Degradation and antibacterial properties of magnesium alloys in artificial urine for potential resorbable ureteral stent applications

A novel near-infrared polymethine dye biosensor for rapid and selective detection of lithocholic acid

Lithocholic acid (LCA), a secondary bile acid, has emerged as a potential early diagnostic biomarker for various liver diseases. In this study, we introduce a novel near-infrared (NIR) polymethine dye-based biosensor, capable of sensitive and selective detection of LCA in phosphate buffer and artificial urine (AU) solutions. The detection mechanism relies on the formation of J-aggregates resulting from the interplay of 3,3-Diethylthiatricarbocyanine iodide (DiSC2(7)) dye molecules and LCA, which induces a distinctive red shift in both absorption and fluorescence spectra. The biosensor demonstrates a detection limit for LCA of 70 μM in PBS solution (pH 7.4), while in AU solution, it responds to an LCA concentration as low as ∼60 μM. Notably, the proposed biosensor exhibits outstanding selectivity for LCA, effectively distinguishing it from common interferents such as uric acid, ascorbic acid, and glucose. This rapid, straightforward, and cost-effective spectrometer-based method underscores its potential for early diagnosis of liver diseases by monitoring LCA concentrations.

Recent development and future application of biodegradable ureteral stents

Ureteral stenting is a common clinical procedure for the treatment of upper urinary tract disorders, including conditions such as urinary tract infections, tumors, stones, and inflammation. Maintaining normal renal function by preventing and treating ureteral obstruction is the primary goal of this procedure. However, the use of ureteral stents is associated with adverse effects, including surface crusting, bacterial adhesion, and lower urinary tract symptoms (LUTS) after implantation. Recognizing the need to reduce the complications associated with permanent ureteral stent placement, there is a growing interest among both physicians and patients in the use of biodegradable ureteral stents (BUS). The evolution of stent materials and the exploration of different stent coatings have given these devices different roles tailored to different clinical needs, including anticolithic, antibacterial, antitumor, antinociceptive, and others. This review examines recent advances in BUS within the last 5 years, providing an in-depth analysis of their characteristics and performance. In addition, we present prospective insights into the future applications of BUS in clinical settings.

Albumin Protein Impact on Early-Stage In Vitro Biodegradation of Magnesium Alloy (WE43)

Mg and its alloys are promising biodegradable materials for orthopedic implants and cardiovascular stents. The first interactions of protein molecules with Mg alloy surfaces have a substantial impact on their biocompatibility and biodegradation. We investigate the early-stage electrochemical, chemical, morphological, and electrical surface potential changes of alloy WE43 in either 154 mM NaCl or Hanks' simulated physiological solutions in the absence or presence of bovine serum albumin (BSA) protein. WE43 had the lowest electrochemical current noise (ECN) fluctuations, the highest noise resistance (Zn = 1774 Ω·cm2), and the highest total impedance (|Z| = 332 Ω·cm2) when immersed for 30 min in Hanks' solution. The highest ECN, lowest Zn (1430 Ω·cm2), and |Z| (49 Ω·cm2) were observed in the NaCl solution. In the solutions containing BSA, a unique dual-mode biodegradation was observed. Adding BSA to a NaCl solution increased |Z| from 49 to 97 Ω·cm2 and decreased the ECN signal of the alloy, i.e., the BSA inhibited corrosion. On the other hand, the presence of BSA in Hanks' solution increased the rate of biodegradation by decreasing both Zn and |Z| while increasing ECN. Finally, using scanning Kelvin probe force microscopy (SKPFM), we observed an adsorbed nanolayer of BSA with aggregated and fibrillar morphology only in Hanks' solution, where the electrical surface potential was 52 mV lower than that of the Mg oxide layer.

Antimicrobial and Antiproliferative Coatings for Stents in Veterinary Medicine-State of the Art and Perspectives

Microbial colonization in veterinary stents poses a significant and concerning issue in veterinary medicine. Over time, these pathogens, particularly bacteria, can colonize the stent surfaces, leading to various complications. Two weeks following the stent insertion procedure, the colonization becomes observable, with the aggressiveness of bacterial growth directly correlating with the duration of stent placement. Such microbial colonization can result in infections and inflammations, compromising the stent's efficacy and, subsequently, the animal patient's overall well-being. Managing and mitigating the impact of these pathogens on veterinary stents is a crucial challenge that veterinarians and researchers are actively addressing to ensure the successful treatment and recovery of their animal patients. In addition, irritation of the tissue in the form of an inserted stent can lead to overgrowth of granulation tissue, leading to the closure of the stent lumen, as is most often the case in the trachea. Such serious complications after stent placement require improvements in the procedures used to date. In this review, antibacterial or antibiofilm strategies for several stents used in veterinary medicine have been discussed based on the current literature and the perspectives have been drawn. Various coating strategies such as coating with hydrogel, antibiotic, or other antimicrobial agents have been reviewed.

Research on the Current Application Status of Magnesium Metal Stents in Human Luminal Cavities

The human body comprises various tubular structures that have essential functions in different bodily systems. These structures are responsible for transporting food, liquids, waste, and other substances throughout the body. However, factors such as inflammation, tumors, stones, infections, or the accumulation of substances can lead to the narrowing or blockage of these tubular structures, which can impair the normal function of the corresponding organs or tissues. To address luminal obstructions, stenting is a commonly used treatment. However, to minimize complications associated with the long-term implantation of permanent stents, there is an increasing demand for biodegradable stents (BDS). Magnesium (Mg) metal is an exceptional choice for creating BDS due to its degradability, good mechanical properties, and biocompatibility. Currently, the Magmaris® coronary stents and UNITY-BTM biliary stent have obtained Conformité Européene (CE) certification. Moreover, there are several other types of stents undergoing research and development as well as clinical trials. In this review, we discuss the required degradation cycle and the specific properties (anti-inflammatory effect, antibacterial effect, etc.) of BDS in different lumen areas based on the biocompatibility and degradability of currently available magnesium-based scaffolds. We also offer potential insights into the future development of BDS.

Review on PLGA Polymer Based Nanoparticles with Antimicrobial Properties and Their Application in Various Medical Conditions or Infections

The rise in the resistance to antibiotics is due to their inappropriate use and the use of a broad spectrum of antibiotics. This has also contributed to the development of multidrug-resistant microorganisms, and due to the unavailability of suitable new drugs for treatments, it is difficult to control. Hence, there is a need for the development of new novel, target-specific antimicrobials. Nanotechnology, involving the synthesis of nanoparticles, may be one of the best options, as it can be manipulated by using physicochemical properties to develop intelligent NPs with desired properties. NPs, because of their unique properties, can deliver drugs to specific targets and release them in a sustained fashion. The chance of developing resistance is very low. Polymeric nanoparticles are solid colloids synthesized using either natural or synthetic polymers. These polymers are used as carriers of drugs to deliver them to the targets. NPs, synthesized using poly-lactic acid (PLA) or the copolymer of lactic and glycolic acid (PLGA), are used in the delivery of controlled drug release, as they are biodegradable, biocompatible and have been approved by the USFDA. In this article, we will be reviewing the synthesis of PLGA-based nanoparticles encapsulated or loaded with antibiotics, natural products, or metal ions and their antibacterial potential in various medical applications.

