Characterization and Application of Nanomaterials 2025, 8(3), 11881. https://doi.org/10.24294/CAN11881 1 Review Nanoreinforcement effects in multifunctional polyurethane foams— Scientific status hitherto and future Ayesha Kausar* National Center for Physics, Quaid-i-Azam University Campus, Islamabad 45320, Pakistan * Corresponding author: Ayesha Kausar, dr.ayeshakausar@yahoo.com Abstract: Polyurethane is a multipurpose polymer with valuable mechanical, thermal, and chemical stability, and countless other physical features. Polyurethanes can be processed as foam, elastomer, or fibers. This innovative overview is designed to uncover the present state and opportunities in the field of polyurethanes and their nanocomposite sponges. Special emphasis has been given to fundamentals of polyurethanes and foam materials, related nanocomposite categories, and associated properties and applications. According to literature so far, adding carbon nanoparticles such as graphene and carbon nanotube influenced cell structure, overall microstructure, electrical/thermal conductivity, mechanical/heat stability, of the resulting polyurethane nanocomposite foams. Such progressions enabled high tech applications in the fields such as electromagnetic interference shielding, shape memory, and biomedical materials, underscoring the need of integrating these macromolecular sponges on industrial level environmentally friendly designs. Future research must be intended to resolve key challenges related to manufacturing and applicability of polyurethane nanocomposite foams. In particular, material design optimization, invention of low price processing methods, appropriate choice of nanofiller type/contents, understanding and control of interfacial and structure-property interplay must be determined. Keywords: polyurethane; nanocomposite; foam; manufacturing; properties; radiation shielding; shape memory; biomedical 1. Introduction Polyurethane forms an important contribution to the thermosetting, thermoplastics, or elastomeric type of polymers due to the range of intrinsic physical features and advanced utilizations [1]. These polymers have flexibility of backbone variations by altering soft or hard units and probable hydrogen bonding between the segments [2]. Worth mentioning application areas of polyurethanes (as coatings, fibers, sponges) expand from defense and devices to medical sectors [3]. Moreover, advancements in the field of polyurethane materials can be seen in the form of nanocomposites with inorganic or carbon nanoadditives [4,5]. Abundant literature reports have been noted on preparation, physical aspects, and technical significance of polyurethane sponges or foams [6]. Similarly, polyurethane foams filled with different types of nanofillers have also been investigated for designs and applied attributes [7]. In this regard, most important types of nanofillers have been noted as graphene and carbon nanotube [8‒10]. These hybrid foams have been manufactured by using variety of self foaming, free rising, foaming agent, freeze drying, in situ, solution, and chemical methods [11]. Consequently, nanocomposite foams own low density, flexibility, mechanical/compression strength, thermal features, other high tech features [12]. The high performance nanocellular polyurethane CITATION Kausar A. (2025). Nanoreinforcement Effects in Multifunctional Polyurethane Foams—Scientific Status Hitherto and Future. Characterization and Application of Nanomaterials. 8(3): 11881. https://doi.org/10.24294/CAN11881 ARTICLE INFO Received: 27 August 2025 Accepted: 31 October 2025 Available online: 24 November 2025 COPYRIGHT Copyright © 2025 by author(s). Characterization and Application of Nanomaterials is published by EnPress Publisher, LLC. This work is licensed under the Creative Commons Attribution (CC BY) license. https://creativecommons.org/licenses/ by/4.0/ Characterization and Application of Nanomaterials 2025, 8(3), 11881. 2 architectures have been applied for important applications concerned to radiation shielding, stimuli responsiveness, and biomedical sectors [13]. This up-to-the-minute review is planned to cover almost every physical and practical facet of polyurethane nanocomposite foams, for first time in the literature so far. In this concern, basics, synthesis, categories of polyurethane hybrid sponges (polyurethane/graphene nanocomposite foams, polyurethane/carbon nanotubes nanocomposite foams), and applications (radiation shields, shape memory, tissue scaffolds) have been conversed. As per reported knowledge, future of polyurethane nanocomposite foams simply relies upon overcoming field challenges of facile processing, design and property optimization, ecofriendliness, and large scale processing. 2. Polyurethane and polyurethane foams Polyurethane is a versatile polymer with thermoplastic, thermosetting, or elastomeric backbone structure [14]. Basically, a polyurethane main chain consists of carbamate or urethane links [15]. In the case of segmented polyurethanes, prepolymers with isocyanate functionalities have been developed to further react with diamine, dihydroxyl, or similar short chain bifunctional compound [16]. Consequently, segmented polyurethanes have two types of segmental units, i.e., isocyanate based hard segments and polyol based soft segments [17]. It is important to mention that secondary interactions or crosslinking may exist between polyurethane chains due to the presence of amine (-N-H) and carbonyl (-C=O) functionalities in the main chain [18]. Notable features of polyurethanes can be listed as mechanical strength, thermal stability, thermal conductivity, electrical conductivity, nonflammability, anticorrosion, chemical resistant, and so on [19]. Subsequently, applications of these remarkable macromolecules have been reported for thermal insulating materials, foams, gaskets/seals, packaging, building, electronics, and transportation to name a few [20]. One of the outstanding behaviors of polyurethanes have been noted as the formation of polymeric sponges or foams [21]. Polyurethane foams may have close or open cell microstructures [22]. These polymeric foams usually have the elasticity, low density, heat stability, heat conductivity, and nonflammability characters [23]. Practical uses of polyurethane foams have been observed for aerospace automobile interiors, industrial packaging, insulating materials, furnishing, and other areas [24‒ 26]. For synthesizing polyurethane foams, numerous facile routes have been practiced, as per literature reports so far. Usually, the synthesis of polyurethane foam may involve reactions of isocyanate and polyols, as shown in Figure 1. An initial attempt by Saint-Michel et. al. [27] reported the polyurethane foam fabrication using 4,4'- diphenylmethanediisocyanate and polypropylene triol in the presence of dibutyltin dilaurate (as catalyst). In this process, in situ produced carbon dioxide from polyisocyanate caused self foaming process [28]. The microstructural analysis revealed close shell cell nanostructures. Consequently, fine electrical conductivity and mechanical properties were observed form these polymeric sponges. Advancements in the field of polyurethane foams led to the development of nanoparticle reinforced hybrid materials [29,30]. Figure 1 shows most probable reactions of isocyanate functionalities involved in the formation of polyurethane foams [31]. Herein, in situ Characterization and Application of Nanomaterials 2025, 8(3), 11881. 3 production of carbon dioxide (key agent for self foaming) can be seen as a result of reactions between isocyanate groups and water [32]. Figure 2A shows scanning electron microscopy images of polyurethane foam having varying isocyanate index (0.88‒1.1). With increasing values of isocyanate index, strength/integrity of cell walls seemed to be enhanced and porosity was decreased due to increasing viscosity, crosslinking, and foam reactions of the system. Figure 2B depicts relationships of tensile strength with isocyanate index and compressive strength vs. isocyanate index at 50% deformation and 20% deformation of foamed samples. According to these results, the linear relationships between the properties were observed due to enhancements in integrity of the cellular foam structure with rising isocyanate index. Figure 2C illustrates glass transition temperature vs. isocyanate index of polyurethane foam. Hither, glass transition temperature was found linearly dependent upon the isocyanate index of polyurethane foams, which may also affect their mechanical properties. It can be suggested that optimal temperature around ~23 ° must be used to attain desirable mechanical properties of these sponges. Figure 1. Common reactions involved in polyurethane foam manufacturing via isocyanate reactions [31]. Reproduced with permission from MDPI. Characterization and Application of Nanomaterials 2025, 8(3), 11881. 