Document Type : Original Research Article
Subjects
Introduction
Nowadays, dental implants are a popular method of replacing lost teeth, giving patients a functional and cosmetic repair. Global demand for dental implants is on an inclining trend, thanks to improved life expectancy and an enhanced focus on quality of life and oral health [1]. Although titanium-based implants have become universally used, considerable interest still exists in the development of newer materials that may counteract specific limitations of metals, namely hypersensitivity reactions, aesthetic issues, and radiopacity [2,3].
Polyaryletherketone (PAEK) polymers, particularly polyetherketoneketone (PEKK), have emerged as promising candidates for dental and orthopedic applications due to their excellent mechanical strength, chemical resistance, radiolucency, and biocompatibility[3]. The mechanical properties of PEKK closely resemble those of natural bone, which can help minimize stress shielding and promote favorable load transfer at the bone-implant interface. However, a major drawback of PEKK and related polymers is their bioinert nature; they lack intrinsic bioactivity and osteogenic potential, which can limit their integration with surrounding bone tissue [4-8].
To cope with this challenge, various recent studies have concentrated on the surface or chemical structure modification of PEKK to advance its biological performance. One viable route is the introduction of bioactive ceramic nanofillers, like silicon dioxide (SiO₂), into the polymer matrix. The incorporation of SiO₂ nanofillers is capable not only of developing the mechanical features of the composite but, more importantly, of enlarging its surface roughness and hydrophilicity, which is helpful in terms of cellular adhesion and osseointegration. Additionally, the homogenous nanofillers dispersion in the polymer matrix is capable of inducing heterogeneous crystallization, and this is able to favor the structural and functional features of the composite further. Considering the latter, the PEKK-based nanocomposites reinforced with SiO₂ nanofillers represent an attractive route in the production of the new-generation dental implant materials. Nonetheless, the optimal nanofillers concentration and their influence on the features of the composite still need detailed research[3,9-13].
The objective of the current work is to assess the influence of different concentrations of SiO₂ nanoparticles on the mechanical, physical, and morphological behavior of PEKK composites. It is hypothesized that the introduction of the SiO₂ nanoparticles will considerably improve the biomechanical and biological features of PEKK and provide an acceptable alternative option compared to the conventional titanium implants.
The materials used in this study included SiO₂ powder obtained from Riedel-de Haën (Germany), 95% ethanol supplied by Scarlab SL (Spain), and PEKK powder provided by Zibo Zichuan Yaodong Chemical Co., Ltd. (China).
Preparation of SiO2/PEKK Composites
The PEKK/SiO2 composites were synthesized via the compression molding process. Initially, the SiO2 powder (average size 0.9 μm) was ultrasonically mixed with 95 % ethanol with varying SiO2:ethanol weight ratios to offer adequate wetting between the powder grains. Subsequently, the PEKK powder (average size 33 μm) was added to the suspension to fill the final composite mixture. For ten more minutes, the resultant mixture was co-dispersed ultrasonically to create a uniform powder blend.
[14]. The powder combination was dried for ten hours at 120°C to eliminate any remaining moisture. After drying, the powder was put into a mold that had already been made [15].
Prior to compression, the mold was preheated to 150°C. A pressure of 15 MPa was used to compress the powder. The composite was kept in situ between heated platens at a maximum temperature of 310°C for 10 minutes in order to guarantee complete mixing of SiO2 particles within the molten PEKK matrix. Following this heating phase, the heaters were shut off while keeping the pressure at 15 MPa until the cooling process was finished.
Sample Preparation and Characterization
The hardened compression-molded sheets were machined into disk-shaped samples with a diameter of 15 mm and a thickness of 2 mm using a turning lathe. Prior to machining, each sheet was measured six times with a vernier caliper to confirm dimensional consistency.
Rectangular specimens measuring 65 mm in length, 10 mm in width, and 3 mm in thickness were prepared, with two samples tested per condition. Flexural strength testing was performed at room temperature using an Instron universal testing machine, operating at a crosshead speed of 2 mm/min, in accordance with ASTM D790-03 standards. The flexural strength (S) was calculated using the following formula:
where:
S = flexural strength (MPa), P = load at a specific point on the load-deflection curve (N), L = support span length (mm), b = specimen width (mm), d = specimen thickness (mm).
Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX)
The microstructure of the samples was examined using a scanning electron microscope (LEO, model 1455VP, UK) operated at an accelerating voltage of 10–20 kV. Elemental composition analysis was conducted simultaneously via energy dispersive X-ray spectroscopy (EDX). EDX relies on the principle that each element emits a characteristic electromagnetic spectrum due to its unique atomic structure. The interaction between the sample and the X-ray excitation source generates elemental-specific emission peaks, enabling qualitative and quantitative elemental analysis.
Atomic force microscopy was employed to obtain roughness. The technique involves scanning a sharp tip attached to a cantilever across the sample surface using piezoelectric scanners. Deflections of the cantilever caused by tip-sample interactions were detected via optical or capacitive tunneling sensors. To minimize surface deformation, measurements were performed under zero standard pressure conditions.
Contact angle measurement (wettability test)
Surface wettability was evaluated by measuring the contact angle using a goniometer equipped with a charge-coupled device (CCD) camera. Images of sessile droplets were captured and analyzed using LabVIEW software to determine the contact angle values.
All quantitative data were analyzed using SPSS software version 24. Descriptive statistics, including mean and standard deviation, were calculated for each test group. Inferential statistical comparisons were performed using paired sample t-tests and analysis of variance (ANOVA), with significance levels set appropriately.
PEKK is an appealing biomaterial with prospective applications in dental, orthopedic, and cranial implants. However, its clinical significance is diminished based on the lack of osteogenic and bioactive features, intrinsic hydrophobicity, inadequate integration with bone tissue, and limited cellular adhesion[16]. To overcome these limitations, bioactive ceramics can be incorporated into the PEKK matrix to enhance its functionality [6]. Nanocomposites, which consist of at least one nanoscale filler uniformly dispersed within a continuous polymer matrix [17], offer a novel approach to improving material properties. This study focuses on reinforcing high-performance thermoplastic PEKK with nanofillers to enhance bioactivity and potentially promote osteogenic differentiation [18].
The result of measuring of the flexural strength for the samples was described in Table 1. The highest mean value obtained for PEKK/ 3% SiO2 (128.6) while the lowest value obtained for PEKK/ 4% SiO2 (116.5).
The flexural strengths of PEKK and SiO₂/PEKK composite materials were evaluated in the present work according to the ISO 178:2010 standard test method. From the results, it was determined that the flexural strength of PEKK enhanced notably with the incorporation of 3% nano-SiO₂. Consistent with the results of Rikitoku et al [19], the introduction of 3% SiO₂ into PEKK is the best way of boosting its mechanical performance, yielding significant flexural strength with respect to neat PEKK. This is attributed to the large surface area of the nanometric SiO₂, giving rise to the formation of an appreciable interphase and broad interfacial contact between the polymer matrix and the filler, thereby promoting mechanical reinforcement. The SEM photos also confirmed the uniform dispersion of the SiO₂ particles into the PEKK matrix, with very minimal particle agglomeration being observed. Pure PEKK and the SiO2/PEKK composite were subjected to SEM examination to investigate the effects of implant texture on cell culture and other physiological responses of PEKK with and without SiO2. There were visible SiO2 particles on the SiO2/PEKK surface (Figure 1). There was a noticeable difference in the surface morphology between the rough and smooth sample surfaces that were prepared for the bioactivity analysis.
SEM images revealed that samples exhibiting smoother fracture surfaces corresponded to higher interfacial adhesion between the composite components. The fractured surfaces of the composites indicated effective fusion. At low filler concentrations, the nanoparticles are able to overcome physical repulsive forces and disperse uniformly throughout the polymer matrix. As the interparticle distance decreases, these repulsive forces diminish, leading to particle agglomeration. This clustering of filler particles can interfere with the fusion of PEKK particles, adversely affecting the composite’s microstructure. Consequently, such filler aggregation results in altered composite properties, often increasing brittleness[20].
