Enhancement of mechanical and thermal properties of poly methyl methacrylate composite bone cements with zinc oxide nanostructures modified carbon fibres additives

Abstract Acrylic bone cement, which primarily consists of polymethyl methacrylate (PMMA), is widely used in orthopaedics, dentistry, and particularly in joint arthroplasty surgery. However, bone cements (BCs) have several limitations, including low mechanical properties, bioactivity issues, and high heat generation during polymerization. In recent years, there has been significant interest in studying the development of mechanical, thermal, and antibacterial properties of bone cement. In this study, ZnO nanostructures modified CFs were added to PMMA BCs at concentrations ranging from 0.10 wt% to 1.00 wt%, and the mechanical and thermal properties of the novel PMMA composite BCs were investigated. The novel composite materials were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR). Mechanical tests including compression and 4-point bending were performed on the composite structures, along with thermogravimetric analysis (TGA). The results revealed that the composite cement containing 0.25 wt% ZnO/CFs reinforcement agent exhibited the best mechanical properties and thermal stability. The flexural strength of the 0.25 wt% ZnO/CFs reinforced PMMA composite BCs increased by 78.9%, while the compression strength increased by 277.4% compared to the control group.


Introduction
Acrylic BCs are mostly composed of PMMA which is a transparent thermoplastic polymer with moderate mechanical and physical properties.PMMA is non-toxic and ceramic compatible so it has been used in orthopaedic surgery for more than forty years, and primarily used as joint sealant in joint replacement operations to transfer the load between the prosthetic implant or/and bone [1,2].In recent years, polymerbased nanocomposites have attracted great interest in many applications such as electronics, optical sensors, environment, energy, biology and medicine [3].Acrylic BCs offer many advantages in terms of ease of preparation and application, rapid polymerization reaction and rapid patient recovery.However, PMMA BCs have several drawbacks, such as poor binding ability, relatively low mechanical strength, and high heat generation during polymerization [4].It's important to note that the thermal properties of PMMA BCs can vary depending on the specific formulation, additives, and manufacturing processes used by different manufacturers.There are various fillers with interesting properties that are currently under investigation for the improvement of mechanical weakness and thermal properties of BCs [5].BCs are often supplemented with certain amount of the reinforcement agents such as graphene oxide [3], reduced graphene oxide [6], glass fiber [7], mineralized collagen [8], multiwalled carbon nanotube (MWCNT) [9,10], calcium carbonate nanoparticles [11], silica nanoparticles [12], hydroxyapatite (HA) [13], carbon fiber (CFs) [14], etc. CFs have been widely used in studies aiming to enhance the mechanical and thermal properties of composite materials, and they offer several advantages compared to other nanomaterials.CFs possess exceptional mechanical properties, making them highly effective as reinforcement agents.Moreover, they are commercially available at a relatively low cost, facilitating their widespread use.Their surface can be easily functionalized, allowing for tailored properties and improved compatibility with the matrix material.Additionally, CFs are suitable for mass production, which is beneficial for large-scale applications.These specific advantages have led to the frequent utilization of CFs as reinforcement agents in the development of high-performance composite materials.The literature contains numerous reports on the use of CFs to enhance the mechanical properties of composite materials [15,16].Zhao et al. reported that the interfacial bond strength between CFs and BCs could be increased, and this improves the mechanical properties of CFs reinforced BCs composite [17].In another study, 1.33% CFs by weight were added to PMMA BCs.According to the result of the study, CFs increased the tensile strength and moduli by 30% and 35.8%, respectively.The compression strength and moduli, however, increased by only 10.7%.Similarly, bending and shear strengths improved by 29.5% and 18.5%, respectively [14].Boehm et al. presented that chemically activated CFs altered the mechanical properties of apatite bone cement in terms of bending strength and work of fracture to a strain of 5.0 wt%.Furthermore, the study demonstrated that the proliferation and activity of osteoblast-like cells were not affected by the addition of fibres or the treatment of fibres [18].Although there have been numerous studies on biocomposites reinforced with CFs, a common challenge is the relatively low strength of the fibres when attempting to fully utilize the excellent physical performance of CFsreinforced polymer composites.The inadequate adhesion at the fiber-matrix interface can negatively affect the physical and mechanical properties of the composites, primarily due to the surface incompatibility between hydrophilic inorganic fillers and non-polar resin [15].Since CFs surfaces are hydrophobic, they do not interface with ceramics, and they disperse poorly in hydrophilic resins.Interfacial properties are being investigated and developed to form, and produce substantial composites [19].