Magnesium-Based Temporary Implants: Potential, Current Status, Applications, and Challenges

Biomedical implants are important devices used for the repair or replacement of damaged or diseased tissues or organs. The success of implantation depends on various factors, such as mechanical properties, biocompatibility, and biodegradability of the materials used. Recently, magnesium (Mg)-based materials have emerged as a promising class of temporary implants due to their remarkable properties, such as strength, biocompatibility, biodegradability, and bioactivity. This review article aims to provide a comprehensive overview of current research works summarizing the above-mentioned properties of Mg-based materials for use as temporary implants. The key findings from in-vitro, in-vivo, and clinical trials are also discussed. Further, the potential applications of Mg-based implants and the applicable fabrication methods are also reviewed.

Incorporation of Magnesium and Zinc Metallic Particles in PLGA Bi-layered Membranes with Sequential Ion Release for Guided Bone Regeneration

Guided bone regeneration (GBR) membranes are commonly used for periodontal tissue regeneration. Due to the complications of existing GBR membranes, the design of bioactive membranes is still relevant. GBR membranes with an asymmetric structure can accommodate the functional requirements of different interfacial tissues. Here, poly(lactic acid-glycolic acid) (PLGA) was selected as the matrix for preparing a bi-layered membrane with both dense and porous structure. The dense layer for blocking soft tissues was incorporated with zinc (Zn) particles, while the porous layer for promoting bone regeneration was co-incorporated with magnesium (Mg) and Zn particles. Mg/Zn-embedded PLGA membranes exhibited 166% higher mechanical strength in comparison with pure PLGA membranes and showed suitable degradation properties with a sequential ion release behavior of Mg²⁺ first and continuously Zn²⁺. More importantly, the release of Zn²⁺ from bi-layered PLGA endowed GBR membranes with excellent antibacterial activity (antibacterial rate > 69.3%) as well as good cytocompatibility with MC3T3-E1 (mouse calvaria pre-osteoblastic cells) and HGF-1 (human gingival fibroblast cells). Thus, the asymmetric bi-layered PLGA membranes embedded with Mg and Zn particles provide a simple and effective strategy to not only reinforce the PLGA membrane but also endow membranes with osteogenic and antibacterial activity due to the continuous ion release profile, which serves as a promising candidate for use in GBR therapy.

Fabrication Procedure for a 3D Hollow Nanofibrous Bifurcated-Tubular Scaffold by Conformal Electrospinning

Electrospinning has shown great potential for the fabrication of 3D nanofibrous tubular scaffolds for bifurcated vascular grafts. However, fabrication of complex 3D nanofibrous tubular scaffolds with bifurcated or patient-specific shapes remains limited. In this study, a 3D hollow nanofibrous bifurcated-tubular scaffold was fabricated by the uniform and conformal deposition of electrospun nanofibers via conformal electrospinning. By conformal electrospinning, electrospun nanofibers are conformally deposited onto a complex shape, such as the bifurcated region, without large pores or defects. Owing to conformal electrospinning, a corner profile fidelity (F_C), a measure of conformal deposition of electrospun nanofibers at the bifurcated region, was increased 4 times at the bifurcation angle (θ_B) of 60°, and all F_C values of the scaffolds reached 100%, regardless of the θ_B. Furthermore, the thickness of the scaffolds could be controlled by varying the electrospinning time. Leakage-free liquid transfer was successfully achieved owing to the uniform and conformal deposition of electrospun nanofibers. Finally, the cytocompatibility and 3D mesh-based modeling of the scaffolds were demonstrated. Thus, conformal electrospinning can be used to fabricate leakage-free and complex 3D nanofibrous scaffolds for bifurcated vascular grafts.

Antifouling and antibacterial performance evaluation of polyethersulfone membranes modified with AZ63 alloy

Antibacterial membranes have attracted researchers' interest in recent years as a possible approach for dealing with biofouling on the membrane surface. This research aims to see if blending AZ63 Mg alloy into a polyethersulphone (PES) membrane can improve antifouling and separation properties. The composite membranes' pure water flux continued to increase from pristine PES to PES/AZ63 2.00 wt%. The results showed that PES/AZ63 2.00 wt% membrane supplied the highest permeate flux of E. coli. The steady-state fluxes of AZ63 composite membranes were 113.24, 104.38 and 44.79 L/m²h for PES/AZ63 2.00 wt%, 1.00 wt%, and 0.50 wt%, respectively. The enhanced biological activity of AZ63 was studied based on antioxidant activity, DNA cleavage, antimicrobial, anti-biofilm, bacterial viability inhibition and photodynamic antimicrobial therapy studies. The maximum DPPH scavenging activity was determined as 81.25% with AZ63. AZ63 indicated good chemical nuclease activity and also showed moderate antimicrobial activity against studied strains. The highest biofilm inhibition of AZ63 was 83.25% and 71.63% towards P. aeruginosa and S. aureus, respectively. The cell viability inhibition activity of AZ63 was found as 96.34% against E. coli. The photodynamic antimicrobial therapy results displayed that AZ63 demonstrated 100% bacterial inhibition when using E. coli.

Dissolution rate and growth performance reveal struvite as a sustainable nutrient source to produce a diverse set of microbial protein

To provide for the globally increasing demand for proteinaceous food, microbial protein (MP) has the potential to become an alternative food or feed source. Phosphorus (P), on the other hand, is a critical raw material whose global reserves are declining. Growing MP on recovered phosphorus, for instance, struvite obtained from wastewater treatment, is a promising MP production route that could supply protein-rich products while handling P scarcity. The aim of this study was to explore struvite dissolution kinetics in different MP media and characterize MP production with struvite as sole P-source. Different operational parameters, including pH, temperature, contact surface area, and ion concentrations were tested, and struvite dissolution rates were observed between 0.32 and 4.7 g P/L/d and a solubility between 0.23 and 2.22 g P-based struvite/L. Growth rates and protein production of the microalgae Chlorella vulgaris and Limnospira sp. (previously known as Arthrospira sp.), and the purple non‑sulfur bacterium Rhodopseudomonas palustris on struvite were equal to or higher than growth on conventional potassium phosphate. For aerobic heterotrophic bacteria, two slow-growing communities showed decreased growth on struvite, while the growth was increased for a third fast-growing one. Furthermore, MP protein content on struvite was always comparable to the one obtained when grown on standard media. Together with the low content in metals and micropollutants, these results demonstrate that struvite can be directly applied as an effective nutrient source to produce fast-growing MP, without any previous dissolution step. Combining a high purity recovered product with an efficient way of producing protein results in a strong environmental win-win.

Current material engineering strategies to prevent catheter encrustation in urinary tracts

Catheters and ureteric stents have played a vital role in relieving urinary obstruction in many urological conditions. With the increasing use of urinary catheters/stents, catheter/stent-related complications such as infection and encrustation are also increasing because of their design defects. Long-term use of antibiotics and frequent replacement of catheters not only increase the economic burden on patients but also bring the pain of catheter replacement. This is unfavorable for patients with long indwelling catheters or stents but inconvenient to replace. In recent years, some promising technologies and mechanisms have been used to prevent infection and encrustation, mainly drug loading coatings, functional coatings, biodegradable polymers and metallic materials for urinary devices. Obvious effects in anti-encrustation and anti-infection experiments of the above strategies in vivo or in vitro have been conducted, which is very helpful for further clinical trials. This review mainly introduces catheter/stent technology and mechanisms in the past ten years to address the potential impact of anti-encrustation coating of catheter/stent materials for the prevention of encrustation and to analyze the progress made in this field.

