Biocorrosion behavior of biodegradable nanocomposite fibers coated layer-by-layer on AM50 magnesium implant

Biomimetic hydrogel coatings for improving the corrosion resistance, hemocompatibility, and endothelial cell growth of the magnesium alloy

The fast biodegradation and poor biocompatibility of Mg alloys in physiological environments are still the main problems restricting their application in cardiovascular stents. In this study, the hydrogel coatings (SBMA-AAM) with different proportions of methacryloyl ethyl sulfobetaine (SBMA) and acrylamide (AAM) were built on the surface of AZ31B magnesium alloy through ultraviolet (UV) polymerization. The corrosion degradation behavior, hemocompatibility, and endothelial cell (EC) growth performance of the samples were studied in detail. The findings revealed that the uniform and dense SBMA-AAM coatings could significantly enhance the corrosion resistance. In addition, the hydrogel coatings showed excellent hydrophilicity, which increased the albumin adsorption while inhibiting the fibrinogen adsorption, and thus reduced the platelet adhesion and activation and hemolysis rate, accordingly significantly enhancing their anticoagulant performance. Furthermore, SBMA-AAM hydrogel coating promoted the EC adhesion and proliferation and the vascular endothelial growth factor (VEGF) and nitric oxide (NO) secretion of ECs, which is conducive to promoting endothelialization. When the concentration ratio of SBMA and AAM was 1: 2, the modified magnesium alloy showed the best corrosion resistance and biocompatibility. Therefore, the SBMA-AAM hydrogel coating could effectively regulate the corrosion degradation performance and biocompatibility of Mg alloys, laying a foundation for the application of Mg alloys in cardiovascular stents.

In Vivo Study of Local and Systemic Responses to Clinical Use of Mg-1Ca Bioresorbable Orthopedic Implants

(1) Background: Resorbable Mg-based implants represent a new direction in orthopedic surgery but have some drawbacks, such as their rapid biodegradation and increased rate of corrosion. Some in vitro studies hypothesized that tissue necrosis, incision dehiscence, risk of gas embolization in vital organs, interference with coagulation processes, and trophocyte viability impairment can occur. (2) Methods: We conducted an in vivo study on ten rabbit cases, in two groups; group one, consisting of six cases, received cylindrical implants of Mg-1Ca alloy in tibial intramedullary bone tissue. Group two, consisting of four cases, received Mg-1Ca parallelepiped implants, in the thigh muscular tissue. We recorded and compared weight (preoperatively and at 2, 4, and 6 weeks postoperatively), complete blood count, serum electrolytes, liver and kidney functional markers, and coagulation parameters, prior to and at 6 weeks after surgery. Local evolution was assessed radiologically and with tissue biopsies with complete pathology analysis. (3) Results: All biological markers and clinical evolution were favorable, showing good integration of the implants with none of the local or systemic signs of degradation. (4) Conclusions: Our study shows that the clinical use of Mg-1Ca bioresorbable alloys can be safe as none of the cited local or systemic complications have been identified.

Surface Modification of Pure Zinc by Acid Etching: Accelerating the Corrosion Rate and Enhancing Biocompatibility and Antibacterial Characteristics

Zinc (Zn) has recently been identified as an auspicious biodegradable metal for medical implants and devices due to its tunable mechanical properties and good biocompatibility. However, the slow corrosion rate of Zn in a physiological environment does not meet the requirements for biodegradable implants, hindering its clinical translation. The present study aimed to accelerate the corrosion rate of pure Zn by utilizing acid etching to roughen the surface and increase the substrate surface area. The effects of acid etching on surface morphology, surface roughness, tensile properties, hardness, electrochemical corrosion and degradation behavior, cytocompatibility, direct cell attachment, and biofilm formation were investigated. Interestingly, acid-treated Zn showed an exceptionally high rate of corrosion (∼226-125 μm/year) compared to untreated Zn (∼62 μm/year), attributed to the increased surface roughness (R_a ∼ 1.12 μm) of acid-etched samples. Immersion tests in Hank's solution revealed that acid etching accelerated the degradation rate of Zn samples. In vitro, MC3T3-E1 cell lines in 50 and 25% conditioned media extracts of treated samples showed good cytocompatibility. Reduced bacterial adhesion, biofilm formation, and dispersion were observed for Staphylococci aureus biofilms cultured on acid-etched pure Zn substrates. These results suggest that the surface modification of biodegradable pure Zn metals by acid etching markedly increases the translation potential of zinc for various biomedical applications.

