The Incorporation of Strontium in a Sodium Alginate Coating on Titanium Surfaces for Improved Biological Properties

Octacalcium Phosphate-Laden Hydrogels on 3D-Printed Titanium Biomaterials Improve Corrosion Resistance in Simulated Biological Media

The inflammatory-associated corrosion of metallic dental and orthopedic implants causes significant complications, which may result in the implant's failure. The corrosion resistance can be improved with coatings and surface treatments, but at the same time, it might affect the ability of metallic implants to undergo proper osteointegration. In this work, alginate hydrogels with and without octacalcium phosphate (OCP) were made on 3D-printed (patterned) titanium alloys (Ti Group 2 and Ti-Al-V Group 23) to enhance their anticorrosion properties in simulated normal, inflammatory, and severe inflammatory conditions in vitro. Alginate (Alg) and OCP-laden alginate (Alg/OCP) hydrogels were manufactured on the surface of 3D-printed Ti substrates and were characterized with wettability analysis, XRD, and FTIR. The electrochemical characterization of the samples was carried out with open circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). It was observed that the hydrophilicity of Alg/OCP coatings was higher than that of pure Alg and that OCP phase crystallinity was increased when samples were subjected to simulated biological media. The corrosion resistance of uncoated and coated samples was lower in inflammatory and severe inflammatory environments vs. normal media, but the hydrogel coatings on 3D-printed Ti layers moved the corrosion potential towards more nobler values, reducing the corrosion current density in all simulated solutions. These measurements revealed that OCP particles in the Alg hydrogel matrix noticeably increased the electrical charge transfer resistance at the substrate and coating interface more than with Alg hydrogel alone.

Advanced applications of strontium-containing biomaterials in bone tissue engineering

Strontium (Sr) and strontium ranelate (SR) are commonly used therapeutic drugs for patients suffering from osteoporosis. Researches have showed that Sr can significantly improve the biological activity and physicochemical properties of materials in vitro and in vivo. Therefore, a large number of strontium containing biomaterials have been developed for repairing bone defects and promoting osseointegration. In this review, we provide a comprehensive overview of Sr-containing biomaterials along with the current state of their clinical use. For this purpose, the different types of biomaterials including calcium phosphate, bioactive glass, and polymers are discussed and provided future outlook on the fabrication of the next-generation multifunctional and smart biomaterials.

Progress in Surface Modification of Titanium Implants by Hydrogel Coatings

Although titanium and titanium alloys have become the preferred materials for various medical implants, surface modification technology still needs to be strengthened in order to adapt to the complex physiological environment of the human body. Compared with physical or chemical modification methods, biochemical modification, such as the introduction of functional hydrogel coating on implants, can fix biomolecules such as proteins, peptides, growth factors, polysaccharides, or nucleotides on the surface of the implants, so that they can directly participate in biological processes; regulate cell adhesion, proliferation, migration, and differentiation; and improve the biological activity on the surface of the implants. This review begins with a look at common substrate materials for hydrogel coatings on implant surfaces, including natural polymers such as collagen, gelatin, chitosan, and alginate, and synthetic materials such as polyvinyl alcohol, polyacrylamide, polyethylene glycol, and polyacrylic acid. Then, the common construction methods of hydrogel coating (electrochemical method, sol-gel method and layer-by-layer self-assembly method) are introduced. Finally, five aspects of the enhancement effect of hydrogel coating on the surface bioactivity of titanium and titanium alloy implants are described: osseointegration, angiogenesis, macrophage polarization, antibacterial effects, and drug delivery. In this paper, we also summarize the latest research progress and point out the future research direction. After searching, no previous relevant literature reporting this information was found.

Novel bilayer coating on gentamicin-loaded titanium nanotube for orthopedic implants applications

Fabricating a multifunctional orthopedic implant which prevents post-surgery infection is highly desirable in advanced materials applications. However, designing an antimicrobial implant, which simultaneously promotes a sustained drug release and satisfactory cell proliferation, remains a challenge. The current study presents a drug-loaded surface-modified titanium nanotube (TNT) implant with different surface chemistry which was developed to investigate the effect of surface coating on drug release, antimicrobial activity, and cell proliferation. Accordingly, sodium alginate and chitosan were coated on the surface of TNT implants with different coating orders through layer-by-layer assembly. The coatings' swelling ratio and degradation rate were around 613% and 75%, respectively. The drug release results showed that surface-coatings prolonged the releasing profile for about 4 weeks. Chitosan coated TNTs demonstrated greater inhibition zone at 16.33mm compared with the other samples where no inhibition zone was observed. However, chitosan and alginate coated TNTs exhibited smaller inhibition zones at 48.56mm and 43.28mm, respectively, compared to bare TNT, which can be attributed to the coatings preventing the antibiotic burst release. Higher viability of cultured osteoblast cells was observed for chitosan-coated TNT as the top layer compared to the bare TNT at 12.18%, indicating improved bioactivity of TNT implants when the chitosan has the most contact with cells. Coupled with the cell viability assay, molecular dynamics (MD) simulations were carried out by placing collagen and fibronectin near the considered substrates. In agreement with cell viability results, MD simulations also indicated that chitosan had the highest adsorption energy approximately 60Kcal/mol. In summary, the proposed bilayer chitosan-coated drug-loaded TNT implant with chitosan and sodium alginate coating as the top and the bottom layers, respectively, can be a potential candidate for orthopedic applications in the light of its bacterial biofilm prevention, better osteoconductivity, and providing an adequate drug release profile.

