Pristine Polyetheretherketone Research Articles

A Comprehensive Review on the Tribological Evaluation of Polyether Ether Ketone Pristine and Composite Coatings.

Polymer coatings have gained a lot of attention in the recent past because of their ability to be easily coated on complex shapes, their low cost, and their ability to reduce friction as compared to other materials. Polyether ether ketone (PEEK) is one such high-performance polymer that has gained significant attention in recent years due to its exceptional mechanical properties, chemical resistance, and thermal stability making it a prominent candidate for applications in industries. However, PEEK in its pristine form exhibits poor wear resistance with a moderate coefficient of friction (0.30-0.38). Many attempts have been made by several researchers to improve its wear resistance and lower the COF by developing composite coatings. Hence, in this review, we aim to summarize and present in detail the tribological evaluation of pristine PEEK and PEEK composite coatings by discussing the various methods adopted by the researchers to improve the properties of PEEK, the different types of reinforcements and various dispersion techniques used to develop PEEK composite coatings. By consolidating and analyzing the existing body of knowledge, we also aim to offer valuable insights into the development of more durable, high-performance PEEK nanocomposite coatings for a broad range of tribological applications.

Dual-functional polyetheretherketone surface modification for enhanced osseointegration and antibacterial activity in pH-responsive manner

Polyetheretherketone (PEEK) has been recognized for its immense potential in hard tissue repair applications due to its mechanical properties resembling those of natural bones. However, the inherent bioinertness of pristine PEEK results in insufficient osseointegration. Moreover, implant-associated infection (IAI) has become a serious threat in orthopedic surgery. These risks usually lead to implant loosening, delayed healing, and even the failure of implantation, hampering many clinical applications of PEEK. In this study, we present a facile strategy to endow PEEK implants with enhanced osseointegration and pH-responsive antibacterial activity. Briefly, pristine PEEK was first treated with mixed acids to obtain a porous structure (referred to as SNPEEK), and then the metal-phenolic networks (MPN) coating was prepared using layer-by-layer (LbL) assembly consisting of Sr2+ and tannin acid (TA) (referred to as ST coating). The results demonstrated that the dual-functional PEEK displayed enhanced antibacterial activity in pH-responsive manner. At pH 7.4, the antibacterial ratios were 71.72% and 66.79% against Staphylococcus aureus (MSSA, ATCC 25,923) and methicillin-resistant Staphylococcus aureus (MRSA, ATCC BAA-40), respectively. Remarkably, at pH 5.5, the antibacterial activities significantly increased, resulting in killing ratios of 99.98% and 100%, respectively. Furthermore, the dual-functional PEEK promoted osteogenic differentiation of pre-osteoblasts (MC3T3-E1) and migration of human umbilical vascular endothelial cells (HUVECs). In addition, the dual-functional PEEK demonstrated effective anti-infection ability and desirable new bone formation ability in vivo compared to both pristine PEEK and SNPEEK implants. Overall, this study provides a promising strategy to endow PEEK implants with effective osseointegration and anti-infective ability, representing a prospective solution to address current clinical challenges associated with PEEK implants.

Chemically heparinized PEEK via a green method to immobilize bone morphogenetic protein-2 (BMP-2) for enhanced osteogenic activity.

Osseointegration remains one of the major challenges in the success of bone-related implants. Recently, polyetheretherketone (PEEK) has emerged as an alternative material in orthopedic and dental applications due to its bone-mimicking mechanical properties. However, its bioinertness resulting in poor osseointegration has limited its potential application. So, the surface modification of PEEK with bone morphogenetic protein-2 (BMP-2) can be a potential approach for improving osseointegration. In this study, we proposed the chemical modification of heparin onto PEEK through an environmentally benign method to exploit the BMP-2 binding affinity of heparin. The heparin was successfully functionalized on the PEEK surface via a combination of ozone and UV treatment without using organic solvents or chemicals. Furthermore, BMP-2 was efficiently immobilized on PEEK and exhibited a sustained release of BMP-2 compared to the pristine PEEK with enhancement of bioactivity in terms of proliferation as well as osteogenic differentiation of MG-63. The significant synergistic effect of BMP-2 and heparin grafting on osteogenic differentiation of MG-63 was observed. Overall, we demonstrated a relatively safe method where no harsh chemical reagent or organic solvent was involved in the process of heparin grafting onto PEEK. The BMP-2 loaded, heparin-grafted PEEK could serve as a potential platform for osseointegration improvement of PEEK-based bone implants.