Cisplatin encapsulated nanoparticles from polymer blends for anti-cancer drug delivery

Synthesis of cubic nanostructure for cisplatin encapsulation.

A biodegradable, mechanically tunable micro-arc oxidation AZ91D-based composite implant with calcium phosphate/chitosan coating promotes long-term bone tissue regeneration

BACKGROUND

To reduce the biodegradable rate and develop the long-term osteogenic ability of magnesium (Mg) alloy, we prepared a new biodegradable micro arc oxidation AZ91D-based composite implant with calcium phosphate/chitosan coating (CaP-CS/MAO/AZ91D) and investigated its mechanical property and long-term bone tissue regeneration ability.

MAIN METHODS AND MAJOR RESULTS

The results showed that the binding force and bioactivity of CaP-CS/MAO/AZ91D was better when the ratio of water to ethanol was 4:6 and MAO constant current was 0.1 A cm^-2 . Compressive strengths of 4:6 sample were more than 1300 N when the soaking time was increased to 21 days. CaP-CS/MAO/AZ91D extracts promoted differentiation and proliferation of rat mesenchymal stem cells (RMSC), which achieved higher proliferation rates over 16 days of culture and exhibited early alkaline phosphatase activity and late bone sialoprotein markers.

CONCLUSIONS AND IMPLICATIONS

CaP-CS/MAO/AZ91D was established to promote RMSC osteogenic differentiation within a proper range for at least 90 days through Wnt/β-catenin pathway activation, which would allow sufficient time for bone healing. Collectively, our findings suggest that the CaP-CS/MAO/AZ91D coating could not only reduce the corrosion rate and lead to better long-term biocompatibility but also promote osteogenic mineralization.

Engineering a Bioactive Hybrid Coating for In Vitro Corrosion Control of Magnesium and Its Alloy

Magnesium (Mg) and its alloys are promising biodegradable metallic implant materials. However, their clinical applications are limited by their fast corrosion rate in the biological environment. In this work, with an outlook to improve the in vitro corrosion resistance of Mg and WE43 Mg alloy, a layer-by-layer interfacially engineered anticorrosive and bioactive coating consisting of a natural oxide lower layer, hydroxyapatite (HA) middle layer, and silk fibroin (SF) top layer was fabricated and investigated. Anodization was used to create natural oxide layer induced microroughness on substrates. The electrochemically deposited HA layer improved the surface microroughness and microhardness but significantly decreased Mg ion release, hydrogen gas evolution, and weight loss in simulated body fluid. The spin-coated SF layer further decreased hydrophilicity, in vitro degradation, and corrosion rate. The nonspecific and specific intermolecular interactions between fabricated layers along with their mechanical interlocking interface contributed to improved adhesion strength and integrity of the coating. The SF+HA-coated samples showed enhanced degradation and corrosion resistance due to a synergistic effect of the underlying HA layer, hindering the ingress of aggressive ions and the top hydrophobic SF layer, preventing the ingress of corrosive solution. The SF+HA-coated Mg and WE43 Mg alloy samples exhibited 50 and 26 times decreased corrosion rate, respectively, compared to uncoated samples. Moreover, in vitro cytotoxicity and cell culture studies using a mouse fibroblast cell showed that the SF+HA hybrid coating improved the cell viability, attachment, and proliferation, with cells exhibiting elongated morphology on coated samples as compared to a round shape on uncoated samples.

Microroughness induced biomimetic coating for biodegradation control of magnesium

