applied to the graphene oxide, culminating in the production of graphene nanosheets (GNs), which possess distinct properties and find utilization across a range of fields such as electronics, energy storage, and material sciences. The preparation methodology for both graphene and nanoclay is depicted in Fig. 2.

Oxidative-exfoliation techniques can produce significant quantities of graphene oxide (GO), a graphene-like nanosheet that typically contains defects and requires additional processing to transform it into reduced graphene oxide (RGO). During oxidation, the addition of oxygen-containing functional groups (OFGs) increases the distance between graphitic layers, weakening van der Waals forces and facilitating exfoliation. Before exfoliation can take place, it is crucial to perform several washing steps to remove oxidizing agents and contaminants from graphite oxide. However, washing graphite oxide on a large scale using conventional methods such as filtration, centrifugation, or dialysis can be quite difficult. Filtration can be particularly tedious because exfoliated graphite oxide particles tend to quickly clog the filter pores. Moreover, high-speed centrifuges are not commonly used in industrial applications due to their limited capacity and high cost. Despite these difficulties, it is important to note that effective washing improves the dispersibility of GO. Regardless of the oxidation method used, the reduction process adds another step to the synthesis workflow, further prolonging the overall production time.

Nanocomposites were created by mixing different amounts of clay (MMT) and graphene nanosheets (GNs) with polypropylene (PP) in a heated internal mixer. The mixing took place at 200 °C and 60 rpm to achieve an even distribution of the fillers within the PP matrix. The process began by adding the PP matrix, followed by the clay (MMT) and/or GNs, and mixing for 5 min until a stable torque was reached. Afterward, the resulting nanocomposite was removed from the heated chamber, cut into smaller pieces, and processed through hot press molding. Compression molding was carried out using an automatic CARVER press with specific settings: a steel mold measuring 100 × 3100 × 1.5 mm³, with both plates heated to 200 °C and a force of 2000 lbs applied. The final nanocomposites were then cooled to room temperature using a combination of air and water cooling. Finally, 3D printing was employed to refine the shape of the samples for testing in sound tube devices. In this section of the article, we present the composition of the investigated formulation expressed in weight percentage (wt. %) across five distinct cases with varying ratios of polypropylene, clay, and graphene. In Case (a), which has a 4:0 ratio, the formulation comprises 96% polypropylene, 4% clay, and 0% graphene. Case (b), with a ratio of 2.75:1.25, contains 96% polypropylene, 2.75% clay, and 1.25% graphene. In Case (c), which features a 2:2 ratio, the composition is 96% polypropylene, 2% clay, and 2% graphene. Case (d) adjusts to a 1.25:2.75 ratio, resulting in 96% polypropylene, 1.25% clay, and 2.75% graphene. Finally, Case (e) employs a 0:4 ratio, comprising 96% polypropylene, 0% clay, and 4% graphene.

The nanocomposite (a) lacks graphene constituents but incorporates clay and polypropylene (PP). Due to the incompatibility between PP and clay, which arises from their differing polar nature, it is essential to modify the clay’s polarity to render it organophilic for successful composite development. The use of maleic anhydride polypropylene as a compatibilizing agent can improve the clay’s distribution within the PP matrix. During the treatment of montmorillonite clay, maleic anhydride polypropylene was integrated with the clay particles to adjust their polarity toward organophility.

The extraordinary surface area-to-volume ratio characteristic of nanoparticles results in notable improvements across various properties, including mechanical performance (such as tensile strength, stiffness, and durability), barrier capabilities, thermal resilience, flame retardance, chemical durability, and dimensional stability. Silicon and carbon-based materials have been effectively utilized in creating anodes for lithium-ion batteries. The reduced permeability of solvents through these polymers is particularly advantageous for manufacturing components within fuel tanks and fuel lines. Addressing challenges like optical issues and the dispersion of nanofillers is essential for optimizing the effectiveness of these materials. The integration of graphene elements into PP/clay nanocomposites can significantly enhance their electrical and thermal conductivity, making them effective as sound-damping materials in nanocomposite formulations.⁴ In scenario (e), graphene is the exclusive component within the nanocomposites. Polymer nanocomposites reinforced with graphene exhibit exceptional properties, including improved tensile strength, Young’s modulus, thermal conductivity, and thermal stability. Patra et al.²⁴ utilized the thermoplastic polymer polypropylene through melt blending to produce nanocomposites enriched with graphene, applying various experimental techniques to rigorously analyze the physicochemical properties of the nanocomposite. Experimental findings suggest that both the amount and size of graphene have distinct positive and negative impacts on filled polypropylene composites. In general, increasing the graphene content in polypropylene yields beneficial results. Our findings indicate that employing 5 µm graphene nanoplatelets is advantageous in many cases, although 15-µm sheets demonstrated enhanced performance concerning flexural and impact strengths.