Surface modification, and coating approaches for CFs have been the focus of recent studies in this field.CFs are functionalized with a wide range of materials to form multi-functional CFs-based composites.Surface functionalization of the CFs can be divided into two main categories; i) surface oxidation, and ii) coating.Functionalization of CFs by surface oxidation is carried out using methods such as plasma treatment, UV light treatment and chemical oxidation, while surface functionalization is carried out using processes such as chemical vapor deposition (CVD), hydrothermal treatment, reactive coating, and galvanic coating.The growth of nanostructured materials on the CFs surfaces, a process commonly known as 'whiskerization' [20].Many researchers have recently focused on enhancing experimental conditions for the whiskerization of CFs surface with metal oxide nanostructures [19,21,22].Xu et al. studied the growth of copper oxide (CuO) nanostructures on CFs surfaces, and presented the superior properties of CuO-functionalized CFs as a super capacitor electrode for electrochemical energy storage [23].In another study, CFs were coated with silver (Ag), and it was emphasized that superior electrical properties were obtained [24].A study carried out by Wu at al. presented the deposition of manganese oxide on CFs surfaces for electrochemical capacitor application [20].Recently, CFs surface modification studies with zinc oxide (ZnO) nanostructures have become widespread.The biocompatibility of ZnO nanostructures, having antimicrobial properties and low-toxicity, allows them to be used in biomedical fields [25].ZnO nanostructures are more prominent than other metal oxides such as relatively high specific surface area, chemical stability [26], electrochemical activity [27], facile synthesis [28].Many different methods such as hydrothermal synthesis, solgel method, electrochemical deposition (ED), electrochemical anodization, atomic layer deposition (ALD), and chemical method have been developed to manufacture highly pure, and desired crystalline ZnO nanostructures on CFs surfaces [29,30].ZnO nanostructures modified CFs (ZnO/CFs) have received great attention due to their wide application area because of their superior properties, such as improved mechanical properties, anti-bacterial features, enhanced interface strength, thermal stability [21].ZnO nanostructures modified CFs applied in many fields such as; ZnO/CFs nanocomposites have been employed in biosensors [31], bio-imaging applications [32], CFs reinforced polymer composite [33], flexible antibacterial material [34], stress-sensor device [35], etc.The number of studies focusing on the effects of CFs and their derivatives on the mechanical behaviour of acrylic BCs is currently limited but being widely investigated.While there have been extensive studies on the raw materials and components of various BCs, there remains a need for further research to enhance their mechanical and thermal properties and reduce their side effects [36].Accordingly, the present study aims to synthesize and characterize the PMMA composite BCs that are reinforced with CFs, Zn/CFs and ZnO/CFs.The study also aims to optimize the wt% amount of the reinforcement material and systematically evaluate the mechanical and thermal properties of the novel PMMA-based composite BCs.It is worth nothing that, to the best of our knowledge, this study represents the first investigation utilizing ZnO/CFs as reinforcement materials for the production of the novel PMMA composite BCs.In this context, bare CF, Zn/CFs, and ZnO/CFs nanostructures were added to PMMA BCs at ratios ranging from 0.10 to 1.00 wt%, and the effects of the reinforcement agent both in mechanical and thermal characteristics were investigated.The results demonstrated that PMMA composite BCs that reinforced with 0.25 wt% of the ZnO/CFs improved the mechanical properties, and thermal stabilities.The findings of this research have the potential to advance the development of composite BCs with enhanced mechanical and thermal properties, leading to improved clinical outcomes and reduced side effects.

Growth of zinc oxide nanostructures on carbon fibres surface
ZnO-coated CFs were manufactured following the procedure previously disclosed by our group [34].Briefly, two sequential reactions were carried out to form ZnO nanostructures on CFs surfaces; electroplating and electrochemical anodization, respectively.Commercially purchased CFs were cut to 6 cm in length for each electroplating and electrochemical anodization experiment.CFs were subjected to ultrasonic cleaning with isopropanol (C 3 H 8 O), water (H 2 O) and ethanol (C 2 H 5 OH), and dried at 50 C in air.Electrodeposition of Zn on CFs was carried out in the commercial zinc bath (pH: 5.5-6.0) at room temperature (25 C).The CFs and Zn electrodes were immersed in the zinc bath and placed in an ultrasonic bath in a beaker with the help of the electrode holder (self-design).The power supply was set to the voltage of 0.9 V for 10 min, for electroplating where Zn plates and CF were used as the anode and cathode, respectively.Similarly, electrochemical anodization was carried out at 25 C, in a 0.05 M solution of KHCO 3 , DC power source was set to 20 V for a duration of 30 min during the anodization process.

