Influence of nitrogen plasma treatment on the wettability of polyetheretherketone and deposited chitosan layers

Biomaterials as Implants in the Orthopedic Field for Regenerative Medicine: Metal versus Synthetic Polymers

Patients suffering bone fractures in different parts of the body require implants that will enable similar function to that of the natural bone that they are replacing. Joint diseases (rheumatoid arthritis and osteoarthritis) also require surgical intervention with implants such as hip and knee joint replacement. Biomaterial implants are utilized to fix fractures or replace parts of the body. For the majority of these implant cases, either metal or polymer biomaterials are chosen in order to have a similar functional capacity to the original bone material. The biomaterials that are employed most often for implants of bone fracture are metals such as stainless steel and titanium, and polymers such as polyethene and polyetheretherketone (PEEK). This review compared metallic and synthetic polymer implant biomaterials that can be employed to secure load-bearing bone fractures due to their ability to withstand the mechanical stresses and strains of the body, with a focus on their classification, properties, and application.

Deposition of Chitosan on Plasma-Treated Polymers-A Review

Materials for biomedical applications often need to be coated to enhance their performance, such as their biocompatibility, antibacterial, antioxidant, and anti-inflammatory properties, or to assist the regeneration process and influence cell adhesion. Among naturally available substances, chitosan meets the above criteria. Most synthetic polymer materials do not enable the immobilization of the chitosan film. Therefore, their surface should be altered to ensure the interaction between the surface functional groups and the amino or hydroxyl groups in the chitosan chain. Plasma treatment can provide an effective solution to this problem. This work aims to review plasma methods for surface modification of polymers for improved chitosan immobilization. The obtained surface finish is explained in view of the different mechanisms involved in treating polymers with reactive plasma species. The reviewed literature showed that researchers usually use two different approaches: direct immobilization of chitosan on the plasma-treated surface or indirect immobilization by additional chemistry and coupling agents, which are also reviewed. Although plasma treatment leads to remarkably improved surface wettability, this was not the case for chitosan-coated samples, where a wide range of wettability was reported ranging from almost superhydrophilic to hydrophobic, which may have a negative effect on the formation of chitosan-based hydrogels.

Characteristics of Hybrid Bioglass-Chitosan Coatings on the Plasma Activated PEEK Polymer

Polyetheretherketone (PEEK) is a biocompatible, chemically and physically stable radiolucent polymer that exhibits a similar elastic modulus to the normal human bone, making it an attractive orthopedic implant material. However, PEEK is biologically inert, preventing strong enough bonding with the surrounding bone tissue when implanted in vivo. Surface modification and composite preparation are the two main strategies for the improvement of the bioactivity of PEEK. In this study, the plasma activated PEEK surfaces with the embedded bioglass, chitosan, and bioglass-chitosan mixed layers applying from the solution dip-coating technique were investigated. The most prominent factors affecting the coating biocompatibility are strictly connected with the composition of its outer surface (its charge and functional groups), hydrophilic-hydrophobic character, wettability and surface free energy, and topography (size of pores/substructures, roughness, stiffness), as well as the personal characteristics of the patient. The obtained surfaces were examined in terms of wettability and surface-free energy changes. Additionally, FTIR (Fourier Transformation Infrared Spectrometry) and SIMS (Secondary Ion Mass Spectrometry) were applied to establish and control the coating composition. Simultaneously the structure of coatings was visualized with the aid of SEM (Scanning Electron Microscopy). Finally, the obtained systems were incubated in SBF (Simulated Body Fluid) to verify the modifications' influence on the bioactivity/biocompatibility of the PEEK surface. Different structures with variable compositions, as well as changes of the wettability, were observed depending on the applied modification. In addition, the incubation in SBF suggested that the bioglass-chitosan ratio influenced the formation of apatite-like structures on the modified PEEK surfaces.

