Biosensitive and antibacterial coatings on metallic material for medical applications

Corrosion Resistance of Biodegradable Zinc Surfaces Enhanced by UV-Grafted Polydimethylsiloxane Coating

Improved living conditions have led to an increase in life expectancy worldwide. However, as people age, the risk of vascular disease tends to increase due to the accumulation and buildup of plaque in arteries. Vascular stents are used to keep blood vessels open. Biodegradable stents are designed to provide a temporary support vessel that gradually degrades and is absorbed by the body, leaving behind healed blood vessels. However, biodegradable metals can suffer from reduced mechanical strength and/or inflammatory response, both of which can affect the rate of corrosion. Therefore, it is essential to achieve a controlled and predictable degradation rate. Here, we demonstrate that the corrosion resistance of biodegradable Zn surfaces is improved by electroless deposition of zinc hydroxystannate followed by UV-grafting with silicone oil (PDMS). Potentiodynamic polarization, electrochemical impedance spectroscopy, respiratory kinetic measurements, and long-term immersion in three simulated body fluids were applied. Although zinc hydroxystannate improves the corrosion resistance of Zn to some extent, it introduces a high surface area with hydroxyl units used to UV-graft PDMS molecules. Our results demonstrate that hydrophobic PDMS causes a 3-fold reduction in corrosion of Zn-based materials in biological environments and reduces cytotoxicity through the uncontrolled release of Zn ions.

Electrophoretic Deposition of 58S Bioactive Glass- Polymer Composite Coatings on 316L Stainless Steel: An Optimization for Corrosion, Bioactivity, and Cytocompatibility

This study presents a facile fabrication of 58S bioactive glass (BG)-polymer composite coatings on a 316L stainless steel (SS) substrate using the electrophoretic deposition technique. The suspension characteristics and deposition kinetics of BG, along with three different polymers, namely ethylcellulose (EC), poly(acrylic acid) (PAA), and polyvinylpyrrolidone (PVP), have been utilized to fabricate the coatings. Among all coatings, 58S BG and EC polymers are selected as the final composite coating (EC6) owing to their homogeneity and good adhesion. EC6 coating exhibits a thickness of ∼18 μm and an average roughness of ∼2.5 μm. Herein, EC6 demonstrates better hydroxyapatite formation compared to PAA and PVP coatings in simulated body fluid-based mineralization studies for a period of 28 days. Corrosion studies of EC6 in phosphate-buffered saline further confirm the higher corrosion resistance properties after 14 days. In vitro cytocompatibility studies using human placental mesenchymal stem cells demonstrate an increase in cellular viability, attachment, and higher proliferation compared to the bare SS substrate. EC6 coatings promote osteogenic differentiation, which is confirmed via the upregulation of the OPN and OCN genes. Moreover, the EC6 sample exhibits improved antibacterial properties against Escherichia coli and Staphylococcus aureus compared to the uncoated ones. The findings of this work emphasize the potential of electrophoretically fabricated BG-EC composite coatings on SS substrates for orthopedic applications.

Fibronectin Conformations after Electrodeposition onto 316L Stainless Steel Substrates Enhanced Early-Stage Osteoblasts' Adhesion but Affected Their Behavior

The implantation of metallic orthopedic prostheses is increasingly common due to an aging population and accidents. There is a real societal need to implement new metal implants that combine durability, good mechanical properties, excellent biocompatibility, as well as affordable costs. Since the functionalization of low-cost 316L stainless steel substrates through the successive electrodeposition of a polypyrrole film (PPy) and a calcium phosphate deposit doped with silicon was previously carried out by our labs, we have also developed a bio-functional coating by electrodepositing or oxidating of fibronectin (Fn) coating. Fn is an extracellular matrix glycoprotein involved in cell adhesion and differentiation. Impacts of either electrodeposition or oxidation on the structure and functionality of Fn were first studied. Thus, electrodeposition is the technique that permits the highest deposition of fibronectin, compared to adsorption or oxidation. Furthermore, electrodeposition seems to strongly modify Fn conformation by the formation of intermingled long fibers, resulting in changes to the accessibility of the molecular probes tested (antibodies directed against Fn whole molecule and Fn cell-binding domain). Then, the effects of either electrodeposited Fn or oxidized Fn were validated by the resulting pre-osteoblast behavior. Electrodeposition reduced pre-osteoblasts' ability to remodel Fn coating on supports because of a partial modification of Fn conformation, which reduced accessibility to the cell-binding domain. Electrodeposited Fn also diminished α5 integrin secretion and clustering along the plasma membrane. However, the N-terminal extremity of Fn was not modified by electrodeposition as demonstrated by Staphylococcus aureus attachment after 3 h of culture on a specific domain localized in this region. Moreover, the number of pre-osteoblasts remains stable after 3 h culture on either adsorbed, oxidized, or electrodeposited Fn deposits. In contrast, mitochondrial activity and cell proliferation were significantly higher on adsorbed Fn compared with electrodeposited Fn after 48 h culture. Hence, electro-deposited Fn seems more favorable to pre-osteoblast early-stage behavior than during a longer culture of 24 h and 48 h. The electrodeposition of matrix proteins could be improved to maintain their bio-activity and to develop this promising, fast technique to bio-functionalize metallic implants.