Herein we explore a combination of anodization induced micro-roughness and biomimetic coating on pure magnesium (Mg) metal at different applied voltages to control adhesion, biodegradation, and corrosion performance in simulated body fluid solution. The anodic film was fabricated using two different potentials, 3 and 5 V, respectively, to create microroughness on the Mg surface. The microroughened Mg surface was subsequently coated with a biomimetic silk thin film; and the characteristics of the treated Mg-substrates were evaluated using various spectroscopic, microscopic, immersion, and electrochemical techniques. A number of independent measurements, including hydrogen evolution, weight loss and electrochemical methods were employed to assess the corrosion characteristics. The silk-coated anodized samples revealed dramatically reduced degradation rate in terms of volume of hydrogen gas generation and weight loss compared to the respective anodized but uncoated, which revealed that optimized biomimetic silk-coated Mg surface (anodized at 5 V and subsequently biomimetic silk-coated ANMg_5V) exhibited the best corrosion performance among all other tested samples. The ANMg_5V Silk showed the highest polarization resistance (46.12 kΩ·cm²), protection efficiency (>0.99) and lowest corrosion rate (only 0.017 mm/year) relative to untreated Mg (8.457 mm/year), and anodized Mg (1.039 for anodized at 3 V and 0.986 for anodized at 5 V) surface due to the formation of a pore-free dense biomimetic protective film over Mg surface. The results of the cytotoxicity test confirm that silk-coated samples are significantly less cytotoxic compared to bare and anodized Mg samples. With enhanced corrosion resistance and cytocompatibility, silk-coated Mg could be a potential material for clinical applications.

Co-incorporation of graphene oxide/silver nanoparticle into poly-L-lactic acid fibrous: A route toward the development of cytocompatible and antibacterial coating layer on magnesium implants

Magnesium (Mg) alloys present great potential for the development of orthopedic implants, whereas, their high degradation rate and poor antibacterial performance have restricted orthopedic applications. In this work, PLLA/GO-AgNP (poly-L-lactic acid/graphene oxide- silver nanoparticle) with different concentration of GO-AgNPs were deposited on Mg alloy via electrospinning method for enhancement of corrosion resistance and antibacterial performance. The result revealed that incorporation of GO into PLLA fibrous considerably slowed down the degradation rate of Mg alloy substrate and reduced the H₂ release rate from the substrate. Also, co-incorporation of GO and AgNPs into PLLA fibrous resulted in substantial escalate in compressive strength after immersion in simulated body fluid (SBF). Antibacterial activity test exhibited that Mg alloy and neat PLLA fibrous presented minimal inhibition area toward Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). In contrast, using PLLA/GO-AgNPs fibrous improved antibacterial performance against both bacteria. Cytocompatibility results indicated that PLLA/GO-AgNPs fibrous with a low amount of GO-AgNPs enhanced cell proliferation and growth while high co-incorporation of GO-AgNPs showed a negative effect on cell proliferation. Taken together, PLLA/1GO-AgNPs fibrous coating shows suitable corrosion resistance, cytocompatibility, and antibacterial function for use in orthopedic applications.

Growth factor releasing core-shell polymeric scaffolds for tissue engineering applications

Tissue engineering is the use of a combination of cells, biomaterials and appropriate signals to repair or improve the functions of damaged tissues. Our group is exploiting various approaches to effectively encapsulate multiple growth factors in polymeric scaffolds for tissue engineering and wound healing applications. In this report, some of the exciting results from our most recent and ongoing projects are outlined with a focus on the use of connective tissue growth factor (CTGF). CTGF is a secreted protein with major roles in angiogenesis, chondrogenesis, osteogenesis and tissue repair. CTGF can play a major role in tissue regeneration by enhancing cell proliferation and promoting cell migration. CTGF was incorporated to electrospun polymeric fibers to provide sustained release. Experimental results demonstrated the ability of scaffolds incorporated with CTGF to promote cell proliferation and cell migration. This study shows the application potential of the developed scaffolds in various tissue engineering applications.

Study of the Morphology and Properties of Biocompatible Ca-P Coatings on Mg Alloy

Magnesium alloys are considered as potential biomaterials for use in orthopedic implantology. The main barrier to the use of Mg alloys in medicine is their overly fast and irregular degradation in body fluids. The use of protective calcium phosphate coatings to increase the corrosion resistance of Mg alloy (AM50 alloy: 4 wt.% Al, 0.3 wt.% Mn, 0.2 wt.% Zn, rest Mg) was examined in this study. The scientific goal of the study was the assessment of the influence of calcium phosphate layer morphology on the corrosion process in Ringer's solution. Modification of the coating morphology was obtained by changing the chemical composition of the phosphatizing bath using NaOH (NaAM50 sample) or ZnSO₄ (ZnAM50 sample). In practice, a more dense and uniform coating could be obtained by the immersion of AM50 alloy in a solution containing ZnSO₄ (ZnAM50 sample). In this study, an adhesion test performed on the ZnAM50 sample indicated that the critical load was 1.35 N. XRD phase analysis confirmed that the obtained coatings included dicalcium phosphate dihydrate (CaHPO₄*2H₂O). The coatings prepared on the NaAM50 and ZnAM50 samples are effective barriers against the progress of corrosion deeper into the substrate. After 120 h immersion in Ringer's solution, the volume of the evolved hydrogen was 5.6 mL/cm² for the NaAM50 and 3.4 mL/cm² for the ZnAM50 sample.

