Surface Reduction of Poly(aryl ether ether ketone) Film: UV Spectrophotometric,3H Radiochemical, and X-ray Photoelectron Spectroscopic Assays of the Hydroxyl Functions

Current surface modification strategies to improve the binding efficiency of emerging biomaterial polyetheretherketone (PEEK) with bone and soft tissue: A literature review

PURPOSE

The aim of this study was to review the literature on current surface modification strategies used to improve the binding efficiency of an emerging biological material, polyetheretherketone (PEEK), with bone and soft tissues.

STUDY SELECTION

This review was based on articles retrieved from PubMed, Google Scholar, Web of Science, and ScienceDirect databases. The main keywords used during the search were "polyetheretherketone (PEEK)," "implant," "surface modification," "biomaterials," "bone," "osseointegration," and "soft tissue."

RESULTS

The suitability of PEEK surface modification strategies has been critically analyzed and summarized here. Many cell and in vivo experiments in small animals have shown that the use of advanced modification technologies with appropriate surface modification strategies can effectively improve the surface inertness of PEEK, thereby improving its binding efficiency with bone and soft tissues.

CONCLUSIONS

Surface modifications of PEEK have revealed new possibilities for implant treatment; however, most results are based on in vitro or short-term in vivo evaluations in small animals. To achieve a broad application of PEEK in the field of oral implantology, more in vivo experiments and long-term clinical evaluations are needed to investigate the effects of various surface modifications on the tissue integration ability of PEEK to develop an ideal implant material.

Evolution of polyetheretherketone (PEEK) and titanium interbody devices for spinal procedures: a comprehensive review of the literature

INTRODUCTION

Interbody fusion is commonly utilized for arthrodesis and stability among patients undergoing spine surgery. Over the last few decades, interbody device materials, such as titanium and polyetheretherketone (PEEK), have been replacing traditional autografts and allografts for interbody fusion. As such, with the exponential growth of bioengineering, a large variety cage surface technologies exist. Different combinations of cage component materials and surface modifications have been created to optimize interbody constructs for surgical use. This review aims to provide a comprehensive overview of common surface technologies, their performance in the clinical setting, and recent modifications and material combinations.

MATERIALS AND METHODS

We performed a comprehensive review of the literature on titanium and PEEK as medical devices between 1964 and 2021. We searched five major databases, resulting in 4974 records. Articles were screened for inclusion manually by two independent reviewers, resulting in 237 articles included for review.

CONCLUSION

Interbody devices have rapidly evolved over the last few decades. Biomaterial and biomechanical modifications have allowed for continued design optimization. While titanium has a high osseointegrative capacity, it also has a high elastic modulus and is radio-opaque. PEEK, on the other hand, has a lower elastic modulus and is radiolucent, though PEEK has poor osseointegrative capacity. Surface modifications, material development advancements, and hybrid material devices have been utilized in search of an optimal spinal implant which maximizes the advantages and minimizes the disadvantages of each interbody material.

Covalently functionalized poly(etheretherketone) implants with osteogenic growth peptide (OGP) to improve osteogenesis activity

Polyetheretherketone (PEEK), as the most promising implant material for orthopedics and dental applications, has bone-like stiffness, excellent fatigue resistance, X-ray transparency, and near absence of immune toxicity. However, due to biological inertness, its bone conduction and bone ingrowth performance is limited. The surface modification of PEEK is an option to overcome these shortcomings and retain most of its favorable properties, especially when excellent osseointegration is desired. In this study, a simple reaction procedure was employed to bind the osteogenic growth peptide (OGP) on the surface of PEEK materials by covalent chemical grafting to construct a bioactive interface. The PEEK surface was activated by N,N′-disuccinimidyl carbonate (DSC) after hydroxylation, and then OGP was covalently grafted with amino groups. The functionalized surface of PEEK samples were characterized by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), water contact angle measurement and biological evaluation in vitro. OGP-functionalized PEEK surface significantly promoted the attachment, proliferation, alkaline phosphatase (ALP) activity and mineralization of pre-osteoblast cells (MC3T3-E1). The in vivo rat tibia implantation model is adopted and micro-CT analyses demonstrated that the OGP coating significantly promoted new bone formation around the samples. The in vitro and in vivo results reveal that the modification by covalent chemical functionalization with OGP on PEEK surface can augment new bone formation surrounding implants compared to bare PEEK and PEEK implant modified by covalently attached OGP is promising in orthopedic and dental applications.

Polyetheretherketone (PEEK), as the most promising implant material for orthopedics and dental applications, has bone-like stiffness, excellent fatigue resistance, X-ray transparency, and near absence of immune toxicity.