3D printing metal implants in orthopedic surgery: Methods, applications and future prospects

Background

Currently, metal implants are widely used in orthopedic surgeries, including fracture fixation, spinal fusion, joint replacement, and bone tumor defect repair. However, conventional implants are difficult to be customized according to the recipient's skeletal anatomy and defect characteristics, leading to difficulties in meeting the individual needs of patients. Additive manufacturing (AM) or three-dimensional (3D) printing technology, an advanced digital fabrication technique capable of producing components with complex and precise structures, offers opportunities for personalization.

Methods

We systematically reviewed the literature on 3D printing orthopedic metal implants over the past 10 years. Relevant animal, cellular, and clinical studies were searched in PubMed and Web of Science. In this paper, we introduce the 3D printing method and the characteristics of biometals and summarize the properties of 3D printing metal implants and their clinical applications in orthopedic surgery. On this basis, we discuss potential possibilities for further generalization and improvement.

Results

3D printing technology has facilitated the use of metal implants in different orthopedic procedures. By combining medical images from techniques such as CT and MRI, 3D printing technology allows the precise fabrication of complex metal implants based on the anatomy of the injured tissue. Such patient-specific implants not only reduce excessive mechanical strength and eliminate stress-shielding effects, but also improve biocompatibility and functionality, increase cell and nutrient permeability, and promote angiogenesis and bone growth. In addition, 3D printing technology has the advantages of low cost, fast manufacturing cycles, and high reproducibility, which can shorten patients' surgery and hospitalization time. Many clinical trials have been conducted using customized implants. However, the use of modeling software, the operation of printing equipment, the high demand for metal implant materials, and the lack of guidance from relevant laws and regulations have limited its further application.

Conclusions

There are advantages of 3D printing metal implants in orthopedic applications such as personalization, promotion of osseointegration, short production cycle, and high material utilization. With the continuous learning of modeling software by surgeons, the improvement of 3D printing technology, the development of metal materials that better meet clinical needs, and the improvement of laws and regulations, 3D printing metal implants can be applied to more orthopedic surgeries.

The translational potential of this paper

Precision, intelligence, and personalization are the future direction of orthopedics. It is reasonable to believe that 3D printing technology will be more deeply integrated with artificial intelligence, 4D printing, and big data to play a greater role in orthopedic metal implants and eventually become an important part of the digital economy. We aim to summarize the latest developments in 3D printing metal implants for engineers and surgeons to design implants that more closely mimic the morphology and function of native bone.

Engineered and Durable Antimicrobial Polymer via Controllable Immobilization of Ionic Liquids onto the Poly(lactic acid) Chains

Nowadays, the development of effective modification methods for PLA has gained significant interest because of the wide application of antimicrobial PLA materials in the medical progress. Herein, the ionic liquid (IL) 1-vinyl-3-butylimidazolium bis(trifluoromethylsulfonyl)imide, has been grafted onto the PLA chains successfully in the PLA/IL blending films via electron beam (EB) radiation for the miscibility between PLA and IL. It was found that the existence of IL in the PLA matrix can significantly improve the chemical stability under EB radiation. The Mn of PLA-g-IL copolymer did not change obviously but was just decreased from 6.80 × 104 g/mol to 5.20 × 104 g/mol after radiation with 10 kGy. The obtained PLA-g-IL copolymers showed excellent filament forming property during electrospinning process. The spindle structure on the nanofibers can be completely eliminated after feeding only 0.5 wt % ILs for the improvement of ionic conductivity. Specially, the prepared PLA-g-IL nonwovens exhibited outstanding and durable antimicrobial activity for the enrichment of immobilized ILs on the nanofiber surface. This work provides a feasible strategy to realize the modification of functional ILs onto PLA chains with low EB radiation doses, which may have huge potential application in the medical and packaging industry.