The research involved measuring both incident (Ii) and transmitted (It) acoustic power through the impedance tube method, utilizing equipment such as microphones, an impedance tube, a conditioning amplifier, a frequency analyzer, and analysis software at room temperature. STL values were recorded for nanocomposites with various filler loadings, including graphene and nanoclay. The impedance tube apparatus consists of a long, cylindrical tube with microphones situated at either end, separated by the sample being tested. Sound waves traverse the sample, allowing the microphones to capture sound pressure levels before and after passing through, which facilitates the calculation of STL. This setup is designed to evaluate the acoustic characteristics of materials for their ability to block or absorb sound, enabling researchers to assess their efficiency in reducing sound transmission—an important factor for tailoring material design for specific applications.

The signal-to-noise ratio (SNR) is determined by assessing the measured signal against the typical baseline noise. This process includes executing a Fourier transform on the current signals over time and examining the frequency spectra.

The Carl Zeiss SUPRA 55 FESEM/EDX system from Germany was employed for a detailed analysis of morphology. With an operating voltage of 30 kV, the electron gun supplied the essential energy for imaging. The system featured an exceptional instrumental resolution of 1.4 nm at 15 kV, facilitating high-quality imaging and precise examination of the sample’s structure and composition. This sophisticated equipment allowed researchers to gather accurate and detailed insights into the sample’s morphology, contributing to a thorough understanding of its properties.

The deployment of scanning electron microscopy (SEM) offered insightful revelations regarding the distribution and arrangement of clay and graphene nanosheets (GNs) within the polypropylene (PP) matrix in this investigation. The SEM imagery presented in Fig. 3 revealed an even distribution of clay and GNs throughout the PP matrix, entirely free from observable filler agglomerations, even in scenario (e). This observation suggests that the melt compounding conditions applied were ideal for fabricating these nanocomposites, indicating a likelihood of beneficial composite characteristics tailored for soundproofing purposes. The study further examined the potential applications of these nanocomposites in brain pacemakers, as illustrated in Figs. 3(a) and 3(b), which depict complex pore architectures interwoven with fibers. The images accentuated the formation of voids resulting from solidified adhesive influenced by the polypropylene matrix, highlighting the composite’s pore development due to gaps between fibers as well as those generated by the polypropylene component.

In addition, the research shed light on the impact of nanocomposite density on sound insulation effectiveness, revealing that the denser sample (case b) demonstrated superior sound transmission loss (STL) values, attributed to its irregular pore configurations and increased density. The analysis also noted a trend wherein escalating graphene proportions led to a reduction in nanocomposite density, subsequently resulting in lower STL values. Moreover, the precise measurements of the hollow polypropylene spheres illustrated in Figs. 3(a) and 3(b)—including inner and outer diameters along with shell thickness—were thoroughly detailed. The primary focus of the research was the formulation of ternary nanocomposites comprising polypropylene, nanoclay, and graphene, with sound insulation assessments indicating remarkable performance, particularly in composite (b), which contained 2.75 wt. % nanoclay and 1.25 wt. % graphene. The presence of nanoclay particles emerged as a pivotal contributor to the enhanced soundproofing capabilities of the nanocomposites, with case (b) exhibiting promising results for sound absorption applications in pacemaker shells, especially when contrasted with case (e) containing 4 wt. % graphene. This extensive investigation illuminates potential advancements in soundproofing technology and provides invaluable insights for future explorations within this field.