PDMS and DLC-coated unidirectional valves for artificial urinary sphincters: Opening performance after 126 days of immersion in urine

In this work, unidirectional valves made of bare polydimethylsiloxane (PDMS) and PDMS provided with a micrometric diamond‐like carbon (DLC) coating were fabricated and characterized, in terms of surface properties and opening pressure. The valve performance was also tested over 1250 repeated cycles of opening/closure in water, finding a slight decrease in the opening pressure after such cycles (10%) for the PDMS valves, while almost no variation for the PDMS + DLC ones. The valves were then immersed in urine for 126 days, evaluating the formation of encrustations and the trend of the opening pressure over time. Results showed that PDMS valves were featured by a thin layer of encrustations after 126 days, but the overall encrustation level was much smaller than the one shown by PDMS in static conditions. Furthermore, the opening pressure was almost not affected by such a thin layer of crystals. DLC‐coated valves showed even less encrustations at the same time‐point, with no significant loss of performance over time, although they were featured by a higher variability. These results suggest that most encrustations can be removed by the mechanical action of the valve during daily openings/closures. Such a self‐cleaning behavior with respect to a static condition opens exciting scenarios for the long‐term functionality of mobile devices operating in the urinary environment.

In vivo urinary compatibility of Mg-Sr-Ag alloy in swine model

A biodegradable metallic ureteral stent with suitable mechanical properties and antibacterial activity remains a challenge. Here we reveal the scientific significance of a biodegradable Mg-Sr-Ag alloy with a favorable combination of balanced mechanical properties, adjustable indwelling time in urinary tract and evident antibacterial activity via in vivo experiments in a swine model. Attributed to the rheo-solidification process, equiaxial microstructure and significantly refined grains (average grain size: 27.1 μm) were achieved. Mg₁₇Sr₂ and Mg₄Ag were found as the primary precipitates in the matrix, due to which the alloy obtained ca. 111% increase in ultimate tensile strength in comparison to pure magnesium. Both the in vitro and in vivo results demonstrated the satisfactory biocompatibility of the alloy. Histological evaluation and bioindicators analysis suggested that there was no tissue damage, inflammation and lesions in the urinary system caused by the degradation process. The stent also improved the post-operative bladder functions viewed from the urodynamic results. Our findings highlight the potential of this alloy as antibacterial biodegradable urinary implant material.

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Innovative biodegradable antibacterial Mg-Sr-Ag alloy.

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In vivo study in pig ureter models.

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Enhanced mechanical properties and adjustable indwelling time.

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Outstanding urinary compatibility and evident antibacterial activity.

Bioresorbable Metals for Biomedical Applications: From Mechanical Components to Electronic Devices

Bioresorbable metals and metal alloys are of growing interest for myriad uses in temporary biomedical implants. Examples range from structural elements as stents, screws, and scaffolds to electronic components as sensors, electrical stimulators, and programmable fluidics. The associated physical forms span mechanically machined bulk parts to lithographically patterned conductive traces, across a diversity of metals and alloys based on magnesium, zinc, iron, tungsten, and others. The result is a rich set of opportunities in healthcare materials science and engineering. This review article summarizes recent advances in this area, starting with an historical perspective followed by a discussion of materials options, considerations in biocompatibility, and device applications. Highlights are in system level bioresorbable electronic platforms that support functions as diagnostics and therapeutics in the context of specific, temporary clinical needs. A concluding section highlights challenges and emerging research directions.

In vitro and in vivo degradation assessment and preventive measures of biodegradable Mg alloys for biomedical applications

Magnesium (Mg) and its alloys have been widely explored as a potential biodegradable implant material. However, the fast degradation of Mg-based alloys under physiological environment has hindered their widespread use for implant applications till date. The present review focuses on in vitro and in vivo degradation of biodegradable Mg alloys, and preventive measures for biomedical applications. Initially, the corrosion assessment approaches to predict the degradation behavior of Mg alloys are discussed along with the measures to control rapid corrosion. Furthermore, this review attempts to explore the correlation between in vitro and in vivo corrosion behavior of different Mg alloys. It was found that the corrosion depends on experimental conditions, materials and the results of different assessment procedures hardly matches with each other. It has been demonstrated the corrosion rate of magnesium can be tailored by alloying elements, surface treatments and heat treatments. Various researches also studied different biocompatible coatings such as dicalcium phosphate dihydrate (DCPD), β-tricalcium phosphate (β-TCP), hydroxyapatite (HA), polycaprolactone (PCL), polylactic acid (PLA), and so on, on Mg alloys to suppress rapid degradation and examine their influence on new bone regeneration as well. This review shows the need for a standard method of corrosion assessment to predict the in vivo corrosion rate based on in vitro data, and thus reducing the in vivo experimentation.

Antibacterial metals and alloys for potential biomedical implants

Metals and alloys, including stainless steel, titanium and its alloys, cobalt alloys, and other metals and alloys have been widely used clinically as implant materials, but implant-related infection or inflammation is still one of the main causes of implantation failure. The bacterial infection or inflammation that seriously threatens human health has already become a worldwide complaint. Antibacterial metals and alloys recently have attracted wide attention for their long-term stable antibacterial ability, good mechanical properties and good biocompatibility in vitro and in vivo. In this review, common antibacterial alloying elements, antibacterial standards and testing methods were introduced. Recent developments in the design and manufacturing of antibacterial metal alloys containing various antibacterial agents were described in detail, including antibacterial stainless steel, antibacterial titanium alloy, antibacterial zinc and alloy, antibacterial magnesium and alloy, antibacterial cobalt alloy, and other antibacterial metals and alloys. Researches on the antibacterial properties, mechanical properties, corrosion resistance and biocompatibility of antibacterial metals and alloys have been summarized in detail for the first time. It is hoped that this review could help researchers understand the development of antibacterial alloys in a timely manner, thereby could promote the development of antibacterial metal alloys and the clinical application.

Microbial fuel cells for remediation of environmental pollutants and value addition: Special focus on coupling diatom microbial fuel cells with photocatalytic and photoelectric fuel cells

With the advent of global industrialisation and adaptation of smart life there is rise in anthropogenic pollution especially in water. Remediation of the pollutants (such as metals, and dyes) present in industrial effluents is possible via microbes and algae present in the environment. Microbes are used in a microbial fuel cell (MFC) for remediation of various organic and inorganic pollutants. However, for industrial scale application coupling the MFCs with photocatalytic and photoelectric fuel cell has a potential in improving the output of power. It can also be used for remediation of pollutants more expeditiously, conserving fossil fuels, cleaning environment, hence making the coupled hybrid fuel cell to run economically. Furthermore, such MFC inbuilt with algae in living or powder form give additional value addition products like biofuel, polysaccharides, biopolymers, and polyhydroxy alkanoates etc. This review provides bird's eye view on the removal of environmental pollutants by different biological sources like bacteria and algae. The article is focussed on diatoms as potential algae since they are rich source of crude oil and high value added products in a hybrid photocatalytic MFC. It also covers bottle necks, challenges and future in this field of research.