4 Besides, waterborne polyurethanes have been considered as an environmentally friendly type of polymers with solvent-borne backbone units [33,34]. These polymers have been studied for valuable thermal, mechanical, anticorrosion/antichemical, barrier, permeability, and other characteristics [35‒37]. Consequently, waterborne polyurethanes have developed in the form of nanocomposites, foams, nanofibers, and other industrially viable materials been and their foams have been reported for advanced applications [38‒40]. Figure 2. (A) Scanning electron microscopy images of polyurethane foam having varying isocyanate index; (B) tensile strength vs. isocyanate index (blue circles) and compressive strength vs. isocyanate index at 50% deformation (red squares) and 20% deformation (brown squares) of foamed samples; (C) glass transition temperature vs. isocyanate index of polyurethane foam [31]. Reproduced with permission from MDPI. Characterization and Application of Nanomaterials 2025, 8(3), 11881. 5 3. Polyurethane foams with carbonaceous nanoreinforcements 3.1. Graphene nanoreinforced polyurethane nanocomposite foam Name of graphene appears first among the most remarkable nanocarbon discoveries [41]. Graphene occurs as a nanosheet of hexagonally organised sp2 hybrid carbon atoms [42]. According to structural specifications, graphene is believed as a single layer out of a stacked graphite structure [43]. Since discovery, countless bottom up or top down strategies have been adopted to form two dimensional graphene nanostructure, including exfoliation, hydrothermal, vapor deposition, plasma/laser, and chemical or electrochemical routes [44]. Subsequently, scientific explorations on graphene unveiled a range of notable attributes, such as superior surface area, Young's modulus (~I TPa), thermal transport (~2000-5000 W/mK), electrical conduction (~200,000 cm2V-1s-1), and other valued characteristics [45]. Amid high-tech applications, worth of graphene has been noted in the fields of space/defense, energy devices (solar cells, fuel cells, capacitors, batteries), electronics (sensors, diodes), civil engineering, textile, environmental remediation, and medical areas [46,47]. Technical implications of graphene have been further enhanced in the form of polymeric hybrids using varying matrices [48]. In this regard, polyurethanes have also been applied as valuable matrices for graphene and derivative nanofillers [49]. Several high performance polyurethane/graphene nanocomposites have been designed and examined for physical properties and advanced industrial uses from energy and environment to biomedical devices [50]. Similar to polyurethanes, hybrid foams or sponges have been prepared with graphene reinforcements [51,52]. Among early attempts, Hodlur et. al. [53] reported coating method for graphene deposition on polyurethane foam. The hierarchical sponges depicted fine percolation and electron conduction behavior under low applied pressures, e.g., ~0.5 atmospheres. Chen et. al. [54] used curing method for the formation of polyurethane/graphene nanocomposite foam. Adding 5‒20 phr graphene contents to polyurethane foam matrix exhibited significantly higher electrical conductivity (1.5 × 10-3 to 1.3 S cm-1), than the unfilled foams (1.0 × 10-11 S cm-1). These superior conductivity properties of hybrid foams seemed to be due to the formation of consistent three dimensional networks in these materials. Kim et. al. [55] preferred catalyst foaming strategy to form polyurethane/graphene nanocomposite foam. These spongy nanomaterials revealed notable sound absorption properties. Herein, including 0.5 phr graphene nanofiller to polyurethane foam caused 7 times higher sound absorption coefficient than the unfilled foams. Patole et. al. [56] prepared a system based on polyurethane/poly(dimethyl siloxane)/graphene foams. Figure 3A shows a facile resin infiltration technique for the formation of hybrid foams. In this regard, initially polyurethane/graphene foam was formed using carbonization process. Later, poly(dimethyl siloxane) was impregnated on the nanocomposite foam to form polyurethane/poly(dimethyl siloxane)/graphene foam hybrids. Figure 3B illustrates scanning electron microscopy micrograph of the hybrid foam, where graphene can be observed with a defect free lattice structure. Such morphology confirmed the effectiveness of synthesis techniques Characterization and Application of Nanomaterials 2025, 8(3), 11881. 6 applied to form these polymeric sponges. Moreover, the hybrid foam had electrical conductivity of ~2.9 S m-1, due to the presence of three dimensional graphene architecture. Figure 3C shows functioning and resistance vs. time plot of a pressure sensor based on polyurethane/poly(dimethyl siloxane)/graphene foam. Pressure was applied using fingertip and resistance variations were measured with a multimeter. The resistance behavior was found directly related to the applied pressure over repeated cyclic process. Such pressure or strain sensors based on polyurethane foams can be useful for future soft robotics applications. Zhong et. al. [57] fabricated polyurethane/graphene oxide and polyurethane/reduced graphene oxide nanocomposite foams. For this purpose, a commercial polyurethane foam (40 × 40 × 30 mm3) was coated with graphene oxide through continuous solution dipping plus squeezing processes (Figure 4A). The as prepared polyurethane/graphene oxide hybrid foam was treated with hydrazine hydrate (reducing agent) to form polyurethane/reduced graphene oxide nanocomposite sponge. Figure 3. (A) Step wise fabrication of polyurethane/poly(dimethyl siloxane)/graphene foam; (B) scanning electron microscopy image of hybrid foam, inset: atomic-resolution image of the same with graphene crystal lattice; (C) resistance vs. time plot for polyurethane/poly(dimethyl siloxane)/graphene foam, inset: experimental setup for hybrid Characterization and Application of Nanomaterials 2025, 8(3), 11881. 7 based pressure sensor with fingertip for applying pressure [56]. PU = polyurethane; PDMS = /poly(dimethyl siloxane); GF = graphene foam; GF-PDMS = graphene foam-poly(dimethyl siloxane); GC-PU = graphene crystal-polyurethane. Reproduced with permission from ACS. Figure 4. (A) Schematic of the formation of polyurethane and reduced graphene oxide based foam and derived pressure or piezo-resistive sensor; (B) scanning electron microscopy images of (a) pristine polyurethane foam; (b, c) reduced graphene oxide based polyurethane foam with different magnifications; (C) current vs. real time scan of polyurethane and reduced graphene oxide based nanocomposite foam under different applied pressures [57]. GO = Characterization and Application of Nanomaterials 2025, 8(3), 11881. 8 graphene oxide; PU = polyurethane; GO/PU = graphene oxide/polyurethane; rGO/PU = reduced graphene oxide/polyurethane. Reproduced with permission from MDPI. Figure 4B a-c present scanning electron microscopy micrographs of pristine polyurethane foam and reduced graphene oxide filled polyurethane foam. In the case of pristine foam, uniform porosity and surface roughness was observed. This surface roughness was found beneficial for the adsorption of graphene oxide in the foam architecture. Consequently, polyurethane/reduced graphene oxide nanocomposite foam revealed typical graphene like wrinkled surfaces. Furthermore, Figure 4C shows a relationship between current and real time for polyurethane/reduced graphene oxide hybrid foam, with increasing applied pressures (0.62-10.4 kPa). It was observed that increasing pressure on the hybrid foam caused continuous rise in current stages due to signal-to-noise ratio and recyclability of the piezoresistive sensor. 