Poly (Ether-Ether-Ketone) for Biomedical Applications: From Enhancing Bioactivity to Reinforced-Bioactive Composites-An Overview

The global orthopedic market is forecasted to reach US$79.5 billion by the end of this decade. Factors driving the increase in this market are population aging, sports injury, road traffic accidents, and overweight, which justify a growing demand for orthopedic implants. Therefore, it is of utmost importance to develop bone implants with superior mechanical and biological properties to face the demand and improve patients' quality of life. Today, metallic implants still hold a dominant position in the global orthopedic implant market, mainly due to their superior mechanical resistance. However, their performance might be jeopardized due to the possible release of metallic debris, leading to cytotoxic effects and inflammatory responses in the body. Poly (ether-ether-ketone) (PEEK) is a biocompatible, high-performance polymer and one of the most prominent candidates to be used in manufacturing bone implants due to its similarity to the mechanical properties of bone. Unfortunately, the bioinert nature of PEEK culminates in its diminished osseointegration. Notwithstanding, PEEK's bioactivity can be improved through surface modification techniques and by the development of bioactive composites. This paper overviews the advantages of using PEEK for manufacturing implants and addresses the most common strategies to improve the bioactivity of PEEK in order to promote enhanced biomechanical performance.

Dual-Functional Polyetheretherketone Surface with an Enhanced Osteogenic Capability and an Antibacterial Adhesion Property In Vitro by Chitosan Modification

A chitosan layer was covalently bonded to a polyetheretherketone (PEEK) surface using a simple facile self-assembly method to address inadequate biological activity and infection around the implant. The surface characterization, layer degradation, biological activity, and antibacterial adhesion properties of chitosan-modified PEEK (PEEK-CS) were studied. Through chitosan grafting, the surface morphology changed, the surface roughness increased, and the contact angle decreased significantly. PEEK-CS boosted cell adhesion, proliferation, increased alkaline phosphate activity, extracellular matrix mineralization, and expression of osteogenic genes. PEEK-CS demonstrated less adhesion to Porphyromonas gingivalis as well as less bacterial adhesion to P. gingivalis and Streptococcus mutans. According to our findings, chitosan modification significantly improved the osteogenic ability and antibacterial adhesion of PEEK in vitro.

A Method for the Immobilization of Chitosan onto Urinary Catheters

A method for the immobilization of an antibacterial chitosan coating to polymeric urinary medical catheters is presented. The method comprises a two-step plasma-treatment procedure, followed by the deposition of chitosan from the water solution. In the first plasma step, the urinary catheter is treated with vacuum-ultraviolet radiation to break bonds in the polymer surface film and create dangling bonds, which are occupied by hydrogen atoms. In the second plasma step, polymeric catheters are treated with atomic oxygen to form oxygen-containing surface functional groups acting as binding sites for chitosan. The presence of oxygen functional groups also causes a transformation of the hydrophobic polymer surface to hydrophilic, thus enabling uniform wetting and improved adsorption of the chitosan coating. The wettability was measured by the sessile-drop method, while the surface composition and structure were measured by X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. Non-treated samples did not exhibit successful chitosan immobilization. The effect of plasma treatment on immobilization was explained by noncovalent interactions such as electrostatic interactions and hydrogen bonds.

Application of biomolecules modification strategies on PEEK and its composites for osteogenesis and antibacterial properties

As orthopedic and dental implants, polyetheretherketone (PEEK) is expected to be a common substitute material of titanium (Ti) and its alloys due to its good biocompatibility, chemical stability, and elastic modulus close to that of bone tissue. It could avoid metal allergy and bone resorption caused by the stress shielding effect of Ti implants, widely studied in the medical field. However, the lack of biological activity is not conducive to the clinical application of PEEK implants. Therefore, the surface modification of PEEK has increasingly become one of the research hotspots. Researchers have explored various biomolecules modification methods to effectively enhance the osteogenic and antibacterial activities of PEEK and its composites. Therefore, this review mainly summarizes the recent research of PEEK modified by biomolecules and discusses the further research directions to promote the clinical transformation of PEEK implants.