Surface Modification of Poly(ether ether ketone) through Friedel-Crafts Reaction for High Adhesion Strength

Poly(ether ether ketone) (PEEK) possesses attractive mechanical and thermal properties but demonstrates poor adhesion. To overcome this disadvantage, in this study, the surface modification of PEEK or PEEK-based carbon-fiber-reinforced thermoplastics (CFRTP) was performed through the Friedel-Crafts reaction and successive epoxidation. Under optimized reaction conditions, surface modification was achieved without surface deterioration, and epoxy groups were introduced. The progress of the Friedel-Crafts reaction and epoxidation was demonstrated by X-ray photoelectron spectroscopy measurements after fluorine labeling through thiol-en reaction and amine addition, respectively. The adhesive strength between CFRTP and epoxy adhesives was increased to 23.5 MPa, and cohesive fracture of epoxy adhesives, rather than interfacial peeling, occurred. In addition, compared with conventional plasma treatment, the durability of the modified surface and thickness of the modified surface layer increased. Therefore, we succeeded in modifying the surface properties through the epoxidation of the PEEK surface.

Synergistic effect of surface phosphorylation and micro-roughness on enhanced osseointegration ability of poly(ether ether ketone) in the rabbit tibia

This study was aimed to investigate the osseointegration ability of poly(ether ether ketone) (PEEK) implants with modified surface roughness and/or surface chemistry. The roughened surface was prepared by a sandblast method, and the phosphate groups on the substrates were modified by a two-step chemical reaction. The in vitro osteogenic activity of rat mesenchymal stem cells (MSCs) on the developed substrates was assessed by measuring cell proliferation, alkaline phosphatase activity, osteocalcin expression, and bone-like nodule formation. Surface roughening alone did not improve MSC responses. However, phosphorylation of smooth substrates increased cell responses, which were further elevated in combination with surface roughening. Moreover, in a rabbit tibia implantation model, this combined surface modification significantly enhanced the bone-to-implant contact ratio and corresponding bone-to-implant bonding strength at 4 and 8 weeks post-implantation, whereas modification of surface roughness or surface chemistry alone did not. This study demonstrates that combination of surface roughness and chemical modification on PEEK significantly promotes cell responses and osseointegration ability in a synergistic manner both in vitro and in vivo. Therefore, this is a simple and promising technique for improving the poor osseointegration ability of PEEK-based orthopedic/dental implants.

Bone-like apatite coating on functionalized poly(etheretherketone) surface via tailored silanization layers technique

Poly(etheretherketone) (PEEK) is a rigid semi-crystalline polymer with outstanding mechanical properties, bone-like stiffness and suitable biocompatibility that has attracted much interest as a biomaterial for orthopedic and dental implants. However, the bio-inert surface of PEEK limits its biomedical applications when direct osteointegration between the implants and the host tissue is desired. In this work, -PO4H2, -COOH and -OH groups were introduced on the PEEK surface by further chemical treatments of the vinyl-terminated silanization layers formed on the hydroxylation-pretreated PEEK surface. Both the surface-functionalized and pristine specimens were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and water contact angle measurements. When placed in 1.5 strength simulated body fluid (SBF) solution, apatite was observed to form uniformly on the functionalized PEEK surface and firmly attach to the substrate. The characterized results demonstrated that the coating was constituted by poorly crystallized bone-like apatite and the effect of surface functional groups on coating formation was also discussed in detail. In addition, in vitro biocompatibility of PEEK, in terms of pre-osteoblast cell (MC3T3-E1) attachment, spreading and proliferation, was remarkably enhanced by the bone-like apatite coating. Thus, this study provides a method to enhance the bioactivity of PEEK and expand its applications in orthopedic and dental implants.

Enhanced osteoblast cells adhesion, spreading, and proliferation to surface-carboxylated poly(etheretherketone)

Poly(etheretherketone) is a rigid semicrystalline thermoplastic that combines excellent mechanical properties, broad chemical resistance, and bone-like stiffness, and is widely used in biomedical fields. However, the hydrophobic bio-inert surface of poly(etheretherketone) tends to hinder its biomedical applications when direct osteointegration between the implants and the host tissue is desired. In this investigation, poly(etheretherketone) surface was functionalized by a method with chemistry analogous to the formation of organosilane self-assembled monolayers on glass or silicon. First, poly(etheretherketone) surface activation with selective carbonyl reduction introduces surface hydroxylation. And then treatment of the hydroxylation-pretreated poly(etheretherketone) samples with a substituted organosilane solution forms the carboxyl (–COOH) functional surface layers. The modified surfaces were characterized using X-ray photoelectron spectroscopy, water contact angle measurements, differential scanning calorimetry, X-ray diffraction, and surface profiler. The effect of cell adhesion, spreading, and proliferation on each specimen was investigated. Pre-osteoblast cells (MC3T3-E1) adhesion, spreading, and proliferation were improved remarkably on surface-carboxylated poly(etheretherketone). Poly(etheretherketone) modified with –COOH on its surface has potential use in orthopedic or dental implants.