3.2. Carbon nanotube filled polyurethane nanocomposite foam Carbon nanotube is one of the most remarkable discovery (1991) in the field of nanocarbon nanoallotropes [58]. It is a one dimensional hollow cylinder shaped carbon nanotecture which is composed of sp2 hybrid atoms [59]. This cylindrical nanostructure may exist as single walled or possess overlapping cylinders to form double walled, or multi walled carbon nanotubes [60]. The diameter of carbon nanotube can be as small as few nm, whereas length has been reported in the range of 100 nm to few µm [61]. Among common synthesis tactics, arc discharge, chemical vapor deposition, laser ablation, catalytic, and chemical approaches have been applied to form carbon nanotube [62]. The precisely designed nanocarbon nanostructures have superior aspect ratio, chirality, optical, electronic, electrical, magnetic, and thermal attributes [63,64]. Subsequently, an endless potential of carbon nanotube can be noted for defense/space, energy/electronics, coatings, construction, textile, sports, and biomedical areas [65‒67]. Besides, carbon nanotube can form the most valuable type of nanocomposites with different polymeric matrices [68]. In this concern, notable scientific attempts can be seen regarding polyurethane and carbon nanotube derived nanocomposites [69]. Consequently, carbon nanotube reinforced thermosetting, thermoplastics, or biobased polyurethanes exhibited countless structural, thermal, mechanical, and tribological features; therefore leading to high end commercial acceptance [70]. Along the similar lines, carbon nanotube has also been reinforced in polyurethane foams to form high performance next level industrial hybrids. As compared to polyurethane/carbon nanotube nanocomposites, the derived hybrid foam revealed exceptional advantages of strength-to-weight ratio, mechanical firmness, flexibility, electrical percolation, thermal transport/stability, and other beneficial properties [71]. Therefore, polyurethane/carbon nanotube foams have been found promising for numerous industrial applications, where polyurethane nanocomposites were found least efficient [72]. Among initial scientific attempts, You et. al. [73] used free rise foaming technique (cyclopentane as foaming agent) to form polyurethane/carbon nanotube hybrid foams. The resulting spongy nanomaterials developed efficient matrix- nanofiller links and percolation effects leading to reasonable electrical conductivity of about 0.2 Scm-1. Later, Zhai et. al. [74] adopted facile water blowing practice to form Characterization and Application of Nanomaterials 2025, 8(3), 11881. 9 carbon nanotube filled polyurethane foam. These hybrid foams revealed valuable compression based stress-strain features due to load transfer effects of increasing carbon nanotube contents. Espadas-Escalante et. al. [75] applied blowing agent based free foam rising practice to design polyurethane/carbon nanotube foams. These spongy hybrids were tested for compressibility, heat conduction, and flame resistance attributes. Accordingly, adding carbon nanotube contents (0.1‒2 wt.%) to polyurethane foams enhanced the flame stability by reducing the flame propagation speed. Huang et. al. [76] adopted an innovative direction dependent freezing process for the formation of carbon nanotube reinforced thermoplastic polyurethane foams. Figure 5A a-c show complete steps, equipment, and mechanism for ice crystal growth involved in the freezing process applied for the formation of thermoplastic polyurethane/carbon nanotube foams. Herein, use of direction dependent freezing led to the formation of aligned hybrid foam architecture. Figure 5B a-c depict scanning electron microscopy micrographs for pristine thermoplastic polyurethane sponges and thermoplastic polyurethane/carbon nanotube hybrid foams. These nanocomposite sponges revealed unique consistently aligned architectures due to the effectiveness of the manufacturing technique used. Hence, polyurethane/carbon nanotube hybrid foams formed unidirectional stairs like nanoarchitectures. Besides, Figure 5C displays a reversible compression behaviour of aligned (freezing method) and irregularly grown nanocomposite foams. As expected, aligned polyurethane/carbon nanotube hybrid foams revealed superior shape reattaining behavior after compression due to structural integrity and synthesis technique used. On the other hand, irregularly grown hybrid foam was suggested to have distorted cell structure and meagre shape recovery on compression cycles. Guo et. al. [77] formed pristine thermoplastic polyurethane and thermoplastic polyurethane/carbon nanotube nanocomposite foams using fused filament fabrication based three dimensional printing technique. Figure 6A demonstrates scanning electron microscopy micrographs of pristine thermoplastic polyurethane and thermoplastic polyurethane/carbon nanotube nanocomposite foams with 1 and 4 wt.% loading level. Relative to the unfilled foam, adding nanofiller contents reduced the cell sizes and enhance the number of cells in the hybrid foams. This effect was observed due to heterogeneous nucleation caused by the nanocarbon nanoparticles in the polyurethane spongy matrix. Figure 6B displays actual compression loading and release processes applied on the hybrid foam at varying compression rates. Accordingly, Figure 6C present relative current vs. time scan of 4 wt.% carbon nanotube filled thermoplastic polyurethane foam. Herein, a constant current changes over different applied compression rates were observed. Similarly, Figure 6D A shows a polyurethane/carbon nanotube nanocomposite foam based wearable sensor for gait recognition (linked to a multimeter). The changes in current were found directly linked to the variations in human gait. Characterization and Application of Nanomaterials 2025, 8(3), 11881. 10 Characterization and Application of Nanomaterials 2025, 8(3), 11881. 11 Figure 5. (A) (a) Manufacturing of thermoplastic polyurethane/carbon nanotube hybrid foam by freezing technique; (b) freezing equipment used; (c) a schematic of process showing directional freezing and growth of ice crystals; (B) scanning electron microscopy images of (a1-3) unfilled thermoplastic polyurethane foams; and (b1-3) thermoplastic polyurethane/carbon nanotube foams; (c-e) as prepared samples of conducting thermoplastic polyurethane/carbon nanotube foams; (C) comparative models showing reversibility processes for aligned and disordered thermoplastic polyurethane/carbon nanotube nanocomposite foams [76]. CNTs = carbon nanotubes; TPU = thermoplastic polyurethane. Reproduced with permission from ACS. Figure 6. (A) Scanning electron microscopy images of pristine TPU foam and TPU/MWCNTs nanocomposite foam (1 & 4 wt.%), left to right, respectively; (B) compression loading and releasing stages of the hybrid foam; (C) relative current vs. time plot of TPU/MWCNTs at varying compression rates; (D) TPU/MWCNTs nanocomposite foam based plantar wearable sensor for gait recognition [77]. TPU = thermoplastic polyurethane; TPU/MWCNTs = thermoplastic polyurethane/multiwalled carbon nanotubes. Reproduced with permission from MDPI. Characterization and Application of Nanomaterials 2025, 8(3), 11881. 12 4. Technical significance of polyurethane/carbonaceous nanocomposite foams 4.1. Radiation shielding Hazardous effects of continuously rising radiation pollution generated by functional electronics and other devices have been observed for the entire ecosystem (human beings, animals, vegetation, electronic systems) [78,79]. To cope the damaging influences of electromagnetic radiations, several solutions have been proposed, including the use of high performance materials/nanomaterials shields [80,81]. In this regard, polymers as well as derived nanocomposites have gained enormous worth to design high tech radiation shields [82]. For polymeric nanocomposites, carbonaceous nanoreinforcements like graphene or carbon nanotubes have attained scientific curiosity to deal with the environmentally interfering radiations [83,84]. Furthermore, polyurethane has been studied as an important matrix material to deal with the challenges of electromagnetic, gamma, or nuclear rays [85]. Particularly, polyurethane foams and derived nanocomposite foams have been noted for low weight, flexibility, facile synthesis, and valuable electrical conductivity and dielectric properties [86]. However, EMI shielding competency of polyurethane nanocomposite foams seemed to be reliant upon polymer backbone, nanoadditive type/content, dispersion, matrix-nanofiller links, and manufacturing route applied [87]. As per literature reports so far, nanocarbons such as graphene, graphene derivatives, carbon nanotubes, carbon nanofibers, carbon black, etc., have been recurrently applied as nanoreinforcements for polyurethane foams [88]. Li et. al. [89] designed polyurethane filled foams with carbon nanotube nanofillers using latex approach. These polyurethane/carbon nanotube sponges exhibited fairly high electrical conductivity (>360 Sm-1) and radiation shielding efficiency (~25 dB). The radiation shielding performance was suggested to be because of the formation of percolation network supporting electron transfer and radiation shielding performance of the hybrids. Jiang et. al. [90] used reduced graphene oxide as nanofiller and CO2 foaming process for polyurethane foams. These nanomaterials revealed lower conductivity (2.5×10-1) than carbon nanotube filled foams, however had reasonable EMI shielding effectiveness (22 dB). In this concern, Gavgani et. al. [91] reported on a outperforming polyurethane and reduced graphene oxide derived foams by adding foaming agents (Voranol/tin). These nanocomposite foams had electrical conductivity of ~4 Sm-1 and enormously high radiation shielding efficiency (>253 dB). Such performance of polyurethane/reduced graphene oxide foams seemed to be because of the effectiveness of synthesis method used for developing hierarchical and inerfacially connected three dimensional porous nanostructures. Oraby et. al. [92] manufactured polyurethane/iron(II,III) oxide/reduced graphene oxide based nanocomposite foams using facile solution sonication and curing routes. These hybrid sponges were investigated for microstructural, mechanical, and radiation absorption properties. Accordingly, Figure 7A a-c show transmission electron microscopy micrographs of iron(II,III) oxide/iron(III) oxide nanoparticles, pristine reduced graphene oxide nanosheet, and iron(II,III) oxide/reduced graphene oxide hybrid nanoparticles, respectively. Characterization and Application of Nanomaterials 2025, 8(3), 11881. 