Tuning high-temperature dielectric properties of poly ether ether ketone by using self-crosslinkable polyetherimide and nanoparticles

Polymer dielectric materials operating at high temperatures are widely needed for advanced electrical and electronic systems. However, currently commercial polymer dielectrics are limited to relatively low operating temperatures. Here, a series of polyether ether ketone (PEEK)-based blends with self-crosslinkable polyetherimide (c-PEI) has been prepared as high temperature dielectrics by melt blending. The obtained polymer blends maintain stable dielectric properties over a wide frequency and temperature range. At 160 °C，the dissipation factor of the blend film is only 0.0019 which is only 14% of the pristine PEEK. Crosslinked networks in polymer blends could efficiently restrict the movement of polymer segments which suppress the dielectric loss and enhance high temperature performance. Furthermore, the introducing of Al2O3 improve the dielectric constant of the polymer blend, which compensated for the decreased dielectric constant due to crosslinking. In addition, the c-PEI/PEEK blends could be produced by industrial-grade continuous production process. This work presents a feasible strategy to large-scale fabrication of high-temperature dielectric materials by melt blending with self-crosslinkable polymers.

PEEK composite resin with enhanced intumescent flame retardancy loaded with Octaphenylsilsesquioxane and nano calcium carbonate and its application in fibers

This study reported a novel strategy of introducing nano Calcium Carbonate (nCC) and Octaphenylsilsesquioxane (OPS) simultaneously into poly ether ether ketone (PEEK) as the intumescent flame retardants for the first time to address the melt flowage and drop in the fire. Good dispersion of nCC and OPS in the PEEK matrix was observed. The nanocomposites displayed lower thermal decomposition rate and higher residual chars compared with those of pristine PEEK. Cone calorimeter tests showed that the peak heat release rate, smoke production rate and the total smoke production of 5%OPS/5%nCC/PEEK decreased by 47.54%, 55.00% and 30.61%, respectively. Furthermore, the combustion mechanism of PEEK and its nanocomposite was investigated by TG-MS, which showed that nCC and OPS had a synergistic flame retardant effect. Finally, as an application verification, the PEEK nanocomposite fiber was prepared and its flame retardant properties were basically the same as the PEEK nanocomposite material, proving its huge application potential in high-performance flame retardant fabrics. This work is expected to pave the pathway about the novel eco-friendly flame retardancy and open a new avenue to develop PEEK nanocomposites.

Improved Mechanical Properties and Bioactivity of Silicate Based Bioceramics Reinforced Poly(ether-ether-ketone) Nanocomposites for Prosthetic Dental Implantology.

Polyether-ether-ketone (PEEK) biomaterial has been increasingly employed for orthopedic, trauma, spinal, and dental implants due to its biocompatibility and in vivo stability. However, a lack of bioactivity and binding ability to natural bone tissue has significantly limited PEEK for many challenging dental implant applications. In this work, nanocomposites based on PEEK reinforced with bioactive silicate-based bioceramics (forsterite or bioglass) as nanofillers were prepared using high energy ball milling followed by melt blending and compression molding. The influence of nanofillers type and content (10, 20 and 30 wt.%) on the crystalline structure, morphology, surface roughness, hydrophilicity, microhardness, elastic compression modulus, and flexural strength of the nanocomposites was investigated. The scanning electron microscopy images of the nanocomposites with low nanofillers content showed a homogenous surface with uniform dispersion within the PEEK matrix with no agglomerates. All nanocomposites showed an increased surface roughness compared to pristine PEEK. It was found that the incorporation of 20 wt.% forsterite was the most effective in the nanocomposite formulation compared with bioglass-based nanocomposites; it has significantly improved the elastic modulus, flexural strength, and microhardness. In vitro bioactivity evaluation, which used biomimetic simulated body fluid indicated the ability of PEEK nanocomposites loaded with forsterite or bioglass nanofillers to precipitate calcium and phosphate bone minerals on its surface. These nanocomposites are expected to be used in long-term load-bearing implant applications and could be recommended as a promising alternative to titanium and zirconia when used as a dental implant material.