Protein repellent hydrophilic grafts prepared by surface-initiated atom transfer radical polymerization from polypropylene

Cross-linked hydrophilic poly(PEGMA) grafts (red) on PP repel fluorescence labelled insulin (green) when the PP plate is pulled out of the protein solution.

Tailoring of poly(ether ether ketone) surface properties via surface-initiated atom transfer radical polymerization

The interfacial properties of commercial poly(ether ether ketone) (PEEK) have been tailored by tethering polymeric brushes to the PEEK surface via surface-initiated atom transfer radical polymerization (SI-ATRP). The immobilization of an ATRP initiator on the PEEK surface was achieved by an unprecedented simple two-step wet chemical method. The keto groups at the PEEK surface were first wet chemically reduced to hydroxyl groups, and then 2-bromoisobutyryl groups were covalently anchored at the PEEK surface as ATRP initiator. SI-ATRP was performed at these functionalized PEEK surfaces with the three different monomers: potassium 3-(methacryloyloxy)propane-1-sulfonate (MPS), monomethoxy-terminated oligo(ethylene glycol)methacrylate (MeOEGMA), and N-isopropylacrylamide (NIPAAm). Atomic force microscopy, scanning electron microscopy, attenuated total reflection infrared spectroscopy, water contact angle measurements, and X-ray photoelectron spectroscopy ascertained the successful grafting of these polymer brushes at the PEEK surface. These brush-modified PEEK surfaces exhibited fully the physiochemical properties of the respective polymer brush: the surface with polyMPS brush showed selective staining by electrostatic interaction, while the polyMeOEGMA-modified surface was biorepellent. The surface modified with polyNIPAAm brush demonstrated a thermally responsive polarity change.

Adhesion and growth of CaCo2 cells on surface-modified PEEK substrata

A series of surface-functionalized poly(ether ether ketone) (PEEK) films has been prepared by selective wet-chemistry; they are hydroxylated polymer (PEEK-OH) obtained by reduction, aminated polymer (PEEK-[]-NH2) prepared by coupling a diisocyanate reagent to PEEK-OH (PEEK-[]-NCO) followed by hydrolysis, and carboxylated and aminocarboxylated polymers (PEEK-[]-GABA and PEEK-Lysine) resulting from the coupling of aminoacids to PEEK-[]-NCO. The aminated and carboxylated substrata promoted the adhesion and growth of CaCo2 cells in the presence of serum. Fibronectin (FN), an extra-cellular matrix protein, has been covalently fixed and/or adsorbed on various PEEK substrata, in the presence or not of a polymeric surfactant (Pluronic F68). The performances of the FN-grafted substrata (PEEK-[]-FN(1) and PEEK-[]-FN(2)) were significantly higher than those of reference substrata simply coated with FN (PEEK-OH(+FN)(1) and (2), PEEK-[]-NH2(+FN)(1) and (2)), considering the adhesion and spreading of CaCo2 cells in the absence of serum. Moreover, the stability of the adherent cells on the FN-adsorbed substrata dramatically depended on the experimental conditions applied during the PEEK coating with FN.

Fibronectin adsorption or/and covalent grafting on chemically modified PEEK film surfaces

Poly(ether ether ketone) (PEEK) films were chemically modified, by surface wet chemistry, into PEEK-OH, PEEK-NH2, and PEEK-NCO. Fibronectin (FN) adsorption, in the presence or absence of two non-ionic surfactants, was compared onto PEEK, PEEK-OH, and PEEK-NH2 on which the protein can only be adsorbed, and onto PEEK-NCO on which FN could be covalently grafted. The amounts of FN present on the various supports were assayed by ELISA and LSC (with 125I-labeled FN). The remarkable effect of Pluronic F68 in preventing non-specific protein adhesion on the less hydrophilic surfaces was pointed out. Accordingly, a procedure could be proposed that allows minimal FN adhesion vs FN fixation on PEEK-NCO. The resulting PEEK-FN film, which immobilized 120-150 ng FN cm(-2), constitutes a new substratum for cell cultivation.

Synthesis and evaluation of RGD peptidomimetics aimed at surface bioderivatization of polymer substrates

Several RGD peptidomimetics have been prepared, in a convergent way, from the common ortho-aminotyrosine template (O-substituted with an anchorage-arm or a methyl group, and alpha N-substituted with a fluorine tag for XPS analysis), and various omega-aminoacid derivatives. The most flexible compounds have shown a biological activity similar to that of the peptide reference (RGDS) in the platelet aggregation test. The compound 16a could be fitted (by modelisation) with DMP 728 and c(RGDfV), two cyclic peptides that are good ligands of integrins. The compound 16b has been covalently fixed on the surface of a poly(ethylene terephthalate) membrane used as support for mammalian cell cultivation.