Preparation of the composite bone cement
PMMA BCs consists of powder and liquid phase that the components are presented in Supplementary Table 1.The sterile and commercial bone cement box contains 40 grams of powder and 20 ml of liquid parts.Powder part includes 35.04 grams of PMMA (87.6%), 0.96 gram BPO (2.4%), and 4 grams of BaSO 4 (10%).The liquid part includes 19.76 millilitres of MMA (98.8%), 0.24 millilitres DmpT (1.2%) and 18-20 ppm hydroquinone.The bone cements used in this study were prepared according to similar studies [9,10].Briefly, a certain amount of PMMA powder was added to the BaSO 4 (radio-opaque agent-powder), and manually mixed.Subsequently, to PMMA-BaSO 4 mixer the reaction initiator BPO was added, and mixed with a sterile stir bar until a homogeneous mixture was obtained.On the other hand, in another container, the liquid phase was prepared by mixing the MMA and DmpT components using ultrasonic mixing with a Digital Sonifier SFX 250.The mixing was done at a 50% amplitude with 30-second intervals and 10-second pauses, repeated for a total of 3 min.During sonication, the liquid monomer was immersed in a water bath maintained at room temperature to prevent overheating, as described in our previous study [46].Thereafter, the powder components were mixed with methyl methacrylate monomer with a constant liquid-to-powder ratio.Neat PMMA BCs prepared as a control group.The novel PMMA composite BCs that contain CFs, Zn/CFs and ZnO/CFs structures were prepared by adding the reinforcement agents at the ratios of 0.10, 0.25, 0.50, 1.00 wt% to the powder component of the cement and mixing randomly.PMMA bone cement undergoes a chemical polymerization reaction, known as curing or setting when the liquid and powder components are mixed together.The process involves the monomer molecules linking together to form a solid polymer network.The polymerization mechanism of the reaction is illustrated in Figure 1.For each handling time, the value for the neat PMMA bone cements was not significantly different from the corresponding value for CFs/Zn/CFs and ZnO/ CFs-PMMA bone cements, and it was about 6 min.This handling time consisted of 3 min.for separately mixing the solid and liquid phases and an additional 3 min.for mixing the solid and liquid phases together.The weight percentage (wt%) of the reinforcement agents was selected based on similar previous studies [9].The novel PMMA composites (PMMA, CFs-PMMA, Zn/CFs-PMMA, and ZnO/CFs-PMMA) were thoroughly mixed and poured into silicone molds.The specimens used for measuring compressive properties were in the form of cylinders with a length of 12 ± 0.1 mm and a diameter of 6 ± 0.1 mm.For the determination of bend properties, the specimens were in the form of rectangular bars with dimensions of 75 ± 0.5 mm in length, 10 ± 0.1 mm in width, and 3.3 ± 0.1 mm in thickness.These dimensions were chosen in accordance with the guidelines specified in ISO 5833-2002 [47].The silicone mould used for the preparation of the specimens and some of the specimen samples are represented in Supplementary Figure 3(a-b).The composite BCs specimens, CFs-PMMA, Zn/CFs-PMMA, ZnO/CFs-PMMA and PMMA (as a control), were stored in a vacuum desiccator at room temperature to avoid any humidity for one week before the test.Subsequently, mechanical tests (bending, compression) and thermo gravimetric analysis tests (TGA) were performed to examine the characterization of composite bone cement.