Potential strategies to prevent encrustations on urinary stents and catheters - thinking outside the box: a European network of multidisciplinary research to improve urinary stents (ENIUS) initiative

Introduction: Urinary stents have been around for the last 4 decades, urinary catheters even longer. They are associated with infections, encrustation, migration, and patient discomfort. Research efforts to improve them have shifted onto molecular and cellular levels. ENIUS brought together translational scientists to improve urinary implants and reduce morbidity.Methods & materials: A working group within the ENIUS network was tasked with assessing future research lines for the improvement of urinary implants.Topics were researched systematically using Embase and PubMed databases. Clinicaltrials.gov was consulted for ongoing trials.Areas covered: Relevant topics were coatings with antibodies, enzymes, biomimetics, bioactive nano-coats, antisense molecules, and engineered tissue. Further, pH sensors, biodegradable metals, bactericidal bacteriophages, nonpathogenic uropathogens, enhanced ureteric peristalsis, electrical charges, and ultrasound to prevent stent encrustations were addressed.Expert opinion: All research lines addressed in this paper seem viable and promising. Some of them have been around for decades but are yet to proceed to clinical application (i.e. tissue engineering). Others are very recent and, at least in urology, still only conceptual (i.e. antisense molecules). Perhaps the most important learning point resulting from this pan-European multidisciplinary effort is that collaboration between all stakeholders is not only fruitful but also truly essential.

Based on the synergistic effect of Mg2+ and antibacterial peptides to improve the corrosion resistance, antibacterial ability and osteogenic activity of magnesium-based degradable metals

To overcome the restricted degradation, poor antiacterial and osteoindctive problems of magnesium and its alloys, this study presented the spinning coating of an antimicrobial peptide (AP)-loaded silk fibroin (SF) composite onto a corrosion-resistant MgO-coated AZ31 Mg alloy via anodization (aMgO) and electrodeposition (eMgO) methods. The composite coatings not only created a smooth and hydrophilic surface, but also obviously improved the corrosion resistance according to the test of corrosion potential and current density. The colonization of E. coli on MgO-AP composite coatings was significantly reduced as compared to the MgO layers, due to the potential synergetic effects of APs and Mg2+. Compared with the bare AZ31, the composite coating inhibited the corrosion of the substrate and the release of Mg2+, supported the adhesion, spreading and proliferation of osteoblasts, and presented a significantly improved osteogenic differentiation trend. Therefore, the MgO-AP composite coating, which had both antibacterial and bone-promoting abilities, was expected to be applied for surface modification of magnesium alloy implants to solve the clinical problems of bacterial infection and poor osseointegration.

In vivo assessment of biodegradable magnesium alloy ureteral stents in a pig model

Today, ureteral stent technology is making progress towards the reduction of complications and patient discomfort. Therefore, magnesium alloys have become excellent candidate materials for manufacturing ureteral stents due to their biodegradability and antibacterial activity. Built on our previous work on biodegradable magnesium alloys, this article reports a semisolid rheo-formed magnesium implant that displays degradability and biocompatibility in vivo, and feasibility as ureteral stents in a pig model. Refined non-dendritic microstructure was observed in the rheo-formed alloy, whose grain size and shape factor were ca. 25.2 μm and ca. 1.56 respectively. Neither post-interventional inflammation nor pathological changes were observed in the urinary system during the implantation period of 14 weeks, and the degradation profile (14 weeks) meets the common requirement for the indwelling time of ureteral stents (8 to 16 weeks). Furthermore, histopathological observation and urinalysis results confirmed that the alloy had significantly higher antibacterial activity than the medical-grade stainless steel control. To our knowledge, this is the first in vivo study of biodegradable magnesium alloy as urinary implants in large animal models. Our results demonstrate that magnesium alloys may be a reasonable option for manufacturing biodegradable ureteral stents.

Evaluation of a novel biodegradable ureteral stent produced from polyurethane and magnesium alloys

Indwelling ureteral stents represent a very frequently used procedure in urological clinical practice that ensures the drainage of urine from the upper urinary tract. However, the stents could result in many stent-associated complications, such as encrustation and patient discomfort. We developed a new type of biodegradable ureteral stents produced from degradable polyurethane and magnesium alloys. In the present study, we investigated the biocompatibility and the property of degradation of the biodegradable ureteral stents. We evaluated the cytotoxicity of biodegradable ureteral stent by the MTT assay in vitro. The rabbit dorsal muscle embedding test was used to assess the biocompatibility of the degradable stents. Inflammation and fibrosis of muscle tissue were noted to evaluate compatibility at 1, 2, 4, 6 weeks after stents implanted in muscle. The degradation of the biodegradable ureteral stents was assessed by measuring the weight loss of the samples in AUS (artificial urine solution). For validating the degradation property of degradable stents in vivo, we inserted a degradable stent or a conventional biostable stent into Bama pigs. Furthermore, blood studies, liver function tests, renal function tests, urine studies, and computerized tomography (CT) were performed postoperatively. Our study confirms that the degradable polyurethane-based biodegradable ureteral stent has good biocompatibility. Our biodegradable ureteral stents were completely degraded within 4 weeks and provided a better ability of drainage than conventional stents. They hold promise for decreasing the need for a secondary procedure and stent related morbidity, such as infections.

An Antibacterial Strategy of Mg-Cu Bone Grafting in Infection-Mediated Periodontics

Periodontal diseases are mainly the results of infections and inflammation of the gum and bone that surround and support the teeth. In this study, the alveolar bone destruction in periodontitis is hypothesized to be treated with novel Mg-Cu alloy grafts due to their antimicrobial and osteopromotive properties. In order to study this new strategy using Mg-Cu alloy grafts as a periodontal bone substitute, the in vitro degradation and antibacterial performance were examined. The pH variation and Mg²⁺ and Cu²⁺ release of Mg-Cu alloy extracts were measured. Porphyromonas gingivalis (P. gingivalis) and Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans), two common bacteria associated with periodontal disease, were cultured in Mg-Cu alloy extracts, and bacterial survival rate was evaluated. The changes of bacterial biofilm and its structure were revealed by scanning electron microscopy (SEM) and transmission electronic microscopy (TEM), respectively. The results showed that the Mg-Cu alloy could significantly decrease the survival rates of both P. gingivalis and A. actinomycetemcomitans. Furthermore, the bacterial biofilms were completely destroyed in Mg-Cu alloy extracts, and the bacterial cell membranes were damaged, finally leading to bacterial apoptosis. These results indicate that the Mg-Cu alloy can effectively eliminate periodontal pathogens, and the use of Mg-Cu in periodontal bone grafts has a great potential to prevent infections after periodontal surgery.

Exposure to New Emerging Bisphenols Among Young Children in Switzerland

Restrictions on the use of bisphenol A (BPA) in consumer products led to its replacement by various bisphenol (BP) analogues, yet young children's exposure to these analogues has been poorly characterized so far. This study aimed to characterize infants' and toddlers' exposure to BPA and 14 emerging BP analogues (i.e., bisphenol AF, bisphenol AP, bisphenol B, bisphenol BP, bisphenol C (BPC), bisphenol E, bisphenol F (BPF), bisphenol G, bisphenol M (BPM), bisphenol P, bisphenol PH, bisphenol S (BPS), bisphenol TMC, and bisphenol Z). We extracted infants' and toddlers' urine from diapers (n = 109) collected in Swiss daycare centers as a practical and noninvasive alternative approach to urinary biomonitoring. Bisphenols were present in 47% of the samples, with BPC and BPM being the most frequently detected (23% and 25% of all samples, respectively). The mean concentrations of urinary BPS and BPF were greater than that of BPA. This contrasts with data reported previously. Furthermore, statistical analysis revealed a significant and negative correlation between urinary BPM concentration and the population's age. Our results provide a first characterization of infants' and toddlers' exposure to bisphenols in Switzerland. This knowledge can be used to support ongoing biomonitoring studies and to prioritize exposure reduction and prevention strategies.