Nanoscale Morphologies on the Surface of 3D-Printed Titanium Implants for Improved Osseointegration: A Systematic Review of the Literature

Three-dimensional (3D) printing is serving as the most promising approach to fabricate personalized titanium (Ti) implants for the precise treatment of complex bone defects. However, the bio-inert nature of Ti material limits its capability for rapid osseointegration and thus influences the implant lifetime in vivo. Despite the macroscale porosity for promoting osseointegration, 3D-printed Ti implant surface morphologies at the nanoscale have gained considerable attention for their potential to improve specific outcomes. To evaluate the influence of nanoscale surface morphologies on osseointegration outcomes of 3D-printed Ti implants and discuss the available strategies, we systematically searched evidence according to the PRISMA on PubMed, Embase, Web of Science, and Cochrane (until June 2022). The inclusion criteria were in vivo (animal) studies reporting the osseointegration outcomes of nanoscale morphologies on the surface of 3D-printed Ti implants. The risk of bias (RoB) was assessed using the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE's) tool. The quality of the studies was evaluated using the Animal Research: Reporting of In Vivo Experiments (ARRIVE) guidelines. (PROSPERO: CRD42022334222). Out of 119 retrieved articles, 9 studies met the inclusion criteria. The evidence suggests that irregular nano-texture, nanodots and nanotubes with a diameter of 40-105nm on the surface of porous/solid 3D-printed Ti implants result in better osseointegration and vertical bone ingrowth compared to the untreated/polished ones by significantly promoting cell adhesion, matrix mineralization, and osteogenic differentiation through increasing integrin expression. The RoB was low in 41.1% of items, unclear in 53.3%, and high in 5.6%. The quality of the studies achieved a mean score of 17.67. Our study demonstrates that nanostructures with specific controlled properties on the surface of 3D-printed Ti implants improve their osseointegration. However, given the small number of studies, the variability in experimental designs, and lack of reporting across studies, the results should be interpreted with caution.

Enhancement of Antibacterial Properties, Surface Morphology and In Vitro Bioactivity of Hydroxyapatite-Zinc Oxide Nanocomposite Coating by Electrophoretic Deposition Technique

To develop medical-grade stainless-steel 316L implants that are biocompatible, non-toxic and antibacterial, such implants need to be coated with biomaterials to meet the current demanding properties of biomedical materials. Hydroxyapatite (HA) is commonly used as a bone implant coating due to its excellent biocompatible properties. Zinc oxide (ZnO) nanoparticles are added to HA to increase its antibacterial and cohesion properties. The specimens were made of a stainless-steel grade 316 substrate coated with HA-ZnO using the electrophoretic deposition technique (EPD), and were subsequently characterized using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), stylus profilometry, electrochemical corrosion testing and Fourier transform infrared (FTIR) spectroscopy. Additionally, cross-hatch tests, cell viability assays, antibacterial assessment and in vitro activity tests in simulated body fluid (SBF) were performed. The results showed that the HA-ZnO coating was uniform and resistant to corrosion in an acceptable range. FTIR confirmed the presence of HA-ZnO compositions, and the in vitro response and adhesion were in accordance with standard requirements for biomedical materials. Cell viability confirmed the viability of cells in an acceptable range (>70%). In addition, the antibacterial activity of ZnO was confirmed on Staphylococcus aureus. Thus, the HA-ZnO samples are recommended for biomedical applications.

Electrophoretic Deposition, Microstructure, and Selected Properties of Poly(lactic-co-glycolic) Acid-Based Antibacterial Coatings on Mg Substrate

There is an urgent need to develop biodegradable implants that can degrade once they have fulfilled their function. Commercially pure magnesium (Mg) and its alloys have the potential to surpass traditional orthopedic implants due to their good biocompatibility and mechanical properties, and most critically, biodegradability. The present work focuses on the synthesis and characterization (microstructural, antibacterial, surface, and biological properties) of poly(lactic-co-glycolic) acid (PLGA)/henna (Lawsonia inermis)/Cu-doped mesoporous bioactive glass nanoparticles (Cu-MBGNs) composite coatings deposited via electrophoretic deposition (EPD) on Mg substrates. PLGA/henna/Cu-MBGNs composite coatings were robustly deposited on Mg substrates using EPD, and their adhesive strength, bioactivity, antibacterial activity, corrosion resistance, and biodegradability were thoroughly investigated. Scanning electron microscopy and Fourier transform infrared spectroscopy studies confirmed the uniformity of the coatings' morphology and the presence of functional groups that were attributable to PLGA, henna, and Cu-MBGNs, respectively. The composites exhibited good hydrophilicity with an average roughness of 2.6 μm, indicating desirable properties for bone forming cell attachment, proliferation, and growth. Crosshatch and bend tests confirmed that the adhesion of the coatings to Mg substrates and their deformability were adequate. Electrochemical Tafel polarization tests revealed that the composite coating adjusted the degradation rate of Mg substrate in a human physiological environment. Incorporating henna into PLGA/Cu-MBGNs composite coatings resulted in antibacterial activity against Escherichia coli and Staphylococcus aureus. The coatings stimulated the proliferation and growth of osteosarcoma MG-63 cells during the initial incubation period of 48 h (determined by the WST-8 assay).