Characterizations
The morphological characterization of the CFs/PMMA, Zn/CFs-PMMA, and ZnO/CFs-PMMA composites with varying weight percentages (0.10-1.00 wt%) was performed using a Carl Zeiss 300VP Scanning Electron Microscope (SEM).The SEM was operated at voltages ranging from 5 to 20 kV.X-ray diffraction (XRD) patterns of the samples were determined using a diffractometer with K-alpha irradiation.Fourier Transform Infrared Spectroscopy (FTIR) analysis was conducted using a Thermo Scientific Nicolet iS50 FTIR spectrophotometer.The spectral range covered was from 4000 cm À1 to 500 cm À1 .Raman spectra of the samples were obtained using a Renishaw Raman spectrometer.The scanning range was from 100 cm À1 to 3000 cm À1 , and a 532 nm laser source was used at room temperature.
To evaluate the mechanical properties of the composite bone cements, both 4-point bending and compression tests were conducted using a SHIMADZU AG-IC universal tensile tester.The test machine configurations can be seen in Supplementary Figure 2(a-b).The compressive and flexural properties of the composite PMMA bone cements were evaluated following the guidelines specified in the International Organization for Standardization (ISO) 5833:2002 standard [47].At least three samples were tested to determine the compression and bending (flexural) properties.The compression test was performed to examine the behaviour and strength of the materials under compressive stresses.The composite BCs specimens for the compression test were prepared with a length of 12.0 ± 0.1 mm and a diameter of 6.0 ± 0.1 mm.The test was conducted at a crosshead speed of 1 mm/min with a load cell of 20 kN.The 4-point bending test was conducted to observe the interfacial bonding properties between the bone cement (matrix material) and the CFs used as the reinforcing material.The composite BCs specimens for the 4-point bending test were prepared with dimensions of 80.0 ± 0.1 mm in length, 10.0 ± 0.1 mm in width, and 4.0 ± 0.1 mm in thickness.The test was performed at a crosshead speed of 1 mm/ min with a load cell of 5 kN.
Thermogravimetric analysis (TGA) tests were conducted to examine the mass changes of the composite bone cement.The samples were analyzed using a TA TGA-SDT Q600 instrument, with temperatures ranging from 0 to 900 C at a heating rate of 20 C/min.This analysis allows for the determination of the thermal stability and decomposition behaviour of the composite bone cements as a function of temperature.

Results and discussion
Table 1 presents the findings of numerous studies that have examined the effects of various additives in reinforcing PMMA BCs, as reported in the literature.It is important to note that several parameters have a significant impact on the preparation of bone cement.These include the purity of the starting materials, the ratio of liquid to solid components, the amount of radiopaque agent, the mixing time, the mixing apparatus, and other physical properties.These factors can lead to variations in both thermal and mechanical properties.Differences in mixing time, mixing rate, and mixing method for PMMA BCs can result in variations in the extent of the reaction and, consequently, in the formation and homogeneous distribution of PMMA BCs [48].Consequently, it is essential to optimize all the aforementioned conditions that can influence the thermal and mechanical properties of the final composite.In the current study, the impact of reinforcement agents (CFs, Zn/CFs, and ZnO/CFs) at a range of 0.10 to 1.00 wt% in PMMA was evaluated.The mixing rate, time, temperature, and apparatus used for preparation were carefully controlled, ensuring consistent parameters across all specimens in this study.We conducted comprehensive investigations on the surface morphology, structural analysis, as well as mechanical and thermal properties of the composite PMMA BCs, which are detailed in the respective section.

Surface morphology study by scanning electron microscope analysis
Surface morphologies of Zn/CFs and ZnO/CFs were determined by SEM analysis.According to SEM results the successful Zn/ZnO-coating on CFs surfaces was observed as shown in Figure 2(a-b), respectively.The SEM images clearly show that the ZnO nanostructures were in a flake-like morphology and uniformly covered the entire surface of CFs.The results were in good agreement with our previous study Al-Janabi et al. [39] PMMA-MWCNTs To evaluate the effect of multiwall carbon nanotubes (CNTs) modified PMMA in terms of fatigue resistance, flexural strength and resilience.Multiwall CNTs (0.5 wt% and 1.0 wt%) significantly improved flexural strength and resilience.Multiwall CNTs modified PMMA for all wt% presented poor fatigue resistance.Reinforcement amount of CNTs above 1.0 wt% showed decrease in mechanical properties.The worst mechanical properties were in the 2.0 wt% multiwall CNTs.

Wang et al. [40]
PMMA-MWCNTs To study the mechanical properties of PMMA BCs that contain multi walled carbon nanotube (MWCNT) with weight loadings ranging from 0.1 to 1.0 wt%.Incorporating low loadings of MWCNTs (less than 0.25 wt.%) to PMMA BCs improved the mechanical properties of the resultant nanocomposite.Higher loadings (more than 0.5 wt %) provided lesser improvements in the mechanical properties Dunne et al. [41] PMMA-MWCNTs To study the fatigue properties and bioactivity of PMMA BCs that contain multi walled carbon nanotube (MWCNT) with weight loadings ranging from 0.1 to 1.0 wt%.Low MWCNT loadings (0.1 wt.%) provided the greatest improvements In addition, MWCNT-COOH provided the greatest improvement in fatigue life of the resultant composite bone cement.