Novel biodegradable magnesium alloy clips compared with titanium clips for hepatectomy in a rat model

Background

The use of surgical metal clips is crucial for ligating vessels in various operations. The currently available metal clips have several drawbacks; they are permanent and interfere with imaging techniques such as computed tomography (CT) or magnetic resonance (MR) imaging and carry the potential risk of endo-clip migration. We recently developed a novel magnesium (Mg) alloy for biodegradable clips that reduces artifacts on CT imaging. This study aimed to examine the tolerance, biodegradability, and biocompatibility of the Mg alloy clips compared with those of standard titanium (Ti) clips in hepatectomy.

Methods

Thirty Wistar rats were divided into two groups based on the clip used (groups A and B). The vascular pedicle, including hepatic artery, portal vein, bile duct, and hepatic vein of the left lateral lobe, was ligated with the Ti clip in group A or the Mg alloy clip in group B, and then the left lateral lobe was removed. The rats were sacrificed at 1, 4, 12, 24, and 36 weeks after surgery. Clinical and histological evaluations were performed. Absorption rate was calculated by measuring the clip volume.

Results

Although the Mg alloy clips showed biodegradability over time, there were no significant differences in the serum concentration of Mg between the two groups. The remaining volume ratio of Mg alloy clips was 95.5, 94.3, 80.0, 36.2, and 16.7% at 1, 4, 12, 24, and 36 weeks, respectively. No side effects occurred. Most of the microscopic changes were similar in both groups.

Conclusions

The new biodegradable Mg alloy clips are safe and feasible in vessel ligation for hepatectomy in a rat model and reduce artifacts in CT imaging compared with the standard Ti clips.

Development of a new biodegradable operative clip made of a magnesium alloy: Evaluation of its safety and tolerability for canine cholecystectomy

BACKGROUND

Operative clips used to ligate vessels in abdominal operation usually are made of titanium. They remain in the body permanently and form metallic artifacts in computed tomography images, which impair accurate diagnosis. Although biodegradable magnesium instruments have been developed in other fields, the physical properties necessary for operative clips differ from those of other instruments. We developed a biodegradable magnesium-zinc-calcium alloy clip with good biologic compatibility and enough clamping capability as an operative clip. In this study, we verified the safety and tolerability of this clip for use in canine cholecystectomy.

METHODS

Nine female beagles were used. We performed cholecystectomy and ligated the cystic duct by magnesium alloy or titanium clips. The chronologic change of clips and artifact formation were compared at 1, 4, 12, 18, and 24 weeks postoperative by computed tomography. The animals were killed at the end of the observation period, and the clips were removed to evaluate their biodegradability. We also evaluated their effect on the living body by blood biochemistry data.

RESULTS

The magnesium alloy clip formed much fewer artifacts than the titanium clip, and it was almost absorbed at 6 months postoperative. There were no postoperative complications and no elevation of constituent elements such as magnesium, calcium, and zinc during the observation period in both groups.

CONCLUSION

The novel magnesium alloy clip demonstrated sufficient sealing capability for the cystic duct and proper biodegradability in canine models. The magnesium alloy clip revealed much fewer metallic artifacts in CT than the conventional titanium clip.

Bi-directional controlled release of ibuprofen and Mg(2+) from magnesium alloys coated by multifunctional composite

Two major problems for magnesium alloy implant are the high degradation rate and easy infection associated with implantation. Herein, a surface drug delivery system (Mg/Epoxy resin-ZnO/PCL-Ibuprofen) which can realize bi-directional controlled release of ibuprofen and Mg(2+) was designed via a dip coating process followed by spraying. The in vitro test demonstrated that the ibuprofen in drug-eluting compound material showed sustained release profiles for 22days, which can effectively solve the local cellular rejection and inflammation during the early stage of implantation. Besides, the drug carrier also exhibited improved corrosion resistance duel to the high combining strength between Epoxy resin-ZnO coating and magnesium alloy, so Mg(2+) can release slowly at first and then speeded up later. This approach may be suitable for coating other implant materials such as stainless steel, titanium alloy etc.