Figures 3(f)–3(j) illustrate the nanocomposites produced using the compatibilizer PP-g-MA. The SEM images presented for these figures correspond to samples that did not utilize compatibilizers. Effective interfacial adhesion between the blended components is crucial for achieving a refined morphology. Compatibilizers can influence the morphology of immiscible blends by preventing coalescence, which enhances both interfacial properties and the adhesion between the polymer components. In Figs. 3(f)–3(j), the compatibilizer produces a non-porous biomaterial that deviates from our objective of creating a sound absorber. In other words, PP-g-MA improves the distribution of graphene and nanoclay within the PP blends, thereby enhancing the mechanical properties of the blend. Consequently, the focus of this work is to exclude the use of a compatibilizer in the production of nanocomposites.

The domain of acoustic insulation materials plays an indispensable role in fostering environments conducive to concentration, relaxation, and general well-being. A heightened sound transmission loss (STL) value signifies enhanced acoustic isolation capabilities, which are pivotal across diverse contexts, including residential, commercial, and industrial environments. The integration of PP/Graphene/Clay within composite formulations has attracted considerable interest due to its favorable mechanical and thermal attributes. These composites exhibit remarkable versatility and applicability spanning various industries, from construction to electronics. This inquiry specifically explores the sound-dampening capabilities of PP/Graphene/Clay composites, with the objective of augmenting our comprehension of their efficacy in mitigating noise transmission. The results indicate that an increased proportion of clay in the composites correlates with superior soundproofing performance in comparison to formulations solely incorporating graphene or clay particulates, particularly across a spectrum of frequencies. Figure 4(a) illustrates the soundproofing efficacy of the PP/Graphene/Clay nanocomposite, providing insights into the behavior of these materials under various frequency conditions. The distinct formulation of PP/2.75%Clay/1.25%GNs is particularly noteworthy for its unique attributes, such as diminutive microspheres and elongated cavities, which enhance the acoustic insulation properties of the nanocomposites when utilized within pacemaker casings. In pacemakers, noise can pose substantial challenges for users, disrupting their daily activities and diminishing their quality of life. Consequently, research initiatives have focused on the development of sound-insulating and absorbing materials to alleviate this challenge across a myriad of applications. The convergence of material science and neurotechnology in this investigation represents a pioneering approach to fulfilling the demand for advanced materials within the realm of neuroscience. By harnessing the characteristics of microshells and innovative electrode architectures, this research aspires to propel the advancement of state-of-the-art technologies that could enhance the functionality and durability of medical devices such as pacemakers.

Implantable pacemakers serve as internal sensors in the body, focusing primarily on monitoring biophysical biomarkers such as temperature, movement, stress, pressure, electrophysiology, and bioimpedance.^27,28 These sensors operate based on established measurement principles, leading to the development of compact and resilient devices with minimal power needs. In certain cases, like electrophysiology in the brain, advanced amplifiers may be necessary to detect faint signals, while bioimpedance could require sophisticated readout systems.^29,30 These sensors are vulnerable to interference from external sources generating similar signals, like external motion and electric fields, with mechanical sensors being affected by changes in temperature. The primary objective of integrating anti-noise composites into pacemakers is to prolong device lifespan and create a serene environment for the patient. In the realm of electrical pacemakers, the transducer might function as an amplifier. Biorecognition heavily relies on post-processing the transducer signal to eliminate unwanted interference or noise from the pacemaker’s response.³¹ This method necessitates a deep understanding of the physiological parameters of biomarker levels over time (frequency, amplitude, etc.) and a thorough comprehension of potential interference factors.

The research explores how sample thickness and bulk density influence sound transmission loss (STL) and sound absorption of two nanocomposites: PP/2.75%Clay/1.25%GNs and PP/0%Clay/4%GNs, both maintaining a uniform bulk density of 100 kg/m³. The findings indicate that increasing sample thickness improves sound absorption and expands the absorption bandwidth, especially at lower frequencies. Furthermore, experiments that varied fiber weights while keeping the material volume consistent demonstrate that higher bulk densities significantly enhance sound absorption across all frequencies. This is primarily attributed to increased energy dissipation and a more complex sound path, as evidenced by the corresponding SEM images. The critical impact of bulk density on sound absorption in nanocomposites is underscored by these results. Figures 4(b) and 4(c) depict the correlation between thicker samples and enhanced sound absorption, leading to a wider absorption bandwidth, particularly at lower frequencies. The data indicate that sound absorption increases with bulk density, supported by SEM images in Fig. 3, which illustrate density distributions. The effect of higher bulk density on sound absorption is more pronounced across frequencies than that of sample thickness. Increased densities contribute to greater energy dissipation within the absorber due to the added complexity of the sound path, as shown in Fig. 4(d).