Surface Properties of Plasma-Activated Chitosan Foils

Thin films of chitosan are often deposited on various surfaces to provide them with antiseptic properties. In the presented research, chitosan foils were obtained using two methods and treated with nitrogen plasma. The obtained materials were characterized by measuring the wettability of the test liquids, and the apparent surface free energy was calculated using the Tadmor equilibrium contact angles. The surface topography was characterized using optical profilometry and SEM. On the other hand, the effect of plasma on surface groups was investigated using the FTIR-ATR technique. Plasma activation of the surface increases the polarity of the surface. This is observed in the changed surface roughness and the share of functional groups on the surface.

The antibacterial and wear-resistant nano-ZnO/PEEK composites were constructed by a simple two-step method

Although the polyether ether ketone (PEEK) has excellent comprehensive properties, its non-antibacterial and low wear-resistant limit the wide application in the field of artificial joint materials. In this paper, Nano-ZnO was generated in situ on the surface of PEEK powder by one-step hydrothermal method, which improved the binding force of Nano-ZnO and PEEK matrix. Then the PEEK-based nanocomposites were prepared by melt blending with the synthesized Nano-ZnO-PEEK powders and PEEK powders. The microstructure, mechanical, biological and tribological properties of PEEK-based nanocomposites were studied. The results showed that the compressive strength of PEEK-based nanocomposites can reach up to 319.2 ± 2.4 MPa. Both PEEK and PEEK-based nanocomposites were non-toxic to cells. Meanwhile, PEEK-based nanocomposites showed good antibacterial activity against E.coli and Staphylococcus aureus, and the antibacterial activity was better with the increase of Nano-ZnO content. In addition, when the Nano-ZnO content was 5%, the wear rate of PEEK-based nanocomposites was about 68% lower than that of pure PEEK materials. Thus, PEEK-based nanocomposites has a dual function of good antibacterial property and excellent wear resistance.

Effect of Extreme Ultraviolet (EUV) Radiation and EUV Induced, N2 and O2 Based Plasmas on a PEEK Surface's Physico-Chemical Properties and MG63 Cell Adhesion

Polyetheretherketone (PEEK), due to its excellent mechanical and physico-chemical parameters, is an attractive substitute for hard tissues in orthopedic applications. However, PEEK is hydrophobic and lacks surface-active functional groups promoting cell adhesion. Therefore, the PEEK surface must be modified in order to improve its cytocompatibility. In this work, extreme ultraviolet (EUV) radiation and two low-temperature, EUV induced, oxygen and nitrogen plasmas were used for surface modification of polyetheretherketone. Polymer samples were irradiated with 100, 150, and 200 pulses at a 10 Hz repetition rate. The physical and chemical properties of EUV and plasma modified PEEK surfaces, such as changes of the surface topography, chemical composition, and wettability, were examined using atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and goniometry. The human osteoblast-like MG63 cells were used for the analysis of cell viability and cell adhesion on all modified PEEK surfaces. EUV radiation and two types of plasma treatment led to significant changes in surface topography of PEEK, increasing surface roughness and formation of conical structures. Additionally, significant changes in the chemical composition were found and were manifested with the appearance of new functional groups, incorporation of nitrogen atoms up to ~12.3 at.% (when modified in the presence of nitrogen), and doubling the oxygen content up to ~25.7 at.% (when modified in the presence of oxygen), compared to non-modified PEEK. All chemically and physically changed surfaces demonstrated cyto-compatible and non-cytotoxic properties, an enhancement of MG63 cell adhesion was also observed.

Evaluation of the Grafting Efficacy of Active Biomolecules of Phosphatidylcholine and Type I Collagen on Polyether Ether Ketone: In Vitro and In Vivo

Biomolecule grafting on polyether ether ketone (PEEK) was used to improve cell affinity caused by surface inertness. This study demonstrated the sequence-polished (P) and sulfonated (SA) PEEK modification to make a 3D structure, active biomolecule graftings through PEEK silylation (SA/SI) and then processed with phosphatidylcholine (with silylation of SA/SI/PC; without SA/PC) and type I collagen (COL I, with silylation of SA/SI/C; without SA/C). Different modified PEEKs were implanted for 4, 8, and 12 weeks for histology. Sulfonated PEEK of SA showed the surface roughness was significantly increased; after the silylation of SA/SI, the hydrophilic nature was remarkably improved. The biomolecules were effectively grafted through silylation, and the cells showed improved attachment after 1 h. Furthermore, the SA/SI/PC group showed good in vitro mineralization. The new bone tissues were integrated into the 3D porous structures of SA/SI/PC and SA/SI/C in vivo making PEEK a potential alternative to metals in orthopedic implants.