Dunne et al. [10]
PMMA-ND To assess the effect of addition of different concentrations of nano diamonds (NDs) on flexural strength, impact strength, and surface roughness of acrylic resin.Mechanical properties neat PMMA compared with PMMA-ND (0.5%wt, 1%wt, and 1.5%wt of ND).The study showed that, the addition of NDs to PMMA improved the flexural strength and surface roughness at low concentrations (0.5 wt%) Al-Harbi et al. [42] (continued) Table 1.Continued.

PMMA Composites
Aim of the Study

Results
Ref.

PMMA-G/GO
The effect of Graphene (G) and graphene oxide (GO) nano-sized powders with loadings ranging from 0.1 to 1.0 wt% were investigated as reinforced agents in PMMA BCs.The mechanical performance of G-PMMA and GO-PMMA BCs has been improved at low loadings ( 0.25 wt%), especially the fracture toughness and fatigue performance.

Paz et al. [43]
PMMA-CNTs To determine the mechanical properties of the composite consists of PMMA and functionalized CNTs by different weight fractions (wt%).Low CNT content, both functionalized and non-functionalized, may cause a decrease in the elastic moduli or produce a similar value as that of the matrix.
Banks-Sills et al. [44] PMMA-CNTs-HNTs-CNFs To investigate the thermo mechanical performance of halloysite nanotubes (HNTs) reinforced polymer nanocomposites and to compare their properties with carbon nanotubes (CNTs) and carbon nano fibres (CNFs) reinforced polymer nano composites.It's concluded as the suitability of particular nanofiller is dependent on requirement of operational parameters.Each of the composite that compared under this study has presented certain pros and cons.
Pal K. [45] PMMA-CNTs and rGO To study the mechanical and biological characteristics of novel bioactive polymethyl methacrylate-hardystonite (PMMA-HT) bone cement reinforced with 0.25 and 0.5 wt% of carbon nanotube (CNT) and reduced graphene oxide (rGO) As a result, low amount of CNT and rGO (0.5 wt%) has been recommended, and some mechanical properties rGO-reinforced BCs, were higher compared to the corresponding values for the nonreinforced cement.
Bakhsheshi-Rad et al. [6] and some other similar studies [30,34].The coating size and thickness of the Zncoated samples were obtained by scratching certain parts of coated CFs, and thickness of coating was found to be 9.5 ± 1 mm.Unmodified CFs diameter was found to be 7.5 ± 1 mm, followed by a successful coating of Zn on CFs surface where the diameter was increased up to 26.5 ± 2 mm in the scratched Zn/CFs image as shown in Supplementary Figure 1.SEM images of the commercial PMMA, and SEM images of the ZnO/CFs functionalized bone cement composites were taken as it shown in   The fracture surfaces of the composites were covered with gold and SEM images compared with the fractured surface of neat PMMA.SEM image of the fractured surface of neat PMMA BCs is presented in Figure 3.The fractured surfaces of the CFs, Zn/CFs, and ZnO/CFs-PMMA BCs with 0.10 wt% and 0.25 wt% reinforcement are depicted in Figure 4(a-f), and 0.50 wt%-1.00wt% reinforced composites in Figure 5(a-f), respectively.Upon studying the fracture surfaces of CFs, Zn/CFs, and ZnO/CFs reinforced PMMA BCs, it was observed that while some regions demonstrated homogeneous dispersion of the reinforcement agent within the PMMA matrix, many other areas showed poor dispersion or a lack of integration of the CFs, Zn/CFs, and ZnO/CFs within the matrix.The addition of a certain amount of  reinforcement agents resulted in smaller voids, a decrease in fracture angle, a reduction in fracture quantity, and a decrease in the presence of voids were observed.However, a higher amount of reinforcement agent in PMMA BCs may increase the number and size of voids due to non-homogeneous matrix formation, as reported in the literature [49,50].Some of the SEM images of PMMA composite BCs showed the presence of CFs and its derivatives, while in other SEM images, the presence of CFs was not observed.This discrepancy is most likely due to the random dispersion of the reinforcement agents.It represents an important challenge that needs to be taken into consideration in this study.