At the outset, baseline noise evaluations involve applying a 0 V signal to the micropipette submerged in a solution while monitoring the time-dependent behavior of the current response at the external connection. Afterward, sinusoidal voltage signals of varying frequencies and amplitudes are introduced, and the resulting current is measured at the external contact. Figure 5(b) illustrates an input voltage signal with an amplitude of 0.5 mV and a frequency of 100 Hz, along with the corresponding recorded current. Next, the frequency spectra of the current signals over time are analyzed using the Fast Fourier transform (FFT) feature in MATLAB.

The baseline noise measured for the proposed nanocomposites reveals distinct values across various cases. In case (a), with a ratio of 4:0, the baseline noise is recorded at 1.81 × 10⁻²⁶ A²/Hz. For case (b), which has a ratio of 2.75:1.25, the baseline noise decreases to 0.50 × 10⁻²⁶ A²/Hz. In case (c), with an equal ratio of 2:2, the baseline noise is noted at 0.89 × 10⁻²⁶ A²/Hz. Finally, in case (d), with a ratio of 1.25:2.75, the baseline noise measures 1.22 × 10⁻²⁶ A²/Hz. Significantly, Case (b) PP/2.75%Clay/1.25%GNs demonstrated diminished Baseline Noise levels, indicating its potential effectiveness for noise attenuation in pacemaker nanocomposites. In stark contrast, Case (c) PP/2%Clay/2%GNs exhibited a noise level that was 78% higher than that of Case (b). An increase in graphene content within the composite can enhance low-frequency sound absorption by modifying its morphology and architecture for improved acoustic energy dissipation. However, such enhancement may be less effective at elevated frequencies, which could inadvertently result in the amplification of acoustic energy.³² Furthermore, our morphological analysis indicated that an elevated percentage of graphene may lead to the emergence of minuscule cavities of limited dimensions, potentially obstructing effective acoustic energy dissipation. Although well-dispersed graphene fillers can reduce the average cell size of polypropylene through nucleation, in this examination, the average cell size of all nanocomposites, excluding Case (e), showed an increase relative to the baseline. The improved soundproofing characteristics noted in the composites are likely due to graphene clustering, resulting in inconsistent cell nucleation and the generation of sizable voids. To mitigate this complication, strategies such as lowering the graphene content in the composites or enhancing the dispersion of graphene within polypropylene may be implemented. Studies on acoustic emission and absorption in composites can illustrate their soundproofing effectiveness, demonstrating the interaction of these materials with acoustic waves across varying conditions.

A study was carried out on soundproofing nanocomposites to find the most effective material based on the frequency characteristics of pacemaker impulse noise. Thicker materials and higher frequency sounds were discovered to enhance sound absorption efficiency, with the addition of an air layer further boosting performance. Incorporating air layers can be achieved through irregular and lengthy microstructures within the polymer matrix.^33,34 Five varieties of sound-absorbing/insulating products were tested, and their effectiveness was evaluated based on noise reduction from actual pacemaker impulse scenarios.

The Fast Fourier transform (FFT) of the measured current response to applied voltage for Case (a) PP/4%Clay/0%GNs is presented in Fig. 6. This figure reveals increased noise power at a frequency of 82 Hz, with the clay-containing nanocomposite displaying more components. The nanoclay structures in these composites consist of roughly 1 nm thick alumina silicate layers stacked in multilayer structures of around 10 nm, offering an impressive aspect ratio and specific surface area of about 657 m²/g. These elongated structures help trap air within the polymer matrix. The FFT of the measured current response to voltage applied for Case (b) PP/2.75%Clay/1.25%GNs is illustrated in Fig. 6. The primary distinction between this composite and those in Fig. 6 is the introduction of graphene into the polymer. The incorporation of graphene can influence these structures by stretching them in different directions. Essentially, adding graphene within the matrix serves to elongate the longitudinal structures and enhance signal transmission.