Enhanced adhesion of copper plating to polyether ether ketone based on active oxygen species generated under ultraviolet irradiation

Polyether ether ketone (PEEK) is a substrate for metal plating to overcome insulation defects and satisfy the increased demands of mechanically robust electronic circuit boards. However, pristine PEEK is hydrophobic; hence, the adhesion between the metal film and PEEK substrate is poor. Therefore, the PEEK surface should be modified to improve hydrophobicity. We have proposed the active oxygen (AOS) treatment under ultraviolet (UV) light as an alternative to a conventional plasma treatment method. Characteristics of the PEEK surfaces obtained by these methods are compared. We explore the effects of reactive‐oxygen and UV light exposure time on the PEEK surface modification. The contact angle of water drop on PEEK after the AOS treatment is lower than that of untreated PEEK. Furthermore, COO groups are observed on the PEEK surface after the treatment. Although plasma treatment has the effect of roughening the surface, it is desirable not to roughen the surface for use in electronic circuit boards. Moreover, we have reported the adhesion strength between PEEK and copper plating without surface roughening.

Fabrication and Characterization of PEEK/PEI Multilayer Composites.

Polyetheretherketone (PEEK)/polyetherimide (PEI) blends (50/50, v/v) keeping the crystal phase of PEEK have been manufactured by alternate PEEK/PEI layer stacking. This strategy avoided the complete miscibility of both polymers, keeping layers of PEEK and PEI unmixed along the sample thickness, as well as promoting the formation of a smooth interfacial layer where PEEK and PEI were mixed. The properties of this interface after processing at molten state and different times was studied by DSC, DMA, and X-Ray synchrotron. These techniques allowed monitoring the evolution of glass transition, where isolated Tg’s for both pristine polymers were observed even after long processing time. PEEK crystallinity slightly decreased during manufacturing, whereas PEEK crystal parameters did not vary. These observations show that, although the interface—the zone where both polymers are mixed—grew, layers with pristine polymers remained even after prolonged processing time. The preservation of the PEEK crystallinity was also observed in the mechanical properties of the multilayer PEEK/PEI films, which were compared with pristine PEEK and PEI films. Multilayer samples processed for shorter times rendered higher young modulus, tensile strength, and strain at break.

Study on the Microstructure of Polyether Ether Ketone Films Irradiated with 170 keV Protons by Grazing Incidence Small Angle X-ray Scattering (GISAXS) Technology

Polyether ether ketone (PEEK) films irradiated with 170 keV protons were calculated by the stopping and ranges of ions in matter (SRIM) software. The results showed that the damage caused by 170 keV protons was only several microns of the PEEK surface, and the ionization absorbed dose and displacement absorbed dose were calculated. The surface morphology and roughness of PEEK after proton irradiation were studied by atomic force microscope (AFM). GISAXS was used to analyze the surface structural information of the pristine and irradiated PEEK. The experimental results showed that near the surface of the pristine and irradiated PEEK exists a peak, and the peak gradually disappeared with the increasing of the angles of incidence and the peak changed after irradiation, which implies the 170 keV protons have an effect on PEEK structure. The influences of PEEK irradiated with protons on the melting temperature and crystallization temperature was investigated by differential scanning calorimetry (DSC). The DSC results showed that the crystallinity of the polymer after irradiation decreased. The structure and content of free radicals of pristine and irradiated PEEK were studied by Fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance (EPR). The stress and strain test results showed that the yield strength of the PEEK irradiated with 5 × 1015 p/cm2 and 1 × 1016 p/cm2 was higher than the pristine, but the elongation at break of the PEEK irradiated with 5 × 1015 p/cm2 and 1 × 1016 p/cm2 decreased obviously.