A biodegradable multifunctional nanofibrous membrane for periodontal tissue regeneration

Biomaterial-based membranes represent a promising therapeutic option for periodontal diseases. Although conventional periodontal membranes function greatly in preventing the ingrowth of both fibroblasts and epithelial cells as well as connective tissues, they are not capable of promoting periodontal tissue regeneration. Here, we report a multifunctional periodontal membrane prepared by electrospinning biodegradable polymers with magnesium oxide nanoparticles (nMgO). nMgO is a light metal-based nanoparticle with high antibacterial capacity and can be fully resorbed in the body. Our results showed that incorporating nMgO into poly(L-lactic acid) (PLA)/gelatin significantly improved the overall properties of membranes, including elevated tensile strength to maintain structural stability and adjusted degradation rate to fit the time window of periodontal regeneration. Acidic degradation products of PLA were neutralized by alkaline ions from nMgO hydrolysis, ameliorating pH microenvironment beneficial for cell proliferation. In vitro studies demonstrated considerable antibacterial and osteogenic properties of nMgO-incorporated membranes that are highly valuable for periodontal regeneration. Further investigations in a rat periodontal defect model revealed that nMgO-incorporated membranes effectively guided periodontal tissue regeneration. Taken together, our data indicate that nMgO-incorporated membranes might be a promising therapeutic option for periodontal regeneration. STATEMENT OF SIGNIFICANCE: Traditional clinical treatments of periodontal diseases largely focus on the management of the pathologic processes, which cannot effectively regenerate the lost periodontal tissue. GTR, a classic method for periodontal regeneration, has shown promise in clinical practice. However, the current membranes might not fully fulfill the criteria of ideal membranes. Here, we report bioabsorbable nMgO-incorporated nanofibrous membranes prepared by electrospinning to provide an alternative for the clinical practice of GTR. The membranes not only function greatly as physical barriers but also exhibit high antibacterial and osteoinductive properties. We therefore believe that this study will inspire more practice work on the development of effective GTR membranes for periodontal regeneration.

The role of magnesium in biomaterials related infections

Magnesium is currently increasing interest in the field of biomaterials. An extensive bibliography on this material in the last two decades arises from its potential for the development of biodegradable implants. In addition, many researches, motivated by this progress, have analyzed the performance of magnesium in both in vitro and in vivo assays with gram-positive and gram-negative bacteria in a very broad range of conditions. This review explores the extensive literature in recent years on magnesium in biomaterials-related infections, and discusses the mechanisms of the Mg action on bacteria, as well as the competition of Mg²⁺ and/or synergy with other divalent cations in this subject.

Advances in Drug Delivery via Biodegradable Ureteral Stent for the Treatment of Upper Tract Urothelial Carcinoma

Drug eluting ureteral stent is an effective means for local drug delivery to the urinary tract. It can potentially solve a variety of upper urinary tract problems, such as stent-related urinary tract infections and discomfort, ureteral stricture, and neoplastic diseases. However, the release of drug elutes on the surface of biostable stents is unsustainable and uncontrollable. With the development of biomaterial science, the emergence of biodegradable ureteral stents (BUSs) provides a new approach for local drug delivery in the urinary tract. The drugs can be continuously released in a controlled manner from a drug-eluting BUS, when the stent degrades. Especially for the delivery of anti-tumor drugs, the stents can obviously improve the therapeutic effectiveness of the drugs by prolonging the contact duration of the drug and tumor cells. In addition, a secondary stent removal procedure can be avoided. The purpose of this review article is to provide an overview of anti-tumor drug-eluting BUSs and discuss the biomaterials and drug delivery systems of BUS that are currently being developed to deliver anti-tumor drugs for upper tract urothelial carcinoma.

In vitro antibacterial activity and cytocompatibility of magnesium-incorporated poly(lactide-co-glycolic acid) scaffolds

BACKGROUND

Bone defects are often combined with the risk of infection in the clinic, and artificial bone substitutes are often implanted to repair the defective bone. However, the implant materials are carriers for bacterial growth, and biofilm can form on the implant surface, which is difficult to eliminate using antibiotics and the host immune system. Magnesium (Mg) was previously reported to possess antibacterial potential.

METHODS

In this study, Mg was incorporated into poly(lactide-co-glycolic acid) (PLGA) to fabricate a PLGA/Mg scaffold using a low-temperature rapid-prototyping technique. All scaffolds were divided into three groups: PLGA (P), PLGA/10 wt% Mg with low Mg content (PM-L) and PLGA/20 wt% Mg with high Mg content (PM-H). The degradation test of the scaffolds was conducted by immersing them into the trihydroxymethyl aminomethane-hydrochloric acid (Tris-HCl) buffer solution and measuring the change of pH values and concentrations of Mg ions. The antibacterial activity of the scaffolds was investigated by the spread plate method, tissue culture plate method, scanning electron microscopy and confocal laser scanning microscopy. Additionally, the cell attachment and proliferation of the scaffolds were evaluated by the cell counting kit-8 (CCK-8) assay using MC3T3-E1 cells.

RESULTS

The Mg-incorporated scaffolds degraded and released Mg ions and caused an increase in the pH value. Both PM-L and PM-H inhibited bacterial growth and biofilm formation, and PM-H exhibited higher antibacterial activity than PM-L after incubation for 24 and 48 h. Cell tests revealed that PM-H exerted a suppressive effect on cell attachment and proliferation.

CONCLUSIONS

These findings demonstrated that the PLGA/Mg scaffolds possessed favorable antibacterial activity, and a higher content of Mg (20%) exhibited higher antibacterial activity and inhibitory effects on cell attachment and proliferation than low Mg content (10%).

A systematic review of the interaction and effects generated by antimicrobial metallic substituents in bone tissue engineering

Changes brought about by metal ions and metal nanoparticles within bacterial cells and the damage caused to the cellular membrane upon contact with negatively charged surface components.

A surface-engineered multifunctional TiO2 based nano-layer simultaneously elevates the corrosion resistance, osteoconductivity and antimicrobial property of a magnesium alloy

Magnesium biometals exhibit great potentials for orthopeadic applications owing to their biodegradability, bioactive effects and satisfactory mechanical properties. However, rapid corrosion of Mg implants in vivo combined with large amount of hydrogen gas evolution is harmful to bone healing process which seriously confines their clinical applications. Enlightened by the superior biocompatibility and corrosion resistance of passive titanium oxide layer automatically formed on titanium alloy, we employ the Ti and O dual plasma ion immersion implantation (PIII) technique to construct a multifunctional TiO₂ based nano-layer on ZK60 magnesium substrates for enhanced corrosion resistance, osteoconductivity and antimicrobial activity. The constructed nano-layer (TiO₂/MgO) can effectively suppress degradation rate of ZK60 substrates in vitro and still maintain 94% implant volume after post-surgery eight weeks. In animal study, a large amount of bony tissue with increased bone mineral density and trabecular thickness is formed around the PIII treated group in post-operation eight weeks. Moreover, the newly formed bone in the PIII treated group is well mineralized and its mechanical property almost restores to the level of that of surrounding mature bone. Surprisingly, a remarkable killing ratio of 99.31% against S. aureus can be found on the PIII treated sample under ultra-violet (UV) irradiation which mainly attributes to the oxidative stress induced by the reactive oxygen species (ROS). We believe that this multifunctional TiO₂ based nano-layer not only controls the degradation of magnesium implant, but also regulates its implant-to-bone integration effectively. STATEMENT OF SIGNIFICANCE: Rapid corrosion of magnesium implants is the major issue for orthopaedic applications. Inspired by the biocompatibility and corrosion resistance of passive titanium oxide layer automatically formed on titanium alloy, we construct a multifunctional TiO₂/MgO nanolayer on magnesium substrates to simultaneously achieve superior corrosion resistance, satisfactory osteoconductivity in rat intramedullary bone defect model and excellent antimicrobial activity against S. aureus under UV irradiation. The current findings suggest that the specific TiO₂/MgO nano-layer on magnesium surface can achieve the three objectives aforementioned and we believe this study can demonstrate the potential of biodegradable metals for future clinical applications.