In Fig. 6, we present the calculated values for the nanocomposites containing PP-g-MA. This figure demonstrates the effect of incorporating PP-g-MA on the structural properties of these nanocomposites. Specifically, it reveals that the addition of PP-g-MA results in the formation of more cohesive nanocomposite structures, which are characterized by noticeably smaller cavities or pores. These larger voids are crucial because they significantly influence the acoustic properties of the nanocomposites. While the tighter structure created by PP-g-MA enhances the overall integrity of the material, it may not be optimal for sound transmission characteristics. However, it is essential to emphasize that the primary aim of this article is to create nanocomposites that effectively absorb a significant portion of sound waves, which is somewhat different from merely improving sound transmission. The findings of this research indicate that integrating PP-g-MA into the nanocomposite formulation notably elevates the baseline noise level of each sample. The data suggest that, on average, the inclusion of PP-g-MA can lead to an increase in baseline noise levels by ∼20%–25%. This contrast with the absence of PP-g-MA underscores the potential of these nanocomposites for noise absorption applications, aligning with the broader objective of developing materials that can help reduce sound pollution.

The foundational noise illustrated in FFT charts is pivotal for precisely evaluating noise power levels. It acts as the intrinsic noise within a signal, impacting the identification of relevant signal components. Establishing a baseline noise threshold allows engineers to differentiate between the target signal and any intrusive noise, aiding in the analysis of signal-to-noise ratios and the assessment of data integrity.³⁵ Accurate measurement of noise power is crucial in sectors like telecommunications and audio engineering. Monitoring and analyzing baseline noise in FFT charts contribute to improved signal processing, the removal of unwanted noise, and the enhancement of overall signal fidelity for reliable data analysis and interpretation.

Figure 7 demonstrates how the signal-to-noise ratio (SNR) of the studied nanocomposite varies with the frequency and amplitude of the applied sinusoidal signal. The findings reveal that incorporating nanoclay and graphene enhances the sound absorption capabilities of polypropylene, particularly at lower frequencies. This enhancement shows promise for the development of sound-absorbing materials intended for pacemakers. Low-frequency sound waves, known for their long wavelengths and slow propagation speeds, present challenges for attenuation and can lead to health risks with prolonged exposure. In the figure, the impact of adding PP-g-MA is represented by a dashed line, which indicates reduced signal transmission values compared to other nanocomposites derived from these biomaterials. The enhanced mechanical performance of the PP nanocomposite due to the addition of PP-g-MA has been validated by the work of Oromiehie et al.,³⁶ as presented in this study.

It is important to highlight that frequencies near pacemakers typically lie within the low-frequency spectrum. Optimal interfacial adhesion is attained when graphene flakes are chemically bonded to the matrix. Conversely, weaker bonding interactions, like hydrogen bonds and van der Waals forces, between graphene and the matrix may lead to insufficient adhesion and load transfer. Hydrogen bonds and van der Waals forces are susceptible to disruption under minimal stress or deformation, only to reform once the stress is alleviated.³⁷ This repetitive cycle results in interfacial sliding (or slip) between filler particles and the matrix, promoting additional dissipation of sound energy through friction. In the present investigation, it seems that strong interfacial adhesion is established when graphene flakes are covalently linked to polypropylene, resulting in decreased interfacial sliding between graphene filler particles and the polypropylene matrix.

The tensile properties of the fabricated samples were evaluated using an Instron 5966 universal testing machine, in accordance with ASTM 638D standards. The tests were conducted on dog-bone-shaped injection-molded samples under tension with a constant strain rate of 4.5 mm/min at room temperature.

For impact strength assessment, a Charpy impact testing instrument (CEAST 9050 Motorized) from Instron Engineering Corp. was utilized. Rectangular bar-shaped PP-based samples (75 mm length, 11 mm width, 4 mm thickness) were prepared, with one-sided notches having a root radius of 0.25 mm at a depth of 2 mm. The notched Charpy impact strength was measured at room temperature, with a drop velocity of 3.8 m/s and an impact energy of 7.2 J.

To investigate the thermal stability, thermogravimetric analysis (TGA) was performed using a TA Instruments TGA Q500 analyzer under a nitrogen atmosphere with a flow rate of 22 ml/min. Samples weighing about 10 mg were heated from room temperature to 900 °C at a rate of 10 °C/min.