In-Situ saxs/waxd analysis on structural evolution in peek irradiated by 1 MeV electrons during tensile deformation

Polyether ether ketone (PEEK) is widely used as an electrical insulation material in aerospace field due to its excellent thermal and electrical properties. The changes in micro structure of the PEEK irradiated by 1 MeV electrons are studied by in-situ analysis of synchronous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) during tensile deformation at room temperature. The tensile strength and the elongation at break of the irradiated PEEK decrease obviously, which is compared with the pristine one. The differential scanning calorimetry (DSC) analysis shows that the pristine PEEK begins to melt at 334.8 °C, the melting peak Tm appears at 339.7 °C and a deeper exothermic crystallization peak Tc appears at 297.8 °C during the cooling process. The crystallization peak temperature decreases with the increase of the irradiation fluences. The pristine PEEK has a significant scattering peak along the meridian direction of the SAXS pattern, which indicates that the crystal lamellae of the material exhibits a certain orientation, and the position of the scattering peak changes little after irradiation. The intensity of SAXS decreases with the increasing of stretching strains, and the descent rate increases with the increasing of the irradiation fluences. According to the WAXD analysis, the width at half height of the diffraction peak increases with the increasing of the stretching strain, and the peak tends to disappear during tensile deformation. The diffraction peak disappearance rate increases with the increasing of the irradiation fluences.

Fabrication of a novel hydroxyapatite/polyether ether ketone surface nanocomposite via friction stir processing for orthopedic and dental applications.

There is increasing interest in the use of polyether ether ketone (PEEK) for orthopedic and dental implant applications due to its elastic modulus (close to that of bone), biocompatibility and radiolucent properties. However, PEEK is still categorized as bioinert owing to its low integration with surrounding tissues. Methods such as depositing hydroxyapatite (HA) onto the PEEK surface could increase its bioactivity. However, depositing HA without damaging the PEEK substrate is still required further investigation. Friction stir processing is a solid-state processing method that is widely used for composite substrate fabrication. In this study, a pinless tool was used to fabricate a HA/PEEK surface nanocomposite for orthopedic and dental applications. Microscopical images of the modified substrate confirmed homogenous distribution of the HA on the surface of the PEEK. The resultant HA/PEEK surface nanocomposites demonstrated improved surface hydrophilicity coupled with better apatite formation capacity (as shown in the simulated body fluid) in comparison to the pristine PEEK, making the newly developed material more suitable for biomedical application. This surface deposition method that is carried out at low temperature would not damage the PEEK substrate and thus could be a good alternative for existing commercial methods for PEEK surface modification.

Improved biotribological properties of polyetheretherketone composites for artificial joints with a ‘soft-on-hard’ structure and brushlike molecules

On the purpose of improving the biotribological performance of polyetheretherketone (PEEK) for artificial joints, mimicking the ‘soft-on-hard’ contact mode of ‘cartilage-subchondral bone’ construction as well as the special brushlike structure of natural articular cartilage, a ‘soft-on-hard’ structure with a poly acrylic acid-poly acrylamide (PAA-PAAm) hydrogel layer connected onto a PEEK substrate was fabricated. Meanwhile, methacrylated sodium alginate (SAGMA) was introduced into the hydrogel layer to form molecular brushes. Compared to the friction coefficient of a pristine PEEK (0.22), that of the PEEK-hydrogel-molecular brush structure was significantly lower (0.02) benefiting from the synergistic effect of biphasic lubrication and boundary lubrication. This work develops a useful method to effectively improve the biotribological properties of artificial joints.

Super tough graphene oxide reinforced polyetheretherketone for potential hard tissue repair applications

Biocompatible polyetheretherketone (PEEK) is a favorable material for hard tissue repair due to its similar elastic modulus to that of the human bone. In this work, graphene oxide (GO) reinforced PEEK nanocomposites with different GO loading have been prepared by injection molding. Mechanical testing reveals that the toughness of the reinforced composite varies with the GO loading, with 0.5% GO giving the greatest elongation at break (86.32% greater than pristine PEEK). The underlying toughening mechanism has been attributed to the well-dispersed GO forming π-π* conjugations at the GO/PEEK interface. These conjugations also acted as the nucleation sites for oriented crystallized region in PEEK. As the GO content increases further (e.g > 0.5%), the fillers tend to agglomerate and would disturb the crystallites of PEEK and serve as stress concentration sites, resulting in decreased toughness. The biocompatibility of the composites has been evaluated in vitro, and the results showed that the addition of GO into PEEK favors the adhesion and spreading of bone marrow stromal stem cells, demonstrating the strong potential of our GO reinforced PEEK composites in applications such as hard tissue repair and replacement.