Strontium-loaded hydrogel scaffolds to promote gingival fibroblast function

Dental implant clinical success is dependent on effective peri-implant tissue attachment to the trans-mucosal portion following placement. Modification of transmucosal implant surfaces can improve cellular adhesion and function leading to formation of an effective soft-tissue seal during healing, of which gingival fibroblasts are prominent cells to migrate to repair wounds and crucial for the development of a collagen rich connective tissue. Biocompatible loaded scaffold materials have been developed to allow local release of molecules with effective biological activity. Our previous studies indicate that strontium can promote gingival fibroblast metabolism, decrease apoptosis and support adhesion to titanium healing abutments. In this study, we developed a strontium-loaded alginate hydrogel scaffold which can be easily personalized to fit over any size and shape of implant transmucosal collar or healing abutment. Results indicate that biologically active strontium ions are effectively released from loaded alginate hydrogel material to promote fibroblast viability and migration to repair in vitro wounds similar to that of strontium citrate solution. Overall, this novel strontium-loaded alginate scaffold device displays good biocompatibility and functionality, demonstrating high potential as a system to provide local delivery of strontium to improve peri-implant mucosal healing following implant placement and clinical success.

Photo-Crosslinkable Hydrogels for 3D Bioprinting in the Repair of Osteochondral Defects: A Review of Present Applications and Future Perspectives

An osteochondral defect is a common and frequent disease in orthopedics and treatment effects are not good, which can be harmful to patients. Hydrogels have been applied in the repair of cartilage defects. Many studies have reported that hydrogels can effectively repair osteochondral defects through loaded cells or non-loaded cells. As a new type of hydrogel, photo-crosslinked hydrogel has been widely applied in more and more fields. Meanwhile, 3D bioprinting serves as an attractive platform to fabricate customized tissue-engineered substitutes from biomaterials and cells for the repair or replacement of injured tissues and organs. Although photo-crosslinkable hydrogel-based 3D bioprinting has some advantages for repairing bone cartilage defects, it also has some disadvantages. Our aim of this paper is to review the current status and prospect of photo-crosslinkable hydrogel-based 3D bioprinting for repairing osteochondral defects.

Bioactive coatings with anti-osteoclast therapeutic agents for bone implants: Enhanced compliance and prolonged implant life

The use of therapeutic agents that inhibit bone resorption is crucial to prolong implant life, delay revision surgery, and reduce the burden on the healthcare system. These therapeutic agents include bisphosphonates, various nucleic acids, statins, proteins, and protein complexes. Their use in systemic treatment has several drawbacks, such as side effects and insufficient efficacy in terms of concentration, which can be eliminated by local treatment. This review focuses on the incorporation of osteoclast inhibitors (antiresorptive agents) into bioactive coatings for bone implants. The ability of bioactive coatings as systems for local delivery of antiresorptive agents to achieve optimal loading of the bioactive coating and its release is described in detail. Various parameters such as the suitable concentrations, release times, and the effects of the antiresorptive agents on nearby cells or bone tissue are discussed. However, further research is needed to support the optimization of the implant, as this will enable subsequent personalized design of the coating in terms of the design and selection of the coating material, the choice of an antiresorptive agent and its amount in the coating. In addition, therapeutic agents that have not yet been incorporated into bioactive coatings but appear promising are also mentioned. From this work, it can be concluded that therapeutic agents contribute to the biocompatibility of the bioactive coating by enhancing its beneficial properties.