The wet weight (ww) and dry weight (wd) were used to calculate the water absorption percentage.

The mechanical characteristics of nanocomposites are vital for their applicability in deep brain stimulator technology. This study investigates how varying weight fractions of clay and graphene impact the tensile strength of these materials. In Fig. 8(a), the stress–strain behavior is depicted, showcasing the relationship between applied stress and resulting strain. In general, the incorporation of nanoparticles into the PP matrix leads to a decrease in tensile strength due to factors like nanoparticle dispersion, interfacial bonding, and composite structure. However, the PP/2.75%Clay/1.25%GNs nanocomposite stands out with the highest tensile strength recorded at 44.6 MPa, surpassing that of other compositions by a small margin. Despite the typical trend of reduced tensile strength with added nanoparticles, the strength levels observed in these nanocomposites are considered suitable for deep brain stimulator applications. This highlights the importance of fine-tuning nanoparticle content to achieve desired mechanical properties in nanocomposites tailored for specific requirements. Further investigation into the underlying mechanisms governing the mechanical behavior of these nanocomposites could yield valuable insights for enhancing performance and broadening their potential applications. Understanding the interplay between filler materials and polymer matrices is crucial for boosting the stiffness and tensile strength of composite materials.³⁸ Robust interfacial bonding between reinforcement agents and polymer matrices can enhance load transfer efficiency and prevent composite failure, ultimately improving mechanical properties. Factors such as polarity mismatch and filler dispersion can influence the performance of polypropylene (PP) nanocomposites. Insufficient load transfer capability may lead to stress concentration in localized regions, impacting overall strength. The inclusion of nanoparticles in PP nanocomposites may expedite degradation during high-temperature processing, potentially diminishing tensile strength. Hence, optimizing interactions between fillers and polymers, as well as ensuring proper dispersion, is essential for enhancing the mechanical properties of these composites. The introduction of clay and graphene nanoparticles notably boosted the elasticity of PP, with elongation-at-break properties being more influenced by the reinforcement rather than the matrix. Specifically, the presence of particles in the PP matrix significantly increased elongation at break, as evidenced by the shift from 101.1% in pure PP to 298% in PP/2.75%Clay/1.25%GNs nanocomposites [Fig. 8(b)].

In Fig. 8(c), it is observed that an increase in the percentage of clay nanoparticles in the polymer leads to a decrease in the impact strength of reinforced PP nanocomposites compared to pure PP. This reduction is attributed to the differing polar and non-polar characteristics of the reinforcing agents and the polymer matrix, resulting in a diminished capacity to absorb mechanical energy before fracturing. This trend mirrors similar behavior seen when incorporating other materials into the PP matrix. The decrease in impact strength is linked to the catalytic degradation of the PP-based nanocomposites, as evidenced by the deterioration of tensile properties. Moving on to Fig. 8(d), changes in the tan delta of both pure PP and PP-nanoparticles nanocomposites are depicted as temperature varies. The introduction of nanoparticles led to a slight broadening of the tan delta peak and an elevation in the glass transition temperature for all PP-nanoparticles nanocomposites in comparison to pure PP. This shift is believed to be caused by the nanoparticles restricting the mobility of PP molecular chains at the interface between the filler and the polymer matrix. Furthermore, there was a marginal increase in the intensity of the tan delta peak in the PP/2%Clay/2%GNs nanocomposites. In contrast, the magnitude of the tan delta peak decreased in the PP/1.25%Clay/2.75%GNs nanocomposites relative to pure PP, indicating that filler particles can only withstand a certain level of stress and allow a specific magnitude to impact the interface. Consequently, energy dissipation occurs within the PP matrix and at the interface, with higher energy dissipation at stronger interfaces and lower energy dissipation at moderate interfaces. In addition, Fig. 8(d) illustrates the viscous and elastic phase relationships of pure PP compared to the reinforced nanocomposites at varying weight fractions of nanoparticles under consistent temperature conditions. Pure PP exhibited a higher tan delta due to increased movement of polymer chains at elevated temperatures, with other nanocomposite reinforcements exhibiting similar behavior at those temperatures.