Biological Assessment of Zn-Based Absorbable Metals for Ureteral Stent Applications

The use of ureteral stents to relieve urinary tract obstruction is still challenged by the problems of infection, encrustation, and compression, leading to the need for early removal procedures. Biodegradable ureteral stents, commonly made of polymers, have been proposed to overcome these problems. Recently, absorbable metals have been considered as potential materials offering both biodegradation and strength. This work proposed zinc-based absorbable metals by firstly evaluating their cytocompatibility toward normal primary human urothelial cells using 2D and 3D assays. In the 2D assay, the cells were exposed to different concentrations of metal extracts (i.e., 10 mg/mL of Zn-1Mg and 8.75 mg/mL of Zn-0.5Al) for up to 3 days and found that their cytoskeletal networks were affected but were recovered at day 3, as observed by immunofluorescence. In the 3D ureteral wall tissue construct, the cells formed a multilayered urothelium, as found in native tissue, with the presence of tight junctions at the superficial layer and laminin at the basal layer, indicating a healthy tissue condition even with the presence of the metal samples for up to 7 days of exposure. The basal cells attached to the metal surface as seen in a natural spreading state with pseudopodia and fusiform morphologies, indicating that the metals were non-toxic.

In vitro and in vivo studies on magnesium alloys to evaluate the feasibility of their use in obstetrics and gynecology

Magnesium and its alloys were widely investigated in many body fluid microenvironments including bone, blood, bile, saliva, and urine; however, no study has been conducted in the intrauterine microenvironment. In this study, the degradation behaviors of HP-Mg, Mg-1Ca, and Mg-2Zn alloys in simulated uterine fluid (SUF) were systematically investigated, and then the biological response of four kinds of uterine cells to these materials was observed. For this purpose, the gluteal muscle of rat was used as the implantation position to study the in vivo biocompatibility as a mimic of the intrauterine device (IUD) fixation part. The 120-day immersion test indicated that the Mg-1Ca alloy had a faster degradation rate than the Mg-2Zn alloy and HP-Mg and dissolved entirely in the SUF. Indirect cytotoxicity assay showed that the extracts of HP-Mg, Mg-1Ca, and Mg-2Zn alloys have positive effects on human uterine smooth muscle cells (HUSMC), human endometrial epithelial cells (HEEC), and human endometrial stromal cells (HESC), especially for the Mg-1Ca alloy group. Furthermore, the in vivo experiment showed that HP-Mg, Mg-1Ca, and Mg-2Zn alloy implants cause a light inflammatory response in the initial 3 days, but they were surrounded mainly by connective tissue, and lymphocytes were rarely observed at 4 weeks. Based on the above facts, we believed that it is feasible for using biomedical Mg alloys in obstetrics and gynecology and proposed three kinds of medical device candidates for future R&D. Statement of Significance Magnesium alloys were widely investigated in various body microenvironments including bone, blood, bile, saliva, and urine; however, no study has been conducted in the intrauterine environment. In this work, the degradation behaviors of Mg alloys in simulated uterine fluid were systematically investigated, and then the biological response of four kinds of uterine cells to these materials was observed. For this purpose, the tibialis anterior of a rat model was used as the implantation position to study the in vivo biocompatibility. The comprehensive in vitro and in vivo testing results indicated that biomedical Mg alloys are feasible for use in obstetrics and gynecology. Further, three kinds of medical device candidates were proposed.

A portable device for studying the effects of fluid flow on degradation properties of biomaterials inside cell incubators

A portable device was designed and constructed for studying the properties of biomaterials in physiologically relevant fluids under controllable flow conditions that closely simulate fluid flow inside the body. The device can fit entirely inside a cell incubator; and, thus, it can be used directly under standard cell culture conditions. An impedance-driven pump was built in the sterile flow loop to control the flow rates of fluids, which made the device small and portable for easy deployment in the incubator. To demonstrate the device functions, magnesium (Mg) as a representative biodegradable material was tested in the flow device for immersion degradation under flow versus static conditions, while the flow module was placed inside a standard cell incubator. The flow rate was controlled at 0.17 ± 0.06 ml/s for this study; and, the flow rate is adjustable through the controller module outside of incubators for simulating the flow rates in the ranges of blood flow in human artery (0.05 ∼0.43 ml/s) and vein (0.02 ∼0.08 ml/s). Degradation of Mg under flow versus static conditions was characterized by measuring the changes of sample mass and thickness, and Mg2+ ion concentrations in the immersion media. Surface chemistry and morphology of Mg after immersion under flow versus static conditions were compared. The portable impedance-driven flow device is easy to fit inside an incubator and much smaller than a peristaltic pump, providing a valuable solution for studying biomaterials and implants (e.g. vascular or ureteral stents) in body fluids under flow versus static conditions with or without cells.

In Vitro Degradation of Absorbable Zinc Alloys in Artificial Urine

Absorbable metals have potential for making in-demand rigid temporary stents for the treatment of urinary tract obstruction, where polymers have reached their limits. In this work, in vitro degradation behavior of absorbable zinc alloys in artificial urine was studied using electrochemical methods and advanced surface characterization techniques with a comparison to a magnesium alloy. The results showed that pure zinc and its alloys (Zn⁻0.5Mg, Zn⁻1Mg, Zn⁻0.5Al) exhibited slower corrosion than pure magnesium and an Mg⁻2Zn⁻1Mn alloy. The corrosion layer was composed mostly of hydroxide, carbonate, and phosphate, without calcium content for the zinc group. Among all tested metals, the Zn⁻0.5Al alloy exhibited a uniform corrosion layer with low affinity with the ions in artificial urine.

Responses of human urothelial cells to magnesium-zinc-strontium alloys and associated insoluble degradation products for urological stent applications

Current urological devices such as ureteral stents and catheters still face serious problems, such as encrustation and biofilm formation. Magnesium (Mg) and its alloys showed great potentials as an alternative material for urological devices, due to their excellent biodegradability and antibacterial property. In this study, a serial of four promising Mg alloys which contain zinc (Zn) and strontium (Sr), i.e., Mg-4Zn-xSr (ZSr41) alloys, were investigated in vitro for potential ureteral stent application. Specifically, these four alloys have 4 wt% Zn in all and 0.15 wt% Sr in ZSr41_A, 0.5 wt% Sr in ZSr41_B, 1.0 wt% Sr in ZSr41_C and 1.5 wt% Sr in ZSr41_D. The cytocompatibility and degradation behaviors of Mg-4Zn-xSr alloys were studied by culturing with human urothelial cells (HUCs) for 24 h and 48 h using exposure culture method. ZSr41_B showed a better cytocompatibility with HUCs among all the Mg-4Zn-xSr alloys in both 24-hour and 48-hour cultures. Moreover, the cytocompatibility of insoluble degradation products of Mg, i.e., MgO and Mg(OH)₂, was also investigated by culturing different concentrations of MgO and Mg(OH)₂ nanoparticles with HUCs for 24 h and 48 h. The concentration of MgO and Mg(OH)₂ particles at 0.5 mg/mL and above, showed a significant decrease of cell density and cell size after 24-hour and 48-hour cultures. The concentration of MgO and Mg(OH)₂ at 1.0 mg/mL and above, showed no viable cells after 24-hour culture. Collectively, it is recommended to further reduce the degradation rates of Mg alloys in order to control possible side effects of the soluble and insoluble degradation products and to take the benefits of Mg-based biodegradable ureteral stents toward the future clinical translation.