Improving surface wettability and lubrication of polyetheretherketone (PEEK) by combining with polyvinyl alcohol (PVA) hydrogel.

Poor surface wettability and relative high friction coefficients of pristine polyetheretherketone (PEEK) have limited its application in orthopedic implants. In this study, inspired by the structure of natural articular cartilage, we presented a novel method to fabricate a "soft-on-hard" structure on the surface of pristine PEEK specimens, which combined a soft polyvinyl alcohol (PVA) hydrogel layer and a three-dimensional porous layer with PEEK substrates. A variety of analytical methods were used to evaluate their properties, our results demonstrated that the hydrogel layer could be seamlessly connected with substrate, and the hydrogel-covered PEEK owned a highly hydrophilic surface, a very low water contact angle of 7° could be obtained. The friction coefficients of untreated and hydrogel-covered PEEK surfaces were measured using a tribometer under water lubrication, due to the presence of the top hydrogel layer and the hard substrate could provide excellent aqueous lubrication and bearing capacity, respectively, the friction coefficient could be reduced from 0.292 to 0.021. In addition, the porous layer under PVA hydrogel layer could work as gel reservoirs, the reserved hydrogel would be released after the surface layer was sheared off, and a regenerable lubrication status was obtained. This work provides a new route for the design of improving the surface wettability and tribological properties of PEEK.

Enhanced Tissue Compatibility of Polyetheretherketone Disks by Dopamine-Mediated Protein Immobilization

Polyetheretherketone (PEEK) disks with hydrophilic and bioactive surface properties were prepared by covalent immobilization of collagen (Col) or insulin (In) on poly-dopamine (D)-coated PEEK samples using WSC (water soluble carbodiimide) as an activating agent. The poly-dopamine on the PEEK disk was coated by carrying out self-assembled polymerization of the dopamine neurotransmitter in a basic medium at pH 8.5. The poly-dopamine coating of the PEEK surface facilitated the deposition of a uniform layer of aligned molecules of collagen, which increased the bioactivity of the PEEK surfaces allowing for adhesion, proliferation, and osteogenic differentiation of MC3T3-E1 cells in a minimum essential medium in the presence of 5% CO2 at 37 °C. The collagen-modified PEEK surface had higher bioactivity for MC3T3-E1 cells, compared to the self-assembled poly-dopamine coated PEEK surface or pristine PEEK alone. Alkaline phosphatase, von Kossa, and Alizarin red staining of MC3T3-E1 cells cultured on a collagen-modified PEEK surface, were all found to be increased compared to staining of cells cultured on other PEEK surfaces. The self-assembled polymerization of dopamine on a PEEK surface was found to be useful for the immobilization of proteins such as collagen and insulin. Thus, collagen-and insulinimmobilized PEEK provide an opportunity to enhance the bioactivity of the PEEK samples allowing for better cells adhesion and tissue integration for potential use in tissue implants.

Enhanced Bioactivity and Bacteriostasis of Surface Fluorinated Polyetheretherketone.

Although polyetheretherketone (PEEK) has been considered as a potential orthopedic and dental application material due to its similar elastic modulus as bones, inferior osseointegration and bacteriostasis of PEEK hampers its clinical application. In this work, fluorinated PEEK was constructed via plasma immersion ion implantation (PIII) followed by hydrofluoric acid treatment to ameliorate the osseointegration and antibacterial properties of PEEK. The surface microstructure, composition, and hydrophilicity of all samples were investigated. Rat bone mesenchymal stem cells (rBMSCs) were cultured on their surfaces to estimate bioactivity. The fluorinated PEEK can enhance the cell adhesion, cell spreading, proliferation, and alkaline phosphatase (ALP) activity compared to pristine PEEK. Furthermore, the fluorinated PEEK surface exhibits good bacteriostatic effect against Porphyromonas gingivalis, which is one of the major periodontal pathogens. In summary, we provide an effective route to introduce fluorine and the results reveal that the fluorinated PEEK can enhance the osseointegration and bacteriostasis, which provides a potential candidate for dental implants.