Figure 9(a) illustrates the thermal profiles of pure PP and PP nanocomposites reinforced with varying amounts of filler. Examination of Fig. 9(a) suggests that introducing the same proportion of graphene and clay filler into the PP matrix results in a slight increase in the thermal degradation temperature at 25% weight loss (from 260 to 265 °C), indicating that equivalent levels of nanoparticles can serve as a thermal barrier during initial degradation phases. However, beyond 25 wt. %, there is no significant enhancement in thermal degradation compared to pure PP in the specified nanocomposite (PP/2%Clay/2%GNs). Adjusting the filler content to 2.75% and 1.25% actually diminishes the inherent thermal stability of pure PP, evident across all weight loss percentages. This decrease implies inadequate dispersion of the filler, particularly in PP/2.75%Clay/1.25%GNs. While the addition of fillers typically boosts thermal stability in polymer nanocomposites by absorbing volatile compounds on the polymer surface, the absence of thermal stability enhancement in the examined PP-based nanocomposites indicates catalytic degradation during the melt processing stage. This phenomenon is likely attributed to peroxide radical reactions during PP–NS nanocomposite melt processing, hindering the reinforcement from effectively acting as a thermal barrier in pure PP, especially at 50% and 60% weight loss levels.

In Fig. 9(b), the water absorption characteristics of both pure PP and PP nanocomposites with varying filler content are depicted over different time periods. The trend observed is associated with the moisture absorption capacities of the materials. It is apparent that the moisture absorption levels change as the days and filler concentrations increase. This variation may be ascribed to the dispersion level influenced by the filler content, which has decreased the tensile stress of the nanocomposites against deformation, potentially leading to the creation of micro-voids in the material that act as pathways for water absorption. Another potential factor could be the clustering of nanoparticles within the matrix, affecting the tensile properties of the reinforced PP.^38,39 The incorporation of reinforcing particles into the polymer structure seems to increase water absorption in the reinforced nanocomposites compared to pure PP. In addition, water absorption appears to rise over the soaking period (from day 0 to 25). While the filler structure’s ability to address the weak mechanical properties in a polymer had minimal impact, it did promote enhanced interfacial bonding between the filler and the matrix. Consequently, the reinforcement properties of NS filler did not demonstrate the anticipated improvement, as pure PP exhibited superior properties compared to the reinforced nanocomposites. In the current study, the PP/4%Clay/0%GNs nanocomposite displays heightened water absorption capabilities due to the filler structures.

Differential scanning calorimetry (DSC) was used to analyze the crystallization behaviors and melting points of both pure polypropylene (PP) and its nanocomposites that contain nanoscale (NS) materials. Figures 9(c) and 9(d) show the crystallization parameters for pure PP and the PP-based nanocomposites. The DSC thermograms displayed in these figures indicate that the addition of nanofillers had a negligible effect on the melting and crystallization temperatures of the pure PP. Temperature variations are crucial in influencing how polymers respond during thermal transitions, affecting the development of crystals or crosslinks. The addition of nanoparticles resulted in a slight decrease in the crystallization temperature of pure PP, while the melting point remained stable, as shown in Figs. 9(c) and 9(d). Specifically, the crystallization temperature of the PP nanocomposites, which included different amounts of clay and graphene nanoparticles, decreased to varying extents compared to that of pure PP, with melting temperatures consistently recorded at 164 °C for both the nanocomposites and pure PP. This drop in crystallization temperature can be linked to the unmodified surfaces of the nanoparticles, which do not possess nucleating capabilities to enhance the crystallization temperature. This trend may indicate a potential reduction in tensile strength and possible catalytic degradation due to peroxide radical reactions during the melt processing phase. Conversely, surface-modified nanoparticles demonstrate nucleating abilities, while non-surface-treated nanoparticles have little effect on the crystallization of the PP matrix. It is also notable to consider the width of the DSC crystallization peak; narrower peaks suggest effective nucleation by the filler, aiding in polymer crystallization, whereas broader melting peaks indicate diminished crystallization efficiency. The greater crystallinity found in pure PP compared to the nanocomposites is due to the interference presented by the nanoparticles in the orderly arrangement of polymer molecules into a highly crystalline structure.