Structural analysis by FTIR, RAMAN and XRD
The Fourier Transform Infrared Spectroscopy (FTIR) technique is commonly used to analyze the chemical composition and molecular structure of materials, including PMMA composite bone cements.The FTIR analysis was performed in the spectral range of 4000-500 cm À1 as shown in Figure 6(a-d).FTIR spectra of neat PMMA and CFs, Zn/CFs and ZnO/CFs reinforced composite PMMA BCs were overlaid for each set of the different weight percent composition (0.10, 0.25, 0.50 and 1.00 wt%).The FTIR spectra of the neat PMMA revealed the characteristic peaks in the FTIR spectrum, including the C¼O stretching vibration peak around 1720-1730 cm À1 and the C-O stretching vibration peak around 1140-1240 cm À1 .Additionally some other peaks are observed in the FTIR spectra at 1065, 978, and 837 cm -1 that correspond to PMMA.Also some other peaks around 3000 is belong to C-H vibration, the peaks around 1600-1700 cm À1 for neat PMMA and the PMMA composites belong to C double bond O, peaks around 1500 cm À1 are belong to C-H as reported in some other similar studies [37,51,52].As it mentioned above, the carbonyl (C¼O) group of neat PMMA contains a strong band at 1720 cm À1 .This band moves and slightly shifts (around ±5 cm À1 ) with lesser intensity in the CFs, ZN/CFs and ZnO/CFs incorporated PMMA composite BCs.It can be observed that when PMMA is reinforced with CFs, Zn/CFs, and ZnO/CFs, the peaks of neat PMMA become wider, the intensity decreases, and the peak positions shift.Additionally, some new peaks are observed around 520-580 cm À1 and 707 cm À1 which are attributed to ZnO stretching and vibration peaks, respectively [34,53].
Raman spectroscopy was also utilized to investigate the interaction between the PMMA polymer matrix and CFs, Zn/CFs, and ZnO/CFs.Raman spectra of neat PMMA, CFs, Zn/CFs, and ZnO/CFs composites with weight percentages ranging from 0.10 wt% to 1.00 wt% are shown in Figure 7(a-d).A decrease in Raman peak intensity and shifting in the D and G peaks of PMMA were observed with the addition of CFs derivatives in PMMA, as described in the literature [54,55].
Figure 8(a-d) illustrates the XRD patterns of neat PMMA and CFs, Zn/CFs, and ZnO/CFs reinforced PMMA composite BCs with weight percentages ranging from 0.10 wt% to 1.00 wt%.PMMA is primarily an amorphous polymer, meaning it does not possess a well-defined crystalline structure.Consequently, the XRD spectrum of PMMA typically lacks sharp and distinct peaks associated with crystalline phases.The  XRD pattern associated with neat PMMA is consistent with the one reported in Ref [56], showing two wide amorphous humps with peaks at 2h ¼ 30 and 43 .The XRD results of this study, when compared with similar studies, clearly demonstrate the presence of CFs, Zn/CFs, and ZnO/CFs in the PMMA BCs. which is consistent with a similar study [52].Briefly, the observed peaks around 30 , 35 , 44 , 48 , correspond to the (100), (002), (101), and (102) planes of the ZnO phase, as described in detail in our previous study [34].In conclusion, the addition of reinforcement agents, even in small weight percentages, was clearly detected in the composite.This was supported by the XRD analysis, which confirmed the presence of CFs, Zn, and ZnO in the composite material.

