Preparation and characterization of chitosan/graphene oxide nanocomposite coatings on Mg-2 wt% Zn scaffold by pulse electrodeposition process

Mg and its alloys are biodegradable and mechanically strong materials, which can be used for an orthopedic implant and device applications, but corrosion rate of these alloys is high. In this research, the nanocomposite coatings of chitosan (CS)/graphene oxide (GO) were fabricated to improve the corrosion resistance of the Mg-2 wt% Zn scaffold. The contents of the GO nanosheets and the pulse electrodeposition process parameters, including peak current density (CD) and duty cycle (DC), will also be investigated. The Mg-2 wt% Zn as a substrate of the scaffold was prepared using a powder metallurgy process. The influence of the porosity was studied on the microstructure fabricated scaffolds. The coating microstructures and morphologies were investigated by Raman spectroscopy, x-ray diffraction, thermogravimetric analysis, and SEM. The atomic force microscopy was performed to study the thickness of the nanocomposite coatings. The zeta potential measurement was conducted for the dispersion of the GO nanosheets in the CS matrix. The obtained results showed that the optimum conditions to fabricate a uniform CS/GO coating on the scaffolds were 2 wt% GO, CD = 20 mA cm^-2, and DC = 0.5. The pH, time and temperature for the fabrication of the coatings were conducted at 5, 20 min, and 37 °C, respectively. Additionally, the potentiodynamic polarization measurement in simulated body fluid indicated that the CS/GO coatings could provide effective protection of the scaffolds against corrosion. Additionally, the optimum sample obtained from the aspect of the corrosion behavior demonstrated adequate biocompatibility with proper adhesion of mouse fibroblast cells (L929) on the CS-2 wt% GO coating.

Polyelectrolyte multilayer composite coating on 316 L stainless steel for controlled release of dual growth factors accelerating restoration of bone defects

A composite coating of polyelectrolyte multilayers (PEMs) consisting of collagen, a chitosan barrier, and poly-γ-glutamic acid was fabricated using a spin coating technique to investigate and overcome the limited osseointegration capacity of 316 L stainless steel (316 L SS). To further enhance the biocompatibility, bone morphogenetic protein 2 (BMP-2) and basic fibroblast growth factor-2 (FGF-2) were loaded separately as dual growth factors, allowing for progressive drug release following the natural process of bone regeneration. The first burst release of FGF-2 triggered the proliferation of surrounding cells, and the subsequent release of BMP-2 stimulated their differentiation. The microstructure, surface potential, hardness, reduced Young's modulus, and wettability were assessed using scanning electron microscopy, nanoindentation, and water contact angle. The formation of apatite layers after immersion in simulated body fluid confirmed the bioactivity of this PEM. PEMs loaded with BMP-2 and FGF-2 showed a long sustained release of growth factors for up to 48 days. The biological properties were studied in vitro with rat bone mesenchymal stem cells (rBMSCs) and in vivo using a rat critical-sized calvarial defect model. PEMs loaded with growth factors further stimulated the proliferation and osteogenic differentiation of rBMSCs and the histology results indicated that new bone tissues could directly grow onto the PEMs. These findings suggest that PEM composite coating possesses significant potential for surface modification and long-term drug release of metallic implants to assist with bone restoration.

Biopolymers as bone substitutes: a review

Human bones have unique structures and characteristics, and replacing a natural bone in the case of bone fracture or bone diseases is a very complicated problem. The main goal of this paper was to summarize the recent research on polymer materials as bone substitutes and for bone repair. Bone treatment methods, bone substitute materials as well as their advantages and drawbacks, and manufacturing methods were reviewed. Biopolymers are the most promising materials in the field of artificial bones and using biopolymers with the shape memory effect can improve the integration of an artificial bone into the human body by better mimicking the structure and properties of natural bones, decreasing the invasiveness of surgical procedures by producing deployable implants. It has been shown that the application of the rapid prototyping technology for artificial bones allows the customization of bone substitutes for a patient and the creation of artificial bones with a complex structure.

Biological properties of calcium phosphate biomaterials for bone repair: a review

This article reviews the recent advances and various factors affecting the improvement of the biological properties of calcium phosphate for bone repair.

Evaluating the osseointegration of nanostructured titanium implants in animal models: Current experimental methods and perspectives (Review)

The aim of this paper is to review the experimental methods currently being used to evaluate the osseointegration of nanostructured titanium implants using animal models. The material modifications are linked to the biocompatibility of various types of oral implants, such as laser-treated, acid-etched, plasma-coated, and sand-blasted surface modifications. The types of implants are reviewed according to their implantation site (endoosseous, subperiosteal, and transosseous implants). The animal species and target bones used in experimental implantology are carefully compared in terms of the ratio of compact to spongy bone. The surgical technique in animal experiments is briefly described, and all phases of the histological evaluation of osseointegration are described in detail, including harvesting tissue samples, processing undemineralized ground sections, and qualitative and quantitative histological assessment of the bone-implant interface. The results of histological staining methods used in implantology are illustrated and compared. A standardized and reproducible technique for stereological quantification of bone-implant contact is proposed and demonstrated. In conclusion, histological evaluation of the experimental osseointegration of dental implants requires careful selection of the experimental animals, bones, and implantation sites. It is also advisable to use larger animal models and older animals with a slower growth rate rather than small or growing experimental animals. Bones with a similar ratio of compact to spongy bone, such as the human maxilla and mandible, are preferred. A number of practical recommendations for the experimental procedures, harvesting of samples, tissue processing, and quantitative histological evaluations are provided.

Tackling Mg alloy corrosion by natural polymer coatings-A review

The field of protective coatings for magnesium and its alloys (e.g., AZ31) using natural polymers is reviewed. Polymers utilized are broadly divided into polysaccharides and proteins. For both polymer classes examples are given focusing on coating processing and characterization. Several analysing methods reported in literature are summarized highlighting the different characterization approaches applied in different studies, which makes difficult a direct comparison of the outcomes. In most cases, the protective behavior of coatings was determined using electrochemical impedance spectroscopy or by assessing hydrogen evolution in different fluids. Mechanical tests and in vitro cell culture studies have been also carried out on selected coating systems. Overall, the results show the possibility of applying protective coatings based on natural polymers on magnesium and its alloys, however, in vivo investigations are scarce so that long-term results in relevant conditions are not yet available. A comparison with the use of synthetic polymers is presented and current challenges and areas for future research are discussed, highlighting the need for further investigations in the field, which should enable broadening the applications of Mg and Mg alloys in medicine. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2628-2641, 2016.