13 Figure 7. (A) Transmission electron microscopy images of: (a) iron(II,III) oxide/iron(III) oxide (Fe3O4/Fe2O3) nanoparticles, inset: particle size distributions; (b) reduced graphene oxide (rGO) nanosheets; (c) iron(II,III) oxide/reduced graphene oxide (Fe3O4/rGO) hybrids; (B) mechanical properties vs. shielding effectiveness (SE) and polyurethane foam with filler loading [92]. Reproduced with permission from MDPI. The iron(II,III) oxide/reduced graphene oxide hybrid had fine dispersion of tiny nanoparticle (~70 nm) over thin transparent graphene surface. In addition, Figure 7B illustrates the effect of increasing iron(II,III) oxide/reduced graphene oxide nanofiller contents as well as compression strength and modulus on shielding effectiveness of the nanocomposite foams. As per results, adding nanoparticle contents (up to 35%) caused notable shielding effectiveness of ~33 dB. This effect was attributed to the formation of continuous percolation network of reduced graphene oxide and iron nanoparticles in the polyurethane foams, so leading to valuable electrical conductivity and radiation absorption properties. Similarly, reasonably high compressive strength and modulus of around 15.6 and 5.3 MPa, respectively, were attained for the hybrid foams. Superior mechanical properties of polyurethane foams reinforced with iron(II,III) oxide/reduced graphene oxide hybrid nanoparticles were visibly linked to the integrity of three dimensional nanoarchitectures due to mutual interfacial compatibility. Into the bargain, polyurethane foams and polyurethane nanocomposite foams (whether open cell or close cell) have been employed in space sector owing to their capabilities towards efficiently attenuating fast moving neutron, γ-rays, and Characterization and Application of Nanomaterials 2025, 8(3), 11881. 14 electromagnetic interfering radiations [93]. In addition, these foams have low densities and nonflammability properties to be employed as promising radiation shields for electronics, energy devices, communication equipment, and defense system of aerospace industry [94]. Hence, using high performance polyurethane foam based radiation shields may open invaluable ways for deployments in advanced future space architectures. For a better literature analysis, Table 1 shows some significant polyurethane nanocomposite foams applied for electromagnetic interference shielding purposes. Table 1. Electromagnetic interference shielding (EMI) shielding effectiveness of polyurethane nanocomposite foams. Foam matrix Nanofiller Fabrication Electrical conductivity (Scm-1) EMI shielding effectiveness (dB) Ref Waterborne polyurethane Carbon nanotube Latex technology 362 25 dB [89] Polyurethane Reduced graphene oxide Supercritical CO2 foaming 2.5×10-1 3.17 vol.%; 22 dB [90] Polyurethane Reduced graphene oxide Tin catalyst and Voranol foaming agent 4.0 253 dB [91] Polyurethane Fe3O4 functional reduced graphene oxide Sonication; curing - 25 wt.%; 23 dB [92] Polyurethane Graphene oxide Solution, heating, casting 3.0 20 wt.%; 17-24 dB [95] Polyurethane/polydopamine Graphene Dip coating; ultrasonic; compression heating - ~ 60 dB [96] Polyurethane Graphene nanoplatelets Supercritical CO2 foaming - 1 wt.%; 16-18 dB [97] Polyurethane Graphene Catalyst; Foaming agent - Acoustic performance [98] 4.2. Shape memory applications Shape memory (stimuli active) polymers own intrinsic ability to change their shape reversibly, when exposed to light, heat, electricity, or any environmental effect [99]. Innumerable shape memory polymers (thermoplastics, thermosets, rubbers, etc.) have been reported in the literature to date [100]. In this concern, polyurethanes have been studied for proficient shape reversibility behaviour [101]. Accordingly, stimuli responsive polyurethane may display one-/two-/or multi-way shape changing phenomenon [102]. As per literature, uses of shape memory polyurethanes can be seen in smart coatings, textiles, and medical appliances [103]. In nanocomposite form, polyurethanes filled with carbon nanoparticles have been investigated for shape memory effects [104]. Mostly studies reported on the thermoresponsive stimuli responsive effects of polyurethane/nanocarbon nanocomposites [105]. Consequently, these smart polyurethane hybrids revealed notable potential for engineering materials, electronics, defense, and medical areas [106]. For example, graphene has been used as an efficient nanofiller to support the stimuli sensitive behavior of polyurethanes [107]. Zarghami Dehaghani et. al. [108] used solution condensation method to form polyurethane from poly(tetramethylene ether) glycol, α,ω-dihydroxy(ethylene- butylene adipate), 1,4-butanediol, and methylene diphenyl diisocyanate. Adding Characterization and Application of Nanomaterials 2025, 8(3), 11881. 15 0.25 wt.% graphene resulted in >92 % enhancement in thermos responsive shape memory effects. Wu et. al. [109] filled carbon nanotube in a commercially available thermoplastic polyurethane using solution method. These nanocomposites depicted water sensitive shape recovery in ~120 s. Similarly, few other reports available for nanocarbon filled shape memory polyurethanes [110]. As per literature reports, polyurethane foam materials have stimuli sensitivity towards photo, thermal, current, pH, and water effects [111]. An earlier effort by Singhal et. al. [112] mentioned the formation of polyurethane via condensation of 2,2',2"-nitrilotriethanol, N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine, and 1,6-diisocyanatohexane. Later, foaming agent method was applied to form polyurethane foams having glass transition temperature up to ~50-70 ºC. Moreover, thermomechanical shape retrieval of 97-98 % was attained. Moreover, In an earlier attempt, Kang et. al. [113] also applied blowing agent technique to form polyurethane foams of polypropylene glycol and 2,4/2,6-toluene diisocyanate with carbon nanotube additives. These nanocomposite foams were tested for thermomechanical shape memory effects. According to results, adding 5 wt.% carbon nanotubes in polyurethan foam caused up to 85% shape recovery properties. Later, Kim et. al. [114] preferred microwave heating technique to form stimuli responsive polyurethane/carbon nanotube foams. These thermoresponsive spongy nanomaterials revealed shape fixity and shape recovery ratio of ~95% and 84%, respectively. Kumar et. al. [115] performed pressure sensitivity studies on shape memory polyurethane foams. In this regard, Figure 8A presents schematic of probable volume changes in shape fixity/recovery of shape memory polyurethane foams. Such changes usually occur around glass transition temperature of the polymer and external pressure was applied in this study. Figure 8B shows Tekscan F scan pressure system used to analyze the effect of applied pressure (male heel) on the shape memory polyurethane foams. Characterization and Application of Nanomaterials 2025, 8(3), 11881. 16 Figure 8. (A) Schematic of volume changes in shape fixity and shape recovery processes of shape memory polyurethane at glass transition temperature (Tg) with strain; (B) Tekscan F scan pressure analysis using male heel; (C) areal pressure distribution of shape memory polyurethane foams under varying surface temperatures and applied force [115]. Reproduced with permission from ACS. Consequently, Figure 8C depicts areal pressure distribution under variable surface temperatures for shape memory polyurethane foam (static force). It was observed that increasing temperature up to 20 °C effectively distributed the applied force and had low modulus due to polymer backbone softening. Contrarily, lower temperatures (10-15 °C) did not efficiently distribute the pressure (concentrated red pressure peaks in Figure 8C) due to rigidity of polyurethane foam. It can be suggested that temperature changes along with the applied pressure play important role in shape memory behavior of polyurethane foams. 