Mechanical properties of the composite bone cements
The specimens for mechanical testing were prepared by injecting the nanocomposite cement into silicone moulds, which were allowed to cure for one week in a vacuum desiccator before mechanical tests.The static mechanical properties of bone cement composites containing CFs, Zn/CFs and ZnO/CFs at different reinforcement amounts versus controlled PMMA BCs are summarized in Table 2.In order to understand the effects of adding bare CFs and modified CFs, such as Zn and ZnO modified CFs, to composite bone cements were compared at different weight percentages.According to the results, the composite reinforced with 0.50 wt% bare CFs presented the best performance in the 4-point bending test.On the other hand, the composite reinforced with 1.00 wt% bare CFs exhibited the best results in the compression test.In contrast, the 0.25 wt% Zn/CFs reinforced composite showed the best results in terms of mechanical properties in both the 4-point bending and compression test.The flexural strength of the composite reinforced with 0.10 wt% Zn/CFs decreased by 6.88%.Similarly, the flexural moduli of the 0.50 wt% Zn/CFs reinforced composite decreased by 6.18%.Furthermore, for the composite reinforced with 1.00 wt% Zn/CFs, a 32.65% decrease in flexural strength and a 41.89% decrease in flexural moduli were observed.It was also observed that Zn/CFs contents exceeding 0.50 wt% in the composite led to increase fragility.Finally, ZnO/CFs reinforced PMMA BCs were also evaluated.Among the other samples the results in the 4-point bending test and compression test were obtained from 0.25 wt% ZnO/CFs-PMMA composite.Compared to the control group, this composite showed an improvement of 78.9% in flexural strength and a 277.4% increase in compression strength.It was determined that reinforcing ZnO/CFs in the range of 0.10-0.50wt% enhanced the mechanical properties of the bone cement, but increasing the reinforcement ratio beyond 0.50 wt% resulted in a gradual decrease.This suggests that the reinforcement ratio should not exceed 1.00 wt% in order to improve the mechanical properties.
The Flexural strength, flexural moduli, compressive strength and compression moduli changes of PMMA composite BCS is depicted in Figure 9(a-d), respectively.
Based on the mechanical data obtained in our study, the 0.25 wt% ZnO/CFs-PMMA composite exhibited the most notable improvement in mechanical properties compared to the other groups.The flexural strength reached 45.9 MPa, while the compressive strength reached 168.3 MPa.These results signify a substantial enhancement, with a 78.9% increase in flexural strength and a remarkable 277.4% increase in compression strength compared to the control group.It is worth emphasizing that achieving a well-organized dispersion of the reinforcement agents within the PMMA matrix can further augment the improvement in mechanical strength.

Thermal properties of the bone cements composite
A typical temperature profile during rapid polymerization of PMMA-based cement shows an initial rise in temperature above room temperature (25 C) until reaching a peak, followed by a decrease.This temperature increase is a result of the exothermic reaction that occurs during the setting process of PMMA bone cement, where the liquid and powder components polymerize.The heat released during this reaction can elevate the temperature of the surrounding tissues.It is important for the cement to maintain its structural integrity without significant softening or degradation under normal physiological conditions [5,57,58].The maximum recorded temperatures were 90.1 C for neat PMMA and 76.9 C for CFs derivative-reinforced bone cement.However, when 1.00 wt% of ZnO/CFs was added as a reinforcement agent to PMMA composite BCs, the polymerization temperature reduced by approximately 15% to around 77 C, which was the lowest recorded temperature in this study.To assess the structural characteristics and identify any impurities in the material, samples taken at different temperatures were subjected to thermal gravimetric analysis (TGA).TGA provided insights into possible structural variations of CFs, Zn/CFs, ZnO/CFs, and their PMMA composites.Figure 10 illustrates the weight loss curve for the composites containing 0.10% and 1.00% ZnO/CFs, as compared to neat PMMA BCs.The TGA curves in Figure 10 shows that the temperature remains constant above 350 C, and weight loss occurs at temperatures below this threshold.The novel composites PMMA (CFs, Zn/CFs, ZnO/CFs) and neat PMMA exhibit no mass loss up to 270 C, after which degradation begins.In the control sample, the sediment content at 600 C measures 10.12% due to the presence of BaSO 4 , which acts as a non-combustible powder component with radioactive properties within the tested temperature range.Figure 11 illustrates the weight loss curve of the derivative as obtained from TGA.The graph demonstrates that all samples experienced decomposition between 200 C and 450 C. Notably, the decomposition percentage slightly increased with higher concentrations of ZnO/CFs in the composite.The peak observed at 300 C can be attributed to the degradation of low molecular weight PMMA polymers or the degradation of unsaturated chain ends [59].The results indicate that the onset of thermal depolymerization began at approximately 280 C [60,61].According to a previously reported study, it was determined that 12% of PMMA decomposed at 200 C, an additional 12% decomposed at 300 C, and the majority, accounting for 64% of PMMA, had decomposed by 400 C [62].The decomposition of PMMA composites can vary, indicating potential structural and chemical differences in the polymer matrix formed in the presence of the modifier [63].
This finding was supported by the presence of a single peak in the DTG curve, as depicted in Figure 11.It should be noted that the peak in the DTG curve corresponds to the thermal degradation temperature (Td), and a higher Td value indicates higher thermal stability.From the DTG curves in Figure 10, it is observed that the Td of the composite PMMA BCs is higher compared to the control sample.It is clear that the