Prospects for the research and application of biodegradable ureteral stents: from bench to bedside

Ureteral stents are commonly used in urological practices but are frequently associated with patient discomfort, encrustation and stent-related infection. And a second procedure is needed to remove the stent. New biomaterials and designs have been attempted to solve these problems. The development of biodegradable ureteral stent shows promising prospects in future clinical applications. This article reviews the biomaterials and preparation methods commonly used in the present study of biodegradable ureteral stents. To date, none of the technological developments has lead to the 'ideal' biodegradable ureteral stent, but much progress has been made in the stent design by improving the physical characteristics and biocompatibility of the biomaterials. The controllability of degradation, the biggest problem faced currently, still needs to be further improved. In the future, the nanotechnology and chemical modification of biomaterials may be able to further optimize the properties of degradation.

Corrosion protection of AZ31 alloy and constrained bacterial adhesion mediated by a polymeric coating obtained from a phytocompound

The prevention of microbial biofilm formation on a biomaterial surface is crucial in avoiding implants failures and the development of antibiotic resistant bacteria. It was reported that biodegradable Mg alloys may show antimicrobial effects due to the alkalinization of the corroding area. However, this issue is controversial and deserves a detailed study, since the processes occurring at the [biodegradable metal/biological medium] interface are complex and varied. Results showed that bacterial adhesion on AZ31 was lower than that of the titanium control and revealed that was dependent on surface composition, depicting some preferential sites for bacterial attachment (C-, P-, O-containing corrosion products) and others that are particularly avoided (active corrosion sites). As a key challenge, a strategy able to improve the performance of Mg alloys by both, reducing the formation of corrosion products and inhibiting bacterial adhesion was subsequently developed. A polymeric layer (polyTOH) was obtained by electropolymerization of thymol (TOH), a phytophenolic compound. The polyTOH can operate as a multifunctional film that improves the surface characteristics of the AZ31 Mg alloy by enhancing corrosion resistance (ions release was reduced to almost the half during the first days) and create an anti-adherent surface (bacterial attachment was 30-fold lower on polyTOH-AZ31 than on non-coated Mg alloy and 200-fold lower than Ti control and was constrained to specific regions). This anti-adherent property implies an additional advantage: enhancement of the efficacy of antibiotic treatments.

Investigation of a novel gradient degradable ureteral stent in a beagle dog model

Ureteral stents are widely used in the department of urology, while the stent could result in many stent-associated complications, such as encrustation, a forgotten stent and patient discomfort. Thus, we developed a novel gradient degradable ureteral stent, which could degrade gradient in vivo, and assessed its effectiveness of the drainage, degradation and biocompatibility in a beagle dog model. In the present study, the degradation time and cytotoxicity were investigated in vitro. And the beagle dogs were inserted with a degradable stent or a biostable stent, and blood studies, liver function tests, renal function tests, urine studies, X-ray, excretory urograms and computerized tomography were performed at immediately, two weeks, four weeks and six weeks postoperative. The results showed that the drainage of the novel stent is similar to the conventional stent, while the biocompatibility and antibacterial ability of the novel stents are better than the conventional stents. The stents we developed provide an alternative for urologists and more assays would be performed in detail to assess the property of the stents.

Anti-fibrotic function of Cu-bearing stainless steel for reducing recurrence of urethral stricture after stent implantation

Recurrent stenosis is the main reason inducing the failure of urethral stricture treatment. Our previous study has found that the 316L type Cu bearing stainless steel (316L-Cu SS) showed antimicrobial activity and anti-encrustation performance when it was used for relieving urethral obstructer. However, whether it can reduce the occurrence of fibrosis or not, we need further investigation to compare the cellular and molecular responses of human urethral scar fibroblast cells (USFCs) on 316L-Cu SS and medical grade 316L stainless (316L SS, as a control). [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4- sulfophenyl)- 2H-tetrazolium (MTS) and Transwell were used to assess the cellular responses, which confirmed that 316L-Cu SS could inhibit proliferation and migration of USFCs. Molecular expressions of fibrosis were evaluated by western blot, real-time quantitative polymerase chain reaction (qPCR), and Cu/Zn superoxide dismutase (CuZnSOD) measurement. The results indicated that up-regulating of CuZnSOD attenuated the transforming growth factor-β1 expression and phosphorylation of Smad3 after exposure to 316L-Cu SS. Besides, the content of collagen type I (COL1) and collagen type III (COL3) secreting into the culture medium measured by enzyme-linked immunosorbent assay were in accord with the results of messenger ribonucleic acids. Both of them exhibited lower levels of COL1/COL3 exposure to 316L-Cu SS, demonstrating the inhibitory performance of 316L-Cu SS against fibrosis. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2019-2028, 2018.

Anodization of magnesium for biomedical applications - Processing, characterization, degradation and cytocompatibility

This article reports anodization of Mg in KOH electrolyte and the associated surface, degradation, and biological properties for bioresorbable implant applications. The preparation procedures for electrodes and anodization setup significantly enhanced reproducibility of samples. The results of anodization performed at the applied potentials of 1.8, 1.9, or 2.0V showed that the sample anodized at 1.9V and annealed, referred to as the 1.9 AA sample, had homogenous surface microstructure and elemental composition, and a reduction in corrosion current density in the electrochemical testing. In comparison with Mg control, the 1.9 AA sample showed a distinct mode of degradation, e.g., continuous growth of a passivation layer enriched with Ca and P instead of typical localized pitting and undermining, and a greater release rate of Mg²⁺ ions when immersed in physiologically relevant media. In the direct culture with bone marrow derived mesenchymal stem cells (BMSCs) in vitro, the 1.9 AA sample did not affect BMSC adhesion and morphology under indirect contact; however, the 1.9 AA sample showed a reduction in cell spreading under direct contact. The change in surface topography/composition at the dynamic interface of the anodized-annealed Mg sample might have contributed to the change in BMSC morphology. In summary, this study demonstrated the potential of anodic oxidation to modulate the degradation behaviors of Mg-based biomaterials and BMSC responses in vitro, and confirmed the value of direct culture method for studying cytocompatibility of Mg-based biomaterials for medical implant applications.

STATEMENT OF SIGNIFICANCE

Magnesium (Mg)-based biomaterials have been specifically designed and actively explored for biodegradable implant applications since the early 2000s. To realize the benefits of Mg-based materials for medical implant applications, it is critical to control the rate of Mg degradation (i.e. corrosion) in the body. We investigated an environmentally friendly anodization process using KOH electrolyte for modifying the surface of Mg-based materials, and the resulted surface, degradation, and biological properties for biomedical applications. This study reported critical considerations that are important for repeatability of anodization process, homogeneity of surface microstructure and composition, and in vitro evaluations of the degradation and biological properties of surface treated Mg samples. The details in preparation of electrodes, anodization setup, annealing, and sample handling before and after surface treatment (e.g. re-embedding) reported in this article are valuable for studying a variety of electrochemical processes for surface treatment of Mg-based metals, because of enhanced reproducibility.