4.3. In biomedical sector Polyurethanes have been noted as significant macromolecules for biomedical purposes [116]. In this concern, polyurethanes have countless valuable attributes including optimum physiological features, biodegradability, biocompatibility, prolonged in vivo stability, nontoxicity, and so on [117]. Looking at the medical applications of polyurethanes, a myriad of uses has been reported for tissue scaffolds, bioimplants, drug delivery, coatings, wound healing, smart devices, etc. [118‒120]. Polyurethane foams have been designed and tested for in vitro and in vivo conditions for biomedical uses [121]. Consequently, these spongy materials depicted fine biocompatibility and long term biosustainability during desirable applications in living systems [122]. Among earliest attempts on biocompatible polyurethane foams, Guelcher et. al. [123] performed condensation of poly(ε-caprolactone-co- glycolide)triol, lysine methyl ester diisocyanate, and tertiary amine. The resulting polyurethane foams were applied as injectable tissue scaffolds [124]. Later, Schreader et. al. [125] explored polyurethane foams reinforced with hydroxyapatite nanoparticles for biocompatibility and bone tissue engineering. Furthermore, an olden attempt by Zawadza et. al. [126] disclosed the use of electrophoretic deposition to coat polyurethane foam with carbon nanotube nanofiller. The resulting polyurethane/carbon nanotube hybrid foams were tested for bone tissue engineering. In this concern, growth, compatibility, noncytoxicity, and hydroxyapatite growth have been studies for the nanocomposite foams. Besides, Shin et. al. [127] formed polyurethane nanocomposite foams with graphene and graphene oxide and studied for skeletal tissue rejuvenation due to biomimetic effects. These polyurethane/graphene nanocomposite foams had minimum cytotoxicity and optimum porosity (~300 μm), which were suitable skeletal cell growth. Hence, both the polyurethane/carbon nanotube and polyurethane/graphene hybrid sponges have been studied for biocompatibility/non cytotoxicity effects towards biomimetic injectable scaffolds or hydroxyapatite growth for bone or skeletal tissue engineering. Future studies must focus on more design combination, long term in vivo stability, and other biomedical uses like drug delivery, bioimaging, etc. Characterization and Application of Nanomaterials 2025, 8(3), 11881. 17 5. Conclusive remarks and future opportunities In summary, polyurethane, being a multiuse polymer, has been studied for variety of physical and practical probabilities. Among well practiced forms of polyurethanes, spongy materials have been manufactured for strategic features and applications. In the form of foam materials, polyurethanes own specific cell sizes, distribution, and open/close structures, so contributing to valuable characteristics. As compared to pristine polyurethanes, development of nanocomposite foams using valued nanocarbons, graphene and carbon nanotube, revealed notable surface area, cellular nanostructures, nanoparticle dispersion, electron and heat transportation, flexibility retaining integrity, barrier, noncytoxicity, biocompatibility, and other beneficial attributes towards high end uses. According to research efforts to date, application areas discovered for polyurethane nanocomposite foams include electromagnetic radiation shielding, stimuli responsiveness, and medical related uses (Figure 9). In polyurethane/graphene nanocomposite foams, polyurethane/carbon nanotube nanocomposite foams, and all the applied fields, adding nanoparticles type, contents, scattering, and interfacial specifications directly influence the materials properties and applied contours. Moreover, feasibility and effectiveness of processing techniques may affect the implication of ultimate spongy architecture. Figure 9. Prospects of multifunctional polyurethane foams. Looking at the valuable properties of polyurethane nanocomposite foams, we can suggest several future applications of these spongy materials. Especially due to thermal conductivity properties, polyurethane hybrid foams can be used to substitute commercial panels and interiors in aerospace and automotive vehicle structures. Characterization and Application of Nanomaterials 2025, 8(3), 11881. 18 Similarly, such materials can be practiced for advanced construction and civil engineering utilizations. Another side of these nanocarbon filled hybrid sponges not discovered yet seemed to be the smart wearable devices and e-electronics. In addition to radiation absorption, these nanocomposite sponges can be used for encounter sound and acoustic effects in relevant fields. Due to limited research so far on medical sides, comprehensive efforts may reveal application of polyurethane nanocomposite foams in smart drug/gene delivery and smart tissues and artificial muscles. Concisely, further applied breakthroughs of polyurethane hybrid aerogels can be protracted by explorations of key mechanisms for ultimate cellular structure and interfacial relationships. In addition, scalable manufacturing of polyurethane nanocomposite foams by achieving global sustainability and environmental demands seem indispensable for future commercial modules in high tech industries, from energy to medical. Conflict of interest: The authors declare no conflict of interest. References 1. Zarmehr SP, Kazemi M, Madasu NGA, et al. Application of bio-based polyurethanes in construction: A state-of-the-art review. Resources, Conservation and Recycling. 2025; 212: 107906. doi: 10.1016/j.resconrec.2024.107906 2. Van Nguyen T, An Y, Kusano Y, et al. Effect of soft segment chemistry on marine-biodegradation of segmented polyurethane elastomers. Polymer Degradation and Stability. 2025; 233: 111149. doi: 10.1016/j.polymdegradstab.2024.111149 3. Shikha, M. Meena, and J. Jacob, Pentaerythritol derived phosphorous based bicyclic compounds as promising flame retardants for thermoplastic polyurethane films. Journal of Applied Polymer Science, 2020: p. 50375. 4. Kausar A, Ahmad I, Lam TD. High-tech graphene oxide reinforced conducting matrix nanocomposites—Current status and progress. Characterization and Application of Nanomaterials. 2023; 6(1). doi: 10.24294/can.v6i1.2637 5. Nguyen TA, Nguyen TB, Tran DQ, et al. Bio-functional nanocellulose/lignocellulose-based polyurethane nanocomposite foams with enhanced flame retardancy, thermal conductivity, and thermal stability. International Journal of Biological Macromolecules. 2025; 305: 141133. doi: 10.1016/j.ijbiomac.2025.141133 6. Karulf L, Singh B, Singh R, et al. Carbon dioxide utilization: CO2-based polyurethane foam. Journal of CO2 Utilization. 2025; 91: 103000. doi: 10.1016/j.jcou.2024.103000 7. Du Y, Wang M, Ye X, et al. Advances in the Field of Graphene-Based Composites for Energy–Storage Applications. Crystals. 2023; 13(6): 912. doi: 10.3390/cryst13060912 8. Ding H, Zhang X. Sodium Intercalation in Nitrogen-Doped Graphene-Based Anode: A First-Principles Study. Crystals. 2023; 13(7): 1011. doi: 10.3390/cryst13071011 9. Jibin K, Augustine S, Velayudhan P, et al. Unleashing the Power of Graphene-Based Nanomaterials for Chromium(VI) Ion Elimination from Water. Crystals. 2023; 13(7): 1047. doi: 10.3390/cryst13071047 10. Nguyen KTD, Nguyen M, Nguyen TA, et al. A novel multifunctional high bio-content polyurethane nanocomposite and comprehensive comparison with its commercial relevance. Composites Part A: Applied Science and Manufacturing. 2025; 191: 108753. doi: 10.1016/j.compositesa.2025.108753 11. Kuo CC, Lu YQ, Farooqui A, et al. Technical Advancements and Applications in Predictive Modeling of Polyurethane Foaming Height. Published online 2024. doi: 10.2139/ssrn.5032941 12. Vothi H, Le V, Nguyen-Ha T, et al. Sustainable polyurethane nanocomposite foam from waste poly(ethylene terephthalate): preparation, thermal stability, and flame retardancy. Macromolecular Research. 2024; 32(12): 1227-1235. doi: 10.1007/s13233-024-00304-3 13. Dong H, Li S, Jia Z, et al. A Review of Polyurethane Foams for Multi-Functional and High-Performance Applications. Polymers. 2024; 16(22): 3182. doi: 10.3390/polym16223182 14. Hu J, Wu X, Ma T. Gradation design and performance evaluation of self-compacting polyurethane mixture. Construction and Building Materials. 2025; 458: 139528. doi: 10.1016/j.conbuildmat.2024.139528 Characterization and Application of Nanomaterials 2025, 8(3), 11881. 