Marginal healing using Polyetheretherketone as healing abutments: an experimental study indogs.

To evaluate the marginal soft and hard tissue healing at titanium and Polyetheretherketone (PEEK) healing implant abutments over a 4-month period. In six Labrador dogs, all mandibular premolars and first molars were extracted. After 4months of healing, flaps were elevated, and two implants were installed at each side of the mandible, one in the premolar and the other in the molar regions. Four different types of healing abutments were positioned on the top of each implant: (i) titanium (Ti); (ii) PEEK material bonded to a base made of titanium (Ti-P), randomly positioned in the premolar region; (iii) PEEK, pristine (P); and (iv) PEEK, roughened (P-R), randomly positioned in the molar region. The flaps were sutured to allow a non-submerged healing, and after 4months, the animals were sacrificed and ground sections obtained for histological evaluation. A higher resorption of the buccal bone crest was observed at the PEEK bonded to a base made of titanium abutments (1.0±0.3mm) compared to those made of titanium (0.3±0.4mm). However, similar dimensions of the peri-implant mucosa and similar locations of the soft tissues in relation to the implant shoulder were observed. No statistically significant differences were seen in the outcomes when the pristine PEEK was compared with the roughened PEEK abutments. The mean apical extension of the junctional epithelium did not exceed the implant shoulder at any of the abutment types used. The coronal level of the hard and soft tissues allows the conclusion that the use of PEEK as healing abutments may be indicated.

Dielectric relaxation behavior of C5+ (70 MeV) swift heavy ion irradiated polyetheretherketone (PEEK) using TSDC technique

The dielectric relaxation characteristics of polyetheretherketone (PEEK) irradiated with C5+ (70 MeV) ion, have been investigated in the temperature range 60–230° as a function of poling temperature TP (50, 100, 150, and 200°C), poling field EP (200, 300, 400, and 500 kV/cm), and storage time ts (2, 24, 48, and 120 h), using thermally stimulated discharge current (TSDC) technique. The TSDC spectra show a prominent maximum around glass transition temperature (Tg ∼ 143°C) named as α-peak. This peak is attributed to the movement of ketone dipoles linked with the main chain. It is observed that the magnitude of α-peak increases with the increase in poling temperature and poling field. The peak current and area under the α-peak are found to be diminished with the increase of storage time ts for electrets. The β-peak (space charge peak) is absent in irradiated PEEK samples as compared to pristine PEEK samples. The results obtained, in the present studies, are compared with the results on pristine samples. The activation energies and pre-exponential factor for PEEK samples determined using Bucci plot method.

Enhanced osteoblast responses to poly ether ether ketone surface modified by water plasma immersion ion implantation

Poly ether ether ketone (PEEK) offers a set of characteristics superior for human implants; however, its application is limited by the bio-inert surface property. In this work, PEEK surface was modified using single step plasma immersion ion implantation (PIII) treatment with a gas mixture of water vapor as a plasma resource and argon as an ionization assistant. Field emission scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy were used to investigate the microstructure and composition of the modified PEEK surface. The water contact angle and zeta-potential of the surfaces were also measured. Osteoblast precursor cells MC3T3-E1 and rat bone mesenchymal stem cells were cultured on the PEEK samples to evaluate their cytocompatibility. The obtained results show that the hydroxyl groups as well as a “ravined structure” are constructed on water PIII modified PEEK. Compared with pristine PEEK, the water PIII treated PEEK is more favorable for osteoblast adhesion, spreading and proliferation, besides, early osteogenic differentiation indicated by the alkaline phosphatase activity is also up-regulated. Our study illustrates enhanced osteoblast responses to the PEEK surface modified by water PIII, which gives positive information in terms of future biomedical applications.