What Can You Learn about Apparent Surface Free Energy from the Hysteresis Approach?

The apparent surface free energy is one of the most important quantities in determining the surface properties of solids. So far, no method of measuring this energy has been found. The essence of contact angle measurements is problematic. Contact angles should be measured as proposed by Young, i.e., in equilibrium with the liquid vapors. This type of measurement is not possible because within a short time, the droplet in the closed chamber reaches equilibrium not only with vapors but also with the liquid film adsorbed on the tested surface. In this study, the surface free energy was determined for the plasma-activated polyoxymethylene (POM) polymer. Activation of the polymer with plasma leads to an increase in the value of the total apparent surface free energy. When using the energy calculations from the hysteresis based approach (CAH), it should be noted that the energy changes significantly when it is calculated from the contact angles of a polar liquid, whereas being calculated from the angles of a non-polar liquid, the surface activation with plasma changes its value slightly.

Synthetic Polymeric Materials for Bone Replacement

Some treatment options available to repair bone defects are the use of autogenous and allogeneic bone grafts. The drawback of the first one is the donor site’s limitation and the need for a second operation on the same patient. In the allograft method, the problems are associated with transmitted diseases and high susceptibility to rejection. As an alternative to biological grafts, polymers can be used in bone repair. Some polymers used in the orthopedic field are poly(methyl methacrylate), poly(ether-ether-ketone), and ultra-high molecular weight polyethylene (UHMWPE). UHMWPE has drawn much attention since it combines low friction coefficient and high wear and impact resistance. However, UHMWPE is a bioinert material, which means that it does not interact with the bone tissue. UHMWPE composites and nanocomposites with hydroxyapatite (HA) are widely studied in the literature to mitigate these issues. HA is the main component of the inorganic phase in the natural bone, and the addition of this bioactive filler to the polymeric matrix aims to mimic bone composition. This brief review discusses some polymers used in orthopedic applications, focusing on the UHMWPE/HA composites as a potential bone substitute.

Microstructure, mechanical properties and heat-resistance properties of bismaleimide composites modified synergistically by alumina and two kinds of thermoplastic resins

Al2O3-PES-SPEEK/MBAE composites has been prepared, polymer matrix (MBAE) was obtained with 4,4’-diamino diphenyl methane bismaleimide (BMI) as reaction monomer, 3,3’-diallyl bisphenol A (BBA) and bisphenol A diallyl ether (BBE) as the reactive diluent, and two kinds of thermal plastic resins (polyether sulfone PES and sulfonated poly(ether ether ketone) SPEEK) as the reinforcements, nano-alumina (Al2O3) prepared by Sol–Gel method as the filler. The microstructure of SPEEK, Al2O3 and the composites were characterized, the mechanical properties and heat resistance of the composites were also studied and analyzed. The results reveal that there are sulfonic acid groups in SPEEK structure and the microstructure is more loose, and the degree of sulfonation is about 41.3%. Al2O3 is a nano-sized short-fibrous crystal with hydroxyl groups on its surface. The micromorphology of Al2O3-PES-SPEEK/MBAE composites show that the proper amount of PES, SPEEK and Al2O3 are uniformly dispersed in the matrix resin, which improves the fracture surface morphology of the composite, the shape of the section is fish scale and the fracture cracks are irregular and divergent, and the composites are ductile fracture. The mechanical properties indicate that the flexural strength, flexural modulus and impact strength of the composite is the maximum value 172.9 MPa, 4.7 GPa and 21.4 kJ/m2, which is 73.1%, 74.1% and 125.3%, higher than the matrix resin, respectively, when the PES content is 3 wt%, 2 wt% SPEEK and 3 wt% Al2O3 in the composite. At this time, the thermal decomposition temperature of the composite material is 453.5°C, which is 15.4°C higher than that of the matrix resin, and the mechanical properties and heat-resistance properties of the Al2O3-PES-SPEEK/MBAE composite are significantly improved.