19 15. Heiran R, Ghaderian A, Reghunadhan A, et al. Glycolysis: an efficient route for recycling of end of life polyurethane foams. Journal of Polymer Research. 2021; 28(1). doi: 10.1007/s10965-020-02383-z 16. Lei W, Zhou X, Fang C, et al. Eco-friendly waterborne polyurethane reinforced with cellulose nanocrystal from office waste paper by two different methods. Carbohydrate Polymers. 2019; 209: 299-309. doi: 10.1016/j.carbpol.2019.01.013 17. Kumar Patel K, Purohit R. Improved shape memory and mechanical properties of microwave-induced thermoplastic polyurethane/graphene nanoplatelets composites. Sensors and Actuators A: Physical. 2019; 285: 17-24. doi: 10.1016/j.sna.2018.10.049 18. Zhang J, Lv S, Zhao X, et al. Surface functionalization of polyurethanes: A critical review. Advances in Colloid and Interface Science. 2024; 325: 103100. doi: 10.1016/j.cis.2024.103100 19. Białkowska A, Kucharczyk W, Zarzyka I, et al. Polylactide-Based Nonisocyanate Polyurethanes: Preparation, Properties Evaluation and Structure Analysis. Polymers. 2024; 16(2): 253. doi: 10.3390/polym16020253 20. De Hoyos-Martinez PL, Mendez SB, Martinez EC, et al. Elaboration of Thermally Performing Polyurethane Foams, Based on Biopolyols, with Thermal Insulating Applications. Polymers. 2024; 16(2): 258. doi: 10.3390/polym16020258 21. Reignier J, Alcouffe P, Méchin F, et al. The morphology of rigid polyurethane foam matrix and its evolution with time during foaming – New insight by cryogenic scanning electron microscopy. Journal of Colloid and Interface Science. 2019; 552: 153-165. doi: 10.1016/j.jcis.2019.05.032 22. Kurańska M, Polaczek K, Auguścik-Królikowska M, et al. Open-cell rigid polyurethane bio-foams based on modified used cooking oil. Polymer. 2020; 190: 122164. doi: 10.1016/j.polymer.2020.122164 23. Fu Y, Qiu C, Ni L, et al. Cell structure control and performance of rigid polyurethane foam with lightweight, good mechanical, thermal insulation and sound insulation. Construction and Building Materials. 2024; 447: 138068. doi: 10.1016/j.conbuildmat.2024.138068 24. Ates M, Karadag S, Eker AA, et al. Polyurethane foam materials and their industrial applications. Polymer International. 2022; 71(10): 1157-1163. doi: 10.1002/pi.6441 25. Sukhawipat N, Saengdee L, Pasetto P, et al. Sustainable Rigid Polyurethane Foam from Wasted Palm Oil and Water Hyacinth Fiber Composite—A Green Sound-Absorbing Material. Polymers. 2022; 14(1): 201. doi: 10.3390/polym14010201 26. Li C, Ye H, Ge S, et al. Fabrication and properties of antimicrobial flexible nanocomposite polyurethane foams with in situ generated copper nanoparticles. Journal of Materials Research and Technology. 2022; 19: 3603-3615. doi: 10.1016/j.jmrt.2022.06.115 27. Saint-Michel F, Chazeau L, Cavaillé JY, et al. Mechanical properties of high density polyurethane foams: I. Effect of the density. Composites Science and Technology. 2006; 66(15): 2700-2708. doi: 10.1016/j.compscitech.2006.03.009 28. Makarov M, Bourguignon M, Grignard B, et al. Advancing Non-isocyanate Polyurethane Foams: exo-Vinylene Cyclic Carbonate–Amine Chemistry Enabling Room-Temperature Reactivity and Fast Self-Blowing. Macromolecules. 2025; 58(3): 1673-1685. doi: 10.1021/acs.macromol.4c02894 29. Soundhar A, Rajesh M, Jayakrishna K, et al. Investigation on mechanical properties of polyurethane hybrid nanocomposite foams reinforced with roselle fibers and silica nanoparticles. Nanocomposites. 2019; 5(1): 1-12. doi: 10.1080/20550324.2018.1562614 30. Alasti Bonab S, Moghaddas J, Rezaei M. In-situ synthesis of silica aerogel/polyurethane inorganic-organic hybrid nanocomposite foams: Characterization, cell microstructure and mechanical properties. Polymer. 2019; 172: 27-40. doi: 10.1016/j.polymer.2019.03.050 31. Olszewski A, Kosmela P, Piasecki A, et al. Comprehensive Investigation of Stoichiometry–Structure–Performance Relationships in Flexible Polyurethane Foams. Polymers. 2022; 14(18): 3813. doi: 10.3390/polym14183813 32. Jin FL, Zhao M, Park M, et al. Recent Trends of Foaming in Polymer Processing: A Review. Polymers. 2019; 11(6): 953. doi: 10.3390/polym11060953 33. Abd El-Fattah M, Hasan AMA, Keshawy M, et al. Nanocrystalline cellulose as an eco-friendly reinforcing additive to polyurethane coating for augmented anticorrosive behavior. Carbohydrate Polymers. 2018; 183: 311-318. doi: 10.1016/j.carbpol.2017.12.084 34. Song S, Xing Y, Wu D, et al. Effect of molecular weight of aliphatic dicarboxylic acids polyester on properties of the waterborne polyurethane sizing agent. Carbon Letters. 2025; 35(3): 1017-1026. doi: 10.1007/s42823-024-00850-x 35. Patti A, Acierno D. Structure‐property relationships of waterborne polyurethane ( WPU ) in aqueous formulations. Journal of Vinyl and Additive Technology. 2023; 29(4): 589-606. doi: 10.1002/vnl.21981 Characterization and Application of Nanomaterials 2025, 8(3), 11881. 20 36. Mekonnen TH, Haile T, Ly M. Hydrophobic functionalization of cellulose nanocrystals for enhanced corrosion resistance of polyurethane nanocomposite coatings. Applied Surface Science. 2021; 540: 148299. doi: 10.1016/j.apsusc.2020.148299 37. Kim MS, Ryu KM, Lee SH, et al. Chitin Nanofiber-Reinforced Waterborne Polyurethane Nanocomposite Films with Enhanced Thermal and Mechanical Performance. Carbohydrate Polymers. 2021; 258: 117728. doi: 10.1016/j.carbpol.2021.117728 38. Sun, J., et al., Asymmetric‐Structured Waterborne Polyurethane Foams for Enhanced Electromagnetic Wave Absorption Performance. Advanced Engineering Materials: p. 2501259. 39. Cao J, Xie X, Liu Y, et al. Advanced waterborne polyurethane/poly(ionic liquids) foam for highly efficient and selective adsorption of 99TcO4-/ReO4-. Chemical Engineering Journal. 2025; 508: 161007. doi: 10.1016/j.cej.2025.161007 40. Tian X, He M, Ding C, et al. Multifunctional waterborne polyurethane microfiber leather with breathable, moisture-wicking, antibacterial, weather-resistant, and high-strength. Progress in Organic Coatings. 2025; 200: 109021. doi: 10.1016/j.porgcoat.2024.109021 41. Wei XX, Pei C, Zhu JH. Towards the large-scale application of graphene-modified cement-based composites: A comprehensive review. Construction and Building Materials. 2024; 421: 135632. doi: 10.1016/j.conbuildmat.2024.135632 42. Geim AK, Novoselov KS. The rise of graphene. Nature Materials. 2007; 6(3): 183-191. doi: 10.1038/nmat1849 43. Lu Z, Han T, Yao Y, et al. Fractional quantum anomalous Hall effect in multilayer graphene. Nature. 2024; 626(8000): 759- 764. doi: 10.1038/s41586-023-07010-7 44. Mbayachi VB, Ndayiragije E, Sammani T, et al. Graphene synthesis, characterization and its applications: A review. Results in Chemistry. 2021; 3: 100163. doi: 10.1016/j.rechem.2021.100163 45. Santra S, Bose A, Mitra K, et al. Exploring two decades of graphene: The jack of all trades. Applied Materials Today. 2024; 36: 102066. doi: 10.1016/j.apmt.2024.102066 46. Lv H, Yao Y, Yuan M, et al. Functional nanoporous graphene superlattice. Nature Communications. 2024; 15(1). doi: 10.1038/s41467-024-45503-9 47. Kong M, Yang M, Li R, et al. Graphene-based flexible wearable sensors: mechanisms, challenges, and future directions. The International Journal of Advanced Manufacturing Technology. 2023; 131(5-6): 3205-3237. doi: 10.1007/s00170-023-12007- 7 48. Zhang H, Zhang G, Tang M, et al. Synergistic effect of carbon nanotube and graphene nanoplates on the mechanical, electrical and electromagnetic interference shielding properties of polymer composites and polymer composite foams. Chemical Engineering Journal. 2018; 353: 381-393. doi: 10.1016/j.cej.2018.07.144 49. Ramasamy RP, Somanathan S, Rafailovich MH, et al. Broadband dielectric spectroscopy and small-angle neutron scattering investigations of polyurethane–graphene foams. Journal of Materials Science: Materials in Electronics. 2020; 31(18): 15843- 15851. doi: 10.1007/s10854-020-04146-4 50. Saganuwan SA. Biomedical Applications of Polyurethane Hydrogels, Polyurethane Aerogels, and Polyurethane-graphene Nanocomposite Materials. Central Nervous System Agents in Medicinal Chemistry. 2022; 22(2): 79-87. doi: 10.2174/1871524922666220429115124 51. Feng C, Yi Z, Jin X, et al. Solvent crystallization-induced porous polyurethane/graphene composite foams for pressure sensing. Composites Part B: Engineering. 2020; 194: 108065. doi: 10.1016/j.compositesb.2020.108065 52. Zhang H, Wang H, Wang T, et al. Polyurethane Foam with High-Efficiency Flame Retardant, Heat Insulation, and Sound Absorption Modified By Phosphorus-Containing Graphene Oxide. ACS Applied Polymer Materials. 2024; 6(3): 1878-1890. doi: 10.1021/acsapm.3c02706 53. Hodlur RM, Rabinal MK. Self assembled graphene layers on polyurethane foam as a highly pressure sensitive conducting composite. Composites Science and Technology. 