Trilateral Multi-Functional Polyamide 12 Nanocomposites with Binary Inclusions for Medical Grade Material Extrusion 3D Printing: The Effect of Titanium Nitride in Mechanical Reinforcement and Copper/Cuprous Oxide as Antibacterial Agents

In this work, for the first time, polyamide 12 (PA12) nanocomposites with binary inclusions in material extrusion (MEX) 3D printing were developed. The aim was to achieve an enhanced mechanical response with the addition of titanium nitride (TiN) and antibacterial performance with the addition of copper (Cu) or cuprous oxide (Cu₂O), towards the development of multi-functional nanocomposite materials, exploiting the 3D printing process benefits. The prepared nanocomposites were fully characterized for their mechanical properties. The thermal properties were also investigated. Morphological characterization was performed with atomic force microscopy (AFM) and scanning electron microscopy (SEM). The antibacterial performance was investigated with an agar-well diffusion screening process. Overall, the introduction of these nanofillers induced antibacterial performance in the PA12 matrix materials, while at the same time, the mechanical performance was significantly increased. The results of the study show high potential for expanding the areas in which 3D printing can be used.

Zn-Mn-Doped Mesoporous Bioactive Glass Nanoparticle-Loaded Zein Coatings for Bioactive and Antibacterial Orthopedic Implants

In recent years, natural polymers have replaced synthetic polymers for antibacterial orthopedic applications owing to their excellent biocompatibility and biodegradability. Zein is a biopolymer found in corn. The lacking mechanical stability of zein is overcome by incorporating bioceramics, e.g., mesoporous bioactive glass nanoparticles (MBGNs). In the present study, pure zein and zein/Zn–Mn MBGN composite coatings were deposited via electrophoretic deposition (EPD) on 316L stainless steel (SS). Zn and Mn were co-doped in MBGNs in order to make use of their antibacterial and osteogenic potential, respectively. A Taguchi design of experiment (DoE) study was established to evaluate the effect of various working parameters on the morphology of the coatings. It was observed that coatings deposited at 20 V for 5 min with 4 g/L concentration (conc.) of Zn–Mn MBGNs showed the highest deposition yield. Uniform coatings with highly dispersed MBGNs were obtained adopting these optimized parameters. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) were employed to investigate the morphology and elemental composition of zein/Zn–Mn MBGN composite coatings. Surface properties, i.e., coating roughness and wettability analysis, concluded that composite coatings were appropriate for cell attachment and proliferation. For adhesion strength, various techniques, including a tape test, bend test, pencil hardness test, and tensile test, were performed. Wear and corrosion analysis highlighted the mechanical and chemical stability of the coatings. The colony forming unit (CFU) test showed that the zein/Zn–Mn MBGN composite coating was highly effective against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) due to the presence of Zn. The formation of a hydroxyapatite (HA)-like structure upon immersion in the simulated body fluid (SBF) validated the in vitro bioactivity of the coating. Moreover, a WST-8 assay depicted that the MG-63 cells proliferate on the composite coating. It was concluded that the zein/Zn–Mn MBGN coating synthesized in this work can be used for bioactive and antibacterial orthopedic applications.

A Brief Insight to the Electrophoretic Deposition of PEEK-, Chitosan-, Gelatin-, and Zein-Based Composite Coatings for Biomedical Applications: Recent Developments and Challenges

Electrophoretic deposition (EPD) is a powerful technique to assemble metals, polymer, ceramics, and composite materials into 2D, 3D, and intricately shaped implants. Polymers, proteins, and peptides can be deposited via EPD at room temperature without affecting their chemical structures. Furthermore, EPD is being used to deposit multifunctional coatings (i.e., bioactive, antibacterial, and biocompatible coatings). Recently, EPD was used to architect multi-structured coatings to improve mechanical and biological properties along with the controlled release of drugs/metallic ions. The key characteristics of EPD coatings in terms of inorganic bioactivity and their angiogenic potential coupled with antibacterial properties are the key elements enabling advanced applications of EPD in orthopedic applications. In the emerging field of EPD coatings for hard tissue and soft tissue engineering, an overview of such applications will be presented. The progress in the development of EPD-based polymeric or composite coatings, including their application in orthopedic and targeted drug delivery approaches, will be discussed, with a focus on the effect of different biologically active ions/drugs released from EPD deposits. The literature under discussion involves EPD coatings consisting of chitosan (Chi), zein, polyetheretherketone (PEEK), and their composites. Moreover, in vitro and in vivo investigations of EPD coatings will be discussed in relation to the current main challenge of orthopedic implants, namely that the biomaterial must provide good bone-binding ability and mechanical compatibility.