Surface analysis of titanium disks with strontium coating

Peri-implantitis is one of the most common complications after dental implant placement. Researchers have demonstrated that the peri-implantitis tends to occur around dental implants with a rough surface rather than those with a smooth surface. We aimed to investigate the ability of a smooth titanium (Ti) surface containing strontium (Sr) to enhance bone formation as a result of strontium's capacity to support osteoblast proliferation and differentiation. A thin titanium oxide film was formed on an as-mirror polished Ti surface by dipping in 5% sodium hypochlorite (NaOCl) solution for 24 h, followed by thermal treatment at 350°C. The Ti surface was then treated with 1% strontium nitrate (Sr(NO₃)₂) solution and turned in spin coater. The surface morphology, chemical composition, and release of strontium ions (Sr²⁺) were evaluated. The results demonstrate that strontium in the form of Sr²⁺ was successfully doped into the titanium dioxide (TiO₂) film by this simple chemical treatment.

Evaluation of fluorohydroxyapatite/strontium coating on titanium implants fabricated by hydrothermal treatment

Titanium and its alloys are considered as appropriate replacements for the irreparable bone. Calcium phosphate coatings are widely used to improve the osteoinduction and osseointegration ability of titanium alloys. To further improve the performance of the calcium phosphate-coated implants, strontium (Sr) was introduced to partially replace the calcium ions. In this study, the effect of Sr ion addition on the fluorohydroxyapatite (FHA)-coated Ti6Al4V alloy was investigated and all the coatings were treated under hydrothermal condition. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the phases and microstructures, respectively. Shear tests were done to evaluate the bond strength of the coating layer. MTT, adhesion, and alkaline phosphatase tests were performed to evaluate the biocompatibility and osteogenic behavior of the samples. Results showed that the average crystallite size for the strontium-doped FHA samples was 48 nm and the bond strength had increased 13.15% in comparison with FHA-coated samples. Analysis of variance showed p value for all MTT tests at more than 0.322 and there was not any evidence of cell death after 7 days. The results of the ALP test showed that the increase of the cell activity in Sr samples from day 7 to 14 is three times higher than the FHA ones.

Alginate Hydrogels with Tuneable Properties

Alginate is a material that has many biomedical applications due to its low toxicity and a variety of favourable physical properties. In particular, the ease in which hydrogels are formed from alginate and the variety of mechanical behaviours that can be imparted on the hydrogels, by understanding alginate chemistry and intuitive design, has made alginate the most widely investigated polysaccharide used for tissue engineering. This chapter provides an overview of alginate, from how the source and natural variations in composition can influence mechanical properties of alginate hydrogels, through to some innovative techniques used to modify and functionalise the hydrogels designed specifically for cell-based therapies. The main focus is on how these strategies of understanding and controlling the chemistry of alginates have resulted in the development of hydrogels that can be tuned to deliver the physical behaviours required for successful application. This will also highlight how research on the physicochemical properties has helped alginate evolve from a structural polysaccharide in brown seaweed into a highly tuneable, multifunctional, smart biomaterial, which is likely to find further biomedical applications in the future.

Application of a Strontium-Loaded, Phase-Transited Lysozyme Coating to a Titanium Surface to Enhance Osteogenesis and Osteoimmunomodulation

Background

To fabricate strontium (Sr)-incorporated titanium (Ti) surfaces by a novel 1-step phase-transited lysozyme (PTL) treatment, and investigate the effects of the prepared samples on osteogenesis and osteoimmunoregulation.

Material/Methods

Five groups of titanium specimens were prepared, including Ti, PTL, PTL@10Sr (PTL coating with 10 mg/mL Sr), PTL@20Sr PTL coating with 20 mg/mL Sr), and PTL@50Sr (PTL coating with 50 mg/mL Sr) groups. Behaviors of bone marrow mesenchymal stem cells (BMSCs) such as initial attachment, spread, proliferation, and migration, on different surfaces were examined by immunofluorescence, MTS assay, and Transwell system. Then the osteogenic differentiation of BMSCs was detected. When an immune response was factored in, the polarization of macrophages induced by the prepared surfaces was detected by real-time PCR, and the response of BMSCs to macrophage-conditioned medium was assessed in terms of cell migration and osteogenic differentiation. Finally, an in vivo study was performed, using the rat femora implant model, to evaluate the potential for osteogenic induction and osteoimmunoregulation of materials.

Results

Our in vitro experiments indicated that PTL coating could improve cell spread and adhesion, and the stable Sr release of PTL@Sr layers could promote cell migration and osteogenesis. Moreover, PTL@Sr surface could regulate the immune response of macrophages resulting in enhanced BMSCs recruitment and osteogenic differentiation. The in vivo evaluation showed less inflammatory infiltration and improved bone formation in the PTL@20Sr group.

Conclusions

The Sr-loaded PTL layers have greater potential for the induction of osteogenic differentiation of BMSCs, meanwhile Sr-loaded PTL layers could adjust the immune response and thus promote osteogenesis both in vitro and in vivo.