Conclusions
In conclusion, novel PMMA composite BCs reinforced with CFs, Zn/CFs, and ZnO/CFs at weight percentages ranging from 0.10% to 1.00% were successfully synthesized and characterized using FTIR, XRD, Raman, and SEM analysis.The effects of CFs, Zn/CFs, and ZnO/CFs as reinforcement agents were investigated through thermogravimetric analysis, flexural strength analysis, and compressive tests.Our findings revealed that PMMA composites BCs reinforced with 0.25% ZnO/CFs exhibited the best mechanical performance and thermal stability among all the composites studied.
The addition of 0.25% ZnO/CFs resulted in significant improvements in flexural strength and compression strength of the novel PMMA composite BCs from 25.66 ± 0.49 MPa to 45.92 ± 0.51 MPa and 44.59 ± 6.94 MPa to 168.29 ± 7.60 MPa, respectively.These improvements correspond to a 78.9% increase in flexural strength and a remarkable 277.4% increase in compression strength compared to the control group.It was found that reinforcing PMMA BCs with CFs, Zn/CFs, and ZnO/CFs derivatives at a rate of 0.50% improved the mechanical and thermal performance of PMMA BCs.However, the addition of CFs, Zn/CFs, or ZnO/CFs powder at high reinforcement amounts !1.00% resulted in poor dispersion in the cement matrix and had adverse effects on the mechanical properties.
In summary, our research highlights that PMMA composite BCs containing 0.10-0.50%CFs, Zn/CFs, and ZnO/CFs offer superior mechanical and thermal properties compared to neat PMMA.While there have been some studies on the biocompatibility of ZnO and CFs, further detailed research is needed to explore their use as reinforcement agents in BCs applications.

Figure 1 .
Figure 1.Polymerization reaction of PMMA BCs, (a) BPO decomposed to benzoyl radical and benzoyl anion, (b) benzoyl radical initiate the polymerization with MMA, (c) chain growth mechanism, and (d) formation of polymer chain.

Figure 2 .
Figure 2. (a) SEM Images of the Zn coated CFs, (b) SEM images of the ZnO nanostructure formation on CFs surface, (c) SEM images of commercial PMMA, and (d) SEM images of the ZnO/CFs doped PMMA BCs.

Figure 3 .
Figure 3. SEM images of bending test specimens fracture surfaces of neat PMMA.

Figure 2 (
Figure 2(c), and Figure 2(d), respectively.The SEM images of the CFs/PMMA and Zn/CFs-PMMA were almost identical with the SEM image of the ZnO/CFs-PMMA.The fracture surfaces of the composites were covered with gold and SEM images compared with the fractured surface of neat PMMA.SEM image of the fractured surface of neat PMMA BCs is presented in Figure3.The fractured surfaces of the CFs, Zn/CFs, and ZnO/CFs-PMMA BCs with 0.10 wt% and 0.25 wt% reinforcement are depicted in Figure4(a-f), and 0.50 wt%-1.00wt% reinforced composites in Figure5(a-f), respectively.Upon studying the fracture surfaces of CFs, Zn/CFs, and ZnO/CFs reinforced PMMA BCs, it was observed that while some regions demonstrated homogeneous dispersion of the reinforcement agent within the PMMA matrix, many other areas showed poor dispersion or a lack of integration of the CFs, Zn/CFs, and ZnO/CFs within the matrix.The addition of a certain amount of

Figure 10 .
Figure 10.Weight loss curve TGA plot of PMMA composite BCs.
increase in thermal stability can be associated with the presence of CFs, Zn/CFs, and ZnO/CFs in the composites.It is worth noting that the DTG analysis provides another crucial insight into the stability of the PMMA composite BCs.It clearly indicates that when the amount of additives exceeds 0.50 wt%, the composite starts to exhibit signs of instability.Supplementary Figures4, 5display both TGA and DTG curves for CFs-PMMA composite BCs and Zn/CFs-PMMA composite BCs.These graphs provide a clearer understanding of how the reinforcement agent and different percentages affect the thermal stability of PMMA BCs.

Figure 11 .
Figure 11.Derivative weight loss curve DTG curves of PMMA composite BCs.

Table 1 .
A summary of different Types of nanomaterials reinforced PMMA composite BCs.Antibacterial activity of AgNPs added BCs improved compared to neat PMMA.The study also indicate that the additives may deteriorate mechanical properties of bone cements and decrease their cyto compatibility, especially at higher content (more than 5.0 wt.%).

Table 2 .
Static mechanical properties (mean ± SD) for CFs-PMMA, Zn/CFs-PMMA and ZnO/CFs-PMMA BCs and the percentage difference compared to the control group (neat PMMA).