Study of High-Density Polyethylene (HDPE) Kinetics Modification Treated by Dielectric Barrier Discharge (DBD) Plasma

In this work, the plasma was used in the dielectric barrier discharge (DBD) technique for modifying the high-density polyethylene (HDPE) surface. The treatments were performed via argon or oxygen, for 10 min, at a frequency of 820 Hz, voltage of 20 kV, 2 mm distance between electrodes, and atmospheric pressure. The efficiency of the plasma was determined through the triple Langmuir probe to check if it had enough energy to promote chemical changes on the material surface. Physicochemical changes were diagnosed through surface characterization techniques such as contact angle, attenuated total reflection to Fourier transform infrared spectroscopy (ATR-FTIR), X-ray excited photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Plasma electronics temperature showed that it has enough energy to break or form chemical bonds on the material surface, impacting its wettability directly. The wettability test was performed before and after treatment through the sessile drop, using distilled water, glycerin, and dimethylformamide, to the profile of surface tensions by the Fowkes method, analyzing the contact angle variation. ATR-FTIR and XPS analyses showed that groups and bonds were altered or generated on the surface when compared with the untreated sample. The AFM showed a change in roughness, and this directly affected the increase of wettability.

Inhibition of hyperplasia during the implantation of the puborectalis-like artificial anal sphincter

OBJECTIVES

This study aims to extend the implantation lifetime of the puborectalis-like artificial anal sphincter by inhibiting the occurrence of hyperplasia following the implantation process.

METHOD

A new transmission structure was designed inside the puborectalis-like artificial anal sphincter to generate an adequate torque to maintain the feces, even if hyperplasia developed around the prosthetic sphincter. An outer shell was added to the prosthetic sphincter to decelerate the occurrence of hyperplasia on the outer shell side. Medical titanium alloy was tested to replace the nylon-12 prosthetic sphincter, while polyetheretherketone was used for the construction of the power supply unit in the puborectalis-like artificial anal sphincter system instead of nylon-12. In vivo experiments were conducted to evaluate all the methods presented in this study with 10 Pa Ma piglets, 1 domestic pig, and 1 beagle dog during the past 2 years.

RESULTS

Compared with the previous prosthetic sphincter that was equipped with a fixed-axle gear transmission, the new transmission structure is equipped with a planet-gear train managed to generate a prosthetic sphincter output with a 53% larger torque but with the same size and type of motor as that used previously and increase the implantation lifetime by 56%. After the replacement of the nylon-12, the new prosthetic sphincter made of medical titanium alloy succeeded in extending the implanted lifetime by 83%. In addition, the lifetime was increased by 143%, when an outer shell was added to the prosthetic sphincter. Polyetheretherketone significantly decreased the growth rate of hyperplasia around the power supply unit by 44% after the replacement of the power supply unit material. After the combination of all the improvements, the longest implantation lifetime of the puborectalis-like artificial anal sphincter during the in vivo experiments was 7 months and 10 days, which reflected an improvement of 249%.

CONCLUSION

All methods posted in this study were evaluated to be effective to prolong the implantation lifetime of the puborectalis-like artificial anal sphincter. Among the methods proposed, the most effective was the addition of the outer shell to the puborectalis-like artificial anal sphincter. The least effective method was the improvement of the transmission structure. Medical titanium alloy and polyetheretherketone were good replacements for nylon-12 that managed to extend the implantation lifetime and yield a moderate improvement.