The results of the water surface roughness and contact angle measurements for the samples are presented in Table 2.
PEKK is an appealing biomaterial with the potential application in dental, orthopedic, and cranial implants. However, its clinical efficacy might be affected because of the lack of osteogenic and bioactive functionalities, intrinsic hydrophobicity, poor integration with the bone tissue, and poor cellular adhesion.[16]. To overcome these limitations, bioactive ceramics can be incorporated into the PEKK matrix to enhance its functionality [6]. Nanocomposites, which consist of at least one nanoscale filler uniformly dispersed within a continuous polymer matrix [17], offer a novel approach to improving material properties. This study focuses on reinforcing high-performance thermoplastic PEKK with nanofillers to enhance bioactivity and potentially promote osteogenic differentiation [18]. The surface roughness (Ra) of the unmodified PEKK discs was quantified, and the introduction of SiO₂ nanoparticles was observed to enhance surface roughness compared with the control. This enhancement is likely due to the introduction of nanofillers in the polymer matrix, which is also responsible for enhanced interfacial adhesion between the composite components [14]. Smoother surfaces are generally less conducive to microbial adhesion and proliferation [16]. Although the addition of SiO₂ raised the surface roughness compared to pure PEKK, the overall roughness remained lower than that of some other materials currently in use.Surface hydrophilicity is an important factor in the physiological performance of dental implants due to its improved interaction with the implant materials and the tissue that is in its vicinity[10]. The water contact angle of the composites and the unmodified PEKK was investigated to determine the level of hydrophilicity and hydrophobicity. The maximum contact angle of the pure PEKK was seen to be about 90°, which shows its level of being hydrophobic. When 3% SiO₂nanofiller was added to the PEKK matrix, the contact angle dropped considerably, to 78.49°, which implies that there is an increase in the level of hydrophilicity, because SiO₂ is inherently hydrophilic[21]. Variations in contact angle measurements between pure PEKK and SiO₂/PEKK nanocomposites were observed, which can be attributed to changes in surface topography induced by the incorporation of nanofillers. Although SiO₂ nanoparticles are hydrophilic, the addition of 3% hydrophobic nano-SiO₂ to the PEKK matrix resulted in modifications to surface roughness. The decrease in surface roughness may be explained by the small particle size of the nanoparticles (20–30 nm) and their uniform dispersion within the PEKK matrix and on the composite surface[22].
This study demonstrates that reinforcing PEKK with nanoscale SiO₂ significantly enhances its mechanical and surface properties, addressing some of the inherent limitations of pure PEKK as a biomaterial for dental, orthopedic, and cranial implants. The incorporation of 3% SiO₂ nanofiller yielded the highest flexural strength, indicating optimal mechanical reinforcement likely due to the large surface area and uniform dispersion of nanosized particles within the polymer matrix. SEM analysis confirmed the effective integration and minimal agglomeration of SiO₂ particles, which contributed to improved interfacial adhesion and composite integrity. Furthermore, the addition of SiO₂ nanoparticles increased surface roughness and enhanced hydrophilicity, as evidenced by a significant reduction in water contact angle compared to pure PEKK. These surface modifications are expected to promote better cellular interactions and bioactivity, which are critical for implant integration and osteogenic differentiation. Although higher filler concentrations (4% SiO₂) led to particle agglomeration and reduced mechanical performance, the results highlight the importance of optimizing nanofiller content to balance mechanical strength and surface characteristics.
Overall, SiO₂/PEKK nanocomposites, particularly those with 3% SiO₂, show great promise as advanced biomaterials with improved bioactivity and mechanical properties suitable for implant applications. Future work should focus on in vitro and in vivo biological evaluations to further validate their clinical potential.
In order to enhance the manuscript’s readability and language, the authors employed artificial intelligence (perplexity.ai) during the writing process. Following the use of this AI, the authors took full responsibility for the content of the published paper and reviewed and amended it as necessary.
No specific grant from a public, private, or nonprofit funding organization was obtained for this study.
The authors declare that they have no conflicts of interest related to this work.