2014; 90: 160-165. doi: 10.1016/j.compscitech.2013.11.005 54. Chen Y, Li Y, Xu D, et al. Fabrication of stretchable, flexible conductive thermoplastic polyurethane/graphene composites via foaming. RSC Advances. 2015; 5(100): 82034-82041. doi: 10.1039/c5ra12515d 55. Kim JM, Kim DH, Kim J, et al. Effect of graphene on the sound damping properties of flexible polyurethane foams. Macromolecular Research. 2017; 25(2): 190-196. doi: 10.1007/s13233-017-5017-9 56. Patole SP, Reddy SK, Schiffer A, et al. Piezoresistive and Mechanical Characteristics of Graphene Foam Nanocomposites. ACS Applied Nano Materials. 2019; 2(3): 1402-1411. doi: 10.1021/acsanm.8b02306 57. Zhong W, Ding X, Li W, et al. Facile Fabrication of Conductive Graphene/Polyurethane Foam Composite and Its Application on Flexible Piezo-Resistive Sensors. Polymers. 2019; 11(8): 1289. doi: 10.3390/polym11081289 Characterization and Application of Nanomaterials 2025, 8(3), 11881. 21 58. Qin LC, Zhao X, Hirahara K, et al. The smallest carbon nanotube. Nature. 2000; 408(6808): 50-50. doi: 10.1038/35040699 59. Baughman RH, Cui C, Zakhidov AA, et al. Carbon Nanotube Actuators. Science. 1999; 284(5418): 1340-1344. doi: 10.1126/science.284.5418.1340 60. Guo H li, Zhang Q xian, Liu Y ping, et al. Properties and Defence Applications of Carbon Nanotubes. Journal of Physics: Conference Series. 2023; 2478(4): 042010. doi: 10.1088/1742-6596/2478/4/042010 61. Syduzzaman M, Islam Saad MS, Piam MF, et al. Carbon nanotubes: Structure, properties and applications in the aerospace industry. Results in Materials. 2025; 25: 100654. doi: 10.1016/j.rinma.2024.100654 62. Mishra S, Kumari S, Mishra AC, et al. Carbon Nanotube – Synthesis, Purification and Biomedical Applications. Current Nanomaterials. 2023; 8(4): 328-335. doi: 10.2174/2405461507666220827092425 63. Yahyazadeh A, Nanda S, Dalai AK. Carbon Nanotubes: A Review of Synthesis Methods and Applications. Reactions. 2024; 5(3): 429-451. doi: 10.3390/reactions5030022 64. Tyagi S, Negi S. Calculation of Density of States of Pristine and Functionalized Carbon Nanotubes: A DFT Approach. Indian Journal Of Science And Technology. 2023; 16(40): 3567-3574. doi: 10.17485/ijst/v16i40.1019 65. Darıcık F, Topcu A, Aydın K, et al. Carbon nanotube (CNT) modified carbon fiber/epoxy composite plates for the PEM fuel cell bipolar plate application. International Journal of Hydrogen Energy. 2023; 48(3): 1090-1106. doi: 10.1016/j.ijhydene.2022.09.297 66. Mishra S, Sundaram B. Efficacy and challenges of carbon nanotube in wastewater and water treatment. Environmental Nanotechnology, Monitoring & Management. 2023; 19: 100764. doi: 10.1016/j.enmm.2022.100764 67. Xavier JR, Sadagopan Pandian V. RETRACTED: Carbon nanotube‐based polymer nanocomposites: Evaluation of barrier, hydrophobic, and mechanical properties for aerospace applications. Polymer Engineering & Science. 2023; 63(9): 2806- 2827. doi: 10.1002/pen.26407 68. Si J, Zhang P, Zhang Z. Road map for, and technical challenges of, carbon-nanotube integrated circuit technology. National Science Review. 2023; 11(3). doi: 10.1093/nsr/nwad261 69. Sulthana YR, Gurusamy Thangavelu SA. Development of nonisocyanate polyurethane–MWCNT nanocomposites: coatings with enhanced antifouling, corrosion resistance and UV protection properties. New Journal of Chemistry. 2025; 49(2): 404- 417. doi: 10.1039/d4nj04917a 70. Pathak R, Punetha VD, Bhatt S, et al. A review on carbon nanofiller-based hyperbranched polyurethane nanocomposites: synthesis strategies, applications and challenges. Journal of Materials Science. 2024; 59(34): 16069-16111. doi: 10.1007/s10853-024-10158-w 71. Iqbal N, Mubashar A, Ahmad S, et al. Improving mechanical properties and ballistic limit of polyurethane foam cores in sandwich panels through multi-walled carbon nanotube reinforcement. Journal of Sandwich Structures & Materials. 2025; 27(6): 1220-1239. doi: 10.1177/10996362251336644 72. Hasani Baferani A, Ohadi A, Katbab AA. Toward mechanistic understanding the effect of aspect ratio of carbon nanotubes upon different properties of polyurethane/carbon nanotube nanocomposite foam. Polymer Engineering & Science. 2021; 61(12): 3037-3049. doi: 10.1002/pen.25816 73. You KM, Park SS, Lee CS, et al. Preparation and characterization of conductive carbon nanotube-polyurethane foam composites. Journal of Materials Science. 2011; 46(21): 6850-6855. doi: 10.1007/s10853-011-5645-y 74. Zhai T, Li D, Fei G, et al. Piezoresistive and compression resistance relaxation behavior of water blown carbon nanotube/polyurethane composite foam. Composites Part A: Applied Science and Manufacturing. 2015; 72: 108-114. doi: 10.1016/j.compositesa.2015.02.003 75. Espadas-Escalante J, Avilés F, Gonzalez-Chi P, et al. Thermal conductivity and flammability of multiwall carbon nanotube/polyurethane foam composites. Journal of Cellular Plastics. 2016; 53(2): 215-230. doi: 10.1177/0021955x16644893 76. Huang W, Dai K, Zhai Y, et al. Flexible and Lightweight Pressure Sensor Based on Carbon Nanotube/Thermoplastic Polyurethane-Aligned Conductive Foam with Superior Compressibility and Stability. ACS Applied Materials & Interfaces. 2017; 9(48): 42266-42277. doi: 10.1021/acsami.7b16975 77. Guo H, Thirunavukkarasu N, Mubarak S, et al. Preparation of Thermoplastic Polyurethane/Multi-Walled Carbon Nanotubes Composite Foam with High Resilience Performance via Fused Filament Fabrication and CO2 Foaming Technique. Polymers. 2023; 15(6): 1535. doi: 10.3390/polym15061535 78. Ramya, K., et al., A Complete Review of Electromagnetic Interference in Electric Vehicle. IEEE Access, 2025. Characterization and Application of Nanomaterials 2025, 8(3), 11881. 22 79. Wang C, Lin X, Xu J, et al. Multifunctional bamboo-derived porous carbon for efficient electrical-thermal energy management and electromagnetic interference shielding. Carbon. 2025; 233: 119872. doi: 10.1016/j.carbon.2024.119872 80. Tang X, Lu Y, Li S, et al. Hierarchical Polyimide Nonwoven Fabric with Ultralow-Reflectivity Electromagnetic Interference Shielding and High-Temperature Resistant Infrared Stealth Performance. Nano-Micro Letters. 2024; 17(1). doi: 10.1007/s40820-024-01590-3 81. Manogaran R, Murugesan M. A review on recent advancements in textile fabrics for electromagnetic interference (EMI) shielding materials. Materials Today Communications. 2025; 44: 111879. doi: 10.1016/j.mtcomm.2025.111879 82. Kumar DA, Murugesan M. Interfacial tailoring of conducting polymer nanocomposite films for high-efficiency X-band EMI shielding. Results in Engineering. 2025; 27: 106639. doi: 10.1016/j.rineng.2025.106639 83. Kamedulski P, Truszkowski S, Lukaszewicz JP. Highly Effective Methods of Obtaining N-Doped Graphene by Gamma Irradiation. Materials. 2020; 13(21): 4975. doi: 10.3390/ma13214975 84. Kumar R, Sahoo S, Joanni E, et al. Heteroatom doping of 2D graphene materials for electromagnetic interference shielding: a review of recent progress. Critical Reviews in Solid State and Materials Sciences. 2021; 47(4): 570-619. doi: 10.1080/10408436.2021.1965954 85. Ghosh S, Ganguly S, Remanan S, et al. Ultra-light weight, water durable and flexible highly electrical conductive polyurethane foam for superior electromagnetic interference shielding materials. Journal of Materials Science: Materials in Electronics. 2018; 29(12): 10177-10189. doi: 10.1007/s10854-018-9068-2 86. Yang J, Liao X, Wang G, et al. Gradient structure design of lightweight and flexible silicone rubber nanocomposite foam for efficient electromagnetic interference shielding. Chemical Engineering Journal. 2020; 390: 124589. doi: 10.1016/j.cej.2020.124589 87. Sultana, S., et al., Recent advances in synthesis and processing of nanomaterial-based polymeric foams for EMI shielding applications. Journal of Materials Science, 2025: p. 1-40. 88. Kaur, R., S.K. Verma, and R. Mehta, Tailoring the Properties of Polyurethane Composites: A Comprehensive Review. Polymer-Plastics Technology and Materials, 2025: p. 1-15. 89. Li H, Yuan D, Li P, et al. High conductive and mechanical robust carbon nanotubes/waterborne polyurethane composite films for efficient electromagnetic interference shielding. Composites Part A: Applied Science and Manufacturing. 2019; 121: 411-417. doi: 10.1016/j.compositesa.2019.04.003 90. Jiang Q, Liao X, Li J, et al. Flexible thermoplastic polyurethane/reduced graphene oxide composite foams for electromagnetic interference shielding with high absorption characteristic. Composites Part A: Applied Science and Manufacturing. 