Wettability and Interfacial Properties of Carbon Fiber and Poly(ether ether ketone) Fiber Hybrid Composite

Studies on carbon fiber (CF)/poly(ether ether ketone) (PEEK) fiber hybrid textiles were initiated several decades ago because their flexibility and conformability make them a promising alternative to traditional prepregs. The adhesion between the CFs and PEEK is mostly controlled by their inherent surface properties and mutual wettability. However, details of these properties remain largely unknown, especially those of PEEK. Therefore, to determine the surface and interfacial properties of these fibers, we performed a comprehensive study and characterized their surface topography (atomic force microscopy, scanning electron microscopy), surface chemistry [X-ray photoelectron spectrometry (XPS), acid-base titration], surface energies (wetting tests, acid-base approach), and interfacial mechanical properties [droplet test, interfacial shear strength (IFSS)]. These experiments were complemented by a theoretical approach to the prediction of the surface energy components (parachor) and contact angles of PEEK. We found good agreement between the results obtained by XPS and wetting tests (base-to-acid surface energy component ratio), as well as between the predicted and measured surface energy and contact angles. The results highlight the consistency and reliability of the proposed methodology. We found that both CFs and PEEK fibers appear to be smooth at the nanoscale and have large dispersive and basic surface energy components. The IFSS of CF/PEEK is significantly higher (44.87 ± 5.76 MPa) compared to that of other thermoplastic systems. The findings not only demonstrate the potential of CF/PEEK hybrid textiles but also emphasize the need to further increase the compatibility between CFs and PEEK fibers by increasing the acidic component of CF surfaces. Surface treatments and the design of a suitable sizing are potential methods to achieve this objective in future studies.

Wetting Properties of Polyetheretherketone Plasma Activated and Biocoated Surfaces

Polyetheretherketone (PEEK) biomaterial is a polymer which has been widely used since the early 90s as a material for human bone implant preparations. Nowadays it is increasingly used due to its high biocompatibility and easily modeling, as well as better mechanical properties and price compared to counterparts made of titanium or platinum alloys. In this paper, air low-temperature and pressure plasma was used to enhance PEEK adhesive properties as well as surface sterilization. On the activated polymeric carrier, biologically-active substances have been deposited with the Langmuir-Blodgett technique. Thereafter, the surface was characterized using optical profilometry, and wettability was examined by contact angle measuring. Next, the contact angle hysteresis (CAH) model was used to calculate the surface free energy of the modified surface of PEEK. The variations of wettability and surface free energy were observed depending on the deposited monolayer type and its components.

Surface bioactivation of PEEK by neutral atom beam technology

Polyetheretherketone (PEEK) is an alternative to metallic implants and a material of choice in many applications, including orthopedic, spinal, trauma, and dental. While titanium (Ti) and Ti-alloys are widely used in many intraosseous implants due to its biocompatibility and ability to osseointegrate, negatives include stiffness which contributes to shear stress, radio-opacity, and Ti-sensitivity. Many surgeons prefer to use PEEK due to its biocompatibility, similar elasticity to bone, and radiolucency, however, due to its inert properties, it fails to fully integrate with bone. Accelerated Neutral Atom Beam (ANAB) technology has been successfully employed to demonstrate enhanced bioactivity of PEEK both in vitro and in vivo. In this study, we further characterize surfaces of PEEK modified by ANAB as well as elucidate attachment and genetic effects of dental pulp stem cells (DPSC) exposed to these surfaces. ANAB modification resulted in decreased contact angle at 72.9 ± 4.5° as compared to 92.4 ± 8.5° for control (p < 0.01) and a decreased average surface roughness, however with a nano-textured surface profile. ANAB treatment also increased the ability of DPSC attachment and proliferation with considerable genetic differences showing earlier progression towards osteogenic differentiation. This surface modification is achieved without adding a coating or changing the chemical composition of the PEEK material. Taken together, we show that ANAB processing of PEEK surface enhances the bioactivity of implantable medical devices without an additive or a coating.

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PEEK is a material of choice for biomaterials except that it is inert and does not integrate with bone.

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Neutral atom beam technology (ANAB) is a surface modification technique that modifies the surface at a nano-scale level and makes the surface more hydrophilic.

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Increased cell attachment and proliferation is seen on ANAB-treated PEEK.

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Dental pulp stem cells differentiate towards osteoblast when grown on ANAB-treated PEEK.

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ANAB makes PEEK bioactive.