The influence of two common sterilization techniques on the corrosion of Mg and its alloys for biomedical applications

This paper studied the influence of two common sterilization techniques, ethylene oxide (EO) and gamma irradiation (GI), on the corrosion rate of four Mg-based materials in CO₂ -bicarbonate buffered Hanks' solution. The four materials were: high-purity (HP)-Mg, ZE41, ultra-high purity (XHP)-Mg, and XHP-ZX00. The corrosion rate was measured through mass loss (P_m ) and hydrogen evolution (P_H ). Two-way analysis of variance (ANOVA) was conducted to assess the effect of the sterilization techniques on the corrosion rates across the four materials. The ANOVA analyzed the variables of (1) material, (2) sterilization condition (EO, GI, and an unsterilized control group), and (3) the interaction between these two independent variables. Neither sterilization technique (EO and GI) significantly influenced the corrosion rate as measured by P_m (p < 0.84) nor P_H (p < 0.08). This result was consistent across the four materials tested, as there was no interaction between the test variables of material and sterilization condition for P_m (p < 0.49) or P_H (p < 0.27). As neither EO nor GI influenced the corrosion rates, either of these techniques warrants consideration for use on Mg-based medical implants and devices. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1907-1917, 2018.

In vivo Study on the Corrosion Behavior of Magnesium Alloy Surface Treated with Micro-arc Oxidation and Hydrothermal Deposition

OBJECTIVE

To study the corrosion behavior of magnesium alloy surface treated with micro-arc oxidation and hydrothermal deposition in living animals.

METHODS

A magnesium oxide (MgO) layer was prepared on Mg alloy using micro-arc oxidation technology, and then a composite coating composed of magnesium hydroxide, hydroxyapatite, and MgO was coated on the MgO layer using the hydrothermal deposition method for 2 h and 24 h. Male 3-month-old white New Zealand rabbits (n = 48) weighting 2200-2300 g, were divided into four groups randomly. The prepared Mg alloy samples with composite coatings were implanted into the femoral medullary cavity of rabbits. For the Mg group, bare Mg samples without any treatment were implanted; for the MgO group, bare Mg samples undergoing MAO treatment were implanted; for the HT2h group, samples of the MgO group undergoing hydrothermal treatment (HT) for 2 h were implanted; and for the HT24h group, samples of group MgO undergoing HT for 24 h were implanted. Then the in vivo corrosion behaviors of implants were evaluated by X-ray observation, micro-CT analysis and serum Mg2+ examination.

RESULTS

The X-ray showed that samples implanted in animals were decreased as time went by. The micro-CT showed that on the fourth week, the residual volume percentages (RVP) of samples of the Mg, MgO, HT2h, and HT24h groups were 72.81% ± 2.10%, 71.68% ± 1.49%, 81.14% ± 1.54%, and 82.04% ± 0.89%, respectively; on the eighth week, the RVP of four groups were 29.45% ± 1.06%, 41.82% ± 1.13%, 53.92% ± 0.37%, and 62.53% ± 2.06%, respectively; while on the 12th week, RVP were 8.45% ± 0.49%, 9.97% ± 0.75%, 37.09% ± 0.89%, 46.71% ± 1.87%. The RVP of the HT2h group and the HT24h group were higher than for the Mg group and the MgO group for all three time points (P < 0.05); the RVP for HT24h was higher than for HT2h at 8 and 12 weeks, and the differences were significant, indicating that the degradation of Mg alloy slowed down after composite coating. In addition, the composite-coated Mg alloy by 24-h hydrothermal treatment exhibited a slower degradation than that treated by 2 h. Serum Mg2+ concentration results showed that on the second week, the Mg2+ concentrations of the Mg, MgO, HT2h, and HT24h groups were 2.24 ± 0.10 mmol/L, 2.12 ± 0.07 mmol/L, 2.06 ± 0.11 mmol/L, and 2.15 ± 0.12 mmol/L, respectively. On the fourth week, these concentrations were 1.99 ± 0.33 mmol/L, 2.18 ± 0.06 mmol/L, 2.17 ± 0.09 mmol/L, and 2.13 ± 0.14 mmol/L, respectively. On the eighth week, the concentrations were 2.22 ± 0.09 mmol/L, 2.20 ± 0.17 mmol/L, 2.06 ± 0.11 mmol/L, and 2.14 ± 0.07 mmol/L, respectively. On the 12th week, the concentrations were 2.18 ± 0.04 mmol/L, 2.20 ± 0.08 mmol/L, 2.09 ± 0.02 mmol/L, and 2.16 ± 0.11 mmol/L.

CONCLUSION

The combination of micro-arc oxidation and hydrothermal deposition can greatly improve the anti-corrosion behavior of Mg alloy, and Mg alloy coated with this composite coating is a promising biomaterial with a satisfactory degradation rate.

Biodegradation behavior of magnesium and ZK60 alloy in artificial urine and rat models

In this work, the biodegradable and histocompatibility properties of pure Mg and ZK60 alloy were investigated as new temporary implants for urinary applications. The corrosion mechanism in artificial urine was proposed using electrochemical impedance spectroscopy and potentiodynamic polarization tests. The corrosion potential of pure magnesium and ZK60 alloy were −1820 and −1561 mV, respectively, and the corrosion current densities were 59.66 ± 6.41 and 41.94 ± 0.53 μA cm⁻², respectively. The in vitro degradation rates for pure Mg and ZK60 alloy in artificial urine were 0.382 and 1.023 mm/y, respectively, determined from immersion tests. The ZK60 alloy degraded faster than the pure Mg in both artificial urine and in rat bladders (the implants of both samples are ø 3 mm × 5 mm). Histocompatibility evaluations showed good histocompatibility for the pure Mg and ZK60 alloy during the 3 weeks post-implantation in rat bladders, and no harm was observed in the bladder, liver and kidney tissues. The results provide key information on the degradation properties and corrosion mechanism of pure Mg and ZK60 alloy in the urinary system.

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ZK60 obtained loose corrosion product layer with poor corrosion resistance in AU.

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ZK60 showed a faster degradation rate than Mg in artificial urine and bladder of rat.

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Mg and ZK60 alloy showed good histocompatibility for the bladder model of rat.

In vivo response of AZ31 alloy as biliary stents: a 6 months evaluation in rabbits

Mg-based metallic materials have been making continuing progress as vascular stents. However, the research of Mg-based materials as non-vascular stents is still at its primary stage. AZ31 stents hereby were implanted into the common bile duct of rabbits for 6 months. The results revealed an existence of 93.82 ± 1.36% and 30.89 ± 2.46% of the original volume after 1 and 3 month, respectively. Whole blood tests indicated an inflammation decreasing to normal level after 3 month implantation. A benign host response was observed via H&E staining. Nonuniform corrosion at the two ends of the stents was observed and considered the results of flow or local inflammation. Moreover, the application of Mg-based materials for different stenting treatment were reviewed and compared. Esophagus was hypothesized most destructive, whilst blood vessel and bile duct considered similar and less destructive. Trachea and nasal cavity were thought to be mildest.