Pacemakers are medical devices that are surgically implanted to help regulate heart rhythms. They consist of electronic circuits connected to batteries and leads fixed to the heart muscle to deliver electrical stimulation. However, these leads can sometimes malfunction and potentially harm surrounding tissue. Once implanted, the position of the leads cannot be altered, which restricts access to different areas of the heart. In addition, the use of rigid metallic electrodes in pacemakers can lead to tissue damage when reactivating the heart after surgery or during the management of arrhythmias.

Pacemakers also face significant challenges from external noise. High-noise environments, such as busy roads or crowded stadiums, can affect the performance of these devices. They function by transmitting signals through electrodes to control blood flow and communication with the brain. Current research lacks comprehensive studies on the materials used in pacemakers. This study aims to introduce a novel polymer-based nanocomposite to enhance signal transmission and reduce noise interference. These nanocomposites—made from nanoclay, graphene, and polypropylene—exhibit lower allergenic potential near body tissues and are classified as biomaterials.

The research employed scanning electron microscopy (SEM) to analyze the distribution of clay and graphene nanosheets within a polypropylene (PP) matrix. The SEM images showed a well-dispersed integration of clay and graphene in the PP, indicating optimal conditions for creating nanocomposites ideal for soundproofing applications. The investigation focused on the use of these nanocomposites in brain pacemakers, examining the intricate pore structures and the effect of nanocomposite density on sound insulation properties. It was observed that higher clay concentrations improved soundproofing performance at different frequencies. In addition, this study examined the impact of adding PP-g-MA on the sound properties of the nanocomposite, revealing that it was not effective for sound absorption due to its more coherent structure.

To assess the noise reduction capabilities of these nanocomposites, signal-to-noise ratio (SNR) evaluations were performed, with particular attention to the performance of the PP/2.75%Clay/1.25%GNs composition, which demonstrated improved soundproofing qualities in pacemaker casings. Fast Fourier transform (FFT) analysis indicated varying current responses depending on the nanocomposite formulation, with the PP/2.75%Clay/1.25%GNs composition significantly reducing baseline noise levels. The study also highlighted the role of graphene content in sound absorption and structural integrity, stressing the importance of well-dispersed graphene within polypropylene for effective acoustic energy dissipation. In addition, in the final section of the research, we examined the thermomechanical properties of nanocomposites that are suitable for use as the primary material in pacemakers within the human body.

Overall, this research offers valuable insights into advancing soundproofing technology and developing sound-absorbing materials specifically designed for pacemakers. It presents innovative ideas and materials for addressing noise-related challenges in these devices. Furthermore, the mechanical and thermal analyses conducted on the nanocomposites affirm their suitability for pacemaker applications.

The authors express gratitude to faculty members for their support and contributions to the research, which is part of Baraa Chasib Mezher’s Ph.D. program funded by Tabriz University (No. IFTU-454578). Special thanks are given to the Head of the Mechanical Engineering faculty, as well as to the SEM Measurement team at Baghdad University of Technology in Iraq and the Nanostructured and Novel Materials Laboratory at the University of Tabriz for their assistance in various tests. The authors thank the Editor-in-Chief and AIP Advances staff for their assistance during the peer-review and publication of this article.

This study was conducted without any external financial support.

The authors have no conflicts to disclose.

Baraa Chasib Mezher (براء جاسب مزهر ال كسار): Conceptualization (equal); Data curation (equal); Formal analysis (equal); Funding acquisition (equal); Investigation (equal); Methodology (equal); Project administration (equal); Resources (equal); Software (equal); Supervision (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Shahab Khameneh Asl (شهاب خامنه اصل): Conceptualization (equal); Data curation (equal); Formal analysis (equal); Funding acquisition (equal); Investigation (equal); Methodology (equal); Project administration (equal); Resources (equal); Supervision (equal); Validation (equal); Visualization (equal); Writing – review & editing (equal). Hamed Asgharzadeh (حامداصغرزاده): Conceptualization (equal); Data curation (equal); Formal analysis (equal); Funding acquisition (equal); Investigation (equal); Methodology (equal); Project administration (equal); Resources (equal); Software (equal); Supervision (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Seyed Jamaleddin Peighambardoust سید جمال الدین پیغمبردوست): Investigation (equal); Methodology (equal); Project administration (equal); Supervision (equal); Writing – review & editing (equal).

The data that support the findings of this study are available from the corresponding author upon reasonable request.