2019; 123: 310-319. doi: 10.1016/j.compositesa.2019.05.017 91. Gavgani JN, Adelnia H, Zaarei D, et al. Lightweight flexible polyurethane/reduced ultralarge graphene oxide composite foams for electromagnetic interference shielding. RSC Advances. 2016; 6(33): 27517-27527. doi: 10.1039/c5ra25374h 92. Oraby H, Tantawy HR, Correa-Duarte MA, et al. Tuning Electro-Magnetic Interference Shielding Efficiency of Customized Polyurethane Composite Foams Taking Advantage of rGO/Fe3O4 Hybrid Nanocomposites. Nanomaterials. 2022; 12(16): 2805. doi: 10.3390/nano12162805 93. Soykan U, Kalkan Y, Kaya S, et al. Remarkable improvement in radiation shielding efficiency, thermal insulation performance and compressive strength of rigid polyurethane foam composites by synergetic effect of PbO and colemanite fillers. Radiation Physics and Chemistry. 2025; 227: 112401. doi: 10.1016/j.radphyschem.2024.112401 94. Soykan U, Akdogan E, Uzun Duran S, et al. A Green and Sustainable Solution for Neutron Shielding: Preparation and Evaluation of Biodegradable Boron‐Incorporated Rigid Polyurethane Foam Composites With Enhanced Radiation Attenuation and Physicomechanical Features. Polymer Engineering & Science. 2025; 65(11): 6275-6290. doi: 10.1002/pen.70131 95. Li Y, Shen B, Yi D, et al. The influence of gradient and sandwich configurations on the electromagnetic interference shielding performance of multilayered thermoplastic polyurethane/graphene composite foams. Composites Science and Technology. 2017; 138: 209-216. doi: 10.1016/j.compscitech.2016.12.002 96. Fan D, Li N, Li M, et al. Polyurethane/polydopamine/graphene auxetic composite foam with high-efficient and tunable electromagnetic interference shielding performance. Chemical Engineering Journal. 2022; 427: 131635. doi: 10.1016/j.cej.2021.131635 97. Pastore Carbone MG, Beaugendre M, Koral C, et al. Thermoplastic polyurethane–graphene nanoplatelets microcellular foams for electromagnetic interference shielding. Graphene Technology. 2020; 5(3-4): 33-39. doi: 10.1007/s41127-020-00034-0 Characterization and Application of Nanomaterials 2025, 8(3), 11881. 23 98. Kiddell S, Kazemi Y, Sorken J, et al. Influence of Flash Graphene on the acoustic, thermal, and mechanical performance of flexible polyurethane foam. Polymer Testing. 2023; 119: 107919. doi: 10.1016/j.polymertesting.2022.107919 99. Kouka MA, Abbassi F, Habibi M, et al. 4D Printing of Shape Memory Polymers, Blends, and Composites and Their Advanced Applications: A Comprehensive Literature Review. Advanced Engineering Materials. 2022; 25(4). doi: 10.1002/adem.202200650 100. Yadav A, Singh SK, Das S, et al. Shape memory polymer and composites for space applications: A review. Polymer Composites. 2025; 46(13): 11647-11683. doi: 10.1002/pc.29707 101. Zhao J, Zhu J, Zhang J, et al. Review of research on thermoplastic self-healing polyurethanes. Reactive and Functional Polymers. 2024; 199: 105886. doi: 10.1016/j.reactfunctpolym.2024.105886 102. Alipour S, Pourjavadi A, Hosseini SH. Magnetite embedded κ-carrageenan-based double network nanocomposite hydrogel with two-way shape memory properties for flexible electronics and magnetic actuators. Carbohydrate Polymers. 2023; 310: 120610. doi: 10.1016/j.carbpol.2023.120610 103. Behera PK, Dhamaniya S, Mohanty S, et al. Advances in thermoplastic polyurethane elastomers. Advances in Thermoplastic Elastomers. Published online 2024: 407-444. doi: 10.1016/b978-0-323-91758-2.00014-3 104. Backes, E.H., et al., Thermoplastic polyurethanes: synthesis, fabrication techniques, blends, composites, and applications. Journal of Materials Science, 2024: p. 1-30. 105. Ma, Q., et al., Nanocomposite‐enhanced polymeric weak gel for conformance control in high‐salinity and high‐temperature reservoir condition. Polymer Engineering & Science, 2025. 106. Zhang H, Zhang G, Li J, et al. Lightweight, multifunctional microcellular PMMA/Fe 3 O 4 @MWCNTs nanocomposite foams with efficient electromagnetic interference shielding. Composites Part A: Applied Science and Manufacturing. 2017; 100: 128-138. doi: 10.1016/j.compositesa.2017.05.009 107. Peng S, Geng Y, Li Z, et al. Investigating the effects of temperature on thermal and mechanical properties of polyurethane/polycaprolactone/graphene oxide nanocomposites: focusing on creating a smart polymer nanocomposite via molecular dynamics method. Molecular Physics. 2024; 123(1). doi: 10.1080/00268976.2024.2351164 108. Zarghami Dehaghani M, Kaffashi B, Haponiuk JT, et al. Shape memory thin films of Polyurethane: Does graphene content affect the recovery behavior of Polyurethane nanocomposites? Polymer Composites. 2020; 41(8): 3376-3388. doi: 10.1002/pc.25627 109. Wu G, Gu Y, Hou X, et al. Hybrid Nanocomposites of Cellulose/Carbon-Nanotubes/Polyurethane with Rapidly Water Sensitive Shape Memory Effect and Strain Sensing Performance. Polymers. 2019; 11(10): 1586. doi: 10.3390/polym11101586 110. Joseph TM, Thomas MG, Mahapatra DK, et al. Adaptive and intelligent polyurethane shape-memory polymers enabling next-generation biomedical platforms. Case Studies in Chemical and Environmental Engineering. 2025; 11: 101165. doi: 10.1016/j.cscee.2025.101165 111. Poser A, Pretsch T. FOIM: Thermal Foaming of Shape Memory Polyurethane Foil. Macromolecular Rapid Communications. 2025; 46(8). doi: 10.1002/marc.202401103 112. Singhal P, Rodriguez JN, Small W, et al. Ultra low density and highly crosslinked biocompatible shape memory polyurethane foams. Journal of Polymer Science Part B: Polymer Physics. 2012; 50(10): 724-737. doi: 10.1002/polb.23056 113. Kang SM, Kwon SH, Park JH, et al. Carbon nanotube reinforced shape memory polyurethane foam. Polymer Bulletin. 2013; 70(3): 885-893. doi: 10.1007/s00289-013-0905-4 114. Kim HM, Park J, Huang ZM, et al. Carbon Nanotubes Embedded Shape Memory Polyurethane Foams. Macromolecular Research. 2019; 27(9): 919-925. doi: 10.1007/s13233-019-7129-x 115. Kumar B, Noor N, Thakur S, et al. Shape Memory Polyurethane-Based Smart Polymer Substrates for Physiologically Responsive, Dynamic Pressure (Re)Distribution. ACS Omega. 2019; 4(13): 15348-15358. doi: 10.1021/acsomega.9b01167 116. Song W, Muhammad S, Dang S, et al. The state-of-art polyurethane nanoparticles for drug delivery applications. Frontiers in Chemistry. 2024; 12. doi: 10.3389/fchem.2024.1378324 117. Dang G peng, Gu J ting, Song J han, et al. Multifunctional polyurethane materials in regenerative medicine and tissue engineering. Cell Reports Physical Science. 2024; 5(7): 102053. doi: 10.1016/j.xcrp.2024.102053 118. Barrioni BR, de Carvalho SM, Oréfice RL, et al. Synthesis and characterization of biodegradable polyurethane films based on HDI with hydrolyzable crosslinked bonds and a homogeneous structure for biomedical applications. Materials Science and Engineering: C. 2015; 52: 22-30. doi: 10.1016/j.msec.2015.03.027 Characterization and Application of Nanomaterials 2025, 8(3), 11881. 24 119. Batool JA, Rehman K, Qader A, et al. Biomedical Applications of Carbohydrate-based Polyurethane: From Biosynthesis to Degradation. Current Pharmaceutical Design. 2022; 28(20): 1669-1687. doi: 10.2174/1573412918666220118113546 120. Singh, J., S. Singh, and R. Gill, Applications of biopolymer coatings in biomedical engineering. Journal of Electrochemical Science and Engineering, 2023. 13(1): p. 63-81. 121. Zhou X, Wei X, Peng Y, et al. Progress on the Structure and Application of Porous Polyurethane Materials. Macromolecular Rapid Communications. 2025; 46(19). doi: 10.1002/marc.202500294 122. Caba V, Borgese L, Agnelli S, et al. A green and simple process to develop conductive polyurethane foams for biomedical applications. International Journal of Polymeric Materials and Polymeric Biomaterials. 2018; 68(1-3): 126-133. doi: 10.1080/00914037.2018.1525732 123. Guelcher SA, Patel V, Gallagher KM, et al. Synthesis and In Vitro Biocompatibility of Injectable Polyurethane Foam Scaffolds. Tissue Engineering. 2006; 12(5): 1247-1259. doi: 10.1089/ten.2006.12.1247 124. Yuan Y, Guo Q, Xu L, et al. Rigid Polyurethane Foam Derived from Renewable Sources: Research Progress, Property Enhancement, and Future Prospects. Molecules. 2025; 30(3): 678. doi: 10.3390/molecules30030678 125. Schreader KJ, Bayer IS, Milner DJ, et al. A polyurethane‐based nanocomposite biocompatible bone adhesive. Journal of Applied Polymer Science. 2012; 127(6): 4974-4982. doi: 10.1002/app.38100 126. Zawadzak E, Bil M, Ryszkowska J, et al. Polyurethane foams electrophoretically coated with carbon nanotubes for tissue engineering scaffolds. Biomedical Materials. 2008; 4(1): 015008. doi: 10.1088/1748-6041/4/1/015008 127. Shin YC, Kang SH, Lee JH, et al. Three-dimensional graphene oxide-coated polyurethane foams beneficial to myogenesis. Journal of Biomaterials Science, Polymer Edition. 2017; 29(7-9): 762-774. doi: